Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 090046
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
646 PM CST Fri Dec 8 2017

.UPDATE...

Initial radar returns not reaching the ground (VIRGA).

&&

.AVIATION(00Z TAFS)...

Still thinking 1 (to 2 inches northeast areas) of dry snow...with
the steadier snow arriving around 03Z northwest and 06Z
southeast. A little light snow or flurries are possible before the
accumulating snow starts but much of that is not reaching the
ground initially. The snow will taper off west to east later
tonight into early Sat morning. Northwest winds pick up with gusts
to 28 knots Saturday.

&&

.PREV DISCUSSION... (Issued 225 PM CST Fri Dec 8 2017)

SHORT TERM...
Tonight and Saturday...Forecast confidence is high:

The first widespread accumulating snowfall of the season is still
expected for later this evening into tonight as low pressure
quickly swings through the area. A little light snow or flurries
are possible in the early evening due to saturation above 5 kft.
Lingering dry air below 5 kft most places (except possibly in the
northeast) will likely get rid of much of the early snow though,
so delayed the start of the accumulating snowfall a couple hours
from the previous forecast. Stuck with amounts of 1-2 inches based
on 12Z models, with the lower amounts in the southwest forecast
area and higher amounts northeast. The snow should taper of west
to east later tonight into very early Sat morning.

After the snow ends in the east early Sat, should see dry weather
and slowly decreasing clouds the rest of the day. Winds will be
gusty behind the departing system. Not out the question to see a
little blowing snow where the snow totals end up higher, but seems
too borderline to put in the forecast for now given only 1-2
inches expected.

Temps will be near normal tonight, not falling too far given the
expected clouds. Temps won`t rise much on Saturday though, as a
colder airmass will be pushing in behind the departing system.
Highs will end up several degrees below normal values.

LONG TERM...
Saturday night through Sunday...Forecast confidence is high:

While northwest flow aloft will continue, the low level flow will
shift the lobe of colder air further east and help to advect some
slightly warmer air into southern Wisconsin for Sunday.

Sunday Night through Monday...Forecast confidence is medium:

The main focus of the extended period is on the chances for snow
or freezing drizzle Monday morning and possibly the afternoon. The
08.12z guidance is fairly in line with timing of this system with
the NAM, GFS, ECMWF and GEM all dropping a mid level trough down
into southern WI/northern IL Monday morning. The question at this
point is where the surface/low level circulation tracks because
most of the precipitation is forecast to develop along and
northeast of the warm front in the area of strongest low level
warm air advection/isentropic lift. The 08.12z GFS/ECMWF solution
is further SW for Monday morning and puts southern WI more in the
snow belt while the 08.12z NAM is further north and keeps most of
the snow toward Green Bay. There is the potential for the loss of
ice development in the southern portion of the system which could
lead to some freezing drizzle. Timing-wise compared to tonight`s
system, this one could have bigger impacts if it comes right at
or slightly before the morning rush hour on Monday.

Monday night through Friday...Forecast confidence is medium:

The northwest, cold flow looks to continue through the rest of the
week with the main cold surge coming in on Tuesday. So, confidence
in temperatures remaining at or below normal for next week is
fairly high. Precipitation chances are not as clear cut with a
number of shortwave troughs propagating through the flow at times
during the week. So, there will likely be another few chances at
getting some light snow, but when and where is uncertain.

AVIATION(21Z TAFS)... Delayed the timing of the steadier
accumulating snowfall a couple hours based on 12Z models coming in
a little slower. Still thinking 1 to 2 inches of dry snow...with
the steadier snow arriving around 03Z northwest and 06Z southeast.
A little light snow or flurries are possible before the
accumulating snow starts. The snow will taper off west to east
later tonight into early Sat morning.

Will see visibilities and ceilings come down with the
accumulating snowfall. Thinking visibilities down to around 2
miles, but will keep an eye on upstream snow as it approaches and
adjust the vis forecast as needed. Ceilings will return to VFR by
late Sat morning. Could see some blowing snow tomorrow with gusty
winds, especially places that see higher amounts toward 2 inches.

MARINE...
Winds continue to slowly ease this afternoon, so the Small Craft
advisory was allowed to expire.

Northwest winds will increase behind a departing low pressure
system tonight, with gusts of 25 to 30 knots possible on
Saturday. Decided to go with another advisory for this period,
from late tonight into Saturday evening.

Winds may reach advisory levels at times again through the first
half of next week under an active northwest flow pattern.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...Small Craft Advisory from 4 AM to 9 PM CST Saturday for
     LMZ643>646.

&&

$$

Update...Hentz
Tonight/Saturday and Aviation/Marine...Davis
Saturday Night through Friday...Halbach



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