Extended Forecast Discussion NWS Weather Prediction Center College Park MD 250 PM EDT Sun May 22 2022 Valid 12Z Wed May 25 2022 - 12Z Sun May 29 2022 ...Heavy/Excessive Rainfall and Strong/Severe Weather Threat to Spread from Eastern Texas to the Lower Mississippi/Tennessee/Ohio Valleys then Appalachians Wednesday into Thursday... ...Weather Pattern Overview... A large scale upper trough will be exiting the Rockies and emerging over the Plains by Wednesday, and this will sustain a surface cold front with multiple waves of low pressure that will slowly track eastward and should reach the East Coast by early Friday. Multiple rounds of heavy to excessive rainfall and strong to severe thunderstorms are likely across the south-central U.S. ahead of the cold frontal passage. Another trough enters the northwestern U.S. by the end of the week with an upper ridge building in ahead of it across the Intermountain West, and this trough will likely spur surface cyclogenesis across the High Plains by next weekend. ...Model Guidance and Preferences... The 00/06/12 UTC guidance bundle continues to offer good synoptic scale agreement across the continental U.S. for the majority of the forecast period, with the normal levels of differences in mesoscale features. The GFS/ECMWF/Canadian are close to their respective ensemble means for a major lead trough over the east-central U.S. mid-later this week and model differences have improved for a second system reaching the western U.S. late week. The basis for the WPC forecast was derived from a blend of the GFS/ECMWF/UKMET/Canadian along with WPC continuity and the National Blend of Models (NBM) Wednesday-Friday. The NBM and the GEFS/ECMWF ensemble means along with best clustered model guidance from the ECMWF and the GFS/Canadian was highlighted for next weekend. ...Sensible Weather/Threat Highlights... Periods of heavy rainfall will continue to make weather headlines going into Wednesday across the south-central U.S., particularly around the ArkLaTex region and extending eastward to Mississippi, where local 2 to 4+ inches of additional rainfall is expected. Portions of this region are forecast to get heavy rainfall early in the week as well, thus the ground will likely be saturated and increases the potential for flooding. Multiple clusters of convection are likely and these may also produce episodes of severe weather as per SPC. The experimental medium range Excessive Rainfall Outlook (ERO) also depicts a "Slight" Risk area for Wednesday into early Thursday from eastern Texas to western Tennessee, with additional potential downstream across the South and up through the Great Lakes/Ohio Valley. Beyond this time, the magnitude of the heavy rainfall threat abates some as the front becomes more progressive across the Appalachians and then the East Coast region, although some instances of repeating convection may also lead to some flooding concerns on a more localized level. 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 some late May mountain snows) from the Pacific Northwest to the Northern Rockies. Storms should emerge over the Plains/Upper Midwest next weekend with system progression. In terms of temperatures, pleasantly cool conditions can be expected across much of the Plains and Midwest in the wake of the cold front for the middle of the week, followed by a warm-up to close out the week with above normal highs returning by the weekend with 90s likely as far north as southern Nebraska, and even some low 100s for portions of western Texas. Hot weather is also expected for the interior valleys of California and the lower elevations of the Desert Southwest for Wednesday through Friday as an upper level ridge is expected to be in place, and then returning closer normal for next weekend. Elsewhere, expect highs to generally be within 5 degrees of climatological averages across most of the eastern U.S., although overnight lows could end up being milder than usual owing to more cloud cover and humidity. Schichtel/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