309 Flashcards
Radar Echoes should be consistent with
- The synoptic situation
- expected or forecast conditions
- knowledge of meteorological theory
2 scales used in weather radar
- Precipitation (rate of fall)
- Echo top (top of detectable precipitation
Precipitation rate (CAPPI) scale on a radar display
- Radar site and type
- setting (rain or snow) (snow is 1/5 as reflective as water equivelant of rain
- rate of fall in mm/hr
- # of pixels in nm (0.5nm/pixel)
- ring scale (25 nm per ring)
- Time of image (utc)
Echo tops scale on radar display
- Radar site and type
- Altitude (elevation in feet)
- Echo top in kms and 100s of feet
- # of pixels in nm (0.5nm/pixel)
- Ring Scale (25 nm per ring)
- Time of image
Features and indicators of stratiform echo systems
Feature Indicator
- Gradient -From weak to moderate
- Persistence -variable, fm hours to days
- Growth -Slow
- Tops -Low and uniform
- Intensity Levels -Low
- Signatures -none
Features and indicators of cumuliform echo systems
Feature Indicator
- Gradient -Moderate to very strong
- Persistence -Variable
- Growth -Can be very rapid
- Tops -Very high, can penetrate tropopause
- Intensity levels -High
- Signatures -Cellular, can be very distinct
4 categories of radar indicators for severe weather
- Echo configuration
- Echo Height
- Echo intensity
- Echo Movement
Echo configuration
- Line Echo Wave Pattern LEWP
- Intersecting lines
- echoes ahead of a line
- Echoes at the trailing edge of a line
- V-notches
- Protuberances or appendages
LEWP
- Damaging winds, Hail and tornadoes
- Discontinuity of speed along a line of echoes
- 2 Meso high caused by TS
- Local wind fields cause low level convergence at the apex of the LEWP
Intersecting Lines
- Occurs where a local effect and a main synoptic feature cross or collide eg. Cold front intersecting with a convergence line (sea breeze)
- Severe Wx at intersecting point (tornadoes)
Echoes ahead of a line
- Isolated echos ahead of a line could indicate a gust front or squall line
- indicator of severe Wx
Echoes at the trailing edge of a line
- The last cell in a solid or broken line often is associated with the most severe weather
- Ensure you are looking at the end of the line
V-Notches
- V is on opposite side from antenna
- Indicates severe precipitation attenuation, Hail
Protuberances or appendages
- Indication of attenuation of tornado hook
- Rear right quadrant relative to storm motion
- Very high reflectivity and echo tops
- Very strong gradient
Severity of weather is indicated by regional echo tops
what are examples of severe Wx tops in NA
- 23000 in Alberta
- 47000 in Ontario
- 58000 in Texas
Taller Echoes
Rapid Growth
Tropopause Penetration
- Echoes taller than their neighbors are more likely to produce severe weather
- Rapid growth can indicate severe weather
- Tropopause Penetration can indicate severe weather
Echo intensity
Strong intensity gradients
High intensity in trailing quadrants
High intensity at long range
- echoes indicating a rate of fall greater than 50mm/hr imply possibility of severe weather
- Strong gradients can indicate hail
- More reliable indicator than protuberances
- indicates severe storms
Echo movement
- Colliding Cells -tornadoes can form at the merge point
- Echo speed-relatively high speed >60km/h =SVR Wx
- Motion to the right of mean flow-deviation of >30’ of mean flow
- Persistence
Other echoes
- Anomalous propagation
- Fringing
- Precipitation attenuation
- Earth curvature distortion
- Migratory birds
Anomalous Propagation
- Super-refraction associated with a strong nocturnal inversion -Ground stations, satellite will show clear
- Echoes are stationary,dissipate with daytime heating - Sub-refraction-Shows clear when ground stations and satellite report cloud
Fringing
- areas of weaker precip may not be detected
- solid echoes are rare with stratiform cloud, but precip can be infered
Earth’s curvature distortion
- causes echoes to end when the precipitation is still occurring
- composite imagery compensates
Angel echoes, Migratory birds
- smaller moving lines
- ground stations and satellite show no precip
Radar terminology
- Type- Convective or stratiform cloud
- Area coverage- Related to size and geography
- Cell- single cell
- Cells- up to three individual cells
- Area- related or similar echoes grouped geographicall
- Line- length of 5-1 and at least 60km at least 30% coverage
Radar coverage values
<1/10- widely scattered 1/10-5/10 - scattered 6/10 - 9/10 - Broken 10/10 - Solid -cell is always solid
Describing convective precipitation
-Describe type with maximum intensity
precipitation scale
VRY STG - very strong STG - strong MDT-STG - moderate to strong WK - MDT - Weak to Moderate VRY WK - Very Weak
Describing Stratiform precipitation
-Describe Maximum coverage
Describing Echo tops
- Convective tops - Always give highest tops
- Stratiform tops - Always give average tops
- In 1000s of feet
Motion and development time units
- Convection - use increments of 15 minutes
- Stratiform - use increments of up to an hour
Remarks
Terminology to avoid
- use for non-standard features or for clarification
- Quantitive rates,technical terms
Canadian Lightning Detection Network
- Overlayed over radar display
- good for confirming convective activity
- Depicted as a small red circle
- Data collected every minute, sent to MSC and Nav Canada
- accurate to 500 m
Azimuth
Noise
Propagation
- A horizontal straight line path represented by a number of degrees rotation from true north
- Any unwanted, usually random fluctuation in signal or emission from a non radar source
- The passage of microwave energy through a medium
Refraction
Process whereby the direction of energy propagation within a medium is changed as a result of varying density of the medium.
