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Area Forecast Discussion (AFD)

Issued by Green Bay, WI (GRB)

                            
000
FXUS63 KGRB 230927
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
427 AM CDT Mon Sep 23 2019

Forecast discussion for routine morning forecast issuance

.SYNOPSIS...
Issued at 423 AM CDT Mon Sep 23 2019

Mild but less humid weather is expected for the work week, with 
another round of showers and thunderstorms Tuesday night into 
Wednesday.

The upper flow across North America will briefly transition away 
from the last week's pattern and into a more zonal regime, then 
flop back into an amplified western trough/eastern ridge 
configuration regime by the weekend. The primary difference 
between next weekend's pattern and last week's pattern will be the
position of the positive height anomaly with the ridge. This time
the anomaly will be centered a little farther south--in the Great
Lakes/southern Ontario region as opposed to near Hudson Bay.

The developing zonal flow aloft will shunt the very moist air 
mass off to the east, allowing the humidity to return to more 
seasonable levels. Temperatures will be mainly above normal, but 
may drop to near normal for a day or two. Although it may not seem
like it given how wet the weather has been lately, normal 
precipitation for a 7 day period has dropped to less than 3/4 of 
an inch (from a max of around an inch during the summer). Two main
precipitation episodes are anticipated during the period, one 
Tuesday night into Wednesday and another late in the work week and
into the start of the weekend. Those will probably be sufficient 
to generate AOA normal amounts. Even wetter conditions could 
return beyond the end of the forecast period if the large scale 
regime forecast by the medium range models verifies.
&&

.SHORT TERM...Today...Tonight...and Tuesday
Issued at 423 AM CDT Mon Sep 23 2019

Quieter weather will settle across the area today and linger
through Tuesday as the remnants of the previous western U.S. upper
trough pull away to the east. Cyclonic flow lingering across the
area will lead to scattered showers across the north. System
clouds will be pulling away, but moist low levels will probably 
lead to diurnal convective cloudiness, so trended a little more 
pessimistic with skycon today.

Any lingering clouds will clear tonight. Fog is a concern, but
the surface pressure gradient and winds aloft begin to increase
overnight. The far north/northeast part of the area seems most at
risk of fog formation. Carried patchy fog in those areas.

South winds will be increasing Tuesday as an upper speed max and  
large shortwave move east across the Plains and Canadian Prairies.
Models were in good agreement that precipitation should hold off 
until after 00Z, so maintained the dry forecast for Tuesday.

Used a combination of a broad-based blend of guidance products 
and recent top performing products for high temperatures. For 
mins, used a blend of bias-corrected MOS products which typically 
does a decent job of capturing the local cool spots.

.LONG TERM...Tuesday Night Through Sunday
Issued at 423 AM CDT Mon Sep 23 2019

Expect showers and thunderstorms as a cold front passes through 
the area late Tuesday night into Wednesday and a upper level 
trough moves into the region. The late arrival of the front should
lessen the likelihood of severe storms, but there may still be 
enough instability and shear for some of the storms to become 
severe. 

Upper level flow across the region is expected to become 
zonal during the latter half of the work week before backing to
southwest by the end of the weekend. Surface high pressure 
should help to keep Wednesday night and Thursday dry and cooler,
with temperatures near normal. The next approaching low will bring
chances for showers, and some storms, back for Thursday night
through Friday night. A surface high moving into the region should
keep rain chances on the low side for the upcoming weekend, but
there is still plenty of uncertainty surrounding next weekend's
forecast.
&&

.AVIATION...for 12Z TAF Issuance
Issued at 423 AM CDT Mon Sep 23 2019

Primarily VFR conditions were across the area early this morning,
with isolated MVFR and IFR ceilings. A brief period of MVFR 
ceilings may develop (especially across the north) as diurnal 
convective cloudiness forms. Marginal LLWS may develop across 
north-central Wisconsin by late tonight.
&&

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

$$

SYNOPSIS.......Skowronski
SHORT TERM.....Skowronski
LONG TERM......MG
AVIATION.......Skowronski