During the past month, enhanced rainfall along a persistent mean frontal boundary draped along the eastern US resulted in substantial drought relief across the Southeast and mid-Atlantic states, although patches of drought remained, particularly across the coastal plain of Georgia and South Carolina.
In contrast, outside of a swath of heavy precipitation from a late season snowstorm along the Iowa/Minnesota border through southern Wisconsin, precipitation was well below average across the northern Plains and western Corn Belt, resulting in an eastward expansion of abnormal dryness (D0) conditions. Temperatures in this region remained well below average for the time of year, which helped to slow the advancement of more severe drought conditions.
As spring transitions to summer, however, these dry incipient conditions leave this region vulnerable to flash drought development should an extended period of hot, dry weather occur. Across the West, drought conditions persisted or expanded slightly under a general regime of above-normal temperatures and subnormal precipitation.
During the next two weeks, a highly active pattern is anticipated across almost the entire contiguous U.S. outside of the climatologically arid Southwest, with the heaviest precipitation over the central and northern Plains, the Southeast, Mid-Atlantic, and southern New England.
The wet conditions favor further drought reductions across the East, and given that both subseasonal and seasonal-scale forecasts favor continued wetness through the JJA period, complete drought removal is forecast by the end of the period. The wet short term forecasts coupled with climatology favor some relief of the most extreme drought conditions across the central Plains, but the absence of a clear wet signal in this region makes full amelioration of the entrenched long-term drought conditions unlikely.
Over southern Texas, a somewhat drier pattern is anticipated over the next two weeks, and climatological precipitation drops off during the summer. Therefore, drought persistence and expansion is favored. Over the West, seasonal guidance favors below-median precipitation for the Northwest, favoring persistence and slow expansion given the drier climatology.
Despite the anticipated onset of monsoon thunderstorms over the Southwest during mid-summer, dry initial conditions including a lack of snow cover, a potential for worsening drought in the short term, and the absence of a clear wet signal in the seasonal guidance makes persistence more likely at any given location than improvement.
No drought conditions currently exist across Alaska, Hawaii, and Puerto Rico, and drought development is unlikely in these regions over the next three months.
Forecast confidence for the Southeast and Mid-Atlantic is high.
- During the past 30 days, anomalous troughing over the Plains and Mississippi Valley regions led to frequent periods of above-average rainfall and temperatures across the Southeast due to southerly flow ahead of the frequent frontal systems.
- The enhanced rainfall resulted in widespread improvements to drought conditions across the Southeast and mid-Atlantic states, although pockets of drought lingered across parts of Florida, southeastern Alabama, and the south Atlantic coastal plain, as above-normal temperatures counteracted the generally favorable precipitation regime.
- Over the next 7 days, southerly flow, including an embedded tropical disturbance, is expected to result in widespread heavy rainfall, with accumulations ranging between 1.5 and 5 inches across much of the Southeast, Mid-Atlantic, and southern New England. The wet pattern is forecast to continue during Week-2 based on the CPC 8-14 day outlook, and both the monthly and seasonal outlooks depict enhanced chances for above-normal precipitation.
- Based on the wet guidance from the short term through the seasonal periods, removal of the remaining drought areas across the eastern CONUS is favored.
Forecast confidence for the Northern Plains, Middle and Upper Mississippi and Ohio Valleys and the Great Lakes region is low.
- Since last month, outside of a late season winter storm that brought a heavy swath of snow to northern Iowa, southern Minnesota, southern Wisconsin and southern Michigan, generally drier conditions prevailed across the northern Plains. Temperatures ranged much below normal during this same period, which helped to slow the expansion of impacts. Still, abnormal dryness (D0) crept eastward across the upper Midwest.
- 30-day percent of normal precipitation values were also low (below 50 percent) across much of the Corn Belt, although the wet winter conditions and cold spring kept impacts at bay outside of longer term drought conditions across northern Missouri and southern Iowa.
- Due to the dry initial conditions, these regions are at increased risk for flash drought development during the summer months if periods of hot, dry weather develop.
