Morning Calm Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Morning Calm Observatory clear sky chart from 2005-11-06 to 2024-11-01.

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% 6% 2 6% 4 4 4 4 6% 8% 42%	101064
	Night	15% 6% 2 6% 4 4 4 3 5% 7% 44%	97827
Transparency	Day	39% 8% 13% 22% 15% 3	100872
	Night	38% 7% 12% 23% 17% 4	97689
Seeing	Day	18% 11% 26% 25% 14% 6%	14986
	Night	17% 7% 27% 33% 15% 2	24632

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	17% 6% 2 6% 4 3 3 3 4 5% 47%	2776
	11th to 20th	Day	13% 8% 3 8% 5% 5% 5% 3 5% 4 41%	2840
	21st to end	Day	16% 9% 3 7% 5% 4 4 3 5% 6% 39%	3124
February	1st to 10th	Day	13% 8% 3 6% 5% 5% 4 4 5% 6% 42%	1710
	11th to 20th	Day	17% 8% 2 6% 3 3 3 4 5% 7% 41%	1668
	21st to end	Day	17% 9% 2 7% 4 4 4 3 6% 5% 39%	1608
March	1st to 10th	Day	21% 7% 2 7% 4 4 4 3 4 6% 39%	3435
	11th to 20th	Day	9% 5% 2 5% 4 4 4 4 6% 6% 52%	3480
	21st to end	Day	20% 8% 2 6% 4 4 4 4 5% 5% 39%	3815
April	1st to 10th	Day	11% 6% 2 5% 4 4 5% 4 6% 7% 47%	2266
	11th to 20th	Day	13% 6% 2 6% 5% 3 4 2 5% 6% 49%	2254
	21st to end	Day	16% 7% 2 6% 5% 5% 4 3 5% 5% 42%	2294
May	1st to 10th	Day	19% 7% 2 8% 5% 5% 4 4 7% 8% 31%	4082
	11th to 20th	Day	23% 6% 3 5% 4 4 4 4 5% 8% 33%	4081
	21st to end	Day	11% 4 2 5% 4 4 5% 5% 7% 9% 43%	4821
June	1st to 10th	Day	11% 5% 2 5% 5% 4 5% 5% 7% 8% 43%	2660
	11th to 20th	Day	10% 5% 2 7% 5% 5% 5% 5% 7% 10% 40%	2660
	21st to end	Day	8% 4 2 5% 4 6% 4 5% 8% 10% 44%	2660
July	1st to 10th	Day	6% 4 2 5% 5% 5% 6% 6% 8% 11% 41%	4378
	11th to 20th	Day	8% 5% 2 6% 5% 6% 5% 6% 8% 12% 37%	4120
	21st to end	Day	11% 8% 2 8% 6% 6% 5% 5% 7% 9% 34%	4466
August	1st to 10th	Day	14% 5% 2 6% 5% 6% 6% 5% 8% 11% 33%	4104
	11th to 20th	Day	8% 5% 2 6% 6% 5% 6% 5% 7% 10% 39%	3948
	21st to end	Day	10% 4 2 5% 4 4 4 4 5% 9% 49%	4180
September	1st to 10th	Day	13% 6% 2 6% 4 4 4 3 5% 7% 46%	2280
	11th to 20th	Day	13% 5% 2 6% 3 3 4 3 6% 8% 48%	2235
	21st to end	Day	22% 7% 3 5% 4 4 4 4 5% 5% 37%	2006
October	1st to 10th	Day	15% 5% 2 5% 4 4 4 3 5% 6% 47%	1900
	11th to 20th	Day	16% 4 1 5% 4 4 3 3 4 5% 52%	1900
	21st to end	Day	14% 5% 2 4 3 3 4 2 4 6% 53%	2090
November	1st to 10th	Day	12% 5% 1 4 4 3 3 3 4 6% 54%	1857
	11th to 20th	Day	14% 5% 2 4 4 3 3 4 5% 6% 50%	1644
	21st to end	Day	15% 4 2 4 4 3 4 4 3 5% 51%	1520
December	1st to 10th	Day	15% 6% 2 6% 4 4 3 4 6% 8% 41%	1520
	11th to 20th	Day	16% 6% 2 4 3 3 2 3 4 6% 51%	1910
	21st to end	Day	20% 6% 2 6% 4 4 4 3 5% 8% 37%	2772
January	1st to 10th	Night	13% 7% 1 4 3 3 4 3 4 5% 51%	4164
	11th to 20th	Night	17% 8% 2 5% 2 3 3 2 4 5% 49%	4120
	21st to end	Night	19% 9% 3 6% 3 3 3 3 4 5% 44%	4532
February	1st to 10th	Night	14% 7% 3 6% 4 4 4 4 6% 6% 42%	2470
	11th to 20th	Night	19% 7% 2 6% 3 4 3 3 5% 5% 43%	2396
	21st to end	Night	15% 8% 3 6% 4 3 3 3 5% 6% 44%	1841
March	1st to 10th	Night	20% 7% 3 6% 4 3 4 3 5% 5% 39%	3418
