Twin Sugars Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Twin Sugars Observatory clear sky chart from 2005-11-06 to 2024-11-05.

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% 8% 3 7% 5% 5% 5% 4 6% 8% 35%	100856
	Night	14% 7% 3 7% 5% 5% 5% 4 6% 7% 37%	98119
Transparency	Day	45% 9% 12% 20% 12% 3	104519
	Night	44% 9% 12% 20% 13% 3	102595
Seeing	Day	23% 16% 25% 20% 11% 5%	15045
	Night	21% 15% 22% 27% 14% 2	25290

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% 13% 4 9% 6% 5% 4 4 5% 7% 30%	2836
	11th to 20th	Day	13% 12% 7% 16% 6% 5% 4 3 4 4 26%	2840
	21st to end	Day	19% 13% 5% 7% 4 3 4 3 5% 5% 31%	3124
February	1st to 10th	Day	13% 9% 3 9% 5% 5% 5% 3 6% 7% 33%	1710
	11th to 20th	Day	16% 8% 3 10% 6% 5% 5% 3 5% 7% 31%	1717
	21st to end	Day	19% 11% 3 9% 4 4 4 3 5% 5% 32%	1611
March	1st to 10th	Day	22% 8% 4 7% 4 4 4 4 6% 7% 31%	3435
	11th to 20th	Day	11% 7% 3 7% 4 4 4 3 5% 7% 45%	3480
	21st to end	Day	15% 10% 3 8% 5% 4 5% 4 5% 7% 34%	3815
April	1st to 10th	Day	11% 8% 4 8% 5% 5% 5% 4 4 7% 39%	2146
	11th to 20th	Day	15% 6% 3 7% 5% 6% 4 4 5% 6% 40%	2254
	21st to end	Day	18% 7% 3 7% 5% 5% 4 4 6% 5% 36%	2465
May	1st to 10th	Day	18% 8% 2 9% 6% 6% 6% 5% 6% 7% 27%	4082
	11th to 20th	Day	23% 7% 2 7% 5% 5% 6% 4 6% 8% 27%	4081
	21st to end	Day	10% 5% 2 7% 6% 6% 6% 6% 8% 10% 35%	4476
June	1st to 10th	Day	13% 6% 2 7% 6% 6% 6% 4 6% 8% 36%	2470
	11th to 20th	Day	10% 5% 2 8% 5% 7% 7% 4 7% 9% 34%	2470
	21st to end	Day	10% 6% 2 7% 7% 6% 6% 5% 7% 10% 35%	2470
July	1st to 10th	Day	8% 5% 2 6% 6% 5% 6% 5% 8% 9% 41%	4120
	11th to 20th	Day	9% 5% 2 5% 5% 5% 6% 5% 8% 9% 41%	4120
	21st to end	Day	16% 9% 3 9% 7% 6% 6% 5% 7% 8% 25%	4466
August	1st to 10th	Day	14% 6% 3 7% 6% 6% 7% 5% 7% 11% 29%	4104
	11th to 20th	Day	10% 5% 2 7% 7% 6% 7% 5% 8% 10% 34%	4044
	21st to end	Day	7% 4 2 6% 4 5% 5% 4 6% 9% 47%	4281
September	1st to 10th	Day	14% 6% 2 6% 4 4 5% 5% 5% 7% 42%	2218
	11th to 20th	Day	14% 7% 2 7% 5% 5% 5% 4 5% 7% 39%	2090
	21st to end	Day	24% 7% 2 6% 4 4 5% 4 5% 6% 33%	2090
October	1st to 10th	Day	16% 6% 1 5% 4 4 4 3 5% 7% 43%	1929
	11th to 20th	Day	15% 9% 2 6% 3 3 4 3 4 6% 44%	1900
	21st to end	Day	16% 8% 2 6% 4 3 4 3 5% 6% 42%	2090
November	1st to 10th	Day	10% 8% 2 5% 5% 4 4 4 5% 7% 47%	1879
	11th to 20th	Day	14% 8% 2 7% 6% 4 4 4 4 7% 40%	1710
	21st to end	Day	14% 7% 2 6% 6% 4 4 4 6% 6% 40%	1645
December	1st to 10th	Day	17% 13% 5% 8% 5% 5% 4 4 6% 6% 27%	1520
	11th to 20th	Day	16% 9% 3 8% 5% 4 4 3 5% 6% 37%	2044
	21st to end	Day	18% 13% 4 8% 6% 5% 5% 5% 6% 7% 23%	3124
January	1st to 10th	Night	11% 10% 5% 13% 6% 6% 6% 5% 6% 7% 25%	4109
	11th to 20th	Night	15% 11% 4 10% 6% 4 4 3 4 5% 34%	4120
	21st to end	Night	21% 11% 4 6% 5% 6% 4 3 5% 6% 30%	4532
February	1st to 10th	Night	13% 7% 4 9% 6% 5% 5% 5% 6% 8% 33%	2470
	11th to 20th	Night	17% 8% 3 8% 6% 6% 6% 5% 6% 5% 30%	2346
