Red n Blue Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Red n Blue Observatory clear sky chart from 2005-11-06 to 2024-01-27.

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% 4 5% 7% 40%	74960
	Night	15% 7% 3 6% 5% 3 4 4 5% 7% 41%	75098
Transparency	Day	43% 6% 12% 23% 15% 2	74666
	Night	43% 5% 11% 22% 16% 3	74913
Seeing	Day	17% 9% 24% 25% 18% 8%	14386
	Night	18% 7% 25% 31% 16% 2	24335

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	18% 11% 4 9% 5% 2 3 4 5% 5% 34%	1517
	11th to 20th	Day	19% 11% 6% 9% 7% 3 4 4 3 5% 30%	1520
	21st to end	Day	16% 11% 4 7% 6% 3 4 3 5% 7% 34%	1790
February	1st to 10th	Day	18% 11% 5% 8% 5% 2 4 4 5% 6% 31%	1800
	11th to 20th	Day	17% 9% 4 7% 6% 3 5% 5% 5% 6% 33%	1748
	21st to end	Day	16% 12% 4 8% 6% 3 5% 4 4 6% 31%	1480
March	1st to 10th	Day	18% 8% 2 6% 5% 3 4 4 4 5% 41%	1800
	11th to 20th	Day	20% 9% 4 7% 5% 3 4 4 5% 6% 34%	1871
	21st to end	Day	19% 10% 4 6% 7% 3 5% 4 4 7% 30%	2333
April	1st to 10th	Day	13% 7% 4 6% 5% 3 4 4 5% 9% 41%	2160
	11th to 20th	Day	17% 7% 3 5% 5% 2 4 4 6% 6% 40%	2134
	21st to end	Day	18% 7% 3 6% 5% 3 4 4 4 7% 39%	2233
May	1st to 10th	Day	17% 6% 3 6% 6% 4 4 4 5% 8% 36%	2340
	11th to 20th	Day	18% 7% 3 6% 6% 4 4 4 5% 7% 38%	2301
	21st to end	Day	9% 6% 3 6% 7% 4 6% 7% 7% 10% 36%	2585
June	1st to 10th	Day	11% 5% 2 5% 5% 3 4 5% 5% 8% 47%	2520
	11th to 20th	Day	6% 5% 3 5% 5% 3 6% 5% 6% 9% 47%	2520
	21st to end	Day	8% 5% 2 4 5% 3 5% 6% 7% 10% 44%	2520
July	1st to 10th	Day	11% 4 2 6% 6% 4 6% 6% 6% 10% 37%	2520
	11th to 20th	Day	7% 5% 2 4 6% 3 6% 5% 8% 10% 44%	2520
	21st to end	Day	9% 5% 2 4 5% 3 6% 6% 8% 10% 42%	2676
August	1st to 10th	Day	8% 5% 2 5% 5% 3 5% 5% 7% 9% 45%	2288
	11th to 20th	Day	9% 5% 3 5% 5% 4 5% 6% 7% 9% 42%	2125
	21st to end	Day	6% 4 3 4 6% 3 5% 5% 5% 9% 50%	2376
September	1st to 10th	Day	11% 6% 2 5% 6% 3 5% 4 5% 8% 46%	2160
	11th to 20th	Day	9% 5% 3 5% 5% 3 4 5% 6% 8% 48%	1985
	21st to end	Day	11% 5% 2 4 3 2 4 4 4 6% 54%	1980
October	1st to 10th	Day	11% 5% 2 3 4 2 3 4 4 6% 55%	1980
	11th to 20th	Day	14% 5% 2 5% 5% 3 5% 4 5% 6% 47%	1864
	21st to end	Day	20% 7% 3 5% 4 2 3 4 4 6% 41%	1782
November	1st to 10th	Day	10% 5% 2 4 4 2 4 4 5% 6% 54%	1672
	11th to 20th	Day	17% 8% 4 5% 4 2 4 4 4 7% 42%	1710
	21st to end	Day	20% 9% 3 5% 4 3 3 4 4 6% 40%	1710
December	1st to 10th	Day	20% 12% 4 6% 5% 3 4 4 4 5% 35%	1710
	11th to 20th	Day	17% 12% 7% 7% 5% 3 4 4 4 6% 31%	1947
	21st to end	Day	24% 17% 6% 7% 6% 3 4 3 3 5% 22%	2783
January	1st to 10th	Night	17% 10% 4 8% 6% 3 4 5% 4 5% 34%	2648
	11th to 20th	Night	19% 12% 6% 8% 6% 3 4 4 3 5% 29%	2660
	21st to end	Night	17% 11% 4 8% 6% 3 4 5% 5% 6% 32%	2706
February	1st to 10th	Night	22% 9% 5% 8% 6% 4 5% 4 4 5% 29%	2160
	11th to 20th	Night	17% 8% 3 7% 6% 3 3 4 5% 7% 36%	2098
	21st to end	Night	20% 11% 4 6% 5% 3 3 4 6% 6% 32%	1776
