Stargate Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Stargate Observatory clear sky chart from 2005-11-06 to 2025-07-21.

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% 10% 4 8% 5% 5% 5% 4 6% 7% 33%	119482
	Night	14% 10% 4 8% 5% 5% 4 4 5% 6% 35%	119696
Transparency	Day	47% 6% 12% 21% 12% 2	123108
	Night	48% 5% 12% 21% 12% 1	124208
Seeing	Day	16% 10% 29% 25% 14% 6%	16269
	Night	18% 9% 29% 30% 12% 1	25859

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	11% 16% 5% 14% 6% 4 4 3 4 5% 27%	3617
	11th to 20th	Day	14% 16% 5% 16% 9% 8% 5% 4 5% 5% 14%	3636
	21st to end	Day	21% 17% 6% 11% 6% 5% 5% 4 4 4 18%	4466
February	1st to 10th	Day	15% 15% 4 13% 8% 6% 5% 3 4 5% 22%	1800
	11th to 20th	Day	13% 14% 5% 12% 8% 4 5% 3 5% 6% 25%	1857
	21st to end	Day	13% 16% 5% 12% 6% 5% 4 4 6% 5% 26%	1650
March	1st to 10th	Day	15% 13% 5% 11% 5% 4 3 3 4 6% 31%	4636
	11th to 20th	Day	12% 12% 4 8% 5% 5% 4 3 5% 7% 34%	4980
	21st to end	Day	19% 14% 4 9% 5% 4 4 3 4 5% 29%	5465
April	1st to 10th	Day	16% 12% 4 8% 5% 4 4 4 5% 6% 31%	2295
	11th to 20th	Day	16% 9% 3 8% 5% 4 4 4 6% 7% 34%	2562
	21st to end	Day	17% 9% 3 8% 5% 4 5% 4 4 6% 35%	2600
May	1st to 10th	Day	18% 8% 3 8% 4 4 4 4 5% 7% 34%	5862
	11th to 20th	Day	16% 8% 3 7% 5% 5% 4 4 6% 7% 35%	5861
	21st to end	Day	13% 6% 3 7% 5% 5% 4 4 5% 7% 41%	6433
June	1st to 10th	Day	9% 6% 3 7% 5% 5% 5% 5% 6% 8% 41%	2959
	11th to 20th	Day	9% 5% 2 7% 4 5% 5% 4 7% 9% 41%	3000
	21st to end	Day	9% 6% 2 6% 5% 6% 6% 5% 7% 10% 38%	2967
July	1st to 10th	Day	9% 6% 2 7% 6% 5% 6% 5% 7% 9% 38%	4580
	11th to 20th	Day	7% 5% 2 5% 4 5% 5% 5% 8% 11% 45%	4580
	21st to end	Day	6% 5% 3 7% 6% 5% 6% 6% 8% 9% 39%	4499
August	1st to 10th	Day	12% 5% 2 5% 5% 5% 6% 4 7% 8% 40%	4104
	11th to 20th	Day	8% 5% 2 7% 5% 5% 6% 5% 8% 10% 39%	4044
	21st to end	Day	9% 5% 3 7% 5% 5% 6% 5% 7% 10% 38%	4532
September	1st to 10th	Day	10% 6% 3 6% 5% 5% 5% 4 6% 9% 41%	2142
	11th to 20th	Day	9% 5% 1 6% 4 4 5% 5% 6% 9% 46%	2090
	21st to end	Day	14% 8% 3 6% 5% 5% 6% 4 6% 8% 35%	2090
October	1st to 10th	Day	11% 7% 3 6% 5% 4 4 4 6% 7% 43%	2014
	11th to 20th	Day	17% 8% 3 7% 5% 6% 5% 4 4 7% 34%	1900
	21st to end	Day	19% 10% 4 9% 4 4 5% 4 4 6% 31%	1959
November	1st to 10th	Day	11% 10% 3 9% 5% 4 4 4 6% 7% 37%	1762
	11th to 20th	Day	14% 11% 4 9% 6% 5% 4 5% 6% 6% 32%	1800
	21st to end	Day	17% 12% 4 10% 5% 5% 4 4 4 6% 27%	1613
December	1st to 10th	Day	13% 14% 6% 12% 6% 5% 4 3 6% 8% 24%	2600
	11th to 20th	Day	19% 20% 4 9% 4 4 3 4 6% 5% 22%	2803
	21st to end	Day	26% 20% 6% 10% 5% 4 4 2 4 4 15%	3724
January	1st to 10th	Night	13% 13% 5% 11% 6% 5% 4 3 5% 6% 29%	6348
	11th to 20th	Night	12% 16% 6% 14% 8% 7% 5% 4 5% 5% 19%	6341
	21st to end	Night	17% 17% 7% 10% 5% 5% 5% 3 4 4 23%	6490
February	1st to 10th	Night	14% 15% 5% 12% 8% 5% 6% 3 5% 4 23%	2600
	11th to 20th	Night	13% 13% 5% 10% 7% 6% 5% 4 6% 5% 28%	2424
