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Presented by Al Fisher
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2009 StormsPart 3
© 2010 Fisher
Aug 19, 2009 11 Tornadoes N+C IL/NW IN
Tornadogenesis: Three ingredients
Development of a persistent, rotating updraft1
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
ILX VAD Wind
ILX Composite
ILX Storm Relative Velocity
FROM WILLIAMSVILLE TO BEASON...THE TORNADO WAS ON THE GROUND FOR 24.5 MILES...FROM 318-402PM.
..WITH A MAXIMUM WIND SPEED OF 140MPH...WITH A TORNADO RATING OF EF3. THERE WERE 7 TOTAL INJURIES .
2 Very Strong Rotation Couplets
Tornado
ILX Base Velocity
ILX Storm Relative Velocity
2 Very Strong Rotation Couplets
ILX AWIPS Storm Relative Velocity 3:18 PM
ILX AWIPS Storm Relative3:27 PM
ILX Base Velocity
ILX Storm Relative Velocity
ILX Storm Relative Velocity
ILX Storm Relative Velocity .5°
Tornado still on ground, you are seeing it, ~5 miles from NWS office near Springfield IL.
T
ILX Storm Relative Velocity 5.1°
Tornado still on ground.
ILX Base Velocity 5.1°
6:44 PM
Joliet tornado: .5° and 3.4°
2 EF0 2 EF1 1 EF2 1 EF3
Front dropping down lake 6/01/09
Front
LOT Base Velocity
TORD Base Velocity
May 7, 2009 LOT Reflectivity lvl 2
LOT Composite
LOT 0.5° Velocity lvl 2
LOT 0.9° Velocity lvl 2
LOT 1.3° Velocity lvl 2
LOT 0.5° Velocity standard
LOT 1.0° Velocity standard
TORD Velocity
TMDW Velocity
LOT VAD Wind
Aug. 16, 2009
Warning needed?
LOT Velocity
TORD Velocity
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!
Tornado
Tornado Cyclone
RFD
Updraft
next to
Supercell
Deep shear,adequate CAPE
Convergence,
tilting of near-
ground SRH
Baroclinic
generation;
arching
Vortex contraction
Processes
States
Development of rear-side precipitationDeep convection
30 min 20 min 5-20 min45-120 min
Thoughts...• Tornadogenesis failure is possibly
generally a failure of contraction of the tornado cyclone.
• Strength of the inner portion of the vortex (the tornado) depends partially on angular momentum in the outer portion, and the removal of mass upward through the vortex (and hence convergence below).
Tornado process success rate only 7.7%
Tornado Siren Activation Questions
Do you have a formal activation policy?
How do you expect the public to respond?
What is the basis (spotter, public, feeling, NWS) for the activation?
How confident are you in that basis?
How many siren false alarms will you accept?
How many siren false alarms will the public accept?
Do you think the public has high confidence in the sirens?
Do you think this confidence level can be improved?
How do you plan to improve the level?
Suggested Tornado Siren guideline
• Your community is in a NWS tornado warning polygon (extreme e fringe?)
• ….OR….• 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)
From reading the Trib today, apparently some communities in Boone and McHenry counties sounded their tornado sirens yesterday evening as a line of showers and isolated tstms moved thru the area between 5:30-6PM. A spotter? reported a funnel cloud from one of the showers.
From the storm theory I have shown, lets remember what minimum atmospheric ingredients are
necessary for even a "chance" of a tornado.
1. Need sufficient instability to make a thunderstorm. The atmosphere could barely make the showers, tops were only 17000 feet. Part of the instability comes from the heat and moisture near the ground. For our area, we need at least temperatures in the 60s and dew points in the mid 50s or higher. Temps due to the rain all day were only near 50 with dew points in the mid 40s. So a NO for this part of the list.
2. We need a sustained rotating updraft. The only thing that can produce that is a thunderstorm, and a rotating thunderstorm (Supercell), especially for March in our area. The atmosphere could only generate 17,000 foot showers, not Supercell thunderstorms. So a NO for this part of the list.
3. Low level storm relative helicity. In other words, the winds with height turn direction in the lower levels. I was looking yesterday afternoon, the wind from the surface to well aloft was all from about the same direction, no low level turning. So a NO for this part of the list.
4. Bulk shear greater than 35 knots. We had this, so a YES for this part of the list.
So out of the minimum 4 necessary ingredients that ALL have to exist to even have a "chance" of a tornado, we had only 1. In other words, was there any chance that the cold air funnel, if it even existed, from the shower would become a tornado? Absolutely NOT.
A complete over reaction on the part of the communities that sounded their sirens. No tornado warnings were issued.
