Forecast Discussion for GRB NWS Office
FXUS63 KGRB 212331

Area Forecast Discussion
National Weather Service Green Bay WI
631 PM CDT Thu Jun 21 2018

Updated aviation portion for 00Z TAF issuance

.SHORT TERM...Tonight and Friday
Issued at 310 PM CDT Thu Jun 21 2018

The main forecast concern remains the northern extent of
precipitation spiraling around a system passing to our south over
the next 24 hours.

The 19Z MSAS surface analysis showed a pair of weak areas of low
pressure over south-central IA and west-central IL. A quasi-
stationary front extended east-southeast from the IL low into the
central Appalachians. To the north, a sprawling area of high
pressure stretched from northeast MN eastward into southern
Quebec. The radar mosaic indicated several bands of showers and
thunderstorms rotating around the surface lows (and its parent
closed upper low) with the northern extent just brushing the
southernmost counties in our forecast area.

The surface lows are expected to congeal into one area of low
pressure and move into central IL tonight, while the closed upper
low heads toward southern IL. Showers and thunderstorms are
expected to continue rotating into southern WI during the night.
The western fringe of the high pressure will be located over the
western Great Lakes region with an influx of dry air (dew points
falling in the 40s to lower 50s) over northeast WI. Depending on
what the radar mosaic is showing at press time, may need to leave
a token minimal pop for a couple of hours into the evening for our
southern tier of counties. Otherwise, dry and cool conditions are
expected with min temperatures in the middle to upper 40s north,
lower to middle 50s south.

The system tracks east-northeast into central sections of IN on
Friday. Even though the high pressure weakens over the western
Great Lakes, enough residual dry air to still be in place to keep
any precipitation locked over southern WI. We should see an
increase in clouds during the afternoon across our southern
counties as moisture does try to push north once again. Prevailing
northeast winds will again keep temperatures in check with higher
winds coming down the bay into Green Bay. Look for max
temperatures to range from near 70 degrees close to Lake MI, lower
to middle 70s east-central WI and middle to upper 70s for north-
central/central WI.

.LONG TERM...Friday Night Through Thursday
Issued at 310 PM CDT Thu Jun 21 2018

The main forecast concerns are small chances for rain at times
and then a more significant weather system bringing a chance for
showers and thunderstorms to the entire area next week.

As surface and 500 mb lows pass southeast of the state there is a
tiny area of slight chance PoPs in part of Manitowoc County
Friday night. There is another slight chance for showers or
storms in central Wisconsin Sunday afternoon with a passing mid
level short wave and a cold front moving across the forecast area
from northeast to southwest. The main chance for showers and
storms is ahead of a system that will traverse the Plains and move
to the Great Lakes early to mid week. Chances for showers and
storms move into most of the area on Tuesday and then continue
through Wednesday. The model blend brings a chance for showers and
storms to about half of the area Thursday afternoon. Not really
sure what caused this, but it fits in with surrounding forecast
grids so have left it alone.

Temperatures should be within a few degrees of normal through
Monday, but there should be a slight warming trend Tuesday through

.AVIATION...for 00Z TAF Issuance
Issued at 626 PM CDT Thu Jun 21 2018

A low pressure system is forecast to move from MO to IN over the
next 24 hours, with any shower activity remaining south of the
forecast area. Meanwhile, Canadian high pressure will remain over
the northern Great Lakes and send drier air into northeast WI.
Mid-level clouds should shift south of the region tonight, then
return to parts of central and east central WI Friday afternoon.
VFR conditions should prevail through the TAF period.

Beach Hazards Statement until 9 PM CDT this evening for WIZ022-


SHORT TERM.....Kallas

NWS GRB Office Area Forecast Discussion