Highlands Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Highlands Observatory clear sky chart from 2005-11-06 to 2024-11-12.

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% 9% 3 8% 5% 5% 5% 4 6% 7% 32%	101491
	Night	17% 9% 3 7% 5% 4 5% 4 6% 7% 34%	97692
Transparency	Day	49% 6% 12% 21% 11% 1	105012
	Night	47% 6% 13% 21% 12% 1	102260
Seeing	Day	25% 16% 27% 19% 10% 3	14853
	Night	23% 15% 27% 24% 9% 1	24036

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	12% 13% 6% 12% 6% 5% 5% 3 5% 6% 27%	2517
	11th to 20th	Day	13% 12% 7% 14% 6% 6% 5% 4 4 5% 22%	2520
	21st to end	Day	20% 14% 6% 11% 6% 4 5% 3 4 6% 21%	3071
February	1st to 10th	Day	16% 12% 4 11% 8% 5% 6% 5% 6% 5% 24%	1710
	11th to 20th	Day	11% 12% 3 9% 6% 5% 5% 4 6% 9% 29%	1765
	21st to end	Day	18% 12% 3 9% 8% 4 4 2 6% 6% 28%	1570
March	1st to 10th	Day	23% 12% 3 10% 5% 4 3 2 4 5% 28%	3116
	11th to 20th	Day	9% 10% 5% 9% 6% 6% 6% 4 6% 7% 32%	3469
	21st to end	Day	19% 11% 2 7% 5% 5% 5% 3 4 6% 33%	4054
April	1st to 10th	Day	17% 12% 3 8% 5% 5% 4 4 4 5% 33%	2280
	11th to 20th	Day	16% 11% 3 7% 5% 5% 5% 3 5% 6% 35%	2254
	21st to end	Day	17% 9% 3 8% 6% 5% 5% 4 4 6% 34%	2280
May	1st to 10th	Day	26% 8% 2 7% 4 4 4 3 4 6% 31%	4254
	11th to 20th	Day	21% 8% 3 8% 6% 6% 5% 4 6% 7% 26%	4398
	21st to end	Day	13% 5% 2 5% 5% 5% 5% 5% 7% 9% 39%	4837
June	1st to 10th	Day	15% 6% 2 8% 6% 5% 6% 4 6% 9% 32%	2660
	11th to 20th	Day	15% 7% 3 6% 7% 5% 6% 5% 7% 8% 32%	2660
	21st to end	Day	14% 6% 3 7% 5% 5% 5% 4 6% 10% 34%	2660
July	1st to 10th	Day	9% 6% 3 7% 6% 6% 6% 6% 7% 10% 35%	4440
	11th to 20th	Day	9% 6% 2 7% 5% 5% 6% 5% 9% 11% 35%	4440
	21st to end	Day	13% 7% 3 8% 5% 5% 5% 4 7% 8% 33%	4814
August	1st to 10th	Day	21% 6% 2 8% 6% 5% 5% 4 6% 8% 29%	4150
	11th to 20th	Day	15% 7% 2 7% 4 5% 6% 4 7% 10% 33%	3803
	21st to end	Day	17% 5% 2 5% 3 4 5% 4 6% 8% 40%	4180
September	1st to 10th	Day	16% 7% 2 6% 5% 4 4 4 5% 8% 38%	2280
	11th to 20th	Day	13% 6% 2 6% 4 4 5% 3 5% 8% 45%	2253
	21st to end	Day	20% 6% 2 6% 4 4 4 4 7% 7% 35%	2081
October	1st to 10th	Day	18% 7% 2 7% 5% 5% 5% 4 5% 7% 34%	1900
	11th to 20th	Day	16% 7% 3 7% 5% 5% 5% 3 7% 6% 36%	1900
	21st to end	Day	21% 10% 3 7% 5% 4 4 4 6% 6% 30%	1986
November	1st to 10th	Day	12% 8% 3 7% 4 5% 4 3 5% 6% 42%	1761
	11th to 20th	Day	16% 11% 3 8% 5% 4 4 4 5% 5% 34%	1710
	21st to end	Day	17% 10% 3 8% 6% 5% 5% 3 6% 7% 29%	1520
December	1st to 10th	Day	18% 13% 5% 9% 6% 6% 5% 4 5% 5% 24%	1520
	11th to 20th	Day	21% 11% 5% 10% 5% 4 3 3 4 6% 29%	1906
	21st to end	Day	19% 15% 7% 12% 5% 5% 5% 3 5% 5% 19%	2772
January	1st to 10th	Night	16% 9% 5% 10% 5% 5% 4 4 6% 8% 28%	4429
	11th to 20th	Night	14% 10% 5% 12% 6% 5% 5% 5% 5% 7% 25%	4440
	21st to end	Night	21% 13% 4 10% 8% 5% 5% 4 5% 5% 21%	4582
February	1st to 10th	Night	14% 10% 4 8% 6% 6% 4 4 5% 7% 31%	2470
	11th to 20th	Night	13% 9% 3 10% 6% 6% 6% 4 7% 8% 29%	2300
