Areal Flood Warning 10, NWS La Crosse, WI

Area Forecast Discussion
National Weather Service La Crosse WI
603 AM CDT Thu Jul 20 2017

.SHORT TERM...(Today and tonight)
Issued at 245 AM CDT Thu Jul 20 2017

Showers/storms on the nose of the low-level jet/stronger moisture
transport producing locally heavy rainfall will continue to shift
eastward as the low-level jet veers early this morning. Otherwise,
it should be a pretty quiet day as the low-level surface boundary
gets shifted southward again. Could not rule out a stray
shower/storm, especially farther south closer to the boundary, but
anything would be isolated. It will still be warm and quite
humid, especially across southern areas closer to the boundary
with highs in the 80s.

Another potential severe event/heavy rain event still appears on
track for Friday. Storms should fire across the northern plains
Thursday night in advance of an upper shortwave trough north of the
surface boundary. Sustained low-level warm advection and increasing
moisture transport north of the surface boundary will help focus
redevelopment of storms as they progress eastward out of the plains
through the day. Once again, the storms likely will focus on the
edge of the stronger instability which will cut across the area.
Deep layer 0-6 km shear around 40 kts would support a severe threat,
including hail and damaging winds. Showers/storms should continue
into Friday night ahead of a weak surface low with continued
moisture transport on the nose of the low-level jet before it veers
westerly and helps end to the precip.

The environment will remain very favorable for heavy rainfall during
this time with seasonably high precipitable water values and very
deep warm cloud depths exceeding 4 km. With a few inches of rain
having fallen in some areas already this week, will have to
carefully watch for flash flood potential Friday/Friday night. See
the hydrology section for more details below.

Confidence is lower in the placement of surface features on Saturday
in the wake of the convection Friday night. Some showers/storms
could linger at least into Saturday morning, though. A strong
upper shortwave trough approaching from the northwest could help
to trigger additional scattered storms in the afternoon and
evening over parts of the area with some potential for strong
storms.

.LONG TERM...(Friday through Wednesday)
Issued at 245 AM CDT Thu Jul 20 2017

A cooler and drier airmass will begin to advect into the area on
Sunday as northwest flow aloft sets up with surface high building
in from the northwest. With upper troughing digging into the
northern Great Lakes, a few showers or storms could develop on
Sunday.

Otherwise, Monday and Tuesday right now look dry under the influence
of high pressure, with highs in the 70s to low 80s.

As the ridge slides eastward by the middle of the week, deeper
moisture will surge northward again as the upper flow pattern
becomes more zonal, with some potential for showers/storms pending
timing of weak embedded upper waves.

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 603 AM CDT Thu Jul 20 2017

All the convection has now pushed southeast of both airports. A
mixed bag of ceiling heights behind the convection with MVFR and
VFR. As the convection continues to move away and high pressure
drops in over the region, expect that ceilings will become all
VFR with the clouds then scattering out late this morning. There
should be more showers and storms that form tonight south of both
airports that will likely bring in a VFR ceiling that should
prevent any fog from forming. Will let the later forecasts detail
these trends.

&&

.HYDROLOGY...
Issued at 555 AM CDT Thu Jul 20 2017

Locally heavy rainfall overnight, locally in excess of 6 inches,
has occurred over parts of western Wisconsin and far southeast
Minnesota with flooding continuing early this morning. Gradually
improving conditions are expected with much of the rain done for
the day.

The rainfall has caused rises on some area rivers, including the
Trempealeau and the Kickapoo, with some locations along these rivers
already at or expected to reach flood stage. The Kickapoo River
at Ontario is peaking in major flood stage with some additional
locations expected to crest near moderate flood stage.

Additional locally heavy rainfall is expected Friday into Friday
night. With several inches of rain having already fallen this week
in some spots, these areas will be particularly susceptible to flash
flooding with more heavy rain. Although there is some uncertainty
where the heaviest rain will occur, the highest chances look to be
south of I-94 at this point. Additional rises and flooding on area
rivers/streams are expected.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Flash Flood Watch until 7 AM CDT this morning for WIZ032>034-041-
     042.

MN...Flash Flood Watch until 7 AM CDT this morning for MNZ079.

IA...None.
&&

SHORT TERM...JM
LONG TERM...JM
AVIATION...04
HYDROLOGY...JM

Hazardous Weather Outlook
National Weather Service La Crosse WI
352 AM CDT Thu Jul 20 2017

IAZ008>011-018-019-029-030-MNZ079-086>088-094>096-WIZ017-029-
032>034-041>044-053>055-061-211200-
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-
352 AM CDT Thu Jul 20 2017

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

.DAY ONE...Today and Tonight

Thunderstorms are likely early this morning with continued
flooding across parts of southeast Minnesota and western
Wisconsin.

A few additional thunderstorms are possible this afternoon and
again overnight tonight mainly south of Interstate 94.

Heat indices may reach 95 to 100 across northeast Iowa into
southwest Wisconsin this afternoon.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday

Thunderstorms are likely Friday into Friday night. Locally heavy
rainfall is expected, with damaging wind gusts and large hail
possible.

Flash flooding is possible in areas that receive repeated
thunderstorms. Rises on some area rivers and streams are expected,
with flooding along rivers where heavier rainfall occurs.

Scattered thunderstorms are possible Saturday into Saturday
evening. A few storms may be severe with locally heavy rainfall,
strong winds, and hail.

Heat indices may reach 95 to 100 across northeast Iowa into
southwest Wisconsin on Saturday afternoon.

Isolated thunderstorms are possible Sunday and again on Wednesday.
It is too early to discern any severe threats at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be requested Friday afternoon and evening.
Rainfall and flooding reports are appreciated.

.EMERGENCY MANAGEMENT COORDINATION...

No webinar is scheduled.

JAM

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