Written by Sig Silber
Updated with minor corrections at 5:06 pm EDT April 3, 2021
It is no longer winter. And the agriculture sector is ramping up. Tonight we review the winter of 2020/2021. We also begin to report more extensively on agriculture via what is sometimes called the State Stories Report. On April 5 more detailed reporting will begin. This article contains all of our regular features and as usual, we include an intermediate-term weather forecast.
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The above was a full report. Now we will just provide two slides that summarize the report for the North Central Region. If you are interested in the full report you can access it here.
Severe Weather
Here is what the SNOTEL data is telling us about Spring runoff.
And here is another way of looking at it.
And here is the water year.
And it is always useful to look at the last seven days.
Let’s look at the current drought situation.
And the week to week change
Here we look at four-time periods: one week, one month, six months, and a full year.
Drought Discussion (The Regional links are live and will take you to the drought map for that Region)
This Week’s Drought Summary
Multiple low pressure systems resulted in widespread precipitation (0.5 to 3 inches, or more) from the Mississippi Valley to the East Coast during late March. Heavy to excessive rainfall (more than 5 inches) soaked southeast Louisiana and triggered flooding across Tennessee this past week. Along with the flooding, a severe weather outbreak affected Alabama, Georgia, Tennessee, and Kentucky on March 25. Mostly dry weather persisted farther to the south, including the Florida Peninsula and south Texas. A cold front brought strong winds to the northern Plains on March 29 but little or no precipitation. Rain and high-elevation snow was limited to coastal Washington and the northern Cascades across the Pacific Northwest, while mostly dry weather prevailed throughout California. 7-day temperatures from March 23-29 averaged below (above) normal across the western (eastern) U.S.
Northeast
Mostly dry weather (less than 0.5 inch) prevailed across northwest Pennsylvania where abnormal dryness (D0) was expanded. Based on 60 to 90-day SPIs, low 28-day average streamflows, and soil moisture below the 20th percentile, moderate drought (D1) was added to parts of northwest Pennsylvania and adjacent areas of western New York. Increasing short-term precipitation deficits along with a number of low 28-day average streamflows support the addition of D0 across western Maryland and parts of West Virginia. Despite the 1 to 1.5 inches of rainfall this past week across southern New England, lower streamflows supported an expansion of D0 across parts of Massachusetts and southern New Hampshire.
Southeast
A second severe weather outbreak during March occurred across Alabama and Georgia on the 25th, with numerous tornado reports and locally heavy rainfall. A 1-category improvement was made to areas that received more than 1.5 inches of rainfall including southern Alabama, the western Florida Panhandle, and parts of northern Georgia. D0 (abnormal dryness) was maintained for parts of eastern Alabama and northern Georgia where rainfall was lighter this past week, and based on 60-day SPIs. Increasing short-term precipitation deficits and low soil moisture conditions support the addition of D0 across the Shenandoah Valley in Virginia, extending northward to southern Pennsylvania. D1 (short-term moderate drought) was introduced to southern Palm Beach County in south Florida, based on 60-day SPI and soil moisture. The D1 areas currently designated for south Florida are consistent with the latest Keetch-Byram Drought Index. The D0 in central Florida was expanded slightly westward this week.
South
On March 23 and 24, heavy rainfall (more than 5 inches) resulted in a 2-category improvement to southeast Louisiana where soil moisture is currently above the 70th percentile. However, much less rain fell across northern Louisiana where an expansion of D0 (abnormal dryness) and D1 (moderate drought) was made. The recent heavy rainfall also led to elimination of abnormal dryness (D0) across the Mississippi Gulf Coast. Heavy rainfall triggered flooding across much of Tennessee during late March and the small areas of D0 were removed from the state. Additional improvements from the previous two weeks continued across the Texas Panhandle, while mostly dry weather and increasing precipitation deficits along with worsening soil moisture conditions resulted in expansion of D1 (short-term moderate drought) across parts of southeast Texas. Soil moisture rapidly declines from east to west across Texas.
