Moondance
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Moondance 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	2 6% 3 8% 5% 5% 6% 5% 7% 9% 45%	135550
	Night	2 6% 3 7% 5% 5% 5% 4 7% 9% 48%	131643
Transparency	Day	30% 9% 15% 23% 17% 6%	130451
	Night	29% 10% 16% 24% 16% 5%	127747
Seeing	Day	9% 16% 28% 28% 16% 3	16890
	Night	5% 9% 27% 41% 17% 1	26891

By Month

Percentage Cloud Cover SW (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	6% 5% 15% 8% 6% 6% 5% 10% 11% 29%	3638
	11th to 20th	Day	1 5% 4 11% 12% 8% 8% 5% 6% 7% 33%	3943
	21st to end	Day	7% 6% 12% 7% 5% 4 3 5% 7% 42%	4510
February	1st to 10th	Day	11% 4 14% 7% 7% 6% 3 6% 9% 34%	1800
	11th to 20th	Day	7% 6% 12% 7% 6% 7% 5% 7% 8% 36%	1830
	21st to end	Day	8% 4 13% 7% 7% 6% 4 6% 8% 36%	1650
March	1st to 10th	Day	6% 6% 12% 6% 4 5% 4 5% 9% 43%	4679
	11th to 20th	Day	1 8% 3 9% 5% 6% 6% 5% 7% 9% 41%	5000
	21st to end	Day	1 9% 4 10% 6% 6% 6% 5% 7% 10% 35%	5661
April	1st to 10th	Day	2 8% 4 9% 6% 5% 6% 4 7% 8% 42%	2400
	11th to 20th	Day	3 9% 4 10% 6% 5% 6% 5% 7% 8% 37%	2371
	21st to end	Day	3 9% 3 8% 5% 6% 6% 6% 8% 8% 38%	2400
May	1st to 10th	Day	3 11% 4 9% 6% 5% 7% 6% 8% 9% 32%	5809
	11th to 20th	Day	3 5% 2 7% 5% 5% 6% 5% 8% 9% 44%	6298
	21st to end	Day	3 6% 2 6% 4 6% 5% 5% 8% 9% 45%	6925
June	1st to 10th	Day	3 5% 2 6% 5% 5% 5% 5% 7% 9% 49%	2800
	11th to 20th	Day	4 4 1 5% 3 4 5% 4 6% 7% 57%	2800
	21st to end	Day	3 3 1 4 4 4 5% 4 6% 8% 57%	2800
July	1st to 10th	Day	2 2 1 4 4 4 5% 5% 8% 8% 55%	6339
	11th to 20th	Day	1 2 1 4 4 6% 7% 6% 12% 12% 45%	6340
	21st to end	Day	3 4 2 7% 6% 5% 7% 5% 9% 8% 45%	6538
August	1st to 10th	Day	4 3 2 5% 4 5% 6% 6% 9% 10% 46%	5779
	11th to 20th	Day	3 4 1 5% 4 5% 5% 5% 9% 10% 49%	5579
	21st to end	Day	4 5% 2 7% 5% 5% 6% 5% 8% 9% 44%	5984
September	1st to 10th	Day	5% 3 2 5% 4 4 4 4 6% 8% 56%	2400
	11th to 20th	Day	4 5% 2 6% 4 4 4 4 6% 8% 53%	2400
	21st to end	Day	5% 5% 2 5% 3 2 3 3 4 6% 61%	2143
October	1st to 10th	Day	3 5% 2 4 3 3 3 2 3 4 69%	3270
	11th to 20th	Day	3 5% 2 4 3 4 5% 4 7% 9% 53%	3230
	21st to end	Day	4 8% 3 5% 3 3 3 3 6% 8% 55%	3438
November	1st to 10th	Day	2 7% 4 5% 4 3 4 4 6% 8% 55%	1771
	11th to 20th	Day	1 9% 4 6% 5% 3 4 3 5% 8% 51%	1775
	21st to end	Day	1 6% 3 10% 4 4 4 3 6% 7% 52%	1600
December	1st to 10th	Day	5% 2 8% 4 4 4 3 5% 9% 54%	2620
	11th to 20th	Day	7% 4 9% 4 4 4 4 5% 10% 48%	3026
	21st to end	Day	1 7% 4 13% 9% 6% 6% 5% 7% 9% 34%	4004
January	1st to 10th	Night	5% 6% 13% 8% 7% 7% 5% 7% 9% 33%	6327
	11th to 20th	Night	5% 4 11% 9% 8% 6% 5% 6% 11% 36%	6068
	21st to end	Night	1 9% 5% 12% 7% 7% 6% 3 5% 9% 37%	6468
February	1st to 10th	Night	1 8% 4 12% 7% 6% 5% 5% 7% 9% 37%	2600
	11th to 20th	Night	1 7% 4 10% 5% 6% 5% 6% 9% 8% 39%	2456
	21st to end	Night	1 8% 5% 11% 7% 5% 5% 4 6% 7% 42%	1980
