July - September 2014

Outlook Graphic: PNG   PDF 

Latest Seasonal Assessment - As of June 10, 2014, widespread ample rains in the Plains reduced drought (D1-D4) coverage to approximately 36% of the contiguous 48 States, according to the U.S. Drought Monitor. This number was down from 38% a month ago, which had not changed much since late January. In addition, the area affected by extreme or exceptional drought (D3 or D4) dropped to 12% of the contiguous States, down from 14.5% in mid-May. Most of the improvement occurred in the southern two-thirds of the Plains, while the Tennessee Valley and central Appalachians also saw improvement. With the late spring and summer months climatologically the wettest time of the year in the Nation’s mid-section, the 4 to 8 inches of rain (locally over a foot) that fell during the past 30-days were quite beneficial. Only a few small areas were degraded since mid-May, but did include the Red River Valley of Oklahoma and Texas. Alaska, Hawaii, Puerto Rico, and areas east of the Mississippi River remained almost entirely drought free (wetter than D1), except for small areas in the south-central Appalachians, extreme southern Florida, and on central Molokai Island in Hawaii.

The seasonal drought outlook valid from June 17 to September 30, 2014, is based primarily on initial conditions, short-, medium-, and long-range forecasts, and climatology. Persistence is extremely likely along the West Coast and in the Intermountain West (but especially in California) where summer and early fall is a normally dry and warm time of year, and both surface and subsoil moisture nearly always decline. Persistence is also forecast, though with less confidence, from southern Oklahoma southward into southern Texas. Drought is forecast to expand eastward into eastern Texas and western Louisiana by the end of September. The anticipated El Niño event, which should commence in the late summer or early fall, is expected to reduce tropical activity (e.g. subnormal rains) across the Caribbean and Atlantic basins, hence the forecast for drought development in Puerto Rico. In contrast, drought improvement or removal is forecast for the Rockies, southern High Plains, central Plains, and western Corn Belt as forecasts from mid-June onward generally favor above-normal precipitation, continuing a trend of wetter weather east of the Rockies the past 30 days. July-September is the wettest time of year in the Southwest (summer monsoon) and southern Rockies (35-55% of its annual precipitation), and also normally wet throughout the High Plains into the upper Midwest, so there is the potential for additional drought improvement in these areas if above normal rainfall is recorded – which is forecast - as a robust fetch of moisture from the eastern Pacific Ocean and Mexico is expected into the southwestern U.S. during this 3-month period.

Tools used in the U.S. Seasonal Drought Outlook (SDO) included the official Climate Prediction Center (CPC) temperature and precipitation outlooks for July 2014 and July–September 2014, various short- and medium-range forecasts and models such as the 5-day and 7-day precipitation totals from the Weather Prediction Center, the 6-10 day and 8-14 day CPC forecasts, the NAEFS precipitation outlooks, the soil moisture tools based on the Constructed Analog on Soil Moisture (CAS), dynamical models (CFSv2, NMME, IRI, and IMME), the 384-hour total precipitation forecasts from several runs of the GFS, the four-month Palmer drought termination and amelioration probabilities, climatology, and initial conditions. The chances of El Niño increase during the 2014 summer, with the June 5, 2014 ENSO Advisory (from CPC and the International Research Institute for Climate and Society (IRI)) indicating a 70% chance during the Northern Hemispheric summer, and reaching 80% during the fall and winter.

For the week following the release of this Outlook (June 19-26, 2014), little or no precipitation is expected to fall west of the Rockies. In contrast, moderate to heavy totals (1 to 3 inches), with isolated higher totals, are expected from the central High Plains eastward to the mid-Atlantic, possibly providing additional drought relief to the southern and central Plains. Heavy rain is also expected in Florida, most likely alleviating short-term dryness (D0) in the south. Elsewhere, lighter amounts (less than 0.5 inches) are forecast along the western Gulf Coast and in New England. The odds for notable rainfall in the south-central Plains drought area continues from the last week of June onward, thus the Seasonal Drought Outlook is based on forecasts for the 7-day period and beyond.

Summer and early fall is a dry and warm time of year along the West Coast, especially in California. Typically, less than 5% of a given year’s precipitation falls during July-September on areas west of Oregon’s Cascades and California’s Sierra Nevada, with very little precipitation falling on most of the Golden State. In the Pacific Northwest, although JAS is normally dry, favorable odds for above-median temperatures in the short, medium, and long-term plus existing abnormal dryness (D0) warranted a small area of development in northern Oregon and central Washington. In the Great Basin and Intermountain West, summer is typically drier than other times of the year, though not so markedly. However, surface and subsoil moisture content declines much more frequently than it increases in these regions during the summer and early fall due to high temperatures, making drought recovery highly unlikely. This is true except in extreme eastern sections of the Great Basin where an expected robust Southwest summer monsoon is forecast to bring above-median rainfall, possibly lower temperatures, and drought improvement to eastern Nevada and Utah (see Southwest regional summary).

