Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
145 AM EST Thu Nov 28 2019
Valid 12Z Sun Dec 01 2019 - 12Z Thu Dec 05 2019
...Major Winter Storm will track from the Upper Midwest to the
Northeast Sunday and Monday...
...Pattern overview and Guidance/Predictability Assessment...
The medium range period (Sunday-Thursday) begins with a developed
low pressure system over the Upper Midwest/Great lakes region with
an attendant cold front sweeping through the Mid-Atlantic and
Southeast. Additional southern stream energy rounding the base of
the associated cold core upper low should allow for the
development of a new surface low off the Mid-Atlantic coast late
Sunday, which then tracks up the New England coast through
Tuesday. Models and ensembles show fairly good agreement on this
system, though the latest run of the CMC is slightly faster than
the remaining deterministic models with the track of the upper
low. There are some minor differences regarding how quickly the
surface low exits the New England coast as well, which of course
would have implications for precipitation along the coast. The GFS
is a tad slower with its exit than the ECMWF, but the means are
roughly in the middle.
Meanwhile, an upper level low off the Northwest coast should drop
southward off the West coast through about Tuesday before a
weakened state of the system begins to shift inland across the
Southwest Wednesday and Thursday. Days 3-5 the deterministic
models show relatively good agreement with this system, with
timing differences arising by day 6 with how quickly the energy
moves inland. The last few runs of the GFS and the latest run of
the CMC are notably faster than the ECMWF. The means are
understandably quite weak and washed out by day 7 with the
shortwave, though it seems they would favor a slower shortwave
closer to the ECMWF.
For both systems of note, the forecast blend for days 3-5 was
based mostly on the ECMWF and GFS, with small contributions from
the UKMET on day 3 and the ECENS/GEFS means on days 4 and 5.
Beyond that, leaned more on the means mainly due to continued
uncertainty with the upper low/trough in the West. This maintains
good continuity with the previous WPC forecast.
...Weather Highlights/Threats...
The major winter storm to start the period over the Upper Midwest
will continue spreading heavy and potentially significant
accumulating snow across the Upper Great Lakes and the interior
Northeast on Sunday, and into New England on Monday. High winds
may also accompany this storm, making for difficult and hazardous
travel across much of the region. To the south, locally heavy
rainfall is possible along the attendant cold front as it shifts
through the Mid-Atlantic and the Southeast on Sunday. Behind the
cold front temperatures should trend cooler up and down the East
Coast through Tuesday, with a moderation back towards normal by
Wednesday and Thursday.
In the West, another round of heavy precipitation affects
California through Monday with heavy mountain snows expected in
northern and central California, and rain in the lower elevations.
Locally heavy rain and mountain snow may also shift into Southern
California and parts of the Southwest next week as well. A chilly
start on Sunday in the West should warm through the period, with
temperature anomalies Monday-Thursday generally less than 10
degrees below normal.
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