Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Green Bay WI
240 PM CDT Tuesday Jun 2 2015
Forecast discussion for routine afternoon forecast issuance
Short term...tonight and Wednesday
issued at 239 PM CDT Tuesday Jun 2 2015
The latest rap analysis and satellite/radar analysis indicate that
high pressure resides over the central and eastern Great Lakes early
this afternoon. Plenty of dry air on the western side of this
high...as evident by the 12z grb sounding. Low pressure and cold
front are hanging around the northern plains where scattered showers
are occurring. Other than high clouds filtering overhead ahead of
this system...conditions have been mostly clear and seasonable so
far today. As the low and cold front move east over the next 24
hours...precipitation chances is the main forecast concern.
Tonight...high pressure will shift to the eastern Great Lakes
tonight...but should be enough dry air on the western periphery to
provide a mostly clear to partly cloudy night. Other than middle and
high clouds invading from the west ahead of the next storm
system...will see quiet conditions with lows in the middle 40s to low
Wednesday...as a shortwave moves into the northern Mississippi
Valley during the morning and western Wisconsin in the
afternoon...will see moisture invade from the west through the day.
Forcing is pretty weak ahead of the wave...but the column moistens
enough for a chance of showers moving into north-central Wisconsin
by midday and central Wisconsin during the afternoon. Have slowed
the timing of the precipitation arrival somewhat due to the dry airmass.
Eastern sections should have enough dry air to keep precipitation at Bay.
Highs ranging from the low to middle 70s away from Lake Michigan.
Long term...Wednesday night through Tuesday
issued at 239 PM CDT Tuesday Jun 2 2015
The main forecast challenge during the late part of the week is
how long it takes a cold front to track through the western Great
Lakes...and thus how long it will rain across the area. There are
significant differences between the nwp models this run regarding
the cold front and attendant low pressure system. While models
such as the European model (ecmwf)...Canadian and GFS maintain a trough feature
tracking through the western Great Lakes...the NAM model develops
a closed low that tracks through Wisconsin Wednesday night and
Thursday...with copious amounts of rain across the region. Closer
inspection of this solution looks a bit suspicious...with the
model appearing to suffer from convective feedback which would
explain the development of a surface low when none of the other
models are in the ballpark of this solution. Therefore will side
with the consensus in this instance in tracking the front through
Wednesday night...stalling out over the area on Thursday. There is
the possibility for heavy rain as this slow moving front tracks
through the area...especially as the front stalls out.
Another shortwave tracking along the Wisconsin and Illinois border
on Friday will pull the front the rest of the way through the
area...setting up a dry Saturday across northeast Wisconsin as
high pressure builds in across the Great Lakes region.
The dry weather will be short lived as another cold front tracks
through the western Great Lakes Saturday night and Sunday as a
fairly vigorous middle level shortwave digs across the western Great
Lakes Sunday night and Monday. This system looks stronger than the
cold front slated to move through during the late part of the
week...with the strong dynamics again bringing the chance for
heavy rain to the western Great Lakes. There are significant model
differences regarding this system as the European model (ecmwf) is progressive and
tracks the low through faster than the more deliberate GFS
solution. With high pressure in place across the eastern Continental U.S. The
faster European model (ecmwf) solution seems a bit too quick this run. A weak ridge
building in for Tuesday should keep the weather dry across the
western Great Lakes region.
High temperatures are expected to be below normal for much of
this forecast period...but likely warmer than they have been the
past few days. Thursday...Monday and Tuesday look to be near or a
little above normal.
Aviation...for 18z taf issuance
issued at 1205 PM CDT Tuesday Jun 2 2015
VFR conditions and good flying weather will be present
through tonight. Clouds will be on the increase on Wednesday ahead
of a slow moving cold front. Showers along the front will move into
central and north-central Wisconsin Wednesday afternoon.