Scenic
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Scenic clear sky chart from 2005-11-06 to 2024-10-20.

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	8% 6% 2 5% 4 4 4 4 6% 8% 51%	101290
	Night	7% 6% 2 6% 4 4 4 4 6% 7% 49%	97593
Transparency	Day	30% 7% 15% 27% 17% 4	101034
	Night	32% 7% 15% 26% 17% 4	97439
Seeing	Day	11% 7% 26% 33% 19% 4	15864
	Night	10% 7% 31% 40% 11%	25773

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 6% 2 10% 5% 5% 4 4 6% 8% 46%	2538
	11th to 20th	Day	3 8% 4 10% 5% 3 3 4 6% 9% 45%	2540
	21st to end	Day	3 6% 2 7% 5% 5% 5% 4 6% 7% 50%	2794
February	1st to 10th	Day	7% 11% 4 8% 7% 5% 4 4 6% 6% 39%	1679
	11th to 20th	Day	6% 9% 3 8% 5% 4 4 4 6% 7% 45%	1849
	21st to end	Day	5% 8% 3 7% 5% 4 5% 4 7% 7% 45%	1570
March	1st to 10th	Day	6% 6% 3 5% 4 4 4 3 5% 8% 53%	3130
	11th to 20th	Day	7% 5% 1 4 3 3 4 3 5% 8% 57%	3253
	21st to end	Day	15% 10% 3 9% 4 4 4 3 6% 7% 34%	4133
April	1st to 10th	Day	13% 8% 3 4 5% 3 4 4 5% 8% 44%	2280
	11th to 20th	Day	13% 7% 3 7% 4 4 4 4 6% 8% 39%	2251
	21st to end	Day	14% 6% 2 5% 4 4 4 4 5% 8% 43%	2453
May	1st to 10th	Day	15% 7% 3 7% 5% 4 4 4 5% 7% 39%	4120
	11th to 20th	Day	9% 5% 2 5% 4 4 4 4 6% 8% 48%	4375
	21st to end	Day	13% 7% 2 5% 3 4 5% 4 6% 8% 42%	4825
June	1st to 10th	Day	9% 4 1 4 3 4 4 4 6% 10% 51%	2660
	11th to 20th	Day	9% 3 2 4 4 3 5% 4 7% 9% 50%	2660
	21st to end	Day	4 3 1 3 3 3 4 4 7% 8% 61%	2660
July	1st to 10th	Day	4 3 2 4 4 4 4 4 7% 9% 54%	4430
	11th to 20th	Day	3 2 1 4 3 3 4 4 7% 11% 58%	4430
	21st to end	Day	3 2 1 3 3 4 4 4 6% 8% 61%	4802
August	1st to 10th	Day	5% 5% 2 5% 4 3 5% 4 7% 10% 51%	4365
	11th to 20th	Day	6% 4 2 5% 4 4 4 4 7% 10% 52%	3917
	21st to end	Day	5% 3 1 4 3 3 3 3 6% 7% 63%	4180
September	1st to 10th	Day	7% 3 1 3 3 3 3 2 4 7% 64%	2280
	11th to 20th	Day	8% 3 1 3 3 3 3 3 5% 6% 63%	2161
	21st to end	Day	10% 3 1 3 2 2 2 3 4 7% 63%	2090
October	1st to 10th	Day	12% 5% 2 4 3 3 3 3 4 7% 54%	2051
	11th to 20th	Day	10% 5% 2 5% 4 3 4 3 4 6% 55%	1822
	21st to end	Day	8% 5% 1 5% 4 4 5% 4 6% 6% 52%	1782
November	1st to 10th	Day	5% 6% 2 6% 3 4 3 4 6% 9% 52%	1673
	11th to 20th	Day	6% 5% 2 5% 5% 4 4 3 6% 7% 53%	1710
	21st to end	Day	5% 8% 2 5% 4 4 3 4 5% 7% 53%	1587
December	1st to 10th	Day	5% 9% 3 8% 4 3 4 4 7% 6% 48%	1520
	11th to 20th	Day	4 7% 2 5% 4 3 4 4 6% 9% 52%	1926
	21st to end	Day	10% 12% 3 6% 4 4 4 3 4 5% 45%	2794
January	1st to 10th	Night	5% 8% 3 10% 5% 4 4 4 5% 7% 45%	4417
	11th to 20th	Night	4 6% 3 9% 7% 6% 5% 4 5% 6% 45%	4430
	21st to end	Night	3 6% 3 8% 5% 4 4 4 6% 7% 51%	4873
February	1st to 10th	Night	8% 12% 4 8% 4 4 4 4 5% 7% 40%	2513
	11th to 20th	Night	4 10% 3 8% 6% 5% 5% 4 6% 7% 42%	2218
	21st to end	Night	6% 9% 4 6% 5% 3 4 4 6% 7% 46%	1884
March	1st to 10th	Night	8% 10% 3 7% 4 3 4 3 5% 6% 46%	3734
