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421
FXUS63 KMKX 250837
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
337 AM CDT Sun Jun 25 2017

.TODAY AND TONIGHT...Forecast Confidence Is Medium.

Area of rain showers over northeast Wisconsin should stay just
north of the forecast area early this morning. Best differential
cyclonic vorticity advection at 500 mb with these showers will
shift to the east, and take any lingering showers in that
direction.

The region will remain in a general northwest flow pattern at 500
mb today and tonight. Differential cyclonic vorticity advection
with an advancing 500 mb vorticity maximum will slide into the
area from the northwest this afternoon and early this evening.

Area forecast soundings are showing rather weak mean layer CAPE
developing this afternoon and early this evening, best in the
northern counties. The weak mean layer CAPE barely reaches the
-10 degree Celsius level in the south, so there is some question
 if any thunder is possible there. For now, will continue PoPs for
 showers and slight chances for thunder across the area this
 afternoon and early this evening.

It appears that another shot of cold air advection mainly tonight
will occur, which will reinforce the unseasonably cool
temperatures. Highs should remain in the middle to upper 60s, with
lows tonight into the upper 40s to lower 50s.

.MONDAY...Forecast confidence is high.

Cyclonic flow prevails aloft as a compact shortwave/vorticity
maximum slides southeast from the Minnesota Arrowhead into the
lower Great Lakes. An anomalously cold pocket aloft will
accompany the wave, with 500 mb temperatures dropping to around
-20 degrees Celsius by evening. This will result in steep lapse
rates, as we build a few hundred Joules of tall, skinny CAPE. This
should provide sufficient instability for scattered showers and a
few thunderstorms during the afternoon and evening, with the
greatest chances to the northeast of Madison. Given the CAPE and
moisture profiles, gusty winds and small hail may be possible with
some of the showers and storms. Temperatures will remain below
seasonal normals, with highs in the 60s and lows right around 50.

.TUESDAY...Forecast confidence is high.

The upper flow becomes somewhat more progressive, with
northwesterly flow and rising heights aloft. This will support
surface high pressure as it slides southeast from Iowa into the
Ohio Valley by evening. Low-level southwesterly return flow will
kick in by the afternoon, with high temperatures reaching into the
mid 70s. We`ll likely see some mid to high level cloud cover
ahead of the next wave approaching from the west.

.WEDNESDAY...Forecast confidence is medium.

Southern stream jet energy advances east-northeast from the Four
Corners region into the mid Missouri valley. This occurs in
concert with northern stream energy cascading southeast from the
northern Rockies into the central Great Plains. At least partial
phasing is suggested by the guidance, with a 90 to 100 knot speed
max developing over Wisconsin Wednesday evening. Southern
Wisconsin should be near the left exit region, with jet-level
divergence maximized around 00z Thursday. The upper wave will help
spin up a surface low over the northern High Plains Wednesday
morning, with the slowly occluding cyclone tracking east into
northern or central Wisconsin Wednesday night. Southern Wisconsin
will be in the warm sector on Wednesday, with south to
southwesterly winds advecting a good supply of warmth and
moisture. As dewpoints climb into the mid to upper 60s, moderate
instability is forecast to build late Wednesday afternoon and
evening, with around 1000 to 1500 J/kg of MLCAPE. We`ll also see
around 30 to 40 knots of west to southwesterly deep layer shear
Wednesday afternoon, becoming largely unidirectional and westerly
overnight. All of this suggests a potential severe weather risk
for Wednesday afternoon into Wednesday night, so keep up with the
forecast. Heavy rain is also possible, given strong moisture
transport, precipitable water values over 2 inches, and deep warm
cloud depth. Precipitation should be on the downswing late
Wednesday night as the surface cold front pushes south into
northern Illinois.

.THURSDAY THROUGH SATURDAY...Forecast confidence is low.

The cold front should be located to our south Thursday morning,
but a series of ripples in the mid to upper flow should initiate a
surface wave on Thursday afternoon into Thursday night. This may
help pull the front back to the north and renew our shower and
thunderstorm chances on Thursday and/or Friday. This scenario is
somewhat supported by both the GFS and ECMWF models, with some
timing differences among them. Rain chances during this period are
a little murky, but seasonal temperatures should prevail.

Another wave will bring clouds and perhaps a chance for showers
on Saturday. Temperatures should remain near seasonal normals.

&&

.AVIATION(09Z TAFS)...

West winds will gust up to around 20 knots at times today. Mainly
broken cumulus clouds are expected by this afternoon, with chances
for showers and a few storms. These may linger into early this
evening. Stratocumulus clouds may linger in far northern portions
of the area tonight, with clearing skies over most of the rest of
the area. Winds should weaken during this time. More chances for
showers and a few storms are forecast for Monday afternoon. Gusty
west to northwest winds are expected once again, possibly gusting
in the 20 to 25 knot range.

&&

.MARINE...

West winds will gust to around 20 knots today, with good low
level mixing and a fairly tight pressure gradient. Any high waves
will be over the open waters of Lake Michigan.

West to northwest winds may reach Small Craft Advisory levels
Monday, with stronger winds aloft mixing down to the surface.
Winds may reach Small Craft Advisory levels again Wednesday
afternoon into Thursday morning, with gusty offshore winds.


&&

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

$$

Today/Tonight and Aviation/Marine...Wood
Monday through Saturday...SPM