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 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	2 6% 3 8% 5% 5% 6% 5% 7% 8% 45%	105276
	Night	2 6% 3 8% 5% 5% 5% 4 6% 8% 48%	102500
Transparency	Day	32% 9% 14% 22% 16% 6%	105028
	Night	31% 10% 15% 24% 16% 5%	102339
Seeing	Day	9% 16% 28% 28% 16% 3	15570
	Night	5% 9% 27% 41% 17% 1	25615

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% 18% 10% 7% 6% 5% 8% 9% 28%	2538
	11th to 20th	Day	1 7% 5% 14% 12% 8% 7% 4 6% 7% 30%	2745
	21st to end	Day	9% 6% 15% 8% 6% 5% 3 6% 7% 34%	3146
February	1st to 10th	Day	11% 4 14% 7% 7% 6% 3 6% 8% 33%	1710
	11th to 20th	Day	6% 6% 12% 7% 6% 6% 4 7% 8% 37%	1736
	21st to end	Day	8% 5% 13% 7% 7% 7% 4 7% 8% 35%	1570
March	1st to 10th	Day	1 7% 6% 13% 6% 5% 6% 4 6% 8% 38%	3253
	11th to 20th	Day	1 9% 4 7% 4 6% 6% 5% 5% 8% 45%	3490
	21st to end	Day	1 9% 5% 12% 7% 7% 7% 5% 7% 9% 29%	3948
April	1st to 10th	Day	2 8% 4 9% 6% 5% 6% 4 7% 8% 41%	2280
	11th to 20th	Day	3 10% 4 10% 7% 5% 6% 5% 7% 8% 36%	2251
	21st to end	Day	3 9% 4 8% 5% 6% 5% 5% 8% 8% 39%	2280
May	1st to 10th	Day	4 14% 5% 11% 7% 6% 7% 6% 6% 8% 28%	4063
	11th to 20th	Day	4 5% 2 7% 6% 5% 6% 5% 7% 10% 43%	4388
	21st to end	Day	4 7% 2 6% 5% 6% 5% 4 7% 8% 46%	4825
June	1st to 10th	Day	3 5% 2 6% 5% 5% 5% 5% 7% 9% 50%	2660
	11th to 20th	Day	4 4 1 5% 3 4 5% 4 6% 7% 57%	2660
	21st to end	Day	3 3 1 4 4 4 5% 5% 6% 9% 56%	2660
July	1st to 10th	Day	3 3 1 4 3 4 5% 4 6% 7% 59%	4430
	11th to 20th	Day	2 2 1 4 4 6% 7% 6% 11% 11% 46%	4430
	21st to end	Day	3 4 2 6% 6% 5% 6% 5% 8% 8% 48%	4549
August	1st to 10th	Day	5% 4 2 6% 5% 6% 7% 6% 10% 11% 38%	4092
	11th to 20th	Day	4 5% 2 6% 5% 5% 6% 6% 10% 10% 42%	3874
	21st to end	Day	3 4 1 5% 4 4 5% 4 8% 9% 51%	4180
September	1st to 10th	Day	5% 3 2 5% 4 4 4 4 6% 8% 56%	2280
	11th to 20th	Day	4 5% 2 6% 4 4 4 4 5% 8% 55%	2280
	21st to end	Day	5% 5% 2 5% 3 2 3 3 4 6% 62%	2036
October	1st to 10th	Day	3 5% 2 4 3 3 2 2 3 4 69%	3170
	11th to 20th	Day	3 5% 1 4 3 4 5% 4 7% 9% 53%	3150
	21st to end	Day	4 8% 3 5% 3 3 3 3 6% 8% 55%	3438
November	1st to 10th	Day	1 6% 3 5% 3 3 4 4 6% 8% 56%	1717
	11th to 20th	Day	2 9% 4 6% 5% 3 4 3 5% 8% 51%	1687
	21st to end	Day	1 6% 3 10% 4 5% 4 3 6% 7% 51%	1520
December	1st to 10th	Day	1 8% 4 13% 7% 5% 6% 5% 8% 8% 35%	1520
	11th to 20th	Day	1 9% 3 10% 5% 5% 6% 6% 7% 9% 39%	1926
	21st to end	Day	1 8% 5% 15% 9% 7% 6% 4 6% 8% 32%	2794
January	1st to 10th	Night	7% 5% 14% 10% 7% 8% 5% 6% 7% 30%	4417
	11th to 20th	Night	7% 5% 14% 11% 7% 6% 4 6% 6% 34%	4242
	21st to end	Night	1 12% 6% 15% 8% 8% 6% 3 5% 7% 29%	4521
February	1st to 10th	Night	1 8% 4 12% 7% 6% 6% 5% 7% 8% 36%	2470
	11th to 20th	Night	1 7% 4 9% 5% 6% 6% 6% 8% 8% 40%	2330
	21st to end	Night	1 8% 5% 11% 7% 5% 5% 4 6% 7% 41%	1884
March	1st to 10th	Night	10% 5% 10% 5% 5% 5% 5% 5% 7% 43%	3611
