893
FXUS63 KARX 030834
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
334 AM CDT Fri May 3 2024

.KEY MESSAGES...

- Areas of fog this morning. This fog may be localized dense. As
  drier air moves into the region and diurnal mixing occurs,
  this fog should burn off rapidly between 8 and 10 AM.

- Rain and scattered storms are expected late tonight and
  Saturday. This rain will likely only last up to 6 hours in any
  location. With better forcing and moisture transport into the
  region, rainfall amounts were increased. They now look to
  range from a tenth to a half-inch. Highest rain totals look to
  be west of the Mississippi River where the forcing and
  moisture transport is the best.

- For early next week (Tuesday and Tuesday night), there
  appears to be risk of severe weather. While the shear looks
  good, still some uncertainty of the amount of instability.

&&

.DISCUSSION...
Issued at 334 AM CDT Fri May 3 2024

This Morning - Areas of fog - potentially dense

The combination of clearing skies, light winds, and recent
rainfall will result in the development of fog across much of
the area early this morning. There may be even some localized
dense fog. As drier air moves into the region and diurnal
mixing develops this fog should quickly dissipate between 03.13z
and 03.15z.

Late Tonight through Saturday - Rain and scattered storms

The 05.03z models are in good agreement that a longwave trough
will move east through the forecast area from late tonight into
Saturday. Ahead of this wave, a 40 to 50-knot 850 mb jet will
increase the moisture transport across the area. Precipitable
water values will increase into the 1 to 1.4 inch range. The
highest values will be south of Interstate 90. This is higher
than the past couple of days. Due to this the precipitation
totals were increased. They now range from a tenth of an inch to
a half-inch. The highest values will be likely west of the
Mississippi River where the forcing and moisture transport will
be the strongest.

The CAMs show that the rain and scattered storms will likely
only affect an area up to 6 hours. Used the CONSShort and the
CAMs to try and add some timing to this precipitation. Even by
doing this, still likely holding onto this precipitation a bit
too long.

While the 0-6 km shear increases into the 40 to 50 knot range
(highest north of Interstate 90), the 0-4 km most-unstable CAPES
remains below 100 J/kg, so not anticipating any severe weather
from these storms.

Monday Night into Tuesday Night - Another round of showers and
storms

The models continue to show that a closed 500 mb low will lift
out of the desert southwest and move into the Northern Plains on
Monday. A negatively-tilted shortwave trough will move
northeast through the area on Tuesday. This will likely result
in a line of showers and storms. Both the deterministic GFS and
ECMWF suggest the potential for the 0-6 km shear will be in the
excess of 40 knots. The main question continues to be the
timing differences with this system which greatly impacts the
amount of instability that will be found across the region.
Colorado State severe probability still shows a 15 to 30% chance
in northeast Iowa and southwest and central Wisconsin.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 958 PM CDT Thu May 2 2024

With increasing probabilities of IFR fog over northeast Iowa,
it appears the Miss river valley could also see some MVFR fog by
morning as well. Through the past several hours, most of the
probabilities in the NBM guidance are consistent with some fog
at KLSE. Have decided to add MVFR fog as a trend. With winds
above the boundary layer at inversion height still 20 kts, think
the valley fog scenario is unlikely. It would be more of a
synoptic fog with possibly a slight preference for the valleys
to have lower visibility with cool air drainage under the surface
ridge axis.

&&

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

&&

$$

DISCUSSION...Boyne
AVIATION...Baumgardt