620
FXUS63 KARX 052350
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
650 PM CDT Sat Oct 5 2024

.KEY MESSAGES...

- Low (20 to 30%) potential for a shower or thunderstorm in
  central and north central Wisconsin late this afternoon into
  this evening. If a thunderstorm does in fact occur, a
  localized strong to severe gust cannot be ruled out.

- Decent to very likely (30-90%) probability temperatures fall
  enough Monday morning for potential frost formation across
  much of the area.

- After a cool and breezy Sunday, temperatures climb back above
  normal through the work week. The chance for precipitation is
  at or close to zero each day.

&&

.UPDATE...
Issued at 648 PM CDT Sat Oct 5 2024

Local 23Z surface analysis really showing some action across
the area. Low pressure is located right near La Crosse WI with a
N->S oriented cold front roughly from west of Winona to near
Waterloo Iowa shifting east rapidly. Vigorous pre-frontal, low-
level warm advection is found over WI, with cold advection over
much of MN/IA. Wind gusts on the cold front have been stronger
than the afternoon pre-frontal gusts with gusts of 30-39mph
right on the front. With some cooling with sundown and
stability, expecting the gusts to be a bit lower as the front
rolls through western/central WI early this evening.

An axis of instability exists pre-frontally but there is also
stout capping. The only weakness in the cap sweeps through
northwest into northcentral WI along the front. Some TSRA
activity is in this area near Hayward at 2330Z, with other
weaker showers to the south. Low storm chances are mainly
north/northeast of La Crosse, and right on the front where
convective inhibition goes to near zero. Otherwise, the area is
capped.

A break in the winds occurs for most of the overnight until a
stronger cold front arrives in the pre-dawn hours with another
moderate-strong cold advection signal. Soundings dont flip to
steep lapse rates right on the front but do shortly after, with
gusts coming up early areawide...30-40 mph with breakfast. The
low-level wind field increases with model consensus of ~40 kts
only 4kft AGL in the morning. The entire day will be breezy, but
that morning period has the highest gust potential.

&&

.DISCUSSION...
Issued at 210 PM CDT Sat Oct 5 2024

Windy Saturday afternoon with low potential for evening showers and
storms

The modest downward trend in top end winds seen in guidance over the
past 1-2 days has been borne out, with top wind gusts generally
around 30-35 mph so far early this afternoon despite mostly clear
skies. Additionally, RH values have fallen less than the most
aggressive guidance suggested it would, largely courtesy of modest
southerly moist advection. Have thus refrained from upgrading part
of the ongoing SPS to a Red Flag Warning. As for wind expectations
this afternoon, progged soundings do still suggest a small window
for a 40 mph gust or two west of the Mississippi River valley during
the 3 to 5 pm time frame but, with things having underachieved thus
far, have also refrained from issuing a Wind Advisory.

Moving ahead to this evening, as the upper low over Lake Winnipeg
and attendant cold front advancing over western Minnesota progress
eastward, a few showers and thunderstorms could presumably occur
east of the Mississippi River where marginal 700/850mb moisture may
be present enough to overcome capping in the 500-650mb layer. While
the 05.12z HREF suggests a decent (30-60%) chance for precip along
and north/east of I-94, the trend in the HREF has been downward over
the 3 runs that cover through tonight. Additionally, most HRRR runs
suggest the cap will not be overcome. Given this HREF trend and
guidance assimilating the latest obs remaining pessimistic, have
continued to shift PoPs toward consensus of CAM guidance, yielding
numbers in the 20-30 percent range, restricted to areas along and
north/east of I-94. As for hazards, expected high cloud bases atop a
fairly well-mixed boundary layer continue to suggest that strong to
perhaps severe gusts could occur with any thunderstorms that do
manage to develop.

Frosty Monday

As the aforementioned upper low barrels eastward to Hudson Bay,
surface high looks to develop in IA in the wake of this feature.
This should lead to mostly clear skies and light winds, causing
surface temperatures to tumble Sunday night into Monday. 05.12z HREF
and NBM indicate much of the CWA has a 30 to 90 percent chance to
fall at or below 36 degrees with best chance for this east of the
Mississippi River, setting the stage for potential frost formation.
Will need to monitor this closely as most areas have yet to see
frost this fall.

Warming trend and lack of precip next work week

Medium range guidance continues to point toward upper ridging
developing over the central CONUS with our forecast area mainly
under northwesterly flow aloft. This should serve to keep things
free of precip as temperatures creep back upward into the 70s and
even 80s after our cool Sunday.

&&

.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 648 PM CDT Sat Oct 5 2024

VFR is expected with impactful winds early on this evening with
front moving through or post-frontal winds...then a break in the
late evening. After 06Z, winds increase aloft with LLWS
indicated with 40kts at 2-3kft. A secondary cold front will move
through in the 09-12Z time period making for a gusty Sunday
morning after sunrise with the potential (25%) for higher gusts
than currently are in the TAF. Winds will remain roughly
18G28kts for the afternoon Sunday.

&&

.FIRE WEATHER...
Issued at 350 AM CDT Sat Oct 5 2024

This afternoon`s fire weather risk is driven heavily by winds.
Southerly winds increase through the morning and by midday will
be sustained around 20 to 25 mph, gusting upwards of 30 to 40
mph. The higher gusts in this range will be west of the
Mississippi River. However, these stronger winds will advect
increasing amounts of moisture northward, raising dewpoints into
the 50s and preventing afternoon relative humidity values from
falling much below 30-45 percent. The lowest humidity values
will also be west of the Mississippi River where temperatures
should climb well into the 80s. The lack of recent rainfall has
resulted in Build Up Indices west of the Mississippi River
pushing 80-100, near critical dryness levels. The GFDIAg values
also support that any harvest-ready fields could be susceptible
to fires. A cold front sweeps through this evening, quickly
switching the wind direction to the northwest for the night.

&&

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

&&

$$

UPDATE...Baumgardt
DISCUSSION...Ferguson
AVIATION...Baumgardt
FIRE WEATHER...Skow