Our local forecasters here said......

Winter Weather Discussion

Moderator: S2k Moderators

Forum rules

The posts in this forum are NOT official forecast and should not be used as such. They are just the opinion of the poster and may or may not be backed by sound meteorological data. They are NOT endorsed by any professional institution or STORM2K.

Help Support Storm2K
Message
Author
User avatar
NCGal
Tropical Storm
Tropical Storm
Posts: 117
Joined: Thu Jan 09, 2003 1:55 pm
Location: Middlesex,North Carolina

Our local forecasters here said......

#1 Postby NCGal » Sun Feb 15, 2004 9:39 pm

that if it hadn't started snowing by 9PM that we probably wouldn't see much.. Currently at 9:37PM it's sleeting like crazy. Does this mean we are likely not to see much snow accumulation?? What are your thoughts? Thanks in advance.
0 likes   

User avatar
Erica
Professional-Met
Professional-Met
Posts: 168
Joined: Sat Feb 14, 2004 2:45 am
Location: Daytona Beach, FL
Contact:

#2 Postby Erica » Sun Feb 15, 2004 10:05 pm

If we look at the 01z sounding from RAH (Raleigh) Both profiles indicate Rain. But if we look at the nexrad out of KRAX, there are some heavier precipitation bands forming across North Carolina, some enhancement may be related to Convective Instability or CSI.

Image

http://www.erh.noaa.gov/radar/latest/DS ... krax.shtml

And the NEXRAD from KMHX shows some very interesting things going on, see the heavy convection forming offshore. that would imply that the atmosphere across much of North Carolina is quite unstable. the sounding above from RAH showed some weak CAPE, but 850-500mb Lapse rates were mostly moist adiabatic between 5.00-6.00 C/km.

http://www.erh.noaa.gov/radar/latest/DS ... kmhx.shtml

The sounding from LKN (Cape Lookout) is another story, there doesn't appear to be any SCAPE, but lapse rates are dry adiabatic; above 6.00 C/km, which would support the convection offshore. It's probably safe to say that with intensifying low level frontogenesis, and some negative EPV, that CSI banding will continue across central North carolina and Most of Virginia, where the environment is cold enough through a deep layer of the column to support all snow, regardless of how strong the vertical motions are.

Image

Further south, precipitation type is going to be dynamically driven until cold air advection can cool the column enough, most of the reason why you are seeing heavy bursts of sleet mixing with snow.
0 likes   

User avatar
JQ Public
Category 5
Category 5
Posts: 4488
Joined: Thu Feb 06, 2003 1:17 am
Location: Cary, NC

#3 Postby JQ Public » Mon Feb 16, 2004 1:57 am

Western wake got alot! i dunno about the rest of the area. Hopefully you'll get more next system on tuesday?!
0 likes   

David
Category 5
Category 5
Posts: 4517
Joined: Mon Apr 21, 2003 9:47 pm
Location: Topeka, Kansas
Contact:

#4 Postby David » Mon Feb 16, 2004 2:08 am

Those graphs are confusing.. lol.
0 likes   

ColdFront77

#5 Postby ColdFront77 » Mon Feb 16, 2004 2:13 am

They are called soundings or Skew-T diagrams. :D 8-)

Once you find out how to use them, they aren't so confusing. :)

I have a fair good idea on how to read them... I am sure at least one of those that are putting this data in this forum will let those that don't know more about them.
0 likes   

Guest

#6 Postby Guest » Mon Feb 16, 2004 2:17 am

JQ Public wrote:Western wake got alot! i dunno about the rest of the area. Hopefully you'll get more next system on tuesday?!


Sorry to say this but i hope not. Well atleast in NC anyways! :lol: You guys have had way more then your fair share of the wintry precip over the last several winters. Its about time to break this horrible pattern and start sharing with areas thats supposed to get it and a few others like SC that havent gotten in on it!! :lol:.

As much as i know about the weather i cannot for the life of me figure out why since 2000 or so NC has become such a snowy/wintry place? Perhaps someone like Erica can enlighten me on this. I mean yea one can expect this area to get hit once in so many winters but for almost every winter now since about 2000 something doesnt add up??? Only thing i can come up with is the screwing up of the Gulfstream?????
0 likes   

User avatar
JQ Public
Category 5
Category 5
Posts: 4488
Joined: Thu Feb 06, 2003 1:17 am
Location: Cary, NC

#7 Postby JQ Public » Mon Feb 16, 2004 2:20 am

maybe it is...since the gulfstream is acting up and nc stick out so far into the ocean we're just prime targets fro these things like we are for hurricanes?!?! NC used to get bigger storms though...especially around gboro charlotte...hickory i really don't know the reason y raleigh is. maybe once again our proximity to the ocean and cold...or maybe its all the good vibes i'm send old man winter's way?
0 likes   

Anonymous

#8 Postby Anonymous » Mon Feb 16, 2004 11:51 am

an excellent writeup concerning the above mentioned CSI (conditional symmetric instability) that Erika mentioned (courtesy FLGuy on Storm2k, professional met):

Cold season convective processes such as CSI (Conditional Symmetric instability) can result in localized higher accumulations under enhanced precipitation bands which cannot be resolved by the models. CSI occurs when the absolute vorticity of the geostrophic flow becomes weakly positive or negative. This results in inertial instability which is mixed out as shear increases. The CSI is the atmospheres response to the disturbance (which of course is the negative absolute vorticity since the earth's natural vorticity is positive).

CSI can be assessed by examining cross sections of theta-e and momentum surfaces (when the slope of the theta-e surfaces is greater than the momentum surfaces, the environment is considered favorable for the release of CSI). While that is a good method, cross-sections of EPV (equivalent potential vorticity) and frontogenesis can give us a better idea of where the environment may be symmetrically unstable.
Remember also that the environment MUST BE SATURATED in order for CSI to develop. Areas of negative EPV located in layers above a sloping frontal boundary normally imply a favorable environment for the release of CSI and development of banding. The frontogenesis can continue to disrupt the environment and result in prolonging the life-cycle of CSI.

Strong vertical motions promoted by negative omega and frontogenesis can lead to heavier QPF, which given favorable snow/liquid ratios can result in heavier accumulations. (Frontogenesis is described by the horizontal tightening of the thermal gradient over a given location)

Thank You !

Ken
0 likes   


Return to “Winter Weather”

Who is online

Users browsing this forum: No registered users and 9 guests