Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 061123
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
523 AM CST Wed Dec 6 2017

.UPDATE...Gusty WSW winds to continue today with gusts up to 30-35
mph later this morning and afternoon. Secondary surge of colder
air and approaching short wave trof should cause clouds to
increase later today and this evening. Flurries likely tonight as
trof passes through.

&&

.AVIATION(12Z TAFS)...Still expect an increase in lower VFR clouds
later today and this evening. A light snow shower or flurrie may
accompany the clouds in some areas later today. Flurries are
likely tonight, possibly causing ceilings to drop to MVFR levels.

&&

.PREV DISCUSSION... (Issued 305 AM CST Wed Dec 6 2017)

SHORT TERM...
Today and Tonight - Confidence...Medium.

Mid-level short wave passing across northern WI this morning causing
scattered -shsn and flurries across northern WI.  Some of the
flurries from this system may push into northern parts of the CWA
this morning.  Secondary surge of cold air associated with this
feature will slide into central WI later today, with some increase
in low to mid level moisture.  This may trigger a few more flurries
or light snow showers across the north and west with an increase in
cloud cover. More widespread flurries are expected tonight when the
upstream weak wave over south central Canada rotates southeast. This
wave will sharpen as it progresses southeast across southern WI
overnight.  Synoptic lift remains weak but deepening column moisture
into the snow growth region should result in at least scattered
flurries developing during the evening and continuing through the
late night.  At this point, any snow accumulation should remain a
dusting to a tenth of two.  Gusty WSW winds to continue today, with
gusts up to 30 mph

LONG TERM...
Thursday through Saturday - Confidence...Medium

The main focus is on Friday night into early Saturday morning as
model trends have come together to put southern Wisconsin more in
line for the first widespread accumulating snowfall of the season.
While amounts are forecast to be on the lighter side at around 1
inch, the first snowfall of the season is an important one as
many motorists are not acclimated to drive in these conditions
yet and accident rates tend to be higher than in later season
snows.

Previous model trends had the 05.12z ECMWF further west with this
system while the 05.12z NAM/GFS were further east but showed at
least some light QPF in eastern Wisconsin. With the 06.00z runs,
the ECMWF and GFS are fairly similar to each other with the
surface low/upper level features while the NAM is a bit faster
with a deeper mid level trough. Following along more in line with
the 06.00z ECMWF/GFS thinking which brings the snow in from the
north early Friday evening and has it exiting southern Wisconsin
around daybreak Saturday. The precipitation type will definitely
be snow as the sounding is all well below freezing. QPF between
the models is generally around 0.05-0.10", with higher amounts
closer to Lake Michigan (not because of lake effect but just
deeper lift). The dendritic growth zone isn`t very deep at 100mb
or less, but there is quite a bit of lift associated with the
digging trough and decent lapse rates going up to 500mb which
should lead to some higher than normal snow ratios of around 18/20
to 1. Thus, have come up with a first run of snow totals running
from around a half inch in southwest Wisconsin to an inch and a
half in east central Wisconsin. Due to the models coming together
to show this solution, have bumped up POPs a bit, but have not
gone to likely due to the potential that the track of the system
could again shift its path.

Saturday night through Tuesday - Confidence...High

After the system moves through early on Saturday, we get into a
brief period of low level warm air advection which will push
temperatures back up toward normal for Sunday and Monday before
another shot of cold air drops down into the Great Lakes in the
northwesterly flow aloft. Could see another light snow/dusting
with that passing trough but the 06.00z GFS/ECMWF aren`t as locked
in on it yet. What they are locked in on is another bout of cold
air coming down for the middle of next week.

AVIATION (09Z TAFS)...Expect an increase in clouds to occur
through today with lower VFR clouds settling in from the north.
Isolated snow showers are possible across parts of the region
today, with scattered flurries tonight. MVFR cigs may accompany
the flurries across the area tonight but not enough confidence at
this point to go with prevailing lower cigs. Gusty WSW winds to
continue today with gusts up to 30 kts.

MARINE...Will continue Gale Warning through 12Z. Forecast
soundings over the near shore waters indicate the potential for wind
gusts reaching 33-35 knots for a few more hours.  Will then post
Small Craft Advisory through tonight as gusty off shore winds to
continue as reinforcing push of cold air moves across the western
Great Lakes.  WSW winds will turn to the NW late today and this
evening as cold front moves through.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...Gale Warning until 6 AM CST early this morning for LMZ643>646.

&&

$$

Update...MBK
Today/Tonight and Aviation/Marine...MBK
Thursday THROUGH Tuesday...Halbach



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