Harding Hill Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Harding Hill Observatory clear sky chart from 2005-11-06 to 2025-02-21.

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	17% 8% 2 6% 4 4 4 4 5% 7% 38%	108385
	Night	17% 8% 2 6% 4 4 4 4 5% 6% 39%	110184
Transparency	Day	44% 5% 11% 22% 15% 3	111940
	Night	44% 5% 10% 23% 15% 3	114780
Seeing	Day	22% 13% 29% 22% 10% 3	15208
	Night	21% 10% 30% 29% 9% 1	24183

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% 7% 3 6% 5% 5% 5% 4 7% 7% 38%	3597
	11th to 20th	Day	12% 8% 3 7% 4 3 3 4 5% 6% 45%	3570
	21st to end	Day	12% 10% 2 6% 4 4 3 3 4 5% 46%	3960
February	1st to 10th	Day	15% 11% 2 7% 4 4 5% 4 6% 6% 37%	1772
	11th to 20th	Day	12% 8% 3 7% 6% 5% 4 4 5% 7% 39%	1948
	21st to end	Day	16% 11% 3 7% 4 5% 5% 4 4 5% 36%	1570
March	1st to 10th	Day	24% 15% 3 7% 4 4 3 4 4 4 29%	3116
	11th to 20th	Day	15% 8% 3 6% 5% 5% 5% 4 6% 6% 39%	3372
	21st to end	Day	22% 11% 2 5% 4 3 3 2 5% 6% 35%	3974
April	1st to 10th	Day	20% 11% 3 6% 4 3 3 3 4 6% 37%	2280
	11th to 20th	Day	17% 7% 3 6% 5% 4 4 5% 5% 6% 39%	2318
	21st to end	Day	23% 8% 3 6% 5% 5% 4 3 4 5% 34%	2470
May	1st to 10th	Day	24% 12% 2 8% 5% 4 4 4 5% 5% 27%	4106
	11th to 20th	Day	20% 8% 3 8% 5% 4 4 4 5% 6% 32%	4203
	21st to end	Day	15% 6% 2 6% 4 4 6% 5% 6% 9% 38%	4837
June	1st to 10th	Day	22% 8% 3 6% 4 4 5% 4 5% 8% 32%	2660
	11th to 20th	Day	17% 6% 2 7% 5% 5% 4 4 6% 7% 38%	2660
	21st to end	Day	21% 7% 3 6% 5% 5% 5% 4 6% 7% 31%	2660
July	1st to 10th	Day	14% 7% 2 6% 5% 4 5% 5% 7% 9% 35%	4440
	11th to 20th	Day	12% 5% 2 6% 4 5% 5% 5% 8% 11% 37%	4440
	21st to end	Day	19% 6% 3 6% 4 4 5% 4 6% 8% 35%	4814
August	1st to 10th	Day	15% 6% 2 8% 5% 5% 5% 4 6% 8% 35%	4180
	11th to 20th	Day	17% 8% 3 7% 5% 4 5% 4 6% 7% 34%	4045
	21st to end	Day	10% 5% 2 5% 5% 4 4 5% 7% 9% 44%	4258
September	1st to 10th	Day	12% 4 2 4 3 4 4 4 6% 8% 48%	2261
	11th to 20th	Day	13% 6% 1 4 3 3 3 3 4 5% 54%	2090
	21st to end	Day	17% 4 2 5% 4 4 5% 3 5% 6% 46%	2090
October	1st to 10th	Day	20% 7% 2 7% 4 4 3 3 4 6% 39%	2090
	11th to 20th	Day	17% 6% 2 5% 4 4 4 3 4 6% 45%	1823
	21st to end	Day	24% 7% 2 5% 4 4 3 3 5% 4 39%	1881
November	1st to 10th	Day	16% 6% 2 5% 3 2 4 3 5% 7% 48%	1761
	11th to 20th	Day	19% 5% 2 4 3 3 4 4 6% 6% 45%	1800
	21st to end	Day	22% 7% 3 4 3 2 4 3 5% 5% 42%	1793
December	1st to 10th	Day	17% 9% 2 6% 5% 4 4 5% 5% 7% 35%	2600
	11th to 20th	Day	19% 7% 2 5% 3 3 3 3 5% 6% 44%	2986
	21st to end	Day	20% 10% 3 5% 4 4 4 4 5% 5% 36%	3960
January	1st to 10th	Night	13% 7% 3 6% 4 4 4 4 6% 7% 42%	6349
	11th to 20th	Night	12% 9% 3 10% 5% 5% 5% 4 5% 6% 36%	6315
	21st to end	Night	14% 8% 3 6% 4 4 4 4 5% 6% 41%	6996
February	1st to 10th	Night	15% 10% 3 7% 5% 4 5% 3 5% 6% 37%	2623
	11th to 20th	Night	12% 10% 2 6% 4 5% 5% 4 5% 5% 42%	2338
	21st to end	Night	14% 9% 2 7% 5% 4 4 3 6% 6% 40%	1885
