Extratropical Synoptic-Scale Processes and Severe Convection

Part 1 Elizabeth Polito Pg ( 27- 43 )Part 2 Terrance Seddon pg ( 44-64 )

Over view

• Synoptic Factors Associated with Severe convection– Topographic influences– Solenoidal Circulations over simple Terrain– Monsoons

• Feedbacks to the synoptic scale• Examples of severe convective events from a

Synoptic perspective

Synoptic Factors

• Vertical motion in convective storms is ~10 m/s

• Vertical motion on synoptic scale is ~10 cm/s• Sub synoptic scale process need to provide

the lift to produce the convective storms

Topographical influences

• Orographic effects– Leeward side, flat terrain, import of low level

moistuer

• Other Topographic effects– Seasonal changes in the effects they have

• Air Mass Characteristics– High lapse rates, low level mositure

Solenodial circulations

• The flow associated with solenoidal circulations– Classic fronts– Land-sea breeze– Convective outflow– Inhomogeneties in underline terrain– Dry lines

Monsoons

• Defined as a season shift in the surface flow• Does not directly initiate convection• Does however initiate process that do initiate

convection– Upslope flows– Embedded solenoidal drive flows

• Also the shift in the wind patterns can provide the low level moisture so important to DMC.

Vertical Shear

• The presence or absence of vertical shear can be the difference between a severe storm, and a short heavy rain shower

• It is difficult to predict the exact effects of vertical shear and helicity on a storm, as the storm’s initial path is not known.

Feed Backs to the synoptic scale

• While synoptic scale processes have been associated with helping to initialize DMC, it is also found that DMC affects synoptic processes.– Ex. US Warm and autumn season effects– Ex. Mediterranean Autumn vs. Spring– Ex. Australian variation

Feed backs con.

• Qualitatively DMC is important to a global heat balance

• Single events of DMC are in themselves are too brief to affect Synoptic scale processes

• However, it is not uncommon for an event of DMC to develop until it is a mesoscale Convective system, which lasts for days.

• These MCSs have the longevity required to affect the synoptic scale processes.

Examples of Severe convective events

• 28 Aug 90 Plainfield Il• 27 Mat 1994 Palm Sunday Outbreak• 17 Aug 1994 Lahoma, OK• 7 June 1982 Kansas City, MO• 14 June 1990 Shadyside OH• 9 June 1972 Rapid City, SD

500 hPA chart, 0000UTC 29 Aug 1990

Plainfield, Il An isolated Tornado event

Sounding at Peoria IL, 0000UTC 29 Aug 1990

Plainfield, Il An isolated Tornado event

Surface Analysis for 1500 UTC on 27 Mar 1994

Palm Sunday Tornado outbreak

Sounding and hodograph for 1700 UTC on 27 Mar 1994 for Jackson, MS

Palm Sunday Tornado outbreak

500 hPa analysis at 1200 UTC on 17 Aug 1994

Lohoma, OK an Isolated intense wind and hail storm

Surface analysis at 1800 UTC on 17 Aug 1994

Lohoma, OK an Isolated intense wind and hail storm

a) Ground relative and b) storm relative wind profiles

Lohoma, OK an Isolated intense wind and hail storm

850hPa analysis at 0000 UTC on 7 June 1982

Kansas City, MO a derecho

500-300 hPa Layer averaged Q-vector divergence field at 000 UTC

Kansas City, MO a derecho

Topeka, KS. Sounding at 0000 UTC on 7 June 1982

Kansas City, MO a derecho

500 hPa Analysis at 0000 UTC 15 June 1990

Shadyside, OH A challenge

Surface Analysis at 0000 UTC 15 June 1990

Shadyside, OH A challenge

500 hPa at 0000 UTC 10 June 1972

Rapid City, SD A western event

Surface analysis at 0000 UTC 10 June 1972

Rapid City, SD A western event

500 hPa at 0000 UTC 10 June 1972

Rapid City, SD A western event

Any questions?