Lecture 4 (9/30) METR 1111 Station Plots and Fronts

Station Plots Station plots are a quick and easy way to view the current weather conditions - Puts METAR data in graphical format There are different kinds of station plots We will be looking at surface plots today

Temperature The temperature is at the upper left side of the station’s circle. Measured in degrees Fahrenheit Temperature here is 64°F

Weather Symbol Located directly below the temperature Weather symbol is not included in the station plot if nothing interesting is happening.

Common Weather Symbols:

Dewpoint Temperature Dewpoint temperature is on the bottom left side of the station. This is also in degrees Fahrenheit

Cloud Cover Cloud Cover is indicated by the amount of shading in the station’s circle no shading = clear 1/4th shaded = few clouds half shaded = scattered clouds 3/4ths shaded* = broken clouds fully shaded = overcast conditions

Sea Level Pressure Sea Level Pressure is on the top right side Need to add a 9 or a 10 in front of numbers on map and a decimal goes between the last two numbers Typical values between 970mb and 1030mb Here, the SLP is mb

Wind Barbs Wind barb indicates wind direction & speed The barb points in the direction FROM where the wind is blowing. Our example = southeast wind, 15kts Wind speed is measured (in knots) by the number and type of flags on the barb. Short flag=5kts, Long flag=10kts, Triangle=50kts

What is a front? At a frontal boundary, some or all of the following changes occur: Temperature change Change in dewpoint Wind Shift Pressure trough

Cold Fronts A cold front is a boundary where cold, dry air is sliding under warm, moist air. A typical temperature change with a cold front is about 20°F but varies greatly

More on Cold Fronts Ahead of a cold front, winds are usually south to southeastrly winds. Behind a cold front, winds usually from the north or northwest. A cold front is denoted on a surface map like this Filled triangles point towards direction of movement

3-D Picture of Cold Front Notice the warm air is lifted up and over the cold air and forms clouds. Warm air is less dense than cold air so it rises where they meet.

Warm Fronts A warm front is a boundary where warm, moist air is advancing against cooler, drier air. Temperature change averages 15°F but varies.

More on warm fronts Ahead of a warm front, winds are usually east or northeasterly winds. Behind it, south to southwesterly winds prevail. A warm front looks like this where the half circles point toward the direction it’s moving.

Stationary Front Boundary between warm, moist air and cold dry air in which neither air mass is advancing. Indicated by alternating blue triangles and red half circles. Often happens when front loses it’s “punch” or is blocked by high pressure.

Occluded front A occluded front, or occlusion, occurs when a warm air mass and a cool air mass come in contact with each other, making boundaries at both the ground as well as aloft. Often associated with showers or snow(in winter) and is the beginning of the end to a storm. Indicated by triangles and half circles on the same side.

For next time: Complete homework 4 (already posted) Read Chapter 5 What Makes Rain? Collect your assignments and quizzes at the back of the room. Don’t forget I drop 1 homework and 1 quiz