Extended Forecast Discussion NWS Weather Prediction Center College Park MD 422 PM EDT Mon May 23 2022 Valid 12Z Thu May 26 2022 - 12Z Mon May 30 2022 ...Weather Pattern Overview... A large scale upper trough (with possible embedded closed low) 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 the weekend. Meanwhile, another trough enters the northwestern U.S. by the end of the week with a brief upper ridge ahead of it across the Intermountain West and Rockies. Models suggest this trough will deepen as it crosses the West this weekend to spur surface cyclogenesis across the northern Plains this weekend. In response to the digging upper trough, an upper ridge should build across the eastern U.S. along with warmer temperatures. ...Model Guidance and Preferences... The 00z suite of model guidance has generally trended slower and more amplified with the deep trough through the eastern third of the nation as the period begins with indications of a closed low over into the Ohio Valley/Mid-Atlantic around Friday-Saturday. The exception to this is the 00z/12z ECMWF which continues to be much quicker and weaker, allowing for ridging to build in much faster behind early next week. The timing in the ensemble means general follow with their deterministic counterparts (albeit weaker) so there continues to be a lot of uncertainty surrounding this feature. Given the trends though, the WPC progs do depict a slower/more amplified system compared to previous WPC continuity, with a proxy closest to the 00z/12z CMC (which is a nice middle ground between the stronger GFS and the weaker ECMWF). Out West, the guidance shows good timing agreement on the initial shortwave into the West late this week, but differ with the evolution into the weekend. The CMC (and UKMET through day 5) are faster and stronger with this leading shortwave developing a closed low over south-central Canada by Sunday. Meanwhile, the GFS and ECMWF aren't as strong with this shortwave as it crosses the West, instead wanting to develop and deepen the next shortwave into the coast around Sunday. The WPC forecast trended towards the ensemble means the second half of the period to account for this uncertainty and generally shows good continuity with the previous WPC forecast as well. ...Sensible Weather/Threat Highlights... Periods of heavy rainfall will continue to make weather headlines going into Thursday and Friday across portions of the Eastern U.S. along and ahead of the cold front, with heavy to excessive rainfall possible in some areas particularly across the Southeast. A Slight Risk area in the Day 4 experimental excessive rainfall outlook is highlighted 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. Santorelli/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 Hazards: - Heavy rain across portions of the Central/Southern Appalachians, the Tennessee Valley, the Southeast, and the Ohio Valley, Thu, May 26. - Flooding possible across portions of the Central Plains, the Middle Mississippi Valley, and the Southern 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 Southern Plains, Sat-Mon, May 28-May 30. 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