Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 231759 AAC
AFDMKX

Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
1259 PM CDT Sun Jul 23 2017

.UPDATE...

Storms are firing now in the south/southwest forecast area. Could
see a storm or two approach/reach severe levels this afternoon.
Something to keep an eye on.

&&

.AVIATION(18Z TAFS)...

Storms are expected this afternoon, mainly across the southern
half of the forecast area. Could see some hail and gusty winds
with these storms. Activity will wind down late afternoon into the
evening, with dry weather then expected through Monday as high
pressure builds into the region.

Still think the winds will switch to northeast by the middle of
this afternoon near Lake Michigan as a lake breeze moves in.

Might be some fog tonight in the west toward the high building in.
A drier airmass will slowly be working in overnight though, which
might limit develop.

Low clouds are expected to develop tonight, lingering into Monday
morning. Should see VFR conditions return north to south late
morning into the afternoon.

&&

.PREV DISCUSSION... (Issued 946 AM CDT Sun Jul 23 2017)

UPDATE...

Showers in the northwest will continue eastward, possibly
diminishing a bit per latest radar and mesoscale model trends.
Models are still suggesting shower/storm activity will then focus
in the southwest forecast area late morning into the afternoon,
with dry weather or isolated showers/storms elsewhere.

Temperatures are already approaching forecast highs many places,
but clouds will likely increase a bit into the afternoon. It also
looks like 925 mb temps may slowly decrease during the afternoon,
so will leave forecast highs alone for now.

MARINE...

Could see winds/waves approach Small Craft Advisory levels on
Monday, but right now it looks like conditions should stay just
below criteria.

PREV DISCUSSION... (Issued 652 AM CDT Sun Jul 23 2017)

UPDATE...

Outflow from the storms that are tracking down the lake are
causing easterly winds and low clouds along the shoreline. The
clouds will scatter out quickly this morning. Mostly clear skies
will give way to mid level clouds moving into south central WI
that are associated with the approaching upper trough.

The HRRR has been consistent with producing thunderstorms over
northeast IA and southwest IL today, although they are looking
more delayed. These should track southeast and have a lower chance
of impacting Kenosha. I have lower confidence about thunderstorm
chances in east central southeast WI this afternoon and evening- I
would lean toward them not developing.

AVIATION(12Z TAFS)...

Outflow from the storms that are tracking down the lake are
causing easterly winds and low clouds along the shoreline. The
clouds will scatter out quickly this morning. Mostly clear skies
will give way to mid level clouds moving into south central WI
that are associated with the approaching upper trough.

Patchy ground fog and associated low clouds will clear out quickly
by 8 or 9 am this morning. A surface front will reach south
central WI by midday. The front is weak in terms of wind and
temperature, but could kick up a few storms south of Madison and
Kenosha today.

PREV DISCUSSION... (Issued 337 AM CDT Sun Jul 23 2017)

SHORT TERM...

Today and Tonight...Forecast Confidence is Medium.

Shortwave energy out ahead of a robust upper trough, upward motion
due to the right entrance region of an upper jet, the nose of an
850mb weak low level jet, and just enough moisture in the
700-800mb layer are allowing for scattered showers and
thunderstorms in areas of east central WI early this morning.
These will diminish as drier air moves in around 12Z/ 7 am this
morning.

The next area to watch for potential showers and thunderstorms
later this morning is over south central WI. The HRRR and some
other mesoscale & synoptic models show some activity developing
along the surface cold front where there is just enough moisture
to allow for it. The forcing is also associated with the upper
trough.

These should remain confined to just south of the I-94 corridor
and there is only a brief window of opportunity that will
translate into southeast WI by early afternoon. If these storms
occur, CAPE and shear are on the weak to moderate side, so a few
stronger storms are possible, but probably sub-severe. They would
be fairly short-lived, so this is not a day to cancel plans. A
half inch would be possible under any strong storm, so we will
monitor this for a potential problem to flooded areas.

LONG TERM...

MONDAY AND TUESDAY...Forecast confidence is high.

Light upper flow will prevail with mid-level ridging taking hold
across the western Great Lakes. Surface high pressure will
progress from near Lake Superior Monday morning towards Lower
Michigan Tuesday afternoon. North to northeasterly surface winds
on Monday will veer southerly on Tuesday with return flow behind
the departing surface high. This will advect a higher theta-E
airmass into southern Wisconsin, with a subsequent increase in
both 850/925 mb temperatures and surface dewpoints. Any
precipitation during this time will remain confined well to our
northwest across the Dakotas and Minnesota in close proximity to
a surface cold front. Look for below normal temperatures on Monday
with onshore flow, followed by a warming trend towards normal on
Tuesday. It will feel more humid on Tuesday, as dewpoints climb
into the mid 60s west of Madison.

WEDNESDAY AND WEDNESDAY NIGHT...Forecast confidence is medium.

The upper flow pattern becomes zonal and progressive, as an 80 to
90 knot speed max traverses the Upper Midwest and western Great
Lakes. A band of mid-level moisture and cyclonic vorticity
advection will progress through the region, reaching southern
Wisconsin Wednesday afternoon and evening. The upper wave will
escort a surface cold front, which should arrive in our area
during the evening. Surface convergence along the front will serve
as a focus for showers and thunderstorms as it arrives. The pre-
frontal environment will be characterized by modest deep layer
shear around 25 knots, 1.5 to 2 kJ/kg of MLCAPE, and mid-level
lapse rates around 7 degrees per kilometer. This suggests some
potential for severe thunderstorms on Wednesday. We`ll also need
to keep a close eye on rainfall, given multiple areas which are
particularly vulnerable given recent flooding. While moisture
parameters are conducive to heavy rainfall, the steering flow
appears fairly progressive. This means that we should keep the
showers and storms moving along, which should hopefully minimize
the risk for additional flooding. Of course, this is still several
days out, so we`ll need to watch for any changes. Keep up with
the forecast. It will feel pretty muggy on Wednesday with highs in
the 80s and dewpoints right around 70.

THURSDAY THROUGH SATURDAY...Forecast confidence is medium.

High pressure will slowly migrate from the western Great Plains
into the Lower Great Lakes, bringing quiet weather to the region.
The 23.00z GFS solution brings shower chances along a weak surface
trough on Saturday night, but this is not supported among the
other guidance at this time. Temperatures during this period will
be seasonal.

AVIATION(06Z TAFS)...

Patchy ground fog and associated low clouds will clear out quickly
by 8 or 9 am this morning. Storms in east central WI are expected
to move out by 12z/7 am. Otherwise, mid level clouds will clear
out this morning until a surface front reaches south central WI
by mid morning and southeast WI this afternoon. The front is weak
in terms of wind and temperature, but could kick up a few storms
south of Madison and Milwaukee today.

MARINE...

Light winds will prevail today. Then northeast winds will increase
from north to south this evening with a weak cold front. The wind
gusts are expected to remain below 22 knots and waves below 4
feet, so I did not issue a small craft advisory.

&&

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

$$

Update...DDV
Today/Tonight and Aviation/Marine...Cronce
Monday THROUGH Saturday...SPM


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