Prognostic Meteorological Discussion
Issued by NWS
Issued by NWS
063 FXUS02 KWBC 081836 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 236 PM EDT Wed May 8 2024 Valid 12Z Sat May 11 2024 - 12Z Wed May 15 2024 ...Emerging Texas/Gulf Coast/Southeast Heavy Rainfall Threat... ...Pattern Overview and Guidance/Predictability Assessment... Guidance continues to show pretty good agreement that mean troughing will linger over the Great Lakes/Eastern U.S. into early next week as a blocky pattern out west takes some time to de- amplify. By early next week, shortwave energy into western Canada will amplify over the Northwestern U.S. allowing a closed low over the Great Basin to shift eastward into the Plains/Midwest Monday- Wednesday. This should also help push troughing over the East out and upper ridging to build across the Southeast. Additional shortwave energy may move into the Southwest late period as well. Overall, the latest models and ensembles show good agreement on the large scale pattern, but plenty of uncertainty in the timing and details of individual systems. The differences in the central U.S. shortwave in particular could have bigger implications on heavy rainfall across parts of the southern Plains into the Gulf Coast/Southeast this weekend and into next week, including areas that have been very wet in the past week. So these areas may be more sensitive than normal to smaller changes in the pattern/details. Despite the differences, it seemed that a general model compromise worked well as a starting point and offered the best continuity with the previous WPC forecast. For days 3-5, was able to use an equal blend of the deterministic solutions, incorporating increasing amounts of the ensemble means into the blend for days 6-7 to mitigate the smaller scale details that are impossible to resolve at these longer time scales. ...Weather/Hazards Highlights... Moderate rainfall will linger this weekend over the Northeast with wrapback moisture and upper trough support as downstream energy transference leads to coastal low genesis, but details remain uncharacteristically uncertain even as we enter short range time frames. Upstream northern stream systems will then periodically offer bouts of mainly lighter rains from the north-central U.S. to the Great Lakes/Northeast this weekend to next midweek, albeit also with uncertainty in focus/timing, but with limited impact. Meanwhile to the south, a cooling/slowing trailing front along with a reinforcing front and upper shortwaves are expected to periodically focus precipitation from the southern Rockies/Plains out through the Gulf of Mexico and Gulf Coast/Florida this weekend through early-mid next week. A growing but still not solidified guidance signal offers support for moisture to increase along the Gulf Coast and vicinity ahead of the returning warm front. Heavy rain may work inland over time as the front edges northward. The WPC Day 5/Sunday into Monday Excessive Rainfall Outlook update this afternoon expanded the previous marginal risk area significantly northward into eastern Texas to far southern Oklahoma. Given soil/streamflow sensitivities across especially southeast Texas, also expanded the slight risk farther north. Heavy rain and a threat of runoff issues may also spread through the central Gulf Coast to the Southeast early-mid next week to monitor. Santorelli/Schichtel Additional 3-7 Day Hazard information can be found on the WPC medium range hazards outlook chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation forecast (QPF), excessive rainfall outlook (ERO), winter weather outlook (WWO) probabilities, heat indices, and Key Messages can be accessed from: https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml https://www.wpc.ncep.noaa.gov/#page=ero https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml https://www.wpc.ncep.noaa.gov/#page=ovw $$