Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 160352 CCA
AFDMKX

Area Forecast Discussion...Corrected.
National Weather Service Milwaukee/Sullivan WI
951 PM CST Thu Feb 15 2018

.UPDATE...

Recent coastal observations suggest that the cold front is
accelerating down Lake Michigan, and is moving through the
Milwaukee area at the moment. This has brought some broken lower
stratus inland along the immediate Lakeshore, but they should be
rather transient, and will progress south with the front. Still
keeping our eyes on an area of flurries and snow showers in the
cold advection regime across eastern portions of Iowa and
Minnesota. Forecast models are consistent in weakening this area
as it pushes towards us, given limited saturation and only weak
lift within the dendritic growth zone. Even so, a period of
flurries or light snow showers remains possible tonight. No
accumulations are expected.

&&

.MARINE...

Expect a period of gustiness and north to northeasterly winds
this evening as a cold front pushes south down the lake. Some of
these gusts may approach Small Craft Advisory conditions.
Thereafter, winds will veer northwesterly late tonight into
Friday, before shifting to southerly on Saturday. Another period
of Small Craft Advisory levels is possible at times on Saturday
through Sunday.

&&

.PREV DISCUSSION... (Issued 602 PM CST Thu Feb 15 2018)

UPDATE...

Low amplitude mid-level troughing will progress from the Upper
Midwest into the western Great Lakes through tomorrow morning. A
secondary cold front, now across central Wisconsin, will push
through our area late this evening with a reinforcing shot of cold
air. A band of lower clouds associated with cold advection behind
the front should arrive after midnight. We may squeeze out a few
flurries or light snow showers (between around midnight and 6 AM)
given
some associated mid-level frontogenesis producing weak lift within
the dendritic growth zone. Only partial saturation is noted
though, so not expecting anything impactful out of this.

Clear and colder conditions are expected for Friday, with our next
shot for precipitation on Saturday. Light snow is the most likely
precipitation type, with a brief shot at freezing drizzle Saturday
evening. Still uncertainty regarding precipitation types and
amounts with the Monday into Tuesday system, but we`ll need to
keep an eye on this one for potential impacts to our area. Some
model solutions suggest a period of freezing rain is possible.

AVIATION(00Z TAFS)...

VFR early this evening, with MVFR ceilings arriving behind a cold
front around Midnight. A few flurries or snow showers are
possible, with no accumulation expected. Northwest winds may gust
to around 20 knots behind the front. Ceilings should rise around
daybreak tomorrow, with rapid clearing thereafter and VFR
conditions for Friday.

PREV DISCUSSION... (Issued 257 PM CST Thu Feb 15 2018)

SHORT TERM...
Tonight and Friday...Forecast confidence is high.

A colder airmass will push into the area tonight in the wake of
cold front that exited this afternoon. The cold air advection and
passage of a weak mid level short wave will bring more clouds and
a small chance for light snow or flurries overnight. Any light
snow will exit east before sunrise with clearing skies and mostly
sunny conditions arriving by mid morning on Friday. High temps on
Friday will be about 20 degrees colder than today (Thursday), but
the full sun will help temper the cold.

LONG TERM...
Friday Night and Saturday...Forecast confidence is high.

Quick moving wave will zip across the region and produce mainly
light snow. There will be a fight with dry air early, so QPF
potential is muted. Will also need to keep an eye on ice presence
aloft as it becomes marginal Saturday afternoon. Overall, expect a
period light snow moving west to east across the region, perhaps
ending as brief period of freezing drizzle. Any accumulation will
be minor with less than an inch of snow.

Saturday night and Sunday...Forecast confidence is high.

A short stretch of quiet weather is on tap. Temperatures will be
above average courtesy of southerly winds. Clouds will be on the
increase during the day Sunday.

Sunday night through Tuesday...Forecast confidence is medium to
low.

The signal for an active period of weather continues, but the
devil is in the details. Confidence in higher PoPs remains solid,
but the biggest headache is the location of the baroclinic zone,
its effects on precipitation types, and the speed with which it
moves with time. The GFS (as well as its ensembles) places the
front the furthest southeast, clipping far southeast Wisconsin.
It is also the quickest to push the boundary out of the area. The
Euro is further to the northwest, bisecting southern Wisconsin,
and slower to exit the region.

Regardless of solution, the airmass to the northwest of the
boundary looks to be at or below freezing. With strong warm
advection associated with this pattern, temperatures southeast of
the boundary will be quite warm. In addition, there will be solid
warm advection aloft, with 925/850mb temperatures well into the
30s/40s across the area and approaching 50 in far southeastern
Wisconsin. As a result, there is increasing concern for a mix of
precipitation types.

Two or three rounds of lift are possible. The first being
associated with warm advection Sunday night into Monday morning
where an initial mix of rain/sleet/snow should transition to all
rain. The second round would be associated with a surface low
riding the front Monday afternoon and Monday night. A third round
is possible Tuesday (especially with the slower Euro solution).
Precipitation types for the 2nd/3rd rounds of precip are the most
in question.

At this juncture, the message for Monday night and Tuesday is for
mainly rain in the far southeast portion of Wisconsin (roughly
along/southeast of a line from Port Washington to Janesville) with
a wintry mix northwest of this line. SLU CIPS analogs have a
notable signal for several hours of freezing rain. Given the
progged thermal profiles from the GFS and Euro, this is plausible.
Bottom line, stay tuned.

Tuesday night onward...Forecast confidence is low.

Much depends on the exit speed of the surface front. There are
lingering PoPs to account for this slower exit. Temperatures look
to be around average for the time of year.

AVIATION(21Z TAFS)... Look for VFR conditions into the early
evening hours. Then a period of MVFR CIGS will overspread southern
Wisconsin as colder air spills into the region in the wake of a
cold front. We could see some light snow or flurries out of these
clouds, but no accumulation is expected. Winds will remain
northwest through the TAF period. The MVFR CIGS will push out
before 12z Friday with clearing skies spreading west to east very
quickly after 12z Friday.

MARINE...
Northwest winds will increase overnight into early Friday morning,
with a few gusts approaching small craft advisory conditions.
Winds will shift to the south by Saturday and may reach small
craft advisory levels at times Saturday through Sunday.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...None.
&&

$$

Update...SPM
Tonight/Friday and Aviation/Marine...Davis
Friday Night through Thursday...Gagan


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