J.S.M. Blue Lake Township Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the J.S.M. Blue Lake Township Observatory clear sky chart from 2005-11-06 to 2025-12-18.

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% 12% 4 11% 6% 5% 4 3 5% 6% 31%	126489
	Night	13% 13% 5% 12% 6% 5% 4 3 4 5% 28%	124738
Transparency	Day	51% 7% 11% 19% 10% 1	129982
	Night	55% 8% 11% 17% 9% 1	129332
Seeing	Day	19% 15% 30% 22% 10% 3	17114
	Night	18% 13% 31% 28% 9% 1	26822

By Month

Percentage Cloud Cover NE (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	8% 17% 10% 30% 7% 5% 4 2 3 3 9%	3617
	11th to 20th	Day	10% 17% 7% 22% 15% 11% 6% 3 3 2 4	3589
	21st to end	Day	12% 16% 9% 22% 8% 4 5% 3 4 4 12%	3982
February	1st to 10th	Day	9% 18% 8% 15% 16% 7% 5% 2 4 5% 11%	1745
	11th to 20th	Day	10% 17% 6% 17% 12% 7% 4 4 4 4 16%	1915
	21st to end	Day	11% 18% 8% 15% 9% 5% 3 3 4 5% 18%	1650
March	1st to 10th	Day	11% 11% 3 14% 7% 5% 4 3 5% 5% 31%	4478
	11th to 20th	Day	10% 12% 5% 14% 6% 5% 5% 4 7% 7% 25%	4904
	21st to end	Day	19% 13% 6% 17% 6% 4 4 3 3 4 21%	5594
April	1st to 10th	Day	16% 16% 5% 10% 5% 4 5% 4 4 5% 26%	2400
	11th to 20th	Day	18% 15% 4 7% 4 3 3 3 4 6% 32%	2501
	21st to end	Day	15% 13% 4 9% 4 4 4 4 6% 7% 30%	2600
May	1st to 10th	Day	16% 10% 3 6% 3 4 4 3 5% 7% 40%	5888
	11th to 20th	Day	10% 11% 3 6% 4 4 4 4 5% 6% 42%	5989
	21st to end	Day	14% 9% 3 7% 5% 4 4 4 5% 7% 39%	6949
June	1st to 10th	Day	14% 7% 2 6% 5% 5% 4 4 6% 8% 40%	2965
	11th to 20th	Day	13% 7% 2 7% 4 5% 5% 4 7% 8% 37%	3000
	21st to end	Day	15% 7% 2 7% 4 5% 5% 4 7% 8% 38%	2953
July	1st to 10th	Day	16% 6% 2 6% 4 3 4 4 6% 9% 40%	6359
	11th to 20th	Day	10% 6% 2 5% 4 4 5% 4 6% 8% 47%	6360
	21st to end	Day	8% 6% 2 6% 4 4 4 4 7% 10% 46%	6926
August	1st to 10th	Day	8% 6% 3 7% 5% 6% 6% 5% 8% 9% 37%	4332
	11th to 20th	Day	14% 7% 2 5% 4 4 4 4 5% 7% 44%	4174
	21st to end	Day	13% 7% 2 7% 5% 4 4 3 5% 6% 42%	4543
September	1st to 10th	Day	14% 6% 3 7% 4 4 4 3 6% 8% 40%	2350
	11th to 20th	Day	13% 6% 2 6% 4 4 4 3 6% 8% 45%	2200
	21st to end	Day	15% 8% 3 7% 4 4 5% 4 6% 8% 36%	2200
October	1st to 10th	Day	17% 11% 3 7% 4 4 4 3 5% 6% 36%	2190
	11th to 20th	Day	23% 17% 4 9% 5% 4 4 4 5% 5% 21%	1910
	21st to end	Day	21% 17% 4 10% 6% 5% 5% 3 6% 6% 18%	1980
November	1st to 10th	Day	16% 18% 5% 7% 5% 4 4 3 5% 6% 25%	1852
	11th to 20th	Day	14% 22% 8% 12% 6% 4 6% 3 5% 5% 16%	1890
