Some days I notice that buildings that fly the American Flag have it
at half mast. Usually the local news gives me the reason for that
particular day, but often I am left in the dark. Being a naturally
curious person it drives me nuts to not know why. Is there a site
online that is updated daily with (for lack of a better term) "Flag
Status" and if it is to be flown at half-mast, the reason? Also, I do
know that it can also be a very local or regional decision and not
just a national one. If possible, isolate the reference to California.

What a truly interesting question!  Thanks for asking. 
The short answer is: Flying the flag at half-staff is governed by
United States law.

The general rule is that flags will be flown at half-staff on Memorial
Day (until noon, when it should be raised to the “top of the staff”),
and on Peace Officers Memorial Day.

The Statute (4 U.S.C. 7(m)) sets forth the requirement that the flag
will be flown at half-staff on the following occasions:

30 days from the death of the President or a former President;

10 days from the day of death of the Vice President, the Chief Justice
or a retired Chief Justice of the United States, or the Speaker of the
House of Representatives;

from the day of death until interment of an Associate Justice of the
Supreme Court, a Secretary of an executive or military department, a
former Vice President, or the Governor of a State, territory, or
possession;

and on the day of death and the following day for a Member of
Congress.

The President of the United States may order the honor:

upon the death of “principal figures of the United States Government
and the Governor of a State, territory, or possession, as a mark of
respect to their memory”;

In the event of the death of other officials or foreign dignitaries,
the flag is to be displayed at half-staff according to Presidential
instructions or orders, or in accordance with recognized customs or
practices not inconsistent with law.

STATE GOVERNORS also have authority under the United States Code: “In
the event of the death of a present or former official of the
government of any State . . . the Governor of that State . . .may
proclaim that the National flag shall be flown at half-staff.”

 http://www4.law.cornell.edu/uscode/4/7.html
The flag, when flown at half-staff, should be first hoisted to the
peak for an instant and then lowered to the half-staff position. The
flag should be again raised to the peak before it is lowered for the
day. See id.
But there is a lot of license taken with the decision to fly the flag
at half-staff. For example, the Modesto City Council has authorized
its mayor to make the decision in certain cases where a prominent
local citizen has passed away:
http://www.modestogov.com/cmo/releases/2002/nr02079.htm
Witnessing the Modesto ordinance, it appears clear that although
United States law (the supreme law of the land) sets forth the
authority to order the flag lowered, and appears to limit that
authority to the President and the governors, anyone with a flag pole
may have been known to make their own decisions.
I was curious too as to whether there was a central clearing house for
instructions on when to fly the flag at half-staff in California. I
have called the State Library who referred me to the California
National Guard who, as far as the Library is concerned, is the point
of dissemination on flag protocol. I talked to a master sergeant in
the Adjutant General’s office, who was also intrigued with this
question, knew there was someone somewhere who did it. She promised to
call me back and I will post a Clarification when I hear from her.
Incidentally, the Veterans Administration web site has a handy
condensation of guidelines:
http://www.va.gov/pubaff/celebAm/halfstaf.htm


This site contains a list of when the flag should be flown:
http://www.americanflagstore.com/etiquette/etiquette.htm

NEW YEAR'S DAY..............January 1
MARTIN LUTHER KING DAY......Third Monday in January
INAUGURATION DAY............January 20 (every 4 years)
LINCOLN'S BIRTHDAY..........February 12
PRESIDENT'S DAY.............Third Monday in February
WASHINGTON'S BIRTHDAY.......February 22
EASTER SUNDAY...............Variable
ARMY DAY....................April 6
V-E DAY.....................May 8
MOTHER'S DAY................Second Sunday in May
ARMED FORCES DAY............Third Sunday in May
MEMORIAL DAY................Last Monday in May
FLAG DAY....................June 14
FATHER'S DAY................Third Sunday in June
INDEPENDENCE DAY............July 4
LABOR DAY...................First Monday in September
V-J DAY.....................September 2
CONSTITUTION DAY............September 17
COLUMBUS DAY................Second Monday in October
NAVY DAY................... October 27
PRESIDENTIAL ELECTION DAY...First Tuesday after first Monday in
November
VETERAN'S DAY...............November 11
THANKSGIVING DAY............Fourth Thursday in November
PEARL HARBOR DAY........... December 7
CHRISTMAS DAY...............December 25

If I can help with anything else, please feel free to ask for
clarification.

Thanks for stopping in.
weisstho-ga



SEARCH TERMS USED:

://www.google.com/search?q=flying+a+flag+at+half-staff&hl=en&lr=lang_en&ie=UTF-8&start=10&sa=N

://www.google.com/search?sourceid=navclient&q=%22flag+code%22+usc\

Flying the flag at half mast (from "Standard Bearer")
http://www.fotw.ca/flags/flagnffa.html

On California, I found this for UCLA:

UCLA Procedure 115.1:
Lowering of University Flag to Half-Mast (Upon Death of Employee or
Elected Student Government Official)
http://www.adminvc.ucla.edu/appm/public/115_1.html


On the news:

UK
Palace flag flies at half mast
http://www.ananova.com/news/story/sm_556937.html

CANADA
(HALF-MASTING OF THE FLAG)
http://www.pch.gc.ca/ceremonial-symb/english/half-masting.html
(Half-masting of flags)
http://www.pch.gc.ca/ceremonial-symb/english/emb_flag_half.html


History:

HALF MAST
During battles, the flag of the surrendering forces was lowered half
way down the flag mast in order to allow the flag of the victor to be
erected above it. Legend says that when a ship lost a crew member, the
flag was lowered to half mast to allow the space above for the flag of
the greatest conqueror of all, the Angel of Death.

(http://www.lostatsea.ca/halfmast.htm)

This may not be the most efficient method for knowing when to fly a
flag at half-staff but it may help with
your question.  Flags are flown at half-staff for different reasons,
one of which is a government proclamation.
For the state of California, one way to determine the days it is
proclaimed to fly at half-staff is to review the
governors' proclamations.  The easiest way to do this is to go to the
California State home page:

www.state.ca.us

Then type (half-staff 2002) in the search box.  This will provide the
various days that were proclaimed because
of tragedy, etc. to be days to fly the flag at half-staff.  Naturally
in subsequent years you would enter
(half-staff 2003, etc.).  You can then browse the various
proclamations.  This is from a statewide perspective.
I'm sure (I haven't checked) that some individual city web pages may
have similiar search capapbilities.

I hope this helps.

There is exactly such a site!  This is a one page website that only
exists to display the current status of the flag.

http://www.flaghalfstaff.com

Note: http://www.flaghalfmast.com seems to also point to the same site
(http://www.flaghalfstaff.com)