Qualitative Verification of the Operational GFS and Ensemble

Mean for 1200 UTC 13 March 2003

Mike RichardsMetr 503

Outline• GFS Initialization• 144 hour forecast

- control run - ensemble mean

- spaghetti plot

• 240 hour forecast- control run

- ensemble mean - spaghetti plot

• 372 hour forecast- control run

- ensemble mean

GFS Initialization500 mb heights

• Zonal Jet over the Pacific

• Strong trough off western coast of U.S.

• Large ridge over the American and Canadian Rockies

Control Run and Ensemble Spread144 h Fcst vt 1200 UTC 3/13/03

• Very strong Zonal Jet over the Pacific Ocean

• Much of Zonal Jet and ridge have low ensemble spread

• Trough off west U.S. Coast not in high ensemble agreement

Ensemble Mean and Normalized Spread144 h Fcst vt 1200 UTC 3/13/03

• Strong Zonal Jet over Pacific Ocean has low Normalized Spread

• Strong trough has relatively low Normalized Spread

• Ridge over Rockies has very low Spread

Spaghetti Plot144 h Fcst vt 1200 UTC 3/13/03

• Spaghetti Plot shows all run variations in high agreement with position of zonal jet over the Pacific and with position of trough and ridge.

Control Run and Ensemble Spread240 h Fcst vt 1200 UTC 3/13/03

• Zonal Jet collapses over the Eastern Pacific. Still existent over Western Pacific.

• Trough off Western U.S. Coast disappears and Ridge over Rockies is replaced by a trough and cut-off low

• Little agreement amongst control runs

Ensemble Mean and Normalized Spread240 h Fcst vt 1200 UTC 3/13/03

• Zonal Jet still strong over Western Pacific. Jet begins to break apart over Eastern Pacific.

• Original trough and ridge no longer existent, relatively high normalized spread

Spaghetti Plot240 h Fcst vt 1200 UTC 3/13/03

• Spaghetti Plot shows run variations not in much agreement on trough and ridge position and Eastern Pacific zonal jet. Stronger agreement on Western Pacific zonal jet.

Control Run and Ensemble Spread372 h Fcst vt 1200 UTC 3/13/03

• Zonal jet has all but collapsed.

• 372 hr. fcst shows strong trough of Western U.S. Coast; strong ridge over U.S. and Canadian Rockies.

• Almost no agreement amongst control runs

Ensemble Mean and Normalized Spread372 h Fcst vt 1200 UTC 3/13/03

• Original trough and ridge are nonexistent.

• Zonal jet breaks up over Eastern Pacific; still slightly existent over Western Pacific.

• Little agreement for all positioning.

In Conclusion: • All 144 hr. forecasts are in strong agreement for existence of zonal jet over the Pacific Ocean. Forecasts are also in strong agreement for position of ridge over Canadian and U.S. Rockies. There is agreement for the trough position albeit with a slightly higher spread.

• All 240 hr. forecasts shows are collapsing of the zonal jet over the Eastern Pacific, with the Western Pacific zonal jet sustaining. These forecasts also do not verify existence of a trough off the Western U.S. Coast and a ridge over the Canadian and U.S. Rockies. Agreement for all run variations is low.

• 372 hr. forecasts show relative elimination of zonal jet but a return of the original trough and ridge position. Agreement for all run variations is extremely low.