Extended Forecast Discussion NWS Weather Prediction Center College Park MD 203 PM EDT Sat May 25 2024 Valid 12Z Tue May 28 2024 - 12Z Sat Jun 01 2024 ***Hot and humid conditions continue for southern Texas and the Florida Peninsula*** ...General Overview... An amplifying upper trough over the Great Lakes region early in the week will result in a pattern change across much of the northeastern quadrant of the U.S. through midweek. A relatively strong cold front will bring a quality airmass from the Northern Plains to the East Coast after recent warm and humid conditions. Another cold front is also forecast to cross the Pacific Northwest and then the Intermountain West through mid-late week, while an upper ridge tries to build northward across the Plains. The heatwave across the Gulf Coast region is expected to abate some by midweek, although it will still be quite warm and humid for the remainder of the week across southern Texas. ...Guidance/Predictability Assessment... The 00z guidance was in reasonable agreement about the overall synoptic pattern evolution across the lower 48 during the medium range period. We went with a general model blend, consisting of the 00z EC/CMC/UKMET and 06z GFS for our days 3 and 4 blends with higher weighting toward the 06z GFS and 00z EC. The 00z European Ensemble mean is introduced to the blend on day 5 to moderate the aggressive mid-level troughing over the Northwest found in the operational GFS and Canadian. We move away from the deterministic GFS on day 6 since the 06z solution had a negatively tilted mid- level trough propagating through the northern tier while the Euro, ensemble means and AI models suggested a more positively tiled trough. The days 6 and 7 blends consist of the 00z EC/ECE/CMCE and 06z GEFS. ...Weather/Hazards Highlights... Moisture convergence along a frontal boundary and east of a dryline across Texas and Oklahoma will likely generate scattered to numerous showers and thunderstorms, with the potential for episodes of locally heavy rainfall early to mid week as some MCS activity develops. The threat of heavy rainfall will be highest in Texas Tuesday into Wednesday as an upper level shortwave moves over the southern Plains, so there is now a planned Day 4 (Tuesday) Slight Risk in the ERO across portions of north-central Texas where the potential exists for storms with rainfall rates approaching 2 inches per hour. Some strong to severe storms are also likely. The coverage of showers and storms will likely expand north across the central and northern Plains later in the week as an organized frontal system moves into the central U.S. from the Rockies. Locally heavy rainfall will be possible across portions of the Rockies going into late Friday and early Saturday as the cold front intercepts an increasingly humid airmass. In terms of temperatures, the Gulf Cast region will continue to remain hot and humid on Tuesday before some limited relief arrives by midweek as a cold front drops southward. However, the heat and humidity will likely continue across Deep South Texas and South Florida with highs running up to 10 degree above average, and heat indices in the 100-110 degree range, especially for southern Texas. Some triple digit heat is also likely for the lower elevations of the Desert Southwest, but very low humidity here will help keep heat indices in check. A quality airmass will deliver a refreshingly cooler airmass from the Upper Midwest to the Mid-Atlantic and points northward as a pair of cold fronts pass through. courtesy of a building upper level trough centered over the Great Lakes and Northeast. Cooler weather is also forecast to reach the northwestern quadrant of the nation as the next upper trough moves inland across the Intermountain West, with highs running 5-15 degrees below normal by the end of the week. Kebede/Hamrick 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