NOAA Updates The Outlook For April 2020 – Major Changes For The West

Written by Sig Silber

At the end of every month, NOAA issues an update to their Early Outlook for the following month, in this case, April 2020, which was issued on the Third Thursday of the month just finished. Today, twelve days later, NOAA has issued their updated Outlook for April. The changes are significant especially for the western part of CONUS. But the overall forecast is wetter so the drought situation is pretty much stable at the current good level except for Florida which is anticipated to be dry.

Some housekeeping: On March 21, 2020, we published Part I of our analysis of the NOAA and JAMSTEC Three- to Four- Season Outlook and that can be accessed here. In that report, the April 2020 Early Outlook was issued. This article presents the NOAA update of their Early temperature and precipitation Outlook for April and the most recent Drought Forecast update for the month of April.

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Now let us address the NOAA Update of the April 2020 Forecast.

First, we will compare the NOAA Early Outlook for April 2020 with the newly issued update.

Early Outlook Temperature

Updated Temperature Outlook

Early Outlook Precipitation

Updated Precipitation

Here is the discussion released today:

30-DAY OUTLOOK DISCUSSION FOR APRIL 2020

The updated outlooks for April are largely similar for the eastern CONUS and Alaska, but reflect substantial changes for the western CONUS. The outlooks make use of shorter term forecasts from WPC, the Week-2 guidance from CPC, Week-3/4 guidance from CFS and ECMWF, and monthly guidance tools based on model combinations. The outlooks also reflect a small bit of contribution from MJO, as the signal has emerged over the Maritime Continent. Some small, MJO-related signals that meet significance testing thresholds, indicate a mid-month flip in temperatures over the eastern CONUS. The AO is predicted to be positive through the first half of the month, and there is little reason to forecast a major change for the second half of the month, so progressive solutions are favored.

With respect to temperatures, model outlooks have strong signals for the first 2-weeks of the month for below normal temperatures over the western CONUS and above normal temperatures over the eastern CONUS. Those signals are likely to moderate in the latter half of the month. ECMWF guidance for the second half of the month is more progressive than that in the CFS, which maintains a more amplified pattern and colder temperatures for much of the CONUS. The official outlook is warmer than CFS guidance, based on guidance through Week-2 and the uncertainty from the ECMWF during the latter half of the month. Across Alaska, a predicted cold start to April favors below normal temperatures for the month over southeastern Alaska and the Alaska Panhandle. Sea surface temperatures have risen quickly while sea ice extent has dropped rapidly during March over the Bering Sea, so that would favor above normal temperatures for the western Alaska.

For precipitation, the first week of April is forecast to be quite wet for portions of central and southern California and the southern Plains, where some locations are predicted to receive more precipitation in one week than what defines the bound for the lower tercile. Model outlooks for the latter half of April differ significantly for the Southeast, with the most overlap in signals for above normal precipitation from the lower Mississippi Valley to the Southern Appalachians, pulled away from the Gulf Coast. The Ohio Valley and and Lower Great Lakes are an area of high uncertainty, as the month is forecast to start dry, then turn slightly wetter through Week-2, followed by a period of elevated uncertainty. Predicted mean ridging south of Alaska would steer storms northward and into central mainland Alaska, favoring above normal precipitation for northern Alaska, and below normal precipitation for southern mainland Alaska and the Alaska Panhandle.

Visual Consistency Testing.

It is useful to see how the full-month forecast fits with the set of partial-month forecasts that we have. These will continue to update in this article. It is important to remember that with the partial-month forecasts, we generally have about 25 days of the subsequent month to look at when we do this at the end of the month as we are doing now. It depends on what day of the week the month ends. So this month, which ended on a Tuesday, we are missing a forecast that includes the last six days of the month. So we are in good shape for the visual consistency testing this month. On Friday when we have the complete picture, we may update the commentary in this article.

First Temperature

The new monthly forecast is to the right. Does it appear to be reflective of the four parts of the month for which we have forecasts? →			↑ ← The Week 3 – 4 forecast was updated Friday so we may want to update the commentary when the Week 3 – 4 update is reissued on April 3, 2020. At this point, we have forecasts for 25 days of the 31 days in April and the fit looks pretty good. But there are questions about the last week of the month that we are not able to answer just yet in this section of the report. .

And Precipitation

The new monthly forecast is to the right. Does it appear to be reflective of the four parts of the month for which we have forecasts? →			↑ ←The Week 3 – 4 forecast was updated Friday so we may want to update the commentary when the Week 3 – 4 update is reissued. At this point, we have forecasts for 25 days of the 31 days in April and the fit looks pretty good. But there are questions about the Southwest dry anomaly so we will be interested in the updated Week 3 – 4 Forecast to be issued this Friday.

Because the end of the month forecast was issued on a Tuesday, we see no point in publishing the prior Week 3 – 4 Discussion as the monthly discussion is a lot more current.

