Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 060446

Area Forecast Discussion
National Weather Service Green Bay WI
1046 PM CST Tue Dec 5 2017

Updated aviation portion for 06Z TAF issuance

Issued at 223 PM CST Tue Dec 5 2017

Seasonably cold weather with snow showers and flurries at times
is expected through at least early next week.

The large scale pattern has transitioned to having strong ridge
along the West Coast and a deep trough centered over the Great
Lakes region. Changes during the forecast period will be
confined to relatively modest fluctuations in amplitude and the
exact position of the eastern North America trough.

Temperatures are likely to run 4-8 F degrees below normal into
the upcoming weekend. A brief moderation is possible late in the
weekend into early next week as the eastern trough temporarily
loses a little amplitude. Reamplification of the trough, and a
turn to even colder temperatures, will probably occur at the end
of the forecast period and beyond.

Disturbances rotating through the long-wave trough will result in
scattered light precipitation at times. Moisture will be limited,
so the total precipitation for the period is likely to end up
below normal. The exception could be the Lake Superior snowbelt,
where the flow regime will favor lake-effect snow showers.

.SHORT TERM...Tonight and Wednesday
Issued at 223 PM CST Tue Dec 5 2017

The latest RAP analysis and satellite/radar imagery show an
intense area of low pressure lifting into northern Ontario early
this afternoon. Base of the longwave trough now swinging through
the southern Great Lakes with drier air punching northeast over
eastern Wisconsin. Winds have perked up a little this afternoon
after a lull this morning, with a few gusts reaching 40 to 45 mph
from the Fox Valley to the Lakeshore. Clouds are hanging tough
over northwest Wisconsin with widespread flurries and brief snow
showers impacting central and north-central Wisconsin. Some of
these relatively stronger snow showers also brought down strong
gusty winds from Wisconsin Rapids to Wausau. Think these snow
showers will persist for the rest of the afternoon and may make a
run at the Fox Valley. As the shortwave exits by early this
evening, think snow showers/flurries will dissipate somewhat. As
for the wind advisory, gusts have been just below advisory levels
(45 mph), but its too close to take down, especially with the
sunshine over eastern WI. Will keep the advisory going, and should
see winds subside after sunset. The gusty winds and snow shower
trends are the main forecast concerns.

Tonight...The strong area of low pressure will continue to spin
over far northern Ontario. The pressure gradient will remain tight
across the region, though should see winds subside somewhat, with
gusts to around 30 or 35 mph through the night. May see a break in
the snow showers/flurries over central & north-central WI this
evening. Then the next shortwave trough over northern Minnesota
will rotate through the region from late evening through
overnight. Deeper moisture will slide from northwest to southeast
behind the shortwave, with saturation depth growing sufficiently
to support light snow showers and flurries, mainly northwest of
the Fox Valley by morning. Accumulations should remain below an
inch, but did increase precip chances after midnight. Cold and
blustery with lows ranging from the low teens north to near 20
degrees by the Lake.

Wednesday...The shortwave trough will exit eastern Wisconsin
during the morning. Though forcing will have shifted to the east,
deep cyclonic flow will remain across the region with various
layers saturated up through 500mb. This appears to be a pretty
good recipe for occasional snow showers and flurries under mostly
cloudy skies or overcast conditions. Will show the highest precip
chances over northern WI. Winds will remain breezy, with highs
ranging from near 20 in the north to upper 20s near the Lake.

.LONG TERM...Wednesday Night Through Tuesday
Issued at 223 PM CST Tue Dec 5 2017

The overall weather scenario for the next week is fairly simple.
Disturbances rotating through the eastern North America long-wave
trough will result in periods of snow showers and flurries. They
will be most numerous/frequent in the Lake Superior snowbelt, but
will affect the entire area to at least some extent. The specifics
of timing and location are difficult to discern. At this point, it
looks like one round could occur Wednesday night, especially
across the north. Another round is possible Friday into Friday
evening, and that appears to have a better chance of affecting the
entire area.

The timing of the lake-effect in the Lake Superior snowbelt is
also tough to pin down. But the cold cyclonic upper flow and
favorable looking low-level trajectories will likely result in at
least several inches of snow in the snowbelt during the period.

Given the cold temperatures and potential for snow showers, it is
possible a light snow cover could gradually begin to become
established across the region. Guidance temperatures look okay for
now, but could require downward adjustment (especially at night)
if a snowcover becomes established.

.AVIATION...for 06Z TAF Issuance
Issued at 1046 PM CST Tue Dec 5 2017

West winds will continue to gust to 20 to 30 knots for much of the
TAF period. Shortwaves in the cyclonic flow over the western Great
Lakes will bring periods of light snow showers and flurries to the
TAF sites through the period. The best chance will be across
northern Wisconsin given better moisture. Conditions will
generally bounce between MVFR and VFR with snow showers, with IFR
possible at times across the far north.

Issued at 223 PM CST Tue Dec 5 2017

A Gale Warning remains in effect through midnight for the Bay and
6 am for the Lakeshore. Sustained west winds of 20 to 30 knots
with gusts of 40 knots can be expected through this evening, then
winds will gradually subside overnight. Gusts to 25 kts will
likely continue on Wed into Thu, so a small craft advisory may be
required following the end of the gale warning.



LONG TERM......Skowronski
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