Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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924
FXUS63 KMKX 210209
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
909 PM CDT WED JUL 20 2016

.UPDATE...

Several concerns on Thursday`s forecast. The biggest centers on
the North Dakota Thunderstorms that should push east across
northern Minnesota tonight. The 18Z GFS and NAM push these mainly
east Thursday morning. However the high resolution HRRR pushes
them southeast after entering Northwest Wisconsin. The 00Z HRRR
has the storms just north of the Dells and Fond du lac at 10 AM.
The mid/upper ridge does begin to flatten at this time. If the
storms continue southeast they would likely mess with the Max
temps and heat indices, especially across the advisory area. Even
so they may recover enough to hit criteria given the high dew
points. Even if the storms don`t reach the far south debris clouds
could keep Max Temperatures down in the warning areas. If the
storms stay north, then heat Indices would likely hit the warning
criteria even in the advisory area across Fond du lac and
Sheboygan.

The new 00Z NAM does not handle the existing Dakota storms well
at all, with no thunderstorms Thursday. Until more 00Z data comes
in is would not be prudent to change headlines yet, either way.

&&

.AVIATION/06Z TAFS/...

Some MVFR vsbys during the early morning until just after sunrise.

There should not be much if any shower or thunderstorm activity
tonight. The biggest concern is on the North dakota Thunderstorms
that should push east across northern Minnesota tonight. The 18Z
GFS and NAM push these mainly east Thursday morning. However the
high resolution HRRR pushes them southeast after entering
Northwest Wisconsin. The 00Z HRRR has the storms just north of the
Dells and Fond du lac at 15z. The mid/upper ridge does begin to
flatten at this time, but the storms could drop into southern
Wisconsin by 17z from the northwest.

Surface winds will gradually veer southwest by later tonight and
linger Thursday across the area. Gusts up to 23 knots or so
possible Thursday afternoon.

&&

.MARINE...

Then there is the marine fog issue with the rising dew points.
So far the shore area visibilities are fairly good on the web
cams, but visibilities should lower later tonight and Thursday
morning north of Port Washington.

Gusty southwest winds Thursday may approach Small Craft Advisory
levels, as a tight pressure gradient develops. It appears that
gusts will get close to the 22 to 25 knot range during this time.
May need a small craft advisory Thursday, if winds continue to
look robust over the waters in computer forecast models. However
the very warm air should reduce gusts over the cooler waters due
to a more stable low level lapse rate.

There is lots of uncertainty with thunderstorm chances into
Thursday. Some of the meso scale models do bring some
thunderstorms into the nearshore waters, especially north of
milwaukee by noon. There is a better shot Thursday night into
early Friday morning, as a complex of thunderstorms may slide
southward across the area. Gusty winds are possible during this
time.

&&

.Beaches...

The new HRRR and Consensus Wind data is higher than the previous
forecast, and would push the swim hazard risk into the moderate
criteria across Sheboygan and Ozaukee counties Thursday.

&&

.PREV DISCUSSION... /Issued 311 PM CDT WED JUL 20 2016/

TONIGHT AND THURSDAY...Forecast Confidence Is Medium.

The convection over portions of south central Wisconsin have
weakened considerably over the past hour or two. Mesoscale models
are generally showing this decreasing trend into this evening across
the area. Some do develop some elevated convection across portions
of northern Wisconsin during this time.

There already is more development in west central Wisconsin. This is
associated with steady warm air advection and the low level jet nose
pointed in that general area. Any of this activity could slide
southeast into the area tonight, with the continued steady warm air
advection. However, the mesoscale models have been struggling lately
with convective trends, mainly overdone over the past few days. So,
am leaning toward low POPs for tonight. It very well may end up dry.

Steady warm air advection into Thursday will bring the hot and humid
airmass into the area. Think any clouds from convection to the north
of the area should remain there. Southwest winds should become gusty
during the day, with all areas seeing lower to middle 90s for highs.
Dew points in the middle 70s should help bring heat index values of
100 to 110 across the area.

The Excessive Heat Warning is in effect for most of the area
beginning Thursday afternoon, except the four northeast counties,
where a Heat Advisory is in effect. May need an upgrade to a Warning
for these counties in later forecasts, if forecast heat index values
remain high.

