Dense Fog in Illinois, April 7 to 8, 2024

Area Forecast Discussion
National Weather Service Paducah KY
521 PM CDT Sun Apr 7 2024

.KEY MESSAGES...

- There remains a conditional risk for a few severe storms this
  afternoon. If supercells are able to develop, all hazards will
  be possible.

- The forecast remains mostly to partly clear for the solar
  eclipse on Monday. There will likely be some high-level cirrus
  clouds, but overall good viewing conditions with dry weather
  is expected.

- A prolong period of stormy and wet weather begins Monday night
  and continues through Wednesday. Heavy rainfall looks to be
  the main concern with some flash flooding issues possible.

&&

.UPDATE...
Issued at 515 PM CDT Sun Apr 7 2024

Updated Aviation discussion for 00Z TAF Issuance.

&&

.DISCUSSION...
Issued at 211 PM CDT Sun Apr 7 2024

Forecast remains on a similar line of thought this afternoon.
Water vapor shows lightly better than originally modeled
diffluence over the quad-state which may be aiding in focusing
some of the shower and thunderstorm activity over SEMO/SRN IL.
Low level moisture is moving in from the southwest. With a
dewpoint 62-63 our surface based convective temperature would be
about 73-74 degrees. Cumulus along the dryline that was
bubbling a few hours ago has dissipated and southwesterly winds
have become more parallel to the dryline, limiting
convergence/forcing. There are still areas of focused cu streaks
over Carter and Ripley County, MO with 63-66 degree dewpoints
moving in ahead of it. 0-1km SRH is about 150, down from earlier
as low level winds veer. Deep layer and low layer shear though
should still remain strong enough to pose a severe weather
threat when and if surface based storms initiate over the next
couple of hours. Dry air entrainment will be a mitigating factor
but low level moisture in general looks rich enough to have a
good chance at sustaining some deep convection this afternoon.

Dryline/front washes out over the area overnight with clouds
likely starting to drop off. We have a fairly neutral upper
level pattern overhead Monday afternoon with southwesterly flow
from 90-100 kts. GFS has fairly high RH aloft, but it shows the
same thing over southwest TX this afternoon that result in only
wispy cirrus clouds. With that we maintainlocalized  a
favorable cloud forecast for the eclipse tomorrow with
temperatures in the mid 70s. Continued some minor hourly T
tweaks in totality, but those will be short lived enough to be
hard to capture on an hourly resolution.

Monday night upper-level flow speeds up as a trough moves off
the Rockies. We end up in a right rear exit region of the upper
jet by midnight or so. The increased ascent tightens up our low
level wind fields, increasing moisture advection, and large
scale ascent. We get pretty good coverage of showers and storms
through the night. Instability is limited but shear will be
strong enough we will at least have to be aware about some
severe thunderstorm risk.

We stay in vicinity of a front through the day Tuesday and into
Wednesday afternoon. By Wednesday afternoon a negative tilt
trough moves into the area greatly increasing large scale ascent
once again. Rain and thunderstorms appear likely. Instability
again looks limited for severe threat, but by this point even
with our dry antecedent conditions think its probable we would
start to develop flooding issues by this point. Too
uncertain/early for a flash flood watch but one may become
necessary depending on exactly where and how heavy rain sets up
through this event. Current GEFS and ECMWF means have 3-4 inches
of rain over our southern counties which has trended up over the
last 12-24 hours increasing our concern for a flood threat.

This system sweeps a front through that moderates temperatures
for the weekend before return flow starts up again ahead of the
next trough warming things up and leading to a sharp increase in
humidity.

&&

.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 515 PM CDT Sun Apr 7 2024

Active convection within/around PAH FA will see VCTS with low
VFR, potentially MVFR SCT-BKN bases at flight terminals thru
early evening...with best chances shifting eastward with time.
After loss of diurnal fuel, these chances diminish and lower
bases scour out. There is some modeling that hints at near
surface moistening, perhaps resulting in IFR bases developing late
tonight, mainly east (KEVV-KOWB). As a first step, we'll
introduce its mention but refrain from carrying CIGS until next
issuance. Either way, it's shallow and burns off quickly tmrw
morning, with time/height cross sections showing the only
moisture AOA H3.

&&

.PAH WATCHES/WARNINGS/ADVISORIES...
IL...None.
MO...None.
IN...None.
KY...None.

&&

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