During the past month, across the Northeast, the coverage of abnormal dryness (D0 on the U.S. Drought Monitor) has dropped and no areas of moderate drought (D1) remains. The development of any new drought over this region during the Dec-Jan-Feb (DJF) winter season is considered unlikely.
Dryness and drought have decreased in coverage over the Midwestern states during the past month, with the exception of Missouri, where moderate to severe drought (D1 to D2) now covers most of the southeastern half of the state.
According to CPC’s official 90-day precipitation outlook, prospects for improvement and/or removal of drought are best for northern and eastern portions of Missouri. Elsewhere across the Midwest, drought removal and/or improvement is expected.
A comparison of the latest drought conditions with those from a month ago across the High Plains region reveals relatively small changes overall, especially in terms of spatial coverage.
Despite CPC’s 30-day and 90-day precipitation outlooks favoring above-normal precipitation in eastern Montana and the Dakotas this winter, precipitation amounts, though likely above normal, may not be enough to overcome prior dryness, as normal amounts in that area are low, therefore drought persistence and/or intensification is likely.
For western Montana, the CPC monthly and seasonal precipitation outlooks also favor above-normal precipitation this winter, but this area has already received substantial precipitation this past month and is closer to seeing drought removal and/or improvement than areas farther east.
In addition, typical La Niña winters favor the proximity of the polar jet stream and the associated storm track, which also supports the idea of improving conditions over western Montana.
Across approximately the southern third of the contiguous U.S., dryness and drought have expanded across the Southwest (especially Arizona), portions of the South (with widespread severe drought (D2) in Arkansas), and the Southeast during the past 30-days.
View United States Seasonal Drought Outlook here.
Most precipitation outlooks on timescales out through 90-days, combined with historical wintertime La Niña-related circulation patterns, favor drought persistence and/or intensification across a broad swath of the southern tier states in DJF. This is due in large part to the polar jet stream and mean storm track usually being displaced well to the north of this region during La Niña winters.
In Hawaii, DJF represents the climatological core of the rainy season, and with CPC outlooks favoring above-normal precipitation this winter, it’s reasonable to expect drought improvement and/or removal across the Islands. There is currently no drought in either Alaska or Puerto Rico.
Confidence for the Southeast is moderate to high.
Thirty-day precipitation anomalies in the Southeast indicate mostly below- to near-normal precipitation, with the exception of far western sections of Virginia and the Carolinas, and over southern Florida, where above-normal precipitation fell.
Typically during the DJF season, most of this region receives 20-30 percent of its annual precipitation. The exception is the Florida Peninsula, where the historical record reveals a gradation of values ranging from 15-20 percent in the north to 5-10 percent in the south.
Existing moderate drought (D1) from the Carolina Piedmont region into southern Virginia (and over a localized area along the southern border of Alabama/Georgia) is expected to persist and/or intensify during the DJF period, as precipitation predictions at nearly all time-scales out to one season in advance support below normal precipitation.
Drought development is also anticipated across portions of the Southeast region. This is a common (though not guaranteed) occurrence during La Niña winters.
Across most of peninsular Florida, drought development is considered much less likely, as it received copious rainfall from both Hurricane Irma earlier in the season and from a record wet season this year.
Confidence for the South is moderate to high.
Across the South, most areas report precipitation deficits during the past 30-days, topping out with 3-5 inch deficits most notably in the Lower Mississippi Valley. In contrast, surpluses of 1-4 inches were reported in Tennessee and south-central Louisiana.
For Oklahoma and all but eastern Texas, the 121-year climatological record indicates only 5-20 percent of the annual precipitation amounts can be expected during the DJF season, with the lowest amounts over the typically drier southern High Plains.
For the remainder of the South (Arkansas, Louisiana, Mississippi, and Tennessee), 20-30 percent of their annual precipitation can normally be anticipated during DJF.
Dryness and drought (D0 to D2) has expanded in coverage during the past month across this region.
According to WPC’s Week 1 precipitation forecast, precipitation amounts are expected to be light (less than 0.5-inch) over most of this region. Beyond that period, precipitation outlooks generally call for below-normal precipitation over this area.
As with the Southeast, drought is likely to persist and/or intensify, as well as develop in other portions of the South, during DJF.
Confidence for the Midwest is low to moderate.
Thirty-day DNPs across the Midwest depict near- to below-normal precipitation over approximately the western half of the Midwest region, and near- to above-normal precipitation over the eastern half.
Precipitation deficits generally ranged from 1-3 inches, while surpluses ranged from 1-5 inches or more. The largest surpluses were noted over areas downwind of Lakes Superior and Huron, where the lake-effect snow season has started.
The DJF season is typically a drier time of year across the Midwestern states, with climatology indicating only 5-20 percent of the area’s annual precipitation can be expected. Dryness and drought (D0 to D2) has been focused primarily in eastern and southern Missouri, and in south-central Iowa.
For Week-1, WPC predicts 0.5-2 inches of precipitation for approximately the eastern half of the region, and less than 0.5-inch elsewhere. Week-2 and experimental Week 3-4 precipitation outlooks favor near to below-normal precipitation.
CPC’s official 30-day and 90-day precipitation outlooks indicate a return to above-normal precipitation amounts over much of the Midwest region, especially northern and eastern sections. It is over these northern and eastern sections that prospects for drought improvement and/or removal are greatest.
Areas to the southwest are considered more likely to experience drought persistence and/or intensification.
Confidence for the High Plains is moderate.
Precipitation deficits ranged from near zero to 2 inches during the past 30-days over most of the High Plains region. On the other hand, precipitation surpluses of 0.5-2 inches (locally greater) were noted over central parts of Montana.
Looked at another way, the 30-day Percent of Normal Precipitation (PNP) map depicts much of eastern Colorado, western Kansas, southern and eastern Nebraska, and portions of the Dakotas, as receiving only 5-25 percent of its normal precipitation during the 30-day period, and central Montana receiving 110-300 percent of normal (locally greater) during the period.
As with the Midwest region, this is also a drier time of year for the High Plains region, with the climatological record indicating the reception of only 5-20 percent of the region’s annual precipitation during winter (DJF).
CPC’s 30-day and 90-day precipitation outlooks favor above- normal precipitation amounts across nearly all of the large, ongoing drought area in the region.
While western Montana may get some relief from the drought this winter (primarily from the expected proximity of the polar jetstream and associated storm track associated with La Niña), substantial relief appears less likely for eastern Montana and the Dakotas which have larger deficits to overcome.
Source: Agfax |