631
FXUS63 KARX 262357
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
657 PM CDT Sun May 26 2024

.KEY MESSAGES...

- Monday morning and afternoon will likely bring a round of
  showers and a few thunderstorms. While a severe thunderstorm
  cannot be completely ruled out in northeastern Iowa, the
  chance for a severe thunderstorm is very low (5%).

- Additional shower and storm chances again Tuesday before drier
  conditions return for mid-week.

&&

.DISCUSSION...
Issued at 228 PM CDT Sun May 26 2024

Immediate term rain:

19z WV satellite shows an upper trough shifting eastward over the MS
River with a broad area of moist fetch east of this feature wrapping
over N WI. Radar returns show associated precip shield shifting
eastward accordingly. After a small pocket of enhanced rain rates
affected the greater La Crosse area around noon, latest dual pol
rain rates have returned to being under a half inch per hour. Aside
from a few reports of urban ponding and a couple rivers reaching
action stage in NE IA, flooding impacts have been minimal. Given
that the best forcing is departing to the east, do not think impacts
will become greater than those already seen.

Monday storms:

Monday, potent shortwave, currently located over MT, looks to eject
southeastward to N IL, passing over the forecast area in the
process. With modest wrap-around 850mb moist advection continuing to
occur as the surface low becomes centered over MI, this should
likely (60%) set the stage for showers and a few thunderstorms,
particularly in NE IA, where cooling ahead of the shortwave looks to
be maximized. In any case, HREF probability of at least 500 J/kg of
CAPE is around 50 percent, so have included mentions of thunder in
the forecast. As for severe thunderstorms, these appear doubtful as,
in addition to questionable instability, the probability of
appreciable (30+ kts) sfc-6km bulk shear remains generally 20
percent or less, with this confined to NE IA. In any case, shallow
surface mixed layer and cold temperatures aloft suggest severe hail
rather than wind would be the favored hazard.

Monday night through the week:

Another shortwave trough is expected to dive down across the region,
keeping shower and storm chances in the forecast for Tuesday. A few
models are hinting towards some showers pushing in a bit earlier in
the day, though there still remain some differences on timing and
extent of these showers. Have some lower chances in for early
Tuesday for now with chances increasing into the afternoon, highest
east of the Mississippi River (40-60%). Showers and storms will be
on the decrease into the late evening/overnight as the shortwave
exits and surface high pressure starts to build into the region
behind it.

By early mid-week model guidance continues to highlight upper level
troughs over the Pacific Northwest and Great Lakes with an upper
level ridge building into the central U.S. Overall, this looks to
bring a short break in rain and storm chances across the local area.
However, the upper level ridge will continue to get pushed eastward
as the upper level trough moves into the region over the weekend,
bringing back shower and storm chances to the forecast. There remain
some uncertainties in timing of this precip, with noted differences
in details such as the strength of the trough among ensemble
solutions. The latest blended model guidance seems to have trended a
bit slower in bringing in precip chances Thursday night/Friday.
Still some time to monitor trends and make refinements as we move
closer in time.

Both the GEFS and ECMWF ens show some general increasing trend in
temperatures into the end of the week, with highs currently forecast
to rise into the 70s for most to end the week. However, will note
that temperature spread among ensemble solutions does begin to
increase further into the period with the aforementioned differences.

&&

.AVIATION /00Z TAFS THROUGH 00Z TUESDAY/...
Issued at 643 PM CDT Sun May 26 2024

MVFR ceilings will give way to VFR ceilings...gradually
scattering out as the area of low pressure over central WI
pulls eastward. Another upstream shortwave trough will already
bring increasing VFR ceilings Monday morning with scattered
showers developing. Increasing instability should lead to
scattered thunderstorms. For now included showers/vcts from mid
or later morning through the afternoon. North to northwest winds
becoming northwest 5 to 15kts. At this time, the greater
instability and shear for severe storms looks to reside
southwest of the TAF sites. Stronger gusts Monday afternoon at
RST.

&&

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

&&

$$

DISCUSSION...Ferguson/EMS
AVIATION...Zapotocny