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 2024-02-05.

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	14% 7% 3 6% 5% 3 5% 5% 5% 7% 40%	78336
	Night	15% 8% 3 5% 5% 3 4 4 5% 7% 42%	80551
Transparency	Day	30% 36% 7% 15% 10% 2	78044
	Night	30% 35% 7% 15% 11% 2	80364
Seeing	Day	15% 8% 21% 24% 21% 11%	14340
	Night	17% 7% 23% 32% 19% 2	24280

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	14% 13% 7% 8% 5% 4 5% 4 3 6% 32%	2527
	11th to 20th	Day	18% 8% 4 9% 9% 6% 7% 4 4 4 27%	2530
	21st to end	Day	27% 14% 9% 5% 4 2 4 4 4 4 23%	3166
February	1st to 10th	Day	19% 10% 5% 6% 6% 3 4 4 4 6% 34%	1840
	11th to 20th	Day	18% 10% 4 6% 6% 3 4 4 5% 7% 33%	1748
	21st to end	Day	18% 9% 5% 8% 5% 3 6% 5% 4 5% 32%	1480
March	1st to 10th	Day	17% 8% 3 6% 6% 3 4 4 4 5% 41%	1800
	11th to 20th	Day	22% 8% 3 6% 5% 2 4 4 5% 7% 33%	1871
	21st to end	Day	19% 9% 4 7% 6% 3 5% 4 5% 6% 32%	2333
April	1st to 10th	Day	13% 6% 2 5% 5% 4 5% 5% 5% 8% 43%	2160
	11th to 20th	Day	16% 7% 3 5% 6% 3 4 4 5% 7% 40%	2134
	21st to end	Day	18% 7% 3 5% 4 2 4 4 5% 6% 41%	2214
May	1st to 10th	Day	17% 6% 3 5% 5% 3 5% 5% 6% 8% 36%	2340
	11th to 20th	Day	18% 6% 3 5% 5% 3 5% 5% 5% 7% 38%	2301
	21st to end	Day	9% 4 3 7% 6% 5% 6% 6% 8% 9% 37%	2537
June	1st to 10th	Day	10% 4 2 5% 5% 3 5% 5% 5% 8% 48%	2520
	11th to 20th	Day	6% 3 2 5% 6% 4 6% 7% 6% 10% 47%	2520
	21st to end	Day	8% 4 2 4 5% 3 6% 5% 8% 10% 45%	2520
July	1st to 10th	Day	11% 5% 2 5% 5% 4 6% 6% 8% 9% 38%	2520
	11th to 20th	Day	7% 4 2 5% 5% 4 6% 6% 8% 9% 46%	2520
	21st to end	Day	8% 4 2 5% 5% 4 6% 7% 7% 10% 41%	2641
August	1st to 10th	Day	7% 4 3 5% 6% 3 6% 6% 8% 10% 42%	2257
	11th to 20th	Day	10% 5% 2 5% 6% 4 5% 5% 6% 9% 43%	2125
	21st to end	Day	8% 5% 2 5% 4 3 4 5% 6% 9% 49%	2376
September	1st to 10th	Day	11% 5% 2 5% 5% 3 5% 5% 5% 8% 45%	2160
	11th to 20th	Day	9% 5% 2 5% 6% 2 4 5% 6% 8% 47%	1980
	21st to end	Day	11% 4 2 5% 5% 2 4 4 5% 5% 53%	1980
October	1st to 10th	Day	10% 4 2 4 4 3 3 4 4 7% 56%	1980
	11th to 20th	Day	13% 5% 3 4 6% 1 4 4 5% 6% 49%	1882
	21st to end	Day	19% 7% 2 5% 4 2 3 3 4 5% 45%	1787
November	1st to 10th	Day	10% 4 3 5% 4 3 4 3 4 6% 55%	1672
	11th to 20th	Day	17% 7% 3 5% 5% 3 3 3 4 5% 46%	1710
	21st to end	Day	20% 7% 3 5% 4 2 4 4 5% 6% 42%	1710
December	1st to 10th	Day	21% 10% 4 6% 4 3 3 4 4 5% 37%	1710
	11th to 20th	Day	16% 11% 6% 8% 5% 3 5% 3 4 6% 33%	2002
	21st to end	Day	21% 15% 5% 7% 5% 3 4 4 4 7% 25%	2783
January	1st to 10th	Night	19% 13% 4 5% 4 2 4 5% 4 6% 34%	4428
	11th to 20th	Night	18% 13% 5% 8% 6% 3 6% 3 4 4 30%	4440
	21st to end	Night	25% 14% 5% 5% 4 3 3 3 4 6% 28%	4489
February	1st to 10th	Night	22% 10% 5% 6% 5% 3 4 4 5% 5% 32%	2215
	11th to 20th	Night	19% 8% 4 6% 5% 3 4 4 4 6% 38%	2098
	21st to end	Night	22% 9% 3 6% 5% 3 4 4 4 5% 35%	1776
March	1st to 10th	Night	18% 8% 2 5% 5% 3 4 4 4 5% 44%	2160
