Scientific Forecaster Discussion
fxus63 kmkx 231136
Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
636 am CDT Fri Jun 23 2017
Light rain from the back of the mesoscale convective system has now moved southeast.
Light rain from the back of the exiting mesoscale convective system has now moved
southeast. Brief period of MVFR ceilings still possible mainly
southeast. Also brief period of MVFR fog northwest areas til 14z.
Skies will gradually clear from the northwest as drier air moves
in. However a mid level shortwave moving in from the northwest
this afternoon will bring sct-bkn VFR cu along with isolated
showers, especially north areas.
Previous discussion... (issued 339 am CDT Fri Jun 23 2017)
today and tonight...forecast confidence medium.
The upper trough over the northern plains continues to drop south
across Lake Superior and Wisconsin tonight, with southern
Wisconsin getting into the entrance region of the 115 knot 250 mb
jet later tonight. Moderate upper divergence through sunrise
today, then weak upper divergence.
A mid level 500 mb shortwave moves across southern Wisconsin late
this afternoon and evening. Only weak 700 mb upward motion due to
the cold advection. However lapse rates steepen, and zero to 1 km
mixed layer cape values increase to around 350 joules/kg.
Therefore expect at least isolated showers late this afternoon
Cold air advection will be occurring today behind the cold front.
Some initial clearing, but then more convective clouds will
develop this afternoon and into the evening with the steepening
Saturday through Monday...forecast confidence is medium.
An upper trough will dominate with a strong shortwave moving
through Saturday afternoon. Models are in agreement showing some
precip and a few hundred j of cape. Temperatures will be cooler
with the influence of the trough. At the surface, low pressure
will remain over southeast Canada with high pressure sliding
south across the norther plains. Low level lapse rates will be
steep so we may tap 850 winds of 20-25 knots. West winds will be
a little gusty on Saturday.
Another shortwave moves through on Sunday creating another chance
for mainly afternoon showers and thunderstorms. There is less
instability on Monday. The European model (ecmwf) shows almost no cape so just have
chance for showers.
Tuesday and Wednesday...forecast confidence is high.
A mid level ridge pushes into the region on Tuesday and
temperatures start to rebound. Surface slides southwest of the
state on Tuesday bringing dry weather. Then the high moves off to
the southeast as the next low approaches the region. Surface flow
becomes southwest and moisture advection increases. Instability
builds and expect showers and thunderstorms Wednesday or Thursday
as the low moves through.
A line of thunderstorms will slowly slide southeast through
southern WI overnight. This line is moving slower than expected.
Scattered storms are possible out ahead of this line. The risk for
severe storms is pretty low for the rest of the night.
Period of MVFR ceilings possible behind the front overnight.
Quiet weather expected Friday.
Thunderstorms are sliding southeastward across the area early this
morning. A period of north winds of 15 to 25 mph with the front.
Then mainly northwest winds later today. Some gusts to 25 knots,
especially north areas this afternoon. As a result have issued a
Small Craft Advisory there for this afternoon and early evening.
Lm...Small Craft Advisory from 1 PM this afternoon to 8 PM CDT this
evening for lmz643.