Renaissance Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Renaissance Observatory clear sky chart from 2005-11-06 to 2026-07-01.

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	14% 7% 3 7% 5% 4 5% 4 5% 7% 40%	137305
	Night	15% 8% 3 6% 4 4 4 3 5% 6% 42%	135210
Transparency	Day	42% 5% 11% 24% 16% 2	140938
	Night	42% 5% 11% 23% 18% 3	139652
Seeing	Day	15% 8% 22% 24% 20% 10%	17644
	Night	17% 7% 24% 31% 18% 2	27427

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	15% 10% 6% 11% 5% 5% 5% 3 4 5% 30%	4691
	11th to 20th	Day	12% 9% 4 10% 6% 6% 4 2 4 5% 38%	4710
	21st to end	Day	20% 11% 6% 7% 5% 4 4 3 4 5% 30%	5888
February	1st to 10th	Day	18% 11% 4 7% 5% 3 4 3 4 6% 35%	2100
	11th to 20th	Day	18% 10% 4 8% 5% 4 4 3 5% 6% 34%	2048
	21st to end	Day	16% 10% 4 9% 4 4 5% 5% 4 5% 34%	1730
March	1st to 10th	Day	19% 10% 4 7% 4 3 3 3 3 5% 39%	4580
	11th to 20th	Day	14% 9% 3 5% 4 3 3 3 5% 7% 46%	4807
	21st to end	Day	14% 8% 3 7% 5% 4 4 3 5% 7% 41%	5998
April	1st to 10th	Day	14% 6% 2 6% 5% 4 5% 4 6% 7% 42%	2520
	11th to 20th	Day	15% 7% 3 6% 5% 3 4 4 5% 7% 41%	2494
	21st to end	Day	16% 7% 3 6% 4 3 4 3 5% 6% 41%	2583
May	1st to 10th	Day	17% 7% 3 7% 5% 5% 5% 4 7% 8% 31%	7616
	11th to 20th	Day	17% 6% 2 7% 4 5% 5% 4 5% 7% 39%	7626
	21st to end	Day	19% 7% 4 8% 5% 5% 5% 4 7% 8% 30%	8425
June	1st to 10th	Day	11% 4 2 6% 4 4 4 4 6% 8% 46%	2940
	11th to 20th	Day	6% 5% 2 6% 5% 5% 6% 5% 6% 9% 45%	2940
	21st to end	Day	8% 4 1 5% 5% 4 6% 4 7% 10% 45%	2940
July	1st to 10th	Day	10% 6% 2 6% 4 4 5% 4 6% 9% 43%	6361
	11th to 20th	Day	7% 4 2 6% 5% 5% 6% 5% 9% 11% 40%	6360
	21st to end	Day	7% 7% 3 9% 6% 7% 7% 5% 7% 11% 30%	6658
August	1st to 10th	Day	6% 4 2 4 4 3 4 4 6% 10% 53%	4104
	11th to 20th	Day	8% 5% 2 6% 5% 5% 5% 4 7% 10% 43%	3849
	21st to end	Day	5% 4 1 4 4 4 4 3 6% 9% 56%	4312
September	1st to 10th	Day	10% 6% 2 6% 4 4 5% 4 5% 8% 47%	2400
	11th to 20th	Day	9% 5% 2 6% 5% 3 5% 4 6% 8% 49%	2200
	21st to end	Day	12% 5% 2 6% 4 4 4 3 4 5% 50%	2200
October	1st to 10th	Day	10% 4 2 5% 3 3 3 3 4 6% 57%	2200
	11th to 20th	Day	12% 5% 2 5% 4 2 4 3 5% 6% 51%	2090
	21st to end	Day	19% 6% 2 5% 3 3 3 2 4 5% 46%	1985
November	1st to 10th	Day	11% 6% 2 6% 3 4 4 3 4 5% 52%	1852
	11th to 20th	Day	16% 8% 2 6% 4 4 3 3 4 6% 45%	1890
	21st to end	Day	19% 9% 4 7% 3 3 3 3 5% 6% 39%	1890
December	1st to 10th	Day	17% 10% 3 6% 4 3 3 2 4 5% 43%	3020
	11th to 20th	Day	16% 11% 5% 10% 5% 4 5% 2 5% 6% 31%	3228
	21st to end	Day	23% 14% 5% 9% 5% 4 4 3 5% 6% 22%	4070
January	1st to 10th	Night	16% 13% 4 8% 4 4 4 3 4 5% 35%	8232
	11th to 20th	Night	15% 12% 4 9% 4 4 5% 2 4 4 38%	8280
	21st to end	Night	19% 11% 4 6% 4 4 3 3 4 5% 38%	8290
February	1st to 10th	Night	21% 11% 4 8% 5% 4 4 3 5% 5% 31%	2520
	11th to 20th	Night	20% 9% 3 8% 4 4 4 3 4 6% 37%	2458
	21st to end	Night	21% 9% 2 7% 5% 4 3 3 4 5% 37%	2076
