Extended Forecast Discussion NWS Weather Prediction Center College Park MD 248 AM EDT Thu May 19 2022 Valid 12Z Sun May 22 2022 - 12Z Thu May 26 2022 ...Excessive heat continues into Sunday for parts of the Mid-Atlantic/Northeast... ...Heavy Rain threat shifts from the central Gulf Coast on Sunday into the Southern Plains early next week... ...Overview... The upper flow pattern during the medium range period should stay amplified and active into mid next week. The period begins Sunday with a shortwave pushing a strong cold front through the Eastern U.S. which should finally bring an end to record or near record heat this upcoming weekend. A digging trough across the Western U.S. will shift east with time, with an increasing signal for a potential multi-day heavy rainfall event for the south-central U.S. early next week. Meanwhile, leading southern stream energy will interact with increasing tropical moisture to fuel heavy rain and storms across the central Gulf Coast and parts of the Southeast on Sunday. ...Guidance Evaluation/Preferences... The guidance continues to show good enough agreement the first half of the period for a purely deterministic model blend between the latest available runs of the GFS, ECMWF, and CMC. The past few days of runs have shown significant uncertainty past the weekend regarding evolution of troughing across the West/Central U.S., but today, models are finally showing much better agreement on a more amplified pattern than previous suggested by some of the guidance. The notable difference was the 12z/yesterday UKMET which continued to show a much weaker/faster shortwave progression through Tuesday, and thus was not included in tonights blend. Tonights 00z run of the UKMET did trend slightly stronger and more towards the consensus. By next Tuesday-Thursday, there are some timing differences which begin to arise with the ECMWF/CMC slightly faster/less amplified than the GFS which holds back the troughing over the southern Plains much longer. The WPC forecast trended towards the ensemble means next Wednesday-Thursday which actually shows a more moderate and middle ground solution. Either way, the trend over the past day has been towards a heavier QPF threat focused over the southern Plains and lower Mississippi Valley early next week. ...Weather/Threat Highlights... The relentless heat that has plagued the southern U.S. for the past week should finally break this weekend as the upper ridge pushes into the East. Ahead of the cold front on Sunday though, excessive heat with some lingering record temps (especially for warm lows) will still be possible. Meanwhile, expect locally heavy rain and possibly strong storms to accompany the cold front as it pushes through the Ohio Valley/East on Sunday. Temperatures behind the front next week should hover near seasonable normal values. Low pressure forming along the trailing front as it begins to lift back north as a warm front may continue a rainfall threat into Monday as well for parts of the southern Mid-Atlantic. Leading southern stream impulse energy may also focus heavy rainfall across parts of the South, especially the Gulf Coast, with tropical moisture surging northward from the Gulf of Mexico on Sunday. At least a localized flood and flash flood threat should exist as the environment could be favorable for high rainfall rates. The next system digging into the south-central U.S. 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. Again, flash flooding is expected to be a concern within a very moist and unstable atmosphere. Depending on flow progression, some guidance suggests the threat could linger for a couple of days. The western-central U.S. trough should keep temperatures below normal across Rockies and Plains through at least Tuesday. With the exception of light precip across the Rockies on Sunday, the Western U.S. should remain dry through the middle of next week as upper ridging builds over the region and warmers than average temperatures expand across the region. 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