March	1st to 10th	Night	8% 5% 9% 5% 5% 5% 4 5% 10% 42%	5199
	11th to 20th	Night	1 6% 3 6% 5% 5% 5% 4 6% 9% 50%	5000
	21st to end	Night	1 8% 3 8% 5% 5% 4 4 7% 9% 45%	5306
April	1st to 10th	Night	2 8% 3 8% 4 4 6% 4 7% 7% 48%	2000
	11th to 20th	Night	4 8% 3 6% 5% 4 5% 6% 6% 8% 45%	1977
	21st to end	Night	4 9% 2 6% 4 4 4 4 6% 8% 51%	2000
May	1st to 10th	Night	4 7% 3 6% 5% 5% 5% 5% 8% 9% 43%	4151
	11th to 20th	Night	4 5% 2 6% 4 5% 6% 5% 7% 10% 46%	3617
	21st to end	Night	2 4 2 5% 3 4 4 4 8% 9% 55%	3972
June	1st to 10th	Night	2 3 1 3 3 3 4 5% 7% 11% 58%	1600
	11th to 20th	Night	3 3 1 4 4 4 4 4 5% 8% 62%	1600
	21st to end	Night	3 2 1 3 3 2 3 4 6% 8% 63%	1600
July	1st to 10th	Night	3 3 1 3 3 4 5% 4 7% 8% 59%	3640
	11th to 20th	Night	1 2 1 3 3 4 5% 5% 11% 11% 55%	3640
	21st to end	Night	2 4 1 5% 4 5% 5% 4 8% 8% 54%	4331
August	1st to 10th	Night	2 3 1 4 3 5% 6% 6% 11% 9% 51%	4033
	11th to 20th	Night	2 3 1 4 3 4 5% 4 10% 9% 55%	4268
	21st to end	Night	4 4 2 6% 4 4 6% 5% 9% 9% 48%	4993
September	1st to 10th	Night	5% 4 1 5% 3 3 4 3 6% 7% 59%	2000
	11th to 20th	Night	3 4 1 5% 3 4 4 3 4 8% 63%	2000
	21st to end	Night	4 4 2 4 3 3 3 3 5% 6% 64%	2252
October	1st to 10th	Night	3 3 1 3 2 2 2 2 4 5% 73%	3920
	11th to 20th	Night	2 4 1 4 3 2 4 4 6% 8% 62%	3874
	21st to end	Night	4 5% 2 5% 3 3 3 3 4 8% 62%	4120
November	1st to 10th	Night	2 7% 2 6% 3 4 3 3 5% 8% 58%	2506
	11th to 20th	Night	1 8% 3 6% 4 4 4 4 5% 7% 54%	2620
	21st to end	Night	1 6% 3 7% 4 4 5% 4 6% 9% 50%	2800
December	1st to 10th	Night	5% 3 7% 5% 4 4 4 5% 19% 45%	4570
	11th to 20th	Night	1 6% 3 6% 5% 4 6% 5% 9% 13% 43%	5181
	21st to end	Night	1 8% 4 12% 8% 7% 6% 6% 8% 12% 28%	6974

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	41% 12% 17% 21% 9% 1	3639
	11th to 20th	Day	43% 8% 20% 15% 12% 2	3943
	21st to end	Day	35% 11% 15% 19% 17% 4	4510
February	1st to 10th	Day	47% 8% 17% 15% 11% 2	1800
	11th to 20th	Day	43% 10% 15% 22% 9% 2	1839
	21st to end	Day	42% 8% 16% 16% 15% 2	1650
March	1st to 10th	Day	33% 8% 15% 23% 17% 4	4679
	11th to 20th	Day	32% 7% 18% 30% 11% 1	5000
	21st to end	Day	38% 12% 20% 24% 5% 1	5661
April	1st to 10th	Day	35% 10% 16% 22% 14% 4	2400
	11th to 20th	Day	41% 10% 15% 18% 15% 2	2374
	21st to end	Day	37% 11% 14% 26% 11% 1	2400
May	1st to 10th	Day	39% 12% 14% 19% 15% 2	5809
	11th to 20th	Day	27% 11% 16% 24% 18% 4	6302
	21st to end	Day	26% 11% 13% 27% 22% 2	6926
June	1st to 10th	Day	26% 9% 14% 21% 21% 8%	2800
	11th to 20th	Day	23% 7% 11% 18% 25% 17%	2800
	21st to end	Day	21% 6% 10% 20% 25% 17%	2800
July	1st to 10th	Day	21% 6% 11% 15% 25% 24%	6271
	11th to 20th	Day	22% 9% 16% 24% 20% 9%	6265
	21st to end	Day	29% 8% 14% 17% 18% 14%	6351
August	1st to 10th	Day	30% 12% 18% 17% 13% 11%	4208
	11th to 20th	Day	30% 10% 16% 18% 20% 7%	4038
	21st to end	Day	26% 8% 15% 19% 23% 9%	4311
