Eye In The Sky YOGO Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Eye In The Sky YOGO Observatory clear sky chart from 2005-11-06 to 2026-03-03.

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	5% 7% 3 7% 5% 5% 5% 4 7% 8% 44%	139934
	Night	4 6% 3 7% 4 4 5% 4 6% 8% 48%	138630
Transparency	Day	35% 6% 14% 24% 16% 5%	134621
	Night	31% 6% 16% 27% 16% 4	134949
Seeing	Day	15% 20% 31% 23% 10% 2	17238
	Night	11% 21% 30% 27% 10% 1	26842

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	1 7% 4 10% 6% 5% 5% 4 8% 10% 40%	4124
	11th to 20th	Day	1 6% 4 10% 7% 9% 8% 4 6% 7% 38%	4260
	21st to end	Day	1 4 2 8% 5% 5% 5% 4 6% 8% 51%	5738
February	1st to 10th	Day	2 9% 5% 11% 6% 6% 5% 4 8% 9% 36%	1890
	11th to 20th	Day	1 8% 5% 13% 7% 6% 6% 4 6% 9% 35%	1845
	21st to end	Day	1 9% 4 10% 7% 4 5% 5% 7% 10% 39%	1573
March	1st to 10th	Day	3 6% 3 8% 5% 5% 5% 4 6% 10% 44%	4880
	11th to 20th	Day	2 6% 4 8% 6% 6% 7% 6% 9% 9% 38%	5000
	21st to end	Day	6% 16% 6% 12% 6% 6% 6% 5% 6% 7% 23%	5486
April	1st to 10th	Day	6% 15% 4 7% 6% 5% 5% 5% 7% 8% 32%	2355
	11th to 20th	Day	8% 13% 5% 11% 6% 5% 5% 4 6% 7% 29%	2545
	21st to end	Day	12% 15% 4 8% 5% 5% 4 5% 5% 7% 29%	2600
May	1st to 10th	Day	13% 13% 4 6% 4 4 4 3 5% 7% 37%	6051
	11th to 20th	Day	13% 10% 3 9% 6% 5% 6% 5% 7% 8% 28%	6298
	21st to end	Day	12% 7% 2 6% 5% 5% 5% 4 7% 7% 40%	7047
June	1st to 10th	Day	13% 8% 3 6% 5% 6% 6% 5% 7% 8% 34%	3000
	11th to 20th	Day	13% 7% 3 6% 5% 5% 5% 6% 7% 9% 34%	3000
	21st to end	Day	4 4 1 6% 5% 4 5% 5% 8% 9% 48%	3000
July	1st to 10th	Day	4 3 1 5% 4 5% 7% 6% 9% 9% 47%	6779
	11th to 20th	Day	6% 2 1 3 3 3 4 3 6% 8% 60%	6780
	21st to end	Day	3 2 1 4 4 5% 6% 5% 7% 9% 55%	6872
August	1st to 10th	Day	5% 3 1 6% 5% 6% 7% 6% 8% 9% 43%	5779
	11th to 20th	Day	3 2 1 4 4 4 5% 5% 7% 9% 56%	5798
	21st to end	Day	5% 4 1 4 4 4 4 4 6% 7% 58%	6451
September	1st to 10th	Day	7% 5% 1 5% 3 4 3 3 5% 7% 58%	2400
	11th to 20th	Day	9% 6% 2 5% 4 5% 4 4 6% 8% 49%	2255
	21st to end	Day	9% 5% 2 5% 3 3 4 3 4 7% 56%	2198
October	1st to 10th	Day	7% 7% 2 4 3 3 2 3 4 6% 59%	3270
	11th to 20th	Day	5% 7% 2 5% 3 3 4 3 5% 6% 56%	3250
	21st to end	Day	3 9% 3 6% 4 3 4 3 7% 7% 50%	3401
November	1st to 10th	Day	4 10% 4 8% 4 5% 5% 4 7% 8% 41%	1673
	11th to 20th	Day	2 7% 3 8% 4 6% 5% 6% 8% 11% 40%	1680
	21st to end	Day	2 9% 3 7% 4 5% 5% 4 8% 9% 44%	1680
December	1st to 10th	Day	1 7% 3 7% 4 4 4 4 7% 9% 50%	2686
	11th to 20th	Day	1 6% 4 8% 5% 5% 5% 5% 7% 9% 45%	2715
	21st to end	Day	2 11% 5% 8% 4 4 4 4 6% 8% 45%	3575
January	1st to 10th	Night	1 7% 4 8% 5% 5% 4 5% 7% 10% 44%	8768
	11th to 20th	Night	1 6% 4 8% 7% 6% 6% 5% 7% 8% 44%	8743
