Area Forecast Discussion
Issued by NWS Paducah, KY

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932
FXUS63 KPAH 192326
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
526 PM CST Fri Jan 19 2018

.UPDATE...
Updated aviation section for 00z taf issuance

&&

.SHORT TERM...(Tonight through Sunday)
Issued at 1241 PM CST Fri Jan 19 2018

Mostly sunny early this afternoon and finally above freezing area
wide. Snow still having an impact, as we are still at a 7 inch
depth here. Evansville is at 2 inches at the airport. The warm up
will continue through Saturday. However we will see an increase
in clouds, as a substantial increase in surface-850mb moisture
takes place Saturday. We continue to see 290k isentropic lift in
the saturated layer and significant lowering of PDEF values.
Minimal QPF still showing up on the short range models. So added
back the afternoon slight chance PoPs Saturday afternoon and
continue them on through Sunday. Mainly a light rain/sprinkles or
drizzle scenario given the moisture generally remains at or below
5k/ft. Only slight chance PoPs at that. There may be some fog
Saturday evening and night, as 32+F dew point air moves over
remaining snow cover. We may be looking at just low clouds. But we
did go ahead an include some minor fog wording to hedge that
direction just in case. HiRes models running too cool for today,
MOS typically too warm. We will continue to follow weighted model
output as it has been the best performer minus localized affects.

.LONG TERM...(Sunday night through Friday)
Issued at 212 PM CST Fri Jan 19 2018

Although the general system pattern remains the same for the Sunday
Night into Monday, then again for next weekend, timing issues
between the model guidance appear to be broadening again with each
of the model runs(within the last 24 hours).

Prior to the initialization of the 12z Friday model data, each of
the models (ECMWF,GFS,Canadian) were underestimating 925 and 850 mb
temperatures by as much as 2C across parts of the Midwest from the
00z Friday run. The ECMWF initialized the best, the GFS the worst.
With the 12z model initialization, this issue is being rectified,
but does not bode well with the models attempt to capture warm air
advection ahead of the trough/developing closed low moving into
southern California this afternoon.  At this point in time, the
Canadian, followed by the ECMWF, then the GFS are handling the
precursor height and temperature fields for the late Sunday/Monday
system.

The last couple of numerical model runs of the ECMWF are slowing
down the system even more than the Canadian/GFS guidance. The ECMWF
solution would provide more residence time for moisture transport
and instability for thunderstorms, while the Canadian/GFS would
keep closer to the status quo (slightly less instability positioned
mainly over southeast Missouri and the Purchase area of west
Kentucky).

At this point, am considering a blend of the 12z Friday Canadian and
00z/12z Friday ECMWF for rain chances. The net effect may be to
increase instability slightly Sunday Night and delay complete
frontal passage through the WFO PAH forecast area later into Monday.
The timing still keeps the overall potential for severe storms low
for the WFO PAH forecast area given this blend. Storm total
precipitation still remains quite consistent, with rainfall amounts
between four and six tenths east of the Mississippi River, and six
to eight tenths west of the Mississippi River.

With respect to the system next weekend, the earliest rainfall
chances will be associated with the warm sector shower activity late
next Friday, with the next frontal passage expected next Saturday.
(January 27th). The late January system will likely produce 1-3" of
rain, especially for parts of southeast Missouri, southwest
Illinois, and Purchase Area of west Kentucky.

&&

.AVIATION...
Issued at 526 PM CST Fri Jan 19 2018

Some low clouds have been streaming northeast into western KY during
the afternoon. The northwest edge of this cloud shield has been
clipping kpah. All of the taf sites will remain fairly close to the
north and west edge of these low clouds, which are mostly based near
3k feet agl. For now, will keep kcgi free of low clouds tonight. The
trend at other sites should be for a gradual increase in the low
clouds. The low clouds will be widespread across the whole region on
Friday. Cigs could lower to ifr by evening, but that should occur
mainly after the valid time of these tafs.

The other main story is strong southwest winds. Low level wind shear
criteria will be met tonight at all taf sites. Winds will be 40 to
50 kt at only 2k feet agl.

&&

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

$$

Aviation...MY



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