Sunset Farm Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sunset Farm Observatory clear sky chart from 2005-11-06 to 2024-11-05.

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	11% 9% 3 8% 6% 5% 5% 4 6% 8% 36%	105526
	Night	9% 9% 4 9% 6% 5% 5% 4 6% 7% 36%	102164
Transparency	Day	44% 8% 16% 24% 8%	105253
	Night	44% 7% 14% 23% 10% 1	102026
Seeing	Day	14% 11% 32% 27% 12% 3	16216
	Night	13% 10% 34% 30% 11% 1	26130

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	5% 17% 6% 13% 8% 7% 5% 5% 6% 7% 21%	2218
	11th to 20th	Day	4 8% 4 15% 13% 10% 10% 7% 9% 8% 12%	2383
	21st to end	Day	7% 12% 5% 15% 7% 6% 6% 4 6% 7% 24%	2794
February	1st to 10th	Day	8% 14% 5% 13% 7% 6% 6% 5% 7% 8% 22%	1589
	11th to 20th	Day	5% 11% 4 10% 9% 8% 7% 6% 9% 7% 23%	1664
	21st to end	Day	7% 11% 5% 13% 6% 6% 7% 6% 6% 8% 25%	1560
March	1st to 10th	Day	11% 12% 4 9% 7% 6% 6% 4 6% 8% 27%	3130
	11th to 20th	Day	8% 12% 5% 11% 12% 6% 4 4 6% 8% 25%	3480
	21st to end	Day	9% 12% 6% 15% 8% 5% 5% 3 6% 5% 26%	3814
April	1st to 10th	Day	9% 13% 5% 9% 5% 4 5% 4 5% 7% 34%	2317
	11th to 20th	Day	13% 13% 4 9% 5% 5% 5% 3 6% 5% 31%	2439
	21st to end	Day	17% 10% 4 9% 5% 4 4 3 6% 6% 33%	2470
May	1st to 10th	Day	19% 11% 3 7% 4 4 3 4 5% 8% 32%	4120
	11th to 20th	Day	19% 9% 3 7% 5% 5% 5% 4 5% 7% 32%	4655
	21st to end	Day	18% 9% 3 8% 5% 4 5% 3 5% 6% 34%	5173
June	1st to 10th	Day	13% 6% 2 6% 5% 5% 5% 4 6% 9% 38%	2850
	11th to 20th	Day	14% 6% 3 6% 6% 5% 5% 4 6% 8% 37%	2850
	21st to end	Day	11% 7% 2 6% 5% 6% 5% 5% 7% 9% 37%	2850
July	1st to 10th	Day	8% 4 2 5% 5% 6% 6% 5% 7% 11% 41%	4750
	11th to 20th	Day	7% 4 2 5% 4 4 5% 4 6% 8% 50%	4750
	21st to end	Day	5% 4 2 5% 4 4 5% 5% 7% 10% 50%	4905
August	1st to 10th	Day	8% 6% 2 7% 5% 4 4 4 5% 8% 45%	4324
	11th to 20th	Day	11% 5% 2 5% 4 4 4 4 7% 8% 46%	4041
	21st to end	Day	9% 6% 2 6% 4 3 3 3 6% 8% 49%	4532
September	1st to 10th	Day	11% 6% 2 4 3 3 4 4 5% 7% 51%	2322
	11th to 20th	Day	15% 7% 2 6% 4 4 4 3 5% 8% 42%	2090
	21st to end	Day	13% 7% 2 5% 4 4 4 3 6% 9% 42%	2090
October	1st to 10th	Day	10% 8% 3 6% 3 3 4 4 4 6% 49%	3299
	11th to 20th	Day	10% 10% 3 7% 4 4 5% 3 6% 9% 40%	2997
	21st to end	Day	12% 11% 4 8% 5% 5% 4 3 6% 8% 33%	3091
November	1st to 10th	Day	14% 13% 5% 11% 6% 4 4 3 5% 6% 29%	1631
	11th to 20th	Day	8% 13% 6% 15% 8% 5% 4 4 5% 6% 26%	1520
	21st to end	Day	9% 16% 5% 13% 8% 6% 5% 3 4 6% 26%	1373
December	1st to 10th	Day	8% 13% 5% 13% 8% 8% 6% 5% 6% 7% 21%	1330
	11th to 20th	Day	9% 13% 5% 15% 8% 6% 6% 4 5% 8% 18%	1683
	21st to end	Day	8% 10% 5% 10% 6% 6% 5% 4 6% 7% 32%	2442
January	1st to 10th	Night	6% 13% 5% 13% 7% 6% 7% 5% 7% 9% 23%	4737
	11th to 20th	Night	5% 10% 5% 15% 10% 9% 8% 6% 7% 8% 17%	4586
	21st to end	Night	8% 14% 6% 14% 8% 6% 5% 4 5% 6% 24%	4873
February	1st to 10th	Night	7% 12% 5% 11% 8% 7% 6% 6% 7% 6% 25%	2590
	11th to 20th	Night	6% 8% 4 9% 7% 7% 7% 5% 8% 8% 32%	2403
