Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1100 AM EST Tue Jan 29 2019

Valid 12Z Fri Feb 01 2019 - 12Z Tue Feb 05 2019

...Overview...

The departure of a deep upper level vortex over Quebec at the
beginning of the forecast period Thursday and gradual weakening of
mean troughing aloft over the eastern U.S. late this week and the
weekend will promote a significant warming trend over the eastern
U.S.  At the same time the short-range West Coast mean ridge aloft
will give way to a series of Pacific systems that will bring a
return of significant precipitation to parts of the West with
moisture that will then spread farther eastward.  By the latter
half of the period, the synoptic scale pattern should evolve
toward a positively tilted mean trough over the West and positive
height anomalies with some degree of ridging over the East.


...Guidance Evaluation/Preferences...

Models and ensembles are in relatively good agreement Friday so
prefer a composite solution. The ECMWF and ECMWF ensemble mean
become faster than most other guidance to dig another arctic shot
southward through the n-central U.S. this weekend into early next
week. While not quite as cold as the short range event, suspect a
solution closer to the ECMWF/ECMWF ensemble mean would be more
likely given pattern history and supporting surface high strength.
Meanwhile, run to run model variance also continues to increase
with systems working underneath across the U.S. southern tier and
with Pacific systems moving into/across the West then downstream.
This suggests transition to an ensemble mean based forecast
process and ECMWF ensembles seem to have the best handle on the
medium range strength of these systems considering they seem
pretty energetic at shorter ranges. WPC accordingly leaned
forecast weighting strongly in favor of the 00 UTC ECMWF ensemble
mean and applied less weight to the 06 UTC GEFS mean for this
period.


...Weather Highlights/Hazards...

Pacific system passage will produce a swath of rain and mountain
snows across CA Friday that further moderates across the Southwest
and southern Great Basin/Rockies. Stronger system approach and
passage over the weekend will spread more robust
winds/precipitation across CA with additional effect over the
Northwest and inland. During the latter half of the period,
ejecting mid-upper level trough energy should spawn surface
cyclogenesis over the central U.S. whose increased moisture focus
into an arctic front offers a significant threat of overrunning
ice/snow to the north, with warm sector rains/convection to the
south. The focus for heaviest coverage will spread eastward
through early next week with system progression.

Hamrick/Schichtel


WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation and winter weather outlook
probabilities are found 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