Extended Forecast Discussion NWS Weather Prediction Center College Park MD 251 AM EDT Wed May 29 2024 Valid 12Z Sat Jun 1 2024 - 12Z Wed Jun 5 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. Widespread 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 Saturday, mainly among the GFS, ECMWF, and UKMET, along with the ensemble means. However, at the time of fronts/pressures preparation and the QPF, the 12Z CMC was an outlier solution near the East Coast with keeping the offshore upper low much closer to the coast, and then it become much stronger with an upper ridge developing across the Northeast later in the forecast period compared to the model consensus. It also did not have much support from the machine learning guidance either, so it was not part of the forecast blend for the entire forecast period. The new 00Z CMC has trended more in line with the consensus and does not linger the upper low near the coast like the 12Z run did. The GFS was a little slower with the storm system crossing the Northern Plains early- mid next week, but still enough ensemble and ML support to warrant keeping it. The WPC fronts/pressures forecast was initially derived from a ECMWF/GFS/UKMET blend, but transitioned to about 40-50% ensemble means by next Tuesday/Wednesday amid increasing model uncertainty. Some previous WPC continuity was also maintained for the Saturday to Tuesday time period. ...Weather/Hazards Highlights... Numerous showers and thunderstorms are likely to remain ongoing across portions of the Southern Plains and eastward to the central Gulf Coast region going into the weekend, with multiple weak disturbances aloft interacting with a warm and humid air mass. A broad Marginal Risk area is planned for the Day 4 Excessive Rainfall Outlook period Saturday from central Texas to southern Nebraska, and a second area across portions of the Deep South and into the southern Ohio Valley. Going into the Day 5 period Sunday, a more organized storm system approaches the Dakotas and Upper Midwest, and convection should be widespread enough to merit a Marginal Risk here, with the potential for a Slight Risk in future updates as the event gets closer in time. Some strong to severe thunderstorms are also likely with favorable parameters in place. The potential exists for scattered QPF maxima of 1-3 inches during this time period for some of these areas that get repeated rounds of convection. There is also an increasing likelihood of a late season heavy rain event across northwestern Oregon and into western Washington on Sunday, potentially an atmospheric river event, and a Marginal Risk area is also planned for this region. The fall-like temperatures across much of the Eastern U.S. are expected to 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 Intermountain West, 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. The exception would be for the Pacific Northwest where widespread clouds and steady rainfall will keep readings cooler. 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