Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
330 AM EDT Sun Sep 29 2019
Valid 12Z Wed Oct 02 2019 - 12Z Sun Oct 06 2019
...Heavy rainfall possible midweek from the southern/central
Plains to the lower Great Lakes...
...Anomalous warmth culminates over the eastern and southeastern
U.S. on Wednesday, while very chilly conditions moderate in the
northern and northwestern states...
...Overview and Guidance/Uncertainty Assessment...
Model guidance continues to indicate that the upper-level pattern
will be generally more zonal and less amplified during the
medium-range period following the ejection of a low pressure
system moving toward the Great Lakes and New England. The
trailing cold front is expected to move more slowly across the
Plains under the more zonal upper-level flow. There is a strong
consensus that moisture drawn northward from Tropical Storm Narda
in the eastern Pacific will interact with the front and result in
a band of heavy rain midweek from northern Texas across the
central Plains and into the lower Great Lakes. Meanwhile, another
upper trough is forecast to move through the Pacific Northwest and
the northern Rockies late this week. The upper trough should be
out into the northern Plains where a low pressure center may
develop during the weekend.
The WPC medium-range grid package is basically a consensus of the
12Z ECMWF and the 12Z/18Z GFS, trending more toward their ensemble
means for Days 6 and 7. The CMC ensemble also agrees well with
the EC and GEFS for Days 6 and 7. Thus, a small percentage of the
12Z NAFES is included as well.
...Weather Highlights/Threats...
Confidence is increasing for a band of heavy rain to impact
portions of the central Plains on Wednesday into early Thursday as
moisture drawn northward from Tropical Storm Narda interacts with
a frontal boundary. A few inches of rain is possible within this
band, which could result in flash flooding in parts of the area.
There is some potential for heavy rain to develop over 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, and could approach the lower Texas coast
during the weekend.
Very chilly conditions over the western U.S. into Northern Plains
are expected to moderate through this week. On the other hand,
many locations from the Gulf Coast to New England will see daily
record high temperatures on Wednesday. As the strong upper ridge
retreats, the heat will gradually abate as we head into the
weekend.
Although uncertainty is high at this point, there is some
potential for heavy rain to develop during the weekend over the
central Plains where a low pressure system may form.
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
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