Morning Star Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Morning Star Observatory clear sky chart from 2005-11-06 to 2025-12-18.

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	13% 6% 2 6% 5% 5% 5% 4 6% 7% 41%	127067
	Night	14% 6% 2 5% 4 4 4 4 5% 7% 44%	123964
Transparency	Day	25% 40% 8% 12% 12% 4	130778
	Night	24% 39% 8% 12% 13% 4	128322
Seeing	Day	19% 13% 23% 23% 15% 8%	16538
	Night	17% 11% 22% 27% 19% 3	26600

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	12% 5% 2 4 3 3 2 2 4 6% 58%	4056
	11th to 20th	Day	10% 6% 2 4 3 2 3 3 3 3 62%	4060
	21st to end	Day	18% 5% 2 5% 4 4 4 2 4 4 48%	4466
February	1st to 10th	Day	15% 6% 2 6% 4 5% 4 3 5% 7% 45%	1900
	11th to 20th	Day	19% 7% 3 4 3 4 3 4 4 5% 43%	1948
	21st to end	Day	17% 7% 3 5% 4 5% 5% 3 5% 5% 42%	1650
March	1st to 10th	Day	19% 7% 3 6% 4 4 4 3 4 5% 42%	4837
	11th to 20th	Day	10% 6% 3 5% 3 3 3 2 4 6% 54%	4980
	21st to end	Day	18% 7% 2 5% 3 4 3 3 5% 5% 45%	5465
April	1st to 10th	Day	12% 5% 2 5% 4 4 5% 4 6% 8% 44%	2200
	11th to 20th	Day	14% 6% 3 4 5% 4 4 3 6% 7% 44%	2379
	21st to end	Day	13% 5% 2 5% 4 4 4 4 5% 7% 47%	2600
May	1st to 10th	Day	11% 8% 3 8% 5% 5% 5% 4 7% 8% 35%	5862
	11th to 20th	Day	19% 7% 3 8% 6% 5% 6% 5% 7% 8% 27%	5861
	21st to end	Day	12% 6% 2 7% 5% 5% 5% 4 7% 9% 38%	6433
June	1st to 10th	Day	11% 7% 2 8% 5% 6% 7% 6% 8% 10% 29%	2600
	11th to 20th	Day	7% 6% 2 7% 7% 6% 7% 7% 9% 10% 33%	2600
	21st to end	Day	8% 5% 2 6% 7% 7% 6% 6% 8% 10% 34%	2600
July	1st to 10th	Day	7% 5% 2 7% 6% 7% 7% 6% 9% 11% 33%	5900
	11th to 20th	Day	8% 6% 3 10% 8% 7% 7% 6% 8% 10% 27%	5900
	21st to end	Day	9% 7% 3 11% 8% 9% 8% 6% 8% 9% 21%	6424
August	1st to 10th	Day	15% 7% 3 8% 7% 7% 7% 5% 8% 9% 23%	4234
	11th to 20th	Day	11% 6% 3 7% 6% 7% 6% 5% 8% 10% 30%	4174
	21st to end	Day	8% 4 2 7% 5% 5% 6% 4 7% 8% 46%	4297
September	1st to 10th	Day	11% 6% 3 7% 6% 5% 5% 5% 6% 9% 37%	2200
	11th to 20th	Day	18% 6% 2 7% 5% 5% 6% 4 6% 8% 33%	2200
	21st to end	Day	18% 6% 2 6% 4 4 4 4 6% 7% 38%	2200
October	1st to 10th	Day	15% 6% 2 4 3 3 4 2 5% 7% 50%	2170
	11th to 20th	Day	12% 5% 2 4 2 2 2 3 4 5% 59%	2000
	21st to end	Day	15% 4 2 4 3 2 3 2 4 5% 56%	2200
November	1st to 10th	Day	12% 6% 1 4 3 2 3 2 4 5% 56%	1969
	11th to 20th	Day	12% 4 2 4 3 3 3 3 5% 7% 55%	1890
	21st to end	Day	14% 5% 2 4 3 3 3 3 5% 6% 53%	1890
December	1st to 10th	Day	13% 7% 2 5% 3 3 3 3 4 5% 51%	3020
	11th to 20th	Day	15% 6% 2 6% 3 3 4 3 5% 7% 45%	3436
	21st to end	Day	20% 6% 2 4 2 3 3 2 5% 6% 47%	4466
January	1st to 10th	Night	13% 5% 2 4 2 2 3 2 3 4 59%	5889
	11th to 20th	Night	9% 5% 2 5% 3 3 3 3 4 5% 57%	5900
	21st to end	Night	18% 5% 2 4 3 3 3 3 5% 5% 49%	6490
February	1st to 10th	Night	13% 6% 2 6% 4 3 3 4 5% 6% 48%	2495
	11th to 20th	Night	18% 7% 2 4 3 3 4 4 4 5% 45%	2338
	21st to end	Night	16% 7% 2 5% 4 4 4 4 5% 7% 44%	1980
