Dolan Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dolan Lake clear sky chart from 2005-11-06 to 2026-06-01.

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	12% 7% 3 7% 5% 4 4 4 6% 8% 41%	131958
	Night	13% 7% 3 7% 4 4 4 3 5% 7% 43%	131398
Transparency	Day	40% 5% 11% 25% 17% 2	135558
	Night	41% 4 10% 24% 18% 3	135861
Seeing	Day	15% 8% 24% 25% 19% 8%	17605
	Night	16% 7% 26% 32% 16% 2	27471

By Month

Percentage Cloud Cover SE (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	13% 10% 4 10% 5% 5% 5% 3 5% 5% 34%	4691
	11th to 20th	Day	10% 7% 3 8% 5% 4 4 3 5% 7% 43%	4728
	21st to end	Day	17% 13% 4 8% 5% 4 3 2 4 5% 34%	5812
February	1st to 10th	Day	16% 10% 4 8% 4 3 4 3 5% 6% 37%	2057
	11th to 20th	Day	16% 10% 4 9% 5% 3 4 3 5% 5% 37%	2048
	21st to end	Day	13% 10% 3 9% 5% 5% 4 3 6% 5% 37%	1730
March	1st to 10th	Day	17% 11% 3 6% 3 3 3 2 3 5% 43%	4580
	11th to 20th	Day	10% 9% 2 5% 3 3 4 3 5% 7% 48%	4814
	21st to end	Day	12% 8% 3 7% 5% 5% 5% 4 6% 7% 39%	6099
April	1st to 10th	Day	12% 6% 3 5% 4 5% 5% 4 6% 8% 43%	2520
	11th to 20th	Day	13% 8% 2 7% 5% 4 4 3 5% 7% 41%	2494
	21st to end	Day	17% 6% 2 6% 4 4 4 4 6% 7% 40%	2520
May	1st to 10th	Day	16% 8% 3 8% 6% 5% 6% 5% 6% 9% 27%	5963
	11th to 20th	Day	16% 8% 3 7% 5% 5% 5% 4 6% 8% 35%	5991
	21st to end	Day	12% 6% 3 8% 5% 5% 5% 4 6% 8% 38%	6968
June	1st to 10th	Day	10% 5% 2 6% 4 4 5% 4 6% 9% 45%	2801
	11th to 20th	Day	6% 5% 2 5% 5% 5% 5% 5% 7% 9% 46%	2800
	21st to end	Day	6% 5% 2 5% 5% 4 5% 4 7% 9% 47%	2800
July	1st to 10th	Day	10% 5% 2 6% 4 5% 5% 4 6% 9% 46%	6360
	11th to 20th	Day	6% 4 3 6% 5% 5% 6% 5% 8% 11% 40%	6360
	21st to end	Day	6% 6% 3 7% 6% 6% 6% 6% 8% 12% 35%	6924
August	1st to 10th	Day	5% 3 1 5% 4 4 4 4 6% 10% 54%	3938
	11th to 20th	Day	8% 5% 2 6% 5% 5% 5% 5% 7% 10% 43%	3849
	21st to end	Day	5% 4 1 5% 4 4 4 4 6% 9% 55%	4312
September	1st to 10th	Day	9% 6% 2 6% 4 4 3 5% 5% 7% 49%	2400
	11th to 20th	Day	7% 6% 2 6% 4 3 5% 4 6% 7% 50%	2270
	21st to end	Day	11% 5% 2 6% 3 3 3 3 4 7% 53%	2200
October	1st to 10th	Day	9% 4 1 5% 3 3 4 2 5% 6% 57%	2178
	11th to 20th	Day	12% 5% 2 5% 4 3 3 3 4 7% 52%	2000
	21st to end	Day	18% 7% 2 5% 4 3 3 3 3 6% 46%	2060
November	1st to 10th	Day	8% 6% 2 5% 5% 4 4 4 5% 5% 52%	1852
	11th to 20th	Day	14% 7% 2 6% 4 4 3 3 5% 6% 46%	1890
