Half Marathon Weather Guide: Race Day Preparation

The half marathon is the sweet spot of distance racing—long enough to require strategy, short enough to push hard. Weather affects your race significantly, but smart preparation can minimize its impact.

Ideal Half Marathon Conditions

<WeatherCard condition="Perfect Half Marathon" temp="48-55°F" humidity="40-60%" wind="Under 10 mph" verdict="great" />

Research shows optimal half marathon temperatures are slightly cooler than shorter races because you're running hard for 1.5-2+ hours.

Temperature Adjustments

Pace Impact by Temperature

| Temperature | Pace Adjustment | |-------------|-----------------| | 45-55°F | Optimal - goal pace | | 55-65°F | +10-20 sec/mile | | 65-75°F | +20-40 sec/mile | | 75-85°F | +40-60 sec/mile | | 85°F+ | +60+ sec, safety first |

Racing in Heat

The half is long enough for heat to accumulate:

• Start 15-20 seconds slower than goal pace
• Take water at every station
• Pour water on head/neck
• Accept a slower finish time

Racing in Cold

Cold half marathons can produce PRs:

• Throw-away layers at start
• Warm up thoroughly
• First 2 miles may feel sluggish
• Body warms quickly at race effort

<QuickTip> For a half marathon, the second half is where weather really matters. Even if you feel good early in heat, the accumulation catches up. Start conservative. </QuickTip>

Humidity and the Half

Why Humidity Hits Hard

At half marathon effort (85-90% max HR), your cooling system works overtime. High humidity prevents efficient cooling.

| Dew Point | Impact | |-----------|--------| | Below 55°F | Minimal | | 55-60°F | Slight slowdown | | 60-65°F | Moderate impact | | 65-70°F | Significant - adjust goals | | Above 70°F | Major adjustment needed |

Wind Strategy

Half Marathon Wind Math

Wind matters for 1.5-2 hours of running:

• Headwind sections: ease effort slightly
• Tailwind sections: don't speed up much
• Net effect is always negative

Drafting in the Half

At half marathon pace, drafting helps:

• Find a group running your pace
• Tuck in behind larger runners
• Take turns at front
• Save 3-5% energy

Clothing Choices

Hot Half Marathon

• Singlet (lightest option)
• Short shorts
• No socks if possible
• Sunglasses
• White arm sleeves for sun (optional)

Cold Half Marathon

• Long sleeve or short sleeve base
• Arm warmers (can remove)
• Shorts or half tights
• Light gloves (can discard)
• Headband for ears

Rainy Half Marathon

• Fitted clothing (less drag when wet)
• Brimmed cap essential
• Anti-chafe everywhere
• Accept getting wet

Week-Before Strategy

Weather Monitoring

• Check forecast daily starting 7 days out
• Note temperature trend
• Prepare multiple race strategies
• Have gear options ready

Mental Preparation

Have three goal times ready:

• A goal: Perfect conditions
• B goal: Challenging conditions
• C goal: Difficult conditions

Race Morning

Final Weather Check

Morning of race:

1. Current conditions at race start
2. Forecast for race duration
3. Wind direction relative to course
4. Any weather warnings

Last-Minute Adjustments

Based on conditions:

• Adjust starting pace
• Modify fueling plan
• Choose appropriate clothing
• Reset mental expectations

During the Race

First 5K

• Assess conditions
• Lock into sustainable effort
• Don't chase others who start too fast

Middle Miles (5K-15K)

• Maintain even effort
• Take all water stations in heat
• Adjust if conditions worsen

Final 5K

• In good conditions: push
• In bad conditions: survive smart
• Race place, not time, if weather is poor

Fueling Adjustments

Hot Races

• More fluids, possibly less fuel
• GI issues more common in heat
• Test fueling in hot training runs

Cold Races

• Normal fueling works
• May feel less thirsty (still drink)
• Gels may be thick (warm in hand)

<AppCTA title="Train for Any Conditions" description="Use Run Window to train in varied weather during half marathon prep. Race day surprises are easier when you've experienced different conditions." />

Key Takeaways

1. 48-55°F is optimal - Expect slower times in heat
2. Humidity above 65°F dew point is brutal - Adjust significantly
3. Start conservative in heat - The second half punishes fast starts
4. Have multiple goals - Let conditions determine which to chase
5. Drafting helps - Find groups to run with
6. Fuel and hydrate appropriately - Weather changes your needs

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Half marathon success requires weather awareness. Run Window helps you prepare by showing what conditions to expect.