Chicago-Mackinac: Cold water, Light winds

The 106th Chicago Yacht Club Race to Mackinac has attracted 320 entrants for the oldest annual freshwater distance race in the world. The fleet departs on July 18 and 19, with the 333 mile course starting at the Chicago Lighthouse, just off Navy Pier, and continuing north through Lake Michigan to Mackinac Island, Michigan, in Lake Huron.

Chris Bedford of Sailing Weather Service is providing the race forecast, and will present a formal weather briefing on Friday at the Skippers’ Meetings. Here’s his preliminary outlook as of Thursday, though he admits that a lot can still change, and with the current information available, he has only average confidence in the following:

There’s been perhaps some modest improvement since Wednesday, but it is still looking like a slow race. The outlook is for weak lake breezes on Friday, Saturday and Sunday, with morning and afternoon calms likely away from the IL/WI shore across the central and MI shore portions of Lake Michigan. A mix of light S/SW gradient and lake breezes will dominate winds over the northern ½ of the lake.

For the boats still on the course after Sunday, the outlook is for a building gradient – especially over the northern 1/3 of the lake – on Monday and especially Tuesday. The best news is that the risk of thunderstorms is LOW.

Friday, July 18 – Cruising Division
Primary high pressure will be over northeast US and move slowly east. A ridge will extend west of the high across the central lakes. Because of the cool water on the lake, local high pressure will settle over southeast Lake Michigan. A broad, light S’ly gradient will be over much of the lake, but lake breezes (7-11 kt) will over-ride the gradient during the PM on the IL/WI shore. The lake breeze will die overnight, leaving weak winds on the shore (< 5 kt), but a persistent, light S’ly gradient (4-7 kt) mid-lake. Mainly sunny/clear and seasonably mild weather.

Saturday, July 19 – All Divisions excluding Cruising Division
High pressure over eastern US with ridge across the central Great Lakes region. Again, the cool water supports weak high pressure over southeastern Lake Michigan. A trough of low pressure will be moving north from the Ohio Valley, killing any S’ly gradient component over the southern half of the lake, leaving light 5-10 kt E/SE lake breezes as the only wind source on the IL/WI shore. Light and variable conditions mid-lake. The S’ly gradient will hold over the northern ½ of the lake, but this too will be light (< 10 kt ). Very soft E/SE breezes (< 5 kt) are expected over the southern ½ of the lake Saturday night into Sunday morning. Weather will continue fine with sunny/clear conditions and mild temps.

Forecast through Tuesday, as of July 17

Updated forecast, as of July 18

Race website