Morton Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Morton Observatory clear sky chart from 2005-11-06 to 2024-11-08.

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	7% 8% 2 6% 4 4 4 3 5% 6% 51%	104836
	Night	8% 8% 3 6% 4 4 4 3 5% 6% 50%	102971
Transparency	Day	31% 4 8% 21% 20% 15%	104601
	Night	34% 4 10% 22% 19% 12%	102795
Seeing	Day	10% 4 16% 32% 28% 9%	14852
	Night	12% 3 13% 41% 28% 4	25377

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	8% 17% 6% 12% 5% 4 3 4 5% 5% 30%	2858
	11th to 20th	Day	11% 20% 6% 12% 5% 3 3 2 3 5% 30%	2860
	21st to end	Day	9% 18% 4 10% 4 3 3 3 4 6% 35%	3146
February	1st to 10th	Day	11% 14% 4 7% 6% 5% 5% 4 5% 6% 33%	1710
	11th to 20th	Day	10% 15% 3 8% 5% 4 4 4 7% 6% 34%	1731
	21st to end	Day	9% 16% 4 11% 5% 4 3 3 6% 7% 32%	1570
March	1st to 10th	Day	8% 15% 5% 9% 5% 4 5% 4 5% 7% 33%	3371
	11th to 20th	Day	6% 11% 3 7% 5% 4 5% 4 5% 7% 42%	3490
	21st to end	Day	13% 19% 4 8% 5% 5% 5% 4 5% 6% 25%	3825
April	1st to 10th	Day	9% 11% 3 7% 5% 5% 4 3 6% 6% 40%	2109
	11th to 20th	Day	9% 11% 3 6% 5% 5% 4 4 6% 6% 42%	2386
	21st to end	Day	10% 9% 2 6% 4 4 4 4 5% 7% 46%	2470
May	1st to 10th	Day	9% 12% 3 7% 4 4 5% 4 6% 7% 39%	4110
	11th to 20th	Day	6% 4 1 5% 3 4 4 4 6% 8% 55%	4071
	21st to end	Day	8% 7% 2 5% 3 4 5% 4 7% 7% 49%	4477
June	1st to 10th	Day	4 4 2 5% 3 4 4 4 6% 8% 56%	2470
	11th to 20th	Day	6% 5% 1 4 3 3 3 3 4 6% 63%	2582
	21st to end	Day	3 3 1 3 3 3 3 3 4 6% 69%	2470
July	1st to 10th	Day	1 2 1 2 2 2 2 2 3 5% 79%	4110
	11th to 20th	Day	2 2 2 4 4 4 5% 4 7% 8% 56%	4110
	21st to end	Day	2 2 1 4 3 3 4 4 6% 7% 64%	4454
August	1st to 10th	Day	2 3 1 4 3 4 4 4 6% 6% 63%	4092
	11th to 20th	Day	2 2 1 5% 4 4 4 3 5% 6% 65%	4028
	21st to end	Day	3 3 1 3 2 3 4 3 4 6% 69%	4469
September	1st to 10th	Day	3 2 1 3 2 2 3 3 5% 6% 69%	2147
	11th to 20th	Day	5% 3 1 3 3 2 4 3 5% 7% 64%	2090
	21st to end	Day	5% 3 1 3 2 2 3 2 4 5% 69%	2090
October	1st to 10th	Day	6% 4 1 3 2 3 3 2 4 4 68%	3330
	11th to 20th	Day	6% 7% 2 5% 3 3 3 3 5% 5% 57%	3150
	21st to end	Day	7% 8% 3 6% 3 3 2 3 4 5% 57%	3438
November	1st to 10th	Day	12% 7% 3 6% 4 3 3 3 5% 5% 48%	1746
	11th to 20th	Day	13% 7% 3 5% 4 4 3 3 4 7% 46%	1710
	21st to end	Day	8% 11% 4 7% 5% 5% 4 3 4 6% 42%	1592
December	1st to 10th	Day	12% 12% 4 7% 4 3 4 3 5% 8% 38%	1520
	11th to 20th	Day	13% 13% 4 9% 6% 5% 5% 4 5% 7% 30%	1926
	21st to end	Day	10% 12% 4 8% 6% 5% 4 4 5% 7% 35%	3128
January	1st to 10th	Night	8% 13% 5% 9% 5% 5% 4 3 6% 7% 36%	4097
	11th to 20th	Night	13% 19% 5% 11% 4 4 3 3 4 6% 28%	4110
	21st to end	Night	10% 16% 3 8% 4 4 4 3 5% 7% 36%	4521
February	1st to 10th	Night	11% 14% 3 7% 4 4 3 4 5% 7% 39%	2470
	11th to 20th	Night	9% 12% 4 7% 5% 4 4 3 5% 5% 42%	2332
	21st to end	Night	8% 13% 5% 9% 4 4 4 4 6% 6% 38%	1884
