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 2023-06-24.

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	5% 2 1 2 2 1 2 2 3 6% 68%	71158
	Night	5% 3 1 2 2 1 2 2 3 5% 67%	70034
Transparency	Day	18% 4 7% 16% 27% 26%	70884
	Night	20% 5% 7% 16% 25% 25%	69830
Seeing	Day	6% 8% 27% 36% 15% 4	13737
	Night	5% 2 14% 36% 32% 7%	23644

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	9% 3 1 3 4 1 3 3 4 6% 57%	1439
	11th to 20th	Day	8% 4 1 2 3 2 3 3 3 6% 61%	1601
	21st to end	Day	11% 4 2 2 3 2 2 2 3 4 60%	1980
February	1st to 10th	Day	9% 3 2 3 2 1 2 2 3 5% 64%	1800
	11th to 20th	Day	9% 2 1 2 2 1 2 3 4 6% 62%	1750
	21st to end	Day	9% 4 1 3 4 1 3 2 4 6% 57%	1480
March	1st to 10th	Day	8% 5% 1 4 4 3 3 3 6% 7% 50%	1800
	11th to 20th	Day	8% 4 1 2 2 2 3 3 5% 7% 57%	1845
	21st to end	Day	6% 3 1 2 3 2 4 4 4 7% 58%	2376
April	1st to 10th	Day	6% 3 1 2 2 2 3 3 4 8% 60%	2160
	11th to 20th	Day	4 3 1 3 2 1 3 2 3 5% 66%	2129
	21st to end	Day	5% 3 1 2 2 1 2 2 3 5% 68%	2160
May	1st to 10th	Day	7% 5% 1 2 2 2 2 3 3 6% 61%	2218
	11th to 20th	Day	5% 3 1 3 3 1 3 2 3 7% 63%	2301
	21st to end	Day	6% 3 1 3 3 2 2 2 4 5% 63%	2530
June	1st to 10th	Day	4 3 1 2 3 2 2 2 3 8% 65%	2354
	11th to 20th	Day	3 3 1 2 1 2 2 2 5% 74%	2520
	21st to end	Day	1 1 1 2 1 2 2 3 4 78%	2425
July	1st to 10th	Day	1 2 1 2 1 2 2 3 5% 74%	2380
	11th to 20th	Day	2 1 1 2 1 1 2 2 5% 78%	2355
	21st to end	Day	1 1 1 1 1 2 3 4 7% 72%	2244
August	1st to 10th	Day	1 1 1 1 1 2 2 4 81%	2029
	11th to 20th	Day	1 1 1 1 1 2 3 84%	2002
	21st to end	Day	1 2 1 2 2 3 5% 78%	2244
September	1st to 10th	Day	2 1 1 1 1 2 3 4 80%	2040
	11th to 20th	Day	2 1 1 1 1 2 4 83%	1916
	21st to end	Day	1 1 1 2 1 1 2 3 4 79%	1870
October	1st to 10th	Day	4 2 1 2 3 1 2 2 3 4 70%	1870
	11th to 20th	Day	4 1 2 1 2 2 2 4 76%	1760
	21st to end	Day	4 2 2 1 1 1 3 3 4 74%	1833
November	1st to 10th	Day	3 2 1 2 3 1 2 2 4 4 71%	1584
	11th to 20th	Day	4 2 2 2 1 2 2 4 5% 70%	1620
	21st to end	Day	5% 1 1 3 3 2 3 2 4 7% 63%	1620
December	1st to 10th	Day	8% 3 1 3 3 2 3 4 3 6% 58%	1620
	11th to 20th	Day	11% 3 1 2 3 1 2 3 4 10% 53%	1620
	21st to end	Day	11% 3 1 2 2 2 3 3 3 6% 58%	1683
January	1st to 10th	Night	10% 4 1 3 2 2 2 4 3 7% 58%	2506
	11th to 20th	Night	7% 3 1 3 2 1 2 2 3 6% 64%	2350
	21st to end	Night	10% 3 1 2 3 1 2 2 2 4 64%	2376
February	1st to 10th	Night	7% 3 1 3 2 1 2 2 3 4 66%	2160
	11th to 20th	Night	8% 3 1 3 3 1 3 2 3 5% 63%	2098
	21st to end	Night	11% 3 1 3 3 2 3 3 3 4 59%	1776
March	1st to 10th	Night	9% 5% 1 3 2 2 3 3 5% 8% 54%	2160
	11th to 20th	Night	8% 3 1 2 3 2 3 4 5% 7% 57%	2109
	21st to end	Night	7% 3 1 2 3 2 4 3 4 7% 59%	1980
April	1st to 10th	Night	6% 4 1 3 3 3 3 3 3 6% 60%	1800
