Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 171751

Area Forecast Discussion
National Weather Service La Crosse WI
1251 PM CDT Thu Aug 17 2017

.SHORT TERM...(Today and tonight)
Issued at 250 AM CDT Thu Aug 17 2017

Satellite imagery clearly shows an impressive frontal cyclone early
this morning, with a 998 mb surface low centered just southwest
of the Twin Cities. The strongly forced band of rain/thunder ahead
of the upper wave that passed across the area during the evening
continues to lift north with the dry slot/upper jet punching in
behind it.

A fall-like day is on tap for today with cool, showery, and breezy
conditions. The surface low will move towards Lake Superior by this
evening with wraparound showers and low stratus gradually shifting
east across the region through the day. With widespread clouds
and periods of showers/drizzle, daytime temps won`t rise much,
probably hovering in the upper 60s to low 70s across much of the
area unless some areas see a period of more sun. Winds will also
become gusty, as 850 mb winds of 35-40 kts wrap around the
backside of the 850 mb low tracking from Minnesota into northern
Wisconsin. With all the clouds and showers, the mixing depth may
be limited, but winds could gust over 30 mph (and stronger if
greater mixing occurs than expected), especially over southeast
Minnesota into northeast Iowa.

Weak surface ridging will spread across the area tonight as the low
pushes off to the northeast. Clearing will occur from west to east
this evening and tonight, although clouds may linger for much of the
night across parts of central into north-central Wisconsin.

.LONG TERM...(Friday through Wednesday)
Issued at 250 AM CDT Thu Aug 17 2017

Another upper shortwave trough will dig southeastward towards the
Upper Mississippi Valley later Friday into Friday night with chances
for showers spreading southeastward from Minnesota and Iowa into
western Wisconsin during this time. Could see a few storms, although
the axis of highest CAPE should remain west of the area.

The weekend is shaping up to be dry as high pressure builds in
behind the departing upper trough. 850 mb temps will climb from
around 12-14C Saturday to around 20C on Sunday with a surge of
warm advection. As a result, high temps could climb well into the
80s on Sunday.

Shower and thunderstorm chances return Sunday night into Monday
night as an upper trough drags a cold front through the region.
Plenty of moisture will surge northward ahead of the front, so a
warm and humid period is expected until frontal passage. Although
confidence in details is low, this system could have more
instability/shear to work with.

Ridging looks to build over the central US for the middle of
next week with current trends favoring a period of mainly dry
weather and seasonable temps.


.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1236 PM CDT Thu Aug 17 2017

Sustained northwest winds in the 15-20 kt range, with higher
gusts, and MVFR ceilings associated with a low pressure system
will continue through the afternoon. A few showers will also be
possible, mainly at KLSE. Ceilings should then lift to VFR levels
this evening at both locations, with cloud coverage decreasing
overnight. Some guidance hinted at fog development overnight, but
current thinking is that relatively strong winds aloft will
prevent this from happening. More clouds will then move in Friday
morning, but ceilings will remain in the VFR category. A few
showers could also approach KRST near the end of the TAF period,
but confidence is not there to include any mention at this time.




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