Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 140430
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1030 PM CST Mon Nov 13 2017

Updated aviation portion for 06Z TAF issuance

.SHORT TERM...Tonight and Tuesday
Issued at 228 PM CST Mon Nov 13 2017

A surface ridge extended from a low in northern Illinois to Lake
Superior at 19Z. What happens overnight into Tuesday as the ridge
moves east is the main question during this part of the forecast.
As it drifts east tonight, winds shift to south and moisture
increases across the area. Expect areas of fog and low clouds to
reach central and north central Wisconsin during the night, and
freezing drizzle is possible during the late night and into Tuesday
morning. Bufkit time/height plot from the 12Z NAM showed more
moisture arriving sooner in central Wisconsin than what the 12Z
GFS indicated. The NAM is likely overdoing the low level moisture,
leading to lower forecast confidence, so have opted to downplay
freezing drizzle a little and not issue an advisory. Any freezing
precipitation will switch to liquid on Tuesday as temperatures
increase due to warm advection.

Lows tonight have been adjusted upward due to increasing clouds
and warm advection, and highs on Tuesday should be warmer than
today.

.LONG TERM...Tuesday Night Through Monday
Issued at 228 PM CST Mon Nov 13 2017

The main forecast concern is the potential for minor LES snow
accumulations over Vilas county Wednesday night, and impacts
from a potentially strong storm Friday into Saturday night.

Light rain will increase Tuesday night as a 30-35 knot low-level
jet develops ahead of a cold front, and a short-wave trof and jet
streak approach the region. The rain should end from west to east
late Tuesday night into Wednesday morning as the cold front exits
the forecast area. Scattered lake effect snow showers should
develop over far north central WI in the afternoon as cold
northwest winds develop in the wake of the front.

One significant change to the forecast is an increase in pops and
snowfall over far north central WI (especially Vilas county) on
Wednesday night. Low-level wind trajectories (north-northwest)
and Lake-850 mb delta-T`s (14-17 C) become more favorable for
lake-effect snow showers, so have bumped pops up to likely in
northwest Vilas county, and increased snowfall totals to 1-2
inches there.

High pressure will bring a brief period of dry weather on
Thursday and early Thursday night.

Models still depict a fairly potent low pressure system moving
through the western Great Lakes late in the week, but have backed
off on the strength of the low a bit. The 12z GFS is up to 12
hours faster than the ECMWF, but the track (through southern Lake
Michigan) and strength are similar. If the weaker solution
verifies, it is unlikely we would see significant snowfall
accumulations in GRB CWA, and the threat of a high end Gale event
would be low. However, several GFS ensemble members still show
the low deepening to 980 mb or lower as it shifts east/northeast
of the region, so the possibly of an intense system still exists.
Most of the precipitation is expected to occur Friday into Friday
night, with a prolonged period of lake-effect snow showers
possible in far northern WI Saturday into Sunday. Low-level wind
trajectories may be too westerly for significant LES accumulations
on this side of the MI/WI border.

Temperatures will start out near normal, then drop back below
normal after the strong storm exits this weekend.
&&

.AVIATION...for 06Z TAF Issuance
Issued at 936 PM CST Mon Nov 13 2017

Conditions expected to deteriorate overnight across the state from
southwest to northeast. An area of IFR cigs and MVFR vsbys from
Iowa into southwest and western Wisconsin continue to work
northeastward late this Monday evening. These lower cigs and vsbys
will spread over central Wisconsin by midnight and continue to
fill over the rest of the region overnight and linger into
Tuesday. Surface and road temperatures will support a mix of
drizzle and freezing drizzle until the boundary warms up enough
later Tuesday morning. Primary period of measurable precipitation
toward Tuesday night as a frontal boundary tracks across the
state.
&&

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

$$

SHORT TERM.....MG
LONG TERM......Kieckbusch
AVIATION.......TDH



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