Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 192327

Area Forecast Discussion
National Weather Service Green Bay WI
627 PM CDT Thu Oct 19 2017

Updated aviation portion for 00Z TAF issuance

.SHORT TERM...Tonight and Friday
Issued at 239 PM CDT Thu Oct 19 2017

Quiet weather with even warmer temperatures can be expected
across the area tonight and Friday.

Surface high pressure is forecast to remain southeast of the
Great Lakes through 00Z Saturday as a low pressure system
approaches Wisconsin from the west. As a result, the surface
pressure gradient will increase and winds are expected to back.
Speeds should drop tonight once daytime heating is lost, but winds
on Friday should be stronger than today. A mid level ridge axis
is forecast to pass across the state tonight causing the upper
flow to become southwest while a more amplified trough over the
western CONUS slowly approaches.

Warm advection and some wind should prevent temperatures from
tanking overnight, so lows should be mainly in the 40s. Continued
warm advection and better mixing during the day on Friday should
lead to much warmer than normal temperatures. Highs will be
around 20 degrees above normal, with most locations inland from
Lake Michigan reaching the 70s.

.LONG TERM...Friday Night Through Thursday
Issued at 239 PM CDT Thu Oct 19 2017

Dry and mild at the very start of the long term forecast, followed
by a pattern change throughout the weekend and next week.
Forecast challenges revolve around precip timing this weekend and
model differences next week.

Clouds expected to increase Friday night which will help keep
overnight temperatures in the 50s. On Saturday, a surface cold
front will move across Minnesota through the afternoon and
evening. Models (with the exception of the Canadian) suggest some
scattered precipitation will develop ahead of this front Saturday
afternoon and evening. Thunderstorms cannot be ruled out due to
CAPE up to 700-800 J/kg and lapse rates around 7 to 7.5 C/km.
Severe weather is not expected. Thunder chances diminish Saturday
night once instability is lost. Models also in fairly good
agreement that the surface front will sweep across the forecast
area throughout Sunday morning. There is a better chance of rain
as the front comes through. However, the GFS, ECMWF, and Canadian
all show 500mb energy splitting around the area at this time,
which lowers confidence on the overall coverage and intensity of
rain. Shower chances linger through Sunday afternoon before
drying out Sunday night.

Beyond Sunday, forecast confidence is low due to model-to-model
and run-to-run inconsistencies. There is a general agreement that
we transition to a northwest flow pattern for much of next week as
an upper trough deepens over the Upper Midwest and progresses
eastward. The Canadian has pulled back from the closed low/rainy
solution it depicted yesterday, but there are still opportunities
for showers as various shortwaves move through. Right now, each
model has a different solution on these details so stuck with a
blended solution, and as a result forecast features a chance of
showers more often than not. Temperatures also look to return to
around normal by next Tuesday. Models vary on how cool 850mb temps
will get, but somewhere around -8 to -4C at times. It`s possible
if everything lined up just right a few snowflakes could mix in
with any showers across northern Wisconsin if pcpn occurred
during one of the cooler mornings late next week, but confidence
in this scenario is too low to put in forecast at this time due
to issues stated above.

.AVIATION...for 00Z TAF Issuance
Issued at 624 PM CDT Thu Oct 19 2017

VFR conditions are expected to prevail through Friday with only
high clouds anticipated. As has been the case for the past several
days, the only significant aviation concern is LLWS, which is
expected to impact the RHI/AUW/CWA TAF sites tonight, and all of
the TAF sites Friday evening. Surface winds will also become
a bit gusty during the late morning and afternoon on Friday,
during peak heating.



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