Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 261630 AAA

Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
1130 AM CDT MON SEP 26 2016


Clear skies this morning will make way to more scattered to broken
cloud cover as boundary layer mixing occurs and returning
moisture moves in, in addition to a mid to upper level trough
that is expected to sag southward. This could bring some isolated
to scattered showers in our northern counties later this
afternoon. Instability looks low at this time, so not expecting
thunderstorms with this shower activity.

Primary hazard for today will be strong west winds, thanks to good
momentum transport of 900-800 mb low level winds to the surface.
Gusts today could reach as high as 30-35 knots inland.



VFR cigs expected to continue through the day, along with gusty
west winds, which should weaken slightly overnight. Gusts up to
35 kts are possible this afternoon due to mixing down of stronger
winds aloft. SCT to BKN stratocumulus is also expected to develop
later this afternoon due to thermal trough over the area.

Sfc winds are expected to weaken this evening, which may lead to
some weak degree of low level wind shear, especially for the MSN
TAF site. Values don`t quite reach 30 kts of shear, so won`t
mention it in the TAF, but shear values could reach near 25 kts



Have kept high-end Small Craft Advisory going through Tuesday, with
west winds frequently gusting to 30 knots with a few Gale Force gust
expected. West wind will cause upwelling of colder water along the
western shore of Lake Michigan, limiting the potential of deep
mixing to the stronger winds aloft. Latest model guidance still
shows winds easing Tuesday evening as pressure gradient relaxes with
passage of surface low across the lake into lower Michigan by
Wednesday morning.


.PREV DISCUSSION... /Issued 316 AM CDT MON SEP 26 2016/

TODAY AND TONIGHT...Forecast Confidence - Medium.

High clouds over southern WI will continue to thin and push off to
the east early this morning.  A cooler and breezy day lies ahead
with mid level clouds returning later this morning and continuing
into tonight in some areas.  Strong low level cold air advection
overnight has lowered 925H temps 5 to 10 degrees from 24 hours ago.
Breezy west winds and the clouds will also help keep temps in check
so expect daytime temperatures rising into the 60s.

A passing mid-level wave may bring a few light showers to the
northern CWA this aftn into the evening.  Despite the increase in
clouds, strong low level mixing and a dry adiabatic lapse rate
will result in gusty west winds from late morning thru late aftn.
Gusts of 30 to 35 mph are expected with sustained winds around 20
mph, still well below Wind Advisory Criteria. Lingering low level
mixing and patchy cloud cover tonight will help keep temperatures
a little warmer, however overnight readings will still tumble into
the 40s most areas, coolest since early June.

TUESDAY AND WEDNESDAY - Confidence...Medium
Large 500 millibar is proggd to shift from just north of Lake
Superior early Tuesday into the vcnty of srn lwr MI or OH area.
Numerous embedded vorticity maxima will be wrapping around this
broad low into WI. System will be essentially stacked as is
slowly plods its way sse across the western Lakes and then slowly
towards the eastern Lakes/OH vly region. So MOS and Superblend POPS
reflect this some chance to at times likely POPS with this scenario.
Low level thermal trough brings 850 temps down into the single
digits celsius so the cool regime will hang around with this slow
moving low. Core of coldest 850 temps arrive Tuesday and Tuesday
night where some 850 temps of 1-3c are proggd with 925 temps/cloud
trends supportive of more of a slightly cooler consensus MOS than
Superblend look. By Wednesday the core of the coldest 850/925
temps shift south though flow turns north then northeast with deep
cyclonic regime remaining in place supportive of more shra and a
possibly favorable delta T depending on how lake temps shift
around especially given the variations out there now. Pretty warm
temps still at mid lake(22c) so will have to see how much lake
influence evolves with some colder waters residing closer to the
shore. needless to say potential there for some sizable delta t
numbers to set up across Lake MI, which is quite typical for this
time of year.

THURSDAY - Confidence...Low to Medium
Trends in the NAM/GFS/GEM support enough progression of the stacked
system that some ridging becomes evident across our area which would
support drier and conditions. However the 00z ECMWF keeps the
influence of the circulation in place with potentially more shra
chances. Will support a going trend in 3 of 4 models at this point
and side with the dry Superblend pops. But confidence is starting to
get shaky since the ECMWF has had multiple runs now in showing this
slower progression and longer period of influence on our wx.

The uncertainty remains with the ECMWF showing the mid level
circulation waffling around the western Lakes right into the
weekend. Meanwhile the GFS has a fairly broad high amplitude ridge
with dry wx with a dominating surface ridge axis. The GEM is sort of
a split in positioning of the circulation though still far enough
east to keep that solution mostly dry for us as well. Will go with
the Superblend pops for now which has brought some small pops in for
the weekend.

AVIATION/12Z TAFS/...Thermal trof over the area and returning
low to mid level moisture should result in sct-bkn stratocumulus
redeveloping later this morning into the afternoon with some of
the clouds lingering into tonight. For now, expecting cigs to
remain VFR.

MARINE...Gusty west winds will continue through Tuesday as low
pressure located north of Lake Superior sags slowly southward,
continuing a tight pressure gradient across southern Lake
Michigan. Off shore flow will result in upwelling of colder lake
water into the nearshore waters. Atwater buoy measuring lake
surface temp in the low 50s while mid-lake buoy remains in the low
70s. This low level inversion will prevent stronger gusts from
mixing to lake surface further offshore. However, stronger low
level mixing is expected over the shore areas and just inland. RAP
soundings at KMKE indicating potential for west gusts getting to
33-35kts from late mrng thru 22z or so. Will need to watch closely
but a few gusts to 35 knots are possible this aftn. However not
expecting gusts to last long enough or be widespread enough at
this point that would require upgrading Small Craft Advisory to
Gale Warning. Waterspout threat increases on Wednesday as weak
convergence moves across southern Lake Michigan.


.MKX Watches/Warnings/Advisories...
LM...SMALL CRAFT ADVISORY until 7 PM CDT Tuesday for LMZ643>646.



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