Day 85: Winds of Change

Posted by pmarsh on 26 Mar 2010 | 0 comments

The winds of change are blowing across Oklahoma this evening as a surface low pressure develops across western Texas.  Wind is the result of air moving from regions of higher pressure to areas of lower pressure.  The faster the pressure change over a given distance, the stronger the winds will be.  While not shown, there is a lot of change in pressure over a relatively small distance, and so the result is strong winds.

In addition to blowing from higher pressure to lower pressure, wind travels counter-clockwise around areas of lower pressure.  Thus, if you stand with your back to the wind, areas of lower pressure will be on your left.  This is known as Buys-Ballot’s law.  Applying this law to the image above, we would expect to find low pressure in western Texas, which is what we have.

The strong winds out of the southeast are allowing moist air from Texas (and ultimately the Gulf of Mexico) to be advected (blown) northwestward into Oklahoma.  The image above displays dewpoint temperatures, which can be understood as a measure of the amount of moisture at a given level.  The 2-meter dewpoint temperatures above (measured at 2 meters above ground level) are highest across southwest Oklahoma were the winds, and advection, are strongest.

Even though the dewpoint temperatures are highest across southwest Oklahoma, moisture is being advected northwestward by the southeast winds throughout all of Oklahoma.  If we examine the change in dewpoint temperatures over the last 3 hours we can see they have increased most everywhere in Oklahoma.

However, if we examine the change over the last 24 hours, it is much easier to see the dramatic increase in southwest Oklahoma.

The strong winds are doing more than bringing in moist air.  The winds are also bringing in warmer air from the south and helping to keep temperatures relatively warm tonight.  Again, notice how the warmest temperatures this evening are found where the winds are strongest.  This is not a coincidence.

Now, as the low pressure moves into and through the state of Oklahoma tomorrow, all the moisture above will be advected east into Arkansas.  This will cause dry air to move into the area, which will bring the change of wildfires to portions of southwest Oklahoma.  Caution is advised of those who might engage in any activity that could result in a spark.

Lastly, as we continue to move into spring, strong low pressure systems, such as this one, tend to bring with them the threat of severe thunderstorms.  Although thunderstorms are certainly possible tomorrow ahead of the low pressure, the lack of substantial moisture will severely limit the severe threat.  (The lack of severe weather this year may change in the coming 10-15 days.  Stay tuned…)