Hard Labor Creek Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hard Labor Creek Observatory clear sky chart from 2005-11-06 to 2025-10-19.

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	12% 6% 2 6% 4 4 5% 4 6% 8% 42%	126384
	Night	13% 6% 2 6% 4 4 4 4 6% 8% 44%	123327
Transparency	Day	38% 6% 11% 20% 18% 6%	130147
	Night	37% 5% 11% 19% 21% 8%	127633
Seeing	Day	17% 9% 22% 24% 19% 9%	16266
	Night	16% 8% 21% 30% 21% 4	26259

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	16% 8% 2 5% 3 3 3 2 4 4 49%	4056
	11th to 20th	Day	12% 6% 2 5% 3 2 3 3 4 6% 54%	4060
	21st to end	Day	22% 7% 2 7% 4 3 3 2 3 5% 42%	4540
February	1st to 10th	Day	15% 7% 2 7% 4 4 4 4 5% 6% 40%	2000
	11th to 20th	Day	22% 7% 2 4 3 4 4 4 4 4 42%	1948
	21st to end	Day	18% 7% 2 6% 4 4 4 3 5% 7% 41%	1650
March	1st to 10th	Day	21% 9% 3 7% 4 4 4 3 4 5% 37%	4725
	11th to 20th	Day	9% 5% 2 5% 4 4 4 3 5% 7% 52%	4980
	21st to end	Day	16% 6% 3 7% 4 4 3 3 4 5% 45%	5465
April	1st to 10th	Day	11% 6% 3 5% 5% 4 4 4 5% 6% 48%	2200
	11th to 20th	Day	10% 5% 2 6% 4 3 4 3 5% 7% 50%	2349
	21st to end	Day	9% 4 2 6% 4 4 4 4 5% 8% 51%	2600
May	1st to 10th	Day	12% 6% 3 7% 5% 5% 5% 4 6% 9% 39%	5862
	11th to 20th	Day	17% 7% 3 8% 5% 5% 6% 5% 7% 8% 30%	5861
	21st to end	Day	12% 6% 2 6% 4 4 4 4 6% 8% 42%	6433
June	1st to 10th	Day	9% 6% 2 7% 6% 6% 6% 5% 8% 10% 34%	2600
	11th to 20th	Day	4 4 2 6% 6% 5% 6% 6% 9% 11% 42%	2600
	21st to end	Day	5% 4 2 5% 6% 6% 6% 6% 8% 11% 41%	2600
July	1st to 10th	Day	6% 6% 3 8% 7% 7% 8% 6% 8% 11% 30%	5900
	11th to 20th	Day	5% 4 2 7% 5% 6% 6% 6% 10% 14% 35%	5900
	21st to end	Day	7% 8% 3 9% 7% 7% 7% 7% 9% 11% 26%	6424
August	1st to 10th	Day	12% 6% 2 7% 5% 6% 6% 5% 9% 12% 31%	4234
	11th to 20th	Day	7% 4 2 6% 5% 6% 6% 4 7% 10% 44%	4014
	21st to end	Day	8% 4 2 5% 4 4 4 4 6% 9% 49%	4246
September	1st to 10th	Day	10% 6% 3 7% 5% 6% 5% 5% 7% 9% 39%	2200
	11th to 20th	Day	14% 6% 2 5% 4 5% 4 4 6% 7% 42%	2200
	21st to end	Day	14% 6% 2 5% 5% 4 4 3 4 7% 46%	2200
October	1st to 10th	Day	13% 5% 2 4 3 3 3 3 4 6% 54%	2200
	11th to 20th	Day	11% 4 1 4 3 3 3 3 4 6% 58%	2030
	21st to end	Day	11% 5% 1 4 3 4 3 3 4 6% 56%	2090
November	1st to 10th	Day	13% 5% 2 5% 4 3 3 3 3 5% 54%	1848
	11th to 20th	Day	14% 5% 1 3 3 3 3 4 4 7% 52%	1800
	21st to end	Day	13% 5% 2 5% 4 4 4 3 5% 7% 49%	1800
December	1st to 10th	Day	16% 7% 2 5% 4 3 3 3 5% 5% 47%	2930
	11th to 20th	Day	16% 8% 2 5% 4 3 3 3 4 5% 44%	3373
	21st to end	Day	22% 6% 2 4 3 3 3 3 5% 6% 42%	4466
January	1st to 10th	Night	14% 5% 2 5% 3 3 3 2 5% 6% 52%	5889
	11th to 20th	Night	12% 7% 2 5% 4 4 4 3 5% 6% 48%	5900
	21st to end	Night	17% 8% 2 5% 4 3 4 3 4 6% 43%	6398
February	1st to 10th	Night	15% 6% 2 6% 5% 4 4 3 4 6% 47%	2400
	11th to 20th	Night	20% 8% 2 5% 4 3 3 3 4 5% 43%	2338
	21st to end	Night	16% 7% 2 6% 4 3 4 3 4 5% 45%	1980
