Appold Planetarium
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Appold Planetarium clear sky chart from 2005-11-06 to 2025-05-11.

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	15% 10% 4 8% 5% 5% 5% 4 5% 7% 33%	113902
	Night	15% 11% 4 8% 5% 4 4 3 5% 6% 35%	115135
Transparency	Day	48% 6% 12% 21% 12% 1	117531
	Night	48% 5% 11% 21% 13% 1	119633
Seeing	Day	20% 13% 29% 22% 11% 4	16227
	Night	20% 11% 28% 27% 12% 1	26152

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	13% 17% 7% 18% 5% 4 4 4 4 4 19%	3617
	11th to 20th	Day	14% 17% 5% 14% 9% 6% 8% 4 4 4 14%	3620
	21st to end	Day	21% 18% 8% 13% 5% 4 4 3 4 4 16%	4464
February	1st to 10th	Day	15% 16% 5% 11% 7% 6% 5% 4 5% 6% 21%	1800
	11th to 20th	Day	14% 12% 5% 12% 8% 6% 5% 3 5% 5% 25%	1931
	21st to end	Day	17% 14% 4 9% 4 5% 4 3 5% 7% 28%	1650
March	1st to 10th	Day	18% 13% 5% 10% 5% 4 5% 4 4 5% 29%	4567
	11th to 20th	Day	12% 13% 3 8% 4 4 4 3 5% 6% 38%	4980
	21st to end	Day	18% 14% 5% 9% 5% 5% 5% 3 4 5% 26%	5465
April	1st to 10th	Day	17% 12% 3 7% 5% 5% 5% 4 5% 7% 30%	2335
	11th to 20th	Day	18% 9% 3 7% 5% 5% 4 4 5% 7% 34%	2509
	21st to end	Day	19% 9% 3 7% 4 4 4 4 5% 7% 35%	2600
May	1st to 10th	Day	18% 9% 2 7% 5% 4 5% 3 6% 7% 33%	4212
	11th to 20th	Day	18% 8% 3 7% 4 5% 5% 4 6% 8% 34%	4081
	21st to end	Day	11% 6% 3 6% 4 5% 5% 4 6% 7% 44%	4476
June	1st to 10th	Day	12% 6% 2 6% 5% 5% 5% 5% 7% 8% 41%	2612
	11th to 20th	Day	10% 6% 2 6% 5% 5% 5% 4 7% 7% 43%	2660
	21st to end	Day	10% 6% 2 6% 5% 5% 6% 5% 7% 10% 39%	2660
July	1st to 10th	Day	11% 6% 2 6% 5% 5% 5% 4 6% 9% 40%	4440
	11th to 20th	Day	7% 3 2 5% 4 5% 5% 4 7% 11% 45%	4440
	21st to end	Day	7% 5% 2 7% 5% 6% 6% 5% 7% 9% 41%	4500
August	1st to 10th	Day	12% 4 2 6% 4 4 5% 4 7% 8% 44%	4104
	11th to 20th	Day	9% 6% 2 6% 5% 5% 6% 5% 8% 10% 37%	4044
	21st to end	Day	9% 5% 2 7% 5% 5% 5% 5% 6% 10% 41%	4415
September	1st to 10th	Day	13% 6% 2 5% 4 4 4 4 6% 7% 44%	2152
	11th to 20th	Day	8% 5% 2 6% 4 5% 5% 4 6% 9% 46%	2090
	21st to end	Day	16% 7% 2 5% 4 3 5% 4 5% 7% 40%	2090
October	1st to 10th	Day	12% 5% 3 6% 4 4 4 4 6% 7% 44%	2059
	11th to 20th	Day	19% 9% 2 7% 4 4 4 3 5% 6% 37%	1900
	21st to end	Day	19% 9% 3 8% 4 5% 5% 4 6% 6% 32%	1935
November	1st to 10th	Day	12% 8% 2 7% 4 4 4 3 6% 7% 41%	1762
	11th to 20th	Day	17% 15% 3 8% 5% 4 4 3 4 5% 32%	1800
	21st to end	Day	20% 14% 4 7% 5% 4 4 4 4 7% 27%	1800
December	1st to 10th	Day	14% 14% 8% 13% 6% 5% 4 4 4 6% 23%	2930
	11th to 20th	Day	21% 19% 7% 7% 7% 4 4 3 4 5% 18%	3220
	21st to end	Day	27% 20% 6% 12% 4 4 3 2 4 4 14%	3982
January	1st to 10th	Night	15% 16% 6% 15% 6% 4 4 3 4 4 22%	6348
	11th to 20th	Night	13% 18% 7% 14% 7% 5% 5% 5% 4 4 17%	6346
	21st to end	Night	20% 16% 6% 10% 4 4 4 3 4 5% 23%	6490
February	1st to 10th	Night	17% 16% 4 10% 6% 5% 4 4 4 5% 25%	2600
	11th to 20th	Night	15% 14% 5% 10% 6% 5% 4 3 5% 6% 28%	2353
