Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
248 PM CDT Friday Mar 14 2014
Tonight - confidence...medium 995 mb surface low shifting east from
extreme northern lower Michigan. This has dragged cold front through southeast WI. Cold
air advection regime settling in. MVFR cloud deck shifting southeast into
southern WI and expect cloud cover to be generous into the evening
hours. Airmass stays mixed into the evening hours...then as surface
ridge axis pushes into SC WI towards 12z...expect combo of
clearing and diminishing winds to allow for a better temperature
Saturday and Saturday night - confidence...medium low level
ridging dominates at the outset...then focus shifts to afternoon
-sn chance as low level...850-700 millibar...frontogenetical
forcing takes hold. The NAM is the strongest solution in this
regard. The 4km WRF and the NAM keep the band focused across the
western County Warning Area during the early and middle afternoon and then gradually
shift the focus southward to the WI/Illinois border into Saturday night.
The GFS and European model (ecmwf) are overall less robust and skewed further
south. All models are not real excited about the eastward push of
precipitation...so highest probability of precipitation in the west and SW County Warning Area. In fact the 12z
European model (ecmwf) just clips the far SW County Warning Area with the GFS more The Middle
Ground. Will expand probability of precipitation into the County Warning Area after 18z. 850 temperatures and
BUFKIT soundings support all snow for this event. 925 temperatures are a
bit warmer on the GFS and NAM than the 12z European model (ecmwf). Overall plenty
of cloud cover and a steady NE wind...it will be on the cool side.
Sunday and Monday...forecast confidence is high.
A sprawling area of high pressure will cover the Great Lakes
region with ridging stretching west into the Central Plains on
Sunday. This will be a cold airmass...so highs on Sunday will stay
in the 20s...coldest across the east. The high will drift east by
Monday...but lingering ridging is expected to keep things dry with
the core of the cold air exiting. Highs by Monday should range
from the middle 20s near Sheboygan to the middle 30s southwest of
Tuesday and Wednesday...forecast confidence is low.
It looked like there was model continuity building last night
on the moderately strong low pressure system moving into the Great
Lakes region during this period. The GFS had the low moving over
Chicago...the European model (ecmwf) over southern Wisconsin...the Canadian so far
south we nearly missed all the precipitation...and the wpc forecast was
largely using the European model (ecmwf) ensemble blend that looked like the GFS.
So it looked like a colder low with snow was going to hit the area.
Never mind...for now. From the 12z runs this morning...the GFS
has gone north and west...the European model (ecmwf) has gone farther north and the
Canadian has shifted a about state farther north with the axis of
the heaviest precipitation over the forecast area. The current GFS and
the European model (ecmwf) from 12z this morning would be a warm solution with the
bulk of any snow potential north of the forecast area. There are
also big time timing issues with the European model (ecmwf) much slower than the
GFS. In this scenario...we would see some initial light
snow...transition over the a mix...then rain...then back to light
snow as the cold air arrives in the wake of the low.
My big concern is how cold the Great Lakes are and if we happen to
get into a decent southeast to east flow ahead of the low...we
could see the influential baroclinic zone tighten up farther
south than the models currently suggest...causing the low to go
farther south. Given the large model fluctuations from run to
run... confidence on any solution right now is low. The energy
with this system is currently south of the Aleutian Islands...in
the Pacific. Stay tuned.
Thursday and Friday...forecast confidence is medium.
At this time it looks like high pressure will return with dry
weather. Warmer by Friday as southerly winds kick in.
Aviation/00z tafs/...cold advection regime takes hold with
northwest winds ramping up into Erly evening. Low level relative humidity forecasts/NAM MOS
bring MVFR ceilings into the area later this afternoon and evening. Already
seeing this dropping in from western WI. Surface ridge axis comes into
play late tonight and Sat am...then will keep an eye on snow trends Sat
afternoon/evening with stronger low passing to our south. European model (ecmwf) squashes
precipitation mostly south of the state while GFS and NAM bring at least
some light snow into SC WI and parts of southeast WI during the afternoon.
Marine...pressure gradient remains tight into the evening hours so
will hang on to the Small Craft Advisory. Northwest winds will persist for
a time in the cold advection regime in the wake of the front that
has pushed off to the east.
Lm...Small Craft Advisory until 1 am CDT Saturday for lmz643>646.
Tonight/Saturday and aviation/marine...collar
Saturday night through Friday...Davis