	21st to end	Night	7% 11% 4 9% 7% 5% 5% 4 7% 8% 31%	1909
March	1st to 10th	Night	8% 11% 5% 10% 8% 6% 6% 4 5% 7% 30%	3720
	11th to 20th	Night	7% 9% 4 9% 8% 4 5% 4 6% 8% 37%	3480
	21st to end	Night	7% 11% 6% 15% 7% 5% 5% 4 5% 5% 30%	3817
April	1st to 10th	Night	7% 8% 4 8% 5% 5% 5% 5% 6% 7% 40%	1861
	11th to 20th	Night	12% 12% 4 8% 5% 4 5% 5% 5% 7% 33%	1689
	21st to end	Night	14% 8% 4 7% 5% 5% 5% 3 5% 7% 37%	1710
May	1st to 10th	Night	21% 8% 3 6% 4 4 4 3 5% 7% 35%	2850
	11th to 20th	Night	14% 10% 3 7% 3 5% 4 3 4 6% 41%	2232
	21st to end	Night	16% 7% 3 5% 3 4 3 3 5% 7% 44%	2414
June	1st to 10th	Night	9% 5% 2 7% 5% 4 4 4 6% 8% 45%	1330
	11th to 20th	Night	12% 6% 2 6% 4 4 4 3 8% 8% 43%	1330
	21st to end	Night	10% 5% 1 5% 3 4 5% 3 8% 10% 47%	1330
July	1st to 10th	Night	8% 4 1 4 3 3 3 4 6% 10% 54%	2220
	11th to 20th	Night	5% 3 1 4 3 3 4 4 5% 9% 60%	2220
	21st to end	Night	3 5% 1 5% 4 4 5% 5% 8% 10% 51%	2657
August	1st to 10th	Night	5% 5% 1 7% 4 4 4 4 6% 7% 53%	2615
	11th to 20th	Night	8% 3 2 5% 4 4 5% 4 6% 9% 50%	2798
	21st to end	Night	11% 6% 2 5% 3 3 3 3 5% 7% 52%	3135
September	1st to 10th	Night	9% 5% 2 5% 3 3 3 4 5% 7% 55%	1856
	11th to 20th	Night	11% 5% 2 6% 3 4 4 3 6% 7% 50%	2090
	21st to end	Night	13% 8% 2 6% 4 4 4 3 5% 6% 45%	2090
October	1st to 10th	Night	11% 8% 3 6% 4 3 4 3 5% 7% 47%	3628
	11th to 20th	Night	9% 9% 2 6% 4 4 4 3 7% 9% 43%	3926
	21st to end	Night	7% 9% 3 9% 5% 5% 4 4 5% 7% 41%	4467
November	1st to 10th	Night	11% 11% 4 10% 6% 4 5% 4 6% 7% 31%	2546
	11th to 20th	Night	9% 14% 5% 11% 8% 6% 4 4 5% 7% 28%	2660
	21st to end	Night	9% 14% 4 11% 7% 5% 5% 3 6% 7% 29%	2806
December	1st to 10th	Night	7% 12% 5% 12% 8% 7% 6% 4 6% 7% 25%	2850
	11th to 20th	Night	9% 14% 6% 15% 8% 7% 5% 3 6% 7% 20%	3514
	21st to end	Night	9% 12% 4 11% 7% 6% 5% 3 5% 6% 32%	5225

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	59% 6% 15% 15% 4	2219
	11th to 20th	Day	64% 8% 11% 11% 5%	2383
	21st to end	Day	57% 6% 9% 21% 6%	2794
February	1st to 10th	Day	57% 6% 11% 18% 8% 1	1589
	11th to 20th	Day	53% 8% 12% 17% 9% 1	1673
	21st to end	Day	54% 7% 13% 17% 9% 1	1560
March	1st to 10th	Day	50% 9% 15% 19% 8%	3130
	11th to 20th	Day	54% 9% 13% 18% 6%	3480
	21st to end	Day	55% 8% 11% 19% 6%	3814
April	1st to 10th	Day	47% 7% 14% 23% 8% 1	2317
	11th to 20th	Day	52% 6% 13% 19% 9% 1	2442
	21st to end	Day	51% 7% 16% 17% 8% 1	2470
May	1st to 10th	Day	48% 7% 15% 20% 9% 1	4120
	11th to 20th	Day	46% 9% 13% 22% 9% 1	4659
	21st to end	Day	48% 8% 12% 23% 9% 1	5173
June	1st to 10th	Day	41% 9% 19% 20% 10% 1	2850
	11th to 20th	Day	43% 9% 15% 22% 9% 1	2850
	21st to end	Day	40% 11% 19% 24% 6% 1	2850
July	1st to 10th	Day	33% 11% 25% 26% 5%	4676
	11th to 20th	Day	28% 8% 21% 36% 7%	4669
	21st to end	Day	27% 8% 25% 31% 9% 1	4750
August	1st to 10th	Day	35% 8% 17% 26% 12% 1	4309
	11th to 20th	Day	33% 7% 19% 34% 7%	4080