	21st to end	Night	20% 12% 4 9% 4 4 4 3 4 6% 29%	1980
March	1st to 10th	Night	17% 12% 4 7% 4 3 4 3 4 6% 38%	5286
	11th to 20th	Night	12% 8% 2 6% 5% 4 4 4 5% 7% 45%	4980
	21st to end	Night	17% 10% 4 8% 4 4 4 3 4 6% 36%	5467
April	1st to 10th	Night	17% 10% 3 7% 5% 4 4 3 5% 6% 36%	2080
	11th to 20th	Night	17% 8% 2 8% 4 4 5% 3 4 7% 37%	1838
	21st to end	Night	16% 9% 2 6% 5% 4 4 4 5% 6% 39%	1800
May	1st to 10th	Night	19% 8% 3 7% 5% 4 5% 3 6% 7% 32%	2903
	11th to 20th	Night	17% 7% 2 6% 4 4 4 3 5% 7% 39%	2818
	21st to end	Night	11% 5% 2 6% 4 4 4 4 6% 8% 48%	3079
June	1st to 10th	Night	10% 5% 2 5% 4 5% 5% 5% 7% 7% 44%	1563
	11th to 20th	Night	11% 5% 2 7% 5% 4 4 4 7% 7% 45%	1520
	21st to end	Night	10% 5% 2 4 4 4 4 6% 7% 10% 44%	1520
July	1st to 10th	Night	10% 3 1 5% 4 3 4 4 6% 10% 50%	2530
	11th to 20th	Night	9% 3 2 4 4 3 4 4 6% 8% 52%	2530
	21st to end	Night	7% 4 2 6% 5% 5% 5% 5% 8% 9% 46%	3051
August	1st to 10th	Night	13% 7% 2 7% 4 3 4 2 5% 8% 44%	2825
	11th to 20th	Night	9% 5% 2 5% 4 4 5% 4 6% 8% 50%	2785
	21st to end	Night	9% 4 2 6% 5% 5% 4 4 5% 7% 50%	3238
September	1st to 10th	Night	10% 5% 2 5% 4 5% 4 3 4 8% 50%	2007
	11th to 20th	Night	9% 5% 1 5% 4 4 3 3 4 7% 55%	2090
	21st to end	Night	15% 6% 3 7% 4 3 4 3 5% 6% 44%	2090
October	1st to 10th	Night	13% 5% 2 6% 5% 4 3 3 5% 7% 46%	2120
	11th to 20th	Night	17% 9% 2 7% 4 4 4 4 4 6% 38%	2280
	21st to end	Night	21% 8% 3 6% 5% 4 4 3 5% 6% 36%	2660
November	1st to 10th	Night	14% 8% 3 6% 4 4 3 3 5% 6% 44%	2536
	11th to 20th	Night	16% 11% 4 8% 4 4 4 4 6% 6% 33%	2600
	21st to end	Night	20% 13% 4 9% 5% 5% 3 4 5% 6% 27%	2600
December	1st to 10th	Night	13% 14% 7% 11% 6% 5% 4 3 4 6% 26%	4250
	11th to 20th	Night	17% 19% 6% 11% 5% 4 4 3 4 5% 22%	4976
	21st to end	Night	29% 19% 6% 9% 4 4 3 3 4 5% 15%	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	68% 5% 9% 14% 4	3618
	11th to 20th	Day	73% 4 9% 7% 7%	3620
	21st to end	Day	73% 4 8% 9% 6%	4464
February	1st to 10th	Day	63% 6% 11% 14% 6%	1800
	11th to 20th	Day	61% 5% 9% 16% 8%	1941
	21st to end	Day	56% 5% 13% 17% 7% 2	1650
March	1st to 10th	Day	59% 4 11% 18% 8% 1	4567
	11th to 20th	Day	45% 5% 16% 23% 9% 1	4980
	21st to end	Day	59% 6% 11% 15% 9% 1	5465
April	1st to 10th	Day	53% 6% 12% 17% 13%	2335
	11th to 20th	Day	48% 6% 12% 21% 11% 2	2509
	21st to end	Day	48% 5% 12% 22% 11% 2	2600
May	1st to 10th	Day	48% 6% 12% 22% 11% 1	4250
	11th to 20th	Day	45% 8% 13% 23% 10% 1	4085
	21st to end	Day	38% 7% 11% 19% 20% 5%	4489
June	1st to 10th	Day	38% 7% 12% 26% 13% 3	2612
	11th to 20th	Day	37% 6% 14% 23% 16% 3	2660
	21st to end	Day	39% 7% 15% 21% 15% 4	2660
July	1st to 10th	Day	40% 6% 12% 23% 17% 2	4371
	11th to 20th	Day	29% 7% 13% 32% 17% 1	4365
	21st to end	Day	36% 8% 14% 19% 21% 2	4357
August	1st to 10th	Day	35% 8% 14% 27% 15% 1	4091
