Area Forecast Discussion
Issued by NWS Paducah, KY

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000
FXUS63 KPAH 200458
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
1158 PM CDT Tue Sep 19 2017

.SHORT TERM...(Tonight through Thursday night)
Issued at 240 PM CDT Tue Sep 19 2017

The 500 mb shortwave trough that brought locally heavy rain over
the past 24 hours will exit to the east of our region early this
evening. In its wake, a sharp 500 mb ridge will quickly develop
over the Lower Ohio Valley late tonight through Thursday. The
ridge will suppress precipitation chances, however the low levels
will remain very moist through Thursday. This means the
recurrence of late night fog and diurnal cumulus clouds will be
forecast concerns.

Late night fog has become a common occurrence the past week or so,
which is to be expected climatologically as we head into the
fall. Given the combination of clearing skies, light winds, and
70-degree dew points tonight, it is hard not to forecast fog.
However, winds aloft will be running 15 knots or so just several
hundred feet agl. This should keep widespread dense fog from
developing, but patchy fog will be mentioned in the normally fog-
prone areas. Also, fog will be mentioned where low stratus has
only just started to break up in parts of southwest Indiana and nw
Kentucky. This persistent stratus has kept relative humidity high
in those areas.

Once the fog burns off early Wednesday, some diurnal cumulus will
develop. The cu rule scheme from the 12z nam indicates scattered
to broken cu, with the best coverage in west Kentucky. The
potential for isolated diurnal showers or storms still cannot be
ruled out. However, there is not enough support from the short-
range models (ruc/nam primarily) to justify 20 percent pops.
High temps will be around 90 given the southwest low-level flow at
850 mb and adequate sunshine. Some heat indices will likely be
around 100 degrees, mainly in the typical corridor of higher dew
points from the Missouri bootheel up into southwest Illinois.

Very little change is expected Wednesday night through Thursday
night. The low levels may dry out just a bit, however surface dew
points are not going to be noticeably lower. Daytime highs will be
around 90, with overnight lows near 70.

.LONG TERM...(Friday through Tuesday)
Issued at 240 PM CDT Tue Sep 19 2017

In the extended period, our region will be underneath an elongated
area of high pressure aloft that will encompass a good part of the
eastern half of the country. With not much in the way of moisture
around, Friday will remain dry but it will continue to be rather
warm. There might be enough moisture for some air mass type storms
over the southern sections on Saturday...but all in all it looks
like most of the area will be dry.

The center of the upper high will start shifting northeast by the
end of the weekend. The upper flow becomes more and more weak and
moisture does increase. With no features at the surface, any
convection that tries to form will likely continue to be of the air
mass variety, i.e. isolated to scattered summer time storms. This
far out, it is difficult to say where the best chances may be but it
would be prudent to at least have a slight chance in the forecast
where the better moisture is given the pattern set up. The GFS
ensemble precip mean also suggests at least a small part of the area
could possibly see some isolated mainly afternoon convection.

We have been watching the arrival of an incoming frontal boundary.
Models differ on the arrival time however, with the 00Z ECMWF
showing a Tuesday/Tuesday night arrival, with the 12Z GFS indicating
the front not arriving until Thursday. The new ECMWF came in and
now is delaying the front`s arrival as well.

The main item of interest during the long term is temperatures. We
will see highs on Friday and Saturday in the upper 80s to lower 90s
with at least upper 80s for the rest of the forecast period. We
could be nearing a few records here and there between Friday and
Tuesday.

&&

.AVIATION...
Issued at 1158 PM CDT Tue Sep 19 2017

Little change from 00z Wednesday WFO PAH TAF issuance. Main
concern will be potential for visibility restriction at KEVV and
KOWB through 12z Wednesday. Most guidance suggest enough mixing
to limit fog at these locations. The 12km NAM suggests the
potential for LIFR fog. Leaned toward MVFR fog conditions at KEVV
and KOWB for now, and update as necessary.

&&

.PAH WATCHES/WARNINGS/ADVISORIES...
IL...None.
MO...None.
IN...None.
KY...None.
&&

$$

SHORT TERM...MY
LONG TERM...CW
AVIATION...Smith



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