Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
319 PM EDT Thu Oct 03 2019
Valid 12Z Sun Oct 06 2019 - 12Z Thu Oct 10 2019
...Overview and Guidance/Uncertainty Assessment...
Model and ensemble guidance shows a fairly progressive and
moderately amplified pattern which averages out to broadly
cyclonic flow in the multi-day means. There will be two primary
upper troughs of note during the period, spaced a few days apart,
supporting leading cold fronts at the surface. The first upper
trough should extend from northwest Ontario into the central
Rockies as of early Sun and then progress through the East during
the first half of next week. The second trough will drop
southeast from the Gulf of Alaska/northeastern Pacific and most
likely reach the northern Plains and central-southern Rockies by
day 7 next Thu.
Starting with adjustments made by the ECMWF/ECMWF mean/CMC in
yesterday's 12Z cycle toward the more progressive GFS/GEFS/UKMET,
guidance now clusters quite well for the Gulf of Alaska to
Plains-Rockies trough. The 00Z CMC may be a bit overdone with its
amplitude late in the period though. The leading trough crossing
the East still presents some forecast problems. Individual models
and ensemble members diverge considerably for if and where some
embedded energy may try to separate from the westerlies. Trends
toward what has been the more consistent and progressive GFS
cluster with the trough coming into the West, and the latest ECMWF
run waiting to close off its upper low until the energy reaches
farther eastward, suggest decreasing potential for meaningful
shortwave energy to linger over the East whether in the form of a
closed low or open wave. The 00Z/06Z GFS runs close off a low
over the Maritimes but northeast of the 00Z ECMWF so there is
still potential for such a feature somewhere over that area.
A blend using the 00Z-06Z GFS and 00Z ECMWF/UKMET/CMC represented
consensus well early in the period while resolving low confidence
detail differences for the shortwave reaching the eastern states.
The forecast transitioned to a model and ensemble mean (06Z
GEFS/00Z ECMWF mean) blend by days 6-7 Wed-Thu to reflect the
large scale agreement in the guidance over most areas.
...Weather Highlights/Threats...
A fairly strong low pressure system tracking north of the Great
Lakes on Sun will bring a reinforcing push a cool air from Canada
into the northern states with a brief period of blustery winds.
The trailing cold front with one or more possible embedded waves
will provide a focus for locally heavy rainfall from the Tennessee
Valley/south-central Mississippi Valley into the Northeast during
Sun-Mon. This rainfall will be beneficial over areas currently
experiencing drought of varying intensity. Also during Sun-Mon
the warm sector ahead of the front will contain will contain much
above normal morning lows. By Tue-Thu the front should settle
over the Florida Peninsula and possibly lead to some rainfall
enhancement in its vicinity. There is considerable uncertainty
for rainfall intensity though.
The upper trough dropping southeast from the Gulf of Alaska will
bring a period of rain and higher elevation snow to the Northwest
during the first half of next week with highest totals over
favored westward-facing terrain. The cold air behind the leading
surface front will progress south and east into the
West/Plains--bringing high temperatures down to at least 10-20F
below normal over the northern Rockies/Plains on Wed and over much
of the northern-central Plains by Thu. Expect some rain to
develop along the front as it reaches the Plains.
Rausch/Kong
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
Hazards:
- Heavy rain across portions of the Central Plains, the Lower
Mississippi Valley, the Southern Plains, the Middle Mississippi
Valley, the Great Lakes, and the Ohio Valley, Thu, Oct 10.
- Heavy rain across portions of the Northeast, the Central
Appalachians, the Tennessee Valley, the Mid-Atlantic, the Southern
Appalachians, the Great Lakes, and the Ohio Valley, Sun-Mon, Oct
6-Oct 7.
- Flooding possible across portions of the Central Plains, the
Middle Mississippi Valley, the Great Lakes, and the Upper
Mississippi Valley.
- Flooding occurring or imminent across portions of the Central
Plains, the Middle Mississippi Valley, the Great Lakes, the Upper
Mississippi Valley, and the Northern Plains.
- Flooding likely across portions of the Central Plains, the
Middle Mississippi Valley, and the Great Lakes.
- Heavy precipitation across portions of the Alaska Panhandle,
Sun, Oct 6.
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