Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 280250
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
950 PM CDT SAT AUG 27 2016

.UPDATE...
Issued at 950 PM CDT Sat Aug 27 2016

Skies continue to ever-so-slowly clear from the west at mid
evening, but clouds are proving stubborn with near saturation at
sunset across the area. Still, do anticipate clearing will
continue the next few hours, with light winds as low level ridging
builds overhead likely to allow for some rapid fog development.
Already seeing hints of this to the west across south-central
Minnesota, and given the light wind/low temp-dew point regime
intact, don`t see any reason things won`t fog up for many areas.
Still seeing some decent flow progged aloft west of the river,
with 12-18 knots just above the shallow surface inversion which
may ultimately favor more of a stratus/lighter fog scenario.
However, can`t rule out the potential for a dense fog advisory
later tonight though confidence just yet isn`t there, especially
given the so far stubborn cloud trends.

&&

.SHORT TERM...(This evening through Monday night)
Issued at 238 PM CDT Sat Aug 27 2016

Tonight could be a good night for fog to form across the area if
the clouds can clear out in time to allow for enough cooling.
Plenty of low level moisture trapped below the clouds today and
with light winds expected through the night but just how much
clearing will take place is the main question. Visible satellite
shows the current cloud deck extends well back into southwest
Iowa. Forecast soundings suggest this back edge of the clouds
should work its way into the area this evening. These sounding
also show the winds just above the surface remaining around 10
knots until late tonight, so this could lead to more of a low
cloud deck forming than fog. For now, will go with more of the low
clouds forming than fog but will show some fog, especially in the
river valleys.

Some small rain chances return to parts of the area Sunday. A weak
short wave trough is expected to come across the northern sections
of Minnesota and Wisconsin. This wave looks to be pretty flat with
very little pv advection, but there is some warm air advection in
the low levels that generates 2 to 4 ubar/s of up glide on the
305K isentropic surface. Not sure if this will be enough forcing
to generate any rain, but will carry a very small chance across
the northern sections Sunday afternoon and night for this.

Another weak short wave trough should pass along the Canadian
border Monday that will push a cold front in to the area Monday
night. Again, the wave looks to be pretty flat with little or no
pv advection and in fact, the upper level ridge could hold pretty
tight over the Upper Midwest. There could be a weak band of
frontogenesis in the 1000-700 mb layer with the front with 1 to 2
ubar/s of up glide on the 310K isentropic surface. The moisture
transport axis is well to the north of the area ahead of the short
wave trough so would only expect some scattered showers and storms
at best with this system.

.LONG TERM...(Tuesday through Saturday)
Issued at 238 PM CDT Sat Aug 27 2016

The GFS and ECMWF are in good agreement with a cold front and any
associated precipitation exiting the area to the south Tuesday
night. A ridge builds to the west, putting the area into northwest
flow until the ridge axis slides through the area later in the week.
While both the GFS and ECMWF slide a few shortwaves and
precipitation through following the ridge, the GFS is a bit faster,
bringing the precipitation in Friday night, while the 27.00Z ECMWF
holds off until Saturday morning and 27.12Z ECMWF keeps the area dry
until late Saturday night. As far as temperatures, seasonable highs
in the mid to upper 70s are expected, with lows in the 50s.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 638 PM CDT Sat Aug 27 2016

Lower stratus intact for much of the day continues to erode from
the west, and will be out of LSE by around 01Z (RST already
improving). Clearing skies will then set up the potential for for
some fog and additional stratus development through the night as
high pressure and lighter winds encounter a fairly humid airmass
and low early evening temp/dew point depressions. With a good deal
of flow just above a shallow inversion later tonight, not sure
just how thick fog will become for LSE but it remains possible
that a period of 1/4SM visibility will occur. Regardless, it does
appear that IFR conditions (be it fog and/or lower stratus) will
occur for the LSE terminal roughly 10-14Z, with a period of IFR
visibility also expected for RST. Will have to watch trends the
next few hours to get a feel for how widespread any dense fog may
become. Otherwise, should see skies clearing after 14Z tomorrow
with a little stronger southerly flow in place supporting winds in
the 10-15 knot range for RST during the afternoon.

&&

.HYDROLOGY...
Issued at 638 PM CDT Sat Aug 27 2016

River levels at both Elkader and Garber on the Turkey River have
fallen below flood stage as of about 3-4 pm, with warnings
cancelled for both locations. Thankfully that leaves us with no
ongoing flooding problems, with not much in the way of any
organized rainfall anticipated through midweek.

&&

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

$$

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



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