Drought coverage continues to decrease across the Lower 48 states, after a relatively wet winter for many areas. CPC’s monthly and seasonal precipitation outlooks, valid for May and May-Jun-Jul (MJJ) respectively, favor large areas of above normal precipitation across the CONUS, especially across remaining areas of drought.
These outlooks, a generally favorable MJJ climatology, and a wide array of dynamical and statistical models and tools, support drought improvement/removal over most residual drought areas of the contiguous U.S.
The exception is Washington state and northwestern Oregon, which recorded large precipitation deficits (12 to 16 inches) this past winter, unlike most other portions of the West. Although some precipitation is expected during the next few weeks, the Pacific Northwest is rapidly approaching the end of its rainy season, and the beginning of its dry season.
Climatological considerations, in addition to CPC’s May and MJJ 2019 precipitation outlooks convincingly tilt the odds towards drought persistence in north-central Washington, with a surrounding region of drought development expected.
The dry signal predicted over the Pacific Northwest during MJJ is expected to also influence the Alaska Panhandle region. The southern Panhandle has been in hydrologic drought for many months, and the low reservoir levels have resulted in reduced hydropower production. Drought may extend northward during this MJJ season to include the northern portion of the Panhandle.
In Hawaii, the climatological rainy season will soon give way to its dry phase, and this dry signal is expected to be reinforced by a weak El Niño. With increasingly persistent trade winds a common feature during the Hawaiian dry season, leeward slopes are expected to miss out on the heavy rainfall amounts that are usually received on the windward slopes.
In Puerto Rico, the northwestern portion of the Commonwealth recently experienced the elimination of drought; but the remaining area of moderate drought (D1 on the U.S. Drought Monitor) over the central part of Puerto Rico is expected to be removed as the climatologically wet MJJ season advances.
Forecast confidence is moderate to high for drought persistence and development across the Pacific Northwest, and moderate for the remaining drought areas in the West.
- Precipitation has averaged at or above normal throughout much of California, the Great Basin, and the Southwest since the start of the current Water Year (October 1, 2018). Basin average snow water content (SWC) is also above average across these areas, ranging from 115% to 260% of average.
- The ample precipitation and snowfall this Water-Year-To-Date (WYTD) resulted in major drought reduction throughout much of the Western region.
- According to the U.S. Drought Monitor, drought coverage (D1-D4) in this region decreased from 59% at the start of October 2018 to 6% by early to mid April 2019. California became drought-free for the first time since December 2011.
- For areas that are still in drought, such as New Mexico, northeast Arizona, and extreme southwestern Wyoming, drought improvement and/or removal is forecast. This is supported by CPC’s monthly and seasonal precipitation outlooks, valid for May and MJJ, respectively, the CFS model, the NMME, and the IMME, which all favor above normal precipitation.
- The onset of spring snowmelt will also assist in the mitigation of residual drought across these areas. In the Pacific Northwest, however, prospects for significant improvement are poor after the next several weeks.
- SWC ranges from 67% to 99% for the area that includes western and central Washington and far northwestern Oregon. WYTD values mostly range from 50%-90% of normal, with a few spots as low as 25% to 50%.
- Precipitation deficits of 12-16 inches are common across this region for the past 90-days. USGS 28-day stream flows are low, with values in the lowest quartile of the historical distribution.
- Based on SWC, WYTD deficits, and stream flow considerations, and both the May and MJJ official precipitation outlooks favoring below normal precipitation and above normal temperatures; and the fact that the rainy season out West is almost over, drought persistence is favored for north-central Washington, with drought development indicated elsewhere.
Forecast confidence is moderate to high for the High Plains region.
- The northern and central Great Plains remain drought-free, and above normal precipitation this winter resulted in major flooding along the Lower to Middle Missouri River Valley.
- Drought development is not anticipated during the outlook period at this time, but these areas are climatologically vulnerable to fast-developing drought with multiple weeks of insufficient rainfall and above average temperatures during the late spring and summer.
- Small areas of moderate drought (D1 on the U.S. Drought Monitor) remain over north-central Wyoming (low snowpack associated with the Big Horn Mountain Range) and far southern Colorado.
- However, MJJ climatology, and the CPC precipitation outlooks for both May and MJJ favor the removal of this drought.
Forecast confidence is moderate across the South.
- Across the South, patchy drought lingers over parts of south-central Texas, and a very tiny area in southwestern Louisiana (immediately west of Vermillion Bay).
- The monthly and seasonal precipitation outlooks from CPC, and climatology in general, favor wetter-than-normal conditions across these small areas. Accordingly, drought removal is anticipated.
Forecast confidence is moderate for the Midwest Region.
- Moderate to major flooding continues across parts of the Midwest region, especially along the banks of the Red River of the North and the Mississippi River.
- During the past 90 days, precipitation surpluses exceeded 4 inches across portions of the Midwest and Ohio Valley, with soil moisture ranking at or above the 95th percentile for this time of year.
- Given such wet initial conditions, drought development is unlikely during the outlook period.
Forecast confidence is moderate for the Southeast Region.
- Moderate drought currently exists over southern Alabama and adjacent parts of the Florida Panhandle, parts of Georgia, and coastal South Carolina.
- Increasingly wet climatology during June and July favors drought removal by the end of July. Precipitation deficits in southeastern Alabama are on the order of 6-8 inches for the past 3-months.
- The CPC precipitation outlooks favor above normal precipitation during both May and MJJ, and this is generally consistent with a weak El Niño at this time of year. Therefore, drought removal is favored.
Forecast confidence is moderate to high for the Northeast Region.
- The Northeast region has remained drought-free since early November. Based on wet initial conditions, near to above average soil moisture values, and the absence of a dry signal among CPC’s monthly and seasonal precipitation outlooks, drought development is unlikely through the end of July.
Forecast confidence is high for Alaska.
- Moderate to severe drought coverage remained nearly steady along the southern Alaska Panhandle this past winter. Since MJJ is a relatively drier time of year, persistence of this long-term drought is forecast, along with drought development possible for the northern Panhandle region.
- Over the southern Panhandle, reduced hydropower caused by low reservoir levels has necessitated the use of diesel generators, having a negative impact on regional air quality.
Forecast confidence is moderate to high for Hawaii.
- Although much of Hawaii became drought-free during February, drier conditions consistent with a weak El Niño have returned. In addition, the oncoming dry season and the increasingly persistent trade winds imply favorable precipitation for windward (east or northeast-facing) slopes.
- However, the outlook for leeward (west-facing) slopes, which are located in rain shadow areas downwind of the mountainous topography, favors drought persistence and/or development.
- The Seasonal Drought Outlook attempts to highlight broad-scale drought features, and not localized microclimates.
- It is interesting to note however, that the Kona Coffee belt area near the western coast of the Big Island, at an approximate elevation range of 1000-3000 feet, is the only leeward area of Hawaii that typically experiences its rainy season during the summer.
Forecast confidence is moderate for Puerto Rico.
- Drought coverage across Puerto Rico peaked at 42.66 percent at the beginning of March, but decreased rapidly to 10.35 percent as of April 9, thanks to drought elimination over the northwestern part of the Island.
- Since the climatology becomes increasingly wet during MJJ and without a strong dry signal in the seasonal precipitation tools, removal of drought is anticipated by the end of July.