197
FXUS63 KARX 122339
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
639 PM CDT Mon Aug 12 2024

.KEY MESSAGES...

- Scattered showers and storms are expected north of Interstate
  94 this afternoon and evening. Better rain chances are
  expected across the entire area from Wednesday into Friday
  night.

- Temperatures will be near normal for much of the next 2 weeks.

&&

.DISCUSSION...
Issued at 1249 PM CDT Mon Aug 12 2024

This Afternoon into Evening...

Water vapor satellite imagery continue to show that a shortwave
trough will move southeast through north-central Wisconsin late
this afternoon and evening. Both the visible and infrared
satellite imagery is showing some shower development along and
in the vicinity of a surface front that extends from the western
tip of Lake Superior to Green Bay. The daytime cloud phase
distinction is even showing some cloud top ice nucleation. This
is resulting in some isolated to scattered storms. With the
congestus clouds field increasing over the the past 2 hours,
opted to increase the shower and storm chances into the 30 to 40
percent range. There is some concern that these rain chances
may be too low and not enough.

Tonight into Tuesday Night...

High pressure will build across the area tonight and remain in
control of the weather into Tuesday night. High temperatures
will range from the upper 70s to mid-80s. Low temperatures will
be in the 50s to lower 60s.

Wednesday into Friday Night...

A front will move slowly east across the forecast area. As waves
of low pressure move along this front, there will be several
rounds of showers and storms. With precipitable water values of
around 1.5 inches and warm cloud depths of 3.5 to 4 km, these
showers and storms will be highly efficient rain producers. WPC
has the area under marginal risk for excessive rain for much of
this period. CSU has a 0.05 to 0.15 probability of severe
weather south of Interstate 90 from Thursday into Thursday
night, so there is a small potential for isolated severe storms.

8-14 Day Period (August 20-26) and Beyond...

An omega ridge will likely remain west and northwest of the
area from mid to the latter portions of August. This will result
in higher probabilities for near-normal temperatures and below-
normal precipitation.

Looking further out, there are signals for a Madden Julian
Oscillation (MJO) to move east into the eastern Indian Ocean
(Phase 3) and possibly into the Maritime Continent (Phase 4).
This may result in a westerly wind burst which could reinforce
the low frequency La Nina base state across the central
equatorial Pacific. Time-lagged MJO composites would suggest
that the upper level ridge may move east across the Upper
Mississippi River Valley and into the Great Lakes and New
England in late August or early September. This could result
in an increase in the probabilities for above-normal
temperatures.

&&

.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 630 PM CDT Mon Aug 12 2024

Surface high pressure remains over the region again through tonight
with light winds and VFR conditions outside of fog chances. Dewpoint
depressions are quite large, thus we`ll need to continue to monitor
trends overnight. Forecast soundings at both RST and LSE show
very light winds through about 3km. KRST has a few mid clouds
nearby. Previous forecast had LIFR conditions at KLSE for dense valley
fog 09-14Z. Conditions appear quite favorable for river valley
fog except for the current dewpoint depressions, thus have left
the tempo group in. KRST may see IFR conditions develop,
however with lower confidence, have left out for now.

&&

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

&&

$$

DISCUSSION...Boyne
AVIATION...Zapotocny