Weather, Pressure gradients, and wind

[rwguinn]

It is my understanding that (In the N hemisphere) a high pressure area generates wind flow clockwise from the center, and a low, counterclockwise.
In fact, the local weatherman show that flow on his maps, every night.
Now, this would mean that a High, to the West of us, would generate winds out of the North. To the N. of us, winds would be from the East, S of us, from the West, and East of us, from the S.
Our winds are consistently at 20 mph, all this spring, yet the "High" is to our S and W. This is counter intuitive.
Anyone got a mechanism for this?

 

[Mikemcc]

It is my understanding that (In the N hemisphere) a high pressure area generates wind flow clockwise from the center, and a low, counterclockwise.
In fact, the local weatherman show that flow on his maps, every night.
Now, this would mean that a High, to the West of us, would generate winds out of the North. To the N. of us, winds would be from the East, S of us, from the West, and East of us, from the S.
Our winds are consistently at 20 mph, all this spring, yet the "High" is to our S and W. This is counter intuitive.
Anyone got a mechanism for this?

Sorry? You've not said from which direction. That they are 20mph is not determined by the position of the pressure systems, but by the pressure gradient. (Rule of thumb in the UK, count the isobars across the country (including the Scilies and the Shetlands) and times by five. That gives you the average ground wind speed across the country.)

Winds are greatly effected by terrain too, any mountains near you?

 

[GungHo]

OP: Sorry for the pedestrian terminology -- Are you near a large body(ies) of water? Does the wind "go the other way" at night? During the day, the wind will come off the water, and come off the land during the evening due to the greater specific heat of water. Same thing can happen in mountains/valleys.

Also, you can have high pressure and low pressure systems about, but that may not have anything to do with surface-level winds until the pressure gradients are differentiated enough to get a flow. At that point, the wind direction will be "channeled" diagonally along the differentiations (represented as isobars) into the area of low pressure. However, this assumes that the pressure-gradient force can overwhelm other effects, like surface friction and the pressure differentials created by surface temperature variations (e.g. water vs land).

 

[rwguinn]

Sorry? You've not said from which direction. That they are 20mph is not determined by the position of the pressure systems, but by the pressure gradient. (Rule of thumb in the UK, count the isobars across the country (including the Scilies and the Shetlands) and times by five. That gives you the average ground wind speed across the country.)

Winds are greatly effected by terrain too, any mountains near you?

OOps--sorry--our winds are from the South, at pretty much a constant 20 mph, day and night, at least for the past 2 months.
I am in the DFW area, and the High is centered somewhere around Midland/Odessa/San Antonio--which places are baking (nearly broiling) in the 110 F range of temperatures.
The Gulf of Mexico is about 500 miles SSE of us, and contributes tremendously to the humidity...

 

[BowlOfRed]

I don't see any significant (low-level) high in TX affecting things.

If you look at this map, the overall gradient in the DFW area is driving air from south to north, but they don't look particularly strong right now (not like the panhandle).
http://www.usairnet.com/weather/maps/current/texas/barometric-pressure/

Even if there is a strong circulation in place, the wind you feel at the surface may be significantly different due to shear from surface effects.

 

[BowlOfRed]

I remember this great picture showing how the horizontal layers of wind under a thunderstorm rotate as altitude changes, but I can't find it. But this page does some explanation about why surface winds don't match up with what you expect from pressure gradients near lows.
http://www.webskite.com/weather-seminar/basic-weather/wind.htm

 

[rwguinn]

I don't see any significant (low-level) high in TX affecting things.

If you look at this map, the overall gradient in the DFW area is driving air from south to north, but they don't look particularly strong right now (not like the panhandle).
http://www.usairnet.com/weather/maps/current/texas/barometric-pressure/

Even if there is a strong circulation in place, the wind you feel at the surface may be significantly different due to shear from surface effects.

Thank you for that link. Finding isobar maps on the Weather Channel and news outlets is damn near impossible.
That actually shows what is currently happening--breeze from the South at about 8-10 mph (it has died down considerably in the last couple of hours)
The high has either weakened, or has moved. None the less, I would not expect surface winds to be in direct opposition to the flow around a high (yes, I am familiar with shears, but they tend to be local effects, do they not?) This stuff has been widespread, for a while, with little or no change between day and night, either in speed or direction. Just trying to understand the mechanism.

 

[Mikemcc]

I remember this great picture showing how the horizontal layers of wind under a thunderstorm rotate as altitude changes, but I can't find it. But this page does some explanation about why surface winds don't match up with what you expect from pressure gradients near lows.
http://www.webskite.com/weather-seminar/basic-weather/wind.htm

Even if you have a stagnant weather system in one position the wind directions may be changed or varied by the positioning of other systems.

I've just tried to look up a synoptic chart for your area. Dear God, your weather guys don't have a clue about how to present data clearly. All I have to do is go to the Mountain Weather Information service in the UK (http://www.mwis.org.uk/synoptic.php). I'm in Hamberg at the moment I can see I may get some light rain on Thursday, but that will clear for a good weekend, with very low winds (20kts S dying down and switching to 20kts N). Read that in the space of 2 minutes. You guys try to drown yourselves in data!

