-- Discussion containing changed information from previous version are highlighted. --
658
FXUS63 KARX 121804
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
104 PM CDT Wed Jun 12 2024

.KEY MESSAGES...

- Scattered strong/severe storms possible between noon and 8 PM
  today. Primary threat is damaging winds with a secondary
  threat of hail.

- Maybe a few strong to severe storms in north-central Wisconsin
  during the mid to late evening.

- Additional strong to maybe severe storms are possible on
  Saturday night.

- Near or record warm lows possible early next week. The highest
  chances at this time look to be Tuesday. Looking further out,
  CPC continues to have a slight (20-40%) risk for excessive
  heat for areas along and south of Interstate 90 from June 19
  through June 25.

&&

.MESOSCALE...
Issued at 1045 AM CDT Wed Jun 12 2024

The 15Z surface analysis shows rapid heating taking place over
northern Iowa south a secondary warm front lifting northward and
arcing from Buffalo Ridge southeast to near Waterloo, Iowa with
temperatures already in the low to mid 80s. Dewpoints to the
south of the boundary area only hovering in the low to mid-60s,
which is resulting in large inverted-V soundings and DCAPE
values of 1000-1400 J/kg. A cluster of elevated storms developed
the eastern flank of the 850-mb theta-e advection wing in
western MN early this morning, with the storm clusters
continuously outrunning the 500-1000 J/kg MUCAPE gradient and
dissipating as they tracked eastward into central and eastern
MN. However, this pool of higher 850-mb theta-e air is
progressing eastward and will move over the region by midday.

The last 30 minutes has already seen an uptick in lightning and
storm organization along the western flank of the multi-cell
cluster west of Mankato, MN, with bowing segments observed from
KMPX. The HRRR has been suggesting this morphology over its last
few runs, with this small MCS tracking along and just north of
I-90 late this morning and early this afternoon. Winds of 60-70
mph would be the main threat given the environment in place, but
hail cannot be ruled out as the 50 dBZ reflectivity heights
have been touching the 1 inch hail heights periodically this
morning and multiple 1-1.5 inch hail reports have occurred
upstream.

The organization of this upstream complex in south-central MN
is occurring a little sooner than the HRRR depicted in its
earlier runs, which may cause it to weaken sooner/farther west
than was suggested given that the MUCAPE axis is still displaced
to the west. However, this complex will present a narrow,
focused window for damaging winds with the HRRR Neural Network
progs depicting a 50% chance of winds in excess of 60 mph within
this complex in southeast Minnesota early this afternoon.

How soon this complex clears out will play an important role in
the degree of destabilization that can take place in its wake
ahead of the cold front sagging southeastward from western
Minnesota. A second round of supercells/multi-cell clusters will
work into the region along and ahead of this front after the
9pm timeframe, but the severe weather risk will hinge on how
much airmass recovery takes place late this afternoon.

&&

.DISCUSSION...
Issued at 356 AM CDT Wed Jun 12 2024

Today...

The CAMs have been gradually coming to some consensus early this
morning. They are more in agreement that scattered showers and
storms will develop north of Interstate 90 during the late
morning and early afternoon as an area of 850 mb moisture
transport moves into the region from the Central Plains.

In the CAMs where convection develop earlier in the day, the
storms are less intense than in the CAMS which develop
convection more in the mid afternoon. This is simply due to the
amount of instability that can develop ahead of storm
initiation. With the area being in the right exit region of a
60-80 knot 250 mb jet, thinking that the convection will be more
scattered. However, still cannot rule out some line segments in
clusters of storms where cold pools can coalesce. With DCAPES
climbing into the 1000 to 1500 J/kg and inverted Vs in the sub-
cloud layer, damaging winds look to have highest probabilities
(up to 25% in the HRRR neural network). In addition, with dry
air aloft, hail looks to be a secondary threat.

Tonight...

