HRH Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the HRH Observatory clear sky chart from 2005-11-06 to 2024-11-05.

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	7% 5% 2 6% 5% 5% 6% 5% 8% 10% 40%	100865
	Night	7% 5% 2 7% 5% 5% 5% 5% 7% 10% 41%	98122
Transparency	Day	36% 11% 18% 19% 13% 4	104669
	Night	36% 10% 18% 20% 13% 4	102457
Seeing	Day	7% 4 17% 26% 27% 19%	15501
	Night	8% 3 16% 34% 29% 10%	25540

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	10% 8% 3 8% 4 4 5% 5% 7% 9% 38%	2836
	11th to 20th	Day	20% 10% 3 7% 4 3 4 3 6% 7% 34%	2840
	21st to end	Day	11% 6% 2 6% 4 4 4 5% 7% 9% 42%	3444
February	1st to 10th	Day	10% 5% 2 5% 4 5% 5% 3 7% 7% 47%	1900
	11th to 20th	Day	6% 4 1 4 4 3 4 4 6% 8% 55%	1848
	21st to end	Day	6% 5% 2 5% 4 4 4 4 5% 8% 55%	1627
March	1st to 10th	Day	6% 5% 2 8% 6% 5% 6% 5% 8% 8% 41%	3435
	11th to 20th	Day	5% 4 2 4 4 4 4 4 8% 11% 51%	3480
	21st to end	Day	8% 4 2 4 3 3 4 3 6% 9% 54%	3815
April	1st to 10th	Day	5% 2 2 4 4 4 5% 4 8% 10% 52%	2090
	11th to 20th	Day	6% 4 2 6% 4 5% 5% 4 6% 9% 48%	2066
	21st to end	Day	4 3 1 4 3 4 5% 5% 7% 9% 55%	2228
May	1st to 10th	Day	2 2 1 3 2 3 4 4 7% 10% 63%	4082
	11th to 20th	Day	7% 5% 2 5% 4 5% 5% 5% 8% 12% 42%	4081
	21st to end	Day	3 4 1 4 4 4 5% 4 6% 9% 58%	4476
June	1st to 10th	Day	8% 7% 2 9% 6% 6% 6% 6% 9% 12% 28%	2470
	11th to 20th	Day	6% 5% 2 7% 7% 8% 8% 6% 10% 12% 29%	2470
	21st to end	Day	7% 7% 3 8% 6% 7% 7% 8% 10% 11% 27%	2470
July	1st to 10th	Day	5% 5% 2 7% 7% 7% 9% 7% 10% 15% 26%	4120
	11th to 20th	Day	4 4 2 8% 7% 9% 10% 7% 12% 14% 23%	4120
	21st to end	Day	4 4 2 8% 7% 8% 9% 7% 12% 15% 23%	4466
August	1st to 10th	Day	5% 4 2 10% 7% 8% 8% 7% 9% 13% 26%	4012
	11th to 20th	Day	3 3 1 7% 5% 7% 9% 7% 11% 12% 35%	3702
	21st to end	Day	6% 4 2 9% 7% 8% 9% 8% 11% 13% 23%	3828
September	1st to 10th	Day	7% 5% 2 7% 7% 8% 9% 8% 11% 12% 24%	2090
	11th to 20th	Day	8% 6% 3 7% 6% 8% 9% 7% 9% 11% 25%	2090
	21st to end	Day	5% 6% 3 8% 7% 6% 7% 6% 9% 11% 32%	2090
October	1st to 10th	Day	8% 6% 3 9% 7% 5% 5% 4 7% 10% 36%	2090
	11th to 20th	Day	5% 5% 2 5% 5% 5% 6% 4 7% 10% 47%	1952
	21st to end	Day	7% 4 2 7% 4 4 5% 4 6% 9% 49%	2090
November	1st to 10th	Day	6% 4 2 5% 4 5% 5% 4 7% 8% 51%	1898
	11th to 20th	Day	7% 6% 3 6% 5% 5% 5% 3 7% 8% 46%	1900
	21st to end	Day	7% 5% 2 5% 5% 4 5% 5% 7% 9% 47%	1772
December	1st to 10th	Day	5% 5% 2 6% 5% 5% 5% 4 7% 10% 47%	1710
	11th to 20th	Day	9% 6% 2 6% 5% 5% 4 4 6% 7% 45%	2153
	21st to end	Day	10% 8% 3 9% 7% 5% 6% 3 5% 7% 36%	3124
January	1st to 10th	Night	11% 7% 3 8% 6% 6% 5% 4 7% 9% 34%	4109
	11th to 20th	Night	17% 11% 4 9% 4 4 4 3 6% 7% 30%	4120
	21st to end	Night	9% 6% 3 8% 5% 5% 6% 5% 8% 8% 38%	4208
February	1st to 10th	Night	9% 7% 2 6% 4 4 5% 4 5% 7% 47%	2280
	11th to 20th	Night	8% 5% 2 5% 4 4 4 3 5% 7% 52%	2218
	21st to end	Night	5% 5% 2 4 4 5% 5% 4 7% 8% 51%	1825
