Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1147 AM EDT Sat Nov 02 2019
Valid 12Z Tue Nov 05 2019 - 12Z Sat Nov 09 2019
...Pattern Overview and Guidance/Predictability Assessment...
Overall, the large scale pattern across the CONUS shows slightly
above average predictability during the medium range. A building
ridge from the northeastern Pacific north across Alaska toward the
Arctic will favor a persistent and broad upper trough across the
north central/northeastern U.S.
The primary difference among the guidance emerged by by late on
day 5 (Thu) into days 6-7 (Fri-Sat) 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. A trend was
noted across some of the 00Z guidance toward a more significant
wave of low pressure, as shown by the ECMWF and CMC. The GFS, on
the other hand, moves any potential weak wave of low pressure
eastward and well offshore much more quickly. Given an increasing
number of ensemble members showing something along the lines of
the ECMWF/CMC, felt compelled to adjust the forecast at least
somewhat in that direction, although confidence in this specific
aspect of the forecast is low, as as typical of such systems in
the medium range.
The WPC medium range forecast was initially derived from a
multi-model deterministic blend including the 00Z
ECMWF/CMC/UKMET/06Z GFS during days 3-5 (Tue-Thu). Weighting of
ensemble means (ECENS and NAEFS) was increased by days 6-7
(Fri-Sat), with some continued emphasis on the deterministic
ECMWF/CMC solutions, showing the potential for an area of low
pressure near/off the Northeast U.S. coastline by late next week.
...Weather Highlights/Threats...
Expect mainly dry conditions for much of the West except into
later next week as Pacific moisture feeds into/through 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 modest snows/light rain swaths
over the U.S. northern tier from the Rockies through the Great
Lakes/Northeast where activity will be prolonged by lake effect.
The latest model runs have shown an increasing signal for a
potential overrunning precipitation north of a surface front
across the Southern Plains Tue night-Thu, with the potential for a
couple inches of rainfall. Strong high pressure and cold
temperature well north of the surface front, from the
Mid-Mississippi Valley to the Ohio Valley, could result in the
potential for at least some areas of wintry precipitation,
although confidence in the specifics is low at this time.
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