677
FXUS63 KGRB 091135
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
635 AM CDT Thu May 9 2024

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

- An unsettled weather pattern will bring intermittent chances of
  showers and a few thunderstorms through the weekend. Severe
  weather is not expected with any of these thunderstorms, but we
  will be watching for the potential for strong storms on Sunday.

- Low temperatures in the lower to middle 30s will be conducive
  for a frost or freeze over north-central and far northeast
  Wisconsin late tonight into early Friday morning.

- Due to rainfall over the past week, river levels remain
  elevated. Some rivers may reach or surpass bankfull.

&&

.DISCUSSION...
Issued at 335 AM CDT Thu May 9 2024

Short Term...Today...Tonight...and Friday

Forecast concerns include minor precipitation chances today,
frost/freeze potential over northern WI tonight, and another
round of showers and thunderstorms arriving Friday afternoon.

A weak frontal boundary and short-wave trough was generating a
band of scattered light showers across far northern WI early this
morning. These showers were drifting slowly south and gradually
weakening. Farther south, showers associated with a short-wave
over northern IA were edging toward the sw part of the forecast
area.

The weak cold front will continue to sag south and eventually
interact with the IA short-wave as it moves east through southern
WI. This should bring a small chance of showers over the far
southern part of the forecast area today. Highs should reach the
upper 50s to lower 60s, except middle 50s near lake Michigan.
Brisk NE winds will occur in the Fox Valley.

Any showers should shift south of the region by evening, followed
by clearing skies as a ridge of high pressure moves into WI.
Light winds will allow temperatures to drop into the upper 20s to
middle 30s north, and upper 30s to lower 40s south. Areas of frost
and localized freezing temperatures will likely occur over north
central and far northeast WI. Frost/freeze headlines look like a
good bet, but will let the day shift make headline decisions this
afternoon.

On Friday, morning sunshine will give way to increasing clouds
and showers as a cold front and potent short-wave trough arrive
in the afternoon. Will keep eastern WI dry until the evening, but
have increased pops to likely over north central and central WI
late in the day. Most of the SBCAPE is expected to remain west of
the forecast area, but mid-level lapse rates of 7.0-7.5 C/km
support a mention of thunderstorms. Highs should reach the lower
60s northwest, and middle to upper 60s elsewhere, except near Lake
Michigan, where temperatures will only reach 55 to 60 degrees.

Long Term...Friday Night Through Wednesday

The forecast continues to call for low impact weather for the next
week as the region will be under northwest flow through next Monday.
Forecast concerns mainly revolve around light rain and
thunderstorm chances.

Rain and thunder chances...A dynamic shortwave will bring light rain
to the region on Friday night.  Minor instability up to 300 J/kg of
most unstable cape is still projected to sneak into central and
north-central WI in the evening that could lead to a slight chance
of a thunderstorm. Otherwise, precipitation amounts of a 0.10-0.25"
remain possible before precip exits late on Friday night.

In the wake of this shortwave, a trailing shortwave will interact
with diurnal instability to produce cloud cover and possibly a few
showers.  0-3 km lapse rates are relatively steep to 8.5 C/km, but
equilibrium levels are quite low at around 650 mb and not sufficient
for thunderstorm development. Will keep precip chances low.  Most
precip will dissipate with loss of heating by early Saturday evening.

Another chance of precip remains projected to arrive on Sunday into
Sunday evening when a warm front, followed by a cold front, move
across the region from the northwest.  Despite weaker dynamics
compared to the Friday night system, instability looks considerably
more robust with mixed layer capes from 700-1000 j/kg over central
and north-central WI.  Thunderstorms look possible, but the severe
threat appears low due to weak deep layer of 20 to 25 kts.

After this system, the chance of rain looks to return during the
middle of next week.

Temperatures...High temperatures in the 60s and 70s are forecast
from Saturday through the middle of next week.  There was some
concern for frost on Saturday night, but cloud cover looks to arrive
earlier ahead of the Sunday system which will mitigate the chance of
frost.  Low temperatures have therefore increased on Saturday night.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 632 AM CDT Thu May 9 2024

Mainly VFR conditions are expected through the TAF period, with
scattered light showers or sprinkles occurring during the daytime
period. NE winds will gust to 15 to 20 kts, especially in the Fox
Valley area. high pressure will bring clearing skies and light
winds tonight.

&&

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

&&

$$

DISCUSSION.....Kieckbusch/MPC
AVIATION.......Kieckbusch