Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1039 AM EST Sun Nov 10 2019
Valid 12Z Wed Nov 13 2019 - 12Z Sun Nov 17 2019
...Record cold to slowly ease later this week...
...Pattern Overview and Guidance/Predictability Assessment...
Upper ridging meandering over California, becomes interrupted by
troughing late Wednesday/early Thursday and then again on Friday,
with broad troughing east of the Rockies. Over Mexico, a closed
low will eventually rejoin the southern edge of the westerlies
Thursday and track across the northern Gulf of Mexico and into the
Southeast/Florida.
Overall, the models/ensembles showed fairly good agreement, with
varying degrees of speed/track/evolution/interaction differences.
The 00Z ECMWF/CMC/06Z GFS offered reasonable clustering near their
ensemble means and previous shift continuity to form the base of
the initial forecast for Wed-Thur. After this time, included
increasing amounts of ensemble means (mainly ECENS/NAEFS) due to
differences in western U.S. height falls starting Friday. The
GFS/CMC remain faster both with shortwave energy entering WA/OR on
Friday and with larger scale troughing/possible closed upper low
around Baja California later in the period. Completely ignored the
CMC after day 5 as it forms a rather amplified/deep upper low over
the Southwest U.S., well north and east of even the GFS (which is
faster than the ECMWF) and the ensemble means, which all keep
energy over Baja or farther west. Along the Gulf coast, the models
continue to struggle somewhat with the evolution of an opening
upper low and possible surface wave development off the Southeast
coast. The GFS is considerably faster/weaker than the ECMWF/means
with this feature, though the slower ECMWF may be too amplified.
At this point, prefer a blend of the ECENS mean with the NAEFS
mean, which brings a solution somewhere in between the operational
GFS/ECMWF.
...Weather Highlights/Threats...
Well below average temperatures that will likely break daily
records across a sizable area of the eastern half of the CONUS on
Wednesday will ease by the end of the week. However, highs will
remain about 10-15 degrees below average along and east of the
Mississippi into Friday and 5-10 degrees below average next
weekend. A sneaky reinforcing shot of cold Canadian air may skirt
through the Northeast Fri/Sat as another surface high moves in.
West of the Rockies (but including parts of the Front Range and
central Plains), temperatures will stay above average by about
5-10 degrees.
Once the southern upper low reaches the Gulf, its interaction with
a frontal boundary could spread rain along the I-10 corridor and
across the Florida peninsula early in the period. The surface low
off the Southeast coast should keep the heaviest rains offshore,
though depending on coastal proximity, heavy rains may clip the
coastline. Next system into the Pacific Northwest will provide
focused rain/snow to coastal/mountain OR/WA Friday-Saturday then
east of the Divide Saturday-Sunday. By then, moisture will be much
more limited and precipitation amounts much lighter. Yet another
system may approach Washington late next Sunday.
Santorelli/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