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 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	2 5% 2 6% 4 5% 5% 5% 7% 8% 50%	101487
	Night	2 5% 2 6% 5% 5% 5% 5% 7% 8% 50%	97660
Transparency	Day	29% 9% 11% 20% 19% 11%	101252
	Night	29% 10% 13% 22% 17% 9%	97485
Seeing	Day	7% 15% 28% 28% 17% 5%	15402
	Night	5% 9% 23% 38% 23% 3	25303

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% 4 11% 7% 8% 9% 7% 10% 9% 29%	2858
	11th to 20th	Day	5% 2 10% 8% 7% 9% 7% 11% 10% 32%	2860
	21st to end	Day	1 9% 5% 13% 7% 8% 8% 6% 7% 8% 28%	3146
February	1st to 10th	Day	1 6% 4 9% 7% 7% 7% 6% 11% 11% 32%	1710
	11th to 20th	Day	1 9% 4 9% 6% 7% 7% 5% 8% 10% 34%	1674
	21st to end	Day	1 8% 3 11% 7% 6% 7% 5% 9% 9% 33%	1570
March	1st to 10th	Day	1 6% 3 9% 7% 7% 7% 7% 9% 10% 34%	3375
	11th to 20th	Day	2 6% 3 5% 4 5% 6% 5% 6% 8% 47%	3490
	21st to end	Day	3 10% 4 11% 8% 7% 8% 6% 8% 9% 26%	3825
April	1st to 10th	Day	4 7% 3 7% 6% 6% 6% 4 8% 8% 41%	2143
	11th to 20th	Day	4 7% 3 6% 6% 6% 6% 6% 7% 9% 41%	2390
	21st to end	Day	4 5% 3 6% 5% 5% 6% 5% 7% 10% 45%	2470
May	1st to 10th	Day	6% 8% 2 7% 5% 6% 8% 5% 8% 9% 35%	4110
	11th to 20th	Day	4 4 1 4 3 3 4 4 6% 8% 57%	4071
	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	5% 6% 2 6% 4 4 5% 4 6% 7% 50%	1969
	11th to 20th	Day	4 5% 1 4 3 4 5% 6% 6% 8% 55%	1900
	21st to end	Day	2 5% 2 6% 4 5% 7% 4 6% 10% 50%	2076
November	1st to 10th	Day	3 6% 3 8% 4 5% 6% 5% 7% 8% 44%	1674
	11th to 20th	Day	2 6% 3 5% 5% 5% 7% 6% 6% 11% 44%	1625
	21st to end	Day	2 6% 4 7% 6% 6% 7% 6% 7% 8% 43%	1520
December	1st to 10th	Day	1 6% 4 9% 7% 7% 7% 6% 9% 9% 36%	1520
	11th to 20th	Day	1 7% 4 10% 7% 8% 8% 9% 9% 10% 27%	1926
	21st to end	Day	1 8% 4 9% 8% 8% 8% 8% 9% 9% 28%	2826
January	1st to 10th	Night	1 5% 4 12% 6% 6% 8% 8% 8% 9% 34%	4097
	11th to 20th	Night	1 5% 3 8% 7% 6% 7% 6% 11% 12% 35%	4110
	21st to end	Night	1 11% 5% 12% 9% 7% 7% 4 7% 9% 26%	4521
February	1st to 10th	Night	1 6% 2 9% 7% 7% 7% 6% 10% 10% 35%	2470
	11th to 20th	Night	1 7% 3 7% 5% 5% 7% 5% 9% 9% 42%	2388
	21st to end	Night	1 5% 3 7% 5% 6% 6% 6% 12% 11% 38%	1884
March	1st to 10th	Night	1 5% 2 5% 4 4 6% 7% 9% 12% 44%	3499
	11th to 20th	Night	1 5% 2 4 3 4 6% 5% 7% 8% 53%	3490
	21st to end	Night	3 9% 3 8% 6% 5% 7% 5% 7% 8% 39%	3828
April	1st to 10th	Night	2 7% 3 6% 4 5% 5% 6% 8% 8% 47%	2035
	11th to 20th	Night	3 6% 2 5% 6% 4 5% 4 7% 8% 48%	1735
	21st to end	Night	5% 5% 1 5% 5% 4 5% 3 7% 9% 52%	1710
May	1st to 10th	Night	5% 7% 2 6% 4 5% 6% 5% 7% 9% 45%	2860