Midwest
Widespread precipitation (1 to 2.5 inches) fell throughout much of the central and eastern Corn Belt. Abnormal dryness (D0) and moderate drought (D1) were decreased in spatial coverage across Illinois and Indiana. Despite this rainfall during late March, soil moisture (below the 20th percentile) and SPIs at various time scales support maintaining D1 across parts of northern Indiana, northern Ohio, and lower Michigan. Northeast Illinois and eastern Indiana missed out on the heavier rainfall during late March, prompting a slight expansion of D0 for these areas. Also, D1 was added to northeast Ohio based on increasing 90-day precipitation deficits, 90-day SPIs, and soil moisture below the 20th percentile. A 1-category improvement was made to eastern Minnesota and western Wisconsin where more than 1.5 inches of rainfall occurred this past week. 1 to 2 inches of rainfall resulted in a reduction in D0-D2 across central Iowa. However, SPIs dating back 9 months continue to support D2-D3 long-term drought for northwest Iowa.
High Plains
Another dry week along with strong winds on March 29 resulted in a slight expansion of extreme drought (D3) across North Dakota and northern South Dakota. This expanding D3 area was based mostly on SPI at EDDI at various time scales. Soil moisture remains below the 5th percentile for much of North Dakota. Based on snow water content running near average and 6 to 12 month SPIs, D3 was improved by one category across north-central Wyoming. Following multiple changes during the previous two weeks across Colorado, only minor improvements were needed this week. Localized improvements were made to small areas of southern Colorado, based in part on WYTD (since Oct 1, 2020) precipitation.
West
Widespread extreme (D3) to exceptional (D4) drought continues to be focused across the Southwest. According to the USDA (for the week ending March 28), nearly two-thirds of the winter wheat is rated as very poor in New Mexico. As of March 27, snow water content is running near 70 percent of average for the Sierra Nevada Mountains. Due to this snow water content along with WYTD (since Oct 1, 2020) precipitation deficits, long-term drought persists for nearly all of California. Since precipitation averaged below normal during March, the impact type was adjusted to include both long and short-term drought for California, along with parts of the Southwest. Based on SPIs at various time scales, D1 (moderate drought) was slightly expanded across north-central Montana while below average snow water content prompted an increase in abnormal dryness (D0) for northwest Montana. To the west across eastern Washington, below average precipitation during March and drying topsoil prompted an expansion of D0 and D1 (short-term moderate drought).
Alaska, Hawaii, and Puerto Rico
Abnormal dryness (D0) continues for northern and eastern Mainland Alaska with no changes this week. The depicted D0 will be reassessed next week as current snowfall data becomes updated.
Based on rainfall during mid to late March, a 1-category improvement was made on Maui, Molokai, Lanai, and Kahoolawe. Therefore, Hawaii is currently drought free with only lingering abnormal dryness (D0). Reports from Hawaii indicate a greening of vegetation on Maui but abnormal dryness continues on the northwest side of the Big Island.
According to AHPS, 7-day precipitation amounts across Puerto Rico averaged at or above normal from March 23 to 29. Due to heavier amounts across inland areas, a slight decrease in D0 (abnormal dryness) and D1 (moderate drought) was made to parts of Puerto Rico.
Pacific Islands
The weather features across the U.S.-Affiliated Pacific Islands (USAPI) during this USDM week (03/24/21-03/30/21) included a persistent near-equatorial trough across Palau and western to southern Yap State, accompanied at times by weak circulations; converging trade winds that formed an Inter-Tropical Convergence Zone (ITCZ) over eastern Micronesia with embedded surface troughs; and seasonally dry trade winds over northern portions of Micronesia, especially over the Marianas. The surface convergence was coupled at times with upper-level divergence. South of the equator, instability in the upper levels of the atmosphere combined with moist surface air to generate showers over American Samoa.
Satellite-based estimates of 7-day precipitation (QPE) showed a band of precipitation stretching eastward across Micronesia (reflecting the surface troughs and ITCZ) and patches of precipitation over the Samoan Islands. Rainfall totals of 2+ inches were widespread from the equator to 10 degrees North latitude over western Micronesia and between 3 N and 8 N over eastern Micronesia, with embedded 4+ inches of rain. Little to no rain was indicated across the Marianas. (It should be noted that the satellite QPE is designed to detect precipitation from showers produced by cold high-topped clouds, whereas showers from diurnal island convection and weak systems are typically produced by warmer clouds with limited vertical development that go undetected by this satellite tool.) The satellite QPE detected a patchwork of 1+ inches of rain across the Samoan Island region with lesser amounts in between the 1+-inch patches.
This week continued the dry (below the 1-inch weekly minimum needed to meet most water needs) streak on Guam (0.18 inch of precipitation recorded) and the Commonwealth of the Northern Mariana Islands. Less than half an inch of rain was reported at Rota (0.02), Saipan NPS (0.34), Saipan IAP (0.49), and Saipan ASOS (0.85). Likewise, with the exception of Dededo (where 4.08 inches was recorded), March has been dry at Guam, Rota, and the stations on Saipan. D0-S continued for Guam and Rota and D1-s continued for Saipan.
