Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 130530

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
1130 PM CST Tue Dec 12 2017


Light flurries continue to push across the area this evening.
Just a few flakes have made it to the ground given very dry low

00Z model guidance continues to point toward an organized band of
snow moving into the northeastern corner of the forecast area
around daybreak, with healthy snow accumulations possible north
and east of a Fond du Lac to Port Washington line. A tight
gradient is still expected on the southwest side of the band.
Besides the main band of snow tomorrow morning and early
afternoon, a period of lake effect snow is possible tomorrow
afternoon and evening, potentially affecting the commute home from
work and school.



Model guidance is coming into somewhat better agreement tonight in
keeping the heaviest band of snow north and east of the terminals
Wednesday morning. The latest TAFs reflect this, with higher
visibilities than the 00Z or 03Z issuances. Still think that all
sites except MSN still have a good shot at seeing some snow
tomorrow, and any slight southward shift in the snow band could
result in much more impactful conditions than currently forecast.
In addition to the main band during the day, will need to watch
for lake effect later Wednesday afternoon and evening, especially
at MKE.



Another Small Craft Advisory is in effect for the nearshore waters
from mid morning Wednesday to mid morning Thursday. Initially
gusty southeast winds will become light for a brief period of time
as the surface low moves overhead, before winds increase again
from the northwest. Waves will build to 3 to 6 feet early in the
day, then build to 5 to 8 feet by Wednesday evening. Winds may
also briefly approach gales late Wednesday night.


PREV DISCUSSION... (Issued 244 PM CST Tue Dec 12 2017)


TONIGHT - Confidence...Medium.

Mid-level clouds from strong upstream warm air advection already
spreading into south central WI this afternoon.  Trend will
continue.  Strongest warm air advection spreads across southern WI
from late evening through the overnight.  Enough low to mid level
moisture connection expected to possibly bring some light snow or
flurries to southern WI during this period.  Bumped up and expanded
pops across most of the area for later tonight.  Potential some
northern areas may receive one half inch to one inch by late
tonight.  Hence Winter Weather Advisory goes into effect for several
north central counties late tonight.

WEDNESDAY into WEDNESDAY EVENING - Confidence...Medium to High.

Short term guidance in good agreement on carrying low level
circulation and surface low pressure across southern WI/northern IL
on Wednesday.  GFS and NAM showing fairly good run to run
consistency with this feature.  Strong layer Q-vector convergence of
up to 50 units passes rapidly across southern WI late tonight and
Wednesday morning.  One worrisome snafu is potential for losing ice
crystals for a time in the southwest CWA as drier air wraps around
low pressure circulation, hence slightly lower confidence.  Did
include small chance for -zl/-zr in the southwest. Low level drying
remains more limited in the eastern CWA during the day. Cross
sections show impressive lift across northeast CWA in the dendritic
growth zone close to an area of sloping frontogenetical forcing.  In
addition, an inverted trof extending northwest from the low level
circulation may increase the convergence along the lakeshore areas
from Milwaukee to Sheboygan in the late afternoon into the early
evening.  Delta-T around 14-15C in the early evening with lake
induced Cape over 250J.  Part of the low level conditionally
unstable layer reaches the snow growth region as well.  With snow
liquid ratios around 15 to 1, expecting synoptic snowfall in the 3
to 6 inch range over northeast CWA.  However snowfall may be locally
heavier due to the elevated instability and lake enhancement.  Added
7" local amounts in the northeast.  Posted Winter Wx Advisory for
all of the northeast, with eastern areas continuing into the

Thursday and Friday...Forecast confidence is medium.

We`ll remain under a cold northwest flow regime through the end of
the work week. Thursday looks cloudy and we could see a few
flurries, but not really worth mentioning. On Friday, there`s a
better looking short wave dropping south through the area and this
could bring a chance for some light snow. At this point, it looks
rather dry, so not too worried about any accumulations.

Saturday and Sunday...Forecast confidence is low.

There continues to be model disagreement with the complicated
pattern this weekend. The upper pattern begins to flatten a bit,
or become less northwest oriented. Low pressure is expected to
develop west of the area on Saturday, but where it goes is rather
uncertain. The GFS has a low moving over Lake Superior while the
ECMWF has a low moving over central/southern Wisconsin. Right
now, most of the precip looks north of the forecast area. We
should warm up into the lower and mid 30s this weekend with the
somewhat milder flow returning. We`ll have to keep an eye on that
low pressure track. These are the kind of system that can drift
south, resulting in some snow for southern Wisconsin. If it stays
north, we`re warmer and drier.

Monday and Tuesday...Forecast confidence is medium.

There`s nothing of significance to latch onto early next week. The
upper flow does look for zonal, and thus more mild than what we`ll
see this week. For now, the forecast is dry, but it`s an active
flow, so we`ll have to watch out for some stronger pieces of
energy that may produce some light, pesky precip.


WI...Winter Weather Advisory from 6 AM to 9 PM CST Wednesday for

     Winter Weather Advisory from 4 AM to 6 PM CST Wednesday for

LM...Small Craft Advisory from 9 AM Wednesday to 9 AM CST Thursday
     for LMZ643>646.



Tonight/Wednesday and Aviation/Marine...Boxell
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