	21st to end	Day	15% 24% 10% 14% 6% 3 3 3 3 4 14%	1732
December	1st to 10th	Day	11% 26% 11% 22% 7% 5% 4 2 3 3 6%	2350
	11th to 20th	Day	12% 22% 11% 20% 10% 5% 5% 2 3 3 7%	2670
	21st to end	Day	19% 24% 8% 19% 6% 4 3 2 3 4 8%	3752
January	1st to 10th	Night	9% 16% 9% 29% 8% 5% 3 2 2 3 13%	6348
	11th to 20th	Night	10% 15% 7% 20% 15% 11% 5% 3 3 3 7%	6316
	21st to end	Night	10% 18% 9% 23% 9% 6% 5% 3 3 4 10%	6996
February	1st to 10th	Night	9% 17% 7% 15% 13% 9% 6% 3 4 4 14%	2655
	11th to 20th	Night	11% 15% 7% 17% 9% 7% 5% 3 4 5% 18%	2368
	21st to end	Night	13% 15% 6% 14% 9% 4 4 3 4 5% 22%	1980
March	1st to 10th	Night	14% 10% 4 8% 7% 4 4 3 4 7% 34%	5362
	11th to 20th	Night	10% 12% 5% 10% 5% 5% 4 4 6% 7% 32%	5055
	21st to end	Night	17% 13% 6% 11% 5% 3 4 3 4 5% 29%	5381
April	1st to 10th	Night	18% 13% 3 10% 5% 4 5% 4 5% 5% 29%	2000
	11th to 20th	Night	20% 12% 4 6% 4 4 4 4 4 6% 33%	1847
	21st to end	Night	16% 12% 4 8% 5% 3 3 4 5% 6% 35%	1800
May	1st to 10th	Night	14% 8% 3 6% 4 4 4 3 5% 7% 40%	4053
	11th to 20th	Night	11% 13% 3 7% 4 4 4 4 5% 6% 39%	3907
	21st to end	Night	17% 8% 3 5% 3 3 3 3 5% 6% 43%	3949
June	1st to 10th	Night	12% 7% 3 6% 5% 4 4 4 6% 7% 42%	1430
	11th to 20th	Night	9% 5% 2 7% 5% 4 6% 4 7% 8% 42%	1400
	21st to end	Night	12% 9% 2 6% 4 4 4 4 6% 7% 43%	1439
July	1st to 10th	Night	12% 7% 2 7% 4 4 5% 4 6% 8% 42%	3620
	11th to 20th	Night	9% 6% 2 5% 4 3 4 3 5% 6% 52%	3620
	21st to end	Night	7% 6% 2 5% 4 3 4 4 5% 7% 52%	3948
August	1st to 10th	Night	10% 7% 2 6% 4 5% 5% 3 6% 8% 43%	2819
	11th to 20th	Night	15% 6% 2 5% 3 3 3 3 5% 6% 49%	2875
	21st to end	Night	10% 7% 2 6% 4 4 5% 4 6% 7% 46%	3352
September	1st to 10th	Night	11% 6% 2 6% 4 3 3 3 5% 7% 50%	2030
	11th to 20th	Night	13% 5% 2 5% 4 3 4 3 4 8% 49%	2200
	21st to end	Night	17% 8% 2 7% 4 4 4 4 6% 6% 38%	2200
October	1st to 10th	Night	17% 7% 3 7% 3 3 4 4 6% 6% 41%	2209
	11th to 20th	Night	20% 14% 4 8% 5% 4 4 4 4 6% 27%	2486
	21st to end	Night	22% 15% 3 8% 5% 5% 5% 4 4 6% 25%	2860
November	1st to 10th	Night	13% 18% 5% 9% 5% 5% 4 3 4 7% 27%	2666
	11th to 20th	Night	13% 20% 7% 12% 5% 5% 5% 3 4 5% 20%	2730
	21st to end	Night	16% 21% 9% 13% 5% 5% 4 3 4 4 14%	2877
December	1st to 10th	Night	10% 19% 10% 22% 7% 5% 4 4 4 4 10%	5060
	11th to 20th	Night	10% 23% 9% 18% 9% 5% 4 3 4 4 11%	5692
	21st to end	Night	20% 24% 10% 16% 5% 4 3 2 4 4 10%	7208