In the Federated States of Micronesia (FSM), it was a dry week (less than the 2-inch weekly minimum needed to meet most water needs) at Lukunor (1.66 inches with 2 days missing), but wet at the rest of the analyzed stations. Rainfall totals for the wet stations ranged from 2.33 inches at Yap to 10.77 inches at Pohnpei. Fananu received 2.64 inches of rain this week (with 3 days missing) and 11.90 inches for March so far (both of these values are above the weekly and monthly minimums). This is the fourth consecutive wet week, and the island has recovered from the earlier drought impacts, so the status was improved from D0-S to No Drought or Abnormal Dryness.
At Kapingamarangi, 2.50 inches of rain was recorded this week and 8.91 inches for March through the 30th (likewise, both of these values are above the weekly and monthly minimums). This is the third consecutive wet week, water levels are reported to be 100%, and vegetation/crops are beginning to recover. The last 12 through 7 months (April-March through August-March) are still the driest on record, but the precipitation ranks for the last 4 months have improved. March (to date) ranks as the 8th driest March (compared to complete Marches) out of 31 years of record, which equates to the 26th percentile or D0; February-March ranks 5th driest out of 31 years (16th percentile, or D1), January-March ranks 3rd driest out of 27 years (11th percentile, or D1), and December-March ranks 3rd driest out of 25 years (12th percentile, D1). Considering the recent wetness and improving conditions, the status at Kapingamarangi was changed from D3-SL to D2-L.
With the previous 2 weeks wet, D-Nothing continued at Lukunor, and D-Nothing continued at the rest of the FSM stations where both this week and the month have been wet.
In the Marshall Islands (RMI), no data was received from Utirik this week and in recent months so an analysis could not be made there. The week was wet (above the 2-inch weekly minimum) at Mili (2.50 inches), Majuro (4.06) and Ailinglaplap (4.78), but dry at Wotje (0.36), Kwajalein (0.73), and Jaluit (1.22). Only Wotje (with 0.81 inch) and Kwajalein (6.21 inches) were dry (below the 8-inch monthly minimum) for the month, so D3-S continued at Wotje and D1-S continued for Kwajalein. The other stations were wet for March (through the 30th), with totals ranging from 15.00 inches at Majuro to 24.05 inches at Ailinglaplap, so D-Nothing continued.
Weekly rainfall totals were above the minimum needed to meet most water needs at Palau IAP (2.61 inches) and Koror COOP (2.15) in the Republic of Palau, and at Pago Pago (2.53) and the automated stations at Siufaga Ridge (1.75) and Toa Ridge (1.16) in American Samoa. Likewise, the monthly totals were above monthly minimums, so D-Nothing continued at Palau and Tutuila.
Virgin Islands
The weather conditions across the U.S. Virgin Islands (USVI) during this USDM week (03/24/21-03/30/21) reflected contrasting forces. An upper-level trough moved through the territory during part of the week, but high pressure ridging, dry air, and stable conditions dominated the upper-level atmosphere for the most part. Patches of low-level moisture moved across the islands at times in the trade-wind flow. The result was scattered showers with limited precipitation totals.
Radar-based estimates of rainfall (QPE) for the 7 days ending at 12z on Tuesday showed areas with half an inch or more of precipitation over parts of the islands, with other parts receiving less than a tenth of an inch. USGS well measurements revealed a continuing steady decline in groundwater levels on all three islands. Due to the dry weather conditions, the Virgin Islands Fire Service has issued a ban on burning across the territory, effective March 15.
Weekly rainfall reports on St. Croix ranged from 0.05 inch at the CoCoRaHS station at Christiansted 4.1 ESE (based on 3 days of data) to 0.45 inch at Christiansted 1.6 E. The East Hill station recorded 0.06 inch and 0.30 inch fell at the Rohlsen AP. Monthly totals for March (through the 30th) ranged from 0.53 inch at Rohlsen AP to 1.69 inches at Frederiksted 0.5 N. For those stations with normals, the month was drier than normal at Rohlsen AP (35% of normal) and East Hill (56%). With Standardized Precipitation Index (SPI) values at Rohlsen AP and East Hill in the D0-D1 range for the last 1 to 12 months, D1-SL continued on St. Croix.
