Moran
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Moran clear sky chart from 2005-11-06 to 2025-11-18.

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	14% 10% 4 9% 5% 5% 4 4 5% 7% 33%	126554
	Night	15% 12% 4 10% 6% 5% 5% 3 5% 6% 30%	123989
Transparency	Day	32% 39% 7% 14% 7% 1	130019
	Night	35% 39% 8% 12% 6% 1	128610
Seeing	Day	19% 14% 33% 23% 8% 2	17014
	Night	20% 12% 31% 26% 10% 1	26476

By Month

Percentage Cloud Cover NE (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	11% 14% 7% 23% 10% 6% 6% 3 5% 5% 11%	3617
	11th to 20th	Day	11% 16% 5% 21% 12% 9% 5% 4 4 4 9%	3589
	21st to end	Day	12% 18% 9% 18% 7% 6% 5% 3 5% 4 12%	3982
February	1st to 10th	Day	9% 15% 6% 12% 7% 7% 5% 4 6% 7% 22%	1705
	11th to 20th	Day	13% 13% 6% 12% 8% 5% 5% 3 6% 7% 21%	1883
	21st to end	Day	11% 14% 6% 14% 9% 5% 5% 3 5% 6% 23%	1650
March	1st to 10th	Day	13% 11% 3 11% 5% 5% 4 3 6% 8% 30%	4478
	11th to 20th	Day	13% 13% 4 11% 7% 5% 5% 4 5% 6% 28%	4888
	21st to end	Day	18% 13% 7% 11% 6% 5% 4 3 4 5% 23%	5598
April	1st to 10th	Day	18% 13% 3 8% 4 5% 5% 4 5% 6% 29%	2400
	11th to 20th	Day	19% 11% 4 7% 4 4 4 3 5% 7% 34%	2522
	21st to end	Day	16% 10% 3 9% 5% 5% 4 4 5% 7% 34%	2600
May	1st to 10th	Day	16% 10% 3 6% 4 3 4 3 5% 6% 41%	5888
	11th to 20th	Day	12% 10% 3 7% 4 4 4 3 5% 7% 40%	6121
	21st to end	Day	12% 9% 3 6% 4 4 4 3 5% 8% 41%	7197
June	1st to 10th	Day	14% 6% 2 6% 4 4 5% 4 6% 8% 41%	3000
	11th to 20th	Day	13% 6% 3 7% 4 5% 5% 4 6% 9% 39%	3000
	21st to end	Day	16% 8% 3 6% 4 4 4 3 6% 8% 40%	3000
July	1st to 10th	Day	14% 7% 2 5% 4 4 4 4 6% 8% 42%	6601
	11th to 20th	Day	10% 5% 2 5% 4 4 4 4 5% 8% 50%	6360
	21st to end	Day	10% 5% 2 4 3 4 4 4 6% 10% 48%	6926
August	1st to 10th	Day	8% 6% 2 6% 5% 5% 6% 5% 7% 9% 41%	4398
	11th to 20th	Day	14% 5% 2 5% 3 3 5% 4 6% 7% 46%	4174
	21st to end	Day	14% 6% 2 6% 4 4 4 3 5% 7% 46%	4587
September	1st to 10th	Day	16% 6% 2 5% 3 5% 4 4 6% 7% 42%	2356
	11th to 20th	Day	13% 7% 2 6% 5% 4 5% 4 7% 8% 41%	2200
	21st to end	Day	14% 8% 3 6% 4 5% 5% 3 6% 8% 37%	2200
October	1st to 10th	Day	18% 8% 3 7% 5% 4 4 3 5% 8% 34%	2175
	11th to 20th	Day	21% 13% 3 9% 6% 5% 5% 5% 5% 7% 21%	1894
	21st to end	Day	22% 13% 4 8% 7% 6% 5% 3 6% 6% 21%	1980
November	1st to 10th	Day	19% 12% 4 10% 6% 5% 5% 4 7% 6% 23%	1852
	11th to 20th	Day	17% 15% 6% 11% 7% 6% 6% 3 6% 6% 18%	1826