- The WPC 7-day forecast, however, depicts widespread heavy rainfall across the region, with the heaviest accumulations (1.5 to 2.5 inches) over parts of the Dakotas and northwestern Minnesota. The CPC 8-14 day outlook favors enhanced precipitation across the Northern Plains and Corn Belt region as well, which should help mitigate the recent dryness.
- The monthly outlook maintains equal chances for below-, near-, and above-normal (EC) precipitation, while the seasonal outlook slightly favors above-normal precipitation across the central and eastern Corn Belt. The seasonal temperature guidance maintains EC.
- Based on these outlooks, no drought development is forecast for the northern Plains or Corn Belt, and drought reduction is forecast for areas receiving heavier precipitation in the short term.
Forecast confidence for the Central and Southern Plains is moderate.
- Widespread extreme (D3) to exceptional (D4) drought conditions persisted across North Texas, western Oklahoma, and southwestern Kansas as of the May 15 U.S. Drought Monitor released on May 17. Although the drought is characterized as short term based on 12-week precipitation deficits of 4 to 12 inches, the annual deficits in this region are also quite high.
- Over the next 7 days, widespread heavy rainfall is forecast over North Texas and west-central Oklahoma. In contrast, little precipitation is expected to fall across southern Texas. Drier conditions are favored over the Southern Plains during Week-2, and both the CPC monthly and seasonal outlooks maintain EC for precipitation across the region.
- Above-normal temperatures are favored during the monthly and seasonal periods, which would promote high evapotranspiration rates and reduce the opportunity for soil moisture recharge during the period.
- Based on the short term forecast and a wet climatology, improvement of the worst drought conditions is favored for eastern New Mexico, North Texas, western Oklahoma, Kansas, and eastern Colorado, but drought conditions are likely to remain throughout the period.
- Drought development is forecast for southern Texas, due to drier conditions forecast through the end of the month, which is a climatologically wet time of year.
Forecast confidence for the Central and Southern Rockies, Southwest, Great Basin, and California is moderate.
- Widespread drought conditions continue to persist over the Four Corners region, southern Great Basin, and southern California. Monsoon convection begins to pick up in July, and the JJA period is a wet time of year climatologically for Arizona and New Mexico, while a dry climatology continues for much of California.
- The CPC seasonal guidance does not depict an enhanced early monsoon pattern, with EC favored across southeastern California, Arizona, and New Mexico. Some tools do depict wetness further north, and the CPC seasonal outlook shows enhanced chances for above-normal precipitation across the central Rockies.
- Despite the monsoon climatology, a lack of snow cover on the southern Rockies, hot, dry weather anticipated over the next two weeks, and high probabilities for above-normal temperatures at the monthly and seasonal time scales make substantial improvements less likely.
- It is also possible that drought will continue to intensify ahead of the start of monsoon convection. Therefore, persistence is indicated in this outlook outside of a small region of eastern Utah and western Colorado where the CPC seasonal outlook has a greater than 40 percent chance of above-median precipitation.
- Due to the monsoon, however, there may be spotty areas of localized improvements within the broader persistence regime.
Forecast confidence for the Northern Intermountain West is moderate.
- Below-normal precipitation and above-normal temperatures promoted drought persistence across central and eastern Oregon and far southwestern Idaho. The JJA period is a climatologically dry time of year for the Northern Intermountain West, which reduces the opportunity for significant drought reduction.
- Short term forecasts do show substantial precipitation across the drought areas, which may ameliorate drought conditions temporarily, but the CPC monthly and seasonal outlooks both depict enhanced chances for below-normal precipitation and above-normal temperatures, which favors persistence through the end of August.
- Slight northward expansion of drought conditions where it is already abnormally dry is also possible.
Forecast confidence for Alaska and Hawaii is high, and moderate for Puerto Rico.
- There is currently no drought depicted for Alaska, Hawaii, and Puerto Rico.
- The CPC seasonal outlook favors above-normal precipitation for Alaska and Hawaii. Although a developing warm event over the equatorial Pacific tends to favor suppressed convection across the Caribbean, the summer months are climatologically wet across Puerto Rico, and drought development is not anticipated.