On St. Thomas, weekly rainfall totals ranged from 0.02 inch at Charlotte Amalie 1.4 NE (based on 4 days of data) to 0.30 inch at King AP. March monthly totals (through the 30th) ranged from 0.32 inch at Anna’s Retreat 2.5 ESE and Charlotte Amalie 5.1 E to 0.83 inch at Charlotte Amalie 1.4 NE. King AP recorded 0.61 inch for the month so far, which is 45% of normal. Reports of cracked ground have been received from the Bordeaux area. Severe drought continued on St. Thomas, but the status was changed from D2-S to D2-SL to reflect mounting dryness at the 12-month SPI time scale.
On St. John, the station at Windswept Beach reported 0.38 inch of rain this week, bringing the March total (through the 29th) to 0.94 inch. The long-term average for March is 1.73 inches, which means March 2021 is about 56% of average. The CoCoRaHS station at Cruz Bay 1.6 E reported 0.46 inch for the week and 0.90 inch for the month. The CoCoRaHS station at Cruz Bay 0.8 NE reported 0.35 inch for the week (with 6 days missing) and 1.14 inches for the month. With moderate and severe drought indicated by the Windswept Beach SPI at 1- to 3-month time scales, D2-S continued on St. John.
Looking Ahead
During the next 5 days (April 1 to 5), much drier weather is forecast for the eastern and central U.S. in the wake of a cold front. Mostly dry weather is also expected for the western U.S. with light precipitation limited to the Pacific Northwest and northern California. A brief period of below normal temperatures are forecast for the eastern U.S. and Gulf Coast States. A freeze may affect areas as far south as the Tennessee Valley and southern Appalachians from April 1 to 3. Meanwhile, a rapid warming trend is likely over the northern and central Great Plains with much above normal temperatures forecast during the first week of April.
The CPC 6-10 day extended range outlook (valid from April 6 to 10) favors above normal temperatures across the central and eastern U.S. with the largest probabilities centered over the central and southern Great Plains. Below normal temperatures are most likely along the West Coast and throughout Alaska. Probabilities of below normal precipitation are elevated from the Southeast westward to the southern Great Plains and southern Rockies. Near to above normal precipitation is favored for the Corn Belt, northern Great Plains, much of the western U.S., and Alaska.
More Regional Reports
The result of the drought is very dry soil conditions
April Drought Outlook
Here is the discussion released with the April Drought Outlook.
Discussion for the Monthly Drought Outlook
Tools used in the U.S. Monthly Drought Outlook (MDO) included the Climate Prediction Center (CPC) temperature and precipitation outlooks for April 2021, various short- and medium-range forecasts and models such as the 7-day quantitative precipitation forecast (QPF) from the Weather Prediction Center (WPC), the 6-10 day and 8-14 day CPC extended-range forecasts (ERFs), the Week 3-4 outlooks and tools from CPC, dynamic models at the monthly time scale, the 384-hour total precipitation forecasts from several runs of the GFS, climatology for April, and initial conditions for parameters such as soil moisture. Existing drought areas in the forecast are based on the March 30, 2021 U.S. Drought Monitor. Forecasts currently reflect the presence of a moderate La Nina, which is expected to remain throughout most or all of April, as there is a ~60 percent chance that conditions will begin transitioning toward ENSO-neutral into the spring months. Therefore, ENSO’s influence remains a factor in the April 2021 MDO.
In the West, snow water equivalent (SWE) and reservoir levels are above-normal for the season leading up to April in the Pacific Northwest and northern Great Basin, falling quickly to below-normal southward in the Western Region. However, March saw below-normal precipitation across the West, leading to some expansion of moderate drought (D1) in some locations in eastern Washington and northern Montana. Odds for below-normal temperatures indicate existing drought conditions will not likely be exacerbated further during April. Additionally, the lack of a precipitation signal, coupled with surplus snowpack and above-normal reservoir levels, suggests no major improvements either. As such, persistence favored for much of the Pacific Northwest, with improvement favored along the western Cascades. Further south, drought persistence is also likely, with no additional development, as temperature and precipitation signals are lacking along the West Coast and western portions of the Great Basin. Further east, in the eastern Great Basin, below-normal precipitation is favored in areas already experiencing moderate to exceptional drought, indicating persistence is likely.
Forecast confidence is moderate to high for the Western Region.