March	1st to 10th	Night	21% 10% 2 6% 5% 4 4 3 4 5% 36%	5493
	11th to 20th	Night	13% 6% 2 6% 4 3 4 3 5% 6% 49%	5372
	21st to end	Night	15% 7% 3 8% 6% 4 5% 3 5% 6% 38%	5216
April	1st to 10th	Night	14% 6% 2 6% 4 4 4 3 5% 7% 46%	2100
	11th to 20th	Night	16% 6% 2 5% 4 4 4 3 4 6% 45%	2075
	21st to end	Night	16% 7% 3 6% 6% 4 4 4 5% 8% 38%	2034
May	1st to 10th	Night	17% 8% 3 7% 5% 4 4 3 7% 8% 33%	5237
	11th to 20th	Night	13% 6% 2 8% 5% 5% 5% 4 6% 8% 37%	5234
	21st to end	Night	16% 7% 3 8% 5% 5% 5% 4 6% 9% 32%	5712
June	1st to 10th	Night	9% 5% 2 6% 4 4 3 5% 6% 9% 47%	1680
	11th to 20th	Night	6% 4 2 4 4 5% 4 4 6% 9% 51%	1680
	21st to end	Night	5% 3 1 4 4 4 5% 5% 8% 11% 50%	1680
July	1st to 10th	Night	8% 5% 2 6% 5% 4 5% 4 6% 8% 47%	3618
	11th to 20th	Night	6% 5% 2 6% 4 4 4 4 6% 10% 48%	3617
	21st to end	Night	7% 6% 3 8% 5% 6% 6% 5% 8% 12% 34%	4199
August	1st to 10th	Night	6% 3 1 4 3 3 4 3 5% 7% 61%	3041
	11th to 20th	Night	6% 3 2 5% 4 4 5% 4 6% 9% 52%	3200
	21st to end	Night	4 3 1 4 3 3 4 4 6% 8% 61%	3586
September	1st to 10th	Night	10% 5% 2 5% 4 4 3 3 5% 7% 53%	2000
	11th to 20th	Night	8% 5% 1 5% 4 4 4 4 6% 7% 52%	2178
	21st to end	Night	13% 5% 1 4 3 4 2 3 4 7% 54%	2200
October	1st to 10th	Night	8% 4 2 4 3 3 4 2 5% 5% 60%	2200
	11th to 20th	Night	14% 5% 2 4 3 4 4 2 3 5% 54%	2305
	21st to end	Night	19% 7% 2 6% 3 3 3 2 4 5% 46%	2852
November	1st to 10th	Night	13% 6% 2 5% 3 3 3 3 4 6% 53%	2666
	11th to 20th	Night	14% 7% 2 5% 3 3 3 3 4 6% 49%	2730
	21st to end	Night	19% 7% 3 5% 4 3 3 2 4 5% 44%	2730
December	1st to 10th	Night	18% 9% 3 7% 4 3 3 3 4 4 42%	4380
	11th to 20th	Night	19% 10% 3 6% 4 4 4 3 4 6% 38%	5189
	21st to end	Night	26% 13% 4 8% 5% 4 4 3 4 4 25%	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	57% 4 13% 20% 6% 1	4692
	11th to 20th	Day	48% 4 7% 26% 14% 1	4710
	21st to end	Day	57% 4 9% 18% 9% 4	5888
February	1st to 10th	Day	52% 3 10% 23% 11% 1	2100
	11th to 20th	Day	52% 4 10% 20% 11% 3	2058
	21st to end	Day	51% 6% 9% 17% 13% 4	1730
March	1st to 10th	Day	50% 3 5% 19% 19% 4	4580
	11th to 20th	Day	40% 4 9% 26% 18% 2	4807
	21st to end	Day	43% 5% 11% 28% 13% 1	6000
April	1st to 10th	Day	40% 6% 15% 22% 16% 1	2520
	11th to 20th	Day	43% 4 11% 23% 17% 3	2494
	21st to end	Day	42% 5% 11% 27% 12% 2	2583
May	1st to 10th	Day	49% 6% 12% 22% 11% 1	7651
	11th to 20th	Day	44% 5% 12% 23% 15%	7630
	21st to end	Day	50% 6% 11% 18% 13% 2	8439
June	1st to 10th	Day	35% 7% 11% 24% 20% 3	2940
	11th to 20th	Day	33% 8% 13% 24% 19% 2	2940
	21st to end	Day	32% 8% 15% 23% 17% 4	2940
July	1st to 10th	Day	38% 5% 11% 28% 17% 2	6292
	11th to 20th	Day	35% 7% 17% 29% 10% 1	6285
	21st to end	Day	46% 6% 19% 21% 7% 1	6468
August	1st to 10th	Day	26% 6% 15% 34% 18%	4091
	11th to 20th	Day	35% 6% 14% 27% 17% 1	3885
	21st to end	Day	25% 6% 12% 37% 17% 3	4311
