Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
124 AM EST Sun Dec 15 2019
Valid 12Z Wed Dec 18 2019 - 12Z Sun Dec 22 2019
...Overview and Guidance/Predictability Assessment...
Stormy period for the Pacific Northwest into Northern California
with successive systems moving inland. The East will be quieter
for the end of the week but a weak system in the central Plains
may become more developed off the Southeast coast next weekend.
The models and ensembles have waffled in their agreement with the
incoming western system on Wednesday and how it travels across the
CONUS. Though the east-west timing (speed) has come into better
agreement, the north-south track lags behind. Clue from ensembles
has shown a trend toward enough separation from northern/southern
stream flow that the farther south track seems to still be
preferred. This included the 12Z ECMWF/UKMET (though they were
rather deep) and the 18Z GFS as the Canadian tracked to the north.
This would allow some cyclogenesis over the northeast Gulf and/or
off the Southeast/FL coast in the Atlantic around next Sat.
Thereafter, ensembles show a wide expanse of solutions, so
preferred to take the system eastward but with low confidence.
Back to the West, next trough will likely take a front into
California after several days of focused rainfall (higher
elevation snowfall) via a modest atmospheric river event.
...Weather Highlights/Threats...
Precipitation will be centered on the West, particularly coastal
OR and northern California. Upper trough in the eastern Pacific
will allow a fetch of moisture from near Hawai'i to reach the
OR/CA coast with a north/south oscillation between fronts as the
trough changes shape upstream. Several inches of precipitation are
expected but over a 2-3 day period with a likely break in between.
Daytime temperatures will likely be below average with the
rainfall but otherwise near average elsewhere and near to above
average for overnight lows. East of the Rockies, temperatures may
be more variable with a quick cold shot skirting through the
Northeast on Thursday (10s/20s for highs and -0s/0s/10s for lows).
Fracasso
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