Tools used in the U.S. Monthly Drought Outlook (MDO) included the Climate Prediction Center (CPC) temperature and precipitation outlooks for June, 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 8-14 day CPC extended-range forecasts (ERFs), the weeks 3-4 outlook from CPC, dynamical models at the monthly time scale, the 384-hour total precipitation forecasts from several runs of the GFS, climatology, and initial conditions (the U.S. Drought Monitor valid on May 31, 2018).
During the past 30 days, above-normal temperatures yielded increased moisture demand across the central and southern Plains and the lower Mississippi Valley. Widespread convection resulted in above-normal precipitation accumulations across western Nebraska, parts of western Kansas, and central Texas, which helped to counteract the heat and even resulted in localized improvements to drought impacts. During June, an amplified summer ridge pattern is expected to develop and persist over the west-central U.S., resulting in a continuation and intensification of excessive heat. The ridge will also prevent westward penetration of moist air from the Gulf of Mexico, limiting additional convection. 7-day precipitation accumulations forecast by WPC are generally below 1 inch for much of Colorado, Kansas, Oklahoma, and Texas, with much of eastern Texas anticipated to remain completely dry. Higher QPF totals are depicted in Arkansas, but amounts are barely enough to keep up with climatology. Based on the anticipated persistent hot, dry pattern, widespread rapid drought development is forecast across northern Colorado, Kansas, Oklahoma, and Texas, as well as western Arkansas and much of Louisiana. This development region includes areas that are not abnormally dry currently. Flash drought conditions may also cause substantial exacerbation of impacts in regions already in drought. MCS activity north of the predicted ridge over Nebraska and Kansas early in the month may help to limit the northward expansion of drought conditions, but this area will be closely monitored due to the potential for much above-normal temperatures, particularly in Week-2.
Forecast confidence is low to moderate for the central Plains, high for the southern Plains, and moderate along the Texas Gulf Coast and the lower Mississippi Valley.
Moderate drought (D1) remains entrenched across northern Missouri, far southern Iowa, and west-central Illinois, as these regions missed out on heavier convective precipitation recently observed over the upper Midwest and east-central corn belt. The remnants of Subtropical Storm Alberto passed over the Ohio River Valley and Great Lakes region, but the heaviest bands of convection remained largely to the east of the core drought areas. Over the next 7 days, MCS activity to the north and east of the building ridge over the central U.S. is expected to bring locally heavy rainfall to southeastern Nebraska, northern Iowa and southeastern Missouri through the Tennessee Valley, but lesser accumulations are depicted across northern Missouri. The CPC 8-14 day outlook slightly favors below-normal precipitation for the middle Mississippi Valley, while the updated June monthly outlook maintains equal chances (EC) for below-, near-, and above-normal precipitation. Above-normal temperatures are favored throughout the month, which will increase evapotranspiration rates and potential crop stress. Due to the potential for convective activity, widespread drought development is not forecast, but degradation of areas already abnormally dry (D0) is favored across northern Missouri, southern Iowa, and northern Illinois. This is a low confidence forecast, as any drought development or the absence thereof will be dictated more by the progression of convective complexes during June than incipient conditions. Should an extended period of dryness occur during June, a greater expansion of drought than depicted in this outlook would be possible.
Forecast confidence across the middle Mississippi Valley is low.
Through the end of May, drought conditions and abnormal dryness generally expanded over the northern Plains due to subnormal rainfall and above-normal temperatures, while heavier precipitation relieved drought conditions over the upper Midwest. During the first days of June, a much wetter pattern is anticipated, with an axis of moderate to heavy precipitation forecast in the 7-day QPF from WPC extending from North Dakota south-southeastward to Iowa and Nebraska. This forecasted rainfall early in the period, should it occur, would provide close to the climatological monthly accumulations for many areas. Therefore, a small area of above-normal precipitation is favored on the CPC monthly outlook across much of North Dakota, with EC maintained elsewhere during the climatologically wet time of year. Based on the short term forecast, a reduction of drought is favored for much of North Dakota. Confidence in further relief is limited by anticipated above-normal temperatures, however, and although there is insufficient confidence to depict any development areas on the outlook, any regions that receive subnormal rainfall during June are at risk for drought development or intensification, particularly western North Dakota and eastern South Dakota, where recent precipitation deficits are highest.
Forecast confidence for the northern Plains is moderate.
June is a climatologically dry time of year for California, the Great Basin, and much of the Four Corners region. Therefore, little change to the current depiction of drought conditions in this region is anticipated.
Forecast confidence for the Southwest, California, and the central Great Basin is high.
Drought conditions persisted across central Oregon, with an eastward expansion during the past 30 days due to above-normal temperatures and generally below-normal precipitation. June is a relatively dry time of year for the Northwest, which makes rapid changes in drought conditions less likely. The CPC updated June outlook maintains enhanced chances for below-normal precipitation and above-normal temperatures during June. Based on these outlooks, continued expansion of drought is anticipated, with the most likely regions to the west and north of the existing drought areas due to recent heavier precipitation across northeastern California, and northwestern Nevada. Some degradations across far northwestern Montana are also possible, but confidence is two low to depict a 2-category degradation of the USDM depiction.
Forecast confidence for the Pacific Northwest and northern Intermountain West is moderate.
Precipitation has been persistently below normal during the past several weeks across parts of New England, particularly from southern New Hampshire through southwestern Maine. During the first week of June, moderate precipitation (1 to 1.5 inches) is depicted on the WPC 7-day QPF outlook. These amounts are not sufficient to erode the 3-4 inch deficits that have been observed over the past 30 days. The CPC monthly outlook has slightly enhanced chances for below-normal precipitation during June. Based on this outlook, degradation of the current D0 area in southern New Hampshire to D1 is anticipated. A lack of significant heat, at least during the first half of June, may help to slow the advancement of drought conditions elsewhere.
Forecast confidence for the Northeast is moderate.
Hawaii, Alaska, and Puerto Rico are currently drought-free and drought is not forecasted to develop through the end of June.
Forecast confidence for Alaska, Hawaii, and Puerto Rico is moderate.
Forecaster: Adam Allgood
Next Monthly Drought Outlook issued: June 30, 2018 at 3 PM EDT