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How to Interpret Advanced Severe Weather Data Sets EAX Severe Weather Seminar March 1, 2006

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How to Interpret Advanced Severe Weather Data Sets EAX Severe Weather Seminar March 1, 2006 Objectives To provide an overview of resources for anticipating severe ... – PowerPoint PPT presentation

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Title: How to Interpret Advanced Severe Weather Data Sets EAX Severe Weather Seminar March 1, 2006


1
How to Interpret Advanced Severe Weather Data
SetsEAX Severe Weather SeminarMarch 1, 2006
2
Objectives
  • To provide an overview of
  • resources for anticipating severe weather
  • severe thunderstorm forecasting parameters

3
Anticipating Severe Weather
Internet Resources
  • Hazardous Weather Outlook
  • Focus on expected threats.
  • Seven day outlook for severe weather.

4
EAX (Watches and Warnings) Web Page
  • Warning Decision Update
  • Watches, Warnings, Polygon Warnings, LSR,
    Hazardous Weather Outlook and etc.
  • EAX URL (www.crh.noaa.gov/eax)

5
SPC Outlook Products
  • Convective Outlooks (www.spc.noaa.gov/products/ou
    tlook)
  • Categorical
  • Probabilistic
  • Mesoscale Discussions
  • Convective Outlooks and Mesoscale Discussions can
    also be found in the Watch and Warning link on
    the EAX homepage

6
Categorical Convective Outlook
7
Probabilistic Convective Outlooks25 mile radius
8
Probabilities You May See In The Probabilistic
Outlooks
  • Day 1 Tornadoes
  • 2, 5, 10, 15, 30, 45, 60
  • Large Hail
  • 5, 15, 30, 45, 60
  • Damaging Wind
  • 5, 15, 30, 45, 60
  • Day 2 Any severe weather
  • 5, 15, 30, 45, 60
  • Day 3 Any severe weather
  • 5, 15, 30, 45

9
Anticipating Severe Weather
Mesoscale discussions
  • When conditions appear favorable for the
    development of severe storms
  • Ideally issued 1 to 3 hours before a watch is
    issued.

10
Severe Weather Parameters
  • CAPE
  • LOW LEVEL
  • SBCAPE
  • MLCAPE
  • MUCAPE
  • DCAPE
  • CIN
  • LAPSE RATE
  • 850 MB 700 MB
  • 700 MB - 500 MB
  • SHEAR
  • EFFECTIVE SHEAR
  • BRN SHEAR
  • 0-6 km
  • 0-3 km
  • 0-1 km
  • SRH
  • 0-3 KM
  • 0-1 KM

Instability
Low Level Shear
11
Severe Weather Parameters, cont.
  • STORM RELATIVE WINDS
  • 0-2 KM
  • 4-6 KM
  • 9-11 KM
  • ANVIL LEVEL
  • LCL
  • LFC
  • EHI
  • 3 KM
  • 1 KM
  • VGP (3 KM)
  • SUPERCELL COMPOSITE PARAMETER
  • SIGNIFICANT TORNADO PARAMETER
  • CRAVEN SIGNIFICANT SEVERE

COMPOSITE INDICES
12
Lifted Condensation Level (LCL) and Level of Free
Convection (LFC)
  • LCL is the level at which the cloud base forms.
  • (the level at which unsaturated parcel lifted
    from surface becomes saturated)
  • Tornadoes often occur with low LCLs
  • - less than 1500 m.
  • Level of free convection is level at which air is
    warmer than its environment and rises on its own.
  • Thunderstorms blossom rapidly when rising air
    reaches the LFC.

13
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14
CAPECONVECTIVE AVAILABLE POTENTIAL ENERGY
  • Is a measure of instability through the depth of
    the atmosphere
  • Directly related to updraft strength in
    thunderstorms
  • Values
  • gt 1000 J/kg weak instability
  • 1000-2500 J/kg-moderate instability
  • 2500-4000 J/kg-strong instability
  • gt 4000 J/kg- extreme instability

Higher number ? stronger storm
15




16
CAPE, cont.
  • Variations
  • Low level Cape - Depicts buoyancy for SR-inflow
    (0-3km) and RFD. Large Cape favors strong
    low-level stretching.
  • SBCAPE- Calculates buoyancy from LFC on up.
    Parcel originates at the surface.
  • MUCAPE- Calculates buoyancy of most unstable
    parcel in the lowest 3 km.
  • MLCAPE- Calculates buoyancy utilizing average
    T/Td in lowest layers in atmosphere (lt 1 km).
  • DCAPE- Estimates potential strength of the
    downdraft

17
CIN
  • CIN is a quantitative measure of the amount of
    work necessary to lift a parcel above LFC
  • Larger CIN (gt 50) ? less threat for
    thunderstorms.