	21st to end	Day	19% 21% 5% 12% 6% 6% 5% 4 5% 5% 13%	1530
December	1st to 10th	Day	14% 20% 6% 14% 8% 6% 6% 5% 5% 5% 11%	2280
	11th to 20th	Day	19% 17% 6% 13% 6% 6% 5% 4 5% 6% 14%	2621
	21st to end	Day	26% 21% 8% 12% 5% 3 3 2 3 4 12%	3476
January	1st to 10th	Night	11% 14% 7% 22% 8% 6% 5% 4 4 5% 13%	6348
	11th to 20th	Night	11% 16% 6% 18% 11% 8% 6% 4 4 5% 12%	6316
	21st to end	Night	11% 17% 8% 15% 8% 6% 6% 4 5% 6% 14%	6996
February	1st to 10th	Night	9% 16% 5% 11% 9% 6% 6% 4 5% 6% 23%	2693
	11th to 20th	Night	11% 14% 5% 14% 7% 6% 5% 3 5% 6% 24%	2402
	21st to end	Night	12% 14% 5% 12% 7% 5% 5% 4 4 6% 25%	1980
March	1st to 10th	Night	16% 10% 3 8% 5% 4 4 3 5% 7% 34%	5362
	11th to 20th	Night	12% 11% 4 10% 5% 5% 4 4 5% 8% 32%	5057
	21st to end	Night	21% 12% 4 9% 5% 4 4 3 4 5% 30%	5376
April	1st to 10th	Night	18% 12% 4 7% 6% 5% 5% 4 6% 6% 29%	2000
	11th to 20th	Night	19% 10% 3 7% 4 3 3 4 5% 5% 36%	1827
	21st to end	Night	18% 9% 4 6% 6% 4 4 3 4 6% 36%	1800
May	1st to 10th	Night	16% 7% 3 6% 4 4 4 4 5% 6% 41%	4053
	11th to 20th	Night	15% 10% 3 8% 5% 4 4 3 4 5% 39%	3782
	21st to end	Night	15% 9% 3 7% 4 4 4 4 5% 7% 39%	3683
June	1st to 10th	Night	12% 5% 3 6% 5% 4 5% 4 8% 8% 40%	1400
	11th to 20th	Night	12% 6% 2 7% 5% 5% 6% 4 7% 7% 41%	1400
	21st to end	Night	14% 8% 3 6% 4 3 4 3 6% 8% 41%	1400
July	1st to 10th	Night	13% 6% 2 6% 4 4 4 4 6% 8% 43%	3360
	11th to 20th	Night	8% 5% 2 5% 4 4 4 4 5% 7% 52%	3620
	21st to end	Night	8% 4 2 5% 3 4 4 3 6% 9% 52%	3948
August	1st to 10th	Night	10% 6% 3 6% 4 5% 5% 4 6% 7% 43%	2755
	11th to 20th	Night	12% 5% 2 5% 4 3 4 3 4 8% 51%	2875
	21st to end	Night	10% 5% 2 5% 4 4 4 3 4 7% 51%	3307
September	1st to 10th	Night	12% 6% 2 6% 4 4 5% 3 5% 7% 46%	2023
	11th to 20th	Night	15% 5% 2 4 4 3 4 3 6% 8% 46%	2200
	21st to end	Night	16% 7% 2 7% 4 4 4 3 6% 6% 39%	2200
October	1st to 10th	Night	17% 8% 2 6% 4 4 4 4 6% 7% 39%	2224
	11th to 20th	Night	22% 10% 3 8% 5% 4 4 4 5% 6% 28%	2504
	21st to end	Night	24% 11% 3 8% 5% 4 5% 3 5% 7% 25%	2860
November	1st to 10th	Night	17% 11% 3 8% 5% 4 5% 4 5% 7% 30%	2666
	11th to 20th	Night	17% 14% 4 10% 7% 6% 6% 3 6% 6% 22%	2727
	21st to end	Night	18% 19% 5% 9% 5% 5% 5% 4 5% 6% 18%	2865
December	1st to 10th	Night	12% 17% 6% 13% 7% 6% 6% 4 6% 6% 15%	4910
	11th to 20th	Night	15% 18% 6% 14% 6% 5% 4 4 5% 6% 17%	5586
	21st to end	Night	25% 20% 9% 11% 5% 4 4 3 3 4 10%	7484

