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Area forecast discussion 
National Weather Service La Crosse WI
1244 PM CDT Friday Sep 4 2015

Short term...(today and tonight)
issued at 400 am CDT Friday Sep 4 2015

Forecast focus is on small rain chances today and into tonight.
Convergent area seen in surface analysis at 08z from northern
Illinois...northwest through northeast Iowa and into Minnesota. Overrunning this
area resulting in northwest to southeast bands of cloud cover.
Some convection over southwest WI last night...but nothing
recently. But satellite imagery shows castellanus across Iowa with
isolated slow-moving -tsra...which has been percolating all night.
Water vapor imagery clearly shows the short wave dropping slowly
across WI and into Illinois. Meanwhile a weak ripple was moving
northeast across the Dakotas. Thus with the main forcings just
outside our forecast area...the rain chances are limited. Models
all have varying degrees of rain chances...with GFS most robust
and NAM most paltry. Despite weak forcing...degree of available
moisture and instability should at least allow for some
possibility for rain.

Long term...(saturday through thursday)
issued at 400 am CDT Friday Sep 4 2015

Area to remain in the hot and sticky ridge until late Sunday.
Closed circulation over the Pacific northwest will eventually
shift far enough east into Manitoba by Monday. This will send a
cold front through the region Sunday night. There is a very good
chance for thunderstorms along this boundary...especially given
the significant airmass change and the amount of moisture and
instability ahead of it. At first blush it appears there would be
a risk for strong or even severe storms as the front passes. But
with the front passing after the peak diurnal timeframe...and with
the best shear lagging it...not overly impressed. Still...it bears
watching. Cooler weather then on tap for the remainder of the
week...more typical of September. Another chance for showers
Monday night into Tuesday the trough moves east across Ontario.
Zonal to slightly northwest flow then prevails through next
weekend.

&&

Aviation...(for the 18z tafs through 18z Saturday afternoon)
issued at 1244 PM CDT Friday Sep 4 2015

A short wave trough moving northeast through Minnesota will bring
a broken deck of 10 to to 15k foot clouds to the area from late
this afternoon through Saturday morning. While the mesoscale models are
showing some isolated to scattered showers and storms...concerned
that the lack of forcing and dry air below 10k feet may result in
mainly virga...so did not add any precipitation to the tafs. With
10 to 20 knot winds just off the surface and a broken deck of
clouds...did not include any fog in either taf site.

&&

Arx watches/warnings/advisories...
WI...none.
Minnesota...none.
Iowa...none.
&&

$$

Short term...mw
long term....mw
aviation...boyne

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