037
FXUS63 KGRB 101150
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
650 AM CDT Fri May 10 2024

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

- A quick moving cold front will bring showers and a few storms to
  the region late this afternoon into this evening. A few storms
  may contain gusty winds to 40 mph and small hail, but severe
  weather is not expected.

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

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

&&

.DISCUSSION...
Issued at 348 AM CDT Fri May 10 2024

Short Term...Today...Tonight...and Saturday

Lingering showers had finally dissipated, but cloud cover was
still prevalent over the southeast third of the forecast area
early this morning. Mostly clear skies and light winds over far
northern WI had allowed temperatures to drop into the upper 20s to
middle 30s where frost/freeze headlines were in effect.

A mix of clouds and sun will be found across the region this
morning, but increasing clouds and showers will overspread the
region from NW to SE as a cold front and potent short-wave trough
move through this afternoon and early evening. SBCAPE is weak and
confined to our far western counties in the late afternoon and
early evening, but 700-500 mb lapse rates of 7-7.5 C/km overspread
the forecast area, so isolated to scattered embedded storms are a
good bet with the main rain band. Forecast soundings show
inverted-v signatures supportive of gusty winds, and low wet-bulb
zero heights of 5500-6000 feet indicative of small hail potential
with the stronger storms. The main bulk of the precipitation will
shift east of the region by mid to late evening, with just a few
lingering showers expected over N WI.

On Saturday, partly to mostly cloudy skies will prevail, and a
slight chance of showers will accompany a short-wave trough,
especially in eastern WI.

Highs today should be in the lower 60s northwest, and mid to upper
60s southeast, except near Lake Michigan, where highs will only be
in the middle to upper 50s. Lows tonight will be in the upper 30s
to middle 40s. Highs on Saturday should be in the lower to middle
60s, except middle to upper 50s lakeside.

Long Term...Saturday Night Through Thursday

Impact potential is greatest during the Sunday afternoon and Sunday
night timeframe when a cold front crosses the region near peak
heating. Focus of this forecast therefore revolves around precip
trends and severe weather potential during this period.

Precipitation and Thunderstorm Chances...The weather system moving
across the region during this time period continues to have an
earlier arrival time. As a potent upper trough digs across northwest
Ontario, a warm front will quickly advance across Wisconsin late on
Saturday night into Sunday morning.  Showers will be possible along
the warm front, but little to no instability likely means the
thunderstorm threat is low.

Thunderstorm parameters turn more interesting on Sunday afternoon
and evening when a cold front can interact with a very unstable
airmass in the warm sector. The gfs in particular points to robust
surface based instability developing on the order of 2000-3000 j/kg
although ensemble means are considerably less (up to 1000 j/kg).
This discrepancy may be due to an over-zealous moisture profile in
which the GFS brings dewpoints in the upper 50s into the region
compared to the ensemble means of around 50 degrees.  Something to
watch for in subsequent forecasts.

Deep layer shear of 20-25 kts remains a limiting factor for severe
weather.  Given the potential for robust instability, think pulse
type storms could become strong at times, but the threat of
organized severe weather is low.

The next chance of precip following this system will arrive in the
late Wednesday-Thursday time frame.

Temperatures:  After a warm day on Sunday (mid and upper 70s),
temperatures cool closer to normal (60s) for the rest of the period.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 643 AM CDT Fri May 10 2024

Patchy fog in NC/C WI will mix out early in the TAF period and
localized MVFR stratus will gradually erode or lift to VFR this
morning, so initial aviation concerns will be short-lived.
However, a band of showers and embedded thunderstorms will
overspread the forecast area from mid-afternoon through the
evening, in association with a cold frontal passage. SW-W winds
will turn NW after the front passes through, and most of the rain
should end. There is a chance for some MVFR ceilings to drop into
NC WI, including the RHI TAF site, late tonight.

&&

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

&&

$$

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