Slater Creek Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Slater Creek Observatory clear sky chart from 2005-11-06 to 2024-12-09.

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	3 6% 2 6% 5% 4 5% 4 6% 8% 50%	105420
	Night	2 5% 2 6% 4 4 4 4 6% 8% 56%	103090
Transparency	Day	27% 7% 13% 22% 22% 9%	105167
	Night	23% 7% 14% 26% 23% 8%	102933
Seeing	Day	10% 17% 33% 25% 12% 2	15616
	Night	5% 12% 36% 33% 13% 1	25694

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	3 2 5% 5% 4 4 3 6% 8% 59%	2538
	11th to 20th	Day	1 3 2 9% 4 4 5% 3 6% 9% 55%	2704
	21st to end	Day	7% 3 8% 4 4 4 3 5% 8% 53%	3146
February	1st to 10th	Day	6% 2 7% 4 4 2 4 5% 7% 57%	1710
	11th to 20th	Day	3 2 4 4 3 4 3 6% 9% 60%	1834
	21st to end	Day	5% 3 6% 4 3 3 3 6% 7% 59%	1570
March	1st to 10th	Day	1 7% 4 7% 4 4 3 2 5% 6% 58%	3130
	11th to 20th	Day	1 10% 5% 11% 6% 5% 5% 4 6% 7% 40%	3485
	21st to end	Day	1 7% 3 6% 5% 4 4 4 7% 9% 51%	4036
April	1st to 10th	Day	2 7% 2 6% 5% 5% 4 4 6% 8% 49%	2280
	11th to 20th	Day	4 9% 3 9% 6% 5% 4 3 6% 7% 45%	2251
	21st to end	Day	4 10% 3 8% 5% 5% 5% 4 7% 7% 41%	2280
May	1st to 10th	Day	4 11% 3 8% 5% 4 4 4 5% 8% 43%	3926
	11th to 20th	Day	5% 8% 2 7% 5% 6% 5% 5% 8% 9% 39%	4345
	21st to end	Day	3 6% 2 5% 4 4 5% 5% 7% 9% 50%	4825
June	1st to 10th	Day	4 6% 2 6% 4 4 6% 4 9% 10% 45%	2660
	11th to 20th	Day	4 4 2 5% 4 4 5% 5% 8% 8% 51%	2660
	21st to end	Day	3 4 2 7% 5% 6% 6% 6% 8% 9% 44%	2660
July	1st to 10th	Day	4 4 2 6% 5% 5% 6% 5% 7% 8% 48%	4430
	11th to 20th	Day	5% 5% 3 8% 7% 5% 7% 5% 8% 10% 39%	4430
	21st to end	Day	6% 6% 3 7% 6% 6% 6% 5% 7% 7% 42%	4614
August	1st to 10th	Day	7% 6% 2 8% 6% 6% 7% 5% 8% 9% 34%	4070
	11th to 20th	Day	4 4 2 6% 6% 6% 7% 5% 8% 9% 44%	3726
	21st to end	Day	4 6% 2 6% 6% 6% 6% 6% 7% 9% 43%	4180
September	1st to 10th	Day	5% 5% 3 6% 5% 4 5% 4 5% 6% 50%	2280
	11th to 20th	Day	6% 4 2 5% 4 4 4 4 6% 6% 55%	2266
	21st to end	Day	5% 4 2 4 3 4 3 3 5% 6% 62%	2090
October	1st to 10th	Day	3 3 1 3 3 2 3 3 4 5% 72%	3175
	11th to 20th	Day	2 4 2 5% 4 4 4 4 6% 8% 57%	3150
	21st to end	Day	2 4 2 3 2 3 3 3 4 5% 69%	3377
November	1st to 10th	Day	1 4 2 4 2 2 4 3 5% 7% 67%	1763
	11th to 20th	Day	3 2 4 3 3 2 3 5% 7% 66%	1800
	21st to end	Day	4 2 6% 3 3 4 3 5% 8% 61%	1725
December	1st to 10th	Day	4 1 6% 3 3 4 3 5% 8% 63%	1584
	11th to 20th	Day	1 4 2 5% 4 3 3 3 7% 9% 58%	1926
	21st to end	Day	4 2 6% 5% 4 5% 4 6% 8% 54%	2794
January	1st to 10th	Night	4 2 9% 6% 4 4 3 5% 8% 56%	4417
	11th to 20th	Night	2 1 4 5% 4 3 4 6% 7% 64%	4293
	21st to end	Night	5% 3 7% 4 4 4 3 5% 8% 57%	4521
February	1st to 10th	Night	4 3 6% 4 3 3 3 6% 8% 60%	2470
	11th to 20th	Night	5% 2 6% 4 3 4 3 5% 8% 59%	2232
	21st to end	Night	5% 2 5% 3 3 3 4 5% 7% 64%	1884
March	1st to 10th	Night	1 8% 3 6% 3 3 4 3 5% 7% 58%	3734
