High Peak Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the High Peak Observatory clear sky chart from 2005-11-06 to 2026-08-15.

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	13% 6% 2 6% 4 4 5% 4 6% 8% 42%	143533
	Night	14% 6% 2 6% 4 4 4 4 5% 7% 44%	138350
Transparency	Day	38% 7% 12% 20% 17% 6%	147205
	Night	38% 6% 11% 20% 19% 6%	142750
Seeing	Day	18% 9% 22% 26% 17% 9%	17547
	Night	16% 7% 22% 32% 19% 3	27578

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	14% 6% 2 5% 3 3 2 2 4 5% 53%	5258
	11th to 20th	Day	9% 5% 2 4 3 3 3 2 3 4 63%	5280
	21st to end	Day	17% 7% 3 6% 3 3 3 2 5% 5% 46%	5780
February	1st to 10th	Day	14% 5% 3 5% 4 4 3 3 6% 8% 44%	1895
	11th to 20th	Day	19% 7% 2 4 4 3 4 3 6% 7% 43%	2048
	21st to end	Day	18% 6% 2 6% 4 3 5% 4 5% 6% 43%	1735
March	1st to 10th	Day	20% 8% 2 5% 3 3 3 3 5% 6% 43%	5045
	11th to 20th	Day	10% 6% 2 5% 3 3 3 3 4 7% 54%	5090
	21st to end	Day	16% 5% 2 6% 4 4 3 3 4 6% 47%	5586
April	1st to 10th	Day	11% 4 2 5% 4 4 4 4 6% 7% 49%	2310
	11th to 20th	Day	14% 5% 1 4 4 3 4 4 5% 8% 48%	2488
	21st to end	Day	13% 5% 2 5% 5% 4 4 4 5% 8% 47%	2730
May	1st to 10th	Day	10% 7% 3 7% 5% 5% 6% 5% 7% 9% 37%	7616
	11th to 20th	Day	16% 6% 2 7% 5% 5% 4 4 6% 8% 38%	7626
	21st to end	Day	16% 6% 3 8% 5% 5% 5% 4 7% 9% 34%	8391
June	1st to 10th	Day	11% 5% 2 6% 6% 6% 6% 5% 7% 9% 36%	2730
	11th to 20th	Day	7% 5% 2 6% 6% 6% 6% 5% 9% 10% 39%	2730
	21st to end	Day	7% 5% 2 6% 5% 5% 7% 5% 9% 11% 39%	2730
July	1st to 10th	Day	5% 4 2 7% 6% 6% 7% 5% 9% 12% 37%	7680
	11th to 20th	Day	10% 6% 3 8% 6% 7% 6% 6% 9% 11% 29%	7680
	21st to end	Day	13% 7% 3 8% 7% 7% 7% 6% 8% 11% 25%	8340
August	1st to 10th	Day	18% 7% 3 7% 5% 5% 7% 5% 8% 10% 24%	4364
	11th to 20th	Day	10% 5% 2 6% 6% 5% 7% 5% 8% 11% 35%	4226
	21st to end	Day	7% 4 2 5% 4 4 5% 4 6% 10% 49%	4403
September	1st to 10th	Day	11% 5% 2 7% 5% 5% 5% 4 6% 9% 42%	2200
	11th to 20th	Day	16% 7% 2 6% 4 5% 5% 4 5% 7% 39%	2200
	21st to end	Day	19% 5% 2 7% 5% 4 5% 4 6% 6% 38%	2200
October	1st to 10th	Day	15% 5% 2 4 3 2 3 2 4 6% 54%	2108
	11th to 20th	Day	13% 4 2 4 3 3 3 2 4 5% 58%	2000
	21st to end	Day	15% 5% 1 4 3 2 3 2 3 4 57%	2200
November	1st to 10th	Day	14% 5% 1 4 3 2 3 3 4 5% 56%	2036
	11th to 20th	Day	13% 4 2 4 3 3 3 3 4 7% 54%	1890
	21st to end	Day	14% 4 1 3 4 3 4 3 5% 7% 52%	1890
December	1st to 10th	Day	13% 7% 2 4 3 3 4 3 5% 5% 52%	3020
	11th to 20th	Day	16% 5% 2 5% 4 3 4 3 5% 6% 46%	3463
	21st to end	Day	20% 6% 2 4 3 3 3 3 5% 7% 45%	4565
January	1st to 10th	Night	13% 6% 2 4 3 2 3 2 4 6% 56%	7635
	11th to 20th	Night	11% 5% 2 5% 3 3 3 2 4 4 59%	7680
	21st to end	Night	16% 6% 2 5% 3 4 4 4 5% 6% 47%	8401
February	1st to 10th	Night	14% 5% 2 5% 4 4 5% 4 5% 6% 46%	2719
	11th to 20th	Night	19% 7% 2 5% 3 3 4 3 4 5% 45%	2458
	21st to end	Night	15% 7% 2 5% 4 4 3 4 6% 6% 43%	2069
