Divide
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Divide clear sky chart from 2005-11-06 to 2025-08-05.

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	3 6% 2 7% 5% 4 5% 4 6% 8% 50%	129658
	Night	2 5% 2 6% 4 4 4 4 6% 8% 57%	127311
Transparency	Day	28% 7% 11% 22% 23% 9%	129361
	Night	23% 6% 12% 25% 25% 8%	127123
Seeing	Day	12% 20% 31% 24% 11% 3	16572
	Night	6% 16% 35% 29% 12% 2	26559

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	4 3 8% 5% 3 3 3 4 7% 59%	3638
	11th to 20th	Day	2 1 7% 6% 6% 6% 4 5% 7% 54%	3851
	21st to end	Day	6% 3 7% 4 3 4 3 5% 5% 59%	4510
February	1st to 10th	Day	6% 3 9% 4 3 3 4 5% 7% 57%	1800
	11th to 20th	Day	1 3 2 5% 4 4 3 4 7% 10% 58%	1941
	21st to end	Day	7% 3 7% 3 3 3 3 4 7% 60%	1650
March	1st to 10th	Day	1 6% 4 7% 4 3 3 2 4 6% 60%	4500
	11th to 20th	Day	1 7% 5% 13% 6% 5% 5% 4 6% 7% 41%	4971
	21st to end	Day	1 8% 3 7% 4 4 5% 5% 6% 9% 48%	5808
April	1st to 10th	Day	3 9% 3 7% 4 5% 4 4 6% 8% 46%	2400
	11th to 20th	Day	4 9% 4 9% 5% 4 5% 3 6% 6% 43%	2371
	21st to end	Day	4 12% 4 8% 6% 5% 4 4 6% 8% 40%	2400
May	1st to 10th	Day	4 11% 3 8% 5% 4 5% 4 6% 7% 43%	5660
	11th to 20th	Day	4 7% 2 7% 4 5% 5% 5% 7% 8% 46%	6209
	21st to end	Day	3 5% 2 5% 4 4 6% 5% 8% 9% 48%	6925
June	1st to 10th	Day	5% 6% 3 6% 4 5% 6% 6% 8% 9% 44%	2800
	11th to 20th	Day	5% 5% 2 5% 4 4 5% 5% 8% 8% 51%	2800
	21st to end	Day	3 5% 2 7% 5% 6% 6% 5% 7% 9% 44%	2800
July	1st to 10th	Day	3 3 1 5% 5% 6% 6% 5% 7% 9% 49%	6339
	11th to 20th	Day	4 5% 2 8% 6% 6% 7% 6% 8% 9% 36%	6340
	21st to end	Day	5% 6% 3 8% 6% 6% 6% 5% 7% 7% 39%	6659
August	1st to 10th	Day	7% 7% 3 9% 6% 7% 7% 5% 8% 9% 33%	4115
	11th to 20th	Day	4 5% 2 6% 5% 6% 8% 6% 7% 9% 43%	3726
	21st to end	Day	4 5% 2 7% 5% 5% 6% 5% 8% 10% 41%	4180
September	1st to 10th	Day	6% 6% 3 6% 5% 4 5% 4 5% 6% 49%	2280
	11th to 20th	Day	6% 4 2 5% 4 5% 4 4 5% 5% 56%	2261
	21st to end	Day	5% 4 2 5% 3 3 3 3 5% 6% 61%	2090
October	1st to 10th	Day	3 3 1 3 2 2 3 2 4 5% 70%	3184
	11th to 20th	Day	3 4 2 5% 4 4 4 4 6% 8% 56%	3150
	21st to end	Day	2 5% 1 4 3 2 3 3 4 5% 67%	3355
November	1st to 10th	Day	1 5% 2 5% 2 3 3 2 5% 6% 65%	1763
	11th to 20th	Day	5% 2 3 4 3 3 3 5% 7% 65%	1800
	21st to end	Day	1 5% 2 6% 3 3 4 3 5% 7% 60%	1732
December	1st to 10th	Day	3 2 6% 3 3 2 2 4 6% 69%	2620
	11th to 20th	Day	1 3 2 5% 3 3 3 3 5% 8% 64%	3026
	21st to end	Day	4 2 7% 5% 4 4 4 6% 8% 55%	4004
January	1st to 10th	Night	4 3 10% 5% 3 3 3 5% 8% 56%	6327
	11th to 20th	Night	2 1 5% 5% 4 4 3 5% 6% 65%	6160
	21st to end	Night	4 2 6% 4 3 3 3 5% 6% 63%	6468
February	1st to 10th	Night	5% 2 6% 4 3 3 3 5% 8% 60%	2600
	11th to 20th	Night	5% 2 7% 5% 3 4 4 5% 7% 58%	2343
	21st to end	Night	5% 2 5% 3 3 3 2 4 6% 65%	1980
March	1st to 10th	Night	1 6% 3 6% 4 3 4 3 5% 7% 59%	5374
	11th to 20th	Night	1 7% 4 9% 3 3 3 2 5% 8% 54%	5013
