Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1130 AM EDT Sun Sep 29 2019
Valid 12Z Wed Oct 02 2019 - 12Z Sun Oct 06 2019
...Heavy rain expected from portions of the Southern Plains to the
Mid-Mississippi Valley...
...Anomalous warmth culminates over the eastern and southeastern
U.S. Wed-Thu, while very chilly conditions moderate in the
northern and northwestern states...
...Overview and Guidance/Uncertainty Assessment...
Relatively zonal/progressive flow is expected to be in place
across the CONUS during much of the medium range south of a more
amplified flow regime in place from Alaska across Canada. The
period of more zonal flow will begin by late Wed into Thu as an
upper trough initially across the Rockies lifts out into the
central U.S. with a wavy surface front progressing through most of
the central and eastern U.S. by late week. Meanwhile, another
upper trough is forecast to move through the Pacific Northwest and
the northern Rockies late this week, prompting developing of a low
pressure system across the Central/Northern Plains by this weekend
the trough moves east.
The WPC medium range forecast was based heavily on the 00Z ECMWF
along with gradually increasing weight on ensemble means
(ECENS/NAEFS) through time. The ECMWF was reasonably well-centered
within the model/ensemble spread through most of the forecast
period, lending to an overall preference toward that solution. The
GFS showed differences even early on with the timing of the
shortwave crossing the Northern Plains/Great Lakes Wed-Thu, and
with the amplitude of the feature as it crosses the Northeast
later in the week. Thus the GFS was not a preferred solution for
this forecast update.
...Weather Highlights/Threats...
Confidence is increasing that a band of heavy rain to impact
portions of the Southern/Central Plains starting as early as Tue
and persisting into the early portion of the medium range (Wed-Wed
night) as moisture drawn northward from Tropical Storm Narda
interacts with a frontal boundary. The potential for several
inches of rainfall could result in the potential for flash
flooding for some areas. Localized heavy rain is possible across
portions of New England on Thursday ahead of a developing low
pressure wave along the front. Meanwhile, deep-layer easterly flow
will bring an influx of tropical moisture across southern Florida
and into the Gulf of Mexico later this week.
Very chilly conditions over the western U.S. into Northern Plains
are expected to moderate through this week. Farther east, many
locations from the Gulf Coast to the Mid-Atlantic will see daily
record high temperatures Wed-Thu. As the strong upper ridge begins
to weaken into the weekend, the heat will begin to gradually abate.
Ryan
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