	11th to 20th	Night	18% 9% 4 6% 5% 3 5% 4 5% 5% 36%	2088
	21st to end	Night	20% 8% 3 6% 5% 3 5% 4 5% 6% 35%	2037
April	1st to 10th	Night	13% 5% 2 5% 5% 3 4 4 5% 7% 47%	1800
	11th to 20th	Night	17% 6% 2 4 4 3 4 4 4 6% 46%	1775
	21st to end	Night	17% 7% 3 6% 6% 2 4 5% 5% 8% 38%	1744
May	1st to 10th	Night	18% 5% 3 5% 6% 3 4 4 6% 7% 40%	1620
	11th to 20th	Night	14% 5% 3 6% 6% 3 5% 4 6% 8% 41%	1592
	21st to end	Night	5% 3 2 6% 7% 4 5% 5% 7% 13% 42%	1734
June	1st to 10th	Night	10% 4 2 5% 4 3 3 6% 6% 9% 49%	1440
	11th to 20th	Night	6% 3 2 3 4 4 5% 5% 6% 9% 53%	1440
	21st to end	Night	5% 2 1 3 5% 3 5% 6% 8% 11% 51%	1440
July	1st to 10th	Night	7% 5% 2 4 4 4 5% 5% 6% 10% 47%	1440
	11th to 20th	Night	6% 4 2 4 4 2 4 5% 5% 9% 54%	1440
	21st to end	Night	9% 3 2 4 4 3 5% 5% 6% 10% 48%	1673
August	1st to 10th	Night	7% 3 2 4 5% 3 4 5% 6% 9% 52%	1677
	11th to 20th	Night	6% 3 2 5% 5% 3 5% 6% 6% 10% 48%	1776
	21st to end	Night	6% 4 2 4 4 2 4 4 6% 10% 53%	1980
September	1st to 10th	Night	11% 4 2 4 4 2 4 4 5% 7% 53%	1800
	11th to 20th	Night	8% 4 2 5% 5% 3 4 5% 6% 7% 51%	1960
	21st to end	Night	11% 5% 1 3 3 3 3 3 4 7% 56%	1980
October	1st to 10th	Night	9% 4 2 3 4 2 4 3 5% 5% 58%	1980
	11th to 20th	Night	16% 5% 2 4 4 3 4 3 3 5% 51%	2074
	21st to end	Night	18% 7% 2 5% 4 3 4 3 3 5% 46%	2566
November	1st to 10th	Night	13% 5% 2 4 4 2 3 3 4 5% 55%	2406
	11th to 20th	Night	15% 6% 2 5% 4 2 4 3 4 6% 49%	2470
	21st to end	Night	19% 6% 3 5% 4 2 4 3 4 6% 45%	2470
December	1st to 10th	Night	20% 9% 3 6% 5% 3 4 4 5% 5% 36%	2470
	11th to 20th	Night	17% 10% 4 7% 5% 3 4 4 4 5% 36%	3189
	21st to end	Night	21% 14% 4 8% 7% 4 5% 4 4 5% 25%	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	44% 25% 9% 16% 5%	2528
	11th to 20th	Day	49% 26% 6% 15% 4	2530
	21st to end	Day	56% 23% 4 13% 3 1	3166
February	1st to 10th	Day	35% 35% 6% 16% 7%	1840
	11th to 20th	Day	33% 37% 6% 14% 8% 3	1758
	21st to end	Day	36% 37% 7% 10% 8% 2	1480
March	1st to 10th	Day	29% 36% 7% 14% 13% 1	1800
	11th to 20th	Day	36% 37% 7% 13% 6% 1	1871
	21st to end	Day	36% 37% 8% 14% 4 1	2333
April	1st to 10th	Day	24% 38% 8% 16% 13% 1	2160
	11th to 20th	Day	28% 36% 5% 16% 14% 2	2134
	21st to end	Day	30% 37% 7% 18% 7% 1	2214
May	1st to 10th	Day	32% 39% 7% 15% 6% 1	2340
	11th to 20th	Day	32% 38% 8% 11% 10% 1	2305
	21st to end	Day	24% 40% 10% 15% 10% 2	2537
June	1st to 10th	Day	23% 38% 8% 17% 13% 2	2520
	11th to 20th	Day	19% 39% 9% 17% 14% 2	2520
	21st to end	Day	21% 39% 8% 14% 13% 5%	2520
July	1st to 10th	Day	24% 40% 8% 16% 10% 3	2451
	11th to 20th	Day	23% 41% 9% 13% 11% 3	2445
	21st to end	Day	23% 42% 11% 18% 6% 1	2494
August	1st to 10th	Day	22% 40% 9% 18% 12%	2244
	11th to 20th	Day	22% 39% 7% 19% 11% 2	2125
	21st to end	Day	19% 38% 8% 16% 14% 6%	2376
September	1st to 10th	Day	28% 37% 7% 13% 12% 3	2160
