Latest Monthly Assessment -
As the winter wet season winds down in the West, little if any significant improvement in current drought conditions is expected during April. In the northern and central
Great Plains, current soil moisture deficits range from 1-5 inches across the western Corn Belt. The CPC updated 30-day outlook for April favors below-median precipitation
in this region. Therefore, drought development is anticipated, especially in Nebraska and South Dakota. Across the southern Plains, forecasts out to 30-days favor
above-median precipitation amounts for approximately the southeastern two-thirds of Texas and southeastern Oklahoma. Above-median precipitation is also favored for the
central Gulf Coast region. Areas of moderate drought (D1) across these regions are expected to be upgraded by one category, resulting in drought removal. It is thought
that the core drought area (D3 and D4) encompassing western portions of Oklahoma and north-central Texas is unlikely to receive a 1-category improvement during the month
of April, and is expected to persist. Drought is forecast to persist and/or intensify in extreme southern Florida, during the height of the climatological dry season. In
Hawaii, the spring season is generally a somewhat drier time of year, and it will be difficult to achieve a one-category improvement in the current drought conditions
across the islands.
Tools used in the U.S. Monthly Drought Outlook (MDO) included the official Climate Prediction Center (CPC) updated temperature and precipitation outlooks
for April 2015,, various short- and medium-range forecasts and models such as the 7-day
precipitation totals from the Weather Prediction Center (WPC), the 6-10 day and 8-14 day CPC forecasts, week 3 and 4 experimental outlooks, the NAEFS precipitation
outlooks, dynamical models (CFSv2), the 384-hour total precipitation forecasts from several runs of the GFS, climatology, the latest official Drought Monitor
analysis (released on March 26), observed precipitation during the previous month, and initial conditions.
As the wet season undergoes its annual transition to the dry season in the western contiguous U.S., precipitation amounts accordingly decline, with the Pacific
Northwest being the region that typically receives the last of the winter season's storms. The Weather Prediction Center (WPC) forecasts 2-4 inches of precipitation
during the next 7-days across the mountainous terrain of both Washington and Oregon. This precipitation, and the week 2 outlook favoring above-median precipitation,
in addition to whatever else is received over the second half of April, is expected to preclude the development of any additional drought. Persistence of current
drought areas is anticipated for the West primarily due to a drier climatology.
Forecast confidence for the West is moderate to high.
Little to no precipitation is predicted across the Four Corners region during the first week of April, and odds favor below-median precipitation for week 2. CPC's
updated monthly outlook for April depicts Equal Chances (EC) of below, near, and above-median precipitation. Climatology favors a rapid decline in precipitation
during April, generally followed by dryness in May and almost all of June, before the traditional onset of the Southwest summer monsoon. Persistence/Intensification
of current drought areas is therefore anticipated for this region.
Forecast confidence for the Four Corners states is moderate to high.
Below-median precipitation is predicted on all time-scales out through 30-days for most of the northern and central Great Plains, with odds favoring above-median
precipitation for much of the Upper Midwest. CPC's updated monthly outlook for April depicts an elevated chance of below-median precipitation for most of this region,
centered on South Dakota and Nebraska. The updated temperature outlook indicates EC for the northern Plains and Upper Midwest, and above-normal mean temperatures in
the central Plains. The latest North American Land Data Assimilation System (NLDAS) ensemble mean, dated March 22, 2015, shows near-current soil moisture anomalies in
the root zone (top 1 meter of soil) ranging from 25-75 mm (1-3 inches) across central and eastern sections of the Dakotas and Nebraska, with even greater
anomalies (75-125 mm, 3-5 inches) over southern Minnesota. CPC's Constructed Analog on Soil moisture (CAS) outlook for the end of April favors the driest conditions
across the Upper Midwest, eastern South Dakota, and Kansas. The area that appears most ripe for drought development in April includes South Dakota and Nebraska,
which is indicated accordingly on the monthly drought outlook map. Although it is still early in the growing season, this area (the western Corn Belt) will need to be
monitored for potential drought development during the spring season.
Forecast confidence for the northern and central Great Plains, and upper Midwest, is moderate.
In the southern Plains, above-median rainfall is favored for approximately the southeastern two-thirds of Texas, and southeastern one-third of Oklahoma, by most
precipitation guidance out to 30-days. Accordingly, areas of moderate drought (D1) are predicted to be removed in the extreme southern and eastern portions of
ongoing drought areas across Texas, and for extreme northwestern Arkansas, with some support from the regional climatology for April. No significant improvement is
anticipated for the core drought region (D3 and D4) in western Oklahoma and north-central Texas.
Forecast confidence for the southern Great Plains is moderate.
Above-median rainfall is expected for most of the central Gulf Coast region at all time-scales out through 30 days, resulting in drought removal. Interestingly,
southeastern Louisiana seems to miss out on the more substantial rainfall amounts during the first week in April, and this same area also has some support from April
precipitation climatology. However, it is unclear whether or not these factors will be enough to override the predicted above-median precipitation amounts at Week 2
and in CPC's updated 30-day precipitation outlook. In extreme southern Florida, the traditional height of the dry season warrants the persistence and/or
intensification of drought conditions there.
Forecast confidence for the central Gulf Coast and interior South Florida is moderate.
In Hawaii, climatology favors a somewhat drier period relative to the antecedent winter season. It will be difficult to get significant drought relief for the
islands in April, therefore the expectation of persistence and/or intensification of current drought areas. Though there is no drought at the present time in Alaska,
there are several things to note. In the east-central Interior, snowpack was near normal on March 1, and precipitation this month has been near to above median. The
eastern Kenai Peninsula has also fared well, with Water-Year-To-Date (WYTD) precipitation (since October 1, 2014) generally near normal. An area of concern, however,
is the southern Southeast, where a continuing lack of snow at elevation could pose a problem for small hydropower operations if precipitation is significantly
below-median during the late spring and early summer. In Puerto Rico, the spring signals the start of the traditional rainy season, as the ITCZ undergoes its seasonal
northward migration toward the area. This is expected to preclude any expansion or intensification of current dryness.
Forecast confidence for Hawaii is moderate to high.