Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 281744
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1244 PM CDT WED SEP 28 2016

Updated aviation portion for 18Z TAF issuance

.SYNOPSIS...
Issued at 347 AM CDT Wed Sep 28 2016

Still fairly cloudy and cool today, with showers--especially in
the East. Sunnier and warmer for the end of the work week.

The northern branch of the flow comprising the small split in the
main westerlies over eastern North America will become dominant as
shortwave and jet drive eastward across northern Canada. That will
leave a seasonably deep upper cyclone cut-off from the main flow,
wandering around the region for several more days. It will
initially drift south as the strongest winds have swung onto the
western side of the system, but will likely return north this
weekend as the strongest winds rotate around to its east. The
remnants of the cyclone should finally get kicked east of the area
early next week as the westerlies increase downstream from a
strong trough developing over the West.

A cool Canadian air mass across the area will result in below
normal temperatures again today, but then readings are expected
to quickly rebound back to AOA normal for the rest of the period.
Precipitation chances will be tied to the movement of the
cyclone, as any rains from the new Western trough likely will hold
off until after the period. Given the slow weakening of the
cyclone, amounts are likely to end up below normal for the period.
&&

.SHORT TERM...Today...Tonight...and Thursday
Issued at 347 AM CDT Wed Sep 28 2016

Today will be similar to yesterday, though precipitation will not
be as widespread and have more of a lake-effect component.
Temperatures will also also probably be a bit warmer, as the air
mass will begin moderating.

A well defined convergence band has developed over Lake Michigan
as the cyclone center reforms to the south. The environment in
which the mid-lake shower band is occurring is very favorable for
waterspouts, so will continue to mention those in the grids/HWO
for this morning. Convergence lessens later today as a more
uniform northeast flow strengthens across the area, so confined
mention to the morning. Continued with likely PoPs in the east for
a time this morning to account for the lake band moving inland.

Sky condition late today and tonight is a bit of a challenge. The
consensus among the models was to have rapid clearing from the
northeast, starting already this afternoon. While that trend is
probably okay, am somewhat skeptical about how rapidly it occurs
in guidance products. Am afraid that fairly moist northeast flow
across lakes Superior and Michigan will make clouds a little
tougher to dislodge, so trended forecast toward a little slower
and less complete clearing, especially in eastern and north-
central Wisconsin.

More sun is expected Thursday, and temperatures should respond by
warming back to above normal. Went with max temps just a little
below a broad-based blend of guidance products, as by tomorrow
afternoon the northeast flow over the lakes will result in a
little cooling of temperatures.

.LONG TERM...Thursday Night Through Tuesday
Issued at 347 AM CDT Wed Sep 28 2016

The latest medium range guidance does not show much change over the
past day of model runs, and still advertise a return of the upper
low this weekend.  Models are in better agreement with the track of
this upper low, so will use a blend of the ecmwf and gfs for much of
this forecast.

Thursday night through Friday night...The upper circulation will be
spinning over the Ohio Valley on Thursday night.  Atlantic moisture
rotating around the low will try to edge westward into a dry high
pressure centered over the northern Mississippi Valley and into
southeast WI late.  Will increase cloud cover a tad.  The upper low
will slowly shift northward on Friday and Friday night bringing
potential of light rain to east-central WI on Friday and much of
northeast and north-central WI on Friday night.  No significant
changes to temps.

Rest of the forecast...The upper low will move into the central
Great Lakes on Saturday and Saturday night before slowly pulling
out.  Small chances of rain will therefore linger into this portion
of the forecast, highest over eastern WI.  Potential is there for
dry weather to resume on Sunday through Tuesday before the next
system arrives by the middle of next week.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1243 PM CDT Wed Sep 28 2016

Ceilings across the area were generally in the 2500 to 4000 foot
range at 17Z, and there were scattered showers. Models started to
bring drier air into eastern Wisconsin this afternoon, so have
showers ending, VFR ceilings by late today, then scattered clouds
for tonight through Thursday morning. Farther to the west,
conditions will improve a couple/few hours later than in the east.
Guidance indicated some reduced visibilities in central and north
central Wisconsin later tonight so have MVFR fog after midnight
dissipating around dawn. Expect mainly VFR conditions Wednesday
morning.
&&

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

$$

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



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