Area Forecast Discussion
Issued by NWS Paducah, KY

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FXUS63 KPAH 141553
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
1053 AM CDT Thu Mar 14 2024

.KEY MESSAGES...

- Another warm day will give way to unsettled weather as a round
  of thunderstorms are forecasted late today into tonight.
  Conditions will be favorable for some storms to turn severe
  with large hail, damaging winds, and isolated tornadoes. 4PM
  to 1AM is when the risk will be the greatest. Localized flash
  flooding is also possible with heavy downpours.

- Conditions will be breezy today with southerly winds. Winds
  gusts between 25 to 35 mph are possible through the afternoon.

- Dry weather returns for the weekend before another cold front
  arrives Sunday night that will cause lows to fall back below
  freezing through Monday night. Temperatures quickly rebound by
  the middle of the week.

&&

.UPDATE...
Issued at 1053 AM CDT Thu Mar 14 2024

Morning convection over southern Illinois may have laid down a
bit of a thermal boundary. But cloud cover over most of the CWA
will probably act to limit how much differential heating can
occur. Will watch this zone, mainly along IL Rte 13 for some
development through early afternoon but the cloud cover is
likely helping us limit our destabilization some. 12z SGF and
local LAPS soundings show a strong inversion from EML advection
at about 850mb which may further inhibit convection through
early afternoon.

By 20-22z though the upper level jet pattern will shift in a way
to put us in fairly strong large scale ascent, the start of
which you can already see in cloud behavior over northwest
Arkansas. Coupled with additional warm advection and at least
some solar heating still expect things will be fairly unstable
(1500-2000 J/kg) by late afternoon with reasonably favorable
shear and steep mid level lapse rates supporting a hail/wind
threat with isolated tornadoes. Given the amount of ascent
forecast storm mode will probably be linear by the time it
arrives in the CWA which would confine us to more of a QLCS
tornado threat.

&&

.DISCUSSION...
Issued at 311 AM CDT Thu Mar 14 2024

A mild start to the morning as a warm front is lifting north across
central Illinois. Upstream over northwest Missouri, a MCS is
currently ongoing and will move downstream along the boundary
through this morning. A few showers or elevated thunderstorms with
MUCAPE over 1000 J/kg is possible along the I-64 corridor due to
frontogenetical forcing. Otherwise, the bulk of the convection is
expected to remain northwest as much of the FA will remain dry into
the afternoon as southerly winds prevail in the warm sector.
RAP/HRRR model soundings both show a EML setting up with a cap
around 850-800 mb as the synoptic flow aloft becomes highly
amplified with a 500 mb rex block setting up over southern
California. This allows for 700-500 mb lapse rates to steepen to 8.0-
8.5 C/km. As an influx of deep layer moisture causes dewpoints to
surge into the mid-60s, pockets of MLCAPE upwards 2000-2500 J/kg
develop as diurnal heating occurs causing maxTs to rise into the mid
to upper 70s.

By late Thursday afternoon, modest upper-level divergence will begin
to favor synoptic scale forcing for ascent beneath the right
entrance region of a 60-80 kt 500 mb jet max over AR/MO as the 0z
CAMs show convective initiation by 21-23z ahead of a cold front.
Initially, isolated discrete supercells with all hazards are
possible across our western counties in the CWA before convection
grows upscale into an MCS in southeast Missouri and southern
Illinois. A line/cluster of storms with bowing segments then
propagates southeast into western Kentucky and southwest Indiana
through 04-06z with damaging winds and isolated tornadoes being the
main concern. One forecast question that remains is the northern
extent as this will be contingent on where residual outflow
boundaries setup from this mornings MCS. Overall, there is higher
confidence in the potential for severe weather as convection will
now be developing during peak diurnal heating. For this reason, the
SPC has maintained a slight risk across most of the CWA in their D1
outlook with an enhance risk now clipping our far western SEMO
counties where the probability of seeing severe storms remains the
greatest.

There is certainly a long list of parameters that favor severe
weather as a low WBZ around 725 mb combined with sfc-6km shear of 40-
50 kts will support the potential for some large hail. Meanwhile,
DCAPE between 900-1100 J/kg combined with a sfc-3km max theta-e
difference of 20K will support damaging winds with downburst. As for
the tornado potential, sfc-1 km SRH values of 100-150 m^2/s^2, sfc-1
km shear of 20 kts, and 3CAPE between 40-60 J/kg will support a few
isolated tornadoes with low LCLs around 950 mb. Although the shear
is still not super robust, some of the CAMs now try to develop a
weak meso low over Missouri that would enhance the wind field with
backing at the sfc. The only other real uncertainty that remains
despite the favorable thermodynamics is how quickly the cap erodes
as the RAP is a bit more stout with the EML compared to the HRRR
which could delay the severe risk initially. One thing that is clear
is the instability quickly wanes by 06z Friday, so any convection
that is still ongoing by this point should transition more into a
heavy rain concern as fropa lags into Friday morning.

As for the flooding potential, models still show PWATs around 1.5
inches that will help to enhance rainfall rates. Due to the
potential for seeing multiple rounds of convection, a localized
flash flooding risk may persist into early Friday morning. The 0z
HREF PMM shows a sharp gradient setting up across southeast Missouri
and western Kentucky with 1-2 inches of QPF while locally 2-4
inches remains more south across the TN/AR borders where the risk
for flooding issues will be the greatest. Meanwhile, further north
across the rest of the FA, QPF amounts are significantly lower
between a quarter to half of an inch where there is more
uncertainty in the evolution of convection.

By Friday afternoon, the aformentioned cold front will have cleared
the FA with the main focus being the arrival of an arctic cold front
Sunday night as a 500 mb trough digs over the Ohio Valley. MinTs
Sunday night and Monday night are likely to fall below freezing in
most of the region as a 1030 mb sfc high pressure builds south of
Manitoba Canada providing tranquil and dry weather through the
middle of the week. Temps do quickly rebound by Wednesday as
unseasonably cold temperatures 10 degrees below normal will be short
lived.

&&

.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 537 AM CDT Thu Mar 14 2024

The main concern in the near term is a cluster of TSRA west of
St Louis that could clip terminals KMVN/KEVV between 12-17z. A
severe storm is not ruled out with hail and wind being the main
concern. Otherwise, MVFR cigs will spread across western
terminals later this morning into the afternoon before lifting
to MVFR as a cold front begins to approach from the west. Have
included PROB30s for a line of strong to severe storms this
evening into tonight when brief vsby and cig reductions will be
possible. Southerly winds between 10-15 kts with gusts 20-25 kts
are expected through this afternoon before diminishing to 5-10
kts tonight.

&&

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

&&

$$

UPDATE...JGG
DISCUSSION...DW
AVIATION...DW


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