Area Forecast Discussion
Issued by NWS Paducah, KY

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FXUS63 KPAH 221728
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
1228 PM CDT Sat Jul 22 2017

.UPDATE...
Updated aviation section for 18z taf issuance

&&

.SHORT TERM...(Today through Monday night)
Issued at 314 AM CDT Sat Jul 22 2017

Given essentially every locale was around Excessive Heat Warning
Criteria (110F) yesterday, will expand the Warning to include all
areas today through Sunday. Nearly all areas will be around
dangerous 110F levels or slightly higher at peak heating. Needless
to say dew points have generally ended up higher than what was
forecast a few days ago, making for even worse conditions. For
Sunday, we will probably be 100-105F north 1/2, 105-110F south,
along with a slight chance of convection. So while Sunday is
borderline for Warning criteria, it`s not worth multiple
headlines. Especially given the fact we have seen high heat index
values since last Tuesday.

Isolated convection seems less likely today, given drier air
aloft working in from the west. That`s not to say one or two
showers or storms will not form. Boundary will push south toward
the area tonight, and enter the region Sunday from the north. Low
chance PoPs for convection are in as a result. Overall deep layer
moisture is lacking, so coverage may not be too impressive until
Sunday afternoon and night across the southern 1/2 of the region
when we tap a bit better moisture. The boundary that enters the
area stalls through Monday, keeping a chance of convection going
in the forecast, best chances southern 1/3 of the area, dropping
off considerably heading north toward I-64. Used a EC/NAM model
blend for PoPs. Used a MOS blend and persistence for Max/MinT`s.

.LONG TERM...(Tuesday through Friday)
Issued at 314 AM CDT Sat Jul 22 2017

Early in the extended forecast period, the medium range models (most
notably the ECMWF) depicted some "weaknesses", i.e., hard-to
forecast perturbations, in the mid level flow on the edge of a
persistent ridge where the PAH forecast area is. Mainly in the heat
of the day, isolated to scattered showers and tstms are a
possibility in parts of our region through at least Wed afternoon.

Thu night/early Fri, in the wake of mid level shortwave energy
sweeping through the Midwest, a surface boundary should move into or
stall just north of our region. This boundary will be the focus for
additional shower and tstm activity for this period in the moist and
unstable airmass as early as Thu morning (possibly), starting in the
north, as convective activity outside our region rides along the
west-northwesterly flow aloft. Some model solutions develop a
surface wave along this boundary, which could enhance rainfall rates
and the coverage of shower and tstm activity Thu or Fri, depending
on when it moves through.

While confidence is better that pcpn will probably happen in most
areas Thu night/Fri, the weather picture is a bit more murky at
other time periods as far as timing of pcpn, as the models have had
trouble with the finer details. Bottom line is that PoPs for any one
location are pretty limited through most of the extended forecast
period.

Surface dewpoints should start out early in the upper 60s north/
lower 70s south, which is not as delightful as the previous
forecast. There should be an increase in the dewpoint numbers by Wed
afternoon as low level moist fetch off the Gulf begins to improve.
We should be back in at least mid 70s soup by Thu/Fri. Thu will be
the warmest day outside of shower and tstm activity, with highs in
the lower 90s and heat indices about 101-106.

&&

.AVIATION...
Issued at 1228 PM CDT Sat Jul 22 2017

An outflow boundary from thunderstorms over the Midwest early this
morning has made it all the way to kevv as of 17z. This boundary is
marked by a line of cumulus clouds and even an isolated shower or
two. The main effect on the taf sites will be a lighter and more
variable wind than earlier expected. Winds at kevv/kowb will be
light and variable much of the afternoon. Otherwise, a southwest
wind flow will continue through tonight. Scattered cumulus clouds
will continue this afternoon, especially near the boundary, where a
few showers or a thunderstorm could occur.

On Sunday, a weak cold front will make it down into southern IL in
the morning. Winds will veer into a west or even northwest direction
in the morning. The potential for thunderstorms exists, but it is
too low to mention in tafs at this time. The exception is at kevv,
where vcts was included in the early morning hours.

&&

.PAH WATCHES/WARNINGS/ADVISORIES...
IL...Excessive Heat Warning until 7 PM CDT Sunday for ILZ075>078-
     080>094.

MO...Excessive Heat Warning until 7 PM CDT Sunday for MOZ076-086-087-
     100-107>112-114.

IN...Excessive Heat Warning until 7 PM CDT Sunday for INZ081-082-
     085>088.

KY...Excessive Heat Warning until 7 PM CDT Sunday for KYZ001>022.

&&

$$

AVIATION...MY



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