	11th to 20th	Day	38% 8% 12% 29% 13% 1	4083
	21st to end	Day	35% 7% 12% 32% 12% 2	4414
September	1st to 10th	Day	38% 6% 15% 22% 17% 3	2152
	11th to 20th	Day	33% 7% 10% 30% 18% 1	2090
	21st to end	Day	41% 6% 12% 25% 15% 1	2090
October	1st to 10th	Day	29% 4 13% 31% 22% 1	3423
	11th to 20th	Day	40% 4 9% 27% 19%	3140
	21st to end	Day	43% 4 13% 25% 15% 1	3159
November	1st to 10th	Day	42% 5% 13% 24% 15% 1	1762
	11th to 20th	Day	55% 4 11% 18% 11% 1	1800
	21st to end	Day	57% 5% 13% 18% 7%	1800
December	1st to 10th	Day	63% 6% 15% 13% 3	2930
	11th to 20th	Day	68% 5% 10% 14% 3	3217
	21st to end	Day	75% 5% 7% 9% 4	3982
January	1st to 10th	Night	65% 4 8% 16% 5%	6348
	11th to 20th	Night	70% 4 10% 9% 6%	6346
	21st to end	Night	64% 4 13% 10% 8%	6490
February	1st to 10th	Night	61% 6% 11% 15% 6% 1	2600
	11th to 20th	Night	57% 5% 10% 19% 8% 1	2354
	21st to end	Night	57% 5% 11% 17% 9% 1	1980
March	1st to 10th	Night	49% 4 12% 24% 10% 1	5286
	11th to 20th	Night	38% 5% 14% 27% 14% 1	4980
	21st to end	Night	49% 5% 10% 21% 14% 1	5467
April	1st to 10th	Night	48% 6% 10% 20% 14% 2	2080
	11th to 20th	Night	47% 5% 11% 19% 17% 2	1838
	21st to end	Night	45% 5% 11% 22% 16% 2	1800
May	1st to 10th	Night	51% 6% 11% 18% 13% 1	2930
	11th to 20th	Night	43% 7% 11% 25% 12% 1	2819
	21st to end	Night	32% 7% 12% 25% 20% 3	3087
June	1st to 10th	Night	35% 6% 12% 27% 18% 2	1563
	11th to 20th	Night	35% 8% 12% 26% 16% 3	1520
	21st to end	Night	33% 8% 14% 25% 19% 1	1520
July	1st to 10th	Night	30% 6% 12% 29% 17% 6%	2490
	11th to 20th	Night	29% 6% 16% 28% 19% 2	2482
	21st to end	Night	31% 8% 17% 19% 21% 3	2954
August	1st to 10th	Night	38% 7% 13% 25% 16% 2	2814
	11th to 20th	Night	31% 7% 13% 31% 18% 1	2812
	21st to end	Night	33% 7% 12% 30% 17% 2	3238
September	1st to 10th	Night	34% 6% 12% 26% 19% 4	2007
	11th to 20th	Night	30% 5% 10% 29% 24% 2	2090
	21st to end	Night	40% 6% 12% 25% 16% 2	2090
October	1st to 10th	Night	25% 4 9% 31% 30% 1	3536
	11th to 20th	Night	38% 4 10% 26% 22%	3779
	21st to end	Night	37% 4 7% 34% 16% 2	4373
November	1st to 10th	Night	41% 5% 11% 25% 17% 1	2536
	11th to 20th	Night	48% 6% 13% 20% 11% 2	2600
	21st to end	Night	58% 5% 12% 19% 6%	2600
December	1st to 10th	Night	59% 5% 13% 18% 5%	4250
	11th to 20th	Night	64% 6% 12% 12% 5% 1	4978
	21st to end	Night	72% 4 10% 8% 5%	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	26% 20% 33% 17% 2 1	300
	11th to 20th	Day	30% 20% 37% 9% 3 1	300
	21st to end	Day	31% 18% 30% 19% 3	330
February	1st to 10th	Day	29% 22% 36% 11% 3	300
	11th to 20th	Day	30% 20% 36% 12% 2	300
	21st to end	Day	28% 27% 34% 9% 2	249
March	1st to 10th	Day	26% 24% 35% 12% 3	335
	11th to 20th	Day	28% 15% 36% 16% 5% 1	500
	21st to end	Day	32% 16% 30% 15% 6%	550
April	1st to 10th	Day	26% 17% 31% 19% 7% 1	500
	11th to 20th	Day	28% 19% 28% 15% 8% 2	492
	21st to end	Day	27% 15% 33% 15% 8% 2	500