March	1st to 10th	Night	21% 7% 2 6% 4 3 5% 3 5% 6% 37%	5125
	11th to 20th	Night	9% 5% 1 4 3 3 4 4 6% 8% 53%	4980
	21st to end	Night	15% 6% 2 5% 4 4 4 4 5% 6% 46%	5467
April	1st to 10th	Night	11% 4 2 5% 3 4 5% 5% 6% 8% 49%	2200
	11th to 20th	Night	12% 5% 1 5% 3 3 4 3 5% 8% 51%	2014
	21st to end	Night	8% 6% 2 5% 4 3 4 4 5% 8% 52%	1800
May	1st to 10th	Night	9% 6% 3 7% 5% 5% 5% 4 7% 10% 38%	4033
	11th to 20th	Night	18% 6% 2 6% 5% 5% 5% 4 6% 8% 34%	4032
	21st to end	Night	10% 5% 2 5% 3 4 4 4 7% 10% 44%	4421
June	1st to 10th	Night	7% 5% 2 7% 5% 5% 7% 5% 7% 11% 38%	1800
	11th to 20th	Night	5% 4 2 6% 4 5% 5% 5% 8% 12% 44%	1800
	21st to end	Night	6% 5% 2 5% 5% 7% 6% 5% 9% 12% 40%	1800
July	1st to 10th	Night	8% 6% 3 9% 6% 6% 6% 5% 7% 12% 30%	4058
	11th to 20th	Night	4 4 2 7% 6% 6% 7% 6% 10% 15% 32%	4057
	21st to end	Night	9% 8% 3 8% 7% 6% 7% 5% 8% 11% 28%	4427
August	1st to 10th	Night	10% 5% 2 7% 5% 6% 7% 6% 9% 13% 29%	2915
	11th to 20th	Night	7% 5% 2 7% 5% 5% 5% 5% 7% 10% 42%	3030
	21st to end	Night	7% 5% 2 5% 4 4 4 4 6% 8% 50%	3617
September	1st to 10th	Night	8% 5% 2 7% 4 5% 6% 5% 7% 11% 39%	2200
	11th to 20th	Night	12% 6% 2 7% 4 4 4 4 5% 9% 43%	2200
	21st to end	Night	12% 6% 2 7% 4 4 4 3 6% 8% 46%	2200
October	1st to 10th	Night	12% 5% 2 5% 4 4 3 4 5% 5% 52%	2200
	11th to 20th	Night	10% 5% 1 5% 3 3 3 3 4 4 59%	2327
	21st to end	Night	12% 4 1 3 3 4 4 3 4 5% 58%	2508
November	1st to 10th	Night	13% 6% 2 4 3 3 3 2 4 6% 54%	2449
	11th to 20th	Night	14% 5% 2 5% 3 3 3 3 4 6% 54%	2600
	21st to end	Night	14% 4 3 4 4 3 4 3 5% 7% 49%	2600
December	1st to 10th	Night	14% 6% 2 5% 3 4 3 3 3 5% 53%	4250
	11th to 20th	Night	16% 6% 2 5% 3 3 3 3 5% 6% 48%	4822
	21st to end	Night	20% 7% 2 6% 4 4 4 3 4 5% 42%	6490

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	38% 4 5% 20% 25% 9%	4057
	11th to 20th	Day	32% 3 4 21% 29% 12%	4060
	21st to end	Day	47% 2 4 17% 21% 9%	4540
February	1st to 10th	Day	44% 4 8% 20% 18% 6%	2000
	11th to 20th	Day	44% 3 6% 19% 22% 6%	1958
	21st to end	Day	42% 5% 7% 16% 21% 8%	1650
March	1st to 10th	Day	50% 4 6% 11% 21% 8%	4725
	11th to 20th	Day	31% 4 7% 14% 23% 20%	4980
	21st to end	Day	42% 3 6% 20% 21% 7%	5465
April	1st to 10th	Day	36% 4 10% 22% 21% 7%	2200
	11th to 20th	Day	34% 4 8% 20% 24% 9%	2349
	21st to end	Day	31% 6% 11% 26% 24% 3	2600
May	1st to 10th	Day	41% 6% 14% 23% 14% 2	5897
	11th to 20th	Day	49% 6% 15% 20% 9% 1	5865
	21st to end	Day	38% 8% 11% 23% 19% 2	6447
June	1st to 10th	Day	41% 10% 16% 21% 10% 2	2600
	11th to 20th	Day	31% 10% 18% 25% 15% 1	2600
	21st to end	Day	32% 11% 19% 22% 12% 3	2600
July	1st to 10th	Day	43% 9% 18% 23% 6% 1	5835
	11th to 20th	Day	35% 11% 28% 21% 3 1	5831
	21st to end	Day	47% 11% 17% 21% 4	6240
August	1st to 10th	Day	42% 8% 17% 28% 5%	4221
	11th to 20th	Day	33% 7% 16% 28% 14% 2	4053
	21st to end	Day	31% 7% 15% 25% 18% 4	4246
