Bell Isle State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bell Isle State Park clear sky chart from 2005-11-06 to 2025-09-19.

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% 6% 2 6% 4 4 4 4 6% 8% 42%	126042
	Night	14% 7% 2 6% 4 4 4 3 5% 7% 44%	123022
Transparency	Day	38% 6% 12% 23% 17% 4	129633
	Night	38% 5% 11% 23% 18% 4	127500
Seeing	Day	17% 11% 29% 26% 14% 4	16291
	Night	17% 11% 28% 29% 13% 2	25797

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	14% 4 1 4 3 3 3 3 4 5% 56%	3754
	11th to 20th	Day	12% 8% 2 6% 3 3 3 3 4 5% 50%	4060
	21st to end	Day	12% 8% 3 8% 4 4 4 3 5% 5% 45%	4466
February	1st to 10th	Day	13% 8% 2 6% 5% 4 5% 4 6% 8% 39%	1800
	11th to 20th	Day	21% 7% 2 4 3 3 4 3 4 6% 44%	1874
	21st to end	Day	16% 6% 3 6% 4 6% 4 4 4 6% 40%	1650
March	1st to 10th	Day	18% 7% 2 6% 4 4 4 4 6% 7% 39%	4791
	11th to 20th	Day	10% 6% 2 5% 3 3 4 3 5% 7% 52%	4980
	21st to end	Day	16% 6% 2 6% 4 4 5% 4 5% 6% 43%	5617
April	1st to 10th	Day	12% 6% 2 5% 4 3 4 3 5% 7% 49%	2400
	11th to 20th	Day	11% 7% 2 5% 4 3 5% 4 5% 6% 48%	2374
	21st to end	Day	15% 6% 2 5% 4 4 4 4 6% 7% 43%	2400
May	1st to 10th	Day	16% 8% 2 7% 4 5% 5% 5% 7% 10% 31%	5532
	11th to 20th	Day	19% 6% 3 7% 5% 5% 5% 4 6% 9% 31%	6130
	21st to end	Day	14% 6% 2 5% 4 4 5% 4 6% 9% 40%	6934
June	1st to 10th	Day	11% 5% 2 6% 4 5% 5% 4 7% 9% 42%	2800
	11th to 20th	Day	11% 5% 2 6% 5% 4 5% 5% 7% 11% 42%	2800
	21st to end	Day	8% 4 1 6% 6% 5% 6% 5% 7% 10% 43%	2800
July	1st to 10th	Day	6% 5% 2 6% 4 5% 5% 5% 8% 11% 42%	6360
	11th to 20th	Day	11% 7% 3 8% 6% 7% 7% 5% 9% 12% 26%	6097
	21st to end	Day	6% 5% 2 6% 5% 5% 6% 5% 8% 12% 39%	6424
August	1st to 10th	Day	14% 8% 3 8% 5% 5% 6% 5% 8% 10% 29%	4234
	11th to 20th	Day	9% 7% 3 8% 6% 6% 6% 5% 7% 9% 36%	3884
	21st to end	Day	9% 4 2 5% 3 4 4 4 6% 11% 49%	4312
September	1st to 10th	Day	13% 6% 2 5% 4 5% 5% 4 6% 7% 44%	2400
	11th to 20th	Day	13% 7% 2 7% 4 4 4 4 5% 7% 42%	2376
	21st to end	Day	21% 8% 3 6% 3 4 3 4 5% 6% 38%	2021
October	1st to 10th	Day	15% 6% 2 6% 4 3 3 2 4 7% 46%	1900
	11th to 20th	Day	16% 5% 2 5% 2 3 4 3 4 5% 52%	1900
	21st to end	Day	13% 4 2 5% 4 3 4 3 4 7% 51%	2090
November	1st to 10th	Day	13% 5% 2 5% 3 3 3 3 4 6% 52%	1852
	11th to 20th	Day	14% 5% 2 5% 3 4 3 3 5% 6% 49%	1800
	21st to end	Day	14% 4 2 5% 3 4 4 3 4 5% 52%	1680
December	1st to 10th	Day	10% 5% 2 5% 4 3 3 3 4 6% 54%	2600
	11th to 20th	Day	18% 8% 2 5% 3 3 3 2 3 4 47%	2990
	21st to end	Day	13% 6% 2 5% 3 4 4 3 5% 7% 48%	3960
January	1st to 10th	Night	13% 6% 3 6% 4 3 3 2 3 5% 52%	6188
	11th to 20th	Night	13% 6% 2 5% 3 3 3 2 3 5% 54%	5900
	21st to end	Night	16% 7% 2 6% 3 3 3 3 4 6% 49%	6490
February	1st to 10th	Night	16% 9% 2 5% 4 4 3 4 6% 6% 42%	2600
	11th to 20th	Night	20% 7% 2 5% 4 3 4 3 4 5% 43%	2411
	21st to end	Night	17% 7% 2 4 4 3 4 3 4 7% 45%	1980
