# The Current Arctic Outbreak 17 January 2018

## Objective Analysis of Point Data

A lot of weather observations are available from specific geographical locations. At various locations, the atmosphere is probed by sending up a balloon that carries an instrument package (rawindsonde), which radios back data measured by on-board sensors consisting of: pressure, temperature, humidity, and position. Few people can look at the numerical telemetry from the various sensors distributed at various points on the landscape and make some sense of them. In ancient times, weather forecasters spent most of their time plotting data on maps by hand and drawing contours of various fields. As a result of such analyses and what they knew about the mathematical interrelationships among the various meteorological fields, they would form a mental picture of the weather situation on a particular day, from which they would make their weather forecasts. Weather forecasting was then both an art and a science.

Some people, well versed in mathematics and physics and also interested in the weather, begin to dream of being able to mathematically fit the various meteorological fields to weather observations and to use these objective analyses as initial conditions to the partial differential equations that govern the weather, in the process  generating numerical weather predictions. Although the feasibility of doing this was demonstrated in a crude way, numerical weather predictions became practical only through the development of

Fig. 1 Depiction of the height field of the 500 mb pressure surface in tens of meter for 1200 Greenwich mean time, 16 January 2018.

computers. Although the it has taken hundreds of man ours (more like man years) to develop numerical prognostic models, objective analysis techniques are simple enough that they can be developed and applied by one person in a reasonable amount of time. Objective analysis is something that I can do in a minute's time after downloading the appropriate sounding files from a NOAA data base.

Today's analysis of the height distribution of a pressure surface that is equal to about half of the average sea level pressure (fig. 1) shows the lowered height imprint of the latest outbreak of chill, Arctic air that is rushing southward out of Canada into the United States Midwest.

(Part 2 continues this discussion.)

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