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Climate, Weather and Property Risk
Presentation to Cat Modeling 2014February 11, 2014
Craig TillmanDave Bachiochi
David Hamilton
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Presentation Outline
Weather Scales, Variability and Volatility
Climate Processes and Weather Outcomes
Severe Convective Storm (SCS) Phenomenology
2
Physical CharacteristicsAssociated Hazards
Recent trends in SCS activity
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Highlights
US SCS activity has increased during the last decade
Increased activity mainly linked to decadal climate variability:
Jet stream modification related to variability in Pacific sea-surfacetemperatures associated with the Pacific Decadal Oscillation (PDO),ENSO and other factors
3
WPC expects key climate signals to continue to favor increased severeconvective storm activity.
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Climate is what we expect,
weather is what we get.
4
Andrew John Herbertson
Modified Version by Robert Heinlein
Also Inspired by Mark Twain
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Natural Sciences Scales of Climate Variability
The atmosphere-ocean system is naturally variable in time and space
Variability in time is apparent in a range of scales from days to many years
Short-term weather and long-term climate impact each other to defineboth the present risk and its future evolution
5
TornadicSupercells
Transient WeatherSystems
(e.g., Cold Front)
Large-Scale,Slow Moving
Patterns(e.g., Polar Jet)
Severe WeatherOutbreak Example
Long-Term NaturalVariability/Global
Warming
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Complex Physical Problem
Changes in the atmosphere and/or ocean can trigger change in the variabilityand overall state of the system locally in time and space
ty
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RemoteForcing
ChangingVariab
ili
C
hangingRisk
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Volatility Vs. Variability
Weather volatility is a measure of variability, dependent on the time andspace scales of interest.
High weather volatility (i.e., extreme variability) can lead to unexpectedresults.
Volatility on smaller space and time scales may have limited impacts
Short-term temperature spikes
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Localized severe weather Volatility on larger scales can lead to significant, negatively impactful events:
Extended droughts
Large-scale floods
Severe weather outbreaks
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Managing the Volatility Property Risk Perspective
Changing ExposureChanging Exposure
Increasing UncertaintyDecreased Quality
Synoptic Variability
Short-Term Intermediate-Term Long-Term
Natural VariabilityClimate Change
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Adaptive StrategiesAdaptive Strategies
Historical RecordHistorical Record
Short-term: Day to Day Variability Intermediate: Global Climate Indices Alter Variability
Long-term: Global warming Shifted Patterns/Strength
Blocked FlowsTropical EventsDry SpellsRain EventsSevere WeatherOutbreaks
ENSONAOAtlantic SSTSnow-coverMJO
Pattern Shifts
Additional CO2Sea Ice Melt
Natural Variability"A New Normal"
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Severe Convective Storms (SCS)Phenomenology
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What is Convection? Convection the movement of a fluid
In Meteorology, convection is the vertical overturning of the atmosphere
Deep Convection is a thunderstorm, whereas
Hot, moist air near the surface rises rapidly in an Updraft
Precipitation falls back to the ground, generating a Downdraft
Updrafts and Downdrafts are responsible for all SCS Perils!!!
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What Causes Convection?
The 3 Ingredients for Thunderstorm Development
Source of Moisture
Gulf of Mexico is the primary source of moisture for US SCS development
Instability
In thunderstorms, unstable air refers to vertical air motion, i.e.
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warm, moist air rising
cold air descending
Source of Lift
Surface HeatingTerrain
Fronts
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What Sustains Convection? Long-lived or organized thunderstorms require vertical wind shear,
i.e. change in wind speed and direction with altitude
Allows for a sustained updraft and downdraft
Delivers abundant low level moisture to fuel the storm
Provides an avenue for depositing precipitation without choking the updraft
Enables storm rotation and motion
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Cold Front liftswarm moist air.
