[FRIAM] Dry Line Report

[Nicholas Thompson]

Here's todays map.  The dry line has backed up a bit and tightened.  The
cold front in NM has moved east to approach the dl.

[image: image.png]
On the surface, it looks like an ideal set up for severe weather in east
TX.  Look at the sounding for Dallas Fort Worth:

[image: image.png]
Pay attention to the relation between the blue line and the redline.  The
redline is the actual temperature path for the rising balloon.  The blue
line is the temperature a parcel would have if it were lifted up through
the atmosphere beside the balloon.  The green line is the dewpoint of the
air.  Notice how the green and red lines form a rough triangle from 900mb
up to nearly 500 mb.  This is an elevated mixed layer.  It is the same warm
dry air that is sitting west of the dry line.  See sounding for lubbock.

[image: image.png]
You see that same triangle, but in Lubbock it is sitting on the ground.  So
between Lubbock and DFW the mixed layer (unstable) has become lifted by the
moister cooler air to the east.  The dry line represents the point at which
the warm, dry, mixed layer has been elevated above the surface.  It's not a
"point"; of course, but a zone in which the dewpoint rises some 50 degrees
between Lubbock and DFW.

Now first notice the "nose" on the eml; in the DFW sounding.   Along the
nostrils of that nose  the temperature of the air rises  with altitude,
despite the lapse rate.  In fact the potential or sea level relative
temperature rises around 7 degrees C in just a few meters.  This nose is
called the cap.  The area to the right of the blue line, the nose itself,
is the amount of lifting that must be be produced by latent heat of
condensation before the cap is broken.  Once we have accumulated that much
lifting we read the level of free convection, where the redline crosses the
blue.  Here every lifted parcel will be warmer than the surrounding air for
the next several thousand feet.  Once the cap is broken, one gets explosive
development of cumulus clouds and because they are developing through the
dry air of the eml, they have that wonderful etched look that characterizes
western thunderstorms.

I don[t know why DFW; has no severe alerts for today.  I suspect once
again, it is the lack of upper air support. The jet over tx is not that
robust and there doesnot appear to be much vorticity with it.  But
whaddoooeyeno.

I will say this:  if ever you wanted to have an illustration of what a dry
line is and how it affects the structure of the atmosphere to the east of
it, the diagrams above are perfect for that purpose.  You might save them
somewhere.

I have to quit now, but I took George over the coals about his estimate of
water loss last night, and he amitted to have not heeded my stipulation
that exertion was low.   So, for low exertsion, half a ltry per hour is the
better estimate.  gutta run  Nick



On Thu, May 15, 2025 at 10:38 AM Nicholas Thompson <thompnickson2 at gmail.com>
wrote:

>
> The Dry line is way east in TX.
>
> [image: image.png]
>
> The chief  implication for Santa Fe is the very low dew points.  Under
> these conditions, George says (and I quote),
>
> *" Given this low humidity and the altitude, your estimated water loss
> from light household chores in one hour would be about 1.46 liters (roughly
> 1.5 liters). "*
>
> REALLY?  It seems to me that at this rate I will be a piece of beef jerky
> by noon
>
> One might ask, why there is no severe weather in east Tx.  The answer
> seems to be in the lack of upper air support.  (Note ridgey configuration
> of jet stream over TX.
> [image: image.png]
> Stay hydrated out there.  I don't know about the rest of you, but I can
> get REALLY CRANKY under these conditions.  .
>
> Nick
>


-- 
Nicholas S. Thompson
Emeritus Professor of Psychology and Ethology
Clark University
nthompson at clarku.edu
https://wordpress.clarku.edu/nthompson
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