Spring Hope Observing Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Spring Hope Observing Site 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	12% 6% 2 6% 4 4 4 4 6% 8% 43%	113574
	Night	13% 6% 2 6% 4 4 4 3 5% 7% 45%	115355
Transparency	Day	38% 6% 12% 21% 18% 5%	117220
	Night	38% 5% 10% 20% 21% 6%	119848
Seeing	Day	17% 11% 25% 25% 17% 6%	15947
	Night	16% 9% 28% 30% 16% 2	26097

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% 5% 2 5% 3 3 2 2 3 4 56%	4056
	11th to 20th	Day	13% 6% 2 5% 3 2 2 2 3 4 57%	4060
	21st to end	Day	13% 7% 2 6% 4 4 4 3 5% 4 47%	4466
February	1st to 10th	Day	14% 6% 3 6% 4 4 4 4 5% 6% 45%	1800
	11th to 20th	Day	22% 6% 2 4 4 3 3 3 4 4 45%	1811
	21st to end	Day	16% 8% 2 6% 4 3 3 3 5% 7% 42%	1740
March	1st to 10th	Day	20% 8% 2 6% 4 4 4 3 5% 6% 39%	4935
	11th to 20th	Day	11% 5% 2 6% 3 3 3 3 4 6% 53%	4980
	21st to end	Day	14% 5% 2 5% 4 4 5% 3 5% 6% 47%	5465
April	1st to 10th	Day	11% 4 2 5% 3 3 4 3 6% 7% 52%	2365
	11th to 20th	Day	11% 5% 2 5% 4 4 4 4 5% 8% 49%	2374
	21st to end	Day	13% 5% 3 6% 4 3 4 4 6% 8% 44%	2400
May	1st to 10th	Day	10% 7% 3 8% 6% 5% 6% 5% 7% 10% 34%	4073
	11th to 20th	Day	17% 7% 3 8% 5% 4 5% 4 6% 8% 33%	4081
	21st to end	Day	8% 4 2 5% 4 4 5% 4 6% 10% 48%	4476
June	1st to 10th	Day	9% 6% 2 6% 5% 5% 6% 5% 7% 10% 39%	2608
	11th to 20th	Day	8% 4 2 6% 5% 5% 5% 5% 8% 9% 43%	2660
	21st to end	Day	7% 5% 2 5% 5% 6% 6% 5% 8% 10% 39%	2501
July	1st to 10th	Day	6% 4 2 6% 6% 7% 7% 6% 9% 12% 34%	4120
	11th to 20th	Day	11% 8% 3 7% 6% 6% 6% 5% 7% 11% 30%	4120
	21st to end	Day	10% 8% 3 9% 7% 6% 6% 5% 8% 10% 29%	4466
August	1st to 10th	Day	18% 10% 3 9% 5% 5% 6% 5% 7% 9% 22%	4104
	11th to 20th	Day	9% 6% 3 8% 6% 6% 6% 4 7% 11% 35%	3838
	21st to end	Day	6% 5% 2 5% 4 4 5% 4 7% 11% 47%	4180
September	1st to 10th	Day	9% 6% 2 5% 5% 4 6% 4 5% 10% 43%	2280
	11th to 20th	Day	15% 6% 2 6% 5% 4 5% 3 6% 7% 41%	2222
	21st to end	Day	19% 7% 4 7% 4 4 4 3 5% 7% 37%	2010
October	1st to 10th	Day	14% 6% 2 5% 4 3 3 3 4 6% 48%	1900
	11th to 20th	Day	12% 5% 2 4 3 3 4 3 4 5% 55%	1900
	21st to end	Day	11% 6% 2 6% 3 4 3 2 4 4 56%	2090
November	1st to 10th	Day	13% 5% 2 5% 4 3 3 3 4 6% 53%	1957
	11th to 20th	Day	14% 6% 2 4 4 3 3 3 5% 6% 51%	1950
	21st to end	Day	14% 4 2 5% 4 3 3 3 5% 5% 52%	1645
December	1st to 10th	Day	12% 5% 2 6% 4 3 4 3 4 5% 52%	2600
	11th to 20th	Day	15% 6% 3 6% 4 4 4 3 4 5% 45%	2990
	21st to end	Day	14% 7% 2 6% 3 3 4 3 5% 7% 45%	4351
January	1st to 10th	Night	12% 6% 2 5% 3 3 3 3 5% 5% 54%	5889
	11th to 20th	Night	13% 7% 2 5% 3 3 3 3 3 4 54%	5900
	21st to end	Night	14% 7% 2 5% 4 3 4 3 5% 5% 48%	6490
February	1st to 10th	Night	18% 6% 2 5% 4 3 4 3 6% 6% 44%	2600
	11th to 20th	Night	20% 6% 3 5% 4 3 4 3 5% 5% 42%	2473
	21st to end	Night	14% 7% 2 4 3 3 3 4 6% 6% 47%	1886
March	1st to 10th	Night	18% 8% 2 6% 4 4 4 3 4 5% 42%	4918
