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000
FXUS63 KGRB 201701
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1201 PM CDT Fri Oct 20 2017

Updated aviation portion for 18Z TAF issuance

.SYNOPSIS...
Issued at 401 AM CDT Fri Oct 20 2017

Unseasonably warm through tomorrow, showers tomorrow night and
Sunday, then much cooler next week.

The upper pattern across North America will remain progressive
while undergoing amplification the next few days. The
amplification will continue into next week, but the progression
will not. There will be a longwave ridge along the West Coast and
a downstream trough near 80W as the progression ends early next
week. Those features may tend to reform a little farther west
during the latter part of the week, but the medium range models
have not reached a consensus on that yet.

Unseasonably warm weather will continue through tomorrow, then a
downward trend will begin. The primary opportunities for
precipitation will be with a frontal system crossing the area this
weekend and as the large scale upper trough develops/sharpens
over the area next week. The weather won`t be as dry as the past
several days, but precipitation amounts will probably end up AOB
normal for the period.
&&

.SHORT TERM...Today...Tonight...and Saturday
Issued at 401 AM CDT Fri Oct 20 2017

A building upper ridge will shift east of the area today.
Soundings still show a lot of dry air across the area, so nothing
more than passing cirrus expected today and tonight. Increased
low-level moisture will start to advect into the area, but mixing
into dry air aloft will probably still bring dew points down
below guidance this afternoon. High temperatures will be well
above normal, with forecast maxes 19-24F above normal everywhere
except near the lake. They still wouldn`t be records though, as
those are in the 80s.

LLJ will strengthen over the forecast area tonight as continued
eastward progression of the ridge and upstream trough brings
Wisconsin into strong, deep southwest flow. Mid-level lapse rates
are forecast to steepen to around 7K/km. That combined with weak
isentropic lift with the LLJ may be able to generate some
sprinkles or light showers out of a accas deck toward morning. The
ECMWF hints at this, but the rest of the guidance pretty much
keeps things dry. Went with the majority for now, but the day
shift will need to take another look at this. Stayed with the
broad-based blend of guidance products for min temps as the
gradient looks sufficient to keep winds from dying off and there
will probably be some clouds spreading in overnight.

The trend on the guidance since yesterday has been to slow the
eastward push of the precipitation on Saturday. That seemed
reasonable given that the mid-level trough will still be back west
in the Plains by 00Z Sunday. Given the lower chance for rain,
edged maxes up a couple degrees at most locations.

.LONG TERM...Saturday Night Through Thursday
Issued at 401 AM CDT Fri Oct 20 2017

The mild weather will come to an end next week as temperatures
return to near normal levels for late October. The slow moving
cold front will bring showers and a few thunderstorms across the
area Saturday night. A new wrinkle to the forecast tonight is the
day 2 outlook from the Storm Prediction Center (SPC) has the
marginal risk of severe thunderstorms into our far western
counties. Will bump up wording in the Hazardous Weather Outlook
(HWO) to include gusty winds as bufkit soundings indicated 40 to
50 knots off the deck. The front will then slowly push east of the
area on Sunday. Most of the rain will be post frontal, thus it
will take some time for the rain to end Sunday across northeast
Wisconsin. Have increased rain chances across northeast Wisconsin
Sunday afternoon as much of the steadier rain may not exit the
area until mid afternoon.

For next week, there is low confidence in the forecast from Monday
night through Wednesday due to where the surface low end up. On
the model runs tonight, the surface low at 12z Tuesday was
positioned as far west as Wisconsin (Canadian) or as far east as
West Virgina (GFS). The European model was located near Lake
Huron. The GFS ensemble members (surface low) indicated numerous
solutions to add to the low confidence in the forecast. Will let
the models converge on a solution over the next few days. It
should still be fairly mild Monday, but temperatures should be
closer to normal for the rest of the work week.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1200 PM CDT Fri Oct 20 2017

VFR conditions will prevail today through the start of Saturday.
Primary aviation concern is the increasing coverage of LLWS
conditions as Southwest winds just off the surface increase.
&&

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

$$

SYNOPSIS.......Skowronski
SHORT TERM.....Skowronski
LONG TERM......Eckberg
AVIATION.......TDH