At 19°N latitude, snow is the last thing you’d expect from a mid-August weekend in Hawaii, especially while much of the Northern Hemisphere is enduring a summer of endless heat and wildfire. Yet, that’s exactly what happened on Mauna Kea Aug. 15-16. Cameras atop Mauna Kea, Hawaii’s highest mountain, captured a few brief but indisputable images of fresh snow falling at the mountain’s summit.
At the time, few Hawaiians were paying much attention to the mountain. That’s because Hurricane Lala (now downgraded to a tropical storm) was making a swipe at Hawaii’s Big Island, bringing torrential rain, destructive winds, and dangerous surf. Only a few weather nerds bothered to locate Webcam images of the snow at Mauna Kea’s top observatory – that is, when the 140-mph (225 kph) wind gusts and nightfall weren’t obscuring the view.
- Related: Snowpack Climates Explained
How Did the Snow Happen?
Although Hawaii lies in the tropics, Mauna Kea rises to 4,207 meters (13,803 feet) above sea level. Mauna Kea is so high that it even preserves evidence of glaciation during past ice ages. Snow can occur on the summit during any month of the year. However, it nearly always falls between October and April. Even atop Mauna Kea, summer snows are rare.
Hurricane Lala is the main driver of this brief snow event. Snow in August requires a specific set of ingredients, even at this altitude. In this case, the hurricane drove moisture-laden air from sea level over Mauna Kea’s summit in a process called orographic lift. Air cools as it rises, and rainfall can add to this cooling through evaporation. Orographic lift and evaporation created just enough of a cold pool to create snowflakes on Mauna Kea’s summit.
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El Niño And Hurricane Lala
Ironically, the powerful Hurricane Lala, which managed to produce snow on Mauna Kea’s summit, was itself a product of intense heat in the Pacific Ocean.
- Related: El Niño Ski Season Outlook
That’s because during El Niño, unusually warm water spreads eastward across the equatorial Pacific. Readers have almost certainly heard about this year’s astonishingly powerful El Niño, which is expected to peak with temperature anomalies as high as 4℃ (7.2℉) above normal.
This creates a much more favorable environment for hurricanes to develop in the central and eastern Pacific. In addition to warmer waters, El Niño also reduces vertical wind shear, which allows storms to organize more easily in the atmosphere.
Lala is now expected to turn north and eventually east, strengthening back into a hurricane in the process. With favorable conditions moving forward, it might not be the last we hear about this storm.
