Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Milwaukee/Sullivan WI
1211 PM CST Thursday Dec 18 2014
The Freezing Rain Advisory continues for
Washington...Ozaukee...Waukesha and Milwaukee counties until 3 PM
CST this afternoon. Areas of light freezing rain are causing icing
on roads across these counties...and should continue for the next
few hours...until surface trough slides south of the area.
Milwaukee forecast soundings do support supercooled droplet
formation into middle afternoon.
Radar trends suggest this light freezing drizzle may be spreading
westward into Dodge and Jefferson counties...perhaps further west.
Will continue to monitor social media reports and Road
conditions...and may add more counties to the advisory if
The freezing drizzle should end by middle afternoon...as surface
trough slides south of the area. Some uncertainty exists here with
the ending time. Otherwise...expect cloudy skies with some
flurries this afternoon. Highs should reach the upper 20s to
Light freezing drizzle is expected at times at Milwaukee and
Waukesha until 21z this afternoon...which may cause icing on
runways. Scattered flurries are expected otherwise this
Expect MVFR ceilings to remain across taf sites this afternoon
and most of tonight. Winds will remain light through this period.
There should be a period of the MVFR ceilings mixing out by 13z
Friday morning at Madison and Waukesha...though there is
uncertainty about this. Milwaukee and Kenosha should remain in
the MVFR ceilings on Friday.
Previous discussion... /issued 315 am CST Thursday Dec 18 2014/
Today and tonight...forecast confidence - medium.
Main concern for this period is cloud cover. High pressure ridge
over western grlakes will suppress any precipitation to the south from short
wave passing across middle-MS valley region.
Nearly stationary area of stratus over northern and central WI is
beginning to inch slowly southward last several hours. 11-3.9 micron
imagery showing edge of stratus has sagged into northern Waukesha and
Jefferson counties extending northwest toward kdll. Weak subsidence
from left entrance region of passing upper jet may have contributed
to stratus remaining stationary much of the night...however this
suppression moving off to the east early this morning. 00z kgrb
sounding showed moisture relatively thick around 3k feet. Lingering
very weak forcing from 850 mb cyclonic curvature and low level winds
turning a bit more north to northwest today. Hence expect stratus
field to continue to spread south and engulf most of County Warning Area through the
Not impossible a few flurries may get shaken out of the stratus due
to very weak lift. Expect only slow clearing later tonight into Friday
Friday - confidence...medium
quiet weather continues as high pressure dominates. Very little
stirring in the column. Low level relative humidity forecasts offer hope at a bit of
sunshine while the NAM shows strong inversion around 900
millibars. Some decrease in 925-850 relative humidity noted during the day so
will have some clouds in the grids but hope for a bit more
sunshine than what the NAM MOS is suggesting.
Saturday - confidence...medium
models continue to show a 500 millibar shortwave moving from
Iowa into northern Indiana. NAM sounding shows column fairly moist
below 800 millibars with no saturation noted in the favored ice
growth region. Meanwhile GFS shows some moistening between 700 and
800 millibars. With weak warm air advection regime setting up was tempted to add
some flurries or drizzle. Per collab with surrounding offices will
leave out. Low level moisture forecasts show the synoptically favored
return of stratus within this weak warm air advection regime.
Sunday and Sunday night - confidence...medium
another shortwave affects the area. Low level warm air advection
is ongoing with sustained southerly flow. Thermal pattern suggests
light snow as the precipitation type with 850 and 925 temperatures at or below 0c and
1000/500 millibar thicknesses 531-537dm. Better ice Crystal growth
saturation noted in western County Warning Area per BUFKIT soundings.
Monday through Wednesday - confidence...low
upper low proggd to evolve and plod through Great Lakes this
period. Models now show secondary and stronger low development
along East Coast. GFS and European model (ecmwf) are in good agreement on this 00z
run but consistency hasn/T been established as yet so confidence
still a bit shaky this far out. Certainly plausible that this is
not the final answer considering this southern and eastern
secondary low development is in the day 6/7 timeframe. Having
said that...should this 00z model consensus show staying power we
would be looking at a warmer scenario Monday into at least the
first part of Tuesday before colder air wraps in and changes
precipitation type to all light snow for later Tuesday into Wednesday
with a potential whitening of the landscape.
Aviation/12z tafs/...expect stratus field over northern County Warning Area to spread
southward into taf sites this morning with MVFR ceilings then likely to continue
into tonight. Possible a few light flurries may get shaken out of the
clouds but no visibility restriction is expected.
Recent ascent kmke tamdar sounding continued to show strong elevated
inversion above 3.8k and 00z kgrb sounding showed the moisture was
relatively deep to the north...around 3k feet.
WI...Freezing Rain Advisory until 3 PM CST this afternoon for wiz059-
today/tonight and aviation/marine...mbk
Friday through Wednesday...collar