Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
1046 am CDT Monday Jul 6 2015
Aviation/18z tafs/...lead elongated band of rain showers/thunderstorms and rain associated
with shortwave and increasing moisture transport expected to make
it all the way into the eastern County Warning Area based on latest trends. Have
been behaving and expect them to stay that way. Plenty of clouds
upstream so projected instability not expected to get as high as
previously thought for any later day/evening pre-frontal
development. Overall 0-6km bulk shear not impressive and middle level
lapse rates poor as well. Upstream stratus is a concern with low level
relative humidity getting a bit moist as the night wears on will probably go with
a trend towards the NAM MOS ceiling height/sref ceiling probs are suggesting.
Front comes through around midnight with thermal trough taking
hold with 850 cold air advection into Tuesday.
Marine...will continue Small Craft Advisory for this afternoon and evening.
Thinning cirrus shield should allow south to southeast winds to turn
more mixy rest of this morning and early afternoon. However upstream
convection over southwest WI may hold together and affect nearshore
waters later this afternoon. Better chance for convection tonight
as cold front moves through southern WI. Recent modis imagery measured
lake surface temperature in the upper 50s. With surface dewpoints in the middle to upper
60s...expect areas of fog to continue over the nearshore waters into
tonight. Will be watching shore webcams closely in case fog thickens.
May need to issue marine dense fog advisory as would expect fog to
persist into tonight...except for when showers and storms cleanse
fog for a time.
Beaches...will continue beach hazard statement for Ozaukee and
Sheboygan counties this afternoon and evening. Tightening pressure gradient
ahead of approaching low pressure and cold front will result in
gusty south to southeast winds this afternoon and evening with a few gusts up
to 25 miles per hour. Currently thinning cirrus shield over southeast WI
slowing down mixing but some thinning expected into the early afternoon.
However beachgoers will need to keep eye on radar as thunderstorms
over southwest WI...may affect Lake Michigan shore during the afternoon. There
is a better chance for a period of storms during the evening.
Previous discussion... /issued 922 am CDT Monday Jul 6 2015/
Update...ramped up probability of precipitation in western County Warning Area to account for rain showers/thunderstorms and rain
developing with lead shortwave and decent moisture transport into
the area. Storms behaving themselves so far with very warm column
and less than ideal middle level lapse rates. 0-6km bulk shear a bit
better in western County Warning Area. Will continue to monitor trends.
Previous discussion... /issued 336 am CDT Monday Jul 6 2015/
Today and tonight...forecast confidence...high
An upper shortwave extends across the Dakotas with a ridge from the
Southern Plains...across southern Wisconsin and the eastern Great
Lakes. The upper level shortwave reaches Lake Superior this evening
as the southwest flow increases to 65 knots from west central to
northern Wisconsin. The flow is diffluent across southern Wisconsin
today. As a result the upper divergence increases this morning and
continues over the southeast to around midnight.
The middle level trough sharpens as it pushes into southern Wisconsin
toward evening. 700 mb upward motion increases today and remains
over southern Wisconsin this evening and across southeast Wisconsin
through late tonight. The GFS brings a 50 knot 700 mb jet maximum into
west central and northeast Wisconsin this afternoon. Southern
Wisconsin is in the entrance region...although speeds increase to
almost 40 knots this evening.
The 850 mb thermal ridge moves into southern Wisconsin by noon over
south central Wisconsin and during the afternoon southeast. 500 mb
temperatures also warm resulting in middle level lapse rates around 5.6
celsius/km...while low level lapse rates are around 8 celsius/km by
middle afternoon. The 850 mb winds increase to around 30 knots by
Zero to 1 km mixed layer cape rises to around 1200 joules/kg on the
GFS by middle afternoon. Zero to 6 km shear is rather low...with the
higher shear across central and northeast Wisconsin.
Most of the mesoscale models bring remnants of the upstream nocturnal
convection...with a second strong area developing along the cold
front later toward evening in south central Wisconsin and overnight
in the southeast.
Precipitable water values increase to 2.1 inches. Therefore the
line of storms with the cold front could produce heavy rains.
Corfidi vectors are weak but with a linear system will not issue
any Flash Flood Watch.
The Storm Prediction Center has a slight risk mainly south of a line
from Lone Rock to north of Madison...to Jefferson and Lake Geneva.
This would be for the thunderstorms along the cold front. The rest
of the forecast area is in a marginal risk...as the instability will
decrease after sunset before the storms reach the far east.
Tuesday and Wednesday...forecast confidence...medium
Any lingering precipitation should wind down in the southeast by early
Tuesday morning...with dry weather then expected though at least
Wednesday morning under high pressure. A shortwave and associated
surface low will approach later Wednesday...moving by south of the
forecast area Wednesday night. The NAM is the most aggressive with
this system across southern Wisconsin. Kept probability of precipitation low per consensus
of other models though...with the best chance in the southeast.
Should see high temperatures running several degrees below normal for
Thursday through Sunday...forecast confidence...medium
Should be mainly dry Thursday under high pressure...with a
shortwave to bring shower storm chances by later Thursday night or
More waves riding through baroclinic zone will bring shower/storm
chances through the weekend. Not great agreement in wave
placement and timing between models...so chance probability of precipitation are spread
out through this period.
Looks like temperatures should warm back to near normal by Friday...then
possibly even somewhat above normal for the weekend. Not a ton of
confidence in temperatures though due to timing of waves and resultant
Except for low chance for some patchy fog in the last few hours
before sunrise...still looking at trend of latest hrrr and previous
NAM runs of bringing a lead band of dying convection into southern
Wisconsin in the middle to late morning hours. Then expect
redevelopment ahead of an approaching cold front that will move
across south central Wisconsin early this evening...and the southeast
tonight. Mainly VFR conditions for much of the day...then MVFR/IFR
in the storms along the cold front. IFR ceilings expected to linger for
a while behind the front.
Southerly winds will increase through the morning...and thus will
leave timing of Small Craft Advisory as is. Prior to winds picking
up...could see some haze/fog that reduces visibilities under 5 miles...and
possibly some patches of dense fog.
Then a line of thunderstorms are expected along a cold front
tonight. Winds will become northwest to north behind the front.
Brisk south winds and 4 foot waves will bring a high swim risk to
Lake Michigan in Sheboygan and Ozaukee counties this afternoon and
early evening with a moderate risk to the south.
WI...beach hazards statement until 10 PM CDT this evening for wiz052-
Lm...Small Craft Advisory until 10 PM CDT this evening for lmz643>646.
Today/tonight and aviation/marine...hentz
Tuesday through Sunday...ddv