September	1st to 10th	Day	36% 7% 9% 24% 19% 5%	2400
	11th to 20th	Day	32% 7% 11% 25% 23% 3	2200
	21st to end	Day	36% 4 7% 23% 25% 4	2200
October	1st to 10th	Day	19% 3 5% 22% 44% 6%	3590
	11th to 20th	Day	23% 3 9% 26% 32% 6%	3382
	21st to end	Day	32% 3 7% 27% 26% 7%	3185
November	1st to 10th	Day	35% 4 9% 27% 20% 5%	1852
	11th to 20th	Day	41% 4 8% 24% 18% 5%	1890
	21st to end	Day	46% 4 8% 23% 17% 2	1890
December	1st to 10th	Day	45% 3 9% 26% 16% 1	3020
	11th to 20th	Day	55% 4 10% 20% 11% 1	3225
	21st to end	Day	62% 4 13% 15% 6%	4070
January	1st to 10th	Night	51% 4 13% 24% 8% 1	8233
	11th to 20th	Night	50% 4 5% 20% 18% 3	8280
	21st to end	Night	50% 3 9% 20% 16% 2	8290
February	1st to 10th	Night	55% 4 10% 20% 10% 1	2520
	11th to 20th	Night	50% 4 8% 23% 14% 2	2459
	21st to end	Night	49% 4 9% 20% 13% 3	2076
March	1st to 10th	Night	50% 4 7% 17% 18% 3	5493
	11th to 20th	Night	36% 5% 9% 23% 21% 6%	5372
	21st to end	Night	47% 4 12% 23% 13% 2	5216
April	1st to 10th	Night	38% 5% 11% 26% 17% 3	2100
	11th to 20th	Night	39% 5% 12% 19% 19% 5%	2075
	21st to end	Night	44% 5% 11% 21% 17% 2	2034
May	1st to 10th	Night	47% 6% 13% 23% 11% 1	5264
	11th to 20th	Night	45% 6% 12% 21% 15% 1	5235
	21st to end	Night	47% 7% 15% 19% 11% 1	5722
June	1st to 10th	Night	32% 7% 12% 24% 21% 4	1680
	11th to 20th	Night	27% 8% 16% 20% 25% 4	1680
	21st to end	Night	24% 10% 16% 27% 18% 6%	1680
July	1st to 10th	Night	34% 5% 11% 28% 19% 2	3580
	11th to 20th	Night	32% 6% 19% 28% 13% 2	3572
	21st to end	Night	42% 6% 20% 22% 9% 1	4076
August	1st to 10th	Night	22% 6% 13% 40% 17% 1	3030
	11th to 20th	Night	27% 6% 16% 29% 20% 1	3230
	21st to end	Night	21% 5% 11% 34% 25% 3	3586
September	1st to 10th	Night	31% 7% 9% 24% 23% 6%	2000
	11th to 20th	Night	29% 6% 10% 24% 26% 5%	2178
	21st to end	Night	32% 4 10% 22% 26% 6%	2200
October	1st to 10th	Night	19% 3 6% 15% 50% 7%	3590
	11th to 20th	Night	22% 3 6% 25% 39% 6%	3752
	21st to end	Night	32% 2 7% 22% 28% 8%	4602
November	1st to 10th	Night	33% 4 9% 25% 24% 5%	2666
	11th to 20th	Night	37% 4 7% 23% 21% 7%	2730
	21st to end	Night	43% 4 8% 24% 17% 3	2730
December	1st to 10th	Night	46% 4 10% 23% 16% 1	4380
	11th to 20th	Night	48% 4 11% 21% 16% 1	5191
	21st to end	Night	62% 5% 8% 17% 6% 1	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	24% 13% 31% 23% 9% 1	330
	11th to 20th	Day	21% 19% 40% 16% 3 1	330
	21st to end	Day	22% 18% 39% 15% 6%	363
February	1st to 10th	Day	25% 14% 35% 20% 5% 1	330
	11th to 20th	Day	27% 15% 40% 16% 2 1	330
	21st to end	Day	26% 16% 33% 20% 5%	273
March	1st to 10th	Day	24% 15% 38% 16% 6% 1	330
	11th to 20th	Day	25% 13% 39% 17% 6% 1	413
	21st to end	Day	23% 18% 31% 19% 8% 1	594
April	1st to 10th	Day	19% 14% 31% 26% 9% 1	540
	11th to 20th	Day	19% 15% 27% 24% 13% 2	532
	21st to end	Day	17% 11% 31% 26% 11% 4	540
