RedShift Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the RedShift Observatory clear sky chart from 2005-11-06 to 2026-02-16.

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% 12% 5% 10% 5% 4 4 3 5% 6% 32%	130748
	Night	14% 14% 6% 13% 6% 5% 4 3 4 5% 27%	130370
Transparency	Day	52% 4 11% 21% 11% 1	134235
	Night	59% 4 10% 17% 9% 1	134945
Seeing	Day	21% 14% 31% 22% 9% 3	17646
	Night	23% 11% 28% 27% 10% 1	27651

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	13% 24% 13% 29% 7% 4 2 1 2 2 4	4691
	11th to 20th	Day	10% 19% 11% 28% 13% 11% 3 1 1 1 2	4710
	21st to end	Day	10% 16% 10% 19% 13% 9% 7% 2 2 2 11%	5156
February	1st to 10th	Day	9% 18% 7% 19% 15% 6% 3 3 2 3 14%	1812
	11th to 20th	Day	11% 16% 7% 17% 13% 6% 4 3 3 4 14%	1998
	21st to end	Day	12% 19% 7% 14% 10% 5% 4 2 4 5% 19%	1650
March	1st to 10th	Day	12% 11% 4 12% 7% 4 4 3 4 6% 31%	4480
	11th to 20th	Day	11% 10% 6% 12% 5% 4 4 4 6% 7% 30%	4784
	21st to end	Day	22% 12% 7% 14% 5% 3 3 2 4 4 23%	5776
April	1st to 10th	Day	17% 14% 4 8% 4 4 4 3 5% 6% 30%	2400
	11th to 20th	Day	20% 12% 2 6% 4 4 3 3 5% 6% 35%	2434
	21st to end	Day	16% 10% 3 7% 4 5% 4 4 6% 7% 33%	2600
May	1st to 10th	Day	14% 8% 2 6% 4 3 4 3 6% 7% 43%	5862
	11th to 20th	Day	11% 9% 2 7% 4 4 4 3 5% 6% 44%	6153
	21st to end	Day	14% 7% 2 6% 4 4 4 3 5% 7% 44%	6935
June	1st to 10th	Day	12% 5% 2 5% 4 4 4 4 6% 8% 45%	2800
	11th to 20th	Day	11% 5% 2 6% 5% 4 4 4 6% 9% 43%	2800
	21st to end	Day	13% 6% 2 6% 3 3 4 4 7% 9% 43%	2800
July	1st to 10th	Day	14% 6% 2 5% 3 3 4 4 6% 9% 44%	6360
	11th to 20th	Day	9% 5% 1 4 3 3 4 4 5% 8% 54%	6360
	21st to end	Day	9% 5% 2 5% 4 3 4 4 6% 9% 49%	6924
August	1st to 10th	Day	9% 6% 2 6% 4 5% 5% 4 7% 9% 43%	4436
	11th to 20th	Day	14% 5% 2 5% 3 3 3 3 5% 6% 51%	4174
	21st to end	Day	12% 6% 2 6% 4 4 4 3 5% 7% 46%	4380
September	1st to 10th	Day	14% 5% 2 6% 5% 4 4 4 6% 7% 44%	2400
	11th to 20th	Day	12% 5% 2 5% 4 3 4 4 5% 9% 47%	2203
	21st to end	Day	15% 6% 3 7% 4 4 4 3 7% 8% 39%	2200
October	1st to 10th	Day	15% 8% 3 7% 4 4 4 3 5% 6% 39%	2200
	11th to 20th	Day	22% 16% 4 8% 5% 4 5% 3 5% 6% 22%	1889
	21st to end	Day	24% 16% 4 8% 5% 4 4 4 5% 5% 22%	1980
November	1st to 10th	Day	19% 18% 3 7% 4 4 4 3 4 6% 28%	1852
	11th to 20th	Day	16% 24% 7% 11% 6% 3 4 3 4 5% 17%	1890
	21st to end	Day	20% 25% 9% 13% 4 3 3 2 3 4 15%	1811
December	1st to 10th	Day	13% 32% 16% 16% 4 3 3 2 2 2 7%	2690
	11th to 20th	Day	12% 25% 13% 21% 9% 4 3 2 3 3 5%	3088
	21st to end	Day	20% 22% 9% 15% 7% 4 4 2 3 3 9%	4070
January	1st to 10th	Night	14% 23% 9% 27% 8% 3 2 2 2 2 8%	8232
	11th to 20th	Night	9% 21% 11% 25% 13% 10% 3 1 1 2 5%	8280
	21st to end	Night	9% 17% 10% 20% 14% 9% 6% 2 2 2 9%	9058
February	1st to 10th	Night	10% 19% 7% 18% 13% 6% 4 2 3 4 13%	2803
	11th to 20th	Night	12% 15% 7% 17% 12% 5% 4 3 4 5% 16%	2399
