Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1045 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. Differences hinge largely in the timing
of a shortwave crossing the Upper Midwest/Great Lakes/Northeast
Thu-Fri. Models were broken into two significant camps surrounding
this feature, with the 00Z ECMWF/CMC slower and a bit deeper with
the shortwave, and the 00Z UKMET and 00Z/06Z GFS quite a bit
faster. The slower solutions develop a more significant wave off
the Eastern Seaboard whereas the faster solutions move the front
out to sea quickly. Another notable differences in the GFS was
that the trailing end of the front interacts with a stronger
southern stream impulse, causing a wave of low pressure to develop
across the Southeast Thu night-Fri night. At this time based on an
assessment of ensembles as well as run-to-run consistency, opted
to go more toward the ECMWF/CMC solutions. This idea 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.
By the end of the forecast period late in the week, a relatively
strong North Pacific flow regime should persist, with forecast
confidence in the timing of specific shortwaves reaching the CONUS
relatively low despite somewhat above average consensus on the
large scale pattern.
The WPC forecast was initially based heavily on the 00Z ECMWF/CMC
solutions during days 3-5 (Tue-Thu). After that time, a blend of
the ECMWF along with majority ECENS/NAEFS ensemble means was used.
...Weather Highlights/Threats...
Expect mainly dry conditions for much of the West except until
late week as Pacific moisture spreads 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 potential 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