 

[rwguinn]

I remember this great picture showing how the horizontal layers of wind under a thunderstorm rotate as altitude changes, but I can't find it. But this page does some explanation about why surface winds don't match up with what you expect from pressure gradients near lows.
http://www.webskite.com/weather-seminar/basic-weather/wind.htm

But that's local effect-- I'm talking about wide-area shears here, with 180 degree difference in upper level and ground level, at relatively high wind speeds.
We're talking a 250000 square mile area, here...

 

[rwguinn]

Even if you have a stagnant weather system in one position the wind directions may be changed or varied by the positioning of other systems.

I've just tried to look up a synoptic chart for your area. Dear God, your weather guys don't have a clue about how to present data clearly. All I have to do is go to the Mountain Weather Information service in the UK (http://www.mwis.org.uk/synoptic.php). I'm in Hamberg at the moment I can see I may get some light rain on Thursday, but that will clear for a good weekend, with very low winds (20kts S dying down and switching to 20kts N). Read that in the space of 2 minutes. You guys try to drown yourselves in data!

Actually, they don't give us data--or it's hard to find--which is why I asked the question in the first place.
They give us the "USA Today" version of what most people merely need to know (hot, muggy, windy), without any "why" available...

 

[Crossbow]

It is my understanding that (In the N hemisphere) a high pressure area generates wind flow clockwise from the center, and a low, counterclockwise.
In fact, the local weatherman show that flow on his maps, every night.
Now, this would mean that a High, to the West of us, would generate winds out of the North. To the N. of us, winds would be from the East, S of us, from the West, and East of us, from the S.
Our winds are consistently at 20 mph, all this spring, yet the "High" is to our S and W. This is counter intuitive.
Anyone got a mechanism for this?

rwguinn:

Please keep in mind that those maps you refer to are often the 'upper air maps' which are quite useful at showing the circulation that is occuring over a wide area. However, because these maps are showing the upper air circulation, then they may, or may not, accurately show what is going on at the ground.

To explain, one often sees a significant shift in the wind direction and/or the wind speed between what is going on at the surface and what is going on in the upper atmosphere due to factors like surface friction (mountians and buildings), local heating (large asphalt parking lots and small lakes can have a big impact here), and other such factors.

If you really want to get a good handle on just what is going on in your area, then I suggest that you consult any parachuting, paragliding, or about any small scale aviation groups in your locale. I expect that they will have a good bit of experience and wisdom concerning the microweather versus the macroweather.

I hope this helps!

 

[rwguinn]

rwguinn:

Please keep in mind that those maps you refer to are often the 'upper air maps' which are quite useful at showing the circulation that is occuring over a wide area. However, because these maps are showing the upper air circulation, then they may, or may not, accurately show what is going on at the ground.

To explain, one often sees a significant shift in the wind direction and/or the wind speed between what is going on at the surface and what is going on in the upper atmosphere due to factors like surface friction (mountians and buildings), local heating (large asphalt parking lots and small lakes can have a big impact here), and other such factors.

If you really want to get a good handle on just what is going on in your area, then I suggest that you consult any parachuting, paragliding, or about any small scale aviation groups in your locale. I expect that they will have a good bit of experience and wisdom concerning the microweather versus the macroweather.

I hope this helps!

And Meteorologist David Finfrock agrees. Just got an e-mail from him, saying basically the same thing.
Thanks, folks.

 

[CORed]

Actually, they don't give us data--or it's hard to find--which is why I asked the question in the first place.
They give us the "USA Today" version of what most people merely need to know (hot, muggy, windy), without any "why" available...

http://weather.unisys.com has some decent surface and upper air maps for the US.

 

[Mikemcc]

http://weather.unisys.com has some decent surface and upper air maps for the US.

It's still a horrible map. At the time of viewing it's showing 10-15kts southerly ground wind speed pretty much throughout Texas. Is this something related to the stagnant weather system causing the drought down that way?

 

[rwguinn]

It's still a horrible map. At the time of viewing it's showing 10-15kts southerly ground wind speed pretty much throughout Texas. Is this something related to the stagnant weather system causing the drought down that way?

Yup. And that upper High I was complaining about in the OP is keeping anything from changing.
It keeps chasing the cool fronts off like a Pit Bull protecting its property....

 

[Delvo]

Your original post had everything turned by 90°. That would be a very rare situation. It's usually a much smaller angle and often pretty close to zero. The natural inclination would be for flow straight from high to low without the Coreolis Effect, and all the Coreolis Effect does is deflect that vector a bit to the right in the Northern Hemisphere or a bit to the left in the Southern Hemisphere. How much of a deflection it causes is variable, but it's usually well under 90° or even 45°, and it's usually less drastic near a high-pressure center than near a low-pressure one.