|Above: A tree rests on a vehicle, Sunday, Feb. 10, 2019, on a residential street in Tacoma, Wash. Pacific Northwest residents who are more accustomed to rain than snow were digging out from a big winter storm over the weekend and bracing for more snow. Image credit: AP Photo/Ted S. Warren.|
An unusually contorted weather pattern across the central and eastern North Pacific has brought mammoth surf and roof-lofting winds to Hawaii, while Seattle grapples with a prolonged bout of crippling snowfall. Between these two centers of action, an atmospheric river may develop later this week, pushing heavy lowland rains and mountain snows to California.
As of Sunday, Feb. 10, Seattle’s Sea-Tac airport had already notched the snowiest February in its 71 years of recordkeeping, with 14.1”. The last time any calendar month produced this much snow at Sea-Tac was November 1985, with 17.5”. There were a couple of snowier Februaries in Seattle prior to 1948, when Sea-Tac became the city’s official weather reporting site. The city recorded 17.4” in February 1923 and an amazing 35.4” in February 1916, when official reports were collected from the roof of the Hogue Building in downtown Seattle.
My favorite photo of the night! Sarah Jean and her 11-year-old sister Jordan Wagner created an adorable 'Snow Snoopy' enjoying the winter view from his doghouse in Lynnwood. Perfection! #WAwx #SeattleSnow pic.twitter.com/vvhsxa4Tmn— Shannon O'Donnell (@ShannonODKOMO) February 9, 2019
This month’s snow has socked Seattle in two clumps: 2.7” on Feb. 3-4, and a more impactful 11.4” on Fri-Sun., Feb. 8-10. Monday could be the fourth consecutive day with at least an inch of snow in Seattle, something that’s happened only eight times in records going back to 1894. However, the city is in line for what Cliff Mass (University of Washington) has already dubbed “Slushmageddon.” Warmer air will be pushing into the Puget Sound region from the southwest, forcing a transition from snow to rain between Monday and Tuesday. Snow amounts will vary tremendously across the Seattle region based on altitude and the precise timing of the warm-up, which in turn hinges on the northward movement of the warm front and an associated surface low. Huge amounts of snow are a safe bet for the Cascades of central and southern Washingotn.
The National Weather Service office in Seattle noted the local challenge they faced with a graphic on its home page that cautioned: “THIS IS AN EXTREMELY CHALLENGING FORECAST.” One NWS forecaster called it "probably the toughest forecast in the 32 plus years I have been here." In a Sunday night blog post, Mass concurred: “This is the kind of forecast that can easily go wrong. If the low ends up 100 km [60 miles] farther south, Slushmageddon becomes Snowmageddon. The ensemble forecasts have a wide spread. But I believe the above is the most probable evolution at this point.”
Over the next couple of days, the jet stream will be settling southward from the Pacific Northwest into California, pulling a ribbon of tropical moisture from east of Hawaii into the West Coast in the form of an atmospheric river (AR). This AR may be more beneficial than harmful, as it will not be exceptionally strong or persistent (the two variables employed to rank ARs in a new scale). Between 1” and 3” of rain are possible at lower elevations, and several more feet of snow are likely to sock the Sierra Nevada, especially above 7000 feet. As of Monday, the water content of snowpack across the Lake Tahoe and Truckee River watersheds was running 140% to 150% of average for this time of year.
See the weather.com article for frequent updates on this western U.S. storm, dubbed Nadia.
|Figure 1. The 500-millibar surface (typically about four miles above sea level) at 7 am EST Monday, February 11, 2019, shows the unusually low heights, corresponding to cold upper-level air, across both Hawaii and the western contiguous U.S. The dark blue over Hawaii indicates 500-mb heights that are at least three standard deviations below average. Image credit: tropicaltidbits.com.|
Hawaii’s wintry pummeling
A strong upper low moved just north of Hawaii over the weekend, bringing high winds to many parts of the islands and pounding north- and west-facing beaches with huge surf, including a record 38-foot significant wave height at the Hanalei buoy just off the north coast of Kauai. The rough seas reportedly killed one man in Napili Bay, off Maui’s northwest coast, and at least five people were injured in falls or by falling objects as high winds raked the Honolulu area. Tens of thousands of people lost power at various points during the blustery weekend. Hawaii News Now reported that at least 78 buildings were unroofed in the Honolulu area, and at least 31 trees were toppled, including three century-old kiawe trees in Hawaii’s largest public park. Top wind gusts across the metro area included 55 mph at the Waianae Boat Harbor and 48 mph at Honolulu International Airport.
