172
FXUS63 KARX 281143
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
643 AM CDT Fri Jun 28 2024

.KEY MESSAGES...

- Periodic showers and thunderstorms will occur through tonight.
  A severe thunderstorm this afternoon and evening cannot be
  ruled out, but this appears increasingly doubtful for our
  forecast area.

- A few sprinkles possible Saturday followed by cooler, drier conditions
  Saturday night into Monday.

- More rounds of showers/storms Monday into Tuesday and again
  next Thursday and Friday. Should details come together, some
  severe storms could occur Tuesday.

&&

.DISCUSSION...
Issued at 425 AM CDT Fri Jun 28 2024

Through Tonight: Periodic Showers and Thunderstorms, Potential
Afternoon/Evening Severe

08z WV satellite shows quasi-zonal flow aloft over the upper midwest
ahead of an upper low over southern Alberta with multiple
perturbations within this flow. An area of showers with sporadic
thunder is ongoing from S MN south through IA and a squall line is
sweeping east through SD.

Today, given increasing 850mb moisture transport as the upper low
churns eastward, expect periodic showers and a few thunderstorms as
the various shortwave eject downstream. Most favorable times will be
this morning as the IA/S MN convection and potential MCV associated
with the E SD squall move eastward and again around 4 to 7 PM as a
shortwave lifts east northeast out of NE. Primary limiting factor
for thunderstorm coverage - and by extension severe
thunderstorm potential - looks to be available instability, as
insolation looks to be greatly limited by the morning round of
activity and mostly cloudy conditions that occur in the wake of
this.

Time period with a conditional risk for a severe storm looks to be 7
PM to 10 PM in mainly our far west as guidance suggests 750-1000
J/kg of MLCAPE could develop as heights aloft fall ahead of the main
upper low. That said, while the mid-levels will cool, am skeptical
enough destabilization will occur at the surface. Should sufficient
destabilization manage to be realized, with progged sfc-6km
bulk shear values of around 40 knots and some turning seen in
hodographs, a severe storm could occur. Progged DCAPE does creep
toward 1000 J/kg so damaging winds and, given potential for a
rotating updraft, hail would be the main concerns.

Saturday through Sunday Night: Potential Sprinkles, Cooler

Saturday, a few sprinkles could occur in the northeastern half of
the CWA as a robust shortwave rotates around the departing upper
trough. As a surface high builds over the Dakotas and shift to the
Great Lakes, temperatures should drop Saturday and Sunday nights,
with values in the lower 40s possible in Taylor County south to the
cranberry bogs of Monroe County.

Monday through Tuesday: Next Round of Showers, Storms

Long range guidance remains in good agreement that the next upper
trough will slowly slide eastward over the northern CONUS Monday
into Tuesday. PWATs once again approach 2" as Gulf moisture is
transported to the region via 850mb moist advection. While the
progressive nature of the system should limit flash flooding risk,
another few inches of rain could fall over these two days, keeping
rivers swollen. LREF joint CAPE/CIN/shear probabilities suggest some
chance for severe storms Tuesday, but would need opportune timing of
the main upper trough to coincide with peak heating Tuesday
afternoon, and this remains uncertain at this time.

Next Thursday through Friday: More Rain Chances

The upper wave train rolls on Thursday into Friday as guidance is
once again in pretty good agreement that the next upper trough will
advance eastward sometime during this period. While the pattern in
some guidance would suggest less optimal moist fetch will occur
compared to our last several waves - i.e. PWATs remain under 1.5" -
still a variety of exact solutions, so will need to monitor this
period in the coming days.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 639 AM CDT Fri Jun 28 2024

Light rain and stratus will lead to MVFR to IFR conditions at
LSE/RST over the next 12-18 hours. Much uncertainty surrounds
the potential for thunder, with some ongoing near RST as of
issuance time. Have attempted to time out most probable time for
thunder at each site and elected to upgrade thunder mentions
from VCTS to PROB30 groups. User should however note that
sporadic TS could occur at all sites at any time this morning
and afternoon and amendments may become necessary.

&&

.HYDROLOGY...
Issued at 425 AM CDT Fri Jun 28 2024

With three more periods of precipitation ahead - today into
tonight, Monday/Tuesday, and Thursday/Friday - area rivers will
remain swollen. Both of those first two rounds in particular
show the potential for many areas to pick up around another
1-2". Given this and the large amount of water flowing
downstream, the Mississippi River is expected remain in minor to
moderate flood through at least the next five days.

&&

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

&&

$$

DISCUSSION...Ferguson
AVIATION...Ferguson
HYDROLOGY...Ferguson