163 
FXUS63 KARX 041906
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
205 PM CDT Sun Apr 4 2021

.SHORT TERM...(Today through Monday)
Issued at 205 PM CDT Sun Apr 4 2021

Forecast concerns will continue to be the elevated fire weather 
conditions today and near record high temperatures, the a return to 
a more active weather pattern this week.

Water vapor satellite imagery and heights show a broad mid-
tropospheric ridge over the Rockies and the Plains. Visible 
satellite imagery had some mid and high level cloudiness across the 
area into northern Wisconsin with a subtle shortwave, mid level warm 
air advection combined with a weakening low level jet. At the 
surface, low pressure was centered over northern Minnesota with a 
warm front lifting north across the region and a trailing cold front 
that will continue to move into the forecast area this evening.  The 
front stalls across northern Iowa and southern Wisconsin, then lifts 
north Monday...meanwhile another subtle shortwave trough will track 
across parts of Minnesota tonight and another wave will push across 
Iowa Monday.

Near critical fire weather conditions continue with the dry 
conditions today and brisk south winds.  Temperatures are warming 
through the 70s.  La Crosse's record for today is 80 degrees set in 
1921, so should get close. The surface winds gusting 20 to 30 mph 
should relax this evening as the trough approaches. Used the RAP for 
surface dewpoints yesterday and delayed the onset of the 50's 
dewpoints.  A look at recent observations show the 50s dewpoints 
into Nebraska and southern Iowa.  The HREF and RAP are handling 
these well and transport deepening moisture northward across western 
Iowa and into southern Minnesota. The HREF is a little faster with 
their arrival after 02Z and north of the IA/MN state line 08Z.  The 
RAP brings them west of the area, but then only the 40s dewpoints 
spread into the forecast area until Monday morning. These higher 
dewpoints and a more active shower and thunderstorm pattern will 
bring an end to low relative humidities and provide some much needed 
moisture.  

Monday will be noticeably more humid with a warm front north of the 
forecast area. There may be something isolated tonight with 
scattered showers and thunderstorms possible late tonight and Monday 
morning with the 40kt low level jet to the south. This jet weakens 
to 25 to 30kts as it spreads into the area Monday. A few stronger 
storms are possible with MLCAPE values of 800 to 1800 J/kg and 0-6 
KM Bulk Shear of 25 to 40 kts. The strongest deep layer shear looks 
to be over parts of the forecast area around 18Z...then shifts 
toward northwest Wisconsin later Monday night. Forecast soundings 
show elevated instability and shear during the morning, the 
afternoon and evening. The is some significant drying around 850mb 
during the afternoon and evening and could contribute to gusty winds 
with any of the showers/tstorms.

.LONG TERM...(Monday Night through Sunday)
Issued at 205 PM CDT Sun Apr 4 2021

Weak cold front becomes quasi-stationary over southern WI/into IA 
going into Tuesday as low pressure ramps up over the Plains. Some 
weak mid-level ridging looks to dry things a bit Tuesday morning 
(maybe a few lingering light showers) but then increasing push of 
850mb moisture transport int/over the front is expected to fuel more 
showers/embedded storms later in the afternoon. Temperatures remain 
warm otherwise with readings topping off in the mid-60s to lower 70s.

For Tuesday night through Friday morning, that Plains low pressure 
closes off and slowly lifts northeast into the region. May have to 
watch Wednesday as we build some small cape while there's pretty 
good curvature in the 0-3km hodograph. May be one of those scenarios 
where we could get a few brief small/weak tornado or two. Otherwise, 
will see an increase in coverage of showers and isolated storms as 
the low approaches. Scattered showers expected to continue Wednesday 
night through Friday morning in cyclonic flow. Look for highs in the 
mid-50s to mid-60s.

A few lingering showers still possible east of the Mississippi River 
Saturday in cyclonic flow of that closed low lifting toward the 
UP/Lake Superior. Otherwise, looking continued mild with highs 
remaining in the mid-50s to lower 60s.

Models bring a ridge of high pressure into the area for Sunday but 
looks like there could be some embedded energy rounding it for the 
possibility of a few showers. Will keeps chances on the very low 
side at this point. Remaining mild though with highs in the 60s.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1258 PM CDT Sun Apr 4 2021

VFR conditions expected through the TAF period. South winds 10 to 
20kts gusting to 20 to 30kts. The pressure gradient will relax as 
the surface front approaches KRST. Wind gusts will diminish towards 
evening as winds back to the south and southeast. Increasing clouds 
Monday morning with showers and thunderstorms. Will include shower/t-
storm mention as confidence increases in timing. 

&&

.FIRE WEATHER...Into Early This Evening
Issued at 205 PM CDT Sun Apr 4 2021

Very low RH values in the teens/lower 20 percent range and southerly 
winds of 10 to 15 mph with gusts up to 25 mph will continue to 
produce near critical fire weather conditions as grasses and other 
fine fuels remain dry. Moisture starts to increase across the area 
tonight with RH values climbing into the upper 60s to upper 80s 
after midnight. Rain chances return on Monday into Monday night, 
then widespread rains are looking likely Tuesday night into 
Wednesday. 

&&

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

$$

SHORT TERM...Zapotocny
LONG TERM...DAS
AVIATION...Zapotocny
FIRE WEATHER...DAS/Wetenkamp