Tools used in the U.S. Monthly Drought Outlook (MDO) included the updated Climate Prediction Center (CPC) temperature and precipitation outlooks for May, various short- and medium-range forecasts and models such as the 7-day quantitative precipitation forecast (QPF) totals from the Weather Prediction Center (WPC), the 6-10 day and 8-14 day CPC extended-range forecasts (ERFs), the Week 3-4 CPC forecasts released on April 28, CFSv2 monthly forecasts of temperature and precipitation, the 384-hour total precipitation forecasts from several runs of the GFS, climatology for May, and recent precipitation. The April 25 U.S. Drought Monitor (USDM) was used for existing drought areas (D1 or drier) in the MDO. 

ENSO-neutral conditions are favored to continue through at least the Northern Hemisphere spring 2017, with increasing chances for El Nino development by late summer and fall. To be consistent with the U.S. Drought Monitor, narratives will use the NCEI region definition (Northeast, Southeast, Midwest, South, High Plains, and West), with outside CONUS states (AK & HI) and territory (PR) grouped together.

In the West, small areas of D1 and D2 were limited to southern sections of California with lingering hydrologic concerns (some below-normal reservoirs and low ground water) as this Water Year precipitation was not quite as bountiful here as it was in the rest of the state and the West. As of April 28, Snow Water Content (SWC) across the Sierras still ranged between 182-200% of normal, or a statewide average of 194%. This should allow for a long and favorable spring and summer snow melt and runoff for California's rivers and reservoirs barring any protracted major heat wave or unseasonably heavy rain event. But given that the climatological dry and warm season normally starts in April (although April has been wet and cool in the northern half of the state) and intensifies during May, no drought relief is anticipated for these lingering drought areas (even though the ERFs show slight odds for above-median rainfall). The same is true for southwestern Arizona where moderate drought is currently depicted.
Forecast confidence for the West (southern California and Arizona) is high.

In the High Plains region, the past 30-days have generally been wetter than normal, allowing for an overall improvement of drought in Wyoming, South Dakota, Nebraska, Colorado, and Kansas. As of April 25, a few small areas of drought (D1) lingered in northeastern Wyoming, north-central and southeastern Colorado, and southwestern Nebraska. Since 12Z April 25, however, additional precipitation, including heavy snow at some locations, fell on these aforementioned areas, and with a favorable May climatology (12-20% of annual precipitation) and most outlooks tilting toward above-median precipitation during this typically wet month, odds greatly favor removal of the remaining moderate drought areas.
Forecast confidence for the High Plains (central High Plains) is moderate (CO) to high (WY & NE).

After a warm and windy late winter and early spring, drought rapidly expanded across the Southern region (southern Plains and lower Mississippi Valley). Since late March, however, rains have inundated this area, bringing broad-brushed improvement. In addition, heavy precipitation has occurred after the 12Z April 25 USDM cutoff, and with more rain forecast by the QPF in early May, the remaining D1 in eastern Oklahoma, western Arkansas, and northwest Louisiana is primed for removal - even though the ERFs favor toward submedian precipitation. But the recent wet trend and precipitation which has fallen and is expect to fall in early May - should be enough for D1 removal that should hold to the end of May. An exception to this was a very small D1 area in extreme southern Texas where all but the Weeks 3-4 outlook (wet) tilted dry or EC. With no clear-cut odds for above or below median rainfall, persistence was left.
Forecast confidence for the South region is moderate (southern TX) to high (OK/AR/LA).

Precipitation during the past 30-days has been a mixed bag across the Southeast, with surplus rains falling on western and northern sections while southern and eastern areas were below normal. Temperatures averaged well above-normal, with 30-day departures of +3 to 7 degF. As a result, USDM improvements were made during the past 4-weeks across northern sections of Mississippi, Alabama, and Georgia, eastern Tennessee, throughout the Carolinas, and southern Virginia. In contrast, deteriorations occurred in southern sections of Alabama and Georgia and central Florida. With heavy rains limited to western and northern sections in early May (QPF), but then drier conditions for the Southeast favored by the ERFs and Weeks 3-4, continued improvement to western and northern areas is probable, while persistence and drought development of existing D0 is likely. An uncertainty is that the wet season in Florida typically starts in late May, so if the onset is early or even on time, some improvement is possible for the state. With the Week 3-4 outlooks for May 13-26 EC for Florida, there is no obvious answer to the start of the wet season.
Forecast confidence for the Southeast is moderate.

Across the Northeast region (New England and mid-Atlantic), the past 30-days have brought near to above normal precipitation and above normal temperatures. In New England, a slow but gradual improvement to the long-term drought and hydrologic conditions has occurred this year, with only a small D1 area left in Connecticut. In the mid-Atlantic the drought is of shorter term, with some D1 left in Pennsylvania, Maryland, and northern Virginia. With the QPF predicting 2.5-4 inches of rain across the Northeast and the 6-10 day ERF with enhanced precipitation chances and subnormal temperatures, the wet trend and drought amelioration should continue during early May and last until month's end across the Northeast.
Forecast confidence for the Northeast (New England and mid-Atlantic) is moderate to high.

In Hawaii, the onset of the dry season usually occurs in late spring, meaning that the odds for heavy rains are unlikely in May. With drought present in the leeward side of the Big Island and on central Maui, and with no guidance from the monthly outlook (EC), persistence was drawn for the existing drought areas. In Alaska, no development was introduced in the existing D0 areas across southern sections as May is still somewhat climatologically dry (wet Jun-Sep), and both ERFs favored above median precipitation statewide. No D0 existed on Puerto Rico, and with the onset of its rainy season, no development is anticipated.
Forecast confidence for Hawaii is moderate.


Forecaster: David Miskus


Next Monthly Drought Outlook issued: May 31, 2017 at 3pm EDT