	21st to end	Night	17% 8% 4 9% 5% 5% 5% 4 5% 7% 31%	1841
March	1st to 10th	Night	23% 10% 3 7% 5% 5% 4 4 5% 5% 29%	3418
	11th to 20th	Night	10% 6% 2 8% 5% 5% 5% 4 6% 7% 42%	3480
	21st to end	Night	15% 7% 2 5% 4 3 4 4 7% 7% 41%	3817
April	1st to 10th	Night	12% 8% 4 8% 5% 5% 5% 4 6% 7% 37%	2033
	11th to 20th	Night	12% 7% 2 5% 5% 5% 5% 4 7% 8% 40%	1875
	21st to end	Night	15% 5% 2 5% 4 5% 5% 4 5% 8% 41%	1729
May	1st to 10th	Night	20% 11% 3 7% 5% 4 5% 4 5% 8% 29%	2813
	11th to 20th	Night	24% 8% 3 6% 3 4 3 3 5% 7% 33%	2812
	21st to end	Night	12% 5% 2 6% 5% 5% 5% 4 7% 11% 38%	3079
June	1st to 10th	Night	9% 5% 2 5% 5% 4 5% 5% 7% 10% 43%	1710
	11th to 20th	Night	12% 5% 2 5% 4 3 5% 5% 7% 9% 43%	1710
	21st to end	Night	10% 5% 2 4 5% 4 5% 5% 7% 11% 43%	1710
July	1st to 10th	Night	8% 4 2 6% 5% 4 6% 5% 8% 11% 43%	2840
	11th to 20th	Night	8% 5% 1 6% 4 3 4 4 6% 10% 49%	2840
	21st to end	Night	13% 8% 3 8% 6% 6% 5% 5% 6% 9% 32%	3087
August	1st to 10th	Night	15% 6% 2 6% 5% 5% 5% 4 6% 8% 37%	2825
	11th to 20th	Night	12% 5% 2 6% 4 6% 6% 4 7% 9% 38%	2785
	21st to end	Night	8% 4 1 5% 4 4 3 4 5% 8% 54%	3343
September	1st to 10th	Night	12% 5% 2 6% 4 4 5% 4 6% 7% 45%	1957
	11th to 20th	Night	14% 7% 2 4 4 3 3 4 5% 7% 47%	2090
	21st to end	Night	20% 6% 3 6% 4 4 4 3 5% 6% 39%	2090
October	1st to 10th	Night	14% 7% 2 6% 3 4 4 4 5% 6% 46%	2250
	11th to 20th	Night	12% 7% 2 7% 4 4 4 3 5% 6% 45%	2280
	21st to end	Night	14% 7% 2 6% 4 4 4 3 5% 7% 45%	2508
November	1st to 10th	Night	11% 7% 2 6% 4 4 3 4 6% 7% 46%	2294
	11th to 20th	Night	14% 6% 2 7% 4 4 5% 4 6% 7% 40%	2470
	21st to end	Night	13% 7% 3 6% 5% 5% 5% 4 5% 8% 38%	2527
December	1st to 10th	Night	17% 9% 4 10% 6% 5% 5% 4 5% 7% 28%	2660
	11th to 20th	Night	14% 8% 3 10% 6% 5% 5% 4 4 7% 34%	3137
	21st to end	Night	18% 8% 6% 9% 5% 6% 6% 4 6% 7% 26%	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	55% 8% 8% 19% 10% 1	2837
	11th to 20th	Day	62% 10% 6% 12% 9% 1	2840
	21st to end	Day	55% 9% 9% 14% 12% 1	3124
February	1st to 10th	Day	50% 8% 10% 19% 11% 2	1710
	11th to 20th	Day	53% 8% 10% 16% 12% 2	1726
	21st to end	Day	54% 8% 8% 15% 12% 3	1611
March	1st to 10th	Day	49% 11% 11% 19% 8% 1	3435
	11th to 20th	Day	38% 9% 12% 19% 19% 2	3480
	21st to end	Day	49% 10% 9% 18% 12% 3	3815
April	1st to 10th	Day	44% 10% 11% 18% 14% 4	2146
	11th to 20th	Day	44% 8% 10% 20% 15% 3	2254
	21st to end	Day	47% 10% 12% 19% 10% 2	2465
May	1st to 10th	Day	54% 11% 10% 17% 8% 1	4120
	11th to 20th	Day	51% 13% 13% 16% 6% 1	4085
	21st to end	Day	38% 14% 18% 16% 10% 3	4489
June	1st to 10th	Day	43% 11% 13% 20% 12%	2470
	11th to 20th	Day	43% 12% 14% 17% 14%	2470
	21st to end	Day	42% 12% 14% 20% 11% 2	2470
July	1st to 10th	Day	38% 10% 21% 19% 8% 4	4055
	11th to 20th	Day	36% 9% 15% 30% 10% 1	4051
	21st to end	Day	55% 8% 11% 18% 7% 1	4324
August	1st to 10th	Day	47% 8% 19% 20% 7%	4091
	11th to 20th	Day	43% 9% 11% 25% 11%	4083