March	1st to 10th	Night	26% 12% 2 5% 4 4 3 3 4 4 33%	3724
	11th to 20th	Night	12% 8% 3 8% 5% 6% 6% 5% 6% 6% 35%	3586
	21st to end	Night	23% 9% 3 6% 3 4 4 3 6% 7% 32%	3641
April	1st to 10th	Night	19% 10% 2 6% 5% 3 3 3 5% 6% 36%	1900
	11th to 20th	Night	18% 7% 3 7% 4 4 4 4 4 6% 38%	1811
	21st to end	Night	22% 7% 2 5% 4 4 4 4 5% 6% 36%	1710
May	1st to 10th	Night	24% 10% 3 8% 5% 4 4 5% 6% 6% 26%	2834
	11th to 20th	Night	17% 8% 3 8% 6% 6% 6% 4 7% 7% 26%	2718
	21st to end	Night	15% 7% 2 7% 5% 4 3 3 5% 7% 41%	2738
June	1st to 10th	Night	21% 7% 3 7% 4 4 4 3 6% 7% 34%	1520
	11th to 20th	Night	18% 7% 2 4 4 4 4 4 5% 8% 39%	1520
	21st to end	Night	21% 6% 2 6% 5% 4 3 3 5% 8% 36%	1520
July	1st to 10th	Night	12% 5% 2 7% 5% 5% 5% 5% 8% 9% 37%	2520
	11th to 20th	Night	14% 5% 2 6% 5% 4 4 4 6% 9% 42%	2520
	21st to end	Night	16% 6% 2 5% 4 4 4 3 7% 8% 42%	2739
August	1st to 10th	Night	22% 7% 3 7% 5% 4 4 4 4 7% 34%	2716
	11th to 20th	Night	16% 8% 3 7% 4 4 5% 4 5% 7% 37%	2782
	21st to end	Night	10% 4 1 6% 4 5% 4 3 6% 9% 48%	3396
September	1st to 10th	Night	13% 5% 2 4 4 4 4 4 5% 6% 50%	1919
	11th to 20th	Night	14% 6% 1 5% 3 2 3 3 5% 6% 52%	2090
	21st to end	Night	15% 6% 3 5% 3 4 3 3 5% 7% 47%	2090
October	1st to 10th	Night	19% 7% 2 7% 4 4 5% 3 5% 6% 38%	2090
	11th to 20th	Night	16% 6% 2 6% 4 4 5% 4 5% 6% 42%	2351
	21st to end	Night	24% 8% 2 4 4 3 4 3 4 6% 37%	2717
November	1st to 10th	Night	15% 7% 2 6% 4 3 4 4 4 7% 45%	2537
	11th to 20th	Night	17% 7% 2 5% 3 4 4 3 5% 6% 45%	2600
	21st to end	Night	17% 8% 2 5% 4 4 3 3 5% 5% 43%	2605
December	1st to 10th	Night	16% 11% 3 7% 4 4 3 3 5% 6% 38%	4580
	11th to 20th	Night	24% 7% 2 5% 4 3 3 3 4 5% 40%	5208
	21st to end	Night	20% 11% 3 7% 4 4 4 2 4 5% 37%	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	43% 5% 8% 28% 16% 1	3598
	11th to 20th	Day	41% 5% 12% 26% 13% 4	3600
	21st to end	Day	41% 4 7% 22% 19% 6%	3960
February	1st to 10th	Day	47% 4 11% 20% 14% 4	1772
	11th to 20th	Day	44% 5% 11% 21% 15% 4	1957
	21st to end	Day	51% 4 9% 19% 14% 4	1570
March	1st to 10th	Day	59% 4 8% 12% 14% 3	3119
	11th to 20th	Day	41% 7% 12% 18% 17% 5%	3372
	21st to end	Day	50% 3 5% 15% 20% 7%	3974
April	1st to 10th	Day	48% 4 8% 20% 16% 4	2280
	11th to 20th	Day	44% 6% 10% 22% 16% 3	2318
	21st to end	Day	52% 4 7% 17% 15% 4	2470
May	1st to 10th	Day	56% 8% 9% 16% 10% 1	4120
	11th to 20th	Day	51% 6% 14% 17% 10% 2	4207
	21st to end	Day	40% 8% 14% 21% 16% 2	4837
June	1st to 10th	Day	50% 5% 11% 22% 11%	2660
	11th to 20th	Day	43% 5% 11% 21% 17% 3	2660
	21st to end	Day	51% 6% 11% 19% 12% 1	2660
July	1st to 10th	Day	43% 6% 12% 25% 13% 1	4370
	11th to 20th	Day	39% 7% 15% 27% 12% 1	4365
	21st to end	Day	46% 5% 11% 21% 15% 1	4661
August	1st to 10th	Day	45% 6% 14% 23% 11%	4166
	11th to 20th	Day	48% 5% 14% 24% 8% 1	4084
