Garden City
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Garden City clear sky chart from 2005-11-06 to 2025-05-11.

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	2 5% 2 6% 5% 5% 6% 5% 7% 8% 50%	118325
	Night	2 5% 2 6% 5% 5% 5% 5% 7% 9% 50%	119502
Transparency	Day	29% 9% 12% 22% 19% 10%	118090
	Night	28% 9% 13% 24% 17% 8%	119327
Seeing	Day	7% 14% 28% 29% 17% 5%	16056
	Night	5% 8% 23% 39% 22% 3	26078

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	5% 3 11% 7% 8% 8% 7% 11% 11% 29%	4098
	11th to 20th	Day	3 2 9% 7% 7% 9% 8% 11% 10% 35%	4100
	21st to end	Day	1 6% 4 11% 6% 6% 6% 5% 7% 9% 39%	4510
February	1st to 10th	Day	1 7% 5% 9% 7% 7% 7% 6% 11% 11% 31%	1800
	11th to 20th	Day	1 9% 4 9% 6% 7% 8% 5% 8% 10% 33%	1765
	21st to end	Day	1 7% 3 10% 7% 6% 7% 5% 9% 9% 35%	1650
March	1st to 10th	Day	1 8% 3 10% 7% 6% 6% 6% 8% 8% 37%	4859
	11th to 20th	Day	2 5% 3 7% 5% 5% 7% 6% 7% 9% 44%	5000
	21st to end	Day	2 8% 4 10% 7% 7% 8% 5% 8% 9% 32%	5486
April	1st to 10th	Day	3 7% 3 7% 6% 5% 6% 4 8% 9% 42%	2256
	11th to 20th	Day	4 7% 2 6% 5% 6% 6% 6% 8% 9% 41%	2518
	21st to end	Day	4 5% 3 6% 5% 5% 6% 5% 7% 10% 44%	2600
May	1st to 10th	Day	6% 8% 2 7% 5% 6% 8% 5% 8% 9% 36%	4240
	11th to 20th	Day	4 4 1 4 3 3 4 4 6% 8% 57%	4073
	21st to end	Day	4 4 2 6% 4 5% 6% 5% 7% 8% 50%	4668
June	1st to 10th	Day	3 4 1 4 4 4 5% 5% 7% 9% 54%	2660
	11th to 20th	Day	4 3 1 4 4 4 5% 4 6% 8% 58%	2664
	21st to end	Day	1 2 1 2 2 3 4 3 4 7% 71%	2850
July	1st to 10th	Day	2 1 1 2 2 2 2 2 4 5% 77%	4380
	11th to 20th	Day	2 2 1 2 2 3 4 4 6% 9% 66%	4110
	21st to end	Day	3 2 1 3 2 3 3 3 5% 7% 67%	4454
August	1st to 10th	Day	2 2 1 3 2 4 3 4 5% 7% 66%	4092
	11th to 20th	Day	2 1 1 3 3 3 4 3 5% 8% 68%	4028
	21st to end	Day	2 1 1 2 2 3 3 3 5% 6% 73%	4473
September	1st to 10th	Day	3 2 1 3 3 3 3 3 6% 7% 68%	2200
	11th to 20th	Day	3 3 1 3 3 4 4 4 4 7% 64%	2090
	21st to end	Day	4 3 1 3 3 3 3 4 4 6% 66%	2090
October	1st to 10th	Day	3 4 2 4 3 3 3 3 5% 6% 65%	3278
	11th to 20th	Day	4 6% 1 4 3 3 4 5% 7% 8% 55%	3150
	21st to end	Day	2 6% 2 6% 4 5% 6% 4 6% 9% 51%	3413
November	1st to 10th	Day	3 6% 3 8% 4 5% 6% 5% 7% 9% 44%	1764
	11th to 20th	Day	1 6% 3 6% 5% 5% 7% 6% 6% 11% 44%	1710
	21st to end	Day	2 6% 4 7% 6% 6% 6% 6% 7% 8% 43%	1600
December	1st to 10th	Day	1 4 3 5% 4 6% 7% 6% 8% 9% 48%	2620
	11th to 20th	Day	5% 3 9% 7% 7% 8% 8% 11% 12% 31%	3026
	21st to end	Day	1 7% 4 11% 8% 9% 9% 7% 10% 9% 26%	4050
January	1st to 10th	Night	4 3 10% 6% 6% 7% 8% 9% 11% 35%	5867
	11th to 20th	Night	1 4 2 7% 6% 6% 7% 6% 11% 12% 38%	5880
	21st to end	Night	1 8% 4 10% 7% 6% 5% 4 6% 8% 40%	6468
February	1st to 10th	Night	1 7% 2 9% 7% 7% 7% 6% 9% 10% 35%	2600
	11th to 20th	Night	1 7% 3 7% 5% 5% 7% 5% 9% 9% 42%	2517
	21st to end	Night	1 5% 3 7% 5% 6% 6% 6% 11% 11% 39%	1980
March	1st to 10th	Night	1 8% 3 7% 4 4 5% 6% 8% 10% 44%	5035
