April - June 2014

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Latest Seasonal Assessment - Long-term drought is predicted to continue across California, interior Oregon, the Great Basin, the Desert Southwest, the southern Rockies, and the southern High Plains, as the traditional winter wet season draws to a close in the next few weeks. Mountain snowpacks are running well below-average across much of this region. The Pacific Northwest still has a while yet before entering their climatological dry season, so there are opportunities for drought improvement and removal there. Across the central portion of the contiguous United States, drought improvement and/or removal is anticipated over the lower central and southern Great Plains and Upper and Middle Mississippi Valley. However, farther west across the High Plains, the odds for improvement or removal are not as good, prompting persistence of drought conditions. Drought is expected to either improve or be removed in Hawaii, as their wet season is forecast to continue well into the AMJ season.

Tools used in the U.S. Seasonal Drought Outlook (SDO) included the official Climate Prediction Center (CPC) temperature and precipitation outlooks for April 2014, the long lead forecast for April - June 2014, various short- and medium-range forecasts and models such as the 5-day and 7-day precipitation totals from the Weather Prediction Center, 6-10 day and 8-14 day CPC forecasts, 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. The phase of ENSO is expected to remain neutral, with a gradual transition to a borderline El Nino by the end of the period.

Persistent upper-level ridging across western North America continued to promote drought conditions across California, the Great Basin, the Desert Southwest, and the southern Rockies. Despite recent precipitation nearly statewide across California 2-4 weeks ago, the most recent two-week period has been dry over the southern half of the state, with Percent of Normal Precipitation (PNP) values ranging within the lowest 10 percent. The wet season is rapidly coming to a close for southern California, and little if any precipitation is predicted for the upcoming two-week forecast period. For the state as a whole, California received only about 25-50 percent of the precipitation that it typical gets during the Water-Year so far (which started on October 1, 2013). In the hardest hit region of south-central California, 10 to 20 inches of precipitation are needed to bring the Long-term Palmer Drought Severity Index (PDI) back up to -0.5 or higher, which is one way of determining the end of a drought. Climatologically, the Great Basin, Desert Southwest, and the southern Rockies are also experiencing the tail end of their winter wet season, especially after April. May and June are generally dry prior to the traditional onset of the Southwest Summer Monsoon in July. CPC’s 30-day and 90-day outlooks, for April and April-June, respectively, call for enhanced odds of below-median precipitation across California, with Equal Chances (EC) elsewhere. With above-normal temperatures also favored throughout this region, Persistence and/or Intensification of drought is anticipated.
Forecast confidence for California, Great Basin, Desert Southwest, and the southern Rockies is moderate to high.

The Pacific Northwest has seen a succession of cyclonic storm systems in recent weeks, in the wake of relatively warm and dry conditions which prevailed earlier this winter in association with the persistent West Coast ridge. PNP values ranged from 125-300 percent over the past 2 weeks, with the higher values over Washington, and the lower values over Oregon and southeast Idaho. Mountain snowpack (as of March 1, 2014) ranged between 70-110 percent of median (Washington, southeast Idaho, and the northern interior of Oregon), and only within the lowest 25 percent in the southern interior of Oregon. Above-median precipitation is favored by CPC’s 6-10 day and 8-14-day outlooks. CPC’s 30-day and 90-day outlooks both favor above-normal temperatures for Oregon, near- to above-normal temperatures for Washington, and EC for southeast Idaho. There are slightly elevated odds of below-median precipitation for Oregon and Washington, and EC is indicated for southeast Idaho. With the climatological rainy season still in progress for a while in the Pacific Northwest, there are opportunities for at least a 1-category improvement across much of this region (which in some cases equates with drought removal), with the possible exception of interior Oregon.
Forecast confidence for the Pacific Northwest is moderate.

Long-term dryness and drought continues to influence the central and southern Plains, in particular the High Plains. PNP values range between 5-25 percent of normal across much of this region, with the notable exception of southern and coastal Texas, which received heavy rainfall (several inches) from frontal systems draped along the Gulf Coast region (14-day PNP values range from 150-400 percent). The PDI shows that 3-6 inches of rain are needed in the drier Texas Panhandle to end the current drought. Some of the impacts of the current drought include significantly reduced surface moisture, which is beginning to affect early-planted crops from the Texas Panhandle into central Texas. Forty to 50 percent (or more) of rangelands in both Texas and Oklahoma are starting the growing season in poor to very poor condition. Low reservoir levels are also a concern. The elevations of Lakes Buchanan and Travis (along the Colorado River in Texas) rival the record and near-record low levels of the early 1950’s and the mid 1960’s. The 6-10 day and 8-14 day precipitation outlooks both favor elevated odds of near- to below-median precipitation over the Texas Panhandle and far southwestern Texas, and above-median precipitation over southern and coastal sections of Texas. There are conflicting and/or weak climate signals for precipitation in the central and southern Plains during both April and AMJ, so EC is deemed the best bet. Near- to above-normal temperatures are anticipated during these same periods. Climatologically, a significant fraction (55-60 percent) of the annual precipitation is received in this region during the AMJ time frame. With no clear precipitation signal from the CPC outlooks, it is reasoned that the lower Plains is more susceptible to the influx of low-level Gulf moisture and frontal boundaries, and has the best odds for drought removal. The odds of getting drought improvement or removal rapidly diminishes westward across the High Plains.
Forecast confidence for the central and southern Plains is low to moderate.

The Upper and Middle Mississippi Valley: Temperatures during the past 30-days have averaged between 6-10 degrees F below-normal over the Upper Mississippi Valley, and 3-5 degrees F below-normal over the Middle Mississippi Valley, in what has been a long winter for this region. From about central Iowa northward, soils are frozen down to 5 feet in some locations. Like last April, this frozen soil will take a while to thaw, especially given the cold temperature outlook for the next few weeks, which will delay planting in this region. According to the National Operational Hydrologic Remote Sensing Center (NOHRSC) snow cover across Minnesota and Wisconsin generally ranges from 10-20 inches, with 20-40 inches on the ground in the Arrowhead region of Minnesota and northern Wisconsin. In drier areas, such as Iowa and northeast Missouri, the PDI shows 3-6 inches of precipitation is needed to bring conditions back to normal. The extended-range outlooks (6-10 day and 8-14 day) anticipate enhanced odds of below-normal temperatures and above-median precipitation for the northern half of the Mississippi Valley. Below-normal temperatures are favored for the Upper Mississippi Valley in both April and April-June. For the Middle Mississippi Valley, near- to below-normal temperatures are favored. Climatologically, these areas experience a ramping up of precipitation in AMJ, receiving between 50-60 percent of their annual total. Removal of drought throughout this region is based on the extended-range outlooks and climatology, since there are no clear indications for precipitation in CPC’s 30-day and 90-day outlooks.
Forecast confidence for the upper and middle Mississippi Valley is low to moderate.

Contrary to the previously issued (February 20th) Seasonal Drought Outlook, there are no drought areas (D1 or higher) to modify in Alaska, so no outlook was made.

Periods of enhanced rainfall during the winter rainy season have promoted drought reduction across the Hawaiian Islands. Small areas of lingering drought are expected to be removed from the Big Island and Kahoolawe, with at least a 1-category improvement anticipated for Molokai. CPC’s precipitation outlook for the AMJ season favors above-median precipitation for the tail end of the Hawaiian wet season.
Forecast confidence for Hawaii is moderate to high.