Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1032 AM EST Mon Feb 18 2019
Valid 12Z Thu Feb 21 2019 - 12Z Mon Feb 25 2019
...Multi-day heavy rain event from the Lower Mississippi/Tennessee
Valleys to Southern/Central Appalachians...
...Wintry heavy precipitation threat for the Southwest and
south-central Great Basin/Rockies Thu into Fri...
1530 UTC Update...
Model solutions remain relatively stable and the forecast was kept
fairly close to continuity in the update this morning. A
multi-model deterministic blend was used as a basis for the
forecast during days 3-4 (Thu-Fri). Starting on day 5 (Sat),
preferred the slower solutions (00Z ECMWF/06Z GFS) to bring
shortwave energy into the southern plains, with support from the
consistent ECENS mean and the latest GEFS mean. Differences emerge
with respect to this system across the Midwest/Great Lakes by Sun,
but decent clustering was evident among ensemble members,
well-centered around the ECMWF. Also of note was a nearly
universal trend among the models/ensembles toward a quicker
progression of shortwave energy and associated surface frontal
system reaching the Pacific Northwest Sat - this was probably the
most significant change to the forecast from overnight. A blend of
the ECMWF/GFS and ECENS/GEFS means was used for days 5-7, with
more weight placed toward the ECMWF/ECENS solutions given somewhat
better clustering and consistency. Previous discussion from
overnight follows below.
Ryan
Previous Discussion (issued at 0552 UTC)...
...Pattern Overview and Weather Highlights/Hazards...
What has proven to be quite the persistent and wintry western U.S.
mean upper trough will again be reinforced into Thu-Fri, spreading
an enhanced precipitation threat to include higher elevation heavy
snows from srn CA to the s-central Great Basin/Rockies. Trough
energy ejects over the central then eastern U.S. over the weekend,
working overtop an amplified and slow to erode Bahamas upper
ridge. A favorable corridor for a multi-day heavy rain/training
episode persists from the lower MS/TN/OH Valleys to the
Srn/Central Appalachians and Mid-Atlantic. Flooding/runoff issues
will be fueled by highly anomalous moisture channeling into a wavy
frontal zone under favorable jet support. A threat for heavy
snow/ice develops from the n-central Plains to the Midwest/Great
Lakes/Northeast as enhanced by less certain but potentially deep
surface cyclogenesis Fri-Mon. Upstream, weaker trough energies dig
into a less unsettled West in transition to less stormy and
moderating lower 48 mean zonal flow.
...Guidance/Predictability Assessment and Preferences...
Models and ensembles overall cluster pretty well into Thu/Fri with
the larger scale flow evolution and a favored composite solution
of the GFS/ECMWF and GEFS/ECMWF ensemble means maintains good WPC
continuity in a pattern with above normal predictability. Recent
ample run to run model variance prompts a quick transition in
favor of these ensemble means over the weekend into early next
week amid growing uncertainty in transitional flow.
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