	11th to 20th	Night	4 5% 1 1 2 1 3 3 3 5% 67%	1779
	21st to end	Night	4 4 1 2 3 2 2 3 3 5% 65%	1800
May	1st to 10th	Night	5% 5% 1 3 4 1 2 3 3 6% 61%	1742
	11th to 20th	Night	4 5% 1 3 4 2 3 2 3 6% 62%	1594
	21st to end	Night	4 4 1 3 3 1 1 2 2 5% 69%	1746
June	1st to 10th	Night	2 3 1 2 4 2 3 3 4 7% 64%	1600
	11th to 20th	Night	1 2 2 3 2 2 2 2 4 75%	1440
	21st to end	Night	1 1 2 2 1 2 2 4 5% 74%	1392
July	1st to 10th	Night	1 2 1 2 1 1 2 2 5% 77%	1360
	11th to 20th	Night	1 1 2 2 1 3 3 4 6% 74%	1381
	21st to end	Night	3 1 1 2 1 2 3 5% 7% 69%	1829
August	1st to 10th	Night	1 2 1 1 1 1 2 2 2 4 77%	1690
	11th to 20th	Night	2 1 1 1 1 3 5% 79%	1680
	21st to end	Night	1 1 1 1 1 1 2 3 4 79%	1870
September	1st to 10th	Night	1 2 2 2 1 2 2 2 3 77%	1700
	11th to 20th	Night	1 1 1 1 1 1 1 3 84%	1823
	21st to end	Night	1 1 1 1 1 1 2 2 5% 81%	1870
October	1st to 10th	Night	3 2 1 2 3 2 2 2 3 3 71%	1870
	11th to 20th	Night	4 2 1 1 1 2 2 2 4 74%	1976
	21st to end	Night	3 2 1 2 2 1 2 2 3 3 74%	2278
November	1st to 10th	Night	4 3 1 1 2 1 2 2 3 5% 70%	2275
	11th to 20th	Night	3 2 1 2 2 1 2 2 2 5% 72%	2340
	21st to end	Night	5% 2 1 2 3 2 3 4 5% 6% 62%	2340
December	1st to 10th	Night	8% 3 1 4 3 1 2 2 4 7% 59%	2340
	11th to 20th	Night	11% 3 2 3 3 2 2 3 4 6% 56%	2340
	21st to end	Night	10% 4 1 2 2 1 2 3 3 5% 62%	2664

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	28% 4 6% 17% 21% 21%	1439
	11th to 20th	Day	24% 4 6% 10% 25% 27%	1601
	21st to end	Day	28% 2 7% 17% 17% 27%	1980
February	1st to 10th	Day	24% 2 5% 14% 24% 28%	1800
	11th to 20th	Day	22% 3 5% 16% 27% 24%	1760
	21st to end	Day	25% 3 9% 18% 24% 19%	1480
March	1st to 10th	Day	30% 4 9% 17% 17% 20%	1800
	11th to 20th	Day	23% 5% 10% 19% 22% 17%	1845
	21st to end	Day	22% 5% 11% 22% 22% 14%	2376
April	1st to 10th	Day	22% 5% 12% 25% 22% 12%	2160
	11th to 20th	Day	18% 3 9% 21% 29% 17%	2132
	21st to end	Day	18% 3 8% 25% 30% 13%	2160
May	1st to 10th	Day	22% 6% 9% 19% 27% 13%	2218
	11th to 20th	Day	21% 6% 7% 22% 30% 12%	2304
	21st to end	Day	21% 5% 7% 27% 29% 8%	2530
June	1st to 10th	Day	21% 5% 9% 18% 29% 15%	2354
	11th to 20th	Day	15% 3 5% 12% 32% 30%	2520
	21st to end	Day	14% 3 3 8% 30% 38%	2425
July	1st to 10th	Day	13% 4 5% 9% 23% 43%	2311
	11th to 20th	Day	12% 5% 6% 17% 29% 28%	2280
	21st to end	Day	11% 5% 8% 21% 32% 19%	2112
August	1st to 10th	Day	10% 2 3 12% 32% 38%	2015
	11th to 20th	Day	7% 3 2 12% 38% 35%	2002
	21st to end	Day	9% 3 5% 10% 37% 33%	2244
September	1st to 10th	Day	9% 2 5% 9% 33% 39%	2040
	11th to 20th	Day	9% 2 2 12% 34% 38%	1916
	21st to end	Day	10% 3 5% 14% 34% 32%	1870
October	1st to 10th	Day	17% 3 5% 17% 23% 31%	1870
	11th to 20th	Day	13% 4 5% 15% 27% 33%	1760