	21st to end	Day	33% 6% 20% 32% 9%	4531
September	1st to 10th	Day	32% 6% 19% 30% 12% 1	2322
	11th to 20th	Day	40% 8% 17% 25% 9% 1	2090
	21st to end	Day	39% 7% 15% 30% 9%	2090
October	1st to 10th	Day	36% 5% 11% 35% 11% 1	3299
	11th to 20th	Day	40% 5% 11% 30% 13%	2997
	21st to end	Day	48% 6% 12% 25% 9%	3091
November	1st to 10th	Day	55% 8% 11% 17% 8% 1	1631
	11th to 20th	Day	58% 7% 15% 13% 6%	1520
	21st to end	Day	59% 8% 12% 15% 7%	1373
December	1st to 10th	Day	60% 8% 14% 13% 5%	1330
	11th to 20th	Day	62% 7% 11% 13% 6% 1	1680
	21st to end	Day	48% 7% 12% 20% 13%	2442
January	1st to 10th	Night	55% 9% 13% 16% 6%	4737
	11th to 20th	Night	61% 9% 11% 14% 5%	4586
	21st to end	Night	59% 7% 9% 19% 6%	4873
February	1st to 10th	Night	54% 7% 12% 16% 10% 1	2590
	11th to 20th	Night	46% 7% 15% 19% 12% 1	2404
	21st to end	Night	48% 6% 13% 21% 11% 1	1909
March	1st to 10th	Night	46% 10% 14% 21% 8%	3720
	11th to 20th	Night	42% 8% 16% 22% 12% 1	3480
	21st to end	Night	52% 9% 11% 19% 8% 1	3817
April	1st to 10th	Night	39% 7% 13% 24% 15% 2	1861
	11th to 20th	Night	50% 7% 11% 18% 13% 1	1689
	21st to end	Night	45% 6% 14% 21% 12% 1	1710
May	1st to 10th	Night	45% 8% 14% 24% 10% 1	2850
	11th to 20th	Night	40% 9% 14% 23% 10% 3	2233
	21st to end	Night	39% 7% 13% 30% 10%	2414
June	1st to 10th	Night	34% 9% 18% 27% 9% 2	1330
	11th to 20th	Night	37% 7% 18% 25% 12% 2	1330
	21st to end	Night	31% 10% 21% 32% 6% 1	1330
July	1st to 10th	Night	25% 10% 28% 29% 7% 1	2185
	11th to 20th	Night	21% 8% 18% 43% 11% 1	2178
	21st to end	Night	26% 7% 24% 33% 10% 1	2573
August	1st to 10th	Night	28% 7% 16% 32% 15% 1	2607
	11th to 20th	Night	28% 8% 21% 33% 9% 1	2825
	21st to end	Night	32% 6% 17% 34% 11% 1	3135
September	1st to 10th	Night	28% 7% 15% 34% 16% 2	1856
	11th to 20th	Night	33% 7% 19% 27% 13% 1	2090
	21st to end	Night	39% 6% 12% 30% 12% 1	2090
October	1st to 10th	Night	36% 6% 13% 29% 15% 1	3628
	11th to 20th	Night	38% 5% 13% 29% 15%	3926
	21st to end	Night	41% 6% 13% 31% 8%	4467
November	1st to 10th	Night	50% 8% 14% 18% 9% 2	2546
	11th to 20th	Night	56% 7% 14% 14% 8% 1	2660
	21st to end	Night	54% 8% 15% 17% 7%	2806
December	1st to 10th	Night	56% 7% 16% 14% 6%	2850
	11th to 20th	Night	61% 7% 15% 12% 4 1	3516
	21st to end	Night	51% 7% 10% 19% 12% 1	5225

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	11% 12% 37% 29% 10% 2	270
	11th to 20th	Day	10% 13% 41% 26% 10% 1	270
	21st to end	Day	15% 11% 38% 25% 10% 2	297
February	1st to 10th	Day	14% 15% 40% 24% 5% 2	270
	11th to 20th	Day	7% 17% 42% 25% 7% 1	270
	21st to end	Day	7% 9% 49% 26% 8%	225
March	1st to 10th	Day	14% 12% 35% 33% 5% 1	270
	11th to 20th	Day	17% 14% 30% 27% 10% 2	270
	21st to end	Day	13% 15% 31% 30% 9% 2	297
April	1st to 10th	Day	11% 20% 34% 25% 8% 2	497
	11th to 20th	Day	20% 13% 32% 25% 9% 1	640
	21st to end	Day	20% 13% 31% 25% 10% 2	650
