Sacramento ( and LA ? ) Snow Disaster 1 Week Away??

[Ed Mahmoud]

OK, it is a week away, and with ground temps progged in middle to upper 30s, it may not stick well anyway, but both the 12Z Canadian and 12Z GFS predict a Sacramento, CA SNOW DISASTER HORROR!

Six inches if it actually stuck, maybe more...

[RL3AO]

Oh...the horror.

[jahrmor]

I'm geting my x-county skis waxed today! It looks by Monday the 15th the 528 thickness line will be south of Sacramento.

[Ed Mahmoud]

Oh...the horror.

[jahrmor]

The Sunday morning 850mb 0 degree isotherm is almost in Mexico; however, the 528 thickness line is hanging more North around Redding on this last run of NOGAPS. Not as much moisture either.

https://www.fnmoc.navy.mil/wxmap_cgi/cgi-bin/wxmap_single.cgi?area=ngp_epac&dtg=2008120912&prod=850&tau=120

https://www.fnmoc.navy.mil/wxmap_cgi/cgi-bin/wxmap_single.cgi?area=ngp_epac&dtg=2008120912&prod=prp&tau=120

[Ed Mahmoud]

The Sunday morning 850mb 0 degree isotherm is almost in Mexico; however, the 528 thickness line is hanging more North around Redding on this last run of NOGAPS. Not as much moisture either.

https://www.fnmoc.navy.mil/wxmap_cgi/cgi-bin/wxmap_single.cgi?area=ngp_epac&dtg=2008120912&prod=850&tau=120

https://www.fnmoc.navy.mil/wxmap_cgi/cgi-bin/wxmap_single.cgi?area=ngp_epac&dtg=2008120912&prod=prp&tau=120

Getting towards the end of the 6 day run, but the 12Z Canadian suggests parts of Northern/Central California not fairly close to the Pacific may see some exciting weather Monday.

I was based in Alameda, CA, did some camping in NorCal, and in Summer time, the first row of hills (the reflection of the Hayward fault) in Oakland and Berkeley could mean a 10ºF temperature differential easily in just a few miles.

Of course, ocean modified warm air might have an easier time climbing those hills with an onshore wind than an ocean modified fog bank...

[Ed Mahmoud]

NWS Oxnard/Los Angeles now showing snow levels dropping below 4000 feet next week, and if models are correct, it could come down lower than that.

GFS model predicts snow at Los Angeles airport next week, but I think snow will not fall West of the coastal ranges.

[Aslkahuna]

Thickness values of 528 dm are not generally low enough for a major snow event in SAC and certainly not in Los Angeles (record snowfall there is only a bit over 1 inch). You need 522 dm thickness and lower for sea level snow in CA and SAC is close to sea level elevation. A 528 will give you snow levels below 2K.

Steve

[jahrmor]

I live at the 1200ft elevation just East of Sacramento and we usualy run a few degrees cooler. It looks like the trajectory of the low is more over land which would imply that it would be able to keep some of its cooler air but sacrifice some of its moisture. I still feel that most of the models over predict these low snow events. I think the record snow for Sacramento is only 3 inches. The majority of the time it is only a flurry and nothing will stick to the ground.

[Ed Mahmoud]

Handy AccuWx PPV MOS still shows thicknesses in mid to upper 520s, 850 mb temps near -5º, surface temps between 2 and 3ºC (touch warmer than I'd prefer, but in this part of the country, GFS tends to be a tad too warm on surface temps with cold air, and I don't know wny Cali would be different) while 12 hour accumulated liquids vary between a tenth and two tenths of an inch, for, potentially, somewhere between wet ground and some elevated surface slush to as much as maybe eight inches.