	21st to end	Day	14% 3 4 11% 22% 43%	1833
November	1st to 10th	Day	15% 3 5% 18% 24% 31%	1584
	11th to 20th	Day	16% 3 6% 16% 19% 37%	1620
	21st to end	Day	20% 4 8% 11% 24% 30%	1620
December	1st to 10th	Day	26% 5% 6% 15% 18% 26%	1620
	11th to 20th	Day	27% 3 10% 18% 22% 16%	1620
	21st to end	Day	27% 3 8% 17% 21% 21%	1683
January	1st to 10th	Night	26% 4 6% 16% 24% 20%	2506
	11th to 20th	Night	23% 3 8% 14% 19% 30%	2350
	21st to end	Night	26% 3 7% 16% 17% 28%	2376
February	1st to 10th	Night	24% 2 6% 14% 22% 29%	2160
	11th to 20th	Night	23% 3 6% 16% 23% 25%	2099
	21st to end	Night	28% 4 7% 15% 22% 21%	1776
March	1st to 10th	Night	29% 4 7% 21% 18% 18%	2160
	11th to 20th	Night	25% 7% 9% 16% 23% 17%	2109
	21st to end	Night	23% 5% 11% 22% 23% 13%	1980
April	1st to 10th	Night	26% 6% 10% 24% 19% 13%	1800
	11th to 20th	Night	19% 6% 9% 22% 24% 17%	1779
	21st to end	Night	20% 7% 10% 23% 28% 10%	1800
May	1st to 10th	Night	23% 8% 9% 21% 24% 11%	1742
	11th to 20th	Night	22% 8% 7% 24% 24% 11%	1595
	21st to end	Night	17% 6% 10% 30% 27% 8%	1746
June	1st to 10th	Night	19% 8% 13% 19% 26% 13%	1600
	11th to 20th	Night	14% 6% 6% 14% 35% 22%	1440
	21st to end	Night	17% 4 6% 8% 30% 32%	1392
July	1st to 10th	Night	13% 5% 4 9% 27% 39%	1320
	11th to 20th	Night	14% 6% 7% 19% 25% 27%	1333
	21st to end	Night	15% 7% 9% 21% 29% 17%	1721
August	1st to 10th	Night	13% 3 5% 9% 36% 31%	1680
	11th to 20th	Night	10% 5% 4 13% 36% 30%	1680
	21st to end	Night	11% 6% 4 10% 37% 29%	1870
September	1st to 10th	Night	14% 4 5% 8% 29% 38%	1700
	11th to 20th	Night	9% 4 3 10% 34% 37%	1823
	21st to end	Night	11% 4 4 13% 35% 30%	1870
October	1st to 10th	Night	18% 4 4 16% 23% 32%	1870
	11th to 20th	Night	16% 5% 3 14% 26% 32%	1976
	21st to end	Night	15% 3 4 10% 23% 42%	2278
November	1st to 10th	Night	16% 4 6% 15% 24% 31%	2275
	11th to 20th	Night	17% 3 7% 14% 19% 38%	2340
	21st to end	Night	23% 4 6% 17% 17% 30%	2340
December	1st to 10th	Night	25% 6% 7% 13% 18% 28%	2340
	11th to 20th	Night	30% 4 8% 16% 24% 15%	2340
	21st to end	Night	25% 3 8% 15% 24% 21%	2664

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% 3 28% 35% 13% 2	160
	11th to 20th	Day	11% 11% 32% 31% 11% 1	309
	21st to end	Day	9% 14% 30% 32% 11% 1	462
February	1st to 10th	Day	11% 10% 29% 30% 13% 3	420
	11th to 20th	Day	11% 17% 31% 31% 6% 1	415
	21st to end	Day	11% 19% 31% 28% 8%	346
March	1st to 10th	Day	13% 17% 34% 23% 10%	420
	11th to 20th	Day	13% 14% 34% 26% 9% 1	420
	21st to end	Day	11% 18% 33% 27% 8%	462
April	1st to 10th	Day	9% 14% 34% 26% 14% 2	420
	11th to 20th	Day	7% 19% 38% 24% 7% 2	412
	21st to end	Day	5% 16% 33% 27% 13% 3	420
May	1st to 10th	Day	11% 13% 34% 27% 10% 2	423
