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 2024-11-05.

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%	101102
	Night	15% 7% 2 6% 4 4 4 3 5% 7% 43%	97896
Transparency	Day	39% 6% 12% 23% 17% 4	104737
	Night	39% 5% 11% 23% 18% 4	102400
Seeing	Day	16% 10% 28% 27% 14% 4	15164
	Night	17% 10% 28% 30% 13% 2	24686

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	16% 6% 1 4 3 3 3 3 4 5% 52%	2618
	11th to 20th	Day	13% 9% 2 7% 4 3 4 3 5% 6% 44%	2840
	21st to end	Day	14% 10% 3 8% 4 3 3 3 5% 5% 40%	3124
February	1st to 10th	Day	13% 8% 2 6% 5% 4 5% 4 6% 8% 39%	1710
	11th to 20th	Day	20% 6% 2 4 3 3 5% 3 4 6% 45%	1777
	21st to end	Day	17% 6% 3 7% 5% 6% 4 4 5% 6% 38%	1570
March	1st to 10th	Day	22% 9% 3 6% 4 3 3 3 5% 6% 36%	3333
	11th to 20th	Day	10% 4 1 4 3 4 4 3 5% 7% 55%	3480
	21st to end	Day	20% 7% 2 5% 4 4 5% 3 4 6% 41%	3925
April	1st to 10th	Day	12% 6% 2 5% 4 3 4 3 5% 7% 50%	2280
	11th to 20th	Day	10% 7% 2 5% 4 3 5% 4 5% 7% 49%	2254
	21st to end	Day	16% 6% 2 5% 4 4 4 4 5% 8% 43%	2280
May	1st to 10th	Day	19% 8% 2 8% 5% 5% 5% 4 6% 9% 30%	3850
	11th to 20th	Day	20% 6% 3 7% 5% 5% 4 4 6% 8% 32%	4266
	21st to end	Day	9% 5% 2 5% 4 4 5% 4 7% 9% 46%	4823
June	1st to 10th	Day	11% 5% 2 5% 4 5% 4 5% 7% 10% 42%	2660
	11th to 20th	Day	10% 5% 2 6% 5% 4 5% 5% 7% 11% 42%	2660
	21st to end	Day	8% 4 1 6% 6% 5% 6% 5% 7% 10% 42%	2660
July	1st to 10th	Day	6% 4 2 5% 4 5% 6% 5% 9% 12% 42%	4440
	11th to 20th	Day	11% 6% 2 7% 6% 5% 6% 5% 8% 11% 34%	4261
	21st to end	Day	8% 6% 3 8% 6% 6% 7% 6% 7% 10% 32%	4466
August	1st to 10th	Day	14% 7% 3 8% 5% 5% 6% 5% 8% 10% 28%	4104
	11th to 20th	Day	9% 7% 3 8% 6% 6% 6% 5% 7% 9% 37%	3763
	21st to end	Day	9% 4 2 5% 3 4 4 4 6% 11% 49%	4180
September	1st to 10th	Day	13% 6% 2 5% 4 5% 5% 4 6% 7% 43%	2280
	11th to 20th	Day	12% 7% 2 7% 4 4 4 4 5% 7% 43%	2280
	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	14% 5% 2 5% 3 3 3 3 4 7% 52%	1799
	11th to 20th	Day	14% 5% 2 5% 3 4 3 3 5% 5% 49%	1710
	21st to end	Day	14% 4 2 5% 3 4 3 3 5% 5% 51%	1596
December	1st to 10th	Day	15% 7% 3 5% 4 4 3 4 6% 7% 43%	1520
	11th to 20th	Day	16% 7% 2 5% 3 3 3 3 3 4 51%	1910
	21st to end	Day	16% 7% 2 6% 4 4 4 3 5% 6% 43%	2772
January	1st to 10th	Night	14% 7% 3 6% 4 3 4 3 4 6% 46%	4324
	11th to 20th	Night	16% 8% 3 6% 3 3 3 3 4 5% 46%	4120
	21st to end	Night	19% 8% 3 6% 3 3 3 3 4 5% 43%	4532
February	1st to 10th	Night	15% 9% 2 6% 4 4 3 4 6% 6% 42%	2470
	11th to 20th	Night	19% 8% 2 5% 4 3 4 3 4 5% 44%	2288
	21st to end	Night	18% 7% 2 4 4 3 3 3 4 7% 45%	1884
