Extended Forecast Discussion NWS Weather Prediction Center College Park MD 258 AM EDT Sun Apr 14 2024 Valid 12Z Wed Apr 17 2024 - 12Z Sun Apr 21 2024 ...Overview... A storm system exiting the Upper Midwest/Great Lakes early in the period will continue to bring a threat for at least locally heavy rainfall to parts of the Upper Midwest/Ohio Valley Wednesday into Thursday. Behind this, another upper trough/low will skirt the northern tier states before ultimately evolving into somewhat more amplified troughing across the Ohio Valley-Northeast late this week. Upper ridging should build over the Northwest by next weekend ahead of another amplified trough across the northern Pacific and the overall pattern across the CONUS turns more zonal/relatively quiet. ...Guidance/Predictability Assessment... Model guidance remains reasonably agreeable on the large scale pattern through the period, but plenty of differences in the smaller scale details and timing of systems. The main uncertainties during the medium range period will be with the second, more broad, upper low across central-eastern Canada and any shortwave energy that swings through the base of the trough through the Ohio Valley/Northeast late week. This presents timing inconsistencies of the surface front through the East and associated generally light precip along it. Additional energy may drop southward through central Canada next weekend, possibly skirting the northern tier, and there are some differences in the strength of ridging across the West as well. Otherwise, the pattern trends pretty quiet overall across the CONUS, except for possible energy through the Southwest which models are showing inconsistency with how much this may increase QPF across Texas by next Sunday. The WPC forecast tonight was based on a blend of the deterministic guidance Days 3-5, increasing the means to help smooth out the smaller scale differences by days 6-7. ...Weather/Hazards Highlights... Precipitation will be ongoing from the Upper Midwest into the Ohio Valley associated with a deep surface low moving through the Upper Midwest on Wednesday. Given ample moisture and instability and a threat for at least locally heavy rainfall, a broad marginal risk remains in place for the Day 4 Excessive Rainfall Outlook (Wednesday- Thursday morning) from the Upper Great Lakes to Ohio Valley and central- northern Appalachians. Some potential for severe weather as well along the cold front, per discussions out of the Storm Prediction Center. Behind the low, some gusty winds could be possible across the Upper Midwest region. The next upper trough right on its heels could bring some notable snow to mainly the higher elevations of the northern/central Rockies mid-week. As systems progress, rain and convection are forecast to move into the eastern U.S. into late week, while lingering across the south- central U.S. as the frontal system stalls briefly. After this, conditions should mostly dry out across the CONUS leading into next weekend, but some enhanced rainfall may make its way back into Texas ahead of weak shortwave energy slides into the Southwest. Expect a broad area of above normal temperatures over the eastern third of the country into the southern Plains Wednesday-Thursday, with advancing frontal systems slowly trimming the western side of the warmth. Expect highs in the eastern U.S. to be around 10F or so above normal with anomalies for morning lows tending to be several degrees higher. The upper trough across the northern tier states will bring below normal highs into the northern Rockies/High Plains by next Wednesday- Thursday while gradually expanding farther south and east behind the secondary cold front late week. Above normal temperatures across the Southwest should gradually expand northward underneath a building Western U.S. ridge. Santorelli 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 forecast (QPF), excessive rainfall outlook (ERO), winter weather outlook (WWO) probabilities, heat indices, and Key Messages can be accessed from: 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 https://www.wpc.ncep.noaa.gov/#page=ovw