Definitive Guide to Skew-Ts and Hodographs - Part 1 - Components of a Skew-T
Summary
TLDRThis video script serves as an introduction to reading skew-T diagrams, which are essential tools for meteorologists and storm chasers. The instructor, Trey, acknowledges the complexity of skew-Ts and aims to simplify the understanding by breaking down the different lines and their meanings. He explains the temperature, pressure, mixing ratio, dry and moist adiabats lines, and how they represent various atmospheric conditions. Trey also provides a historical context for skew-Ts and highlights their importance in forecasting and analyzing severe weather events. With clear explanations and visual aids, this video promises to equip viewers with the foundational knowledge to interpret skew-T diagrams effectively.
Takeaways
- 😀 The video series will teach how to read and interpret skew-T diagrams and hodographs, essential tools for meteorological forecasting.
- 📊 The skew-T diagram consists of temperature lines (isotherms) on the x-axis, pressure lines (isobars) on the y-axis, mixing ratio lines, dry adiabats (representing unsaturated parcel ascent), and moist adiabats (representing saturated parcel ascent).
- 🌡️ The red line on a skew-T diagram represents the environmental temperature profile, while the green line represents the environmental dewpoint profile.
- 🔺 The brown line is the parcel temperature profile, showing the hypothetical temperature of an air parcel if it were pushed upward in the given environment.
- 💧 The mixing ratio is the mass of water vapor per kilogram of dry air, represented by the diagonal lines on the skew-T diagram.
- ⬇️ Pressure decreases logarithmically with height, hence the logarithmic scale for pressure on the y-axis.
- 🌡️ The dry adiabatic lapse rate (9.8°C/km) represents the cooling rate of an unsaturated rising air parcel, while the moist adiabatic lapse rate represents the cooling rate of a saturated rising air parcel.
- 📈 The moist adiabatic lapse rate changes with altitude due to the decrease in moisture content as the air parcel rises and cools.
- 🧭 Properly understanding and using skew-T diagrams and hodographs is crucial for accurate meteorological forecasting, whether for operational meteorologists or storm chasers.
- 🔄 The video series will cover creating skew-T diagrams from raw data, interpreting derived parameters, analyzing different environments, and understanding hodographs.
Q & A
What is a skew-t diagram, and why is it called that?
-A skew-t diagram, also known as a skew-T log-P diagram, is a thermodynamic diagram used in meteorology to analyze and forecast atmospheric conditions. It is called a 'skew-t' because the temperature lines (isotherms) are skewed at a 45-degree angle from the vertical, which allowed for easier analysis techniques when the diagram was invented in the late 1940s.
What are the main components of a skew-t diagram?
-The main components of a skew-t diagram are: 1) The x-axis representing temperature in degrees Celsius, 2) The y-axis representing pressure on a logarithmic scale in millibars, 3) Skewed isotherms (temperature lines), 4) Horizontal isobars (pressure lines), 5) Diagonal mixing ratio lines, 6) Curved dry adiabats, and 7) Curved moist adiabats.
What is the significance of the mixing ratio lines on a skew-t diagram?
-The mixing ratio lines on a skew-t diagram represent the mass of water vapor in grams per kilogram of dry air. These lines provide information about the moisture content of an air parcel, which is crucial for understanding atmospheric stability and the potential for precipitation.
What is the difference between dry and moist adiabats on a skew-t diagram?
-Dry adiabats represent the rate of temperature change for an unsaturated (dry) air parcel as it rises or sinks, which is approximately 9.8°C per kilometer. Moist adiabats, on the other hand, represent the rate of temperature change for a saturated (moist) air parcel as it rises, which varies depending on the amount of moisture present and decreases with altitude.
What do the red and green lines on an observed sounding represent?
-On an observed sounding plotted on a skew-t diagram, the red line represents the environmental temperature profile, and the green line represents the environmental dew point profile. These lines are actual observations from a weather balloon as it ascends through the atmosphere.
What is the significance of the parcel profile (brown line) on a skew-t diagram?
-The parcel profile, represented by the brown line on a skew-t diagram, shows the hypothetical temperature of an air parcel if it were to be lifted from the surface. It follows the dry adiabat initially and then the moist adiabat once the parcel becomes saturated. This profile is crucial for assessing atmospheric stability and the potential for convective activity.
How can skew-t diagrams be useful for forecasters and storm chasers?
-Skew-t diagrams provide valuable information about atmospheric stability, moisture content, and the potential for severe weather events. Forecasters and storm chasers can use skew-t diagrams to analyze the environment and make informed decisions about the likelihood and characteristics of thunderstorms, severe weather, and other atmospheric phenomena.
