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

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.”

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 (v g ) across the frontal zone Classical theory

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

Subjective frontal analysis cited in Sanders and Doswell (1995)

Standard surface analysis = Fishwrap!

A meteorologist’s analysis -  and r L OUN

Frontal passage at OUN? ? ?

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

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

FROPA at OUN Temp (F) and Wind DirPressure (mb) and Wind Speed (kt)

Objective analysis …

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

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

Shortly after OUN FROPA:

More information … ?

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

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

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

More examples … 20 May 08 - a gradual change

Norman FROPA

12 July 08 - Spatial variation, with deep convection

The evolution of convection

By 00Z …

Three locations …

Watonga, OK

El Reno, OK

Norman, OK

10 Apr 2008

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

Passage at several stations … Woodward, OK

Breckinridge, OK

El Reno, OK ?

Cherokee, OK ?

Buffalo, OK

08 Sep 2008

Buffalo, OK ?

Cherokee, OK

Arnett, OK

Woodward, OK

Watonga, OK

Norman, OK

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

What do we get from standard surface analysis?

… compared to:

Issues … Isobars –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?

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

Thank you!