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016
FXUS63 KGRB 051954
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
254 PM CDT Sun May 5 2024

Forecast discussion for routine afternoon forecast issuance

.KEY MESSAGES...

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- Patchy fog is possible late tonight until an hour or two
  after sunrise on Monday.

- Relative humidity values are expected to drop into the middle
  20s and 30s Monday afternoon. Recent rain, lack of strong gusty
  winds and continued green-up will limit fire weather concerns.

- Next round of showers and storms arrives Tuesday morning. Best
  chance for thunderstorms will be Tuesday afternoon and evening.
  There is a small risk for a stronger storm especially for our
  western areas.
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&&

.DISCUSSION...
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Issued at 253 PM CDT Sun May 5 2024

Short Term...Tonight and Monday

Fair weather cumulus clouds developed late this morning and
continued this afternoon away from the bay and Lake Michigan.
Temperatures climbed into the 60s, except only around 50 near the
Lake Michigan shoreline. The lake breeze was beginning to move
westward towards Green Bay and the Fox Cities.

For the rest of the afternoon, the lake breeze should move into
Green Bay and the Fox Cities late this afternoon. The passage of
the lake breeze front will bring a wind shift to the southeast
along with temperatures falling several degrees.

For tonight, the fair weather cumulus clouds should dissipate
around sunset. With clear skies and light winds overnight, some
patchy fog is expected to develop toward sunrise on Monday. The
fog is expected to be patchy and not dense with the amount of
drying taking place today.

On Monday, a sunny and mild day is anticipated with highs in the
middle 60s to lower 70s away from the bay and Lake Michigan.
Afternoon relative humidity values should drop into 25 to 30
percent range across the far north with 30-40 percent away from
the bay and Lake Michigan. Southeast winds will increase Monday
afternoon with gusts of 15 to 20 mph expected at most spots.

Long Term...Monday Night Through Sunday

Several opportunities for rain this week as a general unsettled
pattern dominates. No great signal for anything too significant in
terms of storms or rainfall, though we`ll have to keep eye on late
Tuesday if destabilization can occur.

The Monday night through Tuesday evening time frame will likely
be when the most rainfall occurs this week. Deep low sub 985mb
will be lifting northward across the northern plains. Occluded
front well ahead of the low will be interacting with PWATs up to
1.25 inch approximately the 90th percentile for this time of year.
SE flow ahead of this front will also be drawing in dry air tied
to departing high pressure. Slower trend for rain shower arrival
that started showing up 24hr ago remains today, if not even slower
yet. Expect most cwa to remain dry on Monday night, except maybe
the very far western fringe. Eventually though band of moderate
showers (lasting 3-6 hrs at any one location) will swing across
the area beginning mid to late morning on Tuesday. Lingering dry
air could keep parts of east-central and northeast WI from not
seeing rain arrive until at least early Tuesday afternoon.
Current forecast temperatures show decent range with expected
showers and SE winds keeping central to north-central/northeast WI
cooler while earlier ending of steady showers and winds shifting
to the SW could allow temps to reach near 70 south of Wisconsin
Rapids to Oshkosh.

Best chance for thunderstorms comes Tuesday afternoon and evening
as models show a thin band of instability (MLCAPE now increasing
to 500 to as much as 1000 J/kg) building from western to central
WI. Additionally mid-level lapse rates approach 7.5-8.0 C/km
during this period owing to cooler air aloft as H5 temps drop
below -20c beneath elongated trough from Montana to the western
Great Lakes. Seems another embedded shortwave arrives over west-
central WI late afternoon to kick off the additional convection
chances. Forecast soundings show relatively low wet-bulb zero
heights (6-8kft) with inverted-V look. Effective shear is 30-40
kts. Timing will be key as if initial wave of showers moves
through quicker, then there would be more time to destabilize in
the afternoon. SREF thunder/severe probs point to far southern WI
for better severe potential, but think there is at least a small
risk into our southwest areas. In terms of rainfall amounts the
consensus of the ensembles point to likely (60-80%) of seeing at
least 0.50 inch of rain but tail off to less 30 percent for seeing
over 1".

Wednesday through Thursday...Ensembles have come into decent
agreement with a period of dry weather Wednesday morning as dry
air behind an occluding front filters over the region. Dry
conditions may not last long as the weakening cyclone moving east
out of the northern Plains merges with a developing southern
stream system returning rainfall to the region late Wednesday into
Thursday. Possible some convection may occur late Wednesday mostly
over central and western WI away from more easterly flow developing
off Lake Michigan. These east winds may get a bit gusty on
Thursday as they turn northeast once primary low pressure system
begins to shift more to the central Great Lakes and Ohio Valley.

Rest of the extended...Seems Thursday night into Friday will dry
out. If clearing occurs earlier, some risk for fog or frost over
north-central WI early Friday morning. Rather vigorous trough is
on track to drop across the western Great Lakes by Saturday. Due
to this, the risk for showers has increased for Friday night into
Saturday but the chances for chilly min temps and some frost
Friday night over the north has lessened. Will just have to see
if the trend holds. Unsettled weather continues for the weekend as
low pressure slowly drifts away and a reinforcing cold front drops
across.
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&&

.AVIATION...for 18Z TAF Issuance
Issued at 1157 AM CDT Sun May 5 2024

VFR conditions will prevail through Monday afternoon. The only
exception could be for some MVFR visibilities across far north-
central Wisconsin, especially Vilas County, towards sunrise on
Monday morning. Fair weather cumulus between four and six thousand
feet this afternoon will clear around or shortly after sunset.
Fair weather cumulus clouds will redevelop, generally around
the same height, late Monday morning and afternoon. The next
chance of rain will be on Tuesday morning.

&&

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

&&

$$

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