[FRIAM] The Dry Line Report

Tue May 20 16:57:52 EDT 2025

Dear  Phellow Phriammers,

We have to stop meeting this way.

I am sure you detect procrastination when you see it.  So what explains
Nicks annual obsession with the dry line?  Is this genuine meteorological
passion brought on by the annual development of the dry line.  Or is Nick
procrastinating from getting ready for his annual migration to New
England.  Please don't be surprised if I have to ditch this project
abruptly.

Here is todays  Hazard map.  As you see, things have calmed down a lot on
the high plains.
============================
[image: image.png]
+++++++++++++++++++++=
Here's the current surface map.
======================
[image: image.png]
======================
The Map has simplified itself considerably.  A long surface trough coming
down from  a surface  low in Iowa to the TX Gulf Coast accompanied by a
cold front which has joined forces with dry desert air to produce a very
sharp dry line nw of Corpus Christi.  Further north, it gets more blousy.
======================
[image: image.png]

======================
Here is the 500mb chart which shows a deep trough/ridge sequence across the
central US, along with a vorticity center in Nebraska.
======================

Since you all love skew-T's I thought I would give you a grid of them to
contemplate..  The grid only shows color where there is some Convective
Available Potential Energy, CAPE.  So basically you are interested in the
size of the pink blob in the middle of each sounding.  Big pink is Bad.
======================
[image: image.png]
======================
I am focussing on the sounding at Houston TX because it has the largest
CAPE but DOESN'T seem to be getting much attention.  Why is that?
======================
[image: image.png]
Somebody made the terrible mistake of encouraging me to explain a skew T
Diagram in more detail, so now the rest of you have to suffer.  Focus first
on the two dashed lines angling up to the right, one red, one black.  They
are lines of equal temperature.  I think the black line is freezing and the
red one is -30 C?. They are skewed to the right for graphical convenience.
Now ignore them.  Now pay attention to the nice green line.  That is the
dewpoint tracing of the actual sounding.  There appear to be two elevated
mixed layers in this sounding, shown by where the green line makes a rapid
excursion to the left (dryer air) and then wanders back toward the right;
forming a sort of a triangle.  They are called mixed layers because their
potential temperature is relatively constant; but as the water vapor line
suggests, they get moister as you go up because water vapor is lighter than
the air that it is in and tends to collect at the top of the layer.  Now
pay attention to the redline which is the actual temperature profile of the
sounding.  A stable sounding will be more vertical; an unstable sounding
will drift diagonally off to the left.  Finally, pay attention to the black
dotted line that bulges out to the right.   That is the "lifted parcel
temperature"  So imagine that you took a parcel of that nice soupy air near
the surface and lifted it until it was saturated and then KEPT LIFTING IT.
It would become "warmer" than the air around it (its "environment")  The
pink area between is all the extra buoyancy that that upward moving moist
air would capture because of its water vapor content.   The condensation of
that moist air would, of course, take the form of rapidly rising towering
cumulus.

Now, the soundings above are all calculated and interpolated from  40 plus
actual soundings around the US.  Unfortunately the nearest sounding to our
"juicy" one is Corpus Christi, which is not very near.
==============================
[image: image.png]

==============================
Apparently, SPC has taken note of  my ambivalence about the S TX situation
and has put out a special analysis of that area which shows a the dry line
to the NW and a slight cyclonic curvature in the 500mb height contours, and
a line of showers developing parallel to the coast already in the morning.
======================
[image: image.png]
=============================
I will end with a satellite of the same area.  You can see the cold front
pushing through the coast but thunderstorm development seemsto be confined
to NE Mexico. And there is tons of shear.  Go figure!

=======================================================
https://cdn.star.nesdis.noaa.gov/GOES19/ABI/SECTOR/sp/GEOCOLOR/GOES19-SP-GEOCOLOR-600x600.gif

 ===========================
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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