	11th to 20th	Night	6% 6% 2 4 3 4 3 4 6% 10% 52%	3714
	21st to end	Night	12% 10% 4 8% 4 4 4 4 6% 8% 36%	3493
April	1st to 10th	Night	14% 7% 2 5% 3 5% 4 4 6% 8% 42%	1900
	11th to 20th	Night	14% 7% 3 7% 4 4 3 4 6% 7% 42%	1877
	21st to end	Night	14% 8% 2 5% 4 4 4 4 6% 7% 43%	1725
May	1st to 10th	Night	13% 6% 2 7% 4 5% 5% 4 7% 8% 39%	2850
	11th to 20th	Night	8% 4 1 4 3 3 4 4 8% 9% 52%	2527
	21st to end	Night	15% 6% 2 6% 4 4 4 5% 5% 8% 42%	2762
June	1st to 10th	Night	9% 4 2 4 4 3 4 3 7% 9% 50%	1520
	11th to 20th	Night	10% 3 1 5% 5% 4 4 4 7% 7% 49%	1520
	21st to end	Night	6% 3 1 4 3 4 4 5% 7% 7% 57%	1520
July	1st to 10th	Night	7% 3 1 5% 4 3 5% 4 6% 8% 55%	2540
	11th to 20th	Night	3 3 1 4 3 4 5% 4 6% 8% 59%	2540
	21st to end	Night	3 3 1 4 3 3 4 4 6% 8% 60%	2761
August	1st to 10th	Night	5% 4 2 6% 4 5% 6% 5% 7% 9% 48%	2571
	11th to 20th	Night	6% 5% 2 6% 4 4 5% 4 6% 9% 51%	2919
	21st to end	Night	3 4 1 6% 4 4 4 4 5% 8% 57%	3487
September	1st to 10th	Night	7% 3 1 3 3 3 4 2 5% 5% 64%	1900
	11th to 20th	Night	7% 3 1 3 3 3 3 4 5% 7% 62%	2017
	21st to end	Night	10% 4 1 4 3 3 3 2 3 5% 63%	2090
October	1st to 10th	Night	13% 6% 2 4 3 3 3 3 5% 6% 52%	2127
	11th to 20th	Night	10% 4 2 5% 3 3 4 3 5% 6% 54%	2323
	21st to end	Night	10% 7% 1 5% 3 3 3 3 5% 7% 52%	2574
November	1st to 10th	Night	8% 6% 2 5% 4 4 4 3 6% 8% 49%	2405
	11th to 20th	Night	6% 8% 3 7% 4 3 4 4 5% 6% 51%	2470
	21st to end	Night	6% 7% 2 5% 3 4 4 4 6% 8% 52%	2588
December	1st to 10th	Night	5% 9% 3 6% 4 4 4 4 5% 7% 49%	2660
	11th to 20th	Night	4 6% 2 6% 4 4 5% 4 5% 7% 52%	3271
	21st to end	Night	9% 12% 3 6% 4 3 4 3 5% 7% 43%	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	33% 9% 18% 27% 12% 1	2539
	11th to 20th	Day	35% 8% 17% 27% 11% 3	2540
	21st to end	Day	28% 9% 20% 29% 13% 1	2794
February	1st to 10th	Day	44% 8% 13% 21% 12% 2	1679
	11th to 20th	Day	39% 6% 18% 20% 13% 4	1859
	21st to end	Day	35% 7% 16% 27% 12% 3	1570
March	1st to 10th	Day	28% 6% 12% 27% 23% 5%	3130
	11th to 20th	Day	25% 7% 17% 39% 12% 1	3253
	21st to end	Day	46% 9% 20% 19% 6%	4133
April	1st to 10th	Day	37% 7% 16% 28% 10% 3	2280
	11th to 20th	Day	40% 7% 15% 22% 14% 2	2254
	21st to end	Day	38% 8% 17% 27% 10%	2453
May	1st to 10th	Day	41% 8% 14% 24% 11% 2	4120
	11th to 20th	Day	30% 8% 16% 29% 13% 3	4379
	21st to end	Day	36% 9% 16% 26% 11% 1	4825
June	1st to 10th	Day	27% 8% 21% 27% 14% 2	2660
	11th to 20th	Day	27% 7% 18% 26% 17% 4	2660
	21st to end	Day	19% 7% 13% 33% 22% 6%	2660
July	1st to 10th	Day	24% 6% 13% 31% 24% 3	4361
	11th to 20th	Day	19% 5% 12% 31% 23% 9%	4355
	21st to end	Day	17% 5% 12% 25% 28% 12%	4651
August	1st to 10th	Day	26% 6% 18% 22% 22% 6%	4350
	11th to 20th	Day	27% 7% 15% 29% 17% 5%	3956
	21st to end	Day	20% 4 11% 25% 26% 13%	4179
September	1st to 10th	Day	21% 4 9% 28% 27% 11%	2280
