Extended Forecast Discussion NWS Weather Prediction Center College Park MD 259 AM EDT Thu Mar 30 2023 Valid 12Z Sun Apr 2 2023 - 12Z Thu Apr 6 2023 ***Strong low pressure system develops over the Plains early next week with heavy rain, strong winds, northern Plains snow, and severe thunderstorms from the Deep South to the Ohio Valley*** ...Synoptic Overview... The strong storm system over the eastern U.S. in the short range period should be over southeastern Canada by Sunday morning with improving weather for the East Coast to conclude the weekend as a surface high moves in from the west. A progressive surface low tracks eastward along the U.S./Canada border through Monday with a colder airmass settling in behind it across the northern Plains for the beginning of the week. The main weather story going into next week will be the development of another strong low pressure system as a potent upper trough from the western U.S. ejects eastward across the Plains, spurring surface cyclogenesis over eastern Colorado by Tuesday morning. This low may follow a similar path to the one expected this Friday/Saturday and cross over the Upper Midwest on Wednesday and then over Ontario by Thursday with a strong cold front trailing behind it. The upper ridge from the Gulf of Mexico builds northward across much of the eastern U.S. ahead of this storm system and brings anomalous warmth ahead of the front. ...Model Guidance/Predictability Assessment... The 00Z model guidance suite has above average synoptic scale agreement for this weekend and a general model compromise works well as a starting point in the forecast process for Sunday and Monday. Developing differences with upstream Pacific/Alaska flow start to influence progression of the upper trough moving into the West and then the Plains early next week. The GFS and GEFS mean remain on the slower side of the guidance with the next major storm system over the central/northern Plains compared to the more progressive ECMWF/ECENS, with the CMC also indicating a slower solution. The use of the ensemble means was increased to about 50% by next Thursday to account for these increasing differences. ...Weather/Hazards Highlights... Reloading of upper level troughing over the northwestern U.S. by the weekend and continuing into early next week will support multiple days of rain/mountain snow with terrain enhancement from the Pacific Northwest and northern California into the northern and central Rockies, with the moisture shield pushing gradually farther southeast with time. Heavy snow is likely for the Cascades and the Olympic Mountains where a few feet of snow accumulation is expected at higher elevations. Significant snow may reach central and northern portions of the Sierra Nevada by early next week. For the Day 4 outlook (12Z Sunday-12Z Monday), a Marginal Risk of excessive rainfall exists from eastern Texas into the Lower Mississippi Valley where return flow from the western Gulf increases moisture and instability, with a stationary front beginning to lift north as a warm front to provide some added focus for convection that could be locally heavy, but no strong signals for anything yet on the Day 5 outlook. The big headline will be the developing low over the Plains that develops along a strong frontal boundary early next week. Numerous showers and thunderstorms are likely to make a return to locations from the central Gulf Coast to the Ohio Valley again Tuesday night and especially into Wednesday as this storm system gets better organized across the central Plains and advects copious Gulf moisture northward. Recent model runs suggest this could also be a significant event with heavy snow northwest of the low track, with probabilities for at least three inches of snow steadily increasing along an axis from eastern Wyoming across much of South Dakota and then northern Minnesota Monday night through early Wednesday. There is also the potential for some 6-12 inch totals in the core of this band. The threat of strong to severe storms is increasing in the expansive warm sector, with the Storm Prediction Center already monitoring that possibility on Tuesday as favorable kinematic and thermodynamic parameters are expected. Meanwhile the best potential for the strongest winds with this system extends from the southern Rockies/High Plains into the Upper Midwest, with a much broader area of brisk to windy conditions also possible over the central/eastern U.S. A temperature dichotomy will exist across the nation with well below average readings across much of the western U.S. and central/northern Plains, and well above average temperatures from the Gulf Coast to much of the eastern U.S. going into the middle of next week. Widespread highs of 15 to 25 degrees below early April climatology are expected from the Intermountain West and the Rockies to the northern Plains, with the greatest coverage of this expected during the Tuesday through Thursday time period. The reverse holds true east of the Mississippi River where upper level ridging extending from a Gulf of Mexico upper high should maintain warm and humid conditions ahead of the evolving storm system, with highs 10-20 degrees above average and overnight lows 15-25 degrees above average. Tuesday-Thursday will offer the best potential for some daily records, with warm lows tending to be more numerous than record highs. 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