Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
326 am CST Friday Feb 12 2016
Today and tonight...forecast confidence is high.
The focus this morning is on the fluffy light snow moving across
southwest Wisconsin this morning followed by how low the wind chills
will get tonight.
Currently...a quick moving and weak low pressure system is tracking
to the southwest of the region and is producing some very light and
fluffy snow across southwest Wisconsin. Some low level
frontogenesis has provided enough lift to saturate the column from
around 900-750mb which is right in the middle of the dendritic
growth zone. Upstream observations from the Minneapolis/La Crosse
area have shown some very high snow ratios on the order of 50:1 to
90:1 with about a half inch to an inch of accumulation. Current
radar/observation suggest that the areas just to the southwest of Madison
has the best chance of seeing something similar toward daybreak
before the lift shifts south into northern Illinois around 9am.
The focus then GOES to a cold front which is currently in the
northern Great Lakes. This front will swing through the region
today and will begin to usher some much colder air in. The
combination of gusty winds and cold air look like they will produce
wind chills in the 20 to 25 degrees below zero range overnight into
early Saturday morning...which has been fairly consistent for the
past few days from the models. Based on this confidence...have gone
ahead and issued a Wind Chill Advisory from midnight through 9am
Saturday (advisory criteria is 20 below). If there is one possible
hitch it is that the winds could keep temperatures up if they stay
too strong and promote mixing.
Saturday - confidence...high
after a bitterly cold start 1045 millibar high and subsiding
influence should result in a decent amount of sunshine. Middle level
flow remains strong from the northwest though trending more
anticyclonic. Core of low level thermal trough remains across southern
WI with 925 temperatures at or below -20c in the morning modifying only into the
middle or upper teens celsius during the afternoon. So the superblend
guidance showing many highs struggling to get out of the single digits
continues to look good.
Saturday night - confidence...medium
expecting mainly clear skies during the evening with surface
ridge axis across the state. Continued the trend of a non-
diurnal temperature curve as warm air advection increases later in the night with
increasing middle deck. Continued the slight chance/chance probability of precipitation in our far
SW County Warning Area after midnight as models are showing the leading warm air advection Wing
of light snow nudging into those areas.
Sunday and Sunday night - confidence...medium to high
boosted probability of precipitation even further into the categorical range with the
consistent signal form the models of widespread snow likely with
arriving warm air advection and shortwave trough. Getting some impressive vertical
motion signals with coincident warm air advection and DCVA. BUFKIT...especially
the NAM...shows deep dendritic growth potential. Consensus of quantitative precipitation forecast
is between 0.10 and 0.20 with Cobb ratios anywhere from 16-25/1 so
getting some resulting snowfall totals that may push this event
into the advisory category. Sustained warm air advection and yet to arrive surface/850
trough will likely maintain snowfall right into Sunday night.
Monday - confidence...medium
broad middle level cyclonic flow persists with lingering shortwave
activity still possible. The low level trough expected to shift
east though the GFS lingers this feature a bit longer into the
Tuesday - confidence...low
the 00z GFS looks like what the European model (ecmwf) was showing last night with
a potent clipper type system riding southeast with abundant quantitative precipitation forecast
across the area. The European model (ecmwf) is now dry with cold advection and the
system of concern is proggd to ride from the northern plains into
the middle Mississippi Valley completely missing WI. Meanwhile the
GFS shows the vorticity riding through eastern Iowa with an 850 low just
south of dbq. Will be going the superblend Route on probability of precipitation until a
pattern of consensus and consistency is realized.
Wednesday and Thursday - confidence...medium
GFS and European model (ecmwf) show some low level ridging which appears to be
setting up for a quiet Wednesday. Attention then turns to a potential
warmup beginning Thursday as 850 baroclinic zone lifts northeast
through western Great Lakes. The European model (ecmwf) shows a northwest/southeast oriented area
of light quantitative precipitation forecast associated with the 850 baroclinic zone on Thursday.
All in all broad middle level ridging with increasing heights will be
advancing eastward from the plains this period signaling the start
of a warmup. The GFS shows 925 temperatures appch zero celsius in southern
County Warning Area by later Thursday with the European model (ecmwf) a bit colder.
Aviation/12z tafs/...the main focus at the taf sites is with the
early chances for msn to see some light snow this morning. It
appears as though the main band of snow is staying to the southwest
of msn...but there could still be some brief MVFR ceilings that
get in for a few hours this morning. Beyond that it is mainly just
some gusty northwest winds and clear skies going through the rest
of today into tonight.
Marine...winds will be on the increase through this afternoon on
into tonight with northwesterly winds gusting up into the 25 to
30 knots range over this period. With the off shore flow...the highest
waves will be out toward the open waters of the lake. Winds will
quickly diminish on Saturday as a ridge of high pressure moves
into the western Great Lakes region.
WI...Wind Chill Advisory from midnight tonight to 9 am CST Saturday
Lm...Small Craft Advisory from noon today to 9 am CST Saturday for
Today/tonight and aviation/marine...halbach
Saturday through Thursday...collar