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 2024-01-13.

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% 8% 3 7% 6% 4 5% 5% 6% 7% 32%	74744
	Night	16% 8% 3 6% 5% 3 5% 5% 6% 8% 35%	74989
Transparency	Day	49% 7% 11% 20% 11% 1	74449
	Night	46% 7% 13% 21% 12% 1	74818
Seeing	Day	25% 16% 27% 19% 10% 3	13700
	Night	23% 15% 27% 24% 9% 1	23016

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	11% 10% 5% 9% 7% 5% 6% 4 7% 7% 28%	1517
	11th to 20th	Day	15% 11% 4 10% 8% 4 7% 5% 5% 7% 22%	1462
	21st to end	Day	12% 8% 5% 11% 9% 5% 6% 5% 5% 7% 28%	1757
February	1st to 10th	Day	17% 10% 4 10% 9% 4 7% 6% 6% 5% 22%	1620
	11th to 20th	Day	12% 11% 4 8% 7% 4 6% 5% 5% 9% 29%	1670
	21st to end	Day	19% 11% 4 8% 8% 4 4 3 6% 6% 27%	1480
March	1st to 10th	Day	12% 9% 5% 10% 8% 3 5% 4 5% 8% 31%	1797
	11th to 20th	Day	14% 10% 5% 8% 7% 4 5% 5% 5% 7% 31%	1969
	21st to end	Day	19% 9% 3 6% 7% 3 6% 5% 4 7% 31%	2306
April	1st to 10th	Day	17% 10% 4 7% 6% 3 5% 4 4 5% 34%	2160
	11th to 20th	Day	16% 9% 3 6% 6% 4 5% 4 5% 7% 36%	2134
	21st to end	Day	18% 8% 3 6% 7% 4 5% 4 4 6% 33%	2160
May	1st to 10th	Day	22% 9% 3 6% 6% 4 4 5% 5% 6% 32%	2418
	11th to 20th	Day	20% 6% 2 5% 6% 4 5% 5% 5% 7% 34%	2478
	21st to end	Day	15% 7% 2 5% 6% 3 6% 6% 6% 8% 37%	2725
June	1st to 10th	Day	16% 5% 3 7% 7% 4 6% 6% 6% 9% 32%	2520
	11th to 20th	Day	16% 7% 3 6% 7% 4 6% 6% 6% 8% 32%	2520
	21st to end	Day	14% 6% 3 6% 5% 4 5% 5% 6% 10% 35%	2520
July	1st to 10th	Day	10% 6% 3 7% 6% 5% 6% 7% 7% 10% 34%	2520
	11th to 20th	Day	10% 5% 2 6% 6% 4 6% 7% 8% 10% 37%	2520
	21st to end	Day	12% 6% 3 6% 8% 4 6% 6% 6% 9% 36%	2744
August	1st to 10th	Day	12% 5% 2 7% 7% 4 6% 6% 7% 10% 33%	2359
	11th to 20th	Day	14% 6% 3 7% 6% 5% 6% 6% 6% 9% 32%	2173
	21st to end	Day	16% 5% 2 6% 6% 4 6% 6% 6% 8% 36%	2376
September	1st to 10th	Day	17% 6% 3 6% 5% 4 4 5% 5% 8% 37%	2160
	11th to 20th	Day	14% 6% 2 5% 4 3 4 5% 5% 7% 44%	2135
	21st to end	Day	18% 5% 2 5% 5% 3 5% 5% 7% 7% 36%	1972
October	1st to 10th	Day	19% 7% 3 6% 6% 3 5% 5% 5% 7% 34%	1800
	11th to 20th	Day	16% 7% 3 6% 6% 4 4 5% 7% 7% 35%	1800
	21st to end	Day	23% 10% 3 7% 6% 3 5% 5% 5% 7% 27%	1882
November	1st to 10th	Day	13% 8% 3 7% 5% 3 4 5% 4 6% 42%	1671
	11th to 20th	Day	16% 10% 3 7% 7% 3 4 5% 5% 5% 34%	1701
	21st to end	Day	17% 9% 4 6% 8% 4 6% 4 6% 8% 29%	1520
December	1st to 10th	Day	18% 12% 5% 8% 7% 4 6% 5% 5% 6% 24%	1520
	11th to 20th	Day	21% 10% 5% 9% 6% 3 4 4 4 6% 29%	1906
	21st to end	Day	20% 14% 8% 10% 7% 4 5% 4 5% 5% 19%	2772
January	1st to 10th	Night	14% 9% 4 8% 6% 4 5% 5% 7% 8% 29%	2649
	11th to 20th	Night	17% 9% 4 8% 6% 3 5% 6% 6% 8% 27%	2560
	21st to end	Night	11% 9% 5% 7% 7% 5% 6% 6% 7% 8% 28%	2596
