Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 141918

Area Forecast Discussion
National Weather Service La Crosse WI
218 PM CDT Thu Sep 14 2017

.SHORT TERM...(Tonight through Friday)
Issued at 218 PM CDT Thu Sep 14 2017

Latest water vapor imagery shows an upper level trough over the
Pacific Northwest with a ridge axis over the Central Plains. Surface
analysis shows a weak area of low pressure along the Nebraska/South
Dakota border with a boundary extending to the northeast into
northeast Minnesota. The aforementioned ridge axis over the Central
Plains will move through the area today with the surface pressure
gradient tightening ahead of the low pressure system. The increasing
southerly winds will bring in some warmer air, including 925 mb
temperatures in the 22 to 28 C range, leading to well above normal
high temperatures in the 80s to possibly 90 degrees in a few spots.

For tonight, guidance shows some isentropic lift near/in the western
part of the forecast area after midnight. This will lead to some
cloud formation at the very least, with a few showers possible.
MUCAPE values in the 250-500 J/kg range also indicate the
possibility, albeit very slight, of some thunder.

Friday looks like another warm day, despite some lingering clouds
from overnight showers/storms. Temperatures will be in the 80s to
near 90 once again, with strong southerly winds and 925 mb
temperatures in the 22 to 28 C range.

.LONG TERM...(Friday Night through Thursday)
Issued at 218 PM CDT Thu Sep 14 2017

There will be shower/storm chances Friday night into Saturday as
corridor of weak moisture transport continues ahead of a cold front
moving slowly east across MN into northwest WI. Look for these
chances mainly west of a line from Rochester MN to Medford WI.
Otherwise, 925mb temperature remain unseasonably warm in the 24-27C
range. With good mixing ahead of the front, expecting to see highs
climb well into the 80s, with perhaps near 90 across portions of far
southwest WI/northeast IA.

Scattered showers/thunderstorms are expected to spread east across
the area going into Saturday night as the cold front passes through.
Right now, severe threat looks minimal to marginal as CAPE
diminishes with loss of surface heating as the front comes through.
However, cannot rule out the possibility of a few stronger storms
with small hail and gusty winds.

A few lingering showers/storms may be around Sunday morning but then
a push of dry/cool Canadian air spreads in for Sunday afternoon.
Look for highs in the upper 60s to the middle 70s.

Southwest flow aloft ahead of a deepening trough out west Monday
through Thursday will bring a couple mid-level disturbances across
the area for intermittent small-end shower/thunderstorm chances.
Otherwise, looks like temperatures will be a few degrees above
seasonal normals, especially Tuesday through Thursday.


.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1233 PM CDT Thu Sep 14 2017

VFR conditions expected through the period. Could see a few wind
gusts around 18 kts this afternoon at KRST. Then low level wind
shear is expected at KRST and KLSE tonight. Guidance suggests the
formation of some scattered clouds in the 9000 to 10000 ft range
after midnight, and possibly even some showers, especially at KRST,
but confidence in showers forming is not high enough to include any
mention. Should the showers develop, could see some ceilings, but
they would remain in the VFR category. Southerly winds are expected
to prevail on Friday, with gusts near 20 kts at KRST.




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