Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
935 PM CDT Monday Mar 30 2015
Aviation/06z tafs/...only very brief sprinkles are left over much
of southern WI including the taf sites. Low pressure approaching SW WI
will move across far southern WI during the overnight. The winds will
back northerly after the low passes with stratus of 1-3 kft possible and
light fog of 3-5sm as well. The low stratus and light fog will
improve by late Tuesday am. Scattered-broken cumulus of 3.5-4.5 kft are
expected into the afternoon becoming few by late afternoon and
Previous discussion... /issued 328 PM CDT Monday Mar 30 2015/
Tonight...forecast confidence is medium.
Main issue will be probability of precipitation with passing system into tonight. Area
radars already have northwest to southeast oriented bands of
reflectivity shifting southeast through the area. Initial band is
likely just sprinkles...as low levels are still fairly dry. More
robust band of reflectivity extends from The Dells area northwest
toward Eau Claire. This should be more steady light rain...and
should shift southeast and affect the northeast half of the area
late this afternoon.
Models are showing good upward vertical motion with focused warm air
advection and low level frontogenesis into the early evening...with
passing 500 mb vorticity maximum later this evening and overnight.
Frontogenesis response focuses across the far northeast counties
into early this evening.
Area forecast soundings showing a bit more low level moisture and
saturation in the northeastern portions of the area...with drier low
levels further to the southwest. Mesoscale models trying to bring an
area of light rain through the most of the area late this afternoon
and in the northeast in the evening. Think this may be overdone in
the southwest half of the area...given the relatively dry low levels
Maintained likely probability of precipitation in the northeast counties into the
evening...with lower probability of precipitation to the southwest. Some middle clouds may
linger later tonight in the northeast counties...with some low
clouds possible toward the Sheboygan area. Lows near consensus of
models in the middle to upper 30s are forecast.
Tuesday...forecast confidence is medium.
Kept dry forecast going for Tuesday...as area forecast soundings are
showing quite a bit of dry air. Not seeing a whole lot of forcing
for upward vertical motion...besides a weak surface low sliding
southeast across northeastern Wisconsin. European model (ecmwf) only model with
light quantitative precipitation forecast in the area...with the others keeping it to the
northeast of the area. Highs into the 50s are expected inland...with
a lake breeze turning temperatures colder near Lake Michigan in the
Tuesday night through Wednesday...forecast confidence high.
Though the GFS is a bit more progressive than other models...all
guidance shows northwest flow aloft. In the lower levels...the ridge
passes southeast Wisconsin around 18z on Wednesday as does the onset of warm air advection
ahead of an approaching shortwave. The column appears to be
relatively dry through the period. The warm air advection coupled with the partly
cloudy skies will allow temperatures to reach into the middle 60s
inland of Lake Michigan.
Wednesday night through Thursday...forecast confidence medium
Though the timing and magnitude are a bit uncertain...a rain event
looks likely on Wednesday night/Thursday morning. In the upper
levels...the ridge axis will clear the region by 06z on threshold and a
coupled jet structure will set up near the axis of the
ridge...resulting in large area of divergence just behind ridge. Also
expect to see some modest cva at 500 at roughly the same time. In
the lower levels...a low will pass to our north and an associated
cold front will swing through Thursday morning. Warm air advection expected ahead
of the front and lower portion of the atmosphere will remain near
saturation through just after frontal passage. Though it appears to be coming
more in line with other guidance...GFS still has precipitation arriving
ahead of the front...around 06z threshold...while other models have most
of the precipitation arriving with the front and lingering through the day.
GFS also much more aggressive on precipitation amount...bringing almost an
inch to the southeast.
Finally...models still indicating some elevated instability ahead of
the front...so left thunder in the grids.
Thursday night through Friday...forecast confidence high
Front will push through by Thursday evening...ending all rain by
midnight. Cold air advection will dominate through behind the front...so temperatures will
be cooler than the days prior. Euro and Gem have a low crossing the
Ohio Valley and a few hundredths grazing our southeast...so have slight
chance probability of precipitation in the southeast.
Saturday and Sunday...forecast confidence medium
The weekend looks mostly dry as we will be entrenched in northwest
transitioning to zonal flow. Not much in terms in temperature advection in
the lower levels. However...a weak surface low will pass to our
north on Saturday dragging a weak cold front through the state. The
GFS keeps US dry while the Euro brings some light precipitation. Kept probability of precipitation
out of the grids for now...but Worth keeping an eye on.
Monday...forecast confidence low
Models have a deep low developing in the northern plains and push a
baroclinic zone across Wisconsin. The GFS is much more
progressive...pushing to low towards the upper Great Lakes
states...while the Euro keeps the low in the plains. However...both
models bring precipitation into the area around noon on Monday.
Again...there is some elevated instability with this system so put
thunder in the grids.
VFR conditions are expected tonight into Tuesday across taf sites.
West winds may continue to gust to 15 to 20 knots at times until
sunset...before becoming light and southeasterly. Area of broken
to overcast middle level clouds will continue to move southeast
through the area this evening and into the overnight hours. Light
rain may clip taf sites into this evening...but low confidence in
this occurring so will leave them out of tafs. Could see some
May see an area of low clouds with ceilings around 2000 feet above
ground level later tonight into Tuesday morning approach taf
sites from the north...as low pressure passes southeast away from
the area. Confidence is low in this occurring at taf sites...so will
continue scattered to broken clouds around or above 5000 feet above
ground level. North winds will become northeast at eastern sites
with lake breeze during the afternoon.
Some westerly gusts to around 20 knots are expected until
sunset...before becoming light and southeasterly. Any high waves
will be over the open waters. Thus...will continue to hold off on a
Small Craft Advisory.
Winds will increase somewhat tonight and become northwest to
north...as low pressure passes southeast trough the area. Gusts to
20 knots may occur at times later tonight...with waves in the 2 to 4
foot range. Again...will hold off on a Small Craft Advisory. Better
shot at frequent gusts to 22 knots for the Wednesday into Thursday
tonight/Tuesday and aviation/marine...wood
Tuesday night through Monday...bsh