What information can be derived from the spacing of isobars on a skew-t diagram?
-The spacing of isobars (horizontal pressure lines) on a skew-t diagram reflects the logarithmic decrease of pressure with height in the atmosphere. The closer spacing of isobars near the surface indicates a more rapid decrease in pressure compared to the wider spacing at higher altitudes, where the decrease in pressure is more gradual.
Why is it important to understand how to read and use skew-t diagrams effectively?
-Understanding how to read and use skew-t diagrams effectively is crucial for meteorologists and weather enthusiasts because these diagrams provide a wealth of information about the atmospheric environment. Proper interpretation of skew-t diagrams can lead to more accurate forecasts, better identification of severe weather potential, and improved decision-making for storm chasing or other weather-related activities.
What additional topics will be covered in the subsequent videos mentioned in the script?
-According to the script, the subsequent videos in this series will cover: 1) How skew-t diagrams are actually made and plotted from raw data, 2) What the derived parameters on a skew-t diagram mean and how they are calculated, 3) Analyzing and comparing different skew-t diagrams in various atmospheric environments, and 4) An introduction to hodographs, their construction, and their role in forecasting severe weather and supercell characteristics.
Outlines
🌐 Introduction to Reading Skew-Ts and Hodographs
The video introduces a series aimed at explaining how to read skew-Ts and hodographs, essential tools for forecasting and storm chasing. It highlights the importance of understanding these diagrams for better analysis and forecasting. The skew-T was invented in the late 1940s by the U.S. Air Force to facilitate new analysis and forecast techniques, becoming a staple thermodynamic diagram for meteorologists.
📐 Understanding the Skew-T Diagram
This paragraph delves into the components of the skew-T diagram. The x-axis represents temperature in degrees Celsius, with diagonal lines called isotherms or temperature lines skewed at 45 degrees. The y-axis shows pressure decreasing logarithmically with height, represented by horizontal isobars or lines of equal pressure. A scale conversion to feet or kilometers is often provided to interpret height levels.
💧 Mixing Ratio Lines and Adiabatic Processes
The diagonal dashed lines on the skew-T represent mixing ratio lines, indicating the mass of water vapor per kilogram of dry air. The curved solid lines are dry adiabats, representing the dry adiabatic lapse rate of 9.8°C/km for unsaturated parcel ascent. The curved dashed lines are moist adiabats, depicting the moist adiabatic lapse rate for saturated parcel ascent, which varies with moisture content.
📈 Reading an Observed Sounding
This paragraph explains how to interpret an observed sounding on a skew-T diagram. The red line represents the environmental temperature profile, and the green line is the environmental dew point profile, both observed from a weather balloon. The brown line is the parcel temperature profile, following the dry adiabat initially and then the moist adiabat once saturated, indicating the temperature of a hypothetical rising air parcel.
Mindmap
Keywords
💡Skew-T
💡Log-P
💡Isotherms
💡Isobars
💡Mixing Ratio
💡Dry Adiabats
💡Moist Adiabats
💡Environmental Temperature
💡Environmental Dew Point
💡Parcel Profile
Highlights
This video series aims to explain how to read skew-T diagrams and hodographs, which are crucial tools for forecasting and understanding severe weather environments.
Skew-T diagrams were invented in the late 1940s by the U.S. Air Force to make analysis and forecasting techniques easier.
The x-axis of a skew-T diagram represents temperature in degrees Celsius, with the lines skewed at 45 degrees for historical analysis reasons.
The y-axis shows pressure, decreasing logarithmically with height, which is why the diagram is called a "skew-T log-p" diagram.
The dashed diagonal lines represent the mixing ratio, which is the mass of water vapor per kilogram of dry air.
The curved solid lines are dry adiabats, representing the dry adiabatic lapse rate of 9.8°C per kilometer for an unsaturated rising air parcel.
The curved dashed lines are moist adiabats, representing the moist adiabatic lapse rate for a saturated rising air parcel, which varies with moisture content.
The red line on a sounding is the observed environmental temperature profile, while the green line is the observed environmental dew point profile.
The brown line is the parcel temperature profile, which follows the dry adiabat initially and then the moist adiabat once saturated.
Understanding how to read and use skew-T diagrams and hodographs effectively is crucial for being a better forecaster, whether operational or as a storm chaser.
The mixing ratio lines provide an absolute measure of the moisture content in an air parcel.
