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 2024-01-27.

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	13% 7% 3 6% 5% 3 5% 5% 5% 7% 42%	74928
	Night	14% 7% 3 5% 5% 3 4 4 5% 7% 44%	75144
Transparency	Day	40% 6% 11% 24% 15% 3	74630
	Night	40% 5% 10% 23% 17% 3	74963
Seeing	Day	15% 8% 23% 26% 20% 9%	14408
	Night	16% 7% 26% 32% 17% 2	24367

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	18% 10% 4 8% 5% 2 4 4 4 5% 37%	1517
	11th to 20th	Day	18% 10% 4 7% 5% 3 4 4 5% 6% 33%	1524
	21st to end	Day	14% 12% 4 8% 6% 3 4 4 4 6% 36%	1836
February	1st to 10th	Day	17% 10% 5% 7% 5% 2 4 4 5% 5% 36%	1763
	11th to 20th	Day	16% 9% 5% 8% 5% 3 4 3 5% 6% 35%	1748
	21st to end	Day	15% 10% 4 8% 5% 3 5% 4 5% 6% 35%	1480
March	1st to 10th	Day	16% 8% 3 5% 5% 3 4 5% 4 7% 41%	1800
	11th to 20th	Day	19% 10% 4 7% 5% 3 4 4 5% 6% 34%	1864
	21st to end	Day	19% 9% 5% 7% 6% 4 5% 4 5% 7% 30%	2376
April	1st to 10th	Day	10% 6% 3 5% 4 3 5% 5% 6% 8% 45%	2160
	11th to 20th	Day	14% 8% 3 6% 5% 3 5% 4 5% 7% 40%	2134
	21st to end	Day	18% 6% 2 5% 5% 3 5% 5% 5% 7% 39%	2160
May	1st to 10th	Day	17% 6% 3 6% 6% 3 5% 6% 5% 8% 35%	2326
	11th to 20th	Day	17% 7% 3 5% 5% 3 4 5% 6% 8% 38%	2301
	21st to end	Day	8% 6% 3 6% 6% 4 7% 7% 8% 10% 35%	2677
June	1st to 10th	Day	9% 4 2 5% 5% 2 5% 5% 6% 9% 45%	2520
	11th to 20th	Day	6% 4 2 4 5% 3 6% 6% 7% 9% 48%	2520
	21st to end	Day	6% 4 3 5% 6% 3 5% 6% 7% 9% 47%	2520
July	1st to 10th	Day	10% 4 2 4 5% 4 6% 6% 7% 12% 39%	2520
	11th to 20th	Day	5% 4 3 4 5% 4 5% 5% 7% 10% 48%	2520
	21st to end	Day	7% 3 2 5% 6% 4 6% 7% 8% 10% 43%	2743
August	1st to 10th	Day	7% 4 2 4 6% 4 6% 6% 6% 11% 45%	2179
	11th to 20th	Day	9% 5% 2 5% 6% 3 5% 6% 7% 9% 44%	2125
	21st to end	Day	6% 4 2 5% 5% 3 5% 6% 6% 9% 49%	2376
September	1st to 10th	Day	10% 6% 2 5% 5% 3 4 5% 5% 7% 47%	2160
	11th to 20th	Day	7% 6% 2 5% 5% 2 5% 5% 6% 7% 49%	2044
	21st to end	Day	9% 4 2 5% 4 2 4 4 4 7% 55%	1980
October	1st to 10th	Day	10% 5% 1 4 5% 2 4 4 5% 6% 55%	1961
	11th to 20th	Day	14% 5% 2 4 5% 2 3 4 4 7% 49%	1800
	21st to end	Day	18% 6% 2 4 6% 2 3 4 4 6% 45%	1854
November	1st to 10th	Day	8% 5% 2 3 6% 3 4 4 5% 5% 54%	1672
	11th to 20th	Day	14% 6% 3 6% 5% 3 4 4 5% 5% 46%	1710
	21st to end	Day	18% 9% 3 6% 5% 3 3 4 4 5% 42%	1710
December	1st to 10th	Day	15% 12% 4 6% 5% 2 3 3 4 6% 39%	1647
	11th to 20th	Day	15% 10% 4 7% 6% 3 5% 5% 5% 6% 34%	1918
	21st to end	Day	22% 14% 5% 7% 6% 3 4 4 4 5% 26%	2783
January	1st to 10th	Night	15% 10% 4 7% 5% 3 3 4 5% 6% 38%	2648
	11th to 20th	Night	19% 9% 4 8% 5% 2 4 4 5% 5% 35%	2653
	21st to end	Night	17% 9% 3 7% 6% 3 4 4 5% 6% 35%	2665
February	1st to 10th	Night	19% 11% 5% 7% 5% 3 4 5% 4 5% 31%	2196
	11th to 20th	Night	15% 8% 4 6% 6% 3 4 4 4 5% 40%	2098
	21st to end	Night	19% 9% 3 8% 5% 4 3 5% 4 5% 36%	1776
