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 2025-01-07.

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% 7% 2 6% 4 4 4 4 6% 8% 39%	105007
	Night	17% 7% 2 6% 4 4 4 3 5% 7% 41%	104041
Transparency	Day	42% 6% 12% 23% 14% 2	108582
	Night	42% 5% 12% 24% 15% 2	108554
Seeing	Day	20% 12% 27% 23% 13% 5%	15059
	Night	20% 10% 27% 31% 12% 1	24466

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	14% 7% 2 5% 5% 4 5% 4 6% 7% 42%	2565
	11th to 20th	Day	14% 12% 4 8% 5% 6% 5% 4 5% 7% 31%	2648
	21st to end	Day	20% 10% 4 8% 5% 4 4 3 4 5% 32%	3124
February	1st to 10th	Day	15% 7% 3 6% 6% 4 5% 5% 6% 7% 35%	1710
	11th to 20th	Day	14% 7% 3 7% 5% 4 4 4 6% 8% 37%	1755
	21st to end	Day	19% 9% 3 6% 5% 4 4 3 5% 6% 35%	1570
March	1st to 10th	Day	25% 6% 2 5% 4 4 4 4 6% 6% 35%	3205
	11th to 20th	Day	10% 6% 2 7% 5% 5% 5% 4 7% 7% 43%	3480
	21st to end	Day	21% 8% 2 5% 3 3 3 2 4 5% 43%	3991
April	1st to 10th	Day	16% 7% 2 7% 5% 4 4 3 6% 8% 37%	2280
	11th to 20th	Day	15% 7% 2 7% 4 4 4 4 6% 7% 41%	2254
	21st to end	Day	17% 5% 2 6% 4 5% 4 4 7% 8% 39%	2280
May	1st to 10th	Day	27% 7% 2 6% 4 4 4 4 5% 7% 30%	4119
	11th to 20th	Day	25% 9% 3 7% 5% 4 4 4 6% 7% 27%	4398
	21st to end	Day	13% 5% 2 5% 4 3 5% 4 6% 9% 44%	4837
June	1st to 10th	Day	12% 6% 2 5% 6% 4 5% 5% 6% 10% 38%	2660
	11th to 20th	Day	13% 5% 2 6% 4 5% 5% 5% 7% 9% 37%	2660
	21st to end	Day	11% 4 2 5% 4 5% 5% 5% 7% 11% 41%	2660
July	1st to 10th	Day	7% 4 2 7% 6% 6% 7% 5% 8% 11% 36%	4440
	11th to 20th	Day	9% 6% 2 6% 5% 5% 6% 5% 8% 10% 40%	4440
	21st to end	Day	10% 8% 3 8% 6% 6% 6% 5% 7% 7% 35%	4661
August	1st to 10th	Day	20% 6% 3 6% 5% 5% 6% 4 7% 7% 32%	4104
	11th to 20th	Day	14% 5% 2 5% 4 4 5% 4 7% 8% 41%	3821
	21st to end	Day	13% 5% 2 5% 3 3 4 3 6% 8% 47%	4180
September	1st to 10th	Day	16% 5% 2 6% 4 3 4 4 5% 6% 45%	2280
	11th to 20th	Day	12% 5% 2 4 3 4 3 3 5% 8% 50%	2280
	21st to end	Day	20% 7% 2 7% 4 4 4 3 4 6% 39%	2037
October	1st to 10th	Day	18% 6% 3 5% 3 4 4 3 6% 7% 42%	1900
	11th to 20th	Day	16% 5% 2 6% 4 3 3 3 4 8% 45%	1900
	21st to end	Day	19% 6% 2 5% 3 3 4 3 5% 7% 43%	2061
November	1st to 10th	Day	12% 7% 2 4 3 3 3 3 4 7% 51%	1761
	11th to 20th	Day	16% 6% 2 4 4 4 4 4 5% 8% 44%	1800
	21st to end	Day	17% 6% 2 5% 4 4 5% 4 5% 7% 42%	1600
December	1st to 10th	Day	14% 7% 2 7% 4 4 4 4 6% 7% 39%	2600
	11th to 20th	Day	22% 8% 2 4 3 3 4 4 5% 6% 39%	2986
	21st to end	Day	18% 7% 2 6% 5% 4 5% 4 6% 8% 35%	3960
January	1st to 10th	Night	15% 7% 2 7% 5% 4 4 4 5% 7% 40%	4514
	11th to 20th	Night	17% 9% 3 7% 4 4 4 4 6% 7% 38%	4308
	21st to end	Night	23% 10% 2 7% 4 3 3 3 4 5% 35%	4532
February	1st to 10th	Night	16% 9% 3 6% 4 4 5% 3 5% 7% 38%	2470
	11th to 20th	Night	16% 8% 2 8% 5% 4 4 4 5% 5% 39%	2309
	21st to end	Night	19% 7% 3 6% 3 5% 4 3 5% 7% 39%	1884
March	1st to 10th	Night	22% 10% 2 6% 4 4 3 3 4 5% 37%	3632
	11th to 20th	Night	11% 6% 2 6% 4 4 5% 3 5% 6% 47%	3479
	21st to end	Night	17% 8% 2 6% 4 3 3 2 4 5% 46%	3640
April	1st to 10th	Night	18% 7% 2 5% 5% 4 4 4 6% 7% 38%	1900
	11th to 20th	Night	15% 7% 2 6% 4 4 4 4 5% 7% 42%	1875
	21st to end	Night	19% 5% 2 5% 4 4 4 3 6% 5% 44%	1900
May	1st to 10th	Night	27% 7% 2 7% 3 4 4 3 5% 7% 31%	2848
	11th to 20th	Night	25% 9% 3 8% 4 4 3 4 5% 6% 29%	2495
	21st to end	Night	14% 5% 3 6% 3 4 4 3 6% 9% 41%	2738
June	1st to 10th	Night	14% 6% 2 6% 4 3 3 5% 6% 8% 42%	1520
	11th to 20th	Night	12% 5% 2 5% 5% 5% 4 4 7% 9% 42%	1520
	21st to end	Night	11% 4 2 5% 3 4 5% 5% 7% 10% 43%	1520
July	1st to 10th	Night	8% 5% 2 7% 5% 6% 6% 5% 8% 8% 40%	2520
	11th to 20th	Night	8% 6% 2 7% 6% 5% 6% 5% 8% 11% 38%	2520
	21st to end	Night	14% 7% 2 6% 5% 4 5% 4 6% 8% 38%	2888
August	1st to 10th	Night	20% 6% 2 6% 5% 4 5% 3 6% 7% 35%	2825
	11th to 20th	Night	14% 7% 3 8% 4 4 4 4 5% 7% 41%	2976
	21st to end	Night	13% 6% 1 4 3 4 5% 4 6% 8% 47%	3476
September	1st to 10th	Night	14% 6% 2 6% 3 4 3 3 5% 6% 48%	1900
	11th to 20th	Night	13% 5% 2 4 4 4 4 3 5% 6% 51%	1900
	21st to end	Night	20% 6% 2 6% 4 5% 4 3 6% 5% 41%	2140
October	1st to 10th	Night	20% 6% 2 5% 4 3 3 2 5% 6% 43%	2280
	11th to 20th	Night	16% 6% 2 5% 3 3 3 3 4 7% 48%	2280
	21st to end	Night	19% 5% 2 4 3 3 4 3 5% 7% 46%	2536
November	1st to 10th	Night	11% 5% 2 4 3 4 4 4 5% 6% 52%	2537
	11th to 20th	Night	15% 8% 3 5% 4 3 3 3 4 7% 45%	2600
	21st to end	Night	15% 5% 2 6% 4 4 4 4 6% 8% 43%	2795
December	1st to 10th	Night	13% 8% 3 7% 5% 3 4 4 5% 7% 41%	4580
	11th to 20th	Night	23% 7% 2 5% 3 3 4 4 5% 6% 39%	5208
	21st to end	Night	19% 8% 3 7% 4 4 4 4 6% 6% 35%	6996

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	42% 4 15% 25% 11% 2	2566
	11th to 20th	Day	52% 6% 11% 18% 11% 2	2648
	21st to end	Day	54% 5% 12% 20% 8% 1	3124
February	1st to 10th	Day	46% 6% 13% 22% 12% 1	1710
	11th to 20th	Day	45% 5% 11% 24% 13% 2	1764
	21st to end	Day	52% 4 10% 21% 10% 3	1570
March	1st to 10th	Day	47% 6% 11% 26% 8% 2	3208
	11th to 20th	Day	36% 7% 12% 27% 14% 3	3480
	21st to end	Day	45% 4 10% 19% 19% 3	3991
April	1st to 10th	Day	44% 5% 10% 21% 15% 5%	2280
	11th to 20th	Day	41% 6% 11% 22% 15% 4	2254
	21st to end	Day	42% 6% 10% 22% 16% 5%	2280
May	1st to 10th	Day	53% 6% 10% 19% 10% 2	4131
	11th to 20th	Day	55% 7% 12% 17% 8% 1	4402
	21st to end	Day	34% 7% 14% 27% 16% 2	4837
June	1st to 10th	Day	39% 9% 13% 24% 14% 2	2660
	11th to 20th	Day	41% 8% 14% 24% 11% 3	2660
	21st to end	Day	36% 8% 14% 26% 15% 1	2660
July	1st to 10th	Day	38% 10% 14% 22% 13% 2	4370
	11th to 20th	Day	37% 8% 16% 25% 13% 1	4365
	21st to end	Day	46% 7% 10% 20% 16% 2	4512
August	1st to 10th	Day	48% 8% 11% 22% 10%	4091
	11th to 20th	Day	39% 6% 12% 30% 13% 1	3860
	21st to end	Day	35% 6% 10% 29% 19% 2	4180