	21st to end	Day	34% 7% 13% 25% 19% 2	4258
September	1st to 10th	Day	33% 6% 12% 29% 19% 1	2261
	11th to 20th	Day	33% 3 9% 30% 23% 3	2090
	21st to end	Day	38% 5% 9% 28% 19% 2	2090
October	1st to 10th	Day	46% 5% 8% 23% 17% 1	3480
	11th to 20th	Day	33% 3 9% 30% 23% 2	3000
	21st to end	Day	37% 3 9% 27% 21% 4	3081
November	1st to 10th	Day	36% 4 13% 26% 17% 3	1761
	11th to 20th	Day	38% 4 9% 22% 22% 5%	1800
	21st to end	Day	45% 4 15% 21% 14% 1	1793
December	1st to 10th	Day	46% 4 11% 27% 10% 1	2600
	11th to 20th	Day	41% 4 10% 19% 19% 7%	2986
	21st to end	Day	50% 4 8% 19% 13% 6%	3960
January	1st to 10th	Night	40% 4 10% 30% 13% 2	6349
	11th to 20th	Night	48% 5% 11% 20% 12% 3	6360
	21st to end	Night	44% 4 8% 19% 18% 7%	6996
February	1st to 10th	Night	48% 5% 11% 17% 16% 3	2623
	11th to 20th	Night	44% 5% 9% 22% 17% 4	2340
	21st to end	Night	44% 4 10% 22% 14% 5%	1885
March	1st to 10th	Night	55% 3 9% 17% 12% 3	3734
	11th to 20th	Night	44% 8% 9% 19% 15% 3	3587
	21st to end	Night	51% 4 5% 14% 20% 6%	3641
April	1st to 10th	Night	49% 4 8% 20% 16% 4	1900
	11th to 20th	Night	46% 5% 7% 22% 19% 2	1811
	21st to end	Night	47% 6% 10% 17% 16% 4	1710
May	1st to 10th	Night	56% 7% 10% 17% 8% 2	2840
	11th to 20th	Night	52% 8% 12% 18% 7% 2	2719
	21st to end	Night	41% 7% 16% 21% 13% 2	2739
June	1st to 10th	Night	48% 6% 11% 21% 12% 1	1520
	11th to 20th	Night	44% 6% 14% 20% 15% 2	1520
	21st to end	Night	47% 6% 13% 23% 9% 2	1520
July	1st to 10th	Night	41% 7% 17% 21% 13% 1	2480
	11th to 20th	Night	39% 7% 13% 24% 16%	2472
	21st to end	Night	41% 5% 11% 29% 13% 1	2651
August	1st to 10th	Night	50% 7% 13% 20% 9%	2706
	11th to 20th	Night	45% 6% 15% 22% 12%	2809
	21st to end	Night	32% 6% 15% 28% 18% 1	3396
September	1st to 10th	Night	34% 6% 12% 29% 18% 1	1919
	11th to 20th	Night	33% 5% 10% 28% 21% 2	2090
	21st to end	Night	37% 4 10% 31% 17% 2	2090
October	1st to 10th	Night	45% 5% 11% 23% 14% 1	3480
	11th to 20th	Night	33% 4 9% 27% 25% 3	3900
	21st to end	Night	39% 4 8% 28% 18% 3	4467
November	1st to 10th	Night	40% 4 10% 26% 17% 2	2537
	11th to 20th	Night	40% 4 9% 25% 19% 3	2600
	21st to end	Night	43% 4 13% 24% 14% 1	2605
December	1st to 10th	Night	47% 4 8% 30% 11% 1	4580
	11th to 20th	Night	47% 4 9% 16% 20% 3	5208
	21st to end	Night	51% 4 7% 21% 16% 2	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	25% 18% 30% 21% 6% 1	200
	11th to 20th	Day	24% 20% 25% 25% 6% 2	200
	21st to end	Day	19% 17% 36% 21% 7%	220
February	1st to 10th	Day	26% 19% 35% 17% 3	350
	11th to 20th	Day	22% 21% 35% 18% 4	496
	21st to end	Day	25% 17% 30% 24% 5%	382
March	1st to 10th	Day	26% 15% 32% 23% 4	460
	11th to 20th	Day	23% 20% 32% 17% 7% 1	460
	21st to end	Day	26% 16% 32% 15% 8% 2	506
April	1st to 10th	Day	28% 20% 27% 17% 6% 2	460
	11th to 20th	Day	25% 19% 30% 16% 8% 2	452
	21st to end	Day	29% 18% 29% 15% 7% 2	460
