Unless the forecast changes, visitors attending the People’s Climate March should wear summer attire and be sure to hydrate. A high of 90 on April 29 is 19 degrees above normal and near the average maximum temperature in mid-July.

The warmth will result from a sprawling area of high pressure off the Southeast coast that will pump hot air toward the Mid-Atlantic.

There is some chance that if the cloud cover is more pervasive than forecast, temperatures will not be quite as warm. Some models are predicting highs more in the 80- to 85-degree range rather than near 90.

It is likely to be not only unseasonably warm but also unusually humid. The dew point, a measure of humidity, is expected to reach the mid- to upper-60s.

Any dew point over 65 is considered quite humid and more typical of July than April. Factoring in Saturday’s predicted humidity, the air could feel as hot as 92 to 95 degrees in the mid- to late afternoon.

The hot-weather forecast to end April in Washington is almost certain to catapult the month to its warmest average temperature on record, more than seven degrees above normal.

It will mark Washington’s second record-warm month in the past three (February was also record warm) and seventh record-warm month since 2010.

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