September	1st to 10th	Day	40% 6% 10% 21% 20% 3	2280
	11th to 20th	Day	33% 5% 10% 25% 23% 4	2280
	21st to end	Day	48% 4 9% 18% 20% 2	2037
October	1st to 10th	Day	38% 4 9% 21% 24% 5%	3160
	11th to 20th	Day	29% 4 12% 28% 23% 5%	3140
	21st to end	Day	27% 4 14% 25% 27% 4	3375
November	1st to 10th	Day	34% 4 15% 25% 20% 4	1761
	11th to 20th	Day	38% 5% 11% 25% 18% 2	1800
	21st to end	Day	40% 6% 13% 30% 9% 2	1600
December	1st to 10th	Day	44% 5% 16% 25% 9% 2	2600
	11th to 20th	Day	47% 4 14% 27% 8% 1	2986
	21st to end	Day	45% 6% 13% 21% 12% 2	3960
January	1st to 10th	Night	42% 6% 14% 25% 11% 3	4514
	11th to 20th	Night	45% 6% 14% 23% 10% 2	4308
	21st to end	Night	51% 4 10% 25% 9% 1	4532
February	1st to 10th	Night	45% 4 14% 25% 10% 2	2470
	11th to 20th	Night	46% 5% 9% 20% 17% 3	2311
	21st to end	Night	45% 4 10% 21% 16% 4	1884
March	1st to 10th	Night	49% 5% 9% 23% 12% 2	3642
	11th to 20th	Night	35% 6% 13% 28% 15% 2	3480
	21st to end	Night	42% 4 8% 18% 22% 5%	3640
April	1st to 10th	Night	44% 5% 11% 21% 15% 4	1900
	11th to 20th	Night	41% 6% 11% 21% 19% 3	1875
	21st to end	Night	40% 6% 10% 22% 17% 5%	1900
May	1st to 10th	Night	53% 6% 9% 21% 10% 2	2855
	11th to 20th	Night	54% 8% 14% 13% 10% 2	2496
	21st to end	Night	39% 8% 13% 23% 14% 3	2739
June	1st to 10th	Night	39% 8% 10% 23% 19% 2	1520
	11th to 20th	Night	37% 8% 13% 27% 14% 1	1520
	21st to end	Night	34% 8% 14% 29% 13% 2	1520
July	1st to 10th	Night	40% 9% 15% 17% 15% 4	2480
	11th to 20th	Night	38% 8% 16% 24% 13% 1	2472
	21st to end	Night	41% 8% 13% 18% 18% 1	2796
August	1st to 10th	Night	47% 7% 17% 19% 9% 1	2814
	11th to 20th	Night	43% 6% 12% 23% 16% 1	3003
	21st to end	Night	34% 6% 11% 30% 18% 1	3476
September	1st to 10th	Night	38% 5% 10% 24% 20% 3	1900
	11th to 20th	Night	33% 6% 9% 24% 25% 3	1900
	21st to end	Night	44% 5% 8% 20% 21% 2	2140
October	1st to 10th	Night	43% 4 10% 20% 21% 2	3800
	11th to 20th	Night	28% 4 9% 30% 25% 4	3779
	21st to end	Night	28% 3 12% 32% 24% 2	4172
November	1st to 10th	Night	32% 5% 13% 25% 20% 4	2537
	11th to 20th	Night	41% 4 9% 24% 18% 4	2600
	21st to end	Night	39% 5% 13% 28% 14% 1	2795
December	1st to 10th	Night	42% 4 13% 29% 10% 1	4580
	11th to 20th	Night	47% 4 12% 23% 12% 2	5208
	21st to end	Night	47% 5% 11% 21% 15% 1	6996

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	27% 24% 27% 17% 5% 1	192
	11th to 20th	Day	28% 23% 32% 13% 3	216
	21st to end	Day	23% 22% 33% 16% 4 2	297
February	1st to 10th	Day	24% 20% 34% 18% 3 1	270
	11th to 20th	Day	26% 19% 38% 15% 1	362
	21st to end	Day	31% 14% 31% 21% 3	382
March	1st to 10th	Day	24% 19% 31% 21% 4	460
	11th to 20th	Day	24% 23% 32% 16% 4 1	460
	21st to end	Day	29% 17% 31% 17% 6% 1	506
April	1st to 10th	Day	24% 18% 32% 17% 7% 2	460
	11th to 20th	Day	22% 20% 28% 19% 8% 3	452
	21st to end	Day	27% 13% 32% 19% 6% 3	460
