Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 140742

Area Forecast Discussion
National Weather Service La Crosse WI
242 AM CDT Fri Jul 14 2017

.SHORT TERM...(Today through Sunday)
Issued at 242 AM CDT Fri Jul 14 2017

The focus in this period will be on the thunderstorms chances for
Saturday and Saturday night. Water vapor satellite early this
morning shows a large area of ridging over the Rockies that
extends well into Canada. A cut off upper level low off the
Canadian Pacific coast will send some short wave troughs into and
over the upper level ridging. Right now, the models are in
reasonably good agreement that a wave will top the ridge and drop
southeast across the Great Lakes and southwest Ontario Saturday
afternoon and evening. This projected path takes the wave quite a
ways northeast of the local area with almost no pv advection in
the 500-300 mb layer over the region. This essentially will leave
the low level forcing along a cold front to be the trigger for
any convective activity. The front should move across the region
during the favorable peak heating of the day Saturday afternoon
and into the early evening. A band of weak frontogenesis in the
1000-700 mb layer should accompany the front along with about 3
ubar/s of up glide on the 310K isentropic surface. Interestingly,
both the 14.00Z NAM and GFS show the low level moisture transport
starting post-frontal and coming into the the back side of the
front. This suggest the low level jet will not be involved to feed
any storms on the leading edge of the activity. Forecast
soundings suggest a good low level cap will be in place until
almost the time the front moves through, leaving the concern of
just how much time will there be for convective activity to
develop before the front moves through and the atmosphere begins
to stabilize? Given the relative weak forcing and short window of
opportunity for convection to form, a 20 to 30 percent chance of
storms seems appropriate with this system.

If convection can form, some threat for severe storms with it.
Ample instability will exist ahead of the front with up to 2500
J/Kg of ML CAPE. The shear looks to be pretty much all in the 0-3
km layer and should be around 30 knots or so. This would suggest
that damaging winds and hail would be the primary threats.

.LONG TERM...(Sunday night through Thursday)
Issued at 242 AM CDT Fri Jul 14 2017

The upper level ridge looks like it will get flattened during this
period and possibly also shift more over the central part of the
country. This would set up a near zonal flow across the Upper
Midwest or possibly a bit of a northwest flow. Either way, there
does not look to be a strong short wave troughs currently progged
to impact the area. However, there will be a front that should
drop into the region Monday night and Tuesday and then become
stationary either over the area for very close to it for the
remainder of the period. This will keep some 20 to 40 percent rain
chances in the forecast for each period from Monday night right
through to Thursday.


.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1144 PM CDT Thu Jul 13 2017

Satellite trends show expansive low VFR/MVFR cloud deck across
central MN into northern WI holding together late this evening and
now expect these clouds to continue to impact KLSE/KRST overnight
and into Friday morning. KLSE is on the edge of the slightly lower
cloud base, so will continue this MVFR trend through the
overnight. KRST, conversely, is just above 3000 ft agl and this
should also continue for at least a few hours before possibly
dropping to MVFR thresholds approaching sunrise. Clouds should
finally begin to lift/scatter out late Friday morning and early
afternoon with VFR conditions thereafter. Light north-northwest
wind will be the rule, becoming light and variable by Friday
evening as high pressure builds across the region.


Issued at 242 AM CDT Fri Jul 14 2017

After the recent heavy rains, one river flood warning in effect
along the Kickapoo River at Viola. The river was still rising
Thursday, but looked to be slowing down. See the latest flood
statement for more information.




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