Category Archives: probability forecasts

Five days of rain ahead; interpreting probability forecasts

Five consecutive days of afternoon and, or, evening rains are ahead.  If you don’t believe me, go here, to the University of Washington’s model run from last night‘s GLOBAL data, showing where the rain areas will be (in color!) every three hours for the next FIVE days. You will see that EVERY afternoon and evening has regions of color in our area.  I hope you’re happy now.

Instead of dwelling on yesterday’s drab conditions;  all that water up there, and in the air around us as measured by those high dewpoint temperatures, air that produced almost no rain here in Catalina, I thought I would instead liven things up today with a learning module for you, delimited by a string of dashes for excitement.


Below, is a link to the Environmental Science Services Administration (ESSA) pamphlet that tells you how to interpret today’s probability forecasts (10%, 40%, etc.,  chances of rain).

How to interpret precipitation probability forecasts

While I have provided this information as a public service, if you would like to obtain one of these pamphlets for yourself, you can get them for ten cents from the Superintendent of Documents, Government Printing Office, Washington, D. C.

Alert:  there may be some questions in the days ahead to make sure that you read and understand this information.  A sample test question:

“There is a large Cumulonimbus cloud on the Catalina Mountains but you can’t see them through the rainshaft coming out of that cloud.  There is a flash flood warning for the CDO wash.  The chance of rain is 10%?

True or false?

(The answer to this sample question will be provided in an upside down font when WordPress is able to to that.)

 End of learning module.  (I hope you’re happy now.)


OK, here’s is a tiny sample of clouds from yesterday.  I hope you recorded them correctly in your log book.  Here they are, in case you miss them on some hot day ahead:
12:36 PM  Sprinkles are around.  Altocumulus opacus, could be labeled Stratocumulus underneath.  Above the Altocu, Altostratus, the three layers helping to provide that Seattle drab look.


4:35 PM. Can you spot the Cumulus fractus under this Altostratus translucidus layer?