Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 170151
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
851 PM CDT Mon Apr 16 2018

.UPDATE...
Some very light flurries are moving through eastern Wisconsin.
These are associated with the last remnants of a sheared mid level
short wave pushing east. Most ob sites aren`t picking up the
flurries due to their light nature. But, a brief flurry with vsbys
to 5 miles not out of the question before midnight. Look for some
scattering of the clouds west of Madison overnight. Temps again
drop into the lower and mid 20s tonight.

&&

.MARINE...

A small craft advisory is in effect through Tuesday morning due to
gusty northwest winds. The offshore wind will keep the higher
waves out toward open water.

Another period of gusty winds and building waves is anticipated
for Wednesday night into Thursday morning, as low pressure moves
through the region. A Small Craft Advisory may be needed for this
period.


&&

.PREV DISCUSSION... (Issued 552 PM CDT Mon Apr 16 2018)

UPDATE...
Drier air continues to infiltrate the area this evening. The
forecast is in good shape.

AVIATION(00Z TAFS)...
CIGS will be hovering close to the MVFR/VFR threshold into the
evening hours. Most of the TAF sites have lifted to VFR levels,
but the lower CIGS at or just below 3kft could move in at any
time through the evening. CIGS should scattered from KMSN on west
later tonight. But, CIGS will fill back in diurnally on Tuesday
and should again be hovering close to the MVFR threshold. Look for
the northwest winds to gradually diminish, especially west of
Madison.

PREV DISCUSSION... (Issued 305 PM CDT Mon Apr 16 2018)

SHORT TERM...

Tonight and Tuesday...Forecast Confidence Is Medium.

Drier air moving into the area helping end most of the light snow
shower activity in the southeastern parts of the area. There are
some very light reflectivity values to the northwest of the area.
However, not much in the way of ground truth. May go with
scattered flurries mention for the rest of the afternoon and early
evening.

The main 500 mb low will circle around the central Great Lakes
this evening, before heading east later tonight into Tuesday.
Skies will remain cloudy into this evening, and could linger later
tonight into Tuesday morning in eastern portions of the area.
Could see some breaks in the west during this time, though some
uncertainty here. Low clouds should fill into at least the
northern and eastern areas Tuesday afternoon, and may spread
across the rest of the area.

Gusty northwest winds should linger tonight, before gradually
weakening from west to east on Tuesday. Temperatures should remain
well below seasonal normals tonight into Tuesday, with the fresh
snowpack in place. Lows in the lower to middle 20s are expected
tonight, with middle 30s north and east, to lower 40s southwest on
Tuesday.

Wednesday...Forecast Confidence is Medium.

Another mid level shortwave/closed low will shove through the region
on Wednesday. The associated low level/surface low will drop out of
the Northern Plains and into southern Wisconsin on Wednesday. As the
low develops and moves into the region, a low level baroclinic zone
will be pushed northeast into the region. All guidance holds off on
moving moisture into the region until early Wedensday morning and
this will be roughly when precipitation arrives in our southwest.
The warm front will remain situated on top of our CWA until the
low moves through on Wednesday afternoon.

With the front overhead, ample moisture, and the passing upper
trough/low, I expect at least on and off precip to persist
through much of the day. The real question is what type of
precipitation will we receive? Surface temperatures will be below
freezing on Wednesday morning, and will likely only reach a few
degrees above freezing by the afternoon given a) raw model
guidance, b) snowpack in place, and c) evaporational cooling.

Adding to the complexity of the situation, there is a real question
mark regarding saturation in the dendrite growth region. The GFS
generally keeps the DGZ saturated for the duration of the precip,
but the Euro and NAM are less bullish with moisture in the DGZ.
Without that DGZ moisture, any precip falling into subfreezing
temperatures will like result in freezing rain or drizzle.
Finally, our north appears the most likely to keep a saturated
DGZ, and temperatures in that area may remain cool enough to
support at least some snow through much of this event.

Obviously this is a complex situation where we`re right on the
margins of several precip types. This means the forecast may
change, so please continue to keep your eyes on the forecast.

LONG TERM...

Thursday through Monday...Forecast Confidence is Medium.

Upper level ridging moves back in behind Wednesday`s cyclone and
will remain in place through the remainder of the forecast period.
High pressure at the surface will dominate most of the period.
Thanks to a strong low passing well to the south of the region,
winds never quite turn southerly, so we can only expect a modest
warmup. That said, temperatures will approach normal by the
weekend, and given the weather we`ve seen the last few days, I
think most will be happy with dry and normal late-April
temperatures.

AVIATION(21Z TAFS)...

Any lingering light snow showers should exit the southeastern
parts of the area in the next hour or so. Scattered flurries may
linger into early this evening. Gusty northwest winds will remain
into tonight, before gradually weakening west to east Tuesday.

Ceilings of around 2500 feet above ground level into early
evening should improve above 3000 feet by middle to late evening.
Ceilings down to 2500 feet return for a time later tonight in
southern portions of the area, and again Tuesday afternoon in the
north and east. Should see ceilings scatter out from west to east
later tonight for a time, before gradually filling back in by
Tuesday afternoon.

MARINE...

Small Craft Advisory remains in effect until 1 PM CDT Tuesday
afternoon across the nearshore waters of Lake Michigan. A tight
pressure gradient with good low level mixing is expected to linger
tonight across the area. Frequent gusts of 25 to 30 knots are
expected. The pressure gradient and subsequent winds should weaken
Tuesday morning. The ending time may need to be moved back a few
hours into the morning by later shifts.

Another period of gusty winds and building waves are anticipated
for Wednesday night into Thursday morning, as low pressure moves
through the region. A Small Craft Advisory may be needed for this
period.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...Small Craft Advisory until 1 PM CDT Tuesday for LMZ643>646.

&&

$$

Update...Davis
Tonight/Tuesday and Aviation/Marine...Wood
Tuesday Night through Monday...BSH



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