Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
253 AM EDT Sat Oct 23 2021
Valid 12Z Tue Oct 26 2021 - 12Z Sat Oct 30 2021
...A stormy pattern continues across the nation next week...
...Overview...
The weather pattern during the medium range period should remain
quite active and amplified as a couple of systems impact the CONUS
next week. An upper low initially over the lower Great Lakes on
Tuesday will induce a deepening cyclone with heavy rainfall over
the Northeast U.S. which should lift north and east into the
Canadian maritimes by Thursday. Meanwhile upstream, the next
trough will be ejecting out of the Rockies Tuesday-Wednesday with
another possible closed upper low/deep surface cyclone likely to
form and track from the north-central Plains into the Ohio Valley
and eventually the Northeast by late week/early next weekend.
Organized rainfall will accompany the cold front as it traverses
the eastern half of the nation with rounds of heavy rainfall
possible. A couple of shortwaves may also move into the Pacific
Northwest during the period bringing more heavy rain/mountain
snows to parts of the Northwest.
...Guidance Evaluation/Preferences...
For the most part, the guidance continues to show good agreement
on the overall longwave pattern evolution, but significant
uncertainties in the details regarding strength and track of
individual systems. For the intial Northeast closed low on
Tuesday-Wednesday, there remains some subtle differences in
placement but a general model blend should give a good starting
point. The biggest uncertainties surround the amplified trough
exiting the Rockies into the Plains at the beginning of the
period. By late Wednesday/early Thursday, much of the guidance has
been trending towards closed upper low development, but rather
significant differences in placement and track of the low. The
notable outlier at least right now seems to be the 12z (yesterday)
ECMWF as well as the new 00z run both of which are displaced well
south of the better consensus with the low moving through the
Southern Plains/Tennessee Valley into the Mid-Atlantic. The latest
runs of the GFS and CMC suggest the low center farther north (into
the Midwest/Ohio Valley and Northeast) which is also consistent
with the latest ensemble means as well. The WPC blend leaned more
towards the GFS/CMC along with the ensemble means, which also
maintained fairly good continuity with the previous WPC forecast
as well. Out West, some late period timing differences arise with
another trough moving towards the Pacific Northwest later next
week, so a blend of the ensemble means was preferred.
...Weather/Hazards Highlights...
The leading closed low into the Northeast on Tuesday will allow
for heavy rainfall potential to continue from the end of the short
range period into much of New England early next week. Deepening
coastal low development may induce pockets of enhanced rainfall on
the backside of the low as it lifts northward towards the Canadian
Maritimes but there remains some uncertainty in exact low
placement which will impact where the heaviest rains fall.
The cold front reaching the Plains by Tuesday and onward into the
east-central U.S. Wednesday/Thursday is expected to present an
emerging and expanding lead rainfall/convective focus as ample
Gulf of Mexico moisture streams northward ahead of the system. The
latest guidance suggests the best potential for heavy rainfall
will be across portions of the Gulf Coast states and inland on
Wednesday and then into the Mid-Atlantic/Northeast Thursday-Friday
with closed upper low development and a slowed frontal system
progression. The Storm Prediction Center also is highlighting the
potential for severe weather across parts of the central/southern
Plains on Tuesday, and the central Gulf Coast on Wednesday.
Meanwhile, out west, a sustained moisture plume from the short
range period will continue into the Northwest U.S. on Tuesday
bringing a continued threat for heavy rainfall and mountain snows
to especially the Pacific Northwest/northern California but also
farther inland across the northern Rockies. Another system moving
towards the coast mid next week will continue the active weather
with another round of heavy rainfall and mountain snow impacting
parts of the Pacific Northwest Wednesday into Friday.
In terms of temperature highlights, the southern/central Plains
should be above normal to start, but quickly trend back towards
normal following the passage of the cold front. Daytime highs
could be 10 to 15 degrees above normal on Tuesday for parts of
Texas, Oklahoma, and western Kansas. Successive closed
lows/troughs into the east-central U.S. will keep temperatures
near or below normal through the entire week. Out West,
temperatures may initially begin cold (minus 10 to 15F anomalies),
but should trend warmer and back to normal values as some weak
upper ridging moves through. The Central U.S. may again warm to
slightly above normal by late week as the ridging reaches the
Plains.
Santorelli
Additional 3-7 Day Hazard information can be found on the WPC
medium range hazards outlook 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