Download Understanding Weather Maps - University of Alaska Fairbanks

Understanding Weather Maps Week 1: To the Surface Map…and Beyond! October 17, 2014 Our Founding Father, David LeHerman •  Roll that incriminaLng tape Your Instructor and (tor)Mentor •  Born and raised in North Dakota, where weather is “instrucLve” •  Master’s in Atmospheric Science from Colorado State University •  Meteorologist with NaLonal Weather Service 1993-­‐2011. Science Liaison with UAF’s Geographic InformaLon Office since 2012. •  [email protected] Course Outline •  October 17: The Surface Map, and Beyond •  October 24: Radar: Meteorology’s Best and Only Palindrome •  October 31: Weather Satellites •  November 7: Everything else •  My mission: How can I help you be a beHer consumer of weather informaLon? Uh-­‐Oh: Inadvertent Jargon Ahead, please help me! •  What topics do you want? Time to vote! The Surface Map Challenges of the Surface Map •  Noisy and Confusing –  What do those wiggly lines mean? –  What do those blue, red, and purple Gumi Worms mean? –  Why are random dots and dashes sprinkled about? •  That garish green is simply too much this early in the morning. The Root of the Problem •  The atmosphere is three-­‐dimensional (and changing over Lme, a fourth dimension) •  Weather maps are two-­‐dimensional •  When looking at a 2-­‐D weather map, try to also consider the verLcal dimension –  This is actually very difficult, probably the biggest challenge in this class Let’s Start with Topography •  How is three-­‐
dimensional terrain depicted on a two-­‐
dimensional topographic map? •  Enter the RoseHa Sandbox Let’s Go Hiking •  DNR's map of the Granite Tors Trail Topo Map versus Weather Map Topo Map Weather Map •  Base reference is surface of the earth •  Contours are lines of constant elevaLon of the surface above sea level •  Contours thus depict where certain elevaLons above sea level intersect the surface of the earth •  You will find bulls-­‐eyes around hills and valleys •  Base reference is sea level •  Contours are lines of constant atmospheric pressure at sea level •  Contours thus depict where certain atmospheric pressures intersect sea level •  You will find bulls-­‐eyes around highs and lows Our First Weather Map: D-­‐Day June 6, 1944 More About Pressure Contours •  Contours represent lines of constant atmospheric pressure at sea level •  Units of the contours are millibars (or hectopascals) •  Mean global pressure at sea level is roughly 1013mb •  Modern convenLon is to show a contour only every 4mb Even More About Pressure Contours •  Sea level pressure (SLP) can range from 925mb for a deep low to 1050mb for a big high •  World records are even more extreme •  SLP values are more extreme at higher laLtudes than at lower laLtudes •  SLP values are more extreme in winter than in summer Yet Even More About Pressure Contours •  The Lghtness of spacing between contours is the “gradient” and is proporLonal to wind speed •  Wind flows (roughly) parallel to SLP contours •  Wind flows counter-­‐clockwise around low pressure •  Wind flows clockwise around high pressure •  Northern Hemisphere Bias Enough Contours, Already. What About Fronts? •  A front is the edge of an airmass, the boundary between two different airmasses •  The front is named for the airmass that is advancing –  A cold front (depicted as blue) is the leading edge of advancing cold air –  A warm front (depicted as red) is the leading edge of advancing warm air –  An occluded front (depicted as purple) is a mess •  “Weather” tends to happen along and ahead of fronts Example of SLP Contours and Fronts Let’s Check Out Today’s Weather Maps •  hHp://pafc.arh.noaa.gov/tvwx.php Now for the “Beyond” Part…Up •  There are many different kinds of weather maps, using a variety of verLcal coordinates –  ElevaLon above sea level –  A pressure level, like 500mb –  PotenLal temperature, if you really want to take a walk on the wild side –  “Sigma” surfaces, a constant raLo of atmosphere above terrain, another wild walk •  Each kind of map has its strengths and weaknesses Sprawl of Weather Maps on the Web •  A great place to start is NWS’ Numerical Models: •  hHp://mag.ncep.noaa.gov/ Next Week: Radar Radar: Keew Txen