Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 242327

Area Forecast Discussion
National Weather Service Green Bay WI
627 PM CDT Sun Sep 24 2017

Updated aviation portion for 00Z TAF issuance

.SHORT TERM...Tonight and Monday
Issued at 215 PM CDT Sun Sep 24 2017

The main forecast concern switches from heat/humidity to timing of
precipitation chances on Monday. For those who enjoy the heat, you
have one more day before reality returns to northeast WI autumnal

The 19z MSAS surface analysis showed high pressure situated over
the eastern Great Lakes. A quasi-stationary front extended from
western Ontario south-southwest through western MN into the
central Plains. A prevailing southerly wind between these two
weather features continued to draw very warm/humid air into WI
with another day of record or near record high temperatures.

Subtle changes begin to occur tonight as the upper ridge over the
eastern CONUS slides a bit eastward, thereby allowing the quasi-
stationary front over the Upper MS Valley to edge toward the WI
border by 12z Monday. Central WI will start to see some increase
in high clouds after midnight as showers/few thunderstorms
continue to fire along and behind the front. Otherwise, another
mild/muggy night in store across the forecast area with patchy fog
toward daybreak. Min temperatures to be in the lower 60s north,
middle 60s south.

The frontal boundary is forecast to slowly move across western WI
on Monday, bringing more clouds to central WI along with an
increasing chance for showers/thunderstorms in the afternoon.
Eastern WI should remain dry during the daylight hours, although
mid/high clouds will be on the increase. Do not anticipate any
severe storms as both forcing and shear are weak. Have ignored the
GFS which sends measurable precipitation all the way to the lake
on Monday. This front is a slow-mover and prefer to relegate
precipitation west of a line from IMT-ISW. Look for a wider range
in temperatures on Monday with readings in the upper 70s to lower
80s north-central/along Lake MI, to the middle to upper 80s across
east-central WI. A few record highs could be approached in the
east if the thicker clouds can stay away long enough.

.LONG TERM...Monday Night Through Sunday
Issued at 215 PM CDT Sun Sep 24 2017

Blocky ridge over the eastern CONUS gradually flattens as wave
ejects from western trof and moves across northern Great Lakes.
This begins (temporary) transition to WNW flow for second half of
the week. The warm spell will come to an end Tuesday as cold
front associated with wave moves across Wisconsin. The front will
bring scattered showers and storms.

High pressure will briefly dominate Wednesday into Thursday AM
before next shortwave trof and cold front approaches. The front
will bring a chance of showers to much of the area late Thursday
afternoon or Thursday night. Colder temps to follow for late week
and early in the weekend. 24/12Z ECMWF has backed off a bit from
previous run on amount of cold and is now a bit closer to GFS.
Regardless, temps by end of week will be 30 deg colder than this
weekend. Temps cold enough for lake-enhanced showers in cyclonic
flow in the north.

.AVIATION...for 00Z TAF Issuance
Issued at 627 PM CDT Sun Sep 24 2017

VFR conditions to prevail through the TAF period. The only
exception would be some patchy late night fog which could brief
lower vsbys into the MVFR range. Have kept the LLWS potential for
the RHI, AUW and CWA TAF sites tonight as southwest winds just
above the surface reach 30 to 35 knots. Mid and high clouds are
forecast to increase over the region on Monday with a chance for
showers/thunderstorms reaching central WI Monday afternoon. Placed
a PROB30 group in this set of TAFs to account for this.



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