	11th to 20th	Night	6% 4 1 4 3 3 4 3 5% 8% 60%	2834
	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	4 5% 1 5% 4 3 3 4 5% 6% 59%	2210
	11th to 20th	Night	4 5% 2 5% 3 3 4 3 5% 8% 57%	2280
	21st to end	Night	3 4 1 4 3 4 5% 4 6% 8% 56%	2517
November	1st to 10th	Night	3 5% 2 5% 4 4 6% 5% 7% 9% 48%	2411
	11th to 20th	Night	2 4 2 5% 5% 5% 7% 6% 8% 10% 46%	2532
	21st to end	Night	1 6% 2 5% 5% 6% 8% 6% 8% 9% 45%	2660
December	1st to 10th	Night	2 5% 3 8% 7% 6% 7% 6% 8% 9% 39%	2660
	11th to 20th	Night	2 6% 3 9% 6% 7% 8% 8% 10% 11% 30%	3271
	21st to end	Night	1 6% 3 12% 9% 8% 9% 8% 8% 9% 26%	4869

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	44% 15% 17% 17% 6% 1	2859
	11th to 20th	Day	45% 19% 16% 14% 5% 1	2860
	21st to end	Day	47% 17% 14% 13% 7% 1	3146
February	1st to 10th	Day	43% 14% 18% 16% 7% 1	1710
	11th to 20th	Day	43% 12% 16% 18% 8% 2	1683
	21st to end	Day	43% 14% 16% 17% 9% 1	1570
March	1st to 10th	Day	41% 16% 11% 19% 12% 1	3375
	11th to 20th	Day	30% 12% 19% 27% 12%	3490
	21st to end	Day	51% 13% 13% 17% 4 1	3825
April	1st to 10th	Day	38% 11% 15% 21% 12% 2	2143
	11th to 20th	Day	37% 10% 14% 24% 14%	2393
	21st to end	Day	34% 10% 15% 27% 13%	2470
May	1st to 10th	Day	38% 14% 12% 20% 12% 4	4110
	11th to 20th	Day	23% 7% 11% 35% 18% 5%	4074
	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	31% 6% 11% 25% 20% 7%	1969
	11th to 20th	Day	25% 8% 16% 28% 20% 4	1900
	21st to end	Day	27% 8% 18% 28% 17% 1	2076
November	1st to 10th	Day	36% 10% 17% 23% 13% 2	1674
	11th to 20th	Day	32% 12% 21% 23% 12% 1	1625
	21st to end	Day	35% 9% 17% 23% 14% 1	1520
December	1st to 10th	Day	40% 15% 19% 16% 7% 3	1520
	11th to 20th	Day	44% 14% 19% 16% 7%	1924
	21st to end	Day	42% 14% 14% 17% 12% 2	2826
January	1st to 10th	Night	41% 16% 15% 19% 8% 1	4097
	11th to 20th	Night	44% 19% 15% 15% 6% 1	4110
	21st to end	Night	48% 17% 15% 14% 5% 2	4521
February	1st to 10th	Night	39% 17% 17% 19% 7%	2470
	11th to 20th	Night	34% 13% 17% 21% 13% 2	2389
	21st to end	Night	35% 15% 16% 23% 10% 2	1884
March	1st to 10th	Night	29% 15% 15% 24% 17% 1	3499
	11th to 20th	Night	23% 12% 23% 31% 11% 1	3490
	21st to end	Night	39% 15% 17% 24% 5% 1	3828
April	1st to 10th	Night	33% 12% 18% 21% 11% 6%	2035
	11th to 20th	Night	31% 9% 15% 27% 17%	1735
	21st to end	Night	28% 9% 16% 30% 17%	1710
May	1st to 10th	Night	30% 13% 13% 24% 17% 3	2860
	11th to 20th	Night	22% 6% 13% 32% 22% 5%	2835
	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	25% 6% 11% 27% 25% 7%	2210