	11th to 20th	Night	12% 6% 2 5% 3 3 3 3 5% 6% 53%	4980
	21st to end	Night	14% 5% 2 4 3 4 4 3 5% 6% 50%	5467
April	1st to 10th	Night	14% 6% 2 5% 3 4 3 3 6% 7% 48%	2035
	11th to 20th	Night	13% 5% 1 5% 4 3 3 3 6% 7% 50%	1975
	21st to end	Night	10% 6% 2 5% 4 4 5% 4 6% 6% 48%	2000
May	1st to 10th	Night	11% 9% 2 8% 5% 4 5% 4 6% 7% 40%	3070
	11th to 20th	Night	20% 7% 4 8% 5% 4 4 3 5% 5% 35%	2818
	21st to end	Night	8% 5% 2 5% 4 5% 5% 4 7% 10% 47%	3079
June	1st to 10th	Night	9% 5% 2 6% 5% 5% 6% 7% 8% 9% 39%	1563
	11th to 20th	Night	9% 6% 3 7% 5% 4 5% 6% 7% 9% 39%	1520
	21st to end	Night	8% 6% 2 6% 5% 5% 6% 5% 8% 11% 38%	1667
July	1st to 10th	Night	7% 6% 3 7% 5% 5% 6% 5% 8% 12% 36%	2840
	11th to 20th	Night	14% 8% 3 8% 5% 5% 5% 4 7% 10% 32%	2840
	21st to end	Night	15% 10% 3 9% 5% 5% 4 4 6% 9% 28%	3087
August	1st to 10th	Night	21% 9% 3 8% 5% 5% 5% 5% 7% 9% 24%	2825
	11th to 20th	Night	7% 6% 3 8% 6% 6% 6% 6% 8% 10% 35%	2944
	21st to end	Night	6% 5% 2 6% 4 4 5% 4 7% 11% 45%	3476
September	1st to 10th	Night	11% 5% 2 6% 4 3 4 3 6% 9% 47%	1900
	11th to 20th	Night	12% 7% 3 7% 3 4 5% 3 5% 7% 43%	1953
	21st to end	Night	20% 8% 2 7% 4 4 4 4 5% 6% 36%	2168
October	1st to 10th	Night	14% 6% 2 5% 3 4 3 4 5% 5% 48%	2280
	11th to 20th	Night	13% 5% 2 5% 3 3 3 2 4 5% 55%	2280
	21st to end	Night	11% 4 2 5% 3 3 3 2 4 6% 56%	2508
November	1st to 10th	Night	13% 6% 2 5% 4 3 4 3 4 5% 51%	2341
	11th to 20th	Night	13% 6% 2 5% 4 3 4 3 5% 6% 50%	2445
	21st to end	Night	12% 5% 2 5% 4 3 4 4 5% 6% 52%	2753
December	1st to 10th	Night	11% 6% 2 6% 4 3 4 3 4 4 52%	4580
	11th to 20th	Night	17% 8% 3 8% 5% 4 3 4 5% 4 40%	5205
	21st to end	Night	13% 6% 2 5% 3 3 3 3 5% 7% 48%	6600

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	35% 2 5% 19% 31% 8%	4057
	11th to 20th	Day	32% 3 4 16% 36% 9%	4060
	21st to end	Day	40% 4 6% 23% 20% 8%	4466
February	1st to 10th	Day	39% 5% 11% 22% 18% 5%	1800
	11th to 20th	Day	43% 4 7% 18% 22% 6%	1820
	21st to end	Day	42% 5% 11% 15% 21% 6%	1740
March	1st to 10th	Day	46% 4 7% 17% 16% 10%	4935
	11th to 20th	Day	32% 4 8% 18% 24% 14%	4980
	21st to end	Day	38% 5% 11% 21% 19% 6%	5465
April	1st to 10th	Day	31% 5% 10% 24% 22% 7%	2365
	11th to 20th	Day	32% 6% 13% 23% 21% 6%	2374
	21st to end	Day	38% 5% 13% 22% 17% 4	2400
May	1st to 10th	Day	43% 10% 17% 18% 11% 2	4108
	11th to 20th	Day	47% 7% 12% 23% 10% 1	4085
	21st to end	Day	30% 8% 16% 24% 19% 3	4489
June	1st to 10th	Day	38% 9% 15% 21% 15% 2	2608
	11th to 20th	Day	33% 10% 17% 25% 14% 2	2660
	21st to end	Day	36% 10% 17% 22% 15% 1	2501
July	1st to 10th	Day	37% 12% 19% 20% 10% 3	4055
	11th to 20th	Day	45% 10% 24% 15% 5% 1	4051
	21st to end	Day	48% 10% 16% 15% 11%	4324
August	1st to 10th	Day	56% 8% 18% 13% 5%	4091
	11th to 20th	Day	41% 9% 17% 24% 9% 1	3877
	21st to end	Day	31% 8% 15% 31% 14% 2	4180
