Meaningful Surface Analysis Dr. Charles A. Doswell III Doswell Scientific Consulting – Norman, Oklahoma Lubbock Severe Weather Conference Lubbock, Texas – 17 February 2010

What does meaningful mean? Helps with the diagnosis of the current weather situation Critical to a scientific understanding Forecast = diagnosis + trend Formal: Q is a forecast quantity

Surface analysis The industry standard:

The standard analysis The “Norwegian School” Conceptual model of an extratropical cyclone (ETC) – low pressure Polar Front model was an essential element – Cold fronts, warm fronts, occluded fronts – Definition of a front: a 1 st order discontinuity in density – The line on a map - on the warm side of a baroclinic zone (large thermal gradient)

Dropping isotherm analysis … [surface temperature] is often neither representative nor conservative. It is not representative because of many local or orographic influences, and it is not conservative on account of the preponderance of nonadiabatic irreversible processes in the air closest to the earth’s surface. Petterssen (1940) – Weather Analysis and Forecasting

Evolution of this concept Secondary characteristics – Cyclonic wind shift across a front – A “kink” in the isobars Airmass boundaries – Drylines – moisture discontinuities – Outflow boundaries – Land/sea breeze fronts – Others: gravity waves, density currents, etc. Weakly baroclinic troughs in the pressure field

Uncertainty in frontal analysis Uccellini et al. (1992 AMS Bull.)

An ensemble of analyses … It may be inevitable … but good or bad? – Standard isobars + fronts – Isotherms and isodrosotherms – Pressure changes Consensus is right most of the time – why? – Diversity of plausible ideas is valuable Low probability, high-impact event potential – Analysis and forecasting as a team activity

What tells you the most?

Surface analysis and severe weather A simplified version … Ingredients for severe convective weather: – Deep moist convection … ingredients: Moisture Instability (conditionally unstable lapse rates) Lift – Supercell-based severe convective weather Vertical wind shear – Non-supercellular severe convective weather ?? } CAPE

Manually-analyzed surface features Boundaries – Fronts (baroclinic, by definition) – Drylines (baroclinity is a function of time of day) – Windshifts (weakly baroclinic) – Other … sea breeze fronts, gravity waves, etc. Thermal features (  is preferred) Moisture ( r is preferred) Pressure changes (effects on surface wind)

Diagnosis of features Diagnosis – interpretation of data in terms of physical processes Bad diagnosis usually  bad short-term forecast Use of all available information Any interpretation of the data is necessarily provisional … the best you can do at the time Recognition of bad data

Maddox’s Requirements for Making a Short-Term Forecast 1.An accurate diagnosis, including continuous monitoring, of the current situation 2.An extensive physical understanding of the phenomena occurring, including any anticipated developments

Triple points … Ingredients: Moisture, Instability, Lift, Vertical wind shear

Objective analysis aids What’s the purpose of manual analysis? What do you obtain from machine analysis? – Many variables of interest aren’t easily produced for hand analysis (divergence, vorticity, etc.) Keep the notion of ingredients in mind, though – Machine analysis is consistent (reproducible) – Fast and requires no personal effort at all Something of a 2-edged sword

Case example: 22 May 2008

 e versus dewpoint

T / T d versus  / r

Indices and parameters Source: SPC

More indices/parameters

… and what happened …

What can sfc diagnosis do for you? Not perfect forecasts! Keeps you connected to the data Forces you to think like a meteorologist, not a technician Pattern recognition Ingredients-based thinking

Principles of team forecasting Don’t bring your ego to the office! – No one is always right and no one is always wrong – Disagreement is fine, but keep it scientific, not personal – No one succeeds when any one of you fails to do a good job Shift change is a critical time – Listen carefully and ask questions, if necessary – Ever inherited a mess from the previous shift? – Ever leave your relief with a mess?

Surface analysis as a briefing tool Surface analysis generally is idiosyncratic Every few hours, and especially just prior to a shift change, a “standard” surface analysis should be created – Record of your diagnosis and how it has evolved – A fast way to illustrate your concept of what is going on – Everyone should agree on its format

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