	11th to 20th	Night	1 8% 3 7% 5% 5% 5% 4 5% 8% 47%	3490
	21st to end	Night	1 10% 4 10% 6% 5% 5% 4 7% 8% 41%	3701
April	1st to 10th	Night	2 8% 3 8% 4 4 6% 4 7% 7% 47%	1900
	11th to 20th	Night	4 8% 3 6% 5% 4 5% 6% 6% 8% 45%	1877
	21st to end	Night	4 9% 2 6% 4 4 3 4 6% 8% 50%	1900
May	1st to 10th	Night	4 8% 3 7% 6% 6% 6% 5% 7% 7% 41%	2900
	11th to 20th	Night	5% 6% 2 7% 4 5% 6% 5% 8% 10% 43%	2517
	21st to end	Night	3 5% 2 5% 4 4 4 3 6% 8% 55%	2762
June	1st to 10th	Night	2 3 1 3 3 3 4 4 6% 11% 59%	1520
	11th to 20th	Night	3 3 1 4 4 3 4 4 5% 8% 61%	1520
	21st to end	Night	3 2 1 3 3 2 3 4 7% 9% 63%	1520
July	1st to 10th	Night	2 2 1 3 3 3 5% 4 7% 8% 62%	2540
	11th to 20th	Night	1 2 1 3 3 4 5% 5% 10% 11% 56%	2540
	21st to end	Night	2 3 1 4 4 4 5% 4 7% 8% 59%	3010
August	1st to 10th	Night	2 4 1 5% 4 5% 6% 6% 11% 10% 47%	2847
	11th to 20th	Night	2 3 1 4 3 5% 6% 5% 12% 11% 49%	2963
	21st to end	Night	3 3 1 5% 4 4 6% 5% 7% 9% 53%	3487
September	1st to 10th	Night	5% 4 1 5% 3 3 4 4 5% 7% 59%	1900
	11th to 20th	Night	3 4 1 4 3 3 3 2 4 7% 64%	1900
	21st to end	Night	4 4 1 4 3 3 3 3 5% 6% 64%	2139
October	1st to 10th	Night	3 3 1 3 2 2 2 2 3 5% 74%	3800
	11th to 20th	Night	2 4 1 4 3 2 4 4 6% 8% 62%	3778
	21st to end	Night	4 5% 2 5% 3 3 3 3 4 8% 62%	4120
November	1st to 10th	Night	2 7% 2 5% 3 4 3 3 5% 8% 59%	2441
	11th to 20th	Night	1 8% 3 6% 4 4 4 4 5% 7% 54%	2489
	21st to end	Night	1 6% 3 8% 4 4 5% 4 6% 8% 50%	2660
December	1st to 10th	Night	1 7% 3 9% 7% 5% 5% 5% 6% 7% 45%	2660
	11th to 20th	Night	1 8% 4 9% 7% 6% 7% 6% 9% 10% 35%	3271
	21st to end	Night	1 8% 4 13% 8% 7% 6% 6% 8% 8% 29%	4873

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	46% 11% 16% 19% 7% 1	2539
	11th to 20th	Day	53% 10% 18% 14% 5% 1	2745
	21st to end	Day	43% 14% 16% 19% 7% 1	3146
February	1st to 10th	Day	48% 8% 17% 15% 10% 1	1710
	11th to 20th	Day	43% 10% 14% 22% 9% 2	1745
	21st to end	Day	43% 9% 17% 15% 14% 2	1570
March	1st to 10th	Day	37% 11% 15% 26% 11%	3253
	11th to 20th	Day	31% 10% 20% 31% 8% 1	3490
	21st to end	Day	44% 14% 16% 20% 5% 1	3948
April	1st to 10th	Day	36% 10% 16% 21% 14% 4	2280
	11th to 20th	Day	41% 10% 15% 17% 14% 1	2254
	21st to end	Day	38% 11% 13% 26% 11% 1	2280
May	1st to 10th	Day	46% 13% 12% 16% 13% 1	4063
	11th to 20th	Day	27% 13% 18% 27% 13% 2	4392
	21st to end	Day	28% 10% 12% 26% 21% 2	4825
June	1st to 10th	Day	26% 9% 14% 21% 22% 8%	2660
	11th to 20th	Day	23% 7% 10% 18% 24% 17%	2660
	21st to end	Day	21% 6% 11% 21% 25% 17%	2660
July	1st to 10th	Day	21% 6% 9% 15% 24% 25%	4361
	11th to 20th	Day	23% 9% 15% 22% 19% 12%	4355
	21st to end	Day	27% 8% 12% 18% 18% 17%	4406
August	1st to 10th	Day	30% 12% 18% 17% 12% 11%	4078
	11th to 20th	Day	30% 10% 16% 18% 20% 7%	3913
	21st to end	Day	25% 8% 15% 19% 23% 10%	4179
