Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI
FXUS63 KMKX 271645 AAA
Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
1145 AM CDT SAT AUG 27 2016
Area of rain showers continues to diminish across areas mainly
west and north of Madison, to around the Fond du Lac area. These
should either move northeast out of the area and/or diminish by
early this afternoon.
The main question is whether the clouds will partially mix out and
allow for some heating during the afternoon. Area of low clouds
continues to linger across the area, with a weak surface warm
front remaining just south of the area. There is sunshine south of
the front into northern Illinois.
Synoptic and mesoscale models try to bring this frontal boundary
north into the area this afternoon, as a weak surface low shifts
northeast across Wisconsin. Given the current conditions, it
appears that there should be some partial mixing of the low clouds
with the frontal advance into the area this afternoon. The
southern counties would have the best shot at this.
Will continue to bring in partly cloudy skies into the far
southern counties this afternoon. Also kept lower end chance POPs
for showers and storms in the south and east, as the front and
low move through the area. The area is in the right rear quadrant
of the 250 mb jet streak, though the models do not have much in
the way of divergence over the area this afternoon and early
Overall, upward vertical motion fields are weak, though not much
capping is seen in areas that do mix out and warm up. Deep layer
shear is decent, and mean layer CAPE will depend on where the low
clouds mix out. We were taken out of the marginal risk for severe
storms by SPC, which seems reasonable given the uncertainty with
clouds and the weak upward vertical motion.
Temperatures this afternoon will also depend on cloud cover. Will
continue to keep them cooler in the north, where the clouds should
Low clouds with IFR ceilings should slowly rise this afternoon
across TAF sites, as weak warm front moves north into the area.
May see some sunshine mix through the clouds at times, as the
ceilings slowly rise. Should see VFR ceilings by later this
afternoon at TAF sites.
The front may bring a few showers and storms later this afternoon
into early evening. However, there is a fair amount of uncertainty
with if there will be anything that develops. Not sure if vicinitythunder
will be kept in TAFs between 20Z this afternoon and 03Z Sunday.
East to northeast winds should veer to the south and southwest by
later this afternoon, with the front moving into the area. They
may remain more east to southeast near Lake Michigan, though not
confident Milwaukee and Kenosha will see these winds.
High pressure moving east across the area later tonight into
Sunday should bring a period of quiet weather. Clouds should
gradually mix out later tonight, with scattered diurnal cumulus
development Sunday afternoon.
Should see light fog at TAF sites between 08Z and 13Z Sunday,
with light winds and moist airmass lingering. Easterly winds are
expected Sunday afternoon at Milwaukee and Kenosha, with southeast
to south winds inland.
Adjusted winds to prolong more onshore northeast to east flow for
much of the day. Weakening surface warm front draped across
northern IL expected to make slower northward progress into
southern WI and Lake MI. Expect wind speeds to remain mostly in
the 5 to 15 knot range, resulting in wave heights of 1 to 3 feet.
Higher dew points to remain to the south, so not a lot of time
for dense fog to develop this afternoon over lingering cooler
upwelling waters off Ozaukee and Sheboygan counties. Better chance
for fog tonight, as boundary layer winds weaken, and low levels
remain warm and humid.
.PREV DISCUSSION... /Issued 250 AM CDT SAT AUG 27 2016/
TODAY AND TONIGHT...Forecast Confidence Is Medium.
A strong shortwave exiting the northern plains will reach the lake
Superior and southern canada region late tonight. The entrance
region of a 100 knot 250 mb upper jet with southern and central
Wisconsin in the right entrance region today. This results in
upper divergence and mainly weak upward motion. A 700 mb wind max of
35 knots moves through this morning before moving off to the
northeast by early afternoon. The 850 mb wind max of around 25 to
30 knots also moves across southern Wisconsin this morning. The
resulting moisture convergence was setting off the area of showers
and thunderstorms. These should move off by afternoon south
central, and later this afternoon southeast. The high resolution
HRRR and the GFS are similar.
Precipitable water values get favorable, and mesoscale models
suggest some training of storms are possible. Heavy rainfall is
expected in some of the storms. However, think these storms will be
moving quick enough to limit any mainly urban flooding potential.
Precipitation chances Saturday afternoon are still rather murky, as
forcing weakens, but a surface boundary is expected to first push
north this morning, then back south across the area later
this afternoon and evening.
Zero to 1 km mixed layer CAPE is around 1100 Joules/kg with little
cap. Zero to 6 km shear is around 30 knots during the afternoon.
Will maintain the chance POPs for the afternoon hours. A marginal
severe risk exists across the area today and early this evening.
SUNDAY - Confidence...Medium
Weak mid level ridging sets up with all models showing a weak wave
across nrn WI. The NAM also shows a wave riding across nrn IL though
this is an outlier and within an area of anticyclonic curvature.
Surface/850 ridging also noted so will go with quiet POPS. 925 temps
around 20c though a smidge warmer in the western CWA.
MONDAY - Confidence...Medium
Surface/850 ridge axes shift a bit to the east though still some
lingering low level anticyclonic flow evident. The mid level ridge
collapses with some weak shortwave activity in place. Will have some
POPS in place with models keying more in the western and southern
CWA. 925 temps rise just a smidge into the lower 20s celsius with a
better hint of a return flow.
TUESDAY - Confidence...Medium
Surface/850 boundary expected to focus a little better chance of
shra/tsra. Mid level flow becomes more cyclonic from the northwest
though better vorticity resides to the northeast and southwest of
the CWA. Main cool push arrives Tuesday evening as 925 temps turn
WEDNESDAY THROUGH FRIDAY - Confidence...Medium
Shaping up to be a quiet and cooler period with low level thermal
trough in place. Per collab with LOT decided to trim Superblend a
few degrees in the east. Surface high pressure takes hold and sticks
around into Friday. Any return flow type precip is expected to hold
off to our west.
AVIATION/12Z TAFS/...Expect MVRF and a period of IFR cigs with warm
front passage during the morning hours, with the area of showers
and thunderstorms. Should see a break in the precipitation late
morning into the early afternoon especially south central. Expect
VFR conditions once the warm front lifts north with MVFR cigs/vsbys
with any of the scattered showers and storms late this afternoon.
MARINE...Weak gradient keeps winds, and thus waves, relatively low
through the weekend and into next week. Wind direction will go from
east and southeast early this morning, to southeast and south today
with passage of a warm front, then west tonight behind a weak surface
wave of low pressure. Showers and scattered thunderstorms likely
with the warm front and subsequent passage of the surface low but
only scattered coverage thunderstorms late this afternoon and this
TODAY/TONIGHT AND AVIATION/MARINE...Hentz
Sunday THROUGH Friday...Collar