Downdraft acts
to reinforcefront
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What Causes Convective Outbreaks?The Basic SCS Model
SCS Outbreaks are dictated by jet stream amplification
Jet Stream amplification is a bending and strengthening of upper level flow, leading to: Large scale cold air mass intruding over continent from the north
Surface low pressure that draws gulf air into the countrys midsection
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,
Which is sustained by vertical wind shear organized by the jet stream
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Severe Convective Storms: Large-to-Small Scale
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Vertical wind shear on the large scale dictates storm evolution on small scale
Abundant low-level moisture provides thunderstorm cells with fuel
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What is a Severe Convective Storm?
A thunderstorm is considered Severe if at least one of these exist1:
Hail that is at least 1 inch in diameter
Wind gusts to 58 mph or higher
A tornado
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Courtesy of : The Storm PredictionCenter of the US National Weather
Service
1As defined by NOAAs NWS
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Hail
Precipitating ice pellets ranging from pea to grapefruit size
Updraft strength and freezing altitude govern hail production
Damage dependent on hail size, density, concentration and air motion
Easily detected by Doppler radar
Typically falls in swaths (or hailstreaks)
17Hailstreak from 10 April 2001: Changnon and Burroughs, MWR, 2003
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Hail Video
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Downbursts
A downburst is a strong downdraft and is a localized phenomenon:
Rain-cooled air accelerates downward, hits the ground, and spreads
Strong surface winds create straight-line wind damage
Microburst: a downburst with a diameter of less than 4 km
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Downbursts (cont.)
Macrobursts:
Downdraft diameter > 4 km
Create gust fronts
propagate hundreds of miles
winds recorded up to 130 mph
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SCSs can produce hail streaks or swaths. On April 10, 2001, aparticular strong hail storm produced a hail swath over the entirestate of Missouri.
Times of hail are LST, and locations with hailstones >1 inch indiameter are shown as dots.
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Downburst Video
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Tornadoes
Violently rotating column of air in contact with the surface
Typically only a few hundred meters in diameter and last for only 5-10 min.
Average forward speed of 25-30 mph (40-50 kph)
Damage is localized but often devastating
caused by high winds within and near tornado core, as well as from
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Tornado Ratings Enhanced Fujita Scale
Classifies damage on a six-point scale, with input from engineers & scientists
Considers 28 different damage indicators including construction strength
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Tornado Ratings Enhanced Fujita Scale
Examples of Damage associated with the 6 classes of tornado intensity
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Tornado Ratings Enhanced Fujita Scale
Examples of Damage associated with the 6 classes of tornado intensity
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Tornado Ratings Enhanced Fujita Scale
Examples of Damage associated with the 6 classes of tornado intensity
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Severe Convective Storm TypesPerils associated with the following storm types, in decreasing intensity
Supercells Tornadoes, Straight Line Winds, Hail
Multi-cell Line Straight Line Winds, Hail, and to a lesser extent, tornadoes
Multi-cell Clusters Localized Wind Damage and Hail
Ordinary Cells typically non-severe
Photo by Sean Heavey
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SCS Nomenclature
Supercells
Squall line/Derecho
Micro/Macroburst
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Severe Convective Storm Types Supercells
A persistent, rotating thunderstorm lasting several hours
Strong / tilted / rotating updraft
Sustained downdraft displaced from the updraft
High likelihood of severe weather (hail, high winds, tornadoes)
Typically responsible for the strongest tornadoes
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Severe Convective Storms Derecho
Definition: a convective system producing a wind damage swath over 240miles in length from winds of at least 58 mph
Can travel hundreds of miles over several hours to a couple of days.
Propagate analogously to an ocean wave either ahead of a cold front oralong a stationary front
Squall line expands with broad and intense gust front
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Lyndon State University Course Notes, met130, Ch 14
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Derecho Animation
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Super-Derecho of 2012
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24 Hour Maximum Radar Reflectivity field reveals Derecho path and
expansion after developing from a single cell in southwest Iowa.
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Severe Convective Storms Scale Comparison
Tornado
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Hail
Wind
Increased Size/Impact Potential
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Severe Convective Storms Scale Example
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Severe Convective Storms Climatology
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Climatology: What is expected thunderstorm activity?
