NWS-La Crosse Forecast Discussion

						FXUS63 KARX 212238
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
540 PM CDT Sat Jun 21 2025

.KEY MESSAGES...

- Dangerous heat continues through Sunday with heat indices
  reaching 100F to 105F, potentially climbing above 105F.

- New week brings persistent potential for heavy rain but low
  forecast confidence overall in amounts and locations most
  impacted. Monday through Friday warrant close monitoring for
  potential flooding impacts.

&&

.DISCUSSION...
Issued at 208 PM CDT Sat Jun 21 2025

Dangerous heat through Sunday

Well advertised heat event is unfolding this afternoon as an upper
high over the low to mid Mississippi Valley has brought very warm
temperatures aloft to the region while also bringing low level moist
advection. Additionally, 45/35 knot 850/925mb winds and sunny skies
in most locations are leading to surface winds mainly in the 15 to
25 mph and concomitant efficient mixing. Surface heating has
occurred quickly today with temperatures as of 18z are around 90
with dewpoints in the low to mid 70s, yielding heat indices in the
upper 90s. Expect these to reach the triple digits areawide over the
next few hours as insolation is maximized.

Tonight, with lee cyclogenesis occurring to our west, resulting
surface gradient should help a light breeze continue into the
nighttime hours. While mostly clear skies are expected, have leaned
temperatures upward a bit in line with the expected breeze. Record
warm lows appear to be a good bet as temperatures only fall to the
upper 70s.

Sunday, dangerous heat continues as, while the ridge starts shifting
to the east, low level moist advection refuses to yield as flow
through the column becomes south-southwestwerly. Thus, while air
temperatures may be a touch lower than today, 21.12z HREF suggests a
good chance (50-90%) for heat indices to reach or exceed 100 once
again.

Multiple rounds of heavy rain potential

Aforementioned moist advection should lead to anomalously moist
conditions with 21.00z NAEFS PWAT values near the 99.5th percentile
Monday through Wednesday. With the ridge shifting to the east,
cooler temperatures aloft should allow for deep lift to occur ahead
of numerous disturbances progged to eject downstream. That said, as
time goes on, lapse rates will moderate and best forcing for ascent
looks to increasingly focus along an E-W oriented quasi-stationary
front, introducing the potential for heavy rain to focus on the same
areas depending on how mesoscale processes shake out with respect to
exact frontal position. Given the high amount of moisture available
through the column, should heavy rain in the same location occur
during 1-2 consecutive rounds of precip, flash flooding would be a
concern. Should heavy rain occur within a basin across a few
different rounds, river flooding would easily become a concern. In
any case, 21.00z LREF mean QPF values are in the 2-3.5" range across
most of the CWA and even LREF minimums are around an inch,
suggesting getting appreciable rain at some point next week is a
near certainty.

As for severe convection, with the move toward a more moist
adiabatic profile occurring over time, focus is on Monday when
steeper lapse rates are still present, yielding MLCAPE values of
around 1500 J/kg in the presence of sfc-6km shear of 25-35 knots.
Near-surface shear profiles appear unsupportive of tornadoes but mid-
level lapse rates and aforementioned shear would support potential
for a bit of severe hail and, given modeled DCAPE of around 1000
J/kg, severe wind gusts.

&&

.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 540 PM CDT Sat Jun 21 2025

CIGS: SKC/FEW conditions through Sunday evening. Trends don't favor
an increase in clouds/cigs until Monday afternoon when a sfc front
and bits of shortwave energy bring the promise of showers/storms.

WX/vsby: no impacts through Sunday night. Next shot for shra/ts will
come Monday as a sfc front eases in from the west. This boundary is
likely to wobble across the region, in a northeast-southwest running
orientation, providing a focus for periods of shra and a few ts
through the new work week.

WINDS: relatively strong/gusty from the south will continue tonight
through Sunday night. If the winds do decouple this evening (don't
stay gusty), some threat for LLWS as RAP/HRRR have winds blowing 50+
kts by 2kft through 06z.


&&

.CLIMATE...
Issued at 238 AM CDT Sat Jun 21 2025

Daily record high and warm lows this weekend (record / forecast):

  Maximum              Warm Low
June 21
La Crosse:  	  102 (1988) / 96		74 (1943) / 77
Rochester:   	   99 (1988) / 95		72 (1943) / 76

June 22
La Crosse:  	  97 (1995) / 96		75 (1983) / 80
Rochester:   	  94 (1911) / 94        71 (1983) / 77

Warmest June Lows:

 La Crosse:  80F on June 29, 1931
 Rochester:  77F on June 26, 1943 and June 19, 1953

Warmest All-Time Low Temperatures:

 La Crosse: 81F on July 21, 1901, July 13, 1995, and July 4, 2012
 Rochester: 85F on July 3, 1911

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Heat Advisory until 9 PM CDT Sunday for WIZ017-029-032>034-
     041>044-053>055-061.
MN...Heat Advisory until 9 PM CDT Sunday for MNZ079-086>088-094>096.
IA...Heat Advisory until 9 PM CDT Sunday for IAZ008>011-018-019-029-
     030.

&&

$$

DISCUSSION...Ferguson
AVIATION.....Rieck
CLIMATE...Boyne