Special Weather Statement, NWS La Crosse, WI

Area Forecast Discussion
National Weather Service La Crosse WI
235 PM CDT Tue Aug 7 2018

.SHORT TERM...(This Evening through Wednesday)
Issued at 235 PM CDT Tue Aug 7 2018

Decent-looking compact shortwave continues to edge east out of
southeast Minnesota early this afternoon, with a leading weaker
shortwave spinning across southern Wisconsin as well. Showers and
storms have been gradually redeveloping ahead of that stronger
upper wave the past few hours, with very weak steering flow
resulting in some heavier downpours, with MRMS estimates pushing
2+ inches in a few localized spots.

A gradual eastward jaunt to convection is expected through late
afternoon and into early evening, with activity likely to gradually
fade with time given loss of heating/instability. Severe weather
threat remains very low given paltry low level and deep layer shear,
though as mentioned yesterday, decent low level CAPE/updraft
stretching potential and overall spin with the upper wave could
result in a few funnel clouds, with hints of enhanced NST
(non-supercell tornado) parameters across the area the next few
hours.

Otherwise, looking for skies to slowly clear overnight as the wave
pulls east, leaving light winds in place with shallow ridging
overhead. Given already lower temp/dew point spreads with
clouds/rain in place and recent history of similar airmasses,
suspect we're in for another round of fog development overnight,
particularly in the river valleys. Still some variance about how
much wind may be in the column overnight, so not sure just how
widespread it will be. However, after any fog burns off, should be a
pretty great day with warmer temps and a good deal of sunshine into
much of the afternoon. By late afternoon, will have to keep an eye
on yet another shortwave running down through this northwest flow
aloft regime, with some hints that we may see isolated late day
convection well north of I-94. Given better shear and steeper lapse
rates, can't rule out a rogue stronger storm, but don't expect
coverage to be all that much.

.LONG TERM...(Wednesday Night through Tuesday)
Issued at 235 PM CDT Tue Aug 7 2018

The GFS and EC remain locked in with holding onto the northwest-
north upper level flow into the weekend. Recent trends point to
shifting the amplified west coast ridge eastward by the weekend,
bending the ridge axis into southern Canada. As that occurs, the GFS
and EC suggest the trough to the east would cutoff a low, which
could sit just south of the ridge axis across the eastern Great
Lakes into Monday. The upshot of the pattern is that various bits of
upper level energy could/would spin across the region through the
upcoming weekend, bringing periodic shower/storms chances. Favored
times would be afternoon/evening when instability would play a
supporting role...with Wisconsin looking to have the better chances,
less west where the ridge will have more of a influence.

For temperatures, despite the northwest flow the trend if for
increasing heights aloft along with warming in the lower levels.
Expect temps at or above the normals through the work week, slightly
cooler (esp east) for the weekend if an upper level low does cutoff
over the great lakes.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1242 PM CDT Tue Aug 7 2018

An upper level wave of low pressure will continue pushing through
the region into early evening, delivering an uptick in showers and
embedded thunderstorms for many areas. Overall, conditions will
remain VFR but may dip to MVFR or even briefly IFR under any
heavier rains with storms. Skies should then gradually clear
tonight as high pressure brings another round of light winds.
Given the setup and recent history, suspect we're looking at
another round of river valley fog in and around LSE, though there
is some stronger wind aloft behind our departing system.
Regardless, given the pattern, probably looking at LIFR conditions
once again, with the potential for even a period of 1/4SM in very
dense fog. Thereafter, looking like mainly clear conditions should
return for the morning hours of Wednesday with winds shifting
southwesterly 5-8 knots.

&&

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

SHORT TERM...Lawrence
LONG TERM...Rieck
AVIATION...Lawrence

Hazardous Weather Outlook
National Weather Service La Crosse WI
308 AM CDT Tue Aug 7 2018

IAZ008>011-018-019-029-030-MNZ079-086>088-094>096-WIZ017-029-
032>034-041>044-053>055-061-081130-
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-
308 AM CDT Tue Aug 7 2018

This Hazardous Weather Outlook is for parts of southeast
Minnesota, northeast Iowa, and southwest into central Wisconsin.

.DAY ONE...Today and Tonight

Scattered thunderstorms are possible today. Although the main
hazard with any storm will be lightning, an isolated strong storm,
with gusty winds or hail, cannot be ruled out.

Valley fog is possible again tonight.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday

Additional thunderstorm chances exist Thursday night through
Saturday, especially in Wisconsin. Severe storms are not
expected.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not anticipated.

.EMERGENCY MANAGEMENT COORDINATION...

No webinar is scheduled.

Shea

Special Weather Statement
National Weather Service La Crosse WI
227 PM CDT TUE AUG 7 2018

IAZ009-MNZ095-072000-
Howard-Fillmore-
227 PM CDT TUE AUG 7 2018

...A STRONG THUNDERSTORM WILL AFFECT NORTHWESTERN HOWARD AND
SOUTHWESTERN FILLMORE COUNTIES...

At 226 PM CDT, a strong thunderstorm was located over Lime Springs,
or 10 miles northwest of Cresco, moving east at 10 mph.

Nickel size hail is possible with this storm.

Locations impacted include...
Lime Springs, Cherry Grove, York, Chester, Saratoga, Davis Corners
and Hayden Prairie.

Torrential rainfall is also occurring with this storm, and may cause
localized flooding. Do not drive your vehicle through flooded
roadways.

LAT...LON 4334 9245 4358 9245 4358 9223 4334 9223
TIME...MOT...LOC 1926Z 263DEG 10KT 4345 9229

CA

Special Weather Statement
National Weather Service La Crosse WI
336 PM CDT TUE AUG 7 2018

IAZ009-010-019-029-072130-
Winneshiek-Chickasaw-Howard-Fayette-
336 PM CDT TUE AUG 7 2018

...A LINE OF STRONG THUNDERSTORMS WILL AFFECT PORTIONS OF
NORTHEAST IOWA...

At 336 PM CDT, radar indicated strong thunderstorms were located
along a line extending from near Ridgeway to near Waucoma. Movement
was east at 20 mph.

Winds in excess of 40 mph and half inch hail are possible with these
storms.

Locations impacted include...
Decorah, Cresco, Calmar, Ossian, Lawler, Spillville, Fort Atkinson,
Ridgeway, Protivin, Waucoma, Jerico, St. Lucas, Jackson Junction,
Vernon Springs County Park, Festina, Vernon Springs, Eldorado,
Nordness, and Lake Meyer County Park.

These storms may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.

LAT...LON 4336 9171 4299 9170 4299 9227 4336 9226
TIME...MOT...LOC 2036Z 276DEG 19KT 4330 9208 4310 9208

CA