Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 152333
AFDMKX

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

.UPDATE...

The heavier snow has ended across the area, but occasional light
snow showers will persist overnight into into the first half of
the day on Monday. Additional accumulations will only be an inch
or two at most. Given that any additional accumulation will be
quite minor, will plan on letting the Winter Weather Advisory
and Winter Storm Warning expire at 7 PM.

&&

.AVIATION(00Z TAFS)...

Occasional light snow showers will continue through the first half
of the day tomorrow. Additional accumulations will be light--only
an additional inch or two at most. Ceilings will remain IFR
tonight, improving to MVFR tomorrow. Brief drops to IFR vis are
possible within any snow showers. Winds tonight will initially be
from the north, becoming more northwesterly with time. Some
gustiness is possible.

Snow will finally end during the late morning and afternoon on
Monday, with ceilings lifting to VFR late in the day. Gusty
northwest winds will continue on Monday.

&&

.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!

MONDAY NIGHT THROUGH WEDNESDAY...Forecast Confidence - High
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.

EXTENDED PERIOD...

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.

&&

MARINE...

Blustery winds will continue into Tuesday as slow moving low
pressure moves north through the central and eastern Great Lakes.
Northeast winds will continue to slowly back to the north to
northwest tonight and Monday.  A brief lull in the winds is possible
late this afternoon and evening as the center of the low pressure
system passes close to far southern Lake Michigan.  A Small Craft
Advisory remains in effect through Tuesday morning.

&&

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.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Weather Advisory until 7 PM CDT this evening for
     WIZ058>060-062>072.

     Winter Storm Warning until 7 PM CDT this evening for WIZ046-047-
     051-052-056-057.

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

&&

$$

Update...Boxell
Tonight/Monday and Aviation/Marine...Boxell
Monday Night through Sunday...99



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