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