Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 161739

Area Forecast Discussion
National Weather Service La Crosse WI
1239 PM CDT Sun Jul 16 2017

.SHORT TERM...(Today through Tuesday)
Issued at 238 AM CDT Sun Jul 16 2017

The next couple of days look rather quiet and benign. The cold
front will continue to sink south, dropping into Missouri and
southern Illinois by the end of the day. This will allow an area
of high pressure currently over North Dakota and Ontario to drop
southeast and be over the Great Lakes through Monday. This should
allow for a gradual decrease in the dew point and humidity through
tonight before the flow starts to turn more to the south Monday
with a resulting increase in the moisture again. The moisture will
continue to increase into Tuesday ahead of an approaching cold
front and will help set the stage for the next chance of rain.

The upper level ridge currently extending from the Rockies into
the northern High Plains will shift east with the ridge axis
moving across the Upper Midwest Monday and Monday night. The
center of the upper level high will remain over the central
Rockies, so the ridge will take on a more west to east orientation
allowing zonal flow from the northern Rockies into the Upper
Midwest. The 16.00Z models all agree that a short wave trough
will move across the region Tuesday in association with the cold
front, but some differences on the strength and timing of the
wave. The NAM brings a short wave trough in off the Pacific Coast
Monday and as it moves east, there is the suggestion that it will
maintain its strength and become phased with a stronger wave
moving across Canada. The NAM`s timing would bring it into the
area Tuesday afternoon in the heating of the day with the cold
front. Meanwhile, the GFS dampens the wave as it crosses the
Rockies and does not phase it with the Canadian system. It is also
a bit faster with the timing, bringing it across Tuesday morning.
The 16.00Z ECMWF looks a lot more like the GFS than it does the
NAM. All the models indicate a chance for rain with this system
Tuesday, with the NAM showing the potential for heavy rain and
possibly a severe threat as well. For now, plan to go with an
increasing rain chance, starting late Monday night through Tuesday
with a low end likely chance for the northwest portions of the
forecast area by Tuesday afternoon. As for the severe threat, the
more conservative GFS and ECMWF indicate between 1000 and 1500
J/Kg of ML CAPE across the area Tuesday afternoon but have only
about 20 knots of shear in the 0-3 km layer. The NAM is not much
different with the CAPE, but is much stronger with the shear
indicating around 50 knots in the 0-6 km layer near the front. For
now, will lean toward the GFS and ECMWF and not start playing up
any severe threat.

.LONG TERM...(Tuesday night through Saturday)
Issued at 238 AM CDT Sun Jul 16 2017

The models continue to indicate that the upper level ridge will
remain over the central part of the country for much of the
upcoming week before starting to drift east toward the weekend.
This is expected to maintain a zonal flow over the Upper Midwest
with only weak short wave troughs embedded in the flow. The front
that moves in Tuesday still looks like it will become a nearly
stationary feature that gradually washes out with time. With the
front, or the remains of it, over the area and weak short wave
troughs passing over the region, there will be occasional rain
chances every day.


.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1239 PM CDT Sun Jul 16 2017

Diurnal clouds between 3 and 4K will affect both TAF sites through
late afternoon. These clouds will then dissipate this evening with
the loss of diurnal heating. Winds will gradually shift from
northeast to southeast tonight as a ridge axis moves east through
the region. A few of the models hint that an IFR to MVFR deck of
clouds may affect parts of northeast Iowa and southeast Minnesota.
This will include KRST. Confidence was not high enough to include
them at this time.




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