Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1206 PM EST Fri Nov 29 2019
Valid 12Z Mon Dec 02 2019 - 12Z Fri Dec 06 2019
...Significant winter storm to affect the Northeast into Tuesday...
...Low pressure brings midweek heavy rain to southern California...
...Pattern Overview and Guidance/Predictability Assessment...
A cold core mid/upper low with neutrally tilted trough over the
Southeast over the Mid-Atlantic Monday morning will become
negatively tilted as it slowly tracks northeast along the
Northeastern seaboard through Tuesday. The surface low is expected
to track just off Cape Cod Monday night and across Nova Scotia
Tuesday. Meaningful winter weather effects are expected to the
north/west of the low track. There is excellent agreement among
deterministic guidance with this low to allow a general
deterministic model blend through its exit on Tuesday/Day 4.
The next trough tracks southeast across the Great Lakes Tuesday
night and across the northeast through Wednesday night. Surface
low pressure developing offshore looks to track just east of Maine
Wednesday night which is in decent agreement in the 06Z GFS and
00Z ECWMF.
Meanwhile an upper low in a positively tilted trough lingers off
California through Tuesday. Timing of the ejection east across
southern CA is in better timing agreement with the low/trough axis
crossing on Wednesday. This trough then shifts east across the
southern tier of the CONUS through Friday. Timing differences
increase as this feature moves inland with the 06Z GFS outpacing
the 06Z GEFS which is similar to the 00Z ECMWF/ECENS. An upstream
trough is expected to amplify over the eastern Pacific late in the
week. The 00Z ECMWF/ECENS farther west/more positively tilted than
the 06Z GFS/GEFS which has been common this month for systems
along/off the West Coast. Precipitation may arrive into much of
the West Coast on Day 7 per a 06Z GEFS/00z ECENS blend for that
day.
The model blend preferences were for a general deterministic model
blend weighted toward the 06Z GFS/00Z ECMWF for Days 3/4 with
increasing 06Z GEFS/00Z ECENS weight Day 5-7.
...Weather Highlights/Threats...
The cold core low tracking up the Northeast Monday into Tuesday
will bring a period of significant wintry precipitation in a swath
from the northern Mid-Atlantic, the Hudson Valley, south-central
New England, and eastern Maine. Winds look to be sufficiently
strong to make travel even more difficult/hazardous. The Great
Lakes should expect to see a period of mainly light snow in the
Wednesday timeframe as the trough crosses with preferred lake
effect zones of Erie and Ontario likely having the most notable
threat.
The system moving into the Southwest will bring an episode of
focused precipitation with highest totals most likely over favored
terrain inland from the southern California coast Tuesday night
through Wednesday with a lesser maximum over central Arizona later
Wednesday. High elevation snow likely from the Sierra Nevada
across the ranges of the Great Basin to the central Rockies. This
system would produce an area of mostly rain over and east of the
central-southern Plains into the Southeast Thursday/Friday. Timing
and exact focus of potentially heavy precipitation on the West
Coast is sensitive to lower predictability details with the
trough. Currently the best potential for highest totals remains
over northern California for Day 7.
The eastern states will be chilly to start the week in the wake of
the coast-to-coast storm with much of the Southeast temperatures
10 to 15F below normal Monday. Those anomalies spread to Florida
for Monday night/Tuesday with freezes possible into the northern
Peninsula. Eastern U.S. temperatures will gravitate toward normal
by the latter half of the week. On the other hand expect the
central U.S. to see above normal temperatures for most of the
period with some pockets of plus 10F or greater anomalies for min
and/or max readings from Tue onward. The expected pattern will
support continued moderately below normal highs over the Great
Basin and at times into southern California while most of the West
should see morning lows closer to or above normal.
Jackson
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