Triplet Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Triplet Observatory clear sky chart from 2005-11-06 to 2026-05-02.

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	16% 6% 2 6% 4 4 5% 4 6% 8% 39%	131898
	Night	16% 7% 2 6% 4 4 4 4 5% 7% 41%	130611
Transparency	Day	42% 6% 12% 23% 15% 2	135458
	Night	41% 5% 12% 23% 16% 3	135137
Seeing	Day	20% 12% 27% 23% 13% 5%	16764
	Night	20% 10% 27% 31% 12% 1	26204

By Month

Percentage Cloud Cover NE (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	13% 6% 2 7% 5% 5% 5% 4 6% 7% 40%	4661
	11th to 20th	Day	13% 10% 4 8% 5% 5% 4 3 5% 6% 37%	4902
	21st to end	Day	15% 6% 3 8% 5% 5% 5% 4 6% 7% 37%	5780
February	1st to 10th	Day	14% 7% 3 7% 6% 4 5% 5% 6% 7% 36%	1890
	11th to 20th	Day	15% 8% 3 8% 5% 4 3 3 6% 8% 36%	1945
	21st to end	Day	18% 9% 3 6% 5% 4 4 3 5% 6% 36%	1730
March	1st to 10th	Day	20% 5% 2 5% 3 4 4 3 5% 6% 42%	4710
	11th to 20th	Day	11% 7% 3 7% 4 5% 4 4 6% 7% 43%	5090
	21st to end	Day	17% 6% 2 5% 4 4 4 3 5% 6% 42%	5837
April	1st to 10th	Day	17% 7% 2 7% 5% 4 4 3 6% 8% 37%	2520
	11th to 20th	Day	15% 7% 2 7% 4 4 4 4 6% 7% 41%	2494
	21st to end	Day	17% 5% 2 6% 4 5% 4 4 7% 7% 39%	2520
May	1st to 10th	Day	25% 7% 2 6% 4 4 5% 4 5% 8% 30%	5911
	11th to 20th	Day	25% 8% 3 6% 4 4 4 3 6% 8% 30%	6318
	21st to end	Day	19% 5% 2 5% 4 4 4 4 6% 9% 36%	6949
June	1st to 10th	Day	12% 6% 2 5% 6% 4 5% 5% 6% 10% 38%	2800
	11th to 20th	Day	15% 5% 2 6% 4 5% 5% 5% 7% 9% 37%	2800
	21st to end	Day	11% 5% 2 5% 5% 5% 5% 4 7% 11% 41%	2800
July	1st to 10th	Day	7% 5% 3 7% 5% 6% 6% 5% 8% 10% 38%	6360
	11th to 20th	Day	10% 7% 3 7% 5% 5% 6% 5% 8% 10% 32%	6360
	21st to end	Day	10% 7% 3 7% 5% 5% 5% 4 6% 8% 40%	6703
August	1st to 10th	Day	19% 6% 3 6% 5% 5% 6% 4 7% 7% 33%	4234
	11th to 20th	Day	14% 5% 2 5% 4 4 5% 4 7% 8% 40%	3944
	21st to end	Day	13% 5% 2 5% 3 3 4 3 6% 8% 47%	4312
September	1st to 10th	Day	15% 5% 2 6% 4 4 4 3 5% 6% 45%	2400
	11th to 20th	Day	12% 5% 2 4 3 4 3 3 5% 8% 50%	2400
	21st to end	Day	20% 7% 3 7% 5% 4 4 3 4 6% 38%	2144
October	1st to 10th	Day	18% 6% 2 4 3 3 4 3 6% 7% 44%	2000
	11th to 20th	Day	16% 5% 2 6% 4 3 3 3 4 8% 45%	2000
	21st to end	Day	18% 6% 2 4 3 3 4 3 6% 7% 43%	2169
November	1st to 10th	Day	12% 6% 2 5% 3 3 3 3 5% 7% 51%	1851
	11th to 20th	Day	16% 6% 2 4 4 4 4 4 6% 8% 43%	1890
