Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 221936

Area Forecast Discussion
National Weather Service Green Bay WI
236 PM CDT SAT OCT 22 2016

Forecast discussion for routine afternoon forecast issuance

.SHORT TERM...Tonight and Sunday
Issued at 235 PM CDT Sat Oct 22 2016

Main forecast concern will be the extent of light precipitation
event on Sunday, primarily across the north.

The 19z MSAS surface analysis showed weak high pressure ridge from
Lake MI south to the Ohio River Valley and from the Upper MS
Valley south into the central Plains. A weak area of low pressure
was located over the northern High Plains. Visible satellite
imagery indicated most of the low clouds from this morning has
shifted east, however some stubborn clouds lingered over far
northeast Wisconsin. Closest precipitation was over North Dakota
and it is this shower activity that is headed in our direction.

The Upper MS Valley surface ridge to move through the Great Lakes
tonight, bringing light winds to the area. We will see a band of
mid/high clouds pass through as WAA continues through the night.
Have held off on patchy fog wording for now, but may need to
monitor as temperatures fall to near the dew points late tonight.
Min temperatures to range from the lower to middle 30s north-
central, middle to upper 30s central/far northeast and lower 40s
east-central WI.

Models track the weak surface low across central Wisconsin Sunday
morning and quickly send this low into southeast Lower Michigan by
00z Monday. A cold front will accompany this surface low with
light/variable winds becoming north and increasing to 10 to 15 mph
in the afternoon. There will also be a modest shortwave trough
pushing across northern sections of the Great Lakes on Sunday.
Expect clouds to increase/thicken through the day with
precipitation chances limited to northern Wisconsin where stronger
mid-level forcing to exist with the passage of the shortwave
trough. Max temperatures to range from the lower 50s north-
central, upper 50s to lower 60s south.

.LONG TERM...Sunday Night Through Saturday
Issued at 235 PM CDT Sat Oct 22 2016

The main forecast concerns revolve around a strong low pressure
system that is expected to impact the region Tuesday night into
Wednesday night.

A short-wave trof will shift east of the forecast area by Sunday
evening, with associated subsidence providing for a dry forecast.
Dry and seasonable weather is anticipated Monday and MOnday night,
as Canadian high pressure resides over the region. Clouds should
be on the increase Monday night, as low pressure slowly
approaches from the plains.

Models are struggling a bit with the timing of precipitation
onset, with the NAM/GEM bringing rain into central WI on Tuesday,
and the GFS and ECMWF holding off until late Tuesday night.
Will defer to the preferred model blend for now, but it seems
clear that the main brunt of the system will impact the region
late Tuesday night through Wednesday evening, as an upper level
low moves through. The upper system, combined with significant
isentropic lift, will provide strong dynamic forcing to produce
heavy rainfall in a moist air mass (PWATs 0.75 to 1.00 inch).
Total rainfall for the event may reach 1.5 to 2 inches over
central and east central WI. H8 temperatures, and low-level
thicknesses and wet-bulb temperatures, support a potential for
mixed rain and snow over parts of north central and far northeast
WI, especially on Tuesday night and Wednesday night. The
potential for accumulation is minimal due to mixed precipitation,
and warm surface and soil temperatures. Precipitation should exit
the region early Thursday.

Medium range models suggest a cold frontal passage early in the
weekend, but timing is very sketchy. The front should bring a
chance of showers on Saturday.

.AVIATION...for 18Z TAF Issuance
Issued at 1229 PM CDT Sat Oct 22 2016

VFR low clouds over eastern Wisconsin will shift east early this
afternoon leaving mainly clear skies for the rest of the daylight
hours. A weak area of low pressure over the northern High Plains
is forecast to move into the Upper MS Valley toward daybreak and
bring some mid/high clouds to northeast Wisconsin. There also may
be some patchy fog around that could lower vsbys into the MVFR
range. This low pressure is expected to move across central
Wisconsin Sunday morning and drag a cold front through the region.
Winds will switch to the north and increase into the 10 to 15 knot
range (with higher gusts) Sunday afternoon. Rain chances appear to
be limited to northern Wisconsin Sunday afternoon associated with
the passage of a mid-level shortwave trough passing through the
northern Great Lakes. Even with precipitation in the vicinity,
expect VFR conditions to prevail through Sunday.



LONG TERM......Kieckbusch
AVIATION.......AK is the U.S. government's official web portal to all federal, state and local government web resources and services.