Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 240922
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
322 AM CST Fri Nov 24 2017

Forecast discussion for routine morning forecast issuance

.SYNOPSIS...
Issued at 320 AM CST Fri Nov 24 2017

Warm and rather windy today, then cooler (but still above normal)
for the rest of the holiday weekend. Mild and rather quiet
weather continuing next week.

A broad band of low-amplitude westerlies was across southern
Canada and the northern and central CONUS. The pattern is expected
to gain a little amplitude and become progressive. The strong
westerly component to the upper flow will result in above normal
temperatures. The primary storm track will remain to our north
across Canada. That`s unfavorable for generating an inflow of Gulf
moisture into the region, so only scattered light precipitation
is expected. Amounts are likely to end up below normal for the
period.
&&

.SHORT TERM...Today...Tonight...and Saturday
Issued at 320 AM CST Fri Nov 24 2017

A strong cyclone will track across central Ontario today.
Southwest flow in the warm sector of the system will bring very
mild air from the Plains into the forecast area, resulting in
highs 15-20 F degrees above normal. Mixing won`t be very deep as
is typical of WAA situations at this time of year, but winds will
probably still become gusty. The incoming air mass is actually
pretty moist, with 00Z RAOBS from the northern and central Plains
150-200% of normal. Steep mid-level lapse rates will also
overspread the area during the afternoon. So it`s likely that
showers will develop along/near the Pacific cool front that will
be crossing the area this afternoon and evening. But the coverage
of the showers is still in question. It will probably be greatest
in the north--closer to the parent cyclone. Kept PoPs across the
area generally in the chance category due to the coverage
concerns. A rumble of thunder isn`t even out of the question.

Cooler air will begin pushing into the area behind the front, but
incoming air mass has downsloped the Rockies and won`t be that
cold. Edged mins up a little for tonight. Trajectories and
temperature profiles will be marginal for snow showers in the
Lake Superior snowbelt overnight into Saturday. Will carry a
chance in the forecast, but any accumulation will be minor.

Edged temps toward a blend of top performing guidance products,
on Saturday, as that was a little warmer than the standard
forecast initialization grid.

.LONG TERM...Saturday Night Through Thursday
Issued at 320 AM CST Fri Nov 24 2017

The latest ensemble means and medium range models indicate that the
upper air pattern will evolve from northwest flow aloft to more of a
low amplitude split flow pattern across central North America next
week.  Plenty of model differences as this transition takes place,
so will use a blend of the gfs/ecmwf.

Saturday night through Sunday night...Clearing skies will be taking
place on Saturday evening as a surface ridge axis shifts east across
the area. This trend may occur a little slower than guidance is
indicating, due to a sharp inversion, which the met statistical
guidance also hints at as well.  Low pressure will be tracking north
of Lake Superior on Sunday and will push a weak cold front across
the region from late Sunday morning through the afternoon.  Upper
level dynamics as well as deeper moisture will remain over Lake
Superior and the Upper Peninsula, so think dry air will thwart any
attempts at precip. High pressure then returns on Sunday night,
which looks clear and seasonable.

Rest of the forecast...As the high pressure slides east of the area
and a cold front moves into the northern Mississippi Valley on
Monday, winds will shift to the south and draw in warmer air.  Highs
could be several degrees warmer than indicated by the multi-model
blend.  The front will move through on Monday night into Tuesday
morning.  Once again, the better dynamics will remain north of the
region, and the dry air may win out yet again.  Should see more
cloud cover along the front than the previous frontal passage on
Sunday.  Temps will fall back behind the front for Tuesday and
Wednesday.  Then a small chance of precip will arrive on late Wed
into Thu, when a southern stream low pressure system moves closer to
the region, at the same time as northern stream energy moves over
the northern Great Lakes.
&&

.AVIATION...for 12Z TAF Issuance
Issued at 320 AM CST Fri Nov 24 2017

LLWS will be the main aviation forecast concern for the start of
the 12Z TAF period. Winds around 2K ft will increase to nearly 60
knots today, so opted to keep LLWS in the TAFs through mid-day
despite some mixing and increasing surface winds. The next
concern will be ceilings behind the cool front tonight. Guidance
suggested MVFR cigs would push into at least north-central and
possibly central Wisconsin. Accepted that idea for now, though
confidence in that occurring is not high.
&&

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

$$

SYNOPSIS.......Skowronski
SHORT TERM.....Skowronski
LONG TERM......MPC
AVIATION.......Skowronski



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