As predicted in the previous seasonal drought outlook, drought conditions expanded across much of the West Coast states as subnormal precipitation during the wet season resulted in drying soils, below-average snowpack conditions, and dropping reservoir levels.
A plume of Pacific moisture brought some late season relief to California more recently, but the latest snow water content levels across the Sierras remain below 75 percent of normal.
Further east, while frequent winter storms brought abundant moisture and periods of severe weather to parts of the central and southeastern U.S., relieving drought across parts of central Texas, drought conditions deteriorated substantially across South Texas, and pockets of drought began developing across parts of the immediate Gulf Coast.
Over the next several weeks, Pacific atmospheric-river moisture is favored to continue bringing late season precipitation to the West, though the forecast accumulations are likely insufficient to reverse the deficit that developed during the core of the wet season.
The moisture may be sufficient to stave off additional Spring degradations across southern California, but drought is favored to continue slowly expanding across central Washington, Oregon, northern California, and the Great Basin as a rapidly drying climatological regime sets in.
Across Texas, short term forecasts favor wetness along the northern and eastern extents of the current drought areas, but persistence is the most likely outcome for South Texas. Uncertainty is high, however, as May is the climatologically wettest time of year across Texas.
Further east, short term drought development is highly likely across Florida following an unusually hot Fall 2019 and limited cold front intrusions during the Winter 2019-20. The onset of the seabreeze convective regime in June may begin to ease these drought conditions at the end of the forecast period.
Finally, a lack of snow cover and decreasing streamflow values have increased vulnerability to drought development across parts of the coastal Mid-Atlantic and southern New England regions during the Spring as vegetation breaks dormancy.
Climatological precipitation is high and the seasonal guidance slightly favors above-median precipitation, so widespread long-lasting drought development isn’t anticipated, but chances for development are elevated particularly across southeastern Massachusetts, where 90-day percent of normal precipitation values are the lowest.
Forecast confidence is low to moderate for the Western Region.
- Over the past four weeks, moderate drought (D1) developed over a large portion of the Pacific Coast states, with the most rapid degradation over northern California. The gradual expansion of drought conditions was predicted on the prior seasonal drought outlook due to below-average precipitation during the core of the wet season.
- Reservoir levels across California that were well above-average at the beginning of the water year due to abundant snowpack the previous winter have decreased considerably, although they remain close to the historical average.
- Current snow water content values across the Sierra Nevadas and southern Cascades are below 75 percent of normal, despite an uptick in late season precipitation over the past two weeks. Snowpack conditions are better across the northern Cascades, although drought has expanded across Washington east of the range due to decreasing soil moisture.
- The wet pattern is favored to continue over the next two weeks, with QPF values from the latest WPC 7-day outlook of 3 to 4 inches over the highest elevations of the Sierras.
- While this precipitation in concert with unseasonably cold temperatures will provide a late boost the mountain snowpacks, these accumulations are likely insufficient to overcome the deficits that developed during the core of the wet season.
- Climatological precipitation decreases rapidly during the Spring from south to north across the West Coast, and the CPC seasonal outlook favors below-median precipitation during AMJ, which limits the potential for further relief beyond the next two weeks.
- Therefore, continued slow expansion of drought is favored for northern California, Oregon, and central Washington, albeit with reduced confidence compared to last month.
- The short term precipitation across southern California may be sufficient to delay further drought expansion through the end of June.
- Further east, unseasonably heavy precipitation across southeastern New Mexico eased drought conditions, while long term drought persisted across the Four Corners region.
- Further drought improvements are favored for northeastern New Mexico as climatological precipitation increases during AMJ, while persistence is the most likely outcome for the Four Corners region with the core monsoon season falling beyond the end of the outlook period.
Forecast confidence is moderate for the High Plains Region.
- Drought conditions over the High Plains are limited primarily to Colorado and western Kansas, as an active storm pattern brought widespread heavy precipitation to the central Great Plains, and the Northern Plains have been in winter dormancy.
- River flooding is likely to be a bigger concern than drought during the Spring across the Great Plains.