	11th to 20th	Night	11% 6% 2 4 3 3 3 3 5% 6% 52%	3480
	21st to end	Night	14% 7% 2 5% 4 3 4 3 4 5% 49%	3817
April	1st to 10th	Night	14% 7% 2 5% 4 3 4 4 5% 7% 45%	1914
	11th to 20th	Night	12% 5% 2 5% 4 3 5% 2 5% 7% 50%	1875
	21st to end	Night	16% 5% 2 5% 3 3 4 4 6% 7% 45%	1900
May	1st to 10th	Night	21% 7% 3 7% 4 4 5% 4 5% 9% 32%	2815
	11th to 20th	Night	25% 7% 2 4 4 5% 4 4 6% 6% 33%	2812
	21st to end	Night	12% 5% 2 5% 4 4 4 4 6% 9% 45%	2732
June	1st to 10th	Night	11% 4 2 5% 4 4 4 4 6% 10% 46%	1520
	11th to 20th	Night	11% 6% 3 5% 6% 5% 5% 4 6% 8% 43%	1520
	21st to end	Night	9% 4 2 5% 4 5% 5% 4 8% 10% 44%	1520
July	1st to 10th	Night	7% 4 2 6% 5% 6% 7% 5% 7% 10% 41%	2576
	11th to 20th	Night	7% 6% 2 7% 6% 5% 6% 4 7% 11% 38%	2840
	21st to end	Night	9% 7% 2 8% 6% 5% 5% 5% 8% 9% 34%	3087
August	1st to 10th	Night	16% 6% 2 7% 5% 5% 6% 4 7% 10% 33%	2825
	11th to 20th	Night	10% 7% 3 9% 6% 5% 5% 4 5% 8% 37%	2848
	21st to end	Night	12% 6% 2 6% 4 3 4 3 5% 8% 49%	3476
September	1st to 10th	Night	15% 5% 2 4 3 4 4 3 6% 8% 45%	1900
	11th to 20th	Night	12% 6% 2 6% 5% 3 3 4 5% 6% 48%	1942
	21st to end	Night	23% 6% 2 5% 4 4 3 3 4 6% 40%	2173
October	1st to 10th	Night	19% 5% 2 5% 3 4 4 3 3 6% 46%	2280
	11th to 20th	Night	15% 5% 1 5% 3 3 4 2 5% 6% 51%	2280
	21st to end	Night	15% 4 2 4 3 3 4 3 5% 6% 53%	2508
November	1st to 10th	Night	12% 7% 2 5% 3 3 3 3 5% 5% 53%	2228
	11th to 20th	Night	15% 6% 2 5% 3 3 4 3 5% 6% 50%	2529
	21st to end	Night	14% 5% 1 5% 3 3 4 4 4 6% 51%	2660
December	1st to 10th	Night	16% 7% 2 6% 5% 4 4 3 5% 5% 43%	2660
	11th to 20th	Night	16% 6% 2 5% 3 3 3 3 4 6% 47%	3285
	21st to end	Night	17% 5% 2 6% 4 3 5% 4 6% 6% 41%	4884

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	36% 7% 9% 29% 15% 5%	2777
	11th to 20th	Day	42% 6% 10% 19% 16% 7%	2840
	21st to end	Day	45% 7% 10% 21% 15% 3	3124
February	1st to 10th	Day	42% 6% 12% 24% 14% 3	1710
	11th to 20th	Day	41% 6% 9% 22% 18% 4	1677
	21st to end	Day	45% 6% 13% 15% 17% 5%	1608
March	1st to 10th	Day	46% 6% 9% 19% 14% 6%	3435
	11th to 20th	Day	30% 7% 8% 25% 22% 7%	3480
	21st to end	Day	45% 7% 10% 19% 15% 4	3815
April	1st to 10th	Day	35% 6% 13% 20% 18% 8%	2266
	11th to 20th	Day	35% 6% 11% 20% 21% 6%	2254
	21st to end	Day	43% 7% 11% 22% 14% 4	2294
May	1st to 10th	Day	47% 11% 12% 18% 10% 2	4120
	11th to 20th	Day	46% 11% 12% 20% 10% 1	4085
	21st to end	Day	32% 11% 17% 20% 18% 2	4835
June	1st to 10th	Day	35% 10% 15% 24% 16% 1	2660
	11th to 20th	Day	37% 10% 15% 23% 13% 2	2660
	21st to end	Day	32% 11% 16% 24% 16% 1	2660
July	1st to 10th	Day	35% 8% 22% 19% 10% 5%	4309
	11th to 20th	Day	36% 8% 20% 26% 9% 1	4051
	21st to end	Day	44% 8% 11% 21% 14% 1	4324
August	1st to 10th	Day	43% 8% 19% 24% 6%	4091
	11th to 20th	Day	37% 8% 16% 25% 14% 1	3987
	21st to end	Day	33% 6% 17% 29% 14% 2	4180
