Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
245 AM EDT Sun Oct 06 2019
Valid 12Z Wed Oct 09 2019 - 12Z Sun Oct 13 2019
...Another round of cold/snow for the Northern Rockies/Plains next
Wed/Thu...
...Overview...
A positive height anomaly near Labrador/northeastern Quebec will
favor deepening 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 lurk just offshore New England.
...Guidance/Uncertainty Assessment...
A blend of the 12Z ECMWF/ECMWF ensemble mean and 18Z GEFS mean
offered a reasonable starting point to the forecast through the
period. The 12Z/18Z GFSs were quicker with the timing of the
western trough as it progressed onto the Plains, against the
multi-day trends and the vast majority of the ensembles. The 12Z
Canadian/UKMET showed a similar slower timing comparable to the
ECMWF. Off the New England coast, the 12Z ECMWF was on the
southern third of the ensemble spread with the potentially
subtropical system while the GFS/Canadian were much farther north.
Preferred an ensemble mean consensus with a weight toward the
ECMWF ensemble mean by next Sat/Sun which was slower to lift the
system northward than the 18Z GEFS mean.
...Weather Highlights/Threats...
Strong cold front will push out of the Northern Rockies on
Wednesday which will drag down well below average temperatures
through the region. Record cold is likely for many areas in its
wake for both lows and highs (record cold max temperatures) as
readings may be 20-40 deg F below average. Cooler air will spread
southward to Texas and eastward to the mid-Mississippi Valley by
Friday but with less intensity. Still, a large area of the CONUS
will see temperatures below average by about 5-15 deg F. The
exception will be east and south of the front, mainly from the
Appalachians eastward and into the Southeast/Florida until the
front passes.
Along with colder temperatures, modest accumulating snowfall is
likely for parts of the Northern Rockies and eventually the
Northern Plains and Upper Midwest. 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. Rain
threat in general will decrease farther east as the system lifts
into Canada.
The low off the New England coast will bring a threat for locally
heavy rainfall to at least parts of coastal New England next week,
but this is dependent on how close the low tracks to the coast.
NHC is also monitoring this system for potential tropical or
subtropical development. Regardless, stiff easterly onshore flow
will be prevalent through southern New England into the coastal
Mid-Atlantic around its circulation.
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