February	1st to 10th	Night	15% 10% 4 7% 7% 5% 5% 5% 5% 7% 30%	2340
	11th to 20th	Night	13% 8% 3 9% 7% 4 7% 6% 7% 8% 28%	2175
	21st to end	Night	17% 9% 4 7% 7% 4 6% 6% 4 6% 30%	1776
March	1st to 10th	Night	15% 7% 3 8% 6% 3 5% 5% 6% 8% 34%	2150
	11th to 20th	Night	14% 8% 3 6% 6% 3 5% 5% 5% 8% 35%	1988
	21st to end	Night	15% 8% 3 6% 6% 3 5% 5% 6% 7% 36%	2048
April	1st to 10th	Night	16% 10% 4 7% 6% 5% 6% 5% 5% 7% 31%	1800
	11th to 20th	Night	16% 9% 4 5% 6% 3 5% 4 5% 8% 37%	1775
	21st to end	Night	19% 7% 3 6% 5% 3 5% 5% 4 7% 36%	1800
May	1st to 10th	Night	22% 9% 3 6% 6% 3 4 4 4 6% 34%	1553
	11th to 20th	Night	16% 7% 3 5% 6% 2 5% 5% 6% 6% 38%	1415
	21st to end	Night	14% 7% 2 5% 4 3 5% 5% 6% 9% 41%	1550
June	1st to 10th	Night	16% 5% 3 5% 5% 3 5% 5% 5% 8% 41%	1440
	11th to 20th	Night	15% 5% 3 5% 5% 3 3 3 6% 10% 42%	1440
	21st to end	Night	10% 3 2 4 5% 3 5% 6% 7% 10% 45%	1440
July	1st to 10th	Night	11% 5% 3 5% 5% 3 5% 5% 6% 9% 43%	1440
	11th to 20th	Night	12% 5% 2 4 4 4 4 6% 8% 10% 42%	1440
	21st to end	Night	11% 6% 2 5% 6% 3 5% 5% 6% 9% 43%	1574
August	1st to 10th	Night	11% 4 2 5% 5% 2 6% 7% 7% 10% 41%	1575
	11th to 20th	Night	13% 5% 3 6% 7% 3 6% 5% 6% 8% 37%	1709
	21st to end	Night	15% 5% 3 4 5% 3 3 4 5% 8% 43%	1980
September	1st to 10th	Night	17% 5% 2 5% 5% 2 4 4 5% 7% 43%	1800
	11th to 20th	Night	15% 5% 2 3 3 3 3 4 5% 7% 50%	1823
	21st to end	Night	16% 5% 2 7% 5% 4 4 4 5% 6% 42%	1986
October	1st to 10th	Night	20% 7% 2 5% 4 3 4 4 6% 7% 39%	2160
	11th to 20th	Night	19% 8% 2 5% 4 3 3 4 5% 6% 40%	2160
	21st to end	Night	22% 10% 3 5% 4 3 4 5% 5% 9% 31%	2474
November	1st to 10th	Night	13% 8% 3 6% 5% 3 4 5% 5% 6% 43%	2407
	11th to 20th	Night	19% 7% 3 5% 5% 3 4 5% 6% 8% 36%	2474
	21st to end	Night	14% 7% 4 7% 5% 4 5% 5% 7% 8% 34%	2660
December	1st to 10th	Night	19% 8% 4 7% 7% 4 5% 6% 7% 7% 25%	2660
	11th to 20th	Night	18% 10% 4 7% 5% 4 6% 4 6% 7% 29%	3288
	21st to end	Night	23% 12% 6% 7% 5% 3 5% 5% 5% 7% 22%	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	54% 7% 9% 20% 8% 1	1518
	11th to 20th	Day	60% 7% 11% 14% 6% 3	1462
	21st to end	Day	56% 5% 10% 18% 10% 1	1757
February	1st to 10th	Day	60% 8% 10% 14% 8%	1620
	11th to 20th	Day	52% 6% 9% 21% 11% 1	1679
	21st to end	Day	57% 5% 9% 18% 9% 1	1480
March	1st to 10th	Day	51% 6% 13% 18% 9% 2	1800
	11th to 20th	Day	53% 5% 9% 21% 11% 2	1969
	21st to end	Day	53% 5% 8% 16% 15% 3	2306
April	1st to 10th	Day	52% 4 8% 22% 11% 3	2160
	11th to 20th	Day	47% 6% 11% 20% 14% 2	2134
	21st to end	Day	51% 6% 9% 20% 11% 4	2160
May	1st to 10th	Day	52% 5% 9% 19% 12% 2	2418
	11th to 20th	Day	49% 6% 9% 20% 13% 2	2482
	21st to end	Day	44% 8% 14% 20% 12% 2	2725