May	1st to 10th	Day	18% 11% 26% 30% 11% 3	543
	11th to 20th	Day	18% 7% 22% 28% 17% 8%	567
	21st to end	Day	14% 5% 20% 26% 22% 12%	625
June	1st to 10th	Day	11% 5% 17% 26% 28% 12%	780
	11th to 20th	Day	6% 4 16% 31% 29% 14%	780
	21st to end	Day	8% 3 18% 31% 25% 16%	780
July	1st to 10th	Day	12% 2 10% 22% 29% 26%	722
	11th to 20th	Day	7% 3 10% 28% 32% 20%	718
	21st to end	Day	8% 2 11% 24% 35% 21%	680
August	1st to 10th	Day	10% 3 8% 23% 33% 22%	526
	11th to 20th	Day	12% 2 10% 29% 31% 15%	519
	21st to end	Day	10% 2 8% 22% 35% 22%	583
September	1st to 10th	Day	10% 3 11% 21% 37% 17%	530
	11th to 20th	Day	9% 1 8% 22% 38% 21%	530
	21st to end	Day	16% 5% 17% 22% 27% 12%	530
October	1st to 10th	Day	9% 4 14% 33% 30% 10%	530
	11th to 20th	Day	10% 11% 28% 30% 14% 8%	420
	21st to end	Day	26% 11% 27% 23% 12% 2	363
November	1st to 10th	Day	14% 7% 31% 31% 12% 5%	330
	11th to 20th	Day	18% 15% 29% 23% 12% 2	330
	21st to end	Day	23% 11% 31% 23% 11% 1	330
December	1st to 10th	Day	18% 17% 33% 22% 8% 2	330
	11th to 20th	Day	23% 15% 29% 22% 10%	330
	21st to end	Day	26% 17% 33% 20% 3 1	363
January	1st to 10th	Night	22% 12% 33% 28% 5%	1050
	11th to 20th	Night	25% 13% 35% 22% 4	1050
	21st to end	Night	23% 10% 38% 27% 3	1046
February	1st to 10th	Night	25% 9% 34% 28% 3	840
	11th to 20th	Night	25% 13% 36% 25% 2	823
	21st to end	Night	26% 11% 37% 24% 2	692
March	1st to 10th	Night	22% 12% 31% 30% 5%	840
	11th to 20th	Night	23% 8% 35% 28% 6%	840
	21st to end	Night	22% 9% 29% 32% 7% 1	759
April	1st to 10th	Night	17% 9% 33% 31% 10%	630
	11th to 20th	Night	18% 7% 30% 31% 12% 1	623
	21st to end	Night	19% 7% 27% 34% 12% 1	630
May	1st to 10th	Night	18% 5% 27% 34% 14% 1	630
	11th to 20th	Night	14% 4 21% 35% 24% 2	621
	21st to end	Night	8% 2 18% 39% 28% 4	683
June	1st to 10th	Night	12% 2 16% 40% 28% 2	630
	11th to 20th	Night	9% 2 12% 43% 32% 3	630
	21st to end	Night	6% 1 12% 40% 38% 4	630
July	1st to 10th	Night	9% 3 9% 25% 44% 10%	585
	11th to 20th	Night	6% 2 7% 32% 46% 6%	582
	21st to end	Night	8% 2 8% 35% 39% 7%	657
August	1st to 10th	Night	8% 1 7% 31% 48% 5%	597
	11th to 20th	Night	6% 1 7% 37% 42% 7%	594
	21st to end	Night	7% 1 6% 31% 47% 8%	660
September	1st to 10th	Night	12% 2 9% 34% 38% 6%	600
	11th to 20th	Night	9% 2 9% 33% 41% 6%	778
	21st to end	Night	14% 3 17% 31% 29% 5%	800
October	1st to 10th	Night	10% 4 15% 36% 32% 5%	800
	11th to 20th	Night	15% 7% 22% 35% 20% 2	800
	21st to end	Night	22% 7% 29% 29% 13% 1	880
November	1st to 10th	Night	15% 6% 26% 38% 14% 1	820
	11th to 20th	Night	18% 8% 31% 32% 11%	840
	21st to end	Night	23% 8% 26% 32% 11%	840
December	1st to 10th	Night	23% 8% 31% 32% 6%	840
	11th to 20th	Night	24% 8% 32% 29% 6% 1	952
	21st to end	Night	28% 11% 30% 27% 4	1155

Page generated at 2026-06-28 01:10:50. Version ac07

Copyright © 2026 Attilla Danko.