439
FXUS63 KARX 151905
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
205 PM CDT Sat Jun 15 2024

.KEY MESSAGES...

- Storms tonight into Sunday. A few strong to severe storms
  possible tonight into early Sunday and north of I-90 Sunday
  night. Heavy rain will also accompany the storms.

- Highest shower/storm chances shift farther northwest late
  Sunday through early next week then increase with a cold front
  Tuesday night.

- Hot and humid Sunday through Tuesday. The rain from tonight
  may hold temperatures down somewhat. 70-95% probability of
  temperatures above 90 degrees Sunday for most areas.

&&

.DISCUSSION...
Issued at 205 PM CDT Sat Jun 15 2024

Today through Tuesday: Heat and Storms

The next few days will bring periods of shortwave troughs into the
area providing the area with increased chances of precipitation.
Strong instability and humid conditions are expected each day.
Starting with today, there continues to be an area of showers
passing through. These showers will push off to the northeast during
the afternoon. There will be a slight break in the action this
evening before the next round of precipitation starts up tonight.
Looking ahead to tonight, a warm front will lift north this evening
ahead of the rain. Strong moisture transport and a strong low level
jet, 40 to 50kts, will help to increase instability and PWATs across
the area. PWATS are expected to be near 2" and MUCAPE mostly between
1500 and 2000J/kg during the overnight. As the night progresses,
both PWAT and MUCAPE will continue to increase. The greatest severe
weather threat will be with these storms as they enter a more
unstable airmass. Hail looks to be the main threat with the early to
mid morning storms. With these high values and moisture transport,
there will be a potential for heavy rain to occur. Current forecast
has between 0.75" and 1.75" with the higher totals in western
portions of the local area and lower totals in southwest Wisconsin.

Heading into Sunday, a ridge will strengthen over the eastern CONUS.
As this ridge strengthens, strong southwesterly flow will be in
place through early next week. This will allow for strong
instability and humid conditions over the local area. With our area
being on the western fringes of the ridge, cold and warm fronts will
pass through each day. On Sunday, a cold front will enter the region
from the northwest and bring the next chance of thunderstorms with
it. There are still some uncertainties with exactly where this
boundary will set up. Some models have it further northwest while
the NAM has it centered over our area. Where this boundary sets up
will be where storms fire up. This region will already have the
available moisture and instability to support storms, all it
needs is some shear to work with to maintain the storms. Even
though the cold front itself will have some shear, most of the
shear will remain off to the northwest where the jet stream is
stronger and there are stronger winds aloft. With this in mind,
SPC has given a slight risk (level 2 of 5) for severe weather
for eastern Minnesota and portions of western Wisconsin.

By Monday, the cold front that moved through, stalls out along I-90
through the morning. This will allow for continued chances of
precipitation from the overnight period, to linger on through the
morning. Eventually the warm air overcomes this boundary and pushes
a warm front northward. The highest chances for severe weather and
thunderstorms are expected to be where this boundary is as well as a
surface low situated over the northern Plains. For Tuesday, most of
the local area will be dry through the afternoon, before a cold
front pushes through the area late Tuesday evening into the
overnight period. This boundary will help to bring rain through the
overnight into Wednesday.

The severe weather potential remains low as even though there is
ample instability and moisture, shear is quite low. There could be
some mesoscale processes that help to amplify this severe potential,
however the overall potential looks to be low. Something that
is more consistent with guidance is the chance for heavy rain to
occur. Periods of high moisture transport across the Upper
Midwest remain through the week. Current guidance has between
1" and 2" for most places around the local area with potential
for higher amounts. Something to note is that this pattern we
are in continues to change each day, an example would be that
Monday continues to trend drier and so total precipitation
through the time period is lower than what it was with previous
model runs.

In addition to the rain, temperatures will be quite warm early next
week. Ensemble and deterministic guidance continues to show
strong southwest flow over the area, helping to increase
temperatures. Current NBM probabilities have a high chance,
between 70% and 95%, of most of the local area having 90F+
degrees occurring on Sunday and Monday. With these temperatures
and heat indices approaching 100F, a heat advisory may be needed
either Sunday or Monday. The chances lower for Tuesday, but
there is still a decent signal for temperatures to be in the
upper 80s to near 90F.

Wednesday through the Weekend: More Rain Chances?

As the rest of the week unfolds, the ridge begins to flatten out.
Multiple shortwaves look to move through the region and the
temperatures will cool slightly into the upper 70s to mid 80s. Rain
chances will continue to be with us, as will the potential for heavy
rainfall. This trend is different from yesterday, as the ridge was
forecasted to shift westward and then break apart the following
week. This would have meant warmer temperatures and a decrease in
precipitation chances into the weekend. With the current ensemble
and deterministic guidance, the pattern looks to remain active
through the weekend. We will continue to monitor trends in the
potential for heavy rainfall and severe weather.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1154 AM CDT Sat Jun 15 2024

VFR conditions are expected this afternoon with mid-level
ceilings and areas of mainly light showers. More widespread
showers and thunderstorms will spread across the region late
this evening through early Sunday morning, with a period of
MVFR/IFR conditions possible within storms and in the post-
storm saturated air, before skies clear during the morning on
Sunday. A period of LLWS could occur this evening as a low-level
jet increases, especially at KLSE, with gusty south/southwest
winds into Sunday, particularly at KRST.
 &&

.HYDROLOGY...
Issued at 345 AM CDT Fri Jun 14 2024

At this time, it appears the local area can take the rainfall
amounts expected through tonight. That being said, due to the
higher rainfall potential over local areas, flood
advisories/warnings could occur with repeated storms over the
same area. The FFG of 2 to 3 inches for tonight would likely
decrease after the rain tonight, so will need to assess for the
multiple rounds of rainfall next week. Through Wednesday night,
a large portion of MN could see 3-4"+ of rainfall. This would
likely keep the Mississippi River elevated for the next couple
of weeks. There is a 30% chance that the Mississippi River
reaches Minor Flood Stage over the next 10 days through Winona
(and 40% chance at Wabasha).

&&

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

&&

$$

DISCUSSION...Cecava
AVIATION...JM
HYDROLOGY...Zapotocny