Extended Forecast Discussion NWS Weather Prediction Center College Park MD 326 PM EDT Fri May 28 2021 Valid 12Z Mon May 31 2021 - 12Z Fri Jun 04 2021 ...Record Warm Temperatures Likely Next Week Across the West... ...Heavy Rain Possible Mid-Week Across Southern/Central Plains... ...Overview and Guidance Evaluation and Preferences... Upper ridging over the West Coast and troughing over the Eastern U.S. is expected to start the medium range period (May 31). This pattern is forecast to evolve toward more quasi-zonal flow as the western ridge breaks down with the approach of Gulf of Alaska and Eastern Pacific energy dropping into the Pacific Northwest. At the same time, energy ejecting out into the Plains is likely to carve a more substantial trough over the central U.S. by the end of the period. The latest model guidance offers fairly good predictability and agreement through the period. Early on, the GFS was noted to be faster with shortwave energy across the Northeast. The other area of model differences were later in the period (day 6/7) with the central U.S. trough and how it progresses across the Great Lakes and Northeast. Both the deterministic GFS and ECMWF suggest a closed low forms but the GFS is much further north/northeast (fast) with that feature compared to the ECMWF, which suggests the low would remain over the MS River Valley. Although the WPC preference was for a blend and heavily incorporated the ensemble means for day 6/7, there are fairly notable sensible weather differences for QPF, especially for the eastern U.S. as the closed low could allow for a plume of deeper moisture to overspread the area with more widespread/unsettled weather. In the end, the WPC blend preference maintained continuity given the forecast uncertainty and lower confidence details. ...Weather Highlights/Hazards... The main focus for rainfall during the period will be over the central/southern Plains as Gulf of Mexico moisture intercepts a slow moving cold front. Some locations could see several inches of rain with the best chance at this point from parts of northern Texas into Oklahoma. Much of this area is already over saturated due to above normal precipitation recently which would only increase flooding concerns across the region. High pressure building in behind the front may also aid low level upslope flow to enhance convective development over the High Plains. Rain and scattered thunderstorms are expected to spread eastward into the Mississippi Valley, the Ohio/Tennessee Valleys, and parts of the East by mid to late next week ahead of the main trough, but with less certainty on any areas of focused heavy rainfall totals. Meanwhile, the West should stay dry beneath upper level ridging with maybe some scattered precipitation as shortwave energy moves across the region later next week. Main concern for temperatures during the medium range period is from California into the Great Basin where daytime highs 20 to 25 degrees above average could approach or exceed record values, centered around next Tuesday/Wednesday. As the upper ridge weakens and shifts, values may moderate a bit but still are expected to be above normal across much of the West and into the northern Plains. The south-central U.S./High Plains will be below normal under cloudy and stormy skies the first half of the period, while the Eastern U.S. sits near normal all next week. Santorelli/Taylor 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 Hazards: - Heavy rain across portions of the Southern Plains, Mon-Wed, May 31-Jun 2. - Flooding possible across portions of the Central Plains, the Southern Plains, and the Northern Great Basin. - Flooding occurring or imminent across portions of the Lower Mississippi Valley, the Southern Plains, and the Northern Rockies. - Flooding likely across portions of the Central Plains and the Middle Mississippi Valley. - Much above normal temperatures across portions of California, the Northern/Central Great Basin, the Pacific Northwest, and the Northern Rockies, Mon-Thu, May 31-Jun 3. 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