Severe Weather and Storm Chasing Presentation
Download
Report
Transcript Severe Weather and Storm Chasing Presentation
April 10, 2012
Joe Halvorson, Chris MacIntosh, Tim Marquis
What causes a storm, severe parameters, tools.
The Basics
Thunderstorms need three things to
develop:
Moisture
Instability
Lift/Trigger
Severe storms need one more
ingredient:
Wind shear (directional, speed)
Storm Types
Single cell: “popcorn” storms
Usually not severe, short-lived
Multicell: group of cells moving together
Moderate severe, tornado potential
Squall line: line of storms
Moderate severe, low tornado potential
Supercell: storm with a rotating updraft
(mesocyclone)
Very high severe potential
Main tornado producer
Singe cell
Multicell
Multicell radar
4 cells
Quasi-Linear Convective System (QLCS)
Supercell Structure
Supercell Structure
Parameters
CAPE/CIN(H)
Bulk Shear
Storm-Relative Helicity
Energy Helicity Index
Others
LCL Heights, LI, Lapse Rates.
Supercell Composite, Significant Tornado
Parameter
CAPE
Convective Available Potential Energy
Ability that a parcel has to rise
Large CAPE usually means large vertical
velocities
Different types:
Surface-based
Mixed-layer (Mean layer)
Most unstable
0–3 km
“Skinny” and “Fat” CAPE
Skinny: weaker updrafts
Fat: stronger updrafts
“Fat” CAPE
CAPE!
“Skinny” CAPE
CAPE!
CAPE
Thresholds (in J kg-1):
1–1,000 : Marginally unstable
1,000–2,500 : Moderately unstable
2,500–3,500 : Very unstable
3,500+ : Extremely unstable
For 0–3 km CAPE, 100+ J kg-1 best for
tornadic environment
CIN (CINH)
Convective Inhibition
“Cap,” can prevent instability from being
realized
Negative CAPE
Ways to overcome CIN:
Heating (daytime or warm air advection)
Moisture
Lift
CIN!
CIN (CINH)
Thresholds (in J kg-1):
0–50 : Weak cap
50–200 : Moderate cap
200+ : Strong cap
These values are negative on most
model and mesoanalysis charts.
CAPE/CIN: 24 May 2011
Surface-based
Mixed-layer
Bulk Shear
Change in wind direction and speed with
height put into a single number
Most useful: 0–1 km, Effective
Effective accounts for storm depth (inflow
base to equilibrium level)
Thresholds
0–1 km : 15-20+ kts supportive of tornadoes
Effective : 25–40+ kts supportive of
supercells
Bulk Shear: 27 April 2011
Effective
0–1 km
Storm-Relative Helicity (SRH)
Measure of the potential for a rotating
updraft in a supercell
Higher numbers associated with a
higher potential for tornadoes
Three types:
0–1 km, 0–3 km, effective
Effective is most useful in discriminating
between tornadic and nontornadic storms.
Storm-Relative Helicity (SRH)
Thresholds (in m2 s-2)
0–1 km : 100+
0–3 km : 250+
Effective : 100+
0–1 km SRH: Outbreaks
27 April 2011
24 May 2011
Hodographs
Greensburg EF5
Parkersburg EF5
Outbreak Sounding
Energy Helicity Index (EHI)
Combination of CAPE and SRH
Two types: 0–1 km, 0–3 km
Thresholds
>2.5 : Favorable for tornadoes
Storms must develop for this to be
useful
Can be skewed by high CAPE values
0–1 km EHI: Outbreaks
27 April 2011
24 May 2011
Other Parameters
LCL Heights
Lower heights (<1000 m) associated with
tornadoes
Higher moisture available, keeping RFD warm
Lifted Index (LI)
Another stability index (taken at 500 mb)
The lower the number, the more unstable the
atmosphere
Other Parameters
Supercell Composite
Significant Tornado Parameter
For these two, we shall play a game!
But first… MATH!
MLCAPE EBS sfc ESRH 2000 MLLCL 250 MLCIN
STP
*
*
*
*
1500
20
150
1500
200
MUCAPE EBS ESRH
SCP
*
*
1000
20
50
scary Chen math, but still a nuisance.
