Written by Sig Silber
Our Special Topic this week is the Snow Drought in the West, especially in the Sierra Nevada Mountains. Of course, we have our full set of regular weekly reports and, since we are now publishing on Fridays, our intermediate-term weather forecast covers 28 days. The first 14 days of the forecast updates automatically daily – so you can check it each day. You have to scan down a bit to find it as it follows the weekly NIDIS drought report. We do it that way to make it easier to see if the forecast is favorable or unfavorable relative to drought conditions and other ways the weather impacts the economy.
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Special Topic for this Week
Snow Drought Update.
Additional information and resources on Snow Drought can be found here.
Current Drought Conditions
Now we take a look at Thursday’s U.S. Drought Monitor Report.
The U.S. Drought Monitor is a comprehensive way of understanding the drought situation for the U.S. It is issued every Thursday and reflects the conditions as of the prior Tuesday. Drought is defined as a moisture deficit bad enough to have social, environmental or economic effects. Thus, more factors than recent precipitation are considered and more information on how it is done is found at the end of this report.
U.S. Affiliated Pacific Islands and the U.S. Virgin Islands.
And this shows the U.S. including Alaska, Puerto Rico, and Hawaii.
Below is the map for just CONUS.
Last Week | This Week |
Some might find this animation of twelve weeks of change useful;
The graphic below shows the one-week change in drought intensity. Yellow is bad. Green is good.
Now we show the week to week change information by region. The yellow is where the level of drought has been raised. The green is where the level of drought has been lowered.
Degradation in Northeast Colorado. |
No Change |
No Change |
Degradation in South Texas |
Almost all the change is in Florida and it is mixed |
This is where the problem was. Oregon, California, Nevada, Utah and Colorado were where most of the changes took place. |
Here is the Discussion that was issued with the Drought Report. The Regional Headings can be clicked on to obtain maps and statistics.
This Week’s Drought Summary
The pattern has been less active over the CONUS over the past 7 days, with high pressure dominating over much of the western CONUS. Storm systems riding up and over the Pacific ridge resulted in some precipitation in the Pacific Northwest, but not enough to alleviate the dryness there, particularly for Oregon. Meanwhile a low-pressure system propagated northeastward along the East Coast and out of the domain early in the period, adding to surpluses in the Tennessee and Ohio Valleys. Drought continued to expand in the West, as dry conditions persisted over much of the region. Parts of Oregon and California saw increases in D0 and D1 coverage, while areas of D0 were expanded slightly in Montana. There was some D1 added to northeastern areas of Colorado (High Plains Region), as the past 60 days have seen drier than normal conditions. Drought intensification and expansion also continues in southern Texas (Southern Region), in association with continued dryness, low humidity, and high winds over the past week. The Midwest and Northeast continue to remain as is for now, as 90-day precipitation surpluses are widespread across many of these areas, with other areas near normal. Some D0 reduction in southern Georgia (Southeast Region) was made due to recent heavy rainfall. However, the Florida Peninsula saw some D0 expansion north and east of Tampa, with year-to-date (YTD) precipitation estimates between 25 and 50 percent of normal.
Northeast
Some areas of New England have seen drier than normal conditions since the start of 2020. However, February brought above normal precipitation to much of the Northeast Region, reducing deficits in some of the drier areas in New England and Maine, while adding to surpluses in others, such as western Pennsylvania and southern and western New York. The past week has seen an additional 0.5 to 1.5 inches of precipitation, with pockets of 1.5 to 2 inches, over many of the drier areas. Widespread above-average USGS stream flows are also suggestive of adequate precipitation over the region as a whole. As such, no D0 development was needed this week.