	11th to 20th	Day	22% 5% 11% 28% 25% 9%	2161
	21st to end	Day	22% 4 9% 34% 27% 4	2090
October	1st to 10th	Day	31% 6% 12% 23% 23% 5%	2051
	11th to 20th	Day	29% 5% 10% 30% 20% 5%	1822
	21st to end	Day	30% 7% 16% 28% 15% 5%	1782
November	1st to 10th	Day	29% 5% 14% 26% 19% 6%	1673
	11th to 20th	Day	28% 6% 13% 29% 20% 4	1710
	21st to end	Day	30% 5% 15% 31% 15% 4	1587
December	1st to 10th	Day	34% 6% 15% 27% 16% 2	1520
	11th to 20th	Day	27% 7% 21% 33% 11% 1	1924
	21st to end	Day	41% 5% 10% 30% 12% 1	2794
January	1st to 10th	Night	37% 7% 12% 32% 10% 1	4417
	11th to 20th	Night	38% 8% 14% 26% 13% 1	4430
	21st to end	Night	30% 7% 20% 28% 14% 2	4873
February	1st to 10th	Night	43% 7% 14% 22% 13% 1	2513
	11th to 20th	Night	40% 6% 14% 25% 12% 4	2218
	21st to end	Night	35% 6% 15% 26% 13% 5%	1884
March	1st to 10th	Night	35% 7% 12% 24% 21% 1	3734
	11th to 20th	Night	26% 7% 18% 30% 17% 1	3714
	21st to end	Night	44% 9% 20% 20% 6% 1	3493
April	1st to 10th	Night	38% 8% 15% 25% 12% 2	1900
	11th to 20th	Night	40% 7% 13% 24% 14% 3	1877
	21st to end	Night	39% 8% 15% 25% 13% 1	1725
May	1st to 10th	Night	38% 10% 14% 23% 12% 3	2850
	11th to 20th	Night	24% 8% 18% 37% 10% 2	2528
	21st to end	Night	38% 8% 14% 27% 12% 1	2762
June	1st to 10th	Night	29% 9% 19% 26% 15% 2	1520
	11th to 20th	Night	30% 9% 20% 23% 15% 3	1520
	21st to end	Night	23% 7% 16% 29% 20% 6%	1520
July	1st to 10th	Night	26% 5% 17% 23% 24% 5%	2500
	11th to 20th	Night	21% 5% 14% 30% 22% 7%	2492
	21st to end	Night	20% 6% 13% 27% 26% 8%	2674
August	1st to 10th	Night	29% 8% 17% 21% 19% 6%	2563
	11th to 20th	Night	30% 6% 17% 22% 21% 3	2946
	21st to end	Night	24% 6% 13% 23% 25% 9%	3487
September	1st to 10th	Night	22% 4 10% 28% 28% 9%	1900
	11th to 20th	Night	22% 5% 14% 26% 27% 7%	2017
	21st to end	Night	25% 4 8% 29% 26% 8%	2090
October	1st to 10th	Night	33% 6% 11% 23% 20% 7%	2127
	11th to 20th	Night	30% 5% 11% 27% 22% 7%	2323
	21st to end	Night	32% 6% 15% 23% 19% 6%	2574
November	1st to 10th	Night	30% 6% 15% 24% 19% 6%	2405
	11th to 20th	Night	32% 5% 13% 25% 19% 5%	2470
	21st to end	Night	29% 6% 16% 26% 20% 3	2588
December	1st to 10th	Night	33% 6% 14% 27% 17% 2	2660
	11th to 20th	Night	28% 7% 15% 35% 13% 1	3272
	21st to end	Night	40% 5% 13% 28% 12% 2	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	7% 5% 26% 37% 20% 5%	270
	11th to 20th	Day	14% 5% 29% 37% 13% 2	270
	21st to end	Day	7% 8% 39% 32% 13% 1	297
February	1st to 10th	Day	13% 10% 34% 37% 7%	270
	11th to 20th	Day	12% 8% 37% 34% 9%	270
	21st to end	Day	8% 12% 40% 31% 8% 1	225
March	1st to 10th	Day	10% 13% 31% 32% 12% 2	270
	11th to 20th	Day	11% 8% 33% 30% 16% 3	270
	21st to end	Day	19% 11% 28% 26% 13% 2	487
April	1st to 10th	Day	17% 12% 32% 29% 10%	460
	11th to 20th	Day	19% 16% 31% 25% 8% 1	452
	21st to end	Day	18% 10% 23% 33% 15% 1	633
