Tools used in the U.S. Seasonal Drought Outlook (SDO) include the Climate Prediction Center (CPC) temperature and precipitation outlooks for May 2020 and May-June-July (MJJ) 2020, various short-range 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 Weeks 3-4 outlooks and tools from CPC, dynamical models at the monthly and seasonal time scales, climatology for the MJJ season, snow cover, soil moisture, streamflow values, and initial conditions. ENSO-neutral conditions are favored to remain at least through boreal summer.

Across the Western states during the past 14-days, precipitation amounts ranged between 0.5-3.0 inches for the Cascades, the Coastal Range of the Pacific Northwest, and portions of the Rockies. Amounts in central and southern California were greater, ranging from 2-6 inches (locally higher) across the Sierras and coastal mountains. Northern Nevada generally received a half-inch of precipitation or less, while southern portions of the Silver State observed amounts between 0.5-1.0 inch. These slightly elevated precipitation totals were also noted in the mountainous terrain of central and north-central Arizona and New Mexico. Some of the drier locations included the rain-shadow area of central and eastern Washington, and the Four Corners region, which saw precipitation amounts that ranged from zero up to a half-inch. In terms of Percent of Normal Precipitation (PNP), the southern third of California received the lion's share with 4-6 times (locally greater) their normal precipitation for the period. This was due to a series of late-season storms that rolled across the state from the Pacific, accompanied by heavy rainfall at lower elevations. Snow fell at the higher elevations, adding to the seasonal snowpack. The PNP pattern decreased farther north, with central California seeing PNP values of about 2-3 times their normal precipitation, and northern California primarily 25-75 percent of normal. Elsewhere, PNP values fell within the driest quarter of the historical distribution in Washington state (outside of the Cascades), the Four Corner's region, much of Utah, southern Wyoming, and approximately the southern one-third of both Arizona and New Mexico. As of April 14th, SNOTEL basin-averaged Snow Water Content (SWC) was generally near to above average across the West (75-150 percent of average, the Sierras being on the low end), with the exceptions of Arizona (mostly 25-75 percent of average) and New Mexico, where one-half of the reporting stations are at or below the 25th percentile, and the other half between 25%-90%.

Precipitation across the West during the upcoming week is predicted to be light (less than 0.5-inch) for the valleys and lower elevations, with orographic enhancement leading to somewhat higher amounts (0.5-1.0 inch, liquid equivalent) for the mountainous regions. Little to no precipitation is expected in Arizona, New Mexico, or to the lee of the Cascades in Washington and Oregon. During week-2, near to above normal precipitation is forecast across the West. CPC's May precipitation outlook favors Equal Chances (EC) of below, near, and above normal precipitation for most areas, with two exceptions. The first exception is the Pacific Northwest, where relative dryness is favored. The second exception includes parts of the Central Rockies, where odds modestly favor above normal precipitation. The May-Jun-Jul (MJJ) precipitation outlook favors below normal precipitation across the northwestern CONUS, and EC for remaining areas. This is consistent with the onset of the dry season across most of the West starting in May, and with the climatological onset of the monsoon in late June/early July. Therefore, drought persistence is indicated for the current drought areas depicted across the West. For the Sierras, Water-Year-To-Date precipitation (since Oct 1, 2019) is running well below average, with deficits of about 12-20 inches. SWC values are near 70-80 percent of average. In addition, warm, dry conditions anticipated in MJJ support new drought development for this area, as well as northwestern Nevada, eastern Oregon, and much of Washington state.

Forecast confidence for the West is moderate to high.

During the past 14-days over the High Plains region, moderate precipitation (0.5-2.0 inches) fell across most of the Northern Plains, except near the border between Montana and North Dakota, where measured amounts were less than 0.5-inch. Most of Kansas and Nebraska had little to no precipitation. Departure from Normal Precipitation (DNP) over the past two weeks ranged from 1-2 inch deficits in eastern Kansas and eastern Nebraska. A precipitation surplus of 0.5-1 inch was noted in central and eastern North Dakota.

Up to an inch of precipitation is predicted across the region during the next week, with slightly more possible in eastern Kansas. The Week-2, May, and MJJ precipitation outlooks from CPC all favor above normal precipitation, and generally near to above normal surface temperatures. Given the outlooks, as well as a wet MJJ climatology, there is little reason to go with developing drought at this time. However, this region is prone to flash droughts, which by definition develop quickly, and will need to be monitored in the weeks and months ahead.

Forecast confidence for the High Plains region is moderate.

Moderate precipitation (0.5-2.0 inches) fell across the Midwestern states over the past two weeks, with 2-3 inch totals (locally greater) observed in eastern Kentucky and Ohio. This resulted in rainfall surpluses of 1-3 inches in these two states. In contrast, rainfall deficits of 1-2 inches were noted over much of the Middle Mississippi Valley. Soil moisture anomaly change over the past two weeks reveals soil moisture values have diminished by 0.5-1.5 inches over much of the Midwest.

