Weather Forecasting Elisabeth (Lis) Cohen

Motivation Foxtrot Comic Strip

What will the weather be tonight?

1 – Cloud and Rain Observations 2 – Pressure Systems 3 – Current Observations 4 – Computer Models 5 – Predict & Verify Our Forecasting Steps

Why focus on clouds? Rain/Snow producers Heating and Cooling Indicator of weather Come in interesting shapes

Common Cloud Types

Cloud Levels High Cumulus –Size of top of thumb at arms length Low Cumulus –Size of fist at arms length Photo: WBZ-Mos

Cloud Levels High Stratus –Sun and Moon easily seen Low Stratus –Sun and Moon difficult to see

Sign of moisture high up in the atmosphere. (Storms possible in 6-24 hours). Three Cloud Levels High Clouds

Possible marker of afternoon thunderstorm when clouds seen in the morning are growing or are very tall. Three Cloud Levels Middle Clouds

Cloud Levels Low Clouds Can form drizzle like precipitation

Often indicative of thunderstorms and heavy rain. Cloud Levels Large Vertical Development

Cold and Warm Front Clouds Cold Front Warm Front Frontal Movement

Cloud Levels

Satellites Monitor one area constantly, as it remains stationary with respect to an observer on earth’s surface Scan from north to south

Click here for: Satellite loop of the United States Are the clouds moving in your direction? When will they reach you?

RadioMicrowavesInfraredVisibleUltravioletX RaysGamma Rays Wavelengths of Light Wavelength Increases

Earth Surface Infrared Energy High Cloud Low Cloud Cold Satellite Infrared Image Warm Appears GrayAppears White High and Low Clouds in Infrared Image

Visible image Infrared image

How RADAR works USA Today Weather Book Jack Williams

Click here for: Infrared Satellite loop of the United States Are the clouds moving in your direction? When will they reach you?

Click here for the : Radar Map of the United States Where is the rain moving? Is it getting heavier or lighter? Look at the scale

Clear During the Day Cooler Air Relatively Warmer Air All Solar Energy Received = Warmer

Low Clouds During the Day Some Solar Energy Received = Cooler

Clear at Night

Ground radiatively cools at night and the energy is lost to space. The ground can get very cool on these nights.

Cloudy at Night

The ground radiately cools at night. Some of that radiation is absorbed by the clouds and reradiated in all directions. Some of that radiation reaches the ground and keeps warms the ground. This keeps it warmer at night.

What clouds are outside now? Click on the image to check the clouds in Colorado.

Ingredients for Cloud Formation 1.Condensation Nuclei 2.Moisture 3.Cooling / Lift

Surface Weather Map General Rules Low- –cloudy skies –Sucks air –Lousy High- – mostly clear –blows air –Happy

Click here to see the: United States Surface Weather Map Where are the highs and the lows? Are their lows close by that might be associated with clouds?

Winds Moving Air Masses Warm AirCold Air

Temperature During the Day… Temperatures decrease with height, in this layer of the atmosphere.

At Night…. Air at the ground is often cooler than the air above it. Temperature

Winds at Night Cooler Air Relatively Warmer Air

Local Observations Past and Current –Wind Speed –Wind Direction –Temperature –Humidity

Click here for: Surface Observations in Denver (Mesowest data) find your city on the mapSurface Observations in Denver (Mesowest data) find your city on the map

Click here for: Computer model forecast for United States Weather 6 hours from now

Climate Normals for Boulder

Helpful Hints ObservationForecastReason Night Cooler than day Ground Cools (Outgoing Longwave Radiation> Incoming Shortwave Radiation +Incoming Longwave Radiation) Clear Sky Cool Evening The atmosphere is mostly transparent to the outgoing longwave radiation. Calm Winds Cool Evening Little mixing of air from aloft keeps the air close to the ground cooler. Low Humidity Cool Evening The lack of moisture will mean less heat will be reradiated back to earth.

Your Forecast ObservationForecastReason Clouds -satellite -sky cover -highs/lows Temp -clouds -winds Rain -high/lows -radar Other

Thank you! Questions? Lis Cohen or