Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1234 AM EST Tue Dec 10 2019
Valid 12Z Fri Dec 13 2019 - 12Z Tue Dec 17 2019
...Eastern Seaboard heavy rain threat Friday/Saturday and lead
wintry precipitation risk for the interior
Mid-Atlantic/Appalachians & Northeast...
...Wet Pacific Northwest to snowy N-Central Great Basin/Rockies
flow into the weekend leads to Deep South low/rainfall development
early next week...
...Pattern Overview and Guidance/Predictability Assessment...
A cold upper vortex will reform and persist over Hudson Bay this
period. Over the lower 48, an active and complex pattern remains
as several streams laden with a series of impulses interact. Model
and ensemble solutions have become better clustered, but forecast
confidence remains somewhat tempered by recent run to run
continuity issues and flow complexity. Opted for a composite
GFS/ECMWF and GEFS/ECMWF ensemble mean solution blended with the
National Blend of Models as a basis for the WPC medium range
product suite.
...Weather Highlights/Threats...
Southern stream shortwave progression and subsequent northern
stream flow interaction should support low development and track
from the Gulf of Mexico/Gulf Coast to the Southeast then up the
East Coast Friday/Saturday. This will bring heavy rain up the East
Coast mainly from the Southeast to the Appalachians, Mid-Atlantic
then Northeast. System interaction with lower atmospheric cold air
damming offers an interior snow/ice threat to monitor. The degree
of phasing between two initially separate streams and baroclinic
zone/coastal details will be determining factors of eventual
evolution and potential coastal system threat.
The pattern will also become wet upstream over the Pacific
Northwest into late week as Pacific shortwave energies punch
onshore. Moderate to heavy snows will develop as the system
penetrates inland, especially over favored north-central Great
Basin/Rockies terrain through the weekend. By next Monday into
Tuesday, the exiting wave will eject and then interact with Gulf
moisture to spawn a rainfall focusing low pressure/frontal system
forecast to move over the Deep South, then potentially again up
the East Coast.
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