Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
256 AM EDT Wed Oct 23 2019
Valid 12Z Sat Oct 26 2019 - 12Z Wed Oct 30 2019
...Overview and Guidance/Uncertainty Assessment...
It remains the case that an amplified upper flow pattern will
continue into next week, but forecast spread is more than normal.
The majority of the ensemble/deterministic guidance continue to
forecast a splitting of the flow just east of the Rockies which
will likely result in a slowly moving closed low over New
Mexico/Texas late this week that gets picked back up into the flow
ahead of another incoming and amplifying trough through the
Northwest/West. The GFS and to a lesser extent the GEFS have been
the quickest show the least flow separation for days. The
ECMWF/Canadian/UKMET and ECMWF ensembles remain the least
progressive and show the most southern stream separation. Upstream
flow amplitude, wavelength spacing, guidance trends and WPC
continuity favor a solution most in line with this latter group of
guidance. The WPC medium range product suite was primarily derived
from a blend of the ECMWF/ECMWF ensemble mean into this weekend.
By next Sun-Wed, amplification downstream of a strong Alaskan
storm should favor another trough digging just east of southward
through the Pac NW and Great Basin. This seems to again
favoredECMWF ensembles given the lead-in pattern and its typically
better handling of amplified flow over the GEFS at longer time
frames.
...Weather Highlights/Threats...
A favored slower evolution over the Southern Plains/Lower MS
Valley allows for a longer and continued lead fetch of
deep/tropical moisture out of the Gulf. Several inches of rain are
possible from the Gulf Coast states to the OH Valley with the main
supporting/ejecting system trending more northeastward than
earlier guidance. This occurs a weak wave of low pressure slows
the front through the mid-South. The boundary should slowly push
northeastward through the Ohio Valley this weekend and weaken as
it encounters ridging to its east and as a stronger front to its
west largely absorbs/overtakes it. In the West, incoming cold
front late this week into the weekend will be mostly cut off from
the moisture supply but will still manage to spread moderate
precipitation including mountain snows, especially over the
n-central Rockies as enhanced by upslope fetch. Rain/snow
potential may also spread northeastward next week across the
n-central U.S. with slow system progression and emergence into the
Plains.
Temperatures will trend much colder than average in the West
behind the lead cold front this weekend, with max temperatures
10-25 deg F below average Sunday into next Tuesday along/east of
the Divide from western Montana to eastern Colorado as the front
whooshes southward. Above average temperatures will be confined to
the Southeast to the south and east of the front. Florida will
continue to see high temperatures well into the 80s with some
record highs possible this weekend.
Fracasso/Schichtel
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