Accessing and Interpreting Web-based Weather Data

Accessing and Interpreting Web-based Weather Data Clinton Rockey National Weather Service Portland, Oregon

NOAA Weather Online • Aviation Digital Data Service (ADDs) • Aviation Weather Center (AWC) • National Weather Service (NWS) http://weather.gov • Your Local NWS Office http://weather.gov/portland

A common question I have heard from pilots is, “How can I learn more about the weather?” There really aren’t any stand alone courses out there aimed at pilots, and Taking Atmospheric Sciences 101 from a university isn’t a very helpful option.

A zero cost way for YOU to do it (though it will take time and patience) ….may be to… “AFD” it. • Area Forecast Discussion • Discusses the current weather forecast, • NWS Meteorologist’s view of the weather, • Issued 4 times/day.

So how do you learn more by ‘AFD’ing it? • Read and digest the AFD. • Part 1 – where you can find the AFD • 2) Compare this to data on the Internet. • Forecast Charts Satellite Imagery RADAR Imagery • Part 2 – Interpreting Weather Charts 3) Repeat… Part 3 – this is YOU.

Read Discussions Satellite Troughs and Ridges? Where are the Fronts? Which way are these moving? Model Graphics How Do I Start? http://weather.gov/portland

Visible Images Can see land features Also, Can Infer Low Level Winds When Sun is up, clouds reflect the sunlight. So, clouds are visible. But, when sun goes down, what do we do?

Details Of Visible Images Typical SummerAfternoon

Visible Image Summary PROs: Shows topographic features Shows best detail of cloud features Can infer low to mid-level wind flow CONs: Not available at night See tops of the clouds only (can not tell if precipitation occurring) May be difficult to see clouds over snow covered terrain or layers of clouds.

L Cold Front, with Rain Cold Clear Air Warmer the clouds, darker the shading. Colder clouds tops are white, and may be enhanced with color

L L L H 22 FEB 2007, 1 pm PST

IR Image Summary PROs: Shows cold and warm advection Good for determining areas of increasing or decreasing precipitation Good for showing developing or weakening storms CONs: Best for night time use, but day is good Really cold air can often be mistaken for precipitation areas

Water Vapor Image L Developing low, Along a front (rising moist air) Dry, sinking air Moisture shows as gray/green areas. Dry air indicated by dark areas.

L L L L H H 22 FEB 2007, 1 pm PST

Water Vapor Image Summary Shows moisture/dry air advection (dry areas are candidates for fog and low level inversions) PROs: Good for detecting disturbances in the upper flow that may enhance/weaken low level inversions. Good for showing developing or weakening storms and fronts Hard to determine areas of precipitation as same are could just be clouds CONs:

NOAA Surface Graphics These are basic graphics, mostly focused on fronts and simple weather over the next several days. Best Use: Get idea of fronts And where they will Over the next 48 hrs.

300 mb ~ 30k 500 mb ~ 18k 700 mb ~ 10k 850 mb ~ 5k NOAA Model Graphics Charts use a number that reflects the pressure height. Examples: 500 mb Heights 300 mb Winds 850 mb Humidity

Think of Low as a depression or valley (we call them troughs). Troughs = Lower Pressure. And a High as a mountain or ridge. Ridges = Higher Pressure.

This is another 500 mb (millibar) chart This is a small short-wave trough This is a big long-wave trough

http://weather.gov/portland

More points… 5) Winds flow parallel to the lines of constant height. (True for 700 mb and above). 6) The strength of the winds is proportional to the distance between the lines. Strong winds = lines close together Weaker winds = lines further apart. http://weather.gov/portland

Use of Big 5 Model Charts Jet Stream-location & strength 300 mb 500 mb Troughs, Ridges, and short waves 700 mb Vertical lift and RH = Precipitation 850 mb Temperature, often for rain/snow line. Also, gives 5000 ft level winds Surface Locate Fronts, Surface Highs/Lows. Surface Winds, based on gradients http://weather.gov/portland

300 mb Chart (30k ft) Best Use: Location and Movement of Jet Stream. Remember, Jet Stream steers the Highs and Lows.

500 mb Chart (22k ft) Best Use: Location and Movement Ridges and Troughs. Remember, Also Look for short waves, as they create the weather.

700 mb Chart (10k ft) Best Use: Identify areas of precipitation.Remember,stronger lift & more RH, the better the threat of precipitation

850 mb Chart ( 5k ft ) Best Use: Location and movement of cold & warm air masses. Look for the 0 deg line. +1 deg or colder often results in snow on Cascades.

SFC (surface) Chart ( 5k ft ) Best Use: Location & Movement SFC Lows & Highs, clouds & sfc winds. Remember, closer the lines (or gradient), the stronger the winds.

NOAA’s ADDs Specialized Graphics Freezing Level & Icing Potential These are specialized graphics, produced by the National Aviation Weather Center. Icing Potential available for different altitudes, with probability for severe icing. Best Use: Short-term planning. http://adds.aviationweather.gov

Questions?

Accessing and Interpreting Web-based Weather Data