Extended Forecast Discussion NWS Weather Prediction Center College Park MD 218 PM EDT Thu May 30 2024 Valid 12Z Sun Jun 02 2024 - 12Z Thu Jun 06 2024 ...General Overview... Progressive flow pattern across the northern/middle CONUS through early next week before ridging in the west/troughing in the east becomes dominant through midweek. A trough crossing the Pacific Northwest Monday before developing into a closed low over the northern Plains Tuesday. Frontal systems ahead of this wave favor repeating episodes of showers and thunderstorms over the central/eastern portions of the CONUS. The Southwest remains dry, while hot and humid conditions persist over southern Texas under the northern periphery of an upper ridge anchored over Mexico. This ridge expands over the western U.S. by midweek, bringing widespread and potentially hazardous high temperatures. ...Guidance/Predictability Assessment... Decent agreement in the 00Z ECMWF/06Z GFS with the main synoptic feature which is the Northwest to northern tier trough into low which allowed their dominance in the morning model blend through Day 5. The 00Z UKMET is much more zonal/less amplified with the leading trough from the low that settles off BC allowed it to be removed from the blend by Day 4. The 00Z ECMWF seemed the most reasonable with both the low development over the northern Plains Tuesday and the subsequent ridging in the west, so it becomes the dominant entry into the blend (as well as QPF) by Day 5. The 06Z GFS is more progressive with the northern tier low/trough and is inching more toward the ECMWF with the western ridge through midweek, but remains less dominant with that ridge by Day 7, so it was less included in the morning model blend. ...Weather/Hazards Highlights... Periods of showers and thunderstorms are expected broadly across central and eastern portions of the country Sunday night/Monday with multiple shortwave troughs and accompanying surface frontal systems encountering a humid airmass. Uncertainty with the timing of the waves and their generally progressive nature continue to warrant broad brushes for the Marginal Excessive Rainfall Outlooks (EROs) in Days 4 and 5 over the central sections of the CONUS. For Day 4 (Sunday), this includes the Upper Midwest to central Plains as well as the southern Plains to the central Gulf Coast. An additional round of storms is expected Day 5 (Monday) ahead of the frontal system over the Middle Mississippi Valley and Central/Southern Plains where the Marginal Risk was expanded over the Ozarks. An upper-level wave and atmospheric river into the Pacific Northwest brings heavy rainfall Sunday before tapering off on Monday. Marginal Risks are included on the Days 4/5 ERO along the Washington/Oregon coasts and inland to the Cascades. The warm moist air will keep snow limited to the higher mountain peaks with enhance snowmelt below the snow level, adding to the risk for some isolated flooding concerns. While streamflows are currently low locally, a Slight Risk may be necessary here if focused QPF increases. The precipitation will spread inland over the northern Rockies Monday with the chance for locally heavy amounts over 1 inch, with the Marginal Risk maintained there for Day 5. Ridging then builds in broadly over the West with a dry pattern beginning midweek. This upper-level trough is expected to shift east to the northern Plains Tuesday before digging southeastward into the Midwest. This may bring areas of moderate to heavy rainfall to the Upper Midwest Tuesday and Ohio Valley/Lower Great Lakes by Wednesday, though details retain some uncertainty. Additional weak upper-level energies from the Southern Plains to the Southeast will also keep up the potential for additional storms. Forecast high temperatures will start above average by 10-15 degrees early next week over portions of the Plains then over the northern tier through New England, with generally near-average temperatures with daily bouts of storms for the eastern Plains/ Mississippi Valley/Southeast. South Texas westward through the Rio Grande Valley is where the combination of hot temperatures into the 90s and 100s as well as humidity will keep heat indices in the upper 100s, locally 110+. Below normal temperatures persist early next week over the Pacific Northwest as the system passes through the region. Then the next big story temperature-wise will begin to develop by midweek as ridging builds over the West. Highs broadly will be running 10-15 degrees above average, with even warmer anomalies of 15-20+ degrees for the central California valleys and portions the Great Basin. Forecast highs are into the 100s from west Texas into the Desert Southwest and central California valleys. The Climate Prediction Center has highlighted much of this region with at least a Slight Risk of Excessive Heat with the expectation this heat wave will continue beyond the current forecast period into at least next weekend. Jackson 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