Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
343 am CDT Wednesday Jun 3 2015
Today and tonight...forecast confidence is medium.
Short wave energy stays mainly north of the area in west-southwest flow through
the period. Current showers and storms in northern Minnesota in region of
focused warm advection ahead of a northern short wave trough...with
an mesoscale convective system running along the S Dakota/Nebraska border area toward
western Iowa on the leading edge of a second surge of moisture and
thermal advection. The mesoscale convective system is already taking expected southward turn
along 1000-500 mb thickness gradient and upwind propagation
vectors...passing well southwest of forecast area.
Forecast soundings and moisture cross sections indicate we can
expect to see a gradual thickening of high level clouds blowing off
from mesoscale convective system through the day. Will not limit warm up in southerly wind
flow with near 80 in the west. Areas east of The Kettle Moraine will
be cooler with more of a southeast wind but should see low 70s away from
Models do try to break away a piece of mesoscale convective
vorticity from this complex and bring it into the region ahead of
the slow-moving surface trough...with some light quantitative precipitation forecast across central
WI and portions of southern Wisconsin late this afternoon and
evening. However...dry air around western flank of retreating high
pressure and best moisture return and forcing will keep better pop
chances in the northwest half of the County Warning Area. Elevated cape values only reach
around 300 j/kg so expect mainly showers with an isolated
thunderstorm or two. Not much of a drop in temperatures away from the lake
with upper 50s to lower 60s for lows...with middle 50s closer tot he
Thursday... forecast confidence medium.
Some models are hinting at a dying mesoscale convective system tracking through southern WI
on Thursday... while the 00z European model (ecmwf)... GFS and mesoscale models all
keep southern WI dry. Leaned toward drier solutions with lower
chances of showers and thunderstorms. A light southerly breeze will
allow for mild temperatures in the upper 70s... except middle 70s
Thursday night and Friday...forecast confidence medium.
Southerly flow ahead of a slow-moving shortwave will lead to
increasing moisture over all of WI this period. Precipitable water
values rise to over 1.5. There is weak instability due to poor middle
level lapse rates. The upper jet and main low level jet will not be
in the vicinity of southern WI... but a couple of models suggest
some sort of low level jet enhancement with an 850mb trough. Kept the chance
for showers and thunderstorms during this time period... but
confidence for when and where they will occur is low.
Saturday through Tuesday... forecast confidence medium.
Surface high pressure will drop down from Ontario over the Great
Lakes region Friday night. This will lead to a period of probable
dry weather over southern WI Friday night and Saturday. Models are
coming into better agreement for drier weather. An easterly breeze
will keep lake counties cooler than inland.
An upper level trough will slowly swing across the upper Midwest and
Great Lakes Saturday night through Monday. This will bring chances
for showers and thunderstorms to southern WI during this time. There
are still differences between the models with the speed and strength
of the upper trough which will ultimately determine the thunderstorm
Showers may linger into Monday due to cyclonic flow aloft. Tuesday
is trending drier due to the ridge over the center of the country.
VFR conditions are expected through the day into tonight as high
pressure moves east of the region and a weak trough of low pressure
sags toward southern Wisconsin form the northwest.
High clouds will slowly thicken through the day...with some scattered
diurnal cumulus clouds developing this afternoon...mainly over the
western County Warning Area. Will see chances for showers...and possibly a
thunderstorm or two...slowly increase in the west this evening and
tonight...with eastern areas dry until Thursday morning.
Light south winds expected west of The Kettle Moraine with southeast
winds to the east.
Today/tonight and aviation/marine...rem
Thursday through Tuesday...mrc