Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
130 AM EST Sun Nov 03 2019
Valid 12Z Wed Nov 06 2019 - 12Z Sun Nov 10 2019
...Pattern Overview and Guidance/Predictability Assessment...
The large scale pattern across the CONUS shows above average
predictability during the medium range. A building ridge from the
northeastern Pacific north to Alaska and British Columbia will
favor a mean upper trough downstream over the east-central U.S.
The main difference among the guidance becomes evident Thu into
next weekend with respect to a potential wave of low pressure
along the surface front across the Ohio Valley/Appalachians to off
the Northeast U.S. coast. Guidance has trended over the past 24
hours toward a more significant wave of low pressure, as shown by
the ECMWF/CMC. The GFS/UMKET, on the other hand, moves any
potential weak wave of low pressure eastward and well offshore
much more quickly. There is an increasing number of ECMWF/Canadian
and even GEFS ensemble members supporting a solution more in line
with the ECMWF/CMC. This solution keeps better WPC continuity and
seems more plausible considering favorable upstream ridge
amplitude and baroclinic/dynamic environment to feed upon for
development. However, confidence in this aspect of the forecast is
not high considering the short wavelength spacing between the
progressive impulses embedded with the larger scale flow that dig
and carve out the e-central U.S. upper trough from a distant
source region over northeast Asia and the Arctic/Alaska.
Overall, the WPC medium range forecast was primarily derived from
a blend of the 12 UTC ECMWF/Canadian/ECMWF ensemble mean and the
18 UTC GEFS ensemble mean.
...Weather Highlights/Threats...
Expect mainly dry conditions for much of the West except until
late week as Pacific moisture breaks inland into Pacific Northwest
terrain. The downstream pattern will favor the spread and periodic
reinforcement with colder than normal airmasses from the Rockies
and Central U.S. to the East as post-frontal high pressure cells
spill down from Canada. High temperatures are forecast to be as
much as 10-20 deg F below average across much of the central and
eastern U.S. next week as the strong Canadian high pressure moves
southward into the U.S. Moisture will be mainly limited across the
mid-higher latitudes, but the passage of several clipper lows
should support mainly snows swaths over the cooled U.S. northern
tier from the Rockies through the Great Lakes/Northeast where
activity will be prolonged by lake effect. Recent guidance trends
show an increasing signal for overrunning precipitation north of a
surface front across the Southern Plains Wed into Thu, with the
potential for a couple inches of rainfall. Strong high pressure
and cold temperature well north of the surface front, from the
central Plains and Mid-Mississippi Valley to the Ohio Valley and
Northeast, could result in a risk of wintry precipitation whose
threat would be enhanced with aforementioned organized frontal
then coastal low development.
Schichtel/Ryan
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