The Northern Plains in the High Plains Region is a victim of below-normal seasonal snowfall and above-normal temperatures (6-10 degF above-normal). This has resulted in drought expansion and intensification across the Dakotas and into the upper Midwest in the months leading up to April. The Dakotas are favored to experience above-normal precipitation (33% – 40% chance), with the greatest chances during the first half of the month. Additionally, the Great Plains begins its transition into a wetter time of year climatologically toward the end of April, in addition to a typical slight enhancement of wet precipitation signals across the region during La Nina years. Despite the potential for above-normal precipitation, lower probabilities indicate lower confidence, and any precipitation received will need to be much above-normal to overcome antecedent, long-term severe (D2) and extreme (D3) drought conditions across the Dakotas. However, some removal is favored in areas experiencing moderate (D1) drought in the eastern Dakotas, as drought indicators show weaker signals leading into the April period, suggesting any precipitation received will be more impactful. However, it should be noted that any potential improvements in the Dakotas will be slow to develop. Further south, the Central Plains experienced a major winter storm system in mid-March, which dropped 2-3 feet of snow in portions of eastern Colorado and southeastern Wyoming and anywhere from 5-10 inches of rainfall from the Front Range eastward to the Midwest, which brought major drought improvement. However, with above-normal temperatures and below-normal precipitation favored for the western High Plains, drought conditions are likely to persist during April. Furthermore, drought development is likely in abnormally dry (D0) areas, including those affected by the strong March storm system, as these areas are prone to high-wind events and conditions are favored to dry out again during April.
Forecast confidence is low for the Northern Plains and moderate elsewhere for the High Plains Region.
In the Midwest, portions of the Corn Belt have seen beneficial rainfall in the weeks leading up to April, resulting in drought removal across central Illinois. Elsewhere, however, below-normal precipitation has led to drought expansion across southern Michigan and northern portions of Ohio. Drought development also occurred across northern Minnesota. Above-normal precipitation is weakly favored for much of the Midwest during the next 6 to 10 days, transitioning to below-normal during Week-2 (8 to 14 days). Due to increased odds of above-normal precipitation early in the period, and above-normal precipitation favored in the April precipitation outlook in the upper Midwest, drought removal (D1) is likely across Minnesota. Additionally, standardized precipitation indices (SPIs) have shown gradual improvements in recent months, suggesting above-normal precipitation is likely to have more immediate impacts (although to a lesser extent in farther west in Minnesota and the eastern Dakotas, where dry signals in drought indicators are more pronounced). However, in portions of western and southern Michigan and northern Ohio, drought persistence, with additional expansion into abnormally dry (D0) areas, is likely, with above-normal temperatures strongly favored and precipitation signals transitioning to below-normal eastward toward the eastern Great Lakes and Northeast.
Forecast confidence is moderate for the Midwest Region.
The Texas Panhandle, northern and northwestern Oklahoma, the Tennessee Valley, and portions of the middle and lower Mississippi Valley experienced above-normal precipitation and drought removal during March. This beneficial improvement will be much needed during April, as equal chances of above or below to below-normal precipitation is favored throughout the Southern Region. Predicted weak mid-level height patterns during the middle part of the month increases uncertainty a bit in which location could see continued improvement versus degradation. As such, drought persistence is favored across the Southern Region, with development likely in abnormally dry (D0) areas across portions of west-central and southeastern Texas and southwestern Oklahoma, as well as the Texas and Oklahoma Panhandles. However, further eastward toward the lower Mississippi Valley, greater uncertainty among the model precipitation signals makes persistence (northeastern Louisiana) with no further development likely.
Forecast confidence is moderate for the Southern Region.
Heavy precipitation across the Southeast during the latter half of March led to some drought removal across areas of the Deep South. However, dryness has persisted in Florida, resulting in drought development in southern portions of the Peninsula in the past couple of weeks. In addition to April being a climatologically dry month for Florida, enhanced odds of above-normal temperatures and below-normal precipitation are favored, increasing the likelihood of additional drought expansion across the Florida Peninsula during April.
Forecast confidence is moderate to high for the Southeast Region.
In the Northeast, long-term drought has slowly diminished in recent months. However, D0 to D2 standardized precipitation indices (SPIs), locally D3, are still prominent, extending from western Pennsylvania to northern New England. Unfortunately, relief is not likely to come during April, as below-normal precipitation is favored through the first half of the month. Additionally, recent medium-range model solutions point toward equal chances for above and below to below-normal precipitation at longer leads. Coupled with increased odds of above-normal temperatures and plant growth being ahead of schedule (increasing evapotranspiration and water uptake in the root zones), this is likely to exacerbate existing dryness, suggesting drought development is likely in the driest areas from the Shenandoah Valley into western Pennsylvania, northern and western New York, New England, and western Maine.
