1. Doswell Scientific Consulting - Norman, OK
Variations in the details of cold frontal passages as revealed by mesonetwork data
Chuck Doswell
Doswell Scientific Consulting - Norman, OK
14th Cyclone Workshop

2. A classical definition
From Petterssen (1956; pp ): “…let the term frontal surface denote a sloping surface or zone of transition separating two air masses of different density … the term front will denote the intersection of the frontal surface with a chart.”

3. Classical theory
The so-called Margules Formula for the slope of a frontal zone - ( ) denotes the warm air:
Implies cyclonic wind shear of the along-front geostrophic wind (vg) across the frontal zone

4. Classical theory - the windshift
The “kink” in the isobars at the front and cyclonic wind shear across it
The tail wagging the dog?

5. Subjective frontal analysis
cited in Sanders and Doswell (1995)

6. Standard surface analysis = Fishwrap!

7. A meteorologist’s analysis - q and r
OUN L

8. Frontal passage at OUN? ? ?

9. The Oklahoma Mesonet An opportunity for detailed analysis …
5-min temporal samples

10. Do classical cold fronts exist?
Doswell & Haugland (2007 EJSSM)
From:

11. FROPA at OUN
Temp (F) and Wind Dir
Pressure (mb) and Wind Speed (kt)

12. Objective analysis …

13. But this isn’t always the case!
Doswell and Haugland (2007) ?

14. Is this actually a “cold front”? - ~10 h before OUN FROPA:

15. Shortly after OUN FROPA:

16. More information … ?

17. What’s happening here?
FROPA occurred early in the morning, with a strong surface-based nocturnal inversion
Winds ahead of the front were light and variable and much stronger / gusty behind it
Mixing associated with the strong winds behind the front resulted in the temporary temperature increase

18. Issues … What name should we give to this boundary? Does that matter?
Representation with frontal symbols?
Does the nature of an air mass boundary change in time (or space)?
Surface observations are strongly affected by PBL processes
The PBL is strongly influenced by topography - not limited to orography
Last two - are very important for mesoscale thinking

19. What’s the point of surface analysis?
What classical analysts - e.g., Petterssen - saw as problems with surface temperature (and moisture) analysis are actually good reasons for us to analyze those variables!
The task is not to locate the fronts (or drylines, or troughs, or whatever
Rather, we wish to recognize and understand the atmospheric structure revealed by the data

20. More examples … 20 May 08 - a gradual change
So what boundaries do you insert, and what are they?

21. Norman FROPA

22. 12 July 08 - Spatial variation, with deep convection

23. The evolution of convection

24. By 00Z …

25. Three locations …

26. Watonga, OK

27. El Reno, OK

28. Norman, OK

29. 10 Apr 2008

30. Passage through the state …
Seems straight-
forward, but …

31. Passage at several stations … Woodward, OK

32. Breckinridge, OK

33. El Reno, OK ?

34. Cherokee, OK ?

35. Buffalo, OK

36. 08 Sep 2008

37. Buffalo, OK ?

38. Cherokee, OK

39. Arnett, OK

40. Woodward, OK

41. Watonga, OK

42. Norman, OK

43. Discussion
The OK mesonet reveals considerable space-time variations in the nature of “frontal” passages
Details of this don’t look very classical
Many more examples could be shown
Conventional analysis methods are antiscientific - trying to fit the observations to conceptual models

44. What do we get from standard surface analysis?

45. … compared to:

46. Issues … Isobars Frontal analysis
Representation of the wind field?
How many processes are actually dependent on the value of the sea-level pressure?
Isallobars much more useful …
Frontal analysis
Are all fronts classical?
Along an analyzed front, how well does reality correspond to the associated conceptual model?
How much gradient is enough to qualify as a front?
Is a front truly a line?
Why not let the data speak for themselves?

47. Recommendations for surface analysis - operations / research
I see relatively little value to isobar / frontal analyses - especially fronts - too argumentative and often misleading
The “industry standard” for surface analysis should always include either:
Temperature and dewpoint analysis - or, even better,
Potential temperature and mixing ratio analysis
Actual observations should be on the chart, including wind barbs

48. Thank you! cdoswell@earthlink.net cdoswell@gcn.ou.edu