Area Forecast Discussion
Issued by NWS Paducah, KY

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FXUS63 KPAH 210000

Area Forecast Discussion
National Weather Service Paducah KY
700 PM CDT Thu Apr 20 2017

.SHORT TERM...(Tonight through Friday)
Issued at 301 PM CDT Thu Apr 20 2017

A cold front was located over central Missouri this afternoon,
roughly near a kstl-ksgf line at 19z. A complex of thunderstorms
over southeast Missouri will continue to track east-southeast
across parts of west Kentucky through early this evening. This
complex may impede development of organized showers/storms across
sw Indiana and the I-64 corridor. Therefore, only scattered
showers and a few storms are forecast tonight over those areas.
The heaviest rainfall will likely be over se Missouri tonight,
where some training of convective echoes is possible as the
front becomes more west-east oriented.

On Friday, the cold front will move down across Tennessee and
Arkansas. However, the 850 mb front is expected to stall along the
Interstate 64 corridor. This will result in a moist southwest flow
overrunning the surface front. There may be enough elevated
instability for some thunder south of the 850 mb boundary.
Rain is very likely across the region as a 500 mb closed low
approaches from the Plains. QPF varies greatly among the models.
There are large differences in the placement of the heaviest qpf
from model to model. Locally heavy rain is possible where any
elevated convection becomes persistent. Highs will range from the
mid 50s to mid 60s in the cooler north surface flow.

.LONG TERM...(Friday Night through Thursday)
Issued at 414 PM CDT Thu Apr 20 2017

The long term discussion period includes the latter half of the
heavy rainfall event for the Quad State region. Given WPC, blended
model guidance, and collaborative QPF, at least half of the 2.5 to
3.25 inch rainfall totals from tonight through daytime Saturday
will be centered on Friday night (roughly 1.5 inches).

At this point in time, plan to hold off on any Flash Flood
Watch for parts of the Quad State region for Friday night. The
area of greatest concern for excessive rainfall will likely be
Southeast Missouri, with secondary areas of concern over parts of
extreme Southern Illinois, the Purchase area of West Kentucky, and
central sections of the Pennyrile region of West Kentucky. The
WPC QPF branch does have most of this area under a slight chance
for excessive rainfall for the day 2 time period (covering Friday
night). However, in coordination with our Service Hydrologist and
surrounding offices, the lack of consistent and widespread QPF the
last two to three days may provide enough drainage and percolation
of water through the soil to slow an early runoff potential.

The big key will be the amount of training of thunderstorms over
Southeast Missouri tonight into early Friday. If this antecedent
rainfall can provide enough saturation for the Friday night
convection, a Flash Flood Watch may be warranted, especially for
Southeast Missouri. A lot of this will be dependent on the
amplification of the mid/upper level low as it moves through
Southern Missouri, as well as the degree of moisture advection and
warm cloud processes, given the limited instability (lack of
widespread thunderstorm coverage) with this event.

Will emphasis heavy rainfall and minor flooding potential in the
Hazardous Weather Outlook and other communication avenues for now.

Beyond Saturday, the closed low will slowly shear out in a
northeast to southwest fashion, moving the heaviest rainfall east
of the area. Ridging will build in to the area Monday and Tuesday.

A northern stream, low amplitude trough will develop and amplify
in the northwest quarter of the U.S., with most of the energy and
moisture focused along the warm frontal zone north and northwest
of the WFO PAH forecast area Wednesday into Thursday.

At this time have greater than 50 percent forecast confidence
with the weather systems from Friday night through Tuesday, with
less than 50 percent confidence on the timing and position of
systems Wednesday and Thursday.


Issued at 700 PM CDT Thu Apr 20 2017

The 00z Friday WFO PAH TAF issuance accounts for ongoing
shower activity. Separated forecast groups according to wind shift
with approaching cold front. The majority of ceilings through the
first 15 hours of the forecast period should remain in the VFR
category as the front pushes through overnight. As the boundary
stalls out south of the TAF locations, and the next wave of
precipitation moves in during the last six hours of the TAF
forecast, MVFR ceilings and visibilities will be possible,
especially in the KCGI and KPAH TAF locations.




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