Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1200 PM EDT Sun Oct 06 2019
Valid 12Z Wed Oct 09 2019 - 12Z Sun Oct 13 2019
...N-Central Rockies to Northern Plains/Upper Midwest Autumn Snow
Threat Wed/Thu...
...Guidance/Uncertainty Assessment...
The 06 UTC GFS and 00 UTC ECMWF/UKMET deterministic models offer
reasonably similar guidance Wed-Fri and a composite blend was
adopted for Day 3-5/Wed-Fri. This solution is strongly supported
by ensembles, bolstering forecast confidence. Forecast confidence
remains above normal into day 6/7, but gradually increasing model
variance and run to run continuity issues suggest more influence
into the forecast process may from ensembles may be prudent at
these longer time frames. Accordingly, the WPC forecast during
this period was mainly derived from a composite blend of the 06
UTC GEFS/00 UTC ECMWF ensemble means that cluster best with the 00
UTC ECMWF. The ECMWF was included for increased local detail
consistent with increased forecast confidence. Model trends toward
amplification and decreased progression also seem to better favor
the ECMWF over the other models. This forecast plan maintains good
WPC continuity.
...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, wrapback moisture and upslope flow
supports a heavy snow threat from the Northern and Central
Rockies out across the Northern Plains and Upper Midwest with
frontal low track/development. Ahead of the cold front, rainfall
will expand and offers a risk to become locally heavy from the
s-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.
An organized coastal low off the Mid-Atlantic and New England
offers a significant maritime threat and a risk of locally heavy
rainfall to these coasts next week, but this is dependent on how
close the low tracks to the coast. The models are trending a bit
closer and deeper. 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/Schichtel
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