350
FXUS63 KARX 262345
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
645 PM CDT Thu Sep 26 2024

.KEY MESSAGES...

- Quiet weather continues through the short term. Favorable
  conditions for valley fog late tonight into Friday morning.

- Forecast remains dry (90-100%) through the weekend. Trends
  continue to indicate the mid-level low and remnants of
  Hurricane Helene remain southeast of the area with mid-level
  ridging influencing the Upper Mississippi River Valley.

- More seasonable temperatures expected next week.

&&

.DISCUSSION...
Issued at 138 PM CDT Thu Sep 26 2024

Quiet weather continues through the short term. Favorable
conditions for valley fog late tonight into Friday morning.

High pressure and mid-level ridging located over much of the
central United States will continue to influence the Upper
Mississippi River Valley this afternoon and overnight. Clear
skies and calm to light winds are expected through Friday as a
result of these features leading to another valley fog scenario
late tonight into Friday morning. Will need to continue to
monitor the trends for the potential for valley fog Friday
night into Saturday morning, as there will be a decreased depth
of the light wind layer as seen in RAP soundings. Overall, a
persistence forecast is the expectation in the short term.


Forecast remains dry (90-100%) through the weekend. Trends
continue to indicate the mid-level low and remnants of Hurricane
Helene remain southeast of the area with mid-level ridging
influencing the Upper Mississippi River Valley.

The aforementioned high pressure and mid-level ridging will
continue to influence the Upper Mississippi River Valley through
the weekend as a mid-level cutoff low centered over southern
Illinois slowly shifts eastward and merges with the remnants of
Hurricane Helene. The ECMWF Ens/GEFS/GEPS depict these features
remaining to the southeast of the region and continue to trend
towards a dry solution for the weekend with probabilities of
0-10%.


More seasonable temperatures expected next week.

Model guidance depicts a mid-level shortwave trough diving into
the region early next week. This trough is expected to drag a
cold front southeast through the area Monday night into Tuesday.
However, ample dry air in place over much of the region as well
as better dynamics across northern Minnesota and Wisconsin,
precipitation chances are only 0-15% during this timeframe with
Taylor County being the focus of the higher end chances. Cooler
air will succeed the front, allowing for more seasonable
temperatures into the middle of next week.

&&

.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 645 PM CDT Thu Sep 26 2024

Valley fog for Friday morning continues to remain the primary
aviation concern throughout the forecast period with high pressure
in place allowing for relatively clear skies, light low-level winds,
and falling dewpoint depressions. Minimal adjustments have been made
to the KLSE TAF with forecast trends remaining on track for periods
of IFR/LIFR fog around and just before sunrise. The main question
over the next 6-12 hours remains how dewpoint depressions will trend
and if they will favor 1/4SM. Currently, the dewpoint depression at
KLSE is 22 degrees as of 25.23z, which is marginally favorable for
1/4SM per local research. If this trends similar to previous nights,
likely would favor a more intermittent 1/4SM as opposed to longer
duration dense fog. As a result, opted to hold off on any tempo for
1/4SM this forecast issuance but will likely need to introduce it
for the 26.06z issuance assuming dewpoint depressions behave
similarly to previous nights.

&&

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

&&

$$

DISCUSSION...Falkinham
AVIATION...Naylor