Kept small POPs Thursday for thunderstorms, but mesoscale models are
mainly dry. ECMWF/Canadian try to bring in some QPF in the north by
00Z Friday, but the airmass is likely capped with the hot
temperatures in place. Would need forcing above the 700 mb level to
get convection going, which is going to be tough. Thus, Thursday may
end up dry.

THURSDAY NIGHT AND FRIDAY...Forecast confidence is medium.

A convective complex should be ongoing across some portion of far
northeast Wisconsin or the U.P. of Michigan, near the stationary
warm frontal boundary by the start of this period. Much of our
guidance indicates this will take a dive down the lake. It`s
likely the lake will enhance the cold pool and with a steady
southwest feed into this region, we should see the storms progress
south, then possibly southwest late Thursday ngt into early Friday
morning. This back building scenario is a concern for heavy rain,
but model guidance performance with convective complex evolution
has been poor lately, so confidence isn`t high. If we see a big
complex come through Friday morning, this would likely bring
cooler and drier air to southern Wisconsin. Our heat
warning/advisory goes through Friday, but we`ll have to see if any
storms change that.

For now, still looks like mostly lower 90s on Friday. If those
storms don`t develop, possibly warmer.

SATURDAY AND SUNDAY...Forecast confidence is medium.

Our next best chance for rain arrives Saturday afternoon into
Sunday morning. This is associated with a rather decent low
pressure area/elongated trough moving out of the northern plains
and into the Great Lakes. The focus right now looks to be to our
north, with activity developing south with time. It should fire
upstream on Saturday, and the uncertainty is how long it will
survive into Saturday night before it diminishes as it moves
southeast. That has been the broken record this season.
Unfortunately, our dry conditions highlight that these storms have
not survived that diurnal trend into eastern Wisconsin.

Saturday is still looking quite warm with highs around 90 and dew
points around 70. The temp forecast for Sunday is highly
questionable given uncertainty of precip and frontal passages.
But, for now a few degrees cooler than Saturday, but not by much.

MONDAY AND TUESDAY...Forecast confidence is medium.

Right now, this period looks dry as high pressure builds in in the
wake of the passing low on Sunday. Temps drop down into the 80s
with dew points drying out as well.

WEDNESDAY...Forecast confidence is medium.

We get into a return flow of moist air and possibly a trough
pushing in. A long way off, but this will be our next chance of
rain after Tuesday.

AVIATION/00Z TAFS/...

Expect VFR conditions tonight into Thursday across TAF sites.
Showers and storms are weakening across areas north and south of
Madison. There may not be much more thunderstorm activity for
tonight into Thursday, as a hot and humid airmass works into the
area. Lots of uncertainty here, so will keep TAFs dry during this
time.

There may be a period of MVFR fog later tonight into Thursday
morning, but should be rather shallow and intermittent, with some
south to southwest winds during this time.

South to southwest winds may gust to around 20 knots until sunset at
the eastern sites. Winds will gradually veer southwest by later
tonight and linger Thursday across the area. Gusts up to 23 knots or
so possible Thursday afternoon.

A complex of thunderstorms moving southward may affect TAF sites
Thursday evening or overnight, with gusty winds and MVFR/IFR
visibilities possible.

MARINE...

There may be fog development over the nearshore waters at times
tonight, but should be shallow and intermittent in nature. Think the
winds will be strong enough to limit more widespread fog formation.

Gusty southwest winds Thursday may reach Small Craft Advisory
levels, as a tight pressure gradient develops. It appears that gusts
will get close to the 22 to 25 knot range during this time. Held off
on a Small Craft Advisory for now, but may need one in later
forecasts, if winds continue to look robust over the waters in
computer forecast models.

There is lots of uncertainty with thunderstorm chances into
Thursday. Most or all of this period may end up dry. There is a
better shot Thursday night into early Friday morning, as a complex
of thunderstorms may slide southward across the area. Gusty winds
are possible during this time.

&&

.MKX Watches/Warnings/Advisories...
WI...EXCESSIVE HEAT WARNING from noon Thursday to 7 PM CDT Friday for
     WIZ046-047-056>058-062>072.

     HEAT ADVISORY from noon Thursday to 7 PM CDT Friday for WIZ051-
     052-059-060.

LM...None.
&&

$$

UPDATE...Hentz
TONIGHT/Thursday AND AVIATION/MARINE...Wood
Thursday NIGHT THROUGH Wednesday...Davis



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