September	1st to 10th	Day	37% 8% 16% 17% 18% 4	2280
	11th to 20th	Day	40% 6% 11% 20% 20% 3	2222
	21st to end	Day	47% 5% 10% 20% 14% 4	2010
October	1st to 10th	Day	33% 4 10% 21% 25% 7%	3160
	11th to 20th	Day	21% 3 5% 19% 29% 22%	3140
	21st to end	Day	24% 3 7% 25% 26% 15%	3428
November	1st to 10th	Day	34% 4 8% 22% 26% 6%	1957
	11th to 20th	Day	34% 3 10% 21% 25% 7%	1950
	21st to end	Day	34% 4 8% 23% 26% 6%	1645
December	1st to 10th	Day	35% 4 7% 23% 23% 7%	2600
	11th to 20th	Day	42% 4 10% 20% 19% 6%	2986
	21st to end	Day	39% 4 12% 25% 19% 1	4351
January	1st to 10th	Night	32% 3 6% 17% 30% 12%	5889
	11th to 20th	Night	35% 3 5% 16% 34% 7%	5900
	21st to end	Night	39% 3 6% 19% 28% 6%	6490
February	1st to 10th	Night	41% 4 10% 20% 20% 5%	2600
	11th to 20th	Night	45% 4 9% 16% 20% 7%	2475
	21st to end	Night	36% 5% 9% 20% 21% 8%	1886
March	1st to 10th	Night	46% 4 7% 13% 21% 10%	4918
	11th to 20th	Night	33% 4 8% 14% 24% 17%	4980
	21st to end	Night	35% 4 9% 24% 22% 6%	5467
April	1st to 10th	Night	36% 5% 10% 17% 24% 7%	2035
	11th to 20th	Night	33% 6% 11% 23% 21% 6%	1975
	21st to end	Night	34% 7% 11% 26% 18% 4	2000
May	1st to 10th	Night	42% 7% 15% 21% 12% 2	3100
	11th to 20th	Night	48% 7% 10% 19% 14% 1	2819
	21st to end	Night	30% 8% 19% 24% 18% 1	3087
June	1st to 10th	Night	36% 10% 18% 21% 15% 1	1563
	11th to 20th	Night	39% 9% 16% 19% 16% 2	1520
	21st to end	Night	36% 11% 15% 21% 14% 2	1667
July	1st to 10th	Night	37% 14% 20% 18% 10% 2	2795
	11th to 20th	Night	45% 10% 23% 16% 5% 1	2786
	21st to end	Night	52% 9% 12% 17% 10%	2988
August	1st to 10th	Night	54% 9% 17% 16% 4	2814
	11th to 20th	Night	41% 11% 18% 22% 8% 1	2971
	21st to end	Night	32% 7% 13% 29% 18% 2	3476
September	1st to 10th	Night	34% 9% 15% 22% 16% 5%	1900
	11th to 20th	Night	39% 7% 12% 18% 20% 2	1953
	21st to end	Night	48% 6% 11% 16% 16% 3	2168
October	1st to 10th	Night	39% 4 7% 20% 25% 5%	3800
	11th to 20th	Night	25% 3 6% 17% 27% 22%	3779
	21st to end	Night	22% 3 7% 28% 23% 16%	4120
November	1st to 10th	Night	36% 4 8% 19% 27% 6%	2341
	11th to 20th	Night	35% 5% 8% 16% 25% 11%	2445
	21st to end	Night	33% 4 7% 23% 26% 7%	2753
December	1st to 10th	Night	36% 3 6% 18% 28% 8%	4580
	11th to 20th	Night	47% 4 8% 17% 17% 7%	5208
	21st to end	Night	36% 4 12% 26% 20% 2	6600

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% 24% 32% 15% 3	300
	11th to 20th	Day	24% 27% 32% 13% 4	300
	21st to end	Day	20% 22% 42% 13% 2	330
February	1st to 10th	Day	20% 20% 42% 14% 3	300
	11th to 20th	Day	37% 20% 32% 11% 1	358
	21st to end	Day	24% 21% 32% 18% 5%	414
March	1st to 10th	Day	22% 18% 35% 19% 5% 1	500
	11th to 20th	Day	22% 19% 36% 17% 6% 1	500
	21st to end	Day	22% 17% 39% 16% 6% 1	550
April	1st to 10th	Day	20% 18% 35% 21% 5% 1	500
	11th to 20th	Day	15% 17% 32% 24% 10% 2	492