During Week-1, northern portions of the Midwest are forecast to receive little if any precipitation. Southern portions of the Midwest, however, are predicted to receive up to 1.5-2.0 inches of precipitation. Below to near normal temperatures and above normal precipitation (albeit with modest probabilities) are favored over the Midwest during Week-2 period. CPC's 30- and 90-day outlooks favor elevated odds of above normal rainfall. As was the case with the High Plains region, given favorable precipitation outlooks and MJJ climatology, there is little reason to go with developing drought at this time. However, this region is also prone to rapidly-developing flash drought, and will need to be under careful surveillance in the weeks and months ahead.

Forecast confidence for the Midwest is moderate.    

Across the South, heavy precipitation totals (2-5 inches) were observed over the last 14-days from central Texas generally northeastward across the Arklatex region, most of Arkansas and Tennessee, and the northern half of Mississippi. This wet period is attributed to plentiful low-level Gulf moisture, active baroclinic zones, mid-level disturbances, and severe weather. In contrast, less than a half inch of rain fell across western and northern Oklahoma, and West Texas. Remaining areas of the South saw rainfall totals in the moderate range (0.5-2.0 inches). During the past two weeks, 1-2 inch rainfall deficits were noted in north-central Oklahoma, parts of Louisiana, and southern portions of Mississippi.

A review of precipitation outlooks for time periods of one-week to one-season in advance shows that all agree on the more significant precipitation amounts falling over eastern portions of the Southern region, with little to none across the Oklahoma/Texas Panhandle region. The MJJ seasonal outlook favors above normal rainfall from most of Oklahoma and eastern Texas eastward across the Lower Mississippi Valley and Tennessee. Based on the various rainfall outlooks and favorable climatology, the current drought areas in the Southern Region are expected to either improve or be removed.

Forecast confidence is considered moderate across the South.

Precipitation amounts generally ranged from 2-6 inches over the Central and Southern Appalachians and adjacent Piedmont region, the coastal Carolinas, and southern portions of Alabama and Georgia during the past 14-days. This was due in large part to the very recent passage of an energetic spring storm that featured back-to-back cold fronts and strong upper-level support. Most other areas of the Southeast region reported 0.5-2.0 inches of rain. The only place that observed less than a half-inch of rain was parts of southern Florida. This area has been very dry and hot in recent weeks, which is typical of the latter part of their dry season. The areas that received the heavier rainfall amounts noted earlier in this paragraph registered surpluses of 0.5-3.0 inches. Most remaining areas of the Southeast Region had close to normal rainfall for the two-week period.

Nearly all outlooks, from one week to one season in advance, favor at least a slight tilt in the odds towards above normal precipitation across the Southeast. Given these official outlooks, and the fact that Florida's climatological rainy season begins soon (it's usually in place statewide by late May or early June), a one-category improvement is favored, meaning either improvement or removal of drought areas for the Southeast.

Forecast confidence is moderate to high across the Southeast.

In the Northeast region, 2-4 inches of precipitation fell from the Central Appalachians northeastward across eastern Pennsylvania, New Jersey, Long Island, and New England. Parts of southern Maine and adjacent New Hampshire received 5 inches of precipitation during this period. Moderate precipitation amounts (0.5-2.0 inches) fell across the remainder of the Northeast region. Two-week precipitation surpluses ranged from 0.5 to (locally) 4.0 inches coincident with the band of heavy rain noted above.

Up to an inch of precipitation is forecast for the Northeast during Week-1. Above normal precipitation is predicted for Week-2. There is more uncertainty for the month of May as a whole, with EC indicated. For the MJJ season, odds favor above normal precipitation for most of the Northeast Region, except for northern New York and northern New England, where EC is most likely. At this time, there is little evidence to support significant areas of drought development across the region.

Forecast confidence is low to moderate.
                      
Hawaii: With the rainy season drawing to a close for the Hawaiian archipelago, it becomes increasingly difficult to reduce or eliminate remaining drought. Therefore, the current drought designations for western Molokai (D1 & D2) and western Kahoolawe (D1) remain in place.

Forecast confidence for Hawaii: moderate to high

There is no drought at this time in either Alaska or Puerto Rico. In Alaska, there are mixed climate signals out through the seasonal period (MJJ). For the shorter-term (Week-2), near to above normal precipitation is forecast across the state. The May outlook tilts the odds towards below normal precipitation for the Aleutians and Peninsula, with the vast remainder of the 49th state being EC. For MJJ, below normal precipitation is indicated for the Southeast Panhandle, and above normal precipitation is favored for northwest portions of the state. Given the conflicting and highly variable guidance and outlooks over relevant time periods, there is no clear reason to favor drought development in MJJ.


Forecaster: Anthony Artusa

Next Seasonal Outlook issued: May 21, 2020 at 8:30am EDT