Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 261133
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
633 AM CDT Fri May 26 2017

Updated aviation portion for 12Z TAF issuance

.SHORT TERM...Today...Tonight...and Saturday
Issued at 318 AM CDT Fri May 26 2017

Doppler Radar shows an area of showers steadily making its way
over central and north central Wisconsin early this morning.
Despite the steady march east, mesoscale models dissipate this
area of showers as it tracks east later this morning as it
encounters an increasingly dry airmass with an upper level ridge
in place across the western Great Lakes. However Radar trends have
kept this line fairly in tact as it heads east this morning.
Therefore will keep POPs fairly high this morning as the line
heads east and dissipate it later this morning as the line of
showers tracks east into the drier air. Further east there is
some fog at times along the lakeshore, which is expected to be
mitigated by increasing clouds from the line of showers
approaching from the west.

Showers and a few rumbles of thunder will again be possible this
afternoon and this evening as a shortwave tracks through the
western Great Lakes as the aforementioned ridge flattens out a
bit. However limited moisture will prevent widespread coverage of
these showers, with continued low POPs for this evening.

There will be another chance for showers and some thunder
Saturday afternoon as the ridge tracks east and a trough
approaches from the west and settles in across the northern
Plains. This trough will spin off a shortwave that tracks through
the western Great Lakes Saturday afternoon, bringing the chance
for showers.

Temperatures will generally be around normal or a few degrees
above today and tonight with highs today around 70, with cooler
temperatures by the lake. Lows tonight should be around 50. Highs
Saturday will be noticeably warmer as highs soar into the 70s on
the backside of the retreating ridge.

.LONG TERM...Saturday Night Through Thursday
Issued at 318 AM CDT Fri May 26 2017

Models continue to show the movement of a closed upper low/
shortwave trough across the Great Lakes during the first half of
next week, while an upper ridge moves from the West Coast into the
Rockies. The main forecast challenge will be trying to time
individual shortwaves moving through the upper trough and when to
hit the precipitation chances the hardest. Temperatures will be at
or above normal through Sunday, drop below normal through next
Wednesday, then begin to warm again by next Thursday.

The shortwave trough is forecast to drop southeast into the Upper
MS Valley/central Plains Saturday night and models concur on this
timing. The problem continues to be the movement of a surface low
northeast along a cold front, with the models having some serious
differences which impact precipitation chances. The consensus
solution would take this surface low roughly into northern Indiana
by 12z Sunday with the northern extent of rain showers moving over
the southeast half of WI. Therefore, will have the highest pops
over east-central WI and lowest pops over north-central WI. Min
temperatures to only drop to around 50 degrees north-central,
middle 50s east-central WI.

The shortwave trough moves into the western Great Lakes region on
Sunday, providing a cold pool aloft which in turn steepens lapse
rates and increases instability. The NAM sends CAPES close to 1500
J/KG into central WI, but these values may be a bit overdone with
dew points pushing into the upper 50s. Nevertheless, there will be
sufficient instability to warrant thunderstorms in the forecast,
although severe potential would be marginal at best as shear is
weak. Max temperatures will cool a bit with readings in the upper
60s north-central/lakeshore, lower to middle 70s elsewhere.

Additional shortwave energy is forecast to move through the trough
Sunday night and with a cyclonic flow overhead, shower chances
would persist through the night. The loss of daytime heating would
help to stabilize the atmosphere, thus thunder potential would
diminish in the evening hours. Min temperatures to range from the
middle to upper 40s north, lower 50s south. This broad upper
trough to encompass the entire Great Lakes region on Memorial Day
and with the cyclonic flow still in place, expect to see
additional showers develop over northeast WI. Daytime heating will
also allow for the possibility of mainly afternoon thunderstorms
to pop up, but models show weaker instability with little shear,
thus do not anticipate any severe storms. Temperatures will
continue their downhill slide with readings around 60 degrees
north-central, middle to upper 60s elsewhere (slightly cooler near
Lake MI).

Even though the shortwave trough will gradually shift east toward
the eastern Great Lakes by Tuesday, northeast WI to remain on its
cool, cyclonic side with periodic shortwave passages moving
southeast over the Badger state. While specific timing of these
shortwaves becomes more difficult the farther out in time we get,
there is enough forcing evident to keep chance pops in the
forecast for both Monday night and Tuesday. It appears that
Tuesday could also be our coolest day of the extended period with
max temperatures in the upper 50s north-central, to the middle 60s
over eastern WI (away from Lake MI).

Precipitation chances could linger all the way through Wednesday
as one last shortwave trough dives into the exiting main upper
trough, along with the passage of a weak surface cold front.
Depending o whether we can get any peeks of sunshine, there is a
slim chance for afternoon thunderstorms as CAPE values push 500
J/KG and there is better bulk shear compared to earlier in the
week. Max temperatures for Wednesday to be in the lower 60s
north-central/near Lake MI, middle to upper 60s elsewhere.

It looks like we finally get rid of the precipitation chances by
next Thursday as Canadian high pressure builds south-southeast out
of south-central Canada. The return of sunshine will provide a
boost to temperatures with readings able to get back into the
middle 60s lakeside, upper 60s to around 70 degrees north and
lower 70s south.
&&

.AVIATION...for 12Z TAF Issuance
Issued at 633 AM CDT Fri May 26 2017

Patchy to Areas of MVFR/IFR Fog may linger early in the TAF period
until it mixes out in an hour or so. Otherwise some light showers
or sprinkles will track through the eastern TAF sites early this
morning if they hold together. Clouds will linger over the area
today as additional showers develop across the area during the
afternoon hours. Coverage will be isolated enough to just include
as a VCSH. VFR conditions are expected tonight across much of the
area, save for the western TAF sites where some stratus may
develop along with patchy fog later tonight.
&&

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

$$

SHORT TERM.....Kurimski
LONG TERM......Kallas
AVIATION.......Kurimski



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