Long-term drought over the northern Great Plains is expected to continue during the Oct-Nov-Dec (OND) 2017 season, with the region now in its climatological dry season. Other areas where drought is forecast to persist and/or intensify include eastern portions of the Middle Mississippi Valley, Lower Michigan, far southern Texas, western Nebraska, parts of Utah and Colorado, southern California and southern Arizona.
This is due to a combination of factors, a few of which include sufficient distance from anticipated storm tracks, various dynamical and statistical model output, official precipitation forecasts at all timescales out to 90-days in the future, and the winding down of the summer Monsoon season in the Southwest.
Two areas of potential drought development are indicated over the Middle and Lower Mississippi Valley and nearby areas, in regions where 30-day precipitation deficits are already substantial, and where most of the precipitation is expected to miss.
Drought improvement and/or removal is predicted from the Pacific Northwest to the northern Rockies based on good overall model agreement, and is consistent with what would be expected given the increasing odds of a upcoming cold season La Niña.
Drought improvement and/or removal is also indicated across scattered parts of the Central contiguous U.S., generally from the Middle Rio Grande Valley through Kansas to the Upper Great Lakes region, based in part on the expectation of heavy precipitation in the shorter-term (next two weeks). With the approach of the cold season, and a climatological increase in widespread storm activity, the residual drought in eastern Maine is forecast to be removed.
The OND 2017 season is still a bit before the traditional rainy season for the Hawaiian Islands. Therefore, drought is predicted to either persist and/or intensify across the Hawaiian archipelago during the autumn. There is currently no drought in Alaska or Puerto Rico.
Confidence is moderate for the Southeast.
- There is no drought over the Southeast at this time, but drought development is possible over portions of Alabama which extends across Mississippi and eastern Louisiana, where short-term precipitation deficits have increased. Excessive rain associated with Hurricanes Harvey and Irma fell west and east of this region, respectively.
- Precipitation is predicted to range from below to near-normal during the Week-1 period, and below-normal during Week-2.
- Though the 30-day precipitation outlook lacks a significant signal in this region, the 90-day outlook does favor drier-than-normal conditions, especially if the trend toward a La Niña continues. The CAS and CFS precipitation outlooks for OND 2017 also lend support to this forecast.
Confidence is moderate for the High Plains and South.
- The OND season is climatologically dry for northern sections of both the Great Plains and Mississippi Valley. Long-term drought is well established in this region, though there has been some very beneficial precipitation during the past few weeks.
- Precipitation outlooks at time-scales out to 90-days suggest drought conditions may persist across most of this region, as amounts do not appear to be enough to overcome both a drier climatology and the more durable and entrenched nature of the present drought.
- The exception to this is thought to include extreme eastern portions of the Dakotas and adjacent northwest Minnesota, which are anticipated to be in closer proximity to the mean storm track across the middle portion of the Nation and Upper Great Lakes region.
- For central and southern sections of both the Great Plains and Mississippi Valley, and Lower Michigan, areas of drought removal, improvement, persistence, and development are anticipated.
- Precipitation amounts of 2-5 inches are predicted over western and central sections of both Kansas and Oklahoma for the Week-1 period alone, and this does not take into account the vast majority of the season. Above normal precipitation is also favored in this area during Week-2. The CAS predicts an anomalously wet pattern too, though this does contradict a fairly strong climatological signal for dryness in this region during OND.
- Drought removal is indicated for this area, though there is a greater consensus among tools for drought persistence/intensification farther east over eastern Missouri, central Illinois, Lower Michigan, and farther south over South Texas. These areas are generally expected to miss out on the short-term heavy rains (Week-1; with the exception of the central Rio Grande Valley), and longer-term prospects (30-days and 90-days) both support elevated odds of below normal precipitation.
- In eastern Oklahoma, western Arkansas, and southern Missouri, 30-day observed precipitation deficits already range from 3-5 inches, and long-term prospects favor drought development in this region.
- Drought areas in northeast Kansas and western Iowa are also expected to see improvement and/or removal of drought, though this does not appear to be the case for western Nebraska.
Confidence for the West is moderate to high.
- For the Pacific Northwest and northern Rockies, the 90-day CAS and CFS, CPC’s official 30-day and 90-day precipitation outlooks, regional climatology, and La Niña composites all favor increased odds of above-normal precipitation. In addition, it is easier to erase the short-term deficits in this region than it is for areas that have more entrenched, longer-term drought, in place.
- This notion of a wetter Pacific Northwest and northern Rockies is also consistent with the recent trend towards a La Niña, and would favor drought improvement and/or removal.
- For southern California, southern Arizona, and portions of Utah and Colorado, drought persistence and/or intensification is anticipated.
- For southern portions of California and Arizona, the climatological summer monsoon season is rapidly winding down, and climatology favors a drier autumn.
- The situation is somewhat less clear in Utah and Colorado, and CPC’s OND precipitation outlook depicts little if any useful signal. In the absence of any strong signal to the contrary, it is thought that persistence/intensification of drought was the best bet.
As noted above, confidence for the Northeast is low.
- Moderate drought (D1) remains in eastern Maine. During Week-1, WPC’s QPF forecast depicts the proximity of very heavy rainfall to the New England coast associated with Tropical Storm Jose (2pm EDT on Sep 20). The exact track of Jose will determine if any of the rainbands on the western side of the hurricane come close enough to reach eastern Maine.
- CPC’s Week-2 precipitation outlook calls for a modest tilt in the odds for above-normal precipitation in this area. The October and OND precipitation outlooks both favor Equal Chances (EC) of below, near, and above-normal precipitation.
- The CAS and CFS forecasts for OND favor near-normal conditions for Maine, and drier-than-normal conditions for much of the remainder of the Northeast.
- Soil moisture levels usually increase across the Northeast during the fall, as diminishing sun angles and vegetation entering dormancy reduce evapotranspiration (ET) rates. Long term (12 month) precipitation deficits remain, which may act to resist complete moisture recharge.
- Considering these factors, removal of the D1 area is slightly favored in eastern Maine, but confidence is low.
Confidence for Hawaii, Alaska and Puerto Rico is moderate to high.
- Drought is expected to persist and/or intensify in Hawaii during the OND season, as the beginning of the traditional rainy season is still several months away.
- There is currently no drought in Alaska, and the lingering area of drought across southwestern Puerto Rico was recently removed.