Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
200 AM EST Sun Feb 17 2019
Valid 12Z Wed Feb 20 2019 - 12Z Sun Feb 24 2019
...Multi-day Heavy Rain Threat for Lower Mississippi/Tennessee
Valleys to the Southern/Central Appalachians and Snow/Ice for the
Mid-Mississippi/Ohio Valleys and Northern/Central Mid-Atlantic to
Southern New England...
...Cold weather persists in the western to central U.S., with
unsettled weather focusing into the Southwest...
...Overview...
Persistent western U.S. mid-upper level troughing will be
reinforced during the medium range period by shots of renewed
energy. This feature plus an unyielding Bahamas upper ridge
creates a favorable pattern for a multi-day heavy rain threat this
week from the lower MS/TN Valleys to the Srn/Central Appalachians
and a snow/ice threat from the Mid-MS/OH Valleys to especially for
the n-central Mid-Atlantic to srn New England Wed-Thu.
...Guidance/Predictability Assessment and Preferences...
Guidance seems to agree well with ejection of a lead
mid/upper-level trough from the Plains to Northeast Wed-Thu and an
upstream pattern this week of potent upper troughs/height falls
progressing overtop a northeast Pacific ridge that then dig
sharply southward to reinforce a western U.S. mean trough. This
pattern offers above normal predictability into Friday, but
confidence decreases next weekend as guidance is more mixed with
main upper trough ejection from the Southwest and downstream
phasing and surface cyclogenesis potential over the east-central
U.S. Ensemble means offer more consistent guidance. Accordingly,
the WPC medium range suite was derived from a multi-model blend of
the reasonably well clustered 18 UTC GFS/GEFS mean and 12 UTC
ECMWF/ECMWF ensemble mean, but substantially reduced weighting on
deterministic models next weekend amid gradually growing forecast
spread/uncertainty with pattern transiiton.
...Weather Highlights/Hazards...
An prolonged excessive rainfall threat from the lower MS/TN
Valleys to the Srn/Central Appalachians will be a main story this
week. Deep layered and highly anomalously moist southwest flow
channeled from the Southern Plains to the East will act to sustain
a Southeast ridge and fuel multi-day threats of heavy
rain/training. On the northern edge, a cold surface high and cold
air damming in the Mid-Atlantic region is expected, leading to
frozen precipitation. Potentially heavy snow and ice is a
possibility from the Middle Mississippi Valley to Ohio Valley and
especially the northern Mid-Atlantic into southern New England
Wed-Thu.
With anomalously low heights in the western U.S., much below
average temperatures will prevail for the western and central U.S.
A main low is progged to dig from the Pacific Northwest to
California Wed/Thu to the Southwest by Fri along with enhanced
precipitation including higher elevation heavy snow. The main
system is expected to eject northeastward across the central and
east-central U.S. next weekend.
Schichtel
WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation and winter weather outlook
probabilities are found 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