Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 241716
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1216 PM CDT WED AUG 24 2016

.SHORT TERM...(Today and Tonight)
Issued at 236 AM CDT Wed Aug 24 2016

Dealing with major flash flood scenario across northeast tier of
counties in Iowa early this morning with large swath of 4"+
rainfalls likely. Already issued some site specific river flood
warnings but amount of impact likely to be seen after daybreak
today.

Area is primed with bulls-eye of precipitable water near 2" and low
level jet impacting outflow boundary from nearly steady state
convection. To the south of convection steady low level inflow with
70+ surface dew points continues to advect into this east-west
orientated line of storms. Legacy rainfall estimates off radar are
underestimating rainfall while Dual Pol is just a bit high. Needless
to say, combination of watches and warnings are in effect.

Closed low continues to slowly move east across southern Canadian
prairies leaving western Great Lakes in southwest flow and favorable
jet dynamics for good updrafts/lift. Minor waves moving through this
flow spawned earlier convection, but low level moisture transport
starts to shift east gradually this morning so feeling is convection
will gradually end from west to east to follow suit.

Lower confidence on how later in the day will pan out with some
short term guidance suggesting another wave could advect northeast
in flow and work on slow moving frontal boundary. While rain threat
will shift east, continued small risks in south and southeast areas.

Cooler and drier air begins to shift in for tonight and push any
remaining rain threats off to the southeast.

.LONG TERM...(Thursday through Tuesday)
Issued at 236 AM CDT Wed Aug 24 2016

Medium range guidance suggests closed low opens up and moves east
along US and Canadian border for latter part of week. This will mean
quiet few days with short term upper ridge returning into Friday.
May see some early morning valley fog setup but did not have time to
work those details into the forecast database right now. Will have
to add these features as time permits.

Next wave enters the picture by Friday night with moisture transport
returning. This is a quick moving wave and threat of any severe
weather for Saturday time frame may not fall into place with limited
moisture return. Again, this will have to be watched for later
detail.

Early next week looking quiet behind wave.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1216 PM CDT Wed Aug 24 2016

Cold front with the leading edge of cooler/drier air was located
near a KEAU-KONA-KDSM line at 17z. Diurnal warming/mixing was
raising cigs in the airmass ahead of and just behind the front.
Lower cigs to continue mixing/rising thru the afternoon aided by
drier air filtering in behind the front. Clearing skies (edge of low
clouds) were near KMSP to KMKT, with distance-speed tool moving this
thru KRST around 2030z and KLSE around 00z. Once this moves thru,
generally good VFR expected tonight/Thu morning as cooler/drier Can
high pressure builds into the Upper Midwest. May be a small threat
of late night/early morning BR/FG at/near the KLSE airport. However,
with the high building in and 10-15kts of N-NW wind at the top of
what looks to be a shallow boundary layer late tonight, for now left
mention of BR/FG out of the usual 09-13z period at KLSE. May be more
of a concern for BR/FG at KLSE around 12z Fri with the center of the
sfc high near/overhead.

&&

.HYDROLOGY...
Issued at 236 AM CDT Wed Aug 24 2016

Copious amounts of rain overnight have led to widespread and serious
flash flooding in far northeastern Iowa into southwest Wisconsin.
Rivers on the rise and site specific forecasts put together to get
some flood warnings out with as much lead time as we could.

Some locations could have moderate to major flooding very quickly
today with 5"+ rainfall totals still coming in. Warnings will
continue for much of the region for awhile this morning.

Forecasts from the River Forecast center will be made available as
soon as possible.

&&

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

$$

SHORT TERM...Shea
LONG TERM....Shea
AVIATION.....RRS
HYDROLOGY....Shea


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