379
FXUS63 KARX 122329
AFDARX

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

.KEY MESSAGES...

- Shower and storm risk continues through the afternoon, with a
  secondary round of storms expected to move across the area
  tonight. Some storms tonight may be severe with the primary
  threat strong winds and secondary threat hail.

- Additional chances for showers and storms spot the forecast tomorrow
  and then again over the weekend into early next week.

- Above normal temperatures for early next week with highs
  currently forecast into the mid 80s to potentially low 90s.

&&

.MESOSCALE...
Issued at 310 PM CDT Wed Jun 12 2024

An MCS took shape across south-central Minnesota around midday
and has progressed along the MN/IA border and as of 3pm was
located along a line from Fayette to Winona county. Outflow from
earlier convection has been undercutting this complex from
north to south over the course of the last few hours, limiting
the wind threat to the southern apex of the complex along a line
from Mitchell to Winneshiek counties. The complex as a whole
should weaken as it progresses east of the Mississippi River,
but with DCAPE values of 1000-1400 J/kg ahead of the line,
cannot rule out wind issues throughout the lifespan of the event
as it moves eastward through Grant County.

Attention then turns upstream to the cold front that initiates
convection over northern and western Minnesota later this
afternoon. The CAMSs have failed to adequately handle the
strength of the cold pool in our area from the earlier
convection both from a temperature and convective morphology
standpoint. This does not lend much confidence for how storms
will evolve once they reach this modified airmass this evening.
Overall, the severe threat with the second line looks to be on
par with what is transpiring this afternoon with hail and wind
being the main threats.

&&

.DISCUSSION...
Issued at 150 PM CDT Wed Jun 12 2024

Thursday and Friday:

An upper level shortwave trough is forecast to track north of the
area into the Great Lakes area, with an associated 60-90 kt mid-
level jet moving eastward across the region. At the surface the cold
front will continue to sag down through the area and eventually
south of the local area. Hi-res model guidance shows a line of
showers and perhaps storms developing and moving down across the
forecast area through the day on Thursday. Instability looks to
build south of the front locally across our southern counties in the
afternoon, but continues to get shunted southward. There still
remain some differences in hi-res guidance on the location of storm
development with some showing storms on our southern border and
others south of our local area. For now, SPC has our southern tier
of northeast Iowa and southwest Wisconsin counties in a Marginal
Risk (1 out of 5) for severe weather.

Otherwise, surface high pressure builds across the region for
Friday, with drier conditions and highs forecast in the mid 70s to
lower 80s across the area.

Weekend & Beyond: Additional Shower and Storm Chances

Upper level ridging will continue to build eastward as we head into
the weekend. Model guidance shows a couple shortwave troughs lifting
northeastward, riding on the backside of the ridge. Moisture will be
on the increase with models showing PWATs pushing 1.5+ inches. At
the surface a frontal boundary will be lifting up towards the region
with an axis of instability (~1000 - 2500+ J/kg) building south of
the front. This looks to bring our next chances for showers and
storms across the region, with the current forecast increasing
chances Saturday afternoon and into Saturday night. There still
appear to be some model differences on shower and storm chances
Sunday, with some dependency likely on how convection on
Saturday plays out. Ensembles suggest quite a bit of instability
builds back in Sunday, though current deterministic GFS model
forecast soundings do show capping in place for much of the day
along with weaker shear values.

Overall, will continue to monitor trends in the coming days to
determine the severe weather risk. Otherwise, as was previously
mentioned moisture conditions suggest that locally heavy rainfall
could be a concern for the weekend, especially if storms train over
the same areas. Of note, parts of the forecast area are highlighted
in the Excessive Rainfall Outlook for this time period.

Beyond the weekend, upper level ridging will continue to build
across the eastern U.S. resulting in southwesterly flow over the
local region. There is still plenty to work out in the details with
the potential for various disturbances to move through the flow. The
resulting extended forecast keeps broad precipitation chances (~20-
50%) in across the forecast area for the early part of the week.
However, with a moist and unstable environment in place across the
region, this will be another time to watch for potential strong to
severe thunderstorms. Keep up to date as details are refined in the
coming days.

Early Next Week: Above Normal Temperatures

Another point of interest revolves around increased (above normal)
high/low temperatures across the region. There are still some
differences between the ensemble solutions on just how warm, but
current guidance supports temperatures in the mid 80s to potentially
lower 90s. As a result, the current forecast would suggest that heat
index values could rise into the low 90s for some through the
period.

&&

.AVIATION /00Z TAFS THROUGH 00Z FRIDAY/...
Issued at 626 PM CDT Wed Jun 12 2024

Primary aviation concern over the next 24 hours is the
likelihood for thunderstorms at LSE/RST this evening. At this
time, thunder appears likely at each site, so have continued to
keep a few hours of prevailing TS at each site along with
associated MVFR ceilings. Following the thunder, some valley fog
could affect LSE due to near surface moisture from rainfall and
decreasing winds. At this time, low confidence has precluded
including any mention in the TAF with this update.

&&

.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...Skow
DISCUSSION...EMS
AVIATION...Ferguson
CLIMATE...Boyne