January 3-5 2008 West Coast Extratropical Cyclone

Henry D. BartholomewSan Francisco State University

The purpose of my study

I want to answer questions like…

Why did the low rapidly intensify?

Why did it produce strong negative omega?

Outline Synoptic Overview Strong Winds Heavy Precipitation Quasigeostrophic Equations

Discussion Quasigeostrophic Diagnosis Summary and Conclusions

Synoptic Overview Formed on 3 Jan 2008 First located south of the Aleutian

Islands Moved east and strengthened Reached minimum pressure of 956

mb Impacted California on 4 Jan 2008 Brought heavy rain and strong winds

to CA

Outline Synoptic Overview Strong Winds Heavy Precipitation Quasigeostrophic Equations

Discussion Quasigeostrophic Diagnosis Summary and Conclusions

Strong Winds in California

Concord: 45 mph Chico: 58 mph SFO: 68 mph North Oakland: 71 mph Mt. Diablo: 117 mph

Generally, sustained winds of 20-50 mph

Note the increase in wind speeds with a corresponding pressure drop

Max Gusts:

65 to 70 mph

Minimum

Pressure:

997 mb

January 3-5 2008 West Coast Extratropical Cyclone Synoptic Overview Strong Winds Heavy Precipitation Quasigeostrophic Equations

Discussion Quasigeostrophic Diagnosis Summary and Conclusions

24-hour Precipitation Amounts12Z 4 Jan 08 to 12Z 5 Jan 08

San Francisco: 1.72” Napa: 1.98” Oakland: 2.07” Mt. Diablo: 3.69” Ben Lomond: 5.74”

January 3-5 2008 West Coast Extratropical Cyclone Synoptic Overview Strong Winds Heavy Precipitation Quasigeostrophic Equations

Discussion Quasigeostrophic Diagnosis Summary and Conclusions

Quasigeostrophic Analysis of Storm:QG-Omega Equation and SPDE

QG-Omega Equation LHS: Omega Term RHS: Differential vorticity advection,

temperature advection, sensible heating, friction terms

SPDE LHS: 1000 mb relative vorticity tendency RHS: 500 mb absolute vorticity advection, 1000 mb horizontal temperature advection

terms

QG equations, continued QG-Omega Equation

SPDE

January 3-5 2008 West Coast Extratropical Cyclone Synoptic Overview Strong Winds Heavy Precipitation Quasigeostrophic Equations

Discussion Quasigeostrophic Diagnosis Summary and Conclusions

Quasigestrophic Diagnosis Will be conducted at three times 0000 and 1200 UTC 4 Jan 0000 UTC 5 Jan Terms in each equation analyzed Find out general nature of omega,

and contributing factors Find out general nature of

development, and contributing factors

0000 UTC 4 Jan 2008SPDE Center of low Positive relative vorticity tendency Weak absolute vorticity advection Warm advection Development of system: 976 mb. 12 UTC 3 Jan 2008 964 mb. 00 UTC 4 Jan 2008

0000 UTC 4 J an 2008

0000 UTC 4 Jan 2008QG-Omega Equation San Francisco Negative omega Strong negative vorticity advection Weak warm advection Dominating Term: Temp Advection

1200 UTC 4 Jan 2008\SPDE Center of low Slight negative relative vorticity

tendency Weak absolute vorticity advection Weak temperature advection No change in intensity: Low remains at 964 mb.

1200 UTC 4 Jan 2008QG-Omega Equation San Francisco Negative omega Weak negative vorticity advection Strong warm advection Clear dominating term

0000 UTC 5 Jan 2008SPDE Center of low Slight negative relative vorticity

tendency Weak absolute vorticity advection Warm advection Low remains at 964 mb.

0000 UTC 5 Jan 2008QG-Omega Equation San Francisco Weak omega Negative along coast, positive

inland Mostly warm advection Weak vorticity advection

January 3-5 2008 West Coast Extratropical Cyclone Synoptic Overview Strong Winds Heavy Precipitation Quasigeostrophic Equations

Discussion Quasigeostrophic Diagnosis Summary and Conclusions

Summary and Conclusions QG-Omega Equation SF: Dominating factor: Warm

advection Contributed to strong negative

omega