Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus63 kmkx 191215 aaa 
afdmkx

Area forecast discussion...updated
National Weather Service Milwaukee/Sullivan WI
715 am CDT Wed Sep 19 2018

Update...

Thunderstorms tracking through northern Iowa will continue to
move eastward into southern WI late this morning as they weaken.
The hrrr has the general trend but continues to run a couple hours
too slow. Timing and coverage as this complex moves into the area
is still uncertain.

&&

Aviation(12z tafs)...

IFR to MVFR stratus with ceilings of 400 to 1200 feet has
overspread all of southern Wisconsin this morning. Look for
ceilings to gradually rise and break up through mid morning.
Meanwhile, high clouds are beginning to spread into the area.
These are associated with a cluster of thunderstorms that should
spread into southern WI as it weakens around the noon hour. Timing
and coverage are uncertain.

We can expect more widespread thunderstorms to develop over
southern Minnesota this evening, and expand eastward through central and
southern WI overnight. Central WI has the higher chance of
thunderstorms with heavy rain, although that main area could end
up as far south as Madison and Milwaukee

&&

Previous discussion... (issued 355 am CDT Wed Sep 19 2018)

Short term...

Today and tonight...forecast confidence is medium.

A weakening area of showers will slide across central and
northern WI early this morning. Expect dry weather in southern WI
through the morning hours. Current areas of low clouds will
gradually scatter out through late morning. Temperatures will be
on the rise, so any sunshine will help US get into the lower to
mid 70s.

The convection developing over southeast South Dakota is what we'll watch
as it expands and slides east today. The 07z hrrr model seems to
have a handle on it and tracks it into southern WI by early
afternoon. There will be a weakening trend, so coverage is
uncertain for the precip over southern WI this afternoon.

We can expect more widespread thunderstorms to develop over
southern Minnesota, along the nose of a fairly robust low level jet this
evening. This will expand eastward through central and southern
WI overnight. There are model differences regarding the location
of the 850mb warm front, so the placement of the main area of
thunderstorms is still uncertain. Right now, central WI has the
higher chance of thunderstorms featuring heavy rain, although that
main area could end up as far south as Madison and Milwaukee.

Thunderstorms will be on the north side of the warm front
(elevated) overnight and storm Mode is uncertain. Hail would be
the main threat in any stronger storm cores, due to high shear
and decent elevated instability.

Thursday through Friday night...forecast confidence is medium.

Models are showing the east to west oriented surface warm front
and low level jet nose lingering over the area Thursday morning,
before pushing north in the afternoon. Kept higher end pops for
showers and chances for thunderstorms in the morning, highest in
the northern parts of the area. Convection may not be as robust as
later tonight in the north, with varying amounts of elevated cape
per NAM/GFS forecast soundings. Precipitable water values remain
elevated, so could still see locally heavy rainfall in this area.

Warm sector airmass should move northward into the area during
the afternoon and lingering into the evening, before the cold
front slides east across the area later Thursday night and exiting
to the east early Friday morning. There should be enough daytime
heating for warm and humid conditions to return Thursday afternoon
and evening. Gusty south to southwest winds are expected Thursday,
which should boost highs into the 80s across most of the area.

The timing of the cold frontal passage has slowed down, and the
later Thursday night timing is not ideal for severe storms. Mid
level lapse rates are around 6 degrees celsius per kilometer,
which is not great either. Still, there is strong deep layer bulk
shear and enough mean layer cape present to bring a severe storm
risk, mainly across areas northwest of Madison Thursday evening
into the overnight hours. Some uncertainty here with regard to the
severe potential.

Storms should weaken as they cross the area later Thursday night,
as mean layer cape weakens. Brief heavy rainfall is possible,
though storms should move fairly quickly with the front.

Strong cold air advection is expected after the frontal passage
and into Friday, as gusty winds shift to the west and northwest.
Temperatures should gradually fall during the day Friday, with
drier air working into the area. High pressure moving into the
area Friday night should bring quiet weather with colder
temperatures. Lows Friday night will drop into the 40s inland,
around 50 near the lake. It certainly will feel more like autumn
across the area Friday into Friday night.

Long term...

Saturday through Sunday night...forecast confidence is high.

Models are generally showing the influence of high pressure to the
east of the region keeping things dry across the area Saturday
into Sunday night. 500 mb flow looks to remain zonal during this
period. Temperatures look to remain near or a little below
seasonal normals during this time.

Monday through Tuesday...forecast confidence is medium.

Models are hinting at some warm air advection trying to return to
the area for Monday, with a cold front crossing the region Monday
night, exiting to the east on Tuesday. 500 mb trends suggest a
broad longwave trough developing over the region, into the
northern plains. Kept highest pops for Monday night for now, and
will refine them as things become more clear with trends this far
out in the forecast period.

Aviation(09z tafs)...

There is an area of low (ifr) stratus just west of Madison that
is remaining stationary. Another area of stratus over Fond Du Lac,
Sheboygan, and West Bend is expanding southwestward early this
morning. Expect ceilings to gradually rise and scatter out through
mid morning.

Light showers will slide across central and northern WI this
morning and miss southern WI. The convection developing over
southeast South Dakota is what we'll watch as it expands and slides east
today. The 07z hrrr model seems to have a handle on it, although
it is lagging behind a couple of hours, and tracks it into
southern WI by early afternoon. There will be a weakening trend,
so coverage is uncertain.

We can expect more widespread thunderstorms to develop over
southern Minnesota this evening, and expand eastward through central and
southern WI overnight. Central WI has the higher chance of
thunderstorms with heavy rain, although that main area could end
up as far south as Madison and Milwaukee.

Marine...

Breezy southerly winds are expected Thursday and especially
Thursday night. This will build high waves over the nearshore
waters, with highest waves toward the Open Lake. Winds will
remain gusty out of the west on Friday, and northwest Friday
night, in the wake of a cold front. A Small Craft Advisory will
be needed. A few gale force gusts are possible Thursday night
into Friday afternoon.

&&

Mkx watches/warnings/advisories...
WI...none.
Lm...none.
&&

National Weather Service Glossary of Abbreviations