One-Inch Hail InitiativeOne-Inch Hail Initiative

Spring Media SeminarSpring Media Seminar

March 7March 7thth 2009 2009

Jim SievekingJim Sieveking

National Weather ServiceNational Weather Service

WFO St. Louis, Missouri WFO St. Louis, Missouri

Beginning with the 2005 convective season, Kansas Beginning with the 2005 convective season, Kansas weather forecast offices have conducted a 1” hail weather forecast offices have conducted a 1” hail criteria experiment. These offices have issued severe criteria experiment. These offices have issued severe thunderstorm warnings for thunderstorms producing thunderstorm warnings for thunderstorms producing hail sizes of 1” or greater, therefore raising the severe hail sizes of 1” or greater, therefore raising the severe hail criteria from ¾ inch to 1 inch diameter. hail criteria from ¾ inch to 1 inch diameter.

An optional Significant Weather Alert or Advisory An optional Significant Weather Alert or Advisory issued under the Special Weather Statement (SPS) issued under the Special Weather Statement (SPS) header was used to highlight thunderstorms that header was used to highlight thunderstorms that produced hail less than one inch. produced hail less than one inch.

The Kansas ExperimentThe Kansas Experiment

The Kansas Experiment Cont’dThe Kansas Experiment Cont’d

The reasoning for this change in service was The reasoning for this change in service was based primarily on two factors: based primarily on two factors:

– Scientific research indicates 1” is a more Scientific research indicates 1” is a more meaningful threshold for defining hail meaningful threshold for defining hail associated with property damageassociated with property damage

– Feedback from local partners desiring fewer Feedback from local partners desiring fewer warnings and EAS activations for marginal warnings and EAS activations for marginal eventsevents

• Media outlets located in the Kansas Experiment Media outlets located in the Kansas Experiment have expressed approval. They have received have expressed approval. They have received fewer viewer complaints about breaking into fewer viewer complaints about breaking into programming and they feel the warnings we do programming and they feel the warnings we do issue are more meaningful. issue are more meaningful.

• Media representatives stated that their user Media representatives stated that their user feedback suggests individuals now know that feedback suggests individuals now know that when a Severe Thunderstorm Warning is issued, when a Severe Thunderstorm Warning is issued, the threat of damage is genuine. In essence, the the threat of damage is genuine. In essence, the warning is carrying more credibility to the public.warning is carrying more credibility to the public.

The Kansas Experiment Cont’dThe Kansas Experiment Cont’d

• The Kansas Emergency Management community The Kansas Emergency Management community is in favor of continuing the 1” Hail Initiative. is in favor of continuing the 1” Hail Initiative.

• They noted fewer spotter activations during the They noted fewer spotter activations during the demonstration period helped to alleviate the demonstration period helped to alleviate the weariness that can set in from over-activating weariness that can set in from over-activating volunteers for storms that are not expected to volunteers for storms that are not expected to pose serious threat to life and property. pose serious threat to life and property.

The Kansas Experiment Cont’dThe Kansas Experiment Cont’d

Scientific studies indicate hail alone, smaller than Scientific studies indicate hail alone, smaller than 1” in diameter, is not associated with significant 1” in diameter, is not associated with significant property damage.property damage.

““Hail Damage Threshold Sizes For Common Roofing Materials” (Marshall, et. al. 2002)Hail Damage Threshold Sizes For Common Roofing Materials” (Marshall, et. al. 2002)

““The April 1999 Sydney Hailstorm” (Stephen Yeo, Roy Leigh and Ivan Kuhne, 1999)The April 1999 Sydney Hailstorm” (Stephen Yeo, Roy Leigh and Ivan Kuhne, 1999)

http://www.haagengineering.com/ehail/chas/eHail/hailstorm.html

The Kansas Experiment Cont’dThe Kansas Experiment Cont’d

1”1”Threshold size for damage to most lightweight asphalt composition shingles. Threshold size for damage to most lightweight asphalt composition shingles. Thin and/or deteriorated wood shingles, shakes- occasionally punctured or Thin and/or deteriorated wood shingles, shakes- occasionally punctured or cracked. Single-pane windows, thin skylight shells- cracked or broken.cracked. Single-pane windows, thin skylight shells- cracked or broken.

1 ¼” 1 ¼” Threshold size for damage to most heavy weight asphalt composition Threshold size for damage to most heavy weight asphalt composition shingles, wood shingles, and older medium shakes. Automobile body metal- shingles, wood shingles, and older medium shakes. Automobile body metal- dented; galvanized metal vents- dented. Older plastic skylights- cracked or dented; galvanized metal vents- dented. Older plastic skylights- cracked or broken.broken.

1 ½” 1 ½” Threshold size for damage to clay tile, slate, medium shakes, and modified Threshold size for damage to clay tile, slate, medium shakes, and modified bitumen single-ply membranes. Automobile body metal- extensive denting.bitumen single-ply membranes. Automobile body metal- extensive denting.

