East Central Community College
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the East Central Community College clear sky chart from 2005-11-06 to 2026-01-02.

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	11% 6% 2 6% 5% 5% 5% 4 6% 8% 42%	126702
	Night	13% 7% 2 6% 4 4 4 4 6% 7% 45%	124682
Transparency	Day	39% 5% 11% 20% 19% 6%	130449
	Night	38% 4 10% 19% 20% 8%	129010
Seeing	Day	15% 9% 21% 25% 21% 10%	16418
	Night	15% 7% 22% 29% 22% 5%	26089

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% 9% 5% 6% 3 3 3 3 4 5% 45%	3993
	11th to 20th	Day	12% 7% 2 5% 3 3 3 3 4 6% 52%	4119
	21st to end	Day	22% 10% 3 6% 3 3 3 2 4 4 40%	4972
February	1st to 10th	Day	17% 10% 4 6% 5% 3 3 4 4 6% 38%	2000
	11th to 20th	Day	20% 9% 3 6% 4 3 2 2 5% 5% 41%	1948
	21st to end	Day	16% 9% 3 8% 4 4 4 4 4 5% 40%	1650
March	1st to 10th	Day	20% 8% 3 7% 5% 5% 4 4 5% 5% 34%	4480
	11th to 20th	Day	13% 6% 2 6% 5% 4 5% 4 5% 6% 44%	4883
	21st to end	Day	15% 8% 3 8% 5% 4 5% 3 4 5% 40%	5907
April	1st to 10th	Day	12% 5% 3 6% 5% 5% 5% 4 6% 6% 44%	2400
	11th to 20th	Day	13% 8% 2 6% 4 4 3 3 5% 6% 45%	2374
	21st to end	Day	9% 5% 2 5% 5% 5% 5% 4 6% 8% 47%	2400
May	1st to 10th	Day	14% 7% 3 7% 5% 4 5% 4 6% 8% 38%	5405
	11th to 20th	Day	11% 6% 3 8% 6% 5% 6% 5% 6% 9% 35%	5582
	21st to end	Day	8% 5% 2 7% 5% 5% 5% 5% 6% 10% 42%	6433
June	1st to 10th	Day	10% 6% 2 6% 7% 6% 6% 5% 7% 9% 37%	2600
	11th to 20th	Day	5% 5% 2 6% 6% 6% 7% 6% 8% 9% 40%	2791
	21st to end	Day	5% 5% 2 7% 6% 7% 7% 6% 8% 10% 37%	2800
July	1st to 10th	Day	5% 5% 2 8% 7% 7% 8% 6% 8% 11% 32%	6297
	11th to 20th	Day	6% 5% 2 7% 5% 6% 8% 6% 11% 14% 32%	5818
	21st to end	Day	7% 6% 3 9% 7% 7% 8% 6% 8% 11% 27%	5922
August	1st to 10th	Day	3 2 1 4 4 4 4 4 7% 8% 58%	3905
	11th to 20th	Day	4 3 2 6% 5% 6% 6% 5% 8% 10% 45%	3849
	21st to end	Day	8% 4 2 5% 5% 6% 6% 5% 7% 8% 45%	4312
September	1st to 10th	Day	10% 5% 2 8% 6% 5% 5% 5% 6% 8% 40%	2400
	11th to 20th	Day	13% 6% 2 6% 4 4 5% 3 5% 7% 44%	2282
	21st to end	Day	10% 4 2 4 4 4 5% 4 5% 7% 51%	2200
October	1st to 10th	Day	7% 5% 3 5% 4 4 3 3 4 5% 58%	2200
	11th to 20th	Day	9% 4 2 4 4 3 3 3 6% 6% 56%	2005
	21st to end	Day	12% 5% 2 5% 3 3 3 3 3 6% 56%	2200
November	1st to 10th	Day	10% 5% 2 5% 3 3 4 3 4 6% 54%	1927
	11th to 20th	Day	12% 5% 2 6% 3 2 4 3 4 6% 54%	1890
	21st to end	Day	14% 7% 2 6% 3 4 3 3 5% 7% 46%	1890
December	1st to 10th	Day	17% 9% 2 6% 3 3 3 3 4 7% 43%	3020
	11th to 20th	Day	13% 10% 3 7% 5% 4 4 3 4 5% 43%	3463
	21st to end	Day	16% 8% 2 6% 4 3 4 3 4 5% 46%	4385
January	1st to 10th	Night	17% 10% 4 5% 3 2 2 2 3 4 47%	5977
	11th to 20th	Night	16% 7% 4 6% 3 3 3 3 4 5% 46%	5838
	21st to end	Night	23% 10% 2 6% 3 3 3 2 3 4 41%	5984
February	1st to 10th	Night	17% 8% 2 6% 4 4 3 4 5% 5% 42%	2400
	11th to 20th	Night	21% 8% 3 5% 4 3 3 3 4 5% 42%	2338