Southeast
A large swath of 1 to 2 inches of rain fell across central and eastern Mississippi, northern Alabama and Georgia, and into southern South Carolina, adding to extreme rainfall surpluses. Areas of southern Georgia saw 0.5 to 1 inches of rainfall, warranting D0 removal in southwestern portions of the state. In the Big Bend area of Florida, another 1 to 3 inches of rain fell. However, many of these D0 areas in the Big Bend are dealing with 6-month deficits of more than 5 inches. As such, there was a slight increase in D0 coverage north and east of the Tampa Bay area in favor of YTD precipitation 25 to 50 percent of normal. Areas with greater than 10 inch deficits in the Florida Panhandle have seen modest improvements in recent weeks, despite the heavy rains just to the north and high downstream flows. Although areas right along the coast, near Saint George Island, have missed out on some of the heavier precipitation amounts in recent weeks, some D0 removal up to the Apalachicola River was warranted in association with some locally heavier rainfall in portions of Calhoun, Liberty, and Gulf Counties over the past 7 and 14 day periods.
South
Drought intensification over southern Texas continued, along with expansion into adjacent coastal areas. Stream flows are below normal for many areas, and recent high winds and low humidity have enhanced surface soil moisture loss. YTD percent of normal precipitation was 25 to 50 percent for much of southern Texas, with less than 10 percent along the Rio Grande Valley. This is on top of receiving essentially no precipitation over the past 30 days, and beyond, for many areas south of the I-10 corridor. D0 remains for portions of the immediate Gulf Coast in Louisiana, Mississippi, and Alabama this week, although dryness has crept northward in these areas with the sharp north-south precipitation gradients in recent weeks.
Midwest
Some dryness was noted during the last 30 days in southern Iowa and northern Missouri, but long-term surpluses are widespread across the Midwest, so this is welcomed dryness for many areas. Sub-soil conditions are wetter than normal and USGS average stream flows were near and above normal for most of the region, thus no D0 development was required this week.
High Plains
Some D1 was added over northeast Colorado with YTD precipitation 50 to 65 percent of normal. Stream flows were also running well below normal for this area. Recent ground observations support this addition of D1. SPIs over several time periods also show deterioration. The rest of the High Plains Region has long-term surpluses of precipitation. No D0 development expansion was made elsewhere.
West
Westward D1 expansion into the San Francisco Bay area and Mendocino County, northward D1 expansion into Trinity and Shasta Counties, and southwestward D1 expansion into San Luis Obispo County in California was warranted in association with the continuance of a much drier-than-normal water year to date (since October 1, 2019; WYTD). Many areas are seeing WYTD precipitation of 25 to 50 percent of normal and YTD precipitation 10 to 25 percent of normal. Some locations near San Francisco saw no precipitation for the month of February. However, reservoir levels are in good shape overall across California, despite the below normal snowpack. In addition, there have been several reports of non-managed creeks and streams running dry and severe lack of vegetation, resulting in producers supplementing feed for livestock. In addition, much of the state has seen above normal temperatures over the past week, further exacerbating the dryness and reducing longevity of existing snowpack. D1 was also expanded in central and southwestern Oregon, as stream flow conditions have continued to deteriorate, precipitation was lacking, and snowpack was below normal. Many unregulated rivers have fallen below the 10th percentile (much below-normal). WYTD precipitation deficits are greater than 12 inches across much of southwestern Oregon, including coastal areas. In contrast, Washington’s March 3 basin average SWC was above normal, and has received above normal precipitation over the past 30 days, mainly concentrated in areas with no drought, but this added to the snowpack and near-normal stream flows in drought areas, leading to status quo this week. The Four Corners Region is also status quo this week as the last 14 days has seen enough precipitation to prevent deterioration, but not enough for improvement. Some D0 expansion in Montana in favor of the 90 day SPI. Some D1 expansion in western Utah into Millard County, which has seen 5 to 10 percent of normal precipitation over the past 90 days.
Alaska, Hawaii, and Puerto Rico
An active storm track over Alaska has provided above normal precipitation over the past few weeks over much of the state, with widespread areas of greater than 2 inches of precipitation extending from eastern Kenai Peninsula eastward through the Southeastern Panhandle. Despite above normal precipitation over the last month in the panhandle, D0 (L) remain unchanged this week as a result of long-term dryness (beyond 12 months).
Hawaii received most of its precipitation along the windward slopes over the past week, where no drought existed. With stream flows near normal and recent improvements made the past few weeks, it was status quo for this week.