Not
Game time!
Game time!
Where was the severe weather?
?
The point of STP & SCP
These are best used to pinpoint a region
that severe weather could occur on a
given day.
Should never be used to make any other
decisions without actually analyzing the
environment.
More things to look at!
Jet Stream
Increases shear
Separates downdraft from updraft
Longer-lived storms
Low-level Jet (LLJ)
Brings in moisture and warmer temperatures,
increases shear and helicity
Upper-Level Jet Streaks
Increased shear, upward motion to increase
instability
Upward regions: right entrance, left exit
500 mb Jet: 27 April 2011
LLJ: 9 April 2011
Upper Level Jet Streak
Left
Exit
Right
Exit
Left Entrance
Right Entrance
More things to look at!
Frontal boundaries
Cold and warm fronts, dryline
Can enhance shear, helicity
Source of lift
Surface observations
Gives an idea of what is going on at this
moment
Look for mesoscale features
Satellite Imagery
Look for clearing early, robust CU fields
More things to look at!
Water Vapor Imagery
Shows drying, moistening in the mid- and
upper-levels
See where fronts/shortwaves are located
More things to look at!
Moisture
Storms won’t form without it
Td > 60°F for best environment
700 mb temperatures
Good indicator of cap strength
< 12°C in the spring without a strong lifting
mechanism
Can be slightly higher (<13°C) during
summer months or with strong lift
More things to look at!
Theta-E
Measure of heat and moisture in the
atmosphere
Look for theta-e advection/ridges
Increased instability, convergence
Could be area of convective development
Storm Motion
Calculated average direction and speed of
storms
Gives an idea of how storms will move
Where Do We Look At This Stuff?
SPC Mesoanalysis
TwisterData
COD Analysis
AMS Model Animator
HPC
RAP Weather
How to chase safely and effectively.
The Beginner’s Way
S/SE is safest place to be
Watch for right-turning
Avoid core-punching
Avoid rain-wrapped messes
Pull off on side roads, not main roads
What NOT to expect…
To see a tornado on your first time out…
or second…
or third…
Good chasers usually see a tornado
about once in every seven chases.
Don’t let this deter you from chasing…
Can’t win the game if you don’t play!
What to expect…
LONG car rides
Sitting, waiting, wishing… football and
frisbee!
Lots of gas station/fast food meals
Sketchy dirt roads
And in turn, few rest stops.
The beauty of the Plains
Awesome tunes!
THE TIME OF YOUR LIFE! Memories!
Tips
Wear real shoes or boots, not flip flops.
Watch the skies, not just the computer
screen.
Only your eyes can tell you what’s actually
happening around you.
Try to learn as much as possible, not
just watch.
So we’re not held liable if you act stupid. Just kidding. But seriously.
Safety Tips
CHASE WITH SOMEONE WHO HAS
CHASED BEFORE.
Chase with a partner
Stay in the car as much as possible if
there’s lightning nearby.
Have an escape route
Try to head south if you feel that you’re in
danger.
If that’s not possible, head east until you
can go south.
Good Resource: Titan U.
http://www.youtube.com/watch?v=d_Kh
AhitJE0&list=PL68D75C6534412169&in
dex=4&feature=plpp_video
Don’t Get Close on Big Days!
Going with experience and technology.
Freshman shouldn’t go out with other
freshman alone.
Watch out for power poles!
Things NOT to do:
http://www.youtube.com/watch?v=h84yTN
XCXPQ
http://www.youtube.com/watch?v=CaQ3L1j
ftxs
More Safety Tips
Don’t get out of the car if there’s hail.
Don’t chase at night.
Make sure you pull off the road ALL THE
WAY when you stop to look at
something.
Don’t pull over on highways to look.
Flashers.
Watch out for “those” drivers.
More Safety Tips
Avoid “minimum maintenance” roads
Previous rainfall could have washed them
out.
Don’t drive on flooded roads.
Turn around, don’t drown!
Don’t drive over power lines/debris.
Try to avoid driving through squalls.
This is never possible in Iowa.
WATCH OUT FOR ANIMALS.
They get spooked and like to run out in
front of/into the side of moving vehicles.
[email protected]
[email protected]
[email protected]