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Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 0537Z Oct 14, 2018)
 
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Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
137 AM EDT Sun Oct 14 2018

Valid 12Z Wed Oct 17 2018 - 12Z Sun Oct 21 2018

...Pattern Overview...

Upper ridging over British Columbia and Florida will favor
progressive troughing through the northern tier east of the
Rockies with a closed low in the Southwest. A couple Canadian
fronts with limited moisture will swing through the Great
Lakes/Northeast later this week into the weekend with a renewed
push of cooler air. Florida will remain warm/hot with scattered
showers/storms and the Pacific Northwest should see above average
temperatures and dry conditions.


...Guidance/Predictability Assessment...

A multi-model deterministic blend (GFS/ECMWF/Canadian) sufficed
for the Wed-Fri period as models showed generally good consensus
with respect to the upper low lingering across the Southwest and
with amplifying shortwave energy crossing the Great Lakes. For
Sat/Sun, one point of contention among the guidance becomes how
much erosion/flattening of the western North American ridge occurs
as shortwave energy exits the northeastern Pacific. The ECMWF and
its ensembles have mostly been more aggressive with flattening the
ridge while the GFS/GEFS have maintained it, though the latest
ECMWF guidance was closer to the GFS/GEFS than previous cycles. In
the east, GFS/Canadian were much stronger with the upper trough
and surface low exiting the Northeast but a blend of the solutions
with more ensemble weighting proved to be a reasonable compromise
for now.


...Weather Highlights/Threats...

Below average temperatures will continue late this week into the
weekend for the Southwest through the southern Plains (especially
Texas) northeastward through the Ohio Valley into the Northeast.
On the warm side of the stationary front, Florida will see
warm/hot temperatures that may tie/break record highs at some
locations but the chance of showers/storms will remain for much of
the state.

Precipitation will be generally light except for the Texas coast
just to the northeast of the lingering front along an inverted
trough. This signal has been steady for several model/ensemble
cycles (roughly Victoria to Brownsville). Upper low in the
Southwest will support rain/snow showers for at least the higher
elevations though its focus keeps shifting with the small changes
in the shape of the upper low per the models. The rest of the
lower 48 will be largely dry with some generally light rain/snow
showers around the Lakes and into the Northeast along/ahead of the
cold front next weekend.


Fracasso



WPC medium range 500 mb heights, surface systems, weather grids,
quantitative precipitation, winter weather outlook probabilities
and heat indexes are found 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