explain storm movement

[Jonathan Whitehead]

Hey I was watching the College World Series and they had about an hour rain delay. So I went and looked at radar and satellite and noticed something interesting on satellite. Notice that the weather is moving SE yet their rather mushy disorganized tops are being blown NE. How is that possible? My guess is that its the winds in the mid levels that drives these showers/t-showers and not the upper level winds of which are blowing the tops in different directions. Please explain

 

[rdale]

Is your question asking if winds can be from different directions over one spot? Yes.

Looks at the wind barbs here: http://www.spc.noaa.gov/exper/soundings/06062500_OBS/OAX.gif

 

[Shane Adams]

It's possible because mid level winds steer storms, not upper level. You're seeing blowoff from upper levels while the system itself is being driven southeast by the mid levels. This is a great example of "wind shear".

 

[Blake Michaleski]

Yes, and its probably one of the most important parameters to understand for successful chase forecasting. Vertical wind shear is what differentiates ordinary thunderstorms from severe thunderstorms. It also play a major role in determining convective mode.

 

[Jonathan Whitehead]

Is your question asking if winds can be from different directions over one spot? Yes.

Looks at the wind barbs here: http://www.spc.noaa.gov/exper/soundings/06062500_OBS/OAX.gif
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where are the SWly winds on that sounding. The tops of the hvy rain showers are being blown NE

 

[rdale]

http://www.spc.noaa.gov/exper/soundings/06062500_OBS/DVN.gif

http://www.spc.noaa.gov/exper/soundings/06062500_OBS/SGF.gif

 

[Jeff Snyder]

where are the SWly winds on that sounding. The tops of the hvy rain showers are being blown NE
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There was a little better southwesterly upperlevel flow just east of OAX -- see http://hoot.metr.ou.edu/operations/upperair/250mb.html ... If you look at this tomorrow morning (after the 12z obs come in), just put your mouse under the "-12hr" text on top.

The cloud tops may look like they are being blown more to the northeast than they really are... Even under westerly 250mb flow, a storm that's moving southeast will look as though it's anvil is being "blown" to the northeast if you base that observation on only 1 or 2 images. As the udpraft slides to the southeast, upper-level winds advect the anvils to the east, so the anvils take on a southwest-northeast orientation owing to differential advection/motion. This isn't necessarily the case here, since there some of the upperlevel cloud material does look to be advecting to the east-northeast, but it may help make the upperlevel flow "look" more southwesterly than it really was.

 

[Mike Umscheid]

It's all about your point of reference. In looking at the 25/00z Omaha, NE sounding, the 8-10km AGL (roughly anvil level) flow was around 30 to 35 knots from the west northwest. The storm motion, however, appeared to be southeast at about 20-25 knots. So, in a storm-relative sense, these anvil level winds were roughly from ~230/22kts... or from the southwest. But, observe the motion of the anvils relative to the political boundaries... you'll see the anvils are indeed moving to the southeast or east southeast as well! Your eyes can play tricks on you.... you can read a lot about the wind environment from hodographs.... a very valuable tool. All about vector addition/subtraction

Mike U

 

[Dan Dawson]

It's all about your point of reference. In looking at the 25/00z Omaha, NE sounding, the 8-10km AGL (roughly anvil level) flow was around 30 to 35 knots from the west northwest. The storm motion, however, appeared to be southeast at about 20-25 knots. So, in a storm-relative sense, these anvil level winds were roughly from ~230/22kts... or from the southwest. But, observe the motion of the anvils relative to the political boundaries... you'll see the anvils are indeed moving to the southeast or east southeast as well! Your eyes can play tricks on you.... you can read a lot about the wind environment from hodographs.... a very valuable tool. All about vector addition/subtraction

Mike U
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Indeed. This cannot be stressed enough. What a storm "cares" about is the flow relative to it, not the ground, as well as the magnitude and direction of the wind shear interacting with its updraft (which has absolutely nothing to do with the absolute magnitude of the winds, only the change in wind speed and direction with height). When our eyes are looking at a storm on satellite and radar, we unconciously tend to perceive (well, at least I do) the storm relative flow rather than the ground relative flow, and it's easy to get the two confused.

 

[Jonathan Whitehead]

This has got dynamics (I) written all over it.
Three words: inertial reference frame. I heard that phrase so many times last year that I was ready to poke myself in the eye. That and the merry-go-round just made me all dizzy and confused.
Unfortunately I am having to repeat that class again this fall so better get used to it.
But its good to finally see this stuff in action.

 

[rdale]

Don't make it too complicated ;> Just remember that the storm acts within the environment. You saw the northwesterly winds through the heart of the atmosphere on the sounding - but westerlies at the high levels. If the entire sounding was unidirectional (same direction at all levels) the cirrus canopy would move basically in the same direction as the storms (often you'll see the cirrus move ahead due to stronger winds aloft.)