>20NM <15NM >20NM All Storms Composite produces stormtable & detail picture Data level <15NM Stormlab
Terminal Doppler Radar ORD & MDW
For Storm Rel Velocity only…Use the Composite storm table for the storm motion to enter. Either use table value for particular storm if looks good, or average several storm motions to arrive at a value to enter. TOR warning also an option, look at code at bottom of warning. Do this first before clicking on SRV.
Enter position/spotter data
2 ways to “sample” the warning polygon
Clicking on radar site opens window, shows current watches and warnings Loop control buttons
Naperville shows at 4X, road numbers at 8X .
Stormlab/Interwarn computer configuration 1 PC 2 PC 3 PC * * * Interwarn * * * Composite Reflectivity+Table * * * SPC Mesoanalysis * * * Precipitation * * * VAD Winds L 2 L 2 * Storm Relative Velocity L 2 L 2 * Velocity L 2 L 2 * Reflectivity #1 #2 #3 #1 #2 #1
Doppler Weather Radar Concepts
Radar beam increases in altitude with distance from radar.
Radar beam increases in size with distance from radar.
Radar takes 4-5 minutes to complete full scan when in storm/precip mode.
Reliable doppler wind data limited to about 60-70 nm.
Radar velocity 100% when parallel, 0% when perpendicular to beam direction.
.96 Degree Beam Resolution If R = 60 NM 120 NM 180 NM 240 NM D = 1 NM 2 NM 3 NM 4 NM D D = Beam Width Radar resolution with respect to beam width / range
The Zero Isodop “Problem” When the wind velocity is parallel to the radial, the full component of the wind is measured When the radial is perpendicular to the the wind, the radar displays zero velocity - This “zero zone” is called the “Zero Isodop”. What percentage of actual wind will the radar detect? 0 0 = 100% - Parallel 15 0 = 97% 30 0 = 87% 45 0 = 71% 60 0 = 50% 75 0 = 26% 90 0 = 0% - Perpendicular
Azimuth Resolution Considerations Weak inbound, weak outbound Rotation too small to be resolved Stronger inbound than outbound Strong inbound, strong outbound Azimuth 3 Azimuth 2 Azimuth 1 Enlarged image along a radial. Individual “blocks” represent one sample volume. This graphically shows the radar resolution. Rotational couplet identification can be affected by azimuth resolution. As the diagram shows, the closer a rotation is to the radar the more likely it will be identified correctly. If the rotation is smaller than the 1 0 beam width (possible at long ranges) then the rotation will be diluted or averaged by all the velocities in that sample volume. This may cause the couplet to go unidentified until it gets closer to the radar.
Line of tstms moving thru ne IL
Base velocity locates gust front
Lake breeze in precip mode, how it would look if a gustfront coming out of a tstm or shower.
Lake breeze on base velocity
Bowing squall line
Bowing line with Base velocity, inbound winds 50-64 kts
Bowing line on Composite. Note storm motions 45-60 kts
Bowing squall line over N IL
Composite view, note cell motion of 45 & 52 kts
Base velocity, > 55 kts inbound with stronger cells
VAD winds, note 50-60 kts noted 3-6,000 feet as line is within 20 nm of radar
Reflectivity Book end vortex forms and Inflow jet intensifies Derecho Aug 4, 2008
IA tornado: Mesocyclone & hail symbols, along with pathcast.
IA tornado: Strong inflow and updraft area notch (9,000 ft)
IA tornado: B ounded W eak E cho R egion Extremely strong updraft (16,000 ft)
GA… Nothing special on .5 reflectivity
.5 SRM shows very strong rotation
Note red triangle ( T ornado V ortex S ignature) + Meso value of 12
Height of beam above ground vs distance from radar. Green 10nm Yellow 15nm Red 20nm
Joliet tornado 4/20/04 .5° and 3.4° 1800 ft 300 ft
Joliet tornado: .5° and 3.4° 300 ft 1800 ft
Example of level 2 Base Velocity detail. Microburst of 62+ knots which unroofed apartment complex in Carol Stream April 2007. 1400 ft
One hour rainfall
3 Hour Rainfall
How to evaluate a storm report
Take no report at face value, always question the source of the report
The more accurate, reliable, and timely the report, the better the NWS does with its warnings, and the better local communities do with managing their alert and siren systems. Make sure the report is not a recycled one from a few minutes ago.
Every false alert/warning/siren sounding just leads to public inaction on the next storm.
If a storm report is received, try to verify as best as possible:
The exact time and location
If estimated or measured (how)
If building damage…type of building (structure) and exact damage
If tree damage….size of tree and/or branches…type of tree if known
If reporting rotation…is it clearly visible and not just clouds moving around
If tornado…is there clear ground contact and a connection to the cloud above
If it don’t spin, don’t turn it in!
Tornadic Supercell “Ingredients”
Instability (varies, usually CAPE > 1000 J/Kg)
Deep layer shear (0-6km) bulk shear > 35kt
Low level shear (0-1km) SRH > 150 m 2 /s 2 or
Relatively high RH values (in BL and aloft)
Sfc Td depressions <12°F
Tornadogenesis: Three ingredients Development of a persistent, rotating updraft 1 Ingestion of enhanced SRH (occasionally, large-scale SRH is sufficient) and development of strong low-level rotation 2 Development of a downdraft partially embedded in the rotation that aids in the transport of rotation to the ground, followed by focusing of that rotation through convergence if the downdraft reaches the ground with some very uncommon properties 3
Tornadogenesis in a Nutshell
L Forward Flank Downdraft Inflow RFD June 7, 2008
L Forward Flank Downdraft Inflow RFD
L “ Old” Tornado Becomes Rain-wrapped
TDWR WSR-88D Left over old hook “ eye” New hook developing
Suggested Tornado Siren guideline
Your community is in a NWS tornado warning polygon (extreme e fringe?)
You have a reliable/verified report of a tornado approaching/in your community or a verified funnel cloud (not cold air type) and
You have used Stormlab to verify the report. (rotation at 0.5/1.5/2.5)
Summary of How to Use Stormlab
Use to verify incoming storm report: does it match radar? Sirens?
Use to position or update spotters
Use to time incoming weather: pathcast
Use to see what the radar is detecting : hail, high winds, meso, TVS
Use to monitor potential: flash flooding, cell mergers, strength
Use to know when threat has ended: rain, wind
Use to see visual display of the: warning polygon
Use to monitor weather during festivals: When to shut down?
Be sure to go to SPC meso page to have an idea what to expect
Use Interwarn to monitor: warnings, statements, storm reports