Starfire Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Starfire Observatory clear sky chart from 2005-11-06 to 2024-11-28.

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	12% 6% 2 6% 4 4 4 4 6% 8% 45%	101266
	Night	12% 6% 2 5% 3 3 3 3 5% 7% 50%	98354
Transparency	Day	35% 6% 11% 21% 19% 8%	105022
	Night	32% 6% 11% 21% 20% 11%	102725
Seeing	Day	13% 6% 20% 27% 25% 9%	14975
	Night	13% 7% 26% 36% 17% 2	24870

By Month

Percentage Cloud Cover SE (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	15% 8% 2 4 3 3 4 4 5% 7% 47%	2847
	11th to 20th	Day	17% 5% 1 4 2 2 3 2 4 6% 54%	2850
	21st to end	Day	22% 9% 3 6% 3 2 2 2 3 6% 40%	3135
February	1st to 10th	Day	21% 7% 2 7% 4 4 3 2 4 5% 41%	1900
	11th to 20th	Day	21% 8% 2 5% 4 3 3 2 4 5% 43%	1849
	21st to end	Day	19% 8% 2 5% 3 3 3 2 4 5% 46%	1627
March	1st to 10th	Day	14% 9% 3 7% 5% 5% 5% 4 5% 6% 38%	3436
	11th to 20th	Day	20% 8% 3 8% 5% 5% 5% 5% 5% 6% 32%	3480
	21st to end	Day	15% 9% 2 6% 4 3 4 3 5% 7% 42%	3814
April	1st to 10th	Day	15% 8% 3 7% 4 4 4 3 5% 6% 40%	2090
	11th to 20th	Day	15% 8% 3 7% 4 5% 4 3 5% 6% 41%	2126
	21st to end	Day	13% 7% 2 5% 5% 3 4 3 4 6% 46%	2328
May	1st to 10th	Day	19% 9% 3 8% 5% 5% 4 4 6% 7% 31%	4082
	11th to 20th	Day	14% 6% 2 6% 4 4 4 4 7% 6% 43%	4082
	21st to end	Day	10% 6% 2 7% 5% 5% 6% 5% 8% 10% 36%	4477
June	1st to 10th	Day	5% 4 2 5% 4 5% 5% 5% 7% 10% 47%	2470
	11th to 20th	Day	6% 4 2 5% 4 4 5% 5% 7% 11% 47%	2470
	21st to end	Day	6% 5% 2 5% 7% 6% 6% 6% 8% 11% 38%	2470
July	1st to 10th	Day	7% 4 1 5% 5% 5% 5% 5% 7% 9% 48%	4120
	11th to 20th	Day	5% 5% 2 6% 4 5% 5% 4 8% 11% 45%	4120
	21st to end	Day	10% 7% 3 7% 5% 6% 6% 5% 8% 10% 34%	4465
August	1st to 10th	Day	2 1 1 2 2 3 3 3 5% 9% 69%	4104
	11th to 20th	Day	3 2 1 3 3 4 5% 4 7% 11% 56%	4027
	21st to end	Day	5% 3 2 5% 5% 5% 6% 6% 9% 11% 44%	3867
September	1st to 10th	Day	7% 5% 2 6% 5% 5% 6% 5% 7% 8% 45%	2090
	11th to 20th	Day	10% 6% 3 6% 5% 5% 5% 4 6% 8% 43%	2090
	21st to end	Day	6% 3 2 6% 4 5% 5% 5% 5% 8% 51%	2090
October	1st to 10th	Day	5% 4 2 4 3 3 5% 3 6% 6% 59%	2060
	11th to 20th	Day	12% 5% 2 4 3 3 4 2 3 5% 56%	1900
	21st to end	Day	13% 4 2 4 3 3 2 3 3 4 58%	2090
November	1st to 10th	Day	13% 6% 2 5% 4 4 4 3 5% 6% 47%	1958
