Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 221742
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1242 PM CDT Sat Jul 22 2017

.SHORT TERM...(Today and Tonight)
Issued at 313 AM CDT Sat Jul 22 2017

High Impact Weather Potential: Ongoing flooding remains the #1
concern today, with some areas of likely severe flooding over parts
of Clayton and southern Grant Counties, where storm total rains the
past 24 hours have likely exceeded 6-8 inches. Beyond that, will be
watching the potential for some additional storms this afternoon and
early evening, one or two of which could be severe.

Unfortunately, another heavy rain/flooding event across the area
overnight, with persistent moisture transport up and over a low
level warm front into northern/central Iowa delivering another bout
of very heavy rains. Thankfully, that activity is beginning to wane
and shift south the past few hours with veering of the low level
jet/moisture transport axis, but with ongoing short term flooding of
concern as water works through the system. Additional storms to our
west as of 3 AM are likely to gradually weaken as they try to shift
east, running into decreasing instability with eastward extent, such
that most areas will likely remain dry through the morning. Will
have to closely watch cloud trends with some bouts of stratus
around, though per trends we may manage some sunshine at least by
late morning and afternoon.

Focus then shifts to a robust shortwave currently sliding through
southern Saskatchewan early this morning, with that feature
migrating toward western Lake Superior this evening. Associated
broad ascent on the southern flank of that wave and along a trailing
trough axis interacting with MLCAPE values around 2500+ J/kg later
this afternoon (barring unforeseen cloud issues) should be enough to
ignite some convection just to our north during the afternoon hours,
with some of that activity likely sneaking in our direction for the
late afternoon and evening. Confidence in exactly how things will
unfold remains low, but sufficient deep layer shear is there to
support a few severe storms (maybe a few supercells?), despite
overall veered and quite weak low level flow.

.LONG TERM...(Sunday through Friday)
Issued at 313 AM CDT Sat Jul 22 2017

Thankfully, some much-needed quiet weather will make a return Sunday
into much of Tuesday as Canadian high pressure works down into the
area. That setup should spell some nicer days and much more
comfortable humidity levels, before small storm chances return for
the middle and latter portions of next week. With that said, recent
guidance trends have suggested we may actually return to low level
ridging after a brief window of possible convection toward
Wednesday, so something to watch in coming days. With ongoing
weather, just not much time to digest the details that far out.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1242 PM CDT Sat Jul 22 2017

Broad MVFR/IFR cloud deck along and south of I-90 will continue to
sag southward through the afternoon, but would expect some
lingering MVFR ceilings at both TAF airfields until around 22.21Z
before completely clearing out. Attention then turns to a narrow
line of convection this evening mainly across northern/central WI,
but could drop as far south as KLSE. Will introduce VCTS in a
narrow window from 23.00Z to 23.02Z and monitor observations for
additional refinement. IF thunderstorms impact TAF airfield,
could see brief reductions in ceiling/visibility with gusty winds.

Skies expected to clear tonight with relatively light wind. Fog is
possible, especially in river valleys, but confidence not high
enough at this time to include in 18Z TAFs. If no fog develops
expect VFR conditions at both TAF airfields through the night and
into Sunday morning. Winds away from thunderstorms will be light
from the north-northwest, becoming variable at KLSE this evening
and overnight.

&&

.HYDROLOGY...
Issued at 313 AM CDT Sat Jul 22 2017

Another major flooding event across parts of northeast Iowa into
far southwest Wisconsin overnight. In particular, much of Clayton,
southern Fayette, and southern Grant Counties appear to be
hardest hit, with estimates of 8-10+ inches of rain falling the
past 24 hours and associated widespread flooding concerns. That
water will take a while to work through the system, with the
biggest concerns focused along the Volga River and southern
reaches of the Turkey river, mainly south of Elkader.
Additionally, water continues to percolate down the Kickapoo
River, with the crest having just passed Gays Mills, and along the
Trempealeau River, with Dodge cresting earlier. High water also
remains along the La Crosse River. Suffice it to say that we will
be dealing with ongoing flooding for another few days, though
thankfully a much-needed period of dry weather looks to arrive
this weekend into early next week.

&&

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

$$

SHORT TERM...Lawrence
LONG TERM...Lawrence
AVIATION...Rogers
HYDROLOGY...Lawrence


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