	11th to 20th	Night	1 8% 4 9% 5% 4 3 3 6% 8% 48%	3494
	21st to end	Night	1 6% 3 6% 4 4 4 4 5% 9% 55%	3608
April	1st to 10th	Night	2 7% 2 6% 3 3 4 2 5% 7% 60%	1900
	11th to 20th	Night	3 9% 2 7% 5% 4 4 4 4 7% 51%	1877
	21st to end	Night	4 10% 3 5% 4 4 4 3 6% 7% 50%	1900
May	1st to 10th	Night	3 10% 2 6% 4 4 4 3 5% 7% 51%	3042
	11th to 20th	Night	6% 7% 3 6% 4 4 4 4 7% 8% 47%	2557
	21st to end	Night	3 4 2 6% 4 3 3 4 6% 7% 58%	2762
June	1st to 10th	Night	2 4 2 5% 3 4 5% 5% 7% 10% 54%	1520
	11th to 20th	Night	3 2 1 3 3 3 4 5% 8% 10% 59%	1520
	21st to end	Night	3 3 1 5% 4 5% 5% 5% 7% 10% 51%	1520
July	1st to 10th	Night	4 4 2 7% 5% 5% 4 5% 7% 7% 50%	2540
	11th to 20th	Night	3 4 2 5% 4 4 5% 5% 8% 13% 48%	2540
	21st to end	Night	4 3 1 6% 6% 6% 5% 5% 9% 9% 46%	2944
August	1st to 10th	Night	6% 6% 3 8% 6% 6% 6% 6% 9% 10% 34%	2868
	11th to 20th	Night	3 3 2 5% 5% 5% 6% 5% 8% 11% 46%	3113
	21st to end	Night	3 4 1 4 4 5% 7% 6% 9% 13% 44%	3487
September	1st to 10th	Night	5% 4 2 5% 4 5% 5% 5% 7% 9% 49%	1900
	11th to 20th	Night	4 4 1 4 3 4 3 4 6% 8% 59%	1913
	21st to end	Night	4 4 2 5% 3 4 3 3 5% 5% 62%	2090
October	1st to 10th	Night	2 3 1 3 2 2 3 3 4 5% 71%	3790
	11th to 20th	Night	2 4 2 5% 4 3 3 3 5% 7% 62%	3778
	21st to end	Night	2 3 1 4 2 2 2 3 4 5% 71%	4148
November	1st to 10th	Night	4 2 4 3 2 3 3 5% 7% 66%	2535
	11th to 20th	Night	3 1 3 4 3 4 3 4 7% 69%	2600
	21st to end	Night	1 5% 2 4 3 3 3 3 5% 7% 63%	2670
December	1st to 10th	Night	1 2 2 5% 3 3 3 3 5% 10% 63%	2779
	11th to 20th	Night	4 2 4 4 4 4 5% 7% 9% 55%	3271
	21st to end	Night	1 5% 3 7% 4 4 4 4 6% 7% 54%	4873

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	17% 7% 18% 28% 23% 8%	2539
	11th to 20th	Day	18% 8% 15% 30% 22% 6%	2704
	21st to end	Day	26% 6% 14% 29% 20% 5%	3146
February	1st to 10th	Day	24% 5% 16% 27% 20% 9%	1710
	11th to 20th	Day	19% 5% 13% 26% 29% 8%	1844
	21st to end	Day	23% 5% 10% 23% 26% 14%	1570
March	1st to 10th	Day	22% 6% 9% 21% 30% 12%	3130
	11th to 20th	Day	35% 8% 14% 27% 14% 3	3485
	21st to end	Day	23% 9% 16% 30% 19% 3	4036
April	1st to 10th	Day	28% 8% 14% 21% 20% 9%	2280
	11th to 20th	Day	35% 7% 11% 22% 18% 7%	2254
	21st to end	Day	35% 8% 13% 23% 17% 3	2280
May	1st to 10th	Day	32% 10% 12% 20% 16% 10%	3926
	11th to 20th	Day	33% 12% 16% 19% 16% 5%	4349
	21st to end	Day	21% 12% 15% 19% 23% 10%	4825
June	1st to 10th	Day	28% 11% 16% 19% 18% 8%	2660
	11th to 20th	Day	25% 9% 10% 17% 23% 16%	2660
	21st to end	Day	29% 10% 12% 20% 19% 10%	2660
July	1st to 10th	Day	29% 8% 8% 14% 21% 20%	4361
	11th to 20th	Day	35% 7% 12% 26% 14% 7%	4355
	21st to end	Day	35% 9% 11% 17% 13% 14%	4468
August	1st to 10th	Day	41% 8% 19% 16% 13% 3	4056
	11th to 20th	Day	33% 7% 15% 15% 18% 12%	3762
	21st to end	Day	34% 6% 15% 17% 21% 7%	4179
September	1st to 10th	Day	31% 7% 11% 18% 23% 11%	2280
