Area Forecast Discussion
Issued by NWS Paducah, KY

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FXUS63 KPAH 192015

315 PM CDT Tue Aug 19 2014

.SHORT TERM...(Tonight through Thursday night)
Issued at 315 PM CDT TUE AUG 19 2014

Cloud cover has held down heating across much of southern
Illinois, and is likely a contributor to the lack of robust
convection there. Not sure if the band of showers will ever outrun
the clouds and get to the warmer air currently over southwest
Indiana and the Pennyrile. The cluster of storms over Bollinger
and Cape Girardeau counties seems to be the anchor, representing
the edge of the cap. Figure that the activity will increase in
coverage as it moves east through 00Z, but still don`t know if it
will really morph into a solid line. Large hail has already been
reported with the more isolated storms in southeast Missouri. That
should be the main concern through much of the afternoon, but wind
will begin to dominate if and when it grows upscale.

The convection should be east of the area shortly after sunset,
and really do not feel that there will be any further convection
overnight. The upper ridge really builds over the region Wednesday
through Thursday night. This should limit the convective activity to
the EVV Tri State area for the remainder of the short term. The
consensus of guidance focuses the best chances of convection in
the Tri State Wednesday night, with minimal chances Thursday and
Thursday night.

In the absence of convection, a very low-level inversion will
create disgustingly hot and humid conditions. With highs in the
middle 90s and dewpoints in the low to mid 70s, heat indices will
be in the 100 to 105 degree range. These conditions can be
expected everywhere, but the EVV Tri State Wednesday afternoon,
and throughout the area Thursday afternoon. Will continue to
mention in the HWO, but will not issue a heat advisory at this time.

.LONG TERM...(Friday through Tuesday)
Issued at 315 PM CDT TUE AUG 19 2014

It appears that last week`s deterministic runs of the GFS may
have been on target with the intensity of the ridge
building/subsidence across the WFO PAH forecast area.

The last two runs of the medium range deterministic GFS and ECMWF
have been consistent with strong subsidence (roughly 3-7C cap through
925 mb by 00z during for the August 23rd-26th) in a robustly dry
atmosphere over the area.  Although there will be scattered
antecedent precipitation and a moist boundary layer initially for the
middle of this week, significant insolation and subsidence should
help to dry out the lower atmosphere to support much warmer
temperatures.  The GFS Ensembles are suggesting mean 850 mb mean
temperatures between 20-22 Celsius from next Sunday through next
Tuesday and this is not even accounting for the five to seven degree
Celsius increase near the apex of the subsidence inversion between
925-950 mb.

Agree with WFO LMK to push maximum temperatures at or near the
century mark early next week. Assuming a slight cold bias with the
deterministic GFS, the forecast temperatures in this forecast
package may be closer to the mark.

Could see the potential for an multi-day heat advisory (or even an
excessive heat warning for the WFO PAH forecast area give the
duration) from this Friday through next Monday.  Will definitely
highlight this in the Hazardous Weather Outlook and may consider
a Special Weather Statement as well. If there is more consistency
in the next couple of model runs, an excessive heat watch may be
warranted given the duration and intensity of the heat.


Issued at 1250 PM CDT TUE AUG 19 2014

An outflow boundary is expected to provide a focus for
thunderstorm development over southern Illinois this afternoon.
Best guess is that the storms would impact KEVV and KOWB around
00Z. With plentiful low-level moisture, fog development will be
possible again tonight, but with some southwest wind expected,
LIFR/VLIFR conditions are less likely. If they occur it would most
likely be at KCGI. Just a few cu expected by midday Wednesday,
along with modest west southwest to west winds.




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