March	1st to 10th	Night	9% 7% 3 8% 5% 5% 5% 4 6% 8% 40%	3418
	11th to 20th	Night	3 4 1 5% 4 5% 5% 5% 9% 12% 47%	3480
	21st to end	Night	9% 4 2 5% 3 3 4 3 5% 7% 53%	3817
April	1st to 10th	Night	5% 4 1 4 4 4 4 4 8% 10% 53%	2090
	11th to 20th	Night	5% 4 2 5% 4 4 5% 5% 8% 9% 49%	2063
	21st to end	Night	4 3 2 4 4 4 4 4 7% 9% 56%	1957
May	1st to 10th	Night	3 3 1 4 4 4 5% 4 6% 9% 56%	2820
	11th to 20th	Night	6% 5% 2 6% 4 4 5% 4 6% 9% 49%	2812
	21st to end	Night	3 3 1 4 3 3 4 4 5% 8% 63%	3079
June	1st to 10th	Night	9% 6% 2 7% 5% 5% 5% 5% 7% 10% 38%	1710
	11th to 20th	Night	5% 4 2 6% 6% 6% 7% 6% 9% 13% 38%	1710
	21st to end	Night	5% 5% 3 8% 6% 5% 5% 7% 10% 14% 33%	1710
July	1st to 10th	Night	6% 6% 3 8% 7% 7% 7% 7% 10% 12% 27%	2840
	11th to 20th	Night	3 4 3 8% 7% 7% 8% 6% 11% 14% 28%	2840
	21st to end	Night	4 8% 4 12% 9% 9% 9% 7% 9% 10% 18%	3087
August	1st to 10th	Night	4 5% 3 8% 6% 5% 7% 6% 9% 13% 33%	2910
	11th to 20th	Night	3 4 2 6% 5% 5% 7% 7% 10% 17% 34%	3100
	21st to end	Night	6% 5% 3 8% 7% 8% 8% 7% 10% 14% 25%	3819
September	1st to 10th	Night	4 5% 3 7% 7% 6% 8% 6% 11% 15% 28%	2090
	11th to 20th	Night	8% 6% 2 9% 7% 7% 7% 6% 9% 11% 29%	2090
	21st to end	Night	7% 8% 3 9% 6% 5% 6% 6% 9% 10% 31%	2090
October	1st to 10th	Night	8% 5% 3 7% 5% 5% 7% 5% 7% 10% 38%	2090
	11th to 20th	Night	6% 5% 2 7% 4 4 4 4 6% 8% 49%	2225
	21st to end	Night	7% 5% 2 7% 4 4 4 4 6% 9% 48%	2508
November	1st to 10th	Night	6% 4 2 7% 5% 5% 5% 4 6% 8% 50%	2280
	11th to 20th	Night	7% 6% 2 6% 5% 4 4 4 5% 9% 48%	2280
	21st to end	Night	7% 5% 2 6% 4 5% 5% 4 6% 10% 46%	2403
December	1st to 10th	Night	6% 5% 2 6% 6% 5% 5% 4 6% 9% 47%	2470
	11th to 20th	Night	10% 6% 2 6% 4 4 4 4 6% 8% 46%	3042
	21st to end	Night	12% 8% 3 8% 6% 5% 6% 5% 6% 8% 35%	4532

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	39% 8% 11% 20% 17% 5%	2837
	11th to 20th	Day	49% 5% 6% 17% 18% 6%	2840
	21st to end	Day	36% 7% 10% 22% 20% 5%	3444
February	1st to 10th	Day	34% 7% 10% 21% 18% 10%	1900
	11th to 20th	Day	26% 6% 12% 22% 24% 10%	1858
	21st to end	Day	28% 5% 14% 19% 26% 9%	1627
March	1st to 10th	Day	36% 11% 14% 19% 15% 5%	3435
	11th to 20th	Day	24% 9% 17% 26% 18% 6%	3480
	21st to end	Day	26% 6% 11% 31% 19% 8%	3815
April	1st to 10th	Day	25% 9% 19% 26% 16% 6%	2090
	11th to 20th	Day	30% 9% 16% 18% 21% 6%	2066
	21st to end	Day	25% 7% 14% 24% 25% 6%	2228
May	1st to 10th	Day	14% 8% 20% 34% 19% 5%	4120
	11th to 20th	Day	30% 12% 22% 22% 13% 1	4085
	21st to end	Day	22% 8% 17% 35% 18% 1	4489
June	1st to 10th	Day	44% 13% 22% 17% 3	2470
	11th to 20th	Day	41% 14% 24% 18% 2	2470
	21st to end	Day	45% 16% 24% 13% 2	2470
July	1st to 10th	Day	43% 17% 31% 9% 1	4055
	11th to 20th	Day	44% 18% 33% 5%	4051
	21st to end	Day	43% 20% 26% 10%	4324
August	1st to 10th	Day	44% 15% 30% 8% 3	3999
	11th to 20th	Day	35% 16% 27% 16% 5%	3738
