Area Forecast Discussion
Issued by NWS Paducah, KY

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594
FXUS63 KPAH 182309
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
510 PM CST Thu Jan 18 2018

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

&&

.SHORT TERM...(Tonight through Saturday night)
Issued at 1227 PM CST Thu Jan 18 2018

The warming trend is underway with high pressure off to our south
and east. The return flow has current temps beyond what we saw
yesterday for highs. We will go a tad below MOS again tonight
near WMODEL in house (weighted) data as it did marginally o.k. for
last nights lows. With the wind up tonight, do not think we will
tank despite snow cover. Dry Friday into Friday night, with
increasing clouds with time. For Saturday through Saturday night,
will go with a slight chance of light rain and/or drizzle, due to
a substantial increase in sfc-850mb moisture, and isentropic lift
(290K), WAA forecast both periods. Otherwise considerable cloud
cover. This out ahead of a vigorous H5 trof out west, with s/wv
ridging ahead of it across our area. Used a blend of the GFS and
NAM overall as they are in reasonable agreement.

.LONG TERM...(Sunday through Thursday)
Issued at 1259 PM CST Thu Jan 18 2018

The extended period begins with the approach of the progressive
and slightly westward tilted (with height) low pressure system
moving from southern Colorado at 6 am Sunday to near Omaha
Nebraska by 6 am Monday. The 6am Monday time frame would place
the leading edge of the cold front moving into southeast Missouri
with copious amounts of rainfall covering southeast Missouri and
southwest Illinois at that time.

There will continue to be some timing differences on the eastward
progression of this front, owing mainly due to mesoscale
influences associated with entrance/exit orientation of the jet on
the leading edge of the low. Until the low itself moves into a
denser upper air observational network, sampling and modeling
issues will remain somewhat uncertain.

With all that said, the medium range model guidance suite appears
to be keying in on the Sunday night time frame for the approach
of the cold front into the WFO PAH forecast area. Despite the
strong shear (enhanced by the 80-110 knot south to north 250 mb
jet), the best instability remains elevated, but decreasing over
southeast Missouri and into the Purchase Area of West Kentucky.
Agree with SPC that the uncertainty remains to high for
pinpointing any probability for severe weather potential at this
time for the aforementioned area.

With respect to rainfall, QPF values of 0.5" to 0.75" in a six
hour period remains consistent the last several model runs over
southeast Missouri, with up to one half inch for parts of southern
Illinois and the Purchase Area of west Kentucky.

Much high forecast confidence (60-70%) on general timing of
precipitation event, precipitation amounts, and duration of the
event (with the possible exception of precipitation lingering into
Monday afternoon).

Preferred the 00z/12z ECMWF model solution slightly over the GFS
and Canadian, but accepted the regionally initialized model blend
for most sensible weather elements. One adjustment made was to
increase the influence of the ECMWF temperatures to the forecast
Max/Min temperatures in the extended forecast. The net effect is
to raise temperatures slightly.

&&

.AVIATION...
Issued at 510 PM CST Thu Jan 18 2018

Clear skies will continue through Friday. No obstructions to vsby
are anticipated. Winds will remain from the south to southwest on
the back side of a surface high. Wind speeds will become light
tonight, then increase again to near 10 kt on Friday.

&&

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

$$

LONG TERM...Smith
Aviation...MY



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