Kresge Environmental Education Center
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Kresge Environmental Education Center clear sky chart from 2005-11-06 to 2026-07-16.

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% 10% 4 8% 5% 5% 5% 4 5% 7% 33%	137046
	Night	13% 11% 4 9% 5% 5% 4 4 5% 6% 34%	135731
Transparency	Day	48% 6% 11% 20% 13% 1	140601
	Night	49% 5% 12% 21% 12% 1	140249
Seeing	Day	18% 12% 29% 23% 13% 6%	17660
	Night	19% 11% 30% 29% 11% 1	27252

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	12% 17% 8% 15% 7% 5% 5% 3 4 4 22%	4691
	11th to 20th	Day	12% 17% 7% 18% 11% 8% 5% 3 4 4 11%	4710
	21st to end	Day	16% 15% 5% 12% 9% 6% 6% 3 4 5% 18%	5624
February	1st to 10th	Day	13% 15% 5% 15% 8% 5% 4 3 4 5% 22%	1890
	11th to 20th	Day	13% 14% 5% 12% 8% 6% 5% 3 4 6% 23%	1963
	21st to end	Day	13% 16% 5% 12% 7% 5% 4 3 5% 5% 24%	1730
March	1st to 10th	Day	15% 11% 5% 10% 6% 4 4 3 4 5% 32%	4708
	11th to 20th	Day	11% 14% 5% 9% 5% 5% 5% 4 5% 8% 30%	5090
	21st to end	Day	17% 14% 5% 10% 5% 4 4 3 4 6% 28%	5586
April	1st to 10th	Day	17% 13% 4 9% 5% 4 4 3 5% 6% 30%	2439
	11th to 20th	Day	16% 11% 3 7% 5% 4 4 4 5% 6% 35%	2681
	21st to end	Day	15% 9% 3 8% 6% 5% 4 3 5% 7% 35%	2730
May	1st to 10th	Day	16% 8% 3 8% 5% 5% 5% 4 5% 7% 34%	7616
	11th to 20th	Day	15% 8% 3 7% 5% 5% 5% 4 6% 8% 35%	7626
	21st to end	Day	14% 6% 2 6% 4 4 4 4 5% 6% 44%	8451
June	1st to 10th	Day	10% 6% 2 6% 5% 5% 5% 4 7% 8% 42%	3145
	11th to 20th	Day	10% 6% 3 7% 4 5% 5% 4 7% 8% 41%	3150
	21st to end	Day	10% 7% 2 6% 5% 5% 5% 5% 8% 9% 38%	3114
July	1st to 10th	Day	9% 6% 2 7% 5% 5% 5% 5% 7% 10% 39%	6500
	11th to 20th	Day	7% 5% 2 6% 4 5% 5% 4 7% 9% 46%	6431
	21st to end	Day	8% 5% 2 6% 5% 5% 5% 4 6% 9% 46%	6573
August	1st to 10th	Day	12% 6% 2 6% 5% 5% 5% 4 7% 8% 40%	4234
	11th to 20th	Day	11% 6% 2 6% 5% 5% 5% 4 7% 9% 40%	4174
	21st to end	Day	9% 5% 3 7% 5% 5% 6% 5% 6% 9% 40%	4661
September	1st to 10th	Day	9% 7% 2 8% 5% 6% 6% 5% 6% 9% 39%	2260
	11th to 20th	Day	10% 5% 2 5% 4 4 4 4 6% 9% 47%	2200
	21st to end	Day	16% 7% 3 7% 5% 5% 5% 5% 5% 8% 35%	2200
October	1st to 10th	Day	14% 6% 3 6% 5% 4 5% 3 6% 7% 42%	2131
	11th to 20th	Day	18% 10% 3 7% 5% 5% 5% 4 5% 6% 33%	2000
	21st to end	Day	19% 12% 3 7% 4 4 5% 3 5% 7% 29%	2033
November	1st to 10th	Day	12% 10% 4 8% 6% 5% 4 4 5% 7% 34%	1852
	11th to 20th	Day	14% 12% 5% 11% 6% 5% 4 4 5% 7% 27%	1890
	21st to end	Day	16% 16% 5% 9% 6% 5% 4 4 4 6% 24%	1701
December	1st to 10th	Day	14% 16% 6% 11% 6% 5% 6% 5% 6% 6% 19%	2680
	11th to 20th	Day	17% 20% 6% 9% 5% 4 5% 3 5% 5% 21%	2771
	21st to end	Day	25% 20% 6% 12% 6% 4 4 3 4 5% 12%	3811
January	1st to 10th	Night	14% 13% 6% 12% 5% 5% 5% 4 5% 6% 27%	8232
	11th to 20th	Night	9% 16% 7% 16% 9% 8% 6% 4 4 5% 17%	8280
	21st to end	Night	12% 14% 8% 11% 6% 5% 5% 4 5% 6% 23%	8549
February	1st to 10th	Night	14% 15% 5% 10% 7% 5% 6% 4 5% 5% 24%	2730