September	1st to 10th	Day	25% 5% 11% 19% 24% 15%	2400
	11th to 20th	Day	25% 7% 13% 22% 24% 9%	2400
	21st to end	Day	23% 5% 9% 29% 27% 6%	2143
October	1st to 10th	Day	19% 4 8% 26% 30% 13%	3270
	11th to 20th	Day	24% 5% 14% 33% 20% 3	3230
	21st to end	Day	27% 8% 10% 38% 15% 2	3438
November	1st to 10th	Day	26% 7% 16% 27% 23% 1	1771
	11th to 20th	Day	31% 7% 19% 25% 16% 2	1775
	21st to end	Day	31% 6% 15% 33% 13% 2	1600
December	1st to 10th	Day	28% 8% 19% 35% 9%	2620
	11th to 20th	Day	31% 8% 26% 28% 6%	3024
	21st to end	Day	40% 10% 18% 21% 10% 1	4004
January	1st to 10th	Night	41% 12% 18% 19% 9% 2	6327
	11th to 20th	Night	43% 9% 16% 15% 15% 1	6068
	21st to end	Night	39% 11% 17% 13% 18% 2	6468
February	1st to 10th	Night	43% 13% 15% 17% 10% 2	2600
	11th to 20th	Night	39% 11% 14% 24% 10% 1	2457
	21st to end	Night	40% 10% 13% 20% 15% 2	1980
March	1st to 10th	Night	34% 8% 14% 25% 18% 1	5199
	11th to 20th	Night	25% 6% 18% 31% 20% 2	5000
	21st to end	Night	31% 11% 22% 30% 5% 1	5306
April	1st to 10th	Night	32% 10% 17% 23% 16% 3	2000
	11th to 20th	Night	35% 9% 14% 23% 17% 2	1977
	21st to end	Night	31% 9% 14% 28% 18%	2000
May	1st to 10th	Night	31% 11% 19% 26% 11% 2	4148
	11th to 20th	Night	25% 12% 17% 28% 16% 2	3618
	21st to end	Night	20% 10% 16% 28% 23% 3	3972
June	1st to 10th	Night	18% 8% 18% 28% 21% 8%	1600
	11th to 20th	Night	19% 7% 11% 20% 23% 21%	1600
	21st to end	Night	16% 6% 10% 24% 26% 19%	1600
July	1st to 10th	Night	19% 6% 12% 17% 19% 27%	3600
	11th to 20th	Night	16% 8% 25% 28% 15% 8%	3592
	21st to end	Night	22% 9% 18% 24% 13% 13%	4207
August	1st to 10th	Night	24% 12% 20% 19% 14% 10%	2928
	11th to 20th	Night	22% 14% 20% 16% 17% 11%	3085
	21st to end	Night	25% 9% 14% 17% 25% 10%	3597
September	1st to 10th	Night	22% 7% 12% 20% 24% 16%	2000
	11th to 20th	Night	20% 6% 13% 24% 25% 13%	2000
	21st to end	Night	20% 6% 9% 28% 29% 8%	2252
October	1st to 10th	Night	15% 5% 7% 28% 35% 11%	3920
	11th to 20th	Night	19% 5% 16% 37% 19% 3	3874
	21st to end	Night	23% 6% 13% 37% 20% 2	4120
November	1st to 10th	Night	27% 6% 14% 28% 23% 3	2506
	11th to 20th	Night	28% 7% 16% 30% 16% 2	2620
	21st to end	Night	29% 8% 15% 30% 14% 2	2800
December	1st to 10th	Night	27% 17% 19% 28% 8% 1	4570
	11th to 20th	Night	27% 10% 24% 31% 7%	5182
	21st to end	Night	40% 15% 16% 17% 11% 1	6974

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	9% 17% 26% 32% 14% 3	300
	11th to 20th	Day	9% 18% 32% 33% 8% 1	300
	21st to end	Day	3 15% 37% 32% 11% 2	330
February	1st to 10th	Day	13% 28% 33% 22% 3 1	300
	11th to 20th	Day	12% 24% 32% 29% 4	300
	21st to end	Day	16% 22% 32% 24% 6%	249
March	1st to 10th	Day	13% 25% 30% 23% 8% 2	375
	11th to 20th	Day	11% 26% 32% 21% 9% 1	500
	21st to end	Day	13% 34% 32% 15% 6%	550
April	1st to 10th	Day	15% 26% 32% 17% 8% 2	500
	11th to 20th	Day	15% 36% 27% 16% 5% 1	492
