Extended Forecast Discussion NWS Weather Prediction Center College Park MD 113 AM EDT Sat May 02 2020 Valid 12Z Tue May 05 2020 - 12Z Sat May 09 2020 ...Record heat for the Southwest midweek... ...Guidance/Predictability Assessment... Quasi-zonal and progressive flow across the CONUS at the start of the medium range period is expected to evolve into increased amplification featuring a western US ridge and central/eastern US trough. Model guidance continued to be split in the forecast evolution out of the Pacific as early as 24 hrs with spread increasing into the start of the medium range period. The 12-18Z GFS/GEFS were much slower/deeper with a mid-level feature out of the northern Rockies on Tue compared to the 12Z ECMWF/Canadian/UKMET/ECMWF ensembles, though differences were noted among that larger cluster as well. Preferred the larger cluster around the 12Z ECMWF to start the forecast, taking a flatter wave out of the Southeast late Tue. The 12Z ECMWF continued to offer a most reasonable solution near its ensemble mean, and the forecast trended toward that duo for the end of the period. GEFS ensembles did show an increase in amplitude of the 500mb pattern like the ECMWF ensembles but differed in its handling of a potential shortwave poking through the weakness in the upper ridge over the Pac NW (better anomalies over Alaska and the Southwest). Agreement was better than average by next Sat over the CONUS as low pressure may strengthen to the east of the deep upper trough out of Canada. ...Weather/Hazard Highlights... Record heat will continue to be the main impact into next week. Temperatures 10-20F above normal over the Southern Rockies/Plains will migrate westward into the Southwest and California next week as the upper ridge builds along the West Coast/120W. By contrast, much of the east, and especially around the Great Lakes/Northeast, will see cooler than normal temperatures more typical of early April (about 5-10F below normal) through much of the week. An even colder shot of air could accompany the upper trough axis passage into next weekend. Temperatures could be 20 or so degrees colder than normal which may approach record cold levels for some areas. Farther south, a cold front will likely push all the way into and past southern Florida by the end of the week though in a very modified state. Precipitation will accompany and precede the system out of the Corn Belt Tuesday across the Ohio Valley to the Mid-Atlantic/Southeast overnight. Next frontal system out of the Pac NW Tue will slide eastward into the Plains by Thu with generally light rain and some embedded heavier elements. As this system passes the Mississippi River Valley and enters the base of the eastern trough, rainfall may expand to its east ahead of the cold front before it clear the coast early Saturday. Airmass could be cold enough for some snow at the highest elevations in New England late next Friday into Saturday. Fracasso Additional 3-7 Day Hazards information can be found on the WPC medium range hazards chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation, 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/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml