Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 231925
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
225 PM CDT FRI SEP 23 2016

Forecast discussion for routine afternoon forecast issuance

.SYNOPSIS...
Issued at 205 PM CDT Fri Sep 23 2016

Another round of rain likely this weekend, though with rainfall
totals much lighter than the past few days. Generally above
normal temperatures, though with a short cool-down early next
week.

Despite a rather blocky looking split in the main westerlies
currently over the intermountain West, the flow across North
America is slowly progressive. The progression is expected to
continue throughout the forecast period, though with a gradual
loss of amplitude. That will result in the upper trough now over
the Great Basin crossing the area this weekend, to be followed by
broad ridging building across the area for much of next week.

Temperatures will remain modestly above seasonal normals through
the weekend, then briefly cool down to slightly below normal
levels in the northwest flow behind the departing upper trough
early next week. Readings should rebound back to above normal
levels later next week as large scale ridging shifts into the
area. The primary opportunity for precipitation will be tied to
the passage of the upper trough through the area during the
weekend. Available moisture and the dynamics with the trough
should be sufficient to result in AOA normal precipitation for
the period, though amounts are unlikely to be sufficient to cause
another round of flooding.
&&

.SHORT TERM...Tonight and Saturday
Issued at 205 PM CDT Fri Sep 23 2016

Low impact weather expected in the short term. Current
mesoanalysis shows the 925mb front that had been plaguing our CWA
the past few days pushing south into southern Wisconsin. With
little in the way of any forcing mechanisms in the area and
ridging in the upper levels, not much weather-wise to contend with
for today. Some lingering clouds continue to sit over central
Wisconsin due to moisture trapped between 850-700mb, but over
north central Wisconsin clouds cleared out and it was a beautiful
day. Closer to the lakeshore, clouds steaming in off of Lake
Michigan on easterly winds kept this area in and out of clouds.
Further west in MN into the Northern Plains, an area of showers
and thunderstorms developed in response to a 850mb frontal system.
This this front will stay out of NE WI through the rest of today
and hung tight to the dry and quiet weather through the early
overnight.

As the 850mb warm front moves towards NE WI overnight, there is a
slight chance for showers. There isnt any other forcing to help
the front along, and WAA along the front is weak, so not overly
excited about precip chances. Kept the slight chance PoPs but
trimmed the northern edge back a little since low level moisture
will be slow to edge northward and will be too dry for rain.

Low level moisture will eventually increase Saturday morning.
Continued slight PoPs through around midday Saturday as the 850mb
front moves overhead. By Saturday afternoon, we lose any source
for forcing and then strong upper level ridging takes over, so
dry forecast looks good. Clouds should linger through the day
though as moisture in the mid to low levels pools near and just
behind the front. Overall, not a bad day and wouldnt be surprised
if we stayed dry for the entire period.

.LONG TERM...Saturday Night Through Friday
Issued at 205 PM CDT Fri Sep 23 2016

During the past 24 hours, the models have come into much better
agreement on the passage of the western upper trough across the
area. The most favored time for precipitation will be Sunday
through Sunday evening. Structured forecast with likely PoPs
shifting east across the area during this time. Instability will
be limited, so kept thunder out of the forecast as the leading
edge of the precipitation advances into the area Saturday night.
Then went with primarily showers with just a chance of thunder as
the main rain band crosses the area Sunday into Sunday evening.
There will likely be a break in the showers between the main rain
band and a secondary area of precipitation dropping southeast as
additional energy digs southeast on the backside of the upper
trough. But given uncertainty in timing, this is reflected in the
forecast as a period of lower PoPs rather than an outright dry
period.

No significant changes were necessary to the extended forecast
initialization grids based on a broad blend of guidance products.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1100 AM CDT Fri Sep 23 2016

Current MVFR clouds in east central Wisconsin should rise to VFR
levels later this afternoon. Otherwise, skies will range from
mostly sunny north to partly to mostly cloudy in central and
eastern Wisconsin. Removed PoPs for this afternoon since there is
very little in the way of forcing and moisture is decreasing
across the area.

Quiet conditions will continue overnight with high clouds
scattering out for a time. However, a front approaching from the
west will bring cloud cover back in Saturday morning from west to
east. Fairly confident cigs will lower to MVFR levels, with IFR
cigs possible, mainly in central Wisconsin. Showers may also work
their way into cental and east central Wisconsin later Saturday
morning or early afternoon, however low confidence at this time
and left rain chances out of the TAFs for now. If showers do
develop, rain should remain light.
&&

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

$$

SYNOPSIS.......Skowronski
SHORT TERM.....Allen
LONG TERM......Skowronski
AVIATION.......Allen



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