Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
315 PM EDT Sat Oct 30 2021
Valid 12Z Tue Nov 02 2021 - 12Z Sat Nov 06 2021
...Overview...
An omega block centered over North America will likely maintain
broad troughing across the eastern U.S. while general ridging will
tend to re-establish itself over the western U.S. during the
medium range period. Periodic shortwave energies coming from the
eastern Pacific will attempt to pass under the omega block and
then across the western U.S. towards the central Plains. This is
where much of the model uncertainty lies. A more prominent
shortwave is forecast to track through the central Plains midweek
before reaching the East Coast late next week with some potential
for cyclogenesis to occur off the coast. Another shortwave may
make its way through the western U.S. and move into the southern
Plains by next weekend.
...Guidance/Predictability Assessment...
With the omega block in place over North America, model solutions
appear to split into their own flavors as they try to handle the
relatively amplified pattern with time. The ECMWF solutions tend
to be slower while the GFS faster with bringing the broad upper
trough progressively through the eastern U.S. later next week. In
the mean time, the CMC shows elements seen from both the ECMWF and
the GFS. The slower ECMWF solutions would therefore open up the
possibility for a closed upper low to form over the central U.S.
followed by cyclogenesis off the New England coast by next
weekend. On the other hand, the faster GFS would tend to kick the
energy farther offshore. Meanwhile, recent ECMWF runs have shown
a tendency to speed up this incipient trough progression. Given
this relatively typical biases of these models in the
medium-range, a general model compromise was used to compose the
WPC medium-range forecasts. This consisted of mainly an even
blend of the deterministic and ensemble means from the 00Z
ECMWF/EC mean, the 06Z GFS/GEFS, with smaller percentages from the
00Z CMC/CMC means.
...Weather/Hazards Highlights...
A frontal system with occasional upper-level shortwaves passing
through the West will result in periods of enhanced precipitation
across the area during the second half of the week. One such
shortwave is forecast to make its way into the central to southern
Plains where moderate to heavy rainfall is possible Wednesday into
Thursday. Some precipitation could spread east/northeast during
the latter part of the week, with the higher elevations of the
central Appalachians and the interior Northeast seeing some
possibility for snow, but with low confidence in the specifics.
On the other hand, the slower ECMWF solution continues to indicate
the possibility of cyclogenesis near the East Coast by next
weekend.
Meanwhile, unsettled weather is expected to continue along the
West Coast. Northern California and far southwestern Oregon
should see the heaviest precipitation with normal terrain
enhancements and higher elevation snow. Some of these activities
are expected to spread into the Pacific Northwest with lesser
totals eastward into the Intermountain West and Rockies. Some
snow/rain can be expected in the central High Plains Tuesday night
into Wednesday morning as the upper shortwave heads further toward
the northeast.
Behind the aforementioned front, a cold high pressure system will
maintain well below normal temperatures across the central and
eastern U.S. This will especially be the case for highs which
should be 10-20F below average from the central and eventually
southern parts of the Plains and spreading across the Mississippi
Valley and eastern U.S. Chilly lows in the 20s may reach as far
south as Kansas and Iowa, which would only be minus 5-10F
anomalies but would still bring the first freeze around next
Tuesday or so. Expect above normal low temperatures under the
western ridge aloft, but periods of unsettled weather will keep
highs somewhat below normal over California on most days and near
normal elsewhere.
Kong
Additional 3-7 Day Hazard information can be found on the WPC
medium range hazards outlook 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