May	1st to 10th	Day	30% 16% 27% 20% 5% 2	463
	11th to 20th	Day	20% 15% 36% 18% 8% 3	487
	21st to end	Day	20% 12% 31% 24% 10% 2	529
June	1st to 10th	Day	21% 11% 34% 22% 10% 2	490
	11th to 20th	Day	16% 12% 33% 25% 10% 3	490
	21st to end	Day	23% 11% 31% 20% 12% 2	490
July	1st to 10th	Day	18% 8% 29% 27% 14% 4	485
	11th to 20th	Day	13% 6% 33% 30% 14% 5%	484
	21st to end	Day	16% 5% 28% 31% 16% 4	532
August	1st to 10th	Day	13% 7% 25% 29% 20% 5%	486
	11th to 20th	Day	15% 7% 27% 30% 14% 8%	479
	21st to end	Day	12% 9% 25% 31% 17% 7%	539
September	1st to 10th	Day	15% 8% 27% 26% 17% 7%	490
	11th to 20th	Day	17% 10% 25% 21% 16% 11%	490
	21st to end	Day	17% 10% 28% 26% 14% 6%	490
October	1st to 10th	Day	24% 11% 22% 22% 15% 5%	490
	11th to 20th	Day	18% 14% 27% 22% 15% 2	411
	21st to end	Day	31% 11% 26% 24% 8%	429
November	1st to 10th	Day	22% 14% 30% 23% 9% 2	395
	11th to 20th	Day	27% 14% 30% 21% 7% 1	400
	21st to end	Day	30% 15% 27% 21% 6% 1	393
December	1st to 10th	Day	26% 16% 30% 19% 11%	200
	11th to 20th	Day	27% 19% 35% 15% 5%	200
	21st to end	Day	27% 17% 28% 20% 8%	220
January	1st to 10th	Night	19% 13% 39% 25% 4	800
	11th to 20th	Night	24% 15% 32% 25% 4	800
	21st to end	Night	17% 15% 38% 25% 5% 1	880
February	1st to 10th	Night	22% 13% 37% 25% 2	800
	11th to 20th	Night	19% 15% 39% 24% 3	783
	21st to end	Night	21% 11% 36% 28% 4	629
March	1st to 10th	Night	24% 12% 35% 25% 3	760
	11th to 20th	Night	21% 14% 35% 24% 6%	760
	21st to end	Night	26% 11% 33% 22% 7% 1	836
April	1st to 10th	Night	25% 13% 31% 27% 4	760
	11th to 20th	Night	22% 11% 35% 26% 5%	687
	21st to end	Night	25% 15% 29% 27% 5%	570
May	1st to 10th	Night	24% 10% 29% 30% 6% 1	570
	11th to 20th	Night	20% 13% 27% 30% 9%	506
	21st to end	Night	21% 6% 25% 36% 11% 1	411
June	1st to 10th	Night	25% 5% 27% 31% 12%	380
	11th to 20th	Night	19% 6% 24% 37% 13%	380
	21st to end	Night	23% 2 23% 40% 11% 1	380
July	1st to 10th	Night	15% 4 20% 44% 18%	370
	11th to 20th	Night	14% 3 20% 43% 19% 1	368
	21st to end	Night	14% 3 17% 48% 16% 1	416
August	1st to 10th	Night	16% 3 20% 43% 18%	497
	11th to 20th	Night	15% 5% 25% 33% 19% 2	562
	21st to end	Night	15% 4 22% 36% 20% 2	782
September	1st to 10th	Night	15% 3 28% 35% 18% 1	760
	11th to 20th	Night	18% 6% 23% 29% 20% 4	760
	21st to end	Night	17% 7% 27% 28% 19% 2	760
October	1st to 10th	Night	22% 9% 22% 31% 15% 1	760
	11th to 20th	Night	20% 8% 31% 28% 12% 1	760
	21st to end	Night	29% 9% 29% 27% 7%	836
November	1st to 10th	Night	20% 11% 31% 29% 7% 1	780
	11th to 20th	Night	22% 13% 33% 25% 7% 1	800
	21st to end	Night	22% 16% 34% 24% 5%	800
December	1st to 10th	Night	24% 9% 36% 25% 5% 1	800
	11th to 20th	Night	24% 13% 34% 24% 4	800
	21st to end	Night	26% 12% 33% 25% 4	880

Page generated at 2025-02-18 03:26:29. Version ac07

Copyright © 2025 Attilla Danko.