Thunderstorms can occur during any month and at any time of day
Typically, greatest risk for SCSs is during spring and early summer
In the daily cycle, storms typically peak in the late afternoon and evening
Climatologies (average arrivals) of tornado and hail are quite similar whilederechos have a peak frequency slightly later in season.
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Monthly Severe Hail Climatology (Hail Days)
January February July August
36Cintineo, John L., Travis M. Smith, Valliappa Lakshmanan, Harold E. Brooks, Kiel L. Ortega, 2012: An ObjectiveHigh-Resolution Hail Climatology of the Contiguous United States. Wea. Forecasting, 27, 12351248.
March April
May June
September October
November December
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Severe Convective Storms Tornado Climatology
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Courtesy of Dr. Greg Forbes, The Weather Channel
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Derecho Climatology
Most common in late spring and summer
Most active locations, on average, see more than one derecho per year
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lim P rn n Th ir Im n
Are we in a new norm?
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Large Scale: Jet Stream
Jet streams are the dominant atmospheric force on weather systems
Jet wave patterns often modified by global climate signals
ENSO and PDO are significant climatic modulators of North American weather
Arctic Signals
NAO
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BUT, during any given year or period there are other wildcard signals such as AOor NAO that could reduce or enhance the severe convective storm activity.
ENSO
PDOAMO
Antarctic Signals
Indian-PacificSignals
ENSO
PDO
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Pacific Decadal Oscillation (PDO)
Anomalous sea surface temperatures in North Pacific
Cold or warm phases last about 20 to 30 years.
ENSO events typically persist for 6 18 months
Negative PDO brings stronger northwesterly winds to the Northwest UScoast as well as cold Pacific coastal ocean temperatures.
4141
Cooler water in theNortheast Pacific
2008 La Nina coolerwater in the equatorialPacific
Negative (cold) PDO and La Niaillustrated in sea surface
temperature anomaly field onMarch 6, 2008
Warm water in theNorth Central Pacific
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Estimated Uptick in SCS Activity
0
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dizedSevereWeath
er
EF2+ Count EF2+ Smoothed Radar 55 dBz
Radar Smoothed DPI DPI Smoothed
Average Smoothed
El NioLa Nia
5.4
Large scale climate factors and SCSsare correlated
Enhanced risk indicated in radarand tornado count analyses
Evidence for a cycle tied to PDO
Year-to-year variations tied toENSO
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PDO
Smooth PDO
Warm Epoch Warm EpochCold Epoch Cold
-2
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1970
1972
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197!
19!0
19!2
19!4
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Standar
COLD PDOCOLD PDO WARM PDO
nce , ac v y as
increased to levels to that of the priorcold PDO epoch
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43La Nia + Negative PDO
o a a
Strength and position of jets criticalto the location and amount ofsevere weather activity potential.
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EU Idealized Pattern Plots
Generally Mild
POLAR JET
Arctic Air Mass
LLLLLLLLLLLLLLLL
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Generally
Mild
SUB-TROPCAL JET
HHHHHHHHHHHHHHHH
Lo! le"el #et$
%ot layer o& air &ro'
A&rican Sa%ara and
S(anis% Platea)*
T%e S(anis% +Pl)'e,
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What Does Heightened Activity Mean?
Large-scale climate factors favor increase in:
Upper-level (jet stream) energy
Atmospheric instability
Subsequently increasing the probability of SCS outbreaks
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Higher number of intense supercells
Long-track tornadoes
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Recent Trends In Spatial Pattern
Stormdays
Stormdays
Tornado Days Hail Days
Change in Number of Average Days: 2008-2012 minus 1983-2007
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Atmospheric ingredients conducive to SCS have expanded eastward in recent years.
Eastward expansion in SCS potential coincides primarily with negative PDO and La Nina
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Recent increased likelihood in SCS activity in the US
Changes to atmosphere driven by jet stream changes
Jet stream modulation driven by large-scale patterns
Climate factors expected to persist and influence severe convective stormactivity for at least the next 5 years
Severe Convective Storms
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