March	1st to 10th	Night	18% 8% 2 6% 4 4 4 3 4 5% 42%	5016
	11th to 20th	Night	10% 5% 1 4 3 3 4 4 6% 8% 54%	4980
	21st to end	Night	18% 5% 2 5% 4 4 4 3 4 7% 45%	5467
April	1st to 10th	Night	14% 6% 2 4 3 3 3 3 6% 7% 48%	2200
	11th to 20th	Night	14% 6% 2 4 3 3 3 3 4 7% 51%	1984
	21st to end	Night	12% 6% 1 5% 3 3 4 3 6% 6% 51%	1800
May	1st to 10th	Night	13% 7% 3 7% 5% 4 6% 5% 6% 8% 37%	4033
	11th to 20th	Night	22% 6% 2 6% 4 4 5% 4 6% 9% 31%	4032
	21st to end	Night	15% 5% 2 5% 4 4 4 4 6% 10% 41%	4421
June	1st to 10th	Night	10% 7% 2 8% 5% 6% 6% 5% 8% 12% 33%	1800
	11th to 20th	Night	10% 7% 1 7% 5% 4 5% 6% 6% 11% 39%	1800
	21st to end	Night	7% 5% 2 6% 5% 6% 6% 5% 7% 10% 41%	1800
July	1st to 10th	Night	7% 7% 3 8% 6% 6% 6% 6% 8% 10% 32%	4058
	11th to 20th	Night	8% 7% 3 7% 5% 5% 6% 7% 9% 13% 29%	4057
	21st to end	Night	12% 9% 3 9% 6% 7% 7% 5% 7% 10% 26%	4427
August	1st to 10th	Night	14% 9% 3 8% 6% 5% 6% 5% 7% 9% 28%	2915
	11th to 20th	Night	13% 10% 3 9% 6% 5% 5% 5% 6% 8% 29%	2875
	21st to end	Night	8% 6% 2 6% 5% 5% 5% 4 7% 9% 44%	3548
September	1st to 10th	Night	13% 7% 2 7% 4 5% 5% 4 7% 9% 38%	2200
	11th to 20th	Night	18% 8% 3 7% 5% 4 4 3 5% 7% 35%	2200
	21st to end	Night	19% 7% 2 5% 4 3 4 4 4 7% 42%	2200
October	1st to 10th	Night	15% 5% 2 5% 4 3 4 4 4 6% 48%	2230
	11th to 20th	Night	14% 5% 2 5% 3 3 3 3 4 4 54%	2400
	21st to end	Night	15% 4 1 4 3 3 3 3 4 4 57%	2640
November	1st to 10th	Night	14% 5% 2 3 4 3 3 3 4 5% 55%	2545
	11th to 20th	Night	13% 6% 2 4 2 3 3 3 4 6% 55%	2730
	21st to end	Night	14% 5% 2 4 3 4 4 4 5% 7% 50%	2730
December	1st to 10th	Night	13% 6% 2 5% 2 3 4 3 5% 4 53%	4380
	11th to 20th	Night	16% 8% 2 5% 4 4 4 3 4 5% 46%	4914
	21st to end	Night	21% 6% 2 4 3 3 3 3 5% 5% 46%	6490

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	20% 25% 4 12% 33% 6%	4057
	11th to 20th	Day	17% 27% 4 9% 34% 9%	4060
	21st to end	Day	29% 28% 4 10% 21% 7%	4466
February	1st to 10th	Day	14% 62% 4 9% 8% 2	1900
	11th to 20th	Day	18% 62% 4 6% 7% 3	1958
	21st to end	Day	18% 62% 3 3 11% 3	1650
March	1st to 10th	Day	35% 29% 4 8% 12% 11%	4837
	11th to 20th	Day	20% 29% 4 11% 19% 18%	4980
	21st to end	Day	28% 30% 4 20% 13% 5%	5465
April	1st to 10th	Day	17% 63% 4 7% 8% 2	2200
	11th to 20th	Day	16% 64% 3 9% 5% 2	2379
	21st to end	Day	15% 63% 6% 10% 6% 1	2600
May	1st to 10th	Day	32% 34% 12% 14% 7% 1	5897
	11th to 20th	Day	37% 34% 11% 11% 6%	5865
	21st to end	Day	28% 33% 10% 13% 13% 3	6447
June	1st to 10th	Day	18% 64% 6% 8% 3 1	2600
	11th to 20th	Day	14% 66% 9% 7% 4	2600
	21st to end	Day	15% 64% 9% 8% 4	2600
July	1st to 10th	Day	28% 34% 14% 18% 6%	5835
	11th to 20th	Day	34% 35% 21% 10% 1	5831
	21st to end	Day	42% 34% 11% 9% 4	6240
August	1st to 10th	Day	36% 41% 11% 11% 2	4221
	11th to 20th	Day	24% 42% 16% 8% 7% 3	4213
	21st to end	Day	16% 39% 8% 23% 13% 1	4297