	21st to end	Day	17% 11% 29% 28% 14% 1	500
May	1st to 10th	Day	15% 13% 34% 25% 12% 2	503
	11th to 20th	Day	18% 7% 26% 27% 17% 4	487
	21st to end	Day	17% 5% 22% 24% 24% 9%	529
June	1st to 10th	Day	12% 5% 19% 36% 21% 7%	490
	11th to 20th	Day	10% 4 18% 32% 25% 10%	490
	21st to end	Day	9% 4 19% 34% 28% 7%	490
July	1st to 10th	Day	10% 2 9% 31% 35% 14%	485
	11th to 20th	Day	10% 2 10% 29% 36% 13%	484
	21st to end	Day	8% 2 16% 34% 31% 9%	532
August	1st to 10th	Day	15% 5% 14% 29% 26% 11%	486
	11th to 20th	Day	11% 2 16% 28% 28% 15%	479
	21st to end	Day	10% 3 11% 31% 27% 18%	539
September	1st to 10th	Day	14% 2 15% 26% 26% 17%	490
	11th to 20th	Day	17% 6% 12% 33% 21% 13%	490
	21st to end	Day	23% 7% 25% 24% 16% 4	490
October	1st to 10th	Day	17% 6% 23% 24% 22% 9%	490
	11th to 20th	Day	12% 9% 27% 28% 19% 4	490
	21st to end	Day	13% 11% 24% 30% 17% 5%	539
November	1st to 10th	Day	18% 9% 29% 26% 14% 4	495
	11th to 20th	Day	17% 14% 32% 27% 9% 1	475
	21st to end	Day	22% 14% 27% 22% 13% 2	245
December	1st to 10th	Day	21% 22% 39% 13% 7% 1	200
	11th to 20th	Day	19% 17% 35% 23% 7% 1	200
	21st to end	Day	24% 18% 30% 17% 11%	305
January	1st to 10th	Night	20% 17% 36% 21% 6% 1	800
	11th to 20th	Night	22% 13% 36% 25% 5%	800
	21st to end	Night	19% 13% 40% 25% 3	880
February	1st to 10th	Night	22% 12% 38% 25% 4	800
	11th to 20th	Night	25% 18% 39% 16% 1	783
	21st to end	Night	18% 16% 37% 26% 3	660
March	1st to 10th	Night	17% 16% 34% 28% 5%	800
	11th to 20th	Night	21% 12% 38% 22% 7%	800
	21st to end	Night	18% 12% 42% 22% 5%	880
April	1st to 10th	Night	17% 17% 35% 26% 5%	800
	11th to 20th	Night	16% 13% 35% 27% 9%	791
	21st to end	Night	13% 8% 36% 34% 8%	800
May	1st to 10th	Night	11% 11% 34% 33% 10%	705
	11th to 20th	Night	17% 6% 25% 37% 14% 1	563
	21st to end	Night	12% 2 19% 38% 27% 2	617
June	1st to 10th	Night	10% 2 22% 41% 25%	423
	11th to 20th	Night	11% 2 19% 42% 22% 3	380
	21st to end	Night	8% 2 16% 44% 27% 3	527
July	1st to 10th	Night	9% 1 12% 39% 35% 4	555
	11th to 20th	Night	9% 2 9% 40% 35% 5%	552
	21st to end	Night	9% 3 14% 40% 32% 3	624
August	1st to 10th	Night	12% 3 10% 39% 31% 4	567
	11th to 20th	Night	11% 3 11% 34% 36% 5%	658
	21st to end	Night	12% 3 11% 33% 34% 7%	836
September	1st to 10th	Night	13% 2 12% 34% 34% 6%	760
	11th to 20th	Night	16% 4 15% 33% 28% 4	760
	21st to end	Night	24% 4 19% 31% 21% 1	760
October	1st to 10th	Night	16% 3 21% 30% 25% 5%	760
	11th to 20th	Night	16% 8% 25% 32% 18% 2	760
	21st to end	Night	14% 6% 27% 30% 20% 2	836
November	1st to 10th	Night	16% 7% 29% 31% 14% 2	780
	11th to 20th	Night	16% 11% 30% 31% 11%	800
	21st to end	Night	15% 11% 31% 29% 14% 1	800
December	1st to 10th	Night	21% 11% 35% 26% 8%	800
	11th to 20th	Night	19% 10% 32% 32% 7%	800
	21st to end	Night	20% 12% 31% 30% 7% 1	880

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