Latest Monthly Assessment -
The Monthly Drought Outlook (MDO) for December 2017 is primarily based on official precipitation forecasts from both the Weather Prediction Center (WPC, Week-1), and the Climate Prediction Center (Week 2, Week 3/4, and the 30-day precipitation update for December). Dynamical model precipitation guidance from the CFS, GFS, and ECMWF was also used. The overall picture that emerges is one that is "front loaded"; that is, significant precipitation is predicted to fall during the early stages of the outlook period, in this case Week-1. Beyond this time, a succession of polar air masses and northwesterly flow are expected to dominate the Nation east of the Rockies, which is typically associated with a much drier pattern. Should enhanced convection associated with the tropics-based Madden-Julian Oscillation (MJO) emerge over the West Pacific early in the period as dynamical model forecasts suggest, it may also play a role in the mid-latitude North American circulation pattern by prolonging the duration of colder, drier weather across the United States, compared to what would normally be expected by extratropical influences alone. Precipitation patterns typically associated with cold season La Niñas favor drier conditions across the southern tier of states, and wetter conditions across the northern tier of states (the latter being associated with a poleward-displaced jet stream and main storm track). However, this climate signal is often more robust after the month of December, and the utility of this signal for this MDO is therefore limited.
The factors noted above, as well as climatology based on a long historical record (121 years) favor the maintenance of drought conditions across a significant portion of the contiguous United States during December 2017. Several areas of new drought development are anticipated as well. These potential development regions are indicated over the southern CONUS, and are loosely associated with abnormally dry (D0) regions depicted on the latest U.S. Drought Monitor (valid 28 November). Though some of the tools used favor precipitation across portions of the South and Southeast during Week-1, it does not look like the forecasted amounts will warrant drought improvement or removal. The normally wet winter season in California is off to a slow start this year, and with the possible exception of the end of December, the next few weeks look relatively dry as well. With the approach of Hawaii's core rainy season, most of the islands are expected to see drought improvement and/or removal. One exception may be along and near the leeward slopes of western Maui, which has received well below-normal rainfall during November. The persistent trade wind pattern that has dominated the Hawaiian Islands is forecast to continue in December. There is no drought in Alaska or Puerto Rico at this time.
Forecaster: Anthony Artusa
Next Monthly Outlook issued: December 31, 2017 at 3 PM EST
Monthly Drought Outlook Discussion