September	1st to 10th	Day	16% 59% 8% 9% 7% 1	2200
	11th to 20th	Day	20% 60% 6% 8% 6% 1	2200
	21st to end	Day	19% 59% 7% 9% 4 1	2200
October	1st to 10th	Day	16% 37% 5% 13% 20% 9%	3534
	11th to 20th	Day	9% 35% 4 11% 20% 22%	3240
	21st to end	Day	18% 35% 4 16% 14% 12%	3538
November	1st to 10th	Day	19% 53% 4 10% 10% 4	1969
	11th to 20th	Day	14% 54% 3 11% 14% 4	1890
	21st to end	Day	14% 55% 5% 10% 14% 2	1890
December	1st to 10th	Day	22% 35% 3 12% 22% 6%	3020
	11th to 20th	Day	27% 32% 8% 11% 17% 5%	3433
	21st to end	Day	29% 26% 8% 21% 14% 2	4466
January	1st to 10th	Night	21% 26% 4 13% 30% 6%	5889
	11th to 20th	Night	19% 27% 4 11% 29% 10%	5900
	21st to end	Night	26% 29% 4 12% 21% 8%	6490
February	1st to 10th	Night	14% 62% 4 10% 8% 2	2495
	11th to 20th	Night	19% 61% 4 7% 8% 2	2339
	21st to end	Night	16% 62% 4 7% 8% 3	1980
March	1st to 10th	Night	33% 30% 5% 8% 18% 5%	5016
	11th to 20th	Night	16% 29% 6% 13% 20% 17%	4980
	21st to end	Night	29% 29% 5% 18% 12% 6%	5467
April	1st to 10th	Night	16% 62% 5% 8% 8% 1	2200
	11th to 20th	Night	16% 63% 3 8% 7% 2	1984
	21st to end	Night	13% 64% 5% 11% 7% 1	1800
May	1st to 10th	Night	31% 34% 10% 19% 5% 1	4060
	11th to 20th	Night	35% 32% 13% 14% 5%	4033
	21st to end	Night	27% 33% 11% 19% 9% 2	4429
June	1st to 10th	Night	17% 65% 7% 7% 3 1	1800
	11th to 20th	Night	14% 65% 10% 8% 3	1800
	21st to end	Night	14% 64% 9% 9% 5%	1800
July	1st to 10th	Night	31% 34% 15% 17% 3	4015
	11th to 20th	Night	31% 36% 23% 9% 1	4006
	21st to end	Night	41% 31% 13% 11% 4	4297
August	1st to 10th	Night	36% 41% 14% 8% 1	2904
	11th to 20th	Night	31% 41% 13% 8% 6%	2902
	21st to end	Night	17% 39% 9% 25% 8% 1	3548
September	1st to 10th	Night	16% 60% 8% 8% 7%	2200
	11th to 20th	Night	21% 59% 7% 7% 5% 1	2200
	21st to end	Night	21% 58% 6% 9% 5%	2200
October	1st to 10th	Night	18% 37% 8% 12% 18% 7%	3646
	11th to 20th	Night	9% 36% 5% 12% 19% 19%	3899
	21st to end	Night	20% 35% 3 13% 17% 12%	4252
November	1st to 10th	Night	20% 53% 4 9% 10% 4	2545
	11th to 20th	Night	15% 54% 4 9% 13% 6%	2730
	21st to end	Night	15% 55% 4 11% 12% 3	2730
December	1st to 10th	Night	20% 36% 4 15% 20% 4	4380
	11th to 20th	Night	29% 33% 5% 12% 15% 6%	4916
	21st to end	Night	30% 26% 10% 16% 17% 1	6490

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	30% 24% 36% 8% 3	300
	11th to 20th	Day	30% 24% 27% 15% 4	300
	21st to end	Day	24% 28% 33% 13% 2	330
February	1st to 10th	Day	21% 30% 36% 13% 1	300
	11th to 20th	Day	40% 27% 24% 8% 1	300
	21st to end	Day	32% 25% 31% 10% 1	249
March	1st to 10th	Day	24% 26% 28% 16% 7%	450
	11th to 20th	Day	26% 22% 29% 17% 5% 1	500
	21st to end	Day	25% 23% 28% 18% 6%	550
April	1st to 10th	Day	21% 24% 27% 20% 8% 1	500
	11th to 20th	Day	18% 20% 28% 20% 12% 1	492
	21st to end	Day	20% 11% 31% 22% 12% 4	500
May	1st to 10th	Day	13% 16% 33% 24% 10% 5%	503
