The models remain adamant in their forecast of a very cold, modified (or even unmodified) Arctic airmass settling over most of the West in the 4-10 day period, especially away from the coast. A strong system will be the harbinger of this cold air. This cold frontal band will be pretty strong as it approaches CA, with intense rain, thunderstorms, and gusty winds a likelihood as the system feeds off of the steep thermal and baroclinic gradient. A cold and unstable airmass will then dominate the West Coast for a few days, characterized by numerous showers and scattered thunderstorms with hail. Snow levels near Seattle could actually be around sea level, and the coastal hills below 500 feet in Oregon will see some snow. Snow levels could drop to as low as 500-1000 feet even in Norcal. The -3 degree isotherm at 850 mb will slowly move south, possibly as far as Santa Barbara if the coldest scenario pans out. The -5 degree isotherm could traverse the Bay Area at some point, bringing the possibility of very cold (25-35 degrees) low temperatures to the Bay Area and also a few isolated pockets of frozen precip. This remains to be seen, but the strong jet diving due south out of the Gulf of Alaska does look menacing. If the jet dives further west, or lingers for more than a few days, even colder air could filter down the coast. Meanwhile, temperatures in the interior will be even colder. 850 mb temps approach -22 degrees Celcius in the 6-10 day period, along with very strong winds across the higher elevations. This could be a major and possibly record-breaking cold event for the interior, and if the flow can develop just right, for some coastal areas as well. This is pretty early in the season for a cold event of this magnitude to be developing, especially in an El Nino year. Stay tuned; things may chance rapidly over the next week.
