Old Town Pasadena
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Old Town Pasadena clear sky chart from 2005-11-06 to 2024-07-05.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	6% 4 1 3 3 2 3 2 4 6% 67%	89824
	Night	6% 4 1 3 3 2 3 2 4 6% 65%	89589
Transparency	Day	19% 6% 7% 18% 27% 23%	89549
	Night	21% 8% 8% 18% 24% 21%	89385
Seeing	Day	7% 9% 27% 37% 16% 4	15145
	Night	6% 3 15% 37% 32% 7%	25011

By Month

Percentage Cloud Cover SW (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	7% 3 1 3 2 2 2 2 4 6% 68%	2539
	11th to 20th	Day	10% 4 1 3 2 2 3 3 5% 9% 58%	2813
	21st to end	Day	14% 6% 2 4 3 3 3 3 4 6% 53%	3498
February	1st to 10th	Day	10% 4 2 3 3 2 2 2 4 6% 63%	1900
	11th to 20th	Day	10% 3 1 3 2 3 3 3 4 6% 61%	1850
	21st to end	Day	10% 5% 2 5% 4 3 3 2 5% 7% 55%	1570
March	1st to 10th	Day	10% 8% 2 5% 4 4 4 4 7% 7% 46%	3138
	11th to 20th	Day	6% 4 1 3 2 3 3 3 6% 8% 62%	3277
	21st to end	Day	11% 4 1 4 3 4 4 4 5% 8% 52%	4165
April	1st to 10th	Day	6% 5% 1 3 3 3 3 3 5% 8% 61%	2280
	11th to 20th	Day	5% 4 1 4 3 3 3 2 4 6% 66%	2249
	21st to end	Day	6% 4 1 3 2 2 2 2 3 6% 68%	2280
May	1st to 10th	Day	4 4 1 2 2 2 2 2 3 5% 73%	3910
	11th to 20th	Day	4 7% 2 4 3 2 2 2 4 6% 66%	4071
	21st to end	Day	4 7% 2 4 2 2 2 2 3 5% 67%	4477
June	1st to 10th	Day	4 4 1 3 4 3 2 2 4 8% 65%	2485
	11th to 20th	Day	3 3 1 3 2 2 2 2 3 6% 74%	2660
	21st to end	Day	2 2 1 2 2 2 2 2 3 4 79%	2660
July	1st to 10th	Day	1 2 1 2 2 2 2 2 3 5% 76%	2579
	11th to 20th	Day	2 1 1 2 3 1 2 2 3 4 79%	2494
	21st to end	Day	2 2 2 2 2 3 3 5% 7% 72%	2378
August	1st to 10th	Day	2 1 1 1 2 2 2 2 3 4 81%	2149
	11th to 20th	Day	2 1 2 1 2 1 2 4 84%	2122
	21st to end	Day	1 1 1 2 2 3 2 3 5% 80%	2376
September	1st to 10th	Day	3 2 1 2 1 1 2 2 3 4 79%	2160
	11th to 20th	Day	2 2 1 1 1 1 1 3 5% 82%	2029
	21st to end	Day	2 2 1 1 2 2 2 2 4 5% 78%	1980
October	1st to 10th	Day	4 3 1 3 3 2 3 3 4 5% 71%	1980
	11th to 20th	Day	4 2 1 3 1 1 2 2 2 4 77%	1864
	21st to end	Day	4 3 1 3 1 2 2 2 3 5% 74%	1941
November	1st to 10th	Day	3 3 1 3 3 2 3 2 4 5% 72%	1674
	11th to 20th	Day	5% 3 1 3 2 2 2 2 4 6% 70%	1710
	21st to end	Day	5% 3 1 4 4 3 4 2 5% 7% 63%	1710
December	1st to 10th	Day	8% 4 2 4 3 3 3 4 4 6% 60%	1710
	11th to 20th	Day	17% 5% 2 5% 3 3 3 3 5% 9% 45%	2169
	21st to end	Day	14% 6% 2 5% 4 4 4 3 5% 7% 47%	2977
January	1st to 10th	Night	8% 4 1 3 2 3 2 2 3 5% 67%	4406
	11th to 20th	Night	7% 4 2 5% 3 3 3 3 4 8% 59%	4133
	21st to end	Night	14% 6% 2 3 3 2 3 3 4 6% 54%	4180
February	1st to 10th	Night	10% 5% 1 4 2 2 2 3 3 4 64%	2280
	11th to 20th	Night	9% 4 2 3 3 3 3 2 4 5% 62%	2218
	21st to end	Night	12% 4 1 4 3 4 4 3 3 5% 57%	1884
March	1st to 10th	Night	12% 7% 1 3 2 2 4 3 5% 8% 51%	3736
	11th to 20th	Night	5% 3 1 3 3 2 3 4 5% 7% 63%	3697
