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 2025-02-06.

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	13% 8% 3 7% 5% 4 4 4 5% 7% 39%	108330
	Night	15% 9% 3 7% 4 4 4 3 5% 6% 40%	110029
Transparency	Day	42% 5% 11% 24% 16% 2	111992
	Night	43% 5% 10% 23% 17% 3	114507
Seeing	Day	17% 9% 24% 25% 18% 8%	15786
	Night	18% 8% 26% 31% 16% 2	25712

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% 13% 7% 11% 5% 4 4 4 4 5% 27%	3617
	11th to 20th	Day	13% 12% 5% 13% 8% 5% 5% 3 3 5% 28%	3620
	21st to end	Day	21% 12% 6% 8% 4 4 3 3 4 5% 30%	4385
February	1st to 10th	Day	17% 12% 5% 8% 4 3 4 3 5% 6% 33%	1950
	11th to 20th	Day	16% 10% 3 8% 5% 5% 4 4 5% 6% 35%	1848
	21st to end	Day	16% 12% 4 9% 6% 4 4 3 4 6% 32%	1570
March	1st to 10th	Day	24% 13% 3 7% 4 3 3 2 3 4 34%	3120
	11th to 20th	Day	14% 7% 3 6% 4 3 3 3 5% 6% 45%	3287
	21st to end	Day	13% 9% 3 7% 6% 5% 6% 4 5% 7% 36%	4094
April	1st to 10th	Day	13% 9% 3 6% 5% 4 4 4 4 8% 40%	2280
	11th to 20th	Day	17% 8% 2 6% 5% 3 4 3 6% 6% 41%	2254
	21st to end	Day	18% 7% 2 7% 4 4 4 3 4 7% 39%	2358
May	1st to 10th	Day	17% 7% 3 7% 5% 5% 5% 4 7% 9% 30%	4082
	11th to 20th	Day	19% 6% 2 6% 5% 4 4 3 5% 7% 38%	4081
	21st to end	Day	11% 7% 2 7% 5% 5% 5% 4 6% 8% 40%	4572
June	1st to 10th	Day	11% 6% 2 6% 4 3 4 4 5% 9% 46%	2660
	11th to 20th	Day	6% 5% 2 6% 4 5% 5% 5% 6% 8% 47%	2660
	21st to end	Day	8% 5% 2 5% 5% 4 5% 5% 7% 10% 44%	2660
July	1st to 10th	Day	13% 5% 2 6% 4 4 5% 4 6% 9% 40%	4440
	11th to 20th	Day	6% 4 2 5% 4 4 5% 4 8% 10% 47%	4440
	21st to end	Day	10% 7% 3 8% 6% 7% 7% 6% 8% 9% 29%	4693
August	1st to 10th	Day	7% 5% 1 5% 4 4 4 4 6% 10% 51%	4023
	11th to 20th	Day	8% 5% 3 6% 4 5% 5% 5% 7% 9% 42%	3729
	21st to end	Day	5% 4 2 5% 4 4 4 4 6% 9% 54%	4180
September	1st to 10th	Day	10% 6% 2 6% 5% 4 5% 3 6% 7% 46%	2280
	11th to 20th	Day	9% 5% 2 5% 4 4 4 4 6% 8% 49%	2095
	21st to end	Day	12% 6% 2 6% 3 3 4 3 4 6% 52%	2090
October	1st to 10th	Day	10% 5% 2 4 3 3 3 3 4 6% 56%	2090
	11th to 20th	Day	13% 5% 2 6% 4 4 4 3 5% 6% 48%	1967
	21st to end	Day	19% 8% 3 6% 4 3 4 3 4 6% 42%	1881
November	1st to 10th	Day	9% 5% 1 5% 4 3 4 4 5% 6% 53%	1762
	11th to 20th	Day	16% 9% 4 6% 4 3 4 3 4 6% 42%	1800
	21st to end	Day	20% 10% 3 5% 4 4 3 3 4 5% 39%	1800
December	1st to 10th	Day	15% 10% 3 6% 3 3 4 3 3 4 46%	2930
	11th to 20th	Day	16% 12% 6% 10% 5% 5% 4 3 4 6% 29%	3050
	21st to end	Day	26% 17% 5% 8% 6% 4 3 2 3 5% 20%	3982
January	1st to 10th	Night	18% 14% 6% 9% 4 4 4 4 5% 5% 27%	6348
	11th to 20th	Night	15% 15% 5% 10% 5% 6% 6% 3 3 4 28%	6360
	21st to end	Night	20% 12% 4 6% 4 4 4 3 4 6% 33%	6568
February	1st to 10th	Night	21% 9% 4 9% 5% 5% 4 3 4 5% 30%	2341
	11th to 20th	Night	16% 9% 3 8% 5% 4 3 3 5% 7% 37%	2218
	21st to end	Night	20% 12% 3 7% 4 4 3 3 6% 5% 33%	1884
March	1st to 10th	Night	23% 12% 3 7% 4 4 3 2 4 5% 33%	3733
