Cold storms: tstms and low snow levels

Filed in Uncategorized by on February 21, 2007 26 Comments

A rather significant storm is currently at our doorstep. A steady moderate rain has been falling for much of the day on the far NorCal coast north of Cape Mendocino, with some light showers as far south as the Bay Area. This rain is associated with a strong cold front that is nearly stationary between the OR/CA border and the Eureka area. This front has been trending more towards a north-south orientation through the day (as opposed to a west-east drape) and the lower part of the front is beginning to pivot. A strong wave has developed on the backside of the front along a strong jet stream, which is continuing toslow the southward progression of the front but is also servingto intensify the frontal band. I would expect the front the continue to move south over the next 24 hours, reaching SoCal by Friday. The front will be rather strong, esp. in NorCal, with a 3-6 hour period of heavy rain and possible thunderstorms along with gusty and potentially strong winds as high as 45 mph or so. Total rainfall in the far north could be as high as 4-5 inches, 1-4 inches in the Bay Area, and generally 0.75-3.5 in the Southland. The main story, however, will be the very cold air that wil move in immediately behind the cold front. 850 mb temps plummet to -5 C across far NorCal, as low as -4 C around the Bay Area, as low as -2 C in the Los Angeles area, and as low as -1 C near San Diego. Although the coldest air aloft will not arrive until much of the significant precipitation has ended, some showers will low snow levels will undoubtedly occur across CA on Thursday afternoon and night. Snow levels in the far north will be locally as low as 500 feet…1000-1500 feet in the Bay Area…1500-2000 feet in the Los Angeles area…and 2000-3000 feet in the San Diego area. Local snowfall accumulations of 1-4 inches are possible one many “peaks” that do not normally see snow. In addition to the low snow levels, convective chances will be quite high with this system. Post-frontal convection will be rather strong, especially if some sunny breaks can help to increase lapse rates and further destabilize the atmosphere. Therefore, thunderstorms are a good bet from Thursday PM into Friday AM, at least. Tstms or heavy showers could produce bursts of hail or ice pellets just about anywhere, producing hazardous driving conditions. It will certainly be a good sky-watching period. I’m not even going to tackle the extended forecast at this point…it’s just too messy. There appears to be a strong potential for cold and wet weather to continue and perhaps even intensify for at least the first part of next week…with another one or two systems with low/very low snow levels and the chance for thunderstorms. An interesting period ahead…and even SoCal, it appears, will get in on at least some of the action (though it still won’t be “drought-busting”). Feel free to send any reports of hail/snow/thunder to our Weather West blog…