The dry adiabatic lapse rate represents the rate of cooling for an unsaturated rising air parcel.
The moist adiabatic lapse rate approaches the dry adiabatic lapse rate in the upper atmosphere as moisture is squeezed out.
Subsequent videos will cover how skew-T soundings are made, the meaning of derived parameters, and how to interpret different soundings and hodographs.
Understanding the lines and profiles on a skew-T diagram is the foundation for interpreting atmospheric stability and severe weather potential.
Transcripts
hey everybody trey here and welcome to
this first installment of what's going
to be a
series of videos on how to read sku ts
and hodographs i've gotten a lot of
feedback from some of my recent videos
saying from people saying oh the skuti
stuff was kind of over my head i don't
really know how to read a skew tee
they're pretty complicated etc and i've
gotten some requests from people uh also
asking me to do a video or two
explaining how to read skutees and
hodographs and that's exactly what we're
going to do in this series
we're going to start out with
skutees in this
in this video we'll look at just what
all those lines mean on the diagram and
then in subsequent videos we'll take a
look at how skew t's are actually made
what all those derived parameters mean
and how they're calculated
and finally we'll take a look at some
ski different skew t's in different
environments and kind of compare and
contrast them
and then at the end of the series we'll
take a look at hodographs how they're
made
and how different hodographs can
modulate
the kind of severe severe weather
hazards you might see for a given event
or these characteristics of supercells
in a given environment
um skutees and hodographs are
some of the most important things you
can use when you're making a forecast
and if you know how to use them properly
you will be a much better forecaster
whether you are an operational
meteorologist making a forecast or
you're a storm chaser
picking out a good storm chase target
if you know how to read and use skts and
hodographs effectively
you are going to be a much better
forecaster because they give they can
give so much information on a given
environment and how that environment has
changed over time
that if you don't know how to read
skewed teas and holographs and use them
effectively you're going to be at a
disadvantage
so let's get started here quick word on
the
kind of the history of skutees they were
invented in the late 1940s
at the time there were a few different
um thermodynamic diagrams in use for
example the teflogram and the ammogram
but at this at the time the us air force
was coming up with new analysis and
forecast techniques
and the skew-t was invented to kind of
make
those techniques easier to employ and
they did and it's become kind of the
staple thermodynamic diagram
for meteorologists at least in the
united states
in the last
about 70
70 some odd years since the skt was
invented all right so let's get this
full screen here and let's dive in
to just what each of these lines mean
now if you're just looking at this
diagram for the first time you're new to
meteorology and you're looking at a
skew-t for the first time
it can be quite intimidating
um the
there's a just it looks like a jumble of
lines and why when i first started
looking at skutees it was confusing as
well
but once you get the hang of it and once
you know what each of these lines mean
they do have a specific purpose it'll
become a lot easier to decipher what a
sqt actually is showing
um and it's it's in the end it's it's
fairly simple it looks intimidating but
we're going to help you get the hang of
it here with this video series so
let's start with the
um the x-axis here
so
the x-axis and this will give us a clue
as to why
the
diagram is named skew t log p
the x axis is our temperature axis
it is in degrees celsius and they are
represented by these
diagonal
lines
that run from bottom left to top right
of the diagram these solid diagonal
lines here those are our temperature
lines
or our isotherms
and the reason it's called a skew t is
because the temperature lines are skewed
at 45 degrees from the vertical
for whatever reason it allowed the
analysis techniques back in the 40s to
become a lot easier to use and so
therefore
the
diagram is called a skew-t diagram
because the temperature lines are skewed
now once again it is in
they're all in degrees celsius so keep
that in mind you can see the values here
along the x-axis as well
all right now let's take a look at our
y-axis here let me switch colors all
right so then our y-axis
is our pressure axis
and
you of course the name of the diagram is
a skew-t log-p diagram
and that is because
pressure decreases as you go up in the
atmosphere in a logarithmic fashion
these horizontal lines here are called
isobars or lines of equal pressure
and you'll notice nearer to the surface
the distance between these isobars
is a lot closer
a lot less than it is
versus up higher in the atmosphere where
the spacing is a little bit greater
that's because pressure decreases
logarithmically with height
so if it was a linear decrease where
pressure decreased the same amount from
isobar to isobar then we would see these
the spacing remain the same as you went
higher up in the atmosphere but that's
not the case pressure decreases
logarithmically with height and
therefore we have our skew t
skewed temperature lines log p
