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 2024-11-04.

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% 49%	105110
	Night	2 5% 2 6% 4 4 4 4 6% 8% 56%	102581
Transparency	Day	28% 8% 12% 21% 22% 9%	104857
	Night	24% 7% 13% 25% 23% 8%	102424
Seeing	Day	11% 19% 31% 24% 12% 3	15521
	Night	6% 16% 34% 30% 13% 2	25525

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 8% 6% 3 4 4 5% 8% 57%	2538
	11th to 20th	Day	1 3 2 7% 5% 5% 5% 4 6% 8% 54%	2681
	21st to end	Day	8% 4 9% 4 4 4 3 6% 6% 53%	3146
February	1st to 10th	Day	6% 3 9% 4 3 3 4 5% 7% 56%	1710
	11th to 20th	Day	1 3 2 5% 4 4 3 3 7% 10% 58%	1841
	21st to end	Day	7% 3 7% 4 3 3 3 5% 7% 59%	1570
March	1st to 10th	Day	1 7% 4 7% 4 3 3 2 5% 7% 56%	3130
	11th to 20th	Day	2 9% 6% 13% 7% 5% 4 3 6% 7% 38%	3475
	21st to end	Day	1 9% 3 7% 4 4 5% 5% 6% 9% 49%	4056
April	1st to 10th	Day	3 9% 2 7% 5% 5% 4 4 6% 8% 47%	2280
	11th to 20th	Day	4 10% 4 10% 5% 4 5% 4 6% 6% 43%	2251
	21st to end	Day	4 12% 4 8% 7% 5% 4 4 5% 7% 39%	2280
May	1st to 10th	Day	4 12% 3 7% 5% 5% 5% 4 6% 7% 42%	3950
	11th to 20th	Day	6% 9% 2 7% 4 5% 6% 5% 7% 8% 40%	4325
	21st to end	Day	3 6% 2 5% 4 4 6% 4 7% 9% 50%	4825
June	1st to 10th	Day	5% 5% 3 5% 4 5% 6% 5% 8% 9% 44%	2660
	11th to 20th	Day	5% 5% 2 5% 4 4 5% 5% 8% 8% 50%	2660
	21st to end	Day	3 5% 2 7% 5% 6% 6% 5% 7% 9% 43%	2660
July	1st to 10th	Day	4 4 1 6% 5% 6% 6% 5% 7% 8% 48%	4430
	11th to 20th	Day	4 6% 3 8% 7% 7% 6% 6% 8% 9% 36%	4430
	21st to end	Day	6% 7% 2 7% 6% 6% 5% 5% 7% 7% 42%	4628
August	1st to 10th	Day	7% 7% 3 9% 6% 7% 7% 5% 8% 9% 33%	4062
	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 4 2 4 2 3 3 3 6% 7% 66%	1700
	11th to 20th	Day	5% 2 4 4 3 3 3 6% 7% 64%	1710
	21st to end	Day	1 6% 2 6% 3 3 4 4 5% 7% 60%	1646
December	1st to 10th	Day	4 2 6% 3 4 4 3 5% 10% 59%	1520
	11th to 20th	Day	1 5% 2 6% 3 4 3 4 6% 10% 56%	1926
	21st to end	Day	5% 3 8% 5% 4 4 4 6% 7% 54%	2794
January	1st to 10th	Night	4 2 11% 5% 4 3 3 5% 8% 55%	4417
	11th to 20th	Night	2 1 3 5% 3 5% 4 6% 8% 64%	4306
	21st to end	Night	5% 2 8% 5% 4 3 3 5% 7% 58%	4521
February	1st to 10th	Night	5% 3 6% 5% 3 3 3 5% 8% 59%	2470
	11th to 20th	Night	5% 2 7% 4 3 4 4 5% 7% 59%	2223
	21st to end	Night	6% 2 5% 3 3 3 2 4 6% 65%	1884
March	1st to 10th	Night	1 7% 3 6% 3 3 3 3 5% 7% 58%	3734
	11th to 20th	Night	2 9% 5% 10% 3 3 3 3 5% 7% 50%	3503
	21st to end	Night	1 7% 3 5% 4 3 4 3 6% 8% 56%	3588
April	1st to 10th	Night	3 8% 2 5% 3 3 3 3 5% 6% 59%	1900
	11th to 20th	Night	3 10% 3 7% 4 4 4 3 5% 8% 50%	1877
	21st to end	Night	4 11% 3 7% 3 3 4 4 4 8% 49%	1900
May	1st to 10th	Night	4 9% 2 6% 4 4 4 3 6% 8% 50%	3020
	11th to 20th	Night	6% 8% 2 6% 4 4 4 4 7% 8% 47%	2564
	21st to end	Night	3 5% 2 4 3 3 4 4 5% 8% 60%	2762
June	1st to 10th	Night	3 4 1 5% 3 5% 5% 5% 7% 10% 52%	1520
	11th to 20th	Night	3 2 1 3 3 3 5% 6% 9% 9% 58%	1520
	21st to end	Night	3 5% 1 4 5% 5% 6% 5% 7% 8% 51%	1520
July	1st to 10th	Night	4 5% 2 7% 5% 4 5% 4 6% 8% 50%	2540
