← Previous April 15, 2024 3:30 PM

FXUS63 KARX 152030
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
330 PM CDT Mon Apr 15 2024

.KEY MESSAGES...

- Potent spring storm to bring widespread rainfall with a good
  potential for 1+" amounts (60-100% chance) and gusty winds 30
  to 45 mph

- Severe weather for some Tuesday. There is the potential as far
  north as I90, however the greatest threat will be for parts of
  northeast Iowa and southern Wisconsin, increasing as you head
  south.

- Rain chances return for Thursday with more seasonable weather for 
the weekend. Frost/freeze conditions possible for Saturday morning.
&&

.DISCUSSION...
Issued at 303 PM CDT Mon Apr 15 2024

Overview:

Water vapor satellite imagery and heights show a 500mb ridge of high 
pressure over the local area with a closed area of low pressure over 
the Four Corners region.  This storm system will continue to move 
east toward the Mid and Upper Mississippi Valley Tuesday, opening up 
as it lifts northeast.  A few showers/sprinkles and a few mid clouds 
were noted on the visible satellite images and local radar from the 
MPX area into areas north of I90.  The surface warm front at 19Z 
stretched through central Nebraska into northern Missouri.

Potent spring storm to bring widespread rainfall with a good 
potential for 1+" amounts (60-100% chance), gusty winds, and severe 
weather for some. 

The closed 500mb low pressure over the Rockies moves toward the Mid-
Missouri River Valley by 16.15Z  and eastward to the Mid/Upper 
Mississippi River Valley by 17.12Z. We see very good general 
model agreement on the synoptic/surface pattern and the track of
the surface low is tracking farther north into southeast MN by 
Wednesday morning. 

Broad synoptic lift increases with the approaching closed low 
pressure system.  Upper level support increases with strong warm air 
and deep moisture advection. The CAMs (convective allowing models) 
show showers and thunderstorms increasing across Nebraska and 
South Dakota this evening then filling in along the warm front 
across western Iowa tonight. The showers and storms will become 
more widespread across the region spreading northeastward 
Tuesday morning into the local area with continued strong 
moisture advection. The left front exit region of the jet will 
also help support the showers and storms as they move north.
Multiple rounds of showers and storms are expected until the
storm system exits the area.

Deep layer shear increases through the day Tuesday 45 to 60kts.
The gradient of SBCAPE of 500 to 2000J/kg sets up along the
border to just south into DVN's area by 00Z. Forecast soundings
and forecasts of MLCAPE show 100 to 500 J/kg mainly along and
south of I90 through the day. With the surface front south of
the area and the instability dropping off as you move north, 
with the first few rounds of showers and storms, any storms 
would be elevated with a potential hail/damaging wind threat 
during the day. The frontal system and triple point by late 
afternoon is forecast to approach the local forecast area toward
OLZ. Forecast soundings show strong 0-1km helicity in that 
region, thus tornadoes will be possible along and just north of 
the warm front. 

We continue to see rainfall amounts of 1 to 2.25" in the
forecast for the storm total. 1hr flash flood guidance is 1.5 to
2'" per hour and 2.5" for six hours. The HREF guidance shows the
highest probabilities of from 21-00Z from northeast Iowa into
southwest Wisconsin (10-40%). Heavy downpours could result in 
minor hydro issues related to ponding on roads and filling of 
poor drainage areas, but in general, we should be able to
handle the rain rates. We'll need to watch out for training of
storms due to the multiple rounds though.

We continue to see strong east winds Tuesday with gusts 30 to 
45 mph. As the surface low tracks toward the area Wednesday 
morning, the winds decrease, but increase again Wednesday 
afternoon from the northwest with 30 to 45 mph. A wind advisory
may be needed for much of the area Tuesday, for now, the
strongest winds during the day should be west of the Mississippi
River.

Behind the storm system through mid week, we have a trailing area of 
500mb low pressure that will push across parts of Canada and low 
pressure with more zonal flow will track across the local region. 
Embedded shortwaves in this pattern will result in scattered showers 
with the potential for rain changing to snow if the cold can can 
arrive before the precipitation ends, the rain could mix with or 
change to snow Friday north of I94.  Cold advection through the day 
Friday continues into the weekend.  Frost/freeze conditions still 
look possible for Saturday morning with lows in the 20s to lower 30s 
with some mid 30s.  Seasonable temperatures continue into early next 
week.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1242 PM CDT Mon Apr 15 2024

Deteriorating conditions are forecast for Tuesday as a storm system 
moves in with periods of showers and thunderstorms lasting into 
Wednesday.  Some showers will pass to the north of the TAF sites 
with increasing mid cloud today.  Deeper moisture transport will 
develop after midnight tonight. Ceilings will gradually lower 
to MVFR/IFR and possibly LIFR with the storms, however this 
appears more probable after the end of this set of TAFS. East 
winds will strengthen tonight and continue Tuesday 10 to 20kts 
to 20 to 30kts with gusts 30 to 40kts.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...Wind Advisory from 7 AM to 7 PM CDT Tuesday for MNZ079-086-087-
     094-095.
IA...Wind Advisory from 7 AM to 7 PM CDT Tuesday for IAZ008>010-018-
     019-029.

&&

$$

DISCUSSION...Zapotocny 
AVIATION...Zapotocny