Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
338 PM EDT Tue Apr 02 2019
Valid 12Z Fri Apr 05 2019 - 12Z Tue Apr 09 2019
...Overview...
Noticeable model differences emerge quite early in the
medium-range period. These differences continue to bring more
uncertainties further into the forecast period. Despite these
differences, a general eastward progression of a negatively-tilted
mid to upper-level trough can be expected across the western U.S.
through the weekend. The trough should move into the Plains on
Monday as a low pressure center develops and then tracks toward
the Ohio Valley and the lower Great Lakes by next Tuesday. Best
chance of heavy precipitation will span multiple days across areas
closer to the Pacific Northwest coast, while southeastern Texas
should see the best chance of heavy rain on Saturday. The rain
should continue to spread east and northeast and then move into
the East Coast Monday and Tuesday.
...Guidance Assessment/Preferences...
Model guidance this morning continues to show noticeable
differences starting this Friday over the mid-section of the
country as well as just off the East Coast. These differences
prove to have significant impacts on the model solutions across
the U.S. further into the medium-range period. The first
difference is regarding the placement of a frontal wave in the
vicinity of the Ohio Valley on Friday, where the GFS continues to
indicate that the wave will develop much farther north toward the
Great Lakes whereas the ECMWF maintains that it will develop over
Tennessee. The ECMWF also maintains a secondary low development
off the Carolina coast on Saturday, an idea that the Canadian
model agrees but the GFS continues to reject.
Uncertainties continue to grow as we head into early next week as
models have not yet resolved into a stable solution for much of
the eastern two-thirds of the country. This was indicated by a
large difference between their ensemble means and their
deterministic solutions. Nevertheless, the ensemble means from
the ECMWF, GFS, and Canadian models show quite good agreement for
a low pressure center to track from the central Plains toward the
lower Great Lakes from Monday into Tuesday. A blend of these
ensemble means yielded good continuity from the previous WPC
medium-range package also. Therefore, the WPC morning
medium-range grids were derived from a consensus of the 00Z
ECMWF/00Z EC mean and the 06Z GFS/06Z GEFS with more emphasis
toward the ECMWF solutions for days 6 and 7. Please refer to the
previous discussions for further details on model preferences.
...Weather Highlights/Hazards...
Continue to expect periods of enhanced rainfall/higher elevation
snow from the central/northern West Coast into the northern
Rockies. Some locations along the most favored terrain from
northern California/Sierra Nevada into western Washington/Oregon
may see at least several inches liquid over the Fri-Tue period.
The northern Rockies should see lesser but still significant
totals. Individual systems affecting the Pacific Northwest coast
may also be accompanied by periods of strong winds. Confidence in
precipitation coverage and intensity decreases during the first
half of next week as guidance diverges for amplitude/timing of
significant features.
Leading area of precipitation over the East, possibly including
some snow over New England, should depart after Fri night. Some
pockets of locally heavier precipitation are possible but there is
not a clear signal for where such activity may occur. From Fri
night onward the shortwave aloft approaching/reaching the southern
Plains along with strengthening flow of Gulf moisture interacting
with a stalled front will likely lead to a heavy rainfall threat
over the southern Plains/Lower Mississippi Valley and possibly
extending to the east/northeast. Low pressure tracking
northeastward from the southern Plains should eventually help to
spread moisture over much of the eastern half of the country.
Depending on how this system evolves there may be some bands of
significant rainfall in middle/northern latitudes between the
Plains and East Coast. Plains/Mississippi Valley areas sensitive
to additional rainfall should monitor forecasts for this system.
The overall pattern should favor modestly below normal highs over
the West Coast states into the northern Rockies but with a warming
trend over southern areas. Lows should be above normal through
the period (some plus 10-15F anomalies). Most areas east of the
Rockies should see above to much above normal temperatures, though
with a cooling trend behind the front reaching the eastern states
late in the period. Morning lows may be 15-25F above normal over
parts of the northern Plains and Midwest around Sun-Mon with some
daily record warm low values possible.
Kong/Rausch
Hazards:
- Heavy precipitation across portions of California, the Central
Great Basin, the Pacific Northwest, and the Northern Great Basin,
Fri-Sun, Apr 5-Apr 7.
- Heavy rain across portions of California and the Pacific
Northwest, Fri-Sat, Apr 5-Apr 6.
- Heavy rain across portions of the Lower Mississippi Valley and
the Southern Plains, Sat, Apr 6.
- Heavy rain across portions of the Southeast, the Lower
Mississippi Valley, the Southern Plains, and the Tennessee Valley,
Sun, Apr 7.
- Heavy rain across portions of the Southeast, the Mid-Atlantic,
and the Southern Appalachians, Mon-Tue, Apr 8-Apr 9.
- 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.
- Flooding possible across portions of the Northern Plains.
- 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 Upper 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.
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