[Aslkahuna]

First off, while I can't speak for CA either insofar as GFS forecast temperatures are concerned, I do know that in AZ the GFS tends to overdo cold air. However, that being said again thicknesses in the high 520 dm range over CA does not mean sea level snow but probably snow levels in the 15-2500 ft range. Need much lower thickness in CA for sea level snow (generally 518-522 dm). Secondly, -5C at 850 mb over northen and Central CA is not extraordinarily cold for the winter and again suggests snowlevels around 2500 ft. The cold airmass will most likely be a mPk or mAk type airmass if there's any moisture in the low levels which means a trajectory over the comparitively warm Pacific Ocean and also a very unstable low level temperature profile (which is why CA thunderstorms along the coast occur most often in Winter) so sea level temperatures are likely to be well above freezing as will the dewpoints. If the H85 got down to -10C or lower then you could make a case for either sub 1000 ft snow levels or even convective snowshowers in places but a general snow is very rare. I spent the first 23 years of my life in the SFO Bay Area and saw measureable snow at the house only twice. OTOH we saw snow down to 1000 ft or lower about once a winter.

Steve

[Ed Mahmoud]

If that 2ºC to 3ºC surface temp was correct, and temps 1500 meters up were -5ºC, if the snow was coming down at a decent clip, it'd have time to melt?

I know the frustration of living near the ocean, in Long Island snow would frequently change to rain if the wind came from any direction South of about due Northeast, but as I recall, the change usually happened between 36 and 38ºF. Different ocean, I know, but I had the bad luck of living in Alameda for six years, and even in the Summer, that Pacific is mighty cold.



BTW, off topic, how do they compute 1000-500 mb thickness for places at elevation. If you're in the Rockies, at or above the 850 mb level, how do they figure that (layman terms please, BS in pet eng, so I know some math, but very little met)

[Aslkahuna]

Ordinarily if the H85 temperature is -5C then the sealevel temperature would be higher than 2 or 3C in the Sacramento area since the air would be unstable with a lapse rate rather greater than 1.5C/1000ft. However, I have seen conditions like that in CA and the most we got out of it was a snowline at about 500 ft and at best R-/S- mixed occurring at night. The Pacific Ocean is indeed cold in the Summer due to upwelling resulting in SST's in the 50's due west of SAC. However, the upwelling is very much reduced if present at all so the temperatures don't vary that much season to season off CA-not quite like the ATL where near shore waters get quite cool due to persistent offshore cold air flow. It's just plain hard to get snow in Sacramento under any usual circumstances takes an unusual pattern.

Steve

[jahrmor]

I guess I’ll rely on my old “rules of thumb”. If the solid precipitation falls through a warm layer less than 600ft then it will remain solid. If the warm layer is between 600ft and 1200ft then the precip will be mixed. If the warm layer is thicker than 1200ft then the precip will fall as liquid. I will have to see where the freezing level is going to be on Saturday through Monday and determine if their will be available moisture. The models all most always overdo the cold temp. and available moisture. Most all the snow I’ve seen at low elevations in Northern CA has always come from convective type systems.

[Ed Mahmoud]

GFS usually trends too warm here in Southeast Texas in Winter. If its usual error is too warm in SAC, then maybe the poor school children of the Sacramento and San Joaquin Valley won't get a snow day or two.


GFS raw numbers from 12Z for SAC continue to show fairly light precip at various times Monday through Friday, with surface temps ranging between just below 0º and 3º, 850 mb temps ranging -2 to -6ºC, and thickness running between 523 (at end of six hour period of heaviest 12 hour precip, just over 0.2 inches) and as high as 531.


I know people in SAC, I shall try to remain glass half full optimistic and hope for at least one night with accumulating snow and school cancellations.


I never lived in Sacramento or Fresno, but I've been to both cities, I did spend a Summer in the oilfield in BFL.

FAT numbers a bit cooler surface, a tad warmer (still below freezing) 850 mb, and several periods with the surface around -2ºC

BFL a touch warmer than FAT.

The 6Z and 12Z temps are coolest at all the cities Monday through Friday. The GFS knows day and night, apparently, but the diurnal swings are small, 2 or 3ºC.


It'll be interesting to see what the GFS shows for the freezing level (see post above) when the wxmaps.org meteogram updates.

ETA: This hotlinked meteogram now shows 0Z GFS for SAC, should change in about 2 hours.

[Ed Mahmoud]

12Z NAM loop.

Doesn't look quite cold enough for snow in SAC, but I'm a glass half full kind of w!shcaster.

[jahrmor]

Best chance will be Sunday Night - Monday Morning, but Sacramento usualy will stay just warm enough to prevent snow. Just a wet cold windy storm.