Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 241743
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1243 PM CDT Wed May 24 2017

Updated aviation portion for 18Z TAF issuance

.SHORT TERM...Today...Tonight...and Thursday
Issued at 315 AM CDT Wed May 24 2017

The upper low over northern Missouri was still producing upper
diffluence, which was combining with low level warm advection to
produce showers over all but northcentral Wisconsin early this
morning. The upper low will move further away today and the 850mb
low over northern Illinois will move southeast towards the Ohio
Valley. Therefore, we expect the showers to diminish from northwest
to southeast today. The clouds and showers should keep temperatures
5 to 10 degrees below normal.

Cloudy skies likely to hold tonight with cyclonic upper flow and
no real good push of dry air to be found. If there is any clearing,
some fog might be possible. The clouds will keep low temperatures
around 5 degrees above normal. Thursday should be a little warmer
as a weak surface high builds in and upper heights rise. Highs
should be close to normal for this time of the year.

.LONG TERM...Thursday Night Through Tuesday
Issued at 315 AM CDT Wed May 24 2017

The primary weather feature to watch in the coming days will be
the movement of a closed upper low from southern Saskatchewan
Friday to the northern sections of the Great Lakes by Memorial
Day. This upper low, coupled with the passage of a surface low
(late in the weekend) and a shortwave trough rotating around this
upper low (early next week) will keep northeast WI weather
unsettled for much of the extended forecast. Trying to time the
best chance of showers is the biggest challenge. Temperatures are
expected to be close to normal this weekend, then fall below
normal for the first part of next week.

Despite having an upper ridge overhead Thursday night, clouds will
be on the increase ahead of a mid-level shortwave trough moving
into the Upper MS Valley. In addition, a cold front is forecast to
approach the Upper MS Valley after midnight. Therefore, will have
thickening clouds in the forecast, along with a small chance of
showers reaching central WI during the overnight hours. Min
temperatures should be fairly uniform with most locations in the
middle 40s to around 50 degrees. The shortwave trough and
weakening cold front reach the western Great Lakes on Friday, so
cannot rule out a chance of showers across all of northeast WI.
This precipitation appears to be on the light side, so no negative
impacts on areas rivers of streams that are running high. The
southerly winds ahead of the cold front will pull warmer air into
WI with max temperatures in the lower 60s near Lake MI, upper 60s
to around 70 degrees north and lower 70s south.

Northeast WI appears to reside between systems Friday night as the
initial shortwave trough and cold front dissipate and the next
system of interest to still be located to our west over the
northern/central Plains. Other than a stray evening shower, the
rest of Friday night will be dry, so have removed any pops from
the overnight hours. Min temperatures will drop into the upper 40s
north-central WI, lower to middle 50s elsewhere. By Saturday, the
aforementioned upper low is progged to be located near Lake
Winnipeg with the main upper trough pivoting through the northern
Plains toward the Upper MS Valley. Models are still fine-tuning
the timing of this trough with a slower trend noted on the latest
00z model run. This slower movement may bring a smaller chance of
showers/slight chance of thunderstorms to the area than what was
advertised 24 hours ago. For now, prefer to focus any pops on
Saturday afternoon with a weak frontal boundary for lift and the
onset of cooler air aloft/mid-level forcing starting to increase
as the trough approaches. Temperatures will still be mild with
readings topping out in the upper 60s lakeside, lower 70s north-
central and lower to middle 70s elsewhere.

Chance of showers/possible thunderstorms would then carry into
Saturday night, but tend to diminish in coverage as we lose
daytime heating and better forcing shifts to the east. Models do
get into better agreement on timing of the trough across WI on
Sunday and provide favorable conditions for showers to redevelop,
along with a small chance of thunderstorms. Temperatures to cool a
bit due to thicker clouds/precipitation with readings in the
middle 60s north-central/near Lake MI, upper 60s to around 70
degrees elsewhere.

Precipitation chances will continue Sunday night into Memorial Day
as the upper trough slowly slides east and places northeast WI
under a cyclonic flow. Persistent west-northwest winds will also
usher cooler air into the region which will keep temperatures
below normal to start the week. Look for max temperatures on
Memorial Day to be in the lower 60s north-central/lakeshore,
middle to upper 60s elsewhere. We may not get out of the rain
chances until the end of Tuesday as the models send additional
pieces of shortwave energy through the departed upper trough,
along with the passage of another cold front. Temperatures will
remain 5 to 10 degrees below normal on Tuesday with readings a
degree or two cooler than Monday.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1238 PM CDT Wed May 24 2017

Lower-end MVFR, IFR, and even some LIFR (near the lakeshore)
conditions prevailed at mid-day. Ceilings were generally running
lower than forecast by most of the guidance products. Expect a
gradual improvement during the afternoon. Winds will diminish
tonight, but plenty of low-level moisture will linger. Those sites
that initally lose the low clouds could have some fog and stratus
reform. It will probably take until tomorrow (when the upper-level
ridge axis begins to shift into the area) for a more significant
improvement to occur.
&&

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

$$

SHORT TERM.....RDM
LONG TERM......Kallas
AVIATION.......Skowronski


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