Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 251934
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
234 PM CDT Sun Aug 25 2019

Forecast discussion for routine afternoon forecast issuance

.SYNOPSIS...
Issued at 234 PM CDT Sun Aug 25 2019

Scattered showers and thunderstorms at times through Monday
night, blustery and mild on Tuesday, then windy and much cooler
Wednesday.

Slow progression of the large scale pattern is expected for the
next few days as an upper trough pushing into the area from the
west undergoes strong amplification. The trough will slow mid-
week as it closes off into an upper low over western Ontario. The
bulk of the energy within the trough will lift toward northeast
Canada late in the week, leaving weakening cyclonic upper flow
across the area.

The main precipitation event will occur with the frontal system
crossing the area early in the period with only a few rounds of
scattered light showers are expected thereafter. The result will
probably be near to slightly below normal amounts for most
locations. Despite day-to-day temperature variations due to the
passage of individual weather systems, readings will probably end
up near of slightly below normal for the period as a whole.
&&

.SHORT TERM...Tonight and Monday
Issued at 234 PM CDT Sun Aug 25 2019

The latest RAP analysis and satellite/radar imagery show a
sprawling high pressure system departing over the northeast conus
early this afternoon. Onshore southeast flow around this massive
high and daytime heating has produced another day of widespread
fair weather clouds across the region. Meanwhile, southerly flow
aloft ahead of shortwave energy moving over southeast Minnesota
and an MCV over eastern Kansas is pushing higher moisture into
southwest Wisconsin. A narrow band of showers is accompanying the
leading edge of the more moist air, and its possible that some of
these showers will reach into central Wisconsin late this
afternoon or early evening. Will add a slight chance. As shortwave
energy moves into the region, followed by an approaching cold
front late on Monday, forecast concerns revolve around timing
precip chances and whether a severe threat will develop.

Tonight...Weak moisture convergence on the leading edge of the
more moist air will lead to a chance of light showers or sprinkles
over central to north-central WI this evening. Not sure how far
east to carry slight chances of precip, as the moisture
convergence generally weakens through the night. After a brief
lull in the precip chances, the higher resolution guidance
indicates that showers will expand over northern Illinois into
southeast Wisconsin overnight, which will then approach east-
central WI by early Monday morning. No firm consensus on this
scenario, but given the showers over Illinois this afternoon,
think this is a reasonable scenario. Lows will be warmer and
mostly range from the low 50s near the U.P. border to the low 60s
over the southern Fox Valley.

Monday...Details remain murky in general.  Many of the higher
resolution models indicate the MCV over eastern Kansas will lift
northeast across eastern Wisconsin during the day. If this occurs,
marginal severe weather chances would become even lower.
Otherwise, much of central and northern Wisconsin stand a decent
bet of remaining dry during the morning. With 400 to 600 j/kg of
cape moving in from the west during the afternoon ahead of a cold
front, chances for thunderstorms will gradually increase across
central and north-central WI. Deep layer shear will also be
increasing into the 30-35 kt for thunderstorms to work with if any
can develop. But with the cloud cover and potential for rain with
the MCV, it is possible that thunderstorms will hold off into the
evening with the approaching front. Temps will be similar to
todays readings, though could be cooler over eastern WI if rain
moves in during the morning.

.LONG TERM...Monday Night Through Sunday
Issued at 234 PM CDT Sun Aug 25 2019

The primary change in the guidance since yesterday has been to
pull back significantly on the precipitation amounts during the
next 36 hours. Timing has slowed a little as well.

The decrease in QPF seems to primarily be related to the speed
with which the primary forcing with the frontal system pushes
through the area, and the fact it is now arriving well after dark.
PWATs are still forecast to rise to AOA 1.5" for a time, so brief
heavy rain is possible with the stronger convection. Although
storm motion may be nearly parallel to the front, the front is
expected to remain progressive. The main hydro issue will probably
be ponding of water if the heavy rain occurs in urban areas.
Gusty winds will be possible with the storms, with the potential
for severe being limited at best.

The default forecast initialization grids based on a broad-based
blend of guidance products seemed reasonable for temperatures. In
addition to QPF adjustments toward the latest guidance, also
adjusted PoPs up some as the upper trough settles into the area
mid-week.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1203 PM CDT Sun Aug 25 2019

Another day with widespread fair weather clouds across the
region. A period of broken clouds looks likely away from Lake
Michigan until mid-afternoon. Then a storm system remains on
track to impact the region from late tonight into Monday, but
details remain murky. It appears that the system will impact the
area in pieces. The first piece may pass over the Fox Valley and
Lakeshore areas in the morning, with rain and isolated storms, and
mvfr cigs/vsbys. More showers and storms then look possible
across much of the area from late afternoon into Monday night.
&&

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

$$

SYNOPSIS.......Skowronski
SHORT TERM.....MPC
LONG TERM......Skowronski
AVIATION.......MPC


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