Special Weather Statement, NWS La Crosse, WI

Area Forecast Discussion
National Weather Service La Crosse WI
1242 PM CDT Tue Aug 7 2018

.SHORT TERM...(Today through Wednesday)
Issued at 215 AM CDT Tue Aug 7 2018

Weak low level flow and some recent rainfall leading to fairly
widespread valley fog event again early this morning. Showing up
nicely in area tributaries via GOES 16 channel differences imagery,
area observations, and some webcams.

Besides typical morning fog, a bit of a tricky forecast today, but
anyway you look at it, higher rain threat looks on target.

Tracking a short wave trough this morning as it exits the Dakotas.
This was producing robust convection ahead of it, although
convection is far more widespread closer to I-70 in deeper moisture.
As was the case last evening, much of this approaching activity will
weaken this morning, but given proximity of passing short wave,
expecting more shower and thunderstorm development later today
before threat quickly ends this evening from west to east.

Questions are how strong, if at all, will any of these storms be,
and will there be any "surprises" in the form of isolated severe
weather or funnels. Always a bit worried with this tight of wave
passing through during the dog days of summer. This can fire strong
storms with any build up of instability, and even though shear will
be very weak once again, updrafts aligned with any boundary could
produce a brief funnel cloud or two.

Would not have been surprised with a Day 1 MRGL RISK but lots of
limiting factors that muddle this forecast. Models hint at
possibility of 1000-1500 J/kg mixed layer CAPE later today but
assuming showers from the west will get here this morning, banking
on instability remaining fairly low. In any event, will have to keep
an eye on how things evolve. In addition, will lower highs a bit
today based on expected cloud cover and off and on showers.

Quiet again tonight but given continued weak flow, went ahead and
lowered favored colder valleys and put in fog redevelopment.

Northwest flow continues on Wednesday with generally dry day on tap
and a warm up.

.LONG TERM...(Wednesday Night through Monday)
Issued at 215 AM CDT Tue Aug 7 2018

Trends in medium range guidance on how upper pattern evolves later
this week into the weekend has been interesting. Idea of building
upper ridge from Rockies into northern Midwest still stands true,
but flow may become cutoff over Great Lakes into Ohio Valley with
diurnal convection possibilities. This pattern will likely mean some
off and on rain chances mainly for our Wisconsin counties, and
generally dry and warming conditions for our western areas.

Energy passing through flow in Canada early next week may
temporarily flatten ridge, bringing front through the area.
Predictability in this type of developing flow is rather low
though.

&&

.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...Shea
LONG TERM...Shea
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