Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI
FXUS63 KMKX 180239
Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
939 PM CDT WED AUG 17 2016
.UPDATE...Atmosphere continues to stabilize, at least near the
surface but SPC mesoanalysis continues to show elevated weak Cape
aloft. Passing weak mid-level wave may yet set off another
isolated shower or t-storm, especially in the southwest or west.
Otherwise, expect areas of fog to develop overnight as
temperatures fall to near or slightly below the dewpoint,
especially in the south and west. Added low level moisture from
this morning`s rain will also aid in fog development. Will likely
be some patchy dense fog for several hours.
.AVIATION/06Z TAFS/...Light boundary layer winds and high low
level moisture will result in areas of fog developing overnight.
Fog may become dense for several hours at several TAF sites
including KENW and KMSN.
.MARINE...Expect the light south to southwest winds to turn light
offshore overnight. These light southwest winds may carry some
patchy fog into the near shore waters late tonight but the fog
should quickly dissipate Thursday morning.
.PREV DISCUSSION... /Issued 335 PM CDT WED AUG 17 2016/
TONIGHT AND THURSDAY...Forecast Confidence Is Medium.
Confluent surface boundary/moisture gradient from near La Crosse to
northeast Illinois helping generate a few showers southwest of
Madison into Richland County. More showers and storms were around
and east of Rockford, just south of the area.
Adjusted area forecast soundings and SPC Mesoanalysis suggest an
uncapped airmass should linger into the early evening. So, there
should be at least a few showers and storms into early evening near
and south of the above mentioned boundary.
Not expecting anything severe, with mean layer CAPE modest at best,
and deep layer shear weak. Went with isolated wording in forecast
for now into early evening.
After the cells dissipate early this evening, the rest of tonight
into Thursday should be quiet. Weak high pressure moves through
tonight, with south winds on Thursday. Should see patchy fog later
tonight into early Thursday morning, with light winds and moist dew
points in place. Low areas may see more concentrated fog.
The south winds should bring a very warm and humid airmass, with
highs in the mid to upper 80s inland. Southeast winds with lake
breeze should keep highs near the lake a bit cooler.
Some mesoscale models want to generate scattered showers and storms
Thursday afternoon, along lake breeze boundary. Kept dry forecast
for now, as these models have overdone this quite a bit this summer.
Later shifts may need to revisit this, as forecast soundings are
uncapped but most mean layer CAPE is well aloft.
Thursday night and Friday...Forecast confidence is medium.
An upper trough will sharpen as it moves across the northern
plains. The flow across Wisconsin becomes more southwest as a 105
knot 250 mb jet max approaches the lake Superior area. Most of
the upper divergence remains to the west closer to the right
entrance region. However the GFS does bring a band of moderate
upward motion into south central Wisconsin Friday morning, which
appears to be convective feedback with a linear MCS on the GFS.
This is on the nose of a 45 knot 850 mb west jet max that weakens
to 30 knots as it enters southern Wisconsin. 850 mb dew points are
rather high around 13 Celsius. Elevated CAPE of around 2300
joules/KG late Thursday night if lifted from 850 mb. A rather
strong cap develops Friday, that does weaken late in the
Friday night and Saturday...Forecast confidence is medium.
The GFS takes the lead shortwave trough across the upper
Mississippi valley into western Wisconsin Saturday. The 250 mb
jet max lifts north of lake Superior Saturday afternoon. Upper
divergence and 7090 mb upward motion increases Friday night and
continues saturday morning before lifting northeast Saturday
afternoon. 850 and 700 mb dew points are high until saturday
The atmosphere become more moist adiabatic later friday night and
into saturday morning. Then the mid levels become quite dry
Saturday afternoon from the west. Also lapse rates stabilize above850
mb during the afternoon with just the shallow unstable layer. As
such expect mainly scattered to broken cumulus by mid to late
The GFS/NAM and ECMWF all bring moderate to heavy rainfall Friday
night into Saturday morning. The ECMWF is a little slower in the
drying Saturday afternoon, with the NAM much slower.
SUNDAY... Forecast confidence is medium.
Cyclonic flow will linger over the Great Lakes through Sunday night
leading to plenty of cloud cover, a chance for light showers, and
cool temperatures as 1000 to 500 mb thickness drops to 555
MONDAY AND BEYOND... Forecast confidence is medium.
Surface high pressure will move across the Ohio Valley and begin a
warming trend with south winds by Tuesday that continues into
Wednesday. Warmer air will begin making a comeback on Monday and
continue into Wednesday. A tough drops across southern Wisconsin
Wednesday night pushing a boundary to the south. Models bring a
chance of showers/thunderstorms from time to time, but don`t get
too heavy until the boundary drops to the south Wednesday night
Mainly VFR conditions are expected across TAF sites into this
evening and for most of Thursday. Isolated showers and storms are
possible into early evening, but there is some uncertainty with
areal coverage. Left mention out of TAFs due to low confidence in
them affecting TAF sites. There may be brief MVFR/IFR visibilities
and gusty winds with any storms.
Otherwise, scattered to broken diurnal cumulus clouds are expected
into early evening. Light west to northwest winds should remain,
with winds possibly shifting southeast at Milwaukee and Kenosha into
early evening with a lake breeze. Not sure if the lake breeze will
reach these locations or remain just east of there.
Light southwest winds later this evening into tonight should remain
on Thursday, with southeast winds developing at Milwaukee and
Kenosha with lake breeze Thursday afternoon. After some clearing
later tonight, more scattered to broken diurnal cumulus is expected
by Thursday afternoon. Should see MVFR fog between 08Z and 13Z
Thursday at TAF sites.
Southeast lake breeze should linger into early evening, and should
develop again Thursday afternoon, over the nearshore waters of Lake
Michigan. Light southwest to south winds are expected tonight.
South winds will increase somewhat Friday into Saturday, before cold
front moves southeast through the area Saturday night. Winds should
veer northwest and become gusty on Sunday. Low waves are expected
into Saturday night, building to 2 to 3 feet Sunday.
Isolated showers and thunderstorms may occur into early evening, but
uncertainty remains with where they will form. Chances return for
Friday into Friday night, becoming likely Saturday into Saturday
evening with the cold front moving southeast through the region.
TONIGHT/Thursday AND AVIATION/MARINE...Wood
Thursday NIGHT THROUGH Wednesday...Hentz