570
FXUS63 KPAH 311137
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
637 AM CDT Mon Mar 31 2025

.KEY MESSAGES...

- Another major severe weather outbreak is anticipated for
  Wednesday into Wednesday evening. There is an Enhanced Risk
  (Level 3 of 5) of severe storms for that time period with all
  modes of severe weather possible.

- Very heavy rainfall and significant flooding/flash flooding
  will be major concerns late from Wednesday through at least
  Saturday. Ensemble guidance shows a 90-100% chance of seeing
  greater than or equal to 4 inches of rain from Wednesday
  through Saturday and up to a 60% chance of seeing greater than
  8 inches of rain for the same time period!! There is already a
  Moderate Risk for excessive rainfall for Thursday and Friday,
  which could be extended into next weekend.

&&

.DISCUSSION...
Issued at 318 AM CDT Mon Mar 31 2025

The main focus of this discussion will be on the severe weather
potential for mid week along with the significant flooding/flash
flooding expected for the end of the week into the weekend.

A couple days worth of quiet weather are expected as high pressure
builds and passes through the area for today and most of the day
Tuesday. This will keep dry conditions in places along with cooler
weather. Highs today will only be in the low to mid 50s before
warming to the low to mid 60s on Tuesday.

The next period of concern for severe weather and the beginning of a
protracted period of very heavy rainfall will begin late Tuesday
night. The main time period for severe weather will be Wednesday
into Wednesday evening and possibly another round on Thursday. The
heavy rain potential will begin Wednesday and linger all the way
into Sunday!!

The aformentioned high pressure system is expected to drift east of
the area by Tuesday afternoon as a surface low develops/deepens
across the central Plains. The low is then expected to deepen
further as it lifts northward into Upper Michigan by Wednesday
evening. Southerly flow is expected to increase across the area
behind the departing high and ahead of the deepening low fairly
tight isobars wide open to the Gulf. That points to very strong warm
air and moisture advection into the the lower to mid Mississippi
Valley. In fact, current trends would have dewpoints easily pushing
up into the mid 60s across the entire Quad State region through the
day Wednesday. As mentioned earlier, warm air advection will be in
full force as temperatures push up into the 80s across most of the
area by Wednesday afternoon. Not a good combo for early April!
Current thinking is that a line of thunderstorms would develop over
south central into eastern MO Wednesday afternoon, initially
starting out as supercells before congealing into a line as it
shifts east and traverses the Quad State before stalling or at least
slowing down as it cross the Mississippi River. Still some
uncertainty on exact timing and there still may be some issues with
early day convection/cloud cover.

Thermodynamics: There is a decent consensus of the models with very
steep lapse rates (around 8 C/km) expected to arrive by Wednesday
afternoon. The combination of increasing low-level
moisture/temperatures along with the steeper mid-level lapse rates,
combine to push surface based CAPE (fuel for the storms) levels up
to around 2000-3000 J/kg across nearly all of the Quad State area.
As a first look at the probabilities for surface based instability,
current guidance paints out about a 65%-90% chance of seeing
instability values greater than 1500 J/kg. DCAPE values ahead of the
line are progged to be pushing around 1000 J/kg, owing to some mid
level dry air. That would help to create colder downdrafts and
increases the damaging wind threat.

Dynamics: Aloft, a 130kt upper-level jet is expected to approach the
area during the peak heating hours Wednesday afternoon/evening as
fairly stout mid and low-level jet kick up to around 50-70kts! That
will easily provide deep-layer shear values on the order of about 50-
60kts along and ahead of the line of storms. The shear vectors look
to be orthogonal to the line of storms, which would allow for better
organization along with bowing segments as supercells congeal into a
line. Helicity values are progged to be around 300-400 m2/s2 ahead
of the line of severe storms, which is more concerning with the
upcoming event. Comparing that with this past event (Sunday
afternoon/evening), which was around 100-200 m2/s2. That would be
more supportive of tornado development and the stronger wind fields
could support some stronger tornadoes. Finally, the 0-3km shear
vectors are forecast to be around 40-50kts out of the southwest,
which would be parallel to the line of storms. That would keep the
QLCS potential in place for any segment that orients itself in a
northwest/southeast segment.

Both dynamic and thermodynamic fields continue to support a
widespread severe weather outbreak with all modes of severe weather
possible. Very large hail would be supported with the impressive
lapse rates and increased residence time with stronger shear,
especially early in the event across southeast Missouri into
southern Illinois. Any discrete cells would pose a risk for much
stronger/longer lived tornadoes, very large hail and damaging winds
as the storm develop and before the storms congeal into a line. As
the line of storms congeals/grows upscale through the evening,
expect some bowing segments to become more likely along with a some
QLCS tornadoes as the line treks east through the CWA. CIPS analogs
for this event show 5 out of the top 6 matches having several
tornado and wind reports.  Again, I know it may be a bit early for
these details and I`m sure the details will change, but it is worth
noting that some of these parameters indicate a very good severe
weather potential and definitely warrants the Enhanced Risk of
severe storms.

Heavy Rain and Significant Flooding Concerns: Outside of the severe
weather risk on Wednesday, the associated frontal boundary is
expected to become nearly stationary from west to east or
southwest/northeast across the CWA from Thursday night through at
least Saturday night, leading to a very serious risk of significant
rainfall in excess of 4 inches (100% chance) and even 8 inches or
more (70% chance)!! That would likely result in serious/significant
flooding/flash flooding for much of the Quad State. Precipitable
water values from Wednesday through Saturday are progged to be
around 2 inches through much of that time period, which is about
300% of normal. The WPC has most of the area highlighted in a slight
risk on Wednesday and a Moderate Risk of excessive rainfall on
Thursday and Friday. It is a very good possibility that the moderate
risks will be extended through Saturday night and the risk may even
be increased at some point for each of those days as placement and
totals are fine tuned. Looking at sounding climatology along
with Ensemble Return Intervals, the moisture associated with
this system for this time of year are outside of CFSR range of
values and above the maximum daily observed sounding maxima from
ILX/OHX.

This is a very serious flooding threat for a good portion of
the Quad State! Please stay tuned for updates and keep an eye
out for Flood Watches to be issued in the next few days. It is
especially important to monitor the forecasts if you live in a
flood or flash flood prone area!

&&

.AVIATION /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 558 AM CDT Mon Mar 31 2025

MVFR ceilings this morning will quickly give way to VFR
conditions through the rest of this TAF issuance. North to
northwest winds will gust to 15 kts through most of the day
before diminishing this evening.

&&

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

&&

$$

DISCUSSION...KC
AVIATION...KC