U.S. Drought Outlook-Expansion Continues to Creep Across the South11/21/2016
Across the northern tier of the contiguous U.S., there is a general model consensus regarding a tilt toward above-median precipitation, especially in the DJF outlook. This would be expected during a La Niña event as frequent Pacific storm systems and accompanying upper-level troughs typically track across the northern third of the U.S.
In the West, this expected pattern, combined with near-record October wetness in the Northwest and wet winter climatology in the Far West, should bring additional drought improvement or removal to southwestern Montana, eastern Oregon, northwestern Nevada, and northern California, although drought is forecast to persist farther south.
With above-median winter precipitation also favored in the Great Lakes region and Ohio Valley, drought improvement is similarly forecast for western sections of Pennsylvania and New York where recent heavy rains have provided some drought reduction and primed the region for additional relief.
Precipitation has been spottier farther east, and with no consistent guidance from the models, persistence was left in New England, eastern New York, and northern New Jersey; however, recent dryness to the south and La Niña composites and trends called for some development in the mid-Atlantic.
The southern third of the lower 48 States is predicted to tilt toward above-normal temperatures and sub-median precipitation, especially during the winter, favoring drought persistence or intensification. Combined with recent warmth and near-record dryness, areas of predicted drought development included the remaining non-drought areas of the Gulf Coast, extending westward into central Texas and the south-central Plains, and eastward into the Atlantic Piedmont.
Southern and mid-Atlantic coast areas should remain drought free to the end of February due to copious rains from Hurricanes Matthew and Hermine. Drought expansion was also forecast for parts of the Southwest where the winter outlook tilts toward drier and warmer conditions, and D0 is already present.
The only exception to the widespread dryness in the Southeast is improvement in the northern edge of the drought in the lower Ohio Valley (southern Indiana and northern Kentucky) where somewhat above-median winter precipitation is forecast.
Elsewhere, small areas of remaining drought in Hawaii (leeward sides of Kauai and Maui) are expected to improve or be removed by the end of February, although conditions may somewhat degrade first. The Hawaiian precipitation forecast favors above-median precipitation across the archipelago, consistent with the tendency for wet conditions when ENSO is neutral (which is expected by early 2017).
In Alaska and Puerto Rico, the small remaining (non-drought) D0 areas were not expected to worsen during the winter, so no forecast was made.
Forecast confidence for the Southeast is moderate (northern sections) to high (interior and Gulf Coast regions).
- Longer-term drought (more than 6-months) continued to dominate the interior Southeast (northern two-thirds of Mississippi and Alabama, southern and eastern Tennessee, the western two-thirds of Georgia, and western sections of the Carolinas).
- During the past 30-days, extremely dry (less than 25% of normal rainfall) and warm (temperatures averaging 4-8 degF above normal) weather encompassed all of the Southeast, while also expanding northward into the mid-Atlantic and westward into the lower Mississippi Valley and south-central Plains. Many locations failed to record any measurable rains during this period as 2-6 inch deficits accumulated.
- Hydrologic impacts have increased, including ponds and wells that have dried up, numerous large ongoing wildfires that have reduced visibilities and decreased air quality, record or near-record low river and lake levels, and delays in planting winter crops and cover.
- During the past 90-days, deficits of 8-12 inches were common in Mississippi, Alabama, western Florida Panhandle, northern Georgia, and the western Carolinas, while at 6-months, 12-16 inch shortages were found across northern sections of Mississippi, Alabama, and Georgia, and southeastern Tennessee.
- Not surprisingly, drought (D1 or drier) has expanded across nearly all of the Southeast, westward into the lower Mississippi Valley, and northward into the lower Ohio Valley.
- Unfortunately both the 1- and 3-month outlooks are unfavorable for improvement, and point toward additional deterioration and expansion (development).
- With the weak La Niña favoring sub-median DJF precipitation and above-normal temperatures, the December precipitation outlook tilting toward sub-median Southeast precipitation, the entrenched longer-term drought and recent dry and warm conditions, persistence and deterioration, along with development in existing D0 areas (lower Mississippi Valley, mid-Atlantic), is expected across the Southeast.
- The only area with forecasted improvement is the lower Ohio Valley (southern Indiana and northern Kentucky) as the winter precipitation outlook has favorable chances of above-median precipitation in the Ohio Valley, and the drought is not as entrenched (short-term).
Forecast confidence for the Plains is moderate.
- With very dry, warm, and windy conditions the past 30-days, abnormal dryness and drought (D1 or drier) has expanded across the south-central High Plains (eastern Colorado, western Kansas, Oklahoma Panhandle).
- In the southern Plains (northeastern New Mexico, northern Texas Panhandle, extreme southern and eastern Texas, southeastern Oklahoma), the areas of drought are expected to persist along with drought development in the existing D0 areas by the end of February.
- The drier seasonal drought outlook is consistent with CPC’s precipitation outlooks for DJF which broadbrush most of the southern CONUS with enhanced odds of below-median precipitation, consistent with winter La Niña composites.
- The area of southeastern New Mexico, southwest and central Texas has seen rainfall surpluses at both short (90-days) and medium-term (6-months) periods, and this should keep the region drought free through the end of February despite the odds for sub-median winter precipitation.