	21st to end	Night	19% 7% 3 7% 4 3 4 3 4 6% 40%	1980
March	1st to 10th	Night	19% 11% 3 7% 4 3 4 3 5% 6% 36%	5373
	11th to 20th	Night	11% 7% 2 5% 3 4 4 3 4 6% 49%	5118
	21st to end	Night	17% 7% 3 6% 4 3 3 4 5% 5% 44%	5019
April	1st to 10th	Night	12% 6% 2 7% 5% 4 3 4 5% 6% 47%	2000
	11th to 20th	Night	13% 5% 2 5% 3 4 4 3 6% 6% 48%	1975
	21st to end	Night	8% 4 2 4 5% 4 3 3 7% 7% 52%	2000
May	1st to 10th	Night	14% 6% 2 7% 4 4 4 4 6% 8% 40%	4490
	11th to 20th	Night	14% 7% 3 7% 5% 5% 4 3 7% 8% 37%	4307
	21st to end	Night	8% 6% 2 6% 5% 5% 6% 5% 8% 11% 39%	4421
June	1st to 10th	Night	6% 4 2 7% 5% 6% 5% 4 7% 11% 42%	1800
	11th to 20th	Night	4 4 1 4 5% 4 5% 6% 9% 10% 48%	1601
	21st to end	Night	4 5% 2 6% 6% 4 6% 6% 8% 12% 42%	1600
July	1st to 10th	Night	4 5% 2 7% 7% 6% 6% 5% 10% 13% 36%	3661
	11th to 20th	Night	5% 5% 2 7% 5% 6% 7% 6% 10% 14% 34%	4138
	21st to end	Night	6% 7% 3 8% 6% 6% 6% 7% 9% 13% 30%	4929
August	1st to 10th	Night	2 2 1 4 3 4 4 4 7% 10% 59%	3244
	11th to 20th	Night	4 3 2 5% 5% 5% 5% 5% 7% 13% 47%	3200
	21st to end	Night	6% 4 2 6% 5% 5% 6% 5% 7% 8% 46%	3586
September	1st to 10th	Night	9% 5% 3 6% 5% 4 5% 4 7% 8% 44%	2000
	11th to 20th	Night	10% 6% 3 5% 5% 5% 4 4 6% 6% 48%	2096
	21st to end	Night	7% 5% 2 5% 4 4 5% 4 6% 7% 52%	2200
October	1st to 10th	Night	7% 4 2 5% 3 3 4 3 6% 6% 59%	2200
	11th to 20th	Night	10% 4 2 5% 2 3 3 3 4 6% 58%	2390
	21st to end	Night	13% 7% 2 4 2 2 2 2 3 4 57%	2640
November	1st to 10th	Night	11% 4 2 4 3 3 4 3 4 5% 58%	2587
	11th to 20th	Night	12% 5% 2 4 4 3 3 3 4 6% 55%	2730
	21st to end	Night	14% 7% 2 5% 3 4 3 3 5% 6% 48%	2730
December	1st to 10th	Night	20% 6% 2 5% 3 3 3 3 5% 6% 45%	4380
	11th to 20th	Night	15% 9% 3 7% 4 4 3 2 4 4 44%	4952
	21st to end	Night	18% 9% 2 5% 3 3 2 2 4 6% 45%	6798

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	44% 2 3 26% 21% 4	3994
	11th to 20th	Day	35% 2 5% 21% 30% 8%	4119
	21st to end	Day	50% 2 6% 13% 18% 12%	4972
February	1st to 10th	Day	48% 2 6% 17% 18% 9%	2000
	11th to 20th	Day	48% 2 5% 18% 20% 8%	1958
	21st to end	Day	47% 3 7% 16% 17% 10%	1650
March	1st to 10th	Day	52% 3 6% 12% 21% 6%	4480
	11th to 20th	Day	41% 2 5% 16% 19% 16%	4883
	21st to end	Day	47% 2 7% 17% 19% 7%	5909
April	1st to 10th	Day	40% 3 9% 20% 19% 8%	2400
	11th to 20th	Day	40% 2 6% 18% 25% 8%	2374
	21st to end	Day	35% 4 10% 24% 23% 4	2400
May	1st to 10th	Day	44% 3 11% 26% 13% 2	5440
	11th to 20th	Day	44% 6% 16% 20% 15% 1	5586
	21st to end	Day	37% 4 14% 27% 16% 1	6447
June	1st to 10th	Day	42% 5% 13% 23% 14% 2	2600
	11th to 20th	Day	37% 7% 16% 23% 15% 3	2791
	21st to end	Day	39% 8% 15% 24% 12% 3	2800
July	1st to 10th	Day	40% 11% 18% 23% 8% 1	6229
	11th to 20th	Day	35% 13% 29% 20% 3 1	5749
	21st to end	Day	45% 11% 18% 22% 4	5752
August	1st to 10th	Day	22% 5% 13% 30% 27% 2	3893
	11th to 20th	Day	30% 8% 18% 27% 14% 2	3885
