Latest Seasonal Assessment -
Drought relief is forecast across a large portion of the Plains states, as well as much of the
Northwest. In contrast, little relief is expected from central Montana southward through
Wyoming, and into the Southwest. Some improvement will prevail over the Great Basin and
from southern Wyoming south into New Mexico and west Texas. No drought development is
forecast anywhere. A stormy weather pattern kicks off the start of the forecast period, with no
less than two major systems forecast to spread snow or rain across the West and Plains during the
last 10 days of November. In the West, where winter-spring snow pack will be crucial for easing
the long-term drought afflicting many parts of the region since 1999, snow pack increased sharply
in November. As of November 18, observations showed normal to above-normal snow water
content in the Inter-Mountain region and the northern and central Rockies, with more snow on
the way. However, a lot of storms will be needed from now to spring to bring water supplies
even close to normal levels in the drought-hit West, as soil moisture and reservoirs have been
severely depleted by the extended drought. As of November 1, Wyoming, Utah, Oregon, New
Mexico, and Nevada all reported reservoir storage that was well under one-half of normal. In
Hawaii, the outlook calls for improving drought conditions due to plentiful showers forecast over
the next 1 to 2 weeks, and a winter season that should see normal amounts of rainfall. As of
November 18, Honolulu had accumulated only 7.40 inches of rain so far this year, versus a normal
of 14.48 inches.
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Tools used in the drought outlook included: the official CPC long-lead precipitation outlook for
December-February, the Palmer Drought Index probability projections for Febraury
and various medium and short-range forecasts and models such as the 6-10
day and 8-14 day forecasts.
The forecast again calls for drought improvement in much of the Plains. The medium range
models indicate a snow storm and blizzard during November 22-24 for the central and northern
Plains and upper Midwest, with precipitation totals ranging from around 0.5 inches in South
Dakota to over 1 inch from Iowa into Wisconsin. This should be followed by another storm
toward month's end. Where the drought is more intense and long-lived, and affecting water
supplies, such as northwest Missouri and western Nebraska, the odds for drought relief are lower
this time of the year, and the near-term precipitation forecasts are not as impressive, so more
limited drought relief is forecast. The upper air pattern going into early December, featuring
above-normal heights west of Greenland southward to Newfoundland and below-normal heights
over much of the United States, is consistent with fairly widespread precipitation, so the overall
forecast shows somewhat more improvement than indicated in last month's forecast. The longer
term, however, is ambiguous, with the official Dec-Feb outlook calling for equal chances wet or
dry for the Midwest, central and northern Plains, and most of the Rockies and Inter-mountain
region.
With a number of statistical and dynamic models pointing toward normal to above-normal rain
and snow over the Northwest in the coming 3 months, confidence is relatively high for
continued drought improvement in this region. The official Dec-Feb forecast calls for above-normal
precipitation over Washington and northern parts of Oregon and Idaho. The forecasts for
the next 2 weeks led to expansion of the areas showing some improvement into northwest
Wyoming and eastern Idaho. In the areas shown as persisting drought, even normal precipitation
would have little impact on the hydrological aspects of the drought. This is based on the low
climatological probabilities of significant improvement in the Palmer drought indices or other
indicators of long-term drought. The continued drought shown in southern California is based on
the official CPC forecast of below-normal rainfall for Dec-Feb and the lack of significant rains
expected for the last half of November. The area of some improvement shown farther north in
California is largely based on shorter-term forecasts, which indicate above-normal precipitation.
Below-normal rainfall is forecast for Dec-Feb for the Florida area, so this is an area to be
monitored for possible drought development in coming months, especially as the season
transitions toward the higher temperatures of spring.
A Kona storm (upper level low) is forecast to glide southwestward toward the Hawaiian islands in
coming days. A storm system well to the north should also affect the islands by the end of the
month. Coupled with the likelihood for normal rainfall this winter, the height of the rainy season
in the leeward areas, drought improvement is expected. However, given the size of the rainfall
deficits in some areas, complete drought eradication will be difficult.
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