Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 231652

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
1152 AM CDT Wed Aug 23 2017

.AVIATION(18Z TAFS)...VFR cu field has set up across the area.
This should dissipate within the cooling/dry airmass this evening.
Small chance of shra very late tonight into Thursday morning with
approaching vigorous shortwave and southward sliding cold front.



.PREV DISCUSSION... (Issued 905 AM CDT Wed Aug 23 2017)

MARINE...Arrival of potent mid level shortwave combined with
lower level CAA may still lead to an isolated waterspout or two
overnight into Thursday morning. Passing cold front late tonight
into Thursday morning will shift winds onshore though winds and
resultant waves are expected to remain below small craft criteria.


PREV DISCUSSION... (Issued 646 AM CDT Wed Aug 23 2017)

AVIATION(12Z TAFS)...Still expect VFR cumulus to develop across
southern WI later this morning and continue into the afternoon.
Enough moisture in place to result in sct to bkn for several
hours. Passing vigorous short wave may bring a few showers to
western CWA later tonight. Passing cold front may trigger a few
showers over the lake which may affect lakeshore zones late
tonight into early Thursday.

PREV DISCUSSION... (Issued 340 AM CDT Wed Aug 23 2017)


TODAY AND TONIGHT - Confidence...Medium to High.

Cold air aloft and a surge in low to mid level moisture should
result in sct-bkn cumulus developing this morning, persisting into
the afternoon.  Northwest winds will not be as strong as Tuesday and
will even shift to the NNE this afternoon close to the lake. Some
mesomodels try to develop a few -shra along the lake breeze boundary
in the northeast CWA but forecast soundings show moisture in the 4-
8K foot level limited.  Lake Michigan water temperature near its
peak warmth, in the lower 70s, while very cool air now sits over the
western Great Lakes.  Delta-T values are around 14 degrees.

Expect high temperatures today to be near or slightly below
yesterday`s values due to more clouds during peak heating and
slightly cooler air aloft.

Vigorous mid-level short wave visible on water vapor imagery over
central Sask/Manitoba provinces, moving southeast.  This wave will
continue to track southeast across MN/WI tonight.  Deeper column
moisture will remain mainly west of WI tonight with precipitable
water increasing to over 1".  Layer q-vector convergence and warm
air advection remains to the west of WI overnight as well.  Mid
clouds will increase overnight.  Except for a few sprinkles,
thinking -shra from this system wl remain mostly to the west.
HOWEVER, back door cold front located just north of Lake Superior
will accompany the wave and slide south across Lake Michigan and
southern WI later tonight.  This will usher even cooler air across
the area for Thursday.  Weak convergence along this boundary along
with lake induced instability may generate a few showers over the
lake later tonight.  For now, wl keep -shra mention offshore but if
convergence strengthens in later forecasts, may need to bring -shra
threat in the shore areas of lakeshore counties later tonight.  Deep
convective cloud depth late tonight and high delta-T may cause a
waterspout to form offshore late tonight.



In the wake of the upper level shortwave, southern Wisconsin will
settle into NW flow persisting into the weekend. While the GFS
and NAM each hint at very weak shortwaves on Friday and Saturday
mornings respectively, the next decent shot of CVA won`t arrive
until Saturday night or Sunday morning.

In the lower levels, high pressure will remain anchored over the
region. Southerly flow on the western flank of the high, across
western WI and MN, will usher in some warm, moist air. This warm,
moist advection just to our west is supportive of precipitation in
that area through much of the period and therefore a few showers
may creep into our western areas.

With weak temperature advection beneath the high, temps will remain
cool through the period. In fact, raw model guidance shows highs
struggling to break 70 through Saturday. Given the recent change to
a cooler pattern, bias correction is likely not adding any value, so
will be siding closer to the raw model output.

SUNDAY THROUGH TUESDAY - Confidence...medium.

The pattern turns a bit more active as a sharp upper low drops out
of Canada into the western Great Lakes. A surface low over the
Northern Plains will quickly develop in response to the upper low,
reaching the Arrowhead of MN by Sunday night. Precip chances in
southern WI begin to increase Sunday afternoon as the the low passes
to our west. Both the GFS and Euro show the cold front associated
with the low wiping out a bit on Monday morning before arriving in
southern WI, resulting in only chance PoPs.


Expect sct-bkn cumulus to develop later this morning and continue
through the afternoon. Mostly VFR cigs are expected. West to
northwest winds will turn northeast by the lake this afternoon.


West to northwest winds will turn northeast this afternoon
as the pressure gradient weakens.  Surface lake temperature around
its peak warmth for the season in the low 70s, however offshore
winds yesterday resulted in some upwelling of cooler waters at some
points along the lakeshore.  Lighter winds today should allow these
cooler waters to warm once again.

Weak boundary sliding south across the lake later tonight may
generate a few light showers after midnight.  Lake induced
instability may cause an isolated water spout to develop.



Today/Tonight and Aviation/Marine...MBK
Thursday THROUGH Tuesday...BSH is the U.S. government's official web portal to all federal, state and local government web resources and services.