	21st to end	Night	15% 17% 5% 15% 7% 5% 4 3 5% 5% 19%	1980
March	1st to 10th	Night	16% 10% 4 12% 4 3 3 2 5% 6% 33%	5373
	11th to 20th	Night	11% 11% 4 10% 5% 4 5% 4 5% 7% 35%	5175
	21st to end	Night	20% 12% 5% 11% 4 4 4 3 5% 5% 28%	5197
April	1st to 10th	Night	18% 12% 4 8% 5% 4 4 4 5% 6% 31%	2000
	11th to 20th	Night	21% 10% 3 7% 4 4 4 2 4 6% 35%	1914
	21st to end	Night	18% 9% 3 7% 5% 4 4 3 4 6% 37%	1800
May	1st to 10th	Night	15% 7% 3 6% 4 4 4 4 5% 7% 41%	4033
	11th to 20th	Night	11% 9% 2 7% 5% 5% 4 4 5% 7% 41%	3739
	21st to end	Night	19% 6% 3 5% 3 3 3 3 5% 6% 43%	3942
June	1st to 10th	Night	12% 8% 2 6% 5% 4 5% 4 5% 7% 42%	1600
	11th to 20th	Night	11% 6% 3 7% 6% 4 5% 4 6% 8% 41%	1600
	21st to end	Night	12% 7% 2 6% 4 4 5% 4 5% 7% 44%	1600
July	1st to 10th	Night	13% 8% 2 6% 4 4 5% 4 5% 8% 42%	3618
	11th to 20th	Night	8% 6% 1 4 3 4 5% 3 5% 6% 54%	3617
	21st to end	Night	7% 6% 2 6% 4 4 4 4 6% 8% 49%	3947
August	1st to 10th	Night	12% 5% 2 7% 4 5% 5% 4 6% 8% 43%	2719
	11th to 20th	Night	13% 5% 2 5% 3 4 4 3 5% 7% 51%	2875
	21st to end	Night	9% 6% 2 7% 4 4 4 4 5% 7% 48%	3515
September	1st to 10th	Night	11% 7% 2 6% 4 4 4 3 5% 7% 48%	2000
	11th to 20th	Night	11% 6% 2 5% 3 3 4 3 6% 7% 49%	2176
	21st to end	Night	16% 7% 2 7% 5% 4 4 4 5% 7% 39%	2200
October	1st to 10th	Night	18% 7% 3 7% 4 4 4 3 4 5% 42%	2200
	11th to 20th	Night	24% 13% 4 8% 4 4 4 3 4 6% 26%	2505
	21st to end	Night	26% 14% 4 8% 5% 4 4 3 4 5% 25%	2860
November	1st to 10th	Night	17% 17% 4 8% 5% 3 3 3 5% 6% 28%	2666
	11th to 20th	Night	16% 24% 7% 12% 4 4 4 3 3 4 20%	2730
	21st to end	Night	18% 25% 9% 12% 3 4 4 2 4 4 15%	2808
December	1st to 10th	Night	13% 27% 14% 19% 5% 4 3 2 2 3 9%	4720
	11th to 20th	Night	14% 26% 10% 19% 10% 3 2 2 3 3 8%	5339
	21st to end	Night	22% 21% 9% 14% 5% 4 3 3 3 4 12%	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	91% 2 4 3 1	4692
	11th to 20th	Day	94% 2 2 2 1	4710
	21st to end	Day	82% 3 6% 7% 1	5156
February	1st to 10th	Day	77% 3 7% 12% 1	1812
	11th to 20th	Day	75% 4 8% 9% 4	2008
	21st to end	Day	69% 4 9% 14% 4 1	1650
March	1st to 10th	Day	55% 3 14% 17% 10% 1	4480
	11th to 20th	Day	53% 4 14% 19% 9% 1	4784
	21st to end	Day	66% 4 9% 15% 7%	5778
April	1st to 10th	Day	56% 3 9% 21% 11%	2400
	11th to 20th	Day	51% 3 8% 21% 15% 2	2434
	21st to end	Day	49% 4 12% 19% 14% 2	2600
May	1st to 10th	Day	41% 4 9% 25% 18% 3	5897
	11th to 20th	Day	42% 4 9% 25% 18% 2	6157
	21st to end	Day	40% 4 10% 24% 20% 1	6949
June	1st to 10th	Day	37% 4 12% 29% 16% 2	2800
	11th to 20th	Day	37% 4 14% 26% 17% 1	2800
	21st to end	Day	36% 5% 15% 27% 15% 1	2800
July	1st to 10th	Day	36% 5% 14% 31% 13% 1	6291
	11th to 20th	Day	28% 6% 14% 35% 15% 2	6285
	21st to end	Day	31% 6% 15% 30% 17% 1	6728
August	1st to 10th	Day	36% 5% 14% 31% 13% 1	4421
