Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1200 PM EDT Sun Mar 24 2019
Valid 12Z Wed Mar 27 2019 - 12Z Sun Mar 31 2019
...Overview...
A closed eastern Pacific upper trough will reach the West midweek,
with height falls working eastward over the nation Thu-next Sun.
Surface fronts in the West will support some heavy precipitation
including heavy elevation snows, and 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 some enhanced rain/thunderstorms in those
areas later in the week. The pattern also includes a risk of
wrap-around post-frontal snows on the cooled northwest periphery
of the main precipitation shield.
...Guidance Assessment/Preferences...
For the beginning of the medium range period, a multi-model blend
served us well for the large-scale features (upper trough/low
entering the West with some downstream ridging) while
de-emphasizing the small-scale differences. This blend included
the 00Z GFS, ECMWF, and UKMET, as well as the 00Z EC mean and 06Z
GEFS mean. By day 5 (Fri), preferred the 00Z deterministic GFS
rather than the 06Z run, as most other models have come into
better agreement with the the location/orientation of the closed
upper high in western Canada compared to yesterday, and this
placement is unlike the 06Z GFS. Deterministic models quickly
diverge by day 6-7, especially by day 7 (Sun) as the 00Z EC
combines the northern and southern streams into one deep upper
trough across the central/eastern CONUS, whereas the GFS runs
separate the streams but have been rather inconsistent regarding
placement of troughs in the central to western U.S. Thus preferred
the EC and GEFS means, which were reasonably well-aligned, for
this more uncertain portion of the forecast.
...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
is expected Wed/Thu. Heavy 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. This plus another cold
front dropping southward out of Canada in tandem with deepening
lead return flow from the Gulf of Mexico would fuel an expanding
risk of enhanced rains/convection. The Upper/Middle Mississippi
Valley (where flooding is ongoing) is currently forecast to
receive rainfall by Thu-Fri, with rain expected in the Lower
Mississippi Valley by Sat. Uncertainty remains regarding heaviest
rainfall amounts/placement, but the guidance signal for
development continues to grow. In the cold air behind the
aforementioned cold front coming from Canada, late-season snow is
possible in the Northern/Central Plains to Midwest.
Warmer than average temperatures are expected to prevail across
the Plains/MS Valley before the series of cold fronts dropping
south through those areas changes the regime to cooler than
average temperatures. The Eastern Seaboard could have above normal
temperatures next weekend ahead of these cold fronts.
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