March	1st to 10th	Night	11% 14% 5% 8% 4 5% 4 4 4 6% 34%	3502
	11th to 20th	Night	6% 8% 2 6% 4 4 4 4 6% 8% 49%	3490
	21st to end	Night	12% 17% 4 8% 4 4 4 3 4 6% 34%	3828
April	1st to 10th	Night	13% 11% 3 4 3 3 3 2 4 6% 47%	2070
	11th to 20th	Night	8% 8% 2 5% 4 5% 4 4 5% 7% 48%	1740
	21st to end	Night	11% 8% 3 6% 3 4 4 3 6% 6% 48%	1710
May	1st to 10th	Night	12% 9% 2 6% 4 4 5% 4 6% 8% 42%	2860
	11th to 20th	Night	7% 4 1 4 3 3 3 3 5% 7% 61%	2834
	21st to end	Night	10% 6% 2 4 3 3 3 3 5% 7% 54%	3110
June	1st to 10th	Night	6% 4 2 5% 3 3 4 3 6% 7% 56%	1693
	11th to 20th	Night	5% 4 1 3 2 3 3 2 4 5% 66%	1565
	21st to end	Night	4 2 2 3 2 3 3 3 5% 6% 68%	1710
July	1st to 10th	Night	4 3 1 3 3 3 2 3 3 5% 71%	2860
	11th to 20th	Night	2 3 1 5% 4 6% 7% 5% 7% 9% 50%	2860
	21st to end	Night	3 4 2 5% 5% 4 4 4 5% 6% 57%	3109
August	1st to 10th	Night	3 3 2 5% 3 4 5% 4 6% 7% 59%	2847
	11th to 20th	Night	3 3 2 5% 4 4 5% 4 5% 7% 58%	2811
	21st to end	Night	5% 2 1 2 2 3 3 3 4 5% 69%	3197
September	1st to 10th	Night	3 2 1 4 3 3 4 3 4 5% 67%	2028
	11th to 20th	Night	6% 3 1 3 3 3 3 3 5% 7% 63%	2090
	21st to end	Night	6% 4 1 3 2 2 2 2 3 5% 70%	2090
October	1st to 10th	Night	5% 3 1 3 2 2 3 3 3 4 71%	3645
	11th to 20th	Night	9% 5% 2 3 3 3 3 3 4 5% 59%	3778
	21st to end	Night	6% 5% 2 5% 3 3 4 3 5% 6% 58%	4120
November	1st to 10th	Night	9% 8% 2 4 3 3 3 4 5% 7% 52%	2492
	11th to 20th	Night	11% 6% 2 5% 3 3 3 3 4 7% 52%	2470
	21st to end	Night	9% 10% 3 6% 4 3 3 4 5% 6% 47%	2565
December	1st to 10th	Night	11% 10% 4 6% 3 3 3 3 5% 6% 45%	2660
	11th to 20th	Night	15% 12% 3 6% 4 4 4 4 6% 7% 34%	3271
	21st to end	Night	9% 12% 5% 10% 5% 5% 5% 4 7% 6% 33%	4552

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	53% 8% 13% 21% 4	2859
	11th to 20th	Day	61% 5% 15% 13% 4 1	2860
	21st to end	Day	52% 6% 18% 16% 6% 1	3146
February	1st to 10th	Day	48% 8% 14% 19% 9% 1	1710
	11th to 20th	Day	47% 4 13% 24% 11% 1	1740
	21st to end	Day	47% 3 13% 25% 11% 1	1570
March	1st to 10th	Day	43% 4 12% 28% 11% 2	3371
	11th to 20th	Day	36% 2 10% 39% 12% 2	3490
	21st to end	Day	55% 2 12% 22% 7% 2	3825
April	1st to 10th	Day	40% 2 12% 23% 17% 6%	2109
	11th to 20th	Day	37% 2 11% 27% 19% 4	2389
	21st to end	Day	34% 2 10% 29% 21% 3	2470
May	1st to 10th	Day	39% 2 6% 28% 19% 6%	4110
	11th to 20th	Day	23% 2 6% 34% 30% 5%	4074
	21st to end	Day	29% 3 7% 29% 27% 5%	4477
June	1st to 10th	Day	23% 2 7% 22% 32% 13%	2470
	11th to 20th	Day	21% 2 5% 18% 29% 25%	2582
	21st to end	Day	16% 2 1 11% 28% 42%	2470
July	1st to 10th	Day	10% 2 3 8% 15% 63%	4046
	11th to 20th	Day	19% 4 5% 12% 25% 34%	4041
	21st to end	Day	16% 3 6% 12% 24% 40%	4314
August	1st to 10th	Day	18% 3 6% 19% 28% 27%	4078
	11th to 20th	Day	19% 4 4 15% 31% 27%	4067
	21st to end	Day	15% 3 4 14% 29% 34%	4468
September	1st to 10th	Day	15% 3 5% 17% 30% 31%	2147
