Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI
FXUS63 KMKX 291657 AAA
Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
1157 AM CDT MON AUG 29 2016
Scattered showers with middle to high clouds continue to develop
to the southwest of the area, and push toward the far western
counties. Weak differential cyclonic vorticity advection and some
weak 850 mb moisture pooling helping generate these showers. These
may hold together enough to make it into the far western and
southwestern parts of the area into this afternoon. Added some
POPs to these areas during this period. Enough mean layer CAPE
should develop to bring a few thunderstorms as well.
Outflow boundary from storms to the north also pushing southward
toward the area. This was helping produce some showers to the
north, but not much development has been seen in the past hour.
Will watch this for additional isolated shower/storm development
into this afternoon in the northern counties.
Middle to high clouds may continue to push east across the
southern and central portions of the area this afternoon. Not much
confidence here with trends, though the 500 mb relative humidity
fields on models do show these clouds hanging around the southern
half of the area into tonight.
Will add more clouds to the south and central portions of the
area during this time. This may affect highs this afternoon in
those areas, so lowered temperatures a few degrees.
Middle to high clouds should spread across a good portion of the
area this afternoon into tonight. May see scattered to broken
diurnal cumulus development as well, in case the higher clouds
do not make it all the way across the area. An isolated shower or
storm may affect Madison this afternoon, though not enough
confidence to mention in TAFs at this time. Light east to
southeast winds are expected.
Small chances for showers/storms are forecast for tonight, with a
better chance Tuesday into Tuesday evening with a cold front
passing southeast through the area. Will carry mainly VFR category
ceilings and visibilities into Tuesday, with a possible vicinity
thunder mention Tuesday afternoon. Any storms should be scattered
in nature, with brief heavy rain and MVFR/IFR visibilities
May see light fog later tonight into early Tuesday morning, with
light winds and a moist airmass lingering. Presence of middle to
high clouds may limit dense fog chances to low lying areas. Winds
will become southwest to west on Tuesday, remaining rather light.
Recent MODIS imagery from Sunday continued to show the effect of
recent upwelling of cooler waters in the nearshore waters. MODIS
estimated lake surface temperatures mostly in the low to mid 60s,
while mid-lake temperatures were measured in the low to mid 70s.
Light wind regime will continue through tonight. Onshore winds of
mostly 5 to 10 knots are expected today, becoming offshore
tonight. Lingering warm, humid air over cooler near shore waters
should continue to produce patchy fog and haze until cold front
passes through Tuesday night.
.PREV DISCUSSION... /Issued 300 AM CDT MON AUG 29 2016/
TODAY and TONIGHT...Forecast Confidence Is Medium.
A moderate zonal upper flow extends across Wisconsin today with
a weak ridge trying to briefly build into the south toward evening.
Weak upper divergence this afternoon and into tonight. Little in the
way of any 700 mb upward motion until later tonight. Southern
Wisconsin in in the northern fringe of a mid level ridge with an 850
mb ridge across the southern Great Lakes. Weak 850/700 mb winds.
700 mb RH remains low but does increase late tonight, especially
south. 850 mb dewpoints are around 15 Celsius south and west of
Madison but only around 3 Celsius near Lake Michigan. As a result
there is a tight gradient of Zero to 1 km CAPE this afternoon from
around 1100 Joules/kg along the Illinois border and west of Madison
to less than 150 Joules/KG near Sheboygan.
Patchy dense fog is possible, but more clouds and a weak wind
has limited a lot of the fog to mainly northeast areas.
Any dense Fog should mix out by mid/late morning, which should give
mainly scattered cumulus, and a warm day. Light winds will become
easterly during the afternoon near Lake Michigan. However the GFS
has a cap around 20 Joules/kg just below 850 mb with fairly dry air
above. RAP soundings have the cap weakening. Surface based CAPE is
around 2200 Joules/kg, so an isolated thunderstorm is possible in
the high CAPE region, but lack of forcing will limit the
There will be a small chance of thunderstorms tonight as upper
forcing increases a little along with column moistening and elevated
CAPE is around 1000 Joules/kg.
