Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Milwaukee/Sullivan WI
905 PM CST sun Feb 7 2016
Initial band of light precipitation that produced light snow at Decorah
Iowa over the past hour appears tied to pocket of low
level frontogenetic forcing and weak isentropic lift out ahead of
the cold front. This pocket of brief light snow/flurries is
brushing far western Wisconsin as it drops to the southeast.
More widespread light snow will be moving in around/after midnight with
deepening moisture behind the cold front and forcing with the 500
Seeing spotty reports of unknown precipitation right along the front
before the column cools and moistens into the dendrite growth zone
for all snow so will add a mix of rain/snow/drizzle in a band
right along the wind shift. Rest of forecast looks on track.
VFR conditions will fall to MVFR ceilings/visibilities in light snow behind
a cold front that will move across southern Wisconsin between 06z
and 12z. May see a brief mix of rain/drizzle and snow right along
the cold front...going over to all light snow behind the front
with winds shifting west and then northwest.
Strongest winds hold off until baggy gradient around surface low
pushes east of the forecast area late Monday morning/early
afternoon...with sustained 15 to 20 knot winds and gusts to 25
kts. Still looks like periods of light snow with total
accumulations between 1 inch and 1.5 inch by 06z Tuesday.
Strongest winds associated with low slowly moving east-southeast
from the western u.P. Of Michigan not expected to reach the
Western Shores of Lake Michigan until 00z Tuesday. Looks as if winds
will strengthen to Small Craft Advisory levels around/after 06z
Tuesday. And continue through most of the day Wednesday.
Previous discussion... /issued 212 PM CST sun Feb 7 2016/
Tonight and Monday...forecast confidence...high
Surface trough/cold front will slide through late this evening into
tonight...while an upper level low moves overhead. Looks mainly dry
prior to the front arriving...with snow developing behind the
front/trough. Should see light snow spread all the way east by
Saturation remains pretty deep most of the day Monday...with some
weak lift under the upper low...so will probably see some light snow
persist through much of the day Monday. Snow to liquid ratios will
be on the increase tonight into Monday as a colder airmass moves
in...with around an inch of total snow possible through Monday
After a mild day today...temperatures tomorrow will fall back to around
Monday night and Tuesday...forecast confidence...high
The upper trough near Lake Michigan is still over the Great Lakes
region Tuesday with a weakly cyclonic north/northwest flow into
Tuesday with weak 700 mb upward motion.
The middle levels begin to dry west of Madison...but remain moist in
the 925/850 mb layer.
Should see a little light snow into Tuesday afternoon...with
flurries possible west areas.
Cold air advection continues at 850 mb...dropping to around minus
15 celsius Tuesday afternoon.
Tuesday night and Wednesday...forecast confidence...high
A northwest upper level flow continues with a 150 knot upper jet
maximum dropping down across eastern Minnesota.
700 mb relative humidity remains saturated east into the night...but then finally
dries across Wednesday morning. Even with a deep moist layer
through 700 mb...the steeper lapse rates are below 900 mb.
850 mb winds briefly become north/northeast...and lake snow may
brush the shoreline area...but should not extend inland.
Mainly dry weather is expected Wednesday as a surface high
pressure ridge moves into the upper Mississippi Valley.
Low level winds remain northwest keeping any lake snow out over
Wednesday night and Thursday...forecast confidence...high
The upper flow remains out of the northwest with the European model (ecmwf)
dropping a shortwave across Wisconsin around the large trough
over southeast Canada. The GFS has a slower and more north track.
Both the GFS and European model (ecmwf) are dry with a surface ridge continuing
across the upper Mississippi River valley.
Thursday night and Friday...forecast confidence...medium
The upper level flow becomes just a little more zonal with another
upper low forming near and southeast of James Bay.
A weak surface trough forms across the Great Lakes region...but
only the 06z dgex has any light snow across southern Wisconsin.
Saturday and Sunday...forecast confidence...medium
An upper level ridge builds across the northern rockies and moves
across the northern plains Saturday night and into Wisconsin
Sunday ahead of an approaching shortwave. This shortwave is more
north in the 00z European model (ecmwf).
A strong surface high extends across the western Great Lakes
Saturday. The GFS is a little quicker moving it across the eastern
Great Lakes Sunday. This results in the GFS spreading light
precipitation into south central Wisconsin Sunday afternoon. The
12z European model (ecmwf) has trended toward the 12z GFS.
VFR conditions will likely prevail into the evening hours. Will
eventually see lower clouds and light snow develop late evening into
the night as a trough and cold front push through southern
Wisconsin. Light snow will likely linger through much of the day
Overall snow accumulations will be on the light side...generally
around an inch through Monday afternoon. With temperatures falling
into the 20s tonight and staying there Monday...bulk of snow will
generally be on the dry side...around 15-18 to 1 ratios.
Low clouds are expected to persist through the day Monday as the
system slowly moves through the Great Lakes.
Winds will continue to slowly ease late afternoon into the
Stronger winds and higher waves will likely lead to Small Craft
Advisory conditions from Monday night through at least the day
Wednesday...between low pressure pulling away to the east and high
pressure moving in from the northwest.
tonight/Monday and aviation/marine...ddv
Monday night through Sunday...hentz