	21st to end	Night	11% 6% 1 3 3 3 3 3 4 7% 57%	3488
April	1st to 10th	Night	7% 5% 2 4 3 3 3 3 3 6% 62%	1900
	11th to 20th	Night	5% 6% 1 2 2 2 3 3 3 5% 67%	1879
	21st to end	Night	4 5% 1 3 3 3 3 3 4 6% 66%	1900
May	1st to 10th	Night	5% 5% 2 4 3 1 2 2 3 4 71%	3066
	11th to 20th	Night	3 5% 3 5% 4 2 2 2 4 6% 66%	2834
	21st to end	Night	3 9% 2 4 2 1 1 1 2 4 71%	3110
June	1st to 10th	Night	2 4 1 3 4 3 3 3 5% 7% 65%	1688
	11th to 20th	Night	2 3 1 4 4 2 2 2 3 4 74%	1520
	21st to end	Night	2 2 1 2 2 2 2 3 4 5% 76%	1520
July	1st to 10th	Night	1 3 2 2 2 2 2 2 5% 79%	1475
	11th to 20th	Night	1 1 1 2 2 2 3 2 5% 6% 74%	1462
	21st to end	Night	3 2 2 2 2 2 4 5% 7% 70%	1937
August	1st to 10th	Night	1 3 1 2 2 2 2 2 3 5% 77%	1790
	11th to 20th	Night	1 2 1 2 2 2 2 1 3 6% 79%	1780
	21st to end	Night	1 1 2 1 2 2 2 4 4 80%	1980
September	1st to 10th	Night	3 2 1 3 2 2 2 2 3 4 77%	1800
	11th to 20th	Night	2 2 2 2 1 2 2 2 4 82%	1930
	21st to end	Night	1 2 2 2 1 1 2 2 5% 81%	1980
October	1st to 10th	Night	3 3 1 3 3 3 3 2 3 4 72%	1980
	11th to 20th	Night	5% 2 1 2 2 2 3 2 3 4 75%	2092
	21st to end	Night	4 3 1 3 2 2 2 2 3 4 75%	2412
November	1st to 10th	Night	4 4 1 2 3 2 2 2 4 5% 72%	2405
	11th to 20th	Night	4 3 1 3 2 2 2 2 3 6% 72%	2470
	21st to end	Night	6% 3 1 4 3 3 3 4 5% 7% 62%	2470
December	1st to 10th	Night	8% 3 1 5% 3 3 3 2 4 7% 61%	2470
	11th to 20th	Night	17% 5% 2 5% 3 4 3 3 4 7% 48%	3041
	21st to end	Night	13% 8% 2 4 4 3 4 4 5% 6% 48%	4676

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	19% 4 6% 23% 29% 19%	2539
	11th to 20th	Day	25% 5% 16% 20% 17% 17%	2813
	21st to end	Day	33% 5% 6% 19% 21% 17%	3498
February	1st to 10th	Day	26% 3 6% 14% 24% 27%	1900
	11th to 20th	Day	23% 4 6% 16% 27% 24%	1860
	21st to end	Day	27% 3 9% 19% 23% 18%	1570
March	1st to 10th	Day	32% 7% 11% 20% 17% 14%	3138
	11th to 20th	Day	19% 7% 13% 32% 15% 15%	3277
	21st to end	Day	28% 6% 14% 28% 15% 8%	4165
April	1st to 10th	Day	22% 5% 12% 25% 23% 13%	2280
	11th to 20th	Day	19% 4 9% 21% 29% 18%	2252
	21st to end	Day	17% 5% 8% 25% 32% 13%	2280
May	1st to 10th	Day	14% 7% 8% 17% 39% 16%	3910
	11th to 20th	Day	14% 17% 6% 19% 36% 9%	4074
	21st to end	Day	14% 14% 5% 24% 36% 6%	4477
June	1st to 10th	Day	20% 7% 9% 20% 30% 15%	2485
	11th to 20th	Day	15% 4 5% 13% 32% 30%	2660
	21st to end	Day	14% 4 3 8% 30% 41%	2660
July	1st to 10th	Day	13% 5% 5% 9% 22% 46%	2510
	11th to 20th	Day	12% 5% 6% 17% 31% 29%	2419
	21st to end	Day	12% 6% 8% 22% 33% 19%	2246
August	1st to 10th	Day	11% 3 3 13% 32% 39%	2135
	11th to 20th	Day	8% 4 3 12% 37% 36%	2122
	21st to end	Day	9% 4 5% 10% 36% 36%	2376
September	1st to 10th	Day	10% 3 5% 9% 34% 39%	2160
	11th to 20th	Day	9% 4 2 12% 36% 37%	2029
	21st to end	Day	10% 4 5% 14% 34% 33%	1980
