Area Forecast Discussion
Issued by NWS Green Bay, WI

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000
FXUS63 KGRB 172320
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
620 PM CDT Tue Oct 17 2017

Updated aviation portion for 00Z TAF issuance

.SHORT TERM...Tonight and Wednesday
Issued at 323 PM CDT Tue Oct 17 2017

Flow aloft remains relatively low amplitude across the northern
CONUS in the short term. A weak mid level trough is expected to
pass through the area on Wednesday as a cold front moves into
northwest Wisconsin. Moisture is lacking, models lack QPF, and MOS
PoPs are less than 10 percent, so the forecast remains dry. Would
expect warmer temperatures with continued warm advection and a
warmer start to the day. Highs temperatures on Wednesday are
expected to be quite a bit warmer than normal, reaching the lower
70s at many locations. Winds will be stronger as the surface
gradient increases ahead of the approaching surface system.

.LONG TERM...Wednesday Night Through Tuesday
Issued at 323 PM CDT Tue Oct 17 2017

Quiet weather and well above normal temps will continue through
the end of the work week as a large ridge of high pressure moves
into the Midwest and Great Lakes. Friday looks to be the warmest
day, as 850mb temps climb to around 16C. Locations away from Lake
Michigan will see highs in the 70s. Lowering heights should bring
slight cooler readings on Saturday, but still above normal.
However, if an approaching low pressure system slows down, more
70s will be expected on Saturday. Much cooler air arrives early
next week behind a cold front, with near or slightly below normal
temps expected.

Main forecast issue will be when the next chance for rain arrives
and how much thunder there will be. Models continue to differ up
to 12-15 hours on the arrival of the mid-upper trough and surface
cold front, which of course results in different arrival times of
the best chances for rain and threat for storms. If the slower
solution (ECMWF) verifies, the rain won`t arrive until Saturday
night and linger into at least Sunday morning, plus thunder
chances will be on the low side. If the faster solution verifies
(GFS), the showers will be out of the area by 12z Sunday morning
and thunder chances are higher due to better interaction with
daytime instability Saturday afternoon/evening. That said,
instability would be on the low side (CAPE under 400 J/kg), and
best bulk shear resides behind the front, so not expecting severe
weather. The Canadian is closer to the GFS, but is not as speedy
with the front. Will continue to use a blend for the arrival of
rain, bringing chance POPs into the area Saturday PM and likely
POPs for much of the area Saturday evening, then taper off POPs
overnight.

Smaller chances for showers will linger into the start of next
week, with a northwest flow in full effect by mid-week. It will
definitely feel more like Fall with the cooler temps and rain
chances, plus a couple periods of gusty winds will add to the
chill in the air.
&&

.AVIATION...for 00Z TAF Issuance
Issued at 615 PM CDT Tue Oct 17 2017

VFR conditions will continue through the TAF period. Borderline
LLWS conditions are expected at GRB/ATW/MTW later this evening
through Wednesday morning. Daytime heating will cause stronger
winds aloft to mix to the surface in the late morning and
afternoon on Wednesday, with south-southwest winds gusting to
20 to 25 kts at most airport locations.
&&

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

$$

SHORT TERM.....MG
LONG TERM......Bersch
AVIATION.......Kieckbusch


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