Transcript Outline - AEROSAFETY | Nick Czernkovich

SUMMER SEVERE WEATHER
Transport Canada
Aviation Safety Seminar
March 15, 2006
Nick Czernkovich
Outline
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Scales of Motion
Thunderstorms
Mesoscale Convective Systems
Downbursts
Flight Planning
Weather Systems
Why does weather occur?
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NATURE LOVES AN EQUILIBRIUM !!
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Net energy imbalance
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More incoming energy in the tropics
Less incoming energy at the poles
Scales Of Motion
General
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Can be divided based
on:
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Observations
Energy contained
within the scales
Scales Of Motion
Planetary Scale
Scales Of Motion
Synoptic Scale
Scales Of Motion
Mesoscale
Scales Of Motion
Time- vs. Length-Scales
Scales Of Motion
Limits of Predictability
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Theoretical Limit: 2 weeks
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In General:
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Synoptic Scales: 2-5 days
Mesoscale: 1-6 hours (or less!)
Mesoscale Features
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Thunderstorms
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Mesoscale Convective Systems
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“Garden Variety”/Airmass
Multicell
Supercell
Squall Lines
Bow Echoes
Downbursts
A Note on Humidity
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Relative Humidity = % saturation
Temperature – Dew Point spread is a measure of
RH
Smaller T-Td spread = Higher RH
Ok so far?
Airmass #1 has T=20C and Td=5C
Airmass #2 has T=8C and Td=5C
Which has a higher RH?
Which contains more water vapour?
A Note on Humidity
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Airmass #2 has a higher RH because the
T-Td spread is smaller
They both hold the same amount of water
vapour
Temperature puts a cap on dew point
because T >= Td, ALWAYS
Td is a measure of water vapour available,
not T
Thunderstorms
Thunderstorms
Parcel Theory
Parcel Theory:
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Considers a lifted
parcel to be a closed
system
No mass is exchanged
with the environment
As parcel rises, it
expands to equalize
pressure with
surroundings
700 mb
850 mb
900 mb
Parcel
Thunderstorms
Cloud Formation
Parcel cools at ~1.5 C / 1000 ft
Latent Heat
Release
Phase change Vapour  Liquid
Lifting Condensation Level
RH = 100%
Parcel cools at 3 C / 1000 ft
Rising air
expands and
cools
Thunderstorms
Altitude
An Idealized Example
2 C/1000 ft
Parcel
Environment
Temperature
1.5 C/1000 ft
LFC
LCL
3 C/1000 ft
Thunderstorms
Capping Inversion
Capping Inversion
LCL
Parcel
Thunderstorms
Temperature and Moisture
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Increases in TEMPERATURE and DEW
POINT can destabilize a parcel
An increase in dew point will destabilize a
parcel MORE than an equivalent increase
in temperature.
Thunderstorms
Triggering Mechanisms
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Heating
Moisture
Lifting
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Terrain
Mechanical (Turbulence)
Frontal
Convergence (Southwestern Ontario!)
Upper-level divergence
Thunderstorms
Single Cell
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Cumulus
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Mature
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Air is lifted to LFC
Updrafts only
Parcel reaches maximum
altitude (Tropopause)
Precipitations forms
Updrafts and downdrafts
co-exist
Dissipating
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Precipitation falls
Downdrafts only
Thunderstorms
Single Cell
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Often referred to as “popcorn convection”
or “pulse storms”
Lifetimes ~ 30 min to 1 hr
Difficult to predict location of formation
Usually disorganized
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Form in low shear environments
Thunderstorms
Single Cell
Thunderstorms
Multicell
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Organized group of
single cells
Self sustaining
Each cell goes through
the typical single cell
lifecycle
Outflow from old cells
generates new cells
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Usually on the southern
Warm Moist Inflow
flank
Thunderstorms
Multicell
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Lifetimes ~ 1 to 3 hr
Form in moderate shear environments
Heaviest precipitation on downwind side
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Weather:
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Locally high winds due to outflow
Heavy rainfall
Hail/Tornado possible
Thunderstorms
Multicell
Thunderstorms
Supercell
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MOST SEVERE – Hail/Wind/Tornadoes
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Form in Strong Shear Environments
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Typically, wind direction rotates with height
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Organized and long-lived ~ 1 to 3 hr
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Weather:
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Locally high winds due to outflow
Heavy rainfall
Hail/Tornado possible
Thunderstorms
Supercell
T
Thunderstorms
Supercell
Thunderstorms
Supercell
Thunderstorms
Supercell
Thunderstorms
Supercell
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Sunday March 12,
2006
Kansas – Missouri
2.25” Hail
Damaging Wind
5 Tornado Reports
Thunderstorms
Supercell
Thunderstorms
Supercell
Thunderstorms
Hail
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Form in severe thunderstorms
Strong updrafts / displaced downdrafts
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Hail tends to fall DOWNWIND of storm
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Can fall as far out beneath the anvil
Golf ball and Baseball sized hail possible!
Thunderstorms
Hail
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Storms:
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Fast moving (not necessary)
Long-lived (supercell or multicell)
Radar:
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Dry hail DOES NOT show up well on radar
Look for BWER … Hail down shear
High radar reflectivities (strong rain rates)
Thunderstorms
Hail
Thunderstorms
Motion
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Synoptic systems tend to move with the 500 mb
wind (~18 000 ft)
Individual thunderstorms (single cells) move
with the mean wind in cloud layer
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At 45 deg latitude, ~700 mb (9000 ft) wind
Organized thunderstorms (multi- and supercells)
move due to advection & propagation
Thunderstorms
Motion
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Single Cells
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Multicells
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Move with the mean wind in the cloud layer
At 45 deg latitude, this is ~700 mb (9000 ft)
Advection + Propagation
Embedded cells move with mean wind
Storm system usually moves right of mean wind
Supercells
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Storm system usually moves right of mean wind
Thunderstorms
Motion
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Angle between Mean
Wind and Storm
Motion varies
Larger angle ~ more
organized
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Often more severe
Fast moving storms
often more severe
Propagation
Thunderstorms
Flying Considerations
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Counter-Clockwise isn’t always best!