Since the forecast discussion mentioned the Arctic Oscillation (AO), I thought it useful to show the history and forecast of the AO.

You can see the impact of the different phases in the schematics below (Source: N.C. State Climatologist). PNA Positive in on the left and PNA Negative on the right. PNA Negative is a pattern that is more westerly located than PNA Positive. This has to do with storms entering CONUS in the Northwest and then moving south either closer to the coast or further inland.

………………………..PNA Positive…………………………….. PNA Negative……………..

PNA Negative kind of conflicts with a strong ridge of High Pressure in the Gulf of Alaska but it depends on the location of the Ridge.

Forecasts for these indices and others are always in the Addendum of the LIVE Current weather and forecast article for readers and these forecasts auto-update ( I have not frozen them in this article either).and for those with an interest in more detail, the WEATHER CONTINUALLY LIVE article allows one to access current NOAA Warnings and details associated with those warnings. To read the current version of the WEATHER CONTINUALLY LIVE article, go to the DIRECTORY and click on the version of LIVE which is at the top of the stack.

Impact of the MJO.

In the Directory of the WEATHER CONTINUALLY LIVE Article there is a link to the MORE WEATHER Addendum which basically has what we used to publish on Mondays but with no commentary. But all the graphics are there. So sometimes I use them in the LIVE article or in this case in the End of Month Article. But readers are welcome to visit that page at any time.

Current Location and Forecast Models.

There are a lot of models and I try to read the results from all of them. For access to a variety of models, I refer readers here. Now the first of the three graphics we typically present which shows where the MJO is now and how it got there.

This shows recent history. What next? Please read the MJO Summary carefully. You will have to use the link provided above to obtain the summary as it does not auto-update.

And then a forecast. On this GFS graphic, the light gray shading shows the tracks which fit with 90% of the forecasts and the dark gray shading shows a smaller area that fits with 50% of the forecasts The large dot is the current location.

And then the ECMF forecast.

Then side by side to see if they agree.

Sometimes it is useful to compare the three-month outlook to the forecast for the first of the three months. It shows how much the pattern changes over the three-month period.

One can mentally subtract the First-Month Outlook from the Three-month Outlook and create the Outlook for the last two months in the three-month period.

And with respect to drought, this was also issued on March 31, 2020.

Discussion for the Monthly Drought Outlook

Tools used in the U.S. Monthly Drought Outlook (MDO) include the Climate Prediction Center (CPC) temperature and precipitation outlooks for April, 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 Weeks 3-4 outlooks and tools from CPC, dynamical models at the monthly time scale, the 384-hour total precipitation forecasts from several runs of the GFS, and April climatology. Initial conditions are based on the March 24, 2020 U.S. Drought Monitor released on March 26, 2020. ENSO-neutral conditions are present albeit with warm equatorial SST anomalies across the central Pacific, and recent MJO activity may play a role in the evolution of the tropical convective pattern and any subsequent tropical-extratropical teleconnections.

Drought conditions gradually worsened across the Pacific coastal states and Great Basin during March following a lackluster core of the wet season, although a late season surge of moisture brought some limited improvements to parts of the Sierra Nevadas and southern Great Basin. Following this late season storminess at the end of March, long range forecasts issued prior to the April – June 2020 seasonal drought outlook (SDO) depicted a return to drier conditions to end the wet season. Therefore, gradual drought expansion was favored across the West and Great Basin through the remainder of the Spring and early Summer. More recent forecasts have shifted the pattern considerably, however, and now depict a continuation of the late season moisture surge that began in late March, with troughing bringing below-normal temperatures. In particular, the 7-day QPF from WPC shows a heavy precipitation event across coastal northern California northward to Washington, with heavy snowfall across the Cascades and to a lesser extent the Sierras. This late season moisture boost may bring some drought improvement to the coastal areas of extreme northern California and Oregon as well as the Oregon Cascades. Further south, continued low snowpack conditions and lower accumulations limit the potential for late season improvements across the Sierras, but some improvement to ongoing drought conditions is possible for northeastern Arizona. Due to the unsettled weather and below-normal temperatures expected during the first half of April, no additional drought development is anticipated across the Pacific coastal states or Great Basin. Further east, dry weather has predominated across northeastern New Mexico, and the first half of April is anticipated to remain almost completely dry. Therefore, slow drought expansion is favored across northeastern New Mexico.

Forecast confidence is moderate for the Western Region.

Drought conditions persist across parts of Colorado, western Oklahoma, and western Kansas, as heavier precipitation missed this region both to the north and the south. April weather conditions can be quite variable across the Plains, as moisture surges from the Gulf of Mexico alternate with late season cold pushes from Canada, often resulting in severe weather outbreaks. The updated April monthly outlook from CPC favors above-median precipitation across the northern Plains, while near to below-median precipitation is favored during the first half of the month across southeastern Colorado and southwestern Kansas. Therefore, slight drought expansion may occur across southwestern Kansas, but no additional drought development is anticipated across the High Plains Region.

