Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 291756

Area Forecast Discussion
National Weather Service Green Bay WI
1256 PM CDT THU SEP 29 2016

Updated aviation portion for 18Z TAF issuance

Issued at 304 AM CDT Thu Sep 29 2016

Dry and warmer with plenty of sunshine today, then more clouds
with rain chances returning, especially to east-central Wisconsin.

The main westerlies are now primarily across Canada, with the
remnants of a southern stream upper trough in the form of a cut-
off cyclone over the lower Ohio Valley. The cut-off will slide a
little farther south today, then return north the next several
days. The cut-off will finally get kicked east of the area early
next week as the westerlies increase downstream from a strong
trough developing out west.

A cool Canadian air mass settled into the area the past couple
days. But now that the area is removed from the main westerlies,
little change in air mass is anticipated until next week. The air
mass across the area will continue to modify, and changes in
cloud cover will play a substantial role in daily temperature
variations. Temperatures will be a few degrees above seasonal
normals today, then be tempered a couple days (especially in the
east) due to widespread clouds. Readings should then return to
above normal for the rest of the period. Precipitation chances
will be tied to the cut-off, but given the gradual weakening of
the cyclone, amounts are likely to end up below normal for the

.SHORT TERM...Today...Tonight...and Friday
Issued at 304 AM CDT Thu Sep 29 2016

Quiet weather is expected today, through northeast winds will be
somewhat gusty over the east. The main change to the forecast
involved adjusting PoPs to account for the northward return of the
cut-off. Guidance has trended faster in returning the system,
through there is still some spread in terms of timing when
precipitation from the system will edge back into the area from
the southeast. Trended forecast toward the 00Z GFS and ECMWF,
which had support from the SREF and GFS ensembles. Stayed fairly
close to initialization grids based on a broad-based blend of
guidance products, though tweaked those some based on expected
cloud distribution and local effects.

.LONG TERM...Friday Night Through Wednesday
Issued at 304 AM CDT Thu Sep 29 2016

Precipitation chances this weekend are the main forecast concerns in
this part of the forecast.  Continued to use a blend of the

Friday night through Saturday night...Upper level low pressure will
slowly move from the Ohio Valley to central lower Michigan during
this period.  With ample Atlantic moisture rotating on the northern
periphery of the low across much of central and eastern portions of
the state, should see occasional showers, most numerous over eastern
WI.  Mid-level moisture will scour out at times, which could lead to
showers diminishing to drizzle, or breaks in the rainfall. With the
cloud cover, high temps will be slightly below normal.

Rest of the forecast...The low pressure system will finally start
moving east on Sunday over Lake Huron and into the eastern Lakes on
Sunday night.  Light precip chances will likely linger into Sunday
at least across eastern WI.  But in general, should see the shower
activity and clouds gradually diminish through the day.  High
pressure should lead to a period of nice weather on Monday and
Tuesday before the next widespread precip chance arrives on
Wednesday night.

.AVIATION...for 18Z TAF Issuance
Issued at 1256 PM CDT Thu Sep 29 2016

Skies were clear across most of the forecast area with the
exception of the lakeshore counties and far north central
Wisconsin, where there were MVFR ceilings at 1730Z. Think the
clouds in those areas will depart this afternoon. This will leave
the area mostly clear for the evening hours. Clouds, wrapped
around the surface low to the southeast, will move back into
eastern Wisconsin later tonight and slowly spread across the rest
of the area. Think that some MVFR fog may develop in northern
Wisconsin late tonight. Clouds will be scarce there and winds
light. Rain chances return to eastern Wisconsin during the
morning as the low moves toward Wisconsin.

Issued at 304 AM CDT Thu Sep 29 2016

Persistent modest pressure gradient on the northwest flank of the
cut-off will result in a prolonged period of northeast flow over
the lake and bay. The direction yields a favorable fetch for wave
growth, so extended the Small Craft Advisory through Friday night.



SHORT TERM.....Skowronski
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