Lesson 9: Atmospheric Charts

what are atmospheric charts?

• geographically depict (…) at a given moment of time

• geographically depict state of the atmosphere at a given moment of time

what time is atmospheric charts recorded in? (4 timezones)

• coordinated universal time (UTC)

• greenwich mean time (GMT)

• zulu time (Z)

• mountain standard time (MST)

how do you go from UTC to MST?

• UTC (time) - 7 hours

what are the contours on an atmospheric chart and what do they look like?

• isob… or height…: ()

• isot…: ()

• isota… ()

• isobars or height contours: solid

• isotherms: long dash

• isotachs (short dash)

what is also included on atmospheric charts?

• l…

• h…

• tro…

• rid…

• fro…

• include (…) at given stations

• lows

• highs

• troughs

• ridges

• fronts

• include station models at given stations

what are analysis charts?

• depict (…) obtained at a given observation time

• depict actual data obtained at a given observation time

what are forecast (prognostic charts)?

• () model charts predicting (…); () charts and () charts are created

• computer model charts predicting future conditions of the atmosphere; surface charts and upper-level charts are created

what are the two types of analysis charts you can have?

• constant… charts

• () charts

• constant altitude charts

• isobaric charts

what are constant altitude charts?

• all locations at the () altitude above (…) (for surface analysis, pressures are typically adjusted to () )

• all locations at the same altitude above ground level (for surface analysis, pressures are typically adjusted to MSL)

what are isobaric charts?

• all locations on the chart have the same (); contour lines of () height of the atmospheric column to that pressure level; typically used for () levels of the atmosphere such as () mb, () mb, etc

• all locations on the chart have the same pressure; contour lines of equal height of the atmospheric column to that pressure level; typically used for elevated (upper) levels of the atmosphere such as 700 mb, 500 mb, etc

how are surface analyses created?

• ()/() is the primary source of data in the US: (…) at the surface (typically adjusted to () ), temp…, dew…, wind…, wind…, prec…, visi…, cloud…); similar data collection in other governments

• NOAA/NWS is the primary source of data in the US: atmospheric pressure at the surface (typically adjusted to MSL), temperature, dewpoint, wind direction, wind speed, precipitation, visibility, cloud cover); similar data collection in other governments

what are on surface analyses?

• () contours of pressure ()

• () contours of temperature ()

• (spacing of contours indicates…)

• (l), (h), (t), (r)

• include () and station model…

• result a (…) chart

• solid contours of pressure (isobars)

• dashed contours of temperature (isotherms)

• (spacing of contours indicates gradients)

• lows, highs, troughs (low-dash), ridges (zigzag)

• include fronts and station model symbols

• result: a surface analysis chart

what times are the surface analyses created?

• every () hours

• 00, (), (), (), (), (), (), () UTC daily

• every 3 hours

• 00, 03, 06, 09, 12, 15, 18, 21 UTC daily

how do you read a surface station model?

• Center Circle (): The amount the circle is filled in shows the total cloud coverage (e.g., () for clear, () for partly cloudy, () for overcast).

• Wind Barb (): A line extends from the central circle pointing in the direction from which the wind is blowing. Short feathers represent 5 knots, long feathers represent 10 knots, and flags (triangles) represent 50 knots.

• Top-Left Number (): Plotted as the air temperature, typically in degrees Fahrenheit (°F) or Celsius (°C).

• Bottom-Left Number (): Plotted as the dew point temperature in the same unit as the air temperature.

• Top-Right Number (): Shown as a coded 3-digit sea-level pressure in tenths of millibars (mb). The leading 9 or 10 and the decimal point are omitted. For example, a plotted value of 103 means 1010.3 mb, and 987 means 998.7 mb.

• GREATER THAN 500, add 9 in front, but LESS THAN 500, add 10 in front

• Left Middle Symbol (): A specific symbol (like dots for rain or asterisks for snow) sitting right next to the circle indicating what weather is happening during the observation.

• Bottom-Right / Middle-Right (): Shows how the atmospheric pressure has changed over the past 3 hours, often paired with a small number or plus/minus sign

• Center Circle (Sky Cover): The amount the circle is filled in shows the total cloud coverage (e.g., empty for clear, half-filled for partly cloudy, completely filled for overcast).

• Wind Barb (Speed and Direction): A line extends from the central circle pointing in the direction from which the wind is blowing. Short feathers represent 5 knots, long feathers represent 10 knots, and flags (triangles) represent 50 knots.

• Top-Left Number (Temperature): Plotted as the air temperature, typically in degrees Fahrenheit (°F) or Celsius (°C).

• Bottom-Left Number (Dew Point): Plotted as the dew point temperature in the same unit as the air temperature.

• Top-Right Number (Barometric Pressure): Shown as a coded 3-digit sea-level pressure in tenths of millibars (mb). The leading 9 or 10 and the decimal point are omitted. For example, a plotted value of 103 means 1010.3 mb, and 987 means 998.7 mb.

• GREATER THAN 500, add 9 in front, but LESS THAN 500, add 10 in front

• Left Middle Symbol (Present Weather): A specific symbol (like dots for rain or asterisks for snow) sitting right next to the circle indicating what weather is happening during the observation.

