Case Study: 19 February 1997

• I. Frontal Diagnosis - 19 February 1997/00.00 UTC
  • Overview of satellite imagery for 00.00 UTC
  • Key parameters on isobaric surfaces for 00.00 UTC
  • Use of vertical cross sections for 00.00 UTC
• II. Frontal Diagnosis - 19 February 1997/06.00 UTC
  • Overview of satellite imagery for 06.00 UTC
  • Key parameters on isobaric surfaces for 06.00 UTC
  • Use of vertical cross sections for 06.00 UTC
• III. Diagnosis of Rapid Cyclogenesis and Upper Level Trough Feature - 19 February 1997/00.00 UTC
  • Overview of satellite imagery for Rapid Cyclogenesis 00.00 UTC
  • Key parameters on isobaric surfaces for Rapid Cyclogenesis 00.00 UTC
• IV. Diagnosis of Rapid Cyclogenesis and Upper Level Trough Feature - 19 February 1997/06.00 UTC
  • Overview of satellite imagery for Rapid Cyclogenesis 06.00 UTC
  • Key parameters on isobaric surfaces for Rapid Cyclogenesis 06.00 UTC
  • Relative streams and conveyor belts for Rapid Cyclogenesis 06.00 UTC
• V. Very Short Range Forecast
  • Very Short Range Forecast for the frontal system
  • Very Short Range Forecast for the Rapid Cyclogenesis and the Comma feature
  • Verification of Very Short Range Forecast

19 February 1997 - Key Parameters On Isobaric Surfaces For Rapid Cyclogenesis 06.00 UTC

19 February 1997/06.00 UTC - Meteosat IR image; magenta: height contours 1000 hPa, green: positive vorticity advection (PVA) 500 hPa, red: temparature advection - WA 1000 hPa	19 February 1997/06.00 UTC - Meteosat IR image; black: positive vorticity advection (PVA) 300 hPa, yellow: isotachs 300 hPa

The same relevant parameter combinations as before are presented in the left and right images above (compare Key parameters on isobaric surfaces for Rapid Cyclogenesis 00.00 UTC ). The deepening of the surface low is very distinct as well as the WA maximum; both give hints for the localisation of the Rapid Cyclogenesis. For a better relation between cloudiness and PVA maxima, clarification is expected from curvature and shear vorticity.

The jet streak diagnosis in the right image is much easier now using the knowledge gained before. The dominant jet streak is at the rear side of the Cold Front with a south-west - north-east orientation, and the PVA maximum in its left exit region corresponds to the intensified cloud patches. However there is a second jet streak north of Scotland close to a substructure in the cloud shield there. It is common experience that such secondary jet streaks may develop in connection with a Rapid Cyclogenesis.

Hints for difficult PVA field interpretation

19 February 1997/06.00 UTC - Meteosat IR image; red: vorticity advection 300 hPa, blue: shear vorticity 300 hPa	19 February 1997/06.00 UTC - Meteosat IR image; red: vorticity advection 300 hPa, brown: curvature vorticity 300 hPa

The images above differentiate between shear and curvature vorticity at 300 hPa. The comparison still shows that both vorticity maxima are close together but have a different orientation, hence the PVA maximum related to the curvature maximum influences the Comma feature, while the PVA maximum related to the shear maximum appears together with the Rapid Cyclogenesis.

Summarizing, this case study showed that it was possible to detect and separate two conceptual models - a Rapid Cyclogenesis development and a comma-like cold air feature - by means of a synopsis of all key parameters relevant for the conceptual models mentioned.

One set of key parameters which has not yet been mentioned are relative streams on isentropic surfaces (compare Relative streams and conveyor belts for Rapid Cyclogenesis 06.00 UTC ).