March	1st to 10th	Night	16% 8% 3 5% 4 3 4 4 3 6% 43%	2160
	11th to 20th	Night	16% 8% 4 6% 6% 3 5% 4 4 6% 39%	2110
	21st to end	Night	20% 7% 4 5% 6% 3 4 5% 5% 6% 34%	1980
April	1st to 10th	Night	11% 6% 3 5% 5% 3 3 5% 4 7% 47%	1800
	11th to 20th	Night	16% 6% 2 4 4 3 4 5% 6% 7% 44%	1775
	21st to end	Night	19% 6% 3 5% 5% 3 5% 4 5% 6% 39%	1800
May	1st to 10th	Night	15% 6% 3 5% 6% 3 4 4 5% 6% 44%	1634
	11th to 20th	Night	11% 7% 3 6% 6% 4 4 5% 6% 6% 42%	1592
	21st to end	Night	6% 4 3 6% 6% 4 6% 7% 7% 10% 41%	1595
June	1st to 10th	Night	9% 5% 2 5% 4 3 4 5% 5% 8% 49%	1440
	11th to 20th	Night	5% 3 2 4 5% 3 4 5% 6% 8% 55%	1440
	21st to end	Night	5% 3 2 3 4 3 4 5% 7% 10% 53%	1440
July	1st to 10th	Night	7% 4 2 4 4 2 6% 6% 7% 11% 48%	1440
	11th to 20th	Night	5% 3 2 5% 4 3 4 6% 5% 8% 56%	1440
	21st to end	Night	7% 4 2 5% 5% 3 5% 5% 7% 8% 49%	1575
August	1st to 10th	Night	6% 3 2 4 4 3 5% 4 6% 10% 53%	1754
	11th to 20th	Night	5% 5% 1 5% 4 3 5% 5% 6% 9% 50%	1776
	21st to end	Night	5% 4 2 6% 4 2 4 4 5% 9% 54%	1980
September	1st to 10th	Night	10% 5% 2 5% 4 3 3 5% 4 6% 54%	1800
	11th to 20th	Night	7% 4 2 5% 5% 3 4 5% 5% 8% 53%	1898
	21st to end	Night	11% 5% 2 4 4 2 3 4 5% 7% 55%	1980
October	1st to 10th	Night	7% 5% 2 4 4 3 3 3 5% 6% 57%	1997
	11th to 20th	Night	14% 4 2 5% 4 2 3 3 4 5% 54%	2160
	21st to end	Night	19% 7% 3 5% 4 2 3 3 4 5% 45%	2502
November	1st to 10th	Night	11% 6% 2 3 3 2 3 3 5% 5% 57%	2406
	11th to 20th	Night	13% 5% 2 5% 4 2 3 3 5% 6% 51%	2470
	21st to end	Night	18% 6% 3 5% 4 2 4 3 4 6% 46%	2470
December	1st to 10th	Night	19% 9% 3 6% 5% 3 4 4 5% 6% 37%	2531
	11th to 20th	Night	17% 7% 4 6% 4 3 4 4 5% 5% 40%	3279
	21st to end	Night	20% 14% 5% 7% 6% 3 5% 4 4 5% 26%	4884

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	51% 3 11% 22% 11% 2	1518
	11th to 20th	Day	52% 5% 10% 23% 10%	1524
	21st to end	Day	50% 4 11% 24% 9% 2	1836
February	1st to 10th	Day	50% 5% 11% 21% 11% 1	1763
	11th to 20th	Day	50% 4 9% 21% 13% 2	1758
	21st to end	Day	50% 4 10% 20% 12% 4	1480
March	1st to 10th	Day	44% 5% 8% 23% 17% 2	1800
	11th to 20th	Day	51% 5% 12% 20% 10% 2	1864
	21st to end	Day	54% 5% 12% 19% 9% 1	2376
April	1st to 10th	Day	36% 5% 13% 28% 16% 1	2160
	11th to 20th	Day	43% 6% 11% 22% 15% 3	2134
	21st to end	Day	44% 6% 11% 25% 12% 2	2160
May	1st to 10th	Day	47% 8% 12% 24% 9% 1	2326
	11th to 20th	Day	42% 7% 13% 20% 16% 2	2305
	21st to end	Day	40% 11% 14% 21% 12% 2	2677
June	1st to 10th	Day	34% 8% 12% 25% 18% 2	2520
	11th to 20th	Day	30% 9% 12% 26% 21% 3	2520
	21st to end	Day	32% 8% 15% 23% 16% 6%	2520
July	1st to 10th	Day	35% 10% 14% 23% 14% 4	2451
	11th to 20th	Day	29% 8% 15% 26% 18% 4	2445
	21st to end	Day	32% 10% 14% 28% 14% 2	2591
August	1st to 10th	Day	33% 9% 14% 29% 14% 1	2165
	11th to 20th	Day	34% 8% 14% 27% 15% 2	2125
	21st to end	Day	30% 8% 15% 24% 17% 6%	2376
