992
FXUS63 KARX 161653
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1153 AM CDT Wed Apr 16 2025

.KEY MESSAGES...

- Widespread rain with low potential for strong to severe
  storms late Thursday evening into Friday morning. If severe
  potential is realized, large hail would be the primary
  concern.

- Some locations could top 1" of rainfall across Thursday
  and Friday. With ground now thawed across the area, flooding
  concerns appear very low.

- Additional rain likely Sunday into Monday. Once again, some
  locations could top 1" of rain across the event but flooding
  concerns appear very low.

&&

.DISCUSSION...
Issued at 317 AM CDT Wed Apr 16 2025

Widespread rain Thursday into Friday with low potential for severe
storms, very low potential for flooding

Thursday, surface high, currently centered in AR, will shift to the
eastern CONUS in the wake of the current upper trough over eastern
North America. As this occurs, lee surface cyclogenesis will take
place to our west, setting up good southerly moist advection across
the central CONUS, with ensemble means suggesting around 1-1.25" of
PWAT will eventually be present Thursday evening. Given robust low
level moist advection, should get at least some spotty light showers
through the day with periods of more widespread showers ahead of
shortwaves ejecting northeastward over the CWA.

On the subject of severe thunderstorms, focusing on our forecast
area, guidance continues to suggest low potential for severe
convection, with the limiting factor continuing to be best moisture
arriving after peak heating Thursday evening, confining potential
risk to elevated thunderstorms due to surface inversion. Indeed,
15.12z LREF joint probabilities for surface-based CAPE/CIN and deep
shear suggest only about a 10 percent chance to have ingredients for
a severe storm before sunset. In contrast, probabilities using deep
shear, MUCAPE, and CIN associated with the most unstable parcel
suggest a 20-50% chance for sufficient ingredients for a severe
storm in NE IA and far SW WI, although it must be noted this
probability only uses ECENS members. In any case, progged soundings
continue to illustrate the general pattern, with 16.00z GFS profile
at Decorah depicting around 500-1000 J/kg when lifting from above
the surface inversion - albeit still with around 100 J/kg of CIN.
Given instability and shear, could get some severe hail if updrafts
are able to overcome aforementioned inhibition Thursday night. Due
to said inhibition, the risk, while it cannot be written off,
remains low.

As for flooding, ensemble mean precipitation remains around the
0.25-0.5" range for Thursday into Friday. Additionally, the chance
to receive at least 1" over 6 hours is very low - generally less
than 5% in GEFS/ECENS/GEPS. With soils having thawed, low amounts of
spring snowmelt runoff, and 1/3/6 hour flash flood guidance - itself
generally too low - of 1.5-2/2-2.5/2.5-3", am not concerned about
flooding outside of urban areas with their abundant impervious
surfaces should a thunderstorm pass overhead. Thus, think overall
flash flood risk is in line with WPC excessive rain outlooks for
Thursday and Friday, under 5%. As for rivers, HEFS output keeps vast
majority of sites under action stage even in high end scenarios. In
summary, flooding risk outside of poor drainage urban areas is very
low.

Additional rainfall Sunday into Monday

Sunday into Monday, most operational and ensemble guidance -
operational 16.00z GFS notwithstanding - brings an upper low
northeast from the TX Panhandle to Lake Superior. Robust moist
advection east of this feature should allow for another period with
widespread rainfall. While earlier runs suggested some chance for
wintry precip during this period, progged 850mb temps have trended
warmer, suggesting precip will remain rain. Similar to the rain
Thursday/Friday, probabilities for receiving at least in inch remain
very low - generally under 5% to receive at least that amount over
any 6 hour period and 10-20% over the event. Thus, current thinking
is that flooding risk would once again be very low.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 1154 AM CDT Wed Apr 16 2025

As the high pressure moves east of the area tonight, a
deepening low pressure will move out of the Central Plains. This
will result in a tightening pressure gradient across the region
for tonight and Thursday. Sustained southeast winds will
gradually increase and range from 15 to 20 knots by Thursday
morning. Wind gusts will climb into the 20 to 30 knots.
Depending on the strength of low level inversion tonight, there
may be low level wind shear at KLSE. Confidence was not high
enough to include it at this time.

&&

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

&&

$$

DISCUSSION...Ferguson
AVIATION...Boyne