	11th to 20th	Night	1 6% 3 6% 4 5% 6% 4 7% 10% 48%	5000
	21st to end	Night	3 7% 3 7% 5% 5% 6% 5% 7% 8% 45%	5489
April	1st to 10th	Night	2 6% 3 5% 4 4 5% 6% 8% 8% 47%	2142
	11th to 20th	Night	3 6% 3 5% 6% 4 5% 4 7% 8% 49%	1827
	21st to end	Night	5% 5% 2 5% 5% 4 6% 3 7% 9% 51%	1800
May	1st to 10th	Night	5% 7% 2 6% 4 5% 6% 5% 7% 9% 46%	2950
	11th to 20th	Night	6% 4 1 4 3 3 4 3 5% 8% 60%	2838
	21st to end	Night	5% 4 1 6% 5% 4 4 4 5% 8% 55%	2901
June	1st to 10th	Night	3 3 1 4 3 4 5% 4 7% 10% 57%	1520
	11th to 20th	Night	4 2 1 3 3 3 3 3 6% 9% 63%	1504
	21st to end	Night	2 2 1 2 2 3 4 2 5% 6% 70%	1330
July	1st to 10th	Night	1 1 1 3 3 1 3 3 4 4 77%	2557
	11th to 20th	Night	1 2 1 3 3 3 3 4 6% 9% 66%	2860
	21st to end	Night	2 2 1 3 3 3 3 3 6% 7% 67%	3109
August	1st to 10th	Night	2 2 1 4 3 3 4 3 6% 8% 64%	2847
	11th to 20th	Night	3 4 1 5% 3 3 4 3 5% 6% 63%	2811
	21st to end	Night	2 2 1 2 2 2 3 3 4 6% 74%	3194
September	1st to 10th	Night	2 3 1 3 3 3 3 2 5% 6% 70%	1976
	11th to 20th	Night	4 2 4 3 4 4 3 4 7% 65%	2090
	21st to end	Night	5% 2 1 3 2 3 3 2 4 5% 69%	2090
October	1st to 10th	Night	3 3 1 3 2 2 2 2 3 5% 73%	3694
	11th to 20th	Night	4 5% 2 7% 4 4 4 3 5% 7% 55%	3778
	21st to end	Night	3 6% 2 4 3 4 5% 4 7% 9% 53%	4140
November	1st to 10th	Night	3 5% 2 5% 4 4 6% 5% 7% 9% 48%	2535
	11th to 20th	Night	2 4 2 5% 5% 6% 7% 6% 8% 10% 47%	2666
	21st to end	Night	1 6% 2 5% 5% 6% 8% 5% 8% 10% 45%	2800
December	1st to 10th	Night	1 3 2 5% 4 5% 7% 5% 7% 8% 52%	4570
	11th to 20th	Night	1 5% 3 8% 5% 6% 7% 7% 9% 10% 39%	5181
	21st to end	Night	1 6% 3 13% 9% 8% 9% 8% 8% 9% 26%	6956

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	41% 12% 22% 16% 8%	4099
	11th to 20th	Day	40% 16% 13% 19% 9% 4	4100
	21st to end	Day	37% 12% 12% 23% 14% 1	4510
February	1st to 10th	Day	43% 14% 17% 16% 8% 1	1800
	11th to 20th	Day	45% 11% 16% 18% 8% 2	1774
	21st to end	Day	42% 14% 16% 17% 9% 2	1650
March	1st to 10th	Day	41% 12% 9% 23% 11% 3	4859
	11th to 20th	Day	29% 11% 15% 31% 13%	5000
	21st to end	Day	46% 10% 18% 21% 4	5486
April	1st to 10th	Day	38% 11% 15% 22% 13% 2	2256
	11th to 20th	Day	37% 10% 13% 25% 15%	2521
	21st to end	Day	34% 10% 15% 27% 13%	2600
May	1st to 10th	Day	37% 13% 12% 21% 13% 4	4240
	11th to 20th	Day	23% 7% 11% 35% 18% 5%	4076
	21st to end	Day	27% 11% 11% 31% 18% 1	4668
June	1st to 10th	Day	24% 9% 15% 26% 23% 3	2660
	11th to 20th	Day	24% 7% 9% 21% 28% 12%	2664
	21st to end	Day	13% 5% 6% 19% 33% 24%	2850
July	1st to 10th	Day	10% 4 4 11% 18% 53%	4316
	11th to 20th	Day	13% 5% 4 13% 31% 34%	4041
	21st to end	Day	17% 4 4 12% 32% 31%	4314
August	1st to 10th	Day	17% 5% 5% 18% 30% 25%	4078
	11th to 20th	Day	15% 4 5% 21% 34% 21%	4067
	21st to end	Day	13% 4 5% 14% 39% 25%	4472
September	1st to 10th	Day	15% 6% 7% 19% 33% 21%	2200