	21st to end	Night	17% 9% 3 8% 6% 5% 6% 5% 5% 6% 31%	1884
March	1st to 10th	Night	21% 12% 3 8% 5% 4 4 4 5% 5% 29%	3724
	11th to 20th	Night	10% 9% 4 8% 7% 6% 6% 5% 6% 7% 33%	3488
	21st to end	Night	13% 11% 3 8% 5% 5% 5% 4 5% 6% 36%	3576
April	1st to 10th	Night	15% 11% 3 8% 6% 5% 6% 4 5% 6% 30%	1900
	11th to 20th	Night	17% 10% 3 6% 5% 4 4 3 5% 7% 36%	1875
	21st to end	Night	18% 7% 3 7% 5% 4 5% 4 5% 7% 37%	1900
May	1st to 10th	Night	27% 8% 3 6% 4 4 3 3 4 6% 32%	2711
	11th to 20th	Night	21% 9% 3 7% 5% 4 4 4 6% 6% 31%	2495
	21st to end	Night	12% 8% 2 6% 4 5% 5% 5% 6% 8% 39%	2738
June	1st to 10th	Night	16% 5% 2 6% 5% 4 5% 4 5% 8% 40%	1520
	11th to 20th	Night	14% 5% 2 6% 5% 4 3 3 7% 10% 42%	1520
	21st to end	Night	10% 4 2 5% 5% 4 5% 5% 7% 10% 43%	1520
July	1st to 10th	Night	10% 6% 2 7% 6% 4 5% 5% 7% 8% 40%	2520
	11th to 20th	Night	12% 5% 2 5% 4 4 4 5% 7% 10% 41%	2520
	21st to end	Night	15% 7% 2 5% 4 4 4 4 6% 7% 41%	2739
August	1st to 10th	Night	21% 5% 2 7% 5% 4 5% 4 7% 8% 33%	2761
	11th to 20th	Night	17% 6% 3 6% 4 3 4 3 5% 7% 41%	2993
	21st to end	Night	14% 4 2 4 4 3 4 4 5% 9% 47%	3476
September	1st to 10th	Night	16% 5% 2 6% 4 3 4 3 5% 7% 44%	1900
	11th to 20th	Night	14% 5% 1 4 2 4 3 3 5% 7% 50%	1925
	21st to end	Night	18% 6% 2 7% 5% 4 4 3 5% 6% 40%	2097
October	1st to 10th	Night	19% 8% 2 6% 3 4 4 3 6% 7% 38%	2280
	11th to 20th	Night	18% 8% 2 5% 3 4 3 3 5% 6% 42%	2280
	21st to end	Night	21% 10% 2 6% 3 4 4 4 5% 8% 33%	2612
November	1st to 10th	Night	12% 8% 2 7% 4 4 4 4 5% 6% 44%	2537
	11th to 20th	Night	19% 8% 3 6% 4 4 4 3 6% 7% 35%	2488
	21st to end	Night	14% 8% 3 8% 5% 5% 5% 4 7% 7% 34%	2660
December	1st to 10th	Night	19% 9% 4 8% 6% 5% 6% 5% 6% 7% 25%	2660
	11th to 20th	Night	18% 11% 4 8% 4 5% 5% 4 6% 6% 28%	3288
	21st to end	Night	22% 12% 6% 8% 5% 4 5% 4 5% 7% 21%	4884

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	56% 6% 10% 21% 6% 1	2518
	11th to 20th	Day	63% 6% 9% 15% 5% 2	2520
	21st to end	Day	64% 5% 9% 16% 6%	3071
February	1st to 10th	Day	58% 7% 11% 15% 9%	1710
	11th to 20th	Day	51% 6% 9% 22% 11% 1	1774
	21st to end	Day	56% 5% 10% 19% 8% 1	1570
March	1st to 10th	Day	59% 4 11% 17% 9% 1	3119
	11th to 20th	Day	48% 7% 12% 23% 8% 1	3469
	21st to end	Day	51% 5% 7% 15% 19% 3	4054
April	1st to 10th	Day	53% 4 8% 22% 10% 3	2280
	11th to 20th	Day	48% 6% 10% 20% 13% 2	2254
	21st to end	Day	50% 6% 9% 20% 12% 4	2280
May	1st to 10th	Day	53% 5% 10% 18% 11% 2	4268
	11th to 20th	Day	55% 8% 10% 18% 7% 1	4402
	21st to end	Day	38% 8% 13% 25% 16% 1	4837
June	1st to 10th	Day	47% 7% 12% 21% 13%	2660
	11th to 20th	Day	47% 7% 12% 22% 10% 1	2660
	21st to end	Day	44% 7% 13% 25% 10%	2660
July	1st to 10th	Day	43% 8% 15% 22% 12% 1	4370
	11th to 20th	Day	38% 8% 17% 25% 12%	4365
	21st to end	Day	47% 6% 14% 20% 13% 1	4661
August	1st to 10th	Day	52% 7% 13% 19% 9%	4136