May	1st to 10th	Day	25% 16% 30% 18% 8% 3	503
	11th to 20th	Day	21% 12% 32% 17% 13% 4	487
	21st to end	Day	13% 9% 29% 23% 18% 7%	529
June	1st to 10th	Day	14% 8% 32% 30% 12% 3	632
	11th to 20th	Day	14% 9% 31% 32% 11% 3	680
	21st to end	Day	13% 9% 31% 29% 12% 5%	680
July	1st to 10th	Day	11% 6% 24% 29% 18% 11%	671
	11th to 20th	Day	11% 6% 29% 27% 19% 9%	668
	21st to end	Day	10% 4 27% 31% 19% 9%	553
August	1st to 10th	Day	11% 2 23% 29% 22% 12%	486
	11th to 20th	Day	13% 4 25% 29% 19% 9%	479
	21st to end	Day	11% 4 22% 32% 21% 10%	539
September	1st to 10th	Day	15% 6% 22% 27% 19% 10%	490
	11th to 20th	Day	10% 4 20% 29% 26% 11%	490
	21st to end	Day	22% 9% 25% 22% 16% 7%	490
October	1st to 10th	Day	15% 9% 27% 27% 16% 7%	490
	11th to 20th	Day	21% 18% 30% 21% 8% 2	490
	21st to end	Day	26% 19% 31% 18% 6% 1	384
November	1st to 10th	Day	17% 19% 35% 19% 8% 2	300
	11th to 20th	Day	30% 21% 27% 17% 5% 1	300
	21st to end	Day	31% 20% 33% 14% 2	300
December	1st to 10th	Day	27% 27% 27% 12% 7%	300
	11th to 20th	Day	27% 24% 33% 12% 3	300
	21st to end	Day	32% 18% 35% 10% 4	330
January	1st to 10th	Night	25% 17% 32% 20% 5% 1	1000
	11th to 20th	Night	27% 17% 34% 17% 5% 1	999
	21st to end	Night	24% 17% 32% 22% 4	880
February	1st to 10th	Night	25% 15% 33% 23% 4	800
	11th to 20th	Night	24% 14% 35% 24% 3	783
	21st to end	Night	28% 15% 37% 18% 2	660
March	1st to 10th	Night	23% 14% 31% 26% 6% 1	800
	11th to 20th	Night	20% 18% 34% 22% 6%	800
	21st to end	Night	25% 13% 31% 24% 7%	880
April	1st to 10th	Night	23% 15% 33% 24% 5%	680
	11th to 20th	Night	23% 12% 31% 25% 7% 1	593
	21st to end	Night	21% 10% 35% 25% 9%	600
May	1st to 10th	Night	22% 10% 28% 29% 10% 2	600
	11th to 20th	Night	21% 5% 29% 29% 14% 1	563
	21st to end	Night	12% 4 27% 35% 20% 3	617
June	1st to 10th	Night	13% 4 29% 38% 16%	570
	11th to 20th	Night	12% 4 26% 40% 17% 1	570
	21st to end	Night	12% 4 26% 35% 21% 2	570
July	1st to 10th	Night	10% 2 20% 37% 28% 3	555
	11th to 20th	Night	11% 3 22% 39% 22% 4	552
	21st to end	Night	8% 1 17% 43% 28% 2	624
August	1st to 10th	Night	9% 1 19% 40% 27% 3	567
	11th to 20th	Night	12% 2 16% 35% 30% 5%	564
	21st to end	Night	10% 3 16% 36% 31% 4	627
September	1st to 10th	Night	12% 5% 19% 33% 26% 4	677
	11th to 20th	Night	10% 4 18% 35% 30% 3	760
	21st to end	Night	17% 7% 21% 29% 23% 3	760
October	1st to 10th	Night	16% 9% 25% 29% 18% 3	760
	11th to 20th	Night	22% 14% 30% 23% 10% 2	760
	21st to end	Night	26% 12% 30% 25% 7%	836
November	1st to 10th	Night	19% 14% 29% 25% 11% 1	780
	11th to 20th	Night	24% 15% 32% 22% 7% 1	800
	21st to end	Night	29% 12% 33% 21% 5% 1	800
December	1st to 10th	Night	27% 16% 31% 20% 5%	800
	11th to 20th	Night	27% 16% 32% 21% 4	865
	21st to end	Night	33% 12% 33% 19% 3	1100

Page generated at 2025-05-08 09:33:59. Version ac07

Copyright © 2025 Attilla Danko.