Identifying fronts during HA

[brice.coffer]

I came across something interesting this weekend while reading Tim Vasquez's Weather Analysis and Forecasting Handbook. When talking about cold fronts, Tim said:

Forecasters must remember that like all fronts, a cold front is on the warm side of a transition zone. Therefore the arrival of a cold front at a weather station marks the instant that a transition to colder temperatures begins. Since a cold front is a function of temperature and not any other property, a front should never be placed along wind shift lines...

I found this surprising because it goes against what I had been taught and what I had read in other books. For example in Howie Bluestein's Synoptic-Dynamic Meteorology in Midlatitudes, he says:

Surface fronts are always located along the wind-shift rather than along the zone of maximum horizontal temperature gradient.

Now I tend to agree with Howie, but maybe that is because that's how I've always done it.



What are some of your opinions? How do you identify fronts during hand analysis?

 

[Greg Higgins]

I think it boils down to semantics. Tim, I think, considers the actual air temperature as the line (the next question is; how much of a temperature drop occurs before you draw the line?) while Howie is looking at the "big" picture; the air mass itself. Drawing the line in this case is rather straight forward. I would also think that when one is considering the overall storm setup, how does the wind and / or temperature affect the synoptic weather?

 

[Mark Ellinwood]

It could be either, both or neither... depends on the type of front and the clarity of the boundary using different variables. You can use the wind shift or temperature change if they're obvious enough, but honestly I would never use JUST the temperature to identify a frontal boundary. Dewpoints are usually much more telling, along with a change in the surface pressure gradient. Other variables like theta-e can also be used.

 

[MClarkson]

I almost always place them where the wind shifts.

 

[mikedeason]

Doswell and Sanders wrote a very nice paper on the challenges of surface analysis in 1995 and it's still a good read today: A Case for Detailed Surface Analysis

 

[brice.coffer]

Thanks for that paper Mike. It is all about semantics but I enjoy the semantics of meteorology.

 

[Travis Davis]

I always place them at the wind shift line also.

 

[mikedeason]

The problem is that a front, by definition, is a transition zone of air masses with differing densities. Sometimes, as with the case with prefontal troughs, outflow boundaries, etc., if you analyze for the wind shift line then you're probably placing your front far ahead of it's actual position according to this definition. Experience is the best teacher when it comes to chart analysis and even after years and years of it, you'll still get scenarios thrown in which don't always fit the textbook models. Wind shift lines are certainly valuable, but I generally like to place the greatest attention on temperature gradients/transitions, moisture and then wind/pressure. Mileage may vary.