	11th to 20th	Day	35% 4 15% 30% 16% 1	4213
	21st to end	Day	36% 6% 15% 30% 12% 1	4379
September	1st to 10th	Day	40% 5% 14% 28% 12% 1	2400
	11th to 20th	Day	34% 5% 16% 32% 13% 1	2203
	21st to end	Day	42% 5% 15% 28% 10%	2200
October	1st to 10th	Day	31% 4 8% 38% 19% 1	3590
	11th to 20th	Day	53% 6% 11% 21% 10%	3040
	21st to end	Day	60% 5% 14% 16% 5%	3180
November	1st to 10th	Day	57% 5% 10% 20% 8%	1852
	11th to 20th	Day	70% 4 11% 11% 4	1890
	21st to end	Day	76% 3 10% 8% 2	1811
December	1st to 10th	Day	85% 4 4 6% 1	2690
	11th to 20th	Day	87% 3 6% 4 1	3085
	21st to end	Day	81% 4 6% 8% 1	4070
January	1st to 10th	Night	84% 3 6% 6% 1	8233
	11th to 20th	Night	90% 3 4 3	8280
	21st to end	Night	84% 3 6% 6% 1	9058
February	1st to 10th	Night	77% 3 6% 11% 3	2803
	11th to 20th	Night	71% 4 8% 13% 4	2400
	21st to end	Night	68% 3 11% 14% 4	1980
March	1st to 10th	Night	52% 4 17% 20% 8%	5373
	11th to 20th	Night	48% 5% 18% 21% 8% 1	5175
	21st to end	Night	59% 4 10% 19% 8% 1	5197
April	1st to 10th	Night	55% 4 8% 21% 11% 1	2000
	11th to 20th	Night	53% 3 7% 22% 13% 3	1914
	21st to end	Night	49% 4 9% 22% 14% 3	1800
May	1st to 10th	Night	42% 4 11% 20% 19% 3	4060
	11th to 20th	Night	43% 5% 9% 24% 17% 1	3740
	21st to end	Night	43% 3 10% 25% 14% 5%	3950
June	1st to 10th	Night	40% 5% 10% 29% 15% 2	1600
	11th to 20th	Night	39% 5% 12% 24% 18% 2	1600
	21st to end	Night	39% 5% 13% 26% 15% 2	1600
July	1st to 10th	Night	40% 5% 12% 25% 14% 4	3580
	11th to 20th	Night	29% 5% 13% 32% 19% 3	3572
	21st to end	Night	32% 7% 13% 27% 19% 2	3832
August	1st to 10th	Night	38% 6% 14% 27% 14% 2	2710
	11th to 20th	Night	34% 4 13% 32% 17%	2902
	21st to end	Night	35% 6% 13% 24% 21% 1	3515
September	1st to 10th	Night	35% 4 13% 26% 20% 1	2000
	11th to 20th	Night	33% 5% 14% 33% 15% 1	2176
	21st to end	Night	44% 3 15% 25% 12% 1	2200
October	1st to 10th	Night	38% 4 9% 36% 12%	3590
	11th to 20th	Night	51% 4 9% 25% 12%	4080
	21st to end	Night	52% 4 14% 23% 7%	4610
November	1st to 10th	Night	57% 4 11% 20% 8% 1	2666
	11th to 20th	Night	70% 3 11% 11% 5% 1	2730
	21st to end	Night	74% 3 12% 9% 2	2808
December	1st to 10th	Night	81% 5% 6% 7% 1	4720
	11th to 20th	Night	83% 3 7% 6% 1	5341
	21st to end	Night	76% 4 10% 7% 3	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% 24% 31% 16% 5% 1	330
	11th to 20th	Day	28% 22% 37% 12% 2	330
	21st to end	Day	26% 20% 34% 17% 2 1	363
February	1st to 10th	Day	23% 30% 31% 12% 3 1	330
	11th to 20th	Day	25% 26% 35% 12% 2	315
	21st to end	Day	28% 30% 37% 4 2	249
March	1st to 10th	Day	26% 29% 33% 11% 1	300
	11th to 20th	Day	29% 16% 29% 18% 8%	408
	21st to end	Day	32% 16% 29% 17% 5% 1	550
April	1st to 10th	Day	29% 14% 36% 16% 4 1	500
	11th to 20th	Day	32% 16% 30% 13% 7% 2	492
	21st to end	Day	26% 15% 30% 21% 6% 2	500
May	1st to 10th	Day	22% 15% 37% 18% 6% 2	503
