the forecast process
DESCRIPTION
The Forecast Process. ATMO 4300 Spring 2010. Scales of Motion. Global (Planetary) Scale Synoptic Scale Mesoscale. Figure from www.atmos.washington.edu/2003Q3/101/notes. ITCZ. Average Pressure in January. Average Pressure in July. The Polar Front. - PowerPoint PPT PresentationTRANSCRIPT
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The Forecast ProcessThe Forecast Process
ATMO 4300ATMO 4300Spring 2010Spring 2010
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Scales of MotionScales of Motion
Global (Planetary) ScaleGlobal (Planetary) Scale
Synoptic ScaleSynoptic Scale
MesoscaleMesoscale
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Figure from www.atmos.washington.edu/2003Q3/101/notes
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ITCZ
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Average Pressure in January
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Average Pressure in July
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The Polar Front
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Jet Stream Figure from www.crystalinks.com/jetstream.html
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Seasonal Position of Jet Stream
Figure from www.earth.rochester.edu/fehnlab/ees215/fig17_8.jpg
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Scales of MotionScales of Motion
Global (Planetary) ScaleGlobal (Planetary) Scale
Synoptic ScaleSynoptic Scale
MesoscaleMesoscale
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Synoptic Scale
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Synoptic Scale – 500 mbImage from www.rap.ucar.edu/weather
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Scales of MotionScales of Motion
Global (Planetary) ScaleGlobal (Planetary) Scale
Synoptic ScaleSynoptic Scale
MesoscaleMesoscale
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Mesoscale
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Forecast MethodsForecast Methods
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Forecasting Methods
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Climatology
• Using long-term averages to forecast a particular weather element
• Example:• What’s the problem with using
Climatology?
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Persistence
• Current Weather = Future Weather• Accuracy depends on: 1. Time scale 2. Progressive vs. stagnant weather pattern• Example:
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Trend
• Extrapolating current weather out in time based on steady-state conditions
• Best for approx 0-6 hours (Nowcasting)• Example:• What’s the problem with this method?
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Analogue
• Also called “Pattern Recognition”• Today’s weather similar to a past event• Forecast based on what happened with
the past event• Example:• What’s the problem with this method?
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Analogue - Example
• Go to the following web site:• http://tropical.atmos.colostate.edu• Click on Forecasts• Click first “new” link• Scroll down to No. 5
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Variations on Analogue Method
• Teleconnections – Relationship between weather in one part of the globe to events in another part
• Used in long-range forecasting
• Example: El Nino – connection between tropics and North America
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El Nino
• What is it?
• An event associated with significant warming of sea surface temperatures in the eastern tropical Pacific Ocean.
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Normal Sea Surface Temps
• Ocean temperatures are normally warmer in the west and colder in the east.
• Figures from www.cpc.ncep.noaa.gov
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El Nino EventFigure from www.cpc.ncep.noaa.gov/products
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Effects on AtmosphereFigure from www.cpc.ncep.noaa.gov
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Misconceptions about El Nino
• El Nino or La Nina does not directly cause any one particular weather event.
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Variations on Analogue Method
• Decision Trees / Checklists• Using common parameters associated
with many past events • “Rules of thumb”• Example:
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Example of Decision Trees
• Class Home Page• Click link to All NWS Offices• Click Midland on the map• Click Office Information• Click Local Research• Click on 5th article
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Numerical Weather Prediction
• Using computer models of the atmosphere to predict weather variables
• Model Output Statistics (MOS)• Ensembles
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The Forecast ProcessThe Forecast Process
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The Forecast Process
• With all the data and the different forecasting methods, how do you decide what to forecast?
• Rain or sunny• Snow amount
• Graphic from www.lib.umassd.edu/graphics/judge.gif
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A Systematic Approach
• Start with the Big Picture
- Look at the hemispheric (or partial hemispheric) upper wind flow pattern
- Look at a large scale water vapor satellite animation
(current & recent history)
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A Systematic Approach
• Review Synoptic Scale - Surface map – cyclones/anticyclones, air
mass boundaries - Upper air maps – troughs/ridges,
PVA/NVA, temp advection, meridional vs zonal flow
- Radar/satellite – precip/clouds in and near forecast area
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The Forecast Funnel
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A Systematic Approach
• Associate current weather with causes. Example: Evaluate moisture and lift for precip.
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A Systematic Approach
• What is the time period of your forecast? Example: 0 – 6 hours (Nowcast) Radar, satellite, profilers, detailed surface
analysis Example: Days 1 to 7 Numerical Weather Prediction models
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A Systematic Approach
• Choose a forecast methodology(s)• What weather elements am I forecasting
and what will affect those elements?• When forecasting different weather
elements, usually best to forecast temps last.
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Summary
• What happened and why?
• What is happening and why?
• What is going to happen and why?
• Adapted from Lance Bosart, SUNY, Albany