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	55% 32% 4 5% 2 1	3618
	11th to 20th	Day	56% 31% 4 7% 2	3620
	21st to end	Day	56% 30% 4 7% 3	3982
February	1st to 10th	Day	22% 62% 6% 6% 3	1705
	11th to 20th	Day	25% 61% 4 5% 5%	1892
	21st to end	Day	24% 62% 5% 5% 4	1650
March	1st to 10th	Day	37% 33% 10% 9% 9% 2	4480
	11th to 20th	Day	44% 29% 10% 11% 5% 1	4888
	21st to end	Day	48% 31% 6% 10% 5% 1	5598
April	1st to 10th	Day	22% 62% 4 8% 4	2400
	11th to 20th	Day	20% 62% 2 9% 6% 1	2522
	21st to end	Day	18% 62% 4 8% 6% 1	2600
May	1st to 10th	Day	30% 31% 7% 17% 13% 3	5897
	11th to 20th	Day	29% 32% 6% 18% 14%	6125
	21st to end	Day	30% 30% 8% 16% 11% 4	7197
June	1st to 10th	Day	15% 63% 5% 9% 7% 1	3000
	11th to 20th	Day	19% 62% 5% 9% 4 1	3000
	21st to end	Day	17% 60% 6% 10% 5% 1	3000
July	1st to 10th	Day	33% 26% 11% 20% 9%	6532
	11th to 20th	Day	25% 26% 13% 29% 6%	6285
	21st to end	Day	23% 26% 11% 27% 13%	6728
August	1st to 10th	Day	24% 37% 9% 22% 8%	4383
	11th to 20th	Day	28% 36% 8% 22% 5%	4213
	21st to end	Day	26% 36% 12% 20% 5%	4586
September	1st to 10th	Day	19% 58% 7% 11% 4	2356
	11th to 20th	Day	16% 58% 7% 14% 6%	2200
	21st to end	Day	17% 59% 8% 11% 5%	2200
October	1st to 10th	Day	21% 37% 9% 22% 12%	3539
	11th to 20th	Day	31% 37% 8% 22% 2	3058
	21st to end	Day	40% 37% 7% 13% 3	3180
November	1st to 10th	Day	29% 54% 6% 9% 2	1852
	11th to 20th	Day	30% 56% 6% 6% 2	1826
	21st to end	Day	32% 58% 4 3 2	1530
December	1st to 10th	Day	50% 38% 7% 3 1	2280
	11th to 20th	Day	48% 34% 6% 9% 3	2621
	21st to end	Day	57% 29% 3 8% 4	3476
January	1st to 10th	Night	52% 31% 7% 6% 3	6348
	11th to 20th	Night	54% 31% 7% 5% 3	6360
	21st to end	Night	51% 31% 7% 8% 2	6996
February	1st to 10th	Night	23% 62% 4 7% 4	2693
	11th to 20th	Night	23% 62% 4 9% 2	2403
	21st to end	Night	20% 63% 5% 6% 5%	1980
March	1st to 10th	Night	35% 31% 12% 13% 7% 1	5373
	11th to 20th	Night	38% 29% 14% 12% 5% 1	5058
	21st to end	Night	42% 31% 6% 13% 7%	5376
April	1st to 10th	Night	23% 62% 2 7% 6% 1	2000
	11th to 20th	Night	20% 63% 3 9% 4 2	1827
	21st to end	Night	22% 62% 3 7% 6% 1	1800
May	1st to 10th	Night	30% 31% 7% 17% 12% 3	4060
	11th to 20th	Night	33% 31% 4 20% 11%	3783
	21st to end	Night	34% 31% 8% 15% 7% 5%	3684
June	1st to 10th	Night	15% 63% 5% 9% 8%	1400
	11th to 20th	Night	19% 63% 4 8% 4 2	1400
	21st to end	Night	18% 61% 4 11% 6% 1	1400
July	1st to 10th	Night	32% 26% 11% 18% 11% 1	3321
	11th to 20th	Night	24% 26% 13% 26% 11%	3572
	21st to end	Night	20% 26% 12% 27% 14% 1	3832
August	1st to 10th	Night	27% 36% 8% 20% 10%	2746
	11th to 20th	Night	25% 37% 9% 21% 8% 1	2902
	21st to end	Night	22% 37% 9% 24% 8%	3307
September	1st to 10th	Night	17% 58% 7% 12% 6%	2023
	11th to 20th	Night	16% 57% 7% 13% 6% 1	2200
	21st to end	Night	18% 59% 6% 12% 5%	2200
October	1st to 10th	Night	25% 36% 7% 25% 7%	3640
	11th to 20th	Night	28% 37% 9% 19% 6%	4079
	21st to end	Night	34% 37% 11% 16% 2	4610
November	1st to 10th	Night	28% 54% 6% 8% 4	2666
	11th to 20th	Night	26% 57% 7% 7% 3	2727
	21st to end	Night	29% 59% 5% 4 2	2865
December	1st to 10th	Night	45% 37% 9% 7% 2	4910
	11th to 20th	Night	47% 34% 7% 7% 4	5585
	21st to end	Night	58% 29% 4 6% 2	7484