Forecast confidence for The Far West and the Intermountain West is high.

Climatologically, summer starts out dry across the Southwest and southern Rockies, but precipitation quickly increases in July as monsoonal moisture enters the region from Mexico and the Pacific Ocean, triggering shower and thunderstorm activity. JAS is normally the wettest 3-month period in eastern Arizona, most of New Mexico, and southwest Texas, with over 45% of their annual precipitation occurring. In the short-term, monthly, and seasonal precipitation outlooks, there are enhanced chances for above-normal rainfall across most of this region. Since this is a markedly wet time of the year from eastern Arizona eastward into western Texas, and because of the favorable chances of above median precipitation (e.g. a robust summer monsoon with ample moisture inflow) at all time frames – leading to increased cloud cover, higher humidity, and probable lower temperatures, drought improvement (and removal with areas of moderate drought) is forecast.

Forecast confidence for the Southwest and southern Rockies is moderate to high.

For the drought areas in the southern third of the Great Plains -- from southern Oklahoma southward to the Mexican border and the western Gulf Coast -- drought is expected to persist, with some expansion into south and eastern Texas and western Louisiana. Although the 7-day QPF forecast calls for little or no rain in the eastern half of Texas and western Louisiana, the extended range forecasts (days 6-10 and 8-14) favor above-median precipitation. Thereafter, however, the July and JAS odds tilt toward drier and warmer than normal conditions along the western Gulf Coast and in the southern Mississippi Valley, providing the main reasoning for keeping drought in this region with some southern and eastern expansion by the end of September. Although the July and JAS precipitation outlooks favor below-median out to the western Florida Panhandle, eastern drought expansion stopped in western Louisiana due to surplus rainfall (more than a foot) at 180-days from eastern Louisiana to northern Florida. On the other hand, the areas with drought expansion have 4-8 inch deficits for the same time period.

In contrast, JAS is a relatively wet time of year from western Texas northeastward (including surplus rains the past 30 days) - and since all of the short, medium, and long-term precipitation forecasts point toward above-median rainfall, drought improvement or removal seems the most probable scenario in the southern High Plains.

Forecast confidence for the southern Plains and western Gulf Coast is moderate.

During the past 2 weeks, severe weather and widespread, heavy rains (over 10 inches in southeast South Dakota, northwest Iowa, and southwest Minnesota) have targeted the central Plains and Midwest (specifically the western Corn Belt), providing widespread and ample drought relief. As a result, drought improvement has been made to most of South Dakota, Minnesota, Iowa, Nebraska, and Kansas. With the recent wet pattern, July and JAS a climatologically wet time of the year, heavy rains in the 7-day QPF, and somewhat favorable chances for above-normal rainfall in the 6-10 and 8-14 day, July monthly, and July-September seasonal outlooks, improvement and removal is the only logical forecast. However, one small caveat that can temper seasonal drought forecast confidence in the Midwest and Plains is the possibility of a brief but intense growing season flash drought (extreme temperatures and no rain during critical crop growing stages), especially during mid- to late summer.

Forecast confidence for the central Plains and Midwest is moderate to high.

The small drought area (D1) in the southern Appalachians and abnormal dryness (D0) in eastern Kentucky and Tennessee are possible candidates for improvement based upon the 7-day QPF totals (1.0-2.5 inches) and high probabilities for above-median rainfall during the 6-10 and 8-14 day periods. Accumulated deficits of 4-6 inches over the past 90-days could be erased if the short and medium-term forecasts verify. Although there is no tilt either way in the July and JAS precipitation outlooks, the June and July climatology are somewhat wet, so the short-term precipitation forecasts may be enough for improvement. Thus, removal is forecast, though not with much confidence given the lack of long-term indicators.

Forecast confidence for the southern Appalachians is moderate.

The only remaining Hawaiian drought area (D1) is on central Molokai associated with low water levels on the Kualapuu Reservoir. The July and JAS forecasts favor slight odds toward wetness in this region, although normal summer rainfall amounts at Molokai are much less when compared to the winter totals. However, with the expected odds for above-median monthly and seasonal precipitation throughout Hawaii, this forecast favors drought removal, though with low to moderate confidence.

Forecast confidence for Hawaii is low to moderate.

The past 30 days have been very dry across most of Puerto Rico, especially in southern and eastern sections. With shortages persisting even longer (out to 180-days), abnormal dryness already in place, and the very strong possibility of an El Nino event which would most-likely interrupt the Caribbean and Atlantic tropical season (e.g. less summertime convection and tropical systems), drought development is likely by the end of September.

Forecast confidence for Puerto Rico moderate to high.