Shell Point
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Shell Point clear sky chart from 2005-11-06 to 2024-11-04.

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	10% 5% 2 6% 4 5% 5% 5% 7% 9% 43%	100896
	Night	10% 6% 2 6% 4 4 5% 4 7% 9% 44%	98067
Transparency	Day	32% 10% 17% 19% 15% 7%	104765
	Night	34% 9% 15% 19% 16% 8%	102337
Seeing	Day	10% 3 15% 26% 29% 16%	15043
	Night	11% 4 18% 28% 29% 10%	25022

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% 7% 2 6% 4 4 4 4 5% 6% 45%	2836
	11th to 20th	Day	12% 6% 2 6% 5% 4 4 4 6% 8% 43%	2876
	21st to end	Day	18% 8% 2 5% 4 3 4 3 6% 6% 40%	3476
February	1st to 10th	Day	17% 8% 2 4 5% 5% 4 3 4 6% 42%	1900
	11th to 20th	Day	16% 7% 2 4 3 3 4 3 4 6% 47%	1848
	21st to end	Day	14% 7% 2 6% 5% 4 5% 3 5% 6% 44%	1570
March	1st to 10th	Day	20% 7% 2 5% 4 3 3 3 5% 8% 38%	3269
	11th to 20th	Day	6% 5% 2 6% 4 5% 5% 4 6% 10% 46%	3480
	21st to end	Day	16% 4 1 3 3 3 3 3 5% 7% 52%	3815
April	1st to 10th	Day	9% 5% 1 6% 4 4 5% 4 7% 8% 47%	2090
	11th to 20th	Day	10% 5% 2 5% 4 4 4 3 5% 6% 50%	2219
	21st to end	Day	6% 4 1 4 3 4 4 3 5% 8% 58%	2333
May	1st to 10th	Day	6% 3 1 4 3 4 4 4 6% 9% 56%	4082
	11th to 20th	Day	10% 6% 2 7% 5% 4 5% 5% 6% 7% 43%	4081
	21st to end	Day	4 3 1 4 3 4 4 5% 8% 11% 53%	4476
June	1st to 10th	Day	8% 5% 2 8% 6% 6% 6% 7% 10% 11% 31%	2470
	11th to 20th	Day	6% 4 2 5% 5% 6% 7% 8% 10% 13% 34%	2470
	21st to end	Day	6% 5% 2 7% 6% 7% 7% 8% 10% 12% 30%	2470
July	1st to 10th	Day	6% 4 2 7% 6% 6% 8% 8% 11% 15% 27%	4120
	11th to 20th	Day	4 4 2 5% 4 5% 6% 6% 10% 13% 42%	4120
	21st to end	Day	4 4 2 7% 7% 8% 9% 8% 12% 15% 25%	4466
August	1st to 10th	Day	8% 4 2 6% 6% 6% 7% 6% 9% 13% 32%	3851
	11th to 20th	Day	7% 4 2 5% 4 5% 7% 5% 9% 12% 39%	3729
	21st to end	Day	7% 5% 3 8% 5% 6% 6% 6% 8% 12% 33%	4098
September	1st to 10th	Day	10% 7% 2 7% 5% 7% 6% 7% 9% 12% 29%	2090
	11th to 20th	Day	9% 6% 3 7% 6% 6% 6% 6% 8% 10% 34%	2090
	21st to end	Day	10% 5% 2 6% 3 4 5% 4 6% 8% 47%	2090
October	1st to 10th	Day	8% 6% 2 6% 4 4 5% 3 5% 7% 49%	2090
	11th to 20th	Day	5% 4 1 3 2 3 3 3 4 6% 64%	2045
	21st to end	Day	7% 5% 2 4 4 4 4 4 5% 6% 56%	2090
November	1st to 10th	Day	7% 3 2 4 3 3 4 3 5% 6% 60%	1849
	11th to 20th	Day	9% 5% 2 5% 3 3 3 3 5% 6% 56%	1710
	21st to end	Day	11% 5% 2 5% 3 5% 4 4 6% 6% 50%	1710
December	1st to 10th	Day	12% 7% 2 6% 5% 4 4 4 6% 7% 44%	1710
	11th to 20th	Day	15% 7% 2 6% 4 4 3 3 5% 6% 44%	2153
	21st to end	Day	20% 9% 3 6% 3 4 3 2 4 5% 41%	3124
January	1st to 10th	Night	16% 9% 2 6% 4 3 4 3 5% 6% 42%	4109
	11th to 20th	Night	10% 7% 3 7% 5% 4 5% 4 6% 8% 41%	4079
	21st to end	Night	18% 10% 3 5% 4 4 3 3 4 6% 40%	4180
February	1st to 10th	Night	15% 7% 2 5% 4 4 3 3 5% 6% 45%	2280
	11th to 20th	Night	15% 7% 3 6% 4 3 3 3 4 4 48%	2218
	21st to end	Night	13% 9% 2 7% 5% 3 4 3 4 6% 45%	1884