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	21% 17% 36% 21% 4 1	300
	11th to 20th	Day	23% 15% 41% 16% 4 1	300
	21st to end	Day	24% 15% 34% 22% 5%	330
February	1st to 10th	Day	18% 27% 37% 14% 4 1	300
	11th to 20th	Day	20% 27% 34% 14% 3 1	300
	21st to end	Day	22% 30% 34% 13% 1	249
March	1st to 10th	Day	19% 22% 39% 15% 4	300
	11th to 20th	Day	21% 17% 37% 16% 7% 1	460
	21st to end	Day	27% 18% 27% 19% 7% 1	550
April	1st to 10th	Day	27% 15% 36% 17% 5% 1	500
	11th to 20th	Day	26% 23% 25% 16% 8% 2	492
	21st to end	Day	23% 17% 33% 17% 8% 1	500
May	1st to 10th	Day	24% 16% 31% 18% 9% 2	503
	11th to 20th	Day	19% 13% 37% 23% 7% 3	631
	21st to end	Day	16% 13% 33% 27% 9% 2	789
June	1st to 10th	Day	16% 14% 36% 26% 7% 2	730
	11th to 20th	Day	16% 14% 37% 24% 7% 2	730
	21st to end	Day	22% 10% 33% 26% 8% 1	730
July	1st to 10th	Day	10% 7% 38% 31% 11% 3	721
	11th to 20th	Day	12% 11% 31% 31% 11% 4	718
	21st to end	Day	12% 6% 34% 32% 12% 5%	794
August	1st to 10th	Day	13% 7% 28% 34% 13% 5%	626
	11th to 20th	Day	14% 6% 24% 30% 18% 7%	519
	21st to end	Day	17% 10% 27% 28% 15% 3	583
September	1st to 10th	Day	20% 10% 28% 21% 15% 6%	530
	11th to 20th	Day	13% 8% 28% 32% 14% 5%	530
	21st to end	Day	17% 10% 28% 31% 11% 3	530
October	1st to 10th	Day	22% 16% 30% 19% 11% 2	530
	11th to 20th	Day	26% 18% 35% 17% 3	424
	21st to end	Day	28% 18% 36% 13% 4 1	363
November	1st to 10th	Day	27% 21% 32% 17% 4	330
	11th to 20th	Day	25% 25% 33% 11% 5%	302
	21st to end	Day	24% 26% 39% 11% 2	200
December	1st to 10th	Day	25% 19% 33% 17% 7% 1	200
	11th to 20th	Day	30% 23% 35% 8% 5% 1	200
	21st to end	Day	34% 24% 28% 10% 4 1	220
January	1st to 10th	Night	21% 19% 34% 22% 4	1000
	11th to 20th	Night	22% 15% 35% 21% 6%	1000
	21st to end	Night	20% 14% 36% 24% 6% 1	1100
February	1st to 10th	Night	17% 18% 35% 25% 5%	893
	11th to 20th	Night	19% 18% 32% 23% 7%	783
	21st to end	Night	18% 17% 37% 24% 5%	660
March	1st to 10th	Night	18% 12% 38% 23% 8%	800
	11th to 20th	Night	18% 15% 35% 25% 7% 1	800
	21st to end	Night	19% 12% 31% 29% 8%	840
April	1st to 10th	Night	22% 12% 33% 27% 5% 1	600
	11th to 20th	Night	27% 10% 27% 26% 10% 1	593
	21st to end	Night	22% 10% 31% 27% 9% 1	600
May	1st to 10th	Night	17% 9% 31% 31% 11%	600
	11th to 20th	Night	18% 7% 33% 30% 12% 1	591
	21st to end	Night	13% 8% 31% 33% 15%	540
June	1st to 10th	Night	13% 7% 32% 38% 10%	400
	11th to 20th	Night	14% 7% 30% 32% 17% 1	400
	21st to end	Night	16% 8% 25% 37% 14% 1	400
July	1st to 10th	Night	12% 3 23% 43% 16% 2	469
	11th to 20th	Night	12% 4 25% 31% 24% 3	582
	21st to end	Night	12% 4 23% 39% 20% 2	657
August	1st to 10th	Night	9% 4 24% 39% 22% 1	597
	11th to 20th	Night	11% 4 21% 33% 27% 4	594
	21st to end	Night	13% 7% 22% 40% 17% 1	660
September	1st to 10th	Night	17% 5% 24% 30% 20% 4	623
	11th to 20th	Night	16% 7% 25% 29% 21% 3	800
	21st to end	Night	18% 9% 24% 29% 17% 3	800
October	1st to 10th	Night	20% 11% 29% 26% 12% 1	800
	11th to 20th	Night	26% 15% 30% 23% 6%	800
	21st to end	Night	28% 14% 29% 23% 5%	880
November	1st to 10th	Night	25% 16% 32% 20% 6% 1	820
	11th to 20th	Night	24% 20% 32% 18% 5%	829
	21st to end	Night	27% 20% 33% 17% 3	865
December	1st to 10th	Night	23% 19% 35% 17% 5% 1	1000
	11th to 20th	Night	27% 18% 34% 16% 4 1	1000
	21st to end	Night	32% 13% 32% 19% 4	1100

Page generated at 2025-11-15 00:55:59. Version ac07

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