Forecast Discussion for GRB NWS Office
FXUS63 KGRB 200354

Area Forecast Discussion
National Weather Service Green Bay WI
1054 PM CDT Sun Aug 19 2018

Updated aviation portion for 06Z TAF issuance

.SHORT TERM...Tonight and Monday
Issued at 222 PM CDT Sun Aug 19 2018

Partly cloudy skies prevailed across the region this
afternoon. Temperatures were in the middle 70s to
lower 80s.

For tonight, skies will become mostly cloudy as convection
across the central plains approaches Wisconsin from the
southwest. Some patchy fog is expected, especially across the
north after midnight. Due to increasing cloud cover, not expecting
the fog to become dense at most locations. Our typical low spots
across the far north could see pockets of dense fog. Also, there
is a small chance of showers and storms late tonight as models
depicting some spotty elevated convection across portions of
central into northeast Wisconsin. Did not go as low as numerical
guidance due to expected high clouds across the region.

On Monday, low pressure approaching Wisconsin will bring
increasing chances of showers and storms, especially Monday
afternoon. High temperatures should be cooler than today due
to easterly flow, thick cloud cover and expected showers and
storms during the afternoon. Trended toward the cooler
MAV guidance for highs on Monday.

.LONG TERM...Monday Night Through Sunday
Issued at 222 PM CDT Sun Aug 19 2018

The main forecast concern is heavy rainfall potential with an
unseasonably strong low pressure system impacting the region
Monday night into early Tuesday.

Low pressure over the southeast IA/northeast MO will deepen a
little as it tracks through southern Lake Michigan Monday night,
and heads into southeast Ontario on Tuesday. This will occur in
response to phasing of a northern stream short-wave with the
remnants of an upper low, and upper level divergence with
coupled upper jets. Models agree that widespread shower activity
and locally heavy rainfall will occur over central, northeast and
east central WI Monday night, where forcing will be strongest and
PWATs will be 1.50-1.75 inches. Less precipitation coverage and
QPF is expected over our far northwest counties. With limited
surface-based or elevated instability through the period, only
plan to mention a slight chance or chance of thunderstorms. Local
rainfall amounts of 1 to 2 inches are possible over the southeast
half of the forecast area, which may pose a threat of minor urban

The rain is expected to end quickly on Tuesday, with gusty north
winds and possible Small Craft Advisories on Lake Michigan
lingering through Tuesday night.

High pressure will bring a period of dry and comfortable weather
Tuesday night through Thursday night. As the high shifts east, a
warm front is expected to shift north through the region on Friday
or Friday night, bringing a good chance of showers and
thunderstorms. The warm front should stall out to our north,
setting the stage for a warm and humid weekend, with isolated/
scattered thunderstorms at times.

.AVIATION...for 06Z TAF Issuance
Issued at 1041 PM CDT Sun Aug 19 2018

Visibilities are starting to fall late this evening, and areas of
ground fog remain expected to form across north-central WI
overnight. The fog should not be as dense as previous nights, due
to broken cirrus overhead. Fog will be more patchy elsewhere. Spotty
showers and storms look possible from late morning through the
afternoon as low pressure draws closer to the region. But higher
chances of showers/storms as well as deteriorating flying
conditions look to arrive for Monday evening.




SHORT TERM.....Eckberg
LONG TERM......Kieckbusch

NWS GRB Office Area Forecast Discussion