Area Forecast Discussion
Issued by NWS Paducah, KY

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FXUS63 KPAH 202029

Area Forecast Discussion
National Weather Service Paducah KY
329 PM CDT Fri Oct 20 2017

.SHORT TERM...(Tonight through Sunday night)
Issued at 325 PM CDT Fri Oct 20 2017

Through tonight, a mid level ridge will gradually give way to
southwesterly flow. This will result in high cloudiness
continuing to increase. Southerly low level flow should keep lows
tonight in the lower to middle 50s. Sat will be another warm day,
with very similar temps, but with thicker cloud cover. Subtle
shortwave energy in the flow aloft might result in some sprinkles
over mainly the western half of the PAH forecast area by Sat
afternoon. A few warm advection showers are possible, but we are
going to give it maybe a 10 percent chance of anyone receiving
measurable pcpn.

The weather picture changes rapidly Sat night, especially late,
with the approach of a surface cold front. Showers and scattered tstms
should be common west of the MS River by sunrise, spreading
eastward during the day with the cold front, and reaching even
the easternmost parts of the region by sunset Sun. Simultaneously,
the models suggest a mid level low will begin to develop over AR,
inducing a surface low or trof across our eastern sections by Sun
night. This will tend to distort the surface wind fields and slow
the exit of the pcpn, which should be only showers by then,
especially common in the Pennyrile region of KY.

At this time, it appears the best wind shear will remain to our
west on Sun, and lapse rates do not appear robust enough for
severe convection. We will call it a non-zero chance, but
certainly not probable. 1-2 inches of rain totals are forecast
overall through early next week, possibly somewhat higher, with
the highest amounts in the southern half of the region.

.LONG TERM...(Monday through Friday)
Issued at 325 PM CDT Fri Oct 20 2017

A highly amplified upper level flow pattern will translate into
active weather across our region next week. The models are in
agreement on an impressive deep longwave trough over the eastern and
central states. However, there are large differences in the location
and timing of individual systems within the flow pattern, starting
as early as Monday. The gfs is more progressive with the systems,
while the ecmwf indicates a more blocky pattern.

On Monday, a compact 500 mb low is forecast to pass near or south of
the Lower Ohio Valley. The timing of the ending of the steady rain
hinges on the speed of the low, which varies among the models. The
forecast will hedge toward the faster gfs, but even that solution
means categorical (80 percent plus) pops for much of west Kentucky.
The extensive clouds and rain will hold temps in the 60s all day.

On Tuesday and Wednesday, a northern stream 500 mb shortwave will
phase with the aforementioned closed low. This will result in a
large and strong 500 mb cyclone centered over the Great Lakes
region. A deep northwest flow will bring the coldest 850 mb temps so
far this season. Most of the guidance brings the 850 mb freezing
line near or over our area. Given these cold temps aloft, the model
mos guidance looks suspiciously warm for daytime high temps. The
forecast initialized from the blend of guidance gives highs around
60 both Tuesday and Wed. A look at the 12z gfs ensemble mean 2 meter
temps indicates temps would struggle to get to the mid 50s. Will
shave a degree or two off the forecast blend. A lot will depend on
whether there is any clearing, which appears doubtful in many areas
Tuesday. In fact, a chance of showers is forecast in southwest
Indiana and the Pennyrile. There will be more sun Wednesday, and
possibly warmer southwest winds if the faster gfs is correct.
Overnight lows should be help up by wind and/or clouds. However, any
areas that clear out could have some frost.

For Thursday, the models agree our region will be between systems.
This will allow for a brief return flow of warmer air ahead of the
next cold front. The models vary in the arrival time of the next
front, but it appears rain chances will increase Friday as the front
approaches with strong upper level support.


Issued at 1233 PM CDT Fri Oct 20 2017

VFR conditions will continue through the 24 hr TAF period as ridging
aloft is gradually replaced by southwesterly flow aloft. Surface
winds will be southeasterly, generally 10 knots or less during
daylight hours today, subsiding somewhat tonight, then are forecast
to pick up out of the south on Sat, increasing to 10 knots or more
sustained by midday. High clouds will be on the increase from the
west through the period. The combination of cloudiness and low level
winds should preclude fog formation.




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