Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 151141
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
641 AM CDT Fri Sep 15 2017

.SHORT TERM...(Today through Sunday)
Issued at 300 AM CDT Fri Sep 15 2017

Smattering of light showers, running north-south across the area -
diminishing as a the night wears on. Fueled by a weak frontal
boundary and some moisture transport. Most of the shower/storms
continue well north, over northern MN, associated with an upper
level shortwave. Some hints in a few of the meso models that another
small area of showers could develop over MN late this morning into
the afternoon, likely along another weak boundary/ripple in the
upper level flow. Trends favor keeping chances west/north of the
local area...for now.

The late summery taste to the air will continue for today and
Saturday as an upper level ridge continues to pull warm air
northward. Highs from the mid 80s to around 90 are expected - well
above the low 70s normals for mid Sep. Humidity levels won`t be too
high, but some air conditioners might get their last workout in for
the year. A cold front is slated to sweep west to east across the
Upper Mississippi River valley Sunday, with cooler-more seasonable
air flowing in.

Finally, a decent shot for showers and storms for the local area,
although still can`t say its a slam dunk that everyone will get wet,
nor in amounts that will help the browning grass.

The models have been in good agreement with driving a 500 mb trough
from the PAC NW, across the northern plains Sat, and then northeast
into Canada Sunday. While the bulk of the upper level forcing will
hold west/north of the local area, the system`s associated cold
front is progged to move west-east across the region Sat night. Some
low level moisture transport leads the front in, and there is some
instability that lingers through the overnight hours to aid
shower/storm production. The stronger, deeper shear still displaced
west of the instability axis, but there could be enough overlap for a
stronger (severe?) threat for the late afternoon/evening just to the
west. Bears watching. The GFS and NAM both agree that a sct/bkn line
will be found post the front, with the GFS hinting at a pre frontal
band - mostly moisture transport related. Would expect a diminishing
trend in coverage/intensity as Sat night wears on (weakening
instability).

.LONG TERM...(Monday through Thursday)
Issued at 300 AM CDT Fri Sep 15 2017

The cool down Sunday looks to be brief as the GFS and EC are already
back to upper level ridge building for the start of next week,
digging a trough into the west coast and amplifying the ridge over
the east. It doesn`t look quite as warm as this week, but highs back
into the mid 70s to around 80 look reasonable at this time.

As for rain chances, the GFS remains the more pessimistic (or
optimistic, depending on your viewpoint) model, spinning bits of
shortwave energy into and across the ridge, resulting in periods of
shower/storm chances. The EC is more insistent on the ridge winning
out for much of the next week, favoring a drier forecast (although
still produces some spotty chances here and there). Nothing too
clear when it comes to rain chances at this time - so will stick
with consensus.

&&

.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 623 AM CDT Fri Sep 15 2017

A short wave trough brought a band of scattered showers and
isolated storms to the area overnight. This brought a brief storm
to KLSE around 3 AM. As this wave moves away, watching additional
showers and storms moving toward our area from western Iowa. The
RAP shows that the 850 mb moisture transport associated with these
storms will stay to the west of the area today. In addition, the
meso models show that they will dissipate before moving into our
area. Due to this, kept the forecast dry for now and will continue
to monitor them.

For tonight, it continues to look like the best 850 mb moisture
transport will remain west of the area. Due to this, kept the
mention of precipitation out of the KRST TAF.

With the soundings showing 40 to 50 knots of winds at 2K feet, it
looks like we will have another night with low level wind shear,
so it was included at both TAF sites after 16.02z tonight.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
IA...None.
&&

$$

SHORT TERM...Rieck
LONG TERM....Rieck
AVIATION...Boyne



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