	21st to end	Night	1 6% 3 5% 4 4 4 3 5% 7% 57%	5151
April	1st to 10th	Night	3 7% 2 5% 4 3 3 3 5% 6% 58%	2000
	11th to 20th	Night	3 10% 3 7% 4 4 4 3 5% 8% 51%	1977
	21st to end	Night	4 11% 3 7% 3 3 4 4 4 8% 49%	2000
May	1st to 10th	Night	3 8% 3 8% 5% 5% 5% 4 6% 8% 45%	4320
	11th to 20th	Night	4 7% 2 6% 3 3 4 4 6% 8% 52%	3690
	21st to end	Night	3 5% 2 5% 3 3 4 4 5% 8% 59%	3972
June	1st to 10th	Night	3 4 1 5% 3 5% 5% 4 7% 10% 52%	1600
	11th to 20th	Night	3 2 1 3 3 3 5% 5% 8% 9% 59%	1600
	21st to end	Night	3 5% 1 4 5% 5% 6% 5% 7% 8% 51%	1600
July	1st to 10th	Night	3 4 2 6% 4 4 5% 4 7% 9% 52%	3640
	11th to 20th	Night	2 4 2 4 5% 5% 6% 6% 9% 13% 44%	3640
	21st to end	Night	3 4 1 6% 5% 5% 6% 6% 9% 10% 44%	4197
August	1st to 10th	Night	5% 6% 2 8% 6% 7% 7% 5% 9% 10% 35%	2910
	11th to 20th	Night	3 4 2 5% 5% 6% 5% 5% 8% 12% 45%	3113
	21st to end	Night	3 3 2 5% 4 5% 6% 6% 9% 13% 45%	3487
September	1st to 10th	Night	5% 5% 2 5% 4 5% 5% 4 7% 9% 50%	1900
	11th to 20th	Night	4 3 2 4 3 3 4 3 6% 7% 60%	1919
	21st to end	Night	4 5% 2 4 3 3 4 3 4 6% 62%	2090
October	1st to 10th	Night	3 3 1 3 2 2 3 3 4 5% 71%	3768
	11th to 20th	Night	2 4 2 5% 4 3 4 3 5% 8% 61%	3778
	21st to end	Night	2 4 1 3 2 2 3 2 5% 6% 71%	4169
November	1st to 10th	Night	1 4 2 4 3 2 3 3 5% 8% 66%	2535
	11th to 20th	Night	4 1 4 3 3 3 3 5% 7% 67%	2600
	21st to end	Night	1 5% 3 5% 3 3 3 2 5% 6% 62%	2665
December	1st to 10th	Night	2 1 4 2 2 3 3 4 7% 72%	4570
	11th to 20th	Night	3 1 4 3 3 3 3 5% 8% 65%	5181
	21st to end	Night	6% 3 8% 4 4 5% 4 5% 7% 53%	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	22% 6% 12% 26% 24% 10%	3639
	11th to 20th	Day	24% 6% 11% 22% 28% 10%	3851
	21st to end	Day	23% 6% 10% 24% 26% 11%	4510
February	1st to 10th	Day	26% 5% 14% 26% 19% 11%	1800
	11th to 20th	Day	20% 5% 11% 26% 29% 9%	1951
	21st to end	Day	25% 4 7% 22% 28% 14%	1650
March	1st to 10th	Day	21% 5% 6% 15% 33% 20%	4500
	11th to 20th	Day	35% 8% 10% 21% 21% 5%	4971
	21st to end	Day	26% 8% 12% 36% 16% 2	5808
April	1st to 10th	Day	32% 6% 11% 22% 20% 9%	2400
	11th to 20th	Day	37% 6% 10% 21% 19% 7%	2374
	21st to end	Day	39% 7% 11% 23% 18% 3	2400
May	1st to 10th	Day	33% 9% 10% 24% 18% 7%	5660
	11th to 20th	Day	29% 10% 12% 19% 22% 8%	6213
	21st to end	Day	24% 10% 13% 22% 24% 7%	6926
June	1st to 10th	Day	31% 10% 15% 19% 18% 8%	2800
	11th to 20th	Day	27% 8% 10% 17% 23% 16%	2800
	21st to end	Day	31% 9% 12% 19% 19% 10%	2800
July	1st to 10th	Day	26% 8% 9% 15% 21% 21%	6271
	11th to 20th	Day	36% 9% 15% 23% 12% 5%	6265
	21st to end	Day	38% 9% 13% 14% 16% 10%	6467
August	1st to 10th	Day	42% 11% 17% 16% 12% 3	4101
	11th to 20th	Day	33% 10% 14% 14% 19% 11%	3762
	21st to end	Day	33% 8% 16% 16% 22% 5%	4179
September	1st to 10th	Day	32% 6% 10% 18% 23% 11%	2280
	11th to 20th	Day	28% 5% 9% 18% 28% 12%	2261
