Tue 48tornado forecasting

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Whats ahead in Unit 4?
Tue 4/8 tornado forecasting Wed 4/9 conclude
tornado forecasting intro to MCSs Thu 4/10 MCSs
1 in-class lab (tornado forecasting) Fri
4/11 SEMESTER PROJECT 1-PAGE OVERVIEWS DUE Tue
4/15 MCSs 2 Wed 4/16 MCSs 3 Thu 4/17 derechoes,
flooding, and hailstorms in-class lab (topic
TBD) handout final exam review sheets Mon
4/21 no briefing US severe weather
climatology SEMESTER PROJECT PAPERS DUE Tue
4/22 no briefing in class QA to review for
final exam Wed 4/23 no briefing SEMESTER PROJECT
PRESENTATIONS 1 Thu 4/24 SEMESTER PROJECT
PRESENTATIONS 2 Fri 5/2 FINAL EXAM
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Basics of tornado forecasting
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Tornadogenesis

• Tornadogenesis involves rearranging, twisting,
  and stretching vortex lines so that they become
  vertically oriented and packed tightly together
  at the ground

• Tornadogenesis, if it occurs, is associated with
  the development of the rear-flank downdraft (RFD)
• The temperature of the RFD seems to be important
  to tornadogenesis RFDs that are excessively cold
  apparently are unfavorable for tornadogenesis

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Adapted from Markowski et al. (2002)
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The averaged vertical profiles are generally
similar above 1 km in the tornadic and
nontornadic supercell environments. On the
other hand, considerable differences are found
within 1 km of the ground, with environments
associated with significantly tornadic supercells
having substantially larger low-level vertical
wind shear...
Markowski et al. 2003
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Tornadogenesis

• Best operational means for discriminating between
  significantly tornadic (i.e., F2 and stronger)
  and nontornadic supercells is to use radar data
  in conjunction with information about the
  near-storm environment
• low-level shear (e.g., 0-1 km shear vector
  magnitude, 0-1 km SRH)
• low-level relative humidity (e.g., LCL height)

Nontornadic supercell environments and F0-F1
tornadic supercell environments are
indistinguishable for practical purposes!
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Tornadic (n939) vs. Non-tornadic (n2305)
Supercell Environments
Observed soundings from 0000 UTC, from within 3
hours and 100 mi of storms
tornadic F2 tornado non-tornadic 65kt
gust/2 hail
Tornadic storms likely
Above line 40 tornadic
Below line 4 tornadic
Tornadic storms unlikely
courtesy of Harold Brooks
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Shear between the surface and a height that is
50 of the way to the ML parcels EL
SRH over the layer in which parcels have CAPE gt
500 and CIN lt 250
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Outbreak patterns
Miller type (many key features overlain)
scanned from Doswell (2001)
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Unfortunately, in many situations, outbreaks are
not so synoptically evident
Jon Davies
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Mesoscale boundaries

• Large-scale conditions occasionally support
  significant tornadoes (outbreak days), but more
  commonly, significant tornadoes are only favored
  in relatively small regions where low-level shear
  and/or moisture is locally enhanced

2 June 1995

• Mesoscale boundaries often enhance low-level
  shear and/or moisture, and many supercells have
  been observed to become tornadic upon interacting
  with such boundaries
• But many supercells weaken upon encountering
  mesoscale boundariesclearly not all boundaries
  are favorable!

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OFB
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Mesoscale boundaries

• Large-scale conditions occasionally support
  significant tornadoes (outbreak days), but more
  commonly, significant tornadoes are only favored
  in relatively small regions where low-level shear
  and/or moisture is locally enhanced

2 June 1995

• Mesoscale boundaries often enhance low-level
  shear and/or moisture, and many supercells have
  been observed to become tornadic upon interacting
  with such boundaries
• But many supercells weaken upon encountering
  mesoscale boundariesclearly not all boundaries
  are favorable!

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Mesoscale boundaries
2 June 1995
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• Tornado outbreak pattern recognition
• Triple point/warm front/stationary front
• Dryline
• High Plains upslope
• Cold front/warm sector
• Cold core aloft (mini-supercells)
• Land-falling tropical cyclones

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• Triple point/warm front/stationary front

L
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2. Dryline
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L
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Dryline and/or Triple point/warm front/stationary
front VARIATION Northwest flow
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3. High Plains upslope
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3. High Plains upslope
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Dewpoints are often lower than in Plains/SE
outbreaks, but
Denver 71/54
Raleigh 82/65
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June 7 2001, 20 UTC
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• Cold front/warm sector
• Often, the Miller-type outbreaks

scanned from Doswell (2001)
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• Cold front/warm sector
• Often, the Miller-type outbreaks
• example Super Outbreak

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4. Cold front/warm sector a. Northeastern US
variation
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4. Cold front/warm sector b. Southeastern US
variation
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5. Cold core aloft (mini-supercells)
Jon Davies
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Jon Davies
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6. Land-falling tropical cyclones
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WILMA
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0730 UTC
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dry intrusion
Ivan (2004)
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Ivan (2004)
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