The Impact of Hail:
A Global Perspective
Deon E Terblanche
Seamless prediction
WMO
Nowcasting and Mesoscale Weather Forecasting Research
Nowcasting Research
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The focus of WWRP Nowcasting Research is to promote detection and forecasting
weather over the 0 to 6 hour time frame, to advance nowcasting science, and to
undertake capacity building and expertise sharing within the WMO framework.
•
Nowcasting systems fill an information need for a variety of users (e.g., emergency
services, defence forces, security agencies, the transport industry, hydrologists, the
agricultural community, recreational groups and air quality agencies), since such
(traditional) systems often outperform numerical weather prediction in the first several
hours of a forecast.
Mesoscale Weather Forecasting Research
• The purpose of Mesoscale Weather Forecasting Research is to promote weather
forecasting research on the meso-gamma scale (~500m – 3km), covering time scales
from 0 ~ 48h, and to strengthen international cooperation, knowledge transfer and
capacity building in this field.
• Mesoscale prediction systems are driven toward this high resolution because the largest
impacts on society tend to be regional or even local in nature.
Overview
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Hail and Society
Hail Formation
The Global Distribution of Hail
The Impact of Hail
The Prediction of Hail
Hail in a Changing Climate
Weather Modification – The Status of Hail Suppression
Conclusions
Hail and Society
Global insured losses from catastrophes were USD 45 billion
in 2013, Swiss Re sigma says
• Total economic losses from natural catastrophes and manmade disasters were USD 140 billion in 2013
• Global insured losses were around USD 45 billion in 2013,
with large contributions from flooding and hail events
• Around 26 000 lives were lost in natural catastrophes and
man-made disasters in 2013
• A special chapter on climate change in the sigma says rising
global temperatures are expected to lead to shifts in the
frequency, intensity and duration of extreme weather events
http://www.swissre.com/media/news_releases/nr_20140326_sigma_insured_losses_in_2013.html
Hail and Society
The nation’s (US) top ten loss events during 1950–2006 reveal
a notable temporal increase with most losses in the 1992–
2006 period. Causes for the increases could be an increasing
frequency of very unstable atmospheric conditions leading to
bigger, longer lasting storms, and/or a greatly expanded urban
society that has become increasingly vulnerable to hailstorms.
Stanley A. Changnon, 2009: Increasing major hail losses in the U.S.
Hail Formation
Hail Formation
Schematic vertical cross-section of a multi-cell storm
(Adapted from Browning 1986).
Schematic vertical and horizontal cross-sections of
a supercell storm (Adapted from Knight et al. 1982).
Hail Formation
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List R. 1985: Properties and growth of hailstones. In
‘Thunderstorms: a social, scientific and technological
documentary. Vol 2. Thunderstorm morphology and dynamics.’
2nd edition. Edited by E. Kessler, University of Oklahoma
Press.
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Knight C.A. and Knight N.C., 2001. Hailstorms. In 'Severe
Convective Storms' Ed. Doswell C.A., AMS Met. Mono. Ch 6,
223-254.
Hail Formation
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Hailstones are lumps of ice/water/air mixture with sizes greater
than 5mm that are generally opaque with layered structure.
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Hail and graupel form in the updrafts of convective storms at
temperatures colder than the freezing point of water.
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Hail stone Embryo (formation ~15 minutes)
• An ice crystal or aggregate of ice crystals
• Frozen drop
Hail Formation
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Wet or Dry Growth through riming and accretion – (growth from 1mm
to 20mm ~30 minutes)
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Hailstones smaller than 20mm density range from 50 to 890 kg m-3
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Larger density range from 810 to 915 kg m-3 (density of solid ice is
917 kg m-3)
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10mm particles have fall speeds in the range of 9-17 m s-1 and 50
mm particles have fall speeds in the range of 20-35 m s-1
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Updrafts and downdrafts can be of the order of 10 m s-1 in
thunderstorms
The Global Distribution of Hail
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Hail forms in strong thunderstorms, particularly those with
intense up-draughts, high liquid water content, great vertical
extent, large water droplets, and where a good portion of the
cloud layer is below freezing
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The growth rate is maximized at about −12 °C, and
neglectable below −30 °C as super-cooled water droplets
become rare
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Hail is most common in mid-latitudes during Spring and early
Summer when surface temperatures are warm enough to
create instability for strong thunderstorms, but the upper
atmosphere is still cold enough to support ice
The Global Distribution of Hail
World composite of hail days reproduced from Court and Griffith (1986)
The Global Distribution of Hail
Hail days (> 20 mm) per year (1980-1999) from NSSL
The Global Distribution of Hail
Example of a point hail climatology from NSSL according to day of year
The Global Distribution of Hail
Preliminary climatology of large hail (> 2cm) over Europe showing average number of reports per year
per 10000 km2 in the period 2000-2007. (Reproduced from ttp://www.essl.org/research/ ).
