Special Weather Statement, NWS La Crosse, WI

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

.KEY MESSAGES...

- Shower and storm chances continue this afternoon, with a
  secondary round of showers and storms expected to move across
  the area late this evening into tonight. Some storms may be
  strong to 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 1045 AM CDT Wed Jun 12 2024

The 15Z surface analysis shows rapid heating taking place over
northern Iowa south a secondary warm front lifting northward and
arcing from Buffalo Ridge southeast to near Waterloo, Iowa with
temperatures already in the low to mid 80s. Dewpoints to the
south of the boundary area only hovering in the low to mid-60s,
which is resulting in large inverted-V soundings and DCAPE
values of 1000-1400 J/kg. A cluster of elevated storms developed
the eastern flank of the 850-mb theta-e advection wing in
western MN early this morning, with the storm clusters
continuously outrunning the 500-1000 J/kg MUCAPE gradient and
dissipating as they tracked eastward into central and eastern
MN. However, this pool of higher 850-mb theta-e air is
progressing eastward and will move over the region by midday.

The last 30 minutes has already seen an uptick in lightning and
storm organization along the western flank of the multi-cell
cluster west of Mankato, MN, with bowing segments observed from
KMPX. The HRRR has been suggesting this morphology over its last
few runs, with this small MCS tracking along and just north of
I-90 late this morning and early this afternoon. Winds of 60-70
mph would be the main threat given the environment in place, but
hail cannot be ruled out as the 50 dBZ reflectivity heights
have been touching the 1 inch hail heights periodically this
morning and multiple 1-1.5 inch hail reports have occurred
upstream.

The organization of this upstream complex in south-central MN
is occurring a little sooner than the HRRR depicted in its
earlier runs, which may cause it to weaken sooner/farther west
than was suggested given that the MUCAPE axis is still displaced
to the west. However, this complex will present a narrow,
focused window for damaging winds with the HRRR Neural Network
progs depicting a 50% chance of winds in excess of 60 mph within
this complex in southeast Minnesota early this afternoon.

How soon this complex clears out will play an important role in
the degree of destabilization that can take place in its wake
ahead of the cold front sagging southeastward from western
Minnesota. A second round of supercells/multi-cell clusters will
work into the region along and ahead of this front after the
9pm timeframe, but the severe weather risk will hinge on how
much airmass recovery takes place late this afternoon.

&&

.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 /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 104 PM CDT Wed Jun 12 2024

The main concern this TAF period will be with showers and
thunderstorms currently pushing into the local area. With
satellite imagery showing quite a bit of lightning with these
storms have opted to include it with the current issuance.
Increased wind gusts have also been observed and will be
possible with any stronger storms as well. Will continue to
monitor conditions in the near term and expect there may be
updates through the afternoon and evening. A second round of
showers and storms are expected to move across the area ahead of
a frontal boundary late this evening/into tonight. Some timing
adjustments may be needed with future issuances.

&&

.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...EMS
CLIMATE...Boyne

Hazardous Weather Outlook
National Weather Service La Crosse WI
427 AM CDT Wed Jun 12 2024

IAZ008>011-018-019-029-030-MNZ079-086>088-094>096-WIZ017-029-
032>034-041>044-053>055-061-131100-
Mitchell-Howard-Winneshiek-Allamakee-Floyd-Chickasaw-Fayette-
Clayton-Wabasha-Dodge-Olmsted-Winona-Mower-Fillmore-Houston-
Taylor-Clark-Buffalo-Trempealeau-Jackson-La Crosse-Monroe-Juneau-
Adams-Vernon-Crawford-Richland-Grant-
427 AM CDT Wed Jun 12 2024

This Hazardous Weather Outlook is for portions of southeast
Minnesota...northeast Iowa and southwest into central Wisconsin.

.DAY ONE...Today and Tonight

Scattered storms will be possible from late this morning into
tonight. Some could be severe (level 2 out of 5 risk) with
damaging winds and large hail the main threats between noon and
8 PM tonight.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday

Additional scattered storms are expected for the Father's Day
weekend. Some of these storms could be strong to potentially
severe on Saturday night and Sunday afternoon and evening. The
main threats are damaging winds and large hail.

Throughout the weekend, these showers and storms will be highly
efficient rain producers. This could potentially result in some
localized flooding.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed between noon and 8 PM.

.EMERGENCY MANAGEMENT COORDINATION...

No webinar is scheduled.