	11th to 20th	Day	12% 6% 2 4 3 3 3 3 4 6% 53%	1973
	21st to end	Day	16% 7% 3 6% 5% 3 3 3 5% 5% 45%	1773
December	1st to 10th	Day	15% 8% 2 6% 3 4 4 3 4 6% 45%	1710
	11th to 20th	Day	17% 7% 3 6% 4 4 4 2 5% 5% 44%	2161
	21st to end	Day	16% 7% 2 6% 3 3 3 2 4 4 50%	3135
January	1st to 10th	Night	18% 7% 2 4 2 2 2 2 3 5% 52%	4108
	11th to 20th	Night	16% 6% 2 3 2 2 2 2 3 4 59%	4120
	21st to end	Night	22% 7% 2 6% 4 3 3 2 4 6% 42%	4532
February	1st to 10th	Night	19% 7% 2 6% 4 3 3 2 4 5% 44%	2295
	11th to 20th	Night	20% 7% 2 5% 3 3 3 2 3 4 47%	2218
	21st to end	Night	19% 8% 2 4 2 3 3 3 5% 6% 45%	1824
March	1st to 10th	Night	18% 9% 3 6% 4 3 4 3 5% 6% 38%	3419
	11th to 20th	Night	21% 9% 3 7% 5% 4 4 3 5% 5% 34%	3480
	21st to end	Night	14% 7% 3 7% 4 4 4 3 5% 6% 44%	3817
April	1st to 10th	Night	11% 6% 3 6% 4 3 4 3 6% 7% 48%	2090
	11th to 20th	Night	14% 7% 2 5% 4 4 3 3 5% 7% 46%	2003
	21st to end	Night	13% 7% 2 5% 4 4 3 3 4 5% 49%	1846
May	1st to 10th	Night	20% 10% 2 7% 4 4 3 3 5% 7% 35%	2823
	11th to 20th	Night	12% 6% 2 6% 3 4 4 3 6% 7% 47%	2823
	21st to end	Night	10% 6% 2 6% 5% 4 5% 4 6% 10% 42%	3090
June	1st to 10th	Night	5% 3 1 3 3 3 3 3 6% 10% 59%	1710
	11th to 20th	Night	4 3 1 4 3 3 4 4 7% 9% 60%	1710
	21st to end	Night	4 3 1 5% 4 4 4 4 6% 14% 52%	1710
July	1st to 10th	Night	4 4 1 4 3 3 5% 4 7% 11% 54%	2850
	11th to 20th	Night	4 3 2 4 3 4 4 4 6% 11% 55%	2850
	21st to end	Night	8% 7% 3 7% 4 5% 4 4 7% 11% 41%	3098
August	1st to 10th	Night	1 1 2 1 2 2 2 4 8% 76%	2836
	11th to 20th	Night	3 2 1 3 2 4 4 4 7% 12% 58%	2798
	21st to end	Night	3 3 2 4 3 4 4 4 7% 11% 55%	3782
September	1st to 10th	Night	6% 5% 2 5% 3 4 4 5% 7% 8% 52%	2090
	11th to 20th	Night	9% 5% 2 6% 4 4 5% 4 6% 8% 47%	2090
	21st to end	Night	6% 4 2 4 2 3 4 3 6% 8% 57%	2090
October	1st to 10th	Night	5% 3 1 3 3 3 3 3 4 6% 66%	2099
	11th to 20th	Night	10% 5% 1 4 3 3 3 3 4 6% 60%	2280
	21st to end	Night	13% 5% 1 3 3 2 2 2 4 5% 60%	2508
November	1st to 10th	Night	13% 5% 2 5% 3 3 3 3 4 6% 53%	2340
	11th to 20th	Night	9% 6% 2 5% 4 4 3 3 4 5% 54%	2425
	21st to end	Night	16% 6% 2 5% 4 3 3 3 4 6% 48%	2562
December	1st to 10th	Night	15% 8% 2 5% 3 3 4 2 4 6% 48%	2470
	11th to 20th	Night	15% 9% 3 6% 3 3 2 3 4 6% 45%	3036
	21st to end	Night	17% 7% 2 5% 2 2 3 2 3 4 53%	4532