September	1st to 10th	Day	35% 6% 9% 28% 17% 5%	2160
	11th to 20th	Day	33% 5% 10% 26% 23% 2	2044
	21st to end	Day	30% 5% 8% 26% 28% 4	1980
October	1st to 10th	Day	30% 5% 9% 26% 25% 5%	1961
	11th to 20th	Day	36% 4 8% 25% 22% 6%	1800
	21st to end	Day	41% 5% 7% 25% 19% 3	1854
November	1st to 10th	Day	31% 5% 10% 29% 18% 6%	1672
	11th to 20th	Day	40% 4 7% 25% 19% 5%	1710
	21st to end	Day	45% 3 9% 25% 15% 2	1710
December	1st to 10th	Day	47% 4 12% 23% 12% 1	1647
	11th to 20th	Day	49% 6% 8% 26% 10% 1	1915
	21st to end	Day	60% 4 11% 15% 10% 1	2783
January	1st to 10th	Night	47% 3 10% 23% 15% 1	2648
	11th to 20th	Night	51% 5% 10% 21% 11% 1	2653
	21st to end	Night	50% 4 12% 21% 12% 2	2665
February	1st to 10th	Night	55% 5% 9% 20% 10% 1	2196
	11th to 20th	Night	47% 5% 8% 23% 15% 2	2099
	21st to end	Night	50% 4 10% 19% 13% 3	1776
March	1st to 10th	Night	44% 4 8% 20% 20% 4	2160
	11th to 20th	Night	47% 5% 12% 19% 15% 3	2110
	21st to end	Night	50% 5% 12% 20% 10% 2	1980
April	1st to 10th	Night	37% 5% 12% 26% 18% 3	1800
	11th to 20th	Night	39% 6% 9% 22% 19% 5%	1775
	21st to end	Night	46% 5% 10% 22% 15% 3	1800
May	1st to 10th	Night	41% 7% 10% 27% 14% 2	1634
	11th to 20th	Night	42% 8% 10% 22% 16% 2	1593
	21st to end	Night	35% 9% 15% 23% 16% 4	1596
June	1st to 10th	Night	32% 6% 13% 25% 22% 2	1440
	11th to 20th	Night	25% 6% 14% 25% 25% 5%	1440
	21st to end	Night	24% 7% 17% 26% 19% 7%	1440
July	1st to 10th	Night	28% 9% 16% 24% 16% 6%	1400
	11th to 20th	Night	24% 8% 13% 30% 19% 5%	1392
	21st to end	Night	29% 7% 13% 30% 19% 3	1487
August	1st to 10th	Night	26% 7% 17% 27% 20% 2	1744
	11th to 20th	Night	28% 8% 13% 28% 21% 3	1776
	21st to end	Night	27% 7% 14% 26% 21% 6%	1980
September	1st to 10th	Night	31% 6% 7% 28% 20% 6%	1800
	11th to 20th	Night	29% 6% 8% 28% 24% 5%	1898
	21st to end	Night	29% 4 9% 24% 26% 7%	1980
October	1st to 10th	Night	28% 5% 9% 23% 29% 6%	1997
	11th to 20th	Night	35% 3 7% 25% 23% 7%	2160
	21st to end	Night	42% 4 6% 26% 17% 6%	2502
November	1st to 10th	Night	30% 4 10% 25% 25% 6%	2406
	11th to 20th	Night	35% 3 8% 25% 24% 6%	2470
	21st to end	Night	41% 3 9% 25% 19% 2	2470
December	1st to 10th	Night	48% 5% 11% 22% 13% 1	2531
	11th to 20th	Night	45% 5% 9% 24% 15% 1	3281
	21st to end	Night	61% 4 9% 16% 8% 2	4884

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	26% 14% 29% 23% 7% 1	270
	11th to 20th	Day	27% 17% 33% 19% 5%	270
	21st to end	Day	22% 17% 39% 16% 5%	282
February	1st to 10th	Day	26% 11% 44% 15% 3	240
	11th to 20th	Day	29% 19% 36% 13% 3	240
	21st to end	Day	30% 12% 33% 20% 4 1	198
March	1st to 10th	Day	20% 17% 39% 20% 5%	240
	11th to 20th	Day	25% 19% 29% 21% 6%	248
	21st to end	Day	27% 14% 30% 20% 9% 1	462
April	1st to 10th	Day	13% 14% 35% 26% 11% 1	420
	11th to 20th	Day	19% 14% 25% 24% 15% 1	412