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	78% 7% 6% 6% 3 1	3618
	11th to 20th	Day	85% 6% 5% 3 1	3620
	21st to end	Day	74% 8% 9% 6% 3	3982
February	1st to 10th	Day	75% 6% 8% 9% 2	1745
	11th to 20th	Day	70% 7% 8% 9% 5% 1	1925
	21st to end	Day	66% 6% 10% 14% 3 1	1650
March	1st to 10th	Day	52% 6% 16% 15% 9% 2	4480
	11th to 20th	Day	54% 7% 14% 16% 7% 1	4904
	21st to end	Day	65% 7% 8% 13% 7%	5594
April	1st to 10th	Day	59% 6% 10% 16% 9% 1	2400
	11th to 20th	Day	53% 5% 9% 20% 12% 1	2501
	21st to end	Day	51% 8% 11% 14% 13% 3	2600
May	1st to 10th	Day	43% 7% 11% 19% 17% 3	5897
	11th to 20th	Day	40% 8% 10% 23% 17% 3	5993
	21st to end	Day	43% 7% 10% 19% 18% 3	6949
June	1st to 10th	Day	39% 8% 12% 25% 14% 2	2965
	11th to 20th	Day	40% 9% 13% 21% 16% 1	3000
	21st to end	Day	42% 7% 14% 23% 13% 1	2953
July	1st to 10th	Day	39% 6% 14% 25% 15% 1	6291
	11th to 20th	Day	32% 7% 13% 35% 13% 1	6285
	21st to end	Day	31% 7% 14% 32% 15% 1	6728
August	1st to 10th	Day	38% 10% 14% 26% 12% 1	4317
	11th to 20th	Day	39% 8% 11% 29% 13% 1	4213
	21st to end	Day	41% 7% 13% 29% 9% 1	4542
September	1st to 10th	Day	41% 8% 12% 23% 15% 1	2350
	11th to 20th	Day	35% 8% 15% 28% 13% 1	2200
	21st to end	Day	45% 7% 14% 23% 11%	2200
October	1st to 10th	Day	35% 5% 8% 34% 17%	3567
	11th to 20th	Day	54% 7% 7% 20% 12%	3087
	21st to end	Day	62% 7% 11% 16% 4	3180
November	1st to 10th	Day	57% 7% 11% 17% 7%	1852
	11th to 20th	Day	67% 9% 11% 9% 4	1890
	21st to end	Day	73% 6% 10% 9% 2	1732
December	1st to 10th	Day	81% 7% 6% 5% 1	2350
	11th to 20th	Day	81% 6% 6% 5% 1	2670
	21st to end	Day	80% 6% 5% 5% 4	3752
January	1st to 10th	Night	76% 6% 7% 6% 3 1	6348
	11th to 20th	Night	79% 9% 6% 4 2	6360
	21st to end	Night	75% 9% 6% 8% 2	6996
February	1st to 10th	Night	72% 7% 7% 9% 3 1	2655
	11th to 20th	Night	66% 7% 10% 13% 4	2369
	21st to end	Night	64% 6% 11% 14% 5%	1980
March	1st to 10th	Night	49% 6% 17% 18% 10%	5373
	11th to 20th	Night	48% 8% 18% 18% 7% 1	5056
	21st to end	Night	56% 7% 10% 16% 10% 1	5381
April	1st to 10th	Night	54% 8% 9% 18% 10% 1	2000
	11th to 20th	Night	51% 6% 9% 19% 13% 2	1847
	21st to end	Night	49% 7% 11% 17% 14% 3	1800
May	1st to 10th	Night	42% 7% 11% 18% 19% 4	4060
	11th to 20th	Night	43% 8% 8% 23% 17% 1	3908
	21st to end	Night	41% 6% 12% 22% 14% 5%	3950
June	1st to 10th	Night	39% 7% 12% 24% 17% 1	1430
	11th to 20th	Night	36% 8% 15% 25% 14% 2	1400
	21st to end	Night	39% 9% 12% 24% 15% 2	1439
July	1st to 10th	Night	37% 7% 14% 24% 15% 3	3580
	11th to 20th	Night	31% 7% 12% 32% 18% 1	3572
	21st to end	Night	30% 8% 16% 29% 16%	3832
August	1st to 10th	Night	37% 8% 16% 26% 13% 1	2810
	11th to 20th	Night	34% 6% 16% 30% 13%	2902
	21st to end	Night	34% 8% 16% 25% 16% 1	3352
September	1st to 10th	Night	33% 8% 15% 26% 16% 1	2030
	11th to 20th	Night	34% 7% 17% 29% 13% 1	2200
	21st to end	Night	45% 7% 15% 22% 10% 1	2200
October	1st to 10th	Night	35% 7% 12% 31% 14% 1	3612
	11th to 20th	Night	45% 7% 11% 22% 14%	4048
	21st to end	Night	54% 7% 13% 20% 5%	4610
November	1st to 10th	Night	55% 8% 12% 17% 7%	2666
	11th to 20th	Night	63% 8% 12% 10% 6% 1	2730
	21st to end	Night	71% 8% 11% 8% 1	2877
December	1st to 10th	Night	73% 11% 8% 7% 1	5060
	11th to 20th	Night	75% 8% 7% 8% 2	5691
	21st to end	Night	77% 8% 6% 5% 4	7208

