MCCC Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the MCCC Observatory clear sky chart from 2005-11-06 to 2026-08-15.

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	15% 6% 2 6% 4 4 4 4 6% 8% 40%	144003
	Night	15% 7% 2 6% 4 4 4 3 5% 7% 42%	137890
Transparency	Day	41% 5% 11% 23% 17% 2	147533
	Night	41% 5% 11% 23% 17% 3	142447
Seeing	Day	22% 14% 28% 22% 11% 3	17257
	Night	20% 11% 31% 28% 9% 1	26469

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	14% 6% 2 6% 4 5% 4 3 5% 6% 46%	4661
	11th to 20th	Day	14% 8% 3 8% 4 4 4 3 4 5% 43%	4784
	21st to end	Day	16% 6% 2 6% 5% 5% 6% 4 6% 7% 39%	5780
February	1st to 10th	Day	15% 7% 3 6% 4 4 4 5% 6% 7% 40%	1890
	11th to 20th	Day	16% 9% 2 7% 5% 3 5% 3 4 6% 39%	1995
	21st to end	Day	18% 8% 3 6% 5% 3 4 4 4 6% 39%	1730
March	1st to 10th	Day	21% 5% 2 5% 4 4 4 3 4 5% 43%	4576
	11th to 20th	Day	12% 6% 2 6% 4 4 5% 4 5% 7% 44%	5090
	21st to end	Day	18% 6% 2 6% 4 4 4 3 4 7% 43%	5913
April	1st to 10th	Day	16% 8% 3 6% 4 4 4 4 5% 7% 39%	2520
	11th to 20th	Day	15% 7% 2 6% 4 4 4 4 6% 7% 41%	2494
	21st to end	Day	16% 5% 3 6% 4 4 5% 4 6% 7% 40%	2520
May	1st to 10th	Day	23% 7% 2 6% 4 4 5% 4 6% 8% 33%	7569
	11th to 20th	Day	19% 7% 2 6% 4 4 4 3 5% 7% 38%	8221
	21st to end	Day	24% 7% 2 5% 4 4 4 3 5% 7% 35%	9060
June	1st to 10th	Day	12% 6% 2 5% 4 5% 5% 4 7% 9% 40%	2940
	11th to 20th	Day	13% 6% 2 6% 5% 5% 5% 4 7% 9% 38%	2940
	21st to end	Day	11% 5% 2 6% 4 4 5% 5% 6% 10% 41%	2940
July	1st to 10th	Day	11% 6% 2 7% 5% 4 5% 4 7% 10% 38%	8280
	11th to 20th	Day	8% 7% 3 8% 5% 5% 5% 5% 8% 11% 35%	8280
	21st to end	Day	10% 7% 2 6% 4 5% 5% 4 7% 10% 40%	8858
August	1st to 10th	Day	18% 6% 2 7% 5% 5% 5% 4 7% 8% 35%	4364
	11th to 20th	Day	12% 6% 2 5% 4 4 4 4 7% 8% 43%	3907
	21st to end	Day	11% 5% 2 5% 4 3 4 4 5% 8% 49%	4312
September	1st to 10th	Day	14% 5% 2 5% 5% 3 4 4 5% 6% 46%	2400
	11th to 20th	Day	13% 5% 2 4 2 3 4 3 5% 7% 52%	2370
	21st to end	Day	17% 8% 3 7% 5% 4 4 3 5% 6% 37%	2199
October	1st to 10th	Day	17% 6% 2 4 3 3 4 4 5% 6% 45%	2000
	11th to 20th	Day	16% 5% 2 5% 3 4 4 3 5% 7% 47%	2000
	21st to end	Day	18% 6% 2 5% 3 3 4 3 5% 5% 46%	2129
November	1st to 10th	Day	12% 7% 2 4 3 3 3 3 4 5% 53%	1851
	11th to 20th	Day	15% 5% 1 6% 3 3 4 3 6% 6% 47%	1890
	21st to end	Day	16% 6% 2 5% 3 4 4 4 6% 7% 43%	1746
December	1st to 10th	Day	13% 8% 2 5% 4 3 5% 4 5% 6% 43%	2680
	11th to 20th	Day	20% 10% 2 4 3 3 3 3 4 6% 43%	3066
	21st to end	Day	17% 6% 2 6% 4 5% 6% 4 6% 7% 38%	4048
January	1st to 10th	Night	12% 8% 3 6% 4 4 4 3 5% 6% 46%	8234
	11th to 20th	Night	14% 8% 2 6% 4 3 4 3 4 6% 46%	8097
	21st to end	Night	16% 8% 2 5% 4 4 4 3 4 6% 46%	8401
February	1st to 10th	Night	16% 9% 2 6% 3 4 5% 4 5% 5% 41%	2730
	11th to 20th	Night	19% 8% 2 7% 5% 4 4 3 4 6% 39%	2510
	21st to end	Night	16% 8% 3 6% 3 4 4 3 5% 6% 42%	2076
