Extended Forecast Discussion NWS Weather Prediction Center College Park MD 153 AM EST Tue Dec 31 2019 Valid 12Z Fri Jan 03 2020 - 12Z Tue Jan 07 2020 ...Heavy rainfall threat continues across the Southeast on Friday... ...Overview/Guidance Assessment... Upper troughing shifting from the Central to Eastern U.S. Fri-Sun will induce a heavy rainfall threat ahead of it in the Southeast. The guidance shows pretty good agreement Friday/Day 3 with broad troughing across the Great Plains. After this, the GFS (and the UKMET) has been pretty consistent with wanting to close off an upper low over the Midwest, and race the shortwave eastward through the weekend. The ECMWF/CMC are a bit slower with the upper trough, not quite as developed, and that seems to fit better with the ensemble means. A couple of shortwaves enter the Pacific Northwest on Saturday and again on Sunday, the latter of which guidance shows good agreement will amplify as it crosses the Rockies on Monday, ejecting into the Plains on Tuesday. The latest runs of the GFS/ECMWF have the ECMWF a bit slower/more amplified than the GFS, but run-to-run continuity has been fairly poor with the details. Yet another shortwave trough looks to approach southwest Canada on Tuesday/Day 7, though the deterministic solutions show quite a bit of variability with the evolution of this feature. Preferred a blend more towards the agreeable ensemble means (GEFS/ECENS mean) by the end of the period. ...Weather Highlights/Threats... Gulf of Mexico moisture will get drawn ahead of the trough lifting through the mid-south continuing a threat for heavy rainfall from the end of the short range period into parts of the Southeast/southern Appalachians. Surface low across the Ohio Valley deepens, and reforms off the Northeast coast by Saturday, and depending on development of the upper system, could bring a period of snow north and west of the low from the Upper Midwest to northern/interior New England. Nearly daily bouts of precipitation are likely for the Northwest into the Northern Rockies during the period, focusing more over coastal locations and the Coastal Range/Cascades. Above to well above normal temperatures across the eastern third of the country Friday and Saturday should moderate to near normal following passage of the cold front, with above normal temperatures also moving across the Western U.S. in the Central states this weekend. Santorelli 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