	21st to end	Day	18% 10% 3 7% 4 3 3 2 4 5% 41%	1890
December	1st to 10th	Day	10% 11% 2 7% 3 3 3 2 4 6% 49%	2901
	11th to 20th	Day	13% 9% 4 10% 5% 4 4 4 5% 7% 36%	3088
	21st to end	Day	26% 14% 4 9% 5% 4 4 2 4 5% 23%	4070
January	1st to 10th	Night	15% 10% 4 8% 4 4 4 3 4 6% 37%	8232
	11th to 20th	Night	12% 9% 3 9% 4 4 5% 3 4 5% 41%	8245
	21st to end	Night	18% 9% 4 7% 4 4 4 3 4 6% 38%	8402
February	1st to 10th	Night	18% 11% 4 8% 5% 4 3 5% 4 6% 32%	2561
	11th to 20th	Night	16% 9% 3 7% 5% 4 4 3 4 5% 40%	2458
	21st to end	Night	17% 9% 2 8% 4 4 3 4 4 5% 39%	2076
March	1st to 10th	Night	18% 11% 3 7% 4 4 4 3 4 5% 36%	5493
	11th to 20th	Night	11% 7% 2 6% 4 3 4 3 4 6% 49%	5395
	21st to end	Night	16% 7% 3 8% 5% 5% 4 4 5% 6% 36%	5072
April	1st to 10th	Night	12% 6% 2 6% 5% 4 4 4 5% 7% 46%	2100
	11th to 20th	Night	15% 7% 2 5% 4 4 4 4 6% 6% 43%	2075
	21st to end	Night	18% 7% 3 6% 5% 4 5% 4 5% 6% 39%	2100
May	1st to 10th	Night	15% 9% 3 8% 5% 5% 5% 4 6% 9% 32%	4152
	11th to 20th	Night	12% 7% 3 8% 6% 5% 5% 4 6% 8% 37%	4122
	21st to end	Night	13% 6% 2 7% 5% 5% 5% 4 7% 9% 38%	4129
June	1st to 10th	Night	9% 6% 2 6% 4 4 4 4 5% 8% 48%	1600
	11th to 20th	Night	5% 4 2 5% 5% 4 4 4 6% 8% 54%	1600
	21st to end	Night	4 3 1 4 4 4 5% 4 8% 10% 53%	1600
July	1st to 10th	Night	9% 6% 2 6% 3 4 4 4 6% 8% 49%	3618
	11th to 20th	Night	6% 4 2 6% 4 4 4 5% 7% 9% 50%	3617
	21st to end	Night	6% 5% 3 7% 5% 4 6% 5% 8% 13% 38%	3947
August	1st to 10th	Night	4 3 2 5% 3 4 4 3 5% 9% 59%	3194
	11th to 20th	Night	6% 5% 1 6% 4 4 4 4 6% 8% 52%	3200
	21st to end	Night	3 3 2 5% 3 3 4 4 5% 9% 59%	3586
September	1st to 10th	Night	9% 5% 2 6% 4 3 4 3 4 6% 54%	2000
	11th to 20th	Night	7% 4 2 6% 3 4 4 4 5% 8% 54%	2110
	21st to end	Night	12% 5% 2 5% 3 3 4 3 5% 7% 52%	2200
October	1st to 10th	Night	7% 4 2 5% 3 3 3 3 5% 6% 59%	2219
	11th to 20th	Night	13% 4 2 5% 3 3 3 2 4 5% 56%	2400
	21st to end	Night	19% 7% 2 5% 3 3 3 2 4 5% 46%	2780
November	1st to 10th	Night	11% 6% 2 4 3 3 3 3 5% 6% 55%	2666
	11th to 20th	Night	12% 6% 3 6% 3 3 3 3 5% 6% 51%	2730
	21st to end	Night	18% 7% 3 6% 4 3 3 3 4 6% 45%	2730
December	1st to 10th	Night	17% 9% 3 7% 4 3 3 3 4 4 44%	4500
	11th to 20th	Night	17% 8% 3 6% 4 4 4 3 5% 6% 42%	5339
	21st to end	Night	26% 13% 4 8% 5% 4 4 3 3 4 26%	7150

