Tools used in the U.S. Seasonal Drought Outlook (SDO) included the official Climate Prediction Center (CPC) temperature and precipitation outlooks for May through July (MJJ) 2017, 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), Week 3-4 outlooks, dynamical models (CFSv2, NMME, IRI, IMME, and ECMWF), the 384-hour total precipitation forecasts from several runs of the GFS, the four-month Palmer drought termination and amelioration probabilities, climatology for the MJJ season, and initial conditions (used the 4/18/2017 US Drought Monitor). ENSO-neutral conditions are favored through the Northern Hemisphere spring, with increasing chances for El Niño development by late summer and fall.
In the Northeast, 30-day precipitation departures (DNPs) have been close to normal (between -3 and 3 inches), as have average temperatures across most of New England (between -2 and 2 degF). A few D1 areas persisted in parts of southern New Hampshire and western Connecticut as long-term hydrologic impacts remained. Drought has been ameliorated across western New England as 6-month precipitation has been much above normal; however, to the east, precipitation since mid-October was at or slightly below normal, hence the lingering long-term drought. Farther south in the mid-Atlantic, between 50-75% of normal precipitation (PNPs) has fallen on most of Maryland, Delaware, Virginia, and North Carolina during the past 6-months, and recent 30-day precipitation has also been mostly below normal. With the current drought not as entrenched in the mid-Atlantic as it was in New England last fall, a decent period of surplus rains should be enough for improvement. The WPC 7-day QPF depicts heavy totals (2-5 inches) across the mid-Atlantic and moderate amounts (1-2 inches) in New England, while the 6-10 and 8-14 day ERFs favor sub-median precipitation early and near-median later along the East Coast. The May and MJJ temperature outlooks call for increased chances of above-normal temperatures across the Northeast, and the precipitation outlooks favor Equal Chances (EC) of below-, near-, and above-median precipitation. Although there are no overwhelming indicators for improvement of drought, the recent trend has been for wetter conditions and slow improvement, especially in New England. In the mid-Atlantic, the 7-day QPF forecast may be enough to reverse the regions drying trend and reduce drought.
Confidence is moderate for the Northeast (New England and mid-Atlantic)
For the Southeast, 30-day PNPs varied from 110-175% of normal across northern sections of Alabama and Georgia into the western Carolinas (where long-term drought existed), and across northeastern Florida. In contrast, less than half the normal rain fell on central sections of Alabama and Georgia and southern Florida, and drought (D1 or drier) recently developed or expanded in these areas. With the 7-day QPF keeping the largest totals to the north of MS-AL-GA-SC, the 6-10 and 8-14 day ERFs forecasting below to near-median precipitation and above-normal temperature chances, CPC's 30-day and 90-day temperature outlooks calling for enhanced chances of above-normal temperatures (EC for precipitation), and the onset of the growing season with higher temperatures and increased evapotranspiration and water demand, persistence of drought due to short-term forecasts are likely in existing drought areas while development is likely in areas already at D0. This outlook assumes the lack of any major tropical systems during June and July affecting this region, along with a lack of any definitive longer-term tools, thus lowering its confidence. In southern Florida, removal of drought is considered likely as the tropical rainy season usually begins in late May or early June and continues throughout the remainder of the MJJ season. Note that the drought may increase in intensity and areal coverage early in this period if the start of the rains are delayed or initially weak, but should be erased by the end of July.
Confidence is low (AL-GA-SC) to moderate (FL) for the Southeast.
