Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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263
FXUS63 KMKX 240431
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
1131 PM CDT Tue May 23 2017

.UPDATE...Areas of fog have developed over southern CWA where low
level winds lighter and low level rh higher. Fog likely to stick
around for a few hours and possibly until 12Z and may become dense
in spots until low level winds increase late in the night and
early morning. Also needed to lower temps a few degrees as
northeast winds pulling in cooler temps from over Lake Michigan.

&&

.AVIATION(06Z TAFS)...Areas of fog have developed over southern
CWA where low level winds a bit lighter as rain has diminished.
Fog wl likely stick around through the late night but will be
fighting against cooler air with slightly lower dewpoints settling
in from the north.

&&

.PREV DISCUSSION... (Issued 939 PM CDT Tue May 23 2017)

UPDATE...Strong upper level divergence which produced widespread
showers and a few storms during the late afternoon and early
evening is shifting to the northeast. Heavy rainfall may have
caused localized flooding in the Fond du Lac area and between the
Dells and Reedsburg in Sauk County. Weakening showers over western
CWA still showing little movement but as surface and upper low
slide further south, would expect these showers to begin shiftin
WSW. Report of patchy fog around Beloit via Facebook but
increasing northerly winds and developing low clouds should
prevent fog from becoming widespread overnight. Expect scattered
showers to linger over portions of the area as upper level
deformation weakens and slides south.

MARINE...Webcams show the dense fog has lifted over the northern
near shore zone north of Port Washington. As winds increase from
the northeast ushering in cooler, slightly drier air, thinking fog
will remain more patchy over the near shore waters. Dewpoints
falling into the mid 40s which is near Lake Michigan water surface
temperature. Low pressure passing by to the south will result in a
tightening pressure gradient and increasing north to northeast
winds late tonight into Wednesday. Winds and waves will get close
to Small Craft Advisory levels.

PREV DISCUSSION... (Issued 635 PM CDT Tue May 23 2017)

AVIATION(00Z TAFS)...Widespread showers over eastern CWA will
become more scattered in the south as drier air edges in from the
west. Showers will persist in the northern CWA due to lingering
mid-level deformation as upper low shifts southward. As low level winds
become more ENE, expect lower CIGS over northeast CWA to spread
west and southwest.

PREV DISCUSSION... (Issued 337 PM CDT Tue May 23 2017)

SHORT TERM...

Tonight and Wednesday...Forecast Confidence Is Medium.

500 mb low will continue to slowly slide southeast from north
central Iowa into northeast Missouri tonight. It will then slide
further to the southeast on Wednesday. Differential cyclonic
vorticity advection from several vorticity maxima will continue to
aid upward vertical motion into tonight. In addition, there will
be some low level confluence/convergence from the passing weak
surface low.

Numerous showers should continue across portions of the area into
this evening. They should become more scattered later tonight
into Wednesday. Forecast soundings support some weak low level
CAPE with steep low to mid level lapse rates and cold 500 mb
temperatures. Thus, kept the isolated thunder wording into this
evening. Small hail and brief heavy rainfall will continue to be
possible with any storms.

Cloudy skies and scattered showers tonight into Wednesday should
keep lows in the upper 40s tonight, with highs Wednesday in the
50s lakeside to around 60 well inland.

Wednesday night through Friday...Forecast confidence medium.

Low pressure will be in the vicinity of Lake Erie for Wed nt-Thu
while the upper low tracks from the central MS River Valley to the
east coast. A new round of cyclogenesis will then occur over New
England Thu nt with sfc high pressure finally settling over WI.
Until then, sct showers will linger Wed nt-Thu AM especially over
ern WI. A weak shortwave trough will then track across srn WI on
Fri while the tail end of a Canadian cold front approaches from
the nw with a warm front extending from MO to IN to the south.
Overall, only slight chances of showers over south central WI due
to weak lift. Temps will be near or slightly below normal during
this period.

LONG TERM...Saturday through Tuesday...Forecast confidence
medium.

Another large upper low will settle over Ontario, Canada and the
nrn Great Lakes for the weekend into early next week. Thus,
chances of showers will continue with temps near or slightly below
normal.

AVIATION(18Z TAFS)...

Showers and a few thunderstorms are expected to continue to
develop over the area this afternoon, lingering into this evening.
Small hail and brief heavy rainfall are possible in any of the
storms, as well as some cloud to ground lightning. Scattered
showers may linger later tonight into Wednesday as well.

Ceilings should become VFR category for a few hours this
afternoon, before lowering to MVFR category later this afternoon
into this evening. Low ceilings around or below alternate minimums
are expected southwestward into the area this evening, lingering
into Wednesday morning before improving back above 1000 feet above
ground level.

Light fog is expected to push southwestward onshore near Lake
Michigan later this afternoon and this evening, lingering later
tonight. Visibilities down to around 2 miles are anticipated, with
lower values possible. These should improve above 6 miles by
later Wednesday morning.

MARINE...

Dense fog has developed across the northern marine zone near
Sheboygan, per web cameras and Coast Guard observations. Thus,
issued a Dense Fog Advisory until 03Z Wednesday. This may need to
be extended, until north to northeast winds increase later
tonight. Some fog should develop over the rest of the nearshore
waters of Lake Michigan into tonight as well, until increasing
north to northeast winds develop later tonight.

The pressure gradient will increase Wednesday into early Wednesday
evening, as the surface low moves further to the southeast of the
region. Gusty north to northeast winds are expected by later
Wednesday morning into early Wednesday evening. Frequent gusts to
around 25 knots appear likely during this time. This will help
generate elevated waves of 3 to 5 feet as well. A Small Craft
Advisory will likely be needed during this time.

&&

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

$$

Update...99
Tonight/Wednesday and Aviation/Marine...99
Wednesday Night through Tuesday...99



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