Closed low

[chrisbray]

In my local nws forecast this morning they are talking about the forecast closed low Friday morning, it says "FOR PLACEMENT AND MOVEMENT OF THE CLOSED LOW WHICH IS FORECAST AT
ALMOST THREE STANDARDIZED ANOMALIES BELOW NORMAL AT 500MB..."

What exactly does that mean? Just the intensity of the low at 500mb w respect to height or pressure?

Thanks

 

[rdale]

A closed low is one that has isobars forming a complete circle. I think he's more referring to a cutoff low, which is when the low separates from the main jet streams and hangs out for a few days.

 

[chrisbray]

A closed low is one that has isobars forming a complete circle. I think he's more referring to a cutoff low, which is when the low separates from the main jet streams and hangs out for a few days.

I guess I should clarify, I understand the closed/ cutoff low. Just the 3 standard anomalies part is what I am wondering about.

 

[Kelly Sugden]

Statistics at 500 hPa is usually in terms of geopotential height.

 

[chrisbray]

Right so is the forecaster saying that this low will be below normal in terms of height at 500 hPa?

 

[Kelly Sugden]

Yes, that is correct...

 

[chrisbray]

Yes, that is correct...

Thank you. That's really what I wanted to make sure of.

 

[rdale]

Example at http://www.esrl.noaa.gov/psd/map/images/ens/std_f072_nh.html

At 3 standard deviations that's getting extreme..

 

[Jeff Duda]

Rob is right. If you assume the climatological geopotential height distribution at any one location is approximately normally distributed (Gaussian), then only about 0.2% of the entire distribution is 3 or more standard deviations away from the mean. Quite rare, indeed.

 

[Mike Johnston]

Looks like it is both a closed low and a cutoff low.

At any rate, just sounds like a poor choice of wording. A standard deviation is just that - and there's no need to confuse the term by substituting something like "standard anomaly." I could see the popular press doing that, but not the NWS.

 

[Jeff Duda]

"Standard anomaly" IS the term of choice for ALL weather organizations...operational and research...that I've ever seen.

 

[Mike Johnston]

"Standard anomaly" IS the term of choice for ALL weather organizations...operational and research...that I've ever seen.

I'll defer to you, Jeff, and I stand corrected. As a layman who just took 6 hours of statistics courses (years ago), I had just never heard of that term.

 

[rdale]

Here's the math behind the different terminology... http://journals.ametsoc.org/doi/pdf/10.1175/1520-0493(2001)129<2426:UNCATR>2.0.CO;2