- Over the next week, abundant Pacific moisture will bring heavy snows to the central Rockies.
- As Spring progresses, climatological precipitation increases substantially across the Plains with the core severe thunderstorm season as Gulf moisture penetrates further northward.
- The AMJ seasonal outlook slightly favors below-normal precipitation across the central Rockies, but maintains equal-chances for below-, near- and above-median precipitation across the Plains. Therefore, persistence is favored for western Colorado, while drought improvement is anticipated across eastern Colorado and southwestern Kansas due to a wetter climatology.
Forecast confidence is low for the Southern Region.
- A sharp precipitation gradient was evident across the Southern Region during the Winter, with abundant moisture easing drought across north-central Texas and saturating soils further east across the Tennessee Valley contrasting with pronounced dryness across South Texas and the Gulf Coast.
- Short term drought intensified rapidly across southern Texas, where a small region of exceptional drought (D4) emerged on the latest U.S. Drought Monitor.
- The short-term forecast closely mirrors the pattern that was observed previously, with soaking rains forecast over the next week extending from eastern Texas through the Tennessee Valley that largely miss far South Texas and the north-central Gulf Coast.
- This short term rainfall may bring some relief to the northern and eastern drought areas of Texas, but little improvement is likely for South Texas until climatological precipitation increases in late Spring.
- The CPC AMJ outlook favors below-average precipitation for western Texas.
- Based on these outlooks, drought persistence is the most likely outcome for South Texas, with some improvements further north and east. This is a highly uncertain forecast, as periods of rainfall during May could improve the drought situation, while any lack of rainfall would spark a return of drought to areas that were ameliorated early in the outlook period.
Forecast confidence is moderate to high for the Southeast Region.
- The precipitation gradient mentioned in the above discussion for the Southern Region extended eastward into the Southeast Region, with 90-day precipitation accumulations exceeding 200 percent of normal across the Piedmont regions contrasting with below-average rainfall across most of northern and central Florida.
- Below-average precipitation was also observed across northern Virginia, which is a southward extension of a dry signal across the Northeast that will be discussed in the next section.
- April is a dry time of year for Florida, as cold fronts fail to penetrate that far south and the seabreeze driven wet season begins later. Given the pronounced winter dry signal following an abnormally hot Fall, a Spring drought ahead of the summer thunderstorms is quite likely across much of the state.
- Therefore, development is indicated on this outlook, even though the seasonal outlook tilts slightly towards above-median rainfall. Once the seabreeze convection regime begins in late May and June, the drought conditions will likely ease, but drought impacts from April may linger through much of the outlook period.
Forecast confidence is low for the Northeast Region.
- No drought is currently in place across the Northeast Region, but widespread abnormal dryness (D0) has begun to develop, extending from eastern Pennsylvania through southeastern New England.
- 90-day precipitation amounts were well below-normal extending from northern Virginia through eastern and central New England, and 28-day average streamflow values were generally below-normal as well. Drying brush and topsoils have resulted in scattered brushfire activity.
- Additionally, snow cover is notably absent across much of the Northeast, with deep snow cover currently limited to Maine and the higher elevations of the Adirondack, Green and White Mountains. This reduces a typical source for Spring recharge in addition to new precipitation.
- Based on these factors, the Northeast is vulnerable to drought development should there be a period of abnormally warm or dry weather during the next several months.
- Confidence for drought development is low, however, due to a fairly generous precipitation climatology and a slight tilt towards above-median precipitation favored by the CPC seasonal outlook. Therefore, while drought development has the potential to be more extensive than indicated on the outlook, the most likely area for development shown is across southeastern Massachusetts, where precipitation deficits are the largest.
Forecast confidence is high for Hawaii.
- Drought conditions have gradually eased across Hawaii. The CPC seasonal outlook favors above-median precipitation during the period. Therefore, continued drought reduction is the most likely outcome.
- There is no current drought indicated on the USDM for Alaska and Puerto Rico, and drought is not favored to develop through the end of June.