Extended Forecast Discussion NWS Weather Prediction Center College Park MD 250 AM EDT Tue May 05 2020 Valid 12Z Fri May 08 2020 - 12Z Tue May 12 2020 ...Record cold for the East especially this weekend... ...Overview and Guidance/Predictability Assessment... An amplified pattern will bring in late winter-like chill to much of the East later this week into the weekend as the West will see well above normal temperatures. Guidance remains in good agreement on one upper low swinging through the Great Lakes Friday and out of New England late Saturday with perhaps another one out of central Canada early next week close to Lake Superior. Blend of the deterministic guidance sufficed to start the period as low pressure deepens as it leaves the Ohio Valley toward the Maine coast by early Saturday. Weaker shortwave aloft and surface front will trail behind and bring in additional cooler air to the Plains and MS Valley this weekend, with the 18Z GFS/12Z ECMWF paired well with their ensemble means. By next Mon/Tue, pattern will start to break down, first apparent in the Pac NW as a Pacific system may come ashore by early Tue per the ensemble consensus. About an equal weighting of GFS/ECMWF to the ensembles (60/40) maintained good continuity. ...Weather/Hazard Highlights... Record heat in the parts of the West will slowly diminish over the weekend, with temperatures 10-20F above normal decreasing to about 5-10F above normal by next Tue. Expect mainly dry conditions over the West until perhaps late next Mon over coastal OR/WA when a deep Pacific system may get close enough to spread some rain eastward. Much of the East and especially the Great Lakes/Northeast will see much cooler than normal temperatures, peaking over the weekend, and moderating only a bit by next week. Temperatures will approach/exceed record cold levels for some areas with a late frost/freeze where the growing season has typically started by now. The chill will especially be noticeable during the day when temperatures will climb only to levels typical for March. Precipitation will be mostly confined to southern areas and along/ahead of the front/low pressure Fri-Sat. Northern tier areas could see accumulating snow in higher elevations of New York/New England and even down to higher valley floors, depending on the evolution of the system. Though rare, May snow occurs every so often in the Northeast. Some lake-effect/enhanced rain/snow is also possible behind the system with cold northerly winds and temperatures rising only into the 30s or low 40s. Farther south, some locally heavy rain may occur Friday in the vicinity of an initial stationary boundary across southern Texas as well as with the cold front over the lower Mississippi Valley. Focus may then shift to southern Florida later this weekend as the cold front stalls near the Everglades. 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