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 2024-11-01.

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% 6% 2 6% 4 4 4 4 6% 8% 42%	100637
	Night	14% 7% 2 6% 4 4 4 4 5% 7% 43%	98236
Transparency	Day	39% 7% 13% 21% 17% 4	100445
	Night	39% 6% 11% 20% 19% 5%	98098
Seeing	Day	17% 10% 25% 25% 17% 6%	15305
	Night	16% 8% 27% 31% 16% 2	25339

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% 5% 2 5% 3 3 3 2 3 5% 51%	2836
	11th to 20th	Day	13% 6% 3 6% 4 3 3 3 4 5% 51%	2840
	21st to end	Day	18% 9% 3 6% 3 3 3 3 4 5% 42%	3124
February	1st to 10th	Day	14% 6% 3 6% 4 4 4 3 5% 6% 45%	1710
	11th to 20th	Day	21% 6% 2 4 4 3 3 3 4 4 46%	1718
	21st to end	Day	17% 8% 2 6% 4 3 3 3 5% 7% 41%	1655
March	1st to 10th	Day	23% 9% 2 6% 4 4 4 3 5% 6% 35%	3435
	11th to 20th	Day	11% 4 2 5% 3 3 3 3 5% 7% 54%	3480
	21st to end	Day	19% 7% 2 5% 4 4 4 3 4 6% 43%	3815
April	1st to 10th	Day	11% 4 2 5% 3 3 4 3 6% 7% 53%	2247
	11th to 20th	Day	11% 5% 2 5% 4 4 4 4 5% 8% 49%	2254
	21st to end	Day	14% 6% 3 6% 5% 3 4 3 5% 7% 45%	2280
May	1st to 10th	Day	10% 7% 2 8% 6% 5% 6% 5% 7% 10% 33%	3947
	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% 4 4 3 2 4 4 56%	2090
November	1st to 10th	Day	14% 5% 2 4 4 3 3 2 4 6% 54%	1857
	11th to 20th	Day	14% 6% 2 4 4 2 3 3 5% 6% 51%	1853
	21st to end	Day	14% 4 1 5% 4 3 3 3 5% 5% 52%	1563
December	1st to 10th	Day	18% 6% 2 6% 5% 4 4 3 6% 6% 41%	1520
	11th to 20th	Day	15% 5% 2 4 3 3 3 2 3 6% 54%	1910
	21st to end	Day	16% 7% 2 6% 4 3 4 3 5% 7% 43%	3037
January	1st to 10th	Night	14% 7% 2 6% 3 3 4 3 5% 6% 47%	4109
	11th to 20th	Night	14% 9% 3 6% 4 3 4 4 4 5% 44%	4120
	21st to end	Night	18% 7% 2 6% 4 4 4 3 4 5% 44%	4532
February	1st to 10th	Night	17% 6% 2 5% 4 4 4 3 6% 6% 44%	2470
	11th to 20th	Night	20% 6% 3 6% 4 3 4 3 5% 5% 42%	2346
	21st to end	Night	15% 7% 2 4 3 3 3 4 6% 6% 45%	1795
March	1st to 10th	Night	24% 10% 3 7% 5% 4 4 3 4 4 34%	3418
	11th to 20th	Night	13% 6% 2 5% 3 3 3 3 5% 5% 52%	3480
	21st to end	Night	17% 5% 2 4 3 3 3 3 4 6% 50%	3817
April	1st to 10th	Night	13% 6% 2 5% 4 4 4 3 6% 6% 48%	1933
	11th to 20th	Night	13% 5% 1 4 4 3 3 3 6% 7% 49%	1875
	21st to end	Night	10% 6% 2 5% 4 4 5% 4 6% 6% 48%	1900
May	1st to 10th	Night	11% 9% 2 8% 5% 4 5% 4 6% 7% 40%	2975
	11th to 20th	Night	20% 7% 4 8% 5% 4 4 3 5% 5% 35%	2812
	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 3 3 4 5% 51%	2228
	11th to 20th	Night	13% 5% 2 5% 4 3 4 3 5% 6% 50%	2322
	21st to end	Night	13% 5% 2 5% 4 3 4 3 5% 6% 51%	2615
December	1st to 10th	Night	18% 7% 2 6% 4 3 4 3 5% 5% 41%	2660
	11th to 20th	Night	18% 6% 2 5% 3 3 3 3 5% 4 48%	3285
	21st to end	Night	16% 7% 2 5% 4 3 3 3 5% 6% 46%	4614