	11th to 20th	Day	18% 3 6% 21% 28% 24%	2090
	21st to end	Day	18% 2 4 22% 32% 22%	2090
October	1st to 10th	Day	19% 2 5% 15% 38% 21%	3330
	11th to 20th	Day	25% 4 8% 26% 28% 9%	3150
	21st to end	Day	27% 4 11% 29% 24% 5%	3438
November	1st to 10th	Day	36% 4 11% 25% 20% 4	1746
	11th to 20th	Day	37% 5% 11% 31% 15% 1	1710
	21st to end	Day	41% 8% 13% 24% 14% 2	1592
December	1st to 10th	Day	45% 8% 16% 21% 8% 2	1520
	11th to 20th	Day	53% 8% 12% 22% 6%	1924
	21st to end	Day	48% 11% 12% 18% 11%	3128
January	1st to 10th	Night	49% 7% 12% 26% 5% 1	4097
	11th to 20th	Night	61% 6% 14% 13% 4 1	4110
	21st to end	Night	50% 5% 20% 18% 6% 1	4521
February	1st to 10th	Night	46% 5% 17% 23% 8% 1	2470
	11th to 20th	Night	42% 5% 13% 26% 14% 1	2333
	21st to end	Night	43% 5% 11% 28% 11% 2	1884
March	1st to 10th	Night	47% 4 11% 29% 10%	3502
	11th to 20th	Night	32% 2 9% 39% 15% 2	3490
	21st to end	Night	49% 3 10% 22% 14% 2	3828
April	1st to 10th	Night	37% 3 11% 25% 18% 7%	2070
	11th to 20th	Night	34% 2 10% 26% 24% 4	1740
	21st to end	Night	34% 3 10% 28% 22% 3	1710
May	1st to 10th	Night	37% 2 6% 27% 23% 5%	2860
	11th to 20th	Night	23% 2 5% 32% 30% 8%	2835
	21st to end	Night	28% 3 7% 29% 29% 4	3110
June	1st to 10th	Night	25% 3 6% 22% 30% 13%	1693
	11th to 20th	Night	20% 1 6% 18% 31% 24%	1565
	21st to end	Night	16% 3 2 11% 28% 41%	1710
July	1st to 10th	Night	16% 2 4 7% 11% 60%	2815
	11th to 20th	Night	24% 5% 7% 11% 23% 31%	2806
	21st to end	Night	24% 4 6% 12% 22% 33%	3011
August	1st to 10th	Night	20% 5% 7% 17% 24% 26%	2838
	11th to 20th	Night	22% 5% 7% 14% 25% 27%	2838
	21st to end	Night	17% 3 5% 11% 28% 36%	3197
September	1st to 10th	Night	17% 4 4 15% 26% 34%	2028
	11th to 20th	Night	20% 3 6% 19% 27% 25%	2090
	21st to end	Night	20% 2 3 18% 32% 25%	2090
October	1st to 10th	Night	16% 2 6% 15% 35% 26%	3645
	11th to 20th	Night	25% 3 5% 28% 29% 10%	3778
	21st to end	Night	24% 4 9% 33% 26% 4	4120
November	1st to 10th	Night	31% 3 11% 29% 22% 5%	2492
	11th to 20th	Night	31% 5% 14% 32% 17% 3	2470
	21st to end	Night	37% 6% 11% 31% 13% 2	2565
December	1st to 10th	Night	39% 6% 17% 26% 10% 2	2660
	11th to 20th	Night	49% 7% 14% 23% 8%	3272
	21st to end	Night	50% 8% 14% 19% 8%	4552

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% 3 14% 33% 18% 9%	270
	11th to 20th	Day	16% 3 16% 37% 21% 6%	270
	21st to end	Day	14% 4 12% 39% 23% 7%	297
February	1st to 10th	Day	21% 6% 17% 39% 13% 4	270
	11th to 20th	Day	17% 5% 19% 37% 18% 5%	336
	21st to end	Day	13% 5% 23% 38% 17% 4	382
March	1st to 10th	Day	15% 5% 19% 37% 17% 6%	460
	11th to 20th	Day	13% 3 20% 35% 24% 5%	460
	21st to end	Day	19% 6% 24% 32% 17% 2	506
April	1st to 10th	Day	13% 7% 21% 32% 20% 7%	460
	11th to 20th	Day	14% 9% 26% 29% 18% 4	452
	21st to end	Day	14% 7% 22% 28% 22% 6%	460
