Latest Seasonal Assessment -
Record-breaking rains and flooding in the Pacific Northwest during the first half of November eliminated short-term
dryness concerns, as precipitation amounts reached 1 to 2 feet in western Washington and the adjacent coast of
Oregon. Although a much drier pattern is expected during the winter, it is unlikely that drought will develop within
the next several months. Farther east, however, drought persisted over parts of central and eastern Montana,
southward to Wyoming, and eastward into northern Minnesota and northern Wisconsin. The odds favor drought to largely
persist into February across the region, as below-normal precipitation is forecast for the Montana area, and the
northern Plains usually cannot count on much relief during this time of the year. Drought may even expand across the
eastern Dakotas into western Minnesota, an area where mid-September to mid-November precipitation totaled less than
one-half of normal. Across the southern tier of states, the ongoing El Niño should contribute to improving drought
conditions in the Southwest, the southern Plains, and the Southeast, although many locations will see persisting or
worsening drought conditions before relief arrives later in the outlook period. Prospects for relief gradually
diminish going from south to north in the Plains, with more limited improvement expected in Oklahoma, and persisting
drought in much of Missouri and in southern Kansas and adjacent parts of Oklahoma. In Hawaii, El Niño often brings
dry weather to the islands, and this winter may be no exception. As a result, there is an enhanced risk for drought
development across the islands in coming months.
Tools used in the Drought Outlook included the
official CPC long-lead precipitation outlook for December-February, the four-month drought
termination and amelioration probabilities, 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 Analogue on Soil moisture.
The main change from last month’s Outlook is the removal
of the area of drought development from the Northwest due to the heavy rain and snow that pounded the region
during the first half of November. Although below-normal precipitation is still expected this winter, the current
abundant moisture conditions will make it difficult for drought conditions to develop by the end of February.
Drought development may be seriously considered in future Drought Outlooks, however. April mountain snowpack is a
key drought indicator for the West because of its influence on spring and summer streamflows and reservoir storage,
and much can happen between now and then. Some monthly numerical models are forecasting a change to a more typical
El Niño type of pattern in December, with the latest Japanese model (JMA), for example, showing a change to a
positive Pacific North American Pattern (PNA) by early December, resulting in a high pressure ridge over the
western U.S. and a trough over the East, a pattern favoring dry weather for the Northwest and northern Plains. The
model also shows signs of the subtropical jet developing across the extreme south, indicative of increased rainfall. This
pattern is much more consistent with the canonical El Niño circulation expected during the upcoming winter.
Persisting drought is shown for the northern Rockies and
northern Plains, with expanding drought across the eastern Dakotas into Minnesota. The latest CPC precipitation
outlook for December-February indicates a tendency toward dryness in the Montana-Idaho region, consistent with
drought continuation. This month’s drought outlook is somewhat more pessimistic in the northern Plains, where large
areas of some improvement were indicated in the October release. The change is due in part to the climate, as
precipitation in the plains tends to be light in winter, and also due to indications of a tendency toward
below-normal precipitation from several statistical and numerical models. Both the CFS (Climate Forecast System)
model and the UKMET multimodel, for example, show below-normal precipitation extending eastward into Minnesota
during December-February. Recent drying trends also played a role in the forecast expansion of drought in the
northern Plains. Sixty-day rainfall through November 14 was less than one-half of normal from central South Dakota
into southern Minnesota, resulting in expansion of D0 dryness in the November 14 U.S. Drought Monitor. Confidence
for the development area is not strong, given this is the time of year with low evaporation and reduced water
demands from plants and people, and El Niño winter composites do not indicate unusual dryness east of Montana. Also,
a major Plains winter storm cannot be ruled out in coming weeks.
Farther south, drought is shown as persisting in most of
Missouri, although the area may see some good precipitation events in the next couple of weeks and beyond.
Confidence level is also weak for this region. The persisting outlook comes mostly from the indications of
below-normal precipitation in the 3-month precipitation outlook, but dryness probabilities are weak and the status
of the Arctic Oscillation (AO) has much to do with whether Missouri is wet or dry in the winter during and El Niño,
neutral AO’s tending to bring wet weather to the Middle Mississippi Valley and negative AO’s dry weather.
Given the ongoing El Niño, the odds for wetness increase
toward the south, and a wet winter pattern should result in drought improvement in the Southwest, southern Plains,
and Southeast. Transitioning from the drought in southern Kansas to the drought in Texas, it is difficult to
delineate the boundaries between areas with relatively dim prospects for relief and areas where relief is more
confident. This Outlook was more pessimistic than last month’s in Kansas and northern Oklahoma due to recent trends
and medium-range weather forecasts indicating a good chance that conditions will worsen before they get better in
the southern Plains. Considerable rain will be needed to significantly improve reservoir conditions in some
locations, including the extreme drought area in northern Oklahoma. To the south, the prospects look better in
Texas and southern Oklahoma, where both the monthly and seasonal CPC forecasts show a tilt toward wetness,
consistent with El Niño impacts.
Confidence for improvement on the Florida peninsula is
tempered by the fact that the meteorological drought and water supply situation has been recently deteriorating,
and considerable rain will be needed to turn the situation around.
The official CPC precipitation outlook for December-February
shows an area of dryness centered in the Ohio Valley. Current abundant moisture conditions will make it difficult
for drought to develop by February in most of this region, so no development is indicated in the current Drought
In Hawaii, heavy early November rains banished most of
the dryness on the islands, but below-normal rainfall is expected during December-February, so the risk for drought
is elevated. The main concerns involve the population sensitive to short-term (1-3 month) dryness. This includes
residents dependent on rain water catchment (7000+ homes on the Big Island alone and others on the rest of the
islands) and those dependent on surface water diversions (primarily Big Island and Maui). The north portion of the
Big Island has become more vulnerable to short-term dryness because of damage to the water supply system from
October’s 6.7 earthquake. There is also some concern for out-of-season brush fires if dryness persists long enough.
The drought risk extends well beyond Hawaii to Micronesia, where El Niño-related dryness often begins in November
and lasts until June or July.