Area Forecast Discussion
Issued by NWS Green Bay, WI

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000
FXUS63 KGRB 252255
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
555 PM CDT MON JUL 25 2016

Updated aviation portion for 00Z TAF issuance

.SHORT TERM...Tonight and Tuesday
Issued at 242 PM CDT Mon Jul 25 2016

The main forecast issue to be on precipitation trends across the
north on Tuesday as a slow-moving cold front begins to sag south
from Ontario.

The 19z MSAS surface analysis showed an area of high pressure
extended from the Central Plains north-northeast into the Upper MS
Valley. Otherwise, pleasant conditions were observed across
northeast WI with seasonal temperatures and dew points down a bit
from the weekend.

The weak area of high pressure is expected to slide across the
southern sections of the Great Lakes tonight, providing for mostly
clear skies and a light W-NW wind. There is enough low-level
moisture around (dew points in the mid 50s to lower 60s) such that
patchy fog will likely develop after midnight, especially in low-
lying areas. Min temperatures will range from the middle to upper
50s north, lower to middle 60s south.

As the surface high continues to slide east toward the Eastern
Great Lakes on Tuesday, a return flow will develop across WI
allowing for an increase in moisture to overspread the area. Dew
points are forecast to climb into the lower 60s north, middle to
upper 60s south. By Tuesday afternoon, a modest cold front is
progged to be sagging south across northern MN and Lake Superior.
Increasing WAA, coupled with increased convergence/lift along the
front and moderate instability, should bring a chance of showers
and thunderstorms to Northern WI during the afternoon hours. SPC
has placed the north under a marginal risk of severe storms with
isolated damaging wind gusts possible. Central and east-central WI
should remain dry, but see a general increase in mid/high clouds
Tuesday afternoon. Onset of WAA will also bring an uptick in
temperatures with readings mainly in the middle to upper 80s.

.LONG TERM...Tuesday Night Through Monday
Issued at 242 PM CDT Mon Jul 25 2016

The forecast will hinge upon the movement and placement of a
Canadian cold front during the mid to late part of the week.

A Canadian cold front will sag south across the region Tuesday
night into Wednesday, with the best chance of showers and
thunderstorms expected on Wednesday, when daytime heating will
boost CAPE to 1500-2500 j/kg. Deep layer shear will not be very
strong, but 20-30 kts of shear should be sufficient to support a
few strong to severe storms, especially if discrete cells can
develop.

The GFS/Canadian Models suggest that the front will push well
south of the region after Thursday, with Canadian high pressure
bringing dry conditions through the weekend. However, the ECMWF
stalls the front over northern Illinois, then lifts it back into
southern Wisconsin as a surface low moves through on Thursday and
Friday. This difference is mainly due to the presence of a deep,
slow moving, upper trof/low that the ECMWF tracks through the
western Great Lakes late in the week. This solution could bring a
heavy rainfall to the southeast half of GRB CWA. Right now,
leaning toward the more progressive solutions of the GFS/GEM
models, but confidence is low.

Temperatures should start out near normal during the midweek
period, then cool off several degrees after the cold front
moves through. Gradual warming is anticipated Sunday into Monday,
as south winds develop on the western periphery of the departing
high.
&&

.AVIATION...for 00Z TAF Issuance
Issued at 555 PM CDT Mon Jul 25 2016

VFR conditions are expected through Tuesday morning as a weak
area of high pressure slides across southern sections of the Great
Lakes. Expect mostly clear skies and light winds for tonight.
Some patchy fog could develop late tonight which would lower vsbys
into the MVFR range. As the high pressure starts to pull farther
to the east on Tuesday a return flow will bring warmer, more humid
conditions back to northeast WI with late morning cu field
developing once again. A cold front is forecast to sag south into
Lake Superior Tuesday afternoon and will bring a chance of showers
and thunderstorms to the RHI TAF site late in the TAF period.
&&

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

$$

SHORT TERM.....Kallas
LONG TERM......Kieckbusch
AVIATION.......Kurimski



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