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	53% 2 13% 24% 7% 1	4692
	11th to 20th	Day	43% 3 7% 29% 16% 2	4728
	21st to end	Day	54% 2 10% 17% 10% 6%	5812
February	1st to 10th	Day	48% 4 12% 23% 11% 2	2057
	11th to 20th	Day	50% 4 9% 21% 14% 3	2058
	21st to end	Day	49% 4 9% 20% 14% 4	1730
March	1st to 10th	Day	46% 3 4 20% 23% 4	4580
	11th to 20th	Day	36% 3 9% 28% 19% 4	4814
	21st to end	Day	44% 5% 12% 26% 13% 1	6101
April	1st to 10th	Day	39% 5% 13% 26% 16% 1	2520
	11th to 20th	Day	42% 5% 12% 24% 15% 3	2494
	21st to end	Day	42% 6% 10% 27% 12% 2	2520
May	1st to 10th	Day	51% 8% 11% 19% 11% 1	5999
	11th to 20th	Day	46% 6% 11% 24% 12% 1	5995
	21st to end	Day	42% 6% 10% 21% 19% 2	6982
June	1st to 10th	Day	35% 7% 12% 25% 18% 3	2801
	11th to 20th	Day	31% 8% 11% 25% 21% 3	2800
	21st to end	Day	32% 7% 15% 23% 17% 5%	2800
July	1st to 10th	Day	35% 5% 11% 28% 19% 3	6291
	11th to 20th	Day	36% 5% 17% 28% 12% 1	6285
	21st to end	Day	41% 5% 18% 26% 9% 1	6728
August	1st to 10th	Day	26% 5% 14% 39% 15% 1	3924
	11th to 20th	Day	35% 5% 15% 26% 18% 1	3885
	21st to end	Day	26% 5% 13% 35% 18% 3	4311
September	1st to 10th	Day	34% 5% 9% 28% 19% 5%	2400
	11th to 20th	Day	33% 5% 10% 25% 25% 2	2270
	21st to end	Day	32% 5% 8% 24% 28% 4	2200
October	1st to 10th	Day	18% 3 5% 25% 43% 6%	3542
	11th to 20th	Day	24% 3 8% 23% 36% 7%	3240
	21st to end	Day	32% 3 5% 25% 30% 4	3311
November	1st to 10th	Day	33% 4 10% 29% 18% 6%	1852
	11th to 20th	Day	40% 4 7% 25% 19% 5%	1890
	21st to end	Day	47% 3 8% 25% 15% 2	1890
December	1st to 10th	Day	39% 3 13% 28% 16% 1	2901
	11th to 20th	Day	48% 4 10% 25% 12% 1	3085
	21st to end	Day	65% 3 11% 13% 7%	4070
January	1st to 10th	Night	49% 2 14% 26% 8%	8233
	11th to 20th	Night	46% 4 6% 23% 19% 3	8245
	21st to end	Night	50% 2 10% 20% 17% 1	8402
February	1st to 10th	Night	54% 4 9% 22% 10% 1	2561
	11th to 20th	Night	47% 4 8% 23% 15% 2	2459
	21st to end	Night	47% 4 10% 21% 15% 3	2076
March	1st to 10th	Night	51% 3 6% 18% 19% 3	5493
	11th to 20th	Night	36% 4 10% 23% 21% 6%	5395
	21st to end	Night	48% 5% 11% 24% 11% 1	5072
April	1st to 10th	Night	37% 5% 13% 26% 17% 3	2100
	11th to 20th	Night	39% 6% 10% 22% 19% 4	2075
	21st to end	Night	45% 5% 10% 22% 15% 3	2100
May	1st to 10th	Night	48% 7% 14% 21% 9% 1	4179
	11th to 20th	Night	45% 7% 11% 23% 13% 1	4123
	21st to end	Night	41% 6% 13% 24% 14% 2	4137
June	1st to 10th	Night	33% 6% 13% 25% 21% 3	1600
	11th to 20th	Night	27% 5% 13% 24% 25% 6%	1600
	21st to end	Night	24% 7% 17% 26% 19% 7%	1600
July	1st to 10th	Night	34% 6% 9% 25% 23% 4	3580
	11th to 20th	Night	30% 7% 17% 31% 14% 2	3572
	21st to end	Night	36% 4 21% 26% 11% 1	3832
August	1st to 10th	Night	23% 4 15% 39% 17% 1	3184
	11th to 20th	Night	29% 5% 13% 29% 21% 2	3230
	21st to end	Night	23% 5% 12% 35% 23% 3	3586
September	1st to 10th	Night	31% 6% 7% 28% 22% 6%	2000
	11th to 20th	Night	29% 6% 8% 27% 25% 5%	2110
	21st to end	Night	33% 4 9% 22% 26% 7%	2200
October	1st to 10th	Night	18% 3 5% 16% 49% 9%	3622
	11th to 20th	Night	23% 2 6% 24% 38% 7%	3899
	21st to end	Night	33% 2 6% 25% 25% 9%	4479
November	1st to 10th	Night	32% 4 10% 25% 24% 6%	2666
	11th to 20th	Night	35% 3 7% 25% 23% 6%	2730
	21st to end	Night	43% 3 9% 25% 18% 2	2730
December	1st to 10th	Night	45% 3 9% 26% 17% 1	4500
	11th to 20th	Night	44% 3 12% 24% 17% 1	5341
	21st to end	Night	63% 3 10% 17% 6% 1	7150

