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FXUS63 KPAH 152211
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
511 PM CDT Sat Jun 15 2019

.UPDATE...
Issued at 510 PM CDT Sat Jun 15 2019

After coordination with SPC, dropped the Tornado Watch for three
southeast IL and two southwest IN counties in the WFO PAH forecast
area. The effective boundary has moved north of Knox Co. IL and
the impact from the MCV moving into west Kentucky is of little
influence the counties that were previously in the watch area.

&&

.SHORT TERM...(Tonight through Monday night)
Issued at 353 PM CDT Sat Jun 15 2019

Tornado Watch #360 in effect for five counties along the I-64
corridor in southeast IL and southwest IN. These counties were
along a pre-existing west-east frontal boundary that was still
evident in wind/moisture/temperature fields and was favorable for
enhanced convective development. Convective line is just exiting
the watch area, but the secondary MCV near KCGI (Cape Girardeau)
could still enhance the cumulus field developing along the
differential heating boundary left from the northern MCV earlier
today.

The secondary MCV has also aided in the mixing and downward
transport of winds with non-convective gusts of 32-36 knots
common ahead of it. Moisture fields are somewhat limited ahead of
the second MCV further south into the Purchase/Pennyrile region of
west Kentucky, but may activate updrafts in differential heating
zones in southern Illinois and southwest Indiana left by the
morning cirrus debris field. Less than favorable surface moisture
convergence is hampering any organization of higher theta-e
moisture convergence.

Lake Wind Advisory remains in effect until 7pm CDT. As mentioned
in the morning forecast discussion, raised winds through the
afternoon, with a sharp reduction by this evening as winds
decouple as the boundary layer cools.

Big challenge for tonight into Sunday will be the ability of the
atmosphere to maintain enough instability for showers and
thunderstorms further south in weak ridging, weakening shear, and
instability over the southern section of the WFO PAH forecast
area. Kept higher rain chances over the northern half of the WFO
PAH area overnight with any southward propagation of new MCS
development along and south of the stationary frontal boundary
across northern MO, central IL and IN. May be too aggressive with
PoPS and Weather, especially after midnight, but with generally
unidirectional flow, repeated convection may still be possible
along the northern edge of the WFO PAH forecast area.

The challenge for Sunday night into Monday night will be the
deepening and slowing of the lee side trough into a low over OK
and southern MO. The slow translation of this feature is expected
to gradually increase moisture advection back into the WFO PAH
forecast area, as well increase instability independent of
insolation. Given the overall weaker shear, higher QPF will be
more localized during this time period. However, the northern WFO
PAH counties (I-64 corridor) are still favored for more pronounced
rainfall amounts in the short term period.

.LONG TERM...(Tuesday through Saturday)
Issued at 353 PM CDT Sat Jun 15 2019

The low mentioned in the last paragraph of the short term
discussion will move slowly east across the area Tuesday and
Tuesday evening, with ridging building in Tuesday night into
Wednesday morning.

Have low forecast confidence on the level of PoPs for Tuesday. At
this point, rain chances initialized by NBM may be too broad-
brushed versus reality. Utilized a mix of GFSv3 and ECMWF to
reduce PoP footprint during this time period.

The next shortwave moving into the middle Mississippi Valley on
Wednesday is still in line with previous forecast trends, so
higher PoPs remain in place through Wednesday afternoon and
Evening.

Broad ridging/low amplitude northwest flow will build in behind
the the Wednesday system. So leaned toward a much drier (rain-
wise) from Thursday through Friday.

There is low forecast confidence for rain chances on Saturday, but
kept a small mention for collaborative purposes.

Overall QPF for the forecast period is not impressive from a
widespread flooding perspective, but isolated and episodic flood
potential is still possible in selected corridors across the WFO
PAH forecast area.

&&

.AVIATION...
Issued at 1209 PM CDT Sat Jun 15 2019

Showers and thunderstorms continued to be tied closely to the MCV
(Mesoscale Convective Vortex) centered between KSUS and KMAE
(generally between Hannibal and St. Louis MO) at noon. Most of the
reduction in ceilings occurring along and ahead of this
circulation this afternoon in narrow corridors of space and time.

Given the high cloud bases in the vicinity of the convection, kept
most ceilings in the VFR category this afternoon and tonight.
Added a secondary cloud base to reflect lowering due to rain and
any thunderstorms in the vicinity.

Best potential for MVFR ceilings and visibilities will be at KEVV
and KOWB in the 18z Saturday to 00z Sunday time frame, then after
06z Sunday at KMVN.

Low level mixing and pressure changes ahead of the MCV and in the
vicinity of the frontal zone will keep wind gusts elevated between
25-30 knot mean values in the 180 to 220 degree azimuth range
through 00z Sunday. Could see higher convective gusts in excess of
40 knots around thunderstorms, but timing and placement to
variable at this moment to mention in the 18z Saturday WFO PAH
TAFS.


&&

.PAH WATCHES/WARNINGS/ADVISORIES...
IL...Lake Wind Advisory until 7 PM CDT this evening for ILZ075>078-
080>094.

MO...Lake Wind Advisory until 7 PM CDT this evening for MOZ076-086-
087-100-107>112-114.

IN...Lake Wind Advisory until 7 PM CDT this evening for INZ081-082-
085>088.

KY...Lake Wind Advisory until 7 PM CDT this evening for KYZ001>022.

&&

$$

UPDATE...Smith
SHORT TERM...Smith
LONG TERM...Smith
AVIATION...Smith
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