Amazing Grace Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Amazing Grace Observatory 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	18% 9% 3 7% 5% 5% 5% 4 6% 7% 31%	101372
	Night	18% 10% 3 7% 5% 5% 5% 4 6% 7% 31%	97696
Transparency	Day	48% 6% 13% 21% 12% 1	104884
	Night	47% 6% 13% 21% 11% 1	102273
Seeing	Day	26% 18% 28% 18% 8% 2	14861
	Night	24% 15% 24% 26% 9% 1	23731

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	14% 11% 5% 8% 6% 5% 5% 4 5% 7% 30%	2517
	11th to 20th	Day	15% 12% 6% 11% 10% 5% 5% 4 5% 5% 23%	2520
	21st to end	Day	16% 12% 5% 12% 5% 5% 3 4 6% 5% 26%	2772
February	1st to 10th	Day	15% 13% 3 9% 6% 6% 5% 4 5% 7% 26%	1675
	11th to 20th	Day	12% 10% 4 10% 8% 5% 5% 4 6% 7% 30%	1848
	21st to end	Day	16% 11% 4 10% 5% 4 5% 4 5% 6% 29%	1570
March	1st to 10th	Day	20% 18% 3 9% 6% 4 4 3 4 5% 25%	3116
	11th to 20th	Day	15% 12% 6% 9% 6% 5% 5% 4 5% 6% 28%	3306
	21st to end	Day	19% 11% 3 8% 5% 5% 4 3 5% 7% 30%	4087
April	1st to 10th	Day	21% 11% 3 8% 5% 5% 4 3 4 5% 30%	2280
	11th to 20th	Day	18% 8% 3 6% 5% 4 6% 4 5% 6% 34%	2278
	21st to end	Day	21% 9% 4 9% 5% 4 5% 3 5% 7% 28%	2470
May	1st to 10th	Day	26% 11% 3 9% 5% 4 4 3 4 5% 25%	4106
	11th to 20th	Day	19% 9% 4 8% 6% 5% 5% 4 6% 6% 28%	4324
	21st to end	Day	14% 6% 2 6% 5% 4 6% 5% 7% 8% 37%	4837
June	1st to 10th	Day	20% 8% 2 8% 6% 5% 6% 5% 6% 8% 26%	2660
	11th to 20th	Day	18% 7% 3 5% 5% 5% 6% 5% 5% 7% 35%	2660
	21st to end	Day	20% 8% 3 8% 6% 5% 5% 4 5% 6% 29%	2660
July	1st to 10th	Day	14% 6% 2 6% 5% 5% 6% 5% 8% 10% 32%	4440
	11th to 20th	Day	13% 5% 2 7% 5% 5% 6% 5% 8% 10% 34%	4440
	21st to end	Day	21% 5% 2 6% 4 4 5% 4 6% 7% 35%	4814
August	1st to 10th	Day	16% 6% 3 7% 6% 6% 5% 5% 7% 8% 32%	4277
	11th to 20th	Day	18% 7% 2 8% 5% 5% 6% 5% 8% 9% 27%	4021
	21st to end	Day	11% 4 1 6% 4 5% 6% 5% 8% 9% 41%	4180
September	1st to 10th	Day	12% 5% 2 6% 5% 4 5% 4 6% 8% 43%	2280
	11th to 20th	Day	14% 5% 2 5% 4 4 4 3 4 6% 48%	2111
	21st to end	Day	17% 6% 2 6% 5% 5% 4 3 6% 7% 40%	2090
October	1st to 10th	Day	23% 9% 3 7% 4 4 4 4 4 6% 33%	2090
	11th to 20th	Day	17% 8% 3 7% 5% 5% 5% 3 4 6% 37%	1807
	21st to end	Day	24% 11% 4 7% 4 5% 4 4 4 4 29%	1881
November	1st to 10th	Day	14% 7% 4 7% 6% 4 4 3 6% 7% 36%	1708
	11th to 20th	Day	18% 10% 3 6% 5% 5% 5% 5% 5% 7% 31%	1710
	21st to end	Day	21% 9% 3 6% 5% 6% 5% 5% 7% 6% 29%	1639
December	1st to 10th	Day	21% 12% 5% 9% 5% 6% 6% 4 5% 5% 21%	1520
	11th to 20th	Day	23% 12% 2 6% 4 3 4 3 4 7% 32%	1906
	21st to end	Day	24% 12% 4 7% 6% 5% 5% 4 4 6% 24%	2772
January	1st to 10th	Night	15% 10% 5% 8% 5% 4 5% 4 6% 7% 31%	4429
	11th to 20th	Night	13% 13% 6% 13% 9% 5% 5% 4 5% 6% 21%	4440
	21st to end	Night	17% 14% 5% 11% 5% 5% 5% 4 6% 7% 22%	4884
February	1st to 10th	Night	14% 11% 4 9% 7% 5% 5% 4 6% 7% 28%	2504
	11th to 20th	Night	11% 10% 4 8% 5% 6% 6% 6% 6% 8% 30%	2218
