Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
158 AM EST Wed Jan 01 2020
Valid 12Z Sat Jan 04 2020 - 12Z Wed Jan 08 2020
...Overview/Guidance Assessment...
The pattern across the CONUS during the medium range period
(Sat-Wed) looks to be progressive with an active stream of
shortwave troughs traversing the country. An amplified upper
trough initially in place across the Ohio/Tennessee Valleys on
Saturday will move off the East Coast by Sunday, resulting in a
deepening low pressure system across the Great Lakes and
Northeast. Minor timing differences with this trough (or closed
low), with the GFS/CMC a hair faster than the ECMWF/UKMET days 3
and 4 and the ensemble means in the middle.
To the West, a series of systems moving onshore and tracking
eastward through time continues to show increasing spread in the
guidance, especially toward the end of the forecast period. The
first shortwave enters the West coast day 4, with another
following quickly on day 5. It's with this second one where models
continue to struggle with evolution as it ejects eastward out of
the Rockies and into the Central U.S. day 5 and beyond. The ECMWF
has been quite consistent in showing a much more amplified trough
especially days 6 and 7, which would bring a rapidly deepening
surface low from the south-central Plains on Day 5, into the
Northeast on day 7. The CMC shows a similar evolution, with the
GFS quite a bit flatter/weaker. There is not a ton of ensemble
support yet for that strong of a low as depicted by the ECMWF, but
given the good run-to-run consistency from the ECMWF, and the
pattern set-up, it is not completely unreasonable. Prefer a blend
of the ensemble means at this point, with small contributions from
the ECMWF for some added definition from the means. A third
shortwave moves into the West on day 7, but there is high spread
with timing and strength of this low, that the ensemble means were
heavily favored.
...Weather Highlights/Threats...
Surface low moving through the Northeast on day 3, will bring
precipitation from the Lower Great Lakes into New England,
possibly in the form of snow. Nearly daily bouts of precipitation
are likely for the Northwest into the Northern Rockies during the
period, focusing more over coastal locations and the Coastal
Range/Cascades. Depening on evolution of the trough/surface low
development across the Central U.S. day 5-7, some snow may be
possible north and west of the low across parts of the Ohio Valley
to the Northeast end of the period. ECMWF and CMC show a much
better chance for this, though confidence is low at this time.
Above normal temperatures across the Northeast on Saturday should
moderate to near normal following passage of the cold front. Above
normal temps shift across the Great Plains towards the Midwest
days 3-5, with much of the country near normal by days 6 and 7.
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