Suggestions for the Weather Pages

By Rob Hawley

 

Weather is my hobby and I have been actively following it for about 30 years. It used to be that you could only get easy access to the best information if you were a pilot. The Internet now provides access to all that information and a lot more.

I generally do not like the civilian forecasts because they do not provide enough information. I am also not satisfied in just looking at the Clear Sky Clock. These pages collect the best sources I have found to date. This is probably too much information if you are just interested in answering just the question of whether to observe and where. Here are some suggestions on how to get a more pithy answer.

 

 

Short Term Weather for an Observing Site

Go to the sites page. Here are links to the best info available from current information and forecasts. I have the high resolution satellite images for sites away from the Bay Area. If a Terminal Area Forecast (an Aviation Forecast) site is listed use it for the forecasts. Otherwise use the Clear Sky Clock and/or the Digital Forecast. Both of the latter are extrapolations from other data and, thus, are less reliable than the aviation forecast. The Clear Sky Clock also does not attempt to deal with our summer fog.

 

Overview of the Weather Trends

This is the order I look at the remaining info

Terminal Area Forecasts

The NWS does very detailed aviation forecasts for many airports throughout California.  The aviation forecasts are much more interesting than the civilian forecasts since they are more current and contain detailed information on what the clouds layers are.  Exactly the information an astronomer is interested in.  The aviation forecasts are now decoded so you don’t have to have detailed knowledge. For example

Forecast period:

2000 UTC 25 October 2004 to 0100 UTC 26 October 2004

Forecast type:

FROM: standard forecast or significant change

Winds:

from the SSE (160 degrees) at 14 MPH (12 knots; 6.2 m/s)
gusting to 23 MPH (20 knots; 10.4 m/s)

Visibility:

5 miles (8 km)

Ceiling:

3500 feet AGL

Clouds:

broken clouds at 3500 feet AGL
overcast cloud deck at 8000 feet AGL

Weather:

-RA  (light rain)

 

This link will define some of the common terms used in these forecasts.

The Water Vapor animation

This shows where the weather is moving. It also highlights areas of significant weather. This is the best tool for predicting transparency. The satellite records the density of water vapor in the atmosphere.

Dark areas contain no clouds and little water vapor. The whiter an area is the more water vapor. Green colorized areas denote heavy clouds. Some of the lighter white areas may not have visible clouds, but have reduced transparency due the presence of thin cirrostratus.  You can use the clouds classification (below) to describe the kind of clouds present.

The local VIS satellite

This is basically just a high-resolution photograph. Each pixel is a 1x1 km (about 1/2 mile x 1/2 mile) area.

The Jet Stream

The Jet Stream is a high level (about 29,000 feet) high speed river of air that generally marks the boundary between polar and subtropical air masses. Surface weather systems are steered by its flow. In the winter this becomes very important since changes in the jet stream will influence whether weather systems will visit us. In the summer the Jet Stream generally stays to our north. The dark areas are the strongest portions of the Jet Stream.

The Sacramento Cloud model

This is THE most accurate forecast of clouds. The model is run by the Sacramento NWS office and covers south to Fremont Peak, east to Nevada, and north to Oregon. I don't currently have an equivalent for the LSA area.

Bay Area Winds

This is an improved link to a site maintained by the Navy. It gives surface and upper level winds for the entire Bay Area.

 

 

Nerd Stuff

There are some more advanced tools available on the page as well.

Pressure Annotated Visual Image

U of Washington Map of Fronts

These are low-resolution visual maps annotated with surface winds and pressure.  They display gross weather systems.  The U of Washington Map also displays front boundaries although it seems to display too many Low and High-pressure systems.

700Mb map

This is will give an idea of what the fog will do. The winds at about 10,000 feet are displayed. A subsidence area (negative vertical wind) onshore generally means an offshore flow and clear skies. Areas of convection (positive vertical wind) mark weather systems. The write-up under the diagram gives some more info.

Winds at Alititude

This allows you to see the wind flow on the west coast from the surface to the jet stream.  Similar to the Bay Area Winds above, but provides more detailed information over a broader area.  Watch to see if the winds shift sharply as altitude increases.  This implies a wind shear. Wind shears can decrease seeing.

Cloud Classification

The cloud classification map interprets the raw satellite image to tell what kinds of clouds are present. Sometimes high clouds like Cs (Cirrostratus) are transparent enough to still do astronomy. A progression of Cx ->Ax ->Cx is typical of an approaching weather system.

A preview of this information is not available.

Oakland Upper Air

Twice each day (at 0000Z and 1200Z) weather stations around the world release a weather balloon attached to an instrument package (a radiosonde).  As this ascends it returns the temperature, humidity, and winds. The balloon goes to the very top of the atmosphere.  The balloon is the most direct way to measure what is happening above the bay area.  In the summer it clearly shows the temperature inversion layer that plays a role in our fog. The two drawings displayed here stop at 700 Mb (about 10,000 feet).  This highlights the portion of the atmosphere where the fog is present.  The PDF image is a little easier to use since you can zoom in on details.

Ft. Ord Profiler

The Ft. Ord Profiler is a 21st-century version of the weather balloon. It uses radio waves to get an idea of what the upper air is doing. Since our local fog requires an inversion layer, it shows the layer and how it changes through the day. I believe the mixing height will give us the top of the marine layer, but I am still researching that point

 

 

Input is solicited

Please feel free to give me feedback. I am especially interested in hearing from trained meteorologists.

Rob Hawley 2/12/09