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 2025-03-12.

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	7% 6% 2 6% 4 4 4 4 6% 8% 51%	112624
	Night	7% 7% 2 6% 4 4 4 4 6% 7% 50%	115169
Transparency	Day	30% 6% 14% 28% 17% 5%	112368
	Night	32% 6% 14% 26% 18% 4	115015
Seeing	Day	11% 7% 27% 33% 19% 4	16293
	Night	10% 7% 31% 40% 11%	26451

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 8% 4 12% 7% 6% 5% 4 5% 8% 39%	3638
	11th to 20th	Day	2 8% 5% 12% 5% 4 4 3 5% 7% 44%	3640
	21st to end	Day	2 5% 2 7% 5% 5% 4 4 5% 7% 54%	4004
February	1st to 10th	Day	7% 11% 4 8% 7% 4 4 4 6% 6% 39%	1768
	11th to 20th	Day	6% 10% 4 8% 5% 4 4 4 6% 7% 44%	1949
	21st to end	Day	5% 8% 3 7% 5% 4 5% 4 7% 7% 46%	1650
March	1st to 10th	Day	6% 7% 3 6% 4 4 4 3 5% 8% 53%	3230
	11th to 20th	Day	7% 5% 1 4 3 3 4 3 5% 8% 57%	3263
	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	7% 3 1 3 2 2 2 2 3 5% 71%	3405
	11th to 20th	Day	8% 4 2 3 3 3 3 2 4 7% 61%	3031
	21st to end	Day	10% 6% 2 6% 4 4 4 4 6% 6% 49%	3091
November	1st to 10th	Day	6% 6% 2 6% 3 4 3 4 6% 9% 52%	1763
	11th to 20th	Day	5% 5% 2 5% 5% 4 4 3 6% 7% 54%	1800
	21st to end	Day	5% 8% 3 5% 4 4 3 4 5% 7% 52%	1670
December	1st to 10th	Day	3 8% 3 8% 4 3 4 3 6% 7% 50%	2620
	11th to 20th	Day	3 7% 2 7% 4 4 5% 4 6% 8% 51%	3026
	21st to end	Day	8% 11% 3 7% 4 4 4 3 4 6% 47%	4004
January	1st to 10th	Night	6% 11% 4 11% 6% 4 3 4 4 5% 41%	6327
	11th to 20th	Night	3 8% 3 11% 6% 5% 5% 3 4 5% 46%	6340
	21st to end	Night	2 5% 3 8% 5% 4 4 3 5% 6% 56%	6974
February	1st to 10th	Night	8% 12% 4 8% 5% 4 4 4 6% 7% 39%	2645
	11th to 20th	Night	4 10% 4 9% 6% 5% 5% 4 6% 6% 41%	2338
	21st to end	Night	6% 9% 3 6% 5% 3 4 4 6% 7% 48%	1980
March	1st to 10th	Night	8% 10% 3 7% 4 3 4 3 5% 6% 47%	3854
	11th to 20th	Night	6% 6% 2 4 3 4 3 4 6% 10% 52%	3732
	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	8% 3 1 2 2 2 2 2 3 4 70%	3543
	11th to 20th	Night	8% 4 2 4 3 3 4 3 5% 7% 57%	3865
	21st to end	Night	10% 6% 1 5% 3 4 4 3 5% 8% 51%	4467
November	1st to 10th	Night	8% 6% 2 5% 4 3 4 3 6% 8% 49%	2535
	11th to 20th	Night	6% 7% 3 7% 4 3 4 4 5% 6% 51%	2600
	21st to end	Night	5% 7% 2 5% 4 4 5% 4 6% 8% 52%	2725
December	1st to 10th	Night	3 7% 2 6% 4 5% 4 4 6% 8% 51%	4570
	11th to 20th	Night	3 7% 2 6% 5% 5% 5% 4 6% 8% 47%	5181
	21st to end	Night	8% 11% 3 7% 5% 4 4 3 6% 7% 42%	6974