March	1st to 10th	Night	16% 11% 4 8% 5% 4 4 3 5% 6% 34%	3583
	11th to 20th	Night	9% 5% 2 6% 4 4 4 3 8% 10% 45%	3480
	21st to end	Night	16% 5% 2 5% 4 4 3 3 5% 7% 47%	3817
April	1st to 10th	Night	9% 5% 2 5% 5% 5% 4 4 6% 7% 48%	2090
	11th to 20th	Night	8% 5% 2 7% 4 4 5% 4 6% 7% 49%	1923
	21st to end	Night	5% 3 1 3 4 4 3 4 6% 9% 58%	1843
May	1st to 10th	Night	4 3 1 4 3 3 4 5% 6% 11% 56%	2813
	11th to 20th	Night	9% 5% 2 6% 4 4 4 3 6% 9% 47%	2812
	21st to end	Night	3 3 1 3 3 3 4 4 5% 11% 59%	3079
June	1st to 10th	Night	7% 6% 2 5% 5% 5% 5% 5% 7% 13% 40%	1710
	11th to 20th	Night	4 5% 2 6% 5% 4 5% 4 9% 13% 43%	1710
	21st to end	Night	6% 4 1 6% 5% 5% 6% 5% 8% 12% 41%	1710
July	1st to 10th	Night	5% 5% 2 7% 6% 8% 8% 7% 12% 15% 25%	2840
	11th to 20th	Night	3 3 1 4 4 5% 5% 5% 9% 14% 48%	2840
	21st to end	Night	2 4 2 6% 6% 6% 7% 6% 11% 16% 35%	3087
August	1st to 10th	Night	6% 3 1 6% 5% 5% 5% 5% 10% 14% 39%	3072
	11th to 20th	Night	4 3 1 5% 4 5% 6% 6% 9% 14% 43%	3100
	21st to end	Night	7% 6% 2 8% 5% 6% 8% 6% 10% 13% 28%	3526
September	1st to 10th	Night	8% 7% 3 8% 7% 7% 7% 6% 9% 12% 28%	2090
	11th to 20th	Night	10% 6% 2 8% 6% 6% 7% 5% 8% 10% 33%	2090
	21st to end	Night	9% 4 2 6% 4 5% 5% 5% 6% 9% 46%	2090
October	1st to 10th	Night	8% 5% 3 7% 4 5% 3 3 6% 7% 49%	2090
	11th to 20th	Night	5% 3 1 4 4 4 3 3 5% 6% 61%	2133
	21st to end	Night	7% 4 1 5% 4 4 4 4 6% 6% 54%	2508
November	1st to 10th	Night	6% 5% 2 6% 3 4 4 4 6% 6% 54%	2297
	11th to 20th	Night	10% 6% 2 4 4 3 4 3 4 7% 53%	2470
	21st to end	Night	12% 6% 2 6% 4 3 4 4 4 6% 50%	2470
December	1st to 10th	Night	12% 5% 2 5% 4 4 4 3 5% 8% 46%	2470
	11th to 20th	Night	13% 7% 2 5% 4 3 3 3 5% 7% 47%	3042
	21st to end	Night	17% 8% 3 7% 4 4 4 3 5% 5% 40%	4532

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	38% 6% 9% 15% 19% 12%	2837
	11th to 20th	Day	37% 6% 9% 16% 17% 15%	2876
	21st to end	Day	42% 6% 8% 14% 20% 9%	3476
February	1st to 10th	Day	41% 6% 9% 15% 18% 11%	1900
	11th to 20th	Day	36% 5% 7% 16% 23% 12%	1858
	21st to end	Day	37% 7% 11% 15% 20% 10%	1570
March	1st to 10th	Day	41% 8% 10% 19% 16% 5%	3269
	11th to 20th	Day	29% 9% 17% 17% 20% 8%	3480
	21st to end	Day	30% 6% 14% 26% 14% 10%	3815
April	1st to 10th	Day	32% 8% 14% 17% 17% 12%	2090
	11th to 20th	Day	32% 7% 9% 23% 21% 9%	2219
	21st to end	Day	23% 7% 12% 26% 23% 10%	2333
May	1st to 10th	Day	21% 9% 19% 27% 19% 5%	4120
	11th to 20th	Day	35% 9% 14% 24% 15% 2	4085
	21st to end	Day	18% 10% 20% 31% 18% 2	4489
June	1st to 10th	Day	35% 15% 20% 24% 5% 1	2470
	11th to 20th	Day	30% 17% 24% 21% 8% 1	2470
	21st to end	Day	35% 16% 24% 16% 7% 1	2470
July	1st to 10th	Day	36% 15% 38% 10% 1	4055
	11th to 20th	Day	26% 15% 45% 12% 2	4051
	21st to end	Day	37% 20% 31% 12% 1	4324
August	1st to 10th	Day	34% 15% 25% 18% 7% 1	3838
	11th to 20th	Day	28% 14% 24% 25% 9%	3765
	21st to end	Day	37% 14% 27% 18% 5%	4098
