Topic: Isobars!

[SlowModem]

Step right up!  Get your isobars here!

That sure is a strong Low!

[Chris H.]

Isn't that what used to be Georgette sitting way up there?

[Downlinerz2]

   I was feeling some of those winds today.  Had a gust this morning of 35mph.
It must have been very windy up ovwer the border.  The cold front should be passing us here around now so the winds are expected to die down.

[KeithBC]

I've got more isobars than you.   

[chief-david]

that seems a little too much to me

WU has less..  But I am looking at 7:30 central time.

I was always told that each isobar packed like that equals winds of 5-7 mph.

If so then

12 isobars x 7 mph = 84 mph winds.

Am I right?

[SlowModem]

I was always told that each isobar packed like that equals winds of 5-7 mph.

I've not heard that before.   

But as Billy Joel said, "You may be wrong for all I know, but you may be right."   

[KeithBC]

that seems a little too much to me

WU has less..  But I am looking at 7:30 central time.

I was always told that each isobar packed like that equals winds of 5-7 mph.

If so then

12 isobars x 7 mph = 84 mph winds.

Am I right?

I don't think there is enough information to derive a formula that precise.  It depends on the isobar interval of the map (the map posted by slow modem has a different interval than the one I posted), and of course it depends on exactly how tight "packed like that" really is.  What you really need for a formula is the number of millibars per 100 miles.

The winds right now at my station are showing about 9 km/h average, which means that it is blowing a heck of a gale up above the trees.  The closest official weather station, Comox, is showing 45 km/h gusting to 60.  Considering that the central pressure of the low in the Gulf of Alaska is 955 mb, I am sure glad I'm not on a boat up there!  I don't think Igor got a central pressure that low.

[chief-david]

OK- from very a reputable weather person on KARE 11.


http://www.kare11.com/company/bios/talent_article.aspx?storyid=126276&catid=198

[chief-david]

that seems a little too much to me

WU has less..  But I am looking at 7:30 central time.

I was always told that each isobar packed like that equals winds of 5-7 mph.

If so then

12 isobars x 7 mph = 84 mph winds.

Am I right?

I don't think there is enough information to derive a formula that precise.  It depends on the isobar interval of the map (the map posted by slow modem has a different interval than the one I posted), and of course it depends on exactly how tight "packed like that" really is.  What you really need for a formula is the number of millibars per 100 miles.

The winds right now at my station are showing about 9 km/h average, which means that it is blowing a heck of a gale up above the trees.  The closest official weather station, Comox, is showing 45 km/h gusting to 60.  Considering that the central pressure of the low in the Gulf of Alaska is 955 mb, I am sure glad I'm not on a boat up there!  I don't think Igor got a central pressure that low.

Math on a Friday night
but I am still correcting papers

I like the millibars per 100 miles
But whose map then do we believe? I never really trust weather channel

[KeithBC]

Your best bet would be to take the actual pressure readings from actual stations.  Lines on a map can be drawn anywhere, but unless the instrument is out of whack, the pressure is what it is.

For fun (Yes, math on a Friday night is fun!  Call me a nerd.)  I worked out the pressure gradient between my location and the centre of the Gulf of Alaska low to be 0.043 mb/km or about 7mb/100miles.

[KeithBC]

Well, 7mb/100 miles is enough to blow down trees and knock the power out.  I'm running on generator power this morning.

[Downlinerz2]

   In the DVD course I am taking on Meteorology there are 2 whole lectures devoted to "Whence and Whither the Wind".  The wind is a whole lot more complicated than I had ever imagined.  There are 4 forces that act on the wind that determine how fast and where and when the winds blow.
   The forces are: 1) Pressure Gradient Force   2) Coriolis Force   3) Centripital or Centrifugal (depending on your view but only the centripetal force is real)  and
4) Friction.     Putting these all together is over my head and I will have to watch the lectures a few more times.  It sure is interesting.   The isobar curvature also affects the wind speed. I sure am glad there isn't going to be a test in the morning !!!!
ADD:  I will watch lectures again.  I know the instructor did show some calculations of wind speed over distance and gradient.  For example the wind speed for a gradient of 10 mb over 50 miles.  I cannot remember how he did it off hand.

[Scalphunter]

 In sailing for 35 years up and down the BC and Alaska coast  I have seen and felt some of those closely packed isobars. January 1974 we got into one where we went in circles by Alert Bay. Keith will know where that is. Cape Saint James wasclocking winds of 150 knots. With 500 complaining people on board was not fun listening to there complaing. They quit complaining after it was learned that an lumber ship sank about 100 miles to the west of us. Liberian flag vessel. Also for you perfect storm fans get an copy of the M.V. Leconte
sinking. USCG chopper was recording wave heights of 85 feet out in the Gulf of Alaska.

John

[KeithBC]

... Alert Bay. Keith will know where that is.

Sure do.  That area was hard hit last night.  Port Hardy declared a state of emergency for flooding, roads washed out and trees down on hydro lines.