	11th to 20th	Night	3 4 2 4 4 5% 5% 5% 9% 13% 47%	2540
	21st to end	Night	4 4 1 5% 5% 5% 6% 5% 9% 9% 49%	2918
August	1st to 10th	Night	5% 6% 2 8% 6% 7% 7% 5% 9% 10% 34%	2874
	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 3 3 2 3 3 5% 8% 67%	2451
	11th to 20th	Night	4 1 4 3 3 3 3 5% 7% 66%	2470
	21st to end	Night	1 5% 3 5% 3 3 3 3 5% 6% 62%	2531
December	1st to 10th	Night	1 3 2 5% 3 2 4 4 5% 10% 61%	2660
	11th to 20th	Night	1 5% 1 6% 4 4 4 4 7% 10% 54%	3271
	21st to end	Night	1 7% 3 7% 4 4 5% 4 5% 7% 53%	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	19% 8% 16% 25% 25% 7%	2539
	11th to 20th	Day	22% 7% 13% 30% 21% 6%	2681
	21st to end	Day	26% 8% 13% 27% 21% 5%	3146
February	1st to 10th	Day	26% 5% 14% 26% 19% 9%	1710
	11th to 20th	Day	20% 5% 11% 26% 29% 9%	1851
	21st to end	Day	25% 4 7% 23% 27% 13%	1570
March	1st to 10th	Day	24% 7% 6% 20% 31% 12%	3130
	11th to 20th	Day	37% 10% 11% 26% 14% 3	3475
	21st to end	Day	25% 9% 12% 31% 20% 3	4056
April	1st to 10th	Day	32% 6% 11% 21% 20% 9%	2280
	11th to 20th	Day	37% 6% 10% 21% 19% 7%	2254
	21st to end	Day	40% 7% 11% 22% 18% 3	2280
May	1st to 10th	Day	33% 9% 10% 20% 17% 10%	3950
	11th to 20th	Day	34% 12% 15% 19% 17% 4	4329
	21st to end	Day	23% 10% 12% 21% 24% 10%	4825
June	1st to 10th	Day	30% 10% 15% 19% 18% 8%	2660
	11th to 20th	Day	27% 8% 10% 17% 22% 16%	2660
	21st to end	Day	32% 9% 12% 19% 19% 9%	2660
July	1st to 10th	Day	28% 9% 9% 13% 21% 20%	4361
	11th to 20th	Day	37% 8% 12% 23% 14% 6%	4355
	21st to end	Day	36% 8% 12% 15% 15% 13%	4482
August	1st to 10th	Day	42% 11% 17% 16% 11% 3	4048
	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	17% 4 10% 22% 33% 14%	1700
	11th to 20th	Day	18% 5% 8% 32% 28% 9%	1710
	21st to end	Day	23% 4 9% 24% 27% 13%	1646
December	1st to 10th	Day	20% 6% 16% 26% 24% 8%	1520
	11th to 20th	Day	21% 7% 14% 26% 25% 8%	1924
	21st to end	Day	23% 7% 13% 23% 24% 10%	2794
January	1st to 10th	Night	23% 6% 13% 27% 26% 5%	4417
	11th to 20th	Night	14% 6% 13% 34% 24% 9%	4306
	21st to end	Night	23% 7% 13% 29% 23% 5%	4521
February	1st to 10th	Night	23% 4 13% 30% 22% 8%	2470
	11th to 20th	Night	25% 4 11% 28% 24% 8%	2223
	21st to end	Night	21% 4 8% 26% 29% 12%	1884
March	1st to 10th	Night	22% 5% 9% 22% 34% 8%	3734
	11th to 20th	Night	32% 8% 12% 27% 19% 3	3503
	21st to end	Night	24% 8% 15% 31% 20% 2	3588
April	1st to 10th	Night	25% 6% 11% 27% 25% 6%	1900
	11th to 20th	Night	32% 6% 12% 26% 20% 5%	1877
	21st to end	Night	33% 7% 13% 26% 16% 4	1900
May	1st to 10th	Night	28% 8% 14% 25% 15% 10%	3020
	11th to 20th	Night	29% 11% 17% 25% 15% 2	2565
	21st to end	Night	21% 10% 14% 23% 25% 7%	2762
June	1st to 10th	Night	23% 9% 21% 24% 13% 10%	1520
	11th to 20th	Night	17% 10% 14% 22% 21% 17%	1520
	21st to end	Night	27% 9% 12% 22% 21% 10%	1520
July	1st to 10th	Night	29% 8% 10% 17% 25% 11%	2500
	11th to 20th	Night	24% 8% 19% 34% 12% 4	2492
	21st to end	Night	26% 9% 16% 24% 11% 13%	2826
August	1st to 10th	Night	39% 11% 20% 16% 10% 3	2865