	21st to end	Day	34% 9% 15% 20% 19% 3	4311
September	1st to 10th	Day	41% 6% 12% 18% 16% 6%	2400
	11th to 20th	Day	39% 5% 11% 18% 20% 5%	2282
	21st to end	Day	32% 4 11% 23% 21% 8%	2200
October	1st to 10th	Day	22% 3 6% 14% 28% 27%	3590
	11th to 20th	Day	18% 2 3 15% 33% 29%	3245
	21st to end	Day	23% 2 4 17% 37% 17%	3538
November	1st to 10th	Day	33% 2 6% 19% 28% 12%	1927
	11th to 20th	Day	34% 2 7% 16% 27% 14%	1890
	21st to end	Day	39% 3 7% 17% 23% 10%	1890
December	1st to 10th	Day	42% 3 6% 18% 26% 4	3020
	11th to 20th	Day	46% 3 7% 17% 21% 7%	3460
	21st to end	Day	43% 2 4 23% 26% 2	4385
January	1st to 10th	Night	44% 1 3 21% 26% 5%	5977
	11th to 20th	Night	41% 2 4 16% 26% 10%	5838
	21st to end	Night	49% 2 2 14% 23% 9%	5984
February	1st to 10th	Night	43% 3 6% 16% 22% 10%	2400
	11th to 20th	Night	47% 3 4 16% 20% 10%	2339
	21st to end	Night	47% 3 5% 16% 17% 12%	1980
March	1st to 10th	Night	50% 2 6% 14% 18% 10%	5373
	11th to 20th	Night	37% 3 6% 17% 20% 17%	5118
	21st to end	Night	43% 2 8% 20% 17% 9%	5019
April	1st to 10th	Night	38% 4 10% 18% 20% 10%	2000
	11th to 20th	Night	36% 2 8% 19% 23% 10%	1975
	21st to end	Night	30% 3 10% 24% 26% 6%	2000
May	1st to 10th	Night	42% 4 13% 23% 16% 3	4520
	11th to 20th	Night	45% 5% 14% 23% 13% 1	4308
	21st to end	Night	37% 5% 16% 24% 17% 2	4429
June	1st to 10th	Night	36% 7% 14% 25% 16% 2	1800
	11th to 20th	Night	28% 8% 16% 30% 14% 5%	1601
	21st to end	Night	32% 9% 19% 23% 15% 3	1600
July	1st to 10th	Night	36% 13% 22% 19% 8% 1	3623
	11th to 20th	Night	33% 15% 31% 17% 3 1	4087
	21st to end	Night	41% 13% 19% 23% 4 1	4785
August	1st to 10th	Night	18% 6% 18% 32% 25% 1	3232
	11th to 20th	Night	26% 9% 21% 28% 14% 2	3230
	21st to end	Night	33% 9% 16% 20% 18% 4	3586
September	1st to 10th	Night	36% 6% 15% 19% 17% 7%	2000
	11th to 20th	Night	36% 6% 13% 18% 20% 8%	2096
	21st to end	Night	30% 5% 9% 25% 22% 9%	2200
October	1st to 10th	Night	20% 4 7% 14% 25% 31%	3590
	11th to 20th	Night	19% 2 3 16% 28% 32%	3889
	21st to end	Night	22% 2 5% 15% 35% 21%	4252
November	1st to 10th	Night	30% 3 7% 17% 29% 14%	2587
	11th to 20th	Night	32% 2 7% 17% 28% 14%	2730
	21st to end	Night	38% 3 6% 21% 20% 12%	2730
December	1st to 10th	Night	42% 2 7% 18% 26% 5%	4380
	11th to 20th	Night	44% 3 6% 16% 25% 6%	4954
	21st to end	Night	43% 1 5% 20% 29% 3	6798

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% 19% 37% 14% 3 1	303
	11th to 20th	Day	24% 18% 35% 15% 6% 1	300
	21st to end	Day	26% 22% 34% 14% 3 1	330
February	1st to 10th	Day	24% 20% 34% 16% 6%	300
	11th to 20th	Day	35% 20% 30% 12% 3 1	300
	21st to end	Day	24% 26% 36% 12% 2	249
March	1st to 10th	Day	26% 22% 36% 12% 5%	300
	11th to 20th	Day	28% 19% 32% 19% 3	300
	21st to end	Day	22% 16% 33% 23% 7%	516
April	1st to 10th	Day	21% 14% 31% 23% 9% 1	500
	11th to 20th	Day	22% 16% 25% 25% 10% 2	492