• Bottom-Right / Middle-Right (Pressure Trend): Shows how the atmospheric pressure has changed over the past 3 hours, often paired with a small number or plus/minus sign

how do you read this surface station model?

• wind direction

• wind speed

• sea-level pressure

• pressure trend/tendency

• sky cover

• dewpoint temperature

• present weather

• air temperature

• wind direction: from NNW

• wind speed: 15 kts

• sea-level pressure: 1010.7 mb

• pressure trend/tendency: -0.6 mb over past 3 hours, falling then steady

• sky cover: clear

• dewpoint temperature: 56 degrees F

• present weather: moderate rain

• air temperature: 57 degrees F

what are isobaric charts?

• acquire (), (), and () data from many stations at the same time

• standard pressure levels selected: (8), (7), (5), (3), (2)

• draw atmospheric () contours and ()

• create maps of () and () for a given constant () surface

• acquire weather balloon (radiosonde), satellite, and aircraft data from many stations at the same time

• standard pressure levels selected: 850, 700, 500, 300, and 200 mb

• draw atmospheric height contours and isotherms

• create maps of height and temperature for a given constant pressure surface

what are upper-tropospheric charts?

• () - () mb

• also contain () (….) contours

• 300 - 200 mb so 200, 250, 300

• also contain isotachs (wind speed contours)

what times are isobaric charts available?

• available at 00 and 12 daily (synoptic observations)

what is a characteristic of isobaric (constant pressure) surfaces?

• constant () at all points (altitude varies)

• constant pressure at all points (altitude varies)

another characteristic of isobaric (constant pressure) surface:

• () heights form over () air

• () heights form over () air

• higher heights form over warm air

• lower heights form over cold air

another characteristic of isobaric (constant pressure) surface:

• () heights correspond to regions of () pressure

• () heights correspond to regions of () pressure

• high heights correspond to regions of high pressure

• low heights correspond to regions of low pressure

another characteristic of isobaric (constant pressure) surface:

• () height gradient → () wind

• winds () to height contours ()

• stronger height gradient → stronger wind

• winds parallel to height contours (geostrophic)

is the pressure higher at A or B?

• pressure is higher at point A because high heights correspond to regions of high pressure

how do you read an upper-air station model?

• temperature:

• wind:

• dew point depression:

• height code:

• symbol:

• temperature: -45 degrees C

• wind: WSW at 60 kts

• dew point depression: 4; you can find the dewpoint by subtracting temperature from dew point depression to get the official dewpoint

• height code: height of the pressure level in decameters above sea level (add a zero to the end)

• if the dew point depression is less than 5 degrees C, then the symbol will be filled in

• a circle will indicate radiosonde data; a star is used to indicate satellite data; a square for aircraft observations

what are the standard pressure levels?

• (2), (3), (5), (7), (8)

• 200, 300, 500, 700, 850 mb

what is the height for 200 mb?

• 39,000 ft AGL

what is the height for 300 mb?

• 30,000 ft AGL

what is the height for 500 mb?

• 18,000 ft AGL

what is the height for 700 mb?

• 10,000 ft AGL

what is the height for 850 mb?

• 5,000 ft AGL

what is the height for 1013 mb?

0 ft (standard atmosphere)

the average altitude of a standard level is its…

• () altitude

• however, the actual altitude may differ by more than () ft

• pressure altitude

• however, the actual altitude may differ by more than 1000 ft

a chart for surface analysis is for () altitude AGL; other constant altitude charts may be created for () altitudes above the surface

• a chart for surface analysis is for zero altitude above ground level (AGL); other constant altitude charts may be created for higher altitudes above the surface

what is the importance of upper-air data? (wind information)

• wind is approximately () to height contours

• () where contours () together

• wind is approximately parallel to height contours

• stronger where contours closer together

what is the importance of upper-air data? (location of jet streams)

• bands of () at () level (200-300 mb)

• (), () turbulence near ()

• lead to () and movement of ()

• mix () down into troposphere

• bands of strong wind at tropopause level (200-300 mb)

• clear air turbulence near jet stream

• lead to development and movement of cyclones

• mix ozone down into troposphere

what is the importance of upper-air data? (identify regions of adverse weather)

• () of upper-air () or ()

• downwind of upper-air trough or low

what is the importance of upper-air data? (guides weather forecasters)

• atmospheric () and probability of ()

• initialize computer…

• atmospheric stability and probability of thunderstorms

• initialize computer forecast models

what do these symbols mean? (weather)

what do these symbols mean? (sky cover)

what do these symbols mean? (pressure trend)

decode this model

• temperature: 76 degrees F

• weather: light rain

• dew point: 55 degrees F

• sky cover: overcast

• pressure trend: currently falling (in tenths) so by 0.3

• sea-level pressure: (if you have a number that is less than 500, then you will be a 10 in front of it and then a decimal point at the end, for example 162 would be 1016.2 and anything above 500 you would put a 9 in front of it, for example, 700 would become 970.0) SO this pressure would be 1013.8

• wind speed: 20 kts

• wind direction: NE