	11th to 20th	Day	26% 6% 11% 19% 27% 12%	2266
	21st to end	Day	22% 6% 8% 23% 32% 9%	2090
October	1st to 10th	Day	14% 5% 7% 17% 36% 20%	3175
	11th to 20th	Day	24% 3 8% 32% 26% 8%	3150
	21st to end	Day	16% 4 6% 25% 40% 10%	3377
November	1st to 10th	Day	16% 3 12% 22% 33% 14%	1763
	11th to 20th	Day	15% 5% 9% 32% 29% 10%	1800
	21st to end	Day	20% 4 11% 25% 28% 12%	1725
December	1st to 10th	Day	18% 6% 16% 28% 24% 8%	1584
	11th to 20th	Day	19% 5% 16% 26% 26% 7%	1924
	21st to end	Day	20% 7% 16% 24% 24% 10%	2794
January	1st to 10th	Night	21% 7% 14% 29% 25% 4	4417
	11th to 20th	Night	13% 7% 13% 32% 26% 8%	4293
	21st to end	Night	23% 7% 14% 29% 22% 4	4521
February	1st to 10th	Night	22% 4 14% 31% 22% 7%	2470
	11th to 20th	Night	25% 5% 11% 27% 25% 7%	2232
	21st to end	Night	19% 4 10% 26% 29% 12%	1884
March	1st to 10th	Night	21% 8% 9% 20% 34% 6%	3734
	11th to 20th	Night	31% 7% 14% 27% 18% 2	3494
	21st to end	Night	22% 7% 17% 31% 21% 2	3608
April	1st to 10th	Night	23% 5% 14% 27% 24% 7%	1900
	11th to 20th	Night	30% 6% 12% 26% 19% 5%	1877
	21st to end	Night	31% 7% 15% 27% 16% 4	1900
May	1st to 10th	Night	27% 9% 14% 24% 15% 10%	3042
	11th to 20th	Night	31% 10% 16% 26% 14% 4	2558
	21st to end	Night	23% 9% 14% 22% 24% 8%	2762
June	1st to 10th	Night	23% 9% 22% 22% 14% 10%	1520
	11th to 20th	Night	17% 9% 14% 20% 22% 17%	1520
	21st to end	Night	25% 9% 14% 21% 20% 10%	1520
July	1st to 10th	Night	29% 9% 9% 19% 22% 12%	2500
	11th to 20th	Night	25% 7% 19% 34% 12% 4	2492
	21st to end	Night	28% 10% 16% 23% 8% 14%	2852
August	1st to 10th	Night	42% 8% 21% 16% 9% 4	2859
	11th to 20th	Night	29% 9% 22% 18% 17% 5%	3143
	21st to end	Night	27% 8% 24% 21% 17% 2	3487
September	1st to 10th	Night	29% 8% 13% 22% 20% 8%	1900
	11th to 20th	Night	22% 6% 14% 22% 24% 13%	1913
	21st to end	Night	23% 6% 10% 25% 29% 8%	2090
October	1st to 10th	Night	16% 5% 9% 24% 34% 12%	3790
	11th to 20th	Night	21% 3 12% 32% 24% 8%	3778
	21st to end	Night	15% 3 6% 29% 36% 10%	4148
November	1st to 10th	Night	15% 5% 12% 26% 29% 13%	2535
	11th to 20th	Night	15% 5% 9% 30% 30% 11%	2600
	21st to end	Night	20% 4 10% 24% 30% 11%	2670
December	1st to 10th	Night	18% 6% 15% 28% 25% 8%	2779
	11th to 20th	Night	19% 5% 17% 25% 28% 6%	3272
	21st to end	Night	22% 7% 15% 23% 24% 9%	4873

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	10% 22% 34% 24% 10%	270
	11th to 20th	Day	14% 23% 39% 21% 3 1	270
	21st to end	Day	4 22% 44% 22% 8% 1	297
February	1st to 10th	Day	11% 35% 37% 15% 1 1	270
	11th to 20th	Day	11% 32% 42% 11% 4	270
	21st to end	Day	18% 31% 36% 12% 2	225
March	1st to 10th	Day	15% 23% 37% 20% 6%	270
	11th to 20th	Day	13% 26% 36% 18% 7%	455
	21st to end	Day	18% 32% 35% 13% 2	506
April	1st to 10th	Day	15% 32% 35% 15% 3 1	460
	11th to 20th	Day	20% 33% 32% 13% 2 1	452
	21st to end	Day	17% 32% 31% 16% 3 1	460