September	1st to 10th	Day	41% 15% 22% 14% 7% 2	2090
	11th to 20th	Day	39% 14% 20% 16% 9% 2	2090
	21st to end	Day	34% 8% 14% 22% 16% 6%	2090
October	1st to 10th	Day	42% 6% 9% 13% 17% 13%	3480
	11th to 20th	Day	13% 3 6% 20% 32% 26%	3376
	21st to end	Day	17% 4 5% 20% 39% 14%	3428
November	1st to 10th	Day	25% 5% 11% 20% 22% 16%	1849
	11th to 20th	Day	29% 5% 8% 17% 28% 12%	1710
	21st to end	Day	31% 6% 9% 22% 24% 8%	1710
December	1st to 10th	Day	38% 6% 11% 19% 20% 6%	1710
	11th to 20th	Day	41% 6% 8% 15% 20% 11%	2150
	21st to end	Day	44% 5% 6% 21% 18% 5%	3124
January	1st to 10th	Night	41% 5% 7% 12% 19% 16%	4109
	11th to 20th	Night	40% 5% 7% 15% 23% 10%	4079
	21st to end	Night	45% 6% 7% 13% 20% 9%	4180
February	1st to 10th	Night	39% 6% 9% 14% 21% 11%	2280
	11th to 20th	Night	39% 5% 8% 14% 20% 14%	2219
	21st to end	Night	40% 5% 9% 16% 18% 12%	1884
March	1st to 10th	Night	48% 9% 8% 15% 13% 7%	3583
	11th to 20th	Night	31% 8% 12% 23% 18% 8%	3480
	21st to end	Night	35% 5% 9% 22% 18% 10%	3817
April	1st to 10th	Night	31% 8% 13% 17% 18% 12%	2090
	11th to 20th	Night	32% 6% 9% 20% 23% 10%	1923
	21st to end	Night	22% 7% 11% 28% 22% 10%	1843
May	1st to 10th	Night	18% 10% 22% 27% 18% 6%	2840
	11th to 20th	Night	32% 9% 18% 24% 15% 2	2813
	21st to end	Night	17% 8% 19% 36% 18% 2	3087
June	1st to 10th	Night	33% 11% 21% 25% 9%	1710
	11th to 20th	Night	30% 11% 27% 23% 8%	1710
	21st to end	Night	31% 13% 26% 21% 8% 1	1710
July	1st to 10th	Night	42% 16% 30% 11% 1	2795
	11th to 20th	Night	24% 15% 45% 14% 2	2786
	21st to end	Night	32% 17% 37% 11% 2	2988
August	1st to 10th	Night	30% 13% 30% 18% 9%	3061
	11th to 20th	Night	26% 14% 27% 26% 6%	3130
	21st to end	Night	41% 15% 24% 14% 5%	3526
September	1st to 10th	Night	44% 14% 19% 14% 7% 2	2090
	11th to 20th	Night	44% 13% 18% 16% 8% 1	2090
	21st to end	Night	32% 9% 17% 20% 17% 6%	2090
October	1st to 10th	Night	45% 7% 9% 13% 15% 11%	3480
	11th to 20th	Night	15% 4 6% 21% 31% 23%	3541
	21st to end	Night	18% 5% 6% 18% 38% 14%	4120
November	1st to 10th	Night	29% 6% 9% 22% 20% 15%	2297
	11th to 20th	Night	32% 5% 8% 17% 24% 14%	2470
	21st to end	Night	34% 6% 10% 18% 21% 10%	2470
December	1st to 10th	Night	35% 6% 11% 21% 20% 6%	2470
	11th to 20th	Night	37% 7% 7% 16% 21% 12%	3044
	21st to end	Night	44% 5% 7% 21% 18% 5%	4532

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	11% 6% 37% 34% 10% 1	270
	11th to 20th	Day	7% 8% 28% 37% 17% 4	270
	21st to end	Day	20% 9% 29% 36% 5%	297
February	1st to 10th	Day	17% 8% 28% 28% 18% 1	270
	11th to 20th	Day	20% 6% 26% 34% 14% 1	270
	21st to end	Day	12% 7% 31% 37% 13% 1	225
March	1st to 10th	Day	10% 6% 27% 41% 14% 1	354
	11th to 20th	Day	10% 8% 28% 35% 18% 2	460
	21st to end	Day	11% 8% 27% 32% 20% 2	506
April	1st to 10th	Day	11% 7% 29% 33% 18% 2	460
	11th to 20th	Day	12% 3 26% 32% 25% 3	452
	21st to end	Day	6% 3 20% 37% 29% 5%	460
