Severe Weather Applications Severe Weather Applications David Bright NOAA/NWS/Storm Prediction Center [email protected]AMS Short Course on Methods and Problems of Downscaling Weather and Climate Variables January 29, 2006 Atlanta, GA Where Americas Climate and Weather Services Begin
Severe Weather Applications. David Bright NOAA/NWS/Storm Prediction Center [email protected] AMS Short Course on M ethods and P roblems of D ownscaling W eather and C limate V ariables January 29, 2006 Atlanta, GA. Where Americas Climate and Weather Services Begin. Outline. - PowerPoint PPT Presentation
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Severe Weather ApplicationsSevere Weather Applications
AMS Short Course on Methods and Problems of Downscaling
Weather and Climate VariablesJanuary 29, 2006
Atlanta, GA
Where Americas Climate and Weather Services Begin
OutlineOutline
• Overview of the Storm Prediction Center (SPC)
• Implicit downscaling and hazardous mesoscale phenomena– Parameter evaluation
• SPC ensemble diagnostics
OutlineOutline
• Overview of the Storm Prediction Center (SPC)
• Implicit downscaling and hazardous mesoscale phenomena– Parameter evaluation
• SPC ensemble diagnostics
Overview of the SPC: MissionOverview of the SPC: Mission
The Storm Prediction Center (SPC) exists
solely to protect life and property of the American people
through the issuance of timely and accurate watch and forecast products dealing with hazardous mesoscale
weather phenomena.
• Hail, Wind, Tornadoes
• Excessive rainfall
• Fire weather
• Winter weather
Overview of the SPCOverview of the SPC
HAZARDOUS PHENOMENA
• TORNADO & SEVERE THUNDERSTORM WATCHES
• WATCH STATUS MESSAGE
• CONVECTIVE OUTLOOK
• MESOSCALE DISCUSSION
• FIRE WEATHER OUTLOOK
• OPERATIONAL FORECASTS ARE BOTH DETERMINISTIC AND PROBABILISTIC
Overview of the SPC ProductsOverview of the SPC Products
75% of all SPC products are valid for < 24h period
OutlineOutline
• Overview of the Storm Prediction Center (SPC)
• Implicit downscaling and hazardous mesoscale phenomena– Parameter evaluation
• SPC ensemble guidance
Implicit DownscalingImplicit Downscaling
• We don’t explicitly downscale at the SPC• However, SPC forecasters implicitly incorporate
spatial and temporal downscaling– Models are run at O(10 km) grid spacing– Model output available at O(hours)– Minimum grid spacing to resolve explicitly modeled
convection ~3 km – Even if thunderstorms (and mesocyclones) are explicitly
modeled, severe phenomena (hail, wind, tornadoes) occur at finer scales
• Idealized example…
Trough and associated cold front within the domain of a mesoscale model
ΔX ~ 10 km
ΔX ~ 10 km
Convergence region minimally resolved bymesoscale model at about 4 ΔX
Narrow region of pre-frontal convergence
Thunderstorms are not resolved by mesoscale modelat only 1 to 2 ΔX
ΔX ~ 10 km
Thunderstorms then develop within pre-frontal convergence zone
A grid point model:• does not resolve wavelengths of ~1-3ΔX • minimally resolves wavelengths of ~4ΔX • fully resolves wavelengths of ~10ΔX
ΔX ~ 10 km
The ability to predict phenomena in an NWP model is scale dependent
• Today’s NWP models do not explicitly predict most hazardous mesoscale phenomena of interest to the SPC
• The human needs to understand interactions between the large-scale (well resolved) environment and storm-scale (poorly resolved) phenomena
• Parameter evaluation (e.g., Johns and Doswell 1992)
SPC Downscaling and SPC Downscaling and Parameter EvaluationParameter Evaluation
Parameter Evaluation: Parameter Evaluation: CAPE vs. Deep Layer ShearCAPE vs. Deep Layer Shear
Shear
CAPE
Adapted from AMS Monograph Vol. 28 Num. 50 Pg. 449
Refined Parameter InvestigationsRefined Parameter Investigations A simple product of CAPE and shear
Gradual increase between classes, with discrimination between thunder, severe, and significant severe
90%
10%
50%
75%
25%
A complex parameter space is evaluated for modern severe stormforecasting
OutlineOutline
• Overview of the Storm Prediction Center (SPC)
• Implicit downscaling and hazardous mesoscale phenomena– Parameter evaluation
• SPC ensemble diagnostics
Example 1Example 1
• Basic Ensemble CAPE and Shear Basic Ensemble CAPE and Shear AnalysisAnalysis
Bright et al. (2005), AMS Conf. on Meteor. Appl. of Lightning Data
Essential Ingredients to Cloud Essential Ingredients to Cloud ElectrificationElectrification
• Identify what is most important and readily available from NWP models
• From: Houze (1993); Zipser and Lutz (1994); MacGorman and Rust (1998); Van Den Broeke et al. (2004)– Super-cooled liquid water and ice must be present– Cloud top exceeds charge-reversal temperature zone– Sufficient vertical motion in cloud from mixed-phase region
through the charge-reversal temperature zone
Combine Ingredients into Single Combine Ingredients into Single ParameterParameter
• Three first-order ingredients (readily available from NWP models):– Lifting condensation level > -10o C– Sufficient CAPE in the 0o to -20o C layer – Equilibrium level temperature < -20o C