the logarithm logarithmic scale of
pressure here on the y axis and of
course the pressure
is given
in millibars
and one quick note you know if
someone told you how high up is you know
400 millibars
you wouldn't be able to you know say
that off the top of your head
most likely so a lot of soundings will
have this
some sort of scale showing a conversion
to feet or even kilometers the spc
soundings which we'll take a look at
have a
some
measurements in kilometers above sea
level
and this particular sounding has it in
feet and you can see the values here
um on the right side so
just something to make uh deciphering
how high up a certain level is
you have pressure on the y-axis but you
can also have it in feet here as well
all right next i'm going to clear this
just for to save some space here to make
it a little cleaner so next we'll talk
about these dashed
lines that run diagonal as well from
basically bottom left to top right of
the diagram
and these are our mixing ratio lines and
the mixing ratio which is denoted in
shorthand by the variable w in
meteorology
the mixing ratio is going to be the mass
of water vapor
in grams
over
per kilogram
of dry air
so you might think that those units are
kind of unintuitive which it would be
grams per kilogram
it's kind of weird to have a mass unit
over a mass unit but that's just the way
it is in meteor when we talk about the
mixing ratio here it's the amount of
grams or the mass of water vapor per
kilogram of dry air so quick kind of
example to help you visualize here if we
had one kilogram of dry air here and for
every one kilogram
say in an air parcel
or an imaginary box of air here's our
one kilogram of dry air
we had five grams
of moist air
so we have five grams of water vapor per
one kilogram of dry air so our mixing
ratio would be five grams per kilogram
that's basically all the mixing ratio is
it's an absolute
measure of the moisture in an air parcel
and again they're denoted by these
dashed lines that run diagonal from the
bottom left to the top right of the
diagram
all right now
this is where it can get a little bit
confusing
um i'm gonna change colors here just to
make it a little bit more visible
so these last two lines on the diagram
may be kind of the most important lines
here
and maybe not important so much as
they can be confusing but they're pretty
critical when we're trying to evaluate
the instability in the atmosphere from
skt
so we'll start off with these curved
lines that go from the top sort of top
left of the diagram
and they curve down here
toward kind of the bottom right of the
diagram
these are called the dry
adiabats
now you might be thinking what the heck
is an adiabat well there are two
different kinds of processes really that
we talk about in meteorology there's
there's diabetic and then there's
adiabatic processes
and in an adiabatic process
there is no heat
added or lost
to the system
during that process and really the main
the thing we're talking about here is
the
rising and sinking of air which results
in the
warming and cooling of air parcels so if
you have a parcel near the surface
if it's pushed upward and it goes upward
it's going to expand
it's going to become bigger and that we
can also
have that happen in the opposite fashion
where you have a parcel of air that
starts aloft it's pushed downward as it
sinks it's going to compress
now when an air parcel rises it expands
and through that expansion it cools
that's an adiabatic process just because
it it is expanding the parcel or the box
of air expands it cools
and as a parcel is pushed downward
from aloft toward lower levels
the parcel gets compressed and it warms
those are adiabatic processes
and when we're talking about the our dry
adiabats here these represent the dry
adiabatic lapse rate
which i'll
kind of abbreviate as dry dalr here the
dry adiabatic lapse rate is 9.8 degrees
celsius per kilometer and what that's
basically saying is when you have a dry
parcel of air when it is unsaturated so
we'll say we have a box of air it has no
moisture in it whatsoever
it's going to rise and it's going to
cool
at a rate of 9.8 degrees celsius per
kilometer so for every kilometer this
dry parcel of air goes up
it's going to drop in temperature 9.8
degrees celsius
now let me
clear this and show you these dashed
curved lines that kind of go
sorry a little bit off the line there
but you can see
it's these kind of curved dashed lines
here that go kind of from the bottom of
the diagram and kind of go up towards
the top right of the diagram
these are our moist
adiabats
and the moist adiabats simply represent
a saturated air parcels ascent through
the atmosphere so when we have a box of
air and let's say this time it's full of
water vapor it's completely saturated
it's going to rise but it's not going to
rise and
decrease in temperature as it expands at
the same rate as a completely dry parcel
of air
near the surface and the moist adiabatic
lapse rate
near the surface so we'll just say the
malr for
for short
near the surface
it's usually about four degrees celsius
per kilometer but the moist adiabatic
lapse rate depends on the amount of
water vapor that is in a given air
parcel so it changes as you go up in the
atmosphere
and a simple you know tenet of
meteorology is that
colder air
holds less moisture
than warmer air
and we know that as we go up in the
atmosphere the temperature
decreases
so air as the a saturated parcel rises
all of that moisture is going to get
