Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 251057
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
557 AM CDT Thu May 25 2017

Updated aviation portion for 12Z TAF issuance

.SHORT TERM...Today...Tonight...and Friday
Issued at 406 AM CDT Thu May 25 2017

The old upper low over Indiana will move slowly
east today and reduce it`s influence on our weather. It still was
producing bands of low and middle clouds early today but that
should diminish as the day goes on. Some of the models hint of a
chance of showers today in northeast Wisconsin, likely due to a
convergence area where lake breezes from Lake Superior and
northern Lake Michigan meet. Put in a slight chance for the
possibility of that happening. Highs today should be close to
normal.

Weak upper ridging is forecast to move across the region tonight,
with a surface high centered over eastern Wisconsin. Light winds
and dewpoints near 50 may produce fog over the cool waters of the
lake and bay and adjoining land areas. Some sprinkles or light
showers may move into our central and northcentral counties late
tonight as warm advection begins. Lows tonight should be close to
normal.

A weak trough could produce scattered showers as it moves across the
area Friday. A rumble of thunder is not out of the question in
central Wisconsin.

.LONG TERM...Friday Night Through Wednesday
Issued at 406 AM CDT Thu May 25 2017

Models remain steady with the overall mean flow into the first
half of next week. An eastern Pacific upper ridge will slowly move
east into the western CONUs this weekend and weaken a bit by mid-
week. A closed upper low/associated shortwave trough is projected
to move from Lake Winnipeg/central Rockies Saturday and eventually
reside from Ontario/east-central CONUS by Tuesday. This second
feature, preceded by a surface low, will bring warmer/increasingly
unsettled weather to northeast WI for the latter part of the
holiday weekend. It may take until late Wednesday to finally shake
the effects of this system with temperatures falling below normal
for Tuesday and Wednesday.

The mid-level shortwave trough/accompanying cold front are both
expected to push through WI Friday night, but both in a weakening
state. Expect to see a diminishing area of showers push eastward
with any thunderstorms quickly ending in the evening as daytime
heating wanes. Will carry small chance pops through the night, but
any shower activity should be light and not impact any rivers/
streams that are running high. Min temperatures are forecast to
generally be in the upper 40s to around 50 degrees north/
lakeshore, lower to middle 50s elsewhere.

The remains of the cold front are forecast to hang up from the
Midwest/Mid-MS Valley toward the eastern Great Lakes on Saturday.
Models develop a surface wave on this boundary over northern MO or
west-central IL by Saturday afternoon with weak mid-level
frontogenesis to develop from IA into WI. This could bring shower
chances back into the forecast, mainly toward central sections of
WI during the afternoon. Not much in the way of instability, so
have kept thunder out of the forecast. Max temperatures could
actually move above normal if we can keep the precipitation/
thicker clouds away. Look for readings in the upper 60s near Lake
MI, lower 70s north-central and lower to middle 70s elsewhere. A
few upper 70s are possible west of the Fox Valley if the rain does
not materialize.

This surface wave tracks northeast toward southern sections of the
Great Lakes Saturday night and could bring a chance of showers
across parts of central and east-central WI. The rest of the area
should see partly to mostly cloudy skies adn with the air mass
aloft not changing much, temperatures will be similar to Friday
night. Look for readings in the upper 40s north, lower 50s south.
There continues to be some model disagreement with the timing of
the approaching shortwave trough headed into Sunday. Some models
sweep this trough across the Upper MS Valley, but other models
hold the better mid-level energy back over south-central Canada/
northern Plains. This timing issue makes all the difference
between increasing precipitation chances over WI (steepening lapse
rates/instability) Sunday afternoon or little if any precipitation
and warm temperatures. Since either solution is still plausible,
may need to compromise here and while showers/thunderstorms are
still possible, have lowered pops a bit especially over central
and east-central WI. Temperatures to remain at or above normal
with another day in the upper 60s near Lake MI, around 70 degrees
north and lower 70s south.

The crux of this shortwave trough is progged to be over the
western Great Lakes region Sunday night through Monday. Loss of
daytime heating will again allow any storms to end Sunday evening,
but shower chances to persist through the night as individual
shortwaves move through the trough into WI. Memorial Day still
appears unsettled with the cold pool aloft and daytime heating
allowing for further shower development and a chance for
thunderstorms much like Saturday afternoon. Thicker clouds and
precipitation chances will start a downward tick in temperatures
with readings on Memorial Day in the lower 60s north-central,
middle to upper 60s elsewhere.

Northeast WI to then reside on the cool, cyclonic side of this
broad upper trough for Tuesday and Wednesday with additional
pieces of shortwave energy diving southeast across WI. Anticipate
periodic shower chances (at least thunder chances will end) to
persist for both Tuesday and Wednesday with temperatures to run 5
to 10 degrees below normal as we head into June.
&&

.AVIATION...for 12Z TAF Issuance
Issued at 557 AM CDT Thu May 25 2017

An upper level low pressure system over the northern
Ohio Valley will continue to produce scattered to broken clouds
across the area today. Most of them should be middle clouds, so
generally VFR conditions are expected today and most of tonight.

Some dense fog is possible towards daybreak near Lake Michigan
and the bay. The fog would mostly likely effect 2P2, 3D2, SUE,
GRB, MTW, ATW, MNM and OCQ if it does materialize. Whatever fog
there is should quickly dissipate shortly after sunrise, with VFR
conditions with a slight chance of showers Friday.
&&

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

$$

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


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