- Farther north, the recent addition of D1 to the central High Plains should persist during the winter as the climatology is quite dry, along with no help from the 1- and 3-month precipitation outlooks (EC).
- In the north-central Plains, the long-term drought area in western South Dakota and northeastern Wyoming, along with the small short-term drought areas in eastern South Dakota and central Nebraska, should also persist as the winter is normally dry and the outlooks are either EC or just slightly favor above-median precipitation.
- In addition, the CPC soil moisture model has shown a high frequency of negative changes from mid-November to the end of February across the Plains, so improvement here during the winter is generally not expected.
Forecast confidence for the Southwest is moderate (Four Corner States) to high (southern California).
- Status-quo, with some possible development in existing D0 areas, is expected across the Southwest during DJF. Traditionally, La Niña events tend to favor continuing dryness across this region, and CPC’s winter precipitation outlook has increased odds (albeit low) of below-median precipitation across the Southwest (and eastward across the southern tier of the U.S.).
- Farther north, the 1- and 3-month precipitation outlooks show no tilt either way for Utah, although the probability for above-median precipitation in both December and DJF outlooks were just to the north of the Utah drought area.
- The protracted (4-5 year) drought in southern California is not expected to improve with an ongoing La Niña even though the climatology is quite wet during the winter (40-50% of annual total).
Forecast confidence is moderate to high for the Northwest and California.
- For the Northwest and northern California, the 2016-17 Water Year has gotten off to a wet start. Most of Washington, Idaho, Montana, western Oregon, northern parts of California and Nevada, and western Wyoming have received at least 1.5 times the normal precipitation since October 1. Accordingly, drought was improved or removed across much of the Northwest in the USDM during the past 30-days.
- In the upcoming 7-day period, WPC predicts 4-8 inches (liquid equivalent) of precipitation along the coasts of Washington, Oregon, and northern California, and slightly lower totals in the Cascades and northern Sierra Nevada Mountains. Enhanced odds for above-median precipitation are predicted for nearly all of this area during Week-2.
- CPC’s monthly outlook for December favors above-median precipitation in the northern Rockies and High Plains as does the DJF outlook. Below-median winter precipitation is slightly favored across the southern half of California, with EC in-between.
- With the recent wetness, a very wet winter climatology, and favorable chances of above-median December and DJF precipitation due to the weak La Niña in the Northwest, the odds would be in favor of improvement in southwestern Montana, eastern Oregon, north-central California, and northwestern Nevada.
- In contrast, 4-5 consecutive years of drought in southern California and unfavorable winter precipitation odds point toward persistence there.
Forecast confidence for the Northeast is moderate in western sections (improvement) and low in eastern areas (persistence or development).
- During the past 30 days, the Northeast (New England, eastern Great Lakes region, and northern mid-Atlantic) observed varying amounts of precipitation, with surplus rains in western sections, near-normal totals along coastal locations, and subnormal precipitation in extreme northern and southern sections.
- The U.S. Drought Monitor (USDM) depicted some improvement in extreme western and eastern areas (thus primed for additional improvement), while in-between areas saw some deterioration. Moderate to extreme drought (D1 to D3) remained across this region, albeit an overall smaller area than a month ago.
- The probability of experiencing drought amelioration increases during the cooler half of the year, especially with the climatological increase of mid-latitude storm activity associated with an energized polar jet stream, reduced temperatures, and diminished evapotranspiration and demand.
- In addition, water temperatures across the eastern Great Lakes are considerably above-normal going into the winter season, favoring increased precipitation in areas downwind of the Great Lakes. And with the ongoing but weak La Niña, above-median winter precipitation is favored in the Ohio Valley and Great Lakes region.
- Unfortunately, the drought outlook for this part of the country is quite uncertain because once a drought is firmly established (past 1-2 years), it is often difficult to dislodge it, especially when hydrologic impacts (e.g. low river, lake, and well levels) occur.
- However, with the recent wetness in western sections and a tilt toward above-median winter precipitation in the Ohio Valley and Great Lakes region, continued improvement is favored in western sections of New York and Pennsylvania, and along with the lower Ohio Valley (southern Indiana and northern Kentucky) that is now included in the northward-expanding Southeast drought.
- In contrast, with no clear tilt in odds for above or below median precipitation at 1- and 3-months (EC), and larger long-term (12-months) deficits (8-16 inches) to overcome in eastern areas than in western sections, the region from northern New Jersey and Long Island northward into eastern Maine is more likely to experience drought persistence than improvement.
- A few well-placed Nor’easters during the next few months (before the ground freezes) would be extremely beneficial toward decreasing drought in this region. There are some hints of storminess in the long-range GFS runs during late November, but the uncertainty is too large to use in this outlook.
- In the northern mid-Atlantic, however, recent dryness and La Niña winter trends and composites pointed toward development, and it was added.
Forecast confidence for Hawaii is moderate to high.
- The outlook for the Hawaiian archipelago favors above-median monthly and seasonal rainfall which is fairly consistent with cold-season La Niña episodes.
- In addition, the tendency for wet conditions when ENSO is neutral (which is expected by early 2017) should also assist with improvement or removal of the small drought areas on the leeward sides of Kauai and Maui.