Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 132029
AFDGRB

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

Forecast discussion for routine afternoon forecast 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 18Z TAF Issuance
Issued at 1154 AM CST Mon Nov 13 2017

Mainly VFR conditions prevailed across the area at midday as a
surface ridge extended from a surface high in northern Illinois
to western Lake Superior. Low level moisture will increase across
the area in return flow as the ridge moves east. Expect flying
conditions to deteriorate in central and north central Wisconsin
during the night, especially after about 06Z. IFR ceilings in
stratus already covered all but a small part of Iowa at 18Z and
visibility varied widely in BR/FG as well. Would not be surprised
if freezing drizzle reached the western part of the forecast area
late tonight, but confidence level was not high enough to include
it in TAFs. Any freezing precipitation problems should end during
the morning on Tuesday as surface temperatures warm, but low
clouds and fog will keep conditions from improving to VFR.
&&

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

$$

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



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