Latest Seasonal Assessment -
Scattered heavy showers eased the fire danger over Florida in mid-May, and the Drought Outlook calls for more
improvement as the thunderstorm season gets underway during late May and June. Drought areas in the Carolinas and
along the Gulf Coast are also likely to see improvement. In contrast, hot, dry weather is expected to contribute to
persisting or worsening drought over the High Plains from Texas to Wyoming near the beginning of the outlook period.
Although the forecast for June-August does not show a strong indication for below-normal rainfall in the Plains, it
appears that the drought will largely persist well into summer. The odds for improvement increase farther east, and
some additional relief is anticipated from eastern Oklahoma into Missouri. In the Southwest, where the near-failure
of the winter rain and snow season resulted in severe to extreme drought over much of Arizona and New Mexico, the
summer monsoon rains in July and August will reduce the fire danger, although reservoir levels may continue to drop.
The best odds for short-term drought relief extend from southern Arizona into New Mexico.
Tools used in the Drought Outlook
included the official CPC long-lead precipitation outlook for June-August, the drought
termination and amelioration probabilities for August, various medium and short-range forecasts and models such
as the 6-10 day and 8-14 day forecasts, and the soil moisture tools based on the GFS model and the Constructed
Analogues for the season.
Mid-May thunderstorms brought significant drought relief
to Florida, with some spots recording over 4 inches of rain. The anticipated start of the thunderstorm season
toward the end of May should bring additional relief from dryness and drought, so the Outlook indicates improving
drought conditions for the Florida peninsula. Climatological probabilities for drought relief are also high in the
Carolinas, so improvement is also expected in this region. La Niña soil moisture composites are also consistent
with increased moisture in this area for the summer relative to normal. Although the La Niña has ended, such
composites often remain useful some months after the ENSO event has ended. In the Gulf Coast region, various
degrees of improvement are depicted from Texas to Mississippi. This is consistent with recent trends and
medium-range forecast models suggesting increased convective activity by early June in the Gulf, resulting in the
strong possibility that tropical moisture will surge northward. The May 16 2-week soil moisture forecast from CPC
also shows increased moisture in southern Louisiana. That same forecast shows a strong trend toward decreasing soil
moisture across the Great Plains, and the most recent official 6-10 day and 8-14 day forecasts indicate a large
area of warmth and dryness related to high pressure ridging aloft over the central U.S. With the demise of the La
Niña and the onset of summer, the rainfall outlook for June-August becomes quite uncertain for the Plains, but the
likely intensification of the drought from Texas northward during the early part of the Outlook period tilts the
odds toward drought persistence for the High Plains into summer. There is even a good chance that drought could
redevelop across those areas of western and central Texas that have seen recent relief. The confidence that a
developing drought would persist into August is not high, given that the CPC long-lead outlook depicts equal
chances of above or below-normal rainfall in the Plains states. This Drought Outlook stays with the theme of
indicating better chances for improvement in the lingering drought areas in the Mississippi Valley, although the
area of partial improvement is smaller this month in response to the drier medium-range forecasts. The latest
available GFS model does bring some moisture northward into the eastern Plains and Mississippi Valley and,
although the model may be overdoing the rainfall amounts, this is consistent with the idea of some improvement
from eastern Oklahoma into Missouri.
Medium and long-range models continue to show better odds
for rainfall in the northern Plains and upper Midwest than farther south, so some improvement is indicated for
Montana and South Dakota.
The Outlook for the Southwest mainly hinges on the area
expected to pick up the most rains from the upcoming monsoon season, which typically begins in July over Arizona
and New Mexico. The greatest impact of the rains will likely be the reduction of fire danger in July and August. In
contrast, unless the quantity of rainfall is impressive, most of the reservoirs will continue to drop. Elephant
Butte storage in southern New Mexico, for example, will probably hit 5 percent of normal by September, the lowest
point since October 1971. The confidence in delineating the areas prone to improvement is low. This Outlook
considers both the NCDC drought alleviation probabilities for August, which show much of New Mexico as improving,
and the seasonal statistical precipitation model for the Southwest produced by the Earth System Research
Laboratory (the former Climate Diagnostics Center).