Tools used in the U.S. Seasonal Drought Outlook (SDO) included the official Climate Prediction Center (CPC) temperature and precipitation outlooks for
May 2015 and May-July 2015,
various short- and medium-range forecasts and models such as the 5-day and 7-day precipitation totals forecast (QPFs)
from the Weather Prediction Center (WPC), the 6-10 day and 8-14 day CPC extended-range forecasts (ERFs), the
NAEFS precipitation outlooks, the soil moisture tools
based on the Constructed Analog on Soil Moisture (CAS), dynamical models (CFSv2, NMME, IRI, IMME, and ECMWF), the 384-hour total precipitation forecasts from several
runs of the GFS, the four-month Palmer drought termination and amelioration probabilities,May and May-July climatology, and initial conditions. An El Niño (ENSO)
Advisory is now in effect, with the April 9, 2015 ENSO Diagnostic Discussion indicating a 70 percent chance of El Niño conditions continuing through Northern
Hemisphere summer 2015.
In the southern and eastern U.S., drought is confined to southern Florida and small parts of the central Gulf Coast region. On all time frames from the next few days to
the 3-month May-July 2015 period, above-normal rainfall is favored along the central Gulf Coast. The short-term is not expected to be as wet in southern Florida, but odds
favor above-normal rainfall after the next week or so, and the climatological rainy season will be starting up later in the period. Given these considerations, drought
removal is the most likely outcome.
Confidence in the central Gulf Coast region and in southern Florida is high.
The forecast is uncertain in the swath from the Dakotas eastward through the Great Lakes region, with a lot of different variables to consider. There are enhanced chances
for a drier-than-normal May-July period in the eastern half of this area, with neither abnormal wetness nor dryness favored in the western half of Minnesota and the
Dakotas. Forecasts lean dry for the last half of April, especially from Wisconsin westward. Climatologically, this is a markedly wet time of the year in the northern
Plains, but not farther to the east. In the central and eastern Great Lakes region, soil moisture levels tend to decline from mid-April to the end of July more often than
they increase. Furthermore, climate signals associated with ENSO would argue for a slight tilt of the odds toward increased rainfall late in the period. Given all this,
persistence seems the best forecast, with some expansion (because of the May-July forecast and drier climatology) in the eastern half of the Great Lakes where some degree
of abnormal dryness is already in place. Farther west, it would not be surprising to see some expansion in the short-term, followed by retrenchment toward the end of the
Forecast confidence in the northern Plains and Great Lakes region is low.
In the broad area of drought from the Intermountain West eastward through the central and southern Plains, rainfall forecasts look generally promising, but drought
response may not be as robust as one might expect at first glance. CPC forecasts favor above-normal precipitation for a large part of this region, excepting only (a)
southern Arizona and a small part of adjacent New Mexico, and (b) roughly the eastern half of the Great Plains' drought region outside Texas. This is a wet time of year in
the Plains, but it's neutral or leans drier than other times of the year from the Rockies westward, so above-normal precipitation for the period may not have as much of
an impact on longer-term conditions there as in the lower elevations to the east.
Across central and southern sections of the Rockies and the eastern Great Basin, drought development is relatively recent (near or after the start of the current water
year in October 2014) in most of Colorado and eastern Utah, but has been around considerably longer across the southern Rockies and the Great Basin. For late April, odds
favor above-normal precipitation across Nevada, Utah, and Colorado, but not dramatically so. The threshold for above-normal totals is not particularly high relative to
precipitation at other times of the year. The bottom line is that improvement is forecast where drought is relatively new or may respond more readily to wetness during
the period, including much of western Colorado, northern Utah, northeast Nevada, and southern Idaho. Some improvement is also forecast for the D2 areas in western New
Mexico and eastern Arizona, but persistence is forecast in the surrounding D1 areas in those states, plus the Rio Grande Valley in Colorado, and the southern half of Utah.
Long-term hydrologic impacts are entrenched in these areas, and significant alleviation is unlikely by the end of July. Since any improvement to the existing moderate
drought would mean drought removal on the Drought Monitor, such a change is unlikely, and drought is expected to persist.
Forecast confidence in the Rockies and Intermountain West is moderate.
In the central and southern Plains, improvement or removal is generally expected, with a few notable exceptions. Wet weather is likely before the final week of April in
much of Nebraska, central and west Kansas, western Oklahoma outside the Peninsula, and the High Plains in northeast Colorado and southeast Wyoming. WPC forecasts call for
1 to locally 3 inches of rain. There is no tilt of the odds toward dryness or wetness in late April, and the May-July forecast favors above-normal rainfall across Texas,
the central and southern High Plains, and the western tiers of Oklahoma, Kansas, and Nebraska. Most of the central and southern Plains should anticipate some improvement
or removal of drought by the end of July, with a couple of exceptions. First, despite early-period wetness, precipitation for the upcoming wet season is enough of a
question mark that persistence is forecast in southern Nebraska and eastern Kansas. Second, from north-central Texas through western Oklahoma, drought is more intense and
more entrenched than in other parts of the Plains, and given the significant evaporation that can take place from late spring through mid-summer, it seems conditions will
not be sufficient to bring improvement to this core drought region.
Forecast confidence is low in the central Plains and moderate in the southern Plains.
In the Pacific Coast states and western Nevada, drought is entrenched...this forecast period is a dry and warm time of year...and CPC forecasts show enhanced chances for
above-normal May-July temperatures. Thus, relief is highly unlikely, and persistence or intensification is indicated. This particularly applies to the protracted, extreme
to exceptional drought covering much of California, western Nevada, and adjacent locales.
Forecast confidence in the West is high.
Above-normal rainfall is favored for the next 3 months in the major cities of Hawaii, but chances are not as robust across most other parts of the island chain, and in
any case, this is a relatively dry time of year for most of the state. Therefore, drought should persist or intensify where it now exists, except in east-central Kauai
where climatology is slightly wetter and improvement is more plausible. Drought development is possible in northwest sections of the Big Island. Confidence is reduced a
bit because the forecast for enhanced chances of above-normal May-July precipitation introduces some uncertainty.
Forecast confidence across Hawaii is moderate.
Forecaster: R. Tinker
Next Seasonal Drought Outlook issued: May 21, 2015 at 8:30 AM EDT