Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
907 PM CST Wednesday Nov 26 2014
Update...area of -sn over west central WI diminishing as it
pushes east into western County Warning Area last hour or so as it encounters drier
air and middle-level ridging. However expect several periods of --sn
to sweep into the far west rest of the late evening as it
Fairly sharp middle-level short wave trough upstream over eastern Minnesota will
sweep across area overnight. Weak forcing from this feature
expected to interact with dendritic growth zone. Most likely this
will be a trace event but expect patchy very light snow /just a
nudge more than flurries/ to affect western/central/nrn County Warning Area. Beefed up
probability of precipitation to accounty for --sn with trace accumulations.
Aviation/06z tafs/...increasing northwest boundary layer winds
and some low level drying eroding MVFR stratus over southeast WI.
Expect another period of MVFR clouds to accompany a period of --sn
overnight and low level cold air advection. Expect VFR conditions
to return later Thursday morning or early afternoon.
Marine...tightening pressure gradient late tonight into Thursday morning
and low level cold air advection flowing across nearshore waters
will result in wind gusts to around 20-22 knots for a time. Near
shore soundings for this period shows most gusts should remain
below 22 knots...hence will hold off on Small Craft Advisory. Winds will
diminish later Thursday as pressure gradient weakens...however will
remain gusty until Thursday evening.
Previous discussion... /issued 348 PM CST Wednesday Nov 26 2014/
Tonight and Thanksgiving...forecast confidence is high.
Cloudy skies will continue tonight into Thursday morning as a
shortwave pushes through. Models continue to show very limited
moisture and lift this evening and overnight...so kept probability of precipitation on the
low end. Still thinking not more than a dusting to a couple tenths
of an inch of snow for most places...the best chance across the
northern forecast area.
Will likely see scattered flurries linger in the eastern forecast
area Thanksgiving morning as the shortwave exits. Dry weather and
decreasing clouds from west to east is then expected for the
afternoon. Temperatures aloft will be quite a few degrees cooler tomorrow
behind the shortwave. Highs will thus be pretty chilly for
Thanksgiving...about 15 to 20 degrees below normal.
Short term...Thursday night through Saturday...forecast
confidence is high.
Synoptic models in good agreement with high pressure moving off to
the southeast Thursday night. Area of focused warm air advection
then pushes into the region later Thursday night into Friday.
Best upward vertical motion clips the northern half of the area
during this time. Models all bringing light quantitative precipitation forecast through this area
as well...with southern areas seeing less.
Area forecast soundings showing decent saturation through most of
Friday in the northern portions of the area. Should see an area of
light snow push through that area. Kept likely probability of precipitation going but may
need to be raised in later forecasts if models remain consistent.
Should see up to an inch in the far northern counties...lower
amounts to the south.
Area forecast soundings showing light freezing drizzle remaining
possible as the light snow ends from west to east Friday afternoon
and evening. NAM more aggressive with freezing rain
occurring...but best upward motion will be east of the area. Kept
light freezing drizzle going for now during this time.
Temperatures will rise into the upper 20s to lower 30s
Friday...and into the lower to middle 40s Saturday within warm air
Long term...Saturday night through Wednesday...forecast
confidence is medium.
GFS/European model (ecmwf) are in decent agreement with strong cold front passing
through the area Saturday night and Sunday...though most
precipitation will remain southeast of the area. Strong cold air
advection in the wake of the front will bring another blast of
cold air into the region Sunday into early next week. High
pressure will keep the cold air in place into Monday night.
Warm air advection should then begin a brief warm up Tuesday
across the region. Probability of precipitation late in this period are questionable...as
models become more in opposition with each other with trends. Used
consensus probability of precipitation and temperatures for now this far out in the
Still looks like ceilings will be MVFR for much of the time tonight
into Thursday morning. There could be brief improvements given
upstream conditions...but hard to pinpoint these at this point.
Will keep lower ceilings going in tafs and update if there are
significant improvements approaching.
Light snow will hold off for the most part through late
afternoon...with a dusting or so then possible during the evening
and overnight hours. Could see a little snow linger Thursday
morning in the east...though likely just in the form of flurries.
Northwest winds will be breezy Thursday behind a departing
shortwave. There may be a few gusts to 25 knots...and waves to 4
feet toward open waters. Overall though...conditions seem too
borderline for a Small Craft Advisory.