Latest Seasonal Assessment -
Climatologically, spring (March - May) brings changing precipitation patterns to much of the country. In California and the Far
West, the wet season is winding down during March, and by May precipitation is sparse. In contrast, precipitation normals
increase across the northern and central Plains, the southern High Plains, and northern and eastern parts of the Rockies.
Historically, these areas receive 3 to 7 percent of their annual precipitation during March while 11 to 19 percent falls in
Because patterns are in flux, few locations are markedly wet or dry for March - May as a whole compared to other times of the
year. Distributed evenly, 25 percent of annual precipitation would fall during a 3-month period. In the north-central Rockies
and central Plains, 30 to 40 percent of yearly precipitation falls on average during spring, mainly due to the wet May.
Meanwhile, spring historically delivers less than 20 percent of the annual total to the Florida peninsula and the southern
Rockies. Southern sections of Arizona and New Mexico receive only about 2 percent of their annual total during spring.
These factors weighed heavily on the Drought Outlook for March - May 2013, especially regarding the large area of extreme to
exceptional drought in the Nation's midsection. Precipitation normals increase significantly later in the forecast period, so
less consideration was given to short-term forecasts of 0.5 to 1.5 inches of precipitation during the remainder of February.
The 3-month outlook favors below-median precipitation across roughly the southwest half of this swath of extreme to exceptional
drought; there were equal chances for wetness and dryness in the rest of the area. However, large moisture deficits are deeply
entrenched across the region, and with only one month of the wet season included in this forecast period, improvement seems
Farther west, precipitation forecasts for time periods ranging from the next 5 days to the next 3 months favor dryness for most
or all areas currently in drought, so persistence and areas of development are forecast from the High Plains westward to the
Pacific Ocean. Limited improvement should be restricted to the northern tier near the Montana/Wyoming border, where dryness is
not as universally indicated.
Off to the East, there are enhanced chances for above-normal spring precipitation from the Mississippi Valley eastward into the
Great Lakes region, and moderate precipitation is forecast for the remainder of February into early March. Thus, drought
conditions are expected to improve.
In the Southeast, heavy to excessive rainfall is expected in the areas of drought to the north and west of the Florida
Peninsula during the last week of February. Between 3 and 7 inches is anticipated in a broad stripe from the Louisiana Bayou
northeastward through the western Florida Panhandle, southeastern Alabama, and interior Georgia. One- and three-month outlooks
lean dry in this region, but given the amounts of rain forecast in the short-term, drought is expected to be less intense by
the end of May than it is currently. However, any recovery will occur very slowly, as it will take time for any increased
rainfall to chip away at the large moisture deficits that have accumulated over the course of a multi-year drought. Farther
south, heavy precipitation is forecast to miss the Florida Peninsula, where short-term dryness recently developed. The March
and March - May outlooks favor less rainfall than usual, and given the moisture shortfalls already in place, and that spring
is a dry time of year in the region in any case, drought is forecast to persist, expanding to cover the entire Peninsula by the
end of May.
Elsewhere, mountain snowpack was only 25 to 50 percent of normal on February 1, 2013 across the drought area in north-central
Alaska. Limited improvement is anticipated there over the next 3 months. Finally, drought covers western and (in spots) central
sections of the individual Hawaiian Islands from Oahu southeastward through the Big Island. Drought is expected to persist
where it exists on the Big Island and Maui, with some improvement anticipated to the north and west across Lanai, Molokai, and
Tools used in the U.S. Drought Outlook (USDO) included the official CPC temperature and precipitation outlooks for March
2013 and March through May 2013 (released Feb. 21), various short- and medium-range forecasts and
models such as the 5-day and experimental 7-day HPC precipitation totals (released Feb. 20), 6-10 day and 8-14 day
forecasts (released Feb. 20), the NAEFS precipitation outlooks, the soil moisture tools based
on the Constructed Analog on Soil (CAS) moisture, dynamical models (CFSv2, NMME, and IMME), the 384-hour total
precipitation forecasts from several runs of the GFS, the four-month Palmer drought termination and amelioration
probabilities, climatology, and initial conditions. We are currently in ENSO Neutral conditions as of this forecast
Across the interior Southeast, north of the Florida Peninsula, heavy to excessive rains are expected during late
February, with 3 to 7 inches forecast in a stripe across the Louisiana Bayou, the western Florida Panhandle, southern
Mississippi, southern and eastern Alabama, and interior Georgia. The March and March - May 2013 precipitation outlooks
favor below normal precipitation in this same area, but drought improvement is forecast because of the magnitude of the
rainfall expected in the near-term, and because relative confidence in the long-term outlooks is inherently much lower.
Still, marked dryness during the last half of the period could more than counteract any benefit from the late February
rains, and this seems quite possible (though not likely) in light of the dry 3-month precipitation outlook.
Forecast confidence in the interior Southeast is moderate.