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	42% 7% 15% 26% 9% 1	3639
	11th to 20th	Day	39% 6% 15% 23% 15% 2	3640
	21st to end	Day	26% 7% 15% 34% 14% 3	4004
February	1st to 10th	Day	44% 8% 13% 20% 13% 2	1768
	11th to 20th	Day	39% 6% 17% 19% 15% 4	1959
	21st to end	Day	34% 7% 16% 27% 13% 3	1650
March	1st to 10th	Day	28% 6% 12% 27% 22% 5%	3230
	11th to 20th	Day	25% 7% 17% 39% 12% 1	3263
	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	19% 3 9% 20% 31% 17%	3405
	11th to 20th	Day	25% 4 11% 37% 21% 3	3031
	21st to end	Day	34% 5% 13% 29% 15% 4	3091
November	1st to 10th	Day	29% 5% 14% 26% 20% 6%	1763
	11th to 20th	Day	28% 6% 13% 28% 21% 5%	1800
	21st to end	Day	31% 5% 15% 32% 14% 4	1670
December	1st to 10th	Day	33% 5% 18% 28% 16% 1	2620
	11th to 20th	Day	29% 6% 21% 30% 13% 1	3024
	21st to end	Day	38% 4 9% 35% 13% 1	4004
January	1st to 10th	Night	45% 6% 10% 27% 11% 1	6327
	11th to 20th	Night	39% 6% 13% 23% 18% 1	6340
	21st to end	Night	28% 5% 15% 29% 21% 2	6974
February	1st to 10th	Night	44% 7% 14% 21% 13% 1	2645
	11th to 20th	Night	41% 6% 14% 24% 12% 3	2338
	21st to end	Night	33% 6% 15% 27% 14% 5%	1980
March	1st to 10th	Night	35% 6% 11% 25% 21% 1	3854
	11th to 20th	Night	26% 7% 18% 30% 17% 1	3732
	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	20% 3 7% 20% 30% 20%	3543
	11th to 20th	Night	26% 5% 11% 32% 22% 4	3865
	21st to end	Night	32% 4 12% 26% 19% 7%	4467
November	1st to 10th	Night	31% 6% 14% 24% 19% 6%	2535
	11th to 20th	Night	32% 5% 13% 25% 20% 5%	2600
	21st to end	Night	30% 6% 16% 27% 19% 3	2725
December	1st to 10th	Night	31% 5% 18% 28% 17% 2	4570
	11th to 20th	Night	33% 7% 17% 31% 11% 2	5182
	21st to end	Night	41% 4 10% 30% 13% 1	6974

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% 6% 25% 36% 21% 5%	300
	11th to 20th	Day	13% 6% 30% 38% 12% 2	300
	21st to end	Day	7% 9% 39% 33% 12% 1	330
February	1st to 10th	Day	13% 11% 34% 35% 6%	300
	11th to 20th	Day	12% 8% 38% 33% 9%	300
	21st to end	Day	7% 13% 41% 29% 10% 1	249
March	1st to 10th	Day	10% 13% 31% 32% 13% 2	300
	11th to 20th	Day	11% 8% 34% 30% 15% 3	273
	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	14% 11% 32% 27% 14% 2	300
	21st to end	Day	14% 15% 29% 26% 14% 2	330
November	1st to 10th	Day	11% 10% 35% 29% 14% 2	300
	11th to 20th	Day	10% 9% 35% 32% 12% 2	300
	21st to end	Day	12% 7% 29% 39% 12% 2	300
December	1st to 10th	Day	8% 11% 34% 33% 13% 2	300
	11th to 20th	Day	10% 8% 37% 34% 10% 1	300
	21st to end	Day	13% 9% 33% 30% 13% 2	330
January	1st to 10th	Night	8% 8% 32% 38% 12% 1	1000
	11th to 20th	Night	9% 11% 35% 37% 9% 1	1000
	21st to end	Night	9% 8% 36% 38% 8%	1100
February	1st to 10th	Night	13% 8% 38% 33% 7%	865
	11th to 20th	Night	8% 6% 38% 40% 8%	784
	21st to end	Night	10% 6% 39% 37% 7%	660
March	1st to 10th	Night	12% 8% 33% 39% 8%	800
	11th to 20th	Night	10% 5% 32% 41% 11% 1	719
	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% 31% 38% 14%	809
	21st to end	Night	15% 7% 29% 38% 10%	1045
November	1st to 10th	Night	11% 6% 34% 40% 8% 1	975
	11th to 20th	Night	10% 7% 35% 40% 8%	1000
	21st to end	Night	9% 7% 33% 43% 9%	1000
December	1st to 10th	Night	9% 8% 39% 36% 8%	1000
	11th to 20th	Night	8% 7% 35% 41% 8%	1000
	21st to end	Night	14% 9% 32% 36% 9%	1100

Page generated at 2025-03-09 06:08:47. Version ac07

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