Drought Outlook-Improvements for Midsouth, Not Much Luck Elsewhere01/08/2018
During December, drought and abnormal dryness expanded across wide swaths of the Southwest, the Plains, and the East, with the greatest degradations occurring over the south-central High Plains and the mid-Atlantic region.
In contrast, a series of storm systems moving from the southern Plains across the South drew ample moisture from the Gulf of Mexico, resulting in widespread heavy rains (up to 10 inches) across eastern Texas, the Lower Mississippi Valley, and the Tennessee Valley. The heavy precipitation helped reverse the expansion of short term drought across the region.
At the close of the month, deep troughing over the East brought arctic air into the central and eastern U.S., along with a relatively dry pattern.
During early January, bitter cold over the East and a continuation of the dry pattern for much of the contiguous U.S. is anticipated to continue, with the heaviest precipitation limited to the Northwest and northern California.
Beyond the first week of the month, shortwaves undercutting the ridge across the West may result in a period of enhanced precipitation for California, with the wet signal extending eastward across much of the central U.S. Due to a dry climatology and the potential for most of this precipitation to remain to the west, drought development and intensification are likely across New Mexico and North Texas.
Later in the month, a pattern change, partly influenced by an emerging Indian Ocean MJO signal, favors ridging over the Southeast and a westward shift to the trough, which is fairly consistent with climate anomalies associated with La Niña.
Continued expansion of drought across the mid-Atlantic region is favored due to low streamflow values and the short term dryness, although confidence is low for this region due to the potential pattern change. Continued drought reductions are favored for eastern Texas and the lower Mississippi Valley based on climatology and the wet pattern anticipated during Week-2.
Elsewhere, little change to current drought conditions are expected, although some further improvements are possible for western Montana, where snowpack conditions are favorable and additional precipitation has recently fallen.
Small areas of drought persist across parts of Hawaii, and a reduction of impacts leading to improvement are most likely to occur beyond the forecast period.
Forecast confidence for the Western region is moderate.
- Basin snow water content values have a sharp north-south gradient across the interior West, with near to above-average snowpack conditions over the northern Rockies and Intermountain West, and much below-normal snowpack conditions over the southern Rockies.
- Despite overall generous precipitation for the Northwest during the past month, above-normal temperatures have kept snow water content values below normal across the Cascades.
- The wet season has gotten off to a slower start across central and southern California, but reservoir levels are still in good shape due to the extremely wet previous water year.
- January is a peak month for the California wet season, so adequate precipitation during this period is crucial for maintaining snowpack and reservoir levels. Even if below-average precipitation falls during the month, however, the adequate reservoir levels should preclude any widespread drought development until well beyond the forecast period.
- During the first week of January, the WPC QPF forecast shows widespread light to moderate precipitation (1 to 2 inches) from central California northward, with little to no precipitation falling across existing drought areas of the Southwest.
- A pattern change is suggested by the CPC 8-14 day outlook, with enhanced chances for above-normal precipitation across the entire Southwest, although much of this precipitation appears to be achieved by undercutting of the persistent ridge, rather than deep troughing.
- Dynamical models for the Week 3-4 period do depict troughing over the West, but precipitation tools are mixed, with no clear connection to the tropical Pacific.
- Based on these outlooks, large scale improvements to long term drought conditions over southern California and the Southwest are unlikely, but no further drought development is anticipated.
- Continued expansion of short term drought conditions over New Mexico is likely, however, as climatological precipitation is low and most tools show the heaviest undercutting precipitation staying mainly to the west during Week-2.
- The entire region is currently abnormally dry (D0), and there is uncertainty regarding which areas will degrade by the end of the month. Due to the general worsening conditions across the area, however, development is indicating for much of New Mexico.
- Further trimming of the western extent of drought conditions across Montana is anticipated, due to additional recent precipitation and the favorable snowpack conditions.
Forecast confidence for the High Plains region is moderate.
- Drought and abnormal dryness expanded across southern Kansas and the Dakotas during the past month. January is a dry time of year for the High Plains, and soils and streams typically freeze, limiting the potential for substantive changes to drought conditions.
- Little to no precipitation is anticipated during the first week of January. During Week-2, the CPC 8-14 day outlook depicts enhanced chances for above-normal precipitation across the central Plains.
- Precipitation signals during the Week 3-4 period are weak across the central U.S. Based on climatology and these outlooks, no additional drought development is anticipated, but persistence of existing drought areas is favored.
Forecast confidence for the Southern region is high.
