Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 281055
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
555 AM CDT SUN AUG 28 2016

.UPDATE...
Issued at 329 AM CDT Sun Aug 28 2016

Calls to law enforcement indicated dense fog was reducing
visibility to 1/4 mile or less. As such, will go with a dense fog
advisory through 10 am this morning.

&&

.SHORT TERM...(Today through Tuesday)
Issued at 245 AM CDT Sun Aug 28 2016

Unsettled weather pattern for the next couple days with a
warm/moist/relatively unstable airmass building across the region.
Wind shear is meager at best, while forcing mechanisms leave
something to be desired.

Tonight and Monday night most models develop convective complexes
over northern MN in response to the low level jet, low level warm
air advection, and a weak-elevated frontogenetic region. MCVs are
spawned and expected to slip mostly east. Locally, some shower/storm
threat in the overnight/morning time periods...generally north of I-
94.

Better shot for widespread showers/storms as a cold front sinks
southward across the forecast area - associated with an upper level
trough making its way east across southeast Canada. Weak pressure
gradient alludes to forcing with the boundary, but enough there to
work on warm/unstable airmass to fire scattered to areas of
showers/storms Mon-Tue.

Don`t see a severe weather threat over the next few days. While
instability is progged to peak around 2500 J/KG of SBCAPE Tue
afternoon ahead of the front, wind shear is weak at best. Perhaps
some small hail out of this if it all comes together. Meanwhile,
while sfc pws exceed 1 1/2 inches, the deeper warm cloud depths are
well to the south. Locally heavy downpours possible, but not the
best setup for widespread heavy rains.

Summer temps for the next couple days - especially Monday. Numerical
guidance awfully bullish on the heat prospects Monday...wanting
upper 80s. Gridded data sides about 2-4 degrees cooler. A lot of mid
upper 80s yesterday in the source region though, and can`t rule out
some upper 80s in the usually warmer valley locations. Will temper
expectations a bit for now.

.LONG TERM...(Wednesday through Saturday)
Issued at 245 AM CDT Sun Aug 28 2016

Wed-Fri setting up for a pretty nice stretch for the region as the
area dips its toes into some early fall weather. The passage of the
front on Tue will allow for cooler/drier air to funnel southward
across the Upper Mississippi River Valley. Highs in the mid/upper
70s with lows in the 50s currently on the slate. Thu/Fri mornings
could be decent setups for valley fog - depending on where the sfc
high lies.

Working into the weekend the model flip-flop has continued. The
ECMWF now looks like what the GFS wanted to do a couple days ago,
before it changed to look more like the EC yesterday. The upshot is
the amplifying upper level ridge is back in the latest solutions,
building into the Plains by mid week, holding relatively firm in
strength as it transits east into the eastern Great Lakes by
Fri/Sat. Southerly winds will kick up as the sfc high exits east
Fri, and expect some return of warmer/more moist air. The low level
moisture transport starts to knife back into the region later in the
weekend in this scenario, with an uptick in instability too. Ample
fuel for any forcing mechanism to tap into...and there lies the main
question. Will any ripples in the upper level flow be able to work
into the ridge, dragging any associated sfc boundary into the moist,
unstable airmass? Answer is...uncertain. Model differences and
jumping back and forth keeps confidence on the low end. Some
consensus with bringing the mean upper level trough west-east
across Canada this weekend, moving/flattening the ridge, and
dropping a cold front over the local area. Sat night-Sunday would
have a good shot for showers/storms if this came to pass. For now,
will let consensus solutions dictate pcpn chances. On the whole,
looks dry for the most part through Friday.

&&

.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
Issued at 555 AM CDT Sun Aug 28 2016

Area currently socked in this morning with widespread LIFR dense
fog/stratus as humid air works into the region. Look for the
fog/stratus to lift/burn off by later this morning with daytime
heating and mixing through the lower boundary layer. Also
watching an area of thunderstorms over west-central MN. Models
insist on weakening the storms as they move east through MN...so
not anticipating they will impact the KRST/KLSE taf sites but will
certainly keep an eye on the trends. Otherwise...expecting LIFR
conditions to improve to VFR at KRST by 15z and 17z at KLSE. VFR
conditions then expected to continue into tonight BUT will be
watching for some fog/stratus development once again after 08z
with high pressure overhead and light surface winds. For
now...went with 3-5sm br at KRST/KLSE in the 08-12z time frame
with sct003 as well at KLSE after 10z.

&&

.ARX Watches/Warnings/Advisories...
WI...Dense Fog Advisory until 10 AM CDT this morning for WIZ032>034-
     041>044-053>055-061.

MN...Dense Fog Advisory until 10 AM CDT this morning for MNZ079-
     086>088-094>096.

IA...Dense Fog Advisory until 10 AM CDT this morning for IAZ008>011-
     018-019-029-030.

&&

$$

UPDATE...DAS
SHORT TERM...Rieck
LONG TERM....Rieck
AVIATION...DAS


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