Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 231930
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
230 PM CDT Sun Jul 23 2017

.SHORT TERM...(This evening through Monday)
Issued at 230 PM CDT Sun Jul 23 2017

23.19Z analysis shows a cold front from northeast WI into central
IA with light northwest wind and dewpoints in the upper 50s to
lower 60s behind the boundary. This much more comfortable air mass
will settle across the forecast area tonight as high pressure
moves across northern MN/WI. Will need to watch for some residual
moisture getting stuck under the nocturnal inversion possibly
resulting in some low stratus, but with at least some degree of
clearing and light near surface winds, there could be patchy to
areas of fog overnight.

For Monday, high pressure moves slowly into the western Great
Lakes region resulting in partly to mostly sunny skies, light
easterly winds, and temperatures in the mid to upper 70s.

.LONG TERM...(Monday night through Sunday)
Issued at 230 PM CDT Sun Jul 23 2017

Southerly moist return flow develops on Tuesday as high pressure
drifts farther to the east. At the same time, a strong 500 hPa
closed low will move across the southern Canadian Prairies with a
trailing surface cold front from northwest MN into northeast SD by
00Z Wednesday. This front will serve as the focusing mechanism
for additional showers and thunderstorms, some of which may be
severe. GFS/NAM soundings are in good agreement showing a strong
CAP across the forecast area, keeping things dry through at least
00Z Wednesday. Will need to watch upstream convection Tuesday
night for possible upscale growth into some kind of linear system
farther south, but for now slowly increasing chance POPs seem
reasonable.

Aforementioned cold front drops south across the forecast area on
Wednesday. GFS is much more bullish with instability ahead of the
front compared to NAM, but both models show weak deep layer shear
with perhaps up to 30 kts in the 0-3 km layer. NAM soundings are
more indicative of a heavy rain threat and this makes sense with
PWATS rising back above 2 inches by 00Z Thursday. Cannot rule out
a few isolated severe storms along the front, but think bigger
concern at this time is heavy rain. That said, training
thunderstorms should be limited given rather progressive nature
of the front.

Thursday through Saturday will be mostly sunny and dry as surface
high pressure dominates the regional weather pattern. Temperatures
will be seasonable with daily highs in the upper 70s to lower
80s. The next best chance for some showers and thunderstorms will
be Sunday afternoon.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1210 PM CDT Sun Jul 23 2017

Water Vapor satellite imagery showing a mid-level trough rotating
southeast across the area late this morning. Steep lapse rates exits
under this trough, and this is expected to spark a few shra/ts east
of the Mississippi River (but remaining southeast of the KLSE TAF
site). So, just VFR cumulus expected at both KRST/KLSE. Will then
have to watch for fog at both TAF sites late tonight/early Monday
morning as a ridge of high pressure build in overhead. Light
winds/clear skies and moist lower boundary layer from recent heavy
rain will set the stage for patchy fog. Not totally confident on
coverage or how dense it will be though as models do indicate some
MVFR/VFR stratocumulus drifting over the area along with northeast
winds at 10 to 15kt just off the surface at 500-1000feet. This
will likely inhibit widespread development. Will keep a close eye
on it.

&&

.HYDROLOGY...
Issued at 230 PM CDT Sun Jul 23 2017

The Volga River at Volga crested last night around 1 AM and
continues to fall. It appears the river also crested at Littleport
this morning around 11 AM and has started to fall. Flood waters
will continue to move downstream tonight into Monday, emptying
into the Turkey River and impacting Garber before reaching the
Mississippi River. Water levels have dropped below flood stage
farther upstream along the Turkey River at Elkader.

Elsewhere, flooding continues along portions of the Trempealeau,
La Crosse, and Kickapoo Rivers, although water levels along all
three rivers continue to fall.

Extended the Areal Flood Warnings across southern Fayette and
Clayton Counties for another 24 hours through Monday afternoon
due to river flooding and continued high water issues impacting
roads.

The next best chance for showers and thunderstorms will be Tuesday
night through Wednesday. Some of these thunderstorms may produce
heavy rainfall.

&&

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

$$

SHORT TERM...Rogers
LONG TERM...Rogers
AVIATION...DAS
HYDROLOGY...Rogers



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