Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 200850

Area Forecast Discussion
National Weather Service La Crosse WI
350 AM CDT SAT AUG 20 2016

.SHORT TERM...(Today and tonight)
Issued at 350 AM CDT Sat Aug 20 2016

Main forecast concerns are on the potential for some locally heavy
rainfall today which may lead to flooding in areas already hit by
heavy rain this past week.

Surface low pressure is deepening across the forecast area this
morning as an upper trough digs into the region from the Dakotas.
Ongoing convection across sections of Wisconsin will also help to
deepen the low this morning. So, showers will become widespread this
morning and we could even see some isolated thunderstorms at
times. As the surface low lifts northeast today the heavy rain
environment will be shunted to the east of the forecast area and
we will most likely see the bulk of the rain across northwest into
sections of northern Wisconsin where the deformation zone sets up.
However, until the low starts lifting to the northeast, cannot
rule out some locally heavier rainfall at times. If this rain
would happen to fall over locations recently hit by heavier
rainfall, basically Wabasha County east through Jackson into
Adams County, we may see some areas of flooding develop. However,
the threat for flash flooding appears to be diminishing. Will hold
onto the Flash Flood Watch until the low passes and the heavier
rain environment edges into eastern sections of Wisconsin.
Rainfall amounts of 1 to locally 2 inches appears possible. Warm
cloud depths of 3.5 KM and precipitable water values hover in the
1.6 to 1.8 range and can just see a warm frontal feature near the
interstate 94 corridor across western into central Wisconsin this
morning. However 850 mb moisture transport into this areas is
weak. Showers and isolated thunderstorms will taper off this
afternoon. Showers look to linger across northern Wisconsin this
evening as the low lifts northeast over eastern Lake Superior.

.LONG TERM...(Sunday through Friday)
Issued at 350 AM CDT Sat Aug 20 2016

Surface high pressure edges in from the west on Sunday. Clouds
should gradually clear from west to east through the day, but they
may be stubborn to do so, especially across central into eastern
Wisconsin. A weak shortwave passes  across over northern
Minnesota and Lake Superior Monday night but the forecast area
should remain dry.The surface high pushes off to the east Monday
night into Tuesday as a trough edges east out of the northwest
CONUS. Southerly flow will set up across the region and it could
be rather breezy Monday afternoon and again on Tuesday. The trough
continues its eastward track Tuesday night into Wednesday dragging
a cold front across the area with chances for showers and
thunderstorms. After a slight warmup on Tuesday, with highs
edging into the lower 80s, cooler highs return for late week with
highs slipping back into the 70s. The next chance for rain looks
to arrive this weekend.


.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1205 AM CDT Sat Aug 20 2016

The large area of rain has been dissipating on the southwest side
as the moisture transport shifts off to the east of area. The
20.03Z HRRR has handled this dry slot effect very well and shows
only some occasional light rain for both sites for the rest of
tonight into Saturday morning. The concern then becomes if there
has been enough moisture introduced into the lower sections of the
atmosphere to allow low clouds and fog to form. Looking downstream
to where is was raining most of the evening, the conditions have
remained almost exclusively VFR. However, the office sky cam does
show some lower clouds floating by. With KLSE having received more
rain than KRST, confidence is higher that some low MVFR ceilings
will form at KLSE along with some fog to reduce the visibility to
IFR. With less rain at KRST so far, will only take the forecast
down to MVFR. The rain still looks like it will end Saturday
morning with conditions returning to VFR during the afternoon.


Issued at 350 AM CDT Sat Aug 20 2016

Additional rainfall amounts of 1/2 to locally 2 inches are
expected today. The heaviest rain looks to fall across portions of
west central into northern Wisconsin. While it appears the threat
for flash flooding has diminished, if the axis of steadier rains
sets up across areas hit by heavier rains this week, flooding may
develop. Will continue the Flash Flood Watch with good forecast
model consensus of a heavier deformation band setting up this
morning with 1 to 2 inches of rainfall possible near or over the
Flash Flood Watch area. One hour Flash Flood Guidance in these
areas is only at 1.3 to 1.5 inches. Rainfall rates may not be high
enough for flash flooding, but significant rises are possible on
creeks and streams.


.ARX Watches/Warnings/Advisories...
WI...Flash Flood Watch through this evening for WIZ032>034-042>044.

MN...Flash Flood Watch through this evening for MNZ079.



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