May	1st to 10th	Day	16% 10% 26% 28% 17% 3	653
	11th to 20th	Day	20% 6% 22% 30% 17% 4	675
	21st to end	Day	15% 9% 27% 28% 16% 4	734
June	1st to 10th	Day	6% 6% 22% 33% 24% 9%	680
	11th to 20th	Day	10% 6% 30% 35% 16% 3	680
	21st to end	Day	6% 5% 25% 36% 23% 4	680
July	1st to 10th	Day	5% 3 20% 39% 28% 5%	671
	11th to 20th	Day	5% 2 21% 43% 26% 3	668
	21st to end	Day	5% 2 19% 40% 29% 4	739
August	1st to 10th	Day	6% 3 20% 42% 26% 4	676
	11th to 20th	Day	6% 4 22% 35% 26% 7%	593
	21st to end	Day	5% 6% 20% 34% 28% 8%	539
September	1st to 10th	Day	7% 4 24% 32% 27% 6%	490
	11th to 20th	Day	9% 4 19% 32% 29% 8%	371
	21st to end	Day	12% 8% 26% 29% 19% 7%	300
October	1st to 10th	Day	17% 6% 22% 26% 18% 11%	300
	11th to 20th	Day	13% 12% 32% 26% 14% 2	297
	21st to end	Day	13% 14% 30% 26% 14% 3	297
November	1st to 10th	Day	10% 10% 34% 29% 14% 3	270
	11th to 20th	Day	10% 7% 33% 34% 13% 2	270
	21st to end	Day	13% 7% 29% 39% 10% 2	270
December	1st to 10th	Day	8% 10% 34% 33% 13% 2	270
	11th to 20th	Day	10% 8% 37% 34% 10% 1	270
	21st to end	Day	14% 10% 33% 28% 13% 2	297
January	1st to 10th	Night	7% 9% 32% 38% 13% 1	950
	11th to 20th	Night	9% 11% 33% 37% 9% 1	950
	21st to end	Night	10% 8% 35% 39% 8%	1045
February	1st to 10th	Night	13% 8% 38% 34% 7%	822
	11th to 20th	Night	8% 6% 37% 40% 8%	744
	21st to end	Night	10% 6% 39% 37% 8%	628
March	1st to 10th	Night	12% 8% 33% 39% 8%	760
	11th to 20th	Night	10% 5% 32% 41% 11% 1	713
	21st to end	Night	16% 10% 27% 37% 9%	627
April	1st to 10th	Night	16% 8% 34% 36% 6%	570
	11th to 20th	Night	16% 10% 37% 32% 5%	563
	21st to end	Night	16% 10% 26% 36% 11% 1	570
May	1st to 10th	Night	13% 8% 29% 36% 13% 1	570
	11th to 20th	Night	17% 6% 25% 37% 14%	561
	21st to end	Night	14% 7% 34% 34% 10%	617
June	1st to 10th	Night	9% 7% 28% 41% 14% 1	570
	11th to 20th	Night	11% 5% 36% 40% 8% 1	570
	21st to end	Night	5% 6% 28% 48% 12%	570
July	1st to 10th	Night	6% 3 26% 45% 19% 1	555
	11th to 20th	Night	5% 3 25% 51% 16%	552
	21st to end	Night	4 2 24% 54% 17%	624
August	1st to 10th	Night	6% 2 23% 53% 16%	567
	11th to 20th	Night	5% 3 25% 47% 19%	564
	21st to end	Night	3 5% 26% 50% 17%	627
September	1st to 10th	Night	7% 4 26% 45% 16% 1	570
	11th to 20th	Night	8% 4 26% 44% 18% 1	570
	21st to end	Night	11% 6% 28% 41% 14%	570
October	1st to 10th	Night	17% 6% 24% 36% 16%	607
	11th to 20th	Night	12% 6% 30% 38% 13%	807
	21st to end	Night	15% 7% 29% 38% 11% 1	990
November	1st to 10th	Night	11% 5% 34% 41% 9% 1	925
	11th to 20th	Night	10% 7% 34% 40% 9%	950
	21st to end	Night	9% 7% 33% 42% 9%	950
December	1st to 10th	Night	9% 8% 39% 36% 8%	950
	11th to 20th	Night	9% 6% 35% 42% 9%	950
	21st to end	Night	14% 9% 31% 36% 9%	1045

Page generated at 2024-10-17 11:09:44. Version ac07

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