March	1st to 10th	Night	24% 9% 3 6% 4 3 4 3 4 6% 37%	3517
	11th to 20th	Night	15% 7% 1 4 3 3 3 3 4 6% 51%	3480
	21st to end	Night	17% 8% 3 5% 3 3 3 2 4 4 48%	3705
April	1st to 10th	Night	14% 8% 2 6% 4 3 4 3 6% 7% 42%	1900
	11th to 20th	Night	11% 6% 2 6% 4 3 4 3 4 8% 49%	1875
	21st to end	Night	16% 6% 2 6% 4 3 4 3 5% 7% 44%	1900
May	1st to 10th	Night	21% 7% 2 7% 4 4 4 4 5% 8% 33%	3074
	11th to 20th	Night	23% 8% 2 6% 4 4 4 3 5% 6% 35%	2623
	21st to end	Night	10% 5% 2 5% 4 4 4 4 7% 9% 44%	2732
June	1st to 10th	Night	12% 5% 2 5% 5% 5% 5% 5% 6% 9% 40%	1520
	11th to 20th	Night	10% 6% 1 6% 4 5% 6% 4 8% 11% 39%	1520
	21st to end	Night	7% 5% 2 6% 5% 5% 5% 5% 7% 10% 43%	1520
July	1st to 10th	Night	7% 5% 2 7% 5% 5% 6% 4 8% 11% 40%	2520
	11th to 20th	Night	9% 5% 2 6% 5% 5% 5% 5% 8% 12% 38%	2694
	21st to end	Night	11% 9% 3 9% 7% 5% 5% 5% 6% 8% 32%	3087
August	1st to 10th	Night	16% 8% 4 7% 4 4 5% 4 7% 10% 31%	2825
	11th to 20th	Night	8% 6% 3 8% 5% 5% 5% 4 7% 9% 40%	3032
	21st to end	Night	9% 5% 2 5% 4 4 4 4 5% 8% 50%	3476
September	1st to 10th	Night	12% 5% 2 6% 4 4 4 3 6% 7% 47%	1900
	11th to 20th	Night	10% 6% 2 6% 3 4 5% 3 6% 7% 47%	1900
	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	13% 7% 2 5% 4 3 3 3 4 6% 50%	2379
	11th to 20th	Night	16% 6% 2 4 3 3 3 4 4 6% 48%	2470
	21st to end	Night	12% 5% 2 4 4 3 4 3 5% 7% 50%	2579
December	1st to 10th	Night	17% 8% 2 7% 4 3 4 4 4 6% 42%	2660
	11th to 20th	Night	17% 6% 3 5% 4 4 4 3 4 7% 44%	3285
	21st to end	Night	14% 7% 3 6% 4 4 4 3 6% 7% 43%	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	35% 4 6% 33% 18% 4	2619
	11th to 20th	Day	41% 4 7% 22% 21% 5%	2840
	21st to end	Day	46% 4 10% 24% 14% 3	3124
February	1st to 10th	Day	44% 4 10% 27% 13% 3	1710
	11th to 20th	Day	41% 4 7% 23% 20% 4	1786
	21st to end	Day	47% 4 12% 17% 16% 4	1570
March	1st to 10th	Day	50% 4 9% 17% 15% 5%	3333
	11th to 20th	Day	28% 4 9% 26% 25% 8%	3480
	21st to end	Day	45% 5% 10% 19% 18% 3	3925
April	1st to 10th	Day	34% 5% 11% 23% 20% 7%	2280
	11th to 20th	Day	36% 4 11% 22% 21% 6%	2254
	21st to end	Day	41% 5% 10% 23% 16% 6%	2280
May	1st to 10th	Day	50% 6% 12% 20% 9% 2	3885
	11th to 20th	Day	48% 6% 13% 23% 9% 1	4270
	21st to end	Day	32% 8% 14% 25% 18% 3	4837
June	1st to 10th	Day	36% 7% 15% 27% 13% 2	2660
	11th to 20th	Day	34% 8% 16% 25% 16% 2	2660
	21st to end	Day	35% 7% 15% 24% 17% 2	2660
July	1st to 10th	Day	32% 11% 23% 19% 12% 4	4370
	11th to 20th	Day	42% 8% 21% 22% 7% 1	4187
	21st to end	Day	43% 9% 14% 17% 15% 1	4324
August	1st to 10th	Day	47% 8% 17% 21% 7% 1	4091
