Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 200141
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
841 PM CDT Sat Aug 19 2017

.UPDATE...


&&

.MARINE...

High pressure will become centered over the eastern Great Lakes
Sunday afternoon. This will result in a more south flow, but a
lake breeze is expected with southeast winds late Sunday morning
and afternoon. Wind speeds will gradually increase later Sunday,
but still be below Small Craft criteria.

&&

.PREV DISCUSSION... (Issued 653 PM CDT Sat Aug 19 2017)

UPDATE...

AVIATION(00Z TAFS)...

Clear skies this evening under high pressure. Will see some
IFR/LIFR fog develop late tonight, especially in the river
valleys. After fog dissipates tomorrow morning, there expect
diurnal late morning and afternoon cumulus. Low chances of
thunderstorms west of Madison later in the afternoon and evening
as instability increases and a weak shortwave approaches.

PREV DISCUSSION... (Issued 242 PM CDT Sat Aug 19 2017)

SHORT TERM...

Tonight and Sunday...Forecast confidence is high:

High pressure will slowly slide eastward tonight into Sunday. The
high will hold on long enough for mostly clear skies tonight into
Sunday morning. Will probably see some fog again later tonight
into early Sun morning.

Diurnal cumulus likely again tomorrow, along with increasing
clouds from the west later in the day as a weak shortwave
approaches. May see a few showers/storms mainly in the west by
late afternoon given marginal lift from the waves along with
increasing moisture and instability. Should be a little warmer
tomorrow, as 925 mb temps increase to 22-24C by afternoon. This
will likely yield mid 80s for highs most places.

Sunday Night and Monday...Forecast confidence is Medium.

The upper level flow is zonal with a weak lead shortwave across
Lake Superior and northern Wisconsin Sunday evening. Weak to
moderate upper level divergence. The 700 mb upward motion is
moderate Sunday night and somewhat weaker Monday.

A 20 degree 850 celsius thermal ridge extends across northern
illinois, and a little into southern Wisconsin. The surface
boundary on the GFS is near southern or central Wisconsin. The
NAM and especially the ECMWF is farther south, with the ECMWF
dropping it into northern Illinois Monday.

All three models have some rain Sunday night, with Monday having a
lesser chance. being problematic, with the models developing a
large MCS over Iowa on Monday. Therefore clouds will likely
affect viewing the eclipse in southern Wisconsin on Monday.

Zero to 1 km mixed layer CAPE is near 1400 Joules/kg Sunday
evening, although surface to 3 km lapse rates are only 5.2
Celsius/KM. there are steeper lapse rates above 850 mb, so
elevated thunderstorms are possible.

By Monday Zero to 1 km mixed layer CAPE are near 2000 Joules/kg
with only an initial weak cap, that weakens late in the afternoon.
Stability parameters and shear indicate a marginal severe threat.

LONG TERM...

Monday night and Tuesday... Forecast confidence is High.

The zonal flow becomes more southwest Monday night and Tuesday
ahead of a strong shortwave across south central Canada and the
Northern Plains.

The shortwave will push across Wisconsin Tuesday night.

A surface trough/warm front will be near southern Wisconsin
Monday Night before a strong cold front exits Tuesday morning.

Showers and scattered storms are expected Monday night, ending
Tuesday morning. Look for brisk northwest winds Tuesday.

Wednesday through Saturday...Forecast confidence is High.

A large mid/upper level trough is expected over Southeast canada
and the eastern Great Lakes Wednesday, that slowly reaches the
northeast U.S. Thursday night. A shortwave should drop down
across the western Great Lakes Thursday night and into friday

The cool north wind should diminish Wednesday, with high pressure
and cooler air Thursday. The high is expected to be over the
Great Lakes into saturday.

AVIATION(18Z TAFS)...

Lake breeze is holding fairly stationary just inland early this
afternoon, but may move a bit farther west by mid to late
afternoon. Something to keep an eye on for wind shifts in the far
east.

Few-Sct afternoon cumulus will give way to clear skies this
evening under high pressure. Could see some fog develop again
tonight. After fog dissipates tomorrow morning, there will
probably be another round of diurnal cumulus. Did throw some low
precip chances in west of Madison later in the afternoon as a weak
wave approaches.

MARINE...

Quiet conditions are expected this weekend under high
pressure.

&&

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

$$

Update...Hentz
Tonight/Sunday and Aviation/Marine...DDV
Sunday Night through Saturday...Hentz



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