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The Dry Line

I was glancing over the current surface analysis chart that I have displayed on my desktop and a symbol I don’t recall having seen before caught my eye. After a bit of investigation I found out that the meteorological feature stretching north-south across central Texas was the Dry Line and I went in search of some more information about this phenomena.

As I described in a previous post, I have a variety of current weather charts from the NOAA National Weather Service displayed on my desktop, a number of which come from their Prognostic Charts page. The surface analysis chart as I write this post is shown below.

Surface Analysis Chart

Looking at central Texas you can see the line of orange symbols that caught my eye. A quick glance at the help page for this chart revealed that this marked the location of the Dry Line. This was something I had heard of before but wasn’t covered in the usual meteorological sections of the various FAA tests so I went in search of more information. I turned to Jeppesen’s excellent Aviation Weather textbook (first ed.) and surprisingly found no mention of the Dry Line, similarly my Dictionary of Aeronautical Terms was just as uncommunicative on the subject. The venerable FAA Aviation Weather textbook (AC00-6A, p76) did have this to say on the subject:

“Dew Point Front or Dry Line: During a considerable part of the year, dew point fronts are common in Western Texas and New Mexico northward over the Plains States. Moist air flowing north from the Gulf of Mexico abuts the drier and therefore slightly denser air flowing from the southwest. Except for moisture differences there is seldom any significant air mass contrast across this “front” therefore it is commonly called a ‘dry line’. Night time and early morning fog and low-level clouds often prevail on the moist side of the line while generally clear skies mark the dry side. In spring and early summer over Texas, Oklahoma and Kansas, and for some distance eastward, the dry line is a favored spawning area for squall lines and thunderstorms”

A follow up with the ever-popular google search turned up a nice description courtesy of The University of Illinois online guide to Meteorology. The National Weather Service forecast office for Shreveport, LA has a page for local meteorological inquiries and if you search for ‘dry line’ in the page you will find a number of references to the dry line and the effect it has on the weather in Texas. I also turned up an informative powerpoint presentation about Dry Lines created by Kelvin Droegemeier at the University of Oklahoma School of Meteorology which shows some more technical information includindg a nice description pertinent to aviators in the region:

In Front of the dry line you are likely to find:

  • S or SE winds
  • Hazy or cloudy skies
  • Warm temperatures
  • High moisture

Behind the dry line you are likely to find:

  • Westerly winds (often strong)
  • Clear skies
  • Warm Temperatures
  • Low Moisture

How does this match up to reality? Below is the satellite and weather depiction for the same time period as the previous surface analysis, you can clearly see the IFR and MVFR weather in front of the dry line in eastern Texas.
Front Page Sat

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