Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
325 PM EST Mon Mar 04 2019
Valid 12Z Thu Mar 07 2019 - 12Z Mon Mar 11 2019
...Weather Pattern Overview...
Expect a fairly progressive pattern across the Lower 48 with
systems ejecting from a long-term eastern Pacific/West Coast mean
trough. A leading weak feature may spread some precipitation over
parts of the central/eastern states but with greater than average
uncertainty over coverage and amounts. Following this will be the
strongest system of the period, likely moving into the West by Fri
and then tracking from the central High Plains northeastward
during the weekend. Various weather threats will accompany this
storm during its existence. Another system may approach
California by next Mon.
...Model Guidance Evaluation and Preferences...
Early in the period, there are already guidance discrepancies for
the strength of the weak wave crossing the central/eastern states.
GFS runs are strongest with the shortwave aloft/surface wave
while other solutions are weaker to varying degrees, with
corresponding effects on precipitation coverage/intensity.
Relatively low predictability of such a small scale feature favors
an intermediate/blended approach.
At least in relative terms there is decent clustering for the
system reaching the West on Fri and tracking northeastward from
the Plains. Two significant unknowns will be its interaction with
energy within/around the upper low initially over Vancouver Island
and then possible influence from shortwave energy that may drop
southeastward through Canada. As the system reaches the
Midwest/northwestern Great Lakes the GFS is on the stronger side
of the spread and could be a little overdone considering it has
the greatest influence among guidance of the Canadian shortwave
energy. However it seems likely that the system will be stronger
than at least the ECMWF/CMC ensemble means. Thus a model/mean
compromise provides a reasonable account for detail and
uncertainty. By late in the period the models/ensembles develop
considerable spread regarding the amplitude of upper troughing
reaching the East--GFS/GEFS members the most amplified,
ECMWF/ECMWF members the flattest, and CMC-based guidance
in-between. The mean troughing near the West Coast suggests that
the eastern trough should be weaker than forecast by the GFS to
some degree. At the surface there is a notable trend in the GEFS
mean toward a more inland surface low track late in the period,
toward the ECMWF mean.
The system tracking toward southern California by day 7 Mon shows
better than average agreement for a forecast that far out in time.
Currently a model/ensemble mean compromise represents consensus
well. The primary trend of note over the past 1-2 days is a
faster adjustment in the GEFS mean.
Given a general preference for a blend/intermediate approach, the
updated forecast started with components of the 06Z GFS and 00Z
ECMWF/UKMET/CMC days 3-4 Thu-Fri. The forecast removed the UKMET
after Fri due to straying from consensus over some areas while
introducing some input from the 06Z GEFS/00Z ECMWF means, with a
model/mean blend continuing through day 7.
...Sensible Weather and Potential Hazards...
Over the West expect significant snowfall from the Sierra Nevada
through the Intermountain West and Rockies late this week with a
combination of ongoing activity and the system tracking into the
West by Fri. Some rain will be possible over coastal/low
elevation areas. Precipitation will become lighter and more
scattered during the weekend. The southern half of California may
see an increase of moisture on Mon with the approach of another
system.
The late week system emerging from the West will likely intensify
as it tracks from the central High Plains northeastward during the
weekend. The northern Plains region has the highest potential for
significant snowfall at this time with areas farther east into the
Upper Great Lakes more sensitive to exact storm track. Winds
could become strong enough to produce blizzard conditions
depending on how intense the system becomes. Meanwhile strong low
level Gulf inflow ahead of the advancing strong cold front will
spread widespread rain will develop from the Gulf Coast to the
Ohio Valley and southern Appalachians. The best signal for
heaviest rainfall extends across the south-central Mississippi
Valley and Tennessee River Valley with significant amounts also
possible over other parts of the east. This rainfall combined
with already wet ground may pose some flooding issues.
Strong/severe convection will be another threat that will need to
be monitored. Consult Storm Prediction Center products for the
latest information as specifics become more clear.
During Thu-Fri a weak system may spread some precipitation across
parts of the central/eastern states (snow north/rain south) but
with low confidence in coverage and amounts. Then by the start of
next week there is also significant uncertainty over precipitation
coverage/amounts across parts of the southern tier, depending on
amplitude of flow aloft over the East.
The northern-central Plains will likely continue to see below
normal temperatures most days with highs tending to be 10-20F
below normal with locally more extreme anomalies one or more days.
The West will tend to see below normal highs for much of the
period but morning lows should be above normal late this week.
The South/East will see a brief surge of warmth ahead of the front
associated with the Plains/Great Lakes storm during the weekend.
Rausch
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, Mon, Mar 11.
- Heavy precipitation across portions of the Mid-Atlantic, the
Northeast, and the Great Lakes, Sun, Mar 10.
- Heavy rain across portions of the Central Plains, the Lower
Mississippi Valley, the Tennessee Valley, the Great Lakes, the
Middle Mississippi Valley, the Mid-Atlantic, the Southern
Appalachians, the Upper Mississippi Valley, the Southeast, the
Southern Plains, and the Ohio Valley, Sat-Sun, Mar 9-Mar 10.
- Heavy rain across portions of the Mid-Atlantic, the Northeast,
and the Central Appalachians, Sun-Mon, Mar 10-Mar 11.
- Heavy rain across portions of the Southwest, Mon, Mar 11.
- Heavy snow across portions of the Central Great Basin,
California, and the Southwest, Thu-Fri, Mar 7-Mar 8.
- Heavy snow across portions of the Central Plains, the Middle
Mississippi Valley, the Great Lakes, the Upper Mississippi Valley,
and the Northern Plains, Sat-Sun, Mar 9-Mar 10.
- Flooding occurring or imminent across portions of the Lower
Mississippi Valley, the Tennessee Valley, the Middle Mississippi
Valley, the Mid-Atlantic, the Southeast, and the Ohio Valley.
- Flooding likely across portions of the Central Plains and the
Southeast.
- Much below normal temperatures across portions of the Central
Plains, the Middle Mississippi Valley, the Southern Plains, the
Upper Mississippi Valley, and the Northern Plains, Thu-Mon, Mar
7-Mar 11.
- Much below normal temperatures across portions of the Northeast,
the Central Appalachians, the Mid-Atlantic, the Southern
Appalachians, the Great Lakes, and the Ohio Valley, Thu-Fri, Mar
7-Mar 8.
- Enhanced wildfire risk across portions of the the Southern
Rockies, the Southern Plains, and the Southwest, Thu, Mar 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