3-5 January 2008 West Coast Extratropical Cyclone Cameron G. Loughlin San Francisco State University

Main Points Impact of Storm on Northern California Synoptic History of Cyclone Discussion of Quasigeostrophic Terms Quasigeostrophic Diagnosis Conclusions 3-5 January 2008 West Coast Extratropical Cyclone

Impact of Storm on Northern California Strong wind speeds Rapid Decline in Pressure Heavy Precipitation 3-5 January 2008 West Coast Extratropical Cyclone

Peak Wind 68 MPH Sustained Winds MPH 14 mb Pressure Drop in 10 hrs

Over 1.5” rainfall in 6 hrs

Main Points Impact of Storm on Northern California Synoptic History of Cyclone Discussion of Quasigeostrophic Terms Quasigeostrophic Diagnosis Conclusions 3-5 January 2008 West Coast Extratropical Cyclone

Synoptic Overview Cyclone formed south of Aleutian Islands on 3 January Low Developed over North Pacific Ocean Minimum Central Pressure of 956 mb Low advanced into Northern California on 4 January bringing heavy rains and strong winds 3-5 January 2008 West Coast Extratropical Cyclone

Cyclone Forms

Cyclone Impacts Northern California

Main Points Impact of Storm on Northern California Synoptic History of Cyclone Discussion of Quasigeostrophic Terms Quasigeostrophic Diagnosis Conclusions 3-5 January 2008 West Coast Extratropical Cyclone

Discussion of Quasigeostrophic Terms - Quasigeostrophic (QG) Omega Equation LHS: Omega RHS: Vorticity advection, temperature advection - Sutcliffe Petterssen Equation (SPDE) LHS: Relative vorticity tendency at 1000 mb RHS: 500 mb vorticity advection, 1000 mb horizontal temperature advection 3-5 January 2008 West Coast Extratropical Cyclone

QG Terms Continued… Quasigeostrophic (QG) Omega Equation Sutcliffe-Petterssen Development Equation (SPDE) 3-5 January 2008 West Coast Extratropical Cyclone

Main Points Impact of Storm on Northern California Synoptic History of Cyclone Discussion of Quasigeostrophic Terms Quasigeostrophic Diagnosis Conclusions 3-5 January 2008 West Coast Extratropical Cyclone

Quasigeostrophic Diagnosis Cyclone will be examined at 3 different times at 4 January 00Z, 4 January 12Z and 5 January 00Z Analyze progression of cyclone using QG Omega Equation Terms and SPDE Relate R.H.S. of both equations to L.H.S. For QG Omega equation L.H.S. is Omega and SPDE is Relative Vorticity Tendency 3-5 January 2008 West Coast Extratropical Cyclone

SPDE 4 Jan 00Z Analysis at Center of Low Weak warm advection Positive relative vorticity tendency Weak absolute vorticity advection 3-5 January 2008 West Coast Extratropical Cyclone

0000 UTC 4 J an 2008

QG Omega: 4 Jan 00Z Negative Omega Analyzed at San Francisco Weak warm advection Strong Negative Vorticity Advection 3-5 January 2008 West Coast Extratropical Cyclone

SPDE: 4 Jan 12Z Analyzed at Center of Low Weak absolute vorticity advection Sustained central pressure of 964 mb Weak negative relative vorticity tendency Weak warm advection 3-5 January 2008 West Coast Extratropical Cyclone

QG Omega 4 January 12Z Analysis at San Francisco Negative omega Strong warm advection Weak negative vorticity advection Dominating Term: Temperature Advection 3-5 January 2008 West Coast Extratropical Cyclone

SPDE: 5 Jan 00Z Analyzed at center of low Weak negative relative vorticity tendency Weak absolute vorticity advection Warm advection Low remains at 964 mb. 3-5 January 2008 West Coast Extratropical Cyclone

QG Omega: 5 Jan 00Z Analyzed at San Francisco Weak omega both positive and negative Warm advection Weak vorticity advection 3-5 January 2008 West Coast Extratropical Cyclone

Main Points Impact of Storm on Northern California Synoptic History of Cyclone Discussion of Quasigeostrophic Terms Quasigeostrophic Diagnosis Conclusions 3-5 January 2008 West Coast Extratropical Cyclone

Conclusions QG-Omega Equation Dominating term: warm advection Contributed to overall strong forcing for negative omega Overall weak positive vorticity advection SPDE Relative Vorticity Tendency was mostly positive overall and omega was negative 3-5 January 2008 West Coast Extratropical Cyclone