Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 012020

Area Forecast Discussion
National Weather Service La Crosse WI
220 PM CST Thu Dec 1 2016

.SHORT TERM...(This evening through Friday)
Issued at 220 PM CST Thu Dec 1 2016

At 2 PM, a closed low was located over eastern Ontario and western
Quebec. With this low moving away from the area, much of the area
has been dry this afternoon. The only thing that we will have to
watch tonight is a weak short wave moving south through northern
Minnesota. The radars have been pretty quiet with this system.
However, there was a recent report of unknown precipitation at
Aiken MN. With the soundings not showing much lift across the
region, opted to keep the forecast dry for now.

The only other issue tonight looks to be the low temperatures.
With persistent cloud cover and neutral temperature advection,
the MOS temperature look too cold. As a result, did a trajectory
analysis to see where this air mass was this morning. This
revealed that this air mass was over northern Minnesota and the
temperatures were near 30F this morning. Due to this, opted to
raise the low temperatures closer to these values tonight.

.LONG TERM...(Friday night through Thursday)
Issued at 220 PM CST Thu Dec 1 2016

From Saturday night into Sunday evening...the 01.12z models
continue to show that a short wave trough will move east through
the region. Soundings continue to show that the temperatures aloft
and at the surface will be cold enough for the precipitation to
start out as snow. However there is some indication in the NAM
that there may be a lack of icing initially which could could
result in maybe some patchy freezing drizzle. With surface
temperatures warming into the mid and upper 30s on Sunday, the
boundary layer will sufficiently warm for the snow to change to
either a mix of rain and snow or to all rain. As far as snow
totals, the SPC plumes show that most of the models have snow
totals ranging from a dusting to maybe up to a half inch.

Beyond Monday, the models continue to show a wide variety of
solutions. Some show that the northern and southern streams will
phase over the region. This would result in a strong low moving
through the Midwest. Meanwhile, other models show no phasing at
all. In this scenario, we would be split and would see no
precipitation at all. With the 01.12z ECMWF was running 3 hours
late due to a power failure, did not get a chance to look at that
model at all.

As far as the temperatures, the models continue to show that the
850 mb temperatures will plunge into the -10C to -15C range. While
this will be cold, it is not that unusual for December. The models
continue to show a large spread with standard deviations up to 7.
This is a result of uncertainty on the snow extent across the
region. If the ground remains snow free, high temperatures would
range from the mid-20s to the mid-30s. If we become snow covered,
we would see high temperatures anywhere from the teens to the
mid- 20s. Due to this uncertainty, just stayed with model blends
for now.


.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1103 AM CST Thu Dec 1 2016

Cyclonic flow around low pressure over eastern Canada continues
across the area this afternoon. Plentiful/mostly mvfr status
across our area as a result. Plan on this stratus to linger
through the period with northwest surface winds generally at or
below 10-15kt.




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