This year, runners will face myriad conditions, potentially resulting in a wild swing of weather rarely seen during the event’s 123-year history.

A potent storm system will quickly move up the Ohio River Valley on Sunday afternoon, passing to the west of Boston and eventually ending up in northern New England by Monday. In the meantime, a complex set of fronts associated with an area of low-pressure systems, separating vastly different air masses, will be hovering nearby on Monday morning, right as the starting gun fires.

Similar to the other Abbott World Marathon Majors, the Boston Marathon has staggered start times, beginning with the Men’s Wheelchair event at 9:02 a.m. and ending with the final wave of runners at 11:15 a.m. This year, participants starting toward the end of the staggered start times may find themselves with completely different weather than their early morning counterparts.

Despite being less than 72 hours from the start of the race, forecast uncertainty remains extremely high. The difference in the air masses separated by the fronts is rather stark. North of the boundary, temperatures will be stuck in the upper 40s with a potent east wind (15-20 mph) directly in the face of the runners. South of the boundary, temperatures will soar in the mid-60s, and winds will be strong out of the southwest, or at the back of the runners. With a racecourse that runs due west to east, the direction of the wind matters a great deal to performance.

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As of Friday afternoon, the forecast has the bulk of the expected precipitation falling between midnight and 7 a.m. on Monday morning. However, once the frontal boundary eventually moves north of the racecourse sometime on Monday, the warm and moist air mass that follows may kick-start some isolated thunderstorms with embedded lightning.

Given what happened last year, race organizers are prepared for the worst.