####018006258#### FXUS21 KWNC 131821 PMDTHR US Hazards Outlook NWS Climate Prediction Center College Park MD 300 PM EDT May 13 2024 SYNOPSIS: Mid-level high pressure is forecast to expand across the Southern Tier of the contiguous U.S. (CONUS) early in week-2. This favors a relatively drier pattern compared to week-1, but with increasing chances for anomalously warm temperatures, and excessive heat conditions possibly affecting parts of southern Texas and the Florida Peninsula. Mid-level low pressure is forecast across the northwestern and north-central CONUS, which may help moderate temperatures over some areas by the middle of the period as mid-level heights decrease. A frontal system predicted to move southward across the central CONUS may lead to increased chances for heavy precipitation, initially across the Central Plains and Middle Mississippi Valley, and shifting southward toward the Gulf Coast by the middle of week-2. HAZARDS Moderate risk for excessive heat across southern Texas, Tue-Thu, May 21-23. Slight risk for excessive heat across portions of the Southern Plains and Lower Mississippi Valley, Tue-Mon, May 21-27. Slight risk for excessive heat across the southern Florida Peninsula, Tue-Mon, May 21-27. Slight risk for heavy precipitation across portions of the Great Plains, Mississippi, Tennessee, and Ohio Valleys, and Southeast, Tue-Sat, May 21-25. Rapid onset drought risk across the southern Florida Peninsula. DETAILED SUMMARY FOR THURSDAY MAY 16 - MONDAY MAY 20: https://www.wpc.ncep.noaa.gov/threats/threats.php FOR TUESDAY MAY 21 - MONDAY MAY 27: Subtropical ridging is forecast to expand across portions of the south-central CONUS heading into the week-2 period. This favors increasing chances for anomalously warm temperatures stretching from the Central and Southern Plains eastward to the southern Mid-Atlantic and Southeast coasts. Given the time of year, many areas away from the Gulf Coast are not expected to have temperatures reach excessive heat criteria. The strongest signals for excessive heat are across portions of Texas where the GEFS and ECMWF Probabilistic Extremes Tools (PETs) depict at least a 20 percent chance for maximum temperatures exceeding the 85th climatological percentile and 90 deg F. Probabilities increase above 40 percent across portions of southern and southwestern Texas, with increasing chances for triple digit temperatures. The National Blend of Models depicts an elevated potential for daily record temperatures, with some areas near or exceeding 105 deg F, and the ECMWF/GEFS skill weighted heat risk guidance indicates at least a 30 percent chance heat indices exceed 110 deg F across southern Texas. Given these signals, a moderate risk for excessive heat is posted across south Texas for 5/21-5/23, with a broader slight risk continuing across much of the remainder of Texas (excluding the northern portion and the Panhandle), southeastern New Mexico, and the Lower Mississippi Valley for all of week-2. For the western side of the slight risk area, heat is likely to be temperature driven, but higher dewpoints favored across eastern Texas and the Lower Mississippi Valley may push heat indices above 105 deg F despite the relatively lower temperatures compared to those further west. The slight risk for excessive heat also includes the southern Florida Peninsula for all of week-2. While temperature signals are not as strong compared to Texas, humidity is forecast to be more of a factor. Actual high temperatures in the low- to mid-90s are possible, with elevated dewpoints possibly leading to heat indices above 105 deg F in some areas. Troughing forecast across the northwestern and north-central CONUS favors below-normal temperatures across much of the West, extending into parts of the Northern and Central Plains and Upper and Middle Mississippi Valley. The resulting temperature contrast is likely to lead to enhanced frontal activity across the Central Plains and Middle Mississippi, Ohio, and Tennessee Valleys early in week-2. The ECMWF PET indicates at least a 20 percent chance 3-day precipitation totals exceed the 85th climatological percentile and 1-inch over these areas. By the middle of week-2, this frontal activity is forecast to shift more southward, with both the GEFS and ECMWF PETs indicating the same probabilities across parts of the Lower Mississippi Valley and Central Gulf Coast region. A slight risk for heavy precipitation is posted across portions of the Great Plains, Mississippi, Tennessee, and Ohio Valleys, and Southeast for 5/21-5/25. More northern areas of this shape are favored to receive heavy rainfall early, with the risk moving southward with time. The southward moving front and subsequent decreasing mid-level heights may also moderate temperatures over some areas, although models depict the ridging expanding again by the end of week-2 so this cooling would likely be brief. The flooding possible area is removed along the Gulf Coast and Southeast given the relatively drier conditions favored to develop late in the week-1 period, but this area will continue to be monitored given the increasing precipitation potential in the middle of week-2. Decreasing soil moisture and a more southward displacement from the predicted heaviest rainfall in week-1 lead to an elevated rapid onset drought risk across parts of southern Florida due to the warm and dry pattern predicted in week-2. No hazards are issued for Alaska, with near- to below-normal temperatures favored for most of the state. Snowmelt season is underway and frozen rivers are beginning to break up, leading to the potential for river flooding related to ice-jams. However, there are no indications of impending major river break-ups or serious threat of ice-jamming so no flooding-related hazards are posted at this time. Caution will continue to be exercised as river break-up can be unpredictable and local conditions can change quickly. FORECASTER: Thomas Collow $$