The Weather Patterns Associated with Extremely Heavy Rainfall in Western North Carolina

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The Weather Patterns Associated with Extremely
Heavy Rainfall in Western North Carolina Chip
Konrad Associate Professor Department of
Geography UNC-Chapel Hill Baker Perry Ph.D.
Candidate Department of Geography UNC-Chapel Hill
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Objective Identify the weather patterns
responsible for the heaviest precipitation across
western NC at the local and regional scale.

• Methods
• Determine the heaviest 52 precipitation events
  across western NC. at the regional and local
  scale between 1950 and 2001 (i.e. 52 years).
• These events display a regional recurrence
  interval of 1 year or greater (i.e. the 1 year
  to 52 year storm)
• 2. Classify the events into groups or types
  according to the associated weather pattern.
• 3. Compare the event types to identify weather
  features that best distinguish the very heaviest
  events
• 4. Compare the precipitation and atmospheric
  features associated with Hurricanes Frances and
  Ivan with this climatology

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The Study Area

• Caveats
• Much precipitation variability due to terrain
• Cooperative Observer station network is coarse
• Bias towards valley sites
• ? These have a strong Impact on estimation of
  heaviest rainfall at the local scale

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Classification of the Heaviest 52 events
Tropical Cyclone Mid-latitude Cyclone
L
L
Hurricane Agnes 6/72
October 9, 1976
Wave
September 29, 1964
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Features Associated with the Heaviest Regional
Events
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Monthly Distributions of the Regional Extreme
Events by Type
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Features Associated with the Heaviest Local Events
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Monthly Distributions of the Local Extreme Events
by Type
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Tropical Cyclone Composites of 1000 hPa Height
(i.e. Surface Pressure)
L
L
Heaviest regional events n2 Hurricane Agnes
and Opal
Remainder of Sample n9
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Composites of 1000 hPa height and Precipitable
water for the Tropical Cyclone Type
L
L
Heaviest regional events n2 Hurricanes Agnes
and Opal
Remainder of Sample n9
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Composites of 1000 hPa height and Precipitable
water for the Wave Type
Recall that one out of four of the heaviest local
events is associated with a wave or weak
disturbance.
Heaviest local events n3 Max precipitation
10.0-16.0
Remainder of Sample n10 Max precipitation 8.0
- 9.5
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Note Roughly 90 of tropical cyclones produce
the 1 year or greater rainfall event in
region
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Percent of Tropical Cyclones that pass within 124
miles of Western NC
Only 10-15 of tropical systems ultimately cross
the western NC region
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How does the rainfall associated with Hurricanes
Frances and Ivan stack up against the events in
this climatology?
The Heaviest Regional Events
The Heaviest Local Events
Estimates influenced by the location and number
of rain gauges
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What were the distinctive aspects of Hurricanes
Frances and Ivan that can be tied to the
excessive rainfall?
1. They were both major hurricanes at some point
before making landfall. Frances Category
3 Ivan Category 5
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2. They were both large tropical cyclones
Comparisons with 108 landfalling tropical
cyclones between 1950 and 1993
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3. Frances moved slowly
Frances 8.7 MPH 22
Ivan 15.0 MPH 62
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4. Water vapor contents in the atmosphere were
near record levels.
Maximum 3 Day Precipitable Water Values
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• Concluding Statements
• Tropical cyclones are associated with the vast
  majority of the heaviest rainfall events at the
  regional scale (i.e. 5 year storm and greater).
  
• The wettest systems are bigger, stronger (i.e.
  major hurricane), and have higher amounts of
  water vapor.
• Tropical cyclones and cool season, mid-latitude
  cyclones produce most of the heaviest events at
  the local scale.
• Needs
• More precipitation gauges, particularly at higher
  elevations.
• Research on the development of better
  precipitation estimates in the mountains (e.g.
  blending of observational and radar data).

• Acknowledgements
• David Meaux for assisting me the in the
  development of the software to carry out the
  synoptic analyses.
• NSF Grant BCS-9911315