Why Measure Dewpoint

[P. Thomas]

I have an anemometer. (2 of them as a matter of fact).. I have a thermometer built into my truck and it's fairly accurate.

OK.. If I'm out spotting, why would it be necessary to measure dewpoint for the NWS? Isn't humidity pretty much the same for miles and the NWS can pick it up with their multi-million dollar equipment?

Remember, no question is stupid..

 

[Doug Raflik]

Is your NWS asking spotters to submit dewpoint reports?

 

[rdale]

OK.. If I'm out spotting, why would it be necessary to measure dewpoint for the NWS?

Not sure it is necessary. It's nice though.

Isn't humidity pretty much the same for miles

Absolutely not... It can change quite rapidly near a boundary (look up a 'dryline') and knowing the dewpoint with detailed precision can be critical to storm formation.

NWS can pick it up with their multi-million dollar equipment?

They use ASOS and AWOS sensors for the most part, which while valuable are not multi-millions

- Rob

 

[Chris Bowman]

I have an anemometer. (2 of them as a matter of fact).. I have a thermometer built into my truck and it's fairly accurate.

OK.. If I'm out spotting, why would it be necessary to measure dewpoint for the NWS? Isn't humidity pretty much the same for miles and the NWS can pick it up with their multi-million dollar equipment?

Remember, no question is stupid..

I'm not sure why the NWS would want you to measure dewpoint while spotting. But if you could provide the dewpoint and wind direction near a storm I would definitely use that bit of data in my decision process. I won't turn down free data.

For me personally, dewpoint is one of the most critical elements. It goes into determinng a lot of other critical parameters. CAPE can/will increase significantly with higher dewpoints. This can make the difference between a surface based or elevated environment. Cloud bases can/will be much lower to the ground with higher dewpoints which greatly increase the chances of tornadoes. A plot of dewpoints can determine where a dryline is located and where moisture may be pooling or streaming to. Dewpoint is a direct measure of the moisture in the atmosphere. Relative humidity is not and is dependent on other things like temperature. If you gave me one parameter for a surface analysis for possible severe wx, I would want dewpoint. Wind vectors would come in second.

 

[Greg Blumberg]

I agree. The amount of moisture can make or break a tornado/storm. It would be nice to position yourself near the inflow to measure temperature/dewpoints in order to determine if the storm seems to be getting good enough fuel. I myself would have something similar to a mobile Mesonet, if I had my choice of a chase vehicle because there can be large gaps between weather stations.

 

[Tim Shriver]

I agree with the idea that dewpoints are one of the vital ingredients
to a severe weather event.

A good example was this past Friday in WI We had been dry for sometime
and there was some question as to how much moisture we would
have in place. Need that warm. moist unstable gulf air.

We watched the temps and dewpoints as the other factors were already
in place. (shear, jet, trigger etc)

We did see the dewpoints climb over night into the mid 60's. The only
item missing to some extent was more daytime heating.

I look for temps in the high 70's to mid 80's and dewpoints in the high
60's and above. Ideal is 85 for temps and 70 - 75 for dewpoints.

Add a good trigger with some good shear and life gets interesting...

Tim

 

[Greg Blumberg]

While a high dewpoint (60s, 70s) is important to tornadoes and storms, it is not entirely essential for good storms. Just yesterday (4/26/08) I chased a batch of high based LP supercells that were the most photogenic storms I have seen. It was an absolutely beautiful day for storm photography. No tornadoes, but still an outstanding day. I have photos up on my website.