Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1057 AM EST Tue Feb 19 2019
Valid 12Z Fri Feb 22 2019 - 12Z Tue Feb 26 2019
...Multi-day heavy rainfall/flooding threat from the Lower
Mississippi/Tennessee/Ohio Valleys to the Southern/Central
Appalachians through Saturday...
...Significant snow threat lifts from the Southwest and
south-central Rockies states Friday through the Plains/Upper
Midwest and Great Lakes/Northeast this weekend...
...Pattern Overview and Weather Highlights/Hazards...
A favorable corridor for a multi-day heavy rain/training episode
will persist from the lower MS/TN/OH Valleys to the
Southern/Central Appalachians and Mid-Atlantic through Saturday.
Flooding/runoff issues will be fueled by highly anomalous moisture
channeling into a wavy frontal zone under favorable jet support
initially, then deeper weekend cyclo/frontogenesis.
An amplified upper trough will support terrain enhanced heavy
snows over the Southwest and the South-central Rockies states on
Friday. The trough lifts through the Central and Northeast U.S.
this weekend overtop an amplified and slow to erode
Bahamas/Southeast upper ridge. This system will bring a threat for
significant accumulating snow with some icing possible with a
deepening surface low tracking from the Plains to the Upper
Midwest/Great Lakes/New England. Models have come into better
agreement compared to previous runs on the strength of the surface
low, with most deterministic solutions advertising a surface low
by 12z Saturday in the 980s over the Upper Great Lakes. This would
likely result in gusty winds and potential blizzard conditions
across the Upper Midwest and Great Lakes this weekend.
Troughing out west gets reinforced through the medium range period
thanks to a blocking ridge situated in the Gulf of Alaska and
eastern Pacific. A couple of shortwaves dig southward through the
Northwest this weekend/early next week, albeit should be less
amplified than the lead systems. This should continue an unsettled
weather pattern across the Pacific Northwest and into the
Intermountain West, with the best chance for accumulating snowfall
in the Washington/Oregon Cascades.
...Guidance/Predictability Assessment and Preferences...
Models and ensemble solutions continue to show very good
clustering at the mid-larger scales through the medium range
period. The morning update to the WPC progs favored a majority
blend of the latest runs of the GFS/ECMWF, with smaller
contributions from the GEFS/ECMWF ensemble means. This maintains
excellent WPC continuity within a pattern with above normal
predictability.
Santorelli/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