Across the Southern region (southern Plains and lower Mississippi Valley), excess precipitation during the last 30-days generally ranged between 1 and 3 inches, with 3-8 inch surpluses in southwestern Louisiana, central Mississippi, eastern Texas, and parts of southern Oklahoma. The rains have reversed a dry trend as most areas have seen 1-2 category improvements recently. The 7-day QPF and 6-10 and 8-14 day ERFs favor a continuation of wet weather, especially across northeastern Oklahoma and northern Arkansas, while the CPC monthly and seasonal precipitation outlooks indicate elevated odds of above-median precipitation for the western Gulf Coast, especially eastern Texas and southern Louisiana, and western Texas and Oklahoma for MJJ. In addition, MJJ climatology is fairly wet (30-45% of annual total), especially in western sections. Therefore, recent wetness plus a wet climatology with favorable precipitation outlooks equals drought improvement/removal for the gradually decreasing areas of drought (D1-D2) in this region.
Confidence is moderate to high for the Southern Region (OK-TX-LA).
For the High Plains, PNPs since March 20 ranged from 10-70% of normal across eastern Montana and the Dakotas to much above normal (>150%) across Kansas, eastern Colorado, most of Wyoming, and parts of Nebraska and southwestern South Dakota. With normals generally still low during March and April, surpluses and deficits were less than 3 inches, except in Kansas (3-6 inch surpluses). However, similar to the Southern Region, MJJ climatology is quite wet, with the northern and central High Plains typically receiving one-half to two-thirds of their normal annual precipitation. The rest of the Plains usually sees 40-50% of their yearly precipitation during MJJ. With short-term wetness in the region, an increasingly wet climatology during the next 3 months, unsettled weather during the next 7-days, a tilt toward above-median precipitation in both the 6-10 and 8-14 day ERFs, and a hint of above-median precipitation in both the 1- and 3-month precipitation LLFs, the few remaining areas of drought should be gone by the end of July. An area of concern is that underlying long-term impacts have re-appeared after short but intense periods of dryness, heat, and wind from the south-central Plains 2011-15 drought, so it is unclear if the current and future wetness will be enough to counter long-term hydrologic impacts.
Confidence is moderate to high for the High Plains.
The 2016-17 Water Year (since Oct. 1) in the West continued its incredible run of abundant precipitation. The 30-day PNPs were well above-normal (>150%) in northern and central California, eastern Oregon and Washington, central Idaho, north-central Nevada, much of Utah, and western Wyoming. The rest of the West saw near to above-normal precipitation, except for subnormal precipitation in the Southwest and western Colorado. With the wet season winding down across the West, climatology favors increasing dryness and warmth. After huge drought improvements occurred in California during this near-record wet Water Year (WY), the ongoing problem is to manage the excessive snow melt from the still much above normal Sierra Nevada snow pack (April 19 state snow water content at 187%) into the rivers and reservoirs. In contrast, a few small areas of D1 lingered in southern California due to incomplete recharge of some reservoirs and ground water, and in southwest Arizona where the WY was below normal. While the climatology for May and June is quite dry in the latter area, July rains normally ramp up due to the southwest monsoon, and might provide enough rain for improvement by July 31. However, it is more likely that drought will persist in southern California and the Southwest.
Confidence for the West is high.
Recent dryness has expanded drought (D1 or drier) into eastern Maui and the western Big Island of Hawaii while the remaining islands are in D0. Coming out of the winter wet season, odds favor persistence of drought during the late spring and early summer months as monthly rainfall totals typically decrease. The Hawaii May and MJJ precipitation outlooks call for EC. With respect to development, models favor slight above-normal rainfall odds across the northern islands (Kauai and Oahu) based upon possible El Niño development later this year, thus no development introduced. Similarly in the central islands (Molokai, Lanai, eastern Maui), with no tilt either way for above or below median rainfall (EC), no development was added. Farther south on the Big Island, with EC forecast, persistence was noted for the western (leeward) side. For the eastern (windward) side, the trade winds are expected to return and bring typical showers which should be enough to stave off development during MJJ. There is no drought at this time across Alaska or Puerto Rico, and none is expected.
Confidence is moderate for Hawaii.
Forecaster: David Miskus
Next Seasonal Outlook issued: May 18, 2017 at 8:30 AM EDT