Marine Weather and Tide Forecast for Fennville, MI

DISCUSSION
Issued at 331 PM EDT Thu May 15 2025

- Severe Thunderstorms this Evening

Tonight between 8pm and 2am a round of thunderstorms is expected to move through the area bringing with it the potential for damaging winds, large hail, and tornadoes.

The main source of lift for these storms will be with the occluded front with upper level divergence aloft along with some convergence in the wind fields at 850-700mb. Instability has been gradually building through the day with Mixed Layer CAPE values currently in the 1500 to 2000 J/kg range across much of the area.
Thunderstorms are beginning to develop along the front in Minnesota and are expected to expand south along the front as it moves east this afternoon and into this evening. 0-1km storm relative helicity values peak ahead of the front in the 100 to 150 m2/s2 range and around 200 m2/s2 from 0-3km. Paired with 30 to 40 knots of effective shear and Most Unstable CAPE values around 2000 J/kg this will be a prime environment for rotating updrafts, hence the increased hail and tornado risk.

There is some variability in the storm mode as it heads into western Michigan. Individual storms are expected to develop in Wisconsin and may become clustered or form a line as they move across the lake into western Michigan. If storms take a more linear formation, then winds and quick spin up tornadoes would become the main concern. Any isolated or clustered supercells would be more likely to produce all hazards, especially hail.

With the risk for severe storms late this evening, make sure you have a way to receive warnings and a plan in place to take shelter when warnings are issued.

- Another Round of Strong Friday Evening

Most of Friday will be dry with instability building through the day. Steep lapse rates and ample dry air causing an inverted V in soundings will set the stage for an environment favorable for downbursts. Lift provided by the positive vorticity advection swinging around the 500mb low will move in around 8pm Friday causing showers and thunderstorms to develop. Similar to Thursday evening storms taper off shortly after midnight.

- Windy Saturday, Cooler into Next Week

The same low mentioned in the previous section will gradually track across the northern Great Lakes Saturday. Lingering showers associated with the low should clear early Saturday afternoon, but as the rain and lower clouds clear, gusty westerly winds will develop. Some gusts to 40 mph are possible during the afternoon.
Calmer conditions move in for the remainder of the weekend with highs in the 60s and lows in the 40s and 50s.

AVIATION /06Z TAFS SATURDAY THROUGH 06Z SUNDAY/
Issued at 1258 AM EDT Fri May 16 2025

Strong large scale subsidence in the wake of the thunderstorm complex will support mainly clear skies through the duration of the night and Friday morning. Daytime heating will boost mixing depths resulting in south winds gusting over 20 knots at times by Friday afternoon. The passage of an upper level short wave and late day instability will support a good chance for thunderstors Friday eveing, primaily in the 01Z to 06Z time frame.

MARINE
Issued at 331 PM EDT Thu May 15 2025

A round of thunderstorms is expected between 8 and 10pm with the potential for large hail, damaging winds, and waterspouts. Rough water is expected with this round of storms with southwest winds moving in behind the line. A second round of storms moves in Friday night with the potential for storms to be strong with gusty winds being the primary concern. The low pressure system responsible for these rounds of storms will move through the northern Great Lakes Saturday bringing with it a tight pressure gradient and gusty Westerly winds. A Small Craft Advisory is in effect for Friday through Saturday evening due to winds and high waves.

GRR WATCHES/WARNINGS/ADVISORIES
MI...None.
MARINE...Small Craft Advisory from 11 AM Friday to 2 AM EDT Sunday for LMZ844>849.