447
FXUS63 KARX 051955
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
255 PM CDT Wed Jun 5 2024

.KEY MESSAGES...

- Scattered showers and thunderstorms through early evening.
  Strong to marginally severe storms (5% probability) with hail
  and gusty winds may accompany the stronger storms.

- Gusty winds also possible in general through early evening
  ahead of the cold front. A wind advisory remains in effect for
  parts of southeast Minnesota and northeast Iowa through 7pm.

- More showers hit and miss showers Thursday with more clouds,
  breezy northwest winds, and below normal temperatures.

.DISCUSSION...
Issued at 150 PM CDT Wed Jun 5 2024

Overview:

Water vapor satellite imagery, 500mb heights, and lightning showed
an area of closed low pressure over Saskatchewan and Manitoba with
the troughing extending southward through the Mississippi Valley and
the Southern Plains.  An MCS has pushed well to he south into TX and
storms pushed into Indiana. Clearing was occurring over the
local area in the wake of the rainfall overnight. Rainfall
amounts were quite variable with from less than a tenth of an
inch to as much as an inch or two. Some radar estimates were
higher across parts of Buffalo Co. Upstream, additional showers
were noted across South Dakota into Minnesota with warm
advection ahead of a cold front. Visible satellite imagery
showed cumulus increasing and north to south transverse waves
reflective of the seasonably strong 110-135kt jet nosing into
the region. The latest WSR-88D radar image showed a band of
light rain and sprinkles moving toward the forecast area across
southern Minnesota and additional showers and storms across
northern Minnesota with a new storm forming just to our west in
Goodhue Co. The most recent SPC mesoanalysis page had SBCAPE
around 500-1000J/kg across MN. Effective bulk shear was around
50kts. Where the storms were up north, some pea sized hail had
been reported.

Storms and gusty winds through early evening:

A shortwave trough moving through the larger scale trough across
Minnesota through early evening will drive a cold front through the
region.  Temperatures will warm into the 70s to around 80 this
afternoon.  Depending on the model, MLCAPE increases 250-750 J/kg
(HRRR/RAP) or 1000-2000 J/kg (NAM) along the front and then a second
area of instability during the evening. Convective temperatures are
in the upper 70s. Deep layer shear increases 40 to 70kts and
forecast soundings show effective shear of around 40 to 45kts. Steep
low and mid level lapse rates (inverted v soundings), some
instability, favorable wind shear, and the left exit region of the
jet is forecast to be over the area.  As a result, scattered showers
and thunderstorms, some strong to severe will be possible with hail
and gusty winds. The precipitation should generally decrease in
coverage by 02-03Z, however some showers/an isolated storm may
linger through the evening with some reinforcing cooler air.  The
05/12Z HREF is generally on the light side for precipitation; 0.10"
or less, however the Max 6-hr QPF shows some potential where a storm
could drop 0.25 to .50".

A belt of stronger winds aloft 25 to 45kts at 900mb is forecast
to rotate through southern Minnesota and western Iowa. Some of
these winds are forecast to mix down outside of showers and
storms, and with the showers and storms, wind gusts could be
enhanced. Westerly wind gusts have been 20 to 35kts and we`ll
continue to see conditions for mixing increase, thus have left
the wind advisory in place.

More showers hit and miss showers Thursday with more clouds, below
normal temperatures and continue breezy northwest winds:

We remain under northwest flow aloft through Thursday with continued
cold air advection.  As a result, forecast soundings show the pop-up
showers could develop with convective temperatures in the mid to
upper 60s. Moisture appears limited, however low level mixing could
see winds gusting 20 to 30kts and temperatures topping out in the
60s to lower 70s.  Several of the hi-res models are hint at these
sprinkles and showers.

The extended:

Cyclonic flow aloft will persist through the upcoming weekend as a
broad upper low wobbles just north of the Great Lakes. This will
keep our temperatures near to slightly below normal and also provide
continued diurnally-driven chances for convection. Heading into
Friday night and Saturday, a sheared-out shortwave will be carried
through the area in northwest flow, serving as the focus for
scattered convection. This feature will be accompanied by a brief
push of modest moisture transport from the south and west, leading
to a bump in precipitable water and MUCAPE (up to a few hundred
J/kg). Not enough for any significant activity, but sufficient for
scattered showers and perhaps a few rumbles of thunder.

Another shortwave rotating around the upper low on Sunday will bring
one more round of diurnal showers and possibly a storm before the
system finally departs. Upper level ridging then starts to build
into the region Monday into the middle of next week, setting the
stage for a warming trend. GEFS, Canadian, and European ensembles
are all in good agreement for 850mb temperatures to climb into the
10-15C range, and possibly higher through the latter half of next
week, which aligns with CPC`s 8-14 day outlook calling for warmer
than normal conditions.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 1255 PM CDT Wed Jun 5 2024

Clear skies will give way to increasing clouds as scattered showers
and thunderstorms develop this afternoon into the early
evening. VFR ceilings fl050-150 are expected. Low confidence in
the coverage of thunderstorms. Due to their spotty nature,
included a VCTS at KLSE, but will need to watch KRST. West winds
15 to 30kts into early evening, but should see some stronger
gusts 30 to 40kts near showers and storms. The winds should
decrease this evening, but increase again Thursday from the
northwest.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...Wind Advisory until 7 PM CDT this evening for MNZ086-087-094-
     095.
IA...Wind Advisory until 7 PM CDT this evening for IAZ008-009-018-
     019.

&&

$$

DISCUSSION...Kurz/Zapotocny
AVIATION...Zapotocny