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Extended Forecast Discussion
(Caution: Version displayed is not the latest version. - Issued 0615Z Oct 12, 2018)
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Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
215 AM EDT Fri Oct 12 2018

Valid 12Z Mon Oct 15 2018 - 12Z Fri Oct 19 2018

...Impressive record cold for the central/southern Plains early
next week...

...Pattern Overview...

An upper low near Baffin Island/Davis Strait will slowly translate
southeastward as upper ridging in the Northeast Pacific breaks
down. This will allow troughing initially over the Great Lakes to
split between a northern and southern portion with the former
exiting much quicker than the latter. Across Florida, subtropical
ridging will hold in place, preventing a cold front from slipping
southward to Lake Okeechobee.

...Guidance/Predictability Assessment...

Multi-model/ensemble blend sufficed for a starting point for much
of the period over much of the CONUS, except for a couple areas.
Firstly, exiting compact upper low through the Great Lakes has
been trending slower though the GFS runs remained quicker
(parallel FV3-GFS was a little slower than the operational run).
Relied on the ECMWF/Canadian/UKMET there. Secondly, the embedded
vorticity rounding the base of the trough through the Lakes on
Wednesday has mostly trended slower as well and the 18Z GFS
regained its clustering with the others except for the UKMET which
appeared much too aggressive the break down the upper ridge off
the west coast. By the end of next week, blend of the
deterministic and ensemble guidance smoothed out some uncertain
features in the northern stream around the upper low in
northeastern Canada but maintained the upper low in the Southwest
that should slowly lift northeastward through the week.

...Weather Highlights/Threats...

Well below average temperatures (likely breaking record low minima
and maxima over many stations and states) will sink southward
behind a strong cold front late this weekend into next Monday.
Highs in the 40s are forecast for most of the central Plains into
Texas even to the Big Bend which will be about 25-35 degrees below
average. Some locations may break their record low daytime high
temperature by 5-10 degrees even where records go back over 100
years. The cold will start to relent after Monday as it settles to
the Gulf Coast and Lower Mississippi River Valley. The cold front
will have less bite farther east from the Great Lakes to the
Northeast/Mid-Atlantic where temperatures will only be a few
degrees below average. To the south, Florida will maintain above
average temperatures thanks to upper ridging.

Precipitation may be locally heavy across Texas northeastward as
the upper low behind future ex-Sergio meanders eastward through
the Four Corners region and moisture from the western Gulf flows
northward atop the front. The rain axis will extend to the
Mid-Atlantic but in lessened amounts. The rest of the lower 48
behind the front will be largely dry with some showers around the
Lakes (some snow, some rain). Widespread snow (some lower
elevation rain) will exit the Southern Rockies on Monday with some
snow accumulation thereafter as the upper low swings through.


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