Organizers of the 42nd annual Chevron Houston Marathon expect 250,000 fans to line the course this Sunday, but navigating Houston this weekend will be tricky owing to race-related road closures.

The marathon course begins at Congress and San Jacinto, treks west through Memorial Park, south to Post Oak, east through Rice Village and North on Kirby before finishing on Allen Parkway.

Those who live within that roughly 15-square-mile area, as well as spectators who want to see the race, would be wise to consult the marathon's extensive list of road closures. Streets surrounding the start and finishing areas will be blocked off as early as Thursday through Sunday afternoon, while roads used for the course will be closed on a rolling basis from 6:15 a.m. to 2:20 p.m. Sunday.

Parts of downtown and Midtown will also be closed on Saturday morning for the 5k race.

The marathon has put together a handy list of ten popular viewing locations. Popular perches include Washington Avenue, West Gray, Tanglewood and Memorial Park.

Also worth noting is that runners may ride METRO for free on Sunday with their bibs (just not, of course, during the race).

As for the weather, forecasters predict temperatures will cool down this weekend from near-record highs this week, but still remain about 20 degrees above normal for January. KHOU is calling for highs in the mid-70s Saturday and Sunday, with a chance for a few stray showers during the marathon. The marathon will begin Sunday at 7 a.m. (when, of course, it will still be hot and humid.)

Runners consider temps in the 50s with low humidity as ideal long-distance running weather — so Sunday's unseasonable warmth will likely result in slower times across the board.

The weather takes a turn for the worse on Monday, when heavy rains could bring flooding to the region. We'll keep an eye on that storm system as it approaches and update readers about the flood risk.

The 5k course. Matt Griesmyer

Marathon Course Closures

-Congress from Crawford to Smith

-Smith from Congress to Franklin

-Franklin from Smith to Washington (all lanes except one westbound curb lane)

-Washington from Congress to Waugh (all lanes except one westbound curb lane from Franklin to Houston, and one eastbound curb lane from Studemont to Sawyer)

-Heights/Waugh (southbound) from Washington to West Gray

-West Gray/Inwood from Waugh to Kirby

-Kirby (northbound) from Inwood to San Felipe

-Kirby (southbound) from San Felipe to Bissonnet

-Bissonnet from Kirby to Montrose

-Mandell (southbound) from Bissonnet to Sunset

-Sunset from Mandell to Rice Boulevard

-Rice Boulevard from Sunset to Greenbriar

-Greenbriar from Rice Boulevard to University Boulevard

-University Boulevard from Greenbriar to Weslayan

-Weslayan (from University to Bissonnet

-Weslayan (northbound) from Bissonnet to Westpark

-Westpark from Weslayan to South Rice Boulevard (all lanes closed except one westbound lane from Newcastle to 610/59 northbound feeder road

-Loop 610 feeder (southbound) from Richmond to Westpark

-Post Oak Boulevard (northbound) from Richmond to San Felipe

-San Felipe (westbound) from Post Oak Boulevard to Tanglewood Road

-Tanglewood Road (northbound) from San Felipe to Chimney Rock Road

-Chimney Rock Road (northbound) from Tanglewood to Woodway Drive

-Chimney Rock Road (southbound) from Woodway Drive to Memorial Drive

-Memorial Drive (westbound) from Chimney Rock Road to Loop 610

-Memorial Drive (eastbound) from Loop 610 to Shepherd

-Shepherd (all lanes under overpass) from Memorial Drive to Allen Parkway

-Allen Parkway from Shepherd to Bagby

-Dallas from Allen Parkway to Bagby

-Bagby from Dallas to Lamar

-Lamar from Bagby to Avenida de las Americas

-Avenida de las Americas from Polk to Rusk

-Additional Half Marathon Course Closures

-Montrose from Bissonnet to Main/Mecom Fountain

-Main (southbound) from Mecom Fountain to Bissonnet

-Bissonnet (eastbound) from Main to Montrose

-Montrose (southbound) from Bissonnet to Dallas

-Montrose (northbound) from Dallas to Allen Parkway

-Freeway Exit Ramp Closures

-610 West Loop, southbound, exiting to Hidalgo/Richmond