	11th to 20th	Day	20% 6% 8% 22% 30% 14%	2090
	21st to end	Day	18% 6% 7% 27% 34% 8%	2090
October	1st to 10th	Day	21% 4 6% 21% 31% 17%	3278
	11th to 20th	Day	26% 5% 10% 29% 24% 6%	3150
	21st to end	Day	29% 7% 13% 35% 16% 1	3413
November	1st to 10th	Day	35% 10% 16% 23% 14% 1	1764
	11th to 20th	Day	32% 11% 21% 23% 12% 1	1710
	21st to end	Day	35% 9% 17% 25% 14% 1	1600
December	1st to 10th	Day	29% 12% 21% 29% 8% 2	2620
	11th to 20th	Day	38% 10% 24% 21% 6%	3024
	21st to end	Day	45% 12% 15% 17% 11% 1	4050
January	1st to 10th	Night	36% 14% 16% 24% 9% 1	5867
	11th to 20th	Night	38% 16% 12% 23% 8% 2	5880
	21st to end	Night	38% 12% 13% 22% 13% 1	6468
February	1st to 10th	Night	39% 16% 16% 19% 8% 1	2600
	11th to 20th	Night	34% 13% 17% 22% 13% 2	2518
	21st to end	Night	33% 15% 16% 24% 11% 2	1980
March	1st to 10th	Night	32% 12% 13% 24% 14% 5%	5035
	11th to 20th	Night	28% 9% 17% 33% 13% 1	5000
	21st to end	Night	33% 11% 23% 26% 7% 1	5489
April	1st to 10th	Night	32% 11% 18% 22% 11% 6%	2142
	11th to 20th	Night	31% 9% 15% 27% 18% 1	1827
	21st to end	Night	29% 8% 16% 29% 17%	1800
May	1st to 10th	Night	30% 13% 13% 24% 18% 3	2950
	11th to 20th	Night	22% 6% 13% 32% 22% 5%	2839
	21st to end	Night	25% 9% 11% 33% 20% 1	2901
June	1st to 10th	Night	21% 9% 18% 25% 24% 3	1520
	11th to 20th	Night	17% 6% 11% 24% 29% 13%	1504
	21st to end	Night	14% 4 6% 18% 32% 27%	1330
July	1st to 10th	Night	11% 4 5% 10% 18% 53%	2513
	11th to 20th	Night	15% 4 4 14% 30% 33%	2806
	21st to end	Night	16% 4 6% 13% 35% 27%	3011
August	1st to 10th	Night	17% 5% 6% 17% 30% 25%	2838
	11th to 20th	Night	23% 3 5% 16% 30% 23%	2838
	21st to end	Night	12% 4 6% 13% 34% 30%	3194
September	1st to 10th	Night	16% 4 7% 20% 27% 26%	1976
	11th to 20th	Night	19% 5% 8% 22% 29% 16%	2090
	21st to end	Night	18% 5% 8% 26% 35% 9%	2090
October	1st to 10th	Night	15% 4 6% 22% 40% 13%	3694
	11th to 20th	Night	30% 4 7% 28% 23% 8%	3778
	21st to end	Night	26% 6% 12% 35% 18% 3	4140
November	1st to 10th	Night	30% 10% 16% 24% 17% 3	2535
	11th to 20th	Night	29% 11% 20% 27% 12% 2	2666
	21st to end	Night	30% 9% 17% 27% 13% 3	2800
December	1st to 10th	Night	27% 11% 20% 30% 11% 2	4570
	11th to 20th	Night	33% 11% 24% 26% 6%	5182
	21st to end	Night	45% 10% 15% 21% 7% 2	6956

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	7% 19% 25% 27% 20% 3	300
	11th to 20th	Day	6% 16% 27% 32% 17% 2	300
	21st to end	Day	5% 15% 25% 36% 16% 3	330
February	1st to 10th	Day	9% 26% 36% 24% 5%	300
	11th to 20th	Day	9% 18% 36% 26% 9% 2	310
	21st to end	Day	7% 22% 37% 25% 7% 1	414
March	1st to 10th	Day	8% 24% 33% 26% 8% 2	500
	11th to 20th	Day	7% 20% 33% 28% 11% 1	500
	21st to end	Day	11% 26% 35% 21% 6% 1	550
April	1st to 10th	Day	11% 23% 28% 21% 14% 2	500
	11th to 20th	Day	12% 24% 38% 17% 8% 2	492
	21st to end	Day	11% 24% 28% 21% 13% 3	500
