Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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143
FXUS63 KMKX 090317
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
917 PM CST Thu Dec 8 2016

.UPDATE...

New 00Z Nam is closer to the 12Z ECMWF than the 18Z GFS, with a
slightly slower snow band for saturday afternoon, and a more south
and somewhat weaker low Sunday night and Monday morning. 00Z NAM
and 18Z GFS and 12Z ECMWF are fairly similar in precipitation
amounts with going forecast.

&&

.AVIATION/06Z TAFS/...

MVFR cigs mainly over south central wisconsin while clouds have
scattered out for the most part as the mid level trough pushes
east. Low level moisture gradually decreases, so the clearing
trend may expand during the early morning hours. Very light
flurries still possible.

&&

MARINE...

A Small Craft Advisory remains in effect until 6 AM. A large low
over southeast Canada will still bring brisk west to northwest winds
over Lake Michigan into the early morning. High waves will occur
toward the open waters.

&&

.PREV DISCUSSION... /Issued 226 PM CST Thu Dec 8 2016/

TONIGHT AND FRIDAY - Confidence...Medium
Lingering mid level cyclonic flow/low level thermal trough likely to
keep a good deal of clouds in place into tonight and perhaps at
least some broken cloud cover into Friday. Moisture/lift remains
within the dendritic growth zone so extended the flurry potential a
bit longer into this evening. Notice some drying in the growth zone
later tonight which should cut off ice crystal production. Pressure
gradient proggd to slacken a bit for Friday so expect the west winds
to ease from the windy conditions of these past couple days. 925
temps of -11c to -13c are in place so expect more highs in the
low/mid 20s seem reasonable and this is in line with the MOS numbers.

FRIDAY NIGHT THROUGH SATURDAY MORNING...Forecast confidence is
high.

High pressure will keep it quiet and cold during this brief
period. Snow will be arriving quickly by Saturday afternoon...see
next section.

SATURDAY AFTERNOON THROUGH MONDAY...Forecast confidence is
medium.

Consensus has increased for the weekend snow event to arrive in
two separate events. Two mid level short waves will hit the
Pacific Northwest on Friday and again on Saturday, reaching the
western Great Lakes Saturday night and Sunday night. The first
short wave will have a decent warm air advection component with
weak surface cyclogenesis, while the second wave will be weaker
with the temp advection, but feature stronger sfc cyclogenesis.

Look for snow to spread in quickly Saturday afternoon, and
generally sweep out of here Sunday morning. Low level moisture
remains plentiful, so we could see lingering light snow or
flurries. Freezing drizzle is also possible with the loss of ice
in the snow growth region. Temps will be cold during the snowfall,
with ratios in the 17 to 1 range, so a dry snow. Unlike the snow
last weekend. We could see total snow with the first round in the
3 to 4 inch range.

The second round should arrive late Sunday afternoon or Sunday
evening with the associated surface low tracking across central
Illinois into northern Indiana. The snow would taper off Monday
morning with this second round potentially generating another 3
to 4 inches. Again, air temps will be cold enough to keep this a
dry snow. Pavement temperatures will be solidly below freezing.

The combo of these two events could result in a few spots getting
upwards of 6 to 8 inches over an especially long period.

This is a complicated scenario and these details will likely
change going forward.

TUESDAY THROUGH THURSDAY...Forecast confidence is medium.

This should be our coldest period of the season so far. Surface high
pressure should generally take control. The flow aloft is cyclonic
as troughing extends south into the Great Lakes from a parent low
over Canada. We could see some flurries out of that, but generally
it looks dry. Wednesday lows look to be in the zero to -5 range
with highs on Wednesday remaining in the single digits above zero.
Wind chill readings Wednesday morning could approach 20 below.

AVIATION/00Z TAFS/...Influence of cold trough persists. 500
millibar temps are -36C/-37c noted from 12z ua. Plenty of MVFR
cigs/flurries/shsn around. This pattern will persist into tonight.
While mid level trough trends a little less cyclonic across srn WI
the influence of low level thermal trough will linger so will not be
real quick to scour out the MVFR cigs esp with no clear signal from
the LLVL RH progs and MOS.

MARINE...A Small Craft Advisory remains in effect until 6 AM
Friday. A large low pressure area will move across southern Canada
but still bring brisk westerly winds to Lake MI into early Friday
AM. High waves will occur toward the open waters.

MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...SMALL CRAFT ADVISORY until 6 AM CST Friday for LMZ643>646.

$$

TONIGHT/Friday AND AVIATION/MARINE...Collar

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...SMALL CRAFT ADVISORY until 6 AM CST Friday for LMZ643>646.

&&

$$

UPDATE...Hentz
TONIGHT/Friday AND AVIATION/MARINE...Collar
Friday NIGHT THROUGH Thursday...Davis



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