458
FXUS63 KPAH 141911
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
211 PM CDT Sun Jul 14 2024

.KEY MESSAGES...

- Hot and humid conditions will continue this afternoon into
  next week. A Heat Advisory is now in effect for the entire
  forecast area through Tuesday evening.

- A slow moving cold front arrives Tuesday evening and pushes
  south Tuesday night into Wednesday. Multiple rounds of
  showers and thunderstorms are possible. The potential for
  heavy rainfall and flash flooding is increasing, especially
  across portions of southern Illinois and southwest Indiana.
  The risk for an isolated strong to severe gusty storm remains
  marginal Tuesday evening.

- Dry conditions and unseasonably cool temperatures 5-10 degrees
  below normal arrives during the second half of the week with
  high temperatures only in the 80s. A gradual warming trend
  closer to normal begins over the weekend.

&&

.DISCUSSION...
Issued at 208 PM CDT Sun Jul 14 2024

Another heat wave has begun today as a 597 dam ridge is located over
NM/CO with southerly return flow at the sfc. Visible satellite
imagery shows not much relief with just a few cumulus clouds across
the FA. MaxTs in the low to mid 90s combined with dewpoints
generally in the mid to upper 70s will translate to heat index
values around 105-110 degrees through Tuesday. For this reason, have
extended the Heat Advisory until Tuesday evening as dewpoints are
already overachieving above model guidance. The good news is a cold
front cools maxTs back down into the 80s for the middle of the week.

The synoptic pattern turns more amplified Tuesday night into
Wednesday as the aformentioned ridge retrogrades west and allows for
a 500 mb trough upstream to eject out of Ontario Canada across the
the great lakes. Downstream of the better upper level support, a
shortwave and cold front will slowly approach the FA from the north
Tuesday evening resulting in a period of unsettled weather with
numerous showers and thunderstorms. On the onset Tuesday evening,
there may be a brief window for a few isolated strong to severe
storms mainly in southern IL and southwest Indiana where SPC has a
marginal risk in their D3 outlook. The better deep layer shear lags
behind the front which may inhibit coverage, as model soundings only
show about 20-25 kts of effective bulk shear at best. Given MLCAPE
between 2000-3000 J/kg combined with low-level lapse rates around
7.0 C/km, there may be just enough support for an isolated damaging
wind risk before instability quickly wanes after sunset with the
loss of diurnal heating.

There is higher confidence in the potential for heavy rainfall and
flash flooding Tuesday night into Wednesday as the 850 mb moisture
transport ramps up along a baroclinic zone. Model soundings south of
the frontal boundary transition to more of a long skinny CAPE below
1000 J/kg setup with slow Corfidi vectors around 15 kts. Given PWATs
near the 90th percentile around 2.00 inches and a deep warm cloud
layer above 10 kft, the parameters will support the potential for
both training convection and torrential downpours. While the setup
is favorable, there is still some uncertainty in the placement. Both
the 12z GFS/CMC support the potential for locally 2-4 inches across
portions of southern Illinois and southwest Indiana with even 5+
inches right along the CWA border. Meanwhile, the ECMWF is not as
robust and more in the 1 to 2 inch range. Once the CAMs are in
range, we will likely be able to narrow the meso details a bit
better, but there certainly is a strong signal for heavy rainfall.

As the cold front slowly sags south Wednesday into Wednesday night
into southeast Missouri and western Kentucky, additional rounds of
showers and thunderstorms remain likely with the potential for
localized heavy rainfall and flash flooding. Overall, at least 0.5
to 1 inch is progged across most of the FA, with higher amounts
favored north with the first round as WPC has now expanded the
higher QPF east compared to the previous forecast package. This
makes sense given the strong synoptic scale forcing for ascent.

Pcpn may linger into Thursday morning before trending drier as a
1022 mb sfc high pressure builds across the Ohio Valley to end the
week. Pleasant weather along with unseasonably cool temps 5-10
degrees below normal are in store. In fact, the NAEFS shows 850 mb
temps dropping below the 10th percentile around 10-12C Thursday into
Friday which translates to maxTs in the low 80s and minTs in the low
60s, possibly upper 50s in a few locations. A gradual warming trend
closer to normal follows over the weekend as moisture tries to build
back north.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1134 AM CDT Sun Jul 14 2024

A few CU around 5-6 kft AGL is possible this afternoon as
satellite imagery indicates some development across the region.
Otherwise, VFR conditions prevail through Monday morning with
only a few high cirrus clouds overnight. SWS winds today turn
light & variable tonight before increasing once again in the
morning.

&&

.PAH WATCHES/WARNINGS/ADVISORIES...
IL...Heat Advisory until 8 PM CDT Tuesday for ILZ075>078-080>094.
MO...Heat Advisory until 8 PM CDT Tuesday for MOZ076-086-087-100-
     107>112-114.
IN...Heat Advisory until 8 PM CDT /9 PM EDT/ Tuesday for INZ081-082-
     085>088.
KY...Heat Advisory until 8 PM CDT Tuesday for KYZ001>022.

&&

$$

DISCUSSION...DW
AVIATION...DW