June	1st to 10th	Day	47% 7% 12% 20% 13%	2520
	11th to 20th	Day	48% 7% 12% 21% 10% 1	2520
	21st to end	Day	44% 7% 12% 26% 10%	2520
July	1st to 10th	Day	44% 9% 13% 21% 12% 1	2450
	11th to 20th	Day	39% 9% 14% 25% 13%	2445
	21st to end	Day	43% 8% 13% 21% 13% 2	2591
August	1st to 10th	Day	43% 9% 14% 23% 11%	2345
	11th to 20th	Day	46% 8% 13% 22% 9%	2173
	21st to end	Day	43% 8% 11% 23% 14% 2	2376
September	1st to 10th	Day	45% 6% 11% 23% 13% 1	2160
	11th to 20th	Day	39% 5% 11% 23% 21% 1	2135
	21st to end	Day	44% 6% 11% 22% 15% 2	1972
October	1st to 10th	Day	48% 7% 11% 20% 12% 2	1800
	11th to 20th	Day	46% 6% 12% 23% 12% 1	1800
	21st to end	Day	55% 6% 13% 16% 9% 2	1882
November	1st to 10th	Day	42% 6% 13% 22% 15% 2	1671
	11th to 20th	Day	50% 6% 11% 19% 12% 2	1701
	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	49% 7% 13% 18% 11% 2	2649
	11th to 20th	Night	53% 7% 14% 17% 7% 1	2560
	21st to end	Night	49% 8% 11% 19% 10% 2	2596
February	1st to 10th	Night	53% 6% 13% 18% 9% 1	2340
	11th to 20th	Night	51% 7% 12% 18% 10% 2	2177
	21st to end	Night	53% 5% 9% 19% 11% 2	1776
March	1st to 10th	Night	46% 7% 14% 20% 11% 2	2160
	11th to 20th	Night	48% 6% 12% 22% 12% 1	1989
	21st to end	Night	46% 6% 10% 19% 17% 3	2048
April	1st to 10th	Night	51% 5% 11% 19% 12% 2	1800
	11th to 20th	Night	46% 5% 11% 21% 16%	1775
	21st to end	Night	47% 6% 10% 21% 13% 3	1800
May	1st to 10th	Night	52% 6% 8% 20% 12% 2	1553
	11th to 20th	Night	45% 5% 11% 23% 15% 2	1416
	21st to end	Night	40% 7% 16% 24% 10% 2	1551
June	1st to 10th	Night	42% 5% 12% 24% 15% 1	1440
	11th to 20th	Night	40% 7% 17% 26% 10% 1	1440
	21st to end	Night	32% 11% 17% 27% 14% 1	1440
July	1st to 10th	Night	36% 9% 15% 25% 14% 2	1400
	11th to 20th	Night	36% 8% 16% 28% 11% 1	1392
	21st to end	Night	37% 7% 17% 22% 16% 2	1486
August	1st to 10th	Night	36% 10% 15% 28% 11% 1	1565
	11th to 20th	Night	41% 10% 16% 23% 11%	1709
	21st to end	Night	38% 7% 12% 24% 18% 1	1980
September	1st to 10th	Night	39% 8% 12% 26% 15% 1	1800
	11th to 20th	Night	34% 5% 12% 26% 23% 1	1823
	21st to end	Night	42% 5% 9% 23% 19% 1	1986
October	1st to 10th	Night	44% 7% 13% 22% 14% 1	2160
	11th to 20th	Night	43% 6% 14% 24% 10% 2	2160
	21st to end	Night	50% 6% 12% 21% 10% 1	2474
November	1st to 10th	Night	41% 6% 12% 22% 18% 2	2407
	11th to 20th	Night	46% 5% 13% 20% 13% 3	2474
	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	166
	21st to end	Day	28% 28% 30% 9% 4 1	254
February	1st to 10th	Day	36% 28% 29% 5% 2	240
	11th to 20th	Day	37% 26% 31% 5% 1	338
	21st to end	Day	39% 22% 26% 12% 2	346
March	1st to 10th	Day	33% 20% 29% 15% 2	420
	11th to 20th	Day	32% 24% 27% 12% 4 1	420