May	1st to 10th	Day	29% 12% 27% 19% 10% 3	463
	11th to 20th	Day	23% 11% 31% 21% 10% 3	487
	21st to end	Day	18% 6% 25% 28% 16% 7%	529
June	1st to 10th	Day	15% 11% 31% 24% 15% 4	490
	11th to 20th	Day	18% 9% 27% 24% 18% 4	490
	21st to end	Day	14% 11% 28% 27% 16% 5%	490
July	1st to 10th	Day	12% 4 20% 30% 25% 10%	485
	11th to 20th	Day	7% 6% 21% 32% 26% 8%	484
	21st to end	Day	11% 4 27% 33% 21% 4	532
August	1st to 10th	Day	12% 4 21% 29% 23% 11%	486
	11th to 20th	Day	15% 3 19% 31% 24% 8%	479
	21st to end	Day	14% 4 21% 29% 19% 13%	539
September	1st to 10th	Day	18% 7% 20% 24% 22% 9%	490
	11th to 20th	Day	13% 4 20% 27% 22% 14%	490
	21st to end	Day	26% 11% 20% 22% 17% 4	490
October	1st to 10th	Day	23% 7% 22% 24% 17% 6%	490
	11th to 20th	Day	18% 11% 28% 24% 15% 3	490
	21st to end	Day	21% 11% 31% 23% 12% 2	523
November	1st to 10th	Day	17% 12% 27% 28% 13% 3	395
	11th to 20th	Day	19% 16% 31% 27% 7% 1	400
	21st to end	Day	22% 20% 33% 18% 7% 1	200
December	1st to 10th	Day	28% 18% 33% 16% 6% 1	200
	11th to 20th	Day	27% 22% 29% 17% 5% 1	200
	21st to end	Day	26% 17% 28% 20% 7% 2	220
January	1st to 10th	Night	19% 15% 38% 24% 3	785
	11th to 20th	Night	24% 14% 31% 27% 4	760
	21st to end	Night	18% 16% 36% 28% 3	836
February	1st to 10th	Night	23% 14% 32% 29% 2	760
	11th to 20th	Night	23% 18% 38% 19% 2	743
	21st to end	Night	26% 16% 34% 22% 3	628
March	1st to 10th	Night	22% 16% 33% 25% 5%	760
	11th to 20th	Night	24% 16% 32% 22% 5% 1	760
	21st to end	Night	22% 13% 35% 25% 5%	836
April	1st to 10th	Night	24% 16% 33% 23% 5%	760
	11th to 20th	Night	19% 13% 36% 25% 8%	751
	21st to end	Night	23% 12% 28% 29% 8%	760
May	1st to 10th	Night	26% 8% 27% 31% 8%	585
	11th to 20th	Night	19% 9% 26% 35% 10% 1	374
	21st to end	Night	16% 6% 19% 40% 17% 1	411
June	1st to 10th	Night	16% 6% 22% 37% 19%	380
	11th to 20th	Night	13% 5% 23% 43% 15% 1	380
	21st to end	Night	12% 2 21% 48% 17% 1	380
July	1st to 10th	Night	12% 3 16% 44% 23% 2	370
	11th to 20th	Night	9% 3 16% 42% 29% 1	368
	21st to end	Night	10% 4 14% 45% 25% 1	503
August	1st to 10th	Night	13% 4 9% 43% 29% 2	567
	11th to 20th	Night	15% 4 12% 37% 30% 2	677
	21st to end	Night	15% 4 14% 36% 28% 3	836
September	1st to 10th	Night	16% 3 21% 35% 22% 3	760
	11th to 20th	Night	14% 4 13% 37% 27% 4	760
	21st to end	Night	22% 4 18% 34% 20% 2	760
October	1st to 10th	Night	23% 6% 21% 29% 18% 4	760
	11th to 20th	Night	20% 9% 22% 35% 14% 1	760
	21st to end	Night	22% 9% 26% 32% 10%	836
November	1st to 10th	Night	15% 8% 30% 33% 13% 1	780
	11th to 20th	Night	20% 13% 28% 30% 8% 1	800
	21st to end	Night	19% 13% 29% 33% 7%	800
December	1st to 10th	Night	25% 12% 32% 25% 6% 1	800
	11th to 20th	Night	21% 12% 31% 30% 6%	800
	21st to end	Night	23% 9% 33% 31% 4	880

Page generated at 2025-01-04 03:24:03. Version ac07

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