March	1st to 10th	Night	18% 8% 2 6% 3 3 3 3 4 5% 43%	5466
	11th to 20th	Night	11% 7% 2 6% 3 4 4 3 4 5% 50%	5089
	21st to end	Night	15% 8% 3 6% 4 4 4 3 5% 6% 43%	5260
April	1st to 10th	Night	17% 7% 2 6% 5% 4 4 4 5% 7% 40%	2100
	11th to 20th	Night	15% 7% 2 6% 5% 4 4 4 5% 7% 41%	2075
	21st to end	Night	18% 5% 2 5% 3 3 4 3 6% 8% 43%	2100
May	1st to 10th	Night	20% 8% 3 7% 4 4 5% 4 6% 8% 31%	5386
	11th to 20th	Night	19% 9% 2 7% 3 4 4 4 6% 8% 34%	4639
	21st to end	Night	25% 7% 2 6% 4 3 4 4 5% 7% 33%	5114
June	1st to 10th	Night	14% 7% 2 6% 4 4 4 3 6% 7% 44%	1680
	11th to 20th	Night	11% 7% 2 6% 5% 5% 5% 4 7% 8% 40%	1680
	21st to end	Night	11% 4 2 5% 4 4 5% 5% 8% 10% 41%	1680
July	1st to 10th	Night	11% 6% 2 7% 5% 5% 5% 4 7% 9% 37%	4680
	11th to 20th	Night	10% 8% 3 8% 5% 5% 6% 5% 7% 11% 31%	4680
	21st to end	Night	11% 7% 2 6% 4 4 4 4 6% 9% 41%	5202
August	1st to 10th	Night	20% 7% 3 6% 4 4 5% 4 7% 8% 33%	3005
	11th to 20th	Night	13% 7% 2 7% 4 4 5% 3 6% 7% 41%	3196
	21st to end	Night	11% 5% 2 5% 4 4 4 3 6% 8% 49%	3586
September	1st to 10th	Night	13% 7% 3 6% 4 4 3 3 4 6% 47%	2000
	11th to 20th	Night	11% 6% 2 5% 3 3 3 3 5% 6% 52%	2030
	21st to end	Night	18% 7% 3 5% 4 4 4 3 5% 7% 39%	2200
October	1st to 10th	Night	17% 8% 2 6% 4 4 4 3 4 5% 44%	2397
	11th to 20th	Night	16% 5% 1 5% 3 3 4 3 4 6% 50%	2400
	21st to end	Night	17% 7% 2 4 3 3 3 3 4 5% 49%	2710
November	1st to 10th	Night	12% 5% 2 5% 3 2 3 4 5% 6% 53%	2667
	11th to 20th	Night	16% 7% 2 5% 3 3 4 3 4 5% 48%	2730
	21st to end	Night	14% 5% 2 5% 4 4 4 4 5% 7% 44%	2872
December	1st to 10th	Night	13% 8% 3 5% 4 3 4 3 5% 6% 46%	4720
	11th to 20th	Night	22% 7% 2 4 3 3 4 3 4 6% 41%	5348
	21st to end	Night	19% 8% 3 6% 4 4 4 3 5% 5% 40%	7150

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	39% 3 10% 27% 20% 2	4662
	11th to 20th	Day	41% 3 10% 22% 19% 6%	4814
	21st to end	Day	42% 5% 13% 24% 15% 1	5780
February	1st to 10th	Day	42% 6% 13% 24% 12% 2	1890
	11th to 20th	Day	45% 4 10% 23% 15% 2	2004
	21st to end	Day	45% 4 10% 24% 13% 4	1730
March	1st to 10th	Day	41% 3 10% 22% 16% 7%	4579
	11th to 20th	Day	37% 4 11% 28% 15% 5%	5090
	21st to end	Day	43% 3 10% 16% 22% 5%	5913
April	1st to 10th	Day	42% 5% 11% 22% 16% 4	2520
	11th to 20th	Day	40% 5% 14% 21% 16% 4	2494
	21st to end	Day	41% 6% 11% 21% 17% 4	2520
May	1st to 10th	Day	48% 6% 12% 19% 14% 1	7579
	11th to 20th	Day	45% 5% 9% 25% 14% 1	8225
	21st to end	Day	48% 5% 9% 22% 14% 1	9061
June	1st to 10th	Day	38% 8% 12% 23% 17% 1	2940
	11th to 20th	Day	41% 7% 14% 24% 12% 2	2940
	21st to end	Day	37% 8% 12% 25% 16% 1	2940
July	1st to 10th	Day	41% 9% 13% 19% 16% 2	8210
	11th to 20th	Day	41% 8% 14% 25% 11% 1	8205
	21st to end	Day	39% 6% 10% 22% 21% 1	8662
August	1st to 10th	Day	46% 8% 13% 22% 10%	4351
	11th to 20th	Day	36% 7% 12% 30% 15% 1	3943
	21st to end	Day	33% 6% 10% 28% 22% 2	4312
