847
FXUS63 KGRB 170750
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
250 AM CDT Tue Sep 17 2024

Forecast discussion for routine morning forecast issuance

.KEY MESSAGES...

- Summer-like temperatures continue through Thursday with highs in
  the 80s. Temperatures to stay in the 70s near Lake Michigan.
  Slightly cooler temperatures are expected this weekend, although
  should remain well above normal for this time of year.

- The chances (40-60 percent) of showers and thunderstorms arrive
  Thursday night and linger into Friday as a weak cold front
  moves into and across the area. There is a continued chance for
  storms over the weekend, although there is a lot of uncertainty
  in the timing of the rain.

&&

.DISCUSSION...
Issued at 249 AM CDT Tue Sep 17 2024

Short Term...Today...Tonight...and Wednesday

First off, seeing another early morning with locally dense fog
closer to the warmer/moist waters of Lake Michigan. No real fog on
the water, but the light southeast wind is adding moisture to low-
levels and combining with nighttime cooling to form the fog. Have
issued a special weather statement for the lakeshore counties. A
few obs of fog farther inland, though this is probably more of a
shallower type ground fog.

For the short term looking at largely a persistence forecast through
Wednesday. Little net change in upper-level pattern with higher
heights holding to the north of the upper low over the southeast
and also downstream of western CONUS troughing. Sfc pattern steady
too with ridging continuing to persist out of northeast CONUS
high pressure. Scattered thin high clouds and few-scattered fair
weather cumulus should do little to impact temps. Highs last few
days have shot past guidance and even what would be expected with
full mixing to H85, perhaps due to recent dryness. Used that as
guide to bump up high temps today and Wednesday to as warm as
87-89F. This is quite the contrast to the latest round of NAM MOS
guidance which is much cooler for Wednesday (78 at GRB for example),
but doesn`t seem reasonable given the pattern. Forecast will be
much more in line, but still warmer than, the latest GFS MOS
guidance (86 at GRB). Light southeast winds keep it cooler in the
mid 70s at the Lake Michigan shoreline.

Drying aloft as shown by higher H85 dewpoint depressions working
in from the east resulted in lowering dewpoints/RH values both
afternoons as well. Nighttime cooling will drop min temps tonight
into the lower to mid 50s. Similar to the last few nights, have
kept a mention of patchy fog near the bay and Lake Michigan.

Long Term...Wednesday Night Through Monday

The omega blocking pattern across the CONUS will gradually
break down heading into the weekend. The ECMWF has a closed 500mb
developing across Ontario on Sunday with a fairly zonal flow into
early next week. Well above normal temperatures will continue
into the weekend, then temperatures return closer to normal early
next week.

The best chance for rain will be Thursday night into Friday as an
upper level disturbance and weak cold front move across the area.
Model soundings would support the mention of thunder during this
time frame, although the risk of severe weather is low. The latest
model runs tonight are less bullish on the chances of rain late
Friday night and Saturday. There is a lot of uncertainty in
the rain chances late Saturday night into Sunday, but a better
chance of rain may be on Sunday if the ECMWF and Canadian model
are correct. The GFS kept this period dry at the moment. Based on
model trends, raised high temperatures a few degrees on Thursday
and trended a little higher for Friday and Saturday based on the
latest numerical guidance.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1031 PM CDT Mon Sep 16 2024

Areas of dense ground fog are possible near the bay and Lake Michigan
overnight. MTW and OCQ are likely to see IFR conditions with the
fog. There could be patchy fog elsewhere at places like RRL, EGV
and LNL. Any fog should dissipate by 13z Tuesday. Outside of any
ground fog, VFR conditions are expected with some high clouds at
times.

&&

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

&&

$$

DISCUSSION.....JLA/Eckberg
AVIATION.......RDM