Area Forecast Discussion
Issued by NWS La Crosse, WI

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480
FXUS63 KARX 192324
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
624 PM CDT Thu Apr 19 2018

.SHORT TERM...(This evening through Friday)
Issued at 304 PM CDT Thu Apr 19 2018

At 3 PM, a 1033 mb surface high was centered over southwest
Minnesota and northwest Iowa. This high was providing sunny skies
across the Upper Mississippi River Valley. Temperatures ranged
from upper 30s to upper 40s. The coldest temperatures were found
across the deep snow depth near the Minnesota and Iowa border.

For tonight, high pressure will drift across the region. Soundings
show that a subsidence inversion will trap the moisture from the
snow melt today. This will result in the development of fog
overnight. Visibilities may drop to less than a half mile in the
river valleys and in central Wisconsin.

On Friday, the combination of snow cover and limited mixing will
slow the warm up a bit. High temperatures will range from the mid
40s to mid 50s.

.LONG TERM...(Friday night through Thursday)
Issued at 304 PM CDT Thu Apr 19 2018

Through Monday night, high pressure will provide dry weather
across the Upper Mississippi River Valley. Temperatures will warm
a couple of degree each day. Currently have the high temperatures
around 60 by Monday. However, if the ECMWF is correct, these
temperatures may be on the conservative side for Sunday and
Monday. It would suggest high temperatures mainly in the lower 60s
on Sunday and in the lower and mid 60s on Monday.

Lowered the dew points a bit for the weekend. However, if the
winds increase aloft, these may have to be lowered some more.

There continues to be much uncertainty with the system which may
affect the area from Tuesday into Wednesday. Both the GFS and GEM
bring a Canadian cold front through the region. This front will
bring with it a brief period of rain. In addition, these systems
are bit stronger, so they would bring colder air into the region
in the wake of this front. Meanwhile, the ECMWF is weaker and it
would remain southwest of the area. Due to these differences, just
stayed with the model consensus.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 624 PM CDT Thu Apr 19 2018

Tonight appears to have all the ingredients necessary for fog
development. Clear skies, calm/light winds up to 10 kft, and
higher low-level moisture due to daytime snowmelt. That said,
latest guidance hints at some differences in the degree of near
surface saturation overnight. For now, will not stray too far from
previous forecast, introducing MVFR/IFR restrictions in visibility
by 20.09Z at both TAF airfields and continuing with fog mention
through 20.15Z. Will need to monitor trends in guidance this
evening as well as the dew point depression and adjust as
necessary. Outside of the fog, expect mostly sunny/clear skies
through the period with only some cirrus on Friday. Winds will be
light and variable or calm as surface high pressure dominates the
regional weather pattern.

&&

.HYDROLOGY...
Issued at 304 PM CDT Thu Apr 19 2018

An ideal snow melt will occur through Sunday with daytime
temperatures above freezing and nighttime temperatures below
freezing. This will slow the release of moisture from the
snowpack. The snowmelt will them accelerate for the remainder of
the time period.

Runoff from the melt will lead to rises on area streams and
rivers. Besides the Trempealeau River at Dodge and maybe some
points along the Kickapoo possibly exceeding flood stage this
weekend, the rest of the area streams and rivers are expected to
just see significant within bank rises. Rises on the Mississippi
River will be more into the middle and later part of next week as
it will take some time for the meltwater from central MN and
northern WI to flow south and reach our area. Those with interests
or property close to streams and rivers will want to stay up to
date on latest river forecasts in the coming week.

&&

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

$$

SHORT TERM...Boyne
LONG TERM...Boyne
AVIATION...Rogers
HYDROLOGY...Boyne



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