Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
1059 PM CDT Sat Mar 15 2014
Northeast/east flow off Lake Michigan was brining some light lake
effect flurries. With low level inversion strengthening...do not
anticipate any accumulations.
Clouds/flurries off Lake Michigan. Low level relative humidity decreases as
inversion strengthens....so any precipitation will flurries. Lake clouds
will be at MVFR levels otherwise expecting mainly VFR conditions
into Sunday with clear skies becoming dominate later tonight and
for Sunday inland with high pressure building in.
Previous discussion... /issued 241 PM CDT Sat Mar 15 2014/
Tonight - confidence...medium
frontogenetical band underachieving...hard to get much ground truth
with it. However noting additional development north of kdsm. 4km
WRF shows this band being absorbed into initial mostly aloft band
across SC WI with bulk of this affecting northern Illinois. Tempted to just
go flurries and be done with it. However will keep some probability of precipitation and a
tight gradient in the far south as these bands linger into the
evening. Low level relative humidity forecasts suggest lake effect cloud cover in
parts of eastern WI this evening. Will mention some flurries along the
shore. Collab with kgrb on this. Subsidence/drying really take
hold after 6z...so will end any probability of precipitation and gradually scour out any
lingering cloud cover as well.
Sunday - confidence...high
surface/850 high pressure will dominate. Weak shortwave in the broadly
cyclonic flow will be running into a lot of dry air and lower level
subsidence...so not expecting any impact from that feature. 925 temperatures
bottom out well into the minus teens celsius early with thermal trough
well entrenched...then some modification as the day wears on. Still
quite chilly with highs mostly l-m20s.
Sunday night through Monday night...forecast confidence is high.
Cold high pressure will cover the area at the start of this
period...drifting east with a warmer southerly flow returning by
the end of the period. The increasing southerly flow developing
ahead of approaching low pressure results in some strong warm
advection on Monday into Monday evening...but the atmosphere is
very dry below 8-9kft so will keep things dry for now.
Tuesday through Wednesday...forecast confidence is medium.
No real model swings on the latest runs. Most interesting aspect
since yesterday is the increasing strength of the middle/upper level
short wave. This had been looking like a rather weak open wave and
now is taking on a more closed or nearly closed upper low solution
that becomes negative tilt as it moves into Wisconsin. There is
still some model disparity in the surface low track...but the
consensus suggests the track will be far enough north to keep any
significant precipitation...and snow...north of the forecast area. The
GFS takes the low from Sioux City Iowa to Eau Claire WI to Central
Lake Superior between noon Tuesday and noon Wednesday. The European model (ecmwf) is more like
a Lincoln NE to Des Moines to Green Bay track during the same
time frame. The Canadian is a bit farther south. Either way...the
bulk of any precipitation will be north of this track. Given this...any
precipitation will likely hold off until Tuesday night...when the low
begins to enter the area. We should be deep in the warm sector so
expecting precipitation to start as rain...then transition over to light
snow in the wake of the associated cold front on Wednesday. In
these situations...any snow accumulations would be on the light
side. Again...the heavier snow fall will be well north of the
forecast area...given this track.
Thursday...forecast confidence is medium.
High pressure builds into the area in the wake of the low...but
the upper level flow remains more zonal so the intrusion of any
cold air will be very limited.
Friday and Saturday...forecast confidence is medium.
A fast moving but rather weak trough will move through in the faster
zonal flow for Thursday night into Friday night. Temperatures will
be close to thresholds during the nighttime hours...bringing a
potential for mixed precipitation...but mainly rain on Friday with highs
on Friday ahead of the surface low pushing into the lower 50s
southwest of Madison...but staying quite chilly up toward
Sheboygan where a southeast flow will limit temperatures to the 30s.
Thank you icy Cold Lake Michigan.
Aviation/00z tafs/...frontogenetical band will affect portions of
SC WI Erly this evening. Just starting to get some ground truth in
NE Iowa. Will likely leave -sn out of tafs altogether based on trends.
Favorable Delta T sets up this evening with 850 temperatures into the
negative teens celsius. Clouds/flurries cannot be ruled out. Big
decrease in low level relative humidity after 6z...so any precipitation will be prior to
then...be it from the band or any lake effect precipitation. Not a big deal
either way. Any lake clouds may lower to MVFR levels otherwise
expecting mainly VFR conditions into Sunday with clear skies
becoming dominate later tonight and for Sunday with high pressure
gaining full control.
Marine...a Small Craft Advisory is in effect tonight into Sunday
afternoon south of Port Washington. Brisk northeast winds will
develop tonight and continue into Sunday as the pressure gradient
tightens between low pressure over the lower Mississippi River
valley and polar high pressure moving into the northern Great Lakes.
High waves will develop since most of the ice has melted. The winds
and waves will subside by late Sunday afternoon.
Lm...Small Craft Advisory until 4 PM CDT Sunday for lmz643>646.
tonight/Sunday and aviation/marine...collar
Sunday night through Saturday...Davis