	11th to 20th	Day	44% 7% 16% 26% 7%	3841
	21st to end	Day	39% 6% 11% 32% 11% 1	4180
September	1st to 10th	Day	43% 6% 11% 24% 14% 1	2280
	11th to 20th	Day	38% 5% 11% 23% 21% 1	2253
	21st to end	Day	46% 6% 11% 20% 15% 2	2081
October	1st to 10th	Day	45% 7% 7% 22% 17% 2	3160
	11th to 20th	Day	39% 5% 8% 26% 17% 5%	3140
	21st to end	Day	35% 5% 17% 28% 13% 2	3250
November	1st to 10th	Day	41% 6% 13% 22% 16% 2	1761
	11th to 20th	Day	50% 6% 11% 19% 12% 2	1710
	21st to end	Day	52% 6% 14% 20% 7% 1	1520
December	1st to 10th	Day	59% 7% 14% 13% 7% 1	1520
	11th to 20th	Day	57% 5% 14% 17% 5% 1	1906
	21st to end	Day	67% 6% 9% 13% 5%	2772
January	1st to 10th	Night	51% 7% 13% 20% 8% 1	4429
	11th to 20th	Night	57% 5% 15% 17% 5% 1	4440
	21st to end	Night	63% 7% 8% 16% 6% 1	4582
February	1st to 10th	Night	52% 6% 13% 19% 9% 1	2470
	11th to 20th	Night	50% 7% 13% 18% 11% 2	2302
	21st to end	Night	52% 5% 10% 20% 10% 2	1884
March	1st to 10th	Night	55% 6% 11% 17% 10% 1	3734
	11th to 20th	Night	47% 7% 15% 22% 7% 1	3489
	21st to end	Night	48% 5% 9% 19% 17% 3	3576
April	1st to 10th	Night	52% 5% 11% 18% 12% 2	1900
	11th to 20th	Night	47% 5% 10% 21% 15%	1875
	21st to end	Night	46% 6% 10% 21% 14% 3	1900
May	1st to 10th	Night	53% 6% 9% 22% 8% 2	2717
	11th to 20th	Night	52% 7% 14% 18% 8% 1	2496
	21st to end	Night	41% 8% 14% 22% 14% 1	2739
June	1st to 10th	Night	42% 6% 12% 24% 15% 1	1520
	11th to 20th	Night	39% 7% 17% 27% 10% 1	1520
	21st to end	Night	33% 10% 17% 26% 13% 1	1520
July	1st to 10th	Night	39% 7% 16% 20% 16% 1	2480
	11th to 20th	Night	38% 6% 17% 26% 13% 1	2472
	21st to end	Night	42% 5% 14% 22% 16% 1	2651
August	1st to 10th	Night	48% 8% 16% 21% 7% 1	2751
	11th to 20th	Night	42% 7% 15% 26% 10%	3021
	21st to end	Night	34% 5% 13% 34% 14%	3476
September	1st to 10th	Night	38% 7% 12% 26% 16% 1	1900
	11th to 20th	Night	33% 5% 12% 27% 22% 1	1925
	21st to end	Night	44% 5% 9% 22% 18% 1	2097
October	1st to 10th	Night	44% 6% 10% 24% 15% 1	3800
	11th to 20th	Night	34% 5% 12% 24% 19% 6%	3779
	21st to end	Night	36% 5% 17% 27% 15% 1	4298
November	1st to 10th	Night	40% 5% 12% 22% 18% 2	2537
	11th to 20th	Night	46% 5% 13% 20% 13% 3	2488
	21st to end	Night	46% 6% 16% 23% 9% 1	2660
December	1st to 10th	Night	54% 8% 12% 18% 6%	2660
	11th to 20th	Night	54% 6% 14% 17% 9% 1	3288
	21st to end	Night	60% 7% 13% 15% 5%	4884

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	34% 23% 27% 14% 1 1	180
	11th to 20th	Day	40% 24% 25% 9% 2	180
	21st to end	Day	28% 27% 30% 10% 4 1	285
February	1st to 10th	Day	34% 26% 32% 6% 2	270
	11th to 20th	Day	37% 25% 31% 6% 1	373
	21st to end	Day	38% 21% 27% 12% 2	382
March	1st to 10th	Day	34% 19% 28% 16% 3	460
	11th to 20th	Day	32% 24% 27% 13% 4 1	460
	21st to end	Day	34% 24% 25% 10% 5% 1	506
April	1st to 10th	Day	33% 22% 28% 12% 4 1	460
	11th to 20th	Day	29% 24% 25% 11% 9% 2	452
	21st to end	Day	30% 19% 30% 13% 6% 2	460
