Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
207 AM EDT Mon Mar 25 2019
Valid 12Z Thu Mar 28 2019 - 12Z Mon Apr 01 2019
...Overview...
A potent/closed eastern Pacific upper trough will approach the
West Coast midweek, with these southern stream height falls
working eastward over the nation Thu-Sun. Surface fronts in the
West will support some heavy precipitation including heavy
elevation snows. Low developments in the Plains and subsequent
movement through the MS Valley/Midwest will combine with a surge
of deepening moisture/warmth from the Gulf of Mexico, which may
fuel enhanced rain/thunderstorms in those areas late week into the
weekend. The fronts/waves and moderating precipitation will mainly
exit the East Sun. This pattern also includes a risk of heavy
snows Thu-Sun on the cooled northwest to northern periphery of the
precipitation shield from the n-central Rockies/Plains to the
Midwest/Great Lakes and northern New England.
...Guidance Assessment/Preferences...
A multi-model blend seems quite reasonable Thu into Sat for the
larger-scale features (upper trough/low entering the West with
some downstream ridging all underneath a east-central Canadian
upper trough) while de-emphasizing the small-scale differences.
This blend includes the latest GFS, ECMWF, and UKMET that cluster
well with the latest GEFS/ECMWF ensemble mean during this time
period. Forecast spread and model run to run continuity issues
become more problematic over the weekend and next Mon. Accordingly
preferred a blend of the more compatable GEFS/ECMWF ensemble
means, with more weight assigned to the ECMWF ensembles that
maintain somewhat better WPC continuity.
...Weather Highlights and Hazards...
With the upper trough/low approaching the West, a couple of fronts
will make their way through the West and some heavy precipitation
expected into Thu. Some heavier valley rain/mountain snows will
threaten northern California/Oregon through the Northern Rockies,
with heavy snow forecast for the Central Rockies by Thu/Fri. As
the trough energy ejects out through the West, it is expected to
induce cyclo/frontogenesis in the Plains then Mississippi Valley,
Midwest and Northeast. This plus a northern stream cold front
dropping southward out of Canada will work in tandem with
deepening lead return flow from the Gulf of Mexico to fuel an
expanding risk of enhanced rains/convection. In the cold air
behind the aforementioned cold front coming from Canada,
late-season snow is possible in the Northern/Central Plains to
Midwest/Great Lakes then northern New England.
Schichtel
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