756
FXUS63 KMKX 231807
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
1207 PM CST Mon Dec 23 2024

.KEY MESSAGES...

- Winter Wx Advisory this afternoon into early evening north of
  Madison and for Fond du Lac and Sheboygan Counties with a
  burst of accumulating snow expected.

- A gradual warm up will continue through the end of the week,
  with temperatures well above normal next weekend.


&&

.UPDATE...
Issued 1206 PM CST Mon Dec 23 2024

A compact shortwave trough and associated left exit region of a
jet streak will track across central and srn WI this afternoon.
Fcst soundings do show elevated steep lapse rates and ARX radar
is showing heavier areas of snow. A narrow west to east band of
mdt to heavy snow, probably supported by low to mid level
frontogenesis, will set up north of Madison and across central
WI. Thus kept these counties in the Winter Wx Advisory, but will
have to watch Dodge County ewd if the heavy snow band sets up
farther south. One to three inches is fcst toward central WI.
Farther south a narrow band of rain changing to snow is expected
but with little to no impacts.



Gehring

&&

.SHORT TERM...
Issued 405 AM CST Mon Dec 23 2024

Today through Tuesday:

The dry air continues to win out early this morning and
saturation has not been able to materialize. Thus have been
following the drier trend and cutting back PoPs and precip
timing. Even upstream observations in MN closer to the surface
low and cold front lack any precip/moisture early this morning.
The only precip upstream is anchored to the main mid-level
shortwave trough and even that is small area in northeast SD.
Given these trends along with temperatures running warmer around
or above freezing this morning across southern WI, I do not
have high confidence in seeing precip develop before daybreak.
Thus have delayed the onset of the the Winter Weather Advisory.

While the model soundings eventually saturate the environment
later this morning as the main mid-level shortwave trough moves
in, the timing coincides with warmer diurnal temperatures
around/above freezing. We are beginning to have a concern for
the freezing drizzle to materialize and its associated impacts.
More likely looking at a wintry mix of light snow and freezing
drizzle/drizzle for areas north of I-94, while areas south may
just be warm enough for drizzle with a few flakes mixed in.
Nevertheless, with any wintry precip that may develop later
this morning into the afternoon could result in pockets of
slick conditions especially for untreated and/or elevated
roadways. Will maintain the Winter Weather Advisory for the time
being, but if we continue to see the drier air win out, would
not be surprised to see the headlines be adjusted in
area/timing. Would like to monitor the moisture trends with the
shortwave upstream and get a look at the initial 12z models
before making any more headline decisions.

Otherwise any precip today is progged to end this evening as
the forcing/shortwave pushes east of the area and high pressure
begins to build down across the Upper Great Lakes tonight into
Tuesday. Looking at drier conditions overnight with temps in the
upper 20s to low 30s, but if clouds can clear out a bit could
see a few degrees colder. Influence from high pressure will
continue Tuesday with light winds and temps in the lower 30s.

Wagner

&&

.LONG TERM...
Issued 405 AM CST Mon Dec 23 2024

Tuesday night through Sunday:

The low temperatures for Tuesday night are very uncertain. The
only thing keeping southern WI from having clear skies is a
potential low cloud layer. With subsidence due to high pressure
solidly in place over northern WI, there is a chance that the
low level dry air could erode the cloud cover over southern WI.
In the areas that clear, temps will drop quickly, but in the
areas with clouds, temps will be up to 10 degrees warmer. The
range of possible temperatures is lower 20s toward central WI to
lower 30s toward the WI/IL border.

The low level moisture will steadily increase from southeast to
northwest Wednesday (Christmas) morning as weak lift from warm
air advection moves in. The moisture is loosely associated with an
approaching upper trough from the southern Plains. The added lift
is from an upper trough tracking across Lake Superior. The two
troughs are not expected to phase, but the two areas of forcing
and moisture may come together to produce drizzle or light rain.

If drizzle develops early enough when temperatures are still at
or below freezing, then freezing drizzle could be a short-lived
morning issue. However, the likelihood of below freezing
temperatures and deep enough low level moisture coming together
is very low right now. Temps will increase to the mid-upper 30s
by the afternoon.

Light rain is possible Thursday with a weak mid level
shortwave. With temperatures in the mid 30s to around 40, there
are no travel concerns.

Our upper levels will transition into a southwest flow pattern
with a train of waves rounding the base of an expanding upper
trough over the western U.S. late in the week. The first low
will arrive Friday. Since temperatures at the surface and aloft
will be above freezing, with lows in the upper 30s and highs in
the lower to mid 40s, the precip will be in the form of rain.

This messy and relatively mild upper flow pattern looks like it
will persist into the new year. With this type of pattern, the
timing of rain chances is quite uncertain.

Cronce

&&

.AVIATION...
Issued 1206 PM CST Mon Dec 23 2024

Rain and snow north and west of Madison will spread east this
afternoon with brief heavy snowfall rates toward central WI.
Areas of MVFR Cigs before the precipitation will transition to
600-1900 feet in the precipitation and continuing into tnt.
Vsbys with the snow will range mostly from 3/4sm to 2sm but
lower at times especially toward central WI. There is then
uncertainty whether the stratus clouds will become few or sct
for Tue. Will trend toward sct stratus but beware bkn MVFR Cigs
are possible throughout the day.


Gehring

&&

.MARINE...
Issued 405 AM CST Mon Dec 23 2024

Low pressure over northern IA this morning will gradually drift
across central WI into central Lake Michigan through the afternoon.
Gusty southerly winds ahead of the low will persist this morning
along with small craft advisory for southeast WI nearshore waters,
but winds will weaken as the low and its associated cold front
passes across the lake this afternoon/evening. Winds will then shift
to the northwest tonight as high pressure builds across the Upper
Great Lakes Region through Tuesday. High pressure will continue to
work its way eastward by Wednesday and winds will turn more
southerly through the second half of the week.

Wagner

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Weather Advisory...WIZ046-WIZ047-WIZ056-WIZ057 until 5
     PM Monday.

     Winter Weather Advisory...WIZ051-WIZ052...2 PM Monday to 8 PM
     Monday.

LM...Small Craft Advisory...LMZ643 until 3 PM Monday.

     Small Craft Advisory...LMZ644-LMZ645-LMZ646 until noon Monday.

&&

$$

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