	11th to 20th	Night	13% 7% 2 5% 3 3 3 3 4 5% 49%	3672
	21st to end	Night	16% 8% 3 7% 5% 4 4 3 5% 5% 39%	3565
April	1st to 10th	Night	13% 8% 2 6% 4 4 4 3 6% 7% 42%	1900
	11th to 20th	Night	17% 7% 2 6% 4 3 4 4 5% 7% 43%	1875
	21st to end	Night	18% 7% 2 6% 5% 5% 4 4 6% 7% 37%	1820
May	1st to 10th	Night	17% 10% 2 7% 5% 5% 5% 4 5% 7% 34%	2813
	11th to 20th	Night	17% 6% 2 5% 4 4 4 3 5% 6% 42%	2812
	21st to end	Night	10% 5% 2 6% 4 5% 5% 5% 7% 9% 41%	2969
June	1st to 10th	Night	9% 5% 1 6% 4 3 4 4 7% 8% 48%	1520
	11th to 20th	Night	7% 4 2 5% 5% 4 5% 3 6% 10% 49%	1520
	21st to end	Night	5% 4 2 4 4 4 6% 4 7% 9% 52%	1520
July	1st to 10th	Night	10% 5% 2 5% 4 4 4 4 6% 8% 48%	2530
	11th to 20th	Night	5% 4 2 4 4 3 4 3 6% 9% 57%	2530
	21st to end	Night	9% 7% 3 9% 6% 6% 6% 5% 8% 9% 33%	2863
August	1st to 10th	Night	7% 4 1 4 4 3 3 3 5% 8% 57%	2888
	11th to 20th	Night	6% 4 2 6% 4 4 5% 5% 6% 8% 50%	3100
	21st to end	Night	3 3 2 4 3 4 4 3 6% 9% 60%	3476
September	1st to 10th	Night	10% 4 2 6% 4 4 4 3 6% 7% 51%	1900
	11th to 20th	Night	7% 5% 2 6% 3 3 5% 4 6% 7% 53%	2066
	21st to end	Night	12% 6% 2 5% 4 3 4 3 5% 7% 50%	2090
October	1st to 10th	Night	8% 4 2 5% 3 3 3 3 5% 5% 59%	2090
	11th to 20th	Night	15% 6% 2 5% 3 3 4 3 4 6% 51%	2208
	21st to end	Night	18% 8% 3 5% 4 3 3 2 4 5% 45%	2717
November	1st to 10th	Night	12% 6% 2 6% 4 3 4 3 5% 5% 51%	2536
	11th to 20th	Night	14% 7% 3 6% 3 3 4 3 5% 7% 46%	2600
	21st to end	Night	19% 9% 3 5% 4 3 3 2 4 5% 41%	2600
December	1st to 10th	Night	17% 10% 3 7% 4 3 3 3 3 5% 42%	4250
	11th to 20th	Night	19% 10% 3 7% 3 3 4 3 5% 6% 37%	5151
	21st to end	Night	27% 16% 4 8% 5% 4 3 3 4 4 21%	6996

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	60% 4 10% 19% 7% 1	3618
	11th to 20th	Day	59% 2 10% 18% 10% 1	3620
	21st to end	Day	57% 3 9% 18% 9% 4	4385
February	1st to 10th	Day	51% 4 11% 21% 11% 2	1950
	11th to 20th	Day	49% 5% 10% 22% 12% 2	1858
	21st to end	Day	54% 4 9% 19% 11% 3	1570
March	1st to 10th	Day	56% 4 5% 19% 12% 4	3120
	11th to 20th	Day	39% 5% 11% 27% 16% 2	3287
	21st to end	Day	45% 5% 14% 22% 12% 1	4094
April	1st to 10th	Day	42% 7% 13% 22% 16% 1	2280
	11th to 20th	Day	44% 5% 11% 22% 15% 3	2254
	21st to end	Day	44% 5% 11% 25% 11% 2	2358
May	1st to 10th	Day	47% 9% 16% 21% 8%	4120
	11th to 20th	Day	46% 7% 11% 25% 11% 1	4085
	21st to end	Day	39% 8% 12% 19% 20% 2	4585
June	1st to 10th	Day	35% 6% 12% 26% 18% 3	2660
	11th to 20th	Day	32% 8% 13% 25% 18% 4	2660
	21st to end	Day	33% 8% 14% 22% 18% 5%	2660
July	1st to 10th	Day	39% 7% 11% 24% 16% 2	4371
	11th to 20th	Day	29% 7% 12% 32% 18% 2	4365
	21st to end	Day	47% 9% 16% 17% 10% 1	4544
August	1st to 10th	Day	27% 7% 15% 35% 15% 1	4010
	11th to 20th	Day	35% 7% 13% 26% 18% 1	3765
	21st to end	Day	27% 6% 14% 34% 16% 4	4179
September	1st to 10th	Day	36% 6% 10% 23% 21% 5%	2280
	11th to 20th	Day	32% 5% 11% 29% 21% 3	2095
	21st to end	Day	34% 5% 8% 25% 24% 4	2090
October	1st to 10th	Day	20% 4 5% 27% 42% 3	3480
	11th to 20th	Day	25% 3 9% 26% 33% 4	3247
	21st to end	Day	34% 3 8% 24% 26% 4	3081
November	1st to 10th	Day	32% 5% 10% 30% 18% 6%	1762
	11th to 20th	Day	44% 3 9% 22% 18% 4	1800
	21st to end	Day	48% 3 9% 22% 16% 1	1800
December	1st to 10th	Day	43% 3 13% 26% 15%	2930
	11th to 20th	Day	57% 3 9% 20% 9% 1	3047
	21st to end	Day	68% 3 11% 12% 5%	3982
January	1st to 10th	Night	58% 4 10% 20% 8%	6348
	11th to 20th	Night	61% 3 7% 16% 11% 2	6360
	21st to end	Night	52% 3 8% 21% 15% 1	6568
February	1st to 10th	Night	56% 4 11% 19% 8% 2	2341
	11th to 20th	Night	48% 5% 10% 22% 14% 1	2219
	21st to end	Night	52% 4 11% 19% 11% 3	1884
March	1st to 10th	Night	54% 5% 7% 19% 13% 2	3733
	11th to 20th	Night	36% 6% 13% 24% 20% 3	3672
	21st to end	Night	46% 6% 11% 25% 11% 1	3565
April	1st to 10th	Night	39% 6% 11% 26% 16% 3	1900
	11th to 20th	Night	41% 4 10% 21% 19% 5%	1875
	21st to end	Night	45% 6% 10% 22% 15% 2	1820
May	1st to 10th	Night	48% 8% 15% 21% 7% 1	2840
	11th to 20th	Night	40% 8% 13% 26% 12%	2813
	21st to end	Night	35% 9% 15% 20% 17% 4	2977
June	1st to 10th	Night	32% 7% 12% 25% 22% 4	1520
	11th to 20th	Night	31% 6% 13% 21% 22% 7%	1520
	21st to end	Night	26% 8% 16% 25% 18% 8%	1520
July	1st to 10th	Night	35% 6% 11% 25% 20% 3	2490
	11th to 20th	Night	25% 6% 11% 34% 21% 3	2482
	21st to end	Night	44% 8% 15% 21% 12% 2	2772
August	1st to 10th	Night	25% 6% 16% 38% 14% 2	2877
	11th to 20th	Night	30% 7% 14% 29% 19% 2	3130
	21st to end	Night	21% 5% 14% 31% 26% 4	3476
September	1st to 10th	Night	31% 6% 8% 26% 22% 7%	1900
	11th to 20th	Night	30% 5% 10% 25% 26% 5%	2066
	21st to end	Night	34% 6% 10% 22% 23% 6%	2090
October	1st to 10th	Night	18% 3 7% 17% 50% 5%	3480
	11th to 20th	Night	25% 2 6% 26% 37% 4	3667
	21st to end	Night	32% 3 8% 23% 28% 6%	4467
November	1st to 10th	Night	35% 4 10% 24% 22% 5%	2536
	11th to 20th	Night	39% 3 9% 22% 22% 5%	2600
	21st to end	Night	46% 3 10% 23% 16% 2	2600
December	1st to 10th	Night	47% 3 11% 24% 15%	4250
	11th to 20th	Night	48% 4 13% 21% 13% 1	5153
	21st to end	Night	67% 4 9% 14% 5% 1	6996

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% 17% 31% 20% 6% 1	300
	11th to 20th	Day	26% 21% 32% 18% 3	300
	21st to end	Day	24% 18% 39% 14% 4	330
February	1st to 10th	Day	26% 18% 35% 17% 4 1	285
	11th to 20th	Day	26% 19% 37% 13% 3 1	270
	21st to end	Day	29% 14% 40% 13% 5%	225
March	1st to 10th	Day	26% 16% 38% 17% 3	270
	11th to 20th	Day	26% 17% 35% 15% 6% 1	345
	21st to end	Day	26% 16% 35% 16% 6% 1	506
April	1st to 10th	Day	18% 16% 30% 24% 10% 1	460
	11th to 20th	Day	22% 17% 24% 23% 11% 3	452
	21st to end	Day	21% 12% 33% 22% 8% 3	460
May	1st to 10th	Day	19% 12% 29% 26% 10% 4	463