May	1st to 10th	Day	10% 8% 22% 34% 19% 6%	463
	11th to 20th	Day	9% 3 22% 28% 28% 10%	488
	21st to end	Day	9% 5% 16% 27% 29% 13%	529
June	1st to 10th	Day	4 6% 14% 30% 36% 10%	490
	11th to 20th	Day	7% 5% 18% 33% 29% 7%	602
	21st to end	Day	3 4 20% 34% 31% 8%	490
July	1st to 10th	Day	1 4 9% 34% 39% 13%	486
	11th to 20th	Day	5% 2 7% 35% 42% 9%	484
	21st to end	Day	3 1 8% 29% 44% 15%	531
August	1st to 10th	Day	5% 1 10% 35% 38% 12%	487
	11th to 20th	Day	3 3 15% 25% 39% 14%	477
	21st to end	Day	5% 3 11% 28% 40% 13%	539
September	1st to 10th	Day	4 2 10% 32% 36% 16%	490
	11th to 20th	Day	5% 6% 16% 28% 31% 14%	490
	21st to end	Day	6% 4 14% 28% 34% 13%	490
October	1st to 10th	Day	8% 5% 16% 30% 29% 12%	395
	11th to 20th	Day	8% 4 16% 29% 26% 16%	300
	21st to end	Day	9% 6% 18% 36% 25% 7%	330
November	1st to 10th	Day	18% 6% 13% 31% 21% 11%	291
	11th to 20th	Day	13% 3 14% 38% 20% 12%	270
	21st to end	Day	14% 3 10% 34% 28% 10%	270
December	1st to 10th	Day	15% 3 13% 35% 23% 11%	270
	11th to 20th	Day	16% 6% 9% 41% 24% 4	270
	21st to end	Day	23% 5% 14% 35% 19% 4	297
January	1st to 10th	Night	18% 3 11% 40% 23% 4	760
	11th to 20th	Night	17% 4 12% 36% 27% 4	760
	21st to end	Night	16% 4 11% 42% 23% 4	836
February	1st to 10th	Night	17% 3 14% 47% 16% 3	760
	11th to 20th	Night	14% 3 15% 46% 19% 2	744
	21st to end	Night	13% 4 17% 46% 17% 1	628
March	1st to 10th	Night	17% 4 16% 44% 16% 3	760
	11th to 20th	Night	12% 3 15% 44% 24% 3	760
	21st to end	Night	15% 5% 17% 44% 17% 2	836
April	1st to 10th	Night	19% 4 16% 40% 18% 2	740
	11th to 20th	Night	10% 4 21% 49% 15% 1	563
	21st to end	Night	12% 4 18% 39% 24% 2	570
May	1st to 10th	Night	10% 5% 17% 44% 22% 2	570
	11th to 20th	Night	9% 3 11% 40% 34% 3	561
	21st to end	Night	10% 5% 13% 37% 31% 4	617
June	1st to 10th	Night	8% 5% 11% 39% 34% 3	570
	11th to 20th	Night	7% 4 17% 42% 28% 2	570
	21st to end	Night	5% 1 14% 40% 37% 3	570
July	1st to 10th	Night	5% 2 10% 34% 44% 6%	555
	11th to 20th	Night	5% 1 6% 42% 41% 5%	552
	21st to end	Night	5% 2 4 30% 54% 5%	624
August	1st to 10th	Night	4 1 8% 43% 41% 2	567
	11th to 20th	Night	4 1 9% 39% 41% 5%	564
	21st to end	Night	4 3 7% 38% 45% 3	627
September	1st to 10th	Night	4 2 9% 37% 40% 7%	698
	11th to 20th	Night	7% 3 12% 34% 38% 7%	760
	21st to end	Night	8% 2 11% 33% 39% 7%	760
October	1st to 10th	Night	10% 3 15% 39% 27% 6%	760
	11th to 20th	Night	9% 3 13% 39% 30% 6%	760
	21st to end	Night	11% 2 14% 41% 28% 3	836
November	1st to 10th	Night	13% 3 16% 37% 27% 4	770
	11th to 20th	Night	13% 2 15% 44% 22% 4	760
	21st to end	Night	13% 4 12% 41% 23% 7%	855
December	1st to 10th	Night	16% 3 14% 43% 21% 3	950
	11th to 20th	Night	21% 5% 11% 42% 19% 2	950
	21st to end	Night	21% 4 14% 44% 16% 2	854

Page generated at 2024-11-05 06:15:48. Version ac07

Copyright © 2024 Attilla Danko.