- During late December, storm systems brought widespread rainfall to eastern Texas and the lower Mississippi Valley, resulting in widespread improvements to short term drought conditions, which had been quickly degrading prior to that time. In contrast, North Texas has had little to no precipitation, and drought conditions have been rapidly expanding.
- Little additional precipitation is forecast in the short term, but Week-2 tools and the CPC 8-14 day outlook show a return to wet conditions across eastern Texas and the lower Mississippi Valley.
- Tools are mixed during the Week 3-4 period, with the CFS depicting a drier pattern across the Southern Region, and the ECMWF maintaining above-average precipitation along a frontal boundary extending into eastern Texas.
- Due to the conflicting signals, the CPC Week 3-4 outlook maintains equal chances for below- or above-normal precipitation across the region, with enhanced chances for below-normal precipitation across the remainder of Texas.
- Climatological precipitation for the southern Mississippi River Valley region is high during January.
- Due to improving incipient conditions and an anticipated return to a wetter pattern during Week-2, additional improvement to drought is forecast for eastern Texas, eastern Oklahoma, Arkansas, and the central Gulf Coast states. In contrast, drought development and intensification is favored for North Texas.
Forecast confidence for the Midwestern region is moderate.
- During December, drought and abnormal dryness expanded across parts of Missouri, Illinois, and Iowa, due to subnormal precipitation.
- January is a relatively dry time of year for the Midwest, and streams and soils are typically frozen. Little precipitation is anticipated during the first week of January, with a pattern change favoring enhanced precipitation forecast to occur in the 8-14 day period, as discussed above.
- The highest probabilities for above-normal precipitation during Week-2 are across southern Missouri, where climatological precipitation is also higher than locations further north.
- Tools are somewhat mixed during the Week 3-4 period, but La Niña associated climate anomalies favor a storm track across the Ohio Valley, with enhanced precipitation extending across parts of the Midwest.
- The revised CPC January outlook has enhanced chances for above-normal precipitation across Missouri and Illinois.
- Based on these outlooks, drought improvement is favored for southern Missouri. Persistence is maintained for northern Missouri, Illinois, and Iowa, where incipient conditions are quite dry, and climatology limits the ability for substantive moisture recharge.
Forecast confidence for the Southeast region is low.
- During the past month, drought and abnormal dryness have expanded across parts of southern Georgia and northern Florida.
- During the first week of January, light precipitation (under 0.25 inch) is forecast along the Gulf Coastal Plain. This rainfall may slow drought degradation, but is insufficient to overcome recent deficits.
- Although the CPC 8-14 day outlook favors above-normal rainfall across much of the Southeast, probabilities are low (generally under 40 percent for above).
- Dynamical model forecasts for the Week 3-4 period generally show below-normal precipitation across the Southeast, which is consistent with climate anomalies associated with La Niña.
- The revised CPC January outlook maintains equal chances for below-, near-, and above-normal precipitation.
- Based on recent dryness and the potential for dryness later in the month associated with La Niña, slow expansion of drought across southern Georgia and northern Florida is anticipated. Some slow expansion of drought across the Coastal Plain of North Carolina and Virginia is also possible.
Forecast confidence for the Northeast region is low.
- Widespread light precipitation across New England was sufficient to limit deterioration, but drought conditions and abnormal dryness did expand over southern New York, Pennsylvania, and Maryland during the past month due to a combination of below-normal precipitation and above-normal temperatures.
- More recently, arctic airmasses have invaded the eastern U.S., with mostly dry conditions persisting outside of favored areas for lake effect snowfall (Erie, PA shattered its 1-day snowfall record with 34 inches falling on 25 December).
- Little additional precipitation is favored for the existing drought areas during the first week of January, as the favored storm track is offshore.
- Continued cold temperatures may help slow drought expansion, but given that 28-day streamflow values are below the 10th percentile throughout much of the mid-Atlantic (including some streams falling below the 2nd percentile), continued degradation in the short term is likely.
- By mid-month, a pattern change may favor warmer temperatures and increased precipitation, but there is considerable uncertainty due to a wide range of model depicted outcomes.
- Therefore, further drought expansion across the mid-Atlantic is anticipated in the short term, but confidence is low due to the potential for a pattern change.
Forecast confidence for Hawaii is moderate.
- Small areas of drought persist along the leeward portions of Hawaii’s larger islands.
- January is a wet time of year across Hawaii, although dynamical models favor somewhat suppressed precipitation during the first week of the month.
- While slow improvements are anticipated during the winter months, the effects of wet season precipitation on drought impacts are more likely to be realized after January has passed. Therefore, drought persistence remains the best bet.
- No drought currently exists or is forecast for Alaska and Puerto Rico.
Source: Climate Prediction Center