Tools used in the U.S. Monthly Drought Outlook (MDO) included the official Climate Prediction Center (CPC)
updated temperature and precipitation outlooks for December 2014,
various short- and medium-range forecasts and models such as the 5-day and 7-day
precipitation totals from the Weather Prediction Center, the 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, IMME, and IRI), the 384-hour total precipitation forecasts from several runs of the
GFS, climatology, the latest official Drought Monitor analysis (made on November 25), observed precipitation during the last
few weeks, and initial conditions.
The patches of drought scattered across the Southeast, the Northeast, and the northern Plains are expected to persist through the end of 2014. Odds favor neither above- nor below-normal precipitation for the month as a whole, and short-term indicators show near- to below-normal precipitation in these areas over the next two weeks. As a result, significant drought improvement is unlikely.
Confidence in the forecast across the Northeast, the Southeast, and the northern Plains is moderate to high.
Patchy improvement has been observed across the south-central Plains during the past several weeks, and this general trend is expected to continue through the end of December. After a fairly dry week, heavy precipitation may overspread the region during the second week of the month, and odds favor a wet December as a whole. Still, it was tricky determining how far west to bring improvement. In the central and southwestern Plains, December is one of the drier months of the year, and increased modeled soil moisture totals are observed only 10% to 40% of the time climatologically. Persistence seemed the better forecast here. On the other hand, December soil moisture content increases more frequently from the south-central Plains eastward, and December is not a particularly dry time of the year here. All of this argues for a better chance for improvement in south-central and southeastern sections of the Plains in constrast to areas farther north and west. Improvement or removal is forecast where the expected axis of heavy precipitation and the higher relative frequency of December improvement best coincide.
Confidence for the forecast in the central and southern Plains is high, though less so near the boundary between the improvement/removal and persistence forecasts.
Drought conditions in the southern Rockies, the Great Basin, the Southwest, and the West Coast should persist through the end of December. There are several potential arguments for a forecast of improvement or removal in much of the region, including California: Wetness in the short term across the higher elevations and northwestern section of California and adjacent Oregon; odds favoring above-normal precipitation for December as a whole; the start of the wettest time of year from the western Rockies westward, particularly across central and northern California, where December has brought 20% to 25% of the annual precipitation total on average during the last 15 years. However, persistence is forecast because of (a) the entrenched, multi-year nature of the drought in California, and (b) the fact that the end of December is early in the wet season, and even abundant December precipitation does not guarantee above- nor even near-normal precipitation for the winter as a whole. This is especially true of mountain snowpack.
Confidence in the forecast across the West is high
The odds favor a dry winter across Hawaii, which could spread drought throughout the state by early spring. December 2014 is likewise expected to be drier than normal, but not enough to induce large-scale drought development until after the end of the year. The small areas of drought that exist should persist.
Confidence in the forecast for Hawaii is high.
Forecaster: R. Tinker
Next Monthly Drought Outlook issued: December 31, 2014 at 3:00 PM EDT