	11th to 20th	Day	23% 37% 6% 17% 14% 2	1980
	21st to end	Day	23% 37% 4 15% 18% 4	1980
October	1st to 10th	Day	18% 37% 6% 13% 22% 4	1980
	11th to 20th	Day	25% 37% 5% 17% 14% 3	1882
	21st to end	Day	27% 37% 5% 15% 12% 3	1787
November	1st to 10th	Day	16% 41% 6% 19% 14% 4	1672
	11th to 20th	Day	27% 39% 5% 15% 12% 2	1710
	21st to end	Day	27% 39% 6% 14% 13% 2	1710
December	1st to 10th	Day	33% 40% 7% 15% 5%	1710
	11th to 20th	Day	38% 32% 6% 15% 9% 1	1999
	21st to end	Day	49% 25% 10% 11% 6%	2783
January	1st to 10th	Night	40% 26% 8% 18% 7%	4428
	11th to 20th	Night	46% 25% 6% 15% 7% 1	4440
	21st to end	Night	50% 22% 5% 14% 8%	4489
February	1st to 10th	Night	37% 35% 7% 14% 7% 1	2215
	11th to 20th	Night	33% 36% 4 15% 9% 2	2099
	21st to end	Night	35% 36% 8% 13% 7% 2	1776
March	1st to 10th	Night	28% 36% 5% 14% 14% 3	2160
	11th to 20th	Night	34% 37% 8% 13% 6% 2	2088
	21st to end	Night	34% 38% 9% 13% 5% 1	2037
April	1st to 10th	Night	23% 36% 6% 18% 14% 2	1800
	11th to 20th	Night	26% 35% 6% 13% 15% 4	1775
	21st to end	Night	30% 38% 6% 14% 12% 1	1744
May	1st to 10th	Night	33% 37% 8% 14% 7% 1	1620
	11th to 20th	Night	29% 38% 7% 11% 13% 1	1593
	21st to end	Night	20% 40% 10% 15% 12% 3	1735
June	1st to 10th	Night	19% 38% 8% 17% 16% 2	1440
	11th to 20th	Night	15% 38% 12% 15% 16% 4	1440
	21st to end	Night	15% 40% 11% 16% 12% 7%	1440
July	1st to 10th	Night	21% 39% 9% 18% 11% 3	1400
	11th to 20th	Night	18% 39% 10% 16% 12% 5%	1392
	21st to end	Night	21% 40% 10% 20% 8% 1	1580
August	1st to 10th	Night	18% 38% 10% 18% 15% 2	1666
	11th to 20th	Night	16% 39% 9% 19% 15% 2	1776
	21st to end	Night	18% 37% 7% 16% 16% 5%	1980
September	1st to 10th	Night	24% 38% 6% 13% 14% 5%	1800
	11th to 20th	Night	23% 37% 5% 16% 14% 4	1960
	21st to end	Night	21% 36% 6% 14% 17% 5%	1980
October	1st to 10th	Night	18% 36% 5% 12% 24% 5%	1980
	11th to 20th	Night	25% 37% 5% 15% 15% 4	2074
	21st to end	Night	28% 37% 4 14% 12% 4	2566
November	1st to 10th	Night	16% 40% 6% 17% 17% 4	2406
	11th to 20th	Night	25% 39% 4 14% 13% 5%	2470
	21st to end	Night	26% 39% 6% 14% 12% 2	2470
December	1st to 10th	Night	31% 40% 7% 15% 7%	2470
	11th to 20th	Night	37% 33% 6% 14% 11% 1	3191
	21st to end	Night	50% 26% 8% 10% 6% 1	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	25% 12% 30% 23% 8% 1	270
	11th to 20th	Day	23% 17% 39% 17% 3 1	270
	21st to end	Day	23% 16% 38% 15% 7%	297
February	1st to 10th	Day	25% 14% 37% 17% 6% 1	252
	11th to 20th	Day	29% 15% 38% 17% 2	240
	21st to end	Day	30% 14% 31% 20% 6%	198
March	1st to 10th	Day	21% 16% 40% 18% 5%	240
	11th to 20th	Day	26% 12% 35% 19% 7% 2	311
	21st to end	Day	25% 18% 29% 18% 9% 1	462
April	1st to 10th	Day	16% 14% 30% 28% 11% 2	420
	11th to 20th	Day	20% 12% 25% 25% 16% 3	412
	21st to end	Day	20% 10% 30% 25% 11% 4	420
May	1st to 10th	Day	18% 12% 26% 29% 12% 4	423
