Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 160435

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
1135 PM CDT Sun Apr 15 2018


A small band of heavier snow has developed this evening across far
southern Wisconsin, mainly affecting western Walworth and eastern
Rock Counties, as well as extreme southern Jefferson County.
Snowfall rates may be as high as 1-2" per hour within this band
(which is no more than 10-15 miles wide), so a very localized area
of heavier snow accumulations of 1-3" is likely right along the
Walworth/Rock county line. This is causing some travel issues in
the area, especially along I-43.

Elsewhere, just light snow is expected for the rest of the night.
An additional inch or so is possible through the mid day hours on
Monday, with snow will finally end.



Light snow will remain possible at the TAF sites overnight
tonight, with vis dropping from MVFR to IFR at times within the
heavier bands of snow. Ceilings will likely also bounce around
between MVFR and IFR, with most guidance showing cloud bases right
around 1000 ft. Snow should dissipate later in the morning or
early afternoon on Monday.

Winds will initially be from the north, becoming more
northwesterly early in the morning Monday. Expect gusts to pick
back up as surface low pressure pulls east of the region.


.PREV DISCUSSION... (Issued 946 PM CDT Sun Apr 15 2018)


A few areas of light snow continue this evening. Right now, the
most organized area is along a corridor from Janesville and
Delavan north to Madison and then the Portage area. Snowfall is
generally light, though a few transient areas of enhanced snow
will likely lead to renewed slick spots on roads and localized
reductions in visibility.


North winds will become more northwesterly with time tonight and
tomorrow, with gusts to 25 knots or so continuing. Waves will
slowly diminish tomorrow. A Small Craft Advisory remains in effect
through Tuesday morning.

Winds will increase again on Wednesday from the southeast. This
onshore flow will also lead to building waves across the nearshore


PREV DISCUSSION... (Issued 320 PM CDT SUN APR 15 2018)

TONIGHT AND MONDAY...Forecast Confidence - High.

Strong low pressure will slowly pull away tonight into Monday, with
lingering light snow through tomorrow. Could see up to another inch
tonight...with a half an inch or less on Monday. There could be a
little freezing drizzle at times through this evening in the east
according to model soundings, but not seeing anything in
observations so far.

Decided to move the expiration time of the winter headlines up to 7
pm this evening, with the bulk of steady snowfall winding down.
Winds have backed off quite a bit as well.

Temps will remain well below normal values for mid-April tonight and
tomorrow. The clouds and fresh snowpack will help to keep temps down
tomorrow, with highs only expected to top out in the mid 30s.
Average high temps this time of the year are in the mid 50s!

trending to Medium.

Low pressure over the central and eastern Great Lakes will be taking
longer to exit the area this period.  Hence colder northwest
steering flow and cyclonic curvature will result in some clouds
returning on Tuesday.  Thermal trof begins to ease as deeper
moisture slides off to the east so not expecting any light
precipitation on Tuesday.

Quiet weather will remain brief as short term guidance in good
agreement on sharpening eastward moving 500H short wave trof located
over the northern Plains Tuesday sliding eastward into the upper
midwest Tuesday night.  Further deepening is expected as low
pressure associated with the mid-level short wave moves across the
western Great Lakes Wednesday and Wednesday night. Impressive layer
q-vector convergence with 30 units through the mid-levels. Eastward
progression of this system however continues to slow per latest
ECMWF and NAM, and is slightly farther south. Thinking precip will
spread in during the day on Wednesday, with the heaviest period of
QPF and strongest lift in the afternoon and evening. Temperatures
will be rapidly warming Wednesday morning, but there will be a 1-3
hour window when some -zr may occur.  ECMWF and GFS more aggressive
with deeper moisture and warm air advection surge while NAM slower
and showing more variability.  GEFS and NCEP SREF QPF plumes for the
24 hour period from 12z Wed to 12Z Thu show considerable variability
with variations over an inch in MKE and MSN.  Mean QPF is around a
quarter to a half inch. Leaned on Model Certainty 50 percent heavily
for QPF. Colder air will funnel back into southern WI as the low
pressure system moves off to the east with a period of light to
moderate snow possible Wed night, with minor accumulations possible.


WEDNESDAY NIGHT AND THURSDAY...Forecast Confidence - Medium.

Low pressure moving though the southern Great Lakes will likely
continue to bring snow or a wintry mix to southern Wisconsin
Wednesday night, possibly into Thursday morning. Portions of
northern and western CWA will be most susceptible to receiving light
accumulations. Bulk of Thursday should be dry as low pressure moves
rapidly away from the area.  As mentioned above, there remains
uncertainty regarding the timing and low level thermal structure of
the atmosphere as this system moves through. However Medium range
guidance coming into better agreement on track of this system across
northern IL/southern WI Wednesday night.

THURSDAY NIGHT THROUGH SUNDAY...Forecast Confidence - Medium.

A quiet period is expected with some moderation in temperature.
Amplifying high pressure ridge will move into the central CONUS this
period and then shift eastward into the east over the weekend.
Better agreement in Medium range guidance in deepening slow moving
upper low moving through the central and southern Plains with
precipitation shield from this system remaining south and southwest
of southern WI.  Daytime temperatures should return to the 40s and
possibly lower 50s pending cloud cover.

HYDROLOGY...Expect fresh snow cover over southern WI to slowly
melt this coming week with daytime temperatures rising above
freezing and below freezing at night. Warmest temperatures in the
next week from Friday through the weekend. Latest river
contingency forecasts keep river levels below flood stage through
the week so no significant river rises expected in the next few
days. However will need to watch closely the melting of the much
deeper fresh snowpack over central WI which will drain into the WI
River basin. This could eventually push the WI river at Portage
above flood stage.


LM...Small Craft Advisory until 1 PM CDT Tuesday for LMZ643>646.



Tonight/Monday and Aviation/Marine...Boxell
Monday Night through Sunday...99 is the U.S. government's official web portal to all federal, state and local government web resources and services.