	21st to end	Day	23% 5% 8% 22% 32% 9%	2090
October	1st to 10th	Day	16% 4 7% 17% 39% 16%	3184
	11th to 20th	Day	24% 5% 8% 31% 25% 7%	3150
	21st to end	Day	18% 3 6% 24% 40% 8%	3355
November	1st to 10th	Day	19% 3 10% 22% 32% 14%	1763
	11th to 20th	Day	17% 5% 7% 31% 30% 10%	1800
	21st to end	Day	22% 4 9% 25% 28% 13%	1732
December	1st to 10th	Day	17% 4 10% 32% 28% 10%	2620
	11th to 20th	Day	18% 4 13% 29% 29% 7%	3024
	21st to end	Day	22% 6% 12% 23% 28% 9%	4004
January	1st to 10th	Night	24% 5% 10% 27% 27% 7%	6327
	11th to 20th	Night	17% 5% 10% 27% 26% 15%	6160
	21st to end	Night	20% 6% 10% 23% 29% 12%	6468
February	1st to 10th	Night	22% 4 13% 29% 22% 9%	2600
	11th to 20th	Night	25% 4 11% 28% 23% 7%	2343
	21st to end	Night	21% 3 8% 25% 29% 14%	1980
March	1st to 10th	Night	22% 4 8% 16% 36% 13%	5374
	11th to 20th	Night	28% 6% 9% 19% 31% 8%	5013
	21st to end	Night	24% 6% 17% 35% 17% 2	5151
April	1st to 10th	Night	25% 5% 11% 28% 25% 6%	2000
	11th to 20th	Night	31% 6% 11% 26% 20% 5%	1977
	21st to end	Night	32% 7% 14% 27% 17% 4	2000
May	1st to 10th	Night	31% 10% 14% 28% 11% 7%	4317
	11th to 20th	Night	27% 8% 13% 28% 20% 4	3691
	21st to end	Night	22% 9% 15% 25% 24% 5%	3972
June	1st to 10th	Night	24% 9% 21% 24% 13% 10%	1600
	11th to 20th	Night	17% 10% 14% 21% 22% 17%	1600
	21st to end	Night	27% 8% 12% 21% 21% 11%	1600
July	1st to 10th	Night	25% 7% 11% 18% 30% 10%	3600
	11th to 20th	Night	26% 9% 23% 28% 12% 3	3592
	21st to end	Night	30% 9% 18% 21% 12% 9%	4077
August	1st to 10th	Night	39% 11% 20% 17% 11% 3	2901
	11th to 20th	Night	28% 11% 20% 17% 18% 5%	3143
	21st to end	Night	27% 9% 23% 21% 17% 2	3487
September	1st to 10th	Night	28% 7% 13% 23% 22% 7%	1900
	11th to 20th	Night	22% 5% 12% 22% 26% 13%	1919
	21st to end	Night	24% 5% 9% 25% 30% 7%	2090
October	1st to 10th	Night	16% 5% 9% 22% 37% 10%	3768
	11th to 20th	Night	20% 5% 13% 31% 23% 8%	3778
	21st to end	Night	15% 4 6% 30% 36% 10%	4169
November	1st to 10th	Night	16% 4 12% 25% 30% 13%	2535
	11th to 20th	Night	17% 4 9% 29% 30% 11%	2600
	21st to end	Night	21% 4 10% 23% 30% 12%	2665
December	1st to 10th	Night	13% 4 9% 35% 30% 8%	4570
	11th to 20th	Night	16% 4 10% 30% 34% 5%	5182
	21st to end	Night	26% 6% 12% 20% 29% 7%	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	15% 24% 31% 21% 8%	300
	11th to 20th	Day	14% 30% 32% 20% 4 1	300
	21st to end	Day	7% 29% 39% 18% 6% 1	330
February	1st to 10th	Day	16% 40% 31% 10% 2 1	300
	11th to 20th	Day	14% 37% 36% 9% 4	300
	21st to end	Day	20% 35% 32% 12% 2	249
March	1st to 10th	Day	17% 26% 33% 16% 7%	300
	11th to 20th	Day	17% 28% 33% 15% 6% 1	484
	21st to end	Day	21% 31% 32% 13% 3	550
April	1st to 10th	Day	17% 33% 33% 13% 3 1	500
	11th to 20th	Day	24% 32% 30% 11% 4 1	492
	21st to end	Day	19% 32% 30% 15% 4 1	500
May	1st to 10th	Day	17% 25% 32% 19% 6% 1	593