	11th to 20th	Day	40% 7% 15% 24% 13%	3800
	21st to end	Day	29% 6% 16% 27% 19% 2	4180
September	1st to 10th	Day	39% 7% 14% 19% 18% 4	2280
	11th to 20th	Day	40% 5% 8% 25% 20% 3	2280
	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	34% 4 9% 26% 22% 5%	1799
	11th to 20th	Day	37% 3 10% 21% 23% 6%	1710
	21st to end	Day	36% 3 8% 28% 20% 5%	1596
December	1st to 10th	Day	41% 5% 12% 25% 14% 4	1520
	11th to 20th	Day	39% 3 8% 28% 16% 6%	1906
	21st to end	Day	42% 5% 9% 29% 14% 1	2772
January	1st to 10th	Night	39% 4 7% 26% 19% 5%	4324
	11th to 20th	Night	42% 3 7% 24% 21% 3	4120
	21st to end	Night	46% 3 6% 25% 17% 3	4532
February	1st to 10th	Night	41% 4 11% 25% 17% 2	2470
	11th to 20th	Night	43% 3 7% 22% 20% 6%	2290
	21st to end	Night	41% 4 9% 22% 18% 6%	1884
March	1st to 10th	Night	49% 4 7% 22% 16% 2	3517
	11th to 20th	Night	35% 4 7% 23% 24% 6%	3480
	21st to end	Night	41% 3 8% 23% 20% 5%	3705
April	1st to 10th	Night	41% 5% 9% 18% 23% 4	1900
	11th to 20th	Night	34% 5% 11% 22% 22% 5%	1875
	21st to end	Night	40% 6% 12% 22% 16% 4	1900
May	1st to 10th	Night	50% 5% 14% 20% 10% 2	3104
	11th to 20th	Night	49% 5% 13% 23% 9% 1	2624
	21st to end	Night	34% 7% 16% 25% 16% 1	2739
June	1st to 10th	Night	38% 9% 12% 24% 16% 1	1520
	11th to 20th	Night	37% 7% 15% 23% 15% 2	1520
	21st to end	Night	34% 8% 15% 23% 17% 3	1520
July	1st to 10th	Night	37% 12% 18% 20% 11% 3	2480
	11th to 20th	Night	36% 10% 24% 23% 6% 1	2645
	21st to end	Night	48% 8% 13% 19% 12%	2988
August	1st to 10th	Night	47% 7% 18% 22% 6%	2814
	11th to 20th	Night	38% 8% 18% 22% 13%	3061
	21st to end	Night	31% 6% 12% 25% 25% 1	3476
September	1st to 10th	Night	37% 6% 17% 18% 17% 5%	1900
	11th to 20th	Night	35% 6% 10% 24% 22% 2	1900
	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% 3 10% 25% 20% 5%	2379
	11th to 20th	Night	38% 4 8% 21% 20% 8%	2470
	21st to end	Night	34% 4 9% 27% 22% 5%	2579
December	1st to 10th	Night	44% 3 10% 24% 15% 3	2660
	11th to 20th	Night	41% 3 10% 22% 19% 5%	3288
	21st to end	Night	40% 4 13% 27% 14% 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	22% 18% 40% 15% 4	210
	11th to 20th	Day	24% 23% 36% 14% 2	270
	21st to end	Day	20% 18% 42% 19% 2	297
February	1st to 10th	Day	20% 14% 46% 15% 6%	270
	11th to 20th	Day	28% 19% 37% 14% 2	385
	21st to end	Day	25% 19% 35% 17% 4	382
March	1st to 10th	Day	20% 19% 38% 17% 5% 1	460
	11th to 20th	Day	22% 19% 37% 17% 6% 1	460
	21st to end	Day	19% 17% 38% 22% 4 1	506
April	1st to 10th	Day	15% 18% 42% 18% 7% 1	460
	11th to 20th	Day	13% 16% 35% 26% 8% 3	452
