Area Forecast Discussion
Issued by NWS Paducah, KY

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909
FXUS63 KPAH 202239
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
439 PM CST Tue Feb 20 2018

.UPDATE...
Issued at 437 PM CST Tue Feb 20 2018

Updated Aviation discussion for 00Z TAF Issuance.

&&

.SHORT TERM...(Tonight through Thursday)
Issued at 308 PM CST Tue Feb 20 2018

Will be issuing a Flood Watch for the entire area beginning at 9
PM this evening and running through 6 AM Thursday. Most of the
area will get 2"-3" of rainfall in that period, and with the river
flooding already ongoing in many locations, the runoff will have
no place to go. We are not anticipating flash flooding due to a
lack of prolonged convective rain rates, but rather just a gradual
increase in standing water, especially along tributaries near the
larger rivers.

Most of the 12Z guidance indicates that we will either dry out or
have a serious lull Thursday, especially in the northwest portions
of the area. I fully expect that the watch will be extended
through next weekend, but figured we would get the ball rolling
with this initial shot of heavy rain and then see where we are
heading into the weekend.

SPC has Carter and Ripley counties in a marginal risk of severe
weather for the expected cold frontal QLCS that will move through
that area around 03Z. We will have very strong winds just off the
surface, so any reasonably organized convection has a chance to
transport that momentum to the surface. Definitely looking for
just a very isolated damaging wind threat.

The more intense portion of the frontal line of convection will
be suppressed southward as it tries to move farther east into our
area. We will limit the slight chance of thunder to the southwest
portions of the region late this evening into the overnight
hours. This is where the heaviest rain is also likely to fall
tonight. The leading line of convection will be moving quickly,
which should limit the flash flood threat.

Another concern late tonight and through midday Wednesday is some
potential for freezing rain and icing in our northwest border
areas. Went with more aggressive cooling behind the front given
the intense gradient to our northwest, but we manage to keep the
entire area above freezing. However, with wet bulbing potential in
our far northwest, the potential exists for a period of light
freezing rain and some minor icing. If temperatures trend any
cooler, a Winter Weather Advisory may be needed from Carter County
Missouri through Jefferson County Illinois.

The cold front will clear the entire area Wednesday morning, and
the initial band of rainfall will be diminishing over the
southeast half of the area during the morning. Unfortunately, the
12Z guidance is in decent agreement in bringing another swath of
rain back across the area with another upper-level impulse
Wednesday afternoon and night. The northwest extent of this swath
is uncertain at this time, and the potential exists for northwest
portions of the Flood Watch to be cancelled early.

.LONG TERM...(Thursday Night through Tuesday)
Issued at 308 PM CST Tue Feb 20 2018

The medium range models appeared to be in reasonable agreement
regarding the western trof/eastern ridge longwave mid/upper
pattern over the CONUS, even out in this time range. As usual,
smaller details of timing of shortwave energy bundles moving
through the longwave pattern were less certain. So, you might say
that at least the first half of the extended forecast period will
be a fairly high confidence forecast of a prolonged high PoP
event, especially if you break the forecast into 12 hour
increments.

The PAH forecast area will be under another warm advection pattern
early in the period in response to shortwave energy, with possible
rising temps Thu night. A surface cold front just to our north is
progged to sink partway into the region late Fri, and become quasi-
stationary into the weekend before becoming diffuse. Some tstm
activity will probably occur near this feature, but severe weather
appears to be more likely just to our south. 850 mb moisture
transport into our area will be impressive, especially Thu night/Fri
morning, and again Fri night through Sat. Accompanying these surges,
precipitable water numbers peak above two standard deviations in the
models for this time of year. This scenario should result in several
inches of rainfall for our region, which will tend to aggravate
areal and river flooding conditions from earlier pcpn.
Additional flood watches will be likely.

The mid/upper pattern should become more zonal for the latter half
of the weekend as the Gulf should finally get cut off as a moisture
source. The forecast looks mostly dry and mild through Day 7 (Tue).

&&

.AVIATION...
Issued at 437 PM CST Tue Feb 20 2018

Incoming rains will drop cigs into flight restricted cats
overnight, with IFR possible/best chance time period late
tonight-early tmrw. That is also when vsbys may also briefly
restrict to IFR in heavier showers. After that, IFR cigs linger
into the morning, with MVFR vsbys slow to improve. Rain chances
never go away, but the next best time period will be late in the
forecast, toward the end of the planning period, late tmrw pm.

&&

.PAH WATCHES/WARNINGS/ADVISORIES...
IL...Flood Watch from 9 PM CST this evening through late Wednesday
     night for ILZ075>078-080>094.

     Wind Advisory until 6 PM CST this evening for ILZ075-080-081-084-
     088-092.

MO...Flood Watch from 9 PM CST this evening through late Wednesday
     night for MOZ076-086-087-100-107>112-114.

     Wind Advisory until 6 PM CST this evening for MOZ076-086-087-100-
     109>111.

IN...Flood Watch from 9 PM CST this evening through late Wednesday
     night for INZ081-082-085>088.

KY...Flood Watch from 9 PM CST this evening through late Wednesday
     night for KYZ001>022.

&&

$$



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