May	1st to 10th	Day	16% 14% 28% 28% 12% 2	653
	11th to 20th	Day	19% 12% 30% 24% 12% 3	675
	21st to end	Day	20% 10% 25% 31% 14% 2	734
June	1st to 10th	Day	13% 12% 30% 26% 15% 5%	680
	11th to 20th	Day	15% 13% 35% 24% 11% 2	680
	21st to end	Day	13% 9% 29% 31% 15% 3	680
July	1st to 10th	Day	8% 6% 28% 30% 20% 8%	671
	11th to 20th	Day	11% 8% 30% 26% 19% 5%	668
	21st to end	Day	4 5% 28% 37% 19% 7%	739
August	1st to 10th	Day	7% 8% 29% 31% 19% 6%	676
	11th to 20th	Day	12% 5% 23% 33% 19% 7%	665
	21st to end	Day	11% 9% 27% 31% 17% 4	748
September	1st to 10th	Day	11% 10% 36% 27% 13% 3	532
	11th to 20th	Day	19% 11% 30% 27% 11% 1	300
	21st to end	Day	22% 10% 31% 26% 10% 1	300
October	1st to 10th	Day	20% 16% 27% 25% 12%	300
	11th to 20th	Day	15% 14% 42% 22% 6% 2	300
	21st to end	Day	21% 15% 36% 19% 8% 2	330
November	1st to 10th	Day	23% 13% 32% 23% 8% 1	282
	11th to 20th	Day	14% 15% 42% 22% 6%	270
	21st to end	Day	16% 17% 43% 20% 4	270
December	1st to 10th	Day	12% 13% 39% 27% 7% 2	270
	11th to 20th	Day	15% 15% 43% 23% 3 1	270
	21st to end	Day	11% 10% 39% 28% 9% 3	297
January	1st to 10th	Night	12% 13% 37% 29% 8% 1	950
	11th to 20th	Night	14% 12% 41% 28% 6%	950
	21st to end	Night	13% 13% 40% 25% 7% 1	1045
February	1st to 10th	Night	12% 12% 36% 31% 7% 2	950
	11th to 20th	Night	9% 11% 40% 29% 9% 2	929
	21st to end	Night	11% 11% 40% 28% 9% 1	653
March	1st to 10th	Night	13% 12% 33% 28% 11% 2	759
	11th to 20th	Night	9% 11% 41% 27% 10% 2	570
	21st to end	Night	15% 10% 29% 33% 10% 3	627
April	1st to 10th	Night	9% 11% 39% 30% 9% 1	570
	11th to 20th	Night	17% 8% 35% 30% 9%	563
	21st to end	Night	16% 8% 30% 34% 11% 1	570
May	1st to 10th	Night	17% 8% 32% 31% 11% 1	570
	11th to 20th	Night	16% 9% 31% 29% 15%	561
	21st to end	Night	20% 8% 28% 34% 10%	617
June	1st to 10th	Night	12% 8% 30% 37% 12% 1	570
	11th to 20th	Night	14% 6% 34% 30% 15%	570
	21st to end	Night	10% 6% 27% 39% 17% 1	570
July	1st to 10th	Night	7% 4 25% 40% 23% 2	555
	11th to 20th	Night	6% 5% 28% 40% 20% 1	552
	21st to end	Night	5% 5% 24% 45% 19% 3	624
August	1st to 10th	Night	8% 4 25% 43% 20% 1	567
	11th to 20th	Night	9% 5% 27% 37% 19% 4	564
	21st to end	Night	11% 5% 30% 37% 16% 1	627
September	1st to 10th	Night	11% 4 32% 34% 16% 2	570
	11th to 20th	Night	12% 9% 30% 37% 12% 1	570
	21st to end	Night	16% 8% 34% 29% 12% 1	570
October	1st to 10th	Night	20% 11% 32% 28% 8%	653
	11th to 20th	Night	18% 12% 33% 29% 9%	844
	21st to end	Night	17% 13% 37% 26% 8% 1	1045
November	1st to 10th	Night	16% 15% 35% 26% 8% 1	950
	11th to 20th	Night	14% 14% 40% 23% 7% 2	950
	21st to end	Night	18% 15% 40% 21% 5% 1	950
December	1st to 10th	Night	11% 13% 39% 28% 7% 1	950
	11th to 20th	Night	14% 15% 38% 25% 7% 1	950
	21st to end	Night	19% 9% 36% 27% 8% 1	1045

Page generated at 2024-11-03 01:11:13. Version ac07

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