March	1st to 10th	Night	17% 7% 2 5% 3 3 4 2 4 6% 46%	5059
	11th to 20th	Night	13% 7% 2 5% 3 3 3 3 4 6% 50%	4980
	21st to end	Night	14% 7% 3 5% 3 4 4 3 4 6% 47%	5313
April	1st to 10th	Night	14% 8% 2 6% 4 3 4 3 6% 7% 42%	2000
	11th to 20th	Night	11% 6% 2 6% 4 3 4 4 4 8% 49%	1975
	21st to end	Night	15% 6% 2 6% 4 4 4 3 5% 7% 45%	2000
May	1st to 10th	Night	17% 7% 2 8% 5% 5% 5% 4 6% 9% 32%	4406
	11th to 20th	Night	22% 8% 2 6% 4 4 4 3 6% 7% 33%	3759
	21st to end	Night	15% 7% 3 6% 4 4 4 4 6% 8% 39%	3920
June	1st to 10th	Night	12% 5% 2 6% 5% 5% 5% 5% 6% 8% 40%	1600
	11th to 20th	Night	10% 6% 2 7% 4 5% 6% 4 8% 10% 39%	1600
	21st to end	Night	7% 5% 2 6% 4 5% 5% 5% 7% 11% 43%	1600
July	1st to 10th	Night	9% 5% 3 7% 5% 5% 5% 4 8% 11% 38%	3598
	11th to 20th	Night	9% 6% 3 7% 6% 5% 6% 5% 9% 12% 31%	3841
	21st to end	Night	8% 7% 3 8% 6% 5% 6% 5% 7% 10% 36%	4427
August	1st to 10th	Night	16% 8% 4 7% 4 4 5% 4 7% 10% 31%	2915
	11th to 20th	Night	8% 6% 3 8% 5% 5% 5% 4 7% 9% 39%	3130
	21st to end	Night	9% 5% 2 5% 4 4 4 4 5% 8% 50%	3586
September	1st to 10th	Night	12% 5% 2 6% 4 4 4 3 5% 7% 47%	2000
	11th to 20th	Night	11% 6% 2 6% 3 4 5% 3 6% 7% 46%	1981
	21st to end	Night	20% 8% 3 6% 3 3 4 4 5% 6% 37%	2153
October	1st to 10th	Night	14% 5% 3 6% 4 3 4 3 5% 6% 46%	2280
	11th to 20th	Night	16% 5% 2 5% 4 4 3 2 4 6% 51%	2280
	21st to end	Night	14% 6% 2 4 3 3 3 2 5% 6% 52%	2508
November	1st to 10th	Night	12% 7% 2 5% 4 3 3 3 4 6% 50%	2446
	11th to 20th	Night	17% 6% 2 4 3 3 3 4 5% 6% 47%	2600
	21st to end	Night	12% 5% 2 5% 4 3 4 3 5% 7% 50%	2715
December	1st to 10th	Night	10% 5% 2 5% 3 3 4 3 5% 7% 55%	4580
	11th to 20th	Night	19% 7% 3 6% 4 5% 4 3 5% 6% 39%	5205
	21st to end	Night	12% 7% 2 6% 3 3 3 3 5% 7% 47%	6996

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	31% 3 5% 28% 24% 9%	3755
	11th to 20th	Day	37% 4 5% 22% 25% 7%	4060
	21st to end	Day	41% 3 9% 29% 15% 3	4466
February	1st to 10th	Day	44% 4 10% 27% 13% 3	1800
	11th to 20th	Day	43% 4 7% 22% 20% 4	1883
	21st to end	Day	45% 4 11% 19% 16% 4	1650
March	1st to 10th	Day	44% 4 9% 17% 18% 7%	4791
	11th to 20th	Day	32% 4 9% 23% 24% 8%	4980
	21st to end	Day	42% 5% 10% 18% 19% 6%	5617
April	1st to 10th	Day	35% 5% 11% 23% 20% 7%	2400
	11th to 20th	Day	36% 4 11% 22% 21% 6%	2374
	21st to end	Day	40% 5% 10% 23% 17% 6%	2400
May	1st to 10th	Day	46% 8% 15% 18% 11% 1	5564
	11th to 20th	Day	47% 7% 13% 22% 10% 1	6134
	21st to end	Day	39% 7% 14% 23% 15% 2	6949
June	1st to 10th	Day	36% 7% 15% 26% 14% 3	2800
	11th to 20th	Day	35% 8% 16% 24% 16% 2	2800
	21st to end	Day	34% 7% 16% 25% 17% 2	2800
July	1st to 10th	Day	33% 10% 21% 20% 13% 3	6290
	11th to 20th	Day	46% 11% 21% 16% 5% 1	6023
	21st to end	Day	35% 9% 15% 21% 19% 1	6240
August	1st to 10th	Day	47% 8% 16% 21% 7% 1	4221
	11th to 20th	Day	40% 7% 15% 23% 13%	3921
	21st to end	Day	29% 6% 16% 27% 20% 2	4312