	21st to end	Day	14% 25% 35% 17% 7% 2	500
May	1st to 10th	Day	15% 24% 30% 21% 9% 1	539
	11th to 20th	Day	13% 12% 29% 29% 15% 2	725
	21st to end	Day	8% 15% 28% 30% 16% 3	789
June	1st to 10th	Day	5% 13% 24% 32% 22% 4	730
	11th to 20th	Day	6% 13% 31% 32% 16% 2	730
	21st to end	Day	4 12% 25% 33% 23% 2	730
July	1st to 10th	Day	5% 5% 20% 35% 31% 4	721
	11th to 20th	Day	4 4 20% 35% 30% 6%	718
	21st to end	Day	5% 5% 23% 33% 27% 6%	634
August	1st to 10th	Day	7% 8% 27% 33% 20% 6%	527
	11th to 20th	Day	3 5% 28% 34% 21% 8%	517
	21st to end	Day	5% 7% 28% 34% 21% 5%	583
September	1st to 10th	Day	7% 9% 25% 30% 21% 8%	530
	11th to 20th	Day	6% 12% 30% 31% 16% 5%	530
	21st to end	Day	7% 11% 24% 25% 23% 9%	377
October	1st to 10th	Day	10% 9% 22% 27% 22% 9%	330
	11th to 20th	Day	9% 17% 23% 30% 17% 5%	324
	21st to end	Day	12% 20% 28% 24% 13% 2	330
November	1st to 10th	Day	10% 22% 25% 26% 13% 4	300
	11th to 20th	Day	11% 16% 28% 30% 12% 2	300
	21st to end	Day	6% 15% 33% 31% 14% 1	300
December	1st to 10th	Day	10% 15% 29% 29% 13% 3	300
	11th to 20th	Day	7% 16% 32% 36% 9%	300
	21st to end	Day	10% 17% 38% 26% 8% 2	330
January	1st to 10th	Night	4 17% 28% 40% 12%	1000
	11th to 20th	Night	4 15% 35% 36% 9% 1	884
	21st to end	Night	3 11% 34% 40% 10% 1	880
February	1st to 10th	Night	5% 15% 40% 33% 7% 1	800
	11th to 20th	Night	4 13% 40% 36% 7%	784
	21st to end	Night	5% 10% 42% 39% 4	660
March	1st to 10th	Night	4 10% 36% 40% 10%	800
	11th to 20th	Night	4 8% 30% 45% 12%	800
	21st to end	Night	4 9% 37% 41% 9%	800
April	1st to 10th	Night	6% 13% 38% 38% 5%	600
	11th to 20th	Night	9% 11% 33% 38% 8%	593
	21st to end	Night	8% 12% 29% 40% 10% 1	600
May	1st to 10th	Night	8% 8% 31% 42% 11% 1	600
	11th to 20th	Night	9% 3 23% 43% 21% 1	591
	21st to end	Night	7% 7% 25% 39% 21% 1	650
June	1st to 10th	Night	5% 4 18% 47% 25% 2	600
	11th to 20th	Night	3 5% 26% 49% 17% 1	600
	21st to end	Night	3 3 18% 47% 28% 1	600
July	1st to 10th	Night	4 2 7% 44% 40% 2	585
	11th to 20th	Night	2 1 7% 47% 41% 2	582
	21st to end	Night	4 1 7% 43% 42% 3	657
August	1st to 10th	Night	6% 1 10% 44% 38% 1	597
	11th to 20th	Night	3 2 9% 51% 32% 2	594
	21st to end	Night	5% 1 7% 46% 39% 2	660
September	1st to 10th	Night	5% 2 12% 49% 30% 2	600
	11th to 20th	Night	5% 2 13% 50% 28% 2	600
	21st to end	Night	5% 4 18% 43% 26% 4	700
October	1st to 10th	Night	6% 5% 24% 44% 21% 2	800
	11th to 20th	Night	5% 8% 29% 42% 16% 1	792
	21st to end	Night	8% 10% 25% 42% 13% 2	836
November	1st to 10th	Night	6% 9% 33% 38% 13% 1	946
	11th to 20th	Night	7% 12% 32% 40% 8% 1	1000
	21st to end	Night	4 11% 32% 40% 12%	1000
December	1st to 10th	Night	5% 12% 34% 39% 9% 1	1000
	11th to 20th	Night	5% 13% 36% 37% 9%	1000
	21st to end	Night	5% 17% 34% 35% 8% 1	1100

Page generated at 2025-10-15 23:50:27. Version ac07

Copyright © 2025 Attilla Danko.