March	1st to 10th	Night	18% 6% 2 5% 3 3 4 3 4 6% 45%	5028
	11th to 20th	Night	9% 4 1 4 3 3 4 3 5% 8% 56%	5090
	21st to end	Night	14% 4 2 5% 4 4 4 4 6% 7% 46%	5588
April	1st to 10th	Night	11% 5% 2 5% 3 4 4 4 6% 7% 49%	2310
	11th to 20th	Night	12% 5% 1 4 3 3 4 3 6% 8% 49%	2098
	21st to end	Night	12% 5% 2 7% 4 4 3 3 5% 6% 50%	1890
May	1st to 10th	Night	12% 6% 2 7% 4 5% 5% 4 7% 10% 39%	5237
	11th to 20th	Night	15% 6% 3 7% 5% 5% 4 4 5% 8% 38%	5234
	21st to end	Night	19% 7% 3 8% 4 4 4 3 5% 8% 34%	5761
June	1st to 10th	Night	9% 6% 2 6% 5% 5% 6% 6% 8% 11% 36%	1890
	11th to 20th	Night	11% 6% 2 7% 5% 5% 5% 3 8% 9% 40%	1890
	21st to end	Night	7% 4 2 6% 6% 5% 7% 5% 8% 11% 40%	1890
July	1st to 10th	Night	6% 6% 2 7% 6% 6% 6% 6% 9% 12% 34%	5278
	11th to 20th	Night	12% 7% 3 8% 6% 6% 6% 5% 8% 11% 29%	5277
	21st to end	Night	13% 8% 3 10% 6% 6% 6% 5% 8% 10% 25%	5736
August	1st to 10th	Night	18% 9% 3 8% 6% 5% 5% 5% 8% 9% 25%	3005
	11th to 20th	Night	12% 7% 3 9% 6% 6% 6% 5% 7% 10% 29%	2911
	21st to end	Night	8% 5% 2 6% 5% 5% 5% 4 6% 9% 45%	3443
September	1st to 10th	Night	12% 6% 2 6% 5% 5% 4 4 5% 8% 44%	2200
	11th to 20th	Night	17% 6% 2 8% 4 4 5% 4 5% 7% 37%	2200
	21st to end	Night	20% 6% 2 6% 5% 5% 4 3 5% 5% 40%	2200
October	1st to 10th	Night	17% 5% 2 4 3 4 4 3 5% 5% 49%	2290
	11th to 20th	Night	14% 5% 2 4 3 3 3 3 4 5% 54%	2400
	21st to end	Night	14% 4 1 4 2 3 3 3 3 5% 58%	2640
November	1st to 10th	Night	14% 5% 2 4 4 3 3 3 3 4 55%	2477
	11th to 20th	Night	13% 5% 2 4 3 3 3 3 4 6% 54%	2730
	21st to end	Night	13% 4 2 5% 3 3 3 4 6% 7% 51%	2730
December	1st to 10th	Night	12% 6% 2 5% 3 3 3 3 4 5% 53%	4380
	11th to 20th	Night	18% 8% 2 6% 3 4 4 3 4 5% 43%	4952
	21st to end	Night	19% 5% 1 4 3 3 3 3 5% 7% 46%	6633

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	34% 3 8% 19% 29% 6%	5259
	11th to 20th	Day	27% 2 5% 13% 37% 16%	5280
	21st to end	Day	42% 3 5% 21% 22% 8%	5780
February	1st to 10th	Day	38% 5% 11% 22% 19% 5%	1895
	11th to 20th	Day	41% 4 9% 21% 20% 5%	2058
	21st to end	Day	42% 5% 9% 16% 20% 7%	1735
March	1st to 10th	Day	43% 3 7% 16% 18% 12%	5045
	11th to 20th	Day	31% 5% 6% 17% 22% 19%	5090
	21st to end	Day	39% 4 8% 25% 19% 5%	5586
April	1st to 10th	Day	31% 6% 12% 23% 23% 5%	2310
	11th to 20th	Day	34% 5% 10% 21% 23% 7%	2488
	21st to end	Day	36% 6% 12% 26% 17% 3	2730
May	1st to 10th	Day	41% 8% 15% 22% 13% 1	7651
	11th to 20th	Day	43% 7% 13% 23% 13% 2	7630
	21st to end	Day	46% 8% 14% 17% 13% 3	8405
June	1st to 10th	Day	40% 9% 17% 22% 11% 1	2730
	11th to 20th	Day	36% 11% 18% 21% 13% 1	2730
	21st to end	Day	34% 11% 19% 20% 15% 1	2730
July	1st to 10th	Day	35% 12% 20% 24% 8% 1	7615
	11th to 20th	Day	44% 13% 22% 16% 5% 1	7611
	21st to end	Day	48% 10% 16% 17% 8% 1	8156
August	1st to 10th	Day	49% 12% 17% 18% 4	4351
	11th to 20th	Day	38% 11% 22% 17% 10% 2	4265
	21st to end	Day	28% 7% 15% 35% 13% 2	4403