TUESDAY AND TUESDAY NIGHT - Confidence...Medium
Warm and humid airmass will be in place ahead of frontal boundary
dropping in from the north. Mid level flow will be from the
northwest with no pronounced shortwave within the flow. However the
250 jet strengthens a bit just to our north with some divergence
noted with this jet segment that is proggd to be situated ahead of
the mid/upper level trough axis. Low level forcing will contribute
to a good deal of this lift with the absence of the mid level
shortwave. ECMWF MLCAPE progd to rise to near 1000 j/kg. 0-6km Bulk
shear and 700/500 lapse rates are not impressive. However the
instability combined with the surface/850 lift should be enough to
get some storms going with SPC having the CWA in a Marginal Risk at
this time. Still some uncertainty on convective evolution and timing
with various solutions in this regard. Quite the disparity in the
MOS POPs as well with the NAM showing a dry bias and the GFS a wet
one. Will use the Superblend approach for now in the handling of the
POPs. The cooler post-frontal airmass arrives later Tuesday night as
winds turn decidedly from the north and northeast with some
gustiness expected esp in the eastern CWA in closer proximity to
WEDNESDAY THROUGH FRIDAY - Confidence...Medium
A cool pattern sets up with srn WI situated on western periphery of
large scale upper trough across the eastern Lakes/NE US. Low level
thermal trough showing some chilly temps at 850/925. In fact, seeing
some single digit celsius readings at 850 Wednesday night into
Thursday. Given the warm lake waters and the cooler 850 temps seeing
some delta t values into the teens so at least supportive of a bit
more cloud cover. For now will keep any mention of lake effect
sprinkles/shra out of forecast, but something to monitor for later
Wednesday night into Thursday when combo of favorable onshore traj
overlaps with peak min values within low level thermal trough. By
Friday the cool starts to ease with 588Dm mid level ridge sliding
SATURDAY - Confidence...Medium
Appears that the influence of the mid level ridge will hold with a
return flow setting up in the low levels. The progs are showing a
southerly flow that results in further modification of the low level
SUNDAY - Confidence...Low to Medium
Mid level ridge axis shifts to the east of WI with a southwest
regime taking hold. Both the GFS and ECMWF show a negative tilted
shortwave traversing western/northern WI with some DCVA affecting
the CWA. The 00z ECMWF keeps precip to our west with the wave while
the 00z GFS shows this spreading into the northwest CWA. Will retain
the Superblend approach which shows the better potential in the
northwest CWA. Southerly low level flow strengthens further with 925
temps rising to near 20c.
AVIATION/12Z TAFS/...With a bit more surface pressure gradient than
last night, that is keeping surface winds in the 5 knot range in
the west, and some high clouds, widespread dense fog formation is
still uncertain. Some dense fog is beginning to develop in the
northeast with lesser surface winds. Should see IFR/LIFR conditions
in northeast areas and patchy LIFR in river valleys elsewhere
until 14-15Z. VFR conditions expected after the fog lifts through
the end of the forecast. Scattered cumulus around 4 thsd ft this
afternoon. Isolated thunderstorms possible this afternoon over
south central Wisconsin and across the forecast area tonight.
MARINE...Light easterly winds and a moist boundary layer brings
prospects for fog back to the nearshore waters early this morning.
Web cams are not showing much fog at this time near shoreline.
Will keep mention of areas of fog but no marine fog advisory at
this time. Winds veer to the southeast...today...then south and
southwest late tonight with the approach of a surface trough. Wind
speeds and wave heights will remain below Small Craft Advisory
criteria through tonight.
TODAY/TONIGHT AND AVIATION/MARINE...Hentz
Tuesday THROUGH Sunday...Collar