Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1155 AM EDT Mon Oct 07 2019
Valid 12Z Thu Oct 10 2019 - 12Z Mon Oct 14 2019
...Central Rockies to Northern Plains/Upper Midwest Snow Threat...
...Pattern Overview and Guidance/Uncertainty Assessment...
The main weather driver in the medium range period (Thur-Mon) will
be an amplified trough ejecting out of the Rockies on Thursday,
closing off into a deep upper low over about northern
Minnesota/U.P. Michigan by the weekend. This low should very
slowly drift north/east into eastern Ontario by Monday morning,
driving a cold front east across the Midwest to the East Coast.
Meanwhile, a potential subtropical low should break off from the
larger scale flow and linger off the New England coast through
Saturday, before it gets sling-shot north towards the Canadian
Maritimes.
Across the board, models show above average agreement through day
7, which lends to better than normal forecast predictability
during the medium range. The GFS continues to be a hair faster
with the deep north-central U.S. low, which likely results in it
being quicker to push the New England low northward. It is not
fast enough to completely ignore, but the ECMWF/UKMET show
slightly better continuity with the ensembles and thus were
weighted more in the overall blend. The WPC medium range forecast
suite was mainly derived from a composite blend of the
ECMWF/UKMET/GFS days 3-5, with more ensemble mean weighting
(ECENS/GEFS means) beyond to mitigate smaller scale detail
differences. This maintains good WPC continuity in an active
weather pattern.
...Weather Highlights/Threats...
A strong cold front will dig through the western and central U.S.
into Thu/Fri to bring well below average temperatures through the
region. Some record values may be reached as daytime highs could
be as much as 30-40 degrees below normal. Cooler air will tend to
moderate and spread across the eastern states over the weekend as
well.
Along with colder temperatures, wrapback moisture and upslope flow
supports a heavy snow threat from the Rockies to the Upper Midwest
with upper closed low and surface frontal low track and
development. A period of high winds is possible in this region as
well as the surface low rapidly deepens and a strong pressure
gradient develops on the backside of the storm. Ahead of the
attendant cold front, rainfall will expand and offer a risk of
locally heavy rainfall from the south-central Plains to the mid-MS
Valley/Midwest in a region of enhanced moisture inflow return from
the Gulf of Mexico. The rain threat in general will decrease
farther east as the system lifts into Canada.
Downstream, an organized coastal low off the Mid-Atlantic and New
England will meanwhile offer a significant maritime threat and
some coastal rainfall, dependent on how close the low tracks to
the coast. NHC is also monitoring this system for potential
subtropical development. Regardless, strong easterly onshore flow
will be prevalent through southern New England into the coastal
Mid-Atlantic around its circulation.
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