September	1st to 10th	Day	37% 9% 13% 21% 17% 3	2200
	11th to 20th	Day	43% 7% 12% 18% 17% 3	2200
	21st to end	Day	45% 6% 11% 18% 16% 4	2200
October	1st to 10th	Day	27% 4 8% 20% 30% 9%	3433
	11th to 20th	Day	21% 3 6% 20% 27% 23%	3240
	21st to end	Day	27% 3 7% 24% 22% 16%	3538
November	1st to 10th	Day	32% 4 9% 20% 28% 8%	2036
	11th to 20th	Day	31% 3 8% 24% 27% 7%	1890
	21st to end	Day	33% 4 8% 24% 26% 5%	1890
December	1st to 10th	Day	34% 5% 6% 19% 27% 8%	3020
	11th to 20th	Day	39% 5% 11% 17% 21% 8%	3460
	21st to end	Day	39% 4 10% 28% 17% 3	4565
January	1st to 10th	Night	31% 3 10% 21% 27% 8%	7636
	11th to 20th	Night	29% 3 5% 16% 35% 11%	7680
	21st to end	Night	38% 4 6% 21% 22% 10%	8401
February	1st to 10th	Night	37% 6% 11% 21% 20% 5%	2719
	11th to 20th	Night	43% 4 8% 18% 21% 6%	2459
	21st to end	Night	41% 5% 9% 17% 22% 6%	2069
March	1st to 10th	Night	40% 5% 7% 15% 25% 9%	5028
	11th to 20th	Night	27% 4 7% 18% 26% 18%	5090
	21st to end	Night	37% 5% 7% 26% 18% 7%	5588
April	1st to 10th	Night	33% 6% 13% 21% 23% 5%	2310
	11th to 20th	Night	32% 5% 9% 24% 22% 8%	2098
	21st to end	Night	35% 5% 13% 24% 19% 3	1890
May	1st to 10th	Night	40% 7% 15% 24% 12% 2	5264
	11th to 20th	Night	43% 7% 12% 25% 12% 1	5235
	21st to end	Night	47% 7% 12% 21% 12% 1	5771
June	1st to 10th	Night	37% 12% 17% 21% 12% 1	1890
	11th to 20th	Night	39% 9% 20% 22% 10% 1	1890
	21st to end	Night	34% 11% 17% 20% 14% 3	1890
July	1st to 10th	Night	39% 13% 20% 20% 6% 1	5235
	11th to 20th	Night	46% 13% 22% 14% 4 1	5226
	21st to end	Night	51% 11% 16% 14% 7% 1	5606
August	1st to 10th	Night	53% 10% 18% 14% 4	2994
	11th to 20th	Night	46% 12% 18% 14% 9% 1	2938
	21st to end	Night	32% 10% 14% 31% 11% 2	3443
September	1st to 10th	Night	38% 8% 15% 19% 15% 4	2200
	11th to 20th	Night	44% 9% 11% 18% 17% 1	2200
	21st to end	Night	46% 7% 12% 17% 16% 3	2200
October	1st to 10th	Night	34% 5% 9% 18% 24% 9%	3745
	11th to 20th	Night	22% 3 6% 23% 28% 18%	3899
	21st to end	Night	28% 3 5% 23% 27% 14%	4252
November	1st to 10th	Night	35% 4 8% 19% 25% 9%	2477
	11th to 20th	Night	32% 3 8% 20% 26% 11%	2730
	21st to end	Night	32% 5% 8% 23% 26% 6%	2730
December	1st to 10th	Night	34% 4 8% 21% 27% 7%	4380
	11th to 20th	Night	45% 4 7% 16% 20% 8%	4954
	21st to end	Night	38% 4 14% 22% 21% 2	6633

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	24% 19% 32% 20% 5%	330
	11th to 20th	Day	27% 21% 28% 21% 3	330
	21st to end	Day	23% 21% 34% 18% 3	363
February	1st to 10th	Day	22% 15% 37% 21% 6%	330
	11th to 20th	Day	36% 18% 31% 13% 1	330
	21st to end	Day	29% 19% 34% 14% 4	278
March	1st to 10th	Day	22% 14% 32% 25% 7% 1	540
	11th to 20th	Day	24% 15% 32% 24% 4 1	540
	21st to end	Day	23% 15% 32% 25% 5%	594
April	1st to 10th	Day	20% 14% 32% 21% 12% 2	540
	11th to 20th	Day	16% 16% 27% 27% 12% 2	532
	21st to end	Day	16% 8% 33% 23% 14% 6%	540
