508
FXUS63 KGRB 261923
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
223 PM CDT Wed Jun 26 2024

Forecast discussion for routine afternoon forecast issuance

.KEY MESSAGES...

- Showers and thunderstorms may bring locally heavy rainfall to
  the region Friday and Friday night. The severe weather threat is
  low.

- Small Craft Advisory may be needed from Friday morning through
  Friday night.

- Cool conditions for Sunday and Monday with temperatures around
  10 degrees below normal.

- Some rivers and streams will remain above bankfull and near
  flood stage into the middle of the week.

&&

.DISCUSSION...
Issued at 221 PM CDT Wed Jun 26 2024

Short Term...Tonight and Thursday

A passing shortwave along with warming surface temperatures helped
to develop a scattered cumulus field across the region. A few of
these clouds developed into brief light showers near the Upper
Peninsula border, but any rain should be fairly short-lived and
light. As the afternoon progresses, these showers could also clip
portions of northern Door County, but the rest of the region will
likely remain dry through the afternoon.

High pressure will continue to build across the region tonight,
bringing clearing skies and quiet conditions overnight. Between
the clearing skies and cooler, drier air in the region, expect low
temperatures to get into the middle 40s to middle 50s tonight.
Thursday will start clear and sunny but cloud cover will be on the
increase again in the late afternoon as winds shift to the south
and some warmer air starts to come back in aloft. The cooler air
from overnight will also keep Thursday fairly cool, with highs
ranging from the upper 60s to middle 70s.

Long Term...Thursday Night Through Wednesday



While an upper-level subtropical high pressure sits over the
southern CONUS well into next week, the northern CONUS will see a
progressive northern stream bring systems through the western
Great Lakes. The first impactful system arrives Friday night with
the possibility of strong to severe weather and heavy rains. A
trailing weaker system may bring some showers on Saturday. The
second impactful system is set to arrive late Monday night and
last into Tuesday evening. For the most part, temperatures to be
at or below normal through Monday, then at or slightly above
normal headed toward the middle of next week.

Thursday night and Friday...
As the surface high pulls farther to our east Thursday night,
attention turns to the Upper Midwest where a warm front and cold
front to reside. A strengthening 35-40 knot southerly low-level
jet to begin pulling moisture northward and interact with the
northward moving warm front to bring at least a small chance of
showers toward central WI by daybreak. There will be drier air
initially to overcome, thus most location will only see increasing
clouds through the night. Min temperatures to be in the lower to
middle 50s north, middle to upper 50s south. The warm front lifts
north of WI on Friday, while the trailing cold front to still be
located across the Upper MS Valley. Morning pops appear to be
focused over northern WI (vicinity of the warm front) and central
WI (ahead of an approaching shortwave trough). Precipitation
coverage to expand across all of northeast WI in the afternoon as
this shortwave trough moves into the region. Deeper low-level
moisture to have arrived by the afternoon with PW values of 1.5 to
2.0 inches, thus a potential for brief heavy rains. Severe looks
unlikely during the day with meager (< 200 J/KG) instability.
Temperatures to be held in check with the clouds/precipitation
increasing, thus readings only expected to reach the upper 60s to
lower 70s.

Friday night and Saturday...
The cold front gets a shove east into the western Great Lakes
Friday night by a trailing stronger shortwave trough pushing east
across the northern Plains. Instability still looks weak, but
shear does increase to 40-50 knots. Despite the weak instability,
the strength of the shear may support a threat of supercells with
large hail and damaging winds the main threats. The caveat here is
if we can get sufficient buoyancy which is still uncertain. Models
are hinting at two main areas of heavier precipitation, one over
the northern Great Lakes in the vicinity of a surface low and the
second area over the Midwest/central Plains/mid-MS Valley in the
vicinity of the cold front/better instability). For northeast WI,
will need to watch both the severe potential and rainfall totals.
Min temperatures Friday night to be around 60 degrees far north,
middle to upper 60s east-central WI. The trailing shortwave trough
sweeps across the region on Saturday. While the bulk of the
moisture to have been shunted east by the cold front, there may be
enough mid-level forcing to interact with residual instability and
shear to develop a small chance of showers/thunderstorms,
especially in the afternoon. Otherwise, look for a mix of sun and
clouds with max temperatures to range from the lower 70s north-
central WI, middle 70s to around 80 degrees elsewhere.

Saturday night and Sunday...
Any precipitation would cease Saturday evening as the shortwave
trough departs and high pressure begins to build into the region.
Clearing skies will lead to a cool night with parts of north-
central WI pushing 40 degrees. Sunday is looking like a great day
as the high pressure moves over WI. Plenty of sunshine is
anticipated, but temperatures will be on the cool side with upper
60s to lower 70s.

Sunday night and Monday...
After a quiet Sunday night, the high pressure shifts to our east
on Monday allowing for a return flow to develop over WI. The GFS
wants to already bring WAA-induced precipitation to central WI by
Monday afternoon, but this may be a tad fast with an upper ridge
sliding over the region and dry air to overcome. Expect Monday to
be dry, but may add a slight chance to central WI. Max
temperatures to range from around 70 degrees to the middle 70s.

Monday night and Tuesday...
Showers/thunderstorms look to sweep across the region Monday night
as a 40 knot southerly low-level jet quickly transports moisture
northward into WI ahead of a cold front and another mid-level
shortwave trough. Some of this rain may again be locally heavy.
These showers/storms would continue through most of Tuesday as the
cold front/shortwave trough traverse the area. Max temperatures
Tuesday to be in the lower to middle 70s north/near Lake MI,middle
70s to around 80 degrees south.

Tuesday night and Wednesday...
Precipitation chances finally come to an end later Tuesday night,
however long-range models are showing yet another shortwave trough
that could affect the area by Wednesday afternoon. Will need to
carry small pops for now. Max temperatures Wednesday to warm a bit
with middle to upper 70s north/near Lake MI, upper 70s to lower
80s south.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 109 PM CDT Wed Jun 26 2024

VFR conditions are expected through the TAF period. A few mid to
high clouds will still be in the region for this afternoon, along
with some fair weather cumulus clouds. A few sprinkles are
possible near the Upper Peninsula border this afternoon as well,
but will likely remain as virga. Any cloud cover in the area will
dissipate this evening, bringing in clear skies and light winds
overnight and into Thursday.

&&

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

&&

$$

DISCUSSION.....Uhlmann/Kallas
AVIATION.......Uhlmann