Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
354 AM EDT Tue Oct 01 2019
Valid 12Z Fri Oct 04 2019 - 12Z Tue Oct 08 2019
...Central U.S. heavy rain threat diminishes late this week but
could return/extend eastward by the weekend and early next week...
...Record warmth continues for the Southeast into Thursday...
...Overview and Guidance/Uncertainty Assessment...
A less amplified and more seasonable mean flow aloft is expected
to begin the medium-range period before the pattern possibly
becoming more amplified again by early next week. Models have
come into better agreement with an intensifying low pressure wave
to move quickly off to the east of New England on Friday. The
trailing cold front will bring an end to the record heat over the
eastern U.S. Meanwhile, an upper-level trough is forecast to
progress steadily through the western U.S. and should reach the
Plains during the weekend. Model guidance appears to indicate a
trend toward a more amplified broad scale pattern, with larger
than normal uncertainty regarding the subsequent evolution of this
trough as it heads toward the East Coast early next week.
The WPC forecast grids were derived mostly from a blend of the 18Z
GFS and the 12Z ECMWF, with more weights given to the ECMWF. Some
12Z UKMET and 12Z Canadian solutions were also used. It was noted
that the ECMWF, UKMET, and Canadian models showed a more
amplified/sharper configuration near the base of the upper trough
over the western U.S. which was different from the less amplified
version indicated by the GFS. The most amplified solution, as
shown by the 12Z ECMWF, led to cyclogenesis over the southeastern
U.S. by next Tuesday. This scenario was not yet supported by its
ensemble mean however. Therefore, a more conservative approach
was used to handle the uncertainty by blending the 12Z EC mean,
18Z GEFS, and some 12Z NAEFS for days 6 and 7. This yielded good
continuity with the previous WPC medium range package.
...Weather Highlights/Threats...
The low pressure system moving pass New England Thursday night
will bring focused rainfall to areas near/north of the low track.
Rainfall along the trailing front will diminish except for some
activity persisting over the southern Rockies/High Plains where
the front will stall for a day or so. The system emerging from
the West and into the Plains should bring scattered rain/high
elevation snow to northern parts of the West late this week and
then support some areas of locally moderate to heavy rain over the
central U.S. by this weekend. The forecast becomes more uncertain
by Sun-Mon given poor agreement regarding upper level flow details
that will determine frontal timing/waviness and how much moisture
may flow northward from the Gulf of Mexico. At the very least
there is the potential for some areas to see significant rainfall
but at this time confidence is very low for specifics. Locations
along the eastern half of the Gulf Coast may also see periods of
enhanced rainfall with moisture around the periphery of Gulf of
Mexico low pressure and near a potential upper level weakness/low.
Record warmth over the eastern and southeastern U.S. should
largely come to an end on Friday behind a cold front. Meanwhile,
expect unseasonably cool readings over the Northwest (10-20F below
normal) to persist late this week and then trend closer to normal
over the Pacific Northwest followed by the northern Rockies.
Kong/Rausch
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