Forecast confidence is moderate to high for the Northeast Region.
D0 currently covers much of northern Alaska, extending across the North Slope and Brooks Range southeastward to the Yukon Flats. Basin SWE estimates are currently below-normal (near 60% of normal for the period of record) across central Alaska. However, above-normal precipitation is favored throughout the period across the western Mainland, with equal chances for above or below elsewhere, which will help to stave off drought development throughout April. In Hawaii, many areas received heavy rainfall in recent weeks, with several locations experiencing flooding. As the wet season winds down during April, the state is expected to continue to see above-normal precipitation, making drought removal likely for the entire state. Moderate drought (D1) is currently depicted in northwestern Puerto Rico. Despite above-normal temperatures favored during April, above-normal precipitation is also favored. Coupled with continued improvements in SPIs in recent weeks, this area is primed for continued improvement, making complete drought removal likely for the island.
Forecast confidence is high for Alaska, Hawaii, and Puerto Rico.
Since we are entering fire season it is time to start showing the wildland fire potential outlook. These will update automatically shortly after the month changes.
Crop Conditions
State Agriculture Summary Reports.
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USDA Executive Briefings and other NASS Reports.
There were two Executive Briefings that were released this week. One was on Hogs and Pigs and the other was the first report on Principle Crops. It was not possible for us to present those reports due to lack of time. What we are doing is presenting a key graphic from each and a link to the full report and we may do a more extensive report next week. I think one of the reports is 58 pages. That is a lot of snipping and uploading etc. It is the first report of the new season.
Hogs and Pigs. You can access the full report here.
Grain Stocks, Prospective Plantings and Rice Stocks.
This is a long report covering a number of topics basically two: Prospective Plantings and the carryover inventory (stocks) of grain and rice. The full report can be found here. We may or may not present the full report next week. USDA can produce information faster than I can publish it. It is a large organization and I am one person. The report is definitely worth reading but the first report of the season may reflect a lot more intentions than what the ultimate reality will be. They say they published this on March 31 and sometimes it shows up a little later than the stated publishing date and March 31 is the day that NOAA published their updated forecast for April. So I was busy with that. But you do not need to wait for me as I have provided you with the link to get the PDF of this report. I will now show you what I consider to be the key graphics in this very long report.
Intermediate-Term Weather Forecast
Showing from left to right, Days 1- 5, 6 – 10, 8 – 14, and Weeks 3 – 4 You can click on these maps to have them enlarge. Also, the discussions that go with these forecast maps can be found here (first two weeks) and here (Weeks 3 and 4).
First Temperature
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And then Precipitation
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The Week 3-4 Discussion is always interesting.
Week 3-4 Forecast Discussion Valid Sat Apr 17 2021-Fri Apr 30 2021
In the tropical Pacific, La Nina conditions persist but the anomalously cool sea surface temperature (SST) anomalies have slowly weakened over the last several weeks and the most recent ENSO forecast slightly favors a transition to neutral conditions later this spring. The Madden Julian Oscillation (MJO) is currently active over the Maritime Continent. Dynamical forecast guidance consistently progresses this signal eastward over the West Pacific throughout the next two weeks. As we progress into the spring and summer months, these tropical phenomena will have less of an influence on the US sensible weather. Both the Arctic Oscillation and the North Atlantic Oscillation are in the positive phase and are currently forecast to be neutral/slightly negative by the start of the forecast period. As such, this week’s outlook is largely based on a blend of the dynamical model guidance, with additional considerations from decadal trends.
The agreement among the dynamical models (CFS, ECMWF, JMA, and the SubX multi-model ensemble) is modest regarding the anomalous 500-hPa pattern over the Week 3-4 period. The models consistently forecast ridging centered near the Aleutian Islands over the North Pacific that extends over much of Alaska. The models vary more on the predicted height patterns over the CONUS with the CFS indicating a broad region of positive heights and the JMA favoring weakly negative heights across the northern tier. The ECMWF suggests an intermediate solution with ridging on the West Coast and weak troughing over the East.
