Area Forecast Discussion
Issued by NWS Paducah, KY

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FXUS63 KPAH 171821
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
120 PM CDT WED AUG 17 2016

.UPDATE...
Issued at 120 PM CDT Wed Aug 17 2016

The coverage of pcpn should diminish across the forecast area
overall through sunset. However, showers associated with a mid level
circulation may cause minor flooding through mid afternoon as they
move through western KY.

Updated aviation discussion also.

&&

.SHORT TERM...(Today through Friday night)
Issued at 311 AM CDT Wed Aug 17 2016

Other than minor grid spacing and known model scale resolution
issues, the medium range ECMWF/GFS/Canadian model guidance, as
well as higher resolution NAM-WRF family and RAP guidance are
initializing better with the 00z cycle in the depiction of the
near term convective activity.

Although most of the guidance weakens the Texas cyclonic
circulation detached from the broad low amplitude northern U.S.
flow, the remnant circulation will still interact with the narrow
baroclinic/shear zone around the northern edge of the westward
expanding (west-east oriented) Southeast U.S. ridge. Although the
ridge has been forecast to develop westward, model guidance has
been somewhat inconsistent with the timing and placement of the
ridge during the middle and latter part of the week. This has
created some uncertainty as to the northern extent of rain chances
across the WFO PAH forecast area. It finally appears that the
guidance is moving the shear zone further south into Tennessee.
With little low level (0-1km/0-3km) and deep layer (0-6km) shear
to work with over the WFO PAH forecast area through Thursday
night, rain chances should be significantly lower, except along
the KY/TN border. During the same time period, middle and upper
level ridging develops along the northern stream of the split flow
across the nation, capping any thunderstorm potential further
north after today.

By Friday and Friday night, a shortwave deepening into the Dakotas
lifts heights downstream across the Mississippi River Valley,
shifting the shear zone back into play across the WFO PAH forecast
area, introducing more shear and instability over the area. This
will also increase rain chances from the southwest during the day
on Friday.

Temperatures should gradually rebound into the 80s....still below
normal for this time of year.

.LONG TERM...(Saturday through Tuesday)
Issued at 311 AM CDT Wed Aug 17 2016

Forecast confidence is increasing in a wet start to the weekend, and
then a cold frontal passage that will result in a drying and cooling
trend beginning on Sunday.

A rather large upper-level trough will take shape over the upper
Mississippi Valley Saturday and then shift eastward into the Great
Lakes Sunday. This should be sufficient to push a cold front through
our region Saturday night into early Sunday. Numerous showers and
thunderstorms are expected along and ahead of the cold front
Saturday and Saturday night.

The focus for convection will be over west Kentucky for Sunday, but
the remainder of the area may very well be dry. We will have small
chance PoPs lingering Sunday night into Monday, but this is mostly
the lingering effects of previous model cycles. Figure that Sunday
night and Monday will be dry for the entire area.

Given the strength of the upper-level trough, cannot completely rule
out a few severe storms Saturday afternoon and evening,and possible
over west Kentucky Sunday. However, locally heavy rainfall and
lightning will be the primary concerns.

In the wake of the trough aloft, the flow over our region will
weaken and become nearly zonal Monday into Tuesday. A cool and dry
area of high pressure will be in control at the surface. The surface
high will begin to shift east of the area heading into Wednesday, as
the flow aloft becomes southwesterly. The GFS and ECMWF each develop
a swath of convection northeast through Missouri Wednesday or
Wednesday night, putting our northwestern border areas on the fringe
of some small PoPs.

High temperatures will start out a category below normal Saturday
and trend much cooler. Many areas may struggle to reach 80 for highs
Sunday through Tuesday. Lows will be near normal Saturday night and
then trend much cooler for the work week. Some locations may drop to
the 60 degree mark Monday through Wednesday mornings.

&&

.AVIATION...
Issued at 120 PM CDT Wed Aug 17 2016

MVFR cigs, and in some cases IFR cigs, are expected to improve this
afternoon and early evening as somewhat drier air mixes in from the
north aloft. However, lack of mixing at night will encourage
formation of low clouds, probably IFR level, late in the night.
Vsbys are forecast to dip to MVFR/IFR levels, but confidence is not
high on whether the majority of the moisture available will be
converted to clouds. Conditions should begin to improve in the late
morning Thursday.

&&

.PAH Watches/Warnings/Advisories...
IL...None.
MO...None.
IN...None
KY...None.
&&

$$

UPDATE...DB
SHORT TERM...Smith
LONG TERM...DRS
AVIATION...DB



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