	21st to end	Night	1 6% 3 9% 5% 5% 4 4 6% 7% 49%	8468
February	1st to 10th	Night	2 9% 4 12% 7% 6% 6% 5% 6% 8% 36%	2730
	11th to 20th	Night	1 8% 5% 9% 5% 5% 6% 6% 8% 9% 39%	2662
	21st to end	Night	1 8% 4 8% 7% 5% 5% 5% 8% 10% 39%	2232
March	1st to 10th	Night	2 6% 2 6% 4 4 5% 4 7% 10% 48%	5059
	11th to 20th	Night	1 6% 3 8% 5% 5% 5% 4 6% 8% 47%	5000
	21st to end	Night	5% 11% 4 11% 5% 5% 5% 5% 8% 10% 32%	5489
April	1st to 10th	Night	6% 11% 3 7% 5% 5% 6% 4 7% 9% 39%	2044
	11th to 20th	Night	6% 11% 4 10% 6% 4 5% 5% 6% 8% 34%	1801
	21st to end	Night	11% 10% 2 7% 3 5% 4 4 6% 7% 41%	1800
May	1st to 10th	Night	12% 11% 2 6% 4 3 4 3 4 6% 45%	3926
	11th to 20th	Night	11% 8% 3 7% 4 5% 5% 4 7% 10% 35%	3617
	21st to end	Night	10% 5% 2 5% 3 3 3 3 6% 7% 52%	3840
June	1st to 10th	Night	11% 6% 2 5% 4 5% 5% 4 6% 9% 43%	1400
	11th to 20th	Night	10% 6% 2 6% 5% 5% 4 5% 8% 9% 41%	1400
	21st to end	Night	5% 3 2 4 3 3 4 4 7% 9% 57%	1400
July	1st to 10th	Night	3 3 1 4 3 4 5% 4 6% 9% 58%	3180
	11th to 20th	Night	7% 2 1 3 2 2 3 3 5% 6% 67%	3180
	21st to end	Night	6% 4 1 5% 4 5% 6% 5% 6% 10% 49%	3991
August	1st to 10th	Night	4 4 1 4 3 4 5% 4 8% 11% 51%	4033
	11th to 20th	Night	3 3 1 3 3 3 5% 5% 7% 9% 57%	4051
	21st to end	Night	8% 4 2 5% 3 3 4 4 6% 7% 54%	4526
September	1st to 10th	Night	8% 4 1 4 4 3 4 3 5% 7% 57%	2000
	11th to 20th	Night	9% 5% 2 5% 3 4 4 3 7% 8% 50%	2143
	21st to end	Night	9% 5% 1 3 3 3 4 3 6% 7% 56%	2201
October	1st to 10th	Night	7% 5% 2 4 3 3 3 3 4 5% 62%	3920
	11th to 20th	Night	5% 6% 2 6% 4 4 5% 3 5% 7% 54%	3898
	21st to end	Night	4 6% 2 5% 3 4 4 4 6% 7% 55%	4395
November	1st to 10th	Night	3 8% 2 7% 5% 4 4 5% 7% 9% 45%	2825
	11th to 20th	Night	3 7% 3 6% 4 4 5% 4 7% 8% 49%	2940
	21st to end	Night	1 8% 3 6% 5% 5% 5% 4 6% 10% 46%	2940
December	1st to 10th	Night	1 4 3 6% 5% 5% 4 4 6% 9% 54%	4710
	11th to 20th	Night	2 8% 3 8% 4 4 5% 4 6% 9% 46%	5695
	21st to end	Night	2 8% 4 7% 4 5% 5% 5% 6% 8% 47%	7623

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	34% 8% 17% 29% 12% 1	4125
	11th to 20th	Day	36% 11% 16% 20% 12% 5%	4260
	21st to end	Day	26% 7% 22% 26% 16% 3	5738
February	1st to 10th	Day	44% 7% 20% 17% 11% 2	1890
	11th to 20th	Day	45% 7% 15% 22% 9% 2	1854
	21st to end	Day	40% 5% 17% 22% 13% 3	1573
March	1st to 10th	Day	31% 7% 12% 24% 20% 6%	4880
	11th to 20th	Day	32% 9% 19% 28% 11% 1	5000
	21st to end	Day	56% 7% 14% 19% 4	5486
April	1st to 10th	Day	48% 5% 15% 22% 8% 2	2355
	11th to 20th	Day	54% 5% 12% 20% 8%	2548
	21st to end	Day	54% 4 15% 20% 7% 1	2600
May	1st to 10th	Day	48% 4 10% 26% 12% 1	6051
	11th to 20th	Day	49% 8% 13% 19% 9% 2	6302
