studying meteorological applications using research and technology - advanced seminar session
TRANSCRIPT
Studying Meteorological Applications using Research and Technology -
Advanced Seminar Session
Studying Meteorological Applications using Research and Technology -
Advanced Seminar Session
SMART-ASS
Weather - Advanced TrainingTechnology, Hazards, Education
and Forecasting
Weather - Advanced TrainingTechnology, Hazards, Education
and Forecasting
WAT THE F
Reviewing Algorithms, Definitions, And Resources
Radar Equation
BEAM ME UP!!
You have access to more than one radar for a reason!
Radar “sees”precipitation
Spotters observecloud structures
Outline for this afternoon:
Precipitation Structure*
(The Radar stuff: Kevin & Jim)
Cloud Structure
(The Storm Spotter Stuff: NWS)
* And some non-precipitating too!
Cloud Structure? or Precip Structure?
• VIPIR• Double low level locks• Shear markers• MOAR• Edge• Advantage• WARN• Double/Super/Mega/ Doppler• Doppler (insert large numbers and letters here)
Graphics courtesy of lots of friends with tv sets!
Two sessions for a reason:
Why radar? Why spotter?
Attempt to identify precursors to hazards, and then the hazards themselves.
Attempt to identify precursors to hazards, or the hazards themselves.
Two sessions for a reason:
Radar? Spotter?
What can radar provide that spotters have trouble with?
Seeing through areas of precipitation.
What can spotters provide that radar has trouble with?
Cloud Structure, particularly in precip-free areas
Base versus DerivedBase is raw, Derived has human intervention
Photo by Putnam Reiter
1: 3:30 pm, 4 W Thomas2: 3:30 pm, 4 NNE Custer City3: No time, WNW from 3 WSW Thomas4: 3:25-3:30 pm, WNW from Thomas5: No time, N of Custer City6: 3:30 pm, 4 NW Thomas
7: No time, ENE from 2 NE Custer City8: about 3:35 pm, N of Custer City9: No time, brief N of Custer City
10: No time, N of Custer City11: No time, N/NW from 2 NE Custer City12: Before 3:36 pm, 5 WSW Thomas
Graphic, reports courtesy of Doug Speheger, NWS
We have LOTS of work to do!
Meteorologists: Need to improve algorithms to help identify reflectivity and velocity pattern ID
Spotters: Need to improve cloud description techniques and accurate reporting
Radar Strategies for Pro-Active Spotter Deployment
BEFORE: Look for boundaries (thin lines)!
DURING: Look for the highest reflectivity regions in both base and composite reflectivity data.
Look for tight base reflectivity gradients on the lowest elevation scan – usually on south or southeast side of storm (inflow side)
Look for familiar patterns (bows, hooks, lines, BWERS, etc.)
High reflectivity values
Tight Reflectivity gradients
THEDOPPLERDILEMMA
Pulse rates can be set to acquire highly accurate velocity data, OR highly accurate reflectivity data. Although both are sensed simultaneously, there is
a trade-off!
WSR-88D Radial VelocityRadar site
Reds = outbound motions
Greens = inbound motions
Brighter colors = higher speeds
Cannot “see” motions perpendicular to beam
Radial Velocity Signatures
CYCLONICROTATION
ANTICYCLONICROTATION
DIVERGENCE
CONVERGENCE
Base Velocity vs
Storm Relative Velocity• During some events, it may be beneficial to look at
BOTH products
• Use ___________ for estimating the speed of wind gusts near the surface for straight line winds
• Use ___________ for identifying circulation features or convergence/divergence in or near thunderstorms
Base Velocity
Storm Relative Velocity
1
2
34
5
8000’3400 Feet AGL
12,000’21,000’
3400 Feet AGL 8000’
12,000’
21,000’
3800 Feet AGL 9000’
23,000’ 12,000’
3800 Feet AGL 9000’
12,000’
23,000’
For this grid box, the compositereflectivity would display…….
Composite Reflectivity
50
25
50
30
Courtesy NWSCourtesy NWS
Radar Algorithms• Computer programs to assist in storm
analysis
• Hail size estimation, mesocyclone/ tornado detection, rainfall estimation
• Based on 3-D precipitation structure, empirical and mathematical correlations AND NOT CLOUD STRUCTURE!
• ALGORITHMS ARE TOOLS, NOT GOSPEL!
Dangers of “Pathcasting”
• Exact arrival times used by television (and some NWS) forecasters
• Radar does not allow the level of precision implied by detailed forecasts
• Be Careful!!!
There are quite a few sources for error inherent in the process of estimating precipitation using radar.
* Hail Contamination - Radar-based precipitation measurements are based on the relationship between "reflectivity" of raindrops and the rainfall rate. Wet hail stones within a storm reflect much more energy back to the radar than an equivalent amount of all-liquid precipitation, which results in overestimation.
* Beam Blockage - Mountains, forests, towers, etc., very near the radar can block the radar beams from adequately sampling the atmosphere. This can result in large areas of underestimated rainfall.
* Anomalous Propagation (AP) - Under certain atmospheric conditions, the radar beams actually bend back toward the ground, and reflect off of buildings, hills, etc. This "ground clutter" may appear as “radar indicated” rain where none fell.
* Non-Precipitation Echoes - Radar beams occasionally reflect off of items in the air that are not producing rain at the surface. Examples of this include birds, bats, virga (rain that evaporates before it reaches the surface) and chaff (reflective materials used by the military to confuse/counter enemy radar, and tested occasionally on domestic military bases).
Always “CHECK” your radar data against other data sources (e.g. other radars, other tilts, satellite imagery, etc.)
* Bright Banding - Bright banding occurs due to the reflectivity gradients associated with snow/ice that is melting as it is falling. When the snow is melting, a film of water forms on the outside of the snowflake. These water coated snowflakes show up on radar as high reflectivity bands, resulting in an overestimate of rain.
* Range Degradation - As the radar beams go farther out, they sample higher parts of the storm. Storms with low cloud tops are frequently under-sampled when they are farther away from the radar. This is particularly common with winter weather events.
* Improper Z-R Relationships - Convective storms, tropical storms, and winter storms all require different reflectivity-to-rainfall (Z-R) relationships. An incorrectly set Z-R relationship can seriously impact the rainfall estimates.
“….street corner!!”
Radar is NOT able to tell us EXACTLY where severe weather is occurring! (or headed!)
October 9, 2001 Courtesy Rick Smith, Doug Speheger NWS, OUN
IMPORTANT POINTGO TO THE SOURCE!!!
The National Weather Service!
The have highly trained meteorologists!They SEE the radar data before we do!
They see the derived (algorithm) data before we do!They have more VOLUMETRIC radar data than we have.
They KNOW the RADAR limitations.
PRECIP STRUCTURE vs CLOUD STRUCTURE!This is why THE NWS NEEDS YOU. YOU ARE THEIR
“RADAR” IN THE FIELD..WITH UNIQUE CAPABILITIES!
PRO-ACTIVE and TRAINED SPOTTERS improve the warning process and help save lives.
“LET THY ALGORITHMS GO!!!!”
“THOU SHALT NOT BASE DECISIONS ON ALGORITHM DATA”
RELIANCE on ALGORITHMS, MAGNIFIES STUPIDITY, ENHANCES
SCREWUPS
RELIANCE on ALGORITHMS, MAGNIFIES STUPIDITY, ENHANCES
SCREWUPS
DON’T BE “RAMSES”!
I’ll Take Questions while Jim sets up!!