	21st to end	Day	44% 17% 28% 9% 1	3828
September	1st to 10th	Day	46% 18% 24% 10% 1	2090
	11th to 20th	Day	46% 16% 21% 13% 3	2090
	21st to end	Day	42% 14% 17% 17% 8% 2	2090
October	1st to 10th	Day	52% 11% 15% 10% 8% 4	3480
	11th to 20th	Day	27% 6% 12% 22% 30% 3	3218
	21st to end	Day	28% 5% 8% 26% 25% 8%	3428
November	1st to 10th	Day	29% 7% 12% 22% 18% 12%	1898
	11th to 20th	Day	34% 6% 11% 22% 19% 8%	1900
	21st to end	Day	31% 7% 14% 20% 20% 8%	1772
December	1st to 10th	Day	32% 7% 14% 26% 17% 5%	1710
	11th to 20th	Day	35% 6% 11% 19% 17% 11%	2150
	21st to end	Day	46% 7% 11% 18% 14% 3	3124
January	1st to 10th	Night	43% 8% 11% 19% 15% 4	4109
	11th to 20th	Night	52% 5% 9% 18% 12% 4	4120
	21st to end	Night	38% 8% 12% 17% 20% 5%	4208
February	1st to 10th	Night	34% 7% 11% 20% 20% 9%	2280
	11th to 20th	Night	29% 5% 11% 22% 22% 10%	2219
	21st to end	Night	28% 7% 14% 19% 26% 7%	1825
March	1st to 10th	Night	39% 9% 14% 19% 14% 4	3418
	11th to 20th	Night	24% 9% 23% 23% 17% 4	3480
	21st to end	Night	28% 6% 11% 27% 22% 6%	3817
April	1st to 10th	Night	23% 8% 20% 27% 15% 7%	2090
	11th to 20th	Night	26% 8% 17% 23% 21% 5%	2063
	21st to end	Night	23% 6% 15% 25% 26% 4	1957
May	1st to 10th	Night	19% 10% 18% 30% 17% 5%	2847
	11th to 20th	Night	27% 10% 20% 32% 10% 1	2813
	21st to end	Night	18% 8% 15% 37% 21% 1	3087
June	1st to 10th	Night	38% 10% 22% 23% 6%	1710
	11th to 20th	Night	33% 13% 30% 20% 4	1710
	21st to end	Night	35% 18% 27% 15% 5%	1710
July	1st to 10th	Night	45% 15% 31% 8% 1	2795
	11th to 20th	Night	42% 18% 33% 7%	2786
	21st to end	Night	55% 17% 21% 7%	2988
August	1st to 10th	Night	38% 16% 29% 11% 6%	2899
	11th to 20th	Night	31% 16% 35% 16% 2	3130
	21st to end	Night	44% 17% 31% 8% 1	3819
September	1st to 10th	Night	40% 19% 27% 13% 1	2090
	11th to 20th	Night	45% 14% 22% 16% 3	2090
	21st to end	Night	42% 14% 19% 17% 8% 1	2090
October	1st to 10th	Night	54% 10% 15% 10% 8% 4	3480
	11th to 20th	Night	28% 6% 11% 28% 24% 3	3698
	21st to end	Night	30% 6% 8% 27% 23% 5%	4120
November	1st to 10th	Night	30% 7% 12% 20% 20% 11%	2280
	11th to 20th	Night	33% 7% 12% 22% 19% 8%	2280
	21st to end	Night	32% 7% 13% 22% 19% 7%	2403
December	1st to 10th	Night	32% 7% 13% 27% 17% 4	2470
	11th to 20th	Night	34% 6% 11% 21% 17% 11%	3044
	21st to end	Night	43% 9% 14% 16% 14% 4	4532

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	10% 10% 36% 31% 13% 1	270
	11th to 20th	Day	10% 11% 31% 32% 12% 4	270
	21st to end	Day	11% 13% 44% 25% 6% 1	297
February	1st to 10th	Day	9% 11% 28% 36% 13% 3	270
	11th to 20th	Day	7% 7% 31% 34% 18% 4	270
	21st to end	Day	6% 5% 28% 39% 20% 3	282
March	1st to 10th	Day	5% 5% 38% 35% 16% 1	460
	11th to 20th	Day	7% 6% 28% 34% 24% 2	460
	21st to end	Day	6% 5% 29% 35% 21% 4	506
April	1st to 10th	Day	5% 6% 31% 36% 19% 2	460
	11th to 20th	Day	7% 7% 23% 39% 20% 4	452