Puerto Rico has seen some above normal precipitation (1 to 3 inches) over the past 7 days leading to some reduction along the eastern edge of the D0 area in the northwest. The area is still seeing 75 to 90 percent of normal precipitation over the past 90 days, while the most of the island has seen greater than 150 percent of normal precipitation over the same period.
Pacific Islands
During the Northern Hemisphere winter, the North Pacific subtropical high, and the low latitude Inter-Tropical Convergence Zone (ITCZ), migrate south toward the equator. The seasonal migration brings drier subtropical trade winds to the northern portions of Micronesia and ITCZ rainfall to the southern regions. The weather conditions across the U.S.-Affiliated Pacific Islands (USAPI) during this USDM week (2/26/20-3/3/20) reflected this overall pattern, with a dry season trade-wind regime dominating the Marianas and northern portions of the Federated States of Micronesia (FSM) and Marshall Islands (RMI), while troughs and weak circulations and disturbances within the ITCZ brought rain to parts of southern Micronesia. Divergence aloft aided the surface convergence associated with the southern troughs, enhancing showers. Diffuse shear lines, remnants of fronts, and end-of-week troughs extending northward from the south, brought a few showers to the Marianas. South of the equator, the South Pacific Convergence Zone (SPCZ) remained north of American Samoa with dry stable air dominating the islands.
Satellite-based estimates of 7-day precipitation (QPE) showed a narrow band of 2+ inches of rain across Palau and Yap State, a large area of 2 to over 4 inches of rain over Kosrae State and central to southern RMI, and smaller areas of 1+ inches of rain over other parts of the FSM. The eastern Micronesia 2+ inch rain band extended across the equator southeastward to north and east of American Samoa as the SPCZ. The QPE also showed areas of 2+ inches of rain west of American Samoa. Little to no rain was detected by this satellite over the Marianas and American Samoa.
February rainfall in the Marianas totaled less than 2 inches on some northern locations, including Tinian (1.90 inches, or 58% of normal) and Saipan Airport (1.77 inches, or 68%). Guam International Airport fared a little better, with a February total of 3.79 inches (84% of normal). With rainfall totaling one-half inch or less for 4 consecutive weeks at all observation sites in the Marianas, moderate drought (D1-S) was retained for Saipan, while abnormal dryness (D0-S) persisted on Rota and Guam. The Keetch-Byram Drought Index, indicative of fire danger, was reported by the National Weather Service to be 594, in the high category, on March 2.
In the Republic of Palau, a wetter weather pattern developed in late February, when convergent trade winds northeast of a trough and a weak circulation located south of the main islands of Palau generated sporadic showers and at times continuous rain. The National Weather Service office (WSO) on Koror received 2.06 inches of rain on February 28. For February, rainfall on Koror totaled 7.41 inches (78% of normal), while WSO Palau reported 10.52 inches. However, year-to-date rainfall through March 2 at WSO Koror was significantly below normal, totaling 12.50 inches (59% of normal). As a result, D0-S was retained for the Republic of Palau, pending further assessment of the effects of the recent heavy showers.
In the Federated States of Micronesia (FSM), generally wet conditions on Pohnpei, Pingelap, and Kosrae contrasted with varying degrees of dryness (D0) and drought (D1) across central and western islands. Kosrae was particularly wet, receiving 6.88 inches during the last 4 days of February and reporting a monthly sum in excess of 20 inches. February rainfall was slightly below normal on Pohnpei (8.16 inches) and Pingelap (9.10 inches), but amounts were sufficient to ward off drought concerns. Farther west, February rainfall totaled less than 4 inches at Chuuk Lagoon (2.67 inches, or 37% of normal), Lukunor (2.93 inches, or 30%), Yap (3.28 inches, or 55%), and Ulithi (3.37 inches, or 70%). Chuuk Lagoon and Ulithi remained abnormally dry (D0-S), while Lukunor and Yap retained a moderate drought (D1-S) designation. Elsewhere in the FSM, no changes were made to the depiction for Kapingamarangi (D0-S), Nukuoro (D0-S), and Woleai (D1-S); all three islands received less than 5 inches of February rainfall.