	21st to end	Day	40% 6% 14% 25% 14% 1	7048
June	1st to 10th	Day	47% 5% 18% 23% 6% 1	3000
	11th to 20th	Day	44% 6% 14% 20% 12% 5%	3000
	21st to end	Day	30% 5% 15% 28% 20% 2	3000
July	1st to 10th	Day	24% 9% 14% 27% 20% 6%	6706
	11th to 20th	Day	19% 6% 8% 25% 28% 14%	6699
	21st to end	Day	20% 10% 13% 19% 24% 15%	6673
August	1st to 10th	Day	30% 7% 11% 21% 22% 10%	4208
	11th to 20th	Day	25% 8% 10% 27% 24% 6%	4197
	21st to end	Day	22% 5% 9% 28% 28% 8%	4646
September	1st to 10th	Day	27% 3 8% 30% 22% 10%	2400
	11th to 20th	Day	33% 4 11% 30% 18% 4	2255
	21st to end	Day	29% 4 11% 30% 20% 5%	2198
October	1st to 10th	Day	29% 2 8% 31% 24% 5%	3270
	11th to 20th	Day	29% 4 15% 28% 21% 3	3250
	21st to end	Day	31% 5% 13% 25% 19% 7%	3401
November	1st to 10th	Day	39% 6% 14% 26% 11% 4	1673
	11th to 20th	Day	34% 8% 21% 25% 10% 3	1680
	21st to end	Day	33% 7% 19% 26% 12% 3	1680
December	1st to 10th	Day	28% 8% 24% 25% 12% 3	2686
	11th to 20th	Day	32% 8% 28% 22% 9% 1	2714
	21st to end	Day	37% 5% 10% 23% 16% 8%	3575
January	1st to 10th	Night	30% 8% 17% 30% 13% 2	8769
	11th to 20th	Night	32% 10% 21% 20% 12% 6%	8743
	21st to end	Night	28% 7% 18% 26% 16% 4	8468
February	1st to 10th	Night	44% 8% 17% 19% 9% 3	2730
	11th to 20th	Night	38% 5% 20% 23% 11% 2	2663
	21st to end	Night	37% 6% 18% 23% 13% 4	2232
March	1st to 10th	Night	28% 6% 12% 26% 23% 5%	5059
	11th to 20th	Night	30% 6% 21% 31% 10% 1	5000
	21st to end	Night	45% 6% 20% 22% 7% 1	5489
April	1st to 10th	Night	41% 6% 16% 25% 10% 2	2044
	11th to 20th	Night	46% 5% 14% 24% 9% 1	1801
	21st to end	Night	42% 4 19% 27% 8% 1	1800
May	1st to 10th	Night	41% 3 12% 25% 16% 2	3923
	11th to 20th	Night	41% 6% 14% 27% 10% 1	3618
	21st to end	Night	31% 4 15% 32% 16% 1	3840
June	1st to 10th	Night	38% 6% 24% 23% 8% 1	1400
	11th to 20th	Night	38% 6% 17% 22% 13% 4	1400
	21st to end	Night	23% 4 18% 34% 19% 2	1400
July	1st to 10th	Night	19% 5% 12% 34% 25% 3	3145
	11th to 20th	Night	17% 4 8% 32% 24% 15%	3138
	21st to end	Night	27% 8% 12% 21% 23% 9%	3878
August	1st to 10th	Night	25% 7% 13% 26% 20% 9%	2928
	11th to 20th	Night	25% 6% 11% 32% 22% 5%	2928
	21st to end	Night	24% 5% 9% 34% 23% 4	3262
September	1st to 10th	Night	28% 3 8% 28% 24% 9%	2000
	11th to 20th	Night	32% 4 14% 30% 17% 4	2143
	21st to end	Night	27% 3 13% 29% 23% 4	2201
October	1st to 10th	Night	25% 3 9% 34% 23% 6%	3920
	11th to 20th	Night	30% 4 16% 24% 21% 4	3898
	21st to end	Night	26% 5% 15% 26% 22% 7%	4395
November	1st to 10th	Night	32% 8% 17% 25% 13% 4	2825
	11th to 20th	Night	29% 7% 21% 28% 13% 2	2940
	21st to end	Night	31% 6% 20% 27% 11% 5%	2940
December	1st to 10th	Night	24% 7% 26% 27% 13% 3	4710
