Extended Forecast Discussion NWS Weather Prediction Center College Park MD 120 PM EDT Mon May 25 2020 Valid 12Z Thu May 28 2020 - 12Z Mon Jun 01 2020 ...Much above normal temperatures over the northern Great Basin across the Rockies and Northern High Plains... ...Areas of locally heavy rainfall possible over portions of the Southern Plains to the Southeast... ...Guidance/Predictability Assessment... An upper ridge over the West will drift eastward with time in response to the movement of an upper trough and embedded closed low off the CA coast later this week moves onshore and inland into OR over the weekend. From late this week through the weekend the upper ridge progression will gradually shift emphasis for the most extreme temperature anomalies (and numerous daily record highs/warm lows) from CA/OR/WA across the northern Great Basin, northern-central Rockies and northern High Plains. Over the eastern Pacific/western U.S., guidance is clustering better, with good agreement on the closed low timing among the 00z ECMWF/ECMWF Ensemble Mean, and 06z GEFS Mean. A blend of these solutions was used, with less weighting to the slightly faster 06z GFS solution. around the western ridge. There will be the potential for areas of moderate/heavy rainfall near and to the east of an upper low that drifts northeast out of the Southern Plains and across the Lower Mississippi Valley. The models and means are converging on the timing of the low and its phasing with the northern stream. As a result, a blend of the 00z ECMWF with its mean and the 06z GFS/GEFS Mean was used to mitigate minor differences in the forecast. Expect western Canada upper ridging to support amplification of a downstream trough expected to progress from the Northern Plains and Upper MS valley Thu and across the Great Lakes Fri and Sat, followed by New England Sunday. This trough will be followed by a strong level anticyclone, which will help push a cold front southward into the southeast US Sun 31 May and Mon 01 Jun. ...Weather/Hazard Highlights... Ahead of the upper low, locally heavy rain is possible over the lower half of the Mississippi Valley to the Gulf Coast and southeast late this week, with the threat tapering this weekend. The cold front pushing southward across the Great Lakes and Ohio Valley will provide a focus for showers/thunderstorms Thu and Fri, then across the northeast and mid Atlantic Sat, ending as the front moves off the coast Sun. The upper low brushing the West Coast during the weekend may bring an episode of rainfall that could be moderate/heavy at some locations between extreme northern California and the Pacific Northwest. The models show lingering low level moisture over northern NM and CO with episodes of upper divergence, leading to scattered showers/storms over the weekend. During the Thu-Sat period an area of temperatures 10-25F above normal with numerous daily records for highs/warm lows should occur in the West Coast states. This shifts east Sun-Mon to the northern-central Rockies and High Plains. The axis of greatest anomalies for highs will likely extend from the Central Valley of California across parts of Oregon/Nevada/Idaho and then into Wyoming/Montana. The Great Lakes and Northeast will see above normal temperatures Thu into Fri (plus 10-20F anomalies with some record warm lows possible) followed by a return to near normal after the cold front passes through. Areas of clouds and rainfall as well as the continued southward progress of the eastern U.S. cold front should lead to more below normal highs across the southern half of the central/eastern U.S. As the upper trough departs the Southern Plains and an upper ridge builds in Sun-Mon, highs 5-10F below normal are expected to develop in the high Plains of CO/NM and then into the OK/TX panhandles Mon 01 Jun. Petersen Additional 3-7 Day Hazards information can be found on the WPC medium range hazards chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation, winter weather outlook probabilities and heat indices are at: 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/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml