Spodue Lookout
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Spodue Lookout clear sky chart from 2005-11-06 to 2025-05-11.

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	8% 10% 3 5% 3 3 3 3 4 5% 52%	117957
	Night	10% 10% 3 5% 3 3 3 3 4 6% 49%	119795
Transparency	Day	33% 4 9% 19% 21% 14%	117701
	Night	36% 5% 10% 21% 18% 10%	119640
Seeing	Day	14% 12% 23% 26% 18% 7%	15386
	Night	14% 7% 19% 35% 21% 3	24631

By Month

Percentage Cloud Cover SW (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% 20% 6% 9% 4 4 4 3 3 6% 24%	3639
	11th to 20th	Day	17% 14% 4 4 2 2 2 2 3 4 45%	3640
	21st to end	Day	16% 13% 3 6% 3 2 3 2 3 4 46%	4464
February	1st to 10th	Day	13% 16% 4 7% 4 4 3 3 5% 7% 35%	1800
	11th to 20th	Day	12% 18% 5% 7% 4 4 3 2 4 6% 35%	1793
	21st to end	Day	11% 18% 5% 8% 5% 4 4 3 4 6% 33%	1650
March	1st to 10th	Day	11% 18% 6% 9% 5% 3 3 2 4 7% 33%	4599
	11th to 20th	Day	8% 19% 4 9% 4 4 3 2 4 5% 38%	5000
	21st to end	Day	12% 19% 4 9% 5% 5% 4 3 4 6% 28%	5719
April	1st to 10th	Day	13% 15% 4 8% 5% 4 4 3 4 6% 33%	2400
	11th to 20th	Day	11% 13% 3 7% 4 4 4 4 5% 6% 40%	2369
	21st to end	Day	7% 11% 2 6% 5% 4 3 2 5% 7% 47%	2404
May	1st to 10th	Day	9% 12% 3 5% 3 3 3 3 4 5% 51%	4481
	11th to 20th	Day	6% 5% 2 3 2 2 3 2 4 5% 66%	4380
	21st to end	Day	6% 8% 2 5% 4 4 3 3 4 7% 53%	4813
June	1st to 10th	Day	10% 6% 2 5% 5% 5% 5% 4 5% 7% 47%	2660
	11th to 20th	Day	5% 5% 2 4 3 3 3 3 5% 6% 62%	2660
	21st to end	Day	5% 3 1 3 2 3 2 2 3 5% 72%	2660
July	1st to 10th	Day	1 1 1 1 1 1 1 3 3 86%	4420
	11th to 20th	Day	2 2 1 3 2 2 2 3 2 4 77%	4420
	21st to end	Day	1 1 1 2 1 1 1 3 4 84%	4775
August	1st to 10th	Day	3 3 1 4 3 3 3 3 5% 5% 69%	4091
	11th to 20th	Day	2 1 1 2 2 2 2 2 3 5% 80%	3941
	21st to end	Day	3 2 1 3 2 2 2 1 3 3 78%	4180
September	1st to 10th	Day	2 2 1 2 2 2 2 2 3 5% 78%	2280
	11th to 20th	Day	4 4 1 4 3 3 3 4 4 5% 64%	2280
	21st to end	Day	5% 5% 1 4 3 3 3 2 4 5% 66%	2037
October	1st to 10th	Day	5% 4 1 4 2 1 2 2 4 5% 70%	3180
	11th to 20th	Day	6% 6% 2 5% 3 4 4 5% 6% 8% 52%	3161
	21st to end	Day	12% 10% 3 7% 4 4 3 3 5% 7% 42%	3360
November	1st to 10th	Day	15% 11% 3 7% 4 3 3 3 6% 7% 40%	1764
	11th to 20th	Day	18% 11% 3 6% 4 4 4 5% 7% 8% 33%	1685
	21st to end	Day	11% 16% 3 7% 3 4 3 4 5% 8% 38%	1600
December	1st to 10th	Day	9% 8% 1 5% 4 3 3 3 5% 7% 51%	2620
	11th to 20th	Day	19% 20% 4 8% 4 3 3 3 6% 7% 22%	3028
	21st to end	Day	14% 19% 5% 11% 6% 5% 4 3 5% 6% 20%	4004
January	1st to 10th	Night	15% 21% 4 8% 5% 4 4 3 5% 6% 24%	6306
	11th to 20th	Night	14% 14% 3 6% 2 2 2 2 3 4 48%	6320
	21st to end	Night	15% 13% 3 6% 3 3 3 3 4 5% 43%	6495
February	1st to 10th	Night	13% 14% 4 7% 4 4 3 3 5% 6% 37%	2600
	11th to 20th	Night	13% 15% 3 7% 4 4 3 3 4 5% 38%	2493
	21st to end	Night	11% 14% 5% 6% 4 4 4 4 4 8% 36%	1980
March	1st to 10th	Night	8% 17% 5% 9% 4 4 4 3 5% 6% 35%	5293
	11th to 20th	Night	11% 14% 4 6% 3 3 3 3 4 5% 43%	5000
	21st to end	Night	8% 19% 4 9% 5% 5% 5% 3 5% 7% 28%	5255
April	1st to 10th	Night	13% 12% 3 7% 4 4 4 3 5% 7% 38%	2000
	11th to 20th	Night	9% 11% 3 6% 5% 3 4 4 4 6% 46%	1979
	21st to end	Night	10% 9% 2 5% 3 3 4 4 6% 8% 48%	1993
May	1st to 10th	Night	9% 10% 3 5% 3 3 3 2 4 5% 53%	2699
	11th to 20th	Night	4 4 1 3 2 2 3 2 4 5% 68%	2519
	21st to end	Night	5% 5% 2 4 3 2 3 2 4 6% 63%	2762
June	1st to 10th	Night	11% 6% 2 5% 3 4 3 3 6% 8% 49%	1520
	11th to 20th	Night	5% 5% 2 3 3 3 2 2 4 6% 65%	1520
	21st to end	Night	4 2 1 3 2 3 2 2 3 4 74%	1520
July	1st to 10th	Night	1 1 1 1 1 1 2 3 3 85%	2540
	11th to 20th	Night	1 2 1 3 3 2 2 2 3 4 77%	2540
	21st to end	Night	1 1 2 2 2 2 2 3 3 81%	2761
August	1st to 10th	Night	2 2 1 3 2 2 3 4 5% 5% 70%	2848
	11th to 20th	Night	2 2 1 2 2 2 3 2 4 4 77%	2898
	21st to end	Night	2 3 1 3 2 2 2 2 3 4 78%	3498
September	1st to 10th	Night	1 1 1 2 1 2 2 2 4 4 80%	1900
	11th to 20th	Night	3 4 1 4 2 3 3 2 6% 6% 67%	1900
	21st to end	Night	6% 4 1 3 2 2 2 2 4 5% 69%	2140
October	1st to 10th	Night	3 3 1 3 3 2 3 2 3 4 74%	3800
	11th to 20th	Night	8% 5% 2 4 3 3 3 2 5% 6% 59%	3777
	21st to end	Night	7% 6% 3 5% 4 4 4 4 6% 7% 48%	4206
November	1st to 10th	Night	14% 11% 3 6% 5% 4 4 3 4 7% 40%	2535
	11th to 20th	Night	17% 11% 3 4 4 4 4 4 6% 9% 34%	2710
	21st to end	Night	12% 13% 2 6% 4 3 4 3 4 7% 42%	2800
December	1st to 10th	Night	10% 7% 2 4 3 3 3 3 5% 7% 54%	4560
	11th to 20th	Night	16% 19% 4 9% 5% 5% 5% 4 5% 5% 23%	5176
	21st to end	Night	20% 17% 4 8% 5% 4 4 3 4 6% 26%	6952

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	61% 6% 9% 16% 8%	3639
	11th to 20th	Day	45% 4 7% 24% 16% 3	3640
	21st to end	Day	43% 5% 8% 11% 22% 11%	4464
February	1st to 10th	Day	48% 6% 14% 18% 12% 1	1800
	11th to 20th	Day	48% 7% 12% 16% 13% 3	1802
	21st to end	Day	50% 6% 14% 14% 12% 4	1650
March	1st to 10th	Day	52% 5% 7% 22% 10% 4	4599
	11th to 20th	Day	48% 4 12% 19% 16%	5000
	21st to end	Day	53% 7% 12% 21% 6% 1	5719
April	1st to 10th	Day	51% 7% 12% 18% 10% 3	2400
	11th to 20th	Day	45% 4 12% 20% 15% 3	2372
	21st to end	Day	36% 6% 14% 25% 16% 2	2404
May	1st to 10th	Day	34% 6% 8% 25% 24% 3	4481
	11th to 20th	Day	22% 3 7% 18% 38% 11%	4383
	21st to end	Day	30% 6% 13% 30% 20% 1	4814
June	1st to 10th	Day	34% 7% 12% 25% 20% 1	2660
	11th to 20th	Day	22% 5% 9% 28% 27% 8%	2660
	21st to end	Day	17% 3 6% 23% 33% 17%	2660
July	1st to 10th	Day	7% 1 4 11% 18% 59%	4351
	11th to 20th	Day	12% 3 3 11% 19% 52%	4345
	21st to end	Day	8% 1 3 13% 36% 39%	4624
August	1st to 10th	Day	17% 2 4 11% 25% 40%	4076
	11th to 20th	Day	10% 2 3 20% 42% 24%	3980
	21st to end	Day	13% 1 5% 22% 30% 29%	4179
September	1st to 10th	Day	11% 2 4 15% 32% 35%	2280
	11th to 20th	Day	20% 5% 9% 18% 31% 17%	2280
	21st to end	Day	20% 5% 9% 22% 25% 18%	2037
October	1st to 10th	Day	18% 3 8% 16% 31% 24%	3180
	11th to 20th	Day	27% 5% 13% 31% 19% 6%	3161
	21st to end	Day	40% 4 9% 22% 20% 5%	3360
November	1st to 10th	Day	42% 6% 12% 20% 17% 3	1764
	11th to 20th	Day	47% 7% 17% 14% 12% 3	1685
	21st to end	Day	45% 6% 12% 15% 17% 5%	1600
December	1st to 10th	Day	33% 5% 8% 25% 25% 5%	2620
	11th to 20th	Day	62% 6% 13% 13% 6%	3028
	21st to end	Day	63% 7% 10% 15% 5% 1	4004
January	1st to 10th	Night	58% 8% 11% 16% 6% 1	6306
	11th to 20th	Night	41% 6% 9% 24% 16% 4	6320
	21st to end	Night	44% 5% 7% 15% 16% 13%	6495
February	1st to 10th	Night	45% 7% 14% 18% 13% 3	2600
	11th to 20th	Night	46% 6% 13% 19% 13% 3	2495
	21st to end	Night	45% 8% 15% 18% 12% 2	1980
March	1st to 10th	Night	47% 6% 10% 23% 10% 4	5293
	11th to 20th	Night	41% 5% 11% 25% 18%	5000
	21st to end	Night	51% 11% 13% 18% 7% 1	5255
April	1st to 10th	Night	45% 7% 16% 19% 12% 2	2000
	11th to 20th	Night	39% 6% 15% 21% 15% 4	1979
	21st to end	Night	34% 7% 18% 25% 13% 2	1993
May	1st to 10th	Night	30% 6% 12% 28% 20% 3	2699
	11th to 20th	Night	19% 5% 10% 27% 36% 3	2519
	21st to end	Night	22% 6% 18% 38% 15% 1	2762
June	1st to 10th	Night	32% 7% 15% 28% 17% 1	1520
	11th to 20th	Night	21% 5% 9% 34% 23% 7%	1520
	21st to end	Night	15% 3 8% 30% 33% 12%	1520
July	1st to 10th	Night	6% 2 5% 13% 19% 55%	2500
	11th to 20th	Night	11% 3 4 11% 23% 48%	2492
	21st to end	Night	10% 2 4 12% 34% 39%	2674
August	1st to 10th	Night	15% 3 5% 14% 29% 33%	2839
	11th to 20th	Night	12% 2 4 24% 36% 22%	2925
	21st to end	Night	13% 1 6% 26% 26% 27%	3498
September	1st to 10th	Night	9% 2 4 18% 32% 35%	1900
	11th to 20th	Night	18% 4 9% 21% 30% 18%	1900
	21st to end	Night	19% 3 8% 24% 26% 20%	2140
October	1st to 10th	Night	16% 3 7% 18% 32% 24%	3800
	11th to 20th	Night	26% 3 13% 33% 19% 6%	3777
	21st to end	Night	32% 4 11% 29% 17% 6%	4206
November	1st to 10th	Night	44% 6% 12% 18% 16% 4	2535
	11th to 20th	Night	46% 8% 13% 17% 13% 3	2710
	21st to end	Night	42% 6% 13% 17% 16% 7%	2800
December	1st to 10th	Night	30% 5% 9% 24% 31% 3	4560
	11th to 20th	Night	61% 5% 12% 14% 7% 1	5176
	21st to end	Night	58% 7% 11% 14% 8% 1	6952

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	31% 19% 24% 14% 9% 5%	200
	11th to 20th	Day	30% 12% 18% 22% 14% 5%	200
	21st to end	Day	19% 13% 22% 22% 18% 6%	420
February	1st to 10th	Day	22% 16% 24% 22% 14% 3	400
	11th to 20th	Day	24% 17% 24% 20% 12% 3	415
	21st to end	Day	20% 17% 25% 28% 9% 2	414
March	1st to 10th	Day	25% 18% 27% 21% 8% 1	500
	11th to 20th	Day	23% 15% 25% 21% 14% 3	500
	21st to end	Day	23% 21% 24% 23% 7% 2	550
April	1st to 10th	Day	21% 18% 23% 25% 10% 3	500
	11th to 20th	Day	19% 21% 25% 19% 12% 4	492
	21st to end	Day	14% 18% 26% 22% 15% 5%	500
May	1st to 10th	Day	13% 17% 26% 26% 15% 4	503
	11th to 20th	Day	19% 15% 23% 21% 15% 7%	489
	21st to end	Day	16% 10% 22% 26% 18% 9%	529
June	1st to 10th	Day	10% 12% 24% 24% 21% 8%	490
	11th to 20th	Day	9% 17% 26% 26% 18% 4	490
	21st to end	Day	4 7% 20% 33% 25% 11%	490
July	1st to 10th	Day	3 5% 24% 37% 23% 8%	486
	11th to 20th	Day	3 3 24% 36% 28% 7%	484
	21st to end	Day	2 3 20% 37% 27% 11%	531
August	1st to 10th	Day	2 2 24% 32% 28% 12%	487
	11th to 20th	Day	3 7% 17% 31% 26% 16%	477
	21st to end	Day	4 6% 19% 32% 27% 12%	539
September	1st to 10th	Day	3 5% 21% 36% 24% 12%	490
	11th to 20th	Day	7% 7% 21% 32% 24% 9%	490
	21st to end	Day	6% 12% 23% 27% 25% 7%	490
October	1st to 10th	Day	11% 10% 24% 25% 21% 9%	490
	11th to 20th	Day	15% 10% 21% 23% 24% 7%	490
	21st to end	Day	17% 12% 26% 21% 17% 8%	487
November	1st to 10th	Day	21% 10% 23% 27% 12% 7%	300
	11th to 20th	Day	22% 10% 20% 26% 14% 7%	243
	21st to end	Day	23% 10% 19% 24% 20% 6%	200
December	1st to 10th	Day	23% 9% 19% 24% 12% 16%	200
	11th to 20th	Day	29% 15% 22% 17% 14% 4	200
	21st to end	Day	23% 17% 22% 22% 15% 1	220
January	1st to 10th	Night	23% 10% 24% 25% 13% 4	800
	11th to 20th	Night	21% 11% 21% 24% 19% 5%	800
	21st to end	Night	19% 10% 18% 32% 17% 4	880
February	1st to 10th	Night	20% 7% 23% 32% 16% 2	800
	11th to 20th	Night	19% 10% 23% 32% 14% 2	784
	21st to end	Night	18% 11% 21% 36% 13% 1	660
March	1st to 10th	Night	21% 13% 24% 28% 13% 2	800
	11th to 20th	Night	18% 11% 21% 29% 19% 2	800
	21st to end	Night	21% 12% 25% 29% 12% 1	880
April	1st to 10th	Night	18% 10% 25% 32% 13% 2	800
	11th to 20th	Night	13% 11% 30% 27% 15% 4	791
	21st to end	Night	13% 11% 23% 32% 19% 2	793
May	1st to 10th	Night	10% 5% 30% 34% 20% 1	453
	11th to 20th	Night	9% 7% 18% 40% 23% 2	375
	21st to end	Night	10% 6% 23% 36% 22% 2	411
June	1st to 10th	Night	11% 5% 18% 41% 24% 1	380
	11th to 20th	Night	6% 5% 27% 44% 16% 1	380
	21st to end	Night	4 1 16% 52% 26% 1	380
July	1st to 10th	Night	2 1 14% 53% 29% 1	370
	11th to 20th	Night	1 1 16% 57% 25%	368
	21st to end	Night	2 1 10% 55% 31% 1	416
August	1st to 10th	Night	2 1 7% 48% 39% 3	567
	11th to 20th	Night	2 1 10% 43% 39% 5%	611
	21st to end	Night	4 2 13% 44% 34% 2	836
September	1st to 10th	Night	1 1 16% 43% 35% 4	760
	11th to 20th	Night	5% 4 14% 35% 35% 7%	760
	21st to end	Night	8% 4 16% 36% 29% 7%	760
October	1st to 10th	Night	5% 4 20% 38% 28% 4	760
	11th to 20th	Night	11% 8% 13% 35% 28% 5%	760
	21st to end	Night	13% 7% 18% 34% 21% 7%	836
November	1st to 10th	Night	20% 8% 19% 34% 15% 4	780
	11th to 20th	Night	24% 9% 19% 32% 14% 3	800
	21st to end	Night	17% 9% 19% 32% 20% 4	800
December	1st to 10th	Night	21% 8% 16% 33% 18% 5%	800
	11th to 20th	Night	26% 7% 18% 32% 15% 3	800
	21st to end	Night	27% 15% 21% 27% 9% 1	880

Page generated at 2025-05-08 06:33:57. Version ac07

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