	21st to end	Night	18% 12% 4 9% 5% 6% 4 3 5% 5% 29%	1980
March	1st to 10th	Night	15% 11% 3 9% 5% 4 4 3 4 6% 34%	5217
	11th to 20th	Night	9% 8% 3 8% 5% 5% 5% 4 6% 8% 40%	4980
	21st to end	Night	15% 9% 3 8% 5% 4 4 4 4 5% 39%	5467
April	1st to 10th	Night	17% 10% 4 6% 5% 4 4 4 6% 6% 34%	2121
	11th to 20th	Night	17% 8% 3 6% 4 4 4 4 5% 7% 37%	1786
	21st to end	Night	15% 9% 2 6% 4 4 5% 3 6% 8% 39%	1800
May	1st to 10th	Night	19% 9% 3 8% 5% 4 4 3 5% 6% 34%	4033
	11th to 20th	Night	16% 8% 3 8% 5% 5% 4 4 4 6% 39%	4032
	21st to end	Night	13% 5% 2 6% 4 4 4 4 5% 7% 44%	4404
June	1st to 10th	Night	10% 5% 2 6% 4 4 4 4 6% 9% 46%	1436
	11th to 20th	Night	9% 6% 3 5% 4 4 5% 5% 6% 8% 45%	1400
	21st to end	Night	8% 4 2 6% 5% 4 4 3 6% 8% 50%	1427
July	1st to 10th	Night	8% 4 2 4 4 4 5% 3 6% 11% 49%	2610
	11th to 20th	Night	9% 4 1 5% 3 4 3 3 7% 9% 53%	2610
	21st to end	Night	4 4 2 6% 4 5% 6% 5% 9% 10% 46%	3051
August	1st to 10th	Night	11% 6% 3 6% 3 4 5% 3 6% 8% 46%	2825
	11th to 20th	Night	8% 6% 2 6% 4 4 5% 4 6% 8% 47%	2785
	21st to end	Night	7% 5% 2 7% 5% 5% 5% 4 6% 7% 48%	3124
September	1st to 10th	Night	8% 6% 2 7% 5% 4 4 3 5% 7% 48%	2013
	11th to 20th	Night	9% 5% 2 5% 3 3 4 3 5% 8% 54%	2090
	21st to end	Night	15% 6% 2 6% 4 3 5% 4 5% 7% 44%	2090
October	1st to 10th	Night	13% 6% 2 6% 3 3 4 3 6% 7% 46%	2166
	11th to 20th	Night	17% 9% 3 7% 5% 5% 4 4 5% 5% 36%	2280
	21st to end	Night	20% 9% 3 6% 5% 5% 4 4 5% 7% 32%	2636
November	1st to 10th	Night	13% 9% 2 6% 4 4 4 4 5% 7% 43%	2536
	11th to 20th	Night	15% 10% 4 8% 5% 6% 5% 4 6% 7% 31%	2600
	21st to end	Night	18% 13% 4 8% 5% 5% 4 4 5% 6% 28%	2785
December	1st to 10th	Night	13% 13% 5% 12% 6% 5% 5% 4 6% 6% 24%	4580
	11th to 20th	Night	15% 18% 6% 10% 6% 5% 5% 3 5% 5% 22%	5380
	21st to end	Night	25% 20% 6% 10% 5% 4 3 3 4 4 17%	7249

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	59% 4 13% 15% 7% 2	3618
	11th to 20th	Day	71% 6% 9% 8% 6% 1	3636
	21st to end	Day	69% 4 13% 8% 6%	4466
February	1st to 10th	Day	63% 5% 9% 15% 7%	1800
	11th to 20th	Day	59% 5% 10% 18% 7% 2	1866
	21st to end	Day	60% 3 12% 17% 6% 2	1650
March	1st to 10th	Day	54% 5% 14% 17% 8% 2	4636
	11th to 20th	Day	49% 5% 14% 23% 8% 2	4980
	21st to end	Day	56% 5% 11% 16% 10% 2	5465
April	1st to 10th	Day	51% 5% 11% 20% 11% 1	2295
	11th to 20th	Day	48% 5% 11% 20% 14% 2	2562
	21st to end	Day	48% 6% 13% 19% 13% 2	2600
May	1st to 10th	Day	47% 6% 10% 20% 12% 4	5897
	11th to 20th	Day	47% 6% 12% 21% 12% 2	5865
	21st to end	Day	42% 6% 10% 19% 19% 4	6447
June	1st to 10th	Day	39% 6% 13% 26% 14% 2	2959
	11th to 20th	Day	37% 7% 14% 24% 15% 3	3000
	21st to end	Day	38% 8% 12% 24% 16% 2	2967
July	1st to 10th	Day	39% 8% 13% 22% 16% 2	4511
	11th to 20th	Day	29% 8% 15% 32% 15% 1	4505
	21st to end	Day	35% 10% 14% 17% 22% 2	4357
August	1st to 10th	Day	37% 8% 13% 24% 16% 1	4091
	11th to 20th	Day	36% 8% 12% 32% 10% 1	4083