	21st to end	Day	32% 9% 17% 28% 12% 1	4281
September	1st to 10th	Day	39% 10% 12% 18% 17% 4	2218
	11th to 20th	Day	44% 7% 10% 20% 17% 2	2090
	21st to end	Day	50% 7% 10% 16% 14% 2	2090
October	1st to 10th	Day	30% 5% 10% 21% 27% 7%	3202
	11th to 20th	Day	32% 4 10% 25% 15% 14%	3140
	21st to end	Day	30% 4 10% 30% 15% 12%	3428
November	1st to 10th	Day	36% 7% 10% 21% 21% 4	1879
	11th to 20th	Day	44% 8% 9% 18% 18% 4	1710
	21st to end	Day	43% 9% 12% 19% 15% 2	1645
December	1st to 10th	Day	57% 9% 9% 15% 9% 1	1520
	11th to 20th	Day	49% 7% 10% 17% 16% 2	2041
	21st to end	Day	55% 11% 11% 16% 8%	3124
January	1st to 10th	Night	56% 13% 8% 11% 10% 1	4109
	11th to 20th	Night	53% 8% 8% 17% 12% 2	4120
	21st to end	Night	56% 9% 9% 15% 10% 1	4532
February	1st to 10th	Night	48% 10% 12% 16% 13% 1	2470
	11th to 20th	Night	54% 9% 9% 14% 11% 2	2348
	21st to end	Night	52% 9% 11% 16% 8% 4	1841
March	1st to 10th	Night	54% 8% 11% 16% 9% 2	3418
	11th to 20th	Night	41% 9% 10% 23% 15% 1	3480
	21st to end	Night	40% 10% 12% 19% 16% 3	3817
April	1st to 10th	Night	45% 10% 11% 18% 14% 2	2033
	11th to 20th	Night	41% 9% 13% 18% 15% 4	1875
	21st to end	Night	40% 9% 15% 24% 10% 1	1729
May	1st to 10th	Night	54% 10% 11% 16% 8% 1	2840
	11th to 20th	Night	50% 11% 16% 17% 6% 1	2813
	21st to end	Night	38% 15% 20% 19% 5% 4	3087
June	1st to 10th	Night	35% 13% 18% 22% 12%	1710
	11th to 20th	Night	35% 13% 19% 20% 12% 1	1710
	21st to end	Night	33% 13% 17% 24% 11% 1	1710
July	1st to 10th	Night	35% 10% 20% 20% 12% 2	2795
	11th to 20th	Night	32% 8% 18% 33% 8% 1	2786
	21st to end	Night	49% 9% 13% 21% 8%	2988
August	1st to 10th	Night	44% 9% 18% 23% 5%	2814
	11th to 20th	Night	42% 8% 14% 23% 13%	2812
	21st to end	Night	29% 8% 16% 32% 15% 1	3343
September	1st to 10th	Night	36% 11% 14% 19% 16% 4	1957
	11th to 20th	Night	36% 9% 12% 22% 19% 2	2090
	21st to end	Night	45% 8% 12% 22% 13% 1	2090
October	1st to 10th	Night	33% 5% 8% 24% 26% 4	3757
	11th to 20th	Night	33% 4 9% 21% 21% 12%	3779
	21st to end	Night	26% 4 12% 28% 19% 11%	4120
November	1st to 10th	Night	37% 8% 12% 19% 20% 5%	2294
	11th to 20th	Night	43% 8% 11% 17% 17% 4	2470
	21st to end	Night	44% 8% 11% 18% 15% 3	2527
December	1st to 10th	Night	55% 10% 9% 16% 8% 2	2660
	11th to 20th	Night	52% 8% 10% 15% 14% 1	3139
	21st to end	Night	55% 12% 10% 14% 9%	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	36% 29% 23% 9% 3 1	270
	11th to 20th	Day	44% 24% 26% 6%	270
	21st to end	Day	40% 24% 24% 8% 3	297
February	1st to 10th	Day	36% 25% 26% 11% 2	270
	11th to 20th	Day	49% 24% 21% 5% 1	270
	21st to end	Day	44% 23% 25% 7% 1	266
March	1st to 10th	Day	33% 26% 22% 15% 4	460
	11th to 20th	Day	34% 27% 22% 12% 5% 1	460
	21st to end	Day	29% 27% 25% 15% 4	506
April	1st to 10th	Day	28% 27% 25% 13% 7% 1	460
	11th to 20th	Day	25% 19% 30% 14% 8% 3	452
	21st to end	Day	30% 21% 24% 14% 9% 2	460
