Does anyone know why the sudden chill in the west

[wthrmilagro]

However, it does like warmer air is coming soon

[Aslkahuna]

Well, when you have an offshore ridge that allows systems to dig down out Canada straight into SoCA, it does tend to be rather on the nippy side. Actually though, it's been colder than normal down here since the end of October as the whole month of November had colder than normal temperatures.

Steve

[wthrmilagro]

Well, when you have an offshore ridge that allows systems to dig down out Canada straight into SoCA, it does tend to be rather on the nippy side. Actually though, it's been colder than normal down here since the end of October as the whole month of November had colder than normal temperatures.

Steve

But like the central and east coast when cold air and warm air collide you get snow right? If so, then why not snow in SoCal?

[MGC]

No snow in S Cal? Well, the San Gabriel Mountains get tons of snow and they are just north of LA. Coastal Southern California sees little snow since prevailing winds are from the SW during a rain event there. A SW wind bring in moist Pacific air thus the temps along the coast are too warm for snow........MGC

[Aslkahuna]

Actually, one of those systems did dump snow on much of inland SoCA. But there's another factor involved (actually more than one). First off those inside sliders rarely have the moisture with them needed for any
form of precipitation to result until they get far enough away from the mountain wall of the Sierra to be able to draw moisture in from the Pacific. By that time the system is usually somewhere around 35N or further south. Secondly, although we think of the Pacific as cold-that's only in the Summer when we have the upwelling. Off the SoCA coast, the SSTs in the Pacific are usually in the 50's-60's all year around and it's hard to get snow when the lower layers are warmed up to 14-16C. Dynamically speaking, the structure of the storm systems are different with regards to the thermal structure. The fronts usually outrun the trough. Airmass wise, unless you pick up a ST moisture plume, the air ahead of the front will generally be dry until you get very close to the front. Behind the front you will have mPk air which is very unstable and very moist with the dynamics of the trough acting upon it and this is is where you get the precipitation. But once again mPk airmasses are not cold enough for sea level snow once you get south of Oregon. The cPk air usually comes in behind the trough where subsidence prevents any cloud formation-also cP air has to come in with offshore flow and offshore flow in CA is downslope off the land and in SoCA goes by a special name-Santa Ana so unless the system is very cold aloft and the trajectory is such that the cP or cA air comes around the backside and then off the ocean then snow is unlikely at elevations below 1000 feet or snow in SoCA. The critical thickness value for snow in SoCA is more like 528 dam
rather than 540 dam elsewhere meaning that the upper column has to be really cold.

Steve