408
FXUS63 KARX 241926
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
226 PM CDT Mon Jun 24 2024

.KEY MESSAGES...

- Showers and thunderstorms return to the forecast tonight.
  While some uncertainty remains, confidence has increased that
  at least west central Wisconsin will experience severe
  thunderstorms tonight with primarily a risk for damaging
  winds. An Enhanced Risk (level 3 of 5) for severe weather is
  present east of a Oronoco MN to Dickeyville WI axis. Flash
  flooding may also occur due to high amounts of recent
  rainfall.

- Another brief break for mid-week before additional shower and
  storm chances return late in the period. Details to be refined
  in the coming days.

&&

.DISCUSSION...
Issued at 145 PM CDT Mon Jun 24 2024

This Afternoon and Tonight: Severe Storms and Flash Flooding

19z WV satellite shows an upper trough over Lake Winnipeg with
multiple shortwave in the quasi-zonal flow aloft over ND/SD/MN.
A weak area of thunderstorms has been ongoing all day across
central and northern MN. At the surface, very rich moisture is
advecting northeastward behind a warm front, with dewpoints in
the upper 70s common in NW and N central IA with these beginning
to be seen in S central MN.

This afternoon into tonight, aforementioned rich moisture should
continue to advect northeastward, with convection developing in
central MN this evening. Progged hodographs are long with plenty
of turning in the low levels, so expect initial supercellular
development to our northwest late this afternoon. That said,
relatively straight hodographs suggest upscale growth could
occur quickly with this activity likely an MCS as it approaches
our northwestern CWA. While a strong cap should keep
thunderstorms from developing in our area ahead of this MCS, low
level jet will be on the increase, helping to erode the cap and
allowing any ongoing thunderstorms to propagate southeastward
this evening. Given the strong EML that was advected eastward
today, the probability of moist advection from the 850mb LLJ
allowing the cap to be overcome will increase from west to east
across the forecast area, thus the relatively higher risk for
thunderstorms tonight resides in our east. As for hazards, given
the strong instability, robust deep layer shear, and expected
upscale growth suggests damaging wind is the primary threat.
Additionally, progged PWAT values once again approach 2 inches
so expect around 1 to 3 inches of additional rainfall in areas
affected by the thunderstorms. Given high antecedent rainfall,
This could be enough to see some flash flooding tonight despite
expected quick duration of rainfall. Given aforementioned deep
shear, cannot rule out a severe hailstone. Finally, with sfc-3km
bulk shear vectors of 40 knots but are out of the west-
northwest, obliquely along the axis of the MCS, suggesting the
QLCS tornado risk is low unless any notable bowing segments
developed.

Remaining uncertainties surround the strength of the capping
inversion. Should this cap be weaker than expected, it is
possible a supercell or two could develop in SE MN this
afternoon before the main round of convection described above.
Should this occur, large hail would be the primary risk with
this activity and a tornado could not be ruled out. That said,
the chance this potential afternoon round occurs is low (15%).

Remainder of Forecast:

As expected, blended guidance has trended sharply downward with
PoPs for Tuesday with outflow from the overnight MCS likely
pushing the front well to our south.

After a break from active weather Tuesday through Thursday, next
upper trough approaches Thursday night, leading to a chance for
showers and thunderstorms Thursday night through Saturday.
Operational guidance and ensembles continue to show a variety of
timings with this feature. Given this and active weather in the
short term, elected to let blended guidance ride for all
elements after Tuesday with this update.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1245 PM CDT Mon Jun 24 2024

Thunderstorms will be the primary aviation concern late this evening
and overnight as guidance continues to suggest a line of strong to
severe storms progressing through the region. Uncertainty still
remains with this line in both timing and location, however if
short-range guidance does resolve (40-70% chance) would expect a
period of MVFR/IFR conditions at KLSE, perhaps KRST as well,
between 03z and 09z with the potential for very strong wind
gusts to occur. VFR conditions are generally expected behind
this line of storms aside from some indication for MVFR cigs
(20-40% chance) during the early morning hours. Winds switch
from southerly to northwesterly through the TAF period,
remaining around 5-15 kts with higher gusts possible within
thunderstorms tonight.

&&

.HYDROLOGY...
Issued at 610 AM CDT Mon Jun 24 2024

Heavy rainfall over the previous couple of days has resulted in many
area rivers and streams running high or in flood stage. Flooding
concerns will last well into the week, with the Mississippi
River also continuing to rise. Another round of showers and
thunderstorms will be possible tonight into Tuesday. Although
some details are uncertain at this time, locally heavy rainfall
may be possible. With the already saturated soils, will need to
monitor for any further potential hydro impacts as any
additional heavy rainfall could exacerbate ongoing flooding.
Please continue to reference the latest flood statements for
additional updates and details.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Flood Watch from 7 PM CDT this evening through late tonight
     for WIZ032>034-041>043-053.
MN...Flood Watch from 7 PM CDT this evening through late tonight
     for MNZ079-086>088-094>096.
IA...None.

&&

$$

DISCUSSION...Ferguson
AVIATION...Naylor
HYDROLOGY...EMS