Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI
FXUS63 KMKX 092155 CCA
Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
335 PM CST FRI DEC 9 2016
.TONIGHT AND SATURDAY - Forecast Confidence...Medium.
The big concern tonight is cloud development and resultant impact on
temperatures. Models have been inconsistent and are generally
divided on sky cover overnight. Decided to trend the latest sky
forecast toward less clouds based on current regional conditions. It
does look like there should be a period of at least high clouds
ahead of a weak wave late evening into the night. Went with lows
near the consensus blend of models due to the uncertainty with
clouds. Kept temps mildest tonight toward Lake Michigan where there
will be a bit more wind and there is little to no snow left on the
Skies will become mostly cloudy by Saturday afternoon as clouds
increase ahead of the approaching low that will bring snow to the
area. The snow will likely begin in the southwest half of the
forecast area in the afternoon and is expected to hold off elsewhere
until evening. Below normal temps will continue tomorrow.
.SATURDAY NIGHT THROUGH MONDAY - Forecast
Not enough confidence at this point to upgrade to Winter Storm
Warning or change to Winter Weather Advisory. Expect baroclinic
zone to set up across southern WI later Saturday and strengthen over
the area into Sunday. Nam still most aggressive with QPF amounts
showing axis of .7 to .8 inch across srn tier of counties with .5 to
.6 in the north. ECMWF and GFS QPF lower by 0.1 to 0.2 tenths inch.
Moisture will be plentiful during the period with specific humidity
values 2-3 g/kg for the duration of the evening. Snow-liquid ratios
are expected to be in the 13-17 to 1 range for the majority of the
evening. Despite GFS showing lower QPF, GFS and NAM in good
agreement on sloping frontogenesis developing across srn WI later
Saturday night into Sunday. This frontogenesis intersects dendritic
growth zone region later Sunday night into Monday.
NAM now in better agreement with GFS showing a better potential for
lake enhancement north of Milwaukee Sunday morning. Lake enduced
cape rises to around 200 j at KSBM with delta-t increasing to around
15 degrees. However fetch not as favorable due to more se low level
Will let midnight shift look for consistency /or lack thereof/ in
deciding how to upgrade watch.
MONDAY NIGHT THROUGH FRIDAY - Forecast Confidence...Medium.
Focus of this period will be on a prolonged period of cold
temperatures expected W to NW. Expect widespread fresh snow cover
by the start of the period and 925H temps tumbling into the -20 to
-25 degree range by mid-week as polar low strengthens and settles
into south central Canada. Several periods of snow showers and
flurries likely as several short wave trof rotate around deepening
polar low. High temperatures will be falling into the single digits
so will be watching Wind Chill values closely. Low level flow
remains offshore so no lake affect snow events expected.
The challenge for this evening and tonight is pinning down cloud
cover. Skies ended up sunnier than anticipated this afternoon across
the region. Models do still suggest some low cloud develop is
possible this evening and overnight, but not seeing enough evidence
at this time to go with this. Will likely see at least high clouds
late evening into tonight as a weak wave moves through.
If low clouds don`t develop tonight, expect mainly VFR conditions
through Saturday morning. Cloud bases will lower Sat afternoon into
the evening as the snow arrives from the west. Visibilities will
eventually go down as well. Initial accumulations will be limited to
the southwest half of the forecast area prior to 00Z.
Southerly winds may reach Small Craft Advisory levels for a time
Sunday as low pressure moves through the region. The persistent
along shore flow may also build waves to the 3 to 5 foot range, with
the highest waves toward open waters.
WI...WINTER STORM WATCH from Saturday evening through Sunday evening
WINTER STORM WATCH from Saturday afternoon through Sunday
evening for WIZ046-047-056-057-062-063-067>069.
TONIGHT AND SATURDAY/AVIATION/MARINE...DDV
SATURDAY NIGHT THROUGH FRIDAY...MBK