September	1st to 10th	Day	26% 5% 10% 18% 25% 16%	2280
	11th to 20th	Day	24% 7% 13% 21% 25% 10%	2280
	21st to end	Day	23% 5% 9% 29% 28% 6%	2036
October	1st to 10th	Day	19% 4 8% 26% 30% 13%	3170
	11th to 20th	Day	24% 6% 14% 34% 20% 2	3150
	21st to end	Day	27% 8% 10% 38% 15% 2	3438
November	1st to 10th	Day	25% 7% 16% 27% 24% 1	1717
	11th to 20th	Day	32% 7% 19% 25% 15% 2	1687
	21st to end	Day	32% 6% 16% 32% 13% 2	1520
December	1st to 10th	Day	45% 10% 18% 18% 9% 1	1520
	11th to 20th	Day	38% 8% 18% 28% 7%	1924
	21st to end	Day	45% 11% 11% 20% 12% 1	2794
January	1st to 10th	Night	46% 13% 16% 19% 6% 1	4417
	11th to 20th	Night	51% 11% 13% 16% 7% 2	4242
	21st to end	Night	48% 14% 15% 15% 7% 1	4521
February	1st to 10th	Night	44% 13% 15% 17% 9% 1	2470
	11th to 20th	Night	39% 11% 14% 25% 10% 1	2331
	21st to end	Night	41% 10% 13% 20% 14% 2	1884
March	1st to 10th	Night	35% 10% 12% 28% 15%	3611
	11th to 20th	Night	29% 7% 21% 31% 10% 1	3490
	21st to end	Night	36% 13% 20% 25% 5% 1	3701
April	1st to 10th	Night	32% 10% 17% 21% 17% 3	1900
	11th to 20th	Night	35% 9% 15% 23% 16% 1	1877
	21st to end	Night	31% 9% 14% 27% 18%	1900
May	1st to 10th	Night	35% 11% 14% 25% 13% 2	2900
	11th to 20th	Night	26% 15% 19% 28% 11% 1	2518
	21st to end	Night	24% 9% 13% 28% 23% 3	2762
June	1st to 10th	Night	18% 8% 18% 28% 21% 8%	1520
	11th to 20th	Night	19% 7% 11% 20% 23% 20%	1520
	21st to end	Night	15% 6% 10% 25% 26% 18%	1520
July	1st to 10th	Night	17% 7% 12% 20% 15% 29%	2500
	11th to 20th	Night	17% 8% 21% 28% 16% 10%	2492
	21st to end	Night	18% 9% 15% 27% 14% 16%	2916
August	1st to 10th	Night	24% 12% 21% 19% 13% 10%	2838
	11th to 20th	Night	22% 14% 21% 16% 17% 11%	2990
	21st to end	Night	25% 9% 14% 17% 25% 10%	3487
September	1st to 10th	Night	22% 7% 11% 19% 24% 16%	1900
	11th to 20th	Night	20% 5% 13% 23% 25% 13%	1900
	21st to end	Night	20% 5% 9% 28% 30% 8%	2139
October	1st to 10th	Night	14% 5% 7% 28% 35% 11%	3800
	11th to 20th	Night	19% 5% 17% 37% 19% 3	3778
	21st to end	Night	23% 6% 13% 37% 20% 2	4120
November	1st to 10th	Night	26% 6% 14% 28% 23% 3	2441
	11th to 20th	Night	29% 7% 17% 30% 15% 2	2489
	21st to end	Night	30% 8% 15% 30% 15% 2	2660
December	1st to 10th	Night	38% 10% 18% 22% 11% 1	2660
	11th to 20th	Night	37% 11% 16% 28% 8%	3272
	21st to end	Night	42% 14% 14% 18% 12% 1	4873

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% 16% 24% 32% 15% 4	270
	11th to 20th	Day	10% 18% 32% 31% 8% 1	270
	21st to end	Day	3 15% 38% 30% 11% 2	297
February	1st to 10th	Day	12% 26% 33% 23% 4 1	270
	11th to 20th	Day	12% 23% 32% 30% 4	270
	21st to end	Day	16% 24% 32% 22% 6%	225
March	1st to 10th	Day	13% 26% 30% 22% 7% 2	341
	11th to 20th	Day	9% 24% 34% 23% 9% 1	460
	21st to end	Day	12% 34% 32% 15% 6%	506
April	1st to 10th	Day	15% 26% 33% 16% 8% 2	460
	11th to 20th	Day	15% 36% 27% 16% 5% 1	452