October	1st to 10th	Day	16% 4 5% 18% 24% 32%	1980
	11th to 20th	Day	13% 5% 5% 15% 28% 35%	1864
	21st to end	Day	14% 4 5% 12% 22% 43%	1941
November	1st to 10th	Day	15% 4 5% 18% 25% 33%	1674
	11th to 20th	Day	17% 3 6% 15% 20% 38%	1710
	21st to end	Day	21% 5% 8% 12% 24% 31%	1710
December	1st to 10th	Day	26% 5% 6% 17% 19% 26%	1710
	11th to 20th	Day	37% 4 8% 15% 19% 16%	2168
	21st to end	Day	36% 6% 8% 23% 14% 12%	2977
January	1st to 10th	Night	22% 5% 6% 16% 33% 19%	4406
	11th to 20th	Night	26% 7% 13% 23% 14% 17%	4133
	21st to end	Night	31% 9% 6% 18% 19% 16%	4180
February	1st to 10th	Night	27% 3 6% 15% 21% 28%	2280
	11th to 20th	Night	23% 5% 7% 16% 24% 24%	2219
	21st to end	Night	30% 5% 7% 16% 21% 21%	1884
March	1st to 10th	Night	29% 7% 10% 24% 19% 11%	3736
	11th to 20th	Night	20% 9% 13% 27% 16% 15%	3697
	21st to end	Night	24% 11% 15% 26% 18% 7%	3488
April	1st to 10th	Night	26% 6% 10% 25% 20% 14%	1900
	11th to 20th	Night	19% 8% 9% 22% 25% 17%	1879
	21st to end	Night	20% 8% 10% 24% 28% 10%	1900
May	1st to 10th	Night	17% 11% 7% 20% 37% 8%	3066
	11th to 20th	Night	14% 22% 7% 25% 26% 6%	2835
	21st to end	Night	11% 14% 7% 34% 28% 5%	3110
June	1st to 10th	Night	19% 10% 14% 19% 26% 13%	1688
	11th to 20th	Night	15% 7% 6% 14% 35% 23%	1520
	21st to end	Night	17% 5% 6% 8% 31% 34%	1520
July	1st to 10th	Night	12% 7% 4 9% 26% 42%	1435
	11th to 20th	Night	14% 7% 7% 20% 27% 26%	1414
	21st to end	Night	15% 8% 9% 23% 29% 16%	1829
August	1st to 10th	Night	14% 5% 5% 9% 36% 32%	1780
	11th to 20th	Night	11% 6% 4 13% 36% 30%	1780
	21st to end	Night	12% 7% 4 10% 35% 32%	1980
September	1st to 10th	Night	16% 5% 5% 8% 30% 37%	1800
	11th to 20th	Night	9% 7% 3 11% 33% 36%	1930
	21st to end	Night	11% 5% 4 13% 36% 30%	1980
October	1st to 10th	Night	18% 5% 4 17% 23% 32%	1980
	11th to 20th	Night	16% 6% 4 15% 26% 33%	2092
	21st to end	Night	15% 5% 5% 11% 23% 42%	2412
November	1st to 10th	Night	16% 5% 6% 15% 25% 33%	2405
	11th to 20th	Night	17% 4 7% 14% 20% 38%	2470
	21st to end	Night	23% 5% 7% 17% 18% 31%	2470
December	1st to 10th	Night	25% 7% 7% 14% 18% 28%	2470
	11th to 20th	Night	37% 4 7% 14% 21% 15%	3041
	21st to end	Night	33% 10% 10% 20% 15% 12%	4676

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	16% 4 28% 35% 14% 2	180
	11th to 20th	Day	12% 12% 33% 30% 12% 1	337
	21st to end	Day	10% 14% 30% 33% 12% 1	506
February	1st to 10th	Day	13% 11% 30% 30% 12% 3	460
	11th to 20th	Day	11% 16% 31% 32% 8% 2	455
	21st to end	Day	11% 19% 33% 28% 8% 1	382
March	1st to 10th	Day	13% 18% 34% 23% 11% 1	460
	11th to 20th	Day	12% 16% 35% 26% 9% 2	460
	21st to end	Day	12% 19% 33% 27% 8% 1	506
April	1st to 10th	Day	9% 14% 34% 26% 14% 2	460
	11th to 20th	Day	8% 19% 37% 25% 9% 2	452
	21st to end	Day	5% 16% 32% 29% 14% 4	460
May	1st to 10th	Day	11% 14% 33% 29% 11% 3	463
