Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 170237

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
937 PM CDT Fri Mar 16 2018

.UPDATE...Large area of mixed light rain and snow spreading
northward toward southwest Wisconsin. Expect this area to diminish
as it pushes into the much drier air over southern WI. However
enough synoptic and isentropic lift carries across IL border into
southwest WI for a few hours between 04Z and 10Z, that should be
enough for some light precipitation to fall out of some mid-level
clouds. The dry air will contribute to atmospheric cooling of the
column and mostly -sn is expected. However forecast soundings show
some loss of cloud ice near the top of the saturated layer. Hence
added a chance for some light freezing rain in Lafayette county
for a few hours overnight. Impact from slick roads due to
potential light glaze will be less due to time of day. Due to
timing and uncertainty, will hold off on issuing Winter Wx Advy.


.MARINE...Onshore flow to continue through the night becoming
light and variable later Saturday into Saturday night. Next period
of stronger winds, possibly reaching Small Craft Advisory levels
expected to be on Monday.


.PREV DISCUSSION... (Issued 634 PM CDT Fri Mar 16 2018)

UPDATE...Latest RAP bufkit soundings show low levels remaining
dry in the southwest CWA overnight, while NAM and GFS show more
moisture spreading into this area. Latest Mesoscale guidance
carries period of light precipitation into Lafayette county around
06Z, possibly affecting Green County as well. No changes at this
time since large area of precipitation continues to spread
northward across parts of central and eastern IA this evening.
With drier air feed and low dewpoint depressions, atmospheric
cooling would result in mostly -sn, but can not rule out a brief
period of -zr as forecast soundings show drier air in the -8C and
above layer developing overnight.

AVIATION(00Z TAFS)...Mostly VFR conditions can be expected for
this forecast period. Some areas well southwest and south of
Madison toward the Illinois border will likely lower to low VFR
and possibly experience a brief period of MVFR ceilings. These
lower ceilings would accompany a brief period of light snow, sleet
or light freezing rain. Latest RAP and GFS soundings show low
levels remaining dry with bulk of precipitation remaining to the

PREV DISCUSSION... (Issued 306 PM CDT Fri Mar 16 2018)


Tonight and Saturday...Forecast confidence is high:

Low pressure will pass by to the south tonight, with precip on the
north side of the low brushing the southern forecast area. Still
looks like mainly snow, but not out of the question to see a brief
mix with sleet or freezing rain given a little warm layer aloft
and a possible loss of saturation in the ice crystal growth zone.
The precip should be confined to areas south of a line from Lone
Rock to Kenosha, where forecast snowfall is a half inch or less.

Decreasing clouds and milder temps are expected Saturday, with
highs likely hitting 50 from around Madison westward. It will be
cooler toward the east, especially near Lake Michigan under
onshore winds.


Sunday through Thursday...Forecast confidence is high:

High pressure is expected to bring dry weather Sunday through
Thursday next week. Low pressure will pass by to the south Monday
and Monday night, but the main impacts from this low will be
increased clouds and breezy conditions.

Temps Sunday will be above normal, likely hitting 50 in most
locations. An onshore wind will develop in the afternoon, so
places near Lake Michigan may remain stuck in the 40s. Cooler
temps are likely then from Monday through Thursday behind the
departing low, with highs temps within a couple degrees of normal.

Friday...Forecast confidence is medium:

Another low pressure system will approach the area late in the
week. Decent confidence that there will be some precip in southern
Wisconsin by later Friday into Saturday. There are very large
differences among models though in the evolution of this system
and eventual low track. Thus timing and precip type is still
questionable. In the last 12 hours, models have ranged from a low
far enough north to bring rain and a thunderstorm threat, to a
track to south that would bring heavy snow to southern Wisconsin,
to a low so far south it would stay dry in the forecast area.
Needless to say, more time is needed to get a better idea of what
may happen late next week.


High clouds are expected through Saturday, though some lower
ceilings (mainly VFR) are possible in the southwest tonight closer
to low pressure passing by to the south. The low is still
expected to brush the south with a little precip this evening into
tonight. Mainly light snow is expected (up to a half inch),
though a very brief mix with freezing rain or sleet is not out of
the question. Precip is expected to be limited to an area south of
a line from Lone Rock to Kenosha.

Clearing skies and light winds are expected during the day


Small Craft Advisory conditions are possible later Monday into
Tuesday, as gusty east to northeast winds build higher waves.




Tonight/Saturday and Aviation/Marine...MBK
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