Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI
FXUS63 KMKX 250304
Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
1004 PM CDT SAT SEP 24 2016
.UPDATE...A Flash Flood Watch remains in effect for Sauk and
Marquette County for Sunday. Although only a half an inch of rain
is expected, local amounts of one inch are possible in an area
that is already saturated and experiencing ongoing flooding. A
cold front and approaching strong upper trough will be the trigger
for the showers and storms. The storms will be moving fairly
quickly around 30-35 kts but within a PW airmass of 1.8 inches.
.AVIATION/06Z TAFS/...Mainly VFR conditions for Sun morning.
Showers and storms will increase over south central WI and KMSN by
late Sun morning. Cigs of 1-3 kft will be expected through the
afternoon with rounds of showers and storms. Vsby restrictions are
expected with the precipitation. The precipitation and Cig and
vsby restrictions will reach the se WI taf sites by 20-21z and
last into the early evening.
.MARINE...A Small Craft Advisory is in effect north of Port
Washington on Sun for gusty southeast winds and waves of 3 to 5
feet. A cold front will shift the winds to the west by late Sun
evening and become gusty Mon morning. A Small Craft Advisory may
be needed on Monday for the brisk west winds over all of the
.PREV DISCUSSION... /Issued 334 PM CDT SAT SEP 24 2016/
TONIGHT AND SUNDAY...Forecast Confidence - Medium.
Mid level ridging will slide across the state tonight and surface
winds turn southeast behind high pressure over eastern Ontario.
Patchy fog is possible across southwest WI due to lingering low
level moisture. The pressure gradient will increase Sunday as low
pressure approaches from the west. Warm air advection kicks in
overnight on increasing southwest flow. This brings precip chances
early Sunday morning in the west. This forcing swings east late
morning along with weak shortwave activity so have chance pops
across the rest of the area with these features.
The surface cold front will move through during the afternoon.
Thunderstorms are likely with model consensus of MU CAPE around 500-
1000 J/KG over much of the region with 30 kts of shear. SPC has us
in a Marginal Risk for severe tstorms.
Heavy downpours will accompany the thunderstorms. Low level moisture
transport ramps up a bit during the late night and early morning
hours. PWs are expected to be up to 1.8 or more. As a precaution
have issued a Flash Flood Watch for Sauk and Marquette counties in
collaboration with neighboring offices. Even though rainfall amounts
will generally be roughly up to a half inch in these areas, they are
very sensitive to additional rainfall. Heavy downpours could bring
an 1 inch of rain in some areas.
SUNDAY NIGHT AND MONDAY...Forecast Confidence Medium.
Showers and thunderstorms will be ongoing at start of period but
exiting to the east in the late evening with forcing along and ahead
of surface cold front and deep mid-level trough. Will only carry
slight chance PoPs after 06Z.
Cold advection on gusty west winds will bring low to mid 50s across
CWA by daybreak Monday. In spite of a vigorous vort max swinging
across in the morning, little moisture on forecast soundings to
produce precipitation. Slight warming from subsidence noted on
soundings at and above 800 mb limits instability even as 850 mb
thermal trough swings across the state during the day that drops 850
mb temps down to 3C to 4C by 00Z Tuesday. Will carry a
collaborative slight chance across the north closer to better mid-
level moisture on the ECMWF. Consensus highs in the low to mid 60s
look reasonable with some afternoon sun, especially in the southern
CWA, but gusty winds will make it feel cooler.
MONDAY NIGHT THROUGH TUESDAY NIGHT...Forecast Confidence Medium.
All models keep area under mid-level cyclonic flow with periodic
weak vorticity maxima rotating through but still very little
moisture to work with. ECMWF does brush the eastern CWA Tuesday
evening with some QPF, and the GFS does the same in the far
northeast toward Wednesday morning with a short wave trough with a
bit more northerly wind versus northwest probably bringing some lake-
enhanced moisture into the far east. Will again limit slight chance
PoPs to the northeast half of CWA Tuesday night. Lows in the 40s
both nights with highs Tuesday in the low to mid 60s.
LONG TERM...WEDNESDAY THROUGH SATURDAY...Forecast Confidence
Dry weather for the extended period as mid-level ridging and surface
high pressure build over the region. Only potential problem would be
the ECMWF "tear-dropping" a cut-off low over the mid-Atlantic states
Thursday that retrogrades back toward the Great Lakes for the
weekend, though it does hold the precipitation over mainly the
eastern Great Lakes. Will go with consensus dry forecast and
temperatures that will be at or slightly above normal.
VFR ceilings should continue to become more widespread late this
evening as mixing continues and drier air advects into southeast WI.
Have lower confidence in southwest WI where sub-VFR ceilings may
continue. MVFR or lower ceilings are likely to redevelop in southwest
and parts of south-central WI overnight where low level moisture
will linger. There is good model agreement showing VFR conditions
through Sunday morning in the east. Showers and thunderstorms are
expected on Sunday with reduced ceilings and vsbys but otherwise
VFR conditions are expected for Sunday.
Winds and waves are expected to remain below small craft advisory
levels through the night as winds shift southeast. Winds will
increase on Sunday. Winds and waves will reach small craft levels in
the northern Port Washington to Sheboygan marine zone and will be
near criteria for the other zones. Wind gusts will remain high
Sunday night through Monday as they shift to the west behind a
cold front. A small craft advisory will be needed for Monday and
likely Tuesday. Despite the cooler air moving in for early next
week, cloud depths will not be deep enough for lake effect showers
or water spouts, just some lake effect clouds.
WI...FLASH FLOOD WATCH from 4 AM CDT Sunday through Sunday evening
LM...SMALL CRAFT ADVISORY from noon to 7 PM CDT Sunday for LMZ643.
TONIGHT/Sunday AND AVIATION/MARINE...Marquardt
Sunday NIGHT THROUGH Saturday...REM