922
FXUS63 KARX 050848
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
348 AM CDT Fri Jul 5 2024

.KEY MESSAGES...

- Seasonably cool today with scattered showers and storms.

- Unsettled weather continues through the weekend into early
  next week, however severe weather and additional flooding
  concerns remain low through the weekend.

&&

.DISCUSSION...
Issued at 330 AM CDT Fri Jul 5 2024

Overview:

Latest water vapor satellite imagery, 500mb heights, and lightning
showed the closed low over southern Minnesota.  The convection had
pushed off to the east with showers and a few isolated strokes of
lightning rotating around the closed low.  Rainfall reports included
0.57 at Rochester, 0.51" at La Crosse, and 0.61" here at the NWS.
Winona, Sparta, and Boscobel all reported over and inch. At 08Z,
surface low pressure extended from southeast MN into southern WI.
With the wet ground and low dewpoint depressions we had a variety of
low clouds, patchy fog, and some patchy dense fog.

Patchy morning fog then seasonably cool today with scattered
showers and storms:

The 500mb trough over the Upper Mississippi Valley slowly pushes
across Wisconsin today into the Great Lakes tonight.  A look at the
HREF probabilities show the widespread west to east area of
precipitation across the northern portion of the area of mid-level
low pressure shifts east into the U.P. this morning with the axis
becoming more tilted in a southwest to northeast area around the low
pressure system.  Farther to the southwest, the showers and
thunderstorms are more scattered.  There are hints of higher
probabilities in that axis during peak heating and especially near
and northeast of I94 in the 2-4pm timeframe.  General thunderstorms
are expected today with MLCAPE of up to 500J/kg and little shear.
That being said, did look into the non-supercell tornado parameter
with the upper low nearby.  This value was non-zero from 1 to 3
across parts of the forecast area; near EAU, and I90 around 2 or
3pm. Something to keep in mind during the day if instability
increases or there is a local boundary. The HREF shows some
30-60% 25mi neighborhood probabilities of 1"/6hr rates during
this time. Our current forecast generally has rainfall amounts
of 0.25" or less as the system exits the area, however there
could be pockets of higher amounts where the rainfall is a
little more efficient along and northeast of I94, where there
are thunderstorms, or in general where the precipitation repeats
over the same areas. Temperatures are forecast to be below
normal today generally 69 to 75, being held down by the clouds
and scattered showers/a few storms. If it breaks out more
earlier, temps could top out a little warmer with the July sun.

Unsettled weather continues through the weekend into early next
week, however severe weather and flooding concerns remain low
through the weekend:

An upstream shortwave trough over Alberta, Canada is forecast to
drop southeast Saturday toward Minnesota and continue eastward
Sunday into the Upper Mississippi Valley. Trailing trough energy
lags and deepens over the Northern Plains. This prolongs the
rainfall chance into Sunday night through Tuesday night.
Temperatures warm into the mid 70s to lower 80s Saturday with
isolated showers in the morning and scattered showers/storms in
the afternoon. MLCAPE is modest, 750 to 1500 J/kg with little
shear. The shortwave that moves through the flow Sunday appears
to have little instability to work with. The low level forcing
is a little stronger and the shear increases over parts of
central Iowa. At this time, severe weather and flooding concerns
appear low through the weekend.

With the 500mb trough still in the area Sunday night into Monday and
a surface front in the area, we will remain vulnerable to showers
and thunderstorms.  Spotty showers linger for Wednesday and Thursday
with a large 500mb ridge to the west.  Temperatures for the weekend
into mid-week remain near to below normal in the 70s to lower or mid
80s.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 945 PM CDT Thu Jul 4 2024

Main taf concerns are IFR/MVFR overnight into Friday. Surface
low spins over the region and ceilings will lower to MVFR/IFR
at both taf sites later tonight/early Friday morning. However
confidence in timing of the MVFR/IFR conditions is low. The
lower ceilings linger into the daytime Friday. At this time have
MVFR conditions prevailing at both taf sites...as low stratus
has not developed upstream underneath surface low. Then...the
question is how long MVFR/IFR conditions last at both taf sites
during the day Friday. For now have kept ceilings improving
after 18z Friday. Scattered showers will rotate around the
surface low into both the taf sites Friday. Introduced vicinity
showers at both RST/LSE taf sites.

&&

.HYDROLOGY...
Issued at 300 AM CDT Fri Jul 5 2024

Rainfall amounts were generally less than an inch across the
bulk of the forecast area, however some pockets of 1 to 2"+ did
occur. Some of these localized amounts fell over the Whitewater,
Root River, Kickapoo, Pine River, and Wisconsin River Basins,
and the Mississippi River mainstem. As a result, we are seeing
some river rises and some minor flooding on the Kickapoo and
Pine River. In addition, this widespread rain will prolong the
flooding along the Mississippi River mainstem.

Although rainfall is generally forecast to be a quarter of an
inch or less for most locations today. Some isolated locations
could pick up more. Some of our hi-res guidance shows some low
to medium probabilities of 1" in spots along and east of I94.
Locally higher amounts can occur with any storms.

Through the weekend, the additional rainfall is not expected to
increase flooding concerns.

&&

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

&&

$$

DISCUSSION...Zapotocny
AVIATION...DTJ
HYDROLOGY...Zapotocny