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213
FXUS63 KARX 171948
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
248 PM CDT Mon Jun 17 2024

.KEY MESSAGES...

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- Thunderstorms are possible this afternoon and evening with a
  risk for localized heavy rain, damaging winds, and perhaps
  quarter size hail.

- Hot and humid conditions expected Tuesday, with many locations
  seeing heat indices in the mid 90s.

- An active and wet weather pattern shaping up for mid to late
  week with repeated rounds of storms that have the potential to
  bring heavy rainfall. In particular, Tuesday night into
  Wednesday could see localized flooding.
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&&

.DISCUSSION...
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Issued at 241 PM CDT Mon Jun 17 2024

This Afternoon and Evening: Potential Strong to Severe Thunderstorms

While confidence in occurrence is decreasing, will still need to
monitor for potential severe hail and wind later this afternoon into
this evening in SE MN and along and north of I-90 in WI.

WV satellite shows a large scale upper high centered over the
central Appalachians with southwesterly flow aloft over the upper
midwest. Within this flow, multiple shortwaves are seen extending
from eastern Nebraska to the Upper Peninsula of Michigan with
multiple areas of showers and thunderstorms developing ahead of this
shortwaves along a quasi-stationary front. The opening round of
convection early this morning, taking advantage of a largely non-
worked over atmosphere, packed a bit more punch, causing sporadic
wind damage from Rochester northeastward to Taylor County WI.
Outflow from these storms has stabilized the surface throughout much
of the CWA, where additional showers associated with robust 850mb
warm advection have occurred through the late morning and early
afternoon.

This afternoon and evening, primary forecast questions remain if and
where re-development of strong to severe thunderstorms occurs.
General trend in guidance is for another round of convection to
develop this afternoon in south central Minnesota along the quasi-
stationary front as destabilization occurs as the influence of the
morning cold pool wanes and perhaps 2000 J/kg of MLCAPE builds. With
0-6 km bulk shear values near the front around 35 knots, some more
organized convection could occur with an attendant risk for large
hail and damaging winds. The main issue remains the influence of
that cold pool - the outflow boundary has pushed farther south than
short term guidance suggested so, while southerly warm advection is
ongoing as suggested by the spotty ongoing elevated showers, start
time of this second round of potential severe thunderstorms has
trended later with decreasing confidence that sufficient
destabilization for severe storms will occur. Nevertheless, with a
persistent signal for eventual development of strong to severe
convection, will need to monitor closely this afternoon and
evening.

As for flooding, should the aforementioned thunderstorms
develop, there may be localized flooding concerns, as many of
these locations saw a quick inch of rainfall this morning. That
said, given decreasing confidence in occurrence, have elected
not to issue a Flood Watch with this update.

Tuesday: Hot Temperatures

Precip potential looks to take a break for at least a bit as the
aforementioned front is forced northward. With southerly warm
advection continuing and temperatures aloft warming a bit as well,
this looks to be the warmest day of the next seven, with highs in
the upper 80s to lower 90s expected. Additionally, with surface
dewpoints favored to remain around or a bit above 70, some mid to
upper 90s heat indices may occur. That said, 17.12z HREF
probabilities suggest only a 10 percent chance of reaching a heat
index of 100 in a few spotty locations, so do not think a Heat
Advisory will be needed at this time.

Tuesday Night through Sunday: Multiple Rounds of Heavy Rain Potential

Tuesday night into Wednesday, aforementioned front returns back
southeastward as a cold front as a notable shortwave ejects
northeastward, leading to widespread showers and thunderstorms.
Robust along-boundary 850mb moisture transport will lead to PWAT
values reaching close to the 99th percentile of model climatology in
some locations, with orientation of this moisture transport also
suggesting some pockets of training thunderstorms could occur. While
the heavy rain and flooding concerns look to be mitigated by the
steady southeastward motion of the front, many locations in the
northern CWA have seen plentiful rainfall recently, suggesting some
localized flooding could occur.

Thursday through Saturday, southwesterly flow aloft will continue to
dominate proceedings. Multiple periods of showers and thunderstorms
will likely occur, with exact details focusing on the timing of
approaching shortwaves and the position of any fronts or remnant
boundaries. Given the repeated rain, additional risk for flooding
could manifest itself, particularly if any areas experience rain on
multiple occasions.

Sunday, operational guidance is in good agreement that a longwave
trough will slide eastward, hopefully ending our long period with
recurrent rainfall. Depending on the timing of this wave, could get
some severe thunderstorms, but at this time LREF joint probabilities
of sufficient instability and shear are doubtful and generally
around 10 percent or less.
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&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1246 PM CDT Mon Jun 17 2024

Showers and storms will be the main aviation concern through the
rest of the afternoon and evening. Currently, observing showers and
isolated storms pushing north with a boundary, as it pushes north
instability will push into the region allowing for storms to
potentially initiate later this afternoon. The trouble with
this is the short-range convective guidance is showing
differing solutions with how storms will manifest later this
afternoon. Consequently, deciding to hold with a VCSH group at
both TAF sites through the evening and may need to amend to
include thunder mention as needed. Otherwise, should see
improving conditions into the overnight hours with increasing
southerly winds during the day on Tuesday to around 10-20 kts
with gusts to around 30 kts, mainly in unsheltered areas of
southeast MN and northeast IA.

&&

.HYDROLOGY...
Issued at 400 AM CDT Mon Jun 17 2024

Repeated rounds of heavy rain are expected between today and the
upcoming weekend, with each round of rain increasing the risk of
flash flooding and river flooding. Much of southeast Minnesota
into western Wisconsin will likely see over 3 inches of rain by
the end of the week with a 20-30 percent chance of 4-5 inches.
River flooding concerns, especially along the Mississippi River
and its Minnesota tributaries will need to be monitored closely.
Many locations along the Mississippi River will approach flood
stage towards next weekend (50-70% chance) if rainfall unfolds
as forecast.

&&

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

&&

$$

DISCUSSION...Ferguson
AVIATION...Naylor
HYDROLOGY...Skow