Forecast confidence is low for the High Plains Region.

Developing storm systems associated with an active southern stream brought heavy precipitation and drought relief to parts of central Texas and southwestern Oklahoma, while persistent dryness aggravated the substantial short term drought conditions across South Texas. Precipitation also largely missed the immediate Gulf Coast, resulting in drought expansion across parts of Louisiana. During early April, the active storm pattern is favored to continue, with a southward shift bringing widespread heavy rainfall to southeastern Texas and the central Gulf Coast. Due to the short term nature of the drought conditions, this forecasted wetness should be sufficient to alleviate drought across parts of Texas and the central Gulf Coast. The CPC 8-14 day and updated April outlooks favor a continuation of the wet pattern across eastern Texas and the Gulf Coast, bringing higher confidence for this improvement. Elsewhere, ongoing Spring thunderstorm activity is anticipated to remove drought across southern Oklahoma, while drier conditions further west may promote drought expansion across the far northwestern Texas Panhandle and western Oklahoma Panhandle, similar to the situation in northeastern New Mexico.

Forecast confidence is high for the Southern Region.

No drought is currently in place across the Midwest Region, and no drought development is anticipated. River flooding is likely to be a greater concern for the Midwest than drought during the Spring.

Forecast confidence is high for the Midwest Region.

The mean storm track during March strongly favored excessive wetness across the Tennessee and Ohio Valley regions, with below-normal precipitation observed along the Gulf Coast and much of Virginia. In particular, much below-normal rainfall and hot conditions prevailed across Florida, resulting in a rapid increase of Keetch-Byram Drought Index (KBDI) values across southern Florida, with some moderate drought (D1) developing over interior Southwest Florida. During early April, the 7-day QPF from WPC shows the potential for a wide swath of heavy rainfall along the Gulf Coast, with the 8-14 day ERF and updated April monthly outlooks from CPC continuing the wet pattern. However, the tools maintain a sharp precipitation gradient along the Florida Panhandle, with much less rainfall anticipated across the Peninsula. Abnormally hot conditions are favored to continue across Florida and parts of the Southeast during April as well. Therefore, drought development is forecast for most of the Florida Peninsula. Parts of Virgina may also be susceptible to drought development, but rainfall during the first half of April is anticipated to be adequate to prevent substantial degradation of soil moisture conditions, and the updated April outlook maintains equal chances for below-, near-, and above-median precipitation.

Forecast confidence is high for the Southeast Region.

Late season snowpack conditions remain well below normal across New England, and 30-day percent of normal precipitation ranges generally between 50 and 100 percent across Maryland and much of New England, while moisture conditions are better across western Pennsylvania and the Canadian border region. A late month Nor’easter brought a boost of moisture to southern New England, where precipitation deficits were previously the highest. The updated monthly outlook from CPC shows no tilt towards abnormal dryness. Therefore, while the region remains susceptible to drought development during the Spring and early Summer, drought development is not anticipated to occur during April.

Forecast confidence is moderate for the Northeast Region.

A persistent midlatitude cyclonic circulation west of Hawaii has promoted surges of tropical moisture, resulting in widespread flash flooding and severe weather, particularly across the western islands. An ongoing Maritime Continent MJO event teleconnects to a continuation of this pattern early in the month. While continued MJO activity may flip the pattern later in the period, the recent extreme precipitation and anticipated continuation of the wet pattern in early April favor continued drought reduction for Hawaii, and no additional development.

Forecast confidence is high for Hawaii.

Looking back on March to relate the forecast for April to the actuals in March.

First March Temperature (30 out of 31 days).

And then March Precipitation (30 out of 31 days).

We then show the new forecast and the prior month actuals (less one day) side by side.

Conclusion

The purpose of this article was to present the updated Outlook for April 2020 and compare it with the Early Outlook. It is not to critique the updated Outlook for April based on our opinions but we point out possible inconsistencies if we find them. We have assessed the extent to which the monthly outlook seems to fit with the other forecasts provided by NOAA. In reality, all forecasts are obsolete when issued as the situation changes day by day or six hours by six hours i.e. each new model run. In our other articles, we continually examine the current forecasts from NOAA including the Day 1- 5, 6-10, 8-14 and Week 3 and 4. So we are continually looking at approximately 25 days into the future.

On April 9, 2020, IRI/CBC will issue their ENSO forecast and we will present that and critique it. It is an ongoing process and we attempt to provide our readers with the best current assessment of the next approximately 25 days (except when we cover the Four-Season Analysis or medium-frequency cycles such as ENSO), so our analysis is pretty much ongoing. We also publish a “LIVE” Weather Article which updates in real-time to reflect NOAA Weather Headlines and for those interested provides detailed information down to current warnings in place. All of our reports including past versions of these reports can be located via the Directory/Archive which can be accessed here.