	21st to end	Day	17% 6% 2 6% 4 4 5% 4 5% 6% 41%	1680
December	1st to 10th	Day	14% 8% 2 6% 4 4 4 4 6% 7% 39%	2680
	11th to 20th	Day	22% 8% 2 5% 3 3 4 4 5% 6% 39%	3066
	21st to end	Day	18% 7% 2 6% 5% 4 5% 4 6% 8% 35%	4048
January	1st to 10th	Night	11% 8% 3 8% 5% 5% 4 4 5% 8% 40%	8234
	11th to 20th	Night	13% 9% 3 7% 4 4 4 4 6% 7% 40%	7979
	21st to end	Night	15% 7% 2 6% 4 3 4 3 5% 7% 44%	8401
February	1st to 10th	Night	15% 9% 3 6% 5% 4 5% 3 5% 7% 39%	2730
	11th to 20th	Night	17% 7% 2 8% 5% 4 4 4 5% 6% 38%	2559
	21st to end	Night	17% 7% 3 6% 4 5% 4 3 5% 7% 39%	2076
March	1st to 10th	Night	18% 8% 2 6% 4 4 4 3 5% 5% 42%	5347
	11th to 20th	Night	11% 6% 2 5% 4 4 4 3 5% 6% 50%	5089
	21st to end	Night	15% 7% 2 7% 4 4 4 3 5% 6% 42%	5336
April	1st to 10th	Night	18% 7% 2 5% 5% 4 5% 4 5% 7% 37%	2100
	11th to 20th	Night	15% 7% 2 6% 5% 4 4 4 6% 7% 41%	2075
	21st to end	Night	19% 5% 2 5% 4 4 4 3 6% 6% 44%	2100
May	1st to 10th	Night	26% 7% 2 7% 4 4 5% 3 5% 7% 29%	4093
	11th to 20th	Night	24% 8% 3 7% 4 4 3 4 5% 7% 31%	3575
	21st to end	Night	22% 6% 3 6% 3 4 4 3 5% 7% 37%	3926
June	1st to 10th	Night	15% 6% 2 6% 4 4 3 5% 6% 7% 42%	1600
	11th to 20th	Night	13% 5% 2 5% 5% 5% 5% 4 6% 9% 41%	1600
	21st to end	Night	12% 4 2 5% 3 4 5% 5% 7% 10% 43%	1600
July	1st to 10th	Night	9% 6% 2 8% 6% 5% 6% 4 7% 9% 39%	3600
	11th to 20th	Night	11% 8% 3 9% 6% 5% 6% 5% 7% 10% 31%	3600
	21st to end	Night	12% 6% 2 6% 5% 4 5% 4 5% 9% 43%	4145
August	1st to 10th	Night	20% 7% 2 6% 5% 4 4 3 6% 7% 35%	2915
	11th to 20th	Night	14% 7% 3 8% 4 5% 4 4 5% 7% 41%	3072
	21st to end	Night	13% 5% 2 4 3 4 5% 4 6% 8% 47%	3586
September	1st to 10th	Night	14% 6% 2 6% 3 4 3 3 5% 7% 48%	2000
	11th to 20th	Night	13% 5% 2 4 4 4 4 3 5% 6% 51%	2000
	21st to end	Night	20% 7% 2 6% 4 4 4 3 6% 6% 39%	2253
October	1st to 10th	Night	20% 6% 2 5% 3 3 3 2 5% 6% 45%	2400
	11th to 20th	Night	17% 6% 2 5% 3 3 3 3 4 7% 48%	2400
	21st to end	Night	18% 5% 2 4 3 3 4 3 5% 7% 47%	2670
November	1st to 10th	Night	11% 5% 2 4 3 4 4 4 6% 6% 51%	2667
	11th to 20th	Night	15% 8% 3 5% 4 3 4 3 4 7% 45%	2730
	21st to end	Night	15% 6% 2 6% 4 4 4 4 5% 8% 43%	2935
December	1st to 10th	Night	13% 8% 3 7% 5% 4 4 4 5% 7% 41%	4720
	11th to 20th	Night	22% 7% 2 5% 3 3 4 4 5% 6% 39%	5348
	21st to end	Night	19% 8% 3 7% 4 4 4 4 6% 6% 35%	7150

