Event Title

Life Cycle and Mesoscale Frontal Structure of an Intermountain Cyclone

Presenter Information

Gregory West
W. James Steenburgh

Location

Eccles Conference Center

Event Website

http://water.usu.edu/

Start Date

4-3-2009 8:00 AM

End Date

4-3-2009 8:20 AM

Description

High resolution analyses and surface observations are used to examine the structure and evolution of an lntermountain cyclone and its attendant surface fronts. The cyclone, known locally as the "Tax Day Storm," produced the lowest sea level pressure on record and strongest cold frontal passage (based on the 2 h temperature fall) observed in the past 25 y at the Salt Lake City lnternational Airport (KSLC). Three surface features develop downstream of the Sierra Nevada prior to the incipient cyclogenesis. The first is a barrier parallel lee trough that forms in response to strengthening cross-barrier flow. The second is a decaying elongated trough draped over the northern Great Basin. The third is a confluence zone that extends downstream over the Great Basin normal to the Sierra Nevada. Strong contraction (i.e., deformation and convergence) within this Great Basin Confluence Zone (GBCZ) forms an airstream boundary that is initially nonfrontal, but becomes the locus for surface frontogenesis as it collects isentropes and cooler air from northern Nevada. As the elongated trough rotates into phase with the GBCZ and developing surface front, cyclogenesis occurs as an upper-level cyclonic potential vorticity anomaly traverses the Sierra Nevada and quasi-geostrophic forcing for ascent spreads over the Great Basin. Differential diabatic heating further sharpens the front over northern Utah where dramatic frontal distortions are produced by the local orography. This analysis further establishes the critical role that the GBCZ plays in lntermountain frontogenesis and identifies it as an important mesoscale feature accompanying Nevada cyclogenesis. Recognition of this role may improve short-range forecasting and help advance our understanding of these cyclones and their attendant fronts, which are the primary source of cool season precipitation over the Great Basin.

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Apr 3rd, 8:00 AM Apr 3rd, 8:20 AM

Life Cycle and Mesoscale Frontal Structure of an Intermountain Cyclone

Eccles Conference Center

High resolution analyses and surface observations are used to examine the structure and evolution of an lntermountain cyclone and its attendant surface fronts. The cyclone, known locally as the "Tax Day Storm," produced the lowest sea level pressure on record and strongest cold frontal passage (based on the 2 h temperature fall) observed in the past 25 y at the Salt Lake City lnternational Airport (KSLC). Three surface features develop downstream of the Sierra Nevada prior to the incipient cyclogenesis. The first is a barrier parallel lee trough that forms in response to strengthening cross-barrier flow. The second is a decaying elongated trough draped over the northern Great Basin. The third is a confluence zone that extends downstream over the Great Basin normal to the Sierra Nevada. Strong contraction (i.e., deformation and convergence) within this Great Basin Confluence Zone (GBCZ) forms an airstream boundary that is initially nonfrontal, but becomes the locus for surface frontogenesis as it collects isentropes and cooler air from northern Nevada. As the elongated trough rotates into phase with the GBCZ and developing surface front, cyclogenesis occurs as an upper-level cyclonic potential vorticity anomaly traverses the Sierra Nevada and quasi-geostrophic forcing for ascent spreads over the Great Basin. Differential diabatic heating further sharpens the front over northern Utah where dramatic frontal distortions are produced by the local orography. This analysis further establishes the critical role that the GBCZ plays in lntermountain frontogenesis and identifies it as an important mesoscale feature accompanying Nevada cyclogenesis. Recognition of this role may improve short-range forecasting and help advance our understanding of these cyclones and their attendant fronts, which are the primary source of cool season precipitation over the Great Basin.

https://digitalcommons.usu.edu/runoff/2009/AllAbstracts/45