Scientific Forecaster Discussion

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Area forecast discussion 
National Weather Service Milwaukee/Sullivan WI
314 PM CDT sun Apr 20 2014

Tonight...forecast confidence medium.

A stalled frontal boundary over central Wisconsin is producing light
to moderate showers from La Crosse to Green Bay today. 925-700mb
frontogenesis...weak shortwaves in the 500mb flow...and weak upper
divergence in the right entrance region of an upper jet are allowing
for moderate upward motion/Omega and resultant shower activity.
There are thunderstorms being reported over northeast Iowa...but
that area should remain to our west this evening. There should be a
lull in showers over the northern forecast area this evening. Then
we will wait for the next shortwave to arrive from eastern Iowa
around midnight. There is a chance for scattered showers to pop up
anywhere in the mkx forecast area after midnight...but the better
chance will remain to the northwest of a Madison to Sheboygan line.

Temperatures will remain mild tonight in the lower to middle 50s due to
the increasing clouds. Winds will become light.

Monday...forecast confidence high.

A 500mb shortwave trough slowly moving through the center of the
country will track through Illinois and southern WI Monday. The associated
weak surface low will track across southeast WI during the day. This
will give a little extra lift for numerous showers and also usher
that frontal boundary down through southeast WI. Models are showing
surface-based cape of around 800 j/kg along the cold front as it
moves through southern WI Monday afternoon. Thus...isolated to
scattered thunderstorms are possible. The shear will be weak...but
the cape could be enough to produce brief periods of small hail.

Monday night through Tuesday night...forecast confidence high.

The last of any lingering showers will exit the southeast early
Monday evening. Strong cold advection then kicks in as high
pressure builds south out of Canada. The models offer differing
opinions on how much cold advection cloudiness we/ll see. Believe
the biggest chance for clouds will be in the east. So Tuesday
looks rather chilly across the area...especially along the lake
where a slight northeast component to the northerly wind will cool
it down even more. Clearing skies and light winds under the high
pressure ridge could push some temperatures down to or slightly below
freezing Tuesday night.

Wednesday and Wednesday night...forecast confidence medium.

The surface high pressure ridge will slide east by morning with
strong warm advection arriving by afternoon as the return flow is
quick and pronounced. Showers or even a few storms should move in
during the afternoon...but it will be battling a dry lower level
with southeast surface winds. That flow will also keep it very
chilly across the southeast due to the lake effected airmass.
A decent low level jet blowing across a warm front to the south
of Wisconsin will keep the threat of showers and storms going
into Wednesday night.

Thursday and Friday...forecast confidence is medium.

A rather strong upper level system will push into the western
Great Lakes on Thursday. The upper level divergence and Omega
response should be impressive. The surface low is deepening as it
lifts into the area with the surface cold front expected to sweep
through here during the afternoon. The best chance for any
thunderstorms will likely be along the WI/Illinois border. Given the
track of the surface low...this looks like a classic case of a
leading warm front getting hung up over the far south as the lake
enhanced cold airmass will be tough to budge. The triple point
should then roll across the far south. Clearly the best chance
for any strong or severe thunderstorms should be down south across
Illinois but it/S not a high enough chance for Storm Prediction Center to highlight.
In any looks wet on Thursday with rain chances
diminishing Thursday night into Friday with the low moving slowly
out of the area.

Saturday and Sunday...forecast confidence is low.

Cold high pressure will be in place on Saturday with another
chance for rain arriving later on Sunday as low pressure
approaches the area. The GFS and European model (ecmwf) are at odds for Sunday with
the GFS saying high pressure and dry conditions...while the ec
says the low will get close enough to raise the precipitation chances.
Stay tuned.


Aviation/00z tafs/...

The stationary front producing showers over central WI...along and
north of a dll to fld line...will gradually slip southward
overnight. The better chance for overnight scattered showers and
maybe a rumble of thunder will continue to be west and north of

Lighter winds and area showers could lead to light fog with
MVFR visibility during the early morning hours. Confidence is low.
Expecting VFR ceilings to remain until at least the afternoon when
numerous showers and isolated to scattered thunderstorms are
expected across all of south central and southeast WI. These showers
and thunderstorms will exit southeast WI northwest to southeast through the early
evening with the passage of a cold front.



Winds will gradually diminish overnight as a front sags down through
southeast WI. They will change from southerly this afternoon to
southwesterly overnight into Monday morning...then become northerly
Monday afternoon with the passage of a cold front. Showers are
likely with a chance of thunderstorms Monday afternoon.


Mkx watches/warnings/advisories...


Tonight/Monday and aviation/marine...mrc
Monday night through Sunday...Davis