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	19% 20% 40% 16% 5%	300
	11th to 20th	Day	25% 21% 35% 16% 2	300
	21st to end	Day	22% 18% 37% 18% 5%	330
February	1st to 10th	Day	19% 30% 36% 11% 3 1	300
	11th to 20th	Day	23% 29% 34% 12% 2	300
	21st to end	Day	27% 27% 37% 8% 1	249
March	1st to 10th	Day	23% 27% 35% 13% 2	300
	11th to 20th	Day	24% 16% 36% 17% 6%	463
	21st to end	Day	26% 17% 30% 20% 7% 1	550
April	1st to 10th	Day	26% 18% 33% 16% 6% 1	500
	11th to 20th	Day	30% 19% 27% 12% 9% 2	492
	21st to end	Day	24% 16% 32% 18% 9% 1	500
May	1st to 10th	Day	22% 20% 30% 16% 8% 3	503
	11th to 20th	Day	19% 12% 30% 27% 9% 3	577
	21st to end	Day	17% 14% 28% 28% 11% 3	789
June	1st to 10th	Day	15% 15% 34% 24% 9% 3	730
	11th to 20th	Day	17% 13% 32% 26% 9% 3	730
	21st to end	Day	19% 10% 30% 28% 10% 2	730
July	1st to 10th	Day	10% 9% 29% 32% 14% 7%	721
	11th to 20th	Day	12% 9% 30% 28% 15% 6%	718
	21st to end	Day	10% 7% 32% 31% 15% 4	794
August	1st to 10th	Day	8% 7% 26% 28% 21% 10%	586
	11th to 20th	Day	15% 7% 19% 31% 18% 11%	519
	21st to end	Day	17% 10% 23% 29% 15% 7%	583
September	1st to 10th	Day	18% 9% 25% 24% 15% 8%	530
	11th to 20th	Day	12% 8% 20% 29% 20% 11%	530
	21st to end	Day	18% 11% 23% 29% 14% 5%	530
October	1st to 10th	Day	22% 16% 26% 22% 12% 2	530
	11th to 20th	Day	29% 16% 35% 18% 2	440
	21st to end	Day	29% 22% 30% 13% 4 1	363
November	1st to 10th	Day	27% 20% 33% 15% 4 1	330
	11th to 20th	Day	24% 24% 33% 16% 2	330
	21st to end	Day	24% 26% 34% 14% 2	253
December	1st to 10th	Day	26% 22% 35% 11% 4 2	220
	11th to 20th	Day	29% 21% 38% 12% 1	214
	21st to end	Day	28% 26% 34% 10% 1 1	280
January	1st to 10th	Night	18% 18% 36% 22% 6% 1	1000
	11th to 20th	Night	21% 18% 35% 20% 5%	1000
	21st to end	Night	16% 14% 38% 26% 5% 1	1100
February	1st to 10th	Night	16% 18% 38% 24% 4	855
	11th to 20th	Night	18% 22% 32% 22% 5%	783
	21st to end	Night	21% 17% 35% 23% 3	660
March	1st to 10th	Night	16% 15% 38% 23% 8% 1	800
	11th to 20th	Night	17% 17% 37% 24% 5%	800
	21st to end	Night	20% 12% 31% 29% 7% 1	845
April	1st to 10th	Night	22% 13% 35% 24% 5% 1	600
	11th to 20th	Night	24% 12% 31% 24% 8%	593
	21st to end	Night	19% 13% 31% 30% 7% 1	600
May	1st to 10th	Night	16% 10% 33% 33% 8%	600
	11th to 20th	Night	17% 11% 30% 33% 9% 1	591
	21st to end	Night	14% 8% 27% 36% 13% 1	650
June	1st to 10th	Night	14% 7% 32% 38% 8% 1	430
	11th to 20th	Night	8% 7% 31% 44% 11%	400
	21st to end	Night	13% 7% 29% 37% 13% 1	439
July	1st to 10th	Night	9% 3 21% 45% 20% 1	585
	11th to 20th	Night	9% 4 23% 38% 24% 2	582
	21st to end	Night	10% 4 25% 38% 22% 1	657
August	1st to 10th	Night	11% 4 18% 43% 24% 1	597
	11th to 20th	Night	11% 5% 17% 36% 27% 3	594
	21st to end	Night	14% 6% 21% 38% 20% 1	660
September	1st to 10th	Night	14% 4 23% 34% 21% 4	630
	11th to 20th	Night	15% 6% 20% 34% 22% 4	800
	21st to end	Night	19% 9% 23% 31% 15% 3	800
October	1st to 10th	Night	20% 9% 27% 31% 11% 1	800
	11th to 20th	Night	28% 14% 30% 23% 6%	800
	21st to end	Night	30% 14% 29% 21% 5% 1	880
November	1st to 10th	Night	23% 15% 32% 24% 5% 1	820
	11th to 20th	Night	21% 18% 37% 20% 4	840
	21st to end	Night	25% 16% 38% 20% 2	845
December	1st to 10th	Night	19% 19% 38% 20% 3	1050
	11th to 20th	Night	20% 19% 39% 17% 3 1	1036
	21st to end	Night	25% 16% 37% 18% 3	1100

Page generated at 2025-12-15 01:13:52. Version ac07

Copyright © 2025 Attilla Danko.