Extended Forecast Discussion NWS Weather Prediction Center College Park MD 258 AM EDT Tue May 28 2024 Valid 12Z Fri May 31 2024 - 12Z Tue Jun 04 2024 ...General Overview... The upper trough over the Northeast U.S. late in the week is expected to move offshore by the weekend, with a Canadian surface high providing a quality airmass with pleasantly cool conditions across the East Coast followed by a warming trend by early next week. Meanwhile, a rather unsettled weather pattern is expected to be in place across the Central U.S. with multiple shortwave disturbances aloft fueling multiple rounds of showers and thunderstorms going into the weekend. Showers will also make a return to the Pacific Northwest early next week as a cold front moves inland. Most of the Southwest and the Northeast should remain mostly dry, and the upper ridge likely builds back northward across southern Texas and thus maintaining hot and humid conditions. ...Guidance/Predictability Assessment... The 00Z model guidance suite features good overall synoptic scale agreement on most aspects of the forecast for Friday, but meaningful differences in the models appear as early as Saturday with the arrival of the trough across the Pacific Northwest, and the trough lifting out across the Upper Midwest. The GFS becomes more progressive with the trough crossing the rockies and northern Intermountain West, and by Sunday the CMC is stronger with a shortwave trough over the Midwest and Ohio Valley region, and becoming stronger with a downstream ridge over the Northeast by Monday. Model spread becomes noteworthy by early next week across the northern tier states with limited forecast confidence on specifics, but better agreement with respect to the building upper level ridge across Texas. The WPC fronts/pressures forecast was initially derived from a deterministic model blend, but transitioned to about 50% ensemble means by next Tuesday amid increasing model uncertainty. Some previous WPC continuity was also maintained through the Friday to Monday time period. ...Weather/Hazards Highlights... Numerous showers and thunderstorms are likely to remain ongoing across much of the central and southern Plains going into Friday and the weekend with multiple weak disturbances aloft interacting with a warm and humid air mass. A broad Marginal Risk area continues for the Day 4 Excessive Rainfall Outlook period Friday from central Texas to southern Wisconsin. There is an embedded Slight Risk area planned for the ArkLaTex region, where MCS activity is most likely to develop based on the latest deterministic guidance. There may be some abatement in the coverage of convection on Saturday across the Central U.S., but still enough to merit a few Marginal Risk areas where the best combination of upper level forcing and moisture convergence will likely exist. Some strong to severe thunderstorms are also likely each day. The potential exists for scattered QPF maxima of 2-4 inches for the Friday to Saturday time period for some of these areas that get repeated rounds of convection. The fall-like temperatures across much of the Eastern U.S. are expected to slowly moderate and return to early June levels in time for the weekend as the upper trough exits the region. Readings will also get warmer across much of the Western U.S., with highs generally on the order of 5-10 degrees above average through the weekend, and then spreading eastward across the western High Plains for early next week. This also includes a warm-up for the Great Lakes and into the Northeast. It will remain very hot and humid for much of southern Texas with the upper ridge building back to the north through early next 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