As a result of the uncertainty in the forecast height patterns, equal chances of anomalous temperatures are carved out for much of the eastern and western portions of the CONUS. The temperature forecast tilts toward above normal probabilities through the Southwest and the Central Rockies where long term trends are positive and the dynamical models collectively agree on anomalous ridging. The highest confidence of above normal temperatures is predicted across southern New Mexico and western Texas where probabilities exceed 60 percent. Above normal temperatures are also slightly favored along the Gulf Coast and Florida, consistent with the surrounding positive SST anomalies. Dynamical model guidance favors below normal temperature probabilities over southwest Alaska due to predicted northerly flow while above normal temperature chances increase along the northern regions of the state.
The precipitation forecast favors dry conditions over the Pacific Northwest and along the panhandle and southern coast of Alaska while odds grow for wet conditions in the northern portion of the state.The dynamical models and the SubX ensemble consistently indicate a broad region of below median probabilities across the East Coast extending across the South and through the Central Rockies under the anticipated weak ridging. Elevated probabilities of above median precipitation are forecast over the Northern Plains.
Near normal SSTs are observed surrounding Hawaii and dynamical model guidance suggests equal chances for much of the state with a slight tilt to above normal temperatures over the northwest islands. Dynamical model guidance also indicates equal chances of anomalous precipitation across the region.
International
This week fortunately we do have a map.
Double Dip La Nina Continued
I want to attempt to present a paper that explains why we have more La Ninas than El Ninos. I think you can read the full paper here. I am not positive of that because I am registered with ResearchGate but they did not ask me to log in so I think you can access the full article but hopefully I will present enough for readers to understand the concept.
I have not made any progress on this since I first included it but I am leaving it in the article for those who may want to think about the issue and I will try to expand the discussion when I have the time to really study it. I think it is very important.
The rest of the discussion is later on in the article. And consider this an introduction because some of my readers may be familiar with this but for me, it is uncharted territory. So I need to do a lot more research. But what caught my interest was the part of the discussion not shown here but in the slides that are presented later in this article which suggests that the Pacific Decadal Oscillation or PDO does not explain as much about weather cycles (what I call low-frequency weather cycles) as I have assumed and that there are other factors now that need to be included in the analysis. One of the two is the Pacific Meridional Model or PMM mentioned in the Abstract. If that is the case, and I can come across some other references to this it is very important – let me just say it that way.
I have moved the other slides I made to somewhere close to the end of this article. I will be coming back to this topic very soon. I am not sure yet if this theory if you want to call it that explains why we may have a two-year La Nina this time around. It is not clear that we will but some of the models suggest it. Not all La Nina’s are dry for the Southwest but most are. So if the ratio of two-year La Ninas to one-year La Ninas is increasing, that is very important. I could have held back all this information until was read to fully discuss it but that did not seem to be proper. Some of my readers may know more about this and can leave me messages in the comment section that follows every article I publish.
I also see the possible connection of what is discussed in this paper with the storm we just had. In the article I posted last night on the NOAA four-season forecast I provided some snapshots of the Equatorial Pacific which showed a lack of movement of the cool and warm anomalies. I showed four snapshots which basically covered three months but I could have gone back many more months and it would have looked similar. You can see that set of graphics here. The importance of that is this La Nina is not decaying rapidly. So it could last into next winter or fade for a short period of time and later regain La Nina Status. I am not making any predictions here but I am raising the question of has something fundamentally changed?
I am certainly familiar with the deliveries to Elephant Butte the major reservoir on the Rio Grande and I am familiar with the deliveries to the three beneficiaries of that project namely an irrigation district in New Mexico, a similar irritation district in El Paso County Texas, and Mexico. Shortly after the MegaNino of 1997 and the subsequent La Nina of 1998 deliveries declined to Elephant Butte Reservoir and to the three (there is actually a fourth in good years when there is surplus water available to Hudspeth County Tx under a Warren Act Contract). I concluded that this was a normal change of phase of the PDO but perhaps there is more to it. So that explains my interest in the topic and although I frame the issue in a New Mexico context it impacts essentially all of the U.S.
Just what is the Pacific Meridional Mode?
This may help a bit. It is a second reference to the issue and this time an NOAA article. BTW, the fish are never wrong. We create indices on observed fish behavior. If their behavior deviates from what our indices suggest their behavior should be, it is not because the fish are confused it is because our indices or models no longer are accurate.
