Extended Forecast Discussion NWS Weather Prediction Center College Park MD 152 AM EDT Mon May 04 2020 Valid 12Z Thu May 07 2020 - 12Z Mon May 11 2020 ...Record heat for the Southwest/West Thu-Sat... ...Record cold for parts of the East Fri-Mon... ...Overview and Guidance/Predictability Assessment... Models/ensembles remain in good agreement overall with the amplifying pattern across North America later in the week. An omega block will develop, centered on the North American west coast, with deep winter-like troughing in the East as much of the West bakes in summertime heat. The pattern may start to break down by the start of next week as a Pacific system inches closer to the West coast. Start of the period will feature a deepening Atlantic system just off New England that has trended a bit stronger and closer to the coast than in recent days. As that departs, the upper low over Hudson Bay will sink southward through Ontario and into the Great Lakes, bringing in a much colder airmass to many areas east of the Plains for late in the week through the weekend. Blend of the recent 12Z/18Z guidance served as a good starting point the first few days of the forecast. The GFS became a bit quicker with the upper low moving through the Great Lakes/Northeast vs the larger ECMWF-led consensus. Preferred that group over the quicker GFS though its solution is not out of the question should the track be a bit farther east. Thereafter, trended toward just the 12Z ECMWF with a majority ensemble mean weighting (both 18Z GEFS and 12Z ECMWF ensemble mean) which de-emphasized any unpredictable small-scale system that may very well rotate out of western Canada around the mean upper trough, but has little predictability at this time range. In the PacNW, good agreement exists on trying to bring a Pacific front onshore as the northern upper height anomaly drifts into the Beaufort Sea and the ridging over Mexico/Southwest flattens just a bit. ...Weather/Hazard Highlights... Record heat will continue in the Southwest through about Thu/Fri before shifting into California and Oregon as the upper ridge focuses along the West Coast. Temperatures 10-20F above normal should push readings into record territory for much of Arizona and the lower CO River with highest readings near 110F. The core of the heat will shift northwestward through northern California Fri-Sat into Oregon and northern Nevada as well. By contrast, much of the east, and especially around the Great Lakes/Northeast, will see cooler than normal temperatures by about 10-20F through much of the period. Coldest shot of air may be around Fri-Sat with only some small moderation Sun-Mon. Temperatures may approach record cold levels for some areas with a late frost/freeze where the growing season has typically started by now. Farther south, a cold front will push through all of Florida and into Cuba by the start of the period (Thu) though in a very modified state. A second cold front is forecast to again push into at least southern Florida around next Sun/Mon. Precipitation will generally be light across most 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. In addition to some rainfall for coastal New England Thu around the ocean storm, rainfall may expand through the Ohio Valley into New England as a surface low moves toward Maine late Fri, where temperatures could support accumulating snow over the highest elevations and more conversational snow at middle elevations. Some lake-effect/enhanced rain/snow is possible over Michigan Fri/Sat as the upper low swings through with its cold core of temperatures over still chilly but moderating lakes. In the West, dry conditions are expected until perhaps late next Monday over coastal OR/WA when the Pacific system may get close enough to spread some rain eastward. 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