Extended Forecast Discussion NWS Weather Prediction Center College Park MD 143 AM EDT Sun May 03 2020 Valid 12Z Wed May 06 2020 - 12Z Sun May 10 2020 ...Record heat for the Southwest midweek... ...Guidance/Predictability Assessment... Amplification of the upper pattern is well-forecast by the models/ensembles by next weekend, culminating in a somewhat wintry throwback for much of the Great Lakes/Northeast region. Guidance has finally come into better agreement with the flow out of the Pacific in the short term and through the Ohio Valley to start the medium range. The GFS/GEFS have virtually abandoned their overzealous forecast of a surface cyclone across the northern tier in favor of the flatter solution like the other guidance showed for the past two days. With that, a multi-model blend sufficed to start the period. Thereafter, focus will turn to a weaker but still important shortwave slipping through the Pac NW between the positive height anomaly centers to the north and south, and diving into the base of a digging upper low out of Hudson Bay. This will help spur a surface low out of the mid-Mississippi Valley late Thu into early Fri that will lift northeastward and deepen as it exits New England early Sat. Lowering heights in the east next weekend will usher in a cold airmass for nearly mid-May (reminiscent of winter) and little precipitation for most of the CONUS outside Texas. The 12Z ECMWF offered a reasonable forecast through next weekend though the GFS was acceptable but not preferred. A majority blend of the ensembles helped to downplay any seemingly spurious/overdeveloped feature next weekend in the GFS or ECMWF given the uncertainty in the flow east of the strong upper ridge over Alaska by then. ...Weather/Hazard Highlights... Record heat will continue in the Southwest through about Thu/Fri before shifting slightly into California as the upper ridge focuses along the West Coast. Temperatures 10-20F above normal should push readings into record territory for most of Arizona and the lower CO River with highest readings near 110F. By contrast, much of the east, and especially around the Great Lakes/Northeast, will see cooler than normal temperatures by about 5-10F through much of the week. An even colder shot of air may accompany the upper trough axis passage into next weekend when temperatures could be 20 or so degrees colder than normal. This may approach record cold levels for some areas but not to the extent of the record heat in the Southwest. Farther south, a cold front will push through all of Florida and into Cuba by the end of the week though in a very modified state. A second cold front is forecast to dip into at least central Florida at the end of the period. Precipitation will generally be light across parts of the CONUS. Stationary front around southern Texas will be a focus for perhaps the heaviest rainfall later in the week, but likely more localized than widespread. Rainfall may expand through the Ohio Valley as the surface low moves into New England late Fri, with some lake-effect/enhanced rain/snow through Michigan. Additional snowfall (though light) is looking more likely at the highest elevations in northern New England late next Friday into Saturday behind the front. 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