	11th to 20th	Day	19% 5% 21% 29% 18% 8%	447
	21st to end	Day	11% 4 17% 28% 25% 15%	491
June	1st to 10th	Day	10% 6% 15% 25% 30% 15%	630
	11th to 20th	Day	5% 3 16% 31% 30% 15%	630
	21st to end	Day	7% 3 19% 31% 25% 16%	630
July	1st to 10th	Day	12% 2 8% 21% 29% 28%	621
	11th to 20th	Day	8% 3 10% 26% 33% 21%	618
	21st to end	Day	8% 2 10% 24% 34% 21%	582
August	1st to 10th	Day	10% 3 8% 23% 33% 22%	446
	11th to 20th	Day	14% 3 10% 28% 31% 15%	439
	21st to end	Day	12% 2 8% 22% 35% 22%	495
September	1st to 10th	Day	11% 3 10% 20% 37% 18%	450
	11th to 20th	Day	10% 2 8% 22% 38% 20%	450
	21st to end	Day	15% 5% 17% 21% 29% 13%	450
October	1st to 10th	Day	10% 4 16% 33% 29% 8%	450
	11th to 20th	Day	11% 12% 30% 31% 10% 6%	352
	21st to end	Day	26% 10% 26% 25% 11% 2	297
November	1st to 10th	Day	12% 6% 30% 32% 14% 6%	270
	11th to 20th	Day	17% 14% 28% 25% 13% 3	270
	21st to end	Day	22% 9% 31% 24% 12% 1	270
December	1st to 10th	Day	17% 17% 30% 23% 10% 3	270
	11th to 20th	Day	22% 14% 29% 23% 11%	270
	21st to end	Day	25% 19% 31% 21% 4 1	297
January	1st to 10th	Night	22% 13% 32% 28% 5%	950
	11th to 20th	Night	26% 13% 33% 23% 4	950
	21st to end	Night	24% 10% 36% 27% 3	947
February	1st to 10th	Night	26% 9% 33% 28% 4	739
	11th to 20th	Night	23% 13% 36% 25% 2	703
	21st to end	Night	28% 11% 35% 23% 2	592
March	1st to 10th	Night	21% 11% 32% 31% 5%	720
	11th to 20th	Night	23% 8% 32% 28% 7% 1	720
	21st to end	Night	23% 8% 26% 33% 8% 1	651
April	1st to 10th	Night	16% 8% 32% 33% 11%	540
	11th to 20th	Night	19% 7% 28% 31% 13% 2	533
	21st to end	Night	21% 6% 26% 34% 11% 1	540
May	1st to 10th	Night	18% 5% 27% 34% 16% 1	540
	11th to 20th	Night	14% 4 20% 36% 25% 2	531
	21st to end	Night	5% 2 18% 38% 32% 5%	584
June	1st to 10th	Night	12% 1 14% 40% 30% 3	540
	11th to 20th	Night	7% 2 11% 44% 34% 3	540
	21st to end	Night	5% 1 12% 41% 38% 3	540
July	1st to 10th	Night	8% 3 9% 25% 45% 11%	525
	11th to 20th	Night	6% 2 7% 31% 48% 7%	522
	21st to end	Night	8% 2 8% 36% 38% 8%	591
August	1st to 10th	Night	8% 1 6% 31% 49% 5%	537
	11th to 20th	Night	6% 1 7% 38% 42% 7%	534
	21st to end	Night	7% 1 6% 30% 48% 8%	594
September	1st to 10th	Night	12% 1 9% 32% 39% 7%	540
	11th to 20th	Night	9% 2 10% 32% 41% 6%	700
	21st to end	Night	12% 4 18% 30% 31% 6%	720
October	1st to 10th	Night	10% 4 15% 35% 31% 5%	720
	11th to 20th	Night	17% 6% 23% 34% 18% 2	720
	21st to end	Night	22% 7% 28% 30% 13% 1	792
November	1st to 10th	Night	14% 6% 25% 38% 16% 2	740
	11th to 20th	Night	17% 8% 30% 32% 12%	760
	21st to end	Night	22% 8% 25% 33% 12%	760
December	1st to 10th	Night	23% 8% 29% 32% 7%	760
	11th to 20th	Night	24% 8% 31% 29% 7% 1	860
	21st to end	Night	27% 11% 29% 28% 4	1045

Page generated at 2024-02-02 04:20:30. Version ac07

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