Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1156 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 latest runs of the GFS, ECMWF, and
Canadian, with small contributions from the ECENS/GEFS means,
offered a reasonable starting point as the western U.S. trough
sinks through the Northern Rockies and emerges into the High
Plains. By Fri-Sat, there remains some uncertainty regarding how
quickly a possible cut-off closed low deepens over the Upper
Mississippi Valley/Upper Great Lakes. The GFS continues to be
slightly fast, while the Canadian and ECMWF are slower (Canadian a
hair slower than the ECMWF). The ensemble means generally follow
suit with their respective deterministic counterparts. The 00z
ECMWF continues to represent a good middle ground solution. Though
run-to-run continuity with this system is less than stellar, a
trend may be emerging for a slower and more amplified/deeper upper
low. This is in part because of a slower/farther westward cut-off
low off the New England coast by mid to late next week. For both
systems, a blend between the GFS/ECMWF and ensemble means, with
more weighting on the ECMWF, provided a good blend for the end of
the period. The result was a noticeably deeper system over the
Upper Great Lakes and a surface low closer to the New England
coast from previous WPC continuity.
...Weather Highlights/Threats...
Central U.S. 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 to High Plains Thursday to the
weekend. Cooler air will also spread southward to Texas and
eastward to the mid-Mississippi Valley by Friday but with less
intensity. This system also brings increasing potential for modest
accumulating snowfall across parts of the Northern Rockies, with
snow potential even spreading eastward even to many valley
locations and eventually the Northern Plains. Ahead of the cold
front, 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.
The low off the New England coast has trended a bit westward in
model runs which now brings a threat for locally heavy rainfall to
at least parts of coastal New England by Wednesday-Thursday next
week. There remains plenty of model spread on how close the low
tracks to the coast, so the details of how far west precipitation
extends remains in question.
Santorelli
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