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000
FXUS63 KPAH 231236
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
736 AM CDT Wed Aug 23 2017

.UPDATE...
Issued at 735 AM CDT Wed Aug 23 2017

For aviation section only.

&&

.SHORT TERM...(Today through Friday night)
Issued at 300 AM CDT Wed Aug 23 2017

Much cooler/drier air will work its way southward across the
region today as high pressure continues to build in from the
Midwest. The large dome of high pressure stretches from the
central Plains/Midwest northward all the way through Canada. This
system will move slowly east with time, bringing a prolonged
period of very nice weather (for this time of year) to the
forecast area. Will be down right chilly at night with lows down
in the mid to upper 50s. Highs will only make it into the lower
part of the 80s at most locations.

.LONG TERM...(Saturday through Tuesday)
Issued at 300 AM CDT Wed Aug 23 2017

The overall forecast confidence is moderate to high.

The Quad State region will be under the influence of high pressure
at the surface and troughing aloft through most of the extended
portion of this forecast. Confidence is high that we will remain
well below normal through the period, and there is a pretty good
chance of precipitation mainly Monday into Tuesday, but the
mechanisms vary from model to model and run to run, so the spatial
and temporal details cannot be penned down at this time.

The large fly in the ointment for this forecast is the tropical
system formerly known as "Harvey". This system is expected to reach
at least tropical storm intensity as it moves west through the Gulf
of Mexico, reaching the Texas coast late Friday. The medium range
models agree in this timing, but range anywhere from Houston to
Brownsville for landfall.

The 00Z Canadian is farthest south and takes the system westward
into the higher terrain of northern Mexico and effectively kills it
off. The GFS is in the middle and quickly curves the system
northeast and then eastward through the northern Gulf states early
next week. The ECMWF holds the system nearly stationary just
onshore, putting Houston in a persistent moist onshore flow for 48
hours or so, then lifts it north through western Louisiana to
southwest Arkansas by Wednesday and then moves it more quickly east
northeast through Tennessee beyond this forecast period.

Over our region, a weak inverted surface trough will push slowly
west through west Kentucky and southwest Indiana Sunday into Sunday
night and then farther west Monday. Meanwhile a short wave trough
will descend southward over our region Monday. Enhanced moisture
east of the surface trough may be enough to touch off a few showers
or storms mainly over west Kentucky and southwest Indiana Sunday and
Sunday night and areawide on Monday. The 00Z GFS and GEM are in good
agreement in good coverage of convection Monday along the Ohio and
Wabash Rivers, and the 12Z ECMWF was right with them, too.
Unfortunately, the 00Z ECMWF is not as far south with the shortwave
and is much drier Sunday through Monday.

The interaction of tropical systems with systems in the primary
westerlies is rarely handled well by the models, especially with the
rather large spread of possibilities for "Harvey". Given the
uncertainties, capped PoPs at chance levels. Odds are that some
portion of the area will get wet at some point Monday through
Wednesday from the westerly system, tropical remnant or a
combination of the two. Stay tuned as this all shakes out in the
next 3 to 4 days.

&&

.AVIATION...
Issued at 735 AM CDT Tue Aug 22 2017

Cooler/drier northerly flow will dominate the weather picture for
the next several days. VFR conditions are expected for the next 24
hours, with generally only a few high clouds and northwest to north
winds under 10 kts.

&&

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

$$

UPDATE...GM
SHORT TERM...GM
LONG TERM...DRS