What's this mean?

[Kyle Masters]

Learning, so a question for you guys. What's the circle in East Central SD mean in this image?

[Broken External Image]:http://weather.cod.edu/forecast/ETA/GL/etaGL_850_rhum_30.gif

 

[Mike Peregrine]

Kyle - you are looking at a chart for 850mb, which represents the layer just above the surface (or boundary) layer (it's actually midway up between the surface and 700mb) ... the arrows/lines show wind direction at 850mb ... and they are curving around an area of low pressure ... so what you have there is a low moving across South Dakota.

I'm not sure what day you pulled that map from, but it doesn't look like today: http://weather.cod.edu/analysis/analysis.upr.html

 

[Glen Romine]

850 mb is about a mile above sea level (remeber this because Denver is called the mile high city, and surface pressure there is typically around 850 mb). The color contour is the relative humidity field, and the white lines overlayed on it are streamlines. Streamlines do not tell you the speed of the wind, but do give you an idea of the wind direction along with areas of convergence (such as east of the cyclonic circulation over SD) or divergence (near Minneapolis in this pic) , deformation zones (such as the one in IA), and diffluence (the 'spreading' flow over NE). The yellow line overlays are interstates for further geographic reference, btw.

Glen

 

[mikedeason]

Mike and Glenn explained the streamlines well.

Also, you'll notice a "piling up" of RH values in that area. That is indicative of low level moisture convergence and is a necessary ingredient for thunderstorm development.

Now, the next question might be, where is that moisture advection coming from?

That's the next topic of discussion.

Regards,

Mike

 

[Kyle Masters]

Ahhh...i see. Those are the graphics from today, I got them from the College of DuPage site. I just click on model products and then ETA for Great lakes, and it shows up. I've been trying to get a handle on what all it means. Thanks guys!

 

[Richard Halter]

It means you are getting sleepy, sleepy, sleeeeeeeepy

 

[Michael P. Morris]

Now, the next question might be, where is that moisture advection coming from?

That's the next topic of discussion. Smile

The one drawback of isobaric charts-moisture comes out of nowhere. One would have to use isentropic charts to find out. :x