September	1st to 10th	Day	40% 7% 14% 18% 17% 4	2200
	11th to 20th	Day	40% 6% 11% 19% 21% 2	2200
	21st to end	Day	39% 4 11% 21% 20% 6%	2200
October	1st to 10th	Day	28% 3 6% 15% 36% 12%	3590
	11th to 20th	Day	18% 3 4 16% 29% 29%	3296
	21st to end	Day	24% 3 5% 22% 34% 13%	3428
November	1st to 10th	Day	34% 4 8% 15% 28% 12%	1848
	11th to 20th	Day	33% 4 6% 19% 27% 11%	1800
	21st to end	Day	35% 4 8% 20% 27% 7%	1800
December	1st to 10th	Day	39% 3 5% 18% 26% 9%	2930
	11th to 20th	Day	42% 4 8% 19% 19% 7%	3370
	21st to end	Day	42% 4 7% 23% 22% 2	4466
January	1st to 10th	Night	33% 3 5% 21% 30% 8%	5889
	11th to 20th	Night	36% 3 4 20% 27% 9%	5900
	21st to end	Night	43% 3 5% 15% 28% 7%	6398
February	1st to 10th	Night	40% 3 8% 19% 21% 9%	2400
	11th to 20th	Night	45% 4 5% 17% 21% 9%	2339
	21st to end	Night	41% 4 6% 17% 20% 12%	1980
March	1st to 10th	Night	47% 4 7% 14% 19% 8%	5125
	11th to 20th	Night	28% 4 8% 15% 26% 19%	4980
	21st to end	Night	38% 4 5% 20% 21% 11%	5467
April	1st to 10th	Night	32% 6% 11% 21% 22% 9%	2200
	11th to 20th	Night	32% 4 6% 23% 24% 11%	2014
	21st to end	Night	31% 5% 11% 25% 23% 6%	1800
May	1st to 10th	Night	39% 7% 17% 21% 13% 2	4060
	11th to 20th	Night	47% 6% 15% 19% 11% 1	4033
	21st to end	Night	34% 7% 14% 24% 19% 2	4429
June	1st to 10th	Night	38% 9% 18% 20% 14% 2	1800
	11th to 20th	Night	30% 9% 20% 27% 13% 2	1800
	21st to end	Night	33% 10% 21% 19% 14% 4	1800
July	1st to 10th	Night	46% 9% 20% 20% 4 1	4015
	11th to 20th	Night	36% 13% 29% 18% 4 1	4006
	21st to end	Night	47% 11% 21% 16% 4 1	4297
August	1st to 10th	Night	43% 9% 19% 24% 5%	2904
	11th to 20th	Night	36% 8% 19% 23% 13% 1	3057
	21st to end	Night	32% 7% 14% 25% 20% 2	3617
September	1st to 10th	Night	37% 9% 15% 18% 17% 4	2200
	11th to 20th	Night	38% 8% 12% 20% 18% 4	2200
	21st to end	Night	37% 5% 13% 18% 21% 7%	2200
October	1st to 10th	Night	30% 4 7% 14% 35% 10%	3590
	11th to 20th	Night	18% 3 4 16% 28% 32%	3800
	21st to end	Night	23% 3 4 21% 31% 19%	4120
November	1st to 10th	Night	33% 3 8% 17% 26% 13%	2449
	11th to 20th	Night	33% 3 6% 17% 28% 13%	2600
	21st to end	Night	35% 4 7% 19% 26% 9%	2600
December	1st to 10th	Night	35% 3 5% 18% 31% 8%	4250
	11th to 20th	Night	38% 3 12% 18% 23% 7%	4824
	21st to end	Night	45% 3 6% 26% 19% 2	6490

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% 22% 39% 12% 2	300
	11th to 20th	Day	26% 19% 35% 15% 4 1	300
	21st to end	Day	24% 22% 38% 12% 3	330
February	1st to 10th	Day	21% 18% 40% 17% 3	300
	11th to 20th	Day	40% 15% 30% 14% 1	300
	21st to end	Day	29% 19% 36% 14% 2	249
March	1st to 10th	Day	25% 17% 29% 23% 7%	402
	11th to 20th	Day	21% 15% 35% 21% 6% 1	500
	21st to end	Day	22% 15% 32% 22% 8% 1	550
April	1st to 10th	Day	20% 14% 33% 22% 10% 2	500
	11th to 20th	Day	14% 15% 30% 24% 15% 2	492
	21st to end	Day	14% 10% 25% 29% 18% 4	500