September	1st to 10th	Day	38% 7% 13% 17% 20% 5%	2280
	11th to 20th	Day	34% 7% 10% 27% 19% 4	2235
	21st to end	Day	47% 7% 10% 18% 16% 3	2006
October	1st to 10th	Day	37% 7% 9% 24% 18% 4	1900
	11th to 20th	Day	35% 5% 9% 24% 22% 5%	1900
	21st to end	Day	33% 4 9% 26% 22% 6%	2090
November	1st to 10th	Day	32% 5% 9% 25% 24% 5%	1857
	11th to 20th	Day	34% 5% 12% 20% 22% 7%	1644
	21st to end	Day	34% 4 12% 25% 22% 3	1520
December	1st to 10th	Day	41% 6% 12% 24% 12% 4	1520
	11th to 20th	Day	37% 3 9% 31% 13% 6%	1906
	21st to end	Day	41% 9% 12% 26% 11% 1	2772
January	1st to 10th	Night	33% 5% 10% 26% 21% 5%	4164
	11th to 20th	Night	38% 4 9% 22% 21% 6%	4120
	21st to end	Night	43% 5% 8% 23% 18% 2	4532
February	1st to 10th	Night	41% 6% 11% 24% 16% 3	2470
	11th to 20th	Night	43% 4 8% 21% 18% 7%	2398
	21st to end	Night	41% 6% 11% 20% 17% 6%	1841
March	1st to 10th	Night	43% 8% 10% 22% 14% 3	3418
	11th to 20th	Night	29% 7% 9% 22% 27% 5%	3480
	21st to end	Night	36% 7% 10% 22% 20% 5%	3817
April	1st to 10th	Night	38% 6% 11% 18% 22% 5%	1914
	11th to 20th	Night	34% 6% 12% 22% 20% 6%	1875
	21st to end	Night	37% 7% 11% 26% 13% 5%	1900
May	1st to 10th	Night	49% 9% 12% 18% 10% 3	2842
	11th to 20th	Night	47% 10% 12% 20% 9% 1	2813
	21st to end	Night	33% 10% 17% 25% 12% 3	2739
June	1st to 10th	Night	31% 10% 15% 27% 15% 2	1520
	11th to 20th	Night	37% 10% 15% 23% 13% 2	1520
	21st to end	Night	33% 10% 18% 19% 18% 3	1520
July	1st to 10th	Night	37% 10% 22% 15% 13% 3	2535
	11th to 20th	Night	39% 8% 21% 22% 8% 1	2786
	21st to end	Night	43% 9% 16% 19% 12%	2988
August	1st to 10th	Night	45% 8% 17% 23% 6% 1	2814
	11th to 20th	Night	44% 7% 12% 22% 14% 1	2875
	21st to end	Night	34% 6% 14% 30% 14% 1	3476
September	1st to 10th	Night	38% 7% 12% 21% 16% 6%	1900
	11th to 20th	Night	36% 6% 11% 25% 19% 3	1942
	21st to end	Night	45% 6% 10% 19% 16% 3	2173
October	1st to 10th	Night	40% 5% 11% 23% 18% 4	2280
	11th to 20th	Night	34% 5% 9% 25% 21% 6%	2280
	21st to end	Night	31% 6% 10% 24% 24% 5%	2508
November	1st to 10th	Night	34% 5% 9% 23% 23% 7%	2228
	11th to 20th	Night	36% 4 8% 22% 23% 7%	2529
	21st to end	Night	34% 4 11% 24% 22% 5%	2660
December	1st to 10th	Night	42% 5% 11% 24% 15% 4	2660
	11th to 20th	Night	38% 5% 10% 22% 19% 5%	3288
	21st to end	Night	38% 9% 15% 24% 13% 2	4884

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	25% 21% 33% 17% 4	254
	11th to 20th	Day	28% 23% 29% 16% 3	270
	21st to end	Day	23% 23% 38% 12% 3 1	297
February	1st to 10th	Day	23% 24% 36% 15% 2	270
	11th to 20th	Day	35% 24% 33% 7% 1	275
	21st to end	Day	29% 14% 35% 19% 3	382
March	1st to 10th	Day	23% 18% 33% 21% 5%	460
	11th to 20th	Day	22% 21% 28% 21% 6% 2	460
	21st to end	Day	24% 17% 35% 17% 7% 1	506
April	1st to 10th	Day	20% 25% 24% 21% 9% 2	460
	11th to 20th	Day	18% 17% 26% 23% 12% 3	452
	21st to end	Day	23% 12% 33% 21% 9% 2	460
