Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1058 AM EST Sun Mar 03 2019
Valid 12Z Wed Mar 06 2019 - 12Z Sun Mar 10 2019
...Overview...
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 as
a broad upper trough initially in place across the Great
Lakes/Northeast lifts out.. Shortwave energy ejecting from a mean
upper trough off the West Coast will cross the country every
couple days. A more significant shortwave appears likely to
generate another energetic low pressure system across the central
U.S. by next weekend.
...Model Guidance Evaluation and Preferences...
Models/ensembles continued to show good clustering early in the
medium range with respect to a mid/upper-level shortwave and
surface low moving into California on Wed. As the feature moves
inland Thu-Fri, consensus has improved somewhat on the amplitude,
with the GFS showing a significant reduction in the amplitude of
the wave as it crosses the Rockies and moves into the central
U.S., and a much more suppressed frontal wave by Fri compared to
previous runs. Given the improved consensus, a multi-model
deterministic blend (00Z ECMWF/UKMET/CMC and 06Z GFS) was
preferred from Wed-Fri (days 3-5). There is general consensus now
that the development of a more significant wave of low pressure
across the central U.S. should hold off until Sat when the next
significant shortwave approaches. The ECMWF and GFS showed better
than average consensus with respect to this next wave an the
resultant surface low, which should develop in the central High
Plains Fri night-Sat and then lift northeastward into the Midwest
by Sat night-Sun. Additionally, some semblance of clustering of
ensemble members was also evident with this feature through Sun.
Spread is higher with respect to another shortwave perhaps
approaching the West Coast on Sun, with some solutions keeping the
feature offshore as a closed low (GFS/CMC), while the ECMWF shows
a more open wave. Given these considerations, weighting of the
ECENS and GEFS ensemble means was increased to comprise a majority
of the forecast during days 6-7 (Sat-Sun), with some continued
minor emphasis on the deterministic ECMWF and GFS solutions.
...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 Tennessee Valley and
southern 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.
Ryan/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