Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Green Bay WI
354 am CST sun Feb 14 2016
Forecast discussion for routine morning forecast issuance
Short term...today...tonight...and Monday
issued at 353 am CST sun Feb 14 2016
Main forecast concerns include snow trends and accumulations...
including lake enhancement and potential headlines along the
Lake Michigan shoreline.
Dry air was hanging tough over the forecast area early this
morning...with mainly clear skies and very cold temperatures in the
single digits and teens below zero. Some of the typical cold spots
in NC WI were in the -20 to -25 f range. Middle-level clouds were
thickening up over SW WI...but light snow was just arriving in
southeast Minnesota/NE Iowa.
Have slowed down the arrival of snow in the forecast area a little
bit...with probability of precipitation really ramping up during the late afternoon
and early evg as a short wave trough passes just to our south and warm air advection
increases. Timesections show fairly strong lift occurring below
750 mb...and also a very deep dendritic growth zone in the
900-650 mb layer. Will carry likely/categorical probability of precipitation over the
southeast two-thirds of the County Warning Area late today into tonight...with most
places expected to pick up 1 to 3 inches of powdery snow. The
most interesting aspect of the event is the lake enhancement
potential along the Lake Michigan shoreline...and particularly
over Door County...as low-level winds turn S-southeast today into
tonight. Mesoscale models show lake-effect snow showers
developing this morning...and moving onshore between 16z-18z.
The lake-enhanced band gets more intense tonight as synoptic
scale forcing and deeper moisture arrives. Quantitative precipitation forecast forecasts vary
considerably from model to model...with the WRF-nmm east
the most aggressive...with a forecast of 0.40 to 0.45 inches
for the entire event. This is probably excessive...but quantitative precipitation forecast
amounts around 0.20 to 0.25 inches seem reasonable. With snowfall
to water ratios of nearly 20:1...snowfall amounts should approach
4 or 5 inches in Door County...where wind trajectories are most
favorable. Have decided to issue a Winter Weather Advisory for
Door County this afternoon and tonight.
The snow should taper off across far NE WI Sunday morning...
with perhaps some flurries arriving in NC WI during the
afternoon as another short wave trough approaches.
Used a blend of the better performing guidance sets for temperatures.
Overall...expecting a moderating trend...with highs in the
upper teens to middle 20s today...and middle 20s to lower 30s
Long term...Monday night through Saturday
issued at 353 am CST sun Feb 14 2016
The medium range models continue to advertise a flattening of the
upper air pattern for the upcoming week...which will yield more
progressive weather systems across the northern tier of the Continental U.S..
the result will be a seesaw of temperatures...but precipitation chances
will likely remain on the light side. Will put more weight into the
European model (ecmwf)/sref through 00z Thursday before trending to a blend.
Monday night through Tuesday night...flattened troughing will exist
over the western Great Lakes on Monday night...with an associated
surface trough moving across the western half of the state. The more
robust shortwave activity looks to be bypassing the region to the
south...so think most of the night will be on the dry side. Could
see a few flurries over north-central Wisconsin. The surface trough
will move across eastern Wisconsin on Tuesday...at the same time as
a sharp northern stream shortwave digs over Lake Superior. The tail
end of the vorticity could create light snow or flurries across much of
the region. Not expect much in the way of accums though. The
shortwave exits to the east on Tuesday night while high pressure
builds into the region. Should see a slow clearing trend from west
to east during the night...except in the snow belts where light northwest
flow will be occurring. Temperatures will be mild on Monday night and
Tuesday...the cool off on Tuesday night.
Rest of the forecast...Arctic high pressure will be moving across
the region Wednesday and Wednesday night. Should see mostly clear
and dry conditions...though temperatures will fall back below normal
during this time. Temperatures have potential to tank Wednesday evening
due to clear skies and light winds...but the pressure gradient does
tighten some late as the high departs. Will side with the colder
guidance. Warm advection rapidly increases on Thursday...but will
bring a chance of light precipitation starting Thursday evening. The light
precipitation chances will then continue into Friday. Enough warm air will
be pulled north for a wintry mix precipitation type Thursday afternoon and
night...followed by possibly all rain on Friday. Precipitation mostly
exits Friday night...but temperatures will remain above normal for much of
Aviation...for 06z taf issuance
issued at 901 PM CST Sat Feb 13 2016
Generally good flight conditions /VFR/ expected tonight. Conditions
will start to deteriorate tomorrow as light snow overspreads the
area. In eastern WI...as clouds and some flurries/snow showers off Lake
Michigan will probably bring MVFR conditions to the Lakeshore by
Winter Weather Advisory from 2 PM this afternoon to 8 am CST
Monday for wiz022.