1. Surface Weather Map
a.k.a: Surface Synoptic Chart

3. Available here: http://www.atmos.washington.edu/data/vmaproom/

5. Why Surface Weather Maps?
Summarize weather conditions at the surface (where we are!)
Using a progression of charts can see how weather is evolving.
Summarizes our conceptional model of the atmosphere (fronts).

6. First Surface Weather Map
Perhaps the first surface weather map was created by H. W. Brandes in 1820 for March 6, 1783.
The arrows indicate wind direction and the lines show the deviation of pressure from average conditions

7. One of the weather maps created by Elias Loomis in his groundbreaking paper on the storms of February Surface wind direction is indicated by arrows and the deviations from average pressure are shown by the dashed lines. Temperatures are indicated by dotted lines and the sky or precipitation type by the color shading. This map indicates a strong low-pressure center over the Ohio Valley, rain on the coast, and snow-laden northwesterly winds to the west.

8. The Telegraphic Communication Revolution
By 1849 a telegraphic network was organized in the United States for the transmission of daily meteorological observations for a collection of stations.
In England during the l851 World's Fair, a telegraphic company prepared daily weather maps for display
The internet of the 19th century

9. First Real-Time Weather Maps

10. Fronts
The Norwegian Cyclone Model, around 1920

11. Fronts
Regions of enhanced temperature changes and major weather (clouds and precipitation)

12. 1950 Surface Weather Map

13. Still Used Today

14. What is on surface charts?
Station models: meteorological shorthand describing the observations at locations
Isobars (lines of constant sea level pressure)
Fronts and troughs (locations of low pressure)

15. Surface Observations are plotted using the station model

16. Station Model
In the U.S., the station model uses temperatures in F; other countries used C
Sea level pressure. 3 digits in tenths of a hPa (mb).
Divide by 10 and add either 9 or 10.
237 > 23.7> hPa
When choosing between 9 and 10, use the one that gives one a reasonable pressure (hint: average SLP is around 1000 hPa)

17. Practice
198 is hPa, not hPa
745 is hPa, not hPa
247 is hPa, not hPa

18. Pressure Change over the Past 3 hr
Surface pressure change in tenths of hPa
Over past 3 hr.
3 means pressure increase of .3 hPa in last 3 hr.
Cartoon next to it.

20. Current Weather

21. Sky Coverage

22. Sky Obscured…you are in cloud

23. Wind Pennants

24. Wind Speed

25. Useful to be able to read the station models

27. What kind of observations are plotted on surface charts?

28. ASOS: Automated Surface Observing System: Backbone Observing System in the U.S.

29. Marine Reports

30. Ocean and Lake
Weather Buoys
Anchored

31. Drifting Buoys
Pressure
Wind

32. Ship Reports: Marine VOS Program
Volunteers Observers--generally 6-hourly reports
Highly variable quality and frequency

33. Isobars of sea level pressure are found on station map
Isobars are lines of constant or equal pressure
Everywhere along each line the pressure is the same
Labeled in hPa/mb (e.g., 996, 1000, 1004, etc)

34. Why use sea level pressure rather than station pressure—the pressure at the elevation of the barometer?
Because pressure decreases with height!
The pressure variations on weather maps would be dominated by terrain changes.

35. L L H

36. Terrain effects on pressure would swamp the meteorological signal
So why not take the terrain effects of pressure out?
Adjust the station (surface) pressures to get the pressure at a standard level: sea level.
Called pressure reduction to sea level.
For example, near sea level, pressure drops about 1 hPa for every 8 meters in elevation.

37. Example of Pressure Reduction
* 1024 hPa
64 m
Sea Level
* 1032 hPa

39. Pressure Reduction
In reality, done in a more sophisticated way, but still somewhat artificial
Particular problems for high elevation stations
Sea level pressure is found at all major observing locations and plotted in the station models.
But how make SL pressure maps?

40. Technique called isoplething
Isobars generally drawn every 4 hPa (e.g. 1000, 1004)

41. Once the analysis is done, put on H’s and L’s
High- “H” -high sea level pressure relative to the surroundings. Also known as a ridge or anticylone. Generally associated with fair weather.
Low- “L” - low sea level pressure relative to the surroundings. Also known as a trough or cyclone. Generally associated with cloudy, stormy weather.

43. Pressure patterns are also very important because they influence winds
Strong winds are generally associated with strong horizontal pressure gradients, where pressure changes rapidly with distance.
Weak wind with weak
pressure gradients
strong
weak

44. Winds and pressure
Near terrain winds tend to go directly from high to low pressure
Away from terrain, winds tend to parallel isobars, with a small angle towards lower pressure

45. Typical relationship away from terrain
Surface wind H

46. In the northern hemisphere winds tend to blow countclockwise around lows and clockwise around highs (opposite in the southern hemisphere)

49. Other features on surface charts

50. What are fronts?
The tropics are warmer than the Arctic/Antarctic regions.
But temperatures don’t change gradually between north and south.
There are regions of large horizontal temperature changes, which are known as fronts.
Frontal boundaries are generally located on the warm side of the zone of temperature change.

51. Definition
A front is a boundary between air of relatively uniform warm air and a zone in which temperatures cools rapidly

52. Front
Frontal
Zone
relatively uniform cool air
relatively uniform warm air

53. Four Main Types of Fronts

54. Warm Front

55. Stationary Fronts

56. Occluded Front (a hybrid)

57. Fronts and Pressure

58. Fronts are associated with bands of clouds