	21st to end	Day	12% 11% 30% 29% 15% 3	500
May	1st to 10th	Day	17% 10% 24% 30% 16% 5%	503
	11th to 20th	Day	11% 7% 24% 31% 17% 11%	527
	21st to end	Day	9% 5% 23% 29% 21% 13%	573
June	1st to 10th	Day	14% 2 17% 29% 25% 13%	530
	11th to 20th	Day	6% 4 13% 32% 33% 12%	721
	21st to end	Day	7% 2 11% 31% 32% 17%	730
July	1st to 10th	Day	6% 3 8% 28% 37% 17%	721
	11th to 20th	Day	9% 2 6% 21% 38% 25%	688
	21st to end	Day	7% 3 6% 24% 39% 22%	576
August	1st to 10th	Day	7% 1 8% 22% 37% 25%	526
	11th to 20th	Day	7% 2 5% 22% 38% 26%	519
	21st to end	Day	14% 4 9% 23% 29% 21%	583
September	1st to 10th	Day	10% 2 12% 31% 31% 15%	530
	11th to 20th	Day	12% 3 12% 23% 33% 17%	530
	21st to end	Day	13% 4 13% 29% 30% 11%	530
October	1st to 10th	Day	8% 6% 23% 32% 24% 7%	530
	11th to 20th	Day	7% 8% 28% 34% 19% 4	335
	21st to end	Day	18% 10% 23% 32% 12% 4	363
November	1st to 10th	Day	20% 9% 29% 27% 10% 5%	330
	11th to 20th	Day	18% 11% 36% 23% 12% 1	330
	21st to end	Day	15% 17% 38% 17% 10% 3	330
December	1st to 10th	Day	26% 14% 37% 17% 6% 1	330
	11th to 20th	Day	17% 14% 41% 21% 7%	330
	21st to end	Day	25% 15% 32% 21% 6% 1	363
January	1st to 10th	Night	24% 13% 33% 25% 5%	1006
	11th to 20th	Night	23% 14% 30% 27% 7%	977
	21st to end	Night	23% 13% 36% 26% 3	880
February	1st to 10th	Night	24% 11% 29% 32% 5%	800
	11th to 20th	Night	27% 15% 29% 25% 4	783
	21st to end	Night	22% 16% 38% 22% 2	660
March	1st to 10th	Night	20% 14% 32% 26% 8%	800
	11th to 20th	Night	20% 10% 33% 28% 9%	660
	21st to end	Night	17% 10% 36% 25% 11%	660
April	1st to 10th	Night	18% 11% 33% 26% 12% 1	600
	11th to 20th	Night	16% 10% 33% 27% 13% 1	593
	21st to end	Night	11% 7% 31% 37% 15% 1	600
May	1st to 10th	Night	12% 5% 25% 38% 19% 2	600
	11th to 20th	Night	10% 2 21% 40% 23% 3	591
	21st to end	Night	8% 3 14% 35% 32% 8%	650
June	1st to 10th	Night	8% 2 11% 36% 37% 6%	600
	11th to 20th	Night	4 3 10% 27% 46% 11%	600
	21st to end	Night	6% 3 8% 27% 43% 13%	600
July	1st to 10th	Night	5% 2 4 26% 50% 13%	585
	11th to 20th	Night	5% 1 3 23% 48% 19%	582
	21st to end	Night	4 2 5% 26% 49% 14%	657
August	1st to 10th	Night	5% 1 3 23% 49% 19%	597
	11th to 20th	Night	6% 2 4 24% 47% 17%	594
	21st to end	Night	11% 1 7% 22% 42% 16%	660
September	1st to 10th	Night	12% 3 7% 31% 38% 10%	600
	11th to 20th	Night	12% 3 9% 27% 43% 6%	696
	21st to end	Night	10% 3 12% 34% 37% 5%	800
October	1st to 10th	Night	8% 3 19% 32% 32% 6%	800
	11th to 20th	Night	13% 4 21% 35% 25% 3	800
	21st to end	Night	17% 6% 19% 34% 21% 2	880
November	1st to 10th	Night	13% 6% 20% 37% 21% 4	820
	11th to 20th	Night	15% 6% 28% 35% 14% 1	840
	21st to end	Night	18% 8% 26% 33% 14% 1	840
December	1st to 10th	Night	22% 10% 29% 29% 9%	840
	11th to 20th	Night	22% 8% 31% 29% 10%	840
	21st to end	Night	26% 12% 29% 27% 6%	998

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