September	1st to 10th	Day	38% 7% 14% 20% 18% 4	2400
	11th to 20th	Day	41% 5% 8% 24% 20% 3	2376
	21st to end	Day	48% 5% 7% 22% 15% 4	2021
October	1st to 10th	Day	34% 6% 8% 20% 26% 5%	3160
	11th to 20th	Day	27% 3 5% 21% 35% 9%	3140
	21st to end	Day	22% 3 8% 29% 27% 11%	3428
November	1st to 10th	Day	35% 4 9% 26% 22% 4	1852
	11th to 20th	Day	37% 3 10% 21% 23% 6%	1800
	21st to end	Day	36% 3 8% 28% 21% 4	1680
December	1st to 10th	Day	32% 4 9% 30% 19% 6%	2600
	11th to 20th	Day	43% 3 12% 22% 16% 4	2986
	21st to end	Day	36% 5% 12% 29% 16% 1	3960
January	1st to 10th	Night	36% 3 6% 22% 27% 7%	6188
	11th to 20th	Night	35% 2 5% 26% 25% 6%	5900
	21st to end	Night	39% 3 6% 29% 19% 3	6490
February	1st to 10th	Night	42% 4 11% 24% 16% 2	2600
	11th to 20th	Night	44% 3 7% 21% 19% 6%	2413
	21st to end	Night	41% 4 9% 22% 19% 7%	1980
March	1st to 10th	Night	40% 4 7% 22% 20% 8%	5059
	11th to 20th	Night	36% 4 8% 21% 23% 8%	4980
	21st to end	Night	40% 4 8% 23% 19% 7%	5313
April	1st to 10th	Night	42% 5% 9% 18% 22% 4	2000
	11th to 20th	Night	35% 5% 11% 22% 22% 5%	1975
	21st to end	Night	39% 6% 12% 22% 18% 4	2000
May	1st to 10th	Night	47% 7% 16% 19% 9% 2	4436
	11th to 20th	Night	49% 5% 13% 22% 10% 1	3760
	21st to end	Night	42% 6% 14% 24% 13% 1	3927
June	1st to 10th	Night	38% 9% 12% 23% 17% 2	1600
	11th to 20th	Night	38% 7% 16% 22% 15% 2	1600
	21st to end	Night	33% 8% 15% 23% 18% 3	1600
July	1st to 10th	Night	39% 11% 17% 18% 13% 2	3560
	11th to 20th	Night	42% 12% 24% 17% 4 1	3795
	21st to end	Night	41% 9% 13% 22% 14%	4297
August	1st to 10th	Night	47% 7% 17% 23% 6%	2904
	11th to 20th	Night	38% 9% 18% 22% 13%	3159
	21st to end	Night	31% 6% 12% 24% 25% 1	3586
September	1st to 10th	Night	36% 6% 16% 20% 17% 5%	2000
	11th to 20th	Night	35% 6% 10% 24% 21% 2	1981
	21st to end	Night	47% 6% 9% 17% 17% 3	2153
October	1st to 10th	Night	36% 5% 11% 21% 21% 6%	3800
	11th to 20th	Night	25% 3 8% 23% 31% 9%	3779
	21st to end	Night	21% 2 6% 33% 26% 11%	4120
November	1st to 10th	Night	36% 4 10% 25% 20% 5%	2446
	11th to 20th	Night	39% 4 8% 22% 20% 8%	2600
	21st to end	Night	33% 4 9% 27% 22% 5%	2715
December	1st to 10th	Night	30% 3 10% 29% 24% 4	4580
	11th to 20th	Night	47% 4 12% 20% 13% 5%	5208
	21st to end	Night	37% 4 12% 30% 16% 1	6996

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% 18% 38% 13% 4	234
	11th to 20th	Day	24% 24% 36% 14% 2	300
	21st to end	Day	20% 19% 40% 18% 2	330
February	1st to 10th	Day	22% 16% 43% 14% 5%	300
	11th to 20th	Day	32% 18% 35% 13% 2	422
	21st to end	Day	24% 20% 35% 17% 4	414
March	1st to 10th	Day	20% 20% 37% 17% 5% 1	500
	11th to 20th	Day	22% 19% 36% 17% 6% 1	500
	21st to end	Day	19% 18% 38% 21% 4 1	550
April	1st to 10th	Day	17% 19% 41% 17% 6% 1	500
	11th to 20th	Day	14% 17% 34% 25% 7% 3	492
	21st to end	Day	19% 13% 36% 24% 7% 1	500