September	1st to 10th	Day	38% 6% 11% 20% 22% 3	2400
	11th to 20th	Day	32% 5% 9% 26% 24% 4	2370
	21st to end	Day	48% 6% 8% 17% 20% 2	2199
October	1st to 10th	Day	36% 4 9% 19% 28% 5%	3260
	11th to 20th	Day	25% 4 11% 25% 28% 7%	3240
	21st to end	Day	24% 3 12% 26% 29% 4	3419
November	1st to 10th	Day	33% 4 13% 25% 22% 3	1851
	11th to 20th	Day	37% 4 10% 25% 20% 3	1890
	21st to end	Day	38% 4 14% 30% 12% 2	1746
December	1st to 10th	Day	40% 4 16% 26% 12% 2	2680
	11th to 20th	Day	43% 3 12% 29% 11% 2	3066
	21st to end	Day	42% 5% 13% 21% 17% 1	4048
January	1st to 10th	Night	39% 4 12% 25% 16% 4	8234
	11th to 20th	Night	39% 3 11% 22% 18% 7%	8142
	21st to end	Night	41% 3 8% 25% 21% 3	8401
February	1st to 10th	Night	44% 5% 12% 25% 12% 3	2730
	11th to 20th	Night	46% 3 9% 20% 17% 4	2512
	21st to end	Night	43% 4 7% 23% 17% 4	2076
March	1st to 10th	Night	42% 4 9% 23% 13% 9%	5476
	11th to 20th	Night	36% 5% 14% 26% 15% 5%	5090
	21st to end	Night	43% 4 8% 16% 25% 4	5260
April	1st to 10th	Night	43% 5% 10% 20% 17% 4	2100
	11th to 20th	Night	42% 5% 10% 19% 20% 3	2075
	21st to end	Night	40% 5% 10% 21% 19% 5%	2100
May	1st to 10th	Night	49% 6% 11% 19% 13% 2	5392
	11th to 20th	Night	47% 6% 12% 23% 12% 1	4640
	21st to end	Night	51% 5% 10% 20% 12% 2	5115
June	1st to 10th	Night	39% 5% 12% 22% 21% 2	1680
	11th to 20th	Night	40% 8% 12% 24% 14% 1	1680
	21st to end	Night	35% 9% 14% 25% 15% 2	1680
July	1st to 10th	Night	42% 8% 14% 20% 14% 1	4640
	11th to 20th	Night	43% 9% 15% 22% 10% 1	4632
	21st to end	Night	39% 6% 13% 22% 19% 1	5083
August	1st to 10th	Night	47% 8% 16% 18% 9% 1	2994
	11th to 20th	Night	41% 7% 11% 26% 14% 1	3226
	21st to end	Night	33% 6% 10% 29% 21% 2	3586
September	1st to 10th	Night	38% 6% 10% 20% 22% 3	2000
	11th to 20th	Night	33% 5% 8% 23% 27% 4	2030
	21st to end	Night	44% 6% 8% 20% 21% 2	2200
October	1st to 10th	Night	41% 5% 10% 21% 21% 2	3917
	11th to 20th	Night	25% 4 10% 28% 29% 5%	3899
	21st to end	Night	27% 3 11% 31% 24% 4	4370
November	1st to 10th	Night	31% 5% 12% 25% 21% 5%	2667
	11th to 20th	Night	39% 4 9% 22% 20% 5%	2730
	21st to end	Night	39% 5% 12% 26% 16% 2	2872
December	1st to 10th	Night	39% 4 12% 30% 14% 2	4720
	11th to 20th	Night	44% 3 10% 24% 14% 4	5348
	21st to end	Night	45% 5% 11% 20% 18% 2	7150

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	27% 30% 29% 10% 2 2	220
	11th to 20th	Day	37% 26% 27% 9% 2	243
	21st to end	Day	27% 29% 28% 11% 4 1	363
February	1st to 10th	Day	29% 24% 32% 11% 4 1	330
	11th to 20th	Day	33% 20% 34% 11% 1	483
	21st to end	Day	29% 22% 33% 13% 3	446
March	1st to 10th	Day	29% 19% 30% 18% 4	540
	11th to 20th	Day	27% 21% 33% 15% 3 1	540
	21st to end	Day	28% 25% 30% 12% 5% 1	594
April	1st to 10th	Day	29% 21% 30% 13% 5% 1	540
	11th to 20th	Day	23% 24% 31% 15% 6% 2	532
	21st to end	Day	25% 18% 32% 19% 4 2	540
