Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI
FXUS63 KMKX 240827
Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
327 AM CDT SUN JUL 24 2016
.TODAY AND TONIGHT...Forecast Confidence Is Medium.
An upper level shortwave over the northern plains will move
across Wisconsin and the upper Great Lakes tonight. A 105 knot 250
mb jet max pushes across the Lake Superior area, ahead of the
shortwave today, with southern Wisconsin in the right entrance
region later this afternoon and evening. This brings mainly weak
upper divergence and 700 mb upward motion.
700 mb southwest to west winds increase to around 30 knots early
this morning, and becomes west to northwest at around 35 knots by
evening. The rather strong 35 knot west/southwest low level jet
max, causing the early mornings storms, weakens and pushes off to
the east around sunrise. It does increase a little this afternoon,
ahead of the approaching trough.
850 mb moisture remains high through the day, ahead of the
GFS Forecast soundings show low level lapse rates increase with
the strong heating. There are lingering dew points in the mid 70s
ahead of the approaching cold front. At the same time as 700 mb
temperatures warm, the cap increases, along with mid level
drying. During max heating, the cap is not quite as strong, and
could be broken.
If so, severe thunderstorms will be possible, due to the zero to
1 km CAPE at 4000 Joules/kg. The front does not exit the far
southeast tip until around 7 pm. Zero to 6 km bulk shear is
rather low, around 20 knots ahead of the front, then increases to
30 knots just behind the front.
Parameters are more than enough for the Marginal Risk of severe.
Watch for SPC morning updates for any possible upgrade.
As far as headlines, it looks like today will have heat index
values of 95 to 103 again. The highest in the far southeast
counties. That makes 4 consecutive days with 95 to 99 degree heat
index values or above, and results in a Heat Advisory through
this afternoon for much of southeast and portions of south
Then dew points drop behind the cold front. May still be enough
lingering low level moisture for patchy fog tonight, especially
.MONDAY THROUGH TUESDAY NIGHT...Forecast Confidence Is High.
The models are in pretty good agreement with trends during this
period. They bring high pressure slowly east southeast across Iowa
and northern Illinois Monday into Tuesday, before sliding off to
the east Tuesday night.
The 500 mb shortwave trough will depart the region Monday
morning, with downward motion from differential anticyclonic
vorticity advection. 500 mb flow remains west northwest during
this period, with several 500 mb vorticity maxima moving through
the region Tuesday into Tuesday night.
Looks like a dry period is in store for Monday into Tuesday
across the area. More seasonable temperatures are expected, as a
somewhat cooler and less humid airmass moves into the region
Monday and remains on Tuesday. Lake breeze Tuesday afternoon will
keep lakeshore areas cooler than inland areas.
Models are bringing more clouds into the area Tuesday into
Tuesday night, with weak warm air advection and the passing
vorticity maxima. Kept small POPs in the northwest portions of the
area for Tuesday night.
.WEDNESDAY THROUGH SATURDAY...Forecast Confidence Is Medium.
ECMWF and GFS indicate a rather active period during this time
across the area. 500 mb flow is generally west northwest during
most of this period. The GFS has a potent 500 mb shortwave trough
move through the region Wednesday into Wednesday night, with the
ECMWF not nearly as strong with it. The ECMWF keeps a weaker 500
mb vorticity maximum just south of the area during this time.
Both models show a surface low sliding eastward across northern
Illinois Wednesday night into Thursday. More 500 mb vorticity
maxima cross the region as well. Given the activity during this
period, kept POPs for thunder going. Temperatures should remain
warm, with humid conditions. There should be lake breezes or
onshore winds each day.
Models then bring a deeper 500 mb shortwave trough eastward
through the region Saturday, with continued vorticity maxima
shifting through. Some placement and timing differences with the
low pressure track exist. However, seems that POPs should continue
to go into the weekend. Warm and humid conditions should linger.
Expect lingering showers and thunderstorms to clear the east by
Could be some MVFR fog until just after sunrise. Also areas of
MVFR ceilings, and brief IFR ceilings, with the moist atmosphere
and light winds until mid morning.
Then with mixing, mainly VFR cumulus ahead of an approaching cold
front. There will be more chances of thunderstorms along and ahead
of the approaching front.
Drier air behind the front will end the thunderstorm chances. Dew
points will lower, but some IFR fog possible, especially in river
valleys and low areas later tonight.
Will likely see some patchy fog over the nearshore waters after
showers and storms clear to the east around sunrise. Then another
chance of storms returns today, as a cold front approaches.
Showers and storms will end with the frontal passage by evening.
Southwest winds will gust to around 20 knots, to briefly 25 knots,
ahead of the front. Wind gusts may approach Small Craft Advisory
criteria this afternoon. Look for northwest winds tonight.
WI...HEAT ADVISORY until 7 PM CDT this evening for WIZ058-059-063>066-
TODAY/TONIGHT AND AVIATION/MARINE...Hentz
Monday THROUGH Saturday...Wood