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	37% 3 7% 25% 24% 5%	2837
	11th to 20th	Day	36% 3 6% 17% 32% 6%	2840
	21st to end	Day	44% 5% 6% 18% 18% 7%	3124
February	1st to 10th	Day	39% 5% 11% 22% 19% 5%	1710
	11th to 20th	Day	42% 4 7% 18% 23% 7%	1727
	21st to end	Day	43% 5% 11% 15% 20% 6%	1655
March	1st to 10th	Day	49% 6% 8% 17% 13% 7%	3435
	11th to 20th	Day	31% 5% 8% 20% 24% 13%	3480
	21st to end	Day	43% 5% 9% 20% 18% 5%	3815
April	1st to 10th	Day	31% 5% 10% 24% 23% 7%	2247
	11th to 20th	Day	33% 6% 12% 22% 21% 6%	2254
	21st to end	Day	38% 5% 13% 23% 17% 4	2280
May	1st to 10th	Day	43% 10% 17% 17% 11% 2	3982
	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	37% 4 11% 23% 20% 4	1900
	11th to 20th	Day	32% 5% 8% 26% 22% 9%	1900
	21st to end	Day	32% 4 7% 22% 26% 9%	2090
November	1st to 10th	Day	33% 4 7% 23% 27% 6%	1857
	11th to 20th	Day	34% 3 10% 20% 25% 7%	1853
	21st to end	Day	34% 4 8% 23% 25% 6%	1563
December	1st to 10th	Day	43% 5% 10% 20% 17% 4	1520
	11th to 20th	Day	34% 3 7% 27% 21% 9%	1906
	21st to end	Day	40% 5% 10% 23% 20% 2	3037
January	1st to 10th	Night	37% 5% 8% 21% 25% 5%	4109
	11th to 20th	Night	42% 4 7% 18% 24% 5%	4120
	21st to end	Night	42% 4 6% 19% 22% 7%	4532
February	1st to 10th	Night	41% 4 9% 20% 21% 5%	2470
	11th to 20th	Night	44% 4 8% 16% 20% 7%	2348
	21st to end	Night	37% 5% 10% 20% 20% 7%	1795
March	1st to 10th	Night	54% 5% 7% 14% 15% 5%	3418
	11th to 20th	Night	34% 5% 8% 14% 23% 16%	3480
	21st to end	Night	36% 4 8% 25% 22% 6%	3817
April	1st to 10th	Night	36% 6% 10% 17% 25% 7%	1933
	11th to 20th	Night	33% 6% 11% 22% 21% 6%	1875
	21st to end	Night	34% 7% 11% 26% 18% 5%	1900
May	1st to 10th	Night	41% 7% 16% 22% 12% 2	3005
	11th to 20th	Night	48% 7% 10% 19% 14% 1	2813
	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	37% 5% 9% 21% 23% 5%	2280
	11th to 20th	Night	33% 4 8% 21% 25% 9%	2280
	21st to end	Night	30% 4 8% 22% 26% 10%	2508
November	1st to 10th	Night	36% 4 8% 19% 27% 6%	2228
	11th to 20th	Night	35% 5% 9% 16% 24% 11%	2322
	21st to end	Night	34% 5% 7% 22% 26% 7%	2615
December	1st to 10th	Night	45% 5% 9% 18% 19% 4	2660
	11th to 20th	Night	38% 4 8% 20% 23% 7%	3288
	21st to end	Night	38% 4 8% 25% 22% 3	4614

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	23% 23% 34% 17% 3	270
	11th to 20th	Day	25% 25% 33% 13% 4	270
	21st to end	Day	21% 22% 41% 13% 2	297
February	1st to 10th	Day	20% 20% 41% 16% 4	270
	11th to 20th	Day	35% 19% 33% 12% 1	325
	21st to end	Day	25% 20% 32% 17% 4	382
March	1st to 10th	Day	22% 17% 36% 19% 5% 1	460
	11th to 20th	Day	22% 19% 36% 16% 6% 1	460
	21st to end	Day	23% 16% 37% 17% 6% 2	506
April	1st to 10th	Day	20% 18% 34% 22% 6% 1	460
	11th to 20th	Day	15% 18% 29% 25% 10% 2	452
	21st to end	Day	18% 12% 30% 27% 13% 1	460
May	1st to 10th	Day	15% 13% 33% 24% 13% 2	463
	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	19% 9% 29% 25% 14% 4	455
	11th to 20th	Day	18% 13% 31% 27% 10% 1	438
	21st to end	Day	21% 15% 25% 23% 14% 3	223
December	1st to 10th	Day	22% 21% 37% 12% 7% 1	180
	11th to 20th	Day	18% 17% 34% 23% 7% 1	180
	21st to end	Day	25% 17% 29% 17% 12%	274
January	1st to 10th	Night	20% 16% 36% 22% 6% 1	760
	11th to 20th	Night	22% 12% 36% 25% 5%	760
	21st to end	Night	20% 12% 39% 25% 3	836
February	1st to 10th	Night	21% 12% 38% 26% 4	760
	11th to 20th	Night	24% 18% 40% 16% 1	743
	21st to end	Night	18% 16% 38% 25% 3	628
March	1st to 10th	Night	17% 15% 35% 28% 5%	760
	11th to 20th	Night	21% 12% 37% 22% 7%	760
	21st to end	Night	18% 12% 41% 23% 5%	836
April	1st to 10th	Night	17% 17% 35% 26% 6%	760
	11th to 20th	Night	17% 13% 34% 27% 9%	751
	21st to end	Night	14% 8% 37% 33% 8%	760
May	1st to 10th	Night	11% 11% 34% 33% 10%	670
	11th to 20th	Night	17% 6% 25% 37% 14% 1	561
	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% 21% 2	836
November	1st to 10th	Night	17% 7% 29% 30% 15% 3	743
	11th to 20th	Night	16% 11% 30% 31% 12%	760
	21st to end	Night	14% 10% 31% 30% 14% 1	760
December	1st to 10th	Night	21% 11% 33% 27% 8%	760
	11th to 20th	Night	19% 10% 32% 32% 7%	760
	21st to end	Night	20% 12% 31% 29% 8% 1	836

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