squeezed out and you'll notice here
that in the upper portion of the
atmosphere
our moist adiabats and our dry adiabats
are almost parallel well that's because
the moist adiabatic lapse rate up in
here in the atmosphere
in the higher portions of the atmosphere
begins to
be very similar to the dry adiabatic
lapse rate 9.8 degrees celsius per
kilometer as all that moisture is
squeezed out
it continues to rise in the upper
portion of the atmosphere kind of as a
an unsaturated parcel
so that's what those curved lines mean
you have your your moist adiabats are
these curved lines here
they are your moist adiabats and they
represent saturated parcel ascent
and again the
rate of cooling of a parcel as it
expands and
ascends in the atmosphere
differs based on the amount of moisture
in that parcel
whereas these curved lines here these
curved solid lines
those are your dry adiabats
and they represent that 9.8 degrees
celsius
per kilometer value which is the dry
adiabatic lapse rate
and you know often in meteorology you're
never really going to see
a
parcel that rises the dry adiabatic
lapse rate
although it can happen which is
we would call it can actually go
decrease at a greater amount than the
dry adiabatic lapse rate which is what
we call super adiabatic but that's for a
different video but generally you're
going to see something between this
moist adiabatic lapse rate
and this dry adiabatic lapse rate and
again we'll show you how to use these
lines when making a sounding in the next
video but for now that's pretty much
what all these lines mean so in summary
you've got your temperature lines
those these solid lines here that go
from bottom left to top right those are
your temperature lines t for temperature
actually i'll write it out here
just to make it a little more clear so
those are your temperature lines or
isotherms
these
horizontal lines
are your
pressure contours
or isobars again skew-t the temperature
lines are skewed at 45 degrees from the
vertical
and your pressure lines log p the
pressure scale is logarithmic
as it goes up in the atmosphere
decreases logarithmically
as it as you ascend in the atmosphere
then you have your
mixing ratio lines i'll do green for
moisture here these diagonal lines here
are your mixing ratio lines or for short
w and again that's just the mass of of
water vapor per kilogram of dry air
within a parcel
and then you have your
adiabats your
dry adiabats here these solid curved
lines they go down from the top right to
the bottom
excuse me the top left to the bottom
right of the diagram
those are your dry adiabats and again
they represent that dry adiabatic lapse
rate or unsaturated or dry parcel ascent
which is that 9.8 degrees celsius
per kilometer and then you have your
moist adiabats these
dashed curved lines those are your moist
adiabats
and they represent saturated parcel
ascent
so a parcel of air that is full of water
vapor and again that moist adiabatic
lapse rate changes as you go up in the
atmosphere based on the amount of water
vapor that you have in your parcel
so let's take a look now at an observed
sound we've gone kind of through the
foundation
of the skew-t diagram we've got the the
the what all the lines mean
on kind of the foundation the grid
now what about an observed sounding
so
let's start with the red and green lines
here and of course we'll do an actual
sounding and show you how this sounding
is made in the upcoming video
but
let's go ahead for now just
you know decipher what these actually
mean
the red line
is the environmental temperature which
i'll abbreviate env for environmental
environmental temperature and the green
line here is the environmental dew point
so
these are both
observed profiles
from the instrument pack on the weather
balloon as that weather balloon goes up
it
sort of radios back
uh atmospheric data from from every
different level of the atmosphere
a bunch of different levels of the
atmosphere are plotted and then you get
these profiles the red line is the
environmental temperature the green
lines the environmental dew point so
these are actual actual observed
profiles of the actual atmosphere
this brown line however is the parcel
temperature or the parcel
profile
and there are a few different ways to do
that again we'll do kind of go through
that in the upcoming videos but it's
basically the temperature of a
hypothetical parcel of air
if it were to be pushed upward
in this environment now usually if we're
just doing this on our own we're making
our own sounding usually we
you know start at the surface
and you'll notice here that the
in the kind of lower levels
the parcel profile follows the dry
adiabat
and then once it gets saturated once it
hits
uh
once the mixing ratio line
touches the parcel profile
then it uh the parcel is then saturated
and it rises
following the moist adiabat
we'll talk about that again in detail in
the upcoming videos but just wanted to
give you a kind of baseline of what each
of these lines mean on an observed
sounding so
that's all i've got for this first video
you've kind of got the baseline of what
the lines on the sounding mean
next video we'll put it all together
we'll actually make our own sounding and
see how a sounding skew tea is actually
made
and how we can get from the raw data to
something
like this so that's all i've got for now
we'll see you in the next video thanks
for watching
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