Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 311733
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1232 PM CDT TUE MAY 31 2016

.SHORT TERM...(Today through Thursday)
Issued at 319 AM CDT Tue May 31 2016

Still some ongoing showers across the area early this morning in
the broad warm air advection zone ahead of the cold front over the
Missouri River Valley. This activity should continue to lift north
while slowly weakening and what remains of it should pretty much
be out of the area by 12Z. The concern then becomes if more
activity is going to develop in this warm air advection ahead of a
short wave trough moving out of Iowa. The 31.05Z HRRR does show
more activity blossoming over southern Minnesota into western
Wisconsin that could impact the northwest parts of the forecast
area for awhile this morning.

Once this activity moves out of the area later this morning, there
should be a general lull in the activity. However, given the
persistent warm air advection, cannot rule out some activity
popping up so will maintain at least a low end chance across the
entire area. As the cold front approaches from the west, there
will be a couple of short wave troughs moving across the region to
interact with it. The first will be coming up out of the ongoing
convection over Kansas with the second rotating around the upper
level low as it moves east across North Dakota. These two waves
should provide ample forcing to cause a line of convection to
develop along the front over Minnesota and Iowa early this
afternoon and then move across the local area from mid afternoon
into the evening. The activity looks like it should really slow
down as it reaches the eastern parts of the forecast area. The
initial front is expected to dissipate leaving the tongue of low
level moisture right over the area as another front forms over the
Missouri River Valley off the occluded surface low over North
Dakota. With this second front forming back to the west, the
moisture tongue remains nearly stationary overnight with enough
forcing to keep the showers and storms going for much of the night
before the whole system exits to the east Wednesday morning. Plan
to maintain continuity with the previous forecast and show a line
of 60 to 80 percent rain chances moving east across the forecast
area with the front.

If the hi-res models are close on the timing of the line for this
afternoon, it will be moving into the area during a favorable time
of the day. Still plenty of questions on how much clearing may
occur before the afternoon convection develops and thus how much
CAPE will be in place. The 31.00Z NAM suggests between 1000 and
1500 J/Kg of ML CAPE could be in place by afternoon but then there
is the question of shear. There doesn`t look to much shear until
late this afternoon when the NAM develops around 30 knots in the
0-3 km layer in association with the line of convection and as the
right entrance region of the upper level jet rounds the base of
the upper level low. If the CAPE and shear can develop, there will
be a chance for some severe with damaging winds and large hail
possible. Otherwise, would just expect some strong storms at best.

.LONG TERM...(Thursday night through Monday)
Issued at 319 AM CDT Tue May 31 2016

The rain chances will quickly return to the area for the end of
the week. The zonal flow in the wake of the current system will
buckle ahead of short wave trough coming out of the northern
Rockies. This wave is expected to continue amplifying with an
upper level low forming over the Upper Midwest Friday night. This
system then works into the Great Lakes before becoming almost
stationary into early next week. This will cause the rain chances
to come back Friday and then persist through the weekend.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1232 PM CDT Tue May 31 2016

A line of SHRA/TSRA still on track to move across the the TAF sites
this afternoon into early this evening. SHRA/TSRA were already
developing into north-central IA, with distance-speed tool bringing
them into the KRST area around 20Z. Little fuzzier timing into KLSE,
but in the 22Z-01Z window remains quite valid. Added a tempo group
to both TAFs for MVFR cigs/vsbys, and some gusty west winds, as the
band of SHRA/TSRA would pass across each site. Outside of this
period of convection with the frontal and upper trough passage,
generally good VFR conditions expected at the TAF sites early this
afternoon and again later this evening through Wed.

A concern late tonight/early Wed morning remains potential valley
BR/FG at KLSE. Depending on how much rain falls with the convection
later this afternoon/early this evening, if skies clear overnight
and winds decouple, conditions would be favorable for valley fog
formation at KLSE in the 09Z-13Z time-frame. left this out of the
KLSE taf for now, but will pass along concerns to later shifts to
continue monitor the KLSE BR/FG potential.

&&

.ARX Watches/Warnings/Advisories...
WI...None.
MN...None.
IA...None.
&&

$$

SHORT TERM...04
LONG TERM....04
AVIATION.....RRS


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