Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 211711
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1211 PM CDT Sat Apr 21 2018

.SHORT TERM...(Today through Monday)
Issued at 206 AM CDT Sat Apr 21 2018

Water vapor satellite this morning shows a cut off low over
Colorado with ridging ahead of it over the Mississippi River
Valley. The ridge is expected to get flattened and pushed into the
southeast U.S. today as the upper level low moves slowly to the
east/southeast. This will allow the local area to come under
control of the upper level low with just some very weak forcing as
short wave troughs rotate around the low. Moisture spreading out
ahead of the cut off low was resulting in quite a bit of high
level cloudiness over the area. Not expecting any precipitation to
occur with these clouds and the weak forcing as forecast soundings
show a nice dry wedge in the mid levels. The clouds will persist
through the day before slowly retreating to the south tonight as
the upper level low continues to move slowly to the southeast.

The area of high pressure centered over far southern Ontario today
will re-establish itself over the Great Lakes Sunday with the
ridge axis extending west and back over the area. This will help
provide partly to mostly sunny skies and allow temperatures to
continue slowly warming and be near the seasonal normals for both
days.

.LONG TERM...(Monday night through Friday)
Issued at 206 AM CDT Sat Apr 21 2018

The next chance for precipitation continues to be in the Tuesday
through Wednesday time frame. A short wave trough will move onto
the Pacific Northwest Coast late tonight/early Sunday morning.
Once the wave emerges from the northern Rockies late Monday, the
models differ on how it is handles. The cut off low currently over
Colorado should be over the lower Ohio River Valley/southeast U.S.
The 20.12Z ECMWF has been consistently showing that this upper
level low will slowly weaken and eventually be picked up by a
northern stream system moving across Canada. This causes the short
wave trough coming out of the Rockies to weaken and drop into the
Southern Plains as it runs into the remains of the cut off low.
The northern stream system that picks up the cut off low looks to
move along the Canadian border thus allowing the local area to get
split between the two systems. The 21.00Z GFS shows the short wave
trough phasing with the northern stream system over the High
Plains and strengthening into a closed low over the Missouri River
Valley Tuesday. The low then becomes detached from the northern
stream system and moves slowly southeast across the area through
Wednesday as a closed low. The 21.00Z GEM is more in line with the
ECMWF so plan to only have some small chances for rain for this
system as it passes by. Another northern stream system should
move southeast out of Canada and across the Upper Midwest for
Thursday and Friday. Once again there are strength differences
between the ECMWF and GFS with this system but with similar
timing, will have some small precipitation chances Thursday and
Thursday night.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1211 PM CDT Sat Apr 21 2018

VFR conditions anticipated over the next 24 hours as high pressure
remains in control. Some thicker mid/high clouds will work across
LSE and RST at times, but nothing lower than 8-10kft for the most
part. Will need to watch some small potential for fog development
later tonight across southern Minnesota near the surface ridge,
though at this point it appears we may see just enough lingering
clouds and some wind to prevent anything significant around RST.
Something to watch nonetheless.

&&

.HYDROLOGY...
Issued at 206 AM CDT Sat Apr 21 2018

A flood warning remains in effect for the Trempealeau River at
Dodge with minor flooding expected late this weekend into next
week. See the latest flood statement for more information.

As the recent snow melts and runs off into area streams,
additional flooding will be possible, especially along the
Kickapoo River with additional details in the latest hydrologic
statement.

&&

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

$$

SHORT TERM...04
LONG TERM...04
AVIATION...Lawrence
HYDROLOGY...04



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