Special Weather Statement, NWS La Crosse, WI

Area Forecast Discussion
National Weather Service La Crosse WI
1259 PM CDT MON SEP 5 2016

.SHORT TERM...(Today through Wednesday)
Issued at 356 AM CDT Mon Sep 5 2016

Complex of showers and storms over western Minnesota into
northwest Iowa and South Dakota this morning is tied to the short
wave trough lifting northeast across South Dakota. With the large
scale southwest flow the short wave trough will continue to lift
northeast through this morning. The hi-res meso scale models all
show the convective activity lifting northeast as well but latest
trends suggest the activity is turning into the moisture inflow
and is taking more of an east/northeast trajectory. This would
bring this activity into the area this morning but it should be on
a weakening trend as it moves out of the instability axis. The
rest of the day should then be dry, especially as mid level
temperatures warm with the 05.00Z NAM suggesting the area will get
capped off with 700 mb temperatures warming into the 10 to 12C
range.

As we move into tonight, there will be almost no eastward movement
of the upper level ridge which will keep the mean southwest flow
over just about the same areas as it is this morning. Another
short wave trough is expected to come out of the central Rockies
today and then track northeast tonight into Tuesday morning. The
pv advection in the 500-300 mb layer is shown by both the 05.00Z
GFS and NAM to be weak and stay primarily to the northwest of the
area. Concerned that the mid level cap will remain in place for
the night as 700 mb temperatures stay at or just above 10C across
the area. With the weak forcing and the mid level cap, the hi-res
meso scale models really struggle to produce much convection over
the area keeping this across the northwest half to two-thirds of
Minnesota into northern Wisconsin. Will still bring a small rain
chance across the entire area for late tonight, but will limit the
highest chances to across the northwest sections of the area.

For Tuesday, the surface boundary currently extending from
northwest Minnesota into the Nebraska panhandle, will slip south
into the area. The general model consensus is that this should
extend from northeast Minnesota into northwest Iowa by late
Tuesday afternoon. The GFS indicates there should be some decent
frontogenesis in the 1000-850 mb layer with this boundary. Still
some model differences on whether there will be a short wave
trough coming through to interact with the boundary or not. The
NAM does bring a wave through while the GFS continues to keep the
mean flow to the northwest of the area. Neither model shows any
movement in the upper level ridge axis that would suggest a short
wave trough would be able to move over the area. The low level
moisture transport axis will be in place ahead of the boundary but
this looks to be primarily through the area focused more onto the
northern sections of Wisconsin and Michigan. What will happen with
the mid level capping is also a concern as the GFS keeps this in
place for most of the area while the NAM weakens this since it
allows a short wave trough to move through. Will attempt to
compromise between these two solutions and show a band of showers
and storms along the boundary with the highest values over the
northern sections. Severe chances still look marginal depending on
whether the shear will be able to overlap the cape. The GFS
suggests the ML CAPE will top out around 1500 J/Kg Tuesday
afternoon ahead of the front but the 0-3KM shear values will only
be between 20 and 25 knots with the best shear remaining behind
the front.

The upper level ridge will finally start to give way Tuesday night
allowing height falls to spread over the area through Wednesday
ahead of a much stronger short wave trough that will bring a mean
long wave trough onto the High Plains. Smaller lead short wave
troughs ahead of the mean trough should come across the area and
be able to produce several rounds of moderate pv advection in the
500-300 mb layer. With the height falls and mid level cooling, the
cap should get removed Tuesday night. The moisture transport will
become more favorable into the area, especially for Wednesday
afternoon, with the front still expected to be bisecting the area.
This currently looks to be the most favorable period for showers
and storms and increased the rain chances to around 80 percent along
and south of the expected location of the front. With all the
expected cloud cover and potential rain, the ML CAPE Wednesday may
only get into the 500-1000 J/Kg range which should again keep
severe chances rather marginal despite the potential for the 0-3KM
shear to in the 30 to 40 knot range.

