Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1156 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 higher
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 with ongoing
flooding late week into the weekend. This pattern also includes a
risk of heavy snows Thu-Sun on the cooled northwest to northern
periphery of the precipitation shield from the Northern/Central
Rockies/Plains to the Midwest/Great Lakes and then into northern
New England.
...Guidance Assessment/Preferences...
A multi-model blend seems quite reasonable Thu into Sat for the
larger-scale features (upper trough/low traversing the West
underneath a large east-central Canadian upper low) 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 run to run continuity issues become more problematic over the
weekend and next Mon. This begins day 5/Sat with questions about
the degree of separation in the northern and southern streams,
namely the manner in which a deep upper low in central Canada
phases with troughing across the central CONUS. The 00Z EC and its
mean exhibits more phasing of the features, while the GFS suite
keeps more separation at day 5 and then varies significantly from
run to run as to when the phasing occurs. Preferred a blend of the
00Z GEFS/ECMWF ensemble means as a compromise for now, though by
day 7/next Mon these do have some differences in placement of the
trough axis in the East. Utilized the 00Z GEFS mean rather than
the 06Z due to better handling of the pattern across the West by
early next week.
...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 the Northern Rockies Thu, 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 a 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.
Tate/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