The Global Distribution of Hail
The convective diagnosis procedure (CDP) is used by the UK
Met Office to obtain information about significant weather
events that are not explicitly represented in numerical weather
prediction models
Such events include probability of lightning and maximum hail
size at the ground.
The Global Distribution of Hail
Global distribution of
hail occurrence (number
of events per day per 1
degree square) in DJF
top and JJA bottom
The Impact of Hail: Switzerland, June 2013
The Prediction of Hail
To forecast hail, deep moist convection is required, in addition
to these three basic ingredients:
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Adequate up-draughts to keep hailstones aloft for an
appropriate amount of time.
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Sufficient super-cooled water near the hailstone to enable
growth as it travels through an up-draught.
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A small fragment of ice or snow for it to grow upon.
The Prediction of Hail
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Ideally hail forecasting will utilize outputs from numerical models
capable of resolving the complex processes within convective clouds
and thunderstorms
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Although such models exist, the computing capacity required to run
these operationally over large areas is prohibitive and so hail cannot
be explicitly forecast
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Therefore, in order to provide forecasts, the likelihood of hail is
diagnosed from larger scale variables which can be predicted
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Several predicted parameters need to be used in combination to
provide reliable diagnoses of hail formation (Convectively available
potential energy (CAPE), Wind Shear etc.)
The Prediction of Hail
Brimelow et al (2006) investigated the feasibility of producing
maps of the forecast maximum hail size over the Canadian
prairies using 12-h forecast soundings from an operational
NWP model as input for a numerical hail growth model
(HAILCAST).
HAILCAST comprises a steady-state cloud model linked to a
hail growth model.
Hail in a Changing Climate / World
Intergovernmental Panel on Climate Change (IPCC) in its
latest assessment provides little guidance on how hail
distribution and frequency might change in future
However, a warmer atmosphere capable of carrying more
water vapour will be more energetic. In addition, a growing
population and its expanding infrastructure will be more
vulnerable.
• Increase of composite material in commercial airlines
• Alternative energy infrastructure (solar panels, solar geysers etc)
Hail in a Changing Climate / World
Weather Modification: The Status of Hail
Suppression
WMO Expert Team on Weather Modification
A team of ~10 international experts tasked to review the status
of weather modification and to promote sound scientific
principles in weather modification
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Executive summary of the WMO Statement on Weather
Modification,
WMO Statement on Weather Modification,
Guidelines for the planning of weather modification
activities.
Weather Modification: The Status of Hail
Suppression
Weather Modification: The Status of Hail
Suppression
In terms of hail suppression:
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Extensively practiced glaciogenic seeding technologies have
been used operationally in many parts of the world to reduce
hail damage. Scientific evidence to date is inconclusive and
evaluation of the results has proved difficult and the
effectiveness remains controversial.
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Supercell storms have been recognized as a particular
problem.
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Attempts to seed hailstorms with hygroscopic nuclei have
been made but have not given demonstrable results.
World Weather Open Science Conference
Overarching theme:
•“Seamless Prediction of the Earth System: from minutes to month“
Two Programs in the Conference:
• Science Program
Basic weather research that extends our knowledge of processes and
systems as well as the applied research needed to put prediction systems
together and assess the impacts of weather and climate events
• User, Application & Social Science Program
The goods and services economy and the role of government in disaster risk
reduction and management and the communication of weather information
Date & Venue:
16 - 21 August 2014
Montreal, Canada
Co-organizer:
• WMO
• ICSU
• Environment Canada
• National Research Council Canada
Total Abstract Submission (Closed in 11 March 2014)
1,200 from 73 countries
Early Registration Deadline
5 June 2014
Please visit at www.wwosc2014.org for more information
Thanks