|Figure 2. GOES-West visible image of Hawaii at 0 UTC February 11, 2019 (4 pm HST Sunday). A cold front from an intense winter storm to the north is affecting Maui and the Big Island. Image credit: NOAA/RAMMB.|
If conditions on Hawaii’s higher elevations didn’t set all-time records, they certainly came close. Snowfall was reported near the top of Haleakala, on Maui, and the Hawaii Department of Land and Natural Resources reported on Facebook that Polipoli State Park on Maui, with an elevation of around 6200 feet, was blanketed with snow on Sunday. “It [could be] the lowest elevation snow ever recorded in the state,” said the agency. Given the temperature regime in place, the frozen precipitation at Polipoli State Park may have been graupel (soft hail or snow pellets) rather than classic snowfall (see weather.com for details).
Snowstorm on Maui!! Crazy! pic.twitter.com/sKvCglbdRF— Reel News Hawaii (@reelnewshawaii) February 11, 2019
Temperatures at the observatories near the summit of Mauna Kea, which sits 13,802 feet above sea level on Hawaii’s Big Island, dipped below 12°F at several locations early Sunday, including the Canada France Hawaii Telescope (CFHT). This is almost certainly the coldest place in Hawaii, but changes in instruments and observing practices make it hard to know exactly how cold Mauna Kea has been during the era of modern observing. The NOAA State Climate Extremes Committee lists 12°F from Mauna Kea on May 17, 1979, as the official state record low for Hawaii. However, the observation report for that day shows that the 12°F was incompatible with other temperature readings that day and was later corrected upward to 21°F, according to WU weather historian Chris Burt, who added that a 9°F reading from January 1976 may have also been unreliable. In a 2011 blog post, Burt cited a 15°F reading on Jan. 5, 1975, as the most likely record, which implies that the state record may have fallen several times over the last few years given the growth in observations atop Mauna Kea.
A wind gust to 191 mph was also reported at the CFHT site on Sunday. It wasn’t immediately clear how this gust stood relative to the strongest winds on record at this very windy location. Winds at the Mauna Loa Observatory averaged roughly 16-22 meters per second (36-49 mph) from early Sunday to early Monday, compared to the site’s highest 24-hour average of 24.8 meters per second (55.5 mph), observed on Dec. 25, 2014.
|Figure 3. A flood-destroyed home in April 2018 off Wainiha Powerhouse Road in Kauai. Image credit: Kauai Emergency Management Agency, via NWS/Honolulu.|
It’s official: Hawaii now holds the U.S. 24-hour rainfall record
One record we know is solid (as well as liquid!) is the 49.69” of rain that fell in the 24 hours from 12:45 pm HST April 14 to April 15, 2018, at Waipā Garden on Kauai. NOAA/NCEI’s National Climate Extremes Committee announced: "After considering the observation, the state and condition of the observing equipment, and the meteorological environment in which the observation was recorded, the NCEC has determined, unanimously, that the 49.69 inches of rainfall observed at Waipā Garden is indeed valid, and constitutes a new 24-hour record precipitation value for the United States." The NWS/Honolulu website has a detailed report on the flooding in Kauai and Oahu associated with the rains of April 2018, which affected more than 500 homes and wreaked more than $20 million in damage.
The new record tops the previous 24-hour U.S. record of 43.00” that occurred in association with Tropical Storm Claudette at Alvin, Texas, on July 25-26, 1979.
NCEI has not issued a verdict on the reports of extreme multiday rainfall dumped on Hawaii’s Big Island by Hurricane Lane in August 2018. Two unofficial totals—58.80” at a private weather station and 52.02” at Mountain View—are both higher than the previous state record of 52.00” (Hiki, 1950). That amount also stood as a U.S. record for tropical cyclone rainfall until 2017, when Hurricane Harvey produced 60.58” at Nederland, Texas.
Dr. Jeff Masters contributed to this post.