May	1st to 10th	Day	14% 13% 32% 24% 12% 6%	503
	11th to 20th	Day	16% 5% 24% 27% 17% 10%	527
	21st to end	Day	16% 6% 17% 27% 22% 12%	573
June	1st to 10th	Day	11% 3 18% 31% 25% 12%	530
	11th to 20th	Day	5% 4 17% 28% 27% 20%	530
	21st to end	Day	8% 3 15% 30% 27% 16%	530
July	1st to 10th	Day	9% 2 6% 25% 34% 24%	525
	11th to 20th	Day	9% 2 4 24% 37% 25%	524
	21st to end	Day	6% 3 6% 24% 38% 23%	576
August	1st to 10th	Day	17% 4 12% 22% 28% 18%	526
	11th to 20th	Day	13% 3 7% 21% 35% 21%	519
	21st to end	Day	14% 2 8% 25% 30% 20%	583
September	1st to 10th	Day	11% 3 13% 28% 29% 15%	530
	11th to 20th	Day	17% 3 11% 24% 32% 13%	530
	21st to end	Day	16% 5% 16% 26% 28% 8%	530
October	1st to 10th	Day	17% 3 22% 33% 16% 9%	530
	11th to 20th	Day	12% 9% 23% 27% 23% 5%	522
	21st to end	Day	14% 9% 24% 27% 22% 3	539
November	1st to 10th	Day	22% 5% 25% 30% 17% 2	386
	11th to 20th	Day	18% 16% 35% 25% 6% 1	300
	21st to end	Day	17% 13% 30% 26% 12% 2	300
December	1st to 10th	Day	30% 17% 30% 18% 5% 1	300
	11th to 20th	Day	26% 13% 33% 21% 6% 1	300
	21st to end	Day	32% 14% 30% 17% 5% 2	330
January	1st to 10th	Night	23% 18% 30% 24% 5% 1	800
	11th to 20th	Night	21% 16% 31% 25% 7%	800
	21st to end	Night	21% 16% 34% 25% 4	880
February	1st to 10th	Night	20% 13% 30% 32% 6%	800
	11th to 20th	Night	25% 17% 31% 25% 2	783
	21st to end	Night	20% 14% 35% 28% 3	660
March	1st to 10th	Night	17% 14% 31% 32% 6%	800
	11th to 20th	Night	19% 12% 34% 25% 9% 1	800
	21st to end	Night	16% 14% 31% 30% 9%	880
April	1st to 10th	Night	15% 14% 32% 27% 12% 1	800
	11th to 20th	Night	15% 12% 26% 31% 16% 1	633
	21st to end	Night	12% 7% 25% 36% 20% 1	600
May	1st to 10th	Night	10% 7% 26% 36% 20% 2	600
	11th to 20th	Night	14% 4 20% 35% 21% 5%	591
	21st to end	Night	14% 2 13% 33% 32% 6%	650
June	1st to 10th	Night	10% 3 13% 38% 34% 4	600
	11th to 20th	Night	7% 3 12% 29% 37% 12%	600
	21st to end	Night	8% 2 8% 35% 39% 8%	600
July	1st to 10th	Night	9% 3 6% 26% 44% 12%	585
	11th to 20th	Night	6% 1 3 25% 52% 13%	582
	21st to end	Night	7% 1 6% 30% 46% 10%	657
August	1st to 10th	Night	13% 4 5% 30% 40% 9%	597
	11th to 20th	Night	11% 3 7% 24% 45% 9%	594
	21st to end	Night	14% 4 6% 26% 39% 10%	678
September	1st to 10th	Night	11% 2 10% 30% 38% 10%	800
	11th to 20th	Night	15% 3 9% 27% 42% 5%	800
	21st to end	Night	15% 2 13% 31% 35% 4	800
October	1st to 10th	Night	14% 4 18% 35% 24% 6%	800
	11th to 20th	Night	12% 5% 21% 34% 24% 3	793
	21st to end	Night	15% 6% 19% 33% 23% 3	836
November	1st to 10th	Night	14% 8% 22% 33% 20% 2	780
	11th to 20th	Night	16% 10% 28% 30% 15% 1	800
	21st to end	Night	17% 11% 26% 31% 14% 1	800
December	1st to 10th	Night	19% 15% 25% 30% 9% 1	800
	11th to 20th	Night	20% 11% 28% 31% 10% 1	800
	21st to end	Night	28% 11% 24% 29% 8%	880

Page generated at 2025-10-16 01:50:28. Version ac07

Copyright © 2025 Attilla Danko.