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	43% 4 12% 24% 16% 1	4662
	11th to 20th	Day	47% 4 10% 19% 15% 5%	4934
	21st to end	Day	46% 6% 13% 22% 13% 1	5780
February	1st to 10th	Day	45% 6% 12% 23% 12% 2	1890
	11th to 20th	Day	47% 4 11% 24% 13% 2	1954
	21st to end	Day	50% 4 11% 22% 10% 3	1730
March	1st to 10th	Day	42% 5% 10% 24% 13% 6%	4713
	11th to 20th	Day	39% 6% 13% 27% 11% 5%	5090
	21st to end	Day	43% 5% 11% 16% 21% 4	5837
April	1st to 10th	Day	45% 5% 10% 21% 15% 5%	2520
	11th to 20th	Day	41% 6% 13% 21% 15% 4	2494
	21st to end	Day	42% 6% 10% 23% 15% 4	2520
May	1st to 10th	Day	51% 7% 12% 18% 10% 2	5920
	11th to 20th	Day	52% 6% 10% 21% 11% 1	6322
	21st to end	Day	43% 7% 12% 24% 13% 2	6949
June	1st to 10th	Day	39% 8% 13% 24% 14% 2	2800
	11th to 20th	Day	42% 8% 14% 24% 11% 3	2800
	21st to end	Day	37% 8% 14% 25% 15% 1	2800
July	1st to 10th	Day	38% 10% 13% 22% 15% 1	6290
	11th to 20th	Day	43% 9% 16% 22% 10% 1	6285
	21st to end	Day	40% 6% 10% 21% 22% 1	6510
August	1st to 10th	Day	48% 8% 11% 22% 10% 1	4221
	11th to 20th	Day	39% 6% 12% 30% 12% 1	3983
	21st to end	Day	34% 5% 10% 29% 19% 2	4312
September	1st to 10th	Day	39% 6% 11% 21% 20% 3	2400
	11th to 20th	Day	33% 5% 10% 26% 23% 3	2400
	21st to end	Day	48% 4 9% 17% 19% 2	2144
October	1st to 10th	Day	37% 4 9% 22% 24% 5%	3260
	11th to 20th	Day	29% 3 12% 28% 23% 5%	3240
	21st to end	Day	27% 4 14% 25% 27% 4	3483
November	1st to 10th	Day	34% 4 14% 25% 20% 4	1851
	11th to 20th	Day	39% 5% 11% 24% 18% 3	1890
	21st to end	Day	41% 6% 13% 29% 9% 2	1680
December	1st to 10th	Day	44% 5% 16% 25% 9% 2	2680
	11th to 20th	Day	46% 4 14% 27% 8% 1	3066
	21st to end	Day	46% 6% 13% 21% 12% 2	4048
January	1st to 10th	Night	41% 7% 14% 22% 14% 3	8234
	11th to 20th	Night	43% 5% 12% 19% 16% 5%	8022
	21st to end	Night	40% 4 10% 26% 18% 2	8401
February	1st to 10th	Night	45% 4 14% 25% 10% 2	2730
	11th to 20th	Night	47% 5% 9% 20% 17% 3	2561
	21st to end	Night	45% 4 10% 21% 16% 3	2076
March	1st to 10th	Night	44% 4 10% 22% 12% 7%	5357
	11th to 20th	Night	33% 6% 16% 27% 13% 5%	5090
	21st to end	Night	43% 4 8% 17% 23% 4	5336
April	1st to 10th	Night	45% 5% 11% 21% 15% 4	2100
	11th to 20th	Night	40% 6% 12% 20% 19% 2	2075
	21st to end	Night	40% 6% 10% 22% 17% 5%	2100
May	1st to 10th	Night	54% 6% 10% 17% 10% 2	4100
	11th to 20th	Night	52% 8% 11% 16% 12% 1	3576
	21st to end	Night	46% 6% 10% 23% 12% 2	3927
June	1st to 10th	Night	40% 7% 10% 23% 19% 2	1600
	11th to 20th	Night	39% 8% 13% 26% 14% 1	1600
	21st to end	Night	34% 8% 14% 28% 14% 2	1600
July	1st to 10th	Night	41% 8% 13% 20% 14% 3	3560
	11th to 20th	Night	46% 7% 15% 20% 10% 1	3552
	21st to end	Night	36% 7% 12% 23% 21% 1	4023
August	1st to 10th	Night	47% 7% 17% 19% 10% 1	2904
	11th to 20th	Night	43% 6% 12% 24% 15% 1	3099
	21st to end	Night	34% 6% 11% 30% 18% 1	3586
September	1st to 10th	Night	38% 5% 10% 24% 20% 3	2000
	11th to 20th	Night	33% 5% 9% 25% 25% 3	2000
	21st to end	Night	44% 6% 9% 19% 20% 2	2253
October	1st to 10th	Night	43% 4 10% 20% 22% 2	3920
	11th to 20th	Night	28% 4 9% 30% 25% 4	3899
	21st to end	Night	28% 3 12% 32% 24% 2	4306
November	1st to 10th	Night	32% 5% 13% 25% 20% 4	2667
	11th to 20th	Night	41% 4 9% 24% 18% 4	2730
	21st to end	Night	40% 4 12% 28% 14% 1	2935
December	1st to 10th	Night	42% 4 13% 29% 10% 1	4720
	11th to 20th	Night	46% 4 12% 23% 12% 2	5348
	21st to end	Night	48% 5% 11% 20% 14% 1	7150