May	1st to 10th	Day	26% 21% 28% 13% 9% 3	463
	11th to 20th	Day	22% 16% 30% 16% 12% 4	487
	21st to end	Day	17% 12% 26% 24% 14% 8%	529
June	1st to 10th	Day	16% 13% 27% 24% 13% 7%	490
	11th to 20th	Day	11% 11% 30% 26% 14% 8%	490
	21st to end	Day	11% 12% 32% 26% 13% 6%	490
July	1st to 10th	Day	15% 7% 21% 28% 17% 12%	485
	11th to 20th	Day	6% 7% 26% 34% 17% 11%	484
	21st to end	Day	13% 8% 26% 27% 17% 10%	532
August	1st to 10th	Day	18% 7% 22% 25% 17% 10%	486
	11th to 20th	Day	13% 8% 22% 26% 20% 11%	479
	21st to end	Day	10% 6% 22% 26% 23% 13%	539
September	1st to 10th	Day	15% 7% 21% 26% 20% 12%	490
	11th to 20th	Day	16% 5% 17% 30% 24% 7%	490
	21st to end	Day	27% 12% 21% 24% 12% 3	490
October	1st to 10th	Day	20% 10% 24% 26% 18% 4	490
	11th to 20th	Day	22% 15% 25% 22% 14% 2	490
	21st to end	Day	24% 17% 24% 20% 12% 2	539
November	1st to 10th	Day	19% 19% 25% 25% 10% 3	453
	11th to 20th	Day	34% 16% 26% 19% 4	270
	21st to end	Day	26% 23% 30% 16% 4	239
December	1st to 10th	Day	39% 24% 20% 11% 4 1	180
	11th to 20th	Day	36% 24% 20% 18% 2	222
	21st to end	Day	35% 24% 23% 14% 4	297
January	1st to 10th	Night	32% 26% 24% 16% 3	760
	11th to 20th	Night	32% 22% 26% 17% 2	760
	21st to end	Night	31% 23% 26% 18% 1	836
February	1st to 10th	Night	25% 22% 29% 20% 3	760
	11th to 20th	Night	34% 27% 25% 14% 1	743
	21st to end	Night	28% 27% 28% 16% 1	628
March	1st to 10th	Night	26% 20% 30% 21% 3	760
	11th to 20th	Night	28% 22% 25% 18% 6%	760
	21st to end	Night	23% 23% 29% 20% 6%	836
April	1st to 10th	Night	21% 23% 28% 23% 4	760
	11th to 20th	Night	21% 15% 26% 25% 12%	751
	21st to end	Night	18% 16% 26% 31% 8% 1	589
May	1st to 10th	Night	20% 15% 23% 28% 12% 1	570
	11th to 20th	Night	20% 12% 24% 29% 15%	561
	21st to end	Night	15% 7% 18% 31% 25% 4	617
June	1st to 10th	Night	10% 6% 21% 34% 25% 3	570
	11th to 20th	Night	12% 6% 16% 35% 29% 2	570
	21st to end	Night	12% 4 17% 40% 24% 3	570
July	1st to 10th	Night	12% 3 13% 35% 32% 6%	555
	11th to 20th	Night	8% 3 11% 35% 37% 7%	552
	21st to end	Night	9% 5% 11% 36% 36% 4	624
August	1st to 10th	Night	16% 3 10% 35% 34% 3	567
	11th to 20th	Night	15% 2 12% 34% 34% 4	564
	21st to end	Night	13% 4 11% 34% 32% 6%	755
September	1st to 10th	Night	14% 4 13% 35% 29% 6%	760
	11th to 20th	Night	16% 5% 13% 32% 29% 4	760
	21st to end	Night	24% 8% 16% 27% 23% 2	760
October	1st to 10th	Night	15% 11% 19% 32% 21% 2	760
	11th to 20th	Night	19% 17% 22% 26% 16% 1	760
	21st to end	Night	20% 16% 22% 28% 13% 1	836
November	1st to 10th	Night	18% 12% 26% 31% 12% 2	760
	11th to 20th	Night	25% 16% 22% 28% 9% 1	760
	21st to end	Night	22% 20% 24% 28% 6% 1	760
December	1st to 10th	Night	29% 23% 24% 19% 5%	760
	11th to 20th	Night	23% 24% 25% 24% 4	760
	21st to end	Night	29% 17% 27% 23% 4	836

Page generated at 2024-11-03 02:11:16. Version ac07

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