May	1st to 10th	Day	37% 13% 25% 14% 8% 2	463
	11th to 20th	Day	23% 17% 29% 20% 8% 3	487
	21st to end	Day	19% 12% 28% 22% 14% 5%	529
June	1st to 10th	Day	21% 12% 33% 20% 11% 3	490
	11th to 20th	Day	19% 13% 27% 24% 14% 3	490
	21st to end	Day	18% 13% 31% 24% 10% 3	490
July	1st to 10th	Day	13% 6% 29% 28% 17% 5%	485
	11th to 20th	Day	10% 9% 26% 33% 18% 3	484
	21st to end	Day	15% 8% 36% 25% 12% 4	532
August	1st to 10th	Day	15% 7% 26% 26% 19% 7%	486
	11th to 20th	Day	15% 9% 24% 29% 17% 6%	479
	21st to end	Day	17% 9% 25% 26% 13% 10%	539
September	1st to 10th	Day	23% 11% 20% 21% 18% 8%	490
	11th to 20th	Day	15% 9% 25% 23% 17% 11%	490
	21st to end	Day	25% 10% 27% 21% 13% 4	490
October	1st to 10th	Day	26% 13% 21% 21% 14% 6%	490
	11th to 20th	Day	22% 16% 30% 23% 8% 2	490
	21st to end	Day	30% 17% 27% 18% 8% 1	484
November	1st to 10th	Day	25% 17% 24% 19% 12% 3	395
	11th to 20th	Day	31% 22% 24% 16% 6% 1	364
	21st to end	Day	33% 22% 29% 13% 3	180
December	1st to 10th	Day	32% 25% 28% 8% 7%	180
	11th to 20th	Day	39% 19% 29% 9% 3	180
	21st to end	Day	32% 25% 26% 13% 3 1	198
January	1st to 10th	Night	26% 23% 31% 16% 3	760
	11th to 20th	Night	28% 19% 31% 19% 3	760
	21st to end	Night	22% 24% 35% 16% 3	836
February	1st to 10th	Night	28% 19% 34% 17% 1	760
	11th to 20th	Night	27% 25% 34% 13% 1	743
	21st to end	Night	30% 21% 32% 14% 3	628
March	1st to 10th	Night	27% 22% 31% 16% 3	760
	11th to 20th	Night	28% 21% 29% 19% 3	760
	21st to end	Night	23% 23% 31% 17% 5% 1	836
April	1st to 10th	Night	26% 20% 32% 18% 3	760
	11th to 20th	Night	23% 17% 34% 19% 6% 1	751
	21st to end	Night	24% 17% 30% 22% 6%	760
May	1st to 10th	Night	30% 13% 25% 24% 8% 1	499
	11th to 20th	Night	22% 9% 32% 28% 9% 1	374
	21st to end	Night	18% 7% 24% 36% 15% 1	411
June	1st to 10th	Night	17% 6% 25% 35% 16% 1	380
	11th to 20th	Night	15% 9% 26% 34% 17%	380
	21st to end	Night	12% 5% 22% 46% 15%	380
July	1st to 10th	Night	12% 5% 20% 40% 21% 2	370
	11th to 20th	Night	13% 4 18% 46% 18% 1	368
	21st to end	Night	16% 6% 19% 39% 20%	416
August	1st to 10th	Night	15% 2 19% 40% 21% 3	529
	11th to 20th	Night	16% 4 13% 40% 23% 3	682
	21st to end	Night	18% 6% 16% 33% 26% 2	836
September	1st to 10th	Night	17% 8% 23% 28% 21% 3	760
	11th to 20th	Night	17% 6% 21% 28% 23% 5%	760
	21st to end	Night	21% 8% 22% 31% 16% 3	760
October	1st to 10th	Night	24% 12% 20% 24% 18% 1	760
	11th to 20th	Night	23% 13% 25% 29% 9%	760
	21st to end	Night	28% 17% 28% 21% 6%	836
November	1st to 10th	Night	18% 15% 31% 25% 9% 1	780
	11th to 20th	Night	27% 18% 25% 23% 6% 1	765
	21st to end	Night	21% 19% 32% 22% 5% 1	760
December	1st to 10th	Night	29% 20% 30% 17% 4	760
	11th to 20th	Night	26% 22% 29% 20% 3	760
	21st to end	Night	29% 22% 30% 18% 2	836

Page generated at 2024-11-08 22:45:40. Version ac07

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