May	1st to 10th	Day	6% 3 14% 38% 31% 8%	463
	11th to 20th	Day	8% 3 13% 31% 32% 14%	487
	21st to end	Day	9% 1 7% 25% 38% 19%	529
June	1st to 10th	Day	10% 7% 24% 41% 17%	490
	11th to 20th	Day	8% 1 7% 20% 36% 28%	490
	21st to end	Day	7% 1 4 14% 43% 30%	490
July	1st to 10th	Day	7% 1 6% 10% 34% 42%	485
	11th to 20th	Day	6% 1 3 11% 37% 43%	484
	21st to end	Day	4 5% 11% 41% 39%	532
August	1st to 10th	Day	10% 6% 12% 37% 35%	486
	11th to 20th	Day	9% 1 5% 6% 37% 42%	479
	21st to end	Day	11% 1 5% 15% 36% 32%	539
September	1st to 10th	Day	12% 2 7% 12% 35% 31%	490
	11th to 20th	Day	14% 2 5% 17% 40% 22%	490
	21st to end	Day	11% 1 7% 18% 39% 24%	490
October	1st to 10th	Day	13% 2 13% 30% 31% 11%	490
	11th to 20th	Day	5% 2 14% 27% 39% 14%	490
	21st to end	Day	7% 3 15% 35% 33% 7%	539
November	1st to 10th	Day	10% 3 15% 33% 30% 9%	429
	11th to 20th	Day	11% 3 21% 39% 21% 5%	270
	21st to end	Day	11% 4 23% 37% 20% 6%	270
December	1st to 10th	Day	16% 4 27% 29% 19% 5%	270
	11th to 20th	Day	19% 3 23% 37% 17% 2	270
	21st to end	Day	16% 6% 19% 34% 18% 7%	297
January	1st to 10th	Night	15% 10% 33% 30% 11% 1	760
	11th to 20th	Night	12% 8% 27% 34% 17% 2	760
	21st to end	Night	19% 7% 32% 32% 9% 1	836
February	1st to 10th	Night	17% 6% 27% 33% 17% 1	760
	11th to 20th	Night	18% 8% 24% 35% 13% 1	743
	21st to end	Night	16% 4 30% 36% 13% 1	628
March	1st to 10th	Night	13% 5% 26% 36% 19% 1	760
	11th to 20th	Night	12% 4 23% 35% 24% 2	760
	21st to end	Night	10% 6% 25% 35% 22% 2	836
April	1st to 10th	Night	10% 6% 23% 36% 22% 2	760
	11th to 20th	Night	11% 5% 23% 32% 26% 3	611
	21st to end	Night	6% 5% 19% 35% 31% 4	570
May	1st to 10th	Night	7% 1 16% 34% 34% 7%	570
	11th to 20th	Night	9% 1 14% 34% 34% 8%	561
	21st to end	Night	4 1 7% 29% 46% 13%	617
June	1st to 10th	Night	11% 7% 24% 47% 11%	570
	11th to 20th	Night	6% 1 6% 21% 42% 24%	570
	21st to end	Night	6% 2 4 15% 48% 25%	570
July	1st to 10th	Night	6% 2 5% 11% 44% 32%	555
	11th to 20th	Night	7% 1 2 6% 44% 40%	552
	21st to end	Night	4 4 8% 51% 34%	624
August	1st to 10th	Night	8% 3 10% 46% 33%	567
	11th to 20th	Night	7% 1 3 12% 44% 34%	564
	21st to end	Night	10% 2 5% 17% 39% 26%	651
September	1st to 10th	Night	10% 1 6% 19% 43% 21%	760
	11th to 20th	Night	12% 2 9% 21% 41% 15%	760
	21st to end	Night	10% 2 11% 24% 41% 12%	760
October	1st to 10th	Night	10% 2 18% 30% 31% 8%	760
	11th to 20th	Night	6% 3 17% 32% 35% 7%	760
	21st to end	Night	9% 3 16% 36% 31% 4	836
November	1st to 10th	Night	10% 3 21% 37% 26% 3	755
	11th to 20th	Night	12% 6% 23% 34% 23% 2	760
	21st to end	Night	12% 5% 24% 35% 21% 2	760
December	1st to 10th	Night	15% 6% 24% 31% 21% 4	760
	11th to 20th	Night	16% 5% 25% 33% 19% 2	760
	21st to end	Night	18% 6% 23% 32% 19% 2	836

Page generated at 2024-11-01 22:47:29. Version ac07

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