Boyne

Preliminary Local Storm Report
National Weather Service La Crosse WI
148 PM CDT Wed Jun 12 2024

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0135 PM     Tstm Wnd Gst     4 N Lyle                43.56N 92.95W
06/12/2024  M40 MPH          Mower              MN   Mesonet

            Mesonet station MN144 U.s.218 - Lyle - Mp 4
            Direction was 345 degrees.

&&

db

Special Weather Statement
National Weather Service La Crosse WI
158 PM CDT Wed Jun 12 2024

IAZ008>010-018-019-029-MNZ094-095-122015-
Floyd IA-Winneshiek IA-Howard IA-Chickasaw IA-Fayette IA-Mitchell IA-
Fillmore MN-Mower MN-
158 PM CDT Wed Jun 12 2024

...GUSTY WINDS WITH STRONG THUNDERSTORMS IN NORTHEAST IOWA THROUGH
315 PM...

At 154 PM CDT, the public reported isolated fallen trees near I-35
in northern Iowa with showers and some stronger thunderstorms along
a line extending from 6 miles northeast of Le Roy to Rockford.
Movement was east at 55 mph.

HAZARD...Wind gusts up to 50 mph.

SOURCE...Public.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects.

Locations impacted include...
Decorah, Charles City, Cresco, Osage, New Hampton, West Union,
Nashua, Harmony, Calmar, Fredericksburg, Le Roy, Rockford, Ossian,
Riceville, Elgin, Clermont, Elma, Lime Springs, Hawkeye, and Lawler.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

&&

LAT...LON 4309 9302 4360 9244 4349 9161 4290 9161
      4291 9303
TIME...MOT...LOC 1857Z 265DEG 48KT 4356 9233 4306 9290

MAX HAIL SIZE...0.00 IN
MAX WIND GUST...50 MPH

Baumgardt

Preliminary Local Storm Report
National Weather Service La Crosse WI
224 PM CDT Wed Jun 12 2024

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0218 PM     Tstm Wnd Gst     2 E Elma                43.25N 92.40W
06/12/2024  E60 MPH          Howard             IA   911 Call Center

            Dispatch reports fire department had
            estimated 60 mph winds east of Elma and
            spotted a possible funnel cloud.

&&

Preliminary Local Storm Report
National Weather Service La Crosse WI
231 PM CDT Wed Jun 12 2024

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0210 PM     Tstm Wnd Gst     3 W Saratoga            43.37N 92.47W
06/12/2024  M43 MPH          Howard             IA   Mesonet

            Mesonet station SRGI4 Saratoga Direction is
            350 degrees.

&&

db

Preliminary Local Storm Report
National Weather Service La Crosse WI
255 PM CDT Wed Jun 12 2024

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0252 PM     Tstm Wnd Dmg     1 S Calmar              43.17N 91.86W
06/12/2024                   Winneshiek         IA   Trained Spotter

            A few tree limbs up to 10 inch diameter
            broken off.

&&

Special Weather Statement
National Weather Service La Crosse WI
311 PM CDT Wed Jun 12 2024

IAZ010-011-029-030-WIZ054-061-122115-
Clayton IA-Winneshiek IA-Fayette IA-Allamakee IA-Crawford WI-
Grant WI-
311 PM CDT Wed Jun 12 2024

...STRONG THUNDERSTORMS IN FAR NORTHEAST IOWA MOVING INTO SOUTHWEST
WISCONSIN THROUGH 415 PM CDT...

At 308 PM CDT, automated weather observations and trained spotters
were reporting winds gusting from 40 to 50 mph with strong
thunderstorms along a line extending from near Waukon to near
Postville to near Sumner. Movement was east at 40 mph.

HAZARD...Wind gusts of 35 to 50 mph and pea size hail. Some gusts to
         60 mph are possible.

SOURCE...Automated weather observations.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. Minor hail damage to vegetation is
         possible.

Locations impacted include...
Prairie Du Chien, Waukon, West Union, Guttenberg, Elkader, Postville,
Monona, Fayette, McGregor, Garnavillo, Elgin, Clermont, Marquette,
Harpers Ferry, Farmersburg, Volga, Hardin, Bridgeport, Seneca, and
Eastman.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

&&

LAT...LON 4327 9087 4273 9105 4275 9134 4281 9199
      4306 9171 4331 9163
TIME...MOT...LOC 2008Z 289DEG 36KT 4331 9154 4306 9164 4283 9201

MAX HAIL SIZE...0.25 IN
MAX WIND GUST...50 MPH

Baumgardt