	21st to end	Day	38% 8% 12% 27% 14% 1	4531
September	1st to 10th	Day	39% 6% 15% 25% 13% 2	2142
	11th to 20th	Day	32% 6% 12% 33% 15% 1	2090
	21st to end	Day	44% 6% 13% 25% 12% 1	2090
October	1st to 10th	Day	31% 5% 11% 32% 19% 2	3352
	11th to 20th	Day	40% 5% 11% 26% 18%	3140
	21st to end	Day	45% 6% 13% 23% 13% 1	3209
November	1st to 10th	Day	44% 6% 12% 25% 11% 1	1762
	11th to 20th	Day	51% 5% 14% 19% 10% 1	1800
	21st to end	Day	58% 4 13% 18% 6% 1	1613
December	1st to 10th	Day	58% 5% 18% 15% 4	2600
	11th to 20th	Day	63% 5% 13% 12% 7%	2799
	21st to end	Day	73% 4 9% 9% 6%	3724
January	1st to 10th	Night	54% 5% 11% 20% 7% 2	6348
	11th to 20th	Night	64% 6% 13% 11% 5%	6341
	21st to end	Night	64% 4 11% 15% 7%	6490
February	1st to 10th	Night	61% 6% 10% 15% 7% 1	2600
	11th to 20th	Night	56% 5% 10% 19% 9% 1	2426
	21st to end	Night	55% 3 13% 19% 8% 1	1980
March	1st to 10th	Night	50% 4 15% 21% 10% 1	5217
	11th to 20th	Night	41% 5% 15% 25% 14% 1	4980
	21st to end	Night	47% 5% 11% 21% 15% 1	5467
April	1st to 10th	Night	48% 5% 11% 21% 12% 2	2121
	11th to 20th	Night	45% 5% 11% 19% 18% 2	1786
	21st to end	Night	43% 5% 11% 20% 17% 3	1800
May	1st to 10th	Night	51% 4 11% 16% 14% 5%	4060
	11th to 20th	Night	45% 6% 12% 24% 12% 2	4033
	21st to end	Night	37% 6% 12% 24% 16% 5%	4411
June	1st to 10th	Night	34% 6% 10% 28% 19% 2	1436
	11th to 20th	Night	36% 6% 13% 25% 18% 2	1400
	21st to end	Night	33% 6% 12% 26% 22% 1	1427
July	1st to 10th	Night	29% 5% 14% 31% 15% 6%	2570
	11th to 20th	Night	27% 6% 15% 34% 17% 1	2562
	21st to end	Night	28% 10% 17% 21% 21% 2	2954
August	1st to 10th	Night	34% 6% 15% 27% 17% 1	2814
	11th to 20th	Night	33% 8% 13% 32% 12% 2	2812
	21st to end	Night	33% 8% 12% 32% 15% 1	3124
September	1st to 10th	Night	35% 6% 14% 28% 16% 2	2013
	11th to 20th	Night	29% 5% 14% 31% 21% 1	2090
	21st to end	Night	40% 4 13% 29% 12% 1	2090
October	1st to 10th	Night	26% 4 10% 32% 27% 1	3608
	11th to 20th	Night	43% 4 11% 24% 17% 1	3779
	21st to end	Night	41% 5% 13% 28% 13% 1	4336
November	1st to 10th	Night	41% 5% 13% 26% 14% 1	2536
	11th to 20th	Night	50% 5% 14% 20% 9% 1	2600
	21st to end	Night	56% 4 14% 18% 6%	2785
December	1st to 10th	Night	58% 7% 18% 14% 3	4580
	11th to 20th	Night	62% 5% 12% 14% 6% 1	5383
	21st to end	Night	71% 5% 10% 9% 6%	7249

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	18% 18% 39% 18% 7% 1	300
	11th to 20th	Day	21% 15% 44% 15% 3 1	300
	21st to end	Day	24% 13% 39% 18% 5% 1	330
February	1st to 10th	Day	21% 18% 40% 16% 3 1	300
	11th to 20th	Day	21% 19% 38% 19% 2	300
	21st to end	Day	20% 21% 44% 12% 2	249
March	1st to 10th	Day	22% 17% 39% 18% 4 1	365
	11th to 20th	Day	20% 15% 32% 25% 6% 1	500
	21st to end	Day	27% 14% 30% 23% 5% 1	550
April	1st to 10th	Day	17% 15% 38% 21% 7% 1	500
	11th to 20th	Day	24% 14% 30% 17% 10% 5%	492
	21st to end	Day	22% 12% 29% 24% 11% 2	500