May	1st to 10th	Day	14% 13% 29% 28% 11% 5%	543
	11th to 20th	Day	18% 8% 20% 27% 19% 8%	567
	21st to end	Day	19% 6% 16% 25% 22% 12%	617
June	1st to 10th	Day	12% 6% 15% 33% 23% 10%	570
	11th to 20th	Day	8% 5% 18% 29% 25% 15%	570
	21st to end	Day	9% 2 13% 34% 28% 14%	570
July	1st to 10th	Day	11% 2 9% 22% 32% 25%	565
	11th to 20th	Day	7% 3 8% 27% 30% 26%	564
	21st to end	Day	10% 4 9% 28% 29% 21%	620
August	1st to 10th	Day	17% 3 14% 28% 20% 18%	566
	11th to 20th	Day	13% 3 10% 27% 30% 17%	535
	21st to end	Day	11% 3 11% 23% 30% 23%	583
September	1st to 10th	Day	14% 2 12% 24% 31% 17%	530
	11th to 20th	Day	19% 4 11% 21% 29% 16%	530
	21st to end	Day	23% 3 19% 24% 25% 5%	530
October	1st to 10th	Day	18% 3 16% 28% 25% 9%	530
	11th to 20th	Day	15% 8% 21% 31% 19% 6%	530
	21st to end	Day	20% 8% 19% 32% 17% 4	583
November	1st to 10th	Day	21% 7% 24% 31% 14% 4	514
	11th to 20th	Day	16% 15% 34% 24% 8% 2	330
	21st to end	Day	15% 15% 32% 25% 12% 2	330
December	1st to 10th	Day	27% 13% 31% 25% 5%	330
	11th to 20th	Day	19% 12% 31% 29% 8% 1	330
	21st to end	Day	25% 12% 33% 21% 7% 2	363
January	1st to 10th	Night	18% 13% 33% 30% 6%	840
	11th to 20th	Night	19% 13% 33% 31% 5%	840
	21st to end	Night	18% 9% 39% 31% 3	924
February	1st to 10th	Night	18% 9% 33% 37% 3	840
	11th to 20th	Night	23% 11% 40% 24% 2	823
	21st to end	Night	20% 14% 34% 29% 3	692
March	1st to 10th	Night	18% 10% 32% 35% 5%	840
	11th to 20th	Night	17% 12% 33% 29% 8%	840
	21st to end	Night	19% 10% 34% 31% 7%	924
April	1st to 10th	Night	16% 11% 35% 29% 10%	840
	11th to 20th	Night	16% 10% 29% 32% 12% 1	818
	21st to end	Night	14% 8% 23% 38% 18%	630
May	1st to 10th	Night	14% 6% 29% 35% 16% 1	630
	11th to 20th	Night	16% 6% 17% 36% 23% 2	621
	21st to end	Night	18% 4 11% 32% 29% 6%	683
June	1st to 10th	Night	11% 3 12% 38% 32% 5%	630
	11th to 20th	Night	12% 3 13% 30% 33% 10%	630
	21st to end	Night	7% 1 9% 33% 44% 6%	630
July	1st to 10th	Night	11% 3 5% 25% 48% 8%	615
	11th to 20th	Night	11% 2 3 24% 48% 12%	612
	21st to end	Night	7% 3 7% 31% 43% 10%	690
August	1st to 10th	Night	18% 2 7% 27% 40% 7%	627
	11th to 20th	Night	14% 3 4 33% 37% 9%	606
	21st to end	Night	13% 2 7% 25% 43% 9%	769
September	1st to 10th	Night	13% 2 8% 31% 37% 9%	800
	11th to 20th	Night	19% 3 9% 26% 37% 7%	800
	21st to end	Night	23% 2 14% 31% 27% 3	800
October	1st to 10th	Night	18% 4 15% 30% 27% 7%	800
	11th to 20th	Night	17% 5% 22% 35% 19% 2	800
	21st to end	Night	17% 6% 20% 36% 18% 2	880
November	1st to 10th	Night	17% 5% 21% 39% 15% 3	820
	11th to 20th	Night	15% 7% 29% 38% 11% 1	840
	21st to end	Night	15% 7% 27% 36% 13% 1	840
December	1st to 10th	Night	20% 10% 26% 37% 7%	840
	11th to 20th	Night	20% 6% 31% 36% 7% 1	840
	21st to end	Night	23% 8% 27% 35% 7%	924

Page generated at 2026-08-12 03:37:15. Version ac07

Copyright © 2026 Attilla Danko.