Saturday, January 3, 2015

Hawaiian Blizzard

While much of the U.S., including Alaska, has been short on snow this winter, snow is making some headlines in the least likeliest of places, Hawaii. On Friday night the National Weather Service in Hawaii issued a blizzard warning (yes, blizzard as in snow and wind) for the Big Island summits above 11,000 feet. Winds were expected to gust to 130 mph along with up to a foot of snow, producing near zero visibilities and white-out conditions. The blizzard warnings extended through 6:00 p.m. HST today. High wind warnings were issued for most of the Hawaiian Island chain last night through early this morning.

The warnings were prompted by an unusually strong low pressure system and cold front moving through the islands. The strong pressure gradient around the low produced the high winds near the surface, while a strong upper level trough maintained the strong winds at the higher elevations.

North Pacific surface analysis for 8:00 a.m. HST January 2.
Last night at 6:00 p.m. HST winds at Mauna Kea on the Big Island were west sustained at 79 mph gusting to 139 mph with the temperature at 28°F. The highest wind gust recorded early this morning was 155 mph near the summit of Mauna Kea at the Canada-France-Hawaii Telescope weather station
Timer trace of the wind speed and direction near the summit of Mauna Kea.
The passage of this weather system left thousands without power on most of the islands as the strong winds toppled trees and power lines. Precipitation was also heavy, with amounts from 0.50 to 1.50 inches across the islands. The CoCoRaHS observer at HI-KI-6, Kilauea 0.5 SE measured 2.77 inches of rain this morning.

CoCoRaHS observations for Hawaii the morning of January 3.

Colder air in the wake of this system spread across the island chain today. Island residents were able to observe cold air cumulus today, a common occurrence here in the continental U.S. in the spring and fall but very rare in the tropical Pacific. These clouds develop as much colder air at middle and upper levels creates in a vertical temperature profile that favors the vertical formation of cumulus. As the surface warms cold weather cumulus quickly form and often fill in to result in overcast conditions.

Overcast skies from cold weather cumulus on the north shore of Oahu at 10:30 a.m. HST January 3.

A dry trade wind pattern is forecast to redevelop across the islands early next week.

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