Storm systems tend to move
SOUTHWEST to NORTHEAST
Organized storms tend to move to the
right of the mean wind
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Mean wind ~700 mb (9000 ft)
Thunderstorms
Flying Considerations
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Hail
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Typically falls downwind of storm
Caution under thunderstorm anvil
Turbulence
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Updrafts can reach +3000 ft/min in the core
Under anvil
Stay above cloud base – Gust front – VERY turbulent
Gravity waves – Above thunderstorm
Thunderstorms
Flying Considerations
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New Cell Growth
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Often on the southern flank
Look for Towering Cumulus feeder clouds
TCu’s can become CB’s VERY quickly
TCu’s can be just as turbulent!!!
Torrential Rainfall
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Flameout – Turbines
Rapidly reduced visibility
Local flooding (airports – landing considerations)
Thunderstorms
Flying Considerations
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Lightning
Thunderstorms
Flying Considerations
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Local pressure changes
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Inside thunderstorm
In cold outflow
Downbursts and Wind Shear
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Extreme local changes in wind speed/direction
Microbursts and Macrobursts
More to be discussed …
Mesoscale Convective
Systems
Mesoscale Convective Systems
Characteristics
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Large, organized convection
Lifetime ~ 3 hrs to 1 day
Basic physics are the same as
thunderstorms
Considered here:
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Squall lines
Bow Echoes
Mesoscale Convective Systems
Squall Lines
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Linearity
Leading line of
thunderstorms & trailing
stratiform rain
Embedded Supercells and
Tornadoes
Damaging Winds
Mesoscale Convective Systems
Squall Lines
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Cold fronts
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Ahead of cold fronts (pre-frontal squall)
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100-300 sm ahead of front
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Between 150-500 sm from the low center
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Dry Lines
Mesoscale Convective Systems
Squall Lines
Mesoscale Convective Systems
Squall Lines
Mesoscale Convective Systems
Bow Echoes
Mesoscale Convective Systems
Examples
Mesoscale Convective Systems
Examples
Mesoscale Convective Systems
Things Change Fast!
1042 Z
1142
1242
Downbursts
Downbursts
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Downburst
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Defined by Fujita & Caracena in 1977
An exceptionally strong downdraft
Vertical speed > 750 ft/min at 3000 ft AGL
Areal extent > 800 m
Downdraft
Gust Front
Cold Outflow
HW
DB
TW
Downbursts
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Macroburst
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Outflow > 4 km in diameter
Damaging winds last 5-20 min
Microburst
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Outflow < 4 km in diameter
Peak winds last 2-5 min
DRY and WET microbursts
Downbursts
Environmental Conditions
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DRY Microburst
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Elevated cloud bases (elevated CB’s)
Light rain (< 35 dBZ) and virga
Moist upper-air (~500 mb)
Dry sub-cloud layer (dry adiabatic)
Most common in U.S. southwest
Downbursts
Environmental Conditions
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WET Microburst
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Typical (lower) cloud bases
Heavy rainfall (> 35 dBZ)
Dry mid-level (~500 mb)
Downbursts
Physical Origins of the Microburst
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TWO Causes:
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Precipitation drag
Evaporation
Cloud top
Sides
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Evaporation is ~10x more
efficient
Entrainment:
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Side of CB cell
Overshooting top
Downbursts
Characteristics
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Tend to occur in
families
Peak intensity often
reached after
5-10 min
Can occur from
seemingly innocuous
clouds
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Downdraft
+3000 ft/min
Local pressure change
in outflow
Extreme Wind Shear
Extreme turbulence at
gust front
Downbursts
Characteristics
Extreme Turbulence
Families of Microbursts
Shear Line
Fast Moving
Downbursts
Characteristics
DRY MICROBURST
WET MICROBURST
Downbursts
Characteristics
Sometimes they’re hard to see!!
Blowing Dust
Gust Front
Downbursts
June 24, 1975
Flight Planning
Flight Planning
Synoptic Scale
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Review Surface Analysis
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Low Pressure Areas
Fronts
Observed winds (look for areas of lift)
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Terrain, Fronts, Convergence, etc.
Areas of high temperature and dewpoint
Check Upper Air Charts
Flight Planning
Synoptic Scale
Flight Planning
Flight Planning
Specifics
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Temperatures
Dew Points
Low-level airflow
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Temperature/Dew Point Advection
Check FD’s for vertical winds shear
Locations of convergence and lift
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Lake-Effect, “The Summer Kind”!
Flight Planning
Final Thoughts …
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Shear is the dominant factor in storm
organization
Even a stable atmosphere can be
destabilized by lifting
Nocturnal Thunderstorms:
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TCu’s that last into the overnight can become
unstable due to cloud-top-cooling
Flight Planning
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Nav Canada
Aviation Digital Data Service (ADDS)
Environment Canada
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Storm Prediction Center
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Watches/Warnings
Special Weather Statements
Watches/Warnings
Mesoscale Discussions
Convective Outlooks
Hydrometeorological Prediction Center
Research Applications Program