Extended Forecast Discussion NWS Weather Prediction Center College Park MD 255 AM EDT Mon May 23 2022 Valid 12Z Thu May 26 2022 - 12Z Mon May 30 2022 ...Weather Pattern Overview... A large scale upper trough will be crossing the east-central U.S. through the end of the work week, and this will sustain a surface cold front that will track eastward and should exit the East Coast by Friday afternoon, with a weak surface high following for the weekend. Another trough enters the northwestern U.S. by the end of the week with an upper ridge briefly building in ahead of it across the Intermountain West and Rockies, and this trough will spur surface cyclogenesis across the High Plains by next weekend, although probably weaker than the one that will be in place for the beginning to middle of this week. By next Monday, an upper ridge builds back in across the eastern U.S. along with warmer temperatures. ...Model Guidance and Preferences... The 00Z model guidance suite is initially in good synoptic scale agreement on Thursday across the majority of the nation. However, noteworthy differences in the guidance appear as early as Thursday night and into Friday with the eventual evolution of the trough reaching the East Coast. The 18Z GFS differed considerably from its earlier 12Z run with a much slower solution with a closed low developing, whereas the 12Z model consensus was more progressive and generally did not close off the low. At the time of the fronts/pressures preparation, the 12Z GFS was substituted for the 18Z since the earlier run had more ensemble support. Going forward to the 00Z cycle, the UKMET and CMC trended more amplified and slower across the Ohio Valley, and the large model changes from earlier cycles lowers forecast confidence Friday and into the weekend for the eastern states. The 00Z ECMWF trended only slightly stronger, but overall more of an open wave and close to its ensemble mean. The WPC forecast initially started with a multi-deterministic model blend through Friday, and then more of the ensemble means while still maintaining some of the operational GFS and ECMWF with a little less of the CMC. ...Sensible Weather/Threat Highlights... Periods of heavy rainfall will continue to make weather headlines going into Thursday across portions of the Southeast, with a couple inches of rain likely for parts of the southern Appalachians. This region is forecast to get heavy rainfall through the middle of this week as well, thus the ground will likely be saturated and increases the potential for flooding. A Slight Risk area in the Day 4 experimental excessive rainfall outlook is now in effect from far northern Georgia to southwestern North Carolina where the best orographic forcing will be present in a moist environment. Late week into next weekend, the front moving inland across the northwestern U.S. and eventually the central/northern Plains is expected to bring some showers and thunderstorms (and perhaps some late May mountain snows) from the Pacific Northwest to the Northern Rockies. Storms should emerge over the central/northern Plains to the Upper Midwest next weekend as the low progresses eastward. In terms of temperatures, pleasantly cool conditions can be expected across much of the Midwest and Great Lakes region in the wake of the cold front for the end of the week, followed by a warm-up with above normal highs returning by the weekend across much of the Plains, with 90s likely as far north as central Nebraska, and even some low 100s for portions of western Texas. Hot weather is also expected for the lower elevations of the Desert Southwest for Thursday through the weekend as an upper level ridge is expected to be in place, although a cooling trend will commence for the inland valleys of central California. Elsewhere, expect highs to generally be within 5 degrees of climatological averages across most of the eastern U.S. through Saturday, although overnight lows could end up being milder than usual owing to more cloud cover and humidity. Heat returns to much of the Northeast U.S. and Ohio Valley by early next week as the upper ridge builds back in. Hamrick 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