18
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19
Lapse Rates
  • The rate of temperature change with height (C/km)
  • 850-500 mb (4500-18000 feet)
  • 700-500 mb (10000-18000 feet)
  • Values
  • lt 5.5 6 C/km stable conditions
  • 9.5 C/km absolutely unstable

20
Hodographs of Thunderstorm Types
Typical wind hodographs for (a) single cell, (b)
multicell, and (c) supercell thunderstorms.
Adapted from Chisholm and Renick, 1972.
21
Deep Layer Wind Shear Parameters
  • BRN shear uses a difference between the low
    level wind and a density-weighted mean wind
    through the mid levels.
  • Values of 35-40 m2/s2 or greater have been
    associated with supercells
  • Effective Bulk Shear Similar to 0-6km bulk
    shear. Most unstable layer lifted parcel upward
    to 40-60 of EL.
  • 6 km shear - the boundary layer to 6 km above
    ground level
  • Supercells commonly associated with values of
    35-40kt and greater through this depth
  • Supercells more probable as value increases
    through the 25-40kt range and greater.

22
BL-6 KM shear (5/4/03)
23
Low Level Shear
  • 0-1 KM Shear vector - 15-20 kts or greater
    favors supercells.

24
Bulk Richardson Number
  • A measure of buoyancy to shear ratio.
  • BRN 10-50 range for supercell storms.
  • BRN gt50 multi-cell lines or clusters.

25
Storm Relative Helicity
  • Used to assess potential for storm rotation.

Higher number ? greater potential for tornadoes.
26
Sfc-1 km SR Helicity
  • Sfc-1 km SR helicity 100 m2/s2 indicates and
    increased threat of tornadoes with supercells.

27
0-3 km SR Helicity
  • 0-3km SR Helicity of 250 m2/s2 favors and
    increased threat of tornadoes with supercells.

28
Energy Helicity Index (EHI)
  • Combines CAPE and shear. (SFC up to 1km and 3km)
  • Maximized when CAPE and shear is large.
  • Values larger than 1-2 have been associated with
    significant tornadoes.

29
EHI (5/4/03)
30
More advanced information
www.spc.noaa.gov/exper/mesoanalysis
  • One of my favorite sites for analysis of severe
    weather data.
  • Free of charge.
  • Comprehensive look at severe weather potential.

31
supercell
from SPC mesoanalysis page
EHI analysis Environment suggested strong
potential for storm rotation over C and NE Kansas
32
supercell
from SPC mesoanalysis page
LFC heights were near 3000 m along the track of
the supercell, suggesting minimal threat for a
tornado.
33
Other Mesoscale Analysis Parameters available on
the SPC page
  • VGP (3 KM)
  • EFFECTIVE STORM RELATIVE HELICITY (ESRH)
  • SUPERCELL COMPOSITE
  • SIGNIFICANT TORNADO
  • CRAVEN SIGNIFICANT SEVERE
  • HAIL PARAMETERS

34
VGP
  • Vorticity Generation Parameter
  • Estimates the rate of tilting and stretching of
    horizontal vorticity by a thunderstorm updraft.
  • Values greater than 0.2 m/s2 indicate an
    increasing risk of tornadic storms.

35
EFFECTIVE STORM RELATIVEY HELICITY (ESRH)
  • ESRH
  • Layer restricted to Sfc-3KM
  • Searches for the first parcel (Effective height)
    (starting at the sfc) which has 100 J/Kg and
    greater than -250 J/KG of CIN.
  • Restricts the available streamwise vorticity to
    the layer from the Effective Height to 3km.
  • ESRH graphics plots the SRH and Effective Height.

36
0-3 KM SRH versus 0-3km Effective SRH (5/4/03)
37
Significant Tornado
  • Another multi-parameter index-
  • Includes sfc based effective bulk shear magnitude
  • 0-3km effective storm-relative helicity
  • The 100 mb mean parcel CAPE normalization value
    has increased to 1500 J/KG.
  • MLLCL normalization value of 1500 meters remains
    the same.
  • Values greater than 1 associated with significant
    tornadoes.
  • Most non-tornadic supercells associated with
    values less than 1.

38
Craven Significant Severe
  • The simple product of 100mb MLCAPE and 0-6km
    magnitude of the vector difference (deep layer
    shear)
  • Uses a database of about 60,000 soundings
  • Majority of severe weather events occur when the
    product exceeds 20,000 m3/s3.

39
Supercell Composite
  • Multi-parameter index that includes 0-3km
    effective SRH, CAPE, and effective bulk shear.
  • Each parameter is normalized to supercell
    threshold values.
  • Values greater than 1 suggest increase potential
    for supercells and tornadoes.
  • SCP (muCAPE/1000 J/kg) (Effective SRH3/50
    m2/s2) (effective shear /20 m2/s2)

40
Hail Parameters
  • This image depicts three forecasting parameters
    used to predict hail
  • CAPE in the layer from -20C to -40 C
  • 0-6km shear vector in excess of 30-40 knots
    support persistent updrafts.
  • Freezing level height

41
Bow echoes and Derechoes
  • Favored Environment
  • Sfc-2.5 km shear 15-20 m/s shear or greater
  • CAPE 2000 J/kg or greater
  • Little or no extended shear above 2.5 km

42
Other Tools From the SPC
  • Composite Map
  • http//www.spc.noaa.gov/compmap/
  • Other Forecast Maps
  • http//www.spc.noaa.gov/exper/sref

43
Questions?
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