Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 210347

Area Forecast Discussion
National Weather Service La Crosse WI
1047 PM CDT Fri Sep 20 2019

.SHORT TERM...(This evening through Saturday)
Issued at 312 PM CDT Fri Sep 20 2019

At 3 PM, skies were mostly to partly sunny across northeast Iowa,
and mostly cloudy across the Upper Mississippi River Valley.
Temperatures ranged from the mid-70s to mid-80s.

For late tonight and Saturday morning, the remnants of Imelda will
move northeast through the area. This system will bring with it a
band of showers and storms. With preciptable water values running
close to 2 inches and warm cloud layer depths over 4 km, these
showers and storms will be very efficient rain producers.
Fortunately, it looks like these storms will be rather
progressive, so this will limit the flooding threat.

.LONG TERM...(Saturday night through Friday)
Issued at 312 PM CDT Fri Sep 20 2019

On Saturday night, a cold front will move southeast through the
area. This front will move the fastest north of Interstate 90 and
much slower south of this Interstate. Clouds will likely limit the
instability. While the 0-1 km ML CAPES will be up to 1500 J/kg,
the deep shear will be mainly along and post frontal. Most of the
CAMs are not that impressive with the storms along this front.
However, the latest HRRR would suggest that there may be a few
isolated supercells along this front. The main threat would be
large hail and gusty winds. The main heavy rain threat will be in
southwest Wisconsin and the eastern portion of northeast Iowa
where precipitable water values will be around 2 inches and warm
cloud layer depths will be in the excess of 4 km.

On Sunday, a shortwave will round the base of a longwave trough
moving through the region. It is unclear whether this will bring
additional heavy rain to Grant County in southwest Wisconsin.

From Tuesday night into Wednesday, another longwave trough will
move through the region. Moderate to strong moisture transport
will be found ahead of this system. Precipitable water values will
quickly climb to around 1.6 inches. While 0-1 km ML CAPES will
climb up to 1500 J/kg, the 0-3 and 0-6 km shear looks to be weak,
therefore severe weather is not anticipated at this time.

On Thursday night and Friday, there will be another surge of
moisture into the region as a shortwave trough approaches the
region. Precipitable water values will climb into the 1.6 to 2
inch range. This may result in another bout of heavy rain for the


.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1046 PM CDT Fri Sep 20 2019

VFR conditions expected at the TAF sites through early Saturday
morning until a push of low level moisture arrives towards
daybreak with an approaching disturbance. This will lead to a
quickly developing cloud deck with low end MVFR to IFR ceilings.
Not anticipating much in the way of convection associated with
this passing feature, but limited instability may support some
showers and perhaps a rumble of thunder or two through ~14Z. Due
to expected limited coverage, have only gone with VCSH in the
TAFs. IFR cigs then expected through early afternoon when daytime
heating should initiate a slight rise to MVFR for the remainder of
the period. There is a small chance for additional showers and
storms in the afternoon, but potential activity looks pretty
limited/unorganized due to weak forcing and some capping aloft.
Have therefore stuck with just VCSH. A somewhat better chance for
storms will come after 00Z Sunday as a cold front drops into the
area, so have introduced VCTS Saturday evening.

Southeast winds will gradually increase through early Saturday
morning as the pressure gradient strengthens overhead, becoming
more southerly by daybreak. Winds will turn gusty by mid-morning,
especially at RST where gusts approaching 30 knots are possible
through the afternoon. Gusts will diminish with sunset, but winds
will remain breezy as they shift to the southwest ahead of the




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