Area Forecast Discussion
Issued by NWS Paducah, KY

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FXUS63 KPAH 210237

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

Issued at 937 PM CDT Fri Oct 20 2017

Rather thick cirrus has overspread the region, but it may thin
some later tonight. Guidance shows the pressure gradient weakening
a bit through 06Z and then tightening up a bit 09Z-12Z. With
competing effects of thicker clouds and a weaker pressure
gradient, lows were not changed significantly. However, did alter
the hourly trends to show the lows in the 06Z-09Z period with
steady or slightly warmer readings by 12Z.

UPDATE Issued at 652 PM CDT Fri Oct 20 2017

Updated aviation discussion for 00Z TAFs.


.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 652 PM CDT Fri Oct 20 2017

VFR conditions will persist across the region through the 24 hour
TAF period as ridging is gradually replaced by southwesterly flow
aloft. Winds and moisture will be on the increase as southerly flow
strengthens in response to a cold front approaching from the Plains.
This will result in an increase in high clouds tonight and some mid
clouds on Saturday. In addition, light winds tonight will pick up
from the south around 10 knots with some gusts to 15 to 20 knots by
Saturday afternoon. The combination of cloudiness and low level
winds should by and large preclude fog formation overnight.




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