Extended Forecast Discussion NWS Weather Prediction Center College Park MD 242 PM EDT Fri May 08 2020 Valid 12Z Mon May 11 2020 - 12Z Fri May 15 2020 ...Record cold over the central/eastern U.S. through early next week... ...Wet pattern for southern Florida Sunday onward... ...Overview and Guidance/Predictability Assessment... The synoptic pattern through the medium range period (Mon-Fri May 11-15) is expected to remain relatively persistent featuring the western US ridge and eastern US trough. Toward Day 6/7 there are suggestions in the model guidance that this may begin to break down and change toward a western trough and eastern ridge, or at least more quasi-zonal flow. This should allow a pattern transitioning toward more normal for mid-May unlike the typically colder, winter-like pattern of recent, with surface cyclogenesis potentially developing over the south-central US by day 6/7 as shortwave energy moves from the Rockies eastward. In a large scale sense, the models show relatively good agreement with the pattern but differ quite a bit on the details and individual shortwaves that work through the flow, particularly early on the period over the Great Lakes. The 00Z CMC and 00Z UKMET were discounted given the wide swings in the shortwave rounding the base of the large scale trough. Meanwhile, while the 06Z GFS trended more favorably compared to early runs, it still exhibited typical speed biases and less reliability. The 00Z ECMWF offered a good approach given the average at best forecast confidence early on and then by day 5, there were increasing weights of the ECENS (with some GEFS) as predictability dropped off. ...Weather/Hazard Highlights... The Alaskan/Arctic ridge and broad cyclonic flow farther east will support well below average temperatures across much of the eastern half of the CONUS through early next week, with record cold temperatures possible for a number of locations. Both high and low temperatures are forecast to be 10 to 20 deg F (in some cases as much as 25 deg) below normal Mon-Tue across much of the central and eastern U.S. Scattered records are possible, including record low minimum and maximum temperatures. Temperatures are forecast to gradually moderate Wed-Thu as upper-level flow becomes a bit more zonal, but the Northeast should remain below average into late next week. In terms of precipitation, South Florida will see persistent showers and thunderstorms through much of next week as a trailing frontal boundary stalls in the vicinity. Locally heavy rains will be possible through much of next week, with some locations perhaps seeing several inches of rain. Areas from central/northern California and the Pacific Northwest to the northern Rockies will see precipitation Mon-Wed as the upper low/shortwave move inland. Showers and thunderstorms with at least locally heavy rain will also be possible across portions of the central/southern Plains Mon-Tue along a quasi-stationary frontal boundary and dry line, with convective activity likely lifting northeastward across the central U.S. by the middle to latter portion of next week as shortwave energy crosses the Rockies and reaches the central U.S., resulting in development of a frontal wave. Ryan/Taylor 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