May	1st to 10th	Day	22% 11% 29% 24% 12% 3	503
	11th to 20th	Day	18% 10% 25% 25% 15% 6%	527
	21st to end	Day	14% 6% 23% 29% 20% 8%	573
June	1st to 10th	Day	10% 7% 33% 32% 15% 4	689
	11th to 20th	Day	11% 5% 30% 33% 18% 4	730
	21st to end	Day	11% 7% 26% 32% 19% 5%	730
July	1st to 10th	Day	8% 5% 22% 30% 22% 14%	721
	11th to 20th	Day	8% 5% 24% 34% 20% 9%	718
	21st to end	Day	7% 4 22% 30% 26% 11%	552
August	1st to 10th	Day	9% 5% 18% 27% 27% 15%	486
	11th to 20th	Day	12% 3 14% 32% 24% 15%	479
	21st to end	Day	11% 4 18% 31% 23% 13%	539
September	1st to 10th	Day	11% 5% 23% 24% 24% 12%	490
	11th to 20th	Day	9% 3 18% 22% 31% 16%	490
	21st to end	Day	16% 9% 23% 23% 20% 8%	490
October	1st to 10th	Day	13% 11% 26% 23% 18% 9%	490
	11th to 20th	Day	19% 14% 32% 24% 8% 3	490
	21st to end	Day	23% 13% 38% 18% 7% 1	408
November	1st to 10th	Day	18% 15% 36% 21% 8% 2	300
	11th to 20th	Day	20% 19% 35% 17% 8% 1	300
	21st to end	Day	22% 16% 37% 20% 5%	205
December	1st to 10th	Day	21% 17% 40% 15% 8% 1	200
	11th to 20th	Day	32% 15% 36% 14% 4 1	200
	21st to end	Day	27% 19% 33% 17% 4	273
January	1st to 10th	Night	22% 12% 38% 22% 5% 1	1000
	11th to 20th	Night	24% 12% 35% 25% 4 1	994
	21st to end	Night	20% 10% 35% 28% 6%	880
February	1st to 10th	Night	20% 11% 42% 24% 3	800
	11th to 20th	Night	20% 13% 37% 25% 5%	783
	21st to end	Night	23% 14% 39% 21% 2	660
March	1st to 10th	Night	20% 11% 36% 27% 6%	800
	11th to 20th	Night	16% 13% 38% 26% 6% 1	800
	21st to end	Night	22% 9% 33% 28% 8%	880
April	1st to 10th	Night	22% 12% 34% 28% 4	721
	11th to 20th	Night	21% 9% 33% 27% 8% 2	593
	21st to end	Night	18% 8% 32% 33% 9%	600
May	1st to 10th	Night	18% 7% 30% 35% 10% 1	600
	11th to 20th	Night	20% 6% 26% 32% 16% 1	591
	21st to end	Night	10% 3 23% 41% 21% 2	645
June	1st to 10th	Night	11% 4 26% 44% 14%	400
	11th to 20th	Night	11% 4 24% 46% 15% 1	400
	21st to end	Night	11% 3 20% 46% 21%	427
July	1st to 10th	Night	8% 3 16% 41% 27% 5%	585
	11th to 20th	Night	9% 4 16% 41% 26% 3	582
	21st to end	Night	6% 3 17% 46% 26% 2	624
August	1st to 10th	Night	9% 2 14% 39% 33% 3	567
	11th to 20th	Night	7% 2 17% 38% 32% 4	564
	21st to end	Night	10% 2 17% 35% 32% 3	627
September	1st to 10th	Night	10% 6% 19% 34% 26% 5%	701
	11th to 20th	Night	10% 3 17% 34% 29% 5%	760
	21st to end	Night	16% 5% 20% 34% 20% 5%	760
October	1st to 10th	Night	16% 8% 25% 31% 18% 2	760
	11th to 20th	Night	22% 10% 29% 27% 10% 2	760
	21st to end	Night	25% 9% 33% 29% 5%	836
November	1st to 10th	Night	18% 10% 30% 28% 13% 1	780
	11th to 20th	Night	20% 15% 33% 24% 7% 1	800
	21st to end	Night	25% 12% 35% 22% 6%	800
December	1st to 10th	Night	25% 11% 37% 20% 6%	800
	11th to 20th	Night	23% 12% 38% 24% 4	879
	21st to end	Night	28% 11% 32% 25% 3	1100

Page generated at 2025-07-18 01:09:59. Version ac07

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