Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 PM EDT Wed May 18 2022 Valid 12Z Sat May 21 2022 - 12Z Wed May 25 2022 ...Record Heat to abate over the South-Central U.S., shifting to the Appalachians/Mid-Atlantic/Northeast this weekend... ...Heavy Rainfall and Severe Weather threat for the East-Central U.S. this weekend to redirect over the South-Central U.S. early next week... ...Overview... An amplified weekend upper flow pattern will be highlighted by a trough over the West/north-central U.S. and strong ridging in the East. This yields cooler temperatures across the Rockies and central U.S. and record heat shifting from the south-central U.S. to the East this weekend. A strong cold front across the Midwest and East this weekend will result in increased chances for heavy rainfall and severe weather along and ahead of it. A northward surge of tropical moisture will also increase rain/thunderstorm chances across Florida this weekend. Troughing back into the West Sunday/Monday should dig into the south-central U.S. early next week as upper ridging builds into the Southwest and Florida and flatter flow rides overtop over the northern tier of the lower 48. ...Guidance Evaluation/Preferences... The WPC medium range product suite was primarily derived from a composite blend of reasonably well clustered guidance for the weekend in a pattern with average to above average predictability beyond smaller scale details. Model system timing/amplitude differences become more problematic through early-mid next week with the ECMWF tracking closest to the compatible GEFS/ECMWF ensemble means. The most significant WPC product continuity change into early next week was to promote a more organized and southward shifted heavy QPF threat focus over the southern Plains and lower MS Valley due to the signal for a now more likely development of supporting upper troughing and surface system development in a moist and unstable environment. The resultant WPC QPF is heavier than NBM 4.0. ...Weather/Threat Highlights... The relentless heat across the Southern Plains/Lower Mississippi Valley should finally break by this weekend though record heat continues into Saturday across the East. Numerous daily records could be met or exceeded on Saturday across the Appalachians, Mid-Atlantic, and Northeast with a few lingering records across far southern regions in Texas/Louisiana. A strong cold front will spread rain and thunderstorms through the Mississippi Valley/Ohio Valley on Saturday and into the East on Sunday. Heavy rainfall as well as severe weather is possible along this boundary given above normal moisture and instability present. Flooding and flash flooding could be an issue as well, particularly in places that may be sensitive to additional rainfall given wet antecedent conditions. Lead southern stream impulse energy may also focus heavy rainfall areas across parts of the South, especially the Gulf Coast, as tropical moisture surging northward allows for heavy rainfall across the Florida Peninsula this weekend. To the west, unseasonably cool temperatures will move from the Rockies into the north-central U.S., lowering snow levels across the Rockies Saturday and Sunday. The next system digging into the south-central U.S. into next week has become increasingly likely to re-kindle widespread convection/rainfall across the south-central U.S. as the guidance signal has improved at these longer time frames, albeit still highly dependent on flow details and convective interactions. The Northwest should remain fairly dry, though with some light precipitation accompanying frontal boundaries. The southern half of the West should see a slight warming trend expand from west to east Monday through Wednesday while mean troughing keeps tempeartures near or cooler than normal east of the Rockies. Schichtel/Santorelli 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, experimental excessive rainfall outlook, 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/#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