Area Forecast Discussion
Issued by NWS Green Bay, WI

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223
FXUS63 KGRB 162021
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
221 PM CST Thu Nov 16 2017

Forecast discussion for routine afternoon forecast issuance

.SHORT TERM...Tonight and Friday
Issued at 221 PM CST Thu Nov 16 2017

The latest RAP analysis and satellite/radar imagery show high
pressure moving across Wisconsin early this afternoon. Low clouds
remain stubborn so far today, though partial clearing has taken
place south of route 29. Think clearing will continue to slowly
lift north for the rest of the afternoon. Meanwhile, the jet
stream is already bringing in broken cirrus into western Wisconsin
ahead of the next system. Precip chances and potential impacts
from this system are the main forecast concerns.

Tonight...The high pressure system will exit to the east over the
central Great Lakes. As this occurs, winds will shift to the
southeast, which should continue to cause the low stratus to lift
north over northern WI through the early evening hours. However,
clouds over Lake Michigan may also return west into eastern
Wisconsin. Combined with a thick blanket of cirrus arriving this
evening, will show increasing clouds across areas where skies
cleared for a time. Progged soundings indicate that ample mid-
level dry air will likely hold off precip for most locations
overnight. Some models create a band of precip over northern WI
after midnight despite this dry air, and suppose its possible
that a few snow flakes could survive the trip to reach the ground.
So left a small chance in the forecast, with a tenth or two of
accum possible. As a result, think the threat of impacts to the
roads is rather minimal.

Friday...A stronger push of deeper moisture will occur from west
to east during the morning hours. The mid-level dry wedge will
become significantly eroded as the moisture arrives, with wet
bulb temps aloft rapidly rising into the 3-5C range. This should
lead to a transition into more of a rain/drizzle scenario by mid
to late morning. There may be a brief few hour window when surface
temps are at or just below freezing with liquid precip falling,
which could result in hazardous roadways. Because of such a narrow
window and uncertainty about timing and precip type, will issue
an SPS to draw more attention to this potential hazard. As precip
moves across central and into eastern WI by late morning through
the afternoon, temps should warm into the mid 30s to low 40s.

.LONG TERM...Friday Night Through Thursday
Issued at 221 PM CST Thu Nov 16 2017

The main focus continues to be the beginning of the extended
period for potential wintry mix and high winds through Saturday.

Colder air will move into the region after midnight Friday night.
Initially, primarily drizzle and rain are expected across the
region, with a transition over to snow in the north through the
morning hours. Mixed precipitation is likely across central
Wisconsin in the morning while the Fox Valley keeps mostly rain
chances. Bufkit soundings suggest a brief chance to see mixed
precipitation reach the Fox Valley in the afternoon. There will be
a small chance to see some light snow across the area into the
evening, but currently favor dry air moving in more quickly in the
end of this system, thus kept pops minimal in the evening for
Saturday. The last of the snow showers will be in the far north as
some lake enhancement continues in far northern Wisconsin. Models
have backed off some on the wind speeds over land Saturday, with
gusts closer to around 25 to 30 knots likely Saturday afternoon
and evening.

Drier conditions follow all the active weather on Sunday into
Monday. Models currently suggest the next chance of precipitation
arriving Tuesday into Wednesday as we return to a more meridional
flow, although timing confidence is low at this time.

Temperatures during this time will fluctuate with the passing
systems, with highs hovering in the 30s Saturday, dropping
towards the 20s Sunday, 40s on Monday, and then returning to the
20s and lower 30s through the rest of next week.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1119 AM CST Thu Nov 16 2017

Low clouds remain stubborn late this morning, and delayed clearing
trend until late this afternoon, though some taf sites over
eastern WI will reach vfr before this occurs. Considerable
uncertainty in regards to the return of low clouds and
precipitation exists late tonight into Friday. As low pressure
moves across the northern Plains, winds will shift to the
southeast, and could return mvfr stratus across much of the
region. If and when this occurs is difficult to pinpoint, but a
reasonable guess would be from late evening into the overnight.

A chance of light precip looks to arrive late overnight into
Friday morning from west to east. Precip may start out as a light
snow/freezing drizzle mix, before transitioning to rain/drizzle.
Abundant mid-level dry air should keep precip very light and may
not pose a hazard. The time period of most concern is from 13-16z
Fri.
&&

.MARINE...
Issued at 221 PM CST Thu Nov 16 2017

Another low pressure system could bring additional
chances for gale force winds, first from the south on Friday ahead
of the system, then from the northwest behind the system on
Saturday and Saturday evening. Confidence is high enough to
upgrade to a gale warning for Lake Michigan, but not for Green Bay.
&&

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

$$

SHORT TERM.....MPC
LONG TERM......Uhlmann
AVIATION.......MPC
MARINE.........MPC



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