Day 57: 12 UTC Surface Pressure Chart

Posted by on 26 Feb 2010 | 2 comments

Day 57

Above is this morning (12 UTC; 6 AM CST) surface pressure chart, as analyzed the by the Storm Prediction Center’s surface objective analysis dataset. (Essentially, what this means is that this is a model generated field that is “tugged” back toward truth through the use of observations.)  A couple of things stand out 1) the very strong low pressure centered over the New York City, NY area and 2) the strong high pressure located over the central Rocky Mountains.  The brown dashed lines indicate “troughs” or low pressure, or areas of lower pressure that are not completely closed off.  You’ll notice a trough to the northwest of the strong northeast surface low (this is indicative of strong warm aid advection aloft).  There is also a trough in the southern plains.  This trough is associated with a small, but potent, mid-level shortwave trough / closed low that brought rain (and some snow) to central Oklahoma over night.

  • Greg Blumberg

    I was trying to figure this out at my OWL shift last night…but how do you define an area of pressure that is completely closed off? Is it indicated by whether or not a isobar makes a complete full circle around an area of low pressure? My problem with this definition is that a low being “closed off” would then become a human judgment that can be (prone to error by lack of data in certain areas) call rather than a certain atmospheric state.

    In summary: how exactly do you define this closed off low and what is the significance of it?

  • http://www.patricktmarsh.com pmarsh

    Interesting question. Even though I use the terminology frequently, I don’t think I’ve ever really stopped to think about the answer to your question. There is some subjectivity. I tend to operate under the assumption that if I can visualize or draw a circle in the general vicinity of the lowest pressure without much effort then I’ll consider it a closed low. In other words, I can recognize one when I see one, but am not too sure I can give a specific definition.