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	37% 5% 6% 18% 22% 11%	2848
	11th to 20th	Day	34% 2 6% 20% 30% 8%	2850
	21st to end	Day	47% 3 4 12% 22% 11%	3135
February	1st to 10th	Day	46% 4 6% 11% 21% 12%	1900
	11th to 20th	Day	45% 4 8% 14% 19% 10%	1859
	21st to end	Day	42% 4 6% 17% 16% 14%	1627
March	1st to 10th	Day	44% 7% 8% 15% 20% 7%	3436
	11th to 20th	Day	52% 7% 8% 11% 14% 7%	3480
	21st to end	Day	42% 6% 8% 17% 22% 6%	3814
April	1st to 10th	Day	44% 6% 8% 16% 14% 12%	2090
	11th to 20th	Day	44% 5% 9% 14% 17% 10%	2126
	21st to end	Day	39% 6% 8% 18% 22% 7%	2328
May	1st to 10th	Day	50% 8% 12% 14% 11% 5%	4120
	11th to 20th	Day	39% 7% 11% 17% 23% 3	4086
	21st to end	Day	39% 10% 12% 26% 12% 1	4489
June	1st to 10th	Day	29% 9% 14% 28% 18% 3	2470
	11th to 20th	Day	28% 9% 14% 27% 17% 5%	2470
	21st to end	Day	36% 10% 14% 23% 14% 3	2470
July	1st to 10th	Day	30% 8% 22% 34% 7% 1	4056
	11th to 20th	Day	30% 8% 16% 29% 16% 1	4051
	21st to end	Day	42% 8% 18% 24% 8%	4325
August	1st to 10th	Day	12% 6% 12% 40% 29% 1	4090
	11th to 20th	Day	19% 6% 26% 35% 11% 2	4066
	21st to end	Day	29% 10% 20% 24% 15% 2	3866
September	1st to 10th	Day	35% 9% 12% 20% 17% 8%	2090
	11th to 20th	Day	38% 9% 13% 17% 19% 5%	2090
	21st to end	Day	29% 8% 10% 20% 18% 14%	2090
October	1st to 10th	Day	15% 3 7% 13% 21% 41%	3424
	11th to 20th	Day	20% 3 7% 16% 35% 20%	3140
	21st to end	Day	25% 4 5% 21% 31% 15%	3428
November	1st to 10th	Day	38% 5% 10% 16% 21% 11%	1958
	11th to 20th	Day	33% 4 8% 17% 22% 15%	1973
	21st to end	Day	42% 4 8% 14% 20% 12%	1773
December	1st to 10th	Day	40% 5% 9% 18% 20% 8%	1710
	11th to 20th	Day	42% 6% 7% 12% 22% 11%	2159
	21st to end	Day	39% 4 5% 14% 27% 11%	3135
January	1st to 10th	Night	36% 4 5% 17% 23% 15%	4108
	11th to 20th	Night	31% 3 4 17% 31% 13%	4120
	21st to end	Night	45% 4 4 14% 23% 11%	4532
February	1st to 10th	Night	42% 4 6% 12% 20% 16%	2295
	11th to 20th	Night	42% 3 6% 15% 20% 13%	2218
	21st to end	Night	41% 4 8% 14% 16% 16%	1824
March	1st to 10th	Night	45% 6% 9% 14% 17% 8%	3419
	11th to 20th	Night	50% 6% 10% 14% 14% 7%	3480
	21st to end	Night	41% 6% 9% 14% 22% 8%	3817
April	1st to 10th	Night	36% 5% 10% 18% 17% 13%	2090
	11th to 20th	Night	38% 6% 10% 15% 17% 14%	2003
	21st to end	Night	37% 5% 9% 19% 21% 8%	1846
May	1st to 10th	Night	48% 7% 10% 20% 12% 5%	2850
	11th to 20th	Night	33% 8% 12% 21% 20% 6%	2824
	21st to end	Night	36% 9% 13% 29% 12% 2	3099
June	1st to 10th	Night	20% 6% 19% 30% 22% 3	1710
	11th to 20th	Night	20% 6% 16% 33% 19% 6%	1710
	21st to end	Night	24% 8% 18% 29% 18% 3	1710
July	1st to 10th	Night	23% 8% 26% 36% 7%	2805
	11th to 20th	Night	23% 7% 20% 34% 14% 1	2796
	21st to end	Night	36% 8% 23% 25% 7%	2999
August	1st to 10th	Night	8% 4 15% 41% 30% 2	2826
	11th to 20th	Night	19% 6% 28% 33% 13% 1	2825
	21st to end	Night	22% 11% 23% 29% 14% 2	3782
September	1st to 10th	Night	27% 10% 16% 22% 16% 9%	2090
	11th to 20th	Night	34% 8% 15% 20% 16% 7%	2090
	21st to end	Night	24% 6% 14% 22% 19% 14%	2090
October	1st to 10th	Night	14% 3 7% 15% 19% 42%	3502
	11th to 20th	Night	17% 3 6% 17% 34% 24%	3779
	21st to end	Night	22% 3 5% 22% 31% 18%	4120
November	1st to 10th	Night	32% 6% 8% 19% 22% 13%	2340
	11th to 20th	Night	32% 5% 8% 18% 22% 15%	2425
	21st to end	Night	39% 4 8% 16% 19% 14%	2562
December	1st to 10th	Night	39% 4 7% 21% 18% 11%	2470
	11th to 20th	Night	41% 4 6% 11% 22% 15%	3037
	21st to end	Night	36% 4 5% 14% 29% 12%	4532