Late-February showers swept across the southern sections of the Marshall Islands, providing drought relief. February 26-29 rainfall totaled 6.45 inches on Majuro; 2.92 inches on Mili; 2.79 inches on Ailinglapalap; 1.95 inches on Kwajalein; and 1.93 inches on Jaluit. Some additional showers occurred in early March. As a result, all five island experienced improvement from moderate drought (D1-S) to abnormally dry (D0-S). Between February 15 and 28, Majuro’s reservoir storage jumped 7.04 million gallons (from 21.24 to 28.28 million gallons) – or from 59 to 79 percent of capacity. Farther north, however, severe drought (D2-S) persisted on Utirik and Wotje. Weekly rainfall totaled more than an inch only once during the first 9 weeks of 2020 on Utirik and twice on Wotje.
Despite a few recent days of mostly dry weather, there are no dryness-related concerns in American Samoa. During February, the Pago Pago International Airport received 32.73 inches of rain. However, during the February 26 – March 3 drought-monitoring period, the airport received rainfall totaling just 0.18 inch.
Virgin Islands
Generally tranquil weather prevailed across the U.S. Virgin Islands during the drought-monitoring period ending March 3. Following an unusually wet January, rainfall was much closer to normal during February, which is the heart of the Virgin Islands’ dry season. USGS wells, which in recent weeks had exhibited a response to mid-winter rains, began to show slight increases in depth to water. Most February precipitation totals across the USVI were in the 1- to 2-inch range, although spotty totals in excess of 4 inches were noted.
On St. Croix, February rainfall totaled 0.92 inch (58% of normal) at Rohlsen Airport. However, higher totals were observed at other sites, with 1.23 inches reported by a cooperative observer in East Hill; 1.91 inches noted at a University of the Virgin Islands farm; and more than 4 inches falling at Christiansted Fort. Due to low groundwater levels and other long-term impacts, a moderate drought (D1-L) designation was retained for St. Croix. Farther north, February rainfall reached 1.89 inches (137% of normal) at King Airport on St. Thomas. Meanwhile, a volunteer observer at Windswept Beach on St. John received 2.53 inches of February rainfall, slightly above the long-term mean. There are neither dryness- nor drought-related concerns on St. Thomas and St. John.
Looking Ahead
During the next 5 days (March 5-9), heavy rain will be exiting the Southeast early in the period, leaving behind an estimated 1.5 to 3 inches of rainfall. Light to moderate precipitation is forecast along coastal areas of California, the Sierra Nevada, and the Four Corners Region later in the period. This energy is expected to transition to the central Great Plains by day 5, with estimates of greater than 0.5 inches centered just west of the Mississippi River. The 6-10 day (March 10-14) extended range forecast suggests a more transient pattern over the much of the CONUS (indicated by weak height anomalies and zonal flow), favoring above normal precipitation over much of the country. Enhanced probabilities for above normal precipitation are favored during the 6-10 day period over southern California and the Four Corners Region, in association with a potential mean trough propagating eastward underneath a Pacific ridge of high pressure. Meanwhile, an active storm track is favored to remain in place across Alaska, enhancing probabilities for above normal precipitation over much of the state during the extended range.
And shifting to the Alaska and CONUS Intermediate-Term Weather Forecast
And then Precipitation
Here is the discussion that was released with the Week 3 – 4 forecast today.
Week 3-4 Forecast Discussion Valid Sat Mar 21 2020-Fri Apr 03 2020
There has been a fair bit of tropical wave activity during the past week, superimposed on an ENSO neutral background state. Convection over the western Indian Ocean projects well onto the equatorial Kelvin and Rossby wave bands, as well as the MJO. The CFS forecasts these three modes to maintain their current amplitudes and propagate throughout the next couple of weeks, although the MJO may weaken as it moves into the Central Pacific. Despite three coherent wave modes, there isn’t an obvious teleconnection between the convection over the Indian Ocean and the midlatitude wave pattern over North America.
