Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
330 PM EDT Mon Apr 01 2019
Valid 12Z Thu Apr 04 2019 - 12Z Mon Apr 08 2019
...Overview...
This period will feature a steady progression of Pacific features
into the West that continue onward to produce several episodes of
active weather over the east-central U.S. Heaviest precipitation
should extend from the central/northern West Coast to the northern
Rockies as well as downstream from the southern Plains/South to
the Appalachians/Mid-Atlantic.
...Guidance Assessment/Preferences...
Latest models and ensembles remain remarkably stubborn in
maintaining their spread for shortwave energy aloft and associated
surface lows tracking across the eastern half of the country late
this week into the start of the weekend. As has been the case in
recent days there is decent clustering for low pressure over the
south-central Plains early Thu. Then individual models/ensemble
members rapidly diverge for the latitude of best-defined low
centers farther east. In forecasts valid early Fri the one trend
of note is a reduction of ensemble members in the northern part of
the spread in the Great Lakes. On the other hand recent ECMWF/CMC
runs remain on the southern part of the spread. By early Sat there
is still the potential for low pressure centers anywhere from
northern New England to southern coastal Mid-Atlantic. Confidence
remains low for system specifics due to the sensitivity to small
scale details aloft that include a combination of initial Plains
shortwave and northern tier energy that could interact by Fri. WPC
progs now favor a weakening northern stream surface wave tracking
through the Ohio Valley and Northeast as a southern stream surface
wave focuses potential for deeper moisture/rainfall/convection
underneath over the South and Mid-Atlantic.
Upstream, a fairly strong northeastern Pacific storm should bring
a decent front (with vigorous upper shortwave support) into the
West by Sat, potentially followed a day later by another system
tracking near Vancouver Island and bringing a front/energy aloft
to the Northwest. Guidance has been fairly consistent in weakening
shortwave energy that crosses the Northwest and heads into a
downstream ridge, while southern stream shortwaves cross the
Southwest U.S./northern Mexico and then southern
Plains/Mississippi Valley by the weekend.
There is still a rapid increase in forecast spread for details of
flow aloft from the Pacific into the western U.S., but relative
agreement among the ensemble means.
...Weather Highlights/Hazards...
Aside from the typically variable finer details, there is good
continuity in the forecast of multiple periods of significant
rainfall/higher elevation snow from northern California/Sierra
Nevada and Pacific Northwest into the northern Rockies. Highest
five-day totals will likely be over favored terrain in the West
Coast states with somewhat less moisture reaching the Rockies.
Heaviest precipitation should occur along the West Coast during
Fri-Sun. Meanwhile the system tracking out of the Plains Thu
onward will spread a decent moisture shield across the eastern
half of the country, but with continued lack of confidence in
specifics. Today there is somewhat more of a signal for heavy
rainfall potential over the Lower Mississippi/Tennessee
Valley/Gulf Coast region, and some convection over this area could
be strong to severe. Check SPC outlooks for latest info on severe
threats. Some snow may be possible into the northern Great
Lakes/New England. Behind this system, most guidance continues to
suggest a heavy rainfall threat next weekend/Monday for the
southern Plains/Lower Mississippi Valley. This activity will be
encouraged by the approaching southern stream shortwave aloft and
a healthy flow of Gulf moisture interacting with a stalled front
that should return north as a warm front. Rainfall of varying
intensity should also spread farther northward across the central
and eventually eastern U.S.
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
Hazards:
- Heavy precipitation across portions of California, the Central
Great Basin, the Pacific Northwest, and the Northern Great Basin,
Thu-Sun, Apr 4-Apr 7.
- Heavy rain across portions of California and the Pacific
Northwest, Thu-Sun, Apr 4-Apr 7.
- Heavy rain across portions of the Lower Mississippi Valley and
the Southern Plains, Sat-Sun, Apr 6-Apr 7.
- Heavy rain across portions of the Southeast, the Lower
Mississippi Valley, and the Tennessee Valley, Thu-Fri, Apr 4-Apr 5.
- Heavy snow across portions of the Northern Rockies and the
Northern Great Basin, Sat-Sun, Apr 6-Apr 7.
- Heavy snow across portions of the Northeast, Fri-Sat, Apr 5-Apr
6.
- Severe weather across portions of the Southeast, the Lower
Mississippi Valley, the Southern Plains, and the Tennessee Valley,
Thu, Apr 4.
- Flooding possible across portions of the Middle Mississippi
Valley.
- Flooding occurring or imminent across portions of the Central
Plains, the Lower Mississippi Valley, the Northern Plains, the
Tennessee Valley, the Middle Mississippi Valley, the Upper
Mississippi Valley, the Great Lakes, and the Ohio Valley.
- Flooding likely across portions of the Middle Mississippi Valley
and the Northern Plains.
- High significant wave heights for coastal portions of California
and the Pacific Northwest, Sat-Sun, Apr 6-Apr 7.
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