	11th to 20th	Night	13% 14% 5% 10% 6% 5% 5% 4 5% 5% 28%	2539
	21st to end	Night	17% 12% 5% 9% 5% 5% 5% 4 5% 6% 28%	2076
March	1st to 10th	Night	14% 12% 4 9% 4 3 3 3 4 7% 36%	5364
	11th to 20th	Night	10% 9% 4 8% 5% 4 4 4 6% 8% 37%	5090
	21st to end	Night	15% 10% 3 9% 5% 5% 4 3 5% 5% 36%	5588
April	1st to 10th	Night	18% 11% 3 7% 4 5% 3 3 6% 6% 33%	2199
	11th to 20th	Night	18% 8% 2 8% 4 5% 4 3 5% 7% 36%	1887
	21st to end	Night	17% 9% 2 6% 4 4 4 4 6% 7% 37%	1890
May	1st to 10th	Night	17% 8% 3 8% 4 5% 4 4 5% 7% 35%	5237
	11th to 20th	Night	16% 8% 3 6% 4 4 4 3 5% 7% 41%	5234
	21st to end	Night	15% 6% 2 5% 4 4 4 3 5% 6% 45%	5687
June	1st to 10th	Night	11% 5% 2 6% 3 4 3 4 6% 9% 46%	1470
	11th to 20th	Night	10% 5% 3 6% 3 4 5% 4 6% 9% 45%	1470
	21st to end	Night	9% 6% 2 6% 4 5% 4 4 6% 8% 49%	1499
July	1st to 10th	Night	7% 5% 2 5% 5% 4 5% 3 7% 10% 46%	3698
	11th to 20th	Night	8% 4 2 5% 4 4 4 4 6% 9% 50%	3657
	21st to end	Night	7% 5% 2 7% 4 5% 5% 4 5% 7% 49%	4270
August	1st to 10th	Night	10% 6% 2 6% 4 4 4 3 5% 8% 48%	2915
	11th to 20th	Night	11% 6% 2 5% 4 4 4 4 7% 8% 47%	2875
	21st to end	Night	7% 5% 3 7% 4 4 5% 4 5% 7% 48%	3223
September	1st to 10th	Night	10% 4 2 7% 4 6% 4 4 5% 7% 47%	2118
	11th to 20th	Night	9% 5% 2 5% 3 3 4 3 5% 6% 56%	2200
	21st to end	Night	14% 7% 3 7% 4 4 5% 3 5% 6% 43%	2200
October	1st to 10th	Night	15% 6% 2 6% 4 3 3 4 5% 7% 46%	2267
	11th to 20th	Night	18% 10% 3 7% 4 4 5% 4 5% 6% 35%	2400
	21st to end	Night	20% 9% 3 9% 5% 4 4 3 5% 5% 32%	2805
November	1st to 10th	Night	13% 10% 3 6% 4 4 4 3 5% 7% 41%	2666
	11th to 20th	Night	14% 12% 4 8% 5% 4 5% 5% 6% 7% 29%	2730
	21st to end	Night	18% 15% 3 8% 5% 4 5% 4 5% 6% 25%	2914
December	1st to 10th	Night	12% 16% 6% 12% 6% 5% 4 4 6% 7% 22%	4720
	11th to 20th	Night	14% 18% 6% 12% 6% 5% 4 3 5% 5% 22%	5648
	21st to end	Night	22% 21% 7% 11% 5% 4 3 3 3 4 16%	7404

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	66% 5% 10% 13% 5% 1	4692
	11th to 20th	Day	77% 4 8% 6% 5%	4710
	21st to end	Day	69% 4 9% 10% 7%	5624
February	1st to 10th	Day	63% 6% 8% 16% 7%	1890
	11th to 20th	Day	63% 4 9% 14% 9% 1	1972
	21st to end	Day	61% 6% 10% 15% 7% 2	1730
March	1st to 10th	Day	53% 5% 12% 18% 9% 2	4708
	11th to 20th	Day	51% 5% 13% 21% 8% 1	5090
	21st to end	Day	58% 5% 11% 15% 10% 2	5586
April	1st to 10th	Day	55% 5% 11% 19% 9% 1	2439
	11th to 20th	Day	48% 6% 11% 20% 13% 2	2681
	21st to end	Day	49% 6% 13% 20% 12% 1	2730
May	1st to 10th	Day	47% 6% 11% 21% 12% 3	7651
	11th to 20th	Day	45% 8% 10% 21% 15% 1	7630
	21st to end	Day	40% 5% 7% 20% 23% 4	8465
June	1st to 10th	Day	36% 8% 12% 26% 16% 2	3145
	11th to 20th	Day	38% 7% 12% 24% 16% 2	3150
	21st to end	Day	39% 9% 12% 24% 15% 1	3114
July	1st to 10th	Day	38% 7% 13% 25% 15% 2	6431
	11th to 20th	Day	32% 7% 12% 31% 17% 1	6356
	21st to end	Day	34% 6% 14% 23% 22% 1	6386
August	1st to 10th	Day	39% 7% 13% 22% 17% 1	4221
