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Photo by Patrick Chando
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• What is atmospheric mixing?
• How mixing works
• Evolution through the day
• Case study
• Aviation weather hazards influenced by mixing
o Convective turbulence
o The dry line
o Wildfire smoke
o Haboobs
Learning Objective
Understand the evolution and timing of
atmospheric mixing, so you can better
anticipate the development, intensification
and dissipation of aviation weather
hazards.
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The transfer of momentum from stronger flow aloft to the surface by
thermals and other sources of wind shear (like cold fronts, outflow
boundaries and jet streams).
www.weather.gov/Jetstream/airmass Bubble Thermals
Essentials of Meteorology, C. Donald Ahrens
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https://www.weather.gov/jetstream/heat
Re-radiation
Re-radiation: The ground absorbs then re-radiates
energy at a wavelength air molecules can absorb.
(thermals)
(adapted)
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Adapted from Stull, R. B., 2000: Meteorology for Scientists and Engineers
Surface
Note the nearly calm surface winds
at the bottom of the inversion
and
the region of wind shear
at the top of the inversion
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Adapted from Stull, R. B., 2000: Meteorology for Scientists and Engineers
The descending couplet in
the thermal circulation transfers
stronger momentum aloft downward
causing surface winds to strengthen
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• Today we discuss: o Convective turbulence
o The dry line
o Wildfire smoke
o Haboobs
• On your own consider: o Nocturnal low clouds and fog
o Nocturnal low level jet on the
southern plains
o Some gap wind events, like ABQ’s
notorious east canyon wind
o Thunderstorms
o What else comes to mind?
Many weather hazards
depend on the diurnal cycle
of atmospheric mixing to
develop, intensify, and
diminish
TCC
RTN
LVS
AMA
TAD
11/6/17 (0827-1207Z)
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• Caused by thermals in a well
mixed atmosphere
• To Avoid: o Climb above the cumulus clouds
o Fly before the temperature
inversion breaks
Aviation Weather, FAA AC 00-6A, 1975
Essentials of Meteorology, C. Donald Ahrens
Bubble
Thermals
Chimney
Thermals
Todd Shoemake
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USATODAY.COM
• Dry/moist convergence zone o Daytime advances east
o Nighttime usually retreats west
• Flying hazards o Thunderstorms
o Low Level Wind Shear
• Most common and intense in
spring and early summer
www.tornadochaser.net/dryline.html
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6/24/02 1430Z
6/23/02 1430Z
NWS ABQ Website: www.weather.gov/abq
Mogollon Rim Wildfire
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• Wall of dust that can extend up to
6500 feet high and several
kilometers long o Near zero visibility for up to 45
minutes
o Erratic wind gusts may reach 50
mph or more
• Occur most often when monsoon
thunderstorm outflows merge over
AZ’s central and western deserts
• High risk locations: o Abandoned farmland
o Tilled farmland
o Land disturbed by animals
or ATVs
o Construction sites
o Areas in drought
NWS Phoenix
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• Wall of dust that can extend up to
6500 feet high and several
kilometers long o Near zero visibility for up to 45
minutes
o Erratic wind gusts may reach 50
mph or more
• Occur most often when monsoon
thunderstorm outflows merge over
AZ’s central and western deserts
• High risk locations: o Abandoned farmland
o Tilled farmland
o Land disturbed by animals
or ATVs
o Construction sites
o Areas in drought
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• Wall of dust that can extend up to
6500 feet high and several
kilometers long o Near zero visibility for up to 45
minutes
o Erratic wind gusts may reach 50
mph or more.
• Occur most often when monsoon
thunderstorm outflows merge over
AZ’s central and western deserts
• High risk locations: o Abandoned farmland
o Tilled farmland
o Land disturbed by animals
or ATVs
o Construction sites
o Areas in drought.
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Lubbock, TX, Oct 17, 2011
Emily Davenport
Erin Shaw
• More common with strong back door
cold fronts, especially in drought
• Best developed when buoyant mixing
intensifies mechanical mixing by front
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• What is atmospheric mixing?
• How mixing works
• Evolution through the day
• Case study
• Aviation weather hazards influenced by mixing
o Convective turbulence
o The dry line
o Wildfire smoke
o Haboobs Others to Consider
o Nocturnal low clouds and fog
o Nocturnal low level jet on the southern plains
o Some gap wind events
o Thunderstorms…