Fall 2009 AOS 101Lecture 1
Outline• Observations• Station models• Observation maps• SkewT• Contouring analyses
Class goal: How do you make agood forecast?http://localareaweather.com/images/WeatherComicStrip.jpg• Before tackling this question, we must first learnhow to make a forecast, whether it be bad or good.• The first step is to understand what data is neededto determine weather conditions and how that datais obtained.
Observations• Observations are important to any field• In meteorology, observations are thebuilding blocks in finding relationshipsbetween certain variables in weather• We can use observations to show us whatthe current weather conditions are andgive us an idea of what we can expect theweather to be like in the future
What observations are taken?
What observations are taken?• Pressure• Wind– Direction– Speed• Sky Conditions Is it cloudy or clear orsomewhere in between?• Temperature (in F at the surface and C for upperair observations)• Dewpoint Temperature• Weather Conditions – Is it stormy or nice?• Visibility – How far can a person see?
How do we get this information?• Barometer –measures pressure• Thermometer –measurestemperature• Anemometer –measures wind speedweblogs.newsday.comhttp://www.thedailygreen.comhttp://www.weathernewengland.com• Weather conditions –based onobservations• Cloud Conditions –again, based onobservations bymeteorologists
Viewing observational data• Now that we know how observations arecollected, how do we view them in an efficientand meaningful way?– Station models: compact view of various observations– Observation maps: horizontal maps that are “snapshots”of weather at a specific level in the atmosphere– SkewT diagrams: profiles that show the verticalstructure of the atmosphere• There are many other ways to viewobservational data, those listed above will be thefocus for this class
What is a station model?• Station model – a graphical representationof current weather including, but notlimited to, temperature, dew pointtemperature, wind speed and direction,cloud cover and pressure
Why is a station model necessary?• Because there is a lotof informationcollected in ourobservations, weneed to organize it sothat it is easy tointerpret and not justa big mess.http://www.lizplummer.com/blog/wpcontent/photos2/untidy.jpg
Sample station model
Dissecting the Station Model• Pressure– Measured in hPa or millibars– Data collected from a barometer– Typically, on a station model, the pressure isabbreviated so that if it is less than 600, a 10should be added to the front– If the pressure on the station model is above600, add 9 to the front of the number– The pressure is recorded to a tenth of a hPaso a decimal point must be placed in front ofthe last digit ( i.e. 986 = 998.6hPa )
Pressure versus mean sea level pressure• Atmospheric pressure is the amount of force airmolecules exert over a unit area and is afunction of altitude and temperature• When considering surface pressure, it is difficultto compare the actual pressures recorded forcities at various altitudes to one another• Surface pressure recorded on a station model isactually the mean sea level pressure• To address this problem a calculation ispreformed to adjust for pressure differences dueto varying altitudes• The result of this calculation is known as themean sea level pressure
Visualizing mean sea level pressure• General rule when converting atmosphericpressure to mean sea level pressure: add10hPa for every 100 meters in altitude.
Dissecting the Station Model• Temperature andDewpointTemperature– Measured by athermometer– Reported in degrees Fat surface anddegrees C for upperair
Dissecting the Station Model• Wind speed– Measured in knotsrepresented by barbs(1knot = 1.15mph)– 1 short barb = 5 knots– 1 long barb = 10 knots– Triangle = 50 knots• Wind direction– Ranges from 0 to 360degrees– Points in the directionthe wind is comingFROM
Dissecting the Station Model• Sky Conditions– Represented by the fill of the circle– No fill = clear sky– ¼ fill = few clouds– ½ fill = scattered clouds– ¾ fill = broken clouds– Full = overcast– X = obscured– M = missing
Dissecting the Station Model• Visibility– Is located to the left ofthe weather symbol(represented by VV onthe graph to the left)– It is measured in(statute) miles (up to10)• Weather conditions– Located to the left ofthe cloud cover– Over 90 symbols usedto denote weatherconditions
Weather condition symbols
Weather condition symbols
Station model: practice• Pressure: ??• Temp: ??• Dewpoint temp: ??• Wind speed: ??• Wind direction: ??• Visibility: ??• Cloud Cover: ??• Weather: ??
Station model: practice• Pressure: 1016.2=hPa• Temp: 55• Dewpoint temp: 54• Wind speed: ~20knts• Wind direction: NW• Visibility: 6 mi• Cloud Cover: overcast• Weather: moderaterain