	21st to end	Night	13% 11% 3 8% 6% 6% 5% 5% 7% 7% 31%	1884
March	1st to 10th	Night	23% 14% 3 6% 6% 4 4 4 5% 5% 27%	3724
	11th to 20th	Night	14% 13% 5% 9% 6% 5% 5% 4 4 6% 28%	3653
	21st to end	Night	21% 13% 4 8% 4 3 3 3 5% 6% 30%	3544
April	1st to 10th	Night	19% 10% 3 7% 5% 5% 5% 3 4 6% 34%	1900
	11th to 20th	Night	20% 9% 3 6% 5% 4 4 4 5% 6% 34%	1851
	21st to end	Night	22% 9% 2 6% 4 4 3 4 5% 6% 34%	1710
May	1st to 10th	Night	27% 12% 4 6% 5% 4 5% 4 5% 5% 25%	2834
	11th to 20th	Night	20% 11% 4 7% 5% 5% 5% 5% 5% 6% 26%	2598
	21st to end	Night	15% 7% 2 5% 4 5% 5% 4 6% 8% 39%	2738
June	1st to 10th	Night	21% 8% 3 7% 5% 4 5% 4 5% 8% 30%	1520
	11th to 20th	Night	18% 8% 3 5% 4 4 4 4 5% 6% 37%	1520
	21st to end	Night	18% 7% 3 7% 4 4 5% 4 6% 7% 35%	1520
July	1st to 10th	Night	13% 6% 2 6% 5% 6% 6% 5% 7% 9% 35%	2520
	11th to 20th	Night	18% 6% 2 6% 4 3 4 3 5% 8% 40%	2520
	21st to end	Night	19% 6% 2 6% 4 4 5% 4 6% 6% 38%	2739
August	1st to 10th	Night	21% 9% 3 7% 4 4 4 4 6% 5% 34%	2620
	11th to 20th	Night	18% 8% 3 7% 4 4 5% 4 5% 8% 34%	2803
	21st to end	Night	10% 4 2 5% 4 6% 5% 4 7% 9% 42%	3476
September	1st to 10th	Night	14% 5% 2 5% 4 3 4 4 5% 7% 48%	1900
	11th to 20th	Night	16% 6% 2 4 3 3 4 3 5% 6% 48%	2068
	21st to end	Night	18% 6% 2 5% 4 4 4 3 6% 6% 42%	2090
October	1st to 10th	Night	21% 7% 2 6% 5% 5% 5% 3 6% 6% 33%	2090
	11th to 20th	Night	17% 7% 2 8% 5% 5% 6% 3 5% 7% 34%	2370
	21st to end	Night	23% 9% 3 6% 5% 4 5% 3 6% 7% 29%	2717
November	1st to 10th	Night	14% 7% 3 8% 5% 5% 5% 4 6% 6% 36%	2470
	11th to 20th	Night	17% 7% 4 7% 5% 5% 5% 4 6% 9% 33%	2470
	21st to end	Night	16% 9% 4 7% 5% 5% 6% 4 7% 7% 30%	2540
December	1st to 10th	Night	21% 12% 4 10% 6% 6% 6% 4 5% 5% 22%	2660
	11th to 20th	Night	21% 12% 3 7% 4 4 4 4 6% 7% 27%	3288
	21st to end	Night	23% 14% 5% 9% 5% 4 4 3 5% 5% 23%	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	46% 5% 14% 27% 8%	2518
	11th to 20th	Day	56% 8% 10% 19% 6% 1	2520
	21st to end	Day	55% 6% 11% 19% 9% 1	2772
February	1st to 10th	Day	53% 4 13% 19% 9% 2	1675
	11th to 20th	Day	50% 5% 12% 18% 12% 3	1857
	21st to end	Day	52% 4 12% 16% 13% 2	1570
March	1st to 10th	Day	61% 3 10% 13% 11% 2	3119
	11th to 20th	Day	51% 6% 11% 15% 13% 4	3306
	21st to end	Day	52% 4 5% 16% 19% 4	4087
April	1st to 10th	Day	53% 3 10% 19% 12% 3	2280
	11th to 20th	Day	46% 5% 12% 21% 15% 1	2278
	21st to end	Day	55% 5% 8% 18% 13% 2	2470
May	1st to 10th	Day	60% 5% 9% 17% 7% 1	4120
	11th to 20th	Day	53% 5% 16% 15% 9% 1	4328
	21st to end	Day	40% 7% 14% 24% 14% 1	4837
June	1st to 10th	Day	52% 6% 14% 20% 9%	2660
	11th to 20th	Day	46% 6% 12% 21% 14% 2	2660
	21st to end	Day	52% 6% 11% 19% 10% 1	2660
July	1st to 10th	Day	41% 8% 15% 23% 12%	4370
	11th to 20th	Day	41% 7% 16% 26% 9%	4365
	21st to end	Day	45% 6% 12% 23% 14%	4661
August	1st to 10th	Day	46% 8% 16% 22% 9%	4263
	11th to 20th	Day	48% 7% 16% 22% 6%	4060
