Extended Forecast Discussion NWS Weather Prediction Center College Park MD 253 AM 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 12Z model guidance suite initially has a good overall synoptic scale depiction of the incoming trough for the Pacific Northwest and the downstream ridge over the Rockies on Tuesday. The 12Z CMC differed considerably from the model consensus across the Great Lakes region with the details of the amplifying upper low here, and becomes stronger with the trough axis near the East Coast going into Tuesday. This run was also broader with the Western U.S. trough late in the week. The 12Z UKMET was considerably faster with the progression of this trough across the Rockies through midweek. Neither of these two solutions had much support from the machine learning guidance from the ECMWF nor the ICON model, and taking all of these factors into account, the fronts/pressures forecast only used the GFS and ECMWF, along with some previous WPC continuity since the previous forecast was close to those solutions through Thursday. The 00Z run of the CMC trended more in the direction of the preferred GFS/ECMWF blend, although the UKMET remains progressive with the northwestern U.S. upper trough. Looking ahead to Friday and Saturday, there is good agreement with the upper ridge axis across the Midwest states, but more differences emerge with the trough crossing the Rockies with a faster CMC solution, and also with the trough just off the East Coast, with the 12Z ECMWF slower in moving the trough off the coast. The ensemble means accounted for 30-50% of the forecast for this time period, while having slightly more of the operational GFS compared to the ECMWF and CMC. ...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. 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