May	1st to 10th	Day	29% 20% 29% 15% 6% 1	543
	11th to 20th	Day	23% 13% 31% 22% 8% 2	567
	21st to end	Day	25% 9% 25% 22% 15% 4	617
June	1st to 10th	Day	15% 14% 27% 28% 13% 3	570
	11th to 20th	Day	18% 12% 27% 28% 13% 3	570
	21st to end	Day	15% 9% 29% 29% 14% 4	570
July	1st to 10th	Day	13% 4 21% 32% 23% 6%	565
	11th to 20th	Day	8% 3 27% 30% 26% 6%	564
	21st to end	Day	12% 7% 26% 35% 16% 4	620
August	1st to 10th	Day	12% 6% 24% 32% 20% 6%	566
	11th to 20th	Day	15% 6% 18% 36% 20% 6%	535
	21st to end	Day	13% 8% 26% 29% 17% 8%	583
September	1st to 10th	Day	18% 10% 22% 25% 17% 7%	530
	11th to 20th	Day	16% 6% 23% 30% 16% 9%	530
	21st to end	Day	26% 12% 21% 25% 12% 4	530
October	1st to 10th	Day	23% 7% 26% 21% 14% 8%	530
	11th to 20th	Day	20% 15% 28% 23% 11% 2	530
	21st to end	Day	22% 15% 31% 19% 11% 2	543
November	1st to 10th	Day	21% 12% 30% 24% 12% 2	425
	11th to 20th	Day	23% 18% 31% 22% 5%	430
	21st to end	Day	25% 20% 34% 17% 4 1	286
December	1st to 10th	Day	29% 22% 35% 8% 6%	220
	11th to 20th	Day	35% 19% 31% 11% 4	220
	21st to end	Day	30% 18% 32% 12% 7%	242
January	1st to 10th	Night	22% 18% 37% 20% 3	840
	11th to 20th	Night	26% 18% 30% 24% 3	840
	21st to end	Night	19% 19% 38% 22% 2	924
February	1st to 10th	Night	22% 15% 38% 24% 1	840
	11th to 20th	Night	26% 19% 35% 18% 1	823
	21st to end	Night	23% 17% 39% 17% 3	692
March	1st to 10th	Night	24% 17% 33% 23% 3	840
	11th to 20th	Night	23% 17% 36% 19% 5%	840
	21st to end	Night	21% 13% 41% 19% 5%	924
April	1st to 10th	Night	22% 19% 36% 18% 5%	840
	11th to 20th	Night	19% 14% 37% 25% 5%	831
	21st to end	Night	21% 10% 34% 28% 6%	840
May	1st to 10th	Night	23% 12% 33% 25% 6%	678
	11th to 20th	Night	22% 9% 35% 29% 6%	414
	21st to end	Night	19% 7% 24% 37% 13% 1	455
June	1st to 10th	Night	17% 5% 30% 38% 10% 1	420
	11th to 20th	Night	13% 5% 32% 39% 10%	420
	21st to end	Night	12% 3 27% 47% 11%	420
July	1st to 10th	Night	13% 3 22% 43% 17% 1	410
	11th to 20th	Night	9% 3 24% 41% 22% 1	408
	21st to end	Night	10% 4 25% 39% 21% 1	502
August	1st to 10th	Night	14% 2 16% 43% 24% 2	627
	11th to 20th	Night	14% 3 19% 38% 24% 2	777
	21st to end	Night	14% 4 19% 39% 23% 2	880
September	1st to 10th	Night	17% 3 26% 34% 17% 3	800
	11th to 20th	Night	15% 3 21% 36% 21% 4	800
	21st to end	Night	23% 4 21% 33% 18% 1	800
October	1st to 10th	Night	22% 7% 24% 25% 19% 4	800
	11th to 20th	Night	18% 11% 26% 32% 12% 1	800
	21st to end	Night	20% 12% 32% 27% 9%	880
November	1st to 10th	Night	16% 9% 35% 28% 11% 1	820
	11th to 20th	Night	21% 16% 29% 25% 8% 1	840
	21st to end	Night	18% 16% 34% 26% 7%	840
December	1st to 10th	Night	25% 15% 33% 21% 5% 1	840
	11th to 20th	Night	23% 14% 35% 23% 5%	840
	21st to end	Night	23% 15% 33% 26% 3	924

Page generated at 2026-08-12 03:37:20. Version ac07

Copyright © 2026 Attilla Danko.