Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
327 PM CDT Tuesday Mar 31 2015
Tonight...forecast confidence high
Heights will begin rising aloft as middle-level ridging across the
central Continental U.S. Shifts east into the area. This will support weak and
transient surface ridging overnight...with clear skies and light
winds. As winds slacken...could see some light fog away from the
Lakeshore. 925 mb temperatures support lows ranging from the lower
30s in the NE County Warning Area to the upper 30s in the SW.
Wednesday...forecast confidence high
Upper level ridge axis shifts east of the area in response to a
digging shortwave impulse over the upper Mississippi Valley.
Attendant surface low will track northeast from North Dakota and
occlude as the primary low tracks across southern Canada. Associated
surface troughing will move into northwestern Wisconsin by evening.
Focused low level warm advection will commence during the morning
and continue through the evening. This will support high
temperatures well into the 60s in the western County Warning Area. Southeasterly
winds...off a Cool Lake Michigan...will produce a large temperature
gradient across the area however...and only expecting highs in the
50s along the Lakeshore.
Wednesday night through Friday...forecast confidence medium
A fairly dynamic system will impact southern Wisconsin in this
period...though the exact timing remains somewhat uncertain. Most
models are beginning to come into line with the more progressive
GFS...which has precipitation arriving well before the frontal passage on Thursday
morning. The Euro...which holds precipitation off until 12z...has become
the outlier...due to a lack of warm air advection ahead of the front. While the GFS
is still a little fast...have nudged probability of precipitation on Wednesday evening/threshold
morning. Left thunder in the grids thanks to some elevated
instability threshold morning. Precipitation should clear the area by Thursday
evening. Behind the front...high temperatures will fall off.
On Friday...a low will track across the Ohio River valley. While surface
low tracks well to the south of WI...decent upper level support for
precipitation will be in place. All models bring a shot of precipitation to our
south...so left probability of precipitation in grid for Friday. Additionally...strong cold air advection
will drop 1000-500 thickness below 540 by Friday afternoon...so
added chance snow.
Saturday through Sunday...forecast confidence medium
Northwest flow will dominate the upper levels in this period with a few
embedded shortwaves. Most guidance tracks a low well to our north
with a weak cold front passing through Wisconsin before stalling out
just south of the state. Some question remains as to where this
front will stall. GFS brings front south of the County Warning Area...while Euro
keeps it over the area. Expect to see precipitation as the front
passes/stalls on Saturday night and precipitation will linger through
Sunday. However...if baroclinic zone sets up south of County Warning Area...could
miss out on precipitation. Additionally...positioning of the stalled
front will determine just how warm our temperatures get. Lows look to be
right around freezing Saturday night/Sunday morning and Sunday
night/Monday morning and thickness values support snow...so have
chance snow in grids.
Monday through Tuesday...forecast confidence medium
As low pressure approaches the Great Lakes from the Central
Plains...the aforementioned baroclinic zone will begin to push north
as a warm front. Though there is some disagreement about the timing
and track of this low...all guidance has widespread precipitation affecting
the area starting sometime Monday and lingering into Tuesday.
Again...boundary position makes precipitation type uncertain...but temperatures
and thickness values indicate a chance of winter precipitation
Monday night. Some elevated instability returns to the area on
Monday night and Tuesday...so put in some thunder.
Morning cloud deck has lifted and scattered out with cloud bases
around 3kft early this afternoon...rising to to around 5kft by 21z.
Expect sky clear by 00z. Lake breeze has developed and will impact kmke
and kenw through the evening. Winds at these locations will veer
easterly to southeasterly through tonight. Could see brief MVFR visibility
at msn around/after 08z with light fog. Otherwise...expect VFR visibilities
and ceilings through the taf period.
Winds will ease across the nearshore waters tonight as surface high
pressure takes hold. Light northeasterly winds during the morning
will veer southerly and increase during the day Wednesday. Winds
and waves may near Small Craft Advisory levels Wednesday night
ahead of a trough of low pressure...but appears marginal at this
juncture. Will hold off on any marine headlines for the moment.
Tonight/Wednesday and aviation/marine...spm
Wednesday night through Tuesday...bsh