Area Forecast Discussion
Issued by NWS Paducah, KY

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908
FXUS63 KPAH 250233
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
933 PM CDT TUE MAY 24 2016

.UPDATE...
Issued at 933 PM CDT Tue May 24 2016

The forecast was updated to account for radar trends as the large
area of rain continues to shrivel up as it skirts along the far
southern portions of southeast Missouri and southwest Kentucky. The
net result is a substantial decrease in rain chances through the
remainder of the night. However, kept at least a small chance over
most of the area to account for any potential weak low level jet
induced convergence. However, it appears as though the next chance
of showers and thunderstorms should hold off until the daylight
hours of Wednesday as the next in a series of weak upper level
waves approaches in increasingly moist southwest flow.

&&

.SHORT TERM...(Tonight through Thursday night)
Issued at 250 PM CDT Tue May 24 2016

Short term convective trends will have to be derived from
radar/satellite, and the RAP, as the other models are not
handling well what may be an MCV moving across southern MO. From
there, will trend more toward a NAM/EC blend overnight and on
through the remainder of the short term forecast. We may see a
lull after the current activity does what it will. Late tonight
into Wednesday morning expect another round of convection to move
NE, especially over the NW 1/2 of the area, diminishing by
afternoon with the passage of a mid level s/wv. Likely a lull
Wednesday night, then convective chances slowly increase Thursday
and especially Thursday night as the mid level flow backs in
response to energy digging moving into the Rockies from the SW
U.S. in the form of a mid level low.

The airmass will be rich with deep moisture through the short
term. So any robust convection will produce very heavy rain. Also,
the airmass just to our west and southwest will overspread the
area. Already seeing some pulse near to low end severe cores with
this activity. Models show decent instability, so a few strong,
pulse severe storms cannot be ruled out. Warm and muggy. Split the
difference on MOS and our existing numbers.

.LONG TERM...(Friday through Tuesday)
Issued at 250 PM CDT Tue May 24 2016

Warm and humid conditions will continue through the long term. The
main forecast challenge is precipitation chances. Deep-layer
southwest flow Friday will decrease over the weekend. The flow
pattern will become weak and non-descript by Memorial Day. There
will likely be a corresponding decrease in convective coverage
over the holiday weekend as the flow slackens. Details below...

On Friday, a rather broad 500 mb shortwave trough will emerge from
the Rockies into the western High Plains. This trough will continue
northeastward across the central Plains on Saturday. A moist and
unstable air mass will be in place, but there is no synoptic low-
level boundary apparent in the models. Therefore, precipitation
coverage will be dependent on mesoscale features such as outflow
boundaries and/or convectively-induced vorticity centers. Given the
lack of model skill at longer time ranges with such features, the
forecast will stay the course with 30 to 50 percent chance pops.
Given the moist environment and moderately strong low-level inflow,
locally heavy rain is likely in some thunderstorms. Even small doses
of sun should be enough to push highs into the lower/mid 80s, which
the models have consistently been forecasting for both Fri and Sat.

Sunday into Memorial Day, the upper-level flow will weaken as the
shortwave continues northeast across the Great Lakes region. In the
wake of the shortwave, some mid-level drying is indicated by the
gfs. This is reflected in its lower precipitable water values. The
forecast will follow suit, with pops mainly in the slight chance
category Saturday night into Monday. Highs should be in the 80s
with lows in the 60s during that period.

For Tuesday, the models diverge concerning the evolution of
troughing over the western states. The 12z ecmwf indicates southwest
flow will increase slightly ahead of the trough, but the gfs and
gefs keep the trough much further west. The forecast will indicate
low chance pops for Tuesday. Even the more pessimistic ecmwf does
not suggest widespread coverage of precip.

&&

.AVIATION...
Issued at 634 PM CDT Tue May 24 2016

The 00Z TAFs are VFR. Will keep VFR light rain at KCGI and KPAH
for the first few hours of the forecast...otherwise the forecasts
are dry. Guidance is not doing well in this regime, so will keep
the forecasts dry and simple and await a strong sign on radar
before adding precipitation through this period. At this time,
the best chance of precipitation through this period would be
associated with another complex of showers and thunderstorms
that could potentially impact KCGI and KPAH from midday into the
afternoon on Wednesday.

&&

.PAH Watches/Warnings/Advisories...
IL...None.
MO...None.
IN...None.
KY...None.
&&

$$

UPDATE...RJP
AVIATION...DRS



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