← Previous May 30, 2023 6:09 AM

FXUS63 KARX 301109

Area Forecast Discussion
National Weather Service La Crosse WI
609 AM CDT Tue May 30 2023

.DISCUSSION...(Today through Monday)
Issued at 328 AM CDT Tue May 30 2023

Key Messages:

 - Chance (20-40%) for Showers and Storms Primarily West of the 
   Mississippi River Today

 - Low Confidence For Scattered Storms Through Midweek & Into The

 - Above Seasonable Temperatures Continue Through The Weekend

Today and Tonight: 

A weak shortwave trough gradually pushing across our region today
combined with convergence along the boundary and minimal mixed-
layer CAPE (500-1000 J/kg) will lead to some scattered shower/storm
chances later this afternoon and evening, primarily west of the 
Mississippi River. Limited instability and lack of low and mid- 
level shear insinuates a minimal threat for organized severe 
weather. As the storms progress eastward later into the evening, 
lack of instability should hinder most convection east of the 
Mississippi River which the CAMs tend to agree with.

Latter Half of The Week Storm Chances:

Scattered storm chances continue for much of Wednesday with low 
level moisture advection in the increased low level theta e lobe 
accompanies a weak, open upper level wave lifting through the 
Northern Plains. While increased storm probabilities are shunted to
our west tied to the lifting open wave, high resolution guidance 
(RAP/HRRR 30.03/06Z) suggest elevated instability (1000-2000 J/kg)
primarily along our western periphery into our western counties. 
Latest SREF (29.12Z) agrees with increased confidence (70-100%) 
of MLCAPE/MUCAPE above 1000 J/kg from northeast Iowa and southeast
Minnesota into west-central Wisconsin. Forcing will be isentropic
lift within the warm air advection scheme, pushing 5-10 ubar/s at
times according to the most recent RAP (30.03Z) as well as
diurnal heating influences throughout the day. Similar precipitation
and storm chances expected for Thursday as low level warm air advection
provides isentropic ascent, diurnally building instability pool, and
meager mid level forcing from passing vorticity lobes in upper
level diffluent flow. 

Only other concern through midweek will be lower surface 
dewpoints from increased low level mixing. Potentially inhibiting
precipitation chances outside of storms, limiting heat indices, 
and providing more gusty winds. Given the persistent pattern 
resulting in lower-than-forecasted dewpoints, have decreased them 
area wide away from National Blend during the day Wednesday.

Rainfall Amounts & Impacts

While rainfall totals will be higher within any scattered storms 
(highest confidence (60-100%) for greater than 1.0" PWATS in long 
term probabilistic guidance (GEFS/EPS 30.00Z)), HREF (30.00Z) confidence
suggests widespread amounts nearing 0.1". However, current 
forecast hour nears the terminus of the most recent HREF run, 
limiting membership and forecast continuity through the day 
Wednesday. Ensemble plumes through show little to no agreement for
QPF for much of the area, given the convective, scattered nature 
of storms and attendant precipitation. Maximum, outlier amounts 
near 0.25" at times in all varieties of models. As for storm 
mode, storms are expected to be limited to single cellular 
"popcorn convection" with very limited, if any, directional or 
speed shear given a lack of any sort of frontal boundary. Could 
conclude any shear could be cold pool dependent, however, 
LFCs/LCLs expected to much too high for cold pool to be realized. 

Rest Of The Week Into The Weekend:

Confidence is high (70-100%) for a regressive pattern for the 
latter half of the week into the weekend, according to greater 
than 582 dam heights at 500 mb in the GEFS/EPS advecting west into
the Northern Plains. Timing and location of these regressive 
upper level heights will determine precipitation chances through 
the weekend. At the current forecast hour, probabilistic, 
deterministic, and cluster analysis all disagree on location of 
higher heights and resultant precipitation chances. In all 
aforementioned displayment methods, the GEFS/GFS (30.00Z) is a 
wetter solution through the weekend, containing 50-100% 
probabilities for a hundredth to a tenth of an inch in 24-hour 
rainfall totals. This is the result of a tighter region of upper 
level heights than the ECMWF/EPS, allowing a inverted trough to 
dip into the Upper Midwest. Irregardless, much disagreement at 
this time leaves a lot to be desired, and have therefore 
continued with National Blend, leaving "slight chance" to 
"chance" for storms.

Anomalous Maximum Daytime Temperatures:

Otherwise, confidence remains high for above seasonable 
temperatures (+10 degrees) for the latter half of the week into 
the weekend from the supportive synoptic high pressure. However, 
can expect a slight reprieve from these anomalously high temperatures
within storm activity and attendant cold pools. Similar to aforementioned
precipitation chances, resolving the upper level synoptic pattern through
the weekend into early next week will determine the potential for
a more seasonable, cooler pattern.


.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 608 AM CDT Tue May 30 2023

A weak short wave trough working across Nebraska and South Dakota
was responsible for some showers and a few storms pushing across
parts of Minnesota and Iowa. This activity should dissipate later
this morning as it moves northeast out of the MUCAPE axis and the
low level moisture transport diurnally weakens. Some of this may 
come close the KRST, but expecting it should stay off to the
northeast. Another round of convection should occur late this
afternoon into the early evening as the short wave trough moves
through. This activity could impact KRST and will continue the
inclusion of a VCSH but stay to the west of KLSE.