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	24% 15% 31% 23% 7% 1	330
	11th to 20th	Day	23% 18% 36% 19% 5%	330
	21st to end	Day	21% 17% 41% 17% 5%	363
February	1st to 10th	Day	22% 12% 45% 17% 5%	330
	11th to 20th	Day	26% 19% 39% 13% 2 1	330
	21st to end	Day	25% 16% 36% 19% 3	273
March	1st to 10th	Day	19% 17% 39% 19% 5% 1	330
	11th to 20th	Day	23% 20% 33% 19% 4	341
	21st to end	Day	24% 16% 32% 20% 8% 1	594
April	1st to 10th	Day	17% 14% 34% 24% 10% 1	540
	11th to 20th	Day	19% 16% 27% 23% 14% 1	532
	21st to end	Day	20% 10% 32% 25% 10% 3	540
May	1st to 10th	Day	20% 11% 28% 29% 9% 3	543
	11th to 20th	Day	18% 7% 25% 27% 16% 7%	567
	21st to end	Day	14% 4 24% 29% 21% 9%	788
June	1st to 10th	Day	12% 4 17% 29% 25% 12%	731
	11th to 20th	Day	8% 3 17% 32% 30% 10%	730
	21st to end	Day	8% 2 21% 33% 25% 10%	730
July	1st to 10th	Day	11% 2 11% 24% 26% 25%	721
	11th to 20th	Day	6% 3 13% 31% 31% 16%	718
	21st to end	Day	8% 2 10% 30% 33% 16%	794
August	1st to 10th	Day	8% 2 9% 29% 31% 20%	544
	11th to 20th	Day	12% 1 14% 27% 33% 13%	519
	21st to end	Day	7% 2 10% 24% 37% 21%	583
September	1st to 10th	Day	11% 1 12% 26% 33% 16%	530
	11th to 20th	Day	9% 3 8% 25% 36% 19%	530
	21st to end	Day	13% 5% 21% 26% 23% 13%	530
October	1st to 10th	Day	10% 3 17% 36% 22% 12%	508
	11th to 20th	Day	12% 10% 34% 24% 15% 6%	330
	21st to end	Day	25% 10% 31% 24% 10% 1	363
November	1st to 10th	Day	11% 8% 34% 26% 17% 4	330
	11th to 20th	Day	16% 16% 31% 23% 12% 2	330
	21st to end	Day	25% 13% 28% 22% 11% 1	330
December	1st to 10th	Day	18% 17% 35% 20% 7% 3	330
	11th to 20th	Day	21% 13% 38% 22% 7%	330
	21st to end	Day	29% 17% 33% 17% 5%	363
January	1st to 10th	Night	20% 13% 36% 27% 4	1050
	11th to 20th	Night	23% 14% 37% 21% 4	1050
	21st to end	Night	20% 10% 41% 26% 2	1155
February	1st to 10th	Night	22% 12% 38% 24% 3	881
	11th to 20th	Night	22% 14% 37% 25% 2	823
	21st to end	Night	21% 14% 39% 25% 2	692
March	1st to 10th	Night	21% 13% 33% 29% 4	840
	11th to 20th	Night	21% 10% 35% 28% 6% 1	792
	21st to end	Night	22% 11% 30% 30% 6% 1	693
April	1st to 10th	Night	14% 11% 36% 31% 8%	630
	11th to 20th	Night	18% 10% 30% 29% 12% 1	623
	21st to end	Night	20% 7% 32% 32% 9% 1	630
May	1st to 10th	Night	16% 7% 29% 37% 11%	630
	11th to 20th	Night	16% 5% 25% 32% 21% 2	621
	21st to end	Night	10% 2 18% 42% 24% 3	683
June	1st to 10th	Night	12% 2 17% 41% 25% 3	600
	11th to 20th	Night	6% 3 15% 45% 29% 2	600
	21st to end	Night	5% 2 16% 41% 34% 3	600
July	1st to 10th	Night	11% 1 7% 32% 39% 9%	585
	11th to 20th	Night	6% 2 9% 36% 43% 5%	582
	21st to end	Night	8% 2 10% 36% 38% 6%	657
August	1st to 10th	Night	7% 1 5% 42% 38% 7%	597
	11th to 20th	Night	6% 1 10% 38% 40% 6%	594
	21st to end	Night	7% 1 6% 38% 42% 6%	660
September	1st to 10th	Night	12% 1 10% 34% 37% 6%	600
	11th to 20th	Night	8% 2 11% 32% 41% 6%	710
	21st to end	Night	15% 2 17% 33% 28% 6%	800
October	1st to 10th	Night	9% 3 18% 38% 27% 5%	800
	11th to 20th	Night	16% 6% 27% 32% 17% 3	800
	21st to end	Night	22% 7% 31% 29% 10% 1	880
November	1st to 10th	Night	14% 7% 29% 37% 13% 1	820
	11th to 20th	Night	15% 9% 31% 33% 11% 1	840
	21st to end	Night	23% 9% 29% 29% 10% 1	840
December	1st to 10th	Night	23% 9% 32% 30% 6%	908
	11th to 20th	Night	23% 8% 31% 32% 6%	1050
	21st to end	Night	27% 12% 34% 23% 4	1155

Page generated at 2026-05-29 00:53:30. Version ac07

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