	11th to 20th	Day	39% 6% 13% 28% 12% 1	4213
	21st to end	Day	38% 7% 13% 28% 12% 1	4660
September	1st to 10th	Day	40% 8% 14% 25% 12% 2	2260
	11th to 20th	Day	33% 6% 13% 32% 16% 1	2200
	21st to end	Day	46% 6% 13% 22% 13% 1	2200
October	1st to 10th	Day	32% 4 10% 34% 17% 2	3469
	11th to 20th	Day	42% 4 11% 26% 16%	3240
	21st to end	Day	48% 5% 12% 23% 12% 1	3257
November	1st to 10th	Day	47% 6% 11% 24% 10% 1	1852
	11th to 20th	Day	56% 5% 13% 17% 8%	1890
	21st to end	Day	60% 4 13% 16% 6% 1	1701
December	1st to 10th	Day	64% 6% 17% 11% 3	2680
	11th to 20th	Day	65% 5% 10% 13% 6%	2767
	21st to end	Day	76% 4 8% 8% 5%	3811
January	1st to 10th	Night	58% 5% 12% 17% 7% 2	8233
	11th to 20th	Night	69% 5% 9% 10% 6% 1	8280
	21st to end	Night	61% 5% 9% 18% 7%	8549
February	1st to 10th	Night	61% 7% 9% 15% 7% 1	2730
	11th to 20th	Night	57% 5% 10% 18% 9% 1	2541
	21st to end	Night	57% 5% 12% 18% 7% 1	2076
March	1st to 10th	Night	49% 4 15% 22% 10% 1	5364
	11th to 20th	Night	42% 6% 16% 23% 12% 1	5090
	21st to end	Night	48% 5% 12% 20% 13% 2	5588
April	1st to 10th	Night	51% 5% 10% 20% 12% 2	2199
	11th to 20th	Night	47% 5% 11% 18% 17% 2	1887
	21st to end	Night	44% 6% 12% 20% 15% 3	1890
May	1st to 10th	Night	46% 6% 11% 18% 15% 4	5264
	11th to 20th	Night	44% 5% 10% 25% 14% 2	5235
	21st to end	Night	39% 5% 9% 23% 19% 5%	5697
June	1st to 10th	Night	35% 5% 10% 27% 20% 2	1470
	11th to 20th	Night	35% 6% 15% 23% 18% 2	1470
	21st to end	Night	33% 6% 13% 27% 19% 1	1499
July	1st to 10th	Night	33% 6% 14% 25% 18% 4	3660
	11th to 20th	Night	30% 6% 14% 31% 19% 1	3612
	21st to end	Night	33% 7% 14% 22% 22% 1	4144
August	1st to 10th	Night	34% 6% 15% 28% 16% 1	2904
	11th to 20th	Night	32% 7% 15% 32% 12% 2	2902
	21st to end	Night	34% 7% 13% 31% 14% 1	3223
September	1st to 10th	Night	35% 8% 11% 29% 15% 2	2118
	11th to 20th	Night	29% 7% 12% 32% 19% 2	2200
	21st to end	Night	41% 6% 11% 28% 13% 1	2200
October	1st to 10th	Night	27% 4 12% 32% 25% 1	3709
	11th to 20th	Night	44% 4 11% 23% 17%	3899
	21st to end	Night	44% 4 12% 28% 12% 1	4531
November	1st to 10th	Night	43% 5% 12% 26% 14% 1	2666
	11th to 20th	Night	52% 5% 14% 19% 9% 1	2730
	21st to end	Night	58% 5% 14% 17% 5%	2914
December	1st to 10th	Night	61% 6% 17% 13% 3	4720
	11th to 20th	Night	64% 5% 10% 13% 7% 1	5651
	21st to end	Night	72% 5% 9% 8% 6%	7404

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	23% 18% 38% 14% 6% 1	330
	11th to 20th	Day	20% 18% 45% 14% 4 1	330
	21st to end	Day	27% 18% 34% 17% 4 1	363
February	1st to 10th	Day	23% 22% 36% 15% 4 1	330
	11th to 20th	Day	23% 20% 35% 19% 2	330
	21st to end	Day	25% 28% 33% 12% 2	273
March	1st to 10th	Day	29% 16% 38% 13% 3 1	380
	11th to 20th	Day	22% 16% 34% 22% 7%	540
	21st to end	Day	28% 13% 31% 21% 6% 1	594
April	1st to 10th	Day	24% 16% 33% 19% 8% 1	540
	11th to 20th	Day	27% 15% 30% 17% 8% 4	532
