Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 161133

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
633 AM CDT Fri Jun 16 2017

.UPDATE AND AVIATION(12Z TAFS)...Showers continue to diminish
over northern IL and far southeast WI early this morning as low
level jet shifts off to the east. VFR conditions to continue but
bkn-ovc mid/high clouds to persist most of the day. Still expect
scattered convection to affect southern WI tonight.


.PREV DISCUSSION... (Issued 335 AM CDT Fri Jun 16 2017)


TODAY AND TONIGHT - Confidence...Medium.

Convection passing by across northern IL will cause gusty south
winds for several hours early this morning.  Convection tied to
moisture advection and convergence and passing weak low level jet
across northern IL.  With northern IL convection weakening, isolated
to scattered storms may further develop over parts of southern WI
through early this morning.  Will take some time for mid-high clouds
to thin but expect most areas to see at least filtered sunshine by
late morning or early aftn.  This should allow temps to warm back
into the 80s.  A lake breeze should cool off locations right at the
lakeshore this afternoon.

NAM/GFS focus convection farther south this afternoon on southward
moving outflow boundary.  However with low level moisture return to
southern WI and weakly elevated instability, can not rule out an
isolated storm redeveloping in the mid to late afternoon.  Most of
the day will be dry.

Think a period of t-storms is likely tonight but lack of confidence
on focusing timing on evening or overnight hours.  Hence wl continue
chance wording but with high chance Pops.  Strengthening upper jet
sweeps southeast across the upper midwest tonight as a period of
enhanced synoptic scale forcing sweeps across southern WI. 700mb
jetlet of 35-45knots tied to low level jet development also moves
across southern WI overnight.  Bulk shear increases overnight but
some question as to amount of elevated instability.  May see
Marginal area increase across more of southern WI later today.

Saturday and Saturday night - Confidence...Medium
Highly dynamical system will be moving through the western Great
Lakes this period. A potent mid level wave takes on a negative
tilt with a 90-100 knot speed max at 200-300 millibars riding the
base of the it swings through. There is some evidence
showing the better instability staying south of WI where the SPC
Enhanced Risk is largely focused. However there appears to be
enough CAPE here in srn WI to warrant concern especially with the
appreciable dynamics coming into play. 0-6km shear increased to 50
to 60 knots later in the day and into the evening hours. Of
course prior convection and cloud cover will have a say on the
eventual layout of where the air is best to support the strongest
storms. However the shear is impressive so with even modest CAPE
values some rotating storms could initially evolve before
transitioning to a larger MCS which the models suggest could stay
to our south with some consensus with this in the QPF panels. Also
the CIPS analogs are currently favoring the southern look favoring
the Enhanced Risk. However there is an axis of higher Supercell
composite values that straddle the WI/IL border for a time in the
afternoon though the largest areal extent of this is focused
further south into the Enhanced Risk.

Sunday - Confidence...Medium
A much cooler and less humid airmass will be in place as the low
will be to our northeast with a 850 cold advection which will
continue more gradually into Sunday night. With the mid level
cyclonic flow we may see some SHRA/Isold TSRA development. The
models are showing different QPF distributions but only the GEM is
offering a dry solution so still worthy of a chance at this time.

Monday - Confidence...Medium
Mid level trough axis translates only slowly eastward with still
plenty of lingering cyclonic flow across the area to keep the
chances for SHRA/Isold TSRA in the forecast.

Tuesday - Confidence...Medium
While the primary trough shifts well east the flow remains active
from the northwest with another wave arriving. This will keep the
chance of SHRA/TSRA in the forecast yet again. Some modification
of 850 temps with the ECMWF showing a bit more of a WAA signal.

Wednesday and Thursday - Confidence...Low to Medium
500 millibar heights rise somewhat this period with the northwest
flow regime taking on a more zonal look. An evolving WAA regime
will mean some SHRA/TSRA chances this period. At this time the
better signal for this would arrive Wednesday night or Thursday.
Some modification in 925 temps expected Wednesday but a bigger
jump looks likely Thursday with 925 temps back into the low or mid
20s celsius.

AVIATION(09Z TAFS)...Isolated to scattered t-storms will affect
southern WI through the early morning. Cigs expected to remain
mostly VFR. Widespread mid- high clouds will gradually thin but
more sct-bkn mid clouds will likely develop this aftn. A period of
convection will likely affect southern WI overnight tonight with
briefly lower cigs/vsbys.

MARINE...Outflow from convection passing by to the south will cause
a period of gusty southwest winds to 20 knots across the southern
zones early this morning. Expect southwest winds to once again
turn southeast later this morning or early afternoon as a lake
breeze develops. Possible that patchy fog may develop as moist air
flows over the cooler lake waters, but not enough confidence to
include at this point. Be alert for a period of thunderstorms
affecting the nearshore waters overnight tonight.




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