806
FXUS63 KARX 111728
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1228 PM CDT Sun Aug 11 2024

.KEY MESSAGES...

- Showers are possible (20-40% chance) south of I-90 late
  tonight into Monday, but otherwise precipitation chances are
  low through Tuesday for most areas.

- More active weather is likely later in the week, with
  shower/storm chances trending upward (40-60%) by Thursday.

- Temperatures will be fairly seasonable for mid-August for much
  of the week.

&&

.DISCUSSION...
Issued at 215 AM CDT Sun Aug 11 2024

Today-Tuesday:

Early this morning, surface high pressure extended from the
northern plains southeastward into the Ohio Valley with mostly
clear skies locally. Atmospheric moisture profiles are quite
dry, with precipitable water values in the 10-25% percentiles
relative to climo, per MPX/DVN 00Z soundings. Today should be
similar to yesterday, with scattered diurnal cumulus and
otherwise plenty of sunshine and temps a few degrees warmer than
yesterday as thermal profiles modestly warm. A very low
(10-15%) chance for shower exists across north-central
Wisconsin where mid-levels remain a bit cooler behind the
departing trough across eastern Canada. However, very shallow,
weak instability should keep the thunder threat negligible.

A shortwave trough across the northern Rockies early this morning
will approach the Upper Mississippi Valley region by Monday morning.
Instability continues to look minimal and the stronger moisture
transport and warm advection are expected to remain farther south
across the Mid-Mississippi Valley. As a result, any rain brushing
mainly northeast Iowa or southwest Wisconsin late tonight into
Monday should be light. An isolated diurnal shower/storm could
not be ruled out north of I-94 on Monday with some weak
instability forecast and soundings showing skinny CAPE profiles.

Otherwise, through Tuesday night the mid-level ridge will build
eastward with temps slowly moderating closer to seasonal norms
and rain chances low. With lighter boundary layer flow, early
morning valley fog would be possible Monday/Tuesday mornings if
skies are sufficiently clear.

Wednesday-Saturday:

As the surface ridge passes east into the Great Lakes by later
Wednesday, southerly low-level flow will increase along with a
return of a seasonably moist airmass. There has been a reasonably
consistent signal in the global ensemble suite for a more
pronounced mid-level trough to cross the region, resulting in
increased shower/storm potential, especially towards Thursday.
NBM rain chances have trended upward over the past 24 hours into
the 40-60% range, although among all EPS/GEFS/CPC members,
chances for rain at some point Wednesday night through Thursday
night are greater than 80%. Differences remain with the amplitude
and timing of this trough, limiting confidence in details, but
it seems probable that rain chances will increase as model
spread decreases over the next few days. It at least continues
to look more likely that this will be an opportunity for
meaningful rains across the region with NBM probabilities for at
least 1/2 inch of rain Thursday-Friday of 40-60%. With
predictability remaining lower with the evolution of the trough,
confidence in severe weather potential is also low.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1228 PM CDT Sun Aug 11 2024

Mid and high clouds will increase across the area late this
afternoon and evening as a shortwave moves southeast across
Iowa. These clouds will then move out of the area late tonight.

While there is a deep layer of light winds tonight, the low
level moisture remains rather shallow for KLSE. Due to this,
kept the valley fog out of the forecast.

&&

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

&&

$$

DISCUSSION...JM
AVIATION...Boyne