Area Forecast Discussion
Issued by NWS Green Bay, WI

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413
FXUS63 KGRB 240927
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
427 AM CDT Sat Jun 24 2017

Forecast discussion for routine morning forecast issuance

.SHORT TERM...Today...Tonight...and Sunday
Issued at 426 AM CDT Sat Jun 24 2017

A strong upper low will move across the region
during the afternoon and evening hours. While there is good upper
support, moisture is somewhat lacking, as is the forecasted
instability. There should be lots of showers in the afternoon and
evening. With wet bulb zero heights of 6000` to 7000` and dry air
near the surface, small hail and gusty winds are likely. High
temperatures today will be around 10 degrees below normal. Cold
air funnels are not out of the question.

Showers and scattered thunderstorms should diminish after sunset, except
over northeast Wisconsin where showers could continue overnight. Lows
tonight should be 5 to 10 degrees below normal.

Sunday will have another upper trough move by during the afternoon
and evening with showers and some thunderstorms especially in the
afternoon and evening. Cold temperatures aloft and dry air near
the surface will allow for some gusty winds and small hail. High
temperatures will be 10 to 15 degrees cooler than normal.

.LONG TERM...Sunday Night Through Friday
Issued at 426 AM CDT Sat Jun 24 2017

The mean flow over the CONUS will undergo a transformation from a
western upper ridge/eastern upper trough (early in the week), to
a western upper trough/modest eastern upper ridge (late in the
week). While the models agree that temperatures will warm to or go
slightly above normal by next Thursday/Friday, precipitation
timing remains the main forecast challenge as models struggle with
the mean flow transition. Latest thinking is for a brief period of
dry weather Monday night into Tuesday night, then unsettled
weather returns for mid to late week especially as gulf moisture
gets pulled northward.

A cool, cyclonic flow will persist into Sunday night, along with
the passage of another shortwave trough. Even with the loss of
daytime heating and less instability, still anticipate decent
mid-level forcing through the night, thus a chance of showers will
continue through the night. Despite plenty of clouds around, the
air mass aloft is quite cool, thus min temperatures will be able
to dip into the middle 40s north-central WI, upper 40s central/far
northeast WI and lower 50s east-central WI. One more day of
cyclonic flow over the western Great Lakes region on Monday and
with daytime heating, expect another chance for showers/afternoon
thunderstorms to pop-up. Activity will again be scattered, so
there should be some dry hours in between the showers (i.e., not
washout). Max temperatures to be in the lower to middle 60s
north-central, mainly upper 60s elsewhere.

Any precipitation will end early Monday evening as the upper
trough shifts east, the upper ridge gets shoved toward the
northern/central Plains and upper heights build toward the Great
Lakes. Furthermore, an area of high pressure is forecast to build
into WI Monday night. Look for clearing skies, diminishing winds
and temperatures similar to Sunday night. Tuesday is still shaping
up to be a pleasant day across the forecast area as the high
pressure gradually shifts east-southeast into the eastern Great
Lakes/Ohio Valley. A return to southerly winds and onset of WAA
will bring a boost to temperatures. Under mostly sunny skies, look
for max temperatures to reach the lower 70s north-central/near
Lake MI, to the middle to upper 70s elsewhere.

As the weakening upper ridge reaches the western Great Lakes
Tuesday night, the mean flow will begin to shift to the west-
southwest and the models do bring a shortwave trough into the
Upper MS Valley by 12z Wednesday. The GFS is still a little faster
with this approaching system than the ECMWF, however the timing is
better than what was advertised 24 hours ago. Expect clouds to
increase Tuesday night with a chance of showers/thunderstorms
mainly after midnight. This shortwave trough would then move into
WI on Wednesday with a trailing cold front to push across the
Upper MS Valley. Look for an increasing threat for showers, with
enough instability to support a chance of thunderstorms across
northeast WI on Wednesday. Max temperatures for Wednesday will
continue to run a couple of degrees below normal with lower 70s
north-central/lakeshore, middle to upper 70s elsewhere.

Showers/thunderstorms are progged to continue into Wednesday night
as the cold front drives through WI and interacts with an unstable
atmosphere. Much too early to determine if any of these storms may
become strong to severe, just something to watch in the coming
days. The precipitation is expected to diminish later Wednesday
night into Thursday morning as the cold front settles to our
south. It is looking like most of Thursday will be dry over
northeast WI as the thunderstorm activity fires up to our south
where the cold front is likely to stall as it becomes parallel to
the mean flow aloft. If we can get enough mixed sunshine, max
temperatures on Thursday could get to near normal levels which is
middle 70s north-central/lakeshore, upper 70s to lower 70s
elsewhere.

The chance of showers/thunderstorms return to at least the
southern half of WI Thursday night as a 30 knot southwest low-
level jet pulls gulf moisture northward over the stalled frontal
boundary still situated to our south. The GFS hints at a surface
wave to move along this boundary which adds more lift to generate
precipitation. The forecast for Friday would depend on what
happens to this frontal boundary, whether it remains stationary or
sinks south from the convection. Since this is practically
impossible to determine this far out, prefer to keep a chance of
showers/storms in the forecast Friday with temperatures a little
cooler due to clouds/precipitation chances.
&&

.AVIATION...for 06Z TAF Issuance
Issued at 1034 PM CDT Fri Jun 23 2017

VFR conditions expected tonight into Saturday morning.
Mainly mid level clouds will be on the increase form the northwest
as an upper trough appraoches the region. An upper low pressure
system dropping into the state later Saturday may produce more
showers along with a few thunderstorms. Scattered mvfr cigs may
develop across parts of the area with the showers.
&&

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

$$

SHORT TERM.....RDM
LONG TERM......Kallas
AVIATION.......TDH



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