781
FXUS63 KARX 140354
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1054 PM CDT Tue Aug 13 2024

.KEY MESSAGES...

- Widespread showers/storms likely from late Wednesday
  afternoon/evening into Thursday with locally heavy rainfall
  possible. This looks to be the highest chance for rain over
  the next week with medium to high (40-80%) chances for at
  least 1 inch.

- Below to near-normal temperatures are expected over the next
  10-days and near-normal in the 10 to 14 day period.

&&

.DISCUSSION...
Issued at 307 PM CDT Tue Aug 13 2024

Tonight into Wednesday...

High pressure will move slowly east of the area. As this occurs,
a developing low pressure over the Central and Northern Plains
will move slowly east toward the area. 925 and 850 mb moisture
transport will gradually increase during the afternoon. This
initial moisture transport will result in a gradual decrease in
cloud heights. There are still some differences in the CAMs on
when showers will move into the area on Wednesday afternoon. The
NAM and FV3 has them moving into the area by early afternoon.
Meanwhile, the ARW, HRRR, and RAP keep much of the area dry
through mid- to late afternoon.

Wednesday night through Thursday night...

The models are in good agreement that the low pressure system
will move slowly east northeast through the area and gradually
deepen. Even though it will be deepening, the 0-6 km shear
primarily remains at 30 knots or less. There is a small window
on Thursday afternoon where the 0-6 km shear does climb up to 40
knots in southwest Wisconsin. However, 0-1 km mixed-layer CAPES
at that time ranges from 500 to 1500 J/kg, so the marginal risk
from SPC looks good. With precipitable water values of around
1.5 inches and warm cloud depths of 3.5 to 4 km, these showers
and storms will be highly efficient rain producers. WPC has the
area under marginal to slight risk for excessive rain for this
time period and that seems reasonable. Most areas will likely
see anywhere from 0.75 to 1.5 inches of rain. The 48-hour HREF
QPF has 2 areas where the ensemble probability-matched mean
climbs into the 2 to 3 inch range. The first area is in
northeast Iowa and there is a secondary area from southwest
Minnesota east northeast into the Twin Cities.

From Friday into Saturday...

The surface low continues to move east northeast into the
northern Great Lakes. This will keep scattered showers and maybe
a few storms as shortwaves rotate around this low. With limited
instability and the best moisture to our east, rainfall totals
generally look on the lighter side.

8-14 Day Period (August 21-27)...

The ensembles continue to show that an omega ridge will likely
remain to our west and northwest from mid to to the latter
portions of August. This will favor near- to below-normal
temperatures and below-normal precipitation. The highest
probabilities for below-normal temperatures will be in the 6 to
10 day period (August 19 to 22).

&&

.AVIATION /06Z TAFS THROUGH 06Z THURSDAY/...
Issued at 1055 PM CDT Tue Aug 13 2024

Predominant VFR conditions expected. Some areas of fog will be
possible overnight in river valleys. Southeast winds will
continue overnight and increase to 10 to 20 knots during the
day Wednesday. Rain chances increase in the mid to late
afternoon Wednesday and remain through the rest of the TAF
period. Along with these showers, there is a 25 to 40% chance
for thunderstorms to occur.

&&

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

&&

$$

DISCUSSION...Boyne
AVIATION...Cecava