616
FXUS63 KGRB 141144
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
644 AM CDT Sat Sep 14 2024

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

- There is a 15 to 30% chance of thunderstorms at times from this
  afternoon through Sunday afternoon, primarily over central and
  north-central Wisconsin. Severe weather is not expected.

- Summer-like temperatures through next week with highs ranging
  from the upper 70s to middle 80s.

&&

.DISCUSSION...
Issued at 253 AM CDT Sat Sep 14 2024

Short Term...Today...Tonight...and Sunday

High from mid-upper level rex block is shifting east allowing increasing
plume of higher PWATS over 1.5 inches (up to 175 percent of normal)
to stream into western Great Lakes. Forcing for showers through tonight
comes from a few sources, including piece of energy that broke northward
off of remnants of Francine, weak height falls with approaching northern
branch trough along with jet streak from central MN to northwest Ontario.
That said, the overall net forcing remains weak at best. This along
with limited instability and fact that we still are within purview
of sfc ridge extending westward across the Great Lakes from sfc high
over northeast CONUS/southeast Canada leads to isolated to perhaps
scattered showers and a slight chance of thunder across central and
north-central WI. Dry weather should hold elsewhere, including the
Fox Valley to the lakeshore. High clouds gradually will thicken over
central WI later this morning with filtered sunshine farther east.
Greatest chances for showers and a rumble of thunder tonight will be
over the north closer weak troughing and subtle jet streak. Highs
today will be similar to Friday with upper 70s to near 80 where clouds
are more prevalent and into the low to mid 80s farther east, but
inland from cooling influence of Lake Michigan. Lows tonight will
be more typical of early to mid August versus mid September with
readings only dropping into the lower 60s for much of the area.

On Sunday, shower and thunder chances are looking even more limited
due to even weaker large scale forcing and a wealth of mid-level
dry air. Thus, even as higher levels of low-level moisture and
warmth boost instability with MLCAPES upward of 1000J/kg, short
term models and CAMS are very muted with potential convection. Kept
very small chances (20% or less) from central to north-central WI
during peak heating of the day owing to the greater instability.
Otherwise, appears mid and high clouds will thin out steadily
into the afternoon, allowing temps to be at least a couple degrees
warmer compared to today. A bit more humid as well with afternoon
dewpoints in the lower 60s across the board.

Long Term...Sunday Night Through Friday

Main highlights from this forecast period revolve around the growing
potential for a prolonged period of dry weather for much of the
forecast area, and above normal temperatures continuing through at
least the end of next week.

Dry Weather/Precip Chances...For the first part of the work week,
the forecast area will be under the influence of a ridge of high
pressure centered over the Great Lakes/Northeast US region. Despite
southerly flow advecting moisture into the Northern Plains/Upper
Mississippi Valley during this time, the moisture will struggle to
spread eastward due to the dry air from the nearby high. The only
exception may be on Monday in part of the forecast area (north-
central WI), but the chance is very low (around 15 percent). A ridge
of high pressure will then gradually amplify over the Central Plains
into the Great Lakes with an area of low pressure on either side for
the remainder of the week. Given this pattern, any precip chances
will struggle to move eastward into the forecast area. However, if
the moisture can overcome the dry air, central and north-central WI
will see the best chance for precip towards the end of the work week.

Temperatures...Given ridging will prevail over the area throughout
this forecast period, the above normal temperatures are expected to
continue with highs mainly in the upper 70s to middle 80s. This
pattern will also keep the more moist air away from the area,
leaving comfortable humidity levels in place.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 644 AM CDT Sat Sep 14 2024

Patchy ground fog early again this morning, mainly at RHI and MTW
where brief LIFR/IFR could occur through 13z. Rest of the day will
feature mid and high clouds, thickest from central to north-central
WI. A pop-up shower or storm (prob30 mention) could occur in
those areas this afternoon into early evening, though there will
be no real reduction to cigs or vsby. Tonight will see more
extensive mid and high clouds across the entire area which should
limit ground fog potential. A few showers are possible late tonight
toward daybreak on Sunday over northern WI.

&&

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

&&

$$

DISCUSSION.....JLA/Kruk
AVIATION.......JLA