140
FXUS63 KARX 131733
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1233 PM CDT Tue Aug 13 2024

.KEY MESSAGES...

- Widespread showers/storms likely later Wednesday into Thursday
  with locally heavy rainfall possible. This looks to be the
  highest chance for rain over the next week with medium (40-70%)
  chances for at least 1 inch.

- Seasonable temps generally expected over the next week.

&&

.DISCUSSION...
Issued at 303 AM CDT Tue Aug 13 2024

Today-tonight:

With light winds under the surface ridge, some fog has been
developing early this morning. Expect fog in typical
valley/low-lying areas with guidance also favoring parts of
northeast Iowa and southeast Minnesota. The fog should lift by
mid-morning.

Otherwise, high pressure will continue to drift across the
Upper Midwest today as mid-level ridging works eastward from the
plains. Temps will continue a slow upward trend from the past
few days with highs in the upper 70s to mid 80s. Like the past
few days, an isolated shower/storm could form (10-25% chance)
within a diurnal cumulus field across central Wisconsin where
modest instability and cooler mid-level temps are expected.
Otherwise, the ridge axis will slide east overnight tonight, but
wind fields look to remain light enough to support early
morning fog development in valleys and perhaps parts of central
Wisconsin, but this will depend on timing/thickness of high
level clouds increasing from the west.

Wednesday-Friday:

The highest chances for impactful rainfall over at least the next
week remain on track for later Wednesday into Thursday as a broad
upper level trough gradually organizes from the plains eastward
toward the Great Lakes. As surface ridging pulls east on
Wednesday, an increasing low-level jet will support strong
northward moisture transport with precipitable water values
increasing to near 2" in spots, 175% of normal or higher.
Widespread showers/storms should spread east later Wednesday
into Thursday in conjunction with strong mid-level warm
advection. The high moisture content and deep warm cloud depths
will promote efficient rain production. NBM probabilities for at
least an inch of rain have increased to 40-70% with lower
(20-40%) probabilities for 2". However, the caveat at this time
of year is that rainfall amounts likely will be quite variable
given the convective mode. There are also notable differences
among ensembles, with the majority of EPS members showing a
wetter solution compared with the GEFS.

With the somewhat disjointed nature of the larger trough, deep
layer wind fields are modest and the probabilities for at least
1000 J/kg of SBCAPE drop off considerably northward across
southwest Wisconsin and northern Iowa towards I-90. These,
combined with remaining uncertainty in the evolution of the
trough/surface features limit confidence in severe storms, but
stronger storms cannot be ruled out on Thursday.

Showers/storms remain possible into Friday within cyclonic flow
beneath the upper level trough, but the risk of heavier rains
will mostly be focused late Wednesday into Thursday.

Saturday-Monday:

For the weekend into next week, upper level ridging is forecast to
strengthen across the Rockies into the plain with troughs centered
across the Pacific Northwest and over the eastern Great Lakes. While
this general pattern is supported broadly across global ensembles,
differences exist in the amplitude and degree of progression of
these synoptic features. Regardless of these differences, a
northwest flow pattern is likely across the Upper Midwest this
weekend into next week with generally near to below average temps
favored. Overall, relatively dry conditions are expected through
this period, but some shower potential could linger into the weekend
until the trough pulls east. Any rain chances beyond this time would
be dependent on low predictability shortwaves within the
broader flow.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1233 PM CDT Tue Aug 13 2024

A scattered to broken deck of cumulus clouds will gradually
dissipate with the loss of diurnal heating this evening.

On Wednesday morning, mid- and high clouds will gradually
increase. Southeast winds will increase to around 10 knots by
late morning. There may be even some wind gusts up to 20 knots
west of the Mississippi River.

&&

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

&&

$$

DISCUSSION...JM
AVIATION...Boyne