March	1st to 10th	Night	17% 8% 3 7% 5% 3 3 4 4 6% 40%	2160
	11th to 20th	Night	18% 9% 4 6% 5% 2 4 5% 5% 6% 38%	2088
	21st to end	Night	21% 7% 4 6% 5% 3 5% 4 5% 6% 34%	2037
April	1st to 10th	Night	13% 7% 3 5% 5% 2 4 5% 6% 8% 44%	1800
	11th to 20th	Night	17% 6% 2 5% 4 2 4 5% 5% 7% 43%	1775
	21st to end	Night	18% 6% 3 5% 5% 3 6% 5% 6% 7% 37%	1725
May	1st to 10th	Night	16% 6% 2 5% 5% 4 5% 5% 5% 6% 40%	1620
	11th to 20th	Night	13% 6% 3 6% 6% 3 6% 5% 6% 7% 40%	1592
	21st to end	Night	7% 5% 3 6% 6% 4 6% 6% 7% 12% 39%	1686
June	1st to 10th	Night	9% 5% 1 5% 4 2 4 5% 7% 8% 49%	1440
	11th to 20th	Night	7% 4 2 4 6% 3 6% 4 6% 9% 50%	1440
	21st to end	Night	5% 3 2 3 5% 2 6% 6% 6% 10% 52%	1440
July	1st to 10th	Night	9% 4 2 3 6% 3 5% 4 7% 10% 48%	1440
	11th to 20th	Night	5% 3 2 4 5% 3 4 4 7% 9% 54%	1440
	21st to end	Night	8% 4 2 4 4 3 5% 5% 5% 10% 49%	1638
August	1st to 10th	Night	8% 4 2 4 5% 3 5% 4 6% 10% 51%	1646
	11th to 20th	Night	6% 3 2 5% 5% 3 6% 7% 6% 9% 47%	1776
	21st to end	Night	5% 4 2 4 4 3 4 4 6% 9% 56%	1980
September	1st to 10th	Night	10% 4 2 5% 4 3 4 4 6% 7% 51%	1800
	11th to 20th	Night	7% 5% 2 6% 4 2 4 5% 6% 7% 53%	1957
	21st to end	Night	11% 5% 2 4 4 2 4 4 5% 7% 52%	1980
October	1st to 10th	Night	8% 4 2 5% 3 2 3 3 5% 6% 58%	1980
	11th to 20th	Night	16% 5% 2 4 4 3 4 4 4 6% 49%	2091
	21st to end	Night	18% 7% 3 4 5% 2 3 3 4 5% 44%	2574
November	1st to 10th	Night	12% 6% 2 5% 4 2 4 4 5% 5% 52%	2406
	11th to 20th	Night	14% 6% 4 5% 4 2 4 4 5% 7% 47%	2470
	21st to end	Night	20% 8% 3 5% 5% 2 3 3 4 6% 42%	2470
December	1st to 10th	Night	19% 10% 4 6% 5% 2 5% 4 4 7% 34%	2470
	11th to 20th	Night	19% 10% 4 7% 5% 2 4 4 4 5% 36%	3245
	21st to end	Night	23% 16% 5% 8% 7% 4 4 4 4 4 22%	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	52% 4 11% 20% 12% 1	1518
	11th to 20th	Day	58% 3 12% 19% 8%	1520
	21st to end	Day	51% 4 12% 25% 6% 2	1790
February	1st to 10th	Day	54% 4 10% 20% 10% 1	1800
	11th to 20th	Day	51% 5% 11% 21% 10% 2	1758
	21st to end	Day	55% 4 10% 19% 10% 3	1480
March	1st to 10th	Day	46% 4 8% 24% 16% 1	1800
	11th to 20th	Day	52% 5% 11% 21% 9% 2	1871
	21st to end	Day	54% 5% 11% 21% 8% 1	2333
April	1st to 10th	Day	41% 7% 13% 23% 16%	2160
	11th to 20th	Day	45% 5% 11% 21% 15% 3	2134
	21st to end	Day	44% 5% 12% 25% 11% 3	2233
May	1st to 10th	Day	47% 6% 13% 23% 10% 1	2340
	11th to 20th	Day	47% 6% 13% 19% 14% 1	2305
	21st to end	Day	41% 9% 16% 20% 13% 2	2585
June	1st to 10th	Day	35% 5% 12% 27% 18% 3	2520
	11th to 20th	Day	32% 8% 14% 25% 17% 3	2520
	21st to end	Day	33% 8% 14% 22% 17% 5%	2520
July	1st to 10th	Day	39% 9% 14% 21% 13% 4	2451
	11th to 20th	Day	33% 8% 15% 25% 16% 3	2445
	21st to end	Day	34% 9% 17% 22% 16% 2	2527
August	1st to 10th	Day	33% 9% 15% 27% 15% 1	2275
	11th to 20th	Day	36% 8% 13% 26% 16% 1	2125
	21st to end	Day	32% 7% 14% 24% 17% 7%	2376