May	1st to 10th	Day	15% 26% 35% 18% 5% 1	537
	11th to 20th	Day	11% 17% 33% 29% 10% 2	675
	21st to end	Day	9% 19% 29% 28% 13% 2	734
June	1st to 10th	Day	5% 14% 30% 29% 19% 3	680
	11th to 20th	Day	9% 12% 34% 28% 14% 3	680
	21st to end	Day	3 10% 37% 28% 17% 4	680
July	1st to 10th	Day	6% 6% 24% 33% 26% 5%	671
	11th to 20th	Day	7% 3 20% 38% 26% 7%	668
	21st to end	Day	10% 3 21% 33% 27% 6%	626
August	1st to 10th	Day	12% 5% 27% 35% 17% 4	487
	11th to 20th	Day	7% 6% 30% 35% 17% 6%	477
	21st to end	Day	9% 6% 33% 32% 16% 3	539
September	1st to 10th	Day	8% 10% 28% 32% 18% 5%	490
	11th to 20th	Day	8% 11% 38% 28% 13% 2	476
	21st to end	Day	7% 13% 22% 33% 22% 4	300
October	1st to 10th	Day	8% 11% 29% 26% 19% 6%	300
	11th to 20th	Day	8% 20% 32% 23% 15% 3	300
	21st to end	Day	11% 21% 34% 23% 10% 1	330
November	1st to 10th	Day	12% 18% 36% 22% 10% 2	300
	11th to 20th	Day	10% 17% 39% 25% 8% 1	300
	21st to end	Day	7% 19% 44% 22% 8% 1	300
December	1st to 10th	Day	9% 22% 38% 22% 9% 1	294
	11th to 20th	Day	7% 23% 49% 15% 6%	270
	21st to end	Day	11% 29% 37% 17% 5% 1	297
January	1st to 10th	Night	4 19% 39% 28% 9% 1	950
	11th to 20th	Night	4 23% 42% 22% 7% 1	865
	21st to end	Night	2 13% 49% 30% 6% 1	836
February	1st to 10th	Night	4 17% 55% 20% 4	760
	11th to 20th	Night	4 18% 50% 25% 3	744
	21st to end	Night	3 23% 49% 23% 2	628
March	1st to 10th	Night	3 17% 47% 28% 4	760
	11th to 20th	Night	5% 13% 40% 35% 8%	760
	21st to end	Night	5% 17% 47% 27% 4	706
April	1st to 10th	Night	8% 19% 42% 28% 3	570
	11th to 20th	Night	9% 19% 38% 29% 6% 1	563
	21st to end	Night	10% 15% 39% 29% 7%	570
May	1st to 10th	Night	11% 11% 35% 36% 7% 1	570
	11th to 20th	Night	9% 9% 30% 40% 12% 1	561
	21st to end	Night	6% 11% 34% 34% 14% 1	617
June	1st to 10th	Night	5% 5% 26% 44% 18% 3	570
	11th to 20th	Night	4 6% 30% 46% 14% 1	570
	21st to end	Night	5% 3 21% 45% 25% 2	570
July	1st to 10th	Night	5% 3 15% 44% 31% 2	555
	11th to 20th	Night	6% 1 12% 43% 35% 3	552
	21st to end	Night	6% 1 10% 40% 39% 4	624
August	1st to 10th	Night	8% 3 12% 43% 31% 3	567
	11th to 20th	Night	6% 2 15% 45% 29% 3	564
	21st to end	Night	6% 3 16% 41% 31% 3	627
September	1st to 10th	Night	6% 2 19% 42% 26% 4	570
	11th to 20th	Night	6% 3 23% 44% 21% 3	570
	21st to end	Night	5% 7% 29% 39% 18% 2	570
October	1st to 10th	Night	5% 8% 34% 39% 14% 2	750
	11th to 20th	Night	3 7% 39% 35% 14% 3	760
	21st to end	Night	6% 9% 38% 32% 12% 2	852
November	1st to 10th	Night	4 12% 42% 32% 9% 1	975
	11th to 20th	Night	4 16% 43% 29% 7% 1	1000
	21st to end	Night	5% 14% 41% 32% 8%	1000
December	1st to 10th	Night	3 19% 40% 31% 7%	993
	11th to 20th	Night	4 17% 48% 24% 6%	950
	21st to end	Night	6% 22% 44% 23% 5%	1045

Page generated at 2024-12-06 01:54:49. Version ac07

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