Meteorology 356

Class Notes 9/20/2004

Katherine Cambier

Elizabeth Winchester

 

Weather Radars

 

"We looked at the conceptual diagram of radars on the website.  Explains how when energy is emitted from the radars, some of it comes back and is received by the radar."

It is somewhat similar to the radiation emitted by microwaves

The radar is tailored to detect anything the size of a raindrop or larger.

The computer then creates a chart that shows where all clouds are – those that have precipitation and those that don’t.

"Weather radars are covered by white fabric so you won’t actually see them spinning around.  This fabric is obviously transparent to the radar beam. The fabric also protects the radar from bugs, leaves, and other things that could interfere with its reception.  "

All weather offices are the exact same model in all locations.  They all have a “safe” room that serves as a safe spot in case a tornado or harsh weather comes. The “safe” room is important because personnel are required to stay at the station when a disaster is in progress so they can issue warnings.  All weather stations are also open to the public.  Our closest weather stations are in Santa Cruz and Monterey (one of the few that is not open to the public because it is on military grounds).

 

NWS = National Doppler Radar Sites Webpage – shows where all the sites are in the U.S. 

Stations are usually positioned every 200 miles or so – at least.

Radars can “see” about a 250-mile diameter.

"There are some spots in the U.S. that do not have radars for more than 300 miles.  An example is in Southeastern Oregon.  Why?  Radars are line-of-sight and because the topography of the area consists of mountains the radar is not able to penetrate them. This is the case for many 3rd world countries and will make it hard to implement the radars there, in addition to their high cost."

"Also, people do not want radar beams aimed at them, so they must be aimed 1/2 degree higher than the horizontal. The radar won’t “see” precipitation or rain clouds below its beam, so this limits its use."

"If you click on “National,” you get a plot of rain around the U.S.  The lightest blue color is where the least precipitation is.  The grey background indicates where there is absolutely no radar coverage."

 

We then looked at the present weather map on a Surface Plot

We examined the area around Salt Lake and the other side of the “front” near Nevada and Texas. 

The air was moving from the Northwest to the Southeast and it is cold.

We draw isobars for every 4 millibars.

We noticed that the atmosphere on the East Coast is presently heavier than the West Coast.  The pressure slowly decreased as you headed west. 

 

We then looked at the link to the Pressure Footnotes: Describes what happens at High vs. Low Pressures

 

High pressures

Completely encircled = anticyclone (analogy: mountain peak)

Not Completely encircled = Ridge (analogy; mountain ridge)

 

Low Pressures

Completely encircled by isobar = Cyclone (analogy: Tahoe Valley)

Not completely encircled = Trough (ex; ravine)

 

On today’s weather map we had examples of both: Cyclone = Denver. 

"With a cyclone, you will usually find cloudy skies.  "

Anticyclones usually bring clear skies and fair weather

"There is also a general tendency for air to move from higher pressure to lower pressure.  Why?  Because gas will always escape into vacuums, and high to low pressure creates vacuums  "

 

"Professor then gave us an example of air that is trapped in a room with all the windows and doors shut.  The pressure inside the room is 1000 millibars and outside of the room is 0 millibars.  As soon as a window or door is opened, all of the air will rush outside."

"Nature will always try to equalize this pressure difference, and this is what creates WIND. Without pressure areas there would be no wind."

"However, air doesn’t always move from high to low pressure.  Certain circumstances will cause the reverse.  When?  When there is an interference of topography, such as a canyon.  "

 

"The surface plot for today shows that the only precipitation is in Canada, and this is because it is in places where the weather stations are not located.  So we look at the radar map to see where more of the precipitation is at."

"On the radar, globules of color indicate individual cumulonimbus clouds which are generally thunderstorms."                         

"By using the animate feature, you can infer from the radar where clouds are and how the winds are moving."                    

 

Professor Monteverdi also stressed that we should know the general topography of California because the weather patterns are very much affected by it.                       

Ex;  know the Diablo range from the Santa Cruz mountains