Marine Weather and Tide Forecast for Lawrence, MI

DISCUSSION
Issued at 343 PM EDT Thu Apr 17 2025

- Round of storms late tonight/early Friday

Complicated forecast next 36 hours with main fcst challenge being convective trends/timing and strength.

Northward moving warm front, incoming 50-55kt low level jet, and leading edge of higher PWATs sends a band of showers through the area this evening. This is followed by increasing chances for thunder overnight as MUCapes over 1000 J/KG arrive.

Various CAM runs have been hinting at the possibility of a decent nocturnal MCS rolling through between 4 am and 9 am, favoring areas near and north of I-96. The main threat with these elevated storms would be small hail, heavy downpours and lightning although some isolated stronger wind gusts cannot be ruled out. If Gravity Wave Associated Convection (or GWAC) were to develop/occur then some high gusts could reach the ground despite stable/cool boundary layer conditions. (See recent paper by Borchardt et al on the GWAC subject in Weather and Forecasting.)

After any early morning storms depart, we'll have to watch for the possibility of a few additional stronger, discrete cells developing near the northward moving warm front/on the northern edge of the incoming cap. Guidance shows a few updraft helicity swaths north of I-96 from late morning through mid afternoon, before the warm front lifts far enough north for the cap to become better established. If those storms occur and can become rooted in the boundary layer then a TOR threat may exist for a few hours.
There could also be a mesoscale outflow or two still floating around from any earlier convection.

- Severe storms possible Friday evening

Presence of a capping inversion around 5K ft and CIN values of 200-300 J/KG will likely limit convective convective potential between 18Z and 00Z Friday; possibly longer. The main impetus for new development after 00Z will be the incoming, slow moving sfc cold front but questions remain regarding the coverage and strength of Friday evening convection since the really good mid level lapse rates of 8-9 C/KM may be departing to the east around that same time. If some overlap can exist then damaging winds and/or large hail may occur. Svr potential wanes after Midnight as instability drops off and sfc cold front works through.

- Additional showers Sunday/Monday

Upper low tracking from the srn Plains to WI brings another chance of showers Sunday and Monday. Sfc warm front lifts back north Sunday night but gets quickly pinched off by occlusion/cold front sweeping from the west early Monday, so the thunder and svr threat with that system looks quite low at this time.

AVIATION /06Z TAFS THROUGH 06Z SATURDAY/
Issued at 137 AM EDT Fri Apr 18 2025

Convective trends over the next 24 hours will be the main focus of the 06z set of forecasts. We have a few showers along the I-96 corridor out of the gate with this period. This have been all VFR thus far with little low level moisture present. We will see the thunder threat increase at KMKG and maybe KGRR over the next few hours as convection over WI heads this way. The low level jet is ramping up over the area around 2-4k ft agl, so we have low level wind shear of 55 to 60 knots since sfc winds are much less, and a bit different direction.

Showers and a few storms will remain possible through around noon or 16z or so at KGRR and KMKG. MVFR is likely under these showers/storms, with some IFR possible. Southern terminals will likely not see much at all and stay VFR.

We will likely see conditions dry out during the afternoon hours, and clouds will likely even break out. Then, late in the period beginning around 02z the cold front will approach from the NW and touch off additional showers and storms. They may not reach KJXN by the end of the period at 06z Sat. Additional low level wind shear will be likely with the approach of the front again.

MARINE
Issued at 343 PM EDT Thu Apr 17 2025

A period of hazardous winds and waves is expected on Lk MI through Saturday morning. Strong southerly winds tonight and Friday eventually shift northwesterly on Friday night with a cold frontal passage. Also, rounds of thunderstorms will pose a hazard to mariners from late tonight through Friday night. Can't rule out some areas of fog too once the warmer and more humid air mass arrives on Friday.

GRR WATCHES/WARNINGS/ADVISORIES
MI...None.
MARINE...Small Craft Advisory until 11 AM EDT Saturday for LMZ844>849.