This graphic also might help
4 | DISCUSSION AND SUMMARY
From the present study, it is necessary to discuss two possible factors responsible for modulating La Nina persistence. The first is the preceding El Nino amplitude. From a linear perspective, the discharging amount is proportional to the El Nino amplitude. With strong discharging, significant SSTA cooling could last more than 2 years. The preceding El Nino amplitude also affects the intensity of the interbasin SSTA gradient by influencing the adjustment time of the Indian and tropical Atlantic Oceans to the Pacific SSTA (Wu et al., 2019). More specifically, the delayed response of SST cooling over the Indian and tropical Atlantic Oceans, in comparison with the Pacific cooling, allows the easterly wind anomaly over the western Pacific to be dominated even after the La Nina decaying phase. This initiates a La Nina that tends to persist up to 2 years. However, the role of the Indian Ocean capacitor effect on western Pacific wind anomalies has been questioned by Chen et al. (2016). Using data analysis and numerical experiment, the authors claim that the Indian Ocean basin warming during mature El Nino wintertime events has little effect on the easterly anomalies in the equatorial western Pacific, and the local process over the western Pacific has more influence over the Indian Ocean capacitor effect. Further numerical experiments may provide quantitative insight in to the importance of these factors, which is beyond the scope of this study. The second factor is a recharging/discharging efficiency with respect to anomalous wind-stress/WSC relevant to SSTA patterns, which contributes to ENSO phase transition. This was the focus of this study. An EP-type El Nino preceding a La Nina leads to strong discharge by positive WSC (0 – 15N) that is widely spread over the Pacific basin, which induces a strong and long-lasting La Nina. When a La Nina develops through the mid-latitude connection (PMM or NPO), SSTA cooling and a tropical easterly wind anomaly expand to the North Pacific. In this case, an anomalous negative WSC is weak and, thus, the recharging efficiency by equatorial Rossby waves is low. Consequently, to understand La Nina persistence, it is reasonable to consider both the preceding El Nino amplitude and recharging/discharging efficiency by anomalous SST/wind-stress patterns as the La Nina evolves. In this study, we investigated how the evolution of single- and multi-year La Nina events differs from their onset phase by analysing both observational and climate model data sets. Our analyses showed that there was a significant difference in the evolution between the two types of La Nina events, even from their initial development associated with a mid-latitude connection. These differences are described as follows (Figure 10).
1. A weak CP-type (Nino-4 > Nino-3) El Nino tends to exist one year prior to a single-year La Nina event, whereas a strong EP-type (Nino-3 > Nino-4) El Nino tends to exist prior to a multi-year La Nina event.
2. For single-year La Nina events, negative WSC, associated with CP-type El Nino and confined to the western Pacific, induces weak discharge that leads to a weak La Nina. In contrast, a widely extended negative WSC of a multi-year La Nina in the Pacific basin causes efficient discharge, resulting in a strong La Nina.
3. From the decay of an El Nino to a La Nina developing period, SSTA cooling is initiated by anomalous easterly wind in the eastern Pacific for single-year La Nina. However, for multi-year La Nina events, SSTA cooling is triggered by a mid-latitudinal influence (i.e., PMM/NPO). Such a difference in initiation of a La Nina explains why the meridional width of multi-year La Nina events exceeds that of single-year La Nina events.
4. During a La Nina peak period, single-year La Nina events have an equatorially confined SST cooling structure; however, multi-year La Nina events have intensified SSTA cooling and meridionally expanded easterly wind anomalies. In addition, the overall structure of multi-year La Nina events is shifted westward. Comprehensively, the SST structure of multi-year La Nina events is similar to Mega-ENSO. Thus, the recharging process of a singleyear La Nina is strong due to equatorially confined SST cooling/strong WSC, whereas that of a multi-year La Nina is relatively weak due to meridionally expanded SST cooling/weak WSC.
5. During a La Nina decaying period, the SSTA cooling of a single-year La Nina disappears with strong recharging, resulting in the termination of the La Nina. For multi-year La Nina, the SSTA cooling persists with a weak recharge. Because of the insufficient recharge, the surface cooling in the equatorial Pacific persists until the following summer. Bjerknes feedback is then initiated, resulting in the development of a second La Nina in boreal winter (Chen et al. 2016).
6. The iteration of processes 3 through 5 for a multiyear La Nina may lead to the development of another La Nina in the subsequent winter.
In summary, by analysing the statistically significant differences in precursory signals between single- and multi-year La Nina events, we observed that a midlatitude connection associated with the PMM/NPO, such as the meridional expansion of anomalous SST and wind stress fields, is critical for La Nina persistence. This indicates that there is similar dynamics operating during mega-ENSO and multi-year La Nina events. These results have important implications for improved ENSO prediction and provide an appropriate alternative interpretation to the state-of-the-art climate models in predicting multiyear La Nina events.
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