	21st to end	Day	21% 10% 31% 24% 10% 3	420
May	1st to 10th	Day	20% 11% 27% 29% 9% 4	423
	11th to 20th	Day	19% 6% 24% 27% 17% 7%	447
	21st to end	Day	12% 2 23% 30% 23% 10%	631
June	1st to 10th	Day	11% 4 16% 28% 27% 14%	630
	11th to 20th	Day	7% 3 18% 33% 30% 10%	630
	21st to end	Day	9% 2 22% 33% 25% 10%	630
July	1st to 10th	Day	11% 2 10% 23% 26% 26%	621
	11th to 20th	Day	6% 3 14% 29% 32% 17%	618
	21st to end	Day	8% 2 11% 30% 32% 17%	684
August	1st to 10th	Day	9% 3 9% 28% 31% 20%	463
	11th to 20th	Day	13% 1 13% 26% 33% 13%	439
	21st to end	Day	8% 2 10% 23% 36% 21%	495
September	1st to 10th	Day	12% 2 12% 23% 35% 16%	450
	11th to 20th	Day	9% 3 8% 27% 34% 19%	450
	21st to end	Day	10% 5% 21% 26% 23% 14%	450
October	1st to 10th	Day	11% 3 19% 37% 19% 10%	431
	11th to 20th	Day	13% 11% 37% 24% 11% 3	270
	21st to end	Day	25% 9% 30% 26% 10%	297
November	1st to 10th	Day	10% 6% 34% 26% 20% 5%	270
	11th to 20th	Day	15% 16% 29% 25% 12% 3	270
	21st to end	Day	23% 11% 30% 23% 11% 1	270
December	1st to 10th	Day	17% 18% 33% 20% 9% 3	270
	11th to 20th	Day	22% 12% 36% 24% 7%	270
	21st to end	Day	27% 18% 33% 16% 6%	297
January	1st to 10th	Night	20% 14% 35% 27% 4	950
	11th to 20th	Night	24% 14% 36% 21% 4	950
	21st to end	Night	21% 10% 40% 26% 3	1025
February	1st to 10th	Night	24% 13% 36% 24% 3 1	756
	11th to 20th	Night	21% 14% 38% 25% 2	703
	21st to end	Night	23% 14% 38% 24% 2	592
March	1st to 10th	Night	20% 12% 34% 30% 4	720
	11th to 20th	Night	21% 10% 33% 28% 7% 1	680
	21st to end	Night	23% 10% 29% 31% 7% 1	594
April	1st to 10th	Night	13% 10% 34% 33% 9%	540
	11th to 20th	Night	19% 8% 28% 30% 14% 1	533
	21st to end	Night	21% 6% 31% 32% 9% 1	540
May	1st to 10th	Night	16% 7% 27% 37% 12%	540
	11th to 20th	Night	16% 4 24% 33% 22% 2	531
	21st to end	Night	8% 2 17% 42% 26% 4	584
June	1st to 10th	Night	11% 2 16% 40% 27% 3	540
	11th to 20th	Night	5% 3 15% 45% 29% 3	540
	21st to end	Night	5% 2 17% 41% 32% 3	540
July	1st to 10th	Night	10% 1 7% 31% 41% 10%	525
	11th to 20th	Night	6% 2 9% 35% 43% 5%	522
	21st to end	Night	8% 1 11% 37% 36% 7%	591
August	1st to 10th	Night	7% 1 5% 42% 38% 7%	537
	11th to 20th	Night	6% 1 10% 39% 39% 6%	534
	21st to end	Night	7% 1 6% 36% 43% 7%	594
September	1st to 10th	Night	13% 1 10% 33% 37% 6%	540
	11th to 20th	Night	9% 2 11% 31% 41% 7%	638
	21st to end	Night	13% 2 18% 32% 28% 6%	720
October	1st to 10th	Night	9% 3 19% 38% 26% 5%	720
	11th to 20th	Night	17% 6% 28% 31% 15% 3	720
	21st to end	Night	22% 7% 30% 30% 10% 1	792
November	1st to 10th	Night	14% 6% 28% 38% 14% 1	740
	11th to 20th	Night	15% 9% 30% 33% 12% 1	760
	21st to end	Night	22% 8% 29% 29% 10% 1	760
December	1st to 10th	Night	23% 8% 32% 30% 6%	821
	11th to 20th	Night	24% 8% 29% 33% 6% 1	950
	21st to end	Night	26% 12% 34% 23% 5%	1045

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