Area Forecast Discussion
Issued by NWS Paducah, KY

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FXUS63 KPAH 162106

Area Forecast Discussion
National Weather Service Paducah KY
306 PM CST Mon Jan 16 2017

.SHORT TERM...(Tonight through Wednesday night)
Issued at 205 PM CST Mon Jan 16 2017

A cold front and associated H50 short wave will approach from the
west tonight, as surface low tracks northeastward through through
the Plains and into the Midwest. The slightly negative tilt to the
mid lvl short wave will lead to an area of enhanced upward motion,
especially as we heading into the night time hours. Still believe
the greatest upward motions will occur in the best H50 diffluence
region over wrn KY, and that is where the highest rain amounts
will be placed...on the oder of 1/2 to 3/4 inch.

Turning to the thunderstorm potential with this system, the
strong/severe threat remains low given overall lack of
instability. Mixed layer MU CAPES are still expected to remain the 100-300 J/KG range, with Showalter Index values
in the 0 to -2 range. More likely to be just a few isolated
storms here and there with some locally heavy downpours. Things
could change a bit if more than anticipated instability levels
were to work northeast into the region from AR. Currently, 60+
surface dew points are located just southwest of the forecast
area in northeast AR.

High pressure moving in behind this system will be of Pacific
origin, so should stay with above normal temps as we head into
Tue/Wed time frame. Will be a bit of a cool down from today, but
nothing drastic. Will at least get a nice break in the wet pattern
once precip ends later tonight/early Tuesday.

.LONG TERM...(Thursday through Monday)
Issued at 205 PM CST Mon Jan 16 2017

From a hemispherical perspective, the leading edge of progressive 500
mb zonal flow along the Northern Pacific moves well into the
intermountain region of the Western U.S.  At the same time, the
dominate ridging aloft along eastern Canada/U.S. serves as a
blocking mechanism for the progressive trough stretching from Texas
to the Upper Midwest/Northern Plains as of 6 am CST (12z) Thursday.

With the previous information in mind, this forces the closed low
and shortwave trough on the eastern side of the mean Central U.S.
trough to become negatively tilted and strong flow undercuts the
mean trough across the southwest quarter of the U.S.

With this more dynamic upper flow, stretched a plume of instability
in the form of a differential mention of thunderstorms over parts of
Southern Illinois and West Kentucky mainly during the afternoon and
evening hours on Thursday.

After that time, low amplitude ridging develops across the area
Friday and early Saturday, limiting any chances of precipitation.
Although Gulf of Mexico flow is open for moisture influx, the ECMWF
generates noticeable convection along the Gulf Coast, disrupting
the rich flow of moisture to the WFO PAH forecast area.

The more potent energy forecast by the 00z/12z ECMWF translates a
open wave over Nevada to an intensify low to middle level closed low
over the TX/OK panhandles around midnight Saturday night. This will
push the low in and near the WFO PAH forecast ares Sunday afternoon,
leading to a decent chance of convective activity on Sunday.

Although the Thursday and Sunday weather systems will initially have
some weak shear and instability from 0-3km, the Sunday system may
intensify somewhat, so will be worth watching in later forecasts.

With respect to temperatures, modified temperatures slightly from
the regionally blended numerical guidance initialization, adding a
30% influence of the deterministic ECMWF, NAM-WRF, SREF, European
and EKD MOS. This only modified the maximum/minimum temperatures by
1-2 degrees at most. No other significant changes made.

Forecast confidence has increased with preference toward the ECMWF
solution the past two days for the extended period.


Issued 1230 PM CST Mon Jan 16 2017

Cold front approaching from the west will move through the region
later tonight. Expecting generally IFR cigs AOB 1 kft for much of
the TAF period, tho many areas east of the MS River may break out
in VFR cigs this afternoon before more showers/isolated
thunderstorms arrive in advance of the front. Precipitation
should come to an end at all sites by 12Z Tue but higher IFR or
possibly lower MVFR conditions will probably linger through the
end of the period. Easterly winds AOB 10 knots will gradually veer
around to the southwest with the passage of the front 03Z-09Z




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