Farther south, the heaviest rains should miss the Florida Peninsula, although its northern reaches should pick up 1 or 2
inches. The one- and three-month precipitation outlooks favor below-median precipitation as they do farther north, but
with higher probabilities. Shorter-term, there are enhanced chances for above-median rainfall in late February and early
March across the Peninsula, but this is a dry time of year there. February monthly normals generally range from 2 to 4
inches, except lower near and across the Keys. Therefore, 1-week rainfall totals need not be particularly heavy to be
above-normal, and the below-normal forecast for the upcoming 3-month period - when only 15 to 20 percent of annual
rainfall is recorded under normal circumstances - implies continued surface moisture depletion. All these factors imply
that the ongoing short-term drought will persist and expand through the end of May, and drought is anticipated along the
entire Peninsula by then.
Forecast confidence along the Florida Peninsula is high.
Drought is expected to improve at least somewhat across the northern half of the Mississippi Valley and the western Great
Lakes region. Specifically, some improvement is forecast across most of Missouri and the central and western sections of
Iowa and Minnesota, with more marked improvement anticipated farther east. Moderate precipitation is forecast for the
last week of February in areas south and east of central Minnesota, with amounts topping out between 1.0 and 1.5 inches
in central Missouri. Odds favor a dry start to March in the 8 to 14 day outlook, but the monthly outlook indicates
enhanced chances for March as a whole to be wetter than normal. The 3-month precipitation outlook favors above-median
precipitation for most of the region, except along the western tier. Only some improvement was forecast in this area
where the 3-month outlook did not favor surplus rainfall, with more robust improvement depicted where there was a tilt of
the odds toward wetness in the three month outlook.
Forecast confidence in the Mississippi Valley and western Great Lakes is moderate.
Drought is expected to persist and expand across the Plains, Rockies, Intermountain West, and Far West. This includes the
broad area of extreme to exceptional drought in the middle of the country. The only exceptions are the eastern Dakotas
and along the northern tier of the drought region, where limited improvement is forecast. But the vast majority of the
large area of drought in the central and western states can expect conditions to persist, with no lasting, tangible
improvement anticipated at least through the end of May. In fact, drought is expected to expand, covering most areas not
currently in drought along the southern tier of the country from central Texas through southwestern California. In
addition, drought is expected to expand significantly across central and northern California and adjacent Oregon. This
forecast was motivated by a markedly dry February and forecasts for continued below-median precipitation on time scales
ranging from 5 days to 3 months. In central and northern California, the 3-month precipitation outlook for March - May
2013 calls for significantly enhanced chances (over 50 percent) that spring precipitation totals will rank among the
lower one-third of historic occurrences.
Heavy snow is falling on much of the central Plains Feb. 21 - 22, 2013, including part of the extreme to exceptional
drought area. Every bit of moisture helps, but liquid-equivalent precipitation totals are not expected to be particularly
large - generally 0.5 to 1.5 inches from northernmost Texas northward through Nebraska - and it comes at the end of a
winter with markedly below-normal snowfall. For example, Norfolk, NE, Sioux Falls, SD and Sioux City, IA all received 10
to 13 inches less snowfall than normal this season through Feb. 19 (35 to 65 percent of normal). After this system exits,
another could bring moderate precipitation to the southern Plains and southeastern Rockies during the first week of March.
Otherwise, drier than normal weather is expected to prevail across the central and western states during late February
and early March. In addition, the March and March - May 2013 precipitation outlooks favor below-median precipitation
roughly from the western half of the central and southern Plains westward through most of the Rockies, Intermountain
West, Southwest, and Far West. With dry weather favored for most locations and time periods, and considering the large
precipitation deficits accumulated over the last 6 to 24 months, drought persistence (and in some areas expansion) was
the only reasonable forecast. Even in the eastern Plains, which lies outside the area with enhanced chances for dryness
during March - May, the endurance and/or severity of observed moisture shortages make it unlikely that conditions will
improve by late May. Normal precipitation is fairly low until May, leaving little opportunity for wet-season
precipitation to affect existing precipitation deficits before the outlook period ends. Thus the persistence forecast
reaches eastward through all of Oklahoma, Kansas, Nebraska, southwestern South Dakota, and most of Wyoming.
The one significant wild card is May - a wet month with sizeable precipitation normal as mentioned above. Moisture
deficits could rise or fall quickly once the month gets underway if May precipitation trends significantly above or below
Some improvement was forecast in much of the Dakotas and in some areas near the Montana/Wyoming border for one or more of
the following reasons: (1) moisture deficits of shorter duration and/or smaller magnitude than farther south; (2) close
to normal precipitation since the start of the water year (Oct. 1, 2012); (3) near-average mountain snowpack; (4)
unremarkable Surface Water Supply Index (SWSI); (5) near-normal summer streamflow forecast. All of these factors make it
easier to mitigate impacts.
For the large area of drought from the Plains westward to the Pacific Coast, forecast confidence is moderate to high,
with less certainty along northern and eastern parts of the region, where the monthly and 3-month outlooks do not favor
drier than normal conditions, as they do elsewhere.
Mountain snowpack was only 25 to 50 percent of normal on February 1, 2013 across the drought area in north-central
Alaska. Limited improvement is anticipated there over the next 3 months.
Finally, drought covers western and (in spots) central sections of the individual Hawaiian Islands from Oahu
southeastward through the Big Island. Drought is expected to persist where it exists on the Big Island and Maui, with
some improvement anticipated to the north and west across Lanai, Molokai, and Oahu.
Forecast confidence in Alaska and Hawaii is moderate.