'Bomb Cyclone' Causes Severe Disruptions in California and Oregon, Macy's Thanksgiving Day Parade Under Threat As Storm Moves Northeast

A winter storm warning and winter weather advisory are in effect across northern California and southern Oregon through Wednesday. Heavy snows, strong winds and coastal flooding are expected to cause severe disruptions for the Thanksgiving holiday travel period. The storm hits the northeast on Thursday, possibly disrupting the annual Macy's Thanksgiving Day Parade in New York City.

"A Winter Storm Warning means that severe winter weather is imminent, and poses a threat to life and property," while a "Winter Weather Advisory will be issued for any amount of freezing rain, or when 2 to 4 inches of snow (alone or in combination with sleet and freezing rain), is expected to cause a significant inconvenience, but not serious enough to warrant a warning," the NWS explains.

Commuters in the affected areas are being advised to avoid travel, if possible, or to postpone travels until weather conditions improve, following the damaging effects of a powerful "bomb cyclone" which developed over the eastern Pacific on Tuesday.

A bomb cyclone occurs when a low pressure system drops "at least 24 millibars over 24 hours. A millibar measures atmospheric pressure," the National Oceanic and Atmospheric Administration National Ocean Service explains. "The formation of this rapidly strengthening weather system is a process called bombogenesis, which creates what is known as a bomb cyclone."

A Winter Storm Warning is in place for parts of northern California until 2 p.m. (local time) Wednesday, with total snow accumulations of between 8 and 16 inches likely at elevation level of 2,500 feet in the Del Norte, Humboldt, northeast Mendocino, and Trinity counties (and higher totals above 4,000 feet), coupled with strong winds and small hail, the NWS notes.

"Major travel impacts will continue into Wednesday, with many chain restrictions and delays, particularly across interior mountain roadways above 1500 to 2500 feet in elevation," the NWS warns.

Hail accumulations may occur down to sea level, which will cause slippery roads, while downed trees, power outages, rock slides and coastal flooding from high tides and large seas are also possible across the northern California region, the NWS also notes.

The Bay Area has already seen "pea-sized hail" in Alameda, as the cold front moved through the region on Tuesday, with cold temperatures and widespread rainfall of up to 2 inches and heavy snow expected throughout the week, the NWS predicts.

A Winter Storm Warning remains in effect until 4 p.m. (local time) Wednesday in parts of Oregon including "northeast Siskiyoum, northwest Modoc Counties-Klamath Basin-Northern, Eastern Klamath County and Western Lake County, including the cities of Dorris, Newell, Macdoel, Tulelake, Altamont, Klamath Falls, Beatty, Bly, Chemult, Crescent, Gilchrist, and Sprague River," the NWS confirms.

A Winter Weather Advisory has been issued for the south central coast of Oregon until 10 a.m. (local time) Wednesday for elevation levels above 1,500 feet, possible snow accumulations of more than 10 inches at higher levels and potential wind gusts between 60 and 80 miles per hour.

Storm update - 7:35 pm PST - Intense low pressure down to 972 mb just off the coast OR/CA. #CAwx #ORwx #BombCyclone pic.twitter.com/fvzXCsG1D1

— NWS Medford (@NWSMedford) November 27, 2019

"Travel will be very difficult to impossible, at times, during this time period. Strong winds and heavy snow could create near white-out conditions at times. Strong winds could also cause downed trees and power outages. TRAVEL ON BEAR CAMP ROAD IS STRONGLY DISCOURAGED! Snow will decrease in coverage and intensity Wednesday morning but travel impacts will continue," the NWS warns.

"Significant snow and wind impacts will occur across the area [southern Oregon]. Conditions will improve Wednesday afternoon, so wait until then if you can. However, ICY conditions will develop again Wednesday night," the NWS forecasts.

Several other pockets of Oregon, including the McKenzie Pass, McKenzie Bridge, Oakridge and the Willamette Pass, are under a Winter Storm Warning, while the cities of Parkdale and Odell are under a Winter Weather Advisory until 12 p.m. (local time) on Wednesday.

"Heavy snow and strong winds expected. Total snow accumulations of 12 to 24 inches. Winds gusting as high as 50 mph [miles per hour]" and "travel will be very difficult to nearly impossible at times. Heavy snow and strong gusty winds will create blizzard conditions at times above 3500 feet, including highway 58 over Willamette Pass," the NWS advises.

A powerful storm will continue to push onto the West Coast today, with strong winds and falling snow levels. Wind gusts may reach 70 MPH near the Oregon and northern California coast. The storm will move east later this week and this weekend with potential for more disruptions. pic.twitter.com/R8oNMNbook

— NWS Weather Prediction Center (@NWSWPC) November 26, 2019

Blowing snow with total accumulations of 3 to 6 inches is expected for the Upper Hood River Valley of Oregon and commuters should expect "slippery road conditions and reduced visibility," the NWS warns.

"In the wake of the storm moving off the New England coast early Thanksgiving Day...strong winds will develop across much of the Northeast, threatening portions of the Thanksgiving Day parade in New York City. Wind gusts to 40+ mph [miles per hour] are possible across New York City on Thursday," the NWS adds.

The parade's famous balloons can only be operated if sustained wind conditions stay below 23 miles per hour and wind gusts do not exceed 34 miles per hour under New York City regulations, according to Orlando Veras, a Macy's Parade spokesman.

More than 55 million people will be traveling for Thanksgiving this year—1.6 million more than last year—according to the latest report by INRIX, global transportation analytics company.

The 2018 Macy's Thanksgiving Day Parade in NYC
The 2018 Macy's Thanksgiving Day Parade in NYC. The famous event can only take place if sustained wind conditions stay below 23 miles per hour and wind gusts do not exceed 34 miles per hour under city regulations. Getty Images