Tools used in the U.S. Monthly Drought Outlook (MDO) included the updated Climate Prediction Center (CPC) temperature and precipitation outlooks for October 2018, various short- and medium-range forecasts and models such as the 7-day quantitative precipitation forecast (QPF) totals from the Weather Prediction Center (WPC), the 6-10 day and 8-14 day CPC extended-range forecasts (ERFs), the Week 3-4 outlooks and tools from CPC, dynamical models at the monthly time scale, the 384-hour total precipitation forecasts from several runs of the GFS, climatology for October, predicted soil moisture anomaly from the GFS model, and initial conditions.
Hurricane Rosa is forecast to continue on a northeastward track with its remnant low crossing the desert Southwest at the beginning of October. Heavy rainfall, associated with Rosa, is expected to result in at least a 1-category improvement in drought from the desert Southwest north into Utah. The WPC 7-day precipitation forecast indicates widespread 1 to 3 inches, locally more, across these areas. In addition, an amplified upper-level trough enhances odds for above normal precipitation during the second week of October. Despite the expected drought improvement, long-term drought impacts may persist across the Southwest and Great Basin. Tropical Storm Sergio recently formed in the East Pacific and is forecast to become a major hurricane during the next 48 hours. A number of 6Z GFS ensemble members indicate that Sergio turns more north to northeast during early October which could bring additional rainfall to the desert Southwest. Broad scale persistence is forecast for the remainder of the West since precipitation during the next month is not expected to be sufficient for improving long-term drought. An amplified upper-level ridge is likely to persist offshore of the West Coast, increasing chances for below normal precipitation during early October. The monthly outlook calls for enhanced odds of below normal precipitation across the Pacific Northwest and northern California where persistence is forecast.
Forecast confidence is high for the Pacific Northwest, California, and the desert Southwest and moderate for the Great Basin.
The GFS and ECMWF ensemble means are in good agreement that an amplified upper-level trough persists over the interior West during early October. This persistent longwave trough favors above normal precipitation across Colorado and Wyoming. Despite very dry initial conditions (28-day streamflows and soil moisture ranking in the lowest 10th percentile), a 1-category improvement in drought is forecast for southwest Wyoming and the western half of Colorado. Precipitation amounts are likely to be much lower across southeast Colorado where persistence is forecast. Based on the 7-day WPC forecast and 8-14 day outlook, improvement and removal of drought is forecast across eastern Kansas, parts of the Dakotas, and northwest Minnesota. A relatively dry climatology and predicted lower precipitation amounts during early October favor persistence across northwest North Dakota.
Forecast confidence for the High Plains Region is low.
Recent, heavy rainfall resulted in major drought reduction across most of Oklahoma and Texas since the beginning of September. Although little to no additional decrease in drought coverage is anticipated at the beginning of October, near to above normal precipitation during the remainder of the month is forecast to result in drought improvement. Moderate to locally heavy rainfall during the final week of September eliminated any short-term precipitation deficits across the Tennessee Valley. Therefore, drought removal is likely across this region.
Forecast confidence for the Southern Region is moderate.
Above-normal precipitation during early to mid-October favors improvement and removal of drought across lower Michigan along with Missouri. The WPC 7-day forecast calls for widespread rainfall amounts of 2 to 4inches from the Great Lakes southwest to the middle Mississippi Valley. Drought removal is also forecast for northwest Minnesota, but confidence is lower since precipitation during the next week is likely to be much lower than to the southeast.
Forecast confidence is high for lower Michigan and Missouri but low for Minnesota.
Persistence and development is forecast for parts of Georgia and South Carolina where 30-day precipitation deficits range from 2 to 4 inches. Savannah has received 60 percent of its normal precipitation since June 1, while the precipitation deficit is more than 2 inches from September 1 to 29. Above-normal temperatures with highs well into the 80s to around 90 degrees F during early October will maintain high evapotranspiration rates, further increasing chances of drought development across parts of Georgia and South Carolina. The development area is consistent with the D0 (abnormal dryness) area depicted on the latest U.S. Drought Monitor, valid on September 25.
Forecast confidence is moderate for the Southeast Region.
A small area of moderate to severe drought exists across northern parts of New York and Vermont. Based on a favorable time of year for soil moisture recharge, moderate to heavy rainfall during the first week of October, and increased chances of above normal precipitation during the second week of October, improvement or removal of drought is forecast for these areas.
Forecast confidence is moderate for the Northeast Region.
Moderate to severe drought continues along the southern Alaska Panhandle. October is a relatively wet time of year. Since the monthly outlooks calls for equal chances of below, near, or above normal precipitation, improvement or removal is forecast by the end of October.
Forecast confidence is moderate for Alaska.
Moderate drought continues across the leeward side of the Big Island and a small area of Maui. Since the monthly outlook favors above normal precipitation, removal is forecast for any lingering drought areas in the Hawaiian Islands.
Forecast confidence is moderate for Hawaii.
Abnormal dryness (D0) continues across southern Puerto Rico. The precipitation deficit from September 1 to 29 is more than 2 inches at San Juan. Ongoing rainfall, associated with the remnants of Tropical Storm Kirk, along with enhanced rainfall predicted during the first week of October is likely to limit any drought development through the end of October.
Forecast confidence is high for Puerto Rico.
Forecaster: Brad Pugh
Next Monthly Drought Outlook issued: October 31, 2018 at 3pm EDT