	11th to 20th	Night	25% 6% 12% 31% 21% 5%	2280
	21st to end	Night	23% 7% 19% 31% 17% 3	2517
November	1st to 10th	Night	30% 10% 17% 23% 17% 4	2411
	11th to 20th	Night	29% 11% 20% 26% 12% 2	2532
	21st to end	Night	31% 10% 17% 26% 13% 3	2660
December	1st to 10th	Night	37% 13% 20% 18% 8% 3	2660
	11th to 20th	Night	39% 14% 17% 22% 8%	3272
	21st to end	Night	43% 12% 15% 18% 9% 3	4869

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% 20% 24% 24% 22% 3	270
	11th to 20th	Day	7% 17% 28% 31% 16% 2	270
	21st to end	Day	6% 15% 25% 35% 16% 3	297
February	1st to 10th	Day	7% 27% 36% 24% 6%	270
	11th to 20th	Day	9% 20% 36% 24% 10% 2	279
	21st to end	Day	8% 24% 38% 23% 6%	382
March	1st to 10th	Day	7% 25% 35% 25% 7% 1	460
	11th to 20th	Day	8% 20% 33% 27% 12% 1	460
	21st to end	Day	11% 27% 36% 20% 5%	506
April	1st to 10th	Day	12% 25% 29% 20% 12% 2	460
	11th to 20th	Day	12% 25% 38% 16% 7% 2	452
	21st to end	Day	11% 26% 28% 19% 12% 4	460
May	1st to 10th	Day	11% 23% 33% 21% 10% 2	463
	11th to 20th	Day	11% 13% 33% 28% 13% 2	488
	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% 18% 28% 28% 16% 2	330
November	1st to 10th	Day	13% 17% 27% 24% 12% 8%	270
	11th to 20th	Day	9% 15% 28% 31% 13% 4	270
	21st to end	Day	7% 14% 24% 33% 17% 5%	270
December	1st to 10th	Day	6% 16% 26% 33% 16% 4	270
	11th to 20th	Day	8% 17% 27% 34% 13% 1	270
	21st to end	Day	9% 17% 34% 25% 11% 4	297
January	1st to 10th	Night	4 9% 26% 39% 20% 2	760
	11th to 20th	Night	4 11% 27% 36% 19% 2	760
	21st to end	Night	3 8% 31% 41% 15% 2	836
February	1st to 10th	Night	4 15% 33% 35% 12% 1	760
	11th to 20th	Night	3 12% 30% 38% 14% 2	744
	21st to end	Night	5% 13% 33% 37% 12% 1	628
March	1st to 10th	Night	3 12% 31% 40% 12% 2	760
	11th to 20th	Night	3 8% 26% 44% 17% 1	760
	21st to end	Night	6% 11% 32% 36% 13% 1	836
April	1st to 10th	Night	6% 11% 29% 38% 15% 1	705
	11th to 20th	Night	8% 13% 30% 35% 13% 1	563
	21st to end	Night	6% 11% 27% 34% 19% 2	570
May	1st to 10th	Night	10% 10% 24% 36% 19% 1	570
	11th to 20th	Night	9% 5% 19% 36% 28% 2	561
	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	6% 8% 23% 38% 21% 4	836
November	1st to 10th	Night	6% 9% 24% 38% 20% 3	742
	11th to 20th	Night	4 12% 27% 39% 15% 3	822
	21st to end	Night	5% 12% 25% 37% 18% 3	950
December	1st to 10th	Night	6% 11% 27% 41% 14% 1	950
	11th to 20th	Night	4 11% 30% 41% 12% 1	950
	21st to end	Night	5% 16% 31% 36% 12% 1	1041

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