Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
157 AM EST Sun Mar 3 2019
Valid 12Z Wed Mar 6 2019 - 12Z Sun Mar 10 2019
...Weather Pattern Description...
The flow across the CONUS will begin the medium range in a rather
amplified setup, and then gradually trend more zonal and
progressive by the mid to latter portion of the forecast period.
Shortwave energy ejecting from a mean upper trough off the West
Coast will cross the country every couple days. Meanwhile, a broad
upper trough initially in place across the Great Lakes/Northeast
should gradually lift out by the middle to end of the upcoming
work week.
...Model Guidance Evaluation and Preferences...
The medium range forecast period begins on Wednesday with a West
Coast trough and broad cyclonic flow encompassing the eastern half
of the nation, with a broad upper ridge over the Rockies.
Noteworthy model differences appear as early as Day 4 (Thursday)
with the break down of the ridge as Pacific energy lowers heights
and a quasi-zonal flow pattern returns. The FV3, ECMWF, and UKMET
were in reasonably good agreement on the passage of shortwave
energy across the High Plains and Upper Midwest through Thursday
and Friday, while the GFS was more amplified. Even greater model
differences reside across the West Coast region for Friday and
beyond, with the CMC much slower with the trough axis progression.
This large scale trough and eventual evolution into a closed
upper low will eventually spawn the development of a strong
surface low across the central U.S. Although the chances are good
that a strong storm system will develop, there are major
differences in the placement and track of the low, so future
forecasts are likely to change significantly in the coming days
since confidence is below average in this portion of the forecast.
Given these considerations, the forecast was initially based on a
multi-model deterministic blend (12Z ECMWF/UKMET/FV3) during days
3-5 (Wednesday through Friday). For next weekend, the forecast was
mainly derived from ensemble mean (ECENS and NAEFS) weighting,
with some continued emphasis on the 12Z ECMWF/FV3 solutions as
well.
...Sensible Weather and Potential Hazards...
Although the coldest temperatures will be prior to the start of
this forecast period, it will still be very cold by early March
standards across much of the central and eastern U.S. on Wednesday
and Thursday. A large arctic high will encompass much of the U.S.
east of the Rockies, and temperatures only slowly moderate by the
end of the week with anomalies of 15 to 30 degrees below normal
through Thursday, and a second surge of cold temperatures is
expected for the northern plains and Upper Midwest through next
weekend, keeping readings about 20 degrees below normal. However,
much of the southern and eastern U.S. warms up to near average
levels by the weekend as a storm system gathers strength across
the Plains.
Heavy rain and mountain snow return to the western U.S. by Tuesday
night as an atmospheric river event accompanies a strong Pacific
low headed towards California. The Sierra Nevada will likely get
an additional 1 to 3 feet of snow, thus adding to its extensive
snow pack. Significant snow is forecast for the central and
northern Rockies on Wednesday and Thursday as the moisture plume
advects inland, albeit not to the same degree as California.
With a large storm system possibly affecting the central U.S. next
weekend, widespread rain is expected to develop from portions of
the lower/mid-Mississippi Valley to the Ohio Valley and
Appalachians as a rich supply of Gulf moisture surges northward.
Depending on where the surface low develops, a band of heavy snow
and windy conditions are possible across parts of the northern
plains, Upper Midwest, and western Great Lakes region.
D. Hamrick
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