.LONG TERM...(Wednesday night through Sunday)
Issued at 356 AM CDT Mon Sep 5 2016

With the passage of the long wave trough, the front should get
pushed through the area allowing the rain chances to start
diminishing late Wednesday night with most of the area expected to
be dry Thursday. The front will then start to return back into the
region Thursday night as a surface low forms along it in response
to the next short wave trough. This short wave trough and surface
low then look to move through Friday and off to the east Friday
night with just some lingering rain chances expected into
Saturday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1259 PM CDT Mon Sep 5 2016

Main taf forecast concern is convection possibilities at both the
RST/LSE taf sites through the taf period. Latest mosaic radar shows
a line of showers/thunderstorms southwest of RST taf site into north
central Iowa. This line of convection will continue to lift slowly
northward this afternoon and impact the RST taf site through late
this afternoon. Right now have timed it to end at RST taf site at 21z
today/Monday. This convection is associated with a weak surface
front lifting northward and becomes a focus for redevelopment of
showers/thunderstorms this evening into Tuesday morning. Latest
trends indicate the convection should be north of both RST/LSE taf
sites. However...cannot the rule out the possibility of convection
to develop slightly further south later this evening into tonight
and possibly move over the taf sites. At this time...the
convection is expected to remain north of the taf sites...and VFR
conditions should prevail. Southerly sustained winds will be
around 15 knots with gusts to around 25 knots this afternoon into
early evening...as winds aloft mix down to the
surface...especially at the RST taf site.

&&

.HYDROLOGY...
Issued at 356 AM CDT Mon Sep 5 2016

The main concern for Tuesday night into Wednesday night will be
the potential for heavy rain along the front. The models have been
consistent in showing the precipitable water values reaching or
exceeding two inches. Concerned that these may be too high as the
models may be overdoing the amount of low level moisture that will
be in place. Surface dew points downstream of the area, across
Kansas and Oklahoma ahead of the front, are in the upper 60s. As
the surface crops continue to mature, hard to see how dew points
are going to be able to reach the middle 70s as forecast by
several of the models. Regardless, these will still be high enough
to support the potential for heavy rain, especially with warm
cloud depths expected to be around 4 km. Eventually, there could
be the need for a flash flood watch, but will need to wait and see
where the first round of heavy rain falls to pinpoint where the
threat area will be.

&&

.ARX Watches/Warnings/Advisories...
WI...Flood Watch from 7 PM CDT this evening through late Wednesday
     night for WIZ017-029-032>034-041>044-053.

MN...Flood Watch from 7 PM CDT this evening through late Wednesday
     night for MNZ079-086>088-094>096.

IA...None.
&&

SHORT TERM...04
LONG TERM....04
AVIATION...DTJ

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE LA CROSSE WI
530 AM CDT MON SEP 5 2016

IAZ008>011-018-019-029-030-MNZ079-086>088-094>096-WIZ017-029-
032>034-041>044-053>055-061-052300-
MITCHELL-HOWARD-WINNESHIEK-ALLAMAKEE-FLOYD-CHICKASAW-FAYETTE-
CLAYTON-WABASHA-DODGE-OLMSTED-WINONA-MOWER-FILLMORE-HOUSTON-
TAYLOR-CLARK-BUFFALO-TREMPEALEAU-JACKSON-LA CROSSE-MONROE-JUNEAU-
ADAMS-VERNON-CRAWFORD-RICHLAND-GRANT-
530 AM CDT MON SEP 5 2016

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF NORTHEAST
IOWA...SOUTHEAST MINNESOTA AND WESTERN INTO NORTH CENTRAL
WISCONSIN.

.DAY ONE...TODAY AND TONIGHT

SCATTERED THUNDERSTORMS ARE EXPECTED ACROSS THE AREA THIS
MORNING...MAINLY WEST AND NORTH OF LA CROSSE. THE MAIN
THREAT WITH ANY OF THESE STORMS IS LIGHTNING.

THERE IS A CHANCE OF THUNDERSTORMS TONIGHT...MAINLY ALONG AND
NORTH OF INTERSTATE 90. THE MAIN THREAT LOOKS TO BE LIGHTNING.

.DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SATURDAY

THUNDERSTORMS ARE LIKELY FOR MUCH OF THE AREA TUESDAY AFTERNOON
INTO WEDNESDAY NIGHT. SOME OF THE STORMS TUESDAY AFTERNOON AND
EVENING...AND AGAIN WEDNESDAY AFTERNOON AND EVENING...COULD BE
STRONG TO POSSIBLY SEVERE. THE MAIN THREATS LOOK TO BE LOCALLY
HEAVY RAINFALL AND POSSIBLE FLOODING ALONG WITH DAMAGING WINDS.