	21st to end	Day	5% 2 22% 35% 32% 4	460
May	1st to 10th	Day	4 2 17% 36% 30% 11%	463
	11th to 20th	Day	9% 4 15% 30% 28% 15%	487
	21st to end	Day	5% 2 9% 25% 35% 24%	529
June	1st to 10th	Day	11% 2 10% 24% 31% 22%	490
	11th to 20th	Day	9% 1 7% 21% 30% 31%	490
	21st to end	Day	4 1 5% 12% 30% 47%	490
July	1st to 10th	Day	6% 2 10% 29% 52%	485
	11th to 20th	Day	5% 1 3 7% 35% 50%	484
	21st to end	Day	9% 2 5% 11% 27% 46%	532
August	1st to 10th	Day	7% 1 4 12% 34% 43%	486
	11th to 20th	Day	5% 1 3 10% 30% 51%	479
	21st to end	Day	9% 2 5% 17% 32% 36%	539
September	1st to 10th	Day	7% 2 4 14% 34% 39%	490
	11th to 20th	Day	7% 2 8% 19% 36% 29%	490
	21st to end	Day	6% 2 7% 20% 36% 30%	490
October	1st to 10th	Day	12% 2 13% 31% 32% 10%	490
	11th to 20th	Day	5% 3 17% 33% 31% 12%	490
	21st to end	Day	7% 5% 19% 33% 31% 6%	539
November	1st to 10th	Day	7% 3 17% 34% 32% 6%	472
	11th to 20th	Day	11% 5% 22% 35% 22% 6%	460
	21st to end	Day	8% 5% 24% 35% 23% 5%	332
December	1st to 10th	Day	5% 9% 29% 34% 17% 7%	270
	11th to 20th	Day	7% 7% 30% 30% 23% 3	270
	21st to end	Day	5% 7% 28% 37% 20% 4	297
January	1st to 10th	Night	11% 6% 26% 40% 17% 1	760
	11th to 20th	Night	12% 6% 23% 43% 16% 1	760
	21st to end	Night	11% 8% 30% 39% 12%	836
February	1st to 10th	Night	11% 6% 29% 37% 16%	760
	11th to 20th	Night	10% 5% 24% 42% 18% 1	743
	21st to end	Night	7% 4 22% 47% 20%	628
March	1st to 10th	Night	5% 5% 31% 45% 14% 1	760
	11th to 20th	Night	7% 4 24% 45% 19% 2	760
	21st to end	Night	5% 3 27% 44% 19% 1	836
April	1st to 10th	Night	5% 3 25% 46% 20% 1	760
	11th to 20th	Night	7% 4 23% 47% 18% 1	751
	21st to end	Night	5% 2 22% 47% 22% 1	760
May	1st to 10th	Night	3 1 11% 45% 37% 2	577
	11th to 20th	Night	7% 2 12% 40% 35% 4	561
	21st to end	Night	6% 2 7% 34% 45% 7%	617
June	1st to 10th	Night	10% 5% 25% 48% 13%	570
	11th to 20th	Night	5% 2 4 14% 51% 25%	570
	21st to end	Night	5% 2 3 10% 47% 33%	570
July	1st to 10th	Night	7% 1 3 5% 45% 39%	555
	11th to 20th	Night	4 1 2 7% 41% 45%	552
	21st to end	Night	5% 1 3 7% 46% 38%	624
August	1st to 10th	Night	5% 3 10% 46% 35%	567
	11th to 20th	Night	7% 1 8% 37% 47%	564
	21st to end	Night	11% 1 7% 15% 40% 27%	827
September	1st to 10th	Night	7% 1 4 16% 48% 24%	760
	11th to 20th	Night	10% 2 5% 20% 41% 21%	760
	21st to end	Night	11% 2 6% 26% 42% 14%	760
October	1st to 10th	Night	10% 2 12% 38% 31% 6%	760
	11th to 20th	Night	8% 3 13% 37% 35% 4	760
	21st to end	Night	10% 2 18% 39% 27% 3	836
November	1st to 10th	Night	8% 2 24% 43% 21% 3	760
	11th to 20th	Night	7% 4 22% 43% 22% 3	760
	21st to end	Night	8% 3 23% 45% 20% 1	760
December	1st to 10th	Night	9% 3 20% 39% 28% 1	760
	11th to 20th	Night	10% 4 22% 39% 23% 2	760
	21st to end	Night	10% 4 24% 40% 22% 1	836

Page generated at 2024-11-03 02:11:10. Version ac07

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