Question for Expert

[aveosmth]

As I now have money on this system as far as low snow levels w/a buddy of mine...I need some expert help.....if you look at the 500mb vort map in the latest gfs run...it shows all of socal in a brownish/yellow tint....w/heights at 534...wouldnt this support low snow levels???

TIA,

Avery

[Stormchaser16]

No, wrong model map you got there. Need to take a look at 1000-500 Mb thicknesses and 850 thermals. That is strictly a 500MB vort map.

[Stormchaser16]

http://www.nco.ncep.noaa.gov/pmb/nwprod ... p_168l.gif

Sure it looks cold and all, but often times out west you need even colder thermals to support low level snows. What the GFS shows here IMO is a higher elevation snowfall and nothing more.

[aveosmth]

Thanks for the information there!!! Looks like its gotta get even colder....its been trending that way which is good.....so hopefully it will continue....hopefully the atmosphere will be destablized enough to allow for convection which tends to lower snow levels as well....

Thanks again stormchaser,


Aveo

[Stormchaser16]

Possibly and sometimes models have a hard time with elevation differences. Not sure how the GFS handles it specifically, but sometimes especially out west, those cold readings could be the model picking up on colder readings at higher levels. Actual surface variants may be somewhat different. What IS going for that system though is that the models have it as a closed off 500 low sitting in the STJ over the SW. IF this happens and it gets held back there for awhile, it MAY draw in some colder air from upstream. Strong SLP's tend to draw in towards themselves so if there is enough cold air around to tap, then a closed off 500 lo most certainly will.

[FLguy]

normally the cold air underneath a closed or cutoff low across the southwest is NOT deep enough to produce frozen precipitation down to the surface. looking completely at 1000-500mb thicknesses WILL NOT give you a better idea either. most of the time while 500-850mb partial thicknesses are low enoguh for snow...1000-850mb partial thicknesses are too high (warm) for frozen precipitation to make it down to the surface.

end result...LA sees little more than a cold rain. much is the same up and down the west coast.

[Stormchaser16]

Absolutely true Flguy, however the GFS(as fantasy as it may be) DOES have the 1000-500 MB temps plenty cold enough. Although i personally am more inclined to think that this is a result of it seeing the colder temperatures at a higher elevation and is having a hard time geographically out in the SW especially with this feature(upper level feature as well as surface feature)

[Cumulonimbus]

Fl guy and stormchaser...very true regarding the west. The mountains and ocean totally change things regarding snow near the surface. Even as far north as Seattle where I live 850 temps have to be lower than -6 to -7 and thicknesses below 525 to think about snow falling near sea level. Although Seattle is quite a way north...both the Pacific Ocean and Puget Sound almost always keep the snow level off the surface due to an onshore flow. Earlier this month the arctic air did indeed move south and west into western Washington and the north part of western Oregon but that is the first time since 1998 it has been that strong a push. Winds were north-northeast for 2 days which brought the air south into the western part of both states. Very seldom does it last more than 3-4 days and is soon scoured out by warm ocean air.
1969 was a remarkable January when arctic air DID cover the region for THREE weeks. Seattles(airport) snowfall that January was 45 inches, one of the snowiest Januarys on record. I remember that winter well and it is the snowiest one I have seen while living here.


Alex

[weatherlover427]

Being that I live in this area too (Northwest Orange County, CA) I am watching these models closely. I did observe snow and sleet on a few occasions while I have lived here in southern Cali; but it was a bit further inland than I am now. I have seen temps get down to 31.8 at one point here, which is just cold enough for frozen precip. So if we had moisture at the time, it would have happened.

[FLguy]

Fl guy and stormchaser...very true regarding the west. The mountains and ocean totally change things regarding snow near the surface. Even as far north as Seattle where I live 850 temps have to be lower than -6 to -7 and thicknesses below 525 to think about snow falling near sea level. Although Seattle is quite a way north...both the Pacific Ocean and Puget Sound almost always keep the snow level off the surface due to an onshore flow. Earlier this month the arctic air did indeed move south and west into western Washington and the north part of western Oregon but that is the first time since 1998 it has been that strong a push. Winds were north-northeast for 2 days which brought the air south into the western part of both states. Very seldom does it last more than 3-4 days and is soon scoured out by warm ocean air.
1969 was a remarkable January when arctic air DID cover the region for THREE weeks. Seattles(airport) snowfall that January was 45 inches, one of the snowiest Januarys on record. I remember that winter well and it is the snowiest one I have seen while living here.


Alex

seattle would also need to have a northeast or east wind component through the entire event in order to maintain all snow or frozen precip. if the winds shifts to westerly or northwesterly off the ocean...its over.

[FLguy]

Absolutely true Flguy, however the GFS(as fantasy as it may be) DOES have the 1000-500 MB temps plenty cold enough. Although i personally am more inclined to think that this is a result of it seeing the colder temperatures at a higher elevation and is having a hard time geographically out in the SW especially with this feature(upper level feature as well as surface feature)

the GFS will develop several strong closed lows at H5 several times a winter across the southwest US with 1000-500 thicknesses cold enough to produce snow all the way down to sea-level across the SW US.

the only problem is that while the GFS fantasy land BS like that may get the weenies excited in the MR...but thinking that something as rediculous like that will ACTUALLY VERIFY is about as smart as leving a 4 month old dog home alone and not expect it to poop all over your carpet while your gone.

and if i had just 50 cents for every time the GFS does such things i would make bill gates look like a soup kitchen worker.

[aveosmth]

Obviously the chances of this cold low verifying are very slim....what signs should we look for to see if it would/could verify? Cross-referencing the GFS against other models, Im assuming would be the easiest this far out....

Hey Joshua, nice to see someone else from socal looking at the models as well....the nws up in Hanford said snow levels could get down to 1K feet...of course it has to verify like FL Guy mentioned....

Aveo

[FLguy]

Obviously the chances of this cold low verifying are very slim....what signs should we look for to see if it would/could verify? Cross-referencing the GFS against other models, Im assuming would be the easiest this far out....

Hey Joshua, nice to see someone else from socal looking at the models as well....the nws up in Hanford said snow levels could get down to 1K feet...of course it has to verify like FL Guy mentioned....

Aveo

the GFS actually has it within 24 hours of the verification time...support from all other MR and SR models. correct inspection of soundings to assure that the vertical column is cold enough to support all snow even down to sea-level. which would require most of the sounding to be below freezing. 1000-850mb and 850-500mb partial thicknesses must also support freezing precipitation.

you just cant look at the 850mb temp and 1000-500mb thicknesses fields on the GFS and say...Ok its going to snow or not going to snow. theres more to it than that.