	11th to 20th	Day	14% 17% 33% 25% 9% 2	725
	21st to end	Day	10% 20% 30% 27% 12% 2	789
June	1st to 10th	Day	7% 13% 31% 28% 18% 3	730
	11th to 20th	Day	9% 15% 33% 27% 14% 3	730
	21st to end	Day	6% 14% 31% 29% 16% 5%	730
July	1st to 10th	Day	7% 7% 24% 36% 21% 5%	721
	11th to 20th	Day	7% 3 24% 35% 23% 7%	718
	21st to end	Day	10% 5% 20% 34% 25% 6%	690
August	1st to 10th	Day	11% 8% 28% 35% 15% 3	504
	11th to 20th	Day	8% 6% 33% 32% 16% 5%	477
	21st to end	Day	9% 8% 33% 31% 16% 3	539
September	1st to 10th	Day	8% 11% 28% 34% 14% 5%	490
	11th to 20th	Day	7% 15% 35% 28% 12% 2	471
	21st to end	Day	8% 13% 27% 28% 18% 6%	300
October	1st to 10th	Day	9% 15% 28% 24% 18% 7%	300
	11th to 20th	Day	9% 24% 30% 24% 10% 4	300
	21st to end	Day	14% 22% 33% 21% 9% 2	330
November	1st to 10th	Day	12% 25% 34% 17% 10% 2	300
	11th to 20th	Day	12% 25% 35% 18% 8% 1	300
	21st to end	Day	10% 24% 39% 18% 6% 2	300
December	1st to 10th	Day	12% 28% 33% 20% 6% 1	300
	11th to 20th	Day	11% 30% 39% 15% 6%	300
	21st to end	Day	14% 31% 35% 15% 4 1	330
January	1st to 10th	Night	6% 24% 35% 25% 9% 2	1000
	11th to 20th	Night	5% 29% 36% 21% 7% 1	924
	21st to end	Night	3 18% 46% 27% 5% 1	880
February	1st to 10th	Night	7% 27% 45% 18% 4	800
	11th to 20th	Night	5% 25% 47% 20% 4	784
	21st to end	Night	4 27% 46% 21% 2	660
March	1st to 10th	Night	5% 24% 43% 23% 5% 1	800
	11th to 20th	Night	6% 17% 39% 30% 7%	800
	21st to end	Night	5% 20% 47% 22% 5%	736
April	1st to 10th	Night	10% 21% 43% 23% 5%	600
	11th to 20th	Night	8% 23% 38% 24% 5% 1	593
	21st to end	Night	11% 18% 39% 24% 7% 1	600
May	1st to 10th	Night	11% 11% 37% 32% 8% 1	600
	11th to 20th	Night	9% 10% 31% 37% 12% 1	591
	21st to end	Night	7% 13% 35% 31% 13% 1	650
June	1st to 10th	Night	4 7% 28% 41% 18% 3	600
	11th to 20th	Night	4 9% 32% 40% 14% 2	600
	21st to end	Night	5% 5% 23% 44% 21% 3	600
July	1st to 10th	Night	5% 3 20% 38% 30% 3	585
	11th to 20th	Night	5% 1 17% 40% 33% 4	582
	21st to end	Night	7% 3 12% 38% 37% 4	657
August	1st to 10th	Night	8% 3 15% 40% 30% 4	579
	11th to 20th	Night	6% 3 18% 42% 27% 3	564
	21st to end	Night	7% 3 17% 37% 31% 4	627
September	1st to 10th	Night	5% 3 20% 41% 26% 5%	570
	11th to 20th	Night	4 6% 25% 41% 21% 4	570
	21st to end	Night	5% 8% 30% 36% 18% 3	570
October	1st to 10th	Night	5% 11% 34% 34% 13% 3	741
	11th to 20th	Night	4 13% 35% 32% 13% 3	760
	21st to end	Night	7% 13% 37% 28% 13% 2	861
November	1st to 10th	Night	5% 16% 38% 29% 10% 2	975
	11th to 20th	Night	5% 21% 41% 23% 8% 2	1000
	21st to end	Night	5% 18% 41% 28% 8% 1	1000
December	1st to 10th	Night	5% 25% 35% 27% 7% 1	1000
	11th to 20th	Night	4 25% 45% 19% 6% 1	1000
	21st to end	Night	8% 27% 39% 20% 6%	1100

Page generated at 2025-08-01 23:32:25. Version ac07

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