Extended Forecast Discussion NWS Weather Prediction Center College Park MD 412 PM EDT Thu May 19 2022 Valid 12Z Sun May 22 2022 - 12Z Thu May 26 2022 ...Excessive heat lingering Sunday for South Texas and Mid-Atlantic/Northeast to refocus over interior California/Desert Southwest early-mid next week... ...Heavy Rain/Convection threat from the central Gulf Coast to southern Mid-Atlantic Sunday/Monday then Southern Plains/Lower Mississippi Valley early-mid next week... ...Overview... The upper flow pattern during the medium range period should stay amplified and active into early-mid next week. Shortwaves pushing a strong cold front through the eastern U.S. Sunday should bring an end to record weekend heat. SPC also shows a threat for severe weather Sunday over the northern tier of a warmed Northeast. 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 despite increasing varied model timing issues. Meanwhile, leading southern stream energy will interact with increasing tropical moisture to fuel heavy rain and storms from the central Gulf Coast to the southern Appalachians/Mid-Atlantic Sunday into Monday. ...Guidance Evaluation/Preferences... Guidance shows enough mass field agreement to support a deterministic model blend of the latest GFS/ECMWF/CMC for days 3/4 (Sunday/Monday), but in particular leaned toward solutions with heavier rainfall from the central Gulf Coast states to the Appalachians given overall deeper moisture feed and southern stream impulse/frontal wave support. The 00 UTC UKMET was less amplified with upper troughing across the West into early next week, but the newer 12 UTC run has trended stronger/less progressive. However, forecast predictability quickly lowers to below normal for the rest of the period amid growing forecast spread. By next Tuesday-Thursday, significant timing differences arise with the ECMWF/CMC becoming uncharacteriscally faster/less amplified than the GFS which holds back the amplified trough over the southern Plains much longer. The WPC forecast trended towards the compatible GEFS/ECMWF ensemble means next Tuesday-Thursday which actually shows a more moderate and middle ground solution. ...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. into next week has become increasingly likely to re-kindle widespread convection/rainfall across the south-central U.S. with return flow into another wavy frontal system, albeit dependent on flow details and convective interactions. Again, flash flooding is expected to be a concern within a very moist and unstable atmosphere. The WPC experimental Excessive Rainfall Outlook (ERO) shows a "Slight" risk area Monday into Tuesday. 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 mainly dry through the middle of next week as upper ridging builds over the region and warmer temperatures expand across the region. This may lead to an excessive heat focus over interior California and the Desert Southwest. 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 Hazards: - Heavy rain across portions of the Central/Southern Plains, and the Middle/Lower Mississippi Valley, Mon-Wed, May 23-May 25. - Heavy rain across portions of the Southeast, the Lower Mississippi Valley, the Southern Appalachians, and the Tennessee Valley, Sun, May 22. - Severe weather across portions of the Lower Great Lakes, and the Northeast, Sun, May 22. - Flooding possible across portions of the Middle Mississippi Valley, the Upper Mississippi Valley, and the Northern Plains. - Flooding occurring or imminent across portions of the Upper Mississippi Valley, and the Northern Plains. - Flooding likely across portions of the Northern Plains. - Excessive heat across portions of the Central Great Basin, California, and the Southwest, Mon-Thu, May 23-May 26. - Excessive heat across portions of the Northeast, the Central Appalachians, the Southern Plains, the Mid-Atlantic, the Southern Appalachians, and the Lower Great Lakes, Sun, May 22. 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