	21st to end	Day	34% 23% 26% 11% 5% 1	462
April	1st to 10th	Day	31% 23% 29% 12% 5% 1	420
	11th to 20th	Day	28% 23% 25% 12% 9% 2	412
	21st to end	Day	32% 19% 30% 12% 6% 2	420
May	1st to 10th	Day	37% 13% 26% 14% 8% 3	423
	11th to 20th	Day	24% 17% 30% 19% 7% 2	447
	21st to end	Day	20% 11% 27% 22% 15% 5%	485
June	1st to 10th	Day	22% 12% 33% 19% 11% 3	450
	11th to 20th	Day	20% 14% 27% 23% 13% 3	450
	21st to end	Day	17% 13% 32% 25% 10% 4	450
July	1st to 10th	Day	14% 7% 29% 28% 17% 6%	445
	11th to 20th	Day	10% 8% 26% 34% 18% 4	444
	21st to end	Day	15% 8% 35% 26% 12% 5%	488
August	1st to 10th	Day	14% 7% 26% 26% 20% 8%	446
	11th to 20th	Day	15% 8% 23% 29% 18% 6%	439
	21st to end	Day	16% 9% 25% 26% 14% 9%	495
September	1st to 10th	Day	24% 10% 20% 20% 18% 8%	450
	11th to 20th	Day	16% 10% 27% 22% 17% 10%	450
	21st to end	Day	22% 10% 28% 22% 14% 4	450
October	1st to 10th	Day	27% 12% 20% 20% 14% 6%	450
	11th to 20th	Day	22% 15% 30% 23% 8% 1	450
	21st to end	Day	32% 17% 26% 18% 7%	446
November	1st to 10th	Day	25% 17% 22% 20% 13% 3	365
	11th to 20th	Day	31% 22% 25% 16% 6% 1	361
	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% 18% 31% 20% 3	732
	21st to end	Night	21% 24% 35% 17% 3	792
February	1st to 10th	Night	29% 19% 33% 17% 1	720
	11th to 20th	Night	27% 25% 33% 14% 1	703
	21st to end	Night	30% 22% 31% 14% 2	592
March	1st to 10th	Night	27% 22% 32% 17% 3	720
	11th to 20th	Night	28% 20% 30% 19% 3	720
	21st to end	Night	22% 23% 32% 17% 5% 1	792
April	1st to 10th	Night	26% 21% 32% 18% 4	720
	11th to 20th	Night	22% 17% 35% 20% 6% 1	711
	21st to end	Night	25% 17% 30% 22% 6%	720
May	1st to 10th	Night	29% 14% 24% 24% 8% 1	473
	11th to 20th	Night	22% 10% 33% 26% 8% 1	354
	21st to end	Night	19% 7% 23% 36% 15% 1	389
June	1st to 10th	Night	18% 6% 25% 35% 16% 1	360
	11th to 20th	Night	16% 9% 25% 33% 17%	360
	21st to end	Night	12% 4 22% 48% 15%	360
July	1st to 10th	Night	12% 5% 20% 40% 22% 2	350
	11th to 20th	Night	13% 3 18% 46% 19% 1	348
	21st to end	Night	16% 6% 19% 39% 20%	394
August	1st to 10th	Night	13% 2 19% 41% 22% 3	501
	11th to 20th	Night	16% 4 13% 40% 24% 4	645
	21st to end	Night	18% 6% 16% 33% 26% 2	792
September	1st to 10th	Night	18% 7% 23% 29% 21% 3	720
	11th to 20th	Night	18% 6% 22% 28% 21% 5%	720
	21st to end	Night	19% 8% 23% 31% 16% 3	720
October	1st to 10th	Night	25% 11% 20% 25% 18% 1	720
	11th to 20th	Night	24% 13% 25% 30% 8%	720
	21st to end	Night	29% 17% 28% 20% 6%	792
November	1st to 10th	Night	18% 16% 30% 26% 9% 1	740
	11th to 20th	Night	27% 18% 25% 23% 6% 1	760
	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 2024-01-10 19:35:25. Version ac07

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