	11th to 20th	Day	20% 8% 24% 25% 15% 8%	487
	21st to end	Day	12% 4 27% 26% 18% 12%	586
June	1st to 10th	Day	14% 5% 18% 28% 25% 9%	680
	11th to 20th	Day	8% 4 18% 34% 24% 12%	680
	21st to end	Day	10% 4 24% 30% 22% 11%	680
July	1st to 10th	Day	13% 2 12% 25% 27% 20%	671
	11th to 20th	Day	8% 3 14% 32% 28% 15%	668
	21st to end	Day	10% 3 11% 30% 33% 13%	668
August	1st to 10th	Day	10% 2 11% 28% 31% 18%	486
	11th to 20th	Day	15% 3 11% 31% 29% 11%	479
	21st to end	Day	8% 2 9% 24% 35% 22%	539
September	1st to 10th	Day	9% 3 15% 27% 32% 14%	490
	11th to 20th	Day	8% 4 11% 28% 35% 16%	490
	21st to end	Day	15% 6% 19% 24% 23% 12%	490
October	1st to 10th	Day	10% 4 20% 33% 24% 9%	490
	11th to 20th	Day	14% 11% 35% 23% 13% 5%	376
	21st to end	Day	27% 11% 31% 25% 6% 1	330
November	1st to 10th	Day	12% 11% 33% 26% 12% 5%	300
	11th to 20th	Day	19% 16% 31% 24% 8% 2	300
	21st to end	Day	28% 9% 30% 24% 8% 1	300
December	1st to 10th	Day	18% 21% 34% 17% 7% 3	300
	11th to 20th	Day	25% 13% 34% 20% 7% 1	300
	21st to end	Day	28% 19% 31% 18% 3	330
January	1st to 10th	Night	23% 14% 32% 28% 4	1000
	11th to 20th	Night	24% 14% 36% 22% 3	1000
	21st to end	Night	21% 11% 39% 25% 2	1036
February	1st to 10th	Night	26% 11% 35% 26% 3	781
	11th to 20th	Night	23% 12% 38% 24% 3	743
	21st to end	Night	26% 12% 38% 22% 2	628
March	1st to 10th	Night	23% 12% 34% 26% 4	760
	11th to 20th	Night	24% 10% 34% 25% 7% 1	760
	21st to end	Night	24% 9% 29% 32% 6% 1	687
April	1st to 10th	Night	15% 11% 33% 33% 8%	570
	11th to 20th	Night	21% 10% 27% 29% 13% 1	563
	21st to end	Night	22% 6% 30% 32% 8% 1	570
May	1st to 10th	Night	17% 6% 29% 33% 14% 1	570
	11th to 20th	Night	16% 5% 19% 36% 21% 2	561
	21st to end	Night	10% 3 19% 36% 29% 3	617
June	1st to 10th	Night	12% 3 16% 41% 27% 2	570
	11th to 20th	Night	9% 1 16% 45% 26% 2	570
	21st to end	Night	6% 1 17% 43% 31% 2	570
July	1st to 10th	Night	11% 2 8% 31% 39% 9%	555
	11th to 20th	Night	6% 3 8% 39% 39% 5%	552
	21st to end	Night	10% 2 9% 35% 38% 6%	624
August	1st to 10th	Night	8% 2 9% 36% 40% 6%	567
	11th to 20th	Night	7% 1 9% 40% 38% 5%	564
	21st to end	Night	6% 1 7% 35% 44% 7%	627
September	1st to 10th	Night	12% 3 10% 33% 37% 5%	570
	11th to 20th	Night	9% 2 12% 33% 40% 5%	736
	21st to end	Night	13% 4 20% 31% 28% 4	760
October	1st to 10th	Night	10% 4 18% 38% 25% 6%	760
	11th to 20th	Night	17% 7% 26% 32% 16% 2	760
	21st to end	Night	23% 7% 32% 27% 11%	836
November	1st to 10th	Night	15% 8% 28% 36% 13% 1	780
	11th to 20th	Night	17% 12% 30% 31% 9%	800
	21st to end	Night	24% 12% 25% 29% 9%	800
December	1st to 10th	Night	25% 7% 34% 29% 5% 1	800
	11th to 20th	Night	26% 7% 32% 28% 6% 1	965
	21st to end	Night	29% 12% 32% 24% 3	1100

Page generated at 2025-02-03 03:05:54. Version ac07

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