function [year, day] = snowfall

% snowfall -- First snowfall, Logan Airport, Boston, MA.
%  [year, day] = snowfall (no argument) returns or displays
%   he year and the day of then first trace of snow after
%   September 30, beginning with 1891.
%   Source: Boston Sunday Globe, December 26, 1999,
%   page B8, based on National Weather Service data.
%   The values were taken from the graph using a
%   Gerber scale.
%  yd = snowfall (no argument) returns the snowfall data
%   as a two-column array [year day].
 
% Copyright (C) 1999 Dr. Charles R. Denham, ZYDECO.
%  All Rights Reserved.
%   Disclosure without explicit written consent from the
%    copyright owner does not constitute publication.
 
% Version of 29-Dec-1999 09:15:01.
% Updated    13-Jan-2000 09:19:13.

data = [   % Day and year.
23 1891
35 1892
46 1893
37 1894
52 1895
44 1896
43 1897
56 1898
 3 1899
40 1900
64 1901
29 1902
63 1903
27 1904
44 1905
52 1906
62 1907
44 1908
26 1909
44 1910
33 1911
43 1912
14 1913
27 1914
46 1915
43 1916
24 1917
57 1918
36 1919
46 1920
38 1921
55 1922
39 1923
48 1924
10 1925
36 1926
58 1927
27 1928
52 1929
48 1930
37 1931
50 1932
37 1933
13 1934
46 1935
47 1936
50 1937
47 1938
40 1939
21 1940
24 1941
34 1942
42 1943
37 1944
35 1945
46 1946
43 1947
60 1948
38 1949
52 1950
32 1951
30 1952
37 1953
56 1954
47 1955
42 1956
26 1957
60 1958
39 1959
24 1960
15 1961
25 1962
31 1963
21 1964
32 1965
63 1966
38 1967
41 1968
22 1969
17 1970
41 1971
15 1972
77 1973
62 1974
31 1975
41 1976
44 1977
52 1978
10 1979
41 1980
58 1981
45 1982
45 1983
44 1984
47 1985
42 1986
41 1987
 8 1988
49 1989
39 1990
39 1991
39 1992
55 1993
54 1994
44 1995
58 1996
45 1997
83 1998
105 1999   % And still counting.
];

yr = data(:, 2);
da = data(:, 1);

if nargout > 0
	year = yr;
	day = da;
	if nargout < 2
		year = [yr da];
	else
		year = yr;
		day = da;
	end
else
	help(mfilename)
	x = yr;
	y = da;
	xi = yr;
	p1 = polyfit(x, y, 1);
	p2 = polyfit(x, y, 2);
	p3 = polyfit(x, y, 3);
	y1 = polyval(p1, xi);
	y2 = polyval(p2, xi);
	y3 = polyval(p3, xi);
	subplot(2, 1, 1)
	if exist('hilbert', 'file') == 2
		h = feval('hilbert', y - mean(y));
		hi = abs(h) + mean(y);
		lo = -abs(h) + mean(y);
		plot(x, y, '-bo',x(end), y(end), 'r*', x, hi, 'k-', x, lo, 'k-')
	else
		plot(x, y, '-bo',x(end), y(end), 'r*')
	end
	axis tight
	title('First Trace of Snow at Logan Airport')
	xlabel('Year')
	ylabel('Days After September 30')
	subplot(2, 1, 2)
	plot(x, y, 'o',x(end), y(end), 'r*', xi, y1, xi, y2, xi, y3)
	axis tight
	xlabel('Year')
	ylabel('Days After September 30')
	zoomsafe all
	findpt
	figure(gcf)
	legend('data', '1999', '1st order', '2nd', '3rd', 0)
	set(gcf, 'Name', 'SnowFall', 'ResizeFcn', 'legend')
end