	11th to 20th	Day	17% 11% 37% 24% 9% 2	650
	21st to end	Day	15% 13% 32% 26% 10% 3	789
June	1st to 10th	Day	16% 12% 34% 25% 10% 3	730
	11th to 20th	Day	15% 10% 38% 26% 8% 2	730
	21st to end	Day	17% 9% 34% 27% 11% 3	730
July	1st to 10th	Day	10% 7% 30% 34% 14% 4	721
	11th to 20th	Day	12% 7% 30% 32% 14% 4	718
	21st to end	Day	10% 5% 33% 34% 14% 4	794
August	1st to 10th	Day	12% 5% 26% 31% 20% 7%	651
	11th to 20th	Day	15% 5% 23% 31% 17% 10%	519
	21st to end	Day	16% 7% 26% 29% 17% 5%	583
September	1st to 10th	Day	18% 9% 24% 26% 16% 7%	530
	11th to 20th	Day	11% 5% 26% 32% 20% 6%	530
	21st to end	Day	18% 12% 23% 28% 14% 5%	530
October	1st to 10th	Day	21% 14% 25% 23% 14% 3	530
	11th to 20th	Day	31% 14% 35% 16% 4	365
	21st to end	Day	35% 17% 29% 13% 5%	363
November	1st to 10th	Day	35% 15% 30% 16% 4	330
	11th to 20th	Day	29% 21% 35% 11% 3 1	330
	21st to end	Day	32% 25% 30% 11% 2	330
December	1st to 10th	Day	32% 22% 28% 13% 4 1	330
	11th to 20th	Day	32% 25% 30% 10% 2 1	330
	21st to end	Day	39% 19% 28% 10% 3 1	363
January	1st to 10th	Night	27% 17% 32% 18% 5%	1050
	11th to 20th	Night	25% 18% 32% 19% 6% 1	1050
	21st to end	Night	23% 13% 35% 22% 6%	1155
February	1st to 10th	Night	22% 16% 33% 24% 5%	969
	11th to 20th	Night	22% 21% 28% 23% 5%	804
	21st to end	Night	26% 17% 33% 21% 3	660
March	1st to 10th	Night	20% 15% 32% 25% 7% 1	800
	11th to 20th	Night	19% 14% 35% 25% 6% 1	800
	21st to end	Night	24% 13% 28% 27% 7% 1	765
April	1st to 10th	Night	27% 11% 33% 23% 6% 1	600
	11th to 20th	Night	27% 11% 31% 23% 7% 1	593
	21st to end	Night	23% 10% 31% 28% 8% 1	600
May	1st to 10th	Night	20% 7% 32% 31% 9% 1	600
	11th to 20th	Night	17% 7% 32% 30% 13% 1	591
	21st to end	Night	17% 6% 26% 34% 16% 1	650
June	1st to 10th	Night	16% 4 29% 37% 14% 1	600
	11th to 20th	Night	14% 7% 25% 38% 15% 2	600
	21st to end	Night	15% 4 23% 41% 17% 1	600
July	1st to 10th	Night	12% 2 18% 44% 22% 2	585
	11th to 20th	Night	9% 4 20% 41% 23% 2	582
	21st to end	Night	9% 2 21% 40% 25% 2	657
August	1st to 10th	Night	11% 2 16% 46% 23% 3	597
	11th to 20th	Night	12% 4 18% 35% 26% 5%	594
	21st to end	Night	15% 4 19% 39% 21% 2	660
September	1st to 10th	Night	14% 5% 20% 34% 23% 4	600
	11th to 20th	Night	14% 5% 20% 34% 23% 4	776
	21st to end	Night	20% 8% 20% 31% 19% 3	800
October	1st to 10th	Night	22% 9% 23% 31% 14% 1	800
	11th to 20th	Night	33% 10% 25% 26% 7% 1	800
	21st to end	Night	35% 10% 24% 23% 7% 1	880
November	1st to 10th	Night	29% 13% 28% 23% 6% 1	820
	11th to 20th	Night	31% 17% 28% 20% 4	840
	21st to end	Night	34% 14% 28% 20% 3	918
December	1st to 10th	Night	31% 19% 29% 17% 4	1050
	11th to 20th	Night	30% 18% 30% 16% 4 1	1050
	21st to end	Night	32% 15% 33% 17% 3	1155

Page generated at 2026-02-13 01:42:11. Version ac07

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