Extended Forecast Discussion NWS Weather Prediction Center College Park MD 256 AM EDT Thu May 26 2022 Valid 12Z Sun May 29 2022 - 12Z Thu Jun 2 2022 ...Weather Pattern Overview... A more amplified upper level pattern is expected to become established over the continental U.S. going into the Memorial Day weekend and extending into the middle of next week. Multiple shortwave impulses will reinforce a rather deep synoptic scale trough over the western U.S. whilst a large upper ridge and closed high builds downstream across the Mississippi River Valley and eventually the Eastern U.S. by early next week. This overall pattern will likely become more quasi-zonal by next Thursday with the western trough lifting out and the ridge breaking down some. ...Model Guidance and Preferences... The 00Z model guidance suite is in good overall agreement on most aspects of the forecast going through Memorial Day, and model spread has decreased over the past 24 hours with improved forecast confidence. However, mesoscale differences regarding smaller scale features remain, and this has an effect on the placement of MCS activity and heavier areas of rainfall. There is also increasing model spread regarding the weakening of the upper trough by late in the forecast period. However, there is very good model agreement on the building upper ridge over the Ohio Valley going through the middle of next week. The WPC forecast incorporated some of the GEFS/ECENS means for the Tuesday through Thursday time period to account for the mesoscale uncertainty, whilst still maintaining some of the deterministic CMC/ECMWF/GFS, and generally shows good continuity with the previous WPC forecast as well. ...Sensible Weather/Threat Highlights... The main focus for precipitation will extend from the northwestern U.S. through the northern-central Plains to the western Great Lakes. Showers and storms will initially develop across the Northern Plains and Upper Midwest in response to a developing low pressure and frontal boundary over the north-central U.S. on Sunday, while some precipitation extends back into the northern Rockies and vicinity. Another stronger shortwave is forecast to slowly cross the Rockies and interact with the wavy and slow moving frontal system setting up over the Plains. The result will be late season snow for the higher terrain of the Northern Rockies, with potentially over a foot of accumulation above 8000 feet elevation. There is also an increasing potential for heavy rainfall across much of Montana, northern Wyoming, and the western Dakotas by early next week behind the front with moist upslope flow, with perhaps 2 to 4 inches for the foothills of the Montana Rockies. The focus for heavy rainfall and strong storms is then expected to be across the central Plains by the middle of the week. Temperatures will be quite warm across the central and southern Plains for the weekend with highs reaching well into the 90s from southern Nebraska to the Gulf Coast, and some low-mid 100s across western Texas which could challenge some daily records. The heat then builds eastward to include the Ohio Valley and eventually the East Coast going into early next week, compliments of the building upper ridge and southerly flow ahead of the storm system over the Plains. This will equate to widespread upper 80s to middle 90s for highs going into the beginning of June. Well below normal temperatures will likely encompass areas from the Pacific Northwest to the Northern Rockies and Northern Plains as the upper trough moves in behind the cold front, with highs 15 to 25 degrees below late May averages. 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