Since the midlatitude/tropical connection is lackluster, the main source of midlatitude variability is forecast to be a particularly strong annular pattern [Editor’s Note: for those who are curious there is more information here] over the Northern Hemisphere, characterized by an anomalously strong polar jet that projects strongly onto most midlatitude teleconnections. There is likely to be a weakness over the northwest U.S., resulting in time-mean troughing over the Northwest and time-mean ridging over southwestern Alaska and most of the eastern CONUS. This is a nearly identical forecast to last week and, also like last week, is supported in both Weeks 3 and 4 by the CFS, ECMWF, and JMA.
The temperature forecast follows the predicted height pattern closely. Above normal temperatures are likely throughout the eastern two-thirds of the CONUS and the highest probabilities are found in the Northeast. There is also a 50-60% chance of above normal temperatures in northern Alaska. There is a 50-60% chance of below normal temperatures throughout southern Alaska and along the West Coast of the CONUS and parts of the interior Northwest. The eastern extent of this anomalous cold will depend on the exact position of the trough off the West Coast, which is difficult to pinpoint at this time.
The forecast precipitation pattern features above normal precipitation throughout northern Alaska and below normal precipitation along Alaska’s southern coast. Above normal precipitation is likely throughout the Pacific Northwest, although as mentioned earlier, the exact positioning of the time-mean trough will determine the eastern extent of this area. Below normal precipitation is expected underneath the time-mean ridging over the eastern CONUS, especially throughout the southern Plains and coastal Southeast. Several models, including the CFS, calibrated ECMWF, and SubX multimodel mean, suggest that shortwaves passing through the Midwest will result in above normal precipitation during the forecast period.
There is near unanimous guidance supporting above normal precipitation throughout Hawaii, especially during Week-3 but likely continuing into Week-4. The temperature forecast tilts slightly above normal for Hawaii, which is also supported by all three models.
Some may find the below way of looking at things useful and I hope these graphics are not too small to read. I did not make them so you could click on them individually but you can click on the whole graphic and it may enlarge. But I think you get the picture. It has been a rapid onset and demise. When you read these graphics, remember that the older graphics are not the drought conditions that existed then but the change from then until now.
Let’s focus on the change between February 4, 2020 and March 3, 2020, i.e. one month.
Focusing on the Intermountain West
Drought Forecasts
These two forecasts (Monthly and Season) are issued by the same agency but to obtain them you need to access two different links here and here.
Here is the Three-Month Forecast which was issued on February 20, 2020
Here is the Monthly Drought Outlook which was updated on January 31, 2020. It will be updated as a March Forecast on February 29, 2020 and we will report on it tomorrow night.
Floods
Floods remain a concern.
Last Week | Current Week |
Wildfires
Our usual graphic is not updating so we have deleted it. Bu updates from this source can be found here.
Current Wildfire Risk. This is a new model that updates daily by NOAA (but not automatically in this article) to show the short-term risk.
Click here to update. Red is high risk, blue is low risk. This graphic updates daily but you have to click on the link provided to get the updates More information can be found here.
This explains the model a bit.
The below graphics will update automatically on February 1 or so. So ignore the commentary for the time being. We will update it shortly.
Looking out another month.
Crop and Animal Husbandry Progress. USDA Executive Briefings can be found here (there are none this week). NASS reports can be found here. Foreign Intelligence reports can be found here.
There were a lot of NASS reports this week and we did not have time to prepare them for publication. A good state by state summary report was issued and you can access that here.
This shows the major reports Scheduled.
International
A map helps and is not always available and unfortunately, it was not available this week.
Major Sources of Information
In the box are shown the major resources we use. We will not be using them all each week but the reader is welcome to refer to these resources.
Major Sources of Information Used in this Weekly Report
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Background Information
The sequence of drought occurrence and impacts for commonly accepted drought types. All droughts originate from a deficiency of precipitation or meteorological drought but other types of drought and impacts cascade from this deficiency. (Source: NDMC)
Source: National Drought Mitigation Center, University of Nebraska-Lincoln