September	1st to 10th	Day	37% 6% 10% 24% 19% 4	2160
	11th to 20th	Day	33% 6% 10% 28% 20% 3	1985
	21st to end	Day	32% 5% 8% 26% 25% 4	1980
October	1st to 10th	Day	30% 6% 9% 26% 26% 4	1980
	11th to 20th	Day	37% 4 9% 24% 21% 4	1864
	21st to end	Day	45% 5% 8% 23% 16% 3	1782
November	1st to 10th	Day	31% 5% 11% 30% 18% 6%	1672
	11th to 20th	Day	44% 3 9% 22% 18% 4	1710
	21st to end	Day	46% 3 10% 23% 16% 2	1710
December	1st to 10th	Day	53% 5% 11% 20% 11% 1	1710
	11th to 20th	Day	55% 4 8% 22% 10% 1	1944
	21st to end	Day	65% 4 11% 13% 6%	2783
January	1st to 10th	Night	53% 5% 9% 20% 13% 1	2648
	11th to 20th	Night	58% 4 10% 19% 8% 1	2660
	21st to end	Night	52% 4 11% 21% 9% 1	2706
February	1st to 10th	Night	58% 4 11% 19% 6% 2	2160
	11th to 20th	Night	49% 5% 10% 22% 13% 1	2099
	21st to end	Night	53% 4 11% 18% 10% 3	1776
March	1st to 10th	Night	46% 4 8% 22% 17% 3	2160
	11th to 20th	Night	48% 6% 13% 20% 12% 2	2088
	21st to end	Night	50% 6% 13% 21% 8% 2	2037
April	1st to 10th	Night	38% 6% 11% 27% 16% 3	1800
	11th to 20th	Night	41% 4 11% 20% 19% 5%	1775
	21st to end	Night	46% 6% 10% 21% 15% 2	1725
May	1st to 10th	Night	44% 6% 12% 25% 12% 2	1620
	11th to 20th	Night	42% 9% 12% 19% 17% 1	1593
	21st to end	Night	35% 10% 16% 19% 15% 4	1687
June	1st to 10th	Night	31% 7% 12% 25% 22% 4	1440
	11th to 20th	Night	31% 6% 14% 21% 21% 7%	1440
	21st to end	Night	26% 8% 15% 25% 17% 8%	1440
July	1st to 10th	Night	32% 8% 16% 24% 18% 4	1400
	11th to 20th	Night	27% 7% 14% 27% 19% 5%	1392
	21st to end	Night	29% 7% 13% 29% 19% 3	1547
August	1st to 10th	Night	28% 8% 18% 23% 20% 3	1635
	11th to 20th	Night	30% 8% 15% 27% 17% 3	1776
	21st to end	Night	24% 6% 14% 28% 22% 6%	1980
September	1st to 10th	Night	32% 6% 9% 27% 20% 7%	1800
	11th to 20th	Night	30% 5% 9% 26% 25% 5%	1957
	21st to end	Night	31% 6% 10% 23% 24% 7%	1980
October	1st to 10th	Night	27% 5% 11% 22% 28% 6%	1980
	11th to 20th	Night	37% 4 6% 25% 22% 5%	2091
	21st to end	Night	43% 4 8% 23% 18% 4	2574
November	1st to 10th	Night	34% 4 10% 24% 23% 5%	2406
	11th to 20th	Night	38% 3 9% 23% 22% 5%	2470
	21st to end	Night	45% 4 10% 23% 16% 2	2470
December	1st to 10th	Night	50% 4 12% 21% 12% 1	2470
	11th to 20th	Night	50% 5% 10% 21% 13% 1	3247
	21st to end	Night	65% 5% 10% 13% 7% 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	26% 17% 31% 20% 7% 1	270
	11th to 20th	Day	27% 21% 30% 18% 3	270
	21st to end	Day	26% 18% 37% 14% 5%	282
February	1st to 10th	Day	28% 18% 35% 14% 3 1	240
	11th to 20th	Day	28% 20% 36% 13% 3	240
	21st to end	Day	29% 13% 40% 13% 6%	198
March	1st to 10th	Day	25% 15% 40% 17% 3	240
	11th to 20th	Day	28% 15% 33% 16% 6% 2	311
	21st to end	Day	27% 16% 33% 16% 7% 1	462
April	1st to 10th	Day	16% 15% 32% 25% 11% 1	420
	11th to 20th	Day	22% 16% 24% 23% 12% 3	412
	21st to end	Day	21% 12% 33% 23% 8% 3	420
