Area Forecast Discussion
Issued by NWS Paducah, KY

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182
FXUS63 KPAH 182007
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
307 PM CDT MON JUL 18 2016

.SHORT TERM...(Tonight through Wednesday night)
Issued at 307 PM CDT Mon Jul 18 2016

No changes planned to the heat headline with this forecast
package.

Convection has been dwindling in areal coverage while weakening
over the EVV Tri State this afternoon. Some of the HRRR output
indicates that it will continue to dissipate by 5 PM, as the
outflow pushes into a warmer air mass aloft. To this point the
convective outflow has only impacted the immediate I-57 corridor
through southern Illinois that is in the Advisory. See no reason
to mess with the Advisory given the forecast for Tuesday and
beyond.

The 12Z models continue to amplify the mid/upper-level ridge
through the Plains Tuesday which will put our region in stronger
northwest flow. Certainly cannot disagree with SPC`s Day 2 Marginal
risk which is now just for our northwestern counties. The main
question is just how much convection will be able to survive the
warm mid-level temperatures over the region. Convection certainly
may mess with the Heat Advisory tomorrow, but with the prospect of
little or no convection developing, we will continue with it as
is.

Although there will be weak surface ridging over the region by the
end of the day Tuesday, it remains to be seen how much if any cool
and dry advection there will be into the northeast portions of the
region. The Heat Advisory looks good for the western half of the
region, and may need to be expanded eastward. If there is no
relief from convection Tuesday or Wednesday, portions of southeast
Missouri will likely need to be upgraded to a Warning as we head
into the extended portion of the forecast.

.LONG TERM...(Thursday through Monday)
Issued at 307 PM CDT Mon Jul 18 2016

Above average confidence in the extended.

High pressure both at the surface and aloft dominate the weather
pattern until Sunday. The surface high will start out centered over
the Ohio valley and slowly drift south and east as it washes out.
The mid/upper level high will slowly move west in retrograde motion
to the central plains by the end of the weekend. This will allow for
a vertically stacked low to skirt eastward along the Canadian
border. This low will have a weak cold front associated with it that
will swing through the PAH forecast area around Sunday according to
the latest run of ECMWF. In contrast the GFS is a little slower
indicating more like Monday which is not the typical bias of these
models. They both have similar scenarios just a 24 hour timing
difference. So the overall solution indicates high confidence for
the time period in question.

With temperatures in the 90s and dewpoints in the 70s there will be
plenty of moisture around for isolated afternoon thunderstorms. All
we need is a kicker to ignite them such as an outflow boundary from
previous thunderstorms that form to our north. Also heating
differential could produce a weak boundary to set of storm or two as
well. The best chance of an isolated storm will be for areas east of
the Mississippi River along the edge of the high...especially east
of the Wabash River Valley and the Jackson Purchase areas.

Finally for the bad news we will likely observe apparent
temperatures or heat index values exceeding 105 Thursday through
Saturday. Thus I would anticipate at least a heat advisory for the
aformentioned time frame and possibly before that time.

&&

.AVIATION...
Issued at 1244 PM CDT Mon Jul 18 2016

An outflow boundary from recent convection over KEVV and KOWB is
not expected to push as far west as KCGI and KPAH, so will keep
them both dry this afternoon. Another area of thunderstorms will
try to move southeast behind the boundary back into KEVV and KOWB
this afternoon, so threw MVFR TS in a TEMPO group at both sites.

The convective forecast beyond this afternoon is not certain, so
will keep the rest of the forecasts dry. Winds will be light
through the period, regardless of the boundary. Fog development is
likely at all sites. Will introduce MVFR fog for now, but it may
drop lower.

&&

.PAH Watches/Warnings/Advisories...
IL...Heat Advisory until 7 PM CDT Wednesday for ILZ075-080-081-084-
     085-088-089-092>094.

MO...Heat Advisory until 7 PM CDT Wednesday for MOZ076-086-087-100-
     107>112-114.

IN...None.
KY...Heat Advisory until 7 PM CDT Wednesday for KYZ001>006.

&&

$$

SHORT TERM...DRS
LONG TERM...KH
AVIATION...DRS



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