The weather at El Malpais is dynamic and changes greatly over the span of hours, weeks, and seasons. As a general rule, daily temperatures swing roughly 30 degrees (F) from night lows to afternoon highs.
Broad seasonal patterns are as follows, though visitors should be prepared for a variety of conditions throughout the year:
Summer (June-Mid July): This is the hottest part of the year, before summer monsoon moisture arrives. High winds are less common, but heat builds quickly out on the black lava of the Malpais. Plan your activities around hot, dry afternoons in the high 80's to mid-90's. The forested west side of the monument may be more comfortable than the exposed east-side attractions down Highway 117, and sunscreen, brimmed hats, and plenty of water are "musts." Most plants remain dormant, but resident birds and reptiles are active until the afternoon heat sends them into cooler places to shelter.
Summer Monsoon (Mid-July to September): Within days of the first monsoon soak, this arid landscape explodes with life; the grasses and wildflowers seem to green and bloom almost overnight, and wildlife responds in-turn with an abundance of birds, butterflies, and unexpected critters like toads and frogs easily encountered. Temperatures are generally milder than the previous dry summer months, though heat can still be an issue. Monsoon thunderstorms can be dangerous, both directly from lightning groundstrikes that travel long distances horizontally on lava flows, and from impassible road conditions on any unpaved road surface. A surprisingly small amount of rain can make these roads too slick to drive. Monsoon storms can form very quickly, so keep a constant watch on conditions. If you see the characteristic towering clouds building around you, don't delay - seek shelter in your vehicle. Otherwise, this is a wonderful time to visit the monument, but do be prepared for heat, wind, rain, and dangerous stormy conditions.
Fall (October - Early December): Roads dry and access to many east-side attractions resumes in the fall, when evening temperatures drop to freezing but days are usually sunny and pleasant. Besides the monsoon period, this is probably the second-best time to visit the monument. Be prepared for early snowstorms and cold mornings.
Winter (Late December - February: Cold, with night time lows sometimes reaching -20 degrees (F) and highs usually above freezing, sometimes up into the 50's (F). Snows are usually light within the monument, but roads, especially around the Continental Divide along Highway 53 between El Malpais and El Morro, can be dangerous and/or impassible. Check weather and travel conditions frequently. Winter is a good time to see the sites down Highway 117; the view from the Sandstone Bluffs area is greatly enhanced with snow cover on the lava.