	21st to end	Day	33% 7% 17% 27% 15% 1	4180
September	1st to 10th	Day	35% 6% 13% 29% 15% 1	2280
	11th to 20th	Day	36% 4 9% 31% 18% 2	2111
	21st to end	Day	41% 4 13% 25% 15% 2	2090
October	1st to 10th	Day	45% 6% 10% 22% 15% 1	3480
	11th to 20th	Day	42% 3 14% 24% 14% 2	2971
	21st to end	Day	40% 3 12% 27% 15% 3	3081
November	1st to 10th	Day	44% 4 15% 22% 14% 1	1708
	11th to 20th	Day	47% 3 14% 18% 15% 2	1710
	21st to end	Day	48% 6% 19% 18% 9% 1	1639
December	1st to 10th	Day	57% 5% 14% 17% 6% 1	1520
	11th to 20th	Day	51% 4 10% 18% 15% 1	1906
	21st to end	Day	59% 4 11% 17% 9%	2772
January	1st to 10th	Night	47% 5% 15% 24% 8% 1	4429
	11th to 20th	Night	55% 7% 13% 16% 8% 1	4440
	21st to end	Night	57% 5% 11% 17% 8% 1	4884
February	1st to 10th	Night	50% 5% 14% 19% 11% 2	2504
	11th to 20th	Night	45% 5% 13% 23% 13% 2	2220
	21st to end	Night	46% 4 13% 21% 11% 3	1884
March	1st to 10th	Night	56% 4 11% 17% 10% 2	3734
	11th to 20th	Night	53% 5% 11% 17% 13% 2	3654
	21st to end	Night	52% 4 6% 14% 18% 5%	3544
April	1st to 10th	Night	51% 4 10% 19% 14% 2	1900
	11th to 20th	Night	49% 4 8% 25% 14% 1	1851
	21st to end	Night	47% 4 12% 18% 15% 3	1710
May	1st to 10th	Night	60% 5% 10% 16% 8% 1	2840
	11th to 20th	Night	55% 7% 12% 16% 8% 2	2599
	21st to end	Night	40% 7% 18% 20% 13% 2	2739
June	1st to 10th	Night	50% 6% 14% 19% 11%	1520
	11th to 20th	Night	46% 5% 15% 20% 12% 2	1520
	21st to end	Night	46% 7% 14% 21% 11% 1	1520
July	1st to 10th	Night	40% 8% 17% 21% 13%	2480
	11th to 20th	Night	40% 6% 16% 26% 12%	2472
	21st to end	Night	41% 6% 13% 27% 12% 1	2651
August	1st to 10th	Night	50% 6% 13% 22% 9%	2610
	11th to 20th	Night	45% 8% 17% 20% 11%	2830
	21st to end	Night	30% 9% 19% 28% 14%	3476
September	1st to 10th	Night	32% 7% 15% 31% 15%	1900
	11th to 20th	Night	35% 5% 11% 30% 17% 2	2068
	21st to end	Night	41% 4 12% 28% 14% 1	2090
October	1st to 10th	Night	44% 6% 14% 24% 11% 1	3480
	11th to 20th	Night	38% 6% 12% 25% 17% 3	3945
	21st to end	Night	41% 5% 13% 28% 12% 2	4467
November	1st to 10th	Night	42% 6% 13% 24% 14% 2	2470
	11th to 20th	Night	44% 5% 12% 23% 14% 2	2470
	21st to end	Night	46% 6% 16% 22% 9% 1	2540
December	1st to 10th	Night	56% 5% 13% 19% 6%	2660
	11th to 20th	Night	50% 6% 13% 17% 13% 1	3288
	21st to end	Night	59% 5% 9% 20% 6%	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	29% 23% 28% 16% 3 1	180
	11th to 20th	Day	34% 27% 27% 10% 1 1	180
	21st to end	Day	22% 28% 32% 14% 5%	198
February	1st to 10th	Day	36% 24% 28% 10% 2	286
	11th to 20th	Day	30% 28% 28% 12% 3	456
	21st to end	Day	34% 22% 24% 17% 3	382
March	1st to 10th	Day	29% 24% 28% 14% 4	460
	11th to 20th	Day	35% 24% 24% 12% 4 1	460
	21st to end	Day	34% 20% 24% 14% 5% 2	506
April	1st to 10th	Day	37% 20% 23% 13% 5% 2	460
	11th to 20th	Day	33% 26% 20% 15% 5% 2	452
	21st to end	Day	33% 21% 28% 11% 4 2	460
