Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
158 AM EST Sat Nov 23 2019
Valid 12Z Tue Nov 26 2019 - 12Z Sat Nov 30 2019
...Guidance/Predictability Assessment...
Models seem to be coming into much better agreement regarding the
evolution of a shortwave trough exiting the Central Rockies at the
beginning of the Period (Tuesday), and steadily deepening as it
lifts quickly into the Upper Great Lakes and the Northeast by
Wednesday. This should spin up an impressive cyclone at the
surface which tracks across the Central Plains and Midwest Tuesday
into early Wednesday, and exiting New England by late Wednesday.
Model agreement and run-to-run variability on the timing and
intensity of this system has improved within the past 24-hours,
with most deterministic and ensemble means showing a similar track
for this feature. The exception to this is the 12z/Nov 22 UKMET
which has a much weaker upper shortwave/surface low. The preferred
model blend for this system was a general model compromise of
mostly deterministic 12z/Nov 22 ECMWF and 18z/Nov 22 GFS, with
small contributions from the ECENS and GEFS means. This maintains
good continuity with the previous WPC forecast.
After this, the focus shifts out West where models continue to
show very amplified troughing and an upper level low dropping down
the West Coast in the middle to latter part of next week. Models
and ensembles show good agreement on this feature in the day 3-5
time frame, but there remains question on how far south the height
falls dig and how quickly the energy begins shifting inland by
days 6-7 (Fri-Sat). The GFS remains faster and farther south with
the upper low compared to the ECMWF and CMC, with the ensemble
means representing a good middle ground solution. Thus, preferred
a mostly ensemble mean (ECENS/GEFS) blend on days 6-7, but did
keep a small percentage of the ECMWF because it was the
deterministic model which most closely resembled the ensemble
means.
...Weather Highlights/Threats...
Moderate to locally heavy precipitation is likely Tuesday into
Wednesday on the north and west side of the surface low from the
Central Plains to the Upper Midwest. Some accumulating snows may
be possible on the northern edge of the precipitation shield. As
the storm lifts into the Northeast on Wednesday, wintry
precipitation is possible across northern/interior New England.
Depending on surface low intensity, a period of high winds may
also accompany this system.
Heavy mountain snows are likely from the Washington/Oregon
Cascades and the Sierras on Tuesday, spreading into the Great
Basin and Rockies Wednesday-Friday as the upper trough amplifies
along the coast. Another round of potentially heavy rainfall is
also possible across the Southwest by mid to late next week.
Rainfall is also likely from portions of the Southern Plains to
the Tennessee Valley as multiple shortwave impulses round the base
of the Western U.S. trough.
The biggest temperature anomalies will focus across the Western
U.S. through much of the period with daytime highs averaging 10 to
20 degrees below normal. In response to this trough, ridging
builds across the south-central U.S. which should bring a return
of above normal temps (anomalies +5 to +10 degrees) to this region
by the end of the period. In the East, above normal temperatures
Tuesday and Wednesday should moderate back to normal or slightly
below normal at the end of the week.
Santorelli
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