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fxus63 kgrb 181750 

Area forecast discussion
National Weather Service Green Bay WI
1250 PM CDT Wed Oct 18 2017

Updated aviation portion for 18z taf issuance

issued at 307 am CDT Wed Oct 18 2017

Warm and quiet weather for the rest of the work week, though it
will be quite windy at times. Turning cooler by early next week.

A very energetic band of low-amplitude westerlies was across
Canada and the far northern Continental U.S.. the pattern will undergo some
amplification during the remainder of the work week, with a trough
forming near the West Coast and increased ridging over the Great
Lakes region. Additional changes will quickly follows as a much
stronger trough develops out near 160w. That will flip the
downstream pattern to one with a ridge near the West Coast and
troughing over the Great Lakes region by early next week.

Temperatures 10 to 20 f degrees above normal are expected into
the upcoming weekend, then readings will drop back much closer to
seasonal normals by early next week. The best chance for rain
will be with a frontal system crossing the area this weekend, but
that system seems unlikely to bring substantial rains, so amounts
are likely to end up below normal for the period.

Short Thursday
issued at 307 am CDT Wed Oct 18 2017

Quiet weather is expected throughout the period as a series of
strong cyclones track east across Canada. It will be windy at
times. The main forecast issue is temperatures. Guidance was too
cool yesterday and looks too cool the next couple days as well.
Went with maxes for today that were a couple degrees above
yesterdays observed values at most locations. Thursday won't be
quite as warm as a cool front trailing from one of the Canadian
cyclones will cross the area tonight. But highs are still expected
to be above normal. The forecast pressure gradient and some cold air advection
suggest it's less likely low-levels will decouple completely
tonight. So shaved a couple degrees off mins in the typical cool
spots, but don't expect the drop we've seen at some locations this

Long term...Thursday night through Tuesday
issued at 307 am CDT Wed Oct 18 2017

Unseasonably warm weather will continue on Friday and into
Saturday (not as warm due to cloud cover/chances of rain).
Highs on Friday will be around 20 degrees above normal
away from the Bay and lake, but just shy of the record high
for the date at this point. Have raised high temperatures on
Friday per coordination with surrounding offices.

Still some timing differences among the models with arrival
of the rain and when the cold front will pass through the area
over the weekend. Latest GFS/WRF model depict precipitation
breaking out with the southerly flow on Saturday, with main
precipitation with the cold front Saturday night into early
Sunday morning. Yesterday, the European model (ecmwf) was the slowest model
with the passage of the cold front. The 00z run tonight
has sped up this system. Best available of CAPES were between
200 and 400 j/kg. Will continue the small chances of thunderstorms
Saturday afternoon and evening. Mid level lapse rates were pretty
steep. The cold front will move away from the area Sunday
afternoon, bringing drier conditions to the region. Next system
approaches from the northwest late Sunday night, bringing another
chance of showers Monday into Monday night.

A significant change in the weather pattern is expected by the
end of next week. Northwest flow will become established across
the area, bringing an end to the unusually mild October weather.
In reality, temperatures will return closer to normal next week,
which will be a shock due to the expected warm weather this week.

Aviation...for 18z taf issuance
issued at 1249 PM CDT Wed Oct 18 2017

VFR conditions will continue through Thursday as a passing cold
front and mid level short wave bring only some high and mid level
clouds to the area. Gusty southerly surface flow will weaken with
loss of daytime heating, but low level wind shear then becomes an issue for a few
hours or so prior to 06z. Little, if any, fog should develop since
there should still be some wind overnight.

issued at 307 am CDT Wed Oct 18 2017

Opted to keep the SC.Y rather than upgrade to a gl.W. Some gale
force gusts are still likely, but it does not look as though they
will be widespread/persistent enough to warrant a Gale Warning.
Modis satellite imagery indicated water temperatures over the nsh
waters were in the middle to upper 50s, so low-levels will be
stable as the strongest winds move through aloft.

Persistent strong southwest winds are likely to result in high
waves on Lake Michigan Friday into Sunday morning.

Grb watches/warnings/advisories...


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