May	1st to 10th	Day	18% 15% 34% 22% 9% 2	503
	11th to 20th	Day	22% 7% 30% 29% 9% 2	527
	21st to end	Day	19% 7% 24% 30% 16% 4	573
June	1st to 10th	Day	12% 5% 29% 30% 19% 5%	530
	11th to 20th	Day	12% 5% 23% 35% 19% 6%	530
	21st to end	Day	9% 5% 23% 36% 21% 5%	530
July	1st to 10th	Day	9% 4 19% 36% 24% 7%	525
	11th to 20th	Day	5% 2 14% 41% 29% 9%	524
	21st to end	Day	10% 3 18% 36% 26% 8%	576
August	1st to 10th	Day	13% 3 18% 33% 27% 6%	526
	11th to 20th	Day	10% 3 19% 34% 26% 8%	519
	21st to end	Day	10% 5% 19% 28% 26% 12%	583
September	1st to 10th	Day	15% 5% 19% 29% 20% 12%	530
	11th to 20th	Day	14% 5% 21% 31% 20% 9%	522
	21st to end	Day	29% 6% 26% 22% 13% 4	490
October	1st to 10th	Day	18% 7% 23% 28% 16% 8%	490
	11th to 20th	Day	16% 10% 27% 28% 16% 3	490
	21st to end	Day	15% 10% 34% 25% 12% 4	539
November	1st to 10th	Day	18% 9% 30% 25% 13% 4	442
	11th to 20th	Day	16% 17% 34% 24% 9% 1	400
	21st to end	Day	16% 19% 30% 24% 10% 1	280
December	1st to 10th	Day	18% 13% 48% 16% 6% 1	200
	11th to 20th	Day	23% 13% 38% 19% 8%	200
	21st to end	Day	21% 13% 34% 23% 8%	220
January	1st to 10th	Night	20% 21% 36% 20% 3	800
	11th to 20th	Night	20% 17% 34% 24% 5%	800
	21st to end	Night	19% 18% 36% 24% 2	880
February	1st to 10th	Night	19% 13% 42% 22% 4	800
	11th to 20th	Night	25% 20% 38% 14% 3	783
	21st to end	Night	22% 17% 36% 22% 3	660
March	1st to 10th	Night	19% 18% 36% 24% 5%	800
	11th to 20th	Night	23% 15% 34% 22% 5% 1	800
	21st to end	Night	20% 15% 38% 23% 4	880
April	1st to 10th	Night	20% 16% 40% 20% 4	800
	11th to 20th	Night	14% 13% 37% 28% 8% 1	791
	21st to end	Night	19% 8% 36% 30% 7%	800
May	1st to 10th	Night	17% 11% 35% 29% 7% 1	768
	11th to 20th	Night	18% 5% 30% 35% 11% 1	474
	21st to end	Night	15% 4 21% 36% 23% 2	433
June	1st to 10th	Night	14% 2 20% 44% 18% 2	400
	11th to 20th	Night	14% 4 18% 43% 19% 3	400
	21st to end	Night	10% 2 21% 45% 20% 3	400
July	1st to 10th	Night	12% 4 12% 41% 28% 3	390
	11th to 20th	Night	4 2 12% 43% 34% 5%	488
	21st to end	Night	7% 4 16% 42% 27% 5%	657
August	1st to 10th	Night	12% 3 13% 39% 30% 4	597
	11th to 20th	Night	14% 3 12% 39% 29% 3	747
	21st to end	Night	10% 3 14% 37% 31% 5%	880
September	1st to 10th	Night	15% 3 13% 37% 26% 5%	800
	11th to 20th	Night	13% 3 17% 32% 29% 5%	793
	21st to end	Night	25% 5% 21% 30% 17% 2	760
October	1st to 10th	Night	17% 6% 20% 30% 23% 5%	760
	11th to 20th	Night	17% 11% 25% 30% 15% 2	760
	21st to end	Night	18% 11% 27% 28% 15% 2	836
November	1st to 10th	Night	16% 10% 27% 31% 14% 3	780
	11th to 20th	Night	19% 14% 29% 28% 10% 1	800
	21st to end	Night	15% 16% 30% 29% 10% 1	800
December	1st to 10th	Night	22% 12% 36% 22% 8% 1	800
	11th to 20th	Night	20% 11% 38% 25% 6%	800
	21st to end	Night	19% 14% 30% 33% 5%	880

Page generated at 2025-09-16 01:49:10. Version ac07

Copyright © 2025 Attilla Danko.