1 ¾”1 ¾”Threshold size for damage to heavy shakes and concrete tiles . Metal vents- Threshold size for damage to heavy shakes and concrete tiles . Metal vents- caved in. Bare spots and blisters on deteriorated built-up roofs- bruised or caved in. Bare spots and blisters on deteriorated built-up roofs- bruised or punctured.punctured.

HAIL SIZE (IN) TYPICAL DAMAGE THRESHOLDS HAIL SIZE (IN) TYPICAL DAMAGE THRESHOLDS

• One of the main goals of the initiative was to reduce One of the main goals of the initiative was to reduce the number of overall warnings, and the number of the number of overall warnings, and the number of spotter activations for marginal, non-damaging spotter activations for marginal, non-damaging events. events.

• A process was designed to ascertain a reasonably A process was designed to ascertain a reasonably accurate estimate of the warning issuances each accurate estimate of the warning issuances each office saved by raising the hail criterion to one inch office saved by raising the hail criterion to one inch in diameter. in diameter.

• Results indicated a 35% reduction in the number of Results indicated a 35% reduction in the number of severe thunderstorm warnings issued in the severe thunderstorm warnings issued in the experiment.experiment.

The Kansas Experiment Cont’dThe Kansas Experiment Cont’d

2006-2008 Severe Thunderstorm Warning 2006-2008 Severe Thunderstorm Warning VerificationVerification

What Can We Expect?What Can We Expect?

Based on the experience and evaluations of the Based on the experience and evaluations of the Kansas demonstration project, the decision has Kansas demonstration project, the decision has been made to expand the initiative to all Central been made to expand the initiative to all Central Region offices, including St. Louis. Region offices, including St. Louis.

The official start date of this change in service is The official start date of this change in service is scheduled for April 1scheduled for April 1stst 2009. 2009.

Experiment To Be ExpandedExperiment To Be Expanded

Special Weather Statement Special Weather Statement (SPSLSX)(SPSLSX)

WFO St. Louis will issue Special Weather WFO St. Louis will issue Special Weather Statements with the header outlining the Statements with the header outlining the specific threat for sub-severe t-storms.specific threat for sub-severe t-storms.

So instead of…So instead of…

……SIGNIFICANT WEATHER ADVISORY…SIGNIFICANT WEATHER ADVISORY…

It will say something like…It will say something like…

……STRONG THUNDERSTORM MOVING TOWARD DOWNTOWN ST. LOUIS…STRONG THUNDERSTORM MOVING TOWARD DOWNTOWN ST. LOUIS…

ReferencesReferences

• Gallway, J.G., 1989: The evolution of severe thunderstorm criteria within Gallway, J.G., 1989: The evolution of severe thunderstorm criteria within the weather service. Weather and Forecasting , 4, December 1989, 585-592the weather service. Weather and Forecasting , 4, December 1989, 585-592

• Hales, J.E., 1987: An examination of the National Weather Service sever Hales, J.E., 1987: An examination of the National Weather Service sever local storm warning program and proposed improvements. NOAA Tech. local storm warning program and proposed improvements. NOAA Tech. Memo. NWS NSSFC-15. Memo. NWS NSSFC-15.

• Hales, J.E., 1988: Improving the watch/warning system through use of Hales, J.E., 1988: Improving the watch/warning system through use of significant event data. Preprints. 15significant event data. Preprints. 15thth Conference Severe Local Storms, Conference Severe Local Storms, AMS.AMS.

• Marshall, T.P, R.F. Herzog, S. J. Morrison, and S. R. Smith, 2002: Hail Marshall, T.P, R.F. Herzog, S. J. Morrison, and S. R. Smith, 2002: Hail damage threshold sizes for common roofing materials, damage threshold sizes for common roofing materials, Preprints, 21st Preprints, 21st Conf. on Conf. on Severe Local Storms, Amer. Meteor. Soc., 95-98. Severe Local Storms, Amer. Meteor. Soc., 95-98.

• Stephen Yeo, Roy Leigh and Ivan Kuhne,1999: The April 1999 Sydney Stephen Yeo, Roy Leigh and Ivan Kuhne,1999: The April 1999 Sydney Hailstorm, Reprinted from the Natural Hazards Research Centre, Natural Hailstorm, Reprinted from the Natural Hazards Research Centre, Natural Hazards Quarterly, June 1999, Vol 5 issue 2Hazards Quarterly, June 1999, Vol 5 issue 2

• What do you believe the public’s perception will be to this What do you believe the public’s perception will be to this change, if any? change, if any?

• Do you believe this change in severe hail criteria will cut Do you believe this change in severe hail criteria will cut back on the number of times you will have to interrupt back on the number of times you will have to interrupt regular scheduled broadcasting? regular scheduled broadcasting?

• Do you believe that your station will broadcast the Special Do you believe that your station will broadcast the Special Weather Statement?Weather Statement?

DiscussionDiscussion