609
FXUS63 KARX 070712
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
212 AM CDT Wed May 7 2025

.KEY MESSAGES...

- Seasonal temperatures for midweek with a steady warm up for
  the weekend into next week.

- Essentially a dry forecast through the middle of next week.

&&

.DISCUSSION...
Issued at 210 AM CDT Wed May 7 2025

Today - Thursday: Seasonal Temperatures

A pair of shallow upper tropospheric shortwaves rotating around
a Hudson Bay longwave helped usher a weak cold front across the
Canadian border yesterday afternoon. This quasi-zonal cold
front is steadily marching southward through the forecast area
tonight and was stretching along the I-90 corridor as of 2 am.
Winds are switching to the north/northeast in the wake of the
front and remain from the northeast today off a 1032-mb Ontario
high.

The CAMs have backed down on their mid-level moisture attendant
with the mid-level frontogenesis band this morning and look to
be initiating high-based convection just to the south of the
forecast area in central Iowa this afternoon, thus the going
forecast today is now dry (with PoPs of around 10% along and
west of a line from Dubuque). A high cirrus shield spilling
northward from a cutoff low over the Southern Plains will temper
the sun to some degree along and south of I-90 today while
clearer skies can be found to the north. By Thursday, this low
will shift to the east and clearer skies will be in store
areawide.

The only other item to note is that with the recent green-up
and lows in central Wisconsin falling into the mid-30s tonight,
we may be looking at the need to issue a frost advisory for some
locales in this area. With a weak pressure gradient staying in
place overnight that could keep the near surface layer mixed,
have opted to wait and see how the winds evolve through the day
before issuing headlines.

End of the Week - Early Next Week: Warmer, Still Dry

The synoptic blocking pattern persists well into next week,
with a Rex block building over the western CONUS for the end of
the week, which eventually morphs into a Southern Plains cutoff
low embedded within a broad longwave ridge for the weekend. How
the blocking pattern evolves beyond midweek is a bit uncertain,
but odds are it will take on more of an omega look as a deeper
trough carves out the west coast of North America.

As we transition into the weekend, the lower tropospheric
thermal ridge also builds eastward, opening the door for a
return of above normal temperatures for Friday and beyond. There
is strong agreement in the NBM members that highs will rebound
to the upper 70s to low 80s by Saturday and persist well into
next week. Over the last 48 hours, the NBM temperature
percentiles have been creeping upwards for the middle to latter
part of next week, with 10-20% of the NBM membership pushing
into the mid-80s to near 90 in spots.

The blocking pattern will keep conditions dry for pretty much
the entire forecast period. The only lingering question for
rainfall is Saturday as a shallow trough skirts the MN/Canadian
border. Trends over the last 24-48 hours have been for the wave
energy to remain slightly further to the north, resulting in a
decrease in the number of ensemble members bringing
precipitation this far south. The end result is that the blended
forecast has <10% PoPs for Saturday, but if for some reason
this front were to able to initiate convection, it would present
the only real opportunity for showers before midweek next week
(at which point the longer range guidance breaks down on the
evolution of the blocking pattern).

&&

.AVIATION /06Z TAFS THROUGH 06Z THURSDAY/...
Issued at 1211 AM CDT Wed May 7 2025

VFR conditions expected for the next 24 hours. A weak cold
front is currently dropping south through the area and is
causing winds behind it to shift to the north/northeast. Winds
overnight should remain light at less than 8 kts before picking
up to between 8-12 kts during the morning hours. RST could see
some gusts between 15-20 kts this afternoon so have continued a
prevailing group to account for this possibility. Winds by the
end of the period will have veered more to the east and should
stay close to 10 kts.

&&

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

&&

$$

DISCUSSION...Skow
AVIATION...Barendse