Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
243 AM EDT Sat Oct 05 2019
Valid 12Z Tue Oct 08 2019 - 12Z Sat Oct 12 2019
...Another round of cold/snow for the Northern Rockies next
Tue/Wed...
...Overview...
A positive height anomaly near Labrador will favor troughing in
the western to central states and increased precipitation for the
Mississippi Valley. Western Atlantic ridging is forecast to
compress into the subtropics, allowing a cutoff upper low to
linger just offshore New England and Nova Scotia.
...Guidance/Uncertainty Assessment...
For Tue-Thu, a blend of the 12Z/18Z GFS, 12Z ECMWF/Canadian, and
18Z GEFS mean/12Z ECMWF ensemble mean offered a reasonable
starting point as the western system sinks through the region. By
next Fri/Sat, ensemble spread increases quite markedly with
respect to how quickly (or slowly) the trough moves eastward. The
Canadian represented the slower solutions while the GFSs
represented the quicker/quickest solutions. 12Z ECMWF fell mostly
in line with the ensemble means and this grouping was preferred
for the end of the period. The multi-day trend has been slower and
more amplified but upstream flow may be progressive enough to
prevent a cutoff solution in the central Rockies. To the east,
upper low and surface occluded front are forecast to stay just
offshore enough to prevent any direct impacts to New England, but
a slower/deeper western trough would likely mean that offshore
system could come much closer to the Northeast.
...Weather Highlights/Threats...
Cold front will bring well below average temperatures to the West
Wednesday onward--as much as 30-35 deg F anomalies (temperatures
in the 30s). Montana will be the focus for the cold on Wednesday,
followed by Wyoming on Thursday and the High Plains Fri/Sat.
Precipitation will accompany the front with widespread modest
elevation snow in western Montana spreading eastward even to many
valley locations and eventually to parts of the Plains. Cooler air
will spread southward to Texas and eastward to the mid-Mississippi
Valley by Friday but with less intensity. Rainfall will expand and
offers a risk to become locally heavy from the south-central
Plains to the mid-MS Valley/Midwest later in the period with
moisture inflow return from the Gulf.
Fracasso
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