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Climate Prediction Center


March - May 2013


Outlook Graphic: GIF   PDF Adobe PDF Reader


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 May.

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 unlikely.

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 Oahu.

Discussion for the Seasonal Drought Outlook

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 release date.

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 normal.

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.

NOAA/ National Weather Service
NOAA Center for Weather and Climate Prediction
Climate Prediction Center
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Page Author: Climate Prediction Center Internet Team
Page last modified: February 21, 2013
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