Tools used in the U.S. Seasonal Drought Outlook (SDO) included the official Climate Prediction Center (CPC) temperature and precipitation outlooks for November 2017 and November 2017 through January 2018 (NDJ), 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), Weeks 3-4, dynamical models at the seasonal time scale, the 384-hour total precipitation forecasts from several runs of the GFS, 240-hour total precipitation forecasts from the ECMWF, climatology for the NDJ season including median soil moisture changes, and initial conditions (the U.S. Drought Monitor valid on October 17, 2017). There is an increasing chance (~55-60%) of La Niña during the boreal fall and winter 2017-18.
Moderate drought (D1) expanded recently to include eastern Maine along with parts of Connecticut, Massachusetts, and Rhode Island based on 30 to 90-day precipitation deficits and low streamflows. Since June 1, Portland, Maine is 6.74 inches below normal. Despite the increasing precipitation deficits, the late fall and winter is a favorable time for drought recovery with low evapotranspiration rates, dormant vegetation, and soil moisture recharge. Also, an amplifying upper-level trough over eastern North America is expected to enhance odds for above normal precipitation during the day 6-10 period. There is the potential for heavier precipitation amounts across the Northeast, depending on how the upper-level trough amplifies. Given the likelihood for moderate to heavy precipitation during the remainder of October coupled with climatology, drought removal is forecast for the Northeast.
Confidence for the Northeast is moderate.
Hurricanes Irma and Nate resulted in above-normal rainfall across parts of the Southeast during the past 60 days. Outside areas that received this rainfall, abnormal dryness (D0) and moderate drought (D1) expanded across the Carolinas and Virginia. Although the seasonal outlook favors below normal precipitation across the Southeast, widespread development is not anticipated due to: 1. the heavy rainfall footprint associated with this year's hurricanes and 2. widespread rainfall (locally heavy) during the next week. Persistence is forecast for the ongoing drought area in North Carolina and Virginia with additional development most likely across the piedmont areas of the Carolinas. However, expected rainfall during late October limits forecast confidence in this development.
Confidence for the Southeast is low.
The seasonal outlook calls for an increased chance of below normal precipitation across the lower Mississippi Valley and Texas. However, similar to the Southeast, widespread drought development is not anticipated due to heavy rainfall and flooding, associated with Hurricane Harvey. Persistence is forecast for the moderate drought areas in Mississippi along with northeast and south Texas. Based on 60-day precipitation deficits, the most likely area for additional development across the lower Mississippi Valley is east-central Mississippi. Forecast confidence is slightly higher for development across south Texas and the Big Bend region of Texas since little to no precipitation is expected during the remainder of October. Prospects for drought removal increase across Arkansas and southeast Oklahoma, based on predicted rainfall (1 to 2 inches) during the next week along with a weaker signal for below normal precipitation among seasonal precipitation tools.
Confidence for the South is moderate.
Heavy rainfall (2 to 4 inches, or more) resulted in 1 to 2 category improvements to drought across Iowa and Illinois. Small areas of moderate (D1) drought continue for parts of the middle Mississippi Valley and Corn Belt, to the south and east of the swath of recent heavy rainfall. Although only modest amounts (an inch or less) of precipitation are forecast during the remainder of October, short-term drought is likely to end by the end of January 2018 as the next three months are a favorable time of year for soil moisture recharge.
Confidence for the Midwest is high.
An increase in precipitation since late September resulted in drought ending across parts of the central Dakotas. Prospects for additional, widespread drought amelioration for the Dakotas are expected to decrease, beginning in late October and continuing through January 2018. Only 5 to 10 percent of the annual precipitation occurs during Nov-Dec-Jan across the Dakotas. Due to this dry climatology and the likelihood of little or no precipitation during the next few weeks, persistence is favored for the ongoing moderate to severe drought areas of the Dakotas.
Confidence for the High Plains is moderate.
Following a hot, dry summer that resulted in drought expansion across the Pacific Northwest and northern Idaho, heavy rain and high-elevation snow since mid-September resulted in drought removal across northern Oregon and southeast Washington. Another round of heavy precipitation (2 to 10 inches, locally more) during the next five days is likely to lead to additional removal. The Pacific Northwest and northern Idaho receives 35 to 50 percent of its annual precipitation during Nov-Dec-Jan. Based on this wet climatology, drought removal is likely.
Confidence for the West is high for the Pacific Northwest and northern Idaho.
Long-term drought continues across much of Montana with exceptional drought over northeast parts of the state. As of October 18, the precipitation deficit is 5 inches at Glasgow, Montana which is 53 percent of normal. The seasonal outlook calls for enhanced odds for above normal precipitation throughout Montana which is consistent with increasing chances for La Niña. Despite this wet signal, the eastern third of Montana only receives 5 to 15 percent of its annual precipitation during Nov-Dec-Jan. Due to this relatively dry time of year, persistence is the most likely outcome on a broad scale for the high Plains of eastern Montana. Chances for improvement or removal of drought are more likely closer to the northern Rockies extending west to include northern Idaho, where Nov-Dec-Jan is a relatively wetter time of year compared to the northern Great Plains.
Confidence for the West is low for Montana.
Impacts related to the multi-year drought continue for parts of southern California and Arizona. Without a clear wet signal among precipitation tools at any time scale and increasing chances for La Niña development, persistence or development is forecast for southern California and Arizona.
Confidence for the West is high for Arizona and California.
From January through September 2017, Lihue and Hilo airports have received 78 and 64 percent of their normal precipitation, respectively. An increasingly wet time of year and potential influences from La Niña favor improvement or removal of Hawaii drought later in the outlook period. There is currently no drought in Alaska or Puerto Rico.
Confidence for Hawaii, Alaska and Puerto Rico is high.
Forecaster: Brad Pugh
Next Seasonal Outlook issued: November 16, 2017 at 8:30 AM EST