Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

000
FXUS63 KMKX 130549 AAC
AFDMKX

Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
1149 PM CST Wed Dec 12 2018

.UPDATE...

We still have a large area of dense fog being reported across
central/south central WI, north of I-94. So far, this is all
within the Dense Fog Advisory area that`s in effect until 8 am.
There is a sky clearing trend from southwest to northeast, but
there are still pockets of very low clouds and persistent fog. I
am not sure what affect this clearing will have on areas within
the advisory, as it is still approaching.

&&

.AVIATION(06Z TAFS)...

There is dense fog north of I-94, most of the way eastward to the
lake. There is a sky clearing trend from southwest to northeast,
but there are still pockets of very low clouds and persistent fog
behind this clearing. It is likely that ceilings and visibilities
will bounce around all night before improving Thursday morning.

Portions of southern WI should see a period of partly cloudy
skies (with just high clouds) by midday Thursday. Then expect
MVFR ceilings with possibly IFR to spread into southeast WI with
rain Thursday evening. There is a chance for a wintry mix for MSN
to FLD to SBM as well.

&&

.PREV DISCUSSION... (Issued 836 PM CST Wed Dec 12 2018)

UPDATE...

Observations at Juneau and Fond du Lac have gone down to a quarter
mile or less within the past two hours. A call to Green Lake
confirms dense fog there. Model guidance hits the area from
Marquette county to northeast Columbia county east to northern
Washington and Sheboygan counties hard with low visibility for
most of the night. Given that the surface low is stalling over
northeast WI for the night, it makes sense that conditions that
are developing now should hold for a while.

Temperatures are around or just below freezing. This means there`s
freezing fog that could cause slick spots on untreated roads,
bridges, and sidewalks. A Dense Fog Advisory is in effect for this
area.

MARINE...

Winds will continue to diminish overnight as weakening low
pressure stalls over northeast Wisconsin. Look for increasing
southerly winds Thursday afternoon and night. Winds are expected
to remain below gale levels through the middle of next week.

PREV DISCUSSION... (Issued 605 PM CST Wed Dec 12 2018)

UPDATE...

The freezing drizzle that developed in response to low level cold
air advection and subtle vorticity advection is quickly
diminishing. I will give it another hour to make sure we don`t see
any more drizzle signatures on radar and then cancel the winter
weather advisory. It looks like fog will be an issue tonight,
especially north of I-94, closest to the surface low that is
going to stall overnight. Temperatures are expected to be just
below freezing, so freezing fog could cause icy conditions on
untreated roads, bridges, and sidewalks.

AVIATION(00Z TAFS)...

Freezing drizzle diminished as it got into far eastern Wisconsin
this evening. Expect IFR ceilings and patchy fog for the rest of
the evening. There is an area of clearing in northwest IL that
may expand to the WI/IL border near Janesville and Kenosha. Not
expecting much improvement to ceilings north of there due to low
pressure stalling and weakening over east central/northeast WI.
Some dense freezing fog is possible in the Green Lake, Fond du Lac
and Sheboygan areas overnight.

Southern WI may see a period of clearing skies (with just high
clouds) midday Thursday. Then expect MVFR ceilings with possibly
IFR to spread into southeast WI with rain Thursday evening. There
is a chance for a wintry mix for MSN to FLD to SBM as well.

PREV DISCUSSION... (Issued 317 PM CST Wed Dec 12 2018)

SHORT TERM...
Tonight...Forecast confidence is medium to high:

Main concern is with the hard to detect freezing drizzle and
whether there would be any impacts from it. Surface temperatures
have dropped into the upper 20s, but many area roads are still wet
or treated from the earlier snow that came through. Currently,
some very light, freezing drizzle or snow grains have been
reported, which appears to be tied to a cold front that extends
south of a surface low over Lake Winnebago. As this feature swings
through, it should provide just enough lift to produce this brief
potential for freezing drizzle this afternoon. The support should
then shift east and end as the surface low also weakens and drift
northeast toward Lake Michigan.

Thursday through Thursday night...Forecast confidence is medium:

May get a brief window late Thursday morning/early afternoon where
the clouds clear out before the next system moves in from the
south.

The next focus goes to Thursday evening as an elongated mid level
trough propagates into the region from the west as a surface
trough extends north of a closed low near the gulf. Timing is
fairly consistent between the 12.12z NAM/GFS/ECMWF with the onset
of the precipitation developing in southern Wisconsin in the
evening. The question will be with how far NW the precipitation
makes it and what type it falls as. NAM soundings are showing a
deeper warm layer aloft while the GFS is on the colder side, but
that seems to be an outlier. The ECMWF came in the most robust
with its precipitation shield and a bit further west compared to
the NAM/GFS, but it looks to be on the warmer side as well.
Current thinking is that most, if not all of this precipitation
falls as rain but will have to monitor the western periphery of
it for a changeover to snow. 90th percentile (high end) snow
amounts for this event are only at a half inch with the 10th
percentile (low end) at 0 inches.

LONG TERM...

Friday through Wednesday...Forecast confidence is medium to high:

Precip should wind down quickly Friday morning, with some
clearing likely late morning into the afternoon northwest to
southeast.

High pressure should be in control for much of the time over the
weekend through the first half of next week. Dry weather is
expected through this period. The NAM does clip the southeast with
a little rain Saturday, but all other models are dry, so kept the
bulk of precip chances south of the state line.

Lesser confidence in temps Friday into the weekend. Models show an
inversion not far above the surface for much of the daytime
periods, with very little mixing. Some of this may be due to the
expected snow cover on the ground, which seems to be overdone in
the models. Did nudge the forecast highs up a bit. Given temps
aloft, these forecast values could be underdone and MOS agrees
with that. Soundings look quite dry, though some concern of
stratus given such little flow and mixing under the high. What
happens on Friday should give better direction for what to expect
the remainder of the weekend.

Temps should turn cooler early next week, though will likely
remain a little above normal for mid-December.

AVIATION(21Z TAFS)...
IFR to LIFR conditions becoming more widespread as the backside of
the surface low moves into the area. Expect that these conditions
will linger through much of the evening hours and overnight begin
to slowly improve Friday morning as some drier air moves into the
region.

MARINE...
Winds will begin to weaken going into this evening as a low
pressure system also weakens across central Lake Michigan. As this
system weakens, high pressure will settle in across the lake with
a stronger ridge of high pressure moving in for the weekend. No
issues with stronger winds until potentially next week.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...Dense Fog Advisory until 8 AM CST Thursday for WIZ046-047-051-
     052-057>059.

LM...None.
&&

$$

Update...Cronce
Tonight/Thursday and Aviation/Marine...Cronce
Thursday Night through Wednesday...DDV



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.