Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 AM EDT Fri Apr 22 2022 Valid 12Z Mon Apr 25 2022 - 12Z Fri Apr 29 2022 ...Overview... As upper/surface lows track into south-central Canada as the medium range period begins Monday, the trailing cold front should sweep across the south-central to eastern U.S. and provide a focus for rain and thunderstorms. Upper troughing over the Midwest/Great Lakes should shift eastward as next week progresses and likely form an upper low over/near the Northeast later in the week, promoting a shift from warmer to cooler than average temperatures. Meanwhile model guidance supports mean troughing across the West with likely an embedded upper low, leading to potential for rounds of precipitation in the Northwest. Broad upper ridging is generally forecast in between, leading to warm temperatures across the Southwest to southern/central High Plains. ...Model Guidance Evaluation... Model guidance continues to show fairly good clustering with the large scale pattern described above. Some smaller scale differences exist even at the beginning of the period, particularly with distribution of energy within the trough/low near the Great Lakes region/U.S. Canada border. GFS runs show upstream energy coming into the trough a bit faster which pushes its initial small closed low east compared to other guidance. Associated surface low positions vary a bit but within normal spread. But guidance agrees in principle that this upstream energy will reinforce and strengthen troughing in the northeastern U.S. and track eastward midweek onward. A closed upper low will likely develop--this is showing some timing differences but likely by Wednesday or Thursday (ECMWF runs have been the slowest). At the surface, newer 00Z model guidance is even better clustered than the previous cycle with a low pressure system forming along the New England coast in association with the upper low. An upper low spinning centered west of British Columbia and promoting periods of troughing in the West is also reasonably agreeable in the model guidance, but more differences arise with individual shortwaves embedded within. By Wednesday onward one shortwave tracking east atop the ridge shows considerable spread with its exact track/how much it may suppress the ridge, with CMC runs being the strongest with the energy suppressing the ridge, but GFS runs (especially the 12Z) may not have enough suppression. Leaned toward a solution in between these at this point, closer to the ECMWF and means. Then by Thursday/Friday, the trough axis is finally expected to move eastward somewhat, but there is uncertainty with how much it moves inland given model/ensemble member spread and run to run discontinuities. Overall, a blend of the 12/18Z deterministic guidance favoring the ECMWF a bit worked well for the medium range forecast early on, phasing out the CMC (and UKMET of course) in favor the GEFS and EC ensemble means. This provided good continuity with the previous forecast. ...Sensible Weather/Threats... The cold front trailing from the low moving across Canada early in the workweek will intersect with warm/moist air from the Gulf and lead to widespread rain along the front stretching from the Great Lakes to Ohio/Tennessee Valleys and into the southern Plains Monday, shifting to the Eastern Seaboard Tuesday. While greater potential for excessive rainfall has phased into the short range period, some high rain rates with unstable conditions especially in Texas on Monday could overcome ongoing dry conditions to cause localized flash flooding. Elsewhere, the front should accelerate and lead to lighter overall rainfall amounts over the eastern U.S. Monday-Tuesday. Then as the Northeast upper low develops midweek and surface low pressure pivots over the region, precipitation is forecast to linger especially across New England, with some potential for higher elevations to receive snow. Meanwhile in the West, unsettled weather is likely as a series of shortwaves move through the mean trough south of a closed upper low positioned off British Columbia. Timing and coverage with each episode of rain/high elevation snow will take additional time to resolve given the typical lower predictability of medium to smaller scale of features contained within the mean flow. Warmer than normal conditions for the eastern third of the U.S. Monday-Tuesday will switch to below normal behind the cold frontal passage. The core of that cold air is likely to cause below normal temperatures by 15-30 degrees in the Dakotas and Midwest to the Great Lakes/Central Appalachians for the first half of the week. These temperatures should moderate somewhat as they take hold of the northeastern quadrant of the U.S. as the week progresses. Farther west, upper ridging migrating from the Southwest into the central U.S. will spread warmer than average temperatures from the Southwest (with some record highs possible in southern California Monday) into the Four Corners states and into southern/central parts of the Plains. The High Plains may see temperatures around 15-20F above normal. Tate 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