Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 240830
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
330 AM CDT TUE MAY 24 2016

Forecast discussion for routine morning forecast issuance

.SHORT TERM...Today...Tonight...and Wednesday
Issued at 330 AM CDT Tue May 24 2016

Precipitation trends, severe thunderstorm potential and
temperatures are the main fcst concerns.

Shower and thunderstorm activity has waned a bit over the past
several hours, but a small area of showers and embedded
thunderstorms was moving through north central WI early this
morning. This activity appeared to be sustained by a mid-level
short-wave trof along the leading edge of a moisture axis, and
is expected to wane as the short-wave trof quickly exits the
region this morning.

With most of the pcpn tapering off early and some breaks in the
clouds expected, have increased max temps a few degrees today.
modified fcst sounding (82/60 around GRB) for this afternoon
indicates CAPE increasing to around 1500 j/kg. This, combined
with deep layer shear of 30-40 kts, may be sufficient for isold
strong to severe tstms to develop. SPC has placed the entire fcst
area in a Marginal risk of severe tstms, which seems reasonable.
Activity should be focused along a frontal boundary sagging into
northern WI this afternoon, and possibly near lake/bay breeze
boundaries in eastern WI.

Expect convection to gradually weaken after sunset tonight, and
probably end from north to south as the cold front moves through.
The front will not get very far south of the region on Weds
morning, and is expected to lift back to the north as a warm front
as low pressure approaches from the plains during the afternoon.
the sfc/H8 warm fronts and the arrival of another short-wave trof
will generate additional showers and tstms by Weds afternoon,
especially over our western and southern counties. Instability is
not expected to be as strong as today, but is expected to
increase over c/ec WI during the afternoon. Will need to keep an
eye on our sw counties for severe potential as the warm front
approaches late in the day, but SPC has the Marginal risk just to
our southwest right now. temperatures will be a bit cooler on
Weds, mainly in the 70s, with low to mid 60s along the Lake
Michigan shoreline.

.LONG TERM...Wednesday Night Through Monday
Issued at 330 AM CDT Tue May 24 2016

Mean flow to generally consist of an Eastern Pacific upper ridge,
a broad upper trough over the western half of the CONUS and an
upper ridge to build toward the Mid-Atlantic states. This pattern
to essentially hold into early next week with a SW flow into WI
bringing an active weather pattern with temperatures holding above
normal. Main focus to be on trying to time precipitation chances,
potential for any severe storms and whether we can find a day
where precipitation is not in the forecast.

Prevailing SW flow aloft is expected to persist into the Great
Lakes Wednesday night with the models in agreement with the
movement of a mid-level shortwave trough lifting NE through NE WI
mainly during Wednesday evening. Increasing mid-level forcing...
in concert with increasing isentropic lift...should provide for
showers/thunderstorms across the entire forecast area. The main
frontal boundary is expected to remain to our south through the
night, thus a lack of strong instability would preclude a
widespread severe potential...although an isolated strong storm
cannot be ruled out. Min temperatures to remain mild with readings
in the lower to middle 50s north/lakeshore, upper 50s to around 60
degrees south.

Precipitation chances actually look minimal on Thursday as the
mid-level shortwave trough continues to track away from the
region. The only real concern would the location of the warm front
and whether this feature could set off more showers and storms. If
this front can lift to our north without any precipitation,
Thursday could definitely feel like summer with max temperatures
in the mid to upper 70s north...lower 80s south (cooler lakeside)
and dew points in the upper 50s to lower 60s.

Not surprisingly under this SW flow aloft, models begin to have
difficulty with the timing of the next prominent shortwave trough
to eject NEWD out of the main upper trough situated over the
Rockies. The next of these potential shortwave troughs begins to
lift toward WI Thursday night with the majority of the models
bringing showers/thunderstorms back to NE WI. Have maintained the
medium to high-chc pops per previous forecast with min
temperatures similar to Wednesday night. Shower and thunderstorm
activity looks to carry over into Friday as this lates shortwave
trough moves through the Great Lakes and southerly winds continue
to pump gulf moisture into WI. More clouds with precipitation in
the vicinity will keep temperatures a little cooler than previous
days with readings more in the mid to upper 70s, again cooler near
Lake MI.

This unsettled weather pattern appears to be locked in over the
Great Lakes through most of the upcoming holiday weekend as a
large piece of the main upper trough is progged to move NE through
the Midwest on Saturday, into the Great Lakes Saturday night/
Sunday morning before pulling to the north Sunday afternoon. While
the atmosphere over NE WI to be very moist and unstable, severe
weather threat will come down to whether we can get enough breaks
in the cloud cover to allow instability parameters to really take
off. Another potential problem is the forecast lack of shear by
the models (around 20 kts) to help sustain updrafts. For now,
prefer to try and focus on best time frame for showers/
thunderstorms which looks to be Saturday afternoon into Sundary
morning period. Max temperatures this weekend to remain about 5 to
10 degrees above normal for late May.

Even with the passage and eventual exit of this prominent
shortwave trough headed into Sunday night, NE WI to still be in a
SW flow aloft and there could be a few lingering showers or
thunderstorms Sunday night or even Monday. Pops should be in the
lower chance category by this time with little change in
temperatures anticipated.
&&

.AVIATION...for 06Z TAF Issuance
Issued at 1054 PM CDT Mon May 23 2016

llws possible across eastern wisconsin tonight with
south winds around 30 knots at 500 ft agl and light south winds at
the sfc. vfr conditions should prevail in all but northcentral
wisconsin overnight. a weak frontal system will bring scattered
showers and thunderstorms to northcentral wisconsin late tonight
and across the area tuesday. mvfr cigs and vsbys could accompany
any shower or thunderstorm activity that materializes.
&&

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

$$

SHORT TERM.....Kieckbusch
LONG TERM......Kallas
AVIATION.......RDM



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