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000
FXUS63 KARX 111644
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1145 AM CDT Thu Apr 11 2024

.KEY MESSAGES...

- Rain showers will be increasing across the area into the
  afternoon, with the greatest coverage in central WI near and
  west of I-39. Some thunder is possible, possible small hail
  and wind gusts to 30 mph. Winds will be increasing today from
  west to east with gusts 30-35 mph through Friday.

- A warm and mostly sunny weekend still looking on track but
  there is some uncertainty on just how warm temperatures will
  be. 70s are a sure bet south of I94.

- An active weather pattern early next week with a warm Monday,
  then rain/storms looking likely Monday night and Tuesday,
  severe storms possible, and turning windy. Keep weather aware.

&&

.DISCUSSION...
Issued at 340 AM CDT Thu Apr 11 2024

Rain Showers and Winds Increasing Today, Some Thunder

GOES water vapor showing impressive wave energy in the central
CONUS at 09Z. A moderately strong shortwave trough in northwest
flow is digging into northwest IA with a secondary trough right
behind it near Bismarck ND. A southern stream vigorous
shortwave trough is ripping northeast out of southeast Arkansas,
with both streams combining to cause a deep longwave trough and
cyclogenesis over the next 36 hours at the surface tracking
through the Ohio valley. The northwest flow waves have an
attendant trough from the U.P. of MI southward to near Dubuque
with a few showers/sprinkles on it per radar and surface
observations. This trough stalls in central WI and provides a
focus for afternoon convective north-south bands of showers and
storms aided by weak frontogenesis northwest of the Ohio valley
low per latest RAP runs. MUCAPE values of 100-250 J/Kg areawide by
afternoon are uncapped thus any bump will be a shower or storm
(lightning!). This signal has been consistent for days now. The
two northwest flow mid-level troughs will be in eastern IA by
early afternoon with northern IA/swrn WI in a mild deformation
region north of that low causing what should be a bit more
enhanced showers, so did increase the rain chances there.

Overall, maybe some isolated small hail or gusty winds (30-35
mph?) in somewhat mixed /inverted V/ soundings for the strongest
shower/storms. Most areas should see some rainfall with around
1/4" in central WI, less elsewhere. Winds will be increasing
through the day with 15 to 25 mph expected through Friday, with
gusts in the 30-35 mph range as the deepening low tracks to the
east.


A Warm Spring Weekend

The weather still looks on track for a warm and mostly sunny
weekend. The frontal zone wavers through the weekend with
moderate warm advection Saturday, where temperatures could
overachieve current forecasts with deeper mixing. By evening, a
shower is possible /20-30%/ in the warm advection across
northeast of I-94 but confidence is pretty low on this outcome.
A dry cold front passes Sunday morning with northerly winds and
some cold advection, thus temperatures may underachieve current
forecasts Sunday. However, highs this weekend look to still be
in the 70s both days, cooler north of I94 in northcentral WI.

Monday into Tuesday night: Warm, Showers/Storms Likely, Possibly
Severe, Turning Windy

As we start the next work week, eyes turn to an ejecting upper-level
trough progressing out of the southern rockies into the southern and
central plains. Consensus amongst guidance at this moment has a
deepening surface low collocated with this trough that follows its
motion as it progresses northeast into the Northern Plains with
fairly strong warm advection ahead of it. This would likely
mean that Monday will be fairly warm with model guidance
favoring widespread middle to upper 70s, perhaps making a shot
at 80 in spots. As the low progresses generally northwest of our
region, there already is fairly large agreement amongst
deterministic and ensemble guidance for a fairly strong moisture
fetch associated with low-level southerly flow in the warm
sector. Consequently, the vast majority of ensemble guidance
(11.00z GEFS/EC) support precipitable waters (PW) of over 1
inch pushing into our region which is 90-95th percentile. At
KDVN the PW record for April 16 is 1.11". In addition,
confidence is already fairly high (60-90% chance) in the 11.00z
GEFS and EC ensemble for over 0.5" of QPF during this period.

Cluster analysis of the members of the 11.00z grand ensemble
(GEFS/EC ensemble/Canadian ensemble) currently leans (roughly 65% of
members) more towards an earlier progression of the trough pushing
through Tuesday morning with some members trending towards a later
solution into the afternoon. This difference in timing is important
as a later progression of the trough could bring in the stronger
forcing and ample moisture during more optimal daytime hours where
instability could be maximized. As a result, the April 10.00Z
GEFS-driven CSU machine learning probabilities have a broad
brushed 5-15% risk for severe weather across our region to
account for this potential. Those will update in the next hours
here from the 11.00Z GEFS. Regardless, as the surface low
departs later Tuesday, winds will increase with the tightening
surface pressure gradient with the 11.00z EC ensemble showing
high probabilities (60-80% chance) for wind gusts of 40 mph or
greater.

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1145 AM CDT Thu Apr 11 2024

CIGS: mostly lower VFR cigs through this evening with only low end
MVFR chances (less than 30%) for a short period at KLSE. Movement of
the weather systems favor scattering of the clouds at KRST
overnight, but could hold at KLSE into mid/late morning Fri.

WX/vsby: scattered -shra this afternoon, mostly "done" at both TAF
sites by 00z. Amounts minimal (1/10" or less). Low end thunder risk
(20%).

WINDS: northwest winds chiefly 15-20 kts with gusts into the low/mid
20s kts through Friday. Winds will be erratic with enhanced gusts
(closer to 30kts) around any shower/storm this afternoon. Winds will
slacken as we move into Friday night.

&&

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

&&

$$

DISCUSSION...Baumgardt/Naylor
AVIATION.....Rieck