May	1st to 10th	Day	34% 19% 26% 14% 5% 2	463
	11th to 20th	Day	24% 19% 32% 16% 6% 2	487
	21st to end	Day	22% 16% 30% 23% 7% 2	529
June	1st to 10th	Day	23% 16% 34% 17% 9%	490
	11th to 20th	Day	21% 17% 31% 22% 8% 2	490
	21st to end	Day	21% 17% 32% 20% 8% 1	490
July	1st to 10th	Day	19% 13% 33% 22% 10% 3	485
	11th to 20th	Day	16% 10% 35% 28% 10% 2	484
	21st to end	Day	17% 13% 34% 26% 8% 2	532
August	1st to 10th	Day	14% 14% 29% 25% 15% 2	486
	11th to 20th	Day	19% 14% 28% 20% 13% 6%	479
	21st to end	Day	14% 14% 29% 24% 13% 6%	539
September	1st to 10th	Day	16% 12% 29% 22% 16% 5%	490
	11th to 20th	Day	18% 13% 25% 20% 15% 9%	490
	21st to end	Day	19% 16% 25% 24% 11% 6%	490
October	1st to 10th	Day	30% 15% 20% 19% 12% 4	490
	11th to 20th	Day	27% 16% 25% 21% 10% 2	433
	21st to end	Day	38% 15% 23% 17% 7%	429
November	1st to 10th	Day	25% 18% 23% 25% 9% 1	378
	11th to 20th	Day	32% 18% 23% 20% 7% 1	370
	21st to end	Day	34% 18% 29% 14% 5% 1	299
December	1st to 10th	Day	29% 26% 24% 16% 4	180
	11th to 20th	Day	39% 19% 30% 9% 2	180
	21st to end	Day	34% 19% 28% 15% 3 1	198
January	1st to 10th	Night	24% 22% 28% 23% 3	760
	11th to 20th	Night	29% 18% 25% 24% 3	760
	21st to end	Night	21% 24% 30% 21% 4	836
February	1st to 10th	Night	24% 21% 33% 21% 2	760
	11th to 20th	Night	23% 24% 32% 18% 3	743
	21st to end	Night	25% 21% 27% 23% 3	628
March	1st to 10th	Night	26% 18% 29% 23% 4	760
	11th to 20th	Night	27% 21% 23% 22% 6%	760
	21st to end	Night	27% 19% 24% 23% 6% 1	836
April	1st to 10th	Night	29% 17% 27% 22% 4	760
	11th to 20th	Night	26% 20% 25% 23% 6%	727
	21st to end	Night	28% 17% 27% 22% 6%	570
May	1st to 10th	Night	29% 13% 25% 25% 8%	570
	11th to 20th	Night	22% 13% 25% 31% 9%	438
	21st to end	Night	23% 7% 20% 37% 12% 1	411
June	1st to 10th	Night	26% 9% 23% 32% 9% 1	380
	11th to 20th	Night	23% 9% 23% 31% 14%	380
	21st to end	Night	20% 7% 24% 37% 12% 1	380
July	1st to 10th	Night	16% 5% 22% 42% 15%	370
	11th to 20th	Night	17% 3 21% 37% 20% 2	368
	21st to end	Night	16% 5% 18% 42% 19% 1	416
August	1st to 10th	Night	20% 3 16% 41% 20%	440
	11th to 20th	Night	19% 6% 25% 31% 18% 2	570
	21st to end	Night	18% 5% 19% 33% 22% 3	836
September	1st to 10th	Night	15% 9% 21% 33% 21% 2	760
	11th to 20th	Night	19% 10% 17% 28% 21% 4	760
	21st to end	Night	21% 10% 19% 31% 16% 3	760
October	1st to 10th	Night	26% 10% 20% 27% 16% 2	760
	11th to 20th	Night	23% 16% 24% 25% 12% 1	760
	21st to end	Night	30% 16% 24% 23% 7%	836
November	1st to 10th	Night	21% 16% 23% 30% 8% 1	760
	11th to 20th	Night	27% 18% 22% 25% 8% 1	760
	21st to end	Night	26% 18% 23% 26% 5% 1	760
December	1st to 10th	Night	30% 19% 26% 20% 5%	760
	11th to 20th	Night	32% 17% 25% 21% 4 1	760
	21st to end	Night	31% 22% 24% 21% 3	836

Page generated at 2024-11-03 02:11:30. Version ac07

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