Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 180204
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
904 PM CDT Mon Jul 17 2017

.UPDATE...Light winds and clear skies tnt may lead to light
patchy fog in the early morning hours. Otherwise low temps in the
middle 50s to lower 60s looks good.

A surge of warm, moist advection will then occur on Tue ahead of
a weak shortwave trough that will track across central WI Tue nt.
The sfc-850 mb thermal ridge via a 20-30 kt swly LLJ will move
from central WI to srn WI from the afternoon into the evening
followed by a slow moving cold front. MLCAPEs may rise to 2000
J/kg but there is uncertainty how far south the cold front or
outflow boundaries will reach into srn WI. Thus highest confidence
for storms and heavy rain is central WI with lesser confidence
toward the IL border.


&&

.AVIATION(00Z TAFS)...Patchy light fog may occur over srn WI
during the early morning hours and then quickly dissipate after
sunrise. Otherwise VFR conditions are expected for Tue although
tstorm chances will increase from north to south across the region
during the evening and overnight.

&&

.MARINE...Relatively light winds and low wave heights for tnt
through Thu although locally gusty winds and high waves may occur
with tstorms at times. For Tue, a lake breeze is mainly expected
south of Port Washington for the afternoon hours.


&&

.PREV DISCUSSION... (Issued 319 PM CDT Mon Jul 17 2017)

SHORT TERM...

Forecast Confidence is High.

High pressure will slide east across the Great Lakes region
tonight with low pressure strengthening over the northern Plains
states. Light/variable winds will give way to increasing southerly
flow and a return to warmth and humidity on Tuesday.

Clear skies and light winds tonight may lead to light fog
development. Confidence on this particular aspect of the forecast
is a little bit shaky, but at this point any fog looks patchy.
Will be monitoring convective trends to our northwest tonight,
but current indications are that this activity will either
dissipate and/or stay just to the north of the area by daybreak
Tuesday.

Temperatures tonight will be rather comfortable (50s to low 60s),
but the resurgence in southerly flow will result in high warming
well into the 80s and heat index values in the 90s (especially
away from the lakefront).

Tuesday night night and Wednesday...Forecast Confidence...Medium

A zonal upper flow sets up with one speed max exiting north of
the Great Lakes, with a second stronger one moving across North
Dakota. Moderate upper divergence and 700 mb upward motion is
strongest Tuesday night. Some of the storms could produce
moderate to heavy rain. Precipitable water values are around 2
inches.

Very warm and more humid air is expected Wednesday. Zero to 1 km
CAPE rises to 1500 Joules/kg most areas, but near 3000 Joules/kg
well west of Madison toward the Mississippi River. Low level
shear is weak, with zero to 3 km shear around 20 knots.

LONG TERM...

Wednesday night through Saturday...Forecast Confidence...Medium

This is the period with the greatest heavy rain potential. Also
there could also be a severe potential.

The zonal upper flow becomes a bit more northwest by Friday, as a
broad trough forms near the Hudson Bay area. Several jet max`s
will move across the U.S. Canadian border area. The best chances
of heavy rain are late Wednesday night into Thursday morning and
again Friday, but 3 rounds are possible during this period with
another late friday night into Saturday morning. The storms would
likely produce heavy rain. Precipitable water values are around 2
inches for much of the period.

Zero to 1 km CAPE rises to 2500 Joules/kg most areas, but near
4000 Joules/kg over much of south central Wisconsin. zero to 1 km
shear is around 18 knots with zero to 3 km shear around 25 knots.

Sunday and Monday...Forecast Confidence...Medium

A rather strong shortwave moves across the lake superior region
Sunday with the ECMWF much stronger with the shortwave. The ECMWF
builds an upper ridge across Wisconsin Monday, but the GFS has a
more zonal flow.

The ECMWF is precipitation free, but the GFS still has some
shower possibilities.

AVIATION(18Z TAFS)...

VFR conditions are expected into this evening. Getting a signal
from model and SREF probabilities of light fog potential across
the region tonight, particularly areas adjacent to the lake. Have
gone ahead and included a mention of MVFR during the overnight
hours. Otherwise, some passing high level clouds can be expected
with light variable winds through tonight becoming southerly
Tuesday morning.

MARINE...

Light easterly winds this afternoon and tonight will give way to
increasing southerly winds on Tuesday. Waves should stay at or
below 1 foot. Will continue to monitor wave height forecasts for
Tuesday afternoon into Tuesday evening as wind gusts may approach
20 knots.

&&

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

$$

Update...Gehring
Tonight/Tuesday and Aviation/Marine...Gagan
Tuesday Night through Monday...Hentz


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