	11th to 20th	Day	7% 12% 32% 33% 13% 3	488
	21st to end	Day	9% 11% 34% 31% 13% 3	529
June	1st to 10th	Day	4 7% 28% 40% 17% 5%	490
	11th to 20th	Day	6% 5% 28% 40% 16% 6%	490
	21st to end	Day	2 3 27% 44% 17% 8%	490
July	1st to 10th	Day	2 1 16% 49% 25% 7%	463
	11th to 20th	Day	1 1 10% 49% 26% 13%	444
	21st to end	Day	2 13% 49% 25% 11%	487
August	1st to 10th	Day	2 2 18% 51% 19% 8%	447
	11th to 20th	Day	2 2 14% 49% 24% 10%	437
	21st to end	Day	1 1 18% 50% 25% 5%	495
September	1st to 10th	Day	3 2 24% 45% 19% 6%	450
	11th to 20th	Day	2 4 30% 42% 18% 4	450
	21st to end	Day	2 6% 30% 36% 20% 6%	450
October	1st to 10th	Day	4 9% 30% 34% 19% 3	450
	11th to 20th	Day	3 10% 29% 39% 17% 3	450
	21st to end	Day	5% 8% 25% 36% 21% 5%	456
November	1st to 10th	Day	4 7% 21% 39% 23% 6%	270
	11th to 20th	Day	7% 6% 21% 39% 23% 5%	270
	21st to end	Day	5% 7% 27% 37% 18% 6%	270
December	1st to 10th	Day	10% 5% 23% 41% 19% 3	270
	11th to 20th	Day	6% 6% 27% 37% 21% 4	270
	21st to end	Day	17% 9% 27% 34% 12% 1	248
January	1st to 10th	Night	11% 3 20% 42% 20% 4	760
	11th to 20th	Night	9% 3 21% 42% 23% 2	760
	21st to end	Night	13% 4 21% 41% 18% 3	836
February	1st to 10th	Night	10% 4 19% 40% 23% 4	760
	11th to 20th	Night	8% 5% 22% 38% 22% 4	744
	21st to end	Night	12% 4 23% 40% 19% 2	628
March	1st to 10th	Night	9% 5% 24% 41% 18% 2	760
	11th to 20th	Night	8% 5% 18% 39% 25% 5%	760
	21st to end	Night	8% 6% 21% 42% 21% 3	836
April	1st to 10th	Night	8% 4 16% 46% 23% 3	760
	11th to 20th	Night	5% 7% 19% 40% 26% 3	751
	21st to end	Night	4 6% 21% 37% 27% 6%	760
May	1st to 10th	Night	5% 5% 20% 40% 26% 4	698
	11th to 20th	Night	5% 4 17% 39% 31% 4	561
	21st to end	Night	4 4 21% 38% 30% 4	617
June	1st to 10th	Night	1 2 16% 38% 40% 2	548
	11th to 20th	Night	3 1 6% 33% 52% 5%	380
	21st to end	Night	2 1 4 36% 50% 6%	380
July	1st to 10th	Night	3 1 3 16% 66% 11%	359
	11th to 20th	Night	1 3 15% 67% 13%	370
	21st to end	Night	3 1 2 26% 53% 15%	755
August	1st to 10th	Night	2 1 4 29% 50% 13%	716
	11th to 20th	Night	1 1 5% 20% 55% 19%	712
	21st to end	Night	2 1 5% 23% 53% 17%	792
September	1st to 10th	Night	3 1 7% 27% 47% 15%	720
	11th to 20th	Night	2 1 8% 33% 45% 11%	720
	21st to end	Night	2 2 7% 33% 47% 9%	720
October	1st to 10th	Night	4 2 10% 42% 38% 4	720
	11th to 20th	Night	5% 2 13% 37% 36% 8%	720
	21st to end	Night	4 3 15% 35% 32% 11%	792
November	1st to 10th	Night	5% 2 12% 42% 30% 8%	740
	11th to 20th	Night	4 3 12% 44% 30% 7%	760
	21st to end	Night	6% 2 18% 44% 25% 5%	760
December	1st to 10th	Night	8% 4 18% 42% 23% 4	760
	11th to 20th	Night	12% 5% 17% 44% 19% 3	760
	21st to end	Night	10% 6% 23% 40% 17% 4	836

Page generated at 2024-07-02 03:41:30. Version ac07

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