May	1st to 10th	Day	20% 11% 29% 25% 10% 4	423
	11th to 20th	Day	20% 8% 24% 25% 16% 7%	447
	21st to end	Day	12% 3 26% 27% 20% 13%	539
June	1st to 10th	Day	13% 5% 16% 30% 26% 10%	630
	11th to 20th	Day	8% 4 19% 33% 23% 12%	630
	21st to end	Day	10% 4 24% 29% 22% 11%	630
July	1st to 10th	Day	12% 2 12% 24% 27% 21%	621
	11th to 20th	Day	9% 3 13% 31% 28% 15%	618
	21st to end	Day	10% 3 11% 29% 32% 14%	617
August	1st to 10th	Day	11% 2 11% 28% 30% 18%	446
	11th to 20th	Day	16% 3 10% 30% 29% 11%	439
	21st to end	Day	8% 2 10% 25% 34% 21%	495
September	1st to 10th	Day	10% 4 15% 26% 32% 14%	450
	11th to 20th	Day	8% 4 11% 28% 33% 16%	450
	21st to end	Day	14% 5% 18% 25% 24% 13%	450
October	1st to 10th	Day	11% 4 21% 35% 22% 6%	450
	11th to 20th	Day	15% 11% 36% 23% 13% 2	342
	21st to end	Day	29% 12% 30% 24% 5%	297
November	1st to 10th	Day	13% 10% 33% 28% 11% 6%	270
	11th to 20th	Day	20% 17% 27% 24% 9% 2	270
	21st to end	Day	27% 8% 31% 24% 8% 1	270
December	1st to 10th	Day	19% 21% 33% 17% 8% 3	270
	11th to 20th	Day	25% 13% 35% 20% 7% 1	270
	21st to end	Day	28% 20% 33% 16% 3	297
January	1st to 10th	Night	23% 14% 32% 28% 4	950
	11th to 20th	Night	25% 14% 35% 22% 3	950
	21st to end	Night	22% 11% 39% 25% 2	968
February	1st to 10th	Night	27% 12% 34% 25% 3	720
	11th to 20th	Night	24% 13% 38% 23% 3	703
	21st to end	Night	27% 13% 37% 22% 2	592
March	1st to 10th	Night	21% 12% 35% 27% 4	720
	11th to 20th	Night	25% 9% 33% 25% 7% 1	720
	21st to end	Night	24% 8% 28% 33% 6% 1	651
April	1st to 10th	Night	15% 10% 32% 35% 8%	540
	11th to 20th	Night	21% 10% 26% 29% 14% 1	533
	21st to end	Night	23% 5% 29% 33% 8% 1	540
May	1st to 10th	Night	17% 5% 29% 33% 14% 1	540
	11th to 20th	Night	16% 5% 20% 36% 20% 2	531
	21st to end	Night	10% 3 19% 35% 30% 4	584
June	1st to 10th	Night	12% 2 16% 40% 28% 2	540
	11th to 20th	Night	9% 1 17% 44% 27% 2	540
	21st to end	Night	6% 1 17% 42% 31% 3	540
July	1st to 10th	Night	11% 1 8% 30% 40% 9%	525
	11th to 20th	Night	6% 3 7% 38% 41% 5%	522
	21st to end	Night	8% 2 10% 34% 39% 6%	591
August	1st to 10th	Night	8% 2 8% 36% 40% 6%	537
	11th to 20th	Night	7% 1 9% 39% 40% 5%	534
	21st to end	Night	7% 1 7% 35% 43% 7%	594
September	1st to 10th	Night	12% 3 10% 33% 37% 6%	540
	11th to 20th	Night	8% 2 12% 33% 39% 5%	697
	21st to end	Night	13% 4 20% 30% 29% 4	720
October	1st to 10th	Night	11% 4 18% 37% 25% 6%	720
	11th to 20th	Night	17% 7% 27% 33% 15% 2	720
	21st to end	Night	24% 7% 32% 26% 11%	792
November	1st to 10th	Night	14% 8% 28% 36% 14% 1	740
	11th to 20th	Night	16% 13% 31% 30% 10%	760
	21st to end	Night	23% 12% 25% 29% 10%	760
December	1st to 10th	Night	24% 8% 33% 29% 6% 1	760
	11th to 20th	Night	26% 7% 32% 28% 6% 1	916
	21st to end	Night	28% 12% 33% 24% 4	1045

Page generated at 2024-01-24 09:37:28. Version ac07

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