681
FXUS63 KARX 272344
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
644 PM CDT Mon May 27 2024

.KEY MESSAGES...

- Showers and thunderstorms are expected this afternoon, particularly
  in southeastern Minnesota and northeastern Iowa. A few storms
  may become strong, bringing small hail and strong wind gusts.
  Funnel clouds may also occur with a very low (<2%) chance for
  a brief tornado.

- Tuesday brings another round of potential showers and
  thunderstorms. Strong to severe thunderstorms are not expected
  at this time.

- Drier conditions return by midweek with increasing
  temperatures heading into the weekend.

&&

.DISCUSSION...
Issued at 130 PM CDT Mon May 27 2024

This afternoon thunderstorms:

18z WV satellite shows an upper low churning eastward over MN with
two areas of interest within this flow - a lead shortwave located
over Rochester and the main wave itself located farther west over
New Ulm. The lead shortwave kicked off an axis of light showers in
SE MN and NE IA this morning which have slowly shifted eastward. As
the afternoon goes on, cooling aloft with the main shortwave should,
in conjunction with surface heating, lead to the development of
another round of showers and thunderstorms. Main source of
uncertainty remains the influence of the lead wave with subtle
descent on the back side of this feature and restrained insolation
due to mostly cloudy conditions may delay thunderstorm development.
However, most CAM guidance, including those that assimilate recent
radar data, does continue to suggest sufficient destabilization will
occur, so will continue to be aggressive with PoPs this afternoon.
Progged soundings suggest around 500-1000 J/kg of MLCAPE will be
present so the strongest updrafts could pose a risk for strong wind
gusts and small hail. Deep shear remains anemic, with the
probability for more than 30 knots of sfc-6km shear being present
generally less than 50 percent with this largely confined to NE IA.
Therefore, think the overall chance for severe thunderstorms is low
(5%). However, given the approaching upper low and low level
stretching possible in areas that destabilize, non-supercell tornado
composite has begun to increase. Thus, cannot rule out some stray
funnels along outflow boundaries, particularly in NE IA and NE
MN, and have issued an SPS along these lines.

Tuesday showers and thunderstorms:

Tuesday, yet another wave, currently located over Lake Winnipeg,
looks to approach from the northwest during the morning. Given the
arrival of this wave before peak heating, expect less instability to
work with, leading to more sparse coverage of showers and
thunderstorms and an even lower chance for a severe storm compared
to Monday.

Tuesday Night through Early Next Week:

To start the period the overall pattern looks to feature an upper
level ridge building eastward from the Northern Plains into the
Upper Mississippi Valley, with upper level troughs across the
Northeastern U.S. and Northern Rockies. This will bring drier
conditions resulting in a nice break from rain and storm chances for
the area midweek. However, precipitation chances make a return to
the forecast as this pattern shifts eastward and moisture returns to
the region towards the end of the week. Some slight variability in
details, especially arrival/timing of these showers and storms, is
still noted between individual ensemble solutions. Overall though,
various shortwaves expected to move through the region will keep
precipitation chances mentioned through the weekend.

Highs in the upper 60s to 70s start the period. Though, there
continues to be some hint in model guidance for a slight increasing
trend in temperatures for the weekend and even into early next week.

&&

.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 640 PM CDT Monday May 27 2024

Thunderstorms have fizzled out with waning instability, but
scattered showers will persist through 02 to 03Z and are likely
to still impact the TAF sites until then (especially RST). Later
tonight, the main aviation forecast concern revolves around
potential for MVFR ceilings. Trends seem to be favoring the
potential, but it is not yet for certain. If low stratus does
pan out, there are also questions around its onset and end
times, but impacts generally look to be roughly within the 09 to
17Z Tuesday timeframe. Will monitor trends for 06Z set of TAFs.

Another pronounced shortwave will drop through the region late
Tuesday morning through the afternoon, bringing more shower and
thunderstorm chances. Being so many hours out, have just gone
with VCSH at RST and VCTS at LSE for now, as LSE has a higher
chance of thunderstorms.

NW winds through the period, becoming a tad gusty Tuesday
afternoon.

&&

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

&&

$$

DISCUSSION...Ferguson/EMS
AVIATION...Kurz