901 
FXUS63 KGRB 161855
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
155 PM CDT Sun Jul 16 2023

Forecast discussion for routine afternoon forecast issuance

.SHORT TERM...Tonight and Monday
Issued at 155 PM CDT Sun Jul 16 2023

The main concerns for the short term forecast will be:
-Rain and a few storms this afternoon and evening
-Lingering smoke aloft from the Canadian wildfires
-Another small showers chance tomorrow

Storms Today:
A weak cold front will work its way across the region this
afternoon and evening, bringing showers with a chance of thunder
to the region. The main front is still in northwestern WI, but
some of the showers and a few storms will work their way into
north-central WI by the mid afternoon. Dynamics along the front
will be the main driver for any thunderstorm development, with
fairly impressive bulk shear around 35 knots and strong vorticity
advection along the left exit region of an upper level jet.
Despite the forcing however, instability remains at a premium,
with more modest CAPE values around 500 to 700 J/kg and only
modest mid-level lapse rates. As a result, storms will likely be
fairly scattered with the frontal passage. Stronger storms will
likely be relatively brief, arising only where the strongest
forcing aligns with the better instability. The main thunderstorm
concerns will be wind gusts mixing to the surface and small hail.
Severe weather still seems unlikely at this time. 

Smoke:
Smoke has rapidly improved over the course of the day, with
surface visibility from smoke around 3 miles this morning lifting
to relatively unlimited visibility at the surface. Some hazy skies
and light smoke at the surface will remain through at least
midnight however, especially across central to east-central
Wisconsin, including the Fox Valley. There area a few hints that
some haze will return Monday afternoon, but for the most part the
worst of the smoke will be out of the region for now.

Showers Monday:
Another weak shortwave will work its away across the north on
Monday, producing cloudy skies along the Upper Peninsula border.
Some light precipitation will be possible out of this layer at
times, but no thunder is currently expected. The rest of the area
will predominantly see dry conditions.

Aside from the concerns above, temperatures will be a few degrees
cooler than last night, with lows in the upper 40s to middle 50s.
Tomorrow, high temperatures are forecast to be in the upper 60s to
upper 70s.

.LONG TERM...Monday Night Through Sunday
Issued at 155 PM CDT Sun Jul 16 2023

Overall, no significant changes to the long term portion of this
forecast package.

As far as the big picture is concerned, large-scale upper-level 
pattern will undergo a rapid transition as the upper-level low 
that has been loitering around southern Hudson Bay finally 
releases to the northeast by 12Z Tuesday allowing upper-level 
heights to rebound over the western Great Lake with flow becoming 
strongly zonal. Unfortunately, consensus of medium range guidance
is also locking in on another pesky upper-level circulation over 
southern Canada that will slowly drift southeast and becoming 
situated somewhere just north of Lake Superior by 12Z Thursday. 
With the fast zonal flow in place, confidence remains low during 
the mid-week in terms of timing of aforementioned upper-low and 
any weaker impulses that may eject from this primary system into 
the forecast area. 

In response to the approaching upper-level system, broad upper-
level PVA in concert with low-level WAA will increase late 
Wednesday over the northwest portion of the forecast area, in 
concert with an approaching cold front. At least initially, deeper
boundary layer moisture, steep mid-level LRs and best overall 
instability will be somewhat limited as these will be mostly 
bottled up across the central plains near a strong W-E baroclinic 
zone that will be host to MCS activity there. Thus, it appears 
precipitation late Wednesday into Wednesday night will be on the 
lighter side and mostly confined to the Northwest half of the 
forecast area. 

On Thursday, the upper-level low pressure system and associated
surface low pressure system and cold front will likely be located
somewhere over Wisconsin with additional shower and thunderstorm
activity probable. Whether or not any of the convective activity 
is able approach severe limits later in the day will largely 
depend on cloud cover, extent of lingering morning activity and
how progressive the surface cold front will translate across the
forecast area. Regardless, the period from roughly 06Z Thursday
through 00Z Friday will be rather unsettled. Given the above 
uncertainty, stayed close to blended temperature guidance during 
this period. 

Model consensus for Friday suggests that although surface low
pressure will be east of the forecast area, some E-W orientated surface
troughing may persist suggesting perhaps some diurnal shower
activity, especially into the afternoon.  

By early next weekend, it appears we will be back into a more NW
flow regime with some potential for some weaker, moisture limited
impulses dropping southeast across the area from time to time.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1252 PM CDT Sun Jul 16 2023

A weak cold front will pass through the region this afternoon and
evening, keeping scattered mid-level clouds in place and producing
some rain showers a few thunderstorms. Confidence on location was
not high enough to make the prevailing group for any one site, but
made a mention of vicinity precipitation for each TAF site as the
cold front crosses the region. Aside from the active weather,
smoke and gusty winds will also hang around into the evening
before departing by late overnight. Quieter conditions are
expected for Monday morning, before winds begin to increase again
for portions of the region. There is some potential for an MVFR
cloud deck across the far north tomorrow, which may work its way
into RHI Monday afternoon.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

SHORT TERM.....Uhlmann
LONG TERM......ESB
AVIATION.......Uhlmann