AFTER A BREAK THURSDAY...THUNDERSTORM CHANCES RETURN FOR THURSDAY
NIGHT THROUGH FRIDAY NIGHT. IT IS TOO EARLY TO DETERMINE IF THERE
IS A SEVERE RISK WITH ANY OF THESE STORMS.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT EXPECTED THROUGH TONIGHT...BUT MAY BE
NEEDED AT TIMES FROM TUESDAY AFTERNOON INTO WEDNESDAY EVENING.
RAINFALL REPORTS ARE ALWAYS APPRECIATED.

.EMERGENCY MANAGEMENT COORDINATION...

NO WEBINAR IS SCHEDULED.

RRS/04

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE LA CROSSE WI
126 PM CDT MON SEP 5 2016

MNZ087-088-094-095-051915-
WINONA-MOWER-FILLMORE-OLMSTED-
126 PM CDT MON SEP 5 2016

...A LINE OF STRONG THUNDERSTORMS WILL AFFECT SOUTHWESTERN WINONA...
NORTHEASTERN MOWER...NORTHERN FILLMORE AND OLMSTED COUNTIES...

AT 124 PM CDT...RADAR INDICATED STRONG THUNDERSTORMS WERE LOCATED
ALONG A LINE EXTENDING FROM NEAR ROCHESTER TO 7 MILES EAST OF
BROWNSDALE. MOVEMENT WAS EAST AT 35 MPH.

WIND GUSTS UP TO 50 MPH AND HALF INCH HAIL ARE POSSIBLE WITH THESE
STORMS.

LOCATIONS IMPACTED INCLUDE...
ROCHESTER...STEWARTVILLE...ST. CHARLES...CHATFIELD...EYOTA...
RUSHFORD...LEWISTON AND LANESBORO.

FREQUENT CLOUD TO GROUND LIGHTNING IS OCCURRING WITH THIS STORM.
LIGHTNING CAN STRIKE 10 MILES AWAY FROM A THUNDERSTORM. SEEK A SAFE
SHELTER INSIDE A BUILDING OR VEHICLE.

PERSONS IN CAMPGROUNDS SHOULD CONSIDER SEEKING STURDY SHELTER UNTIL
THESE STORMS PASS.

LAT...LON 4385 9269 4385 9268 4387 9268 4407 9259
      4407 9177 4374 9175 4368 9277
TIME...MOT...LOC 1824Z 255DEG 24KT 4396 9248 4372 9273

DTJ

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE LA CROSSE WI
149 PM CDT MON SEP 5 2016

IAZ008>010-MNZ086>088-094-095-051945-
WINNESHIEK-MITCHELL-HOWARD-WINONA-DODGE-MOWER-FILLMORE-OLMSTED-
149 PM CDT MON SEP 5 2016

...A LINE OF STRONG THUNDERSTORMS WILL AFFECT NORTHERN HOWARD...
NORTHERN MITCHELL...NORTHWESTERN WINNESHIEK...WESTERN WINONA...
MOWER...FILLMORE...SOUTHERN DODGE AND OLMSTED COUNTIES...

AT 148 PM CDT...RADAR INDICATED STRONG THUNDERSTORMS WERE LOCATED
ALONG A LINE EXTENDING FROM NEAR HAYFIELD TO NEAR LYLE. MOVEMENT WAS
EAST AT 40 MPH.

WIND GUSTS UP TO 50 MPH ARE POSSIBLE WITH THESE STORMS.

LOCATIONS IMPACTED INCLUDE...
ROCHESTER...AUSTIN...PRESTON...STEWARTVILLE...ST. CHARLES...
CHATFIELD...SPRING VALLEY...LEWISTON...ST. ANSGAR...HARMONY...
LE ROY...LANESBORO...DOVER AND LYLE.

FREQUENT CLOUD TO GROUND LIGHTNING IS OCCURRING WITH THIS STORM.
LIGHTNING CAN STRIKE 10 MILES AWAY FROM A THUNDERSTORM. SEEK A SAFE
SHELTER INSIDE A BUILDING OR VEHICLE.

PERSONS IN CAMPGROUNDS SHOULD CONSIDER SEEKING STURDY SHELTER UNTIL
THESE STORMS PASS.

LAT...LON 4396 9299 4413 9185 4347 9197 4337 9302
      4350 9303 4350 9304
TIME...MOT...LOC 1848Z 257DEG 37KT 4390 9292 4346 9298

DTJ