A shortwave trough will move east through the area. This will
result in an additional round of scattered showers and storms.
With CAPE values decreasing, the threat for severe storms will
be diminishing. However, there is some concern that HRRR is now
showing a line of strong to potentially severe storms moving
south into Taylor and Clark counties during the mid- to late
evening. This is likely associated with southern extent of a
shortwave moving through northern Minnesota and northern
Wisconsin. Definitely something to watch in the CAMs today.

Thursday...

Another shortwave trough will move east through the region. As
this occurs, a cold front will move south into Iowa and northern
Illinois. During the mid- to late afternoon, the right exit of
a 60 to 80 knot 250 mb jet will be moving into the region. This
will enhance the lift across the southern half of the forecast
area. At this time, it looks like the better instability and
steeper lapse rates will be just south of the forecast area.
However, there are a couple of CAMs suggest that Fayette and
Clayton counties in northeast Iowa and Grant County in southwest
Wisconsin could potentially see a few strong storms before they
move south of the area.

Fathers Day Weekend...

A 500 mb ridge will build northward and eastward though the
region. As this occurs, a warm front will lift northward into
the region. 0-1 km mixed layer CAPES will range from 1000 to
2500 J/KG south of this front. As a 30-40 knot 850 mb jet focus
moisture into the region, it continues to look like a mesoscale
convective complex will develop ahead and approaching shortwave
trough moving east out of the Northern Plains. Deep shear (0-6
km) of 25 to 35 knots in the ECMWF and 30 to 50 knots in the
GFS will be potentially found for areas along and south of
Interstate 90. With the soundings showing surface-based storms,
there could be the potential for damaging winds.

In the wake of the shortwave trough, a cold front will push
south into northern Iowa, far southern Wisconsin, and northern
Illinois on Fathers Day and then move back to the north as a
warm front on Sunday night as the upper level ridge build across
the region. The GFS continues to have much higher (2500-3500
J/kg) 0-1 km mixed-layer CAPES values than the ECMWF (1000-2000
J/kg). Unlike Saturday night, the 0-3 km and 0-6 km shear is
rather light with values generally less than 20 knots.

With a mean precipitable water value around 1.5 inches and warm
cloud layer depths climbing to around 4 km, these showers and
storms will be efficient rain producers from Saturday night into
Sunday night. If these storms train over the same region, there
could be some localized flooding.

Monday through Tuesday...

500 mb heights will be climbing across the southern Great Lakes
into the Mid-Atlantic Region. This will result in anomalous
warmth (85th percentile or higher). Record highs and warm lows
will be possible in this region. For our area, the highest
chances will be on Tuesday when some warm low temperatures along
and south of Interstate 90 could be tied or broken.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
-- Changed Discussion --
Issued at 104 PM CDT Wed Jun 12 2024

The main concern this TAF period will be with showers and
thunderstorms currently pushing into the local area. With
satellite imagery showing quite a bit of lightning with these
storms have opted to include it with the current issuance.
Increased wind gusts have also been observed and will be
possible with any stronger storms as well. Will continue to
monitor conditions in the near term and expect there may be
updates through the afternoon and evening. A second round of
showers and storms are expected to move across the area ahead of
a frontal boundary late this evening/into tonight. Some timing
adjustments may be needed with future issuances.
-- End Changed Discussion --

&&

.CLIMATE...
Issued at 224 AM CDT Wed Jun 12 2024

A strong upper level ridge will build northward into the region
for early next week. Both high and low temperatures will likely
climb into the 85th or higher from at least Monday into
Tuesday. While high temperatures (mid-80s to around 90) look to
be too low for records to be tied or broken, the low
temperatures (around 70 to the mid-70s) along and south of
Interstate 90 will be warm enough for some potential warm low
records to be tied or broken. At this time, the highest chances
look be on Tuesday.

Looking further out, CPC continues to have a slight (20-40%)
risk (20-40%) for excessive heat for areas along and south of
Interstate 90 from June 19 through June 25.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
IA...None.

&&

$$

MESOSCALE...
DISCUSSION...Boyne
AVIATION...EMS
CLIMATE...Boyne