	11th to 20th	Day	7% 12% 31% 33% 12% 3	448
	21st to end	Day	9% 10% 35% 29% 13% 2	485
June	1st to 10th	Day	4 7% 28% 40% 15% 4	450
	11th to 20th	Day	5% 5% 25% 40% 16% 6%	450
	21st to end	Day	2 2 25% 43% 17% 8%	423
July	1st to 10th	Day	1 15% 50% 24% 6%	406
	11th to 20th	Day	10% 49% 25% 12%	404
	21st to end	Day	1 13% 49% 24% 11%	443
August	1st to 10th	Day	2 1 17% 51% 19% 8%	407
	11th to 20th	Day	1 12% 50% 24% 9%	397
	21st to end	Day	18% 50% 23% 5%	451
September	1st to 10th	Day	1 1 24% 46% 18% 6%	410
	11th to 20th	Day	2 3 29% 42% 18% 4	410
	21st to end	Day	1 6% 30% 37% 18% 6%	410
October	1st to 10th	Day	4 9% 30% 34% 17% 3	410
	11th to 20th	Day	3 9% 28% 38% 16% 2	410
	21st to end	Day	5% 7% 24% 36% 21% 5%	414
November	1st to 10th	Day	5% 7% 19% 39% 23% 5%	240
	11th to 20th	Day	5% 4 19% 41% 23% 5%	240
	21st to end	Day	5% 6% 27% 37% 17% 6%	240
December	1st to 10th	Day	10% 5% 23% 41% 16% 3	240
	11th to 20th	Day	5% 5% 27% 37% 20% 4	240
	21st to end	Day	16% 9% 27% 33% 12% 1	220
January	1st to 10th	Night	11% 1 18% 42% 21% 4	720
	11th to 20th	Night	9% 2 20% 42% 23% 2	720
	21st to end	Night	12% 3 20% 41% 18% 2	792
February	1st to 10th	Night	8% 3 18% 41% 23% 4	720
	11th to 20th	Night	8% 4 21% 37% 22% 4	704
	21st to end	Night	11% 4 21% 40% 19% 2	592
March	1st to 10th	Night	9% 4 22% 41% 19% 2	720
	11th to 20th	Night	8% 4 17% 38% 25% 5%	720
	21st to end	Night	7% 4 20% 41% 21% 3	792
April	1st to 10th	Night	7% 4 15% 46% 23% 2	720
	11th to 20th	Night	5% 6% 19% 38% 27% 2	711
	21st to end	Night	3 5% 20% 37% 27% 6%	720
May	1st to 10th	Night	5% 4 20% 39% 26% 4	662
	11th to 20th	Night	5% 3 16% 38% 31% 4	531
	21st to end	Night	3 2 21% 38% 29% 3	584
June	1st to 10th	Night	1 2 15% 37% 40% 2	520
	11th to 20th	Night	2 1 6% 31% 53% 5%	360
	21st to end	Night	2 1 4 34% 51% 6%	348
July	1st to 10th	Night	2 3 13% 67% 11%	330
	11th to 20th	Night	1 3 15% 65% 13%	349
	21st to end	Night	2 1 2 26% 51% 16%	713
August	1st to 10th	Night	2 1 4 26% 51% 14%	676
	11th to 20th	Night	1 4 18% 55% 19%	672
	21st to end	Night	1 4 22% 53% 17%	748
September	1st to 10th	Night	2 7% 25% 48% 15%	680
	11th to 20th	Night	2 1 6% 32% 45% 11%	680
	21st to end	Night	1 1 7% 33% 46% 9%	680
October	1st to 10th	Night	4 1 10% 40% 38% 3	680
	11th to 20th	Night	5% 1 12% 37% 35% 7%	680
	21st to end	Night	4 2 13% 34% 33% 11%	748
November	1st to 10th	Night	5% 1 12% 41% 30% 8%	700
	11th to 20th	Night	3 2 11% 43% 30% 7%	720
	21st to end	Night	6% 1 17% 43% 25% 5%	720
December	1st to 10th	Night	8% 3 18% 41% 23% 4	720
	11th to 20th	Night	12% 4 17% 43% 19% 2	720
	21st to end	Night	10% 5% 23% 39% 17% 3	792

Page generated at 2023-06-21 16:40:08. Version ac06

Copyright 2023 Attilla Danko