May	1st to 10th	Day	22% 14% 28% 22% 11% 4	463
	11th to 20th	Day	21% 9% 28% 26% 12% 4	487
	21st to end	Day	19% 5% 26% 27% 16% 7%	529
June	1st to 10th	Day	13% 6% 27% 28% 20% 7%	490
	11th to 20th	Day	12% 8% 25% 32% 15% 8%	490
	21st to end	Day	9% 6% 25% 35% 18% 7%	490
July	1st to 10th	Day	13% 3 14% 33% 27% 11%	485
	11th to 20th	Day	5% 4 17% 32% 29% 13%	484
	21st to end	Day	11% 4 17% 33% 25% 10%	532
August	1st to 10th	Day	10% 4 20% 27% 25% 13%	486
	11th to 20th	Day	11% 3 19% 29% 25% 12%	479
	21st to end	Day	9% 3 17% 32% 24% 15%	539
September	1st to 10th	Day	15% 5% 17% 28% 20% 15%	490
	11th to 20th	Day	17% 3 19% 25% 23% 12%	490
	21st to end	Day	29% 8% 19% 24% 15% 4	490
October	1st to 10th	Day	20% 5% 20% 31% 17% 6%	490
	11th to 20th	Day	14% 14% 26% 27% 16% 3	490
	21st to end	Day	17% 11% 32% 26% 12% 3	539
November	1st to 10th	Day	15% 11% 31% 27% 12% 4	455
	11th to 20th	Day	19% 11% 29% 28% 12% 2	304
	21st to end	Day	19% 13% 39% 22% 6%	180
December	1st to 10th	Day	19% 14% 41% 20% 6% 1	180
	11th to 20th	Day	24% 11% 37% 19% 8% 1	180
	21st to end	Day	22% 17% 34% 21% 6%	198
January	1st to 10th	Night	19% 13% 38% 26% 4	760
	11th to 20th	Night	19% 10% 34% 31% 5%	760
	21st to end	Night	19% 10% 39% 31% 3	836
February	1st to 10th	Night	17% 8% 40% 31% 4	760
	11th to 20th	Night	25% 15% 37% 22% 2	743
	21st to end	Night	20% 11% 40% 25% 3	628
March	1st to 10th	Night	17% 14% 36% 29% 4	760
	11th to 20th	Night	20% 14% 34% 25% 6% 1	760
	21st to end	Night	18% 12% 37% 26% 6%	836
April	1st to 10th	Night	19% 14% 33% 28% 6%	760
	11th to 20th	Night	15% 11% 33% 29% 10% 1	751
	21st to end	Night	19% 9% 30% 34% 8% 1	760
May	1st to 10th	Night	21% 7% 25% 29% 17% 1	572
	11th to 20th	Night	19% 4 25% 33% 18% 1	561
	21st to end	Night	16% 1 19% 39% 22% 3	411
June	1st to 10th	Night	11% 3 18% 44% 23% 2	380
	11th to 20th	Night	14% 2 15% 41% 26% 2	380
	21st to end	Night	9% 3 14% 47% 24% 2	380
July	1st to 10th	Night	13% 2 13% 35% 33% 5%	399
	11th to 20th	Night	6% 2 9% 37% 42% 5%	552
	21st to end	Night	9% 1 13% 39% 33% 5%	624
August	1st to 10th	Night	13% 1 10% 42% 30% 4	567
	11th to 20th	Night	12% 2 12% 38% 31% 4	601
	21st to end	Night	14% 2 12% 35% 33% 5%	836
September	1st to 10th	Night	17% 2 13% 34% 28% 5%	760
	11th to 20th	Night	14% 3 14% 35% 29% 5%	760
	21st to end	Night	28% 2 18% 30% 20% 3	760
October	1st to 10th	Night	20% 5% 17% 32% 21% 4	760
	11th to 20th	Night	15% 7% 27% 33% 16% 1	760
	21st to end	Night	17% 6% 26% 37% 12% 2	836
November	1st to 10th	Night	15% 6% 29% 35% 13% 2	743
	11th to 20th	Night	17% 8% 32% 33% 9% 1	760
	21st to end	Night	15% 8% 33% 31% 12% 1	760
December	1st to 10th	Night	18% 9% 35% 29% 9%	760
	11th to 20th	Night	17% 6% 35% 36% 6% 1	760
	21st to end	Night	19% 10% 29% 38% 4	836

Page generated at 2024-10-29 11:20:45. Version ac07

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