817
FXUS63 KARX 041714
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1214 PM CDT Tue Jun 4 2024

.KEY MESSAGES...

- Two rounds of showers and storms are expected today -
  scattered storms this afternoon favoring the eastern two
  thirds of the area and more extensive storms sweeping west to
  east across the entire area this evening. The primary concern
  with these storms will be the potential for locally heavy
  rainfall and flooding. Additionally, a severe storm or two
  could occur, primarily with the evening round as the storms
  traverse southeast Minnesota and northeast Iowa.

- Below normal temperatures with diurnal potential for showers
  are expected for the remainder of the forecast period.
  Additionally, gusty winds appear probable Wednesday and
  Thursday afternoon, particularly in southeast Minnesota and
  northeast Iowa.

&&

.DISCUSSION...
Issued at 359 AM CDT Tue Jun 4 2024

* TODAY AND TONIGHT: Showers and thunderstorms, heavy rain and
  severe potential

08z WV satellite reveals a robust upper disturbance over Kansas City
embedded within a broad area of southwesterly flow ahead of a
longwave trough located over the Rockies. At the surface, broad area
of low pressure is present from the Canadian Prairies south to SD
with an associated cold front beginning to shift eastward through
the Dakotas.

Today, southerly low level flow looks to increase as the longwave
trough and the associated surface low shift eastward, strengthening
the surface pressure gradient across the CWA. As a result, moisture
will be on the increase once again, with PWAT values approaching
1.5"-1.75", near the high end of climatology for DVN RAOBs. As this
occurs, the Kansas City shortwave will approach from the southwest
this afternoon. Should sufficient destabilization occur, expect
convection to develop as temperatures aloft cool ahead of this wave.
Guidance suggest that around 750-1000 J/kg of MLCAPE will be
present, so could get a couple strong storms with this activity.
That said, progged 0-6km shear is an anemic 10-15 knots, so am not
expecting severe storms with this round of convection. Given the
anomalously moist airmass, main concern would be heavy rain and
flooding potential, particularly if any areas of NE IA and SW WI
that saw heavy rain yesterday are impacted once again.

Moving ahead to this evening, as the lead disturbance departs,
expect a short respite as subtle subsidence occurs. As the main
upper trough and its associated cold front arrive from the west,
widespread convection should occur as temperatures aloft cool ahead
of main trough and plenty of convergence occurs along the front.
With MLCAPE remaining around 750-1000 J/kg, best shot for a severe
storm would be in our far west as shear values do become marginally
supportive of organized convection. That said, weak mid-level lapse
rates, shallow boundary mixed layers, and winds through the column
of 35 knots or less all suggest only a stray severe gust or hail
report would occur. Once again, main risk would be locally heavy
rainfall and flooding, with the saving grace being the quick motion
of the front and relatively short duration of rainfall.

* WEDNESDAY THROUGH MONDAY: Diurnal showers, breezy winds

Wednesday through Monday feature mainly northwesterly flow aloft as
an upper low remains in place to our northeast. Resulting cool
temperatures aloft should lead to diurnal showers most afternoons
when insolation is maximized. Gusty winds may develop Wednesday and
Thursday afternoon as winds of 30-60 knots look to be present in the
mid-levels - indeed NBM probabilities for a 45 mph gust at Rochester
are near 50 percent for Thursday. Have attempted to raise winds
above blended guidance, especially considering their known low bias
on windier days.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1214 PM CDT Tue Jun 4 2024

General VFR conditions prevail at moment but trends next 12 hours
will focus on where convection is. Convective disturbance rotating
across eastern Iowa will help new, scattered convection form this
afternoon. But as cold front approaches from the west going into
this evening, will be watching for more of a solid line of storms
move in from the west with likely /70%/ periods of MVFR conditions
and even a chance /30-40%/ of brief IFR as main line of storms pass.

The good news this should be relatively short-lived with strong
subsidence behind main trough passage and clearing skies, at least
for Wednesday morning.

&&

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

&&

$$

DISCUSSION...Ferguson
AVIATION...Shea