	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	15% 4 12% 25% 30% 13%	2451
	11th to 20th	Night	17% 4 9% 30% 29% 10%	2470
	21st to end	Night	22% 4 10% 23% 29% 12%	2531
December	1st to 10th	Night	19% 6% 16% 26% 25% 9%	2660
	11th to 20th	Night	22% 6% 14% 24% 28% 6%	3272
	21st to end	Night	24% 8% 12% 22% 24% 10%	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	14% 23% 30% 23% 9%	270
	11th to 20th	Day	15% 30% 31% 19% 4 1	270
	21st to end	Day	6% 28% 39% 19% 6% 1	297
February	1st to 10th	Day	10% 41% 34% 11% 2 1	270
	11th to 20th	Day	11% 37% 38% 9% 5%	270
	21st to end	Day	20% 36% 31% 11% 2	225
March	1st to 10th	Day	17% 25% 34% 16% 8%	270
	11th to 20th	Day	16% 27% 34% 16% 6% 1	445
	21st to end	Day	20% 31% 33% 13% 3	506
April	1st to 10th	Day	16% 33% 33% 14% 3 1	460
	11th to 20th	Day	24% 31% 30% 12% 4 1	452
	21st to end	Day	19% 31% 31% 15% 4 1	460
May	1st to 10th	Day	16% 26% 33% 18% 5% 1	548
	11th to 20th	Day	13% 16% 34% 26% 10% 2	675
	21st to end	Day	9% 20% 29% 27% 13% 2	734
June	1st to 10th	Day	7% 13% 31% 28% 18% 3	680
	11th to 20th	Day	10% 15% 33% 27% 13% 3	680
	21st to end	Day	5% 13% 31% 29% 17% 5%	680
July	1st to 10th	Day	7% 6% 24% 35% 22% 6%	671
	11th to 20th	Day	8% 3 24% 34% 24% 8%	668
	21st to end	Day	10% 5% 19% 34% 26% 6%	640
August	1st to 10th	Day	11% 8% 27% 36% 15% 3	487
	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	11% 24% 34% 18% 10% 3	279
	11th to 20th	Day	10% 24% 37% 19% 9% 1	270
	21st to end	Day	10% 23% 39% 19% 7% 2	270
December	1st to 10th	Day	13% 30% 33% 17% 7% 1	270
	11th to 20th	Day	10% 30% 38% 16% 6%	270
	21st to end	Day	13% 32% 34% 16% 4 1	297
January	1st to 10th	Night	6% 24% 35% 25% 9% 2	950
	11th to 20th	Night	5% 30% 35% 21% 7% 1	878
	21st to end	Night	2 17% 45% 28% 6% 1	836
February	1st to 10th	Night	4 26% 47% 19% 4	760
	11th to 20th	Night	4 24% 47% 21% 4	744
	21st to end	Night	5% 28% 45% 21% 2	628
March	1st to 10th	Night	4 24% 43% 24% 5% 1	760
	11th to 20th	Night	6% 16% 39% 31% 8%	760
	21st to end	Night	5% 20% 47% 23% 5%	699
April	1st to 10th	Night	10% 20% 41% 24% 5%	570
	11th to 20th	Night	9% 22% 37% 25% 6% 1	563
	21st to end	Night	11% 18% 38% 25% 8% 1	570
May	1st to 10th	Night	11% 10% 37% 32% 8% 1	570
	11th to 20th	Night	9% 9% 29% 39% 12% 1	561
	21st to end	Night	7% 13% 34% 31% 14% 1	617
June	1st to 10th	Night	4 6% 27% 42% 18% 3	570
	11th to 20th	Night	4 10% 30% 41% 14% 2	570
	21st to end	Night	5% 4 22% 45% 22% 3	570
July	1st to 10th	Night	5% 3 18% 39% 32% 3	555
	11th to 20th	Night	5% 1 16% 40% 34% 4	552
	21st to end	Night	7% 2 10% 38% 38% 4	624
August	1st to 10th	Night	8% 3 14% 39% 31% 4	567
	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	4 16% 37% 29% 11% 2	943
	11th to 20th	Night	5% 20% 41% 24% 8% 2	950
	21st to end	Night	5% 18% 40% 29% 8% 1	950
December	1st to 10th	Night	5% 27% 35% 26% 6% 1	950
	11th to 20th	Night	4 25% 44% 20% 7% 1	950
	21st to end	Night	7% 28% 38% 21% 6%	1045

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