Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 271732
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1232 PM CDT SAT AUG 27 2016

.SHORT TERM...(Today through Monday)
Issued at 245 AM CDT Sat Aug 27 2016

Latest watervapor satellite imagery depicting a shortwave driving
northeast into IA. It, coupled with the nose of low level moisture
transport/jet, was firing the areas of convection across eastern IA.
The shortwave and jet continue to push northeast this morning, and
so will the areas of showers/storms. Meso models in step with this
trend. The deeper warm cloud depths (4Km) hold south and east of the
local area, although pws approach 2 inches. Still some threat for
heavy rain through mid morning, but currently it looks like it
should miss the locations that received the heavy rains from a few
days ago. The rest of today looks like it should be dry.

Tonight into Sunday...low level warm air advection and the 850 mb
jet/moisture transport get together across southern MN, with the
likely result being an area of showers/storms. The GFS/NAM gradually
lift the favorable thermodynamics, tied with a sfc warm front, north
during the day Sunday, favoring central MN/northern WI with any pcpn
chances. Not much for forcing mechanisms evident aside from the
front/warm air advection locally, but a warm/moist/unstable airmass
does build across the region Sun/Mon. Any weak, small scale features
could tap into the fuel to spark showers/storms. Farther south, the
NAM/GFS/EC all suggest a region of upper level vorticity hanging out
in the weak flow from the southern plains into Iowa. It would be a
broad source region of lift, likely leading to areas of pcpn.
Whether it creeps far enough north to impact the local area is in
question. As mentioned, its a messy pattern with not a lot of clear
cut signals, but the fuel to work with. Will focus pcpn chances in
areas where confidence is higher, and run with smaller pops
elsewhere.

.LONG TERM...(Monday night through Friday)
Issued at 245 AM CDT Sat Aug 27 2016

Somewhat messy pattern continues for the new week. GFS and ECMWF
both point to broad ridging to start, giving way to northwest flow
for a couple days, then a amplification of the upper level ridge
over the plains for the end of the week. The GFS is significantly
stronger with relationship to the ridge building compared to the EC,
which results in a higher likelihood or shortwaves topping the ridge
and dropping across the Upper Mississippi River valley. The EC would
shunt these north. A shortwave slides west-east across southern
Canada Mon/Tue, with perhaps a few ripples south of the mean trough.
Sfc boundary progged to slip across the region though, although
overall weak sfc flow points to weak frontogenetic forcing.
Increasing sfc dewpoints will result in increasing instability in
this period, and likely enough lift for small shower/storm chances.
Currently, any wind shear looks well north.

Less humid, cooler air should move in post this system for Wed/Thu.
Models in conflict with how the end of the week will turn out. As
mentioned, the EC is more moderate while GFS a bit more
rambunctious. The GFS would mean a return to more summery warmth and
rain chances. The EC would be seasonable and likely dry. Believe the
GFS is overdoing it and will lean toward the EC for now.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1232 PM CDT Sat Aug 27 2016

cyclonic low level flow, recent rains an abundant low level moisture
have combined to produce rather widespread IFR/MVFR cigs across much
of IA/southern MN/southwest WI thru this morning. With weak gradient
flow and a broader passing trough aloft, the lower clouds to persist
thru the afternoon into early this evening, with only a gradual slow
rise of cig hgts with the diurnal warming/mixing thru the afternoon.
Passage of the main mid level trough and the lower level cyclonic
circulation should allow for a decrease of clouds this evening.
However a moist/cool boundary layer with smaller temp-dew point
spreads will be left behind, with conditions very favorable for
radiational fog formation in the 08z-14z timeframe Sun morning. In
the 10-15z period, continued with IFR conditions in BR at KLSE and
added some MVFR vsbys to KRST. Will have to watch KLSE for LIFR
cigs/vsbys in FG around 12z Sun. Once any BR/FG lifts/dissipates Sun
morning, generally good VFR expected thru the remainder of Sun into
Sun evening.

&&

.HYDROLOGY...
Issued at 245 AM CDT Sat Aug 27 2016

Still some ongoing river flooding across parts of northeast Iowa.
All the rivers have either crested and are on their way down. See
the latest flood statements for specific river information.

Warm cloud depths/sfc pws still supportive of heavy rain potential
this morning - but generally south of the local area. Current radar
trends and meso models suggest the same thing, keeping the stronger
returns/storms south of the areas that took the hardest hit from a
few days ago. Don/t anticipate any further flash flooding threat as
a result.

&&

.ARX Watches/Warnings/Advisories...
WI...None.
MN...None.
IA...None.
&&

$$

SHORT TERM...Rieck
LONG TERM....Rieck
AVIATION.....RRS
HYDROLOGY....Rieck


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