Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 242003
AFDARX

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

.SHORT TERM...(This evening through Thursday)
Issued at 303 PM CDT Wed Aug 24 2016

Latest water vapor satellite imagery indicating upper level closed
low over southern Canada. Latest 19z surface analysis shows cold
front extending from southern Canada into central Iowa and is
producing light rain/sprinkles or drizzle along and ahead of cold
front per latest KARX radar.

The 24.12z GFS/NAM/ECMWF are in agreement in moving surface front
southeast over Lake Michigan and northern Missouri tonight. The
deterministic models indicate shortwave trough embedded in the
southwesterly flow aloft to move along the surface front this
evening/tonight and the combination of moisture
convergence/lift...the far southern parts of the forecast area
will have the possibility of showers and thunderstorms tonight.
Heavy rain or any severe threats looks very low across the far
southern forecast area.

Surface ridge builds into the western half of Minnesota and the
Dakotas Thursday and provide mainly dry weather across the forecast
area.

.LONG TERM...(Thursday night through Wednesday)
Issued at 303 PM CDT Wed Aug 24 2016

Surface ridge dominates the forecast area Thursday night into
Friday. The 24.12z GFS/NAM bufkit soundings suggest light winds near
the surface...with winds aloft above 10 knots...this will inhibit
fog potential in the Mississippi river valley. However...fog
formation will be possible in river valleys Friday morning. For
now have left out any mention of fog in forecast...based on if
winds will be light enough for development.

Upper level closed low weakens and moves over southern Ontario
Canada Friday night into Saturday. The Upper midwest remains in
southwest flow aloft...as another upper level trough digs over the
Northern Plains states. Shortwave trough tracks into the Upper Great
Lakes region...with forcing/lift/moisture convergence. This will
spread another round of showers and thunderstorms into the forecast
area after 06z Saturday. The 24.12z GFS/NAM indicate 20 to 30 0-3km
shear Saturday and both models show increasing instability.
However...the 24.12z GFS/NAM/ECMWF show differences in timing of
convection. Based on timing...severe threat remains low.

Main forecast concerns Saturday night through Wednesday are
precipitation chances through much of the period. The 24.12z
GFS/ECMWF/GEM show upper level low/trough moving into the Great
Lakes region Sunday into Monday. The 24.12z deterministic long range
models indicate differences in timing of the upper level
trough...this will have impacts on lingering precipitation chances
into Monday. Shortwave ridge builds into the Northern Plains and
Upper Midwest Tuesday and Wednesday. The 24.12z GFS/ECMWF suggest
timing differences on strength and break down of shortwave ridge
over the Upper Midwest Tuesday into Wednesday. Concern is timing
of next piece of energy overtopping ridge and impacting the
forecast area during this time frame. For now will continue with
small chances of showers and thunderstorms across forecast area
through much of forecast period.

&&

.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 303 PM CDT Wed Aug 24 2016

Minor to major flooding is occurring along the
Kickapoo...Cedar...Upper Iowa and Turkey rivers. See the latest
flood statements for the latest forecast information.

Next round of convection to impact the forecast area is expected
Friday night into Saturday. The 24.12z GFS/NAM suggest precipitable
water values approaching 1.5 inches during this time frame. The
potential for 1 to 3 inches of rainfall is possible across the
forecast area...though exact timing and placement is still in
question. With saturated soils...this could lead to further flash
flooding or river flooding threat.

&&

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

$$

SHORT TERM...DTJ
LONG TERM...DTJ
AVIATION.....RRS
HYDROLOGY...DTJ



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