Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 142351

Area Forecast Discussion
National Weather Service La Crosse WI
551 PM CST Wed Feb 14 2018

Issued at 550 PM CST Wed Feb 14 2018

Dense fog is moving northward into Clayton and Grant Counties this
evening. Will continue to monitor the northward progression of the
fog this evening and may have to issue a dense fog advisory if
visibilities continue to worsen this evening. Highest confidence
for dense fog across Grant County at this time.


.SHORT TERM...(This evening through Thursday)
Issued at 200 PM CST Wed Feb 14 2018

At 1 PM, high pressure was centered over the Carolinas and a cold
front was located over Montana.  A moderate pressure gradient
between this system is producing southwest of 10 to 20 mph. Abundant
sunshine has allowed temperatures to climb well above-normal. At
this hour, they range from 35F at Rochester MN to 47F at Black River
Falls WI and Boscobel WI.

For tonight, skies will remain mainly clear through the early
overnight.  They will then increase from northwest and south.  The
increase from the northwest is due to an approaching cold front.
Meanwhile, the increase in the clouds from the south is due to a
short wave trough moving northeast the Mid Mississippi River Valley.
Due to the melting snow today and a lighter surface pressure
gradient along and south of the Interstate 90 corridor overnight,
expect areas of fog to develop after 3 AM.  Low temperatures on
Thursday morning will range from the mid-20s to mid-30s.

Early on Thursday morning, weak 925 and 850 mb moisture will
increase across southwest Wisconsin.  This may result in some small
chances of light rain.  Amounts will range from a trace to maybe a
couple hundreths of an inch.

During the remainder of the morning and early afternoon, a cold
front will move through the region.  This frontal passage looks to
be delayed some, so bumped up the high temperatures anywhere from 2
to 5F. Overall, the soundings look dry through much of the day, so
only have a small precipitation chance across southeast Minnesota
and north-central Wisconsin during the mid to late afternoon. If
precipitation occurs, it will likely start of as light rain or snow
and then transition to light snow.  However, the chances look very
low for this to even occur.

.LONG TERM...(Thursday night through Wednesday)
Issued at 200 PM CST Wed Feb 14 2018

The upper level trough axis swings through Thursday night with
models indicating sufficient forcing for some light snow through the
evening, but with minimal accumulations. However, high pressure will
build in later Thursday night and Friday with dry and colder
weather. Highs on Friday will likely top out in the teens to low

There is good agreement with the upper air pattern evolution heading
into early this weekend with another upper trough forecast to
advance eastward out of the northern plains on Saturday. Milder
air will return for Saturday with highs in the upper 20s to low
30s. Some light snow is possible Saturday with the trough passage,
but any accumulations would be minor.

Zonal flow aloft will gradually transition to southwest flow as an
upper-level longwave trough digs across the western CONUS Sunday
into Monday. Models are in good agreement with surface cyclogenesis
over eastern CO/western KS Sunday night, tracking northeast towards
Lake Michigan Monday night. Precipitation should develop along the
baroclinic zone by Monday morning, but possibly as early as Sunday
evening. Thermal profiles indicate all types of wintry precipitation
are possible. Arctic high pressure pushing down from Canada into the
north-central CONUS could push the track of the low further south,
as indicated by the 14.12Z GFS ensemble mean. A lot of uncertainty
remains with this system, but it is starting to look like our next
chance of impactful weather. The longwave trough will progress
eastward Tuesday into Wednesday, but timing differences begin to
emerge in model guidance.


.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 550 PM CST Wed Feb 14 2018

LLWS will continue this evening at both KLSE and KRST through
around 06Z. Patchy to areas of fog are possible later tonight
into Thursday morning but given mixing of the lower atmosphere
visibilities should stay in the VFR to MVFR range. Conditions will
be worse across northeast Iowa into far southwest Wisconsin where
low stratus and fog is expected. Any fog should improve by mid
morning Thursday. Look for MVFR stratus to move into the TAF sites
after 18Z Thursday with cloud bases in the 1500 to 2500 ft range.




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