Area Forecast Discussion
Issued by NWS Paducah, KY

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FXUS63 KPAH 182039

Area Forecast Discussion
National Weather Service Paducah KY
339 PM CDT Fri May 18 2018

.SHORT TERM...(Tonight through Sunday night)
Issued at 339 PM CDT Fri May 18 2018

The negatively tilted closed low over centered just northwest of
St. Louis Missouri, with an axis stretching down into the
Missouri Bootheel at 230 pm CDT, will continue to slowly drift
northeast this evening and and overnight. The highest rain chances
will continue to the east of the low/trough axis, where enhanced
lift in the moist adiabatic environment will produce effective
rainfall amounts with a minimum of 3/4 of an inch or higher per
hour. Given the extremely isolated nature of the pockets of heavy
rainfall, will just utilize hydrological advisories for local
drainage/minor flooding issues.

With the sharper vorticity gradients aloft, non-supercell based
landspouts will be possible again, especially over southeast
Missouri this afternoon and this evening. We have been carrying
statements the last couple of days hinting at that potential.

The 13km RAP and 12km NAM-WRF continue to perform rather will in
placement and general intensity of afternoon convection within the
favorable isentropic lift zone.

With the loss of daytime heating, any convection should be
limited to the very narrow zones of enhanced lift aloft overnight.
With near calm and saturated condition at the surface, added a
mention of fog for the western sections of the WFO PAH forecast
area (mainly southeast MO and southwest IL) late this evening and

A very narrow ridge will continue to move in behind the closed low
tonight and Saturday, capping the coverage of convective activity
across most of the WFO PAH forecast area on Saturday and Saturday
evening. Worked to keep as much of the area dry as possible,
limiting any spurious model generated pockets of rain chances.

Rain chances will initially develop late Saturday night and early
Sunday along an impressed surface (warm frontal) boundary along
the interstate 64 corridor, then expand southward as diurnal
heating generates scattered convection over the remainder of the
area ahead of channeled vorticity in the southwest flow ahead of
a closed low in eastern Nebraska and wester Iowa.

.LONG TERM...(Monday through Friday)
Issued at 339 PM CDT Fri May 18 2018

Have rather low forecast confidence in the coverage and timing of
the precipitation through the work week next week.

The previously mentioned closed low over Nebraska and Iowa is
forecast to move little on Monday, with minor ridging possible
early in the day. The placement of the PoPs/Weather seem a little
too far west into the WFO PAH forecast area, but for
collaborative and regionally blended model guidance initialization
purposes, left a low chance PoP across most of the area.

There is a disparity among the ECMWF, GFS, and the Canadian medium
range guidance on how dominate the ridge building will take place
along and west of the WFO PAH forecast area. The GFS and Canadian
generate a low over the southeast U.S., southeast of the central
U.S. ridge. With the significant uncertainty associated with this
forecast low, leaned toward lesser PoPs/Weather for the latter
half of the week.

Temperatures were a blend of the regional model initialization,
the national blend of models, and the Canadian guidance.


Issued at 1203 pM CDT Fri May 18 2018

Given the moist atmosphere in place, conditional ceilings due to
convective activity have been in the 300-800 ft AGL (LIFR/IFR
category) range this morning given the lift associated with the
upper low just west of the WFO PAH TAF sites. The 18z Friday
forecast continues this trend into the first 1-4 hours of the
forecast period. KCGI should see the best improvement in ceilings
this afternoon and overnight, as the main convective shower and
thunderstorm bands remain generally east of this location. There
will be a lull in convective activity this evening at most
locations, picking up again after 12z Saturday. This will increase
the probability of MVFR ceilings and visibilities due to




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