316
FXUS63 KARX 122000
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
300 PM CDT Sun May 12 2024

.KEY MESSAGES...

- Scattered showers/storms into the evening with rain chances
  shifting south of I-90 Monday. Gusty winds, lightning and
  small hail possible through this evening.

- Air quality alerts for MN/Parts of WI through Monday Morning.
  Extensions may be needed.

- Seasonable temps with the next better chance for widespread
  rain Wednesday night into Thursday

&&

.DISCUSSION...
Issued at 255 PM CDT Sun May 12 2024

Overview:

Showers and thunderstorms have developed this afternoon with
heating with increasing 850mb moisture and warm air/theta-e
advection. The HRRR seemed to pick up on these showers/storms
over northeast Iowa the best. We did have a gust to 50mph near
New Hampton and some small hail. The SPC had SBCAPE around
1500J/kg and very steep low level lapse rates of 9-10deg. C/km.
Downdraft CAPE was 900-1100J/kg...and inverted-v soundings favor
gusty winds. The effective shear has decreased from earlier
today over southwest WI and is generally 25kts or less.

Water vapor satellite imagery, 500mb heights, and lightning show a
trough over CO/western Plain and also over the Ontario.
Lightning was noted between the two systems from northern WI
into parts of southern MN along the cold front and the area
across northern Iowa The surface cold front at 19Z was moving
through the Twin Cities.

Scattered showers/storms into the evening with pcpn chances
shifting south of I-90 Monday (15-85% higher toward DBQ):

The storm system over the Plains does phase somewhat with the
northern stream wave, however the cold front does push through
areas north of I90, then slow down. We`ll see the scattered
showers and thunderstorms continue per the CAMs with a southern
area and an area along the cold front, generally pushing south I
90 by 03-04Z with a weakening trend there, but continuing across
parts of eastern IA and southwest WI.

Smoke/Air Quality Alerts

Smoke from wildfires in Canada continue to affect parts of the
area today. The HRRR Smoke forecast calls for the near surface
smoke/integrated smoke to continue to push south with the cold
front into southeast MN/much of central WI and into northern IA
through Noon Monday. As a result, both MN and WI have issued air
quality alerts through Monday morning. We`ll continue to
monitor conditions for extensions Monday.

Extended:

Tuesday through Wednesday we should generally be in-between weather
systems with seasonable temperatures in the 60s to lower 70s.

The next full latitude trough will move through Wednesday night into
Thursday night.  It appears to deepens as it exits the area with
increasing areal coverage of precipitation, taking the higher
rainfall amounts to the east.  Per the European/GFS/Canadian
ensembles, the probability for 0.25" for the 24hrs ending 7am
Friday is 20 to 50% with the higher probabilities toward far
southern WI. We have a better chance of seeing a wetting rain
(0.10"), 50 to 70%.

Friday should generally be dry unless the storm system slows down
and precipitation chances linger across the far southern portion of
the forecast area.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 100 PM CDT Sun May 12 2024

A cold front will move through the TAF sites late this afternoon
and evening. This front will produce scattered showers at KRST
between 12.22z and 13.01z and at KLSE between 12.23z and 13.02z.
There may be even some thunderstorms, but confidence was not
high enough to include in the forecast at this time.

In the wake of the front, wildfire smoke will move into the
area. It looks like this smoke could reduce visibilities to
MVFR.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...Air Quality Alert until noon CDT Monday for MNZ079-086>088-
     094>096.
IA...None.

&&

$$

DISCUSSION...Rieck/Zapotocny
AVIATION...Boyne