May	1st to 10th	Day	10% 21% 31% 20% 13% 4	503
	11th to 20th	Day	11% 13% 33% 28% 13% 2	489
	21st to end	Day	10% 12% 26% 26% 21% 5%	642
June	1st to 10th	Day	5% 12% 25% 30% 23% 5%	680
	11th to 20th	Day	6% 14% 29% 32% 17% 2	680
	21st to end	Day	2 7% 27% 38% 21% 5%	680
July	1st to 10th	Day	2 6% 25% 39% 22% 6%	569
	11th to 20th	Day	4 5% 28% 34% 22% 6%	484
	21st to end	Day	4 3 22% 37% 27% 7%	531
August	1st to 10th	Day	5% 4 31% 30% 21% 8%	487
	11th to 20th	Day	3 4 26% 34% 26% 6%	477
	21st to end	Day	3 6% 24% 36% 22% 9%	539
September	1st to 10th	Day	3 9% 23% 30% 22% 13%	490
	11th to 20th	Day	6% 13% 28% 26% 18% 10%	490
	21st to end	Day	5% 13% 22% 28% 23% 8%	490
October	1st to 10th	Day	5% 12% 22% 21% 30% 10%	369
	11th to 20th	Day	8% 14% 20% 27% 23% 9%	300
	21st to end	Day	8% 19% 28% 28% 16% 2	330
November	1st to 10th	Day	11% 16% 26% 27% 12% 7%	300
	11th to 20th	Day	9% 15% 29% 30% 12% 4	300
	21st to end	Day	7% 13% 25% 35% 17% 4	300
December	1st to 10th	Day	5% 14% 24% 31% 17% 8%	300
	11th to 20th	Day	7% 16% 29% 34% 12% 1	300
	21st to end	Day	8% 17% 35% 25% 12% 4	330
January	1st to 10th	Night	4 9% 27% 39% 19% 2	800
	11th to 20th	Night	4 11% 27% 37% 19% 2	800
	21st to end	Night	3 8% 32% 41% 15% 2	880
February	1st to 10th	Night	4 14% 34% 35% 11% 1	800
	11th to 20th	Night	4 12% 30% 39% 14% 2	784
	21st to end	Night	5% 12% 33% 38% 12% 1	660
March	1st to 10th	Night	3 12% 30% 41% 13% 2	800
	11th to 20th	Night	3 9% 26% 44% 17% 1	800
	21st to end	Night	5% 11% 32% 37% 14% 1	880
April	1st to 10th	Night	6% 11% 29% 39% 16% 1	742
	11th to 20th	Night	8% 12% 30% 36% 13% 1	593
	21st to end	Night	7% 11% 26% 36% 19% 2	600
May	1st to 10th	Night	10% 10% 23% 37% 20% 2	600
	11th to 20th	Night	9% 5% 19% 36% 28% 2	563
	21st to end	Night	8% 6% 21% 35% 27% 3	617
June	1st to 10th	Night	3 7% 20% 37% 30% 3	570
	11th to 20th	Night	5% 7% 23% 41% 24%	554
	21st to end	Night	3 2 13% 44% 35% 3	380
July	1st to 10th	Night	1 12% 38% 46% 2	458
	11th to 20th	Night	2 2 12% 45% 38% 1	552
	21st to end	Night	3 1 7% 42% 43% 4	624
August	1st to 10th	Night	2 1 10% 46% 39% 2	567
	11th to 20th	Night	4 2 9% 45% 38% 3	564
	21st to end	Night	4 3 12% 37% 40% 5%	627
September	1st to 10th	Night	3 4 13% 38% 37% 5%	646
	11th to 20th	Night	4 6% 13% 36% 36% 6%	760
	21st to end	Night	5% 5% 15% 33% 33% 8%	760
October	1st to 10th	Night	5% 6% 20% 36% 29% 4	760
	11th to 20th	Night	6% 9% 19% 36% 26% 4	760
	21st to end	Night	5% 8% 23% 38% 21% 4	836
November	1st to 10th	Night	6% 9% 24% 38% 19% 3	780
	11th to 20th	Night	4 12% 28% 40% 14% 2	866
	21st to end	Night	5% 12% 26% 37% 17% 3	1000
December	1st to 10th	Night	6% 10% 27% 41% 15% 1	1000
	11th to 20th	Night	4 11% 32% 41% 12% 1	1000
	21st to end	Night	4 15% 32% 35% 12% 1	1095

Page generated at 2025-05-08 07:33:59. Version ac07

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