	21st to end	Day	20% 13% 36% 23% 7% 1	460
May	1st to 10th	Day	18% 14% 32% 24% 9% 2	463
	11th to 20th	Day	23% 6% 28% 31% 10% 2	487
	21st to end	Day	18% 5% 23% 32% 18% 4	529
June	1st to 10th	Day	12% 4 27% 32% 20% 5%	490
	11th to 20th	Day	11% 5% 22% 36% 20% 6%	490
	21st to end	Day	10% 5% 25% 36% 20% 4	490
July	1st to 10th	Day	9% 4 19% 35% 25% 8%	485
	11th to 20th	Day	5% 1 14% 40% 31% 9%	484
	21st to end	Day	11% 2 19% 36% 24% 7%	532
August	1st to 10th	Day	13% 3 17% 33% 28% 6%	486
	11th to 20th	Day	9% 4 19% 33% 27% 8%	479
	21st to end	Day	10% 5% 16% 29% 27% 13%	539
September	1st to 10th	Day	15% 4 17% 30% 21% 13%	490
	11th to 20th	Day	13% 4 20% 31% 21% 10%	490
	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% 14% 4	425
	11th to 20th	Day	16% 17% 32% 25% 10% 1	370
	21st to end	Day	16% 17% 30% 26% 10% 1	256
December	1st to 10th	Day	17% 12% 47% 16% 7% 1	180
	11th to 20th	Day	22% 13% 37% 20% 8%	180
	21st to end	Day	22% 12% 35% 21% 9% 1	198
January	1st to 10th	Night	19% 19% 37% 21% 4	760
	11th to 20th	Night	20% 18% 33% 24% 5%	760
	21st to end	Night	20% 17% 36% 25% 2	836
February	1st to 10th	Night	18% 13% 42% 23% 4	760
	11th to 20th	Night	23% 21% 39% 15% 3	743
	21st to end	Night	22% 17% 35% 22% 3	628
March	1st to 10th	Night	18% 17% 36% 24% 5%	760
	11th to 20th	Night	23% 15% 34% 22% 5% 1	760
	21st to end	Night	20% 14% 37% 24% 5%	836
April	1st to 10th	Night	20% 16% 40% 20% 4	760
	11th to 20th	Night	13% 13% 37% 29% 8% 1	751
	21st to end	Night	19% 8% 35% 31% 7%	760
May	1st to 10th	Night	18% 11% 34% 28% 8% 1	730
	11th to 20th	Night	18% 5% 29% 36% 11% 1	450
	21st to end	Night	15% 3 20% 36% 24% 2	411
June	1st to 10th	Night	14% 2 21% 42% 19% 2	380
	11th to 20th	Night	13% 4 18% 44% 19% 3	380
	21st to end	Night	10% 2 21% 46% 19% 3	380
July	1st to 10th	Night	11% 4 13% 41% 29% 3	370
	11th to 20th	Night	4 2 11% 44% 33% 5%	463
	21st to end	Night	7% 4 16% 42% 27% 4	624
August	1st to 10th	Night	11% 2 13% 39% 31% 3	567
	11th to 20th	Night	14% 3 12% 39% 29% 3	709
	21st to end	Night	11% 2 13% 36% 32% 6%	836
September	1st to 10th	Night	15% 2 13% 37% 27% 5%	760
	11th to 20th	Night	13% 3 17% 32% 30% 6%	760
	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% 9% 27% 31% 14% 3	760
	11th to 20th	Night	19% 14% 28% 29% 11% 1	760
	21st to end	Night	14% 15% 29% 30% 10% 1	760
December	1st to 10th	Night	22% 12% 35% 21% 8% 1	760
	11th to 20th	Night	19% 11% 39% 25% 6%	760
	21st to end	Night	19% 14% 29% 33% 5%	836

Page generated at 2024-11-03 02:11:12. Version ac07

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