	11th to 20th	Day	19% 11% 23% 25% 14% 8%	527
	21st to end	Day	17% 10% 18% 24% 20% 12%	573
June	1st to 10th	Day	12% 8% 19% 31% 18% 11%	530
	11th to 20th	Day	10% 6% 22% 24% 26% 13%	530
	21st to end	Day	10% 5% 17% 34% 20% 14%	530
July	1st to 10th	Day	9% 4 10% 25% 32% 19%	525
	11th to 20th	Day	8% 2 10% 27% 32% 21%	524
	21st to end	Day	8% 3 11% 28% 28% 22%	576
August	1st to 10th	Day	21% 3 13% 25% 19% 18%	526
	11th to 20th	Day	14% 3 13% 28% 24% 17%	519
	21st to end	Day	15% 3 12% 25% 28% 17%	583
September	1st to 10th	Day	11% 3 17% 26% 28% 15%	530
	11th to 20th	Day	19% 5% 13% 25% 26% 12%	530
	21st to end	Day	21% 7% 18% 28% 21% 5%	530
October	1st to 10th	Day	20% 7% 20% 26% 19% 8%	530
	11th to 20th	Day	15% 12% 28% 27% 15% 4	530
	21st to end	Day	22% 9% 24% 28% 13% 3	583
November	1st to 10th	Day	22% 15% 28% 23% 9% 3	447
	11th to 20th	Day	17% 25% 35% 17% 6% 1	330
	21st to end	Day	18% 23% 33% 18% 6% 1	330
December	1st to 10th	Day	27% 24% 33% 15% 2	330
	11th to 20th	Day	21% 17% 37% 18% 6%	321
	21st to end	Day	25% 19% 34% 16% 5% 1	330
January	1st to 10th	Night	22% 23% 28% 22% 6%	800
	11th to 20th	Night	18% 21% 32% 25% 4	800
	21st to end	Night	18% 20% 35% 24% 3	880
February	1st to 10th	Night	18% 17% 34% 28% 4	800
	11th to 20th	Night	23% 22% 36% 18% 1	783
	21st to end	Night	18% 21% 36% 22% 2	660
March	1st to 10th	Night	19% 21% 30% 26% 4	800
	11th to 20th	Night	22% 17% 31% 23% 6% 1	800
	21st to end	Night	20% 18% 31% 24% 6%	880
April	1st to 10th	Night	18% 17% 32% 25% 8%	800
	11th to 20th	Night	19% 14% 28% 26% 12% 1	697
	21st to end	Night	14% 9% 28% 33% 16% 1	600
May	1st to 10th	Night	13% 9% 27% 33% 17% 1	600
	11th to 20th	Night	18% 8% 17% 34% 22% 2	591
	21st to end	Night	15% 5% 12% 28% 31% 8%	650
June	1st to 10th	Night	10% 2 15% 35% 33% 5%	600
	11th to 20th	Night	11% 3 14% 28% 34% 11%	600
	21st to end	Night	8% 2 12% 32% 41% 7%	600
July	1st to 10th	Night	11% 2 8% 25% 43% 10%	585
	11th to 20th	Night	8% 1 6% 23% 49% 13%	582
	21st to end	Night	9% 1 8% 25% 45% 11%	657
August	1st to 10th	Night	20% 3 7% 22% 40% 9%	597
	11th to 20th	Night	17% 3 7% 24% 40% 8%	594
	21st to end	Night	15% 3 7% 22% 42% 11%	715
September	1st to 10th	Night	14% 5% 11% 29% 35% 8%	800
	11th to 20th	Night	21% 3 11% 25% 34% 6%	800
	21st to end	Night	21% 4 16% 30% 26% 3	800
October	1st to 10th	Night	17% 8% 17% 26% 25% 7%	800
	11th to 20th	Night	18% 9% 24% 29% 17% 3	800
	21st to end	Night	18% 9% 23% 31% 17% 3	880
November	1st to 10th	Night	17% 9% 22% 33% 17% 3	820
	11th to 20th	Night	16% 15% 25% 31% 11% 1	840
	21st to end	Night	15% 17% 26% 29% 13% 1	840
December	1st to 10th	Night	21% 18% 26% 28% 7%	840
	11th to 20th	Night	19% 11% 32% 32% 6%	829
	21st to end	Night	25% 14% 24% 30% 6%	880

Page generated at 2025-12-15 01:13:49. Version ac07

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