	21st to end	Day	20% 12% 30% 24% 11% 2	540
May	1st to 10th	Day	20% 14% 31% 23% 9% 2	543
	11th to 20th	Day	19% 11% 30% 22% 12% 6%	567
	21st to end	Day	16% 7% 27% 26% 16% 8%	638
June	1st to 10th	Day	12% 9% 30% 31% 12% 5%	780
	11th to 20th	Day	13% 9% 31% 28% 15% 4	780
	21st to end	Day	12% 8% 29% 30% 16% 5%	780
July	1st to 10th	Day	9% 4 24% 31% 21% 11%	771
	11th to 20th	Day	9% 7% 26% 30% 19% 9%	744
	21st to end	Day	9% 4 23% 30% 23% 10%	647
August	1st to 10th	Day	9% 5% 19% 27% 25% 15%	526
	11th to 20th	Day	12% 4 18% 29% 24% 13%	519
	21st to end	Day	11% 8% 19% 27% 23% 12%	583
September	1st to 10th	Day	11% 7% 25% 25% 18% 15%	530
	11th to 20th	Day	10% 4 17% 23% 28% 18%	530
	21st to end	Day	18% 12% 19% 24% 20% 8%	530
October	1st to 10th	Day	16% 9% 27% 23% 17% 8%	530
	11th to 20th	Day	20% 15% 34% 23% 7% 1	530
	21st to end	Day	27% 14% 33% 19% 6% 1	416
November	1st to 10th	Day	16% 20% 35% 21% 7% 1	330
	11th to 20th	Day	22% 21% 34% 15% 6% 2	330
	21st to end	Day	26% 23% 33% 14% 3	231
December	1st to 10th	Day	24% 17% 36% 15% 7% 1	220
	11th to 20th	Day	25% 27% 33% 11% 4	220
	21st to end	Day	29% 21% 36% 12% 3	303
January	1st to 10th	Night	21% 16% 37% 20% 5% 1	1050
	11th to 20th	Night	23% 16% 34% 22% 4 1	1050
	21st to end	Night	20% 13% 35% 27% 5%	981
February	1st to 10th	Night	22% 13% 39% 22% 3	840
	11th to 20th	Night	22% 17% 32% 23% 5%	823
	21st to end	Night	24% 18% 34% 22% 2	692
March	1st to 10th	Night	20% 14% 35% 24% 6%	840
	11th to 20th	Night	17% 16% 36% 25% 5% 1	840
	21st to end	Night	22% 12% 31% 28% 7% 1	924
April	1st to 10th	Night	24% 14% 35% 23% 4	729
	11th to 20th	Night	22% 11% 34% 23% 7% 2	623
	21st to end	Night	20% 10% 31% 32% 7%	630
May	1st to 10th	Night	17% 7% 33% 32% 10% 1	630
	11th to 20th	Night	22% 5% 28% 33% 12%	621
	21st to end	Night	12% 4 26% 38% 18% 2	683
June	1st to 10th	Night	11% 5% 28% 44% 12%	420
	11th to 20th	Night	12% 6% 30% 39% 13%	420
	21st to end	Night	10% 5% 25% 46% 14%	449
July	1st to 10th	Night	8% 3 18% 43% 26% 3	615
	11th to 20th	Night	11% 3 17% 44% 21% 4	597
	21st to end	Night	7% 3 19% 46% 24% 2	657
August	1st to 10th	Night	9% 3 14% 44% 29% 3	597
	11th to 20th	Night	10% 3 16% 40% 28% 4	594
	21st to end	Night	10% 4 18% 38% 28% 2	660
September	1st to 10th	Night	12% 5% 20% 34% 23% 6%	720
	11th to 20th	Night	11% 4 16% 35% 30% 4	800
	21st to end	Night	17% 6% 21% 33% 18% 4	800
October	1st to 10th	Night	18% 6% 26% 31% 18% 1	800
	11th to 20th	Night	22% 12% 31% 26% 10%	800
	21st to end	Night	24% 11% 33% 26% 5%	880
November	1st to 10th	Night	18% 13% 32% 25% 11% 1	820
	11th to 20th	Night	19% 16% 34% 23% 6% 1	840
	21st to end	Night	25% 15% 36% 19% 5%	840
December	1st to 10th	Night	23% 16% 35% 21% 5%	840
	11th to 20th	Night	21% 16% 40% 20% 3	992
	21st to end	Night	30% 12% 35% 20% 2	1155

Page generated at 2026-07-13 03:14:50. Version ac07

Copyright © 2026 Attilla Danko.