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	24% 10% 35% 23% 7% 1	270
	11th to 20th	Day	21% 13% 34% 21% 9% 1	270
	21st to end	Day	21% 10% 40% 20% 8%	297
February	1st to 10th	Day	29% 13% 28% 23% 7%	270
	11th to 20th	Day	29% 16% 29% 21% 5%	270
	21st to end	Day	26% 18% 37% 16% 3	225
March	1st to 10th	Day	21% 13% 36% 23% 6% 1	270
	11th to 20th	Day	18% 20% 33% 23% 4 2	270
	21st to end	Day	17% 13% 39% 24% 7% 1	297
April	1st to 10th	Day	21% 14% 40% 19% 6%	270
	11th to 20th	Day	19% 16% 35% 21% 8% 1	324
	21st to end	Day	17% 10% 37% 25% 10% 2	508
May	1st to 10th	Day	13% 11% 35% 31% 9%	653
	11th to 20th	Day	15% 7% 27% 33% 15% 4	675
	21st to end	Day	13% 5% 24% 36% 19% 4	734
June	1st to 10th	Day	5% 2 14% 37% 31% 11%	680
	11th to 20th	Day	8% 1 11% 41% 32% 7%	680
	21st to end	Day	7% 1 11% 30% 37% 13%	680
July	1st to 10th	Day	6% 2 6% 33% 36% 17%	671
	11th to 20th	Day	3 3 27% 47% 18%	668
	21st to end	Day	5% 1 5% 27% 46% 17%	739
August	1st to 10th	Day	3 1 3 23% 51% 20%	676
	11th to 20th	Day	6% 3 23% 50% 18%	664
	21st to end	Day	8% 2 5% 17% 36% 32%	356
September	1st to 10th	Day	7% 1 3 23% 35% 31%	300
	11th to 20th	Day	6% 3 6% 19% 41% 25%	300
	21st to end	Day	8% 2 8% 27% 35% 20%	300
October	1st to 10th	Day	4 1 12% 34% 37% 12%	300
	11th to 20th	Day	11% 2 22% 31% 25% 8%	300
	21st to end	Day	19% 10% 23% 21% 22% 5%	330
November	1st to 10th	Day	19% 5% 20% 34% 17% 6%	300
	11th to 20th	Day	18% 7% 24% 30% 16% 5%	300
	21st to end	Day	19% 15% 31% 19% 13% 3	291
December	1st to 10th	Day	19% 7% 29% 24% 13% 7%	270
	11th to 20th	Day	24% 13% 32% 24% 6% 1	270
	21st to end	Day	22% 11% 37% 20% 9% 1	297
January	1st to 10th	Night	20% 10% 32% 30% 7% 1	950
	11th to 20th	Night	22% 11% 29% 31% 7%	950
	21st to end	Night	19% 11% 32% 30% 7%	1045
February	1st to 10th	Night	24% 11% 34% 26% 5%	775
	11th to 20th	Night	23% 12% 37% 24% 4	744
	21st to end	Night	24% 13% 42% 19% 2	568
March	1st to 10th	Night	21% 11% 39% 25% 4	570
	11th to 20th	Night	18% 12% 36% 28% 6%	570
	21st to end	Night	14% 11% 44% 27% 4	627
April	1st to 10th	Night	11% 12% 45% 28% 3	570
	11th to 20th	Night	15% 12% 39% 29% 5%	563
	21st to end	Night	16% 9% 40% 25% 9%	570
May	1st to 10th	Night	10% 10% 44% 31% 5% 1	570
	11th to 20th	Night	12% 5% 35% 34% 12% 1	561
	21st to end	Night	7% 5% 31% 41% 15% 1	617
June	1st to 10th	Night	5% 2 18% 47% 26% 2	570
	11th to 20th	Night	5% 1 24% 51% 18% 2	570
	21st to end	Night	4 1 11% 48% 32% 3	570
July	1st to 10th	Night	5% 1 8% 47% 34% 4	555
	11th to 20th	Night	3 9% 50% 35% 2	552
	21st to end	Night	3 1 6% 51% 37% 2	624
August	1st to 10th	Night	1 4 54% 38% 3	567
	11th to 20th	Night	5% 1 6% 51% 34% 4	564
	21st to end	Night	4 1 6% 40% 43% 6%	627
September	1st to 10th	Night	7% 1 9% 38% 40% 6%	570
	11th to 20th	Night	9% 2 10% 33% 41% 5%	570
	21st to end	Night	9% 1 11% 40% 34% 6%	570
October	1st to 10th	Night	6% 1 11% 49% 30% 4	579
	11th to 20th	Night	11% 4 22% 41% 21% 1	760
	21st to end	Night	13% 8% 28% 32% 17% 2	836
November	1st to 10th	Night	14% 5% 23% 39% 18% 1	780
	11th to 20th	Night	11% 9% 27% 38% 14% 1	825
	21st to end	Night	18% 11% 28% 29% 14% 1	986
December	1st to 10th	Night	18% 8% 29% 33% 11% 1	950
	11th to 20th	Night	22% 12% 27% 33% 6%	950
	21st to end	Night	19% 10% 30% 33% 7%	1045

Page generated at 2024-11-24 23:22:19. Version ac07

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