Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Green Bay WI
638 am CDT sun Mar 16 2014
Updated aviation portion for 12z taf issuance
Short term...today...tonight...and Monday
issued at 404 am CDT sun Mar 16 2014
Main forecast concerns include temperatures...and minor precipitation chances
late tonight into Monday.
Arctic high pressure over Lake Superior was slowly sagging south
early this morning. Skies had cleared over almost all of the
forecast area...although cold NE flow was producing lake-effect
clouds along the Lake Michigan shoreline...and some flurries
in the Two Rivers and Manitowoc areas.
Expect the lake-effect clouds and flurries near Lake Michigan
to diminish this morning as very dry air advects south across
the lake...and the surface high builds into the region. Sunny
skies and much below normal temperatures will prevail across
the area...with highs in the upper teens to middle 20s.
As the surface high shifts east tonight...southerly return flow and
associated warm air advection will develop. Models are fairly similar in keeping
most of the forecast area dry overnight...although enough
saturation may occur over the far northwest part of the County Warning Area to generate
some flurries late. Low temperatures should range from the single digits
over NE WI to around 10 degrees in our SW counties.
Continued warm air advection will result in thickening cloud cover...and a chance
of light snow or flurries over about the northwest half of the forecast
area. High temperatures should warm into the upper 20s and lower 30s.
Long term...Monday night through Saturday
issued at 404 am CDT sun Mar 16 2014
The main concern during this part of the forecast is the system
that will impact the area Tuesday night and Wednesday as a middle
level trough and surface low make their way across Wisconsin.
Have a chance for snow across the north on Monday night in warm
advection ahead of an approaching surface low pressure system and
middle level trough. This should shift to the north on Tuesday so
mainly slight chance probability of precipitation for snow during the morning and rain or
snow in the afternoon.
Went with likely and categorical probability of precipitation for Tuesday night as both the
surface low and middle level trough reach Wisconsin...but precipitation
type is a major concern. Warm advection should allow for rain
across much of the area during the evening...before the boundary
layer cools bringing the potential for freezing rain to part of
the area. There should be some rain or snow in the east on
Wednesday before the system passes to the east and snow becomes
the predominant precipitation type. Models were in better
agreement during this period but there were still enough
differences to result in some uncertainty regarding precipitation
types and their location. The 00z GFS surface low track was
farther north than the 00z European model (ecmwf) and would bring more warm air
into the area...leading to more liquid and mixed precipitation.
Divergence of model solutions later in the week leads to little
confidence in the forecast moving ahead into next weekend.
Low amplitude flow across the region during the period should keep
temperatures from falling more than a little below normal...even
behind the departing surface low. Higher sun angle should help to
warm things up on days without many clouds.
Aviation...for 12z taf issuance
issued at 631 am CDT sun Mar 16 2014
Lake-effect snow showers and clouds were still occurring along
the Lake Michigan shoreline...and were actually edging farther
inland. Will add a tempo group for a couple hours of light snow
showers at mtw...and keep MVFR ceilings until around 16z. Think that
the low clouds will stay southeast of the grb/atw taf sites...but will
have to watch trends over the next few hours. Drier air does
appear to be overspreading Northern Lake Michigan...as there has
been a decrease in lake cloud development there. This should
aid in a decreasing trend in the lake effect as the morning
progresses. Aside from the lake effect concerns...VFR conditions
will prevail...with sunny skies today...followed by increasing
middle/high clouds tonight. A few flurries may make it into NC WI
toward daybreak Monday.