	21st to end	Day	14% 26% 34% 17% 7% 2	460
May	1st to 10th	Day	16% 24% 31% 20% 8% 1	497
	11th to 20th	Day	13% 11% 27% 30% 16% 2	675
	21st to end	Day	8% 15% 28% 29% 16% 3	734
June	1st to 10th	Day	5% 13% 23% 32% 22% 4	680
	11th to 20th	Day	6% 13% 31% 31% 16% 2	680
	21st to end	Day	4 11% 25% 34% 24% 2	680
July	1st to 10th	Day	5% 5% 19% 35% 31% 4	671
	11th to 20th	Day	4 5% 19% 35% 31% 6%	668
	21st to end	Day	5% 5% 22% 33% 28% 7%	587
August	1st to 10th	Day	7% 6% 26% 34% 21% 6%	487
	11th to 20th	Day	4 5% 29% 34% 21% 7%	477
	21st to end	Day	5% 7% 28% 34% 22% 4	539
September	1st to 10th	Day	7% 10% 24% 29% 21% 9%	490
	11th to 20th	Day	6% 12% 30% 30% 16% 6%	490
	21st to end	Day	8% 12% 25% 25% 22% 8%	345
October	1st to 10th	Day	10% 9% 21% 27% 23% 10%	300
	11th to 20th	Day	8% 17% 22% 30% 18% 6%	300
	21st to end	Day	12% 20% 28% 24% 13% 2	330
November	1st to 10th	Day	9% 22% 26% 26% 13% 4	282
	11th to 20th	Day	11% 16% 27% 30% 12% 3	270
	21st to end	Day	6% 14% 32% 31% 15% 1	270
December	1st to 10th	Day	10% 16% 31% 28% 12% 3	270
	11th to 20th	Day	7% 17% 29% 37% 10%	270
	21st to end	Day	10% 16% 38% 27% 8% 2	297
January	1st to 10th	Night	4 17% 26% 40% 12%	950
	11th to 20th	Night	5% 16% 34% 36% 9% 1	840
	21st to end	Night	3 12% 34% 40% 10% 1	836
February	1st to 10th	Night	4 13% 40% 35% 7% 1	760
	11th to 20th	Night	4 12% 40% 37% 7%	744
	21st to end	Night	5% 11% 42% 39% 4	628
March	1st to 10th	Night	4 10% 36% 40% 10%	760
	11th to 20th	Night	4 7% 30% 46% 13%	760
	21st to end	Night	4 8% 37% 42% 9%	760
April	1st to 10th	Night	6% 13% 37% 38% 5%	570
	11th to 20th	Night	9% 12% 33% 39% 8%	563
	21st to end	Night	9% 12% 29% 39% 11% 1	570
May	1st to 10th	Night	8% 8% 32% 41% 10% 1	570
	11th to 20th	Night	9% 3 22% 43% 22% 1	561
	21st to end	Night	7% 7% 24% 39% 21% 1	617
June	1st to 10th	Night	4 5% 18% 46% 25% 2	570
	11th to 20th	Night	3 5% 25% 50% 16% 1	570
	21st to end	Night	3 2 18% 48% 28% 1	570
July	1st to 10th	Night	4 2 7% 43% 42% 2	555
	11th to 20th	Night	2 1 6% 46% 42% 3	552
	21st to end	Night	4 1 6% 42% 44% 3	624
August	1st to 10th	Night	5% 1 9% 43% 40% 1	567
	11th to 20th	Night	3 2 9% 51% 32% 2	564
	21st to end	Night	5% 1 7% 45% 40% 2	627
September	1st to 10th	Night	5% 2 11% 49% 30% 2	570
	11th to 20th	Night	5% 2 13% 49% 29% 2	570
	21st to end	Night	5% 4 18% 43% 26% 4	665
October	1st to 10th	Night	6% 5% 24% 42% 21% 2	760
	11th to 20th	Night	5% 7% 28% 43% 16% 1	760
	21st to end	Night	8% 10% 25% 42% 13% 2	836
November	1st to 10th	Night	6% 9% 32% 38% 13% 1	921
	11th to 20th	Night	7% 12% 31% 40% 9% 1	950
	21st to end	Night	4 11% 31% 41% 13%	950
December	1st to 10th	Night	6% 12% 34% 39% 9%	950
	11th to 20th	Night	5% 13% 34% 38% 9%	950
	21st to end	Night	6% 16% 34% 35% 8% 1	1045

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