Area Forecast Discussion
Issued by NWS Green Bay, WI

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809
FXUS63 KGRB 231913
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
213 PM CDT Sat Sep 23 2017

Forecast discussion for routine afternoon forecast issuance

.SYNOPSIS...
Issued at 208 PM CDT Sat Sep 23 2017

A couple more unseasonably warm and humid days are expected before
temperatures begin to trend back toward seasonal normals.

The upper pattern across North America remains highly amplified,
with a trough around 115W and a ridge centered over the Great
Lakes region. The flow through the CONUS will begin to weaken the
next few days as energy begins to lift northeast out of the
western trough. That will result in the main westerlies
consolidating across Canada and the northern CONUS into a slowly
progressive flow regime by the middle of the upcoming work week.

After a couple more unseasonably warm days, temperatures will
trend downward to near normal by mid-week, and possibly to a
little below normal by next weekend. Precipitation amounts will
be heavily dependent on what falls with the frontal system
crossing the area early to mid-week. Given the high moisture
content of the air mass, at least some areas are likely to end up
with above normal rainfall. But it`s also possible some areas will
miss out on much of the rain. There will also be another
opportunity for rain late in the week.
&&

.SHORT TERM...Tonight and Sunday
Issued at 208 PM CDT Sat Sep 23 2017

Main forecast challenge remains on temperatures as synoptic
conditions are not expected to change much over the next 24 hours.

The 19z MSAS surface analysis indicated an area of high pressure
located over the eastern Great Lakes region, while a quasi-
stationary front stretched from the MN arrowhead southwest into
the central Plains. Visible satellite imagery showed only
scattered fair weather cumulus clouds across northeast WI, with
any precipitation situated along and west of the frontal boundary.
Temperatures were again unseasonably warm with several records
likely to be tied or surpassed.

Not much change is expected in the overall, highly-amplified
pattern with a deep upper trough over the western CONUS and an
upper ridge over the eastern CONUS. This keeps northeast WI locked
in a southerly flow through the end of the weekend with
unseasonably warm and humid conditions. The northern edge of the
quasi-stationary front may edge east just enough tonight such that
a few showers/thunderstorms would reach northwest WI and impinge
upon north-central WI through the night. Therefore, may mention a
slight chance pop for parts of Vilas county, while the rest of the
region stays dry, muggy and mild. There could be some patchy fog
once again, mainly over the north and along the lakeshore
including the nearshore waters. Min temperatures to primarily
settle into the middle 60s.

On Sunday, the quasi-stationary front edges back to the west, thus
a dry forecast is expected across northeast WI under mostly sunny
skies. Another unseasonably warm and humid day is on tap, although
temperatures aloft do cool a couple of degrees. Look for max
temperatures to range from the lower 80s near Lake MI, to the
middle 80s north and upper 80s south.

.LONG TERM...Sunday Night Through Saturday
Issued at 208 PM CDT Sat Sep 23 2017

The models were in fairly good agreement on the timing of the
frontal system crossing the area, though they were perhaps a
little slower than previous runs. Given the very moist air mass in
place ahead of the front, opted to include thunder in the Wx grids
until the front clears the area.

After a period of cooler and much drier weather mid-week, the
chance for rain will return as shortwave energy digs through the
area and into the large scale trough that will begin shifting east
of the region by that time. The dynamics look much stronger at
that time, but the available moisture won`t be nearly as high as
with the initial frontal system.

Overall, the forecast initialization grids generated from a
broad-based blend of guidance products looked reasonable and no
significant changes were necessary.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1149 AM CDT Sat Sep 23 2017

Mainly VFR conditions to persist over the next 24 hours, other
than some patchy late night fog which could lower vsbys into the
MVFR range. The lake breeze has already passed through MTW with an
east-southeast wind through the afternoon. The rest of the region
will see steady southwest winds and unseasonably warm conditions
as high pressure remains parked to our east. Only thing to add was
adding some LLWS to the RHI TAF site for later tonight as winds
just above the surface could reach 30 knots.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SYNOPSIS.......Skowronski
SHORT TERM.....Kallas
LONG TERM......Skowronski
AVIATION.......Kallas



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