Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
146 AM EST Thu Jan 02 2020
Valid 12Z Sun Jan 05 2020 - 12Z Thu Jan 09 2020
...Overview/Guidance Assessment...
Models and ensembles generally show good agreement that the
synoptic pattern across the U.S. will be dominated by a
progressive west-to-east flow. Some uncertainty regarding track
and intensity of embedded shortwaves is the main concern, one of
which could amplify into a significant cyclone for the eastern
half of the country by the middle to later part of next week.
The medium range period begins Sunday with an initial deep cyclone
exiting the Northeast coast. The UKMET and CMC are displaced
farther away from the coast with the low center, with the
ECMWF/GFS and ensemble low clustering closer to the coast.
Preferred a blend of the ECMWF/GFS with this system which also
fits with previous shift continuity.
Meanwhile, another shortwave will be entering the West Coast on
Sunday, and models generally agree that this feature will track
across the Rockies, and emerge into the Plains late Monday. There
remains some question on amplitude which in turn translates to
potential development of a surface low over the Central U.S. on
Monday, deepening as it moves into the Northeast on Wednesday. The
ECMWF has remained consistent in showing a rather amplified
shortwave, though the GFS has trended more amplified with its
previous past couple of runs. The latest CMC is by far the slowest
and strongest with the shortwave and was not a preferred solution.
The GEFS mean is quite a bit slower than its deterministic
counterpart, with the ECENS mean and NAEFS mean more closely in
line with the GFS/ECMWF (just weaker/more washed out). Prefer a
blend of the GFS/ECMWF with contributions from the ECENS/NAEFS
means. Put a bit more weight on the ECMWF over the GFS only
because of its better/more consistent run to run continuity. It is
important to note there is still quite a bit of uncertainty in the
track of the surface low, or even if one will exist at all. At
this point, WPCs forecast does show low pressure tracking from the
Southern Plains on Monday to off the Northeast Coast by Wednesday,
though not nearly as strong as some of the deterministic guidance
would suggest.
Another shortwave enters the West Coast by Day 7, and again there
are questions on both amplitude and timing of this shortwave.
Given the time range at this point, preferred to stick close to
the ensemble means with this feature for now.
...Weather Highlights/Threats...
Some wintry precipitation should be exiting New England with the
departing surface low on Sunday, with favorable
westerly/northwesterly flow providing some lake effect snows
downwind of the Great Lakes. Daily surges of moisture will keep
precipitation likely across the Northwest into the Northern
Rockies during the period, focusing more over coastal locations
and the Coastal Range/Cascades. Depending on the evolution of the
trough/surface low development across the Central U.S. day 4-6,
some snow may be possible north and west of the low across parts
of the Ohio Valley to the Northeast toward the end of the period,
with rainfall farther south. Confidence remains low at this time
regarding the details.
With a fast west-to-east flow across the country, no severe
outbreaks of arctic air is anticipated. This will lead to
temperatures averaging near to slightly above normal with
relatively short periods of colder than normal temperatures behind
departing storms.
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