Area Forecast Discussion
Issued by NWS Paducah, KY

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000
FXUS63 KPAH 231533
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
1033 AM CDT Sun Apr 23 2017

.UPDATE...
Issued at 1033 AM CDT Sun Apr 23 2017

Made some short term adjustsments to reflect mesoscale changes
around closed low in northwest sections of central Tennessee this
morning and into tonight.

Given the slight sharpening and deepening of the closed low, the
vertical profile of temperatures aloft (i.e. sharpening lapse
rates) has been enough to support updrafts for isolated
thunderstorm development (as evidenced by lightning strikes on the
ENTLN lightning network) centered in the northeast and north
quadrant of the low within the zone of maximum vorticity. The high
resolution (4km) NAM-WRF, (ARW) version, seems to be initializing
this zone of instability quite well and was used in the short term
spatial placement of thunderstorms in the gridded/text forecast
updates this morning.

The precipitation shield and the gradient of precipitation versus
no precipitation was sharpened around the low pressure with some
diurnal expansion northwestward this afternoon. Although not
mentioned in the gridded forecast, isolated small hail may not be
out of the question. In discussion with another forecaster, the
potential for cold air funnels is not out of the question as well
in this environment.

Given the sharp pressure gradient, antecedent rainfall, cold air
advection, and differential heating over the rest of the WFO PAH
forecast area not impacted by the upper low, decided to modify
several sensible weather elements. Where there was rainfall the
past few days, more energy and insolation may be required to mix
out near surface ground moisture in parts of Southwest Illinois
and Southeast Missouri, therefore, slightly lowered temperatures
and kept dewpoints slightly elevated in those areas. Increased
winds over parts of the forecast area not covered by clouds and
rain.


UPDATE Issued at 649 AM CDT Sun Apr 23 2017

Updated aviation discussion for 12Z TAFs.

&&

.SHORT TERM...(Today through Tuesday night)
Issued at 249 AM CDT Sun Apr 23 2017

The upper level low responsible for the cool wet start to the
weekend was positioned near northwest Tennessee early this morning.
This low is forecast to continue on a very gradual southeastward
track into the Tennessee Valley and southeastern U.S. through
Monday. As it does, a general trend towards decreasing clouds and
warmer temperatures should progress northwest to southeast across
the forecast area. However, clouds and the potential for scattered
showers will likely persist over southeastern portions of the area
today with wrap-around moisture and lift in the deformation zone
north of the low.

The contrast between sunshine and lingering clouds will result in a
large temperature gradient across the area. Highs today should
approach 70 degrees northwest of the Ohio River. Meanwhile,
temperatures will likely remain in the 50s east of the Land Between
the Lakes in the southern Pennyrile region of western Kentucky where
stubborn clouds and showers persist. A relatively strong pressure
gradient northwest of the surface low will also make for breezy
conditions today. From late morning into the afternoon, northwest
winds around 15 mph will gust as high as 20 to 25 mph at times.

After a small chance of lingering showers in far southeastern
portions of the area this evening, dry weather is expected through
the remainder of the short term as a ridge of high pressure passes
through. Highs should range from 70 to 75 on Monday. Strengthening
southerly flow on Tuesday in response to developing low pressure
over the Plains will bring even warmer air northward as highs
approach the 80 degree mark. A cold front associated with this low
is forecast to reach western Illinois and central Missouri by 12Z
Wednesday. Any precipitation with this front should stay just west
of the immediate forecast area through daybreak Wednesday.

.LONG TERM...(Wednesday through Saturday)
Issued at 249 AM CDT Sun Apr 23 2017

An active pattern is expected in the long term. Decent confidence in
Days 4-5, lower confidence Days 6-7. We blended the 00z GFS and EC
for days 4 and 5, and their handling an ejecting H5 s/wv that will
move northeast from the Central Plains Wednesday to the Great Lakes
Thursday. For Days 6-7, Friday through Saturday, the overall trend
in the operational models, is slower and deeper with a developing
closed low near the 4 corners region by 00z Saturday. If this trend
develops, supported somewhat by the smoother ensemble mean solutions
from the GEFS/ECENS, we should see a more amplified pattern, which
will have impacts on our Friday through Saturday precipitation
forecast. For temperatures, we used an even blend of MOS and
ensemble MOS.

For Wednesday through Thursday, we`ll see increasing chances of
convection from west to east by Wednesday afternoon, with the band
of convection forecast to move across the area Wednesday afternoon
and evening, departing late. We may see strong to severe storms with
this activity, especially SEMO, southern IL, far west KY. Still a
few days to assess that potential in more detail. But shear and
thermal profiles are suggestive. We will see a lull, break in the
activity Thursday. Will carry low chance PoPs for weaker convection
Thursday night as mid level energy moves toward, and then across the
area.

For Friday through Saturday, greater amplification would likely mean
chance PoPs for convection as a warm front lifts north across the
area Friday/Friday night, coupled with some weak mid level support.
Saturday is where we may see a more significant change to the
forecast. The models now warm sector us, showing a much lower chance
of convection as the system out west closes off and backs our mid
level flow more strongly southwest. We have lowered PoPs quite a bit
for Saturday into early Saturday night, and abandoned the 6 hourly
PoPs forecast given such uncertainty and change in timing and
evolution.

&&

.AVIATION...
Issued at 649 AM CDT Sun Apr 23 2017

An upper level low over Tennessee will keep MVFR ceilings and
scattered showers across the Pennyrile region of western Kentucky
through much of the day. Elsewhere including the forecast terminals,
gradual clearing should continue with VFR conditions through the
forecast period. It will be quite breezy with north to northeast
winds 10 to 15 knots and gusts as high as 20 to 25 knots at times.
Winds will diminish after sunset.


&&

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

$$

UPDATE...Smith
SHORT TERM...RJP
LONG TERM...CN
AVIATION...RJP



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