Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI
FXUS63 KMKX 210248
Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
948 PM CDT SAT AUG 20 2016
.AVIATION/06Z TAFS/...Few-sct cloud cover may become broken during
the early morning hours of Sunday as a weak surface trough
approaches and passes through S WI. Low level instability may lead
to isold showers during the daylight hours on Sunday as well. MVFR
cigs will likely develop from 09z to the late morning hours with
cigs rising to 4 kft or becoming scattered.
.MARINE...A small craft advisory will continue until 10 am Sunday.
Breezy wly winds will continue tonight into Sunday morning as
strong low pressure moves away across Canada. The winds will turn
nwly after sunrise due to the passage of a weak surface trough.
The winds will gradually weaken through the afternoon as high
pressure approaches from the west.
.PREV DISCUSSION... /Issued 318 PM CDT SAT AUG 20 2016/
TONIGHT AND SUNDAY...Forecast Confidence...Medium
An upper-level wave with an associated sfc low pressure will move
through the region. Current sfc pressure analysis shows the center of
the low over northeastern WI this afternoon. A cold front
will move through southern WI, exiting by this evening. Instability
appears to be mainly absent later this afternoon, so not expecting
anything in terms of thunderstorms, just shower activity.
Mid-level deformation zone on the backside of the sfc low, along
with some lingering positive vorticity advection from a mid-level
shortwave, will support some slight chances of a shower through the
day tomorrow as the upper-level wave slowly moves to the east.
Cold air advection behind the cold front will bring some of the
coolest air of the summer into southern WI, as shown by the 925 mb
temperatures as the GFS, NAM and ECMWF are progging 925 mb temps near
11-12 C. This would support lows overnight in the mid 50s. A bit of a
rebound in these 925 mb temps up to 15 C will support highs Sunday
into the lower 70s.
Sunday night and Monday...Forecast Confidence Is Medium.
A mid/upper level trough exits the great Lakes with a weak zonal
flow across southern Wisconsin Monday afternoon.
Weak 700 mb upward motion begins Monday afternoon as the 700 mb RH
increases along the nose of a 35 knot west speed max.
Only expect increasing altocumulus with no zero to 1 km mixed
laker CAPE and dry air both just above and below 700 mb.
A large high extending from Wisconsin to the lower Mississippi
valley will be centered over the Ohio valley Monday with a south
Monday night and Tuesday...Forecast Confidence Is Medium.
The zonal flow continues with slight riding ahead of the next
shortwave north of Montana. Weak upper divergence and 700 mb
upward motion into Tuesday morning before weakening.
Elevated CAPE of 350 Joules/kg Monday night may bring as few
showers mainly north area.
The south low level flow continues.
Tuesday night and Wednesday...Forecast Confidence Is Medium.
ECMWF/GFS are in decent agreement with features during this
period. They shift the weak 500 mb ridge to the east Tuesday night,
with a weak subtle lead shortwave trough moving across southern
Wisconsin Tuesday night and Wednesday.
Both the GFS and ECMWF bring a moderate amount of precipitation
late Tuesday night and Wednesday as the trough moves into southern
Wisconsin. Kept consensus POPs for this period.
Wednesday night through Saturday...Forecast Confidence is
The Main Mid/Upper level trough moves across the Upper Great
Lakes Thursday and Thursday night with a second shortwave moving
across Wisconsin Saturday on the ECMWF. The GFS is stronger but
slower with this trough, not really reaching the forecast area
Both the GFS and ECMWF keep precipitation over southeast Wisconsin
High pressure then moves across the mid Mississippi Valley Friday
and across the Great Lakes and Ohio Valley Friday night and into
Saturday, with the GFS pushing it off east faster Saturday.
Mainly MVFR cigs from this afternoon will improve to VFR this
evening as a cold front passes through S WI this afternoon and exits
this evening. Gusty winds up to 25 kts are possible as the cold front
More MVFR cigs expected overnight and Sunday morning as cooler air
behind the cold front moves in, supporting a lower stratus deck.
Small craft advisory is in effect until 10 am Sunday morning due to
gusts up to 30 kts and waves of 3 to 5 feet. Low pressure over
northeastern Wisconsin will continue to move off to the northeast
this afternoon and evening, which will result in increasing westerly
winds as a cold front moves through. There will be a chance of
showers with the cold front.
Strengthening low pressure passing through Wisconsin tonight will
result in increasing west winds this afternoon and evening after a
cold front moves through. Waves are expected to be 3 to 5 feet
resulting in a moderate swim risk at Lake Michigan beaches into this
LM...SMALL CRAFT ADVISORY until 10 AM CDT Sunday for LMZ643>646.
TONIGHT/Sunday AND AVIATION/MARINE...JTS
Sunday NIGHT THROUGH Saturday...Hentz