Accessing and Accessing and Interpreting Web-based Interpreting Web-based

Weather DataWeather Data

Clinton Rockey

National Weather ServicePortland, Oregon

NOAA Weather OnlineNOAA Weather Online

Aviation Digital Data Service (ADDs)Aviation Digital Data Service (ADDs) Aviation Weather Center (AWC)Aviation Weather Center (AWC)

National Weather Service (NWS)National Weather Service (NWS)http://weather.govhttp://weather.gov

Your Local NWS OfficeYour Local NWS Officehttp://weather.gov/portlandhttp://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.

1) Read and digest the AFD.

Part 1 – where you can find the AFD

2) Compare this to data on the Internet.

Forecast ChartsSatellite ImageryRADAR Imagery

Part 2 – Interpreting Weather Charts

So how do you learn more by ‘AFD’ing it?

3) Repeat… Part 3 – this is YOU.

How Do I Start?How Do I Start?

• Read DiscussionsRead Discussions

• SatelliteSatellite Troughs and Ridges?Troughs and Ridges? Where are the Fronts?Where are the Fronts? Which way are these Which way are these

moving?moving?

• Model GraphicsModel Graphics

http://weather.gov/portland

Visible ImagesVisible Images

When Sun is up, clouds reflect the sunlight. So, clouds are visible.

But, when sun goes down, what do we do?

Can see land features

Also, Can Infer Low Level Winds

DetailsOf VisibleImages

Typical SummerAfternoon

Visible Image SummaryVisible Image Summary

PROs: Shows topographic features

Shows best detail of cloud features

CONs: Not available at night

See tops of the clouds only(can not tell if precipitation occurring)

Can infer low to mid-level wind flow

May be difficult to see clouds over snow covered terrain or layers of clouds.

Warmer the clouds, darker the shading. Colder clouds tops are white, and may be enhanced with color

Cold Front, with Rain

Cold Clear Air

L

L

22 FEB 2007, 1 pm PST

HL

L

IR Image SummaryIR Image Summary

PROs: Shows cold and warm advection

Good for determining areas of increasing or decreasing precipitation

CONs: Best for night time use, but day is good

Really cold air can often be mistaken for precipitation areas

Good for showing developing or weakening storms

Water Vapor ImageWater Vapor Image

Moisture shows as gray/green areas.Dry air indicated by dark areas.

Developing low,Along a front(rising moist air)

Dry, sinking air

L

L

22 FEB 2007, 1 pm PST

L

L

H L

H

Water Vapor Image SummaryWater Vapor Image Summary

PROs: Shows moisture/dry air advection(dry areas are candidates for fog and low level inversions)

Good for detecting disturbances in the upper flow that may enhance/weaken low level inversions.

CONs: Hard to determine areas of precipitation as same are could just be clouds

Good for showing developing or weakening storms and fronts

NOAA NOAA Surface Surface GraphicsGraphics

These are basicgraphics, mostlyfocused on frontsand simple weatherover the next severaldays.

Best Use:Get idea of frontsAnd where they willOver the next 48 hrs.

850 mb ~ 5k

700 mb ~ 10k

500 mb ~ 18k

300 mb ~ 30k

NOAA NOAA Model Model GraphicsGraphics

Charts use a numberthat 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 big long-wave trough

This is a small short-wave trough

A point to remember:

I n general, High pressure (highs, ridges) producebetter weather than Low pressure (lows, troughs).

Ridges = good weather, lack of cloudsDownward motion in the atmosphere

Associated with surf ace Highs/ ridges

Troughs = poor weather, clouds/ precipitation Upward motion in the atmosphere Associated with surf ace Lows/ troughs

http://weather.gov/portland

Points to remember #4 through..... .....ahhh whatever..........

LARGE long-wave ridges and troughs aredefi ned by how the jetstream (or storm-track)flows around the entire hemisphere.

Smaller short-waves are embedded in this storm-track.

Short-waves actually move along, up over thelong-wave ridges and down around the long-wave troughs.

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 ChartsUse of Big 5 Model Charts

300 mb300 mb

500 mb500 mb

700 mb700 mb

850 mb850 mb

SurfaceSurface

Jet Stream-location & strength

Troughs, Ridges, and short waves

Vertical lift and RH = Precipitation

Temperature, often for rain/snow line.Also, gives 5000 ft level winds

Locate Fronts, Surface Highs/Lows.Surface Winds, based on gradients

http://weather.gov/portland

300 300 mbmb

ChartChart(30k ft)(30k ft)

Best Use:Location and Movement ofJet Stream.

Remember, Jet Stream steers the Highs and Lows.

500 500 mbmb

ChartChart(22k ft)(22k ft)

Best Use:Location and Movement Ridges and Troughs.

Remember, Also Look for short waves, as they create the weather.

700 700 mbmb

ChartChart(10k ft)(10k ft)

Best Use:Identify areas of precipitation.

Remember,stronger lift & more RH, the better the threat of precipitation

850 850 mbmb

ChartChart( 5k ft )( 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 SFC (surface)(surface)

ChartChart( 5k ft )( 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 NOAA’s ADDs SpecializedSpecializedGraphicsGraphics

These are specializedgraphics, produced bythe National AviationWeather Center.

Icing Potential availablefor different altitudes, with probability for severe icing.

Best Use:Short-term planning.

Freezing Freezing Level & Level & Icing Icing PotentialPotential

http://adds.aviationweather.gov

Questions?Questions?