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	25% 24% 29% 18% 4 1	220
	11th to 20th	Day	27% 25% 33% 12% 3	265
	21st to end	Day	20% 21% 36% 17% 4 1	363
February	1st to 10th	Day	23% 20% 32% 20% 4 1	330
	11th to 20th	Day	28% 19% 35% 17% 1	432
	21st to end	Day	27% 14% 32% 24% 3	446
March	1st to 10th	Day	24% 19% 31% 22% 4	540
	11th to 20th	Day	23% 23% 30% 17% 5% 1	540
	21st to end	Day	26% 20% 32% 16% 5% 1	594
April	1st to 10th	Day	25% 18% 31% 17% 7% 2	540
	11th to 20th	Day	21% 20% 28% 19% 8% 3	532
	21st to end	Day	25% 13% 31% 19% 8% 3	540
May	1st to 10th	Day	29% 12% 29% 18% 10% 3	507
	11th to 20th	Day	23% 11% 31% 21% 10% 3	527
	21st to end	Day	19% 7% 25% 27% 16% 6%	573
June	1st to 10th	Day	15% 11% 30% 24% 15% 5%	530
	11th to 20th	Day	19% 8% 27% 24% 17% 4	530
	21st to end	Day	14% 10% 26% 27% 17% 5%	530
July	1st to 10th	Day	12% 4 19% 29% 26% 10%	525
	11th to 20th	Day	7% 6% 21% 32% 27% 8%	524
	21st to end	Day	11% 4 25% 34% 22% 5%	576
August	1st to 10th	Day	12% 4 20% 30% 23% 12%	526
	11th to 20th	Day	15% 3 18% 30% 24% 9%	519
	21st to end	Day	14% 4 21% 29% 19% 13%	583
September	1st to 10th	Day	17% 8% 20% 24% 23% 9%	530
	11th to 20th	Day	12% 5% 19% 27% 23% 14%	530
	21st to end	Day	25% 10% 19% 23% 17% 5%	530
October	1st to 10th	Day	22% 7% 21% 25% 18% 8%	530
	11th to 20th	Day	18% 13% 28% 24% 14% 3	530
	21st to end	Day	20% 12% 31% 24% 11% 2	565
November	1st to 10th	Day	16% 13% 28% 27% 12% 3	425
	11th to 20th	Day	18% 17% 30% 26% 7% 1	430
	21st to end	Day	23% 20% 33% 17% 6% 1	220
December	1st to 10th	Day	27% 18% 31% 17% 5% 1	220
	11th to 20th	Day	25% 22% 30% 17% 5%	220
	21st to end	Day	27% 17% 29% 19% 7% 2	242
January	1st to 10th	Night	19% 16% 38% 25% 3	840
	11th to 20th	Night	23% 15% 31% 26% 4	840
	21st to end	Night	17% 15% 38% 28% 2	924
February	1st to 10th	Night	22% 14% 32% 30% 3	840
	11th to 20th	Night	23% 18% 36% 21% 2	823
	21st to end	Night	24% 14% 35% 24% 3	692
March	1st to 10th	Night	23% 16% 32% 25% 5%	840
	11th to 20th	Night	23% 16% 32% 23% 5%	840
	21st to end	Night	22% 13% 35% 25% 5%	924
April	1st to 10th	Night	25% 15% 33% 23% 5%	840
	11th to 20th	Night	19% 12% 36% 26% 8%	831
	21st to end	Night	22% 11% 28% 31% 7%	840
May	1st to 10th	Night	26% 8% 27% 31% 8%	621
	11th to 20th	Night	19% 9% 27% 35% 10% 1	394
	21st to end	Night	18% 6% 20% 39% 16% 1	433
June	1st to 10th	Night	16% 6% 22% 37% 19%	400
	11th to 20th	Night	15% 5% 23% 43% 15% 1	400
	21st to end	Night	12% 2 20% 47% 18% 1	400
July	1st to 10th	Night	12% 3 16% 43% 24% 3	390
	11th to 20th	Night	9% 4 15% 42% 29% 1	388
	21st to end	Night	10% 4 14% 44% 26% 1	530
August	1st to 10th	Night	13% 4 9% 43% 30% 2	597
	11th to 20th	Night	15% 4 11% 37% 31% 2	713
	21st to end	Night	15% 4 14% 37% 27% 3	880
September	1st to 10th	Night	16% 3 20% 35% 23% 3	800
	11th to 20th	Night	14% 4 13% 38% 27% 4	800
	21st to end	Night	22% 4 17% 34% 21% 2	800
October	1st to 10th	Night	22% 6% 20% 29% 20% 4	800
	11th to 20th	Night	20% 9% 22% 35% 14% 1	800
	21st to end	Night	22% 9% 26% 33% 10%	880
November	1st to 10th	Night	15% 9% 30% 33% 13% 1	820
	11th to 20th	Night	20% 13% 29% 30% 8% 1	840
	21st to end	Night	18% 13% 29% 32% 7%	840
December	1st to 10th	Night	25% 12% 33% 25% 5% 1	840
	11th to 20th	Night	21% 12% 31% 30% 5%	840
	21st to end	Night	23% 9% 34% 30% 4	924

Page generated at 2026-04-29 02:21:47. Version ac07

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