	11th to 20th	Night	32% 7% 27% 25% 8% 1	5696
	21st to end	Night	31% 6% 12% 28% 15% 9%	7623

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	23% 26% 25% 16% 8% 2	220
	11th to 20th	Day	16% 35% 30% 12% 4 3	220
	21st to end	Day	11% 35% 40% 11% 3 1	342
February	1st to 10th	Day	15% 35% 35% 11% 3	330
	11th to 20th	Day	10% 34% 32% 21% 3 1	330
	21st to end	Day	21% 29% 30% 14% 4 1	289
March	1st to 10th	Day	13% 32% 35% 14% 4 1	509
	11th to 20th	Day	13% 28% 34% 18% 5% 1	500
	21st to end	Day	20% 23% 32% 16% 7% 2	550
April	1st to 10th	Day	20% 26% 35% 15% 2 1	500
	11th to 20th	Day	17% 30% 34% 14% 4	492
	21st to end	Day	25% 14% 34% 19% 7% 1	500
May	1st to 10th	Day	20% 12% 29% 24% 13% 3	570
	11th to 20th	Day	22% 12% 26% 24% 12% 4	725
	21st to end	Day	22% 12% 23% 23% 17% 3	789
June	1st to 10th	Day	15% 14% 26% 25% 13% 6%	730
	11th to 20th	Day	19% 22% 29% 21% 7% 1	730
	21st to end	Day	9% 14% 29% 30% 16% 2	730
July	1st to 10th	Day	8% 9% 31% 31% 16% 4	721
	11th to 20th	Day	4 11% 33% 37% 13% 2	718
	21st to end	Day	4 7% 33% 36% 17% 2	724
August	1st to 10th	Day	9% 10% 35% 34% 11% 2	527
	11th to 20th	Day	9% 6% 34% 32% 17% 2	517
	21st to end	Day	7% 12% 33% 29% 15% 3	583
September	1st to 10th	Day	9% 10% 37% 29% 12% 2	530
	11th to 20th	Day	15% 15% 33% 23% 10% 3	530
	21st to end	Day	16% 17% 30% 25% 11% 2	528
October	1st to 10th	Day	17% 16% 34% 16% 13% 4	330
	11th to 20th	Day	18% 25% 30% 16% 8% 2	330
	21st to end	Day	17% 33% 28% 15% 6% 2	363
November	1st to 10th	Day	22% 28% 28% 14% 5% 2	330
	11th to 20th	Day	15% 43% 25% 13% 3 1	330
	21st to end	Day	13% 35% 28% 18% 5% 1	330
December	1st to 10th	Day	20% 40% 20% 14% 6% 1	329
	11th to 20th	Day	24% 33% 25% 14% 4 1	220
	21st to end	Day	20% 29% 29% 15% 6% 1	242
January	1st to 10th	Night	12% 34% 31% 17% 6% 1	1050
	11th to 20th	Night	11% 35% 34% 14% 6% 1	1025
	21st to end	Night	9% 33% 36% 16% 6%	924
February	1st to 10th	Night	9% 31% 31% 19% 7% 1	840
	11th to 20th	Night	6% 29% 35% 23% 6% 1	824
	21st to end	Night	12% 24% 33% 21% 9% 1	692
March	1st to 10th	Night	7% 24% 37% 22% 9% 1	808
	11th to 20th	Night	7% 25% 33% 27% 8% 1	800
	21st to end	Night	12% 17% 34% 27% 9% 1	880
April	1st to 10th	Night	13% 16% 35% 29% 8% 1	644
	11th to 20th	Night	12% 18% 33% 30% 7% 1	593
	21st to end	Night	18% 10% 29% 32% 10% 2	600
May	1st to 10th	Night	17% 12% 19% 35% 15% 1	600
	11th to 20th	Night	18% 7% 22% 36% 14% 2	591
	21st to end	Night	20% 8% 18% 35% 16% 2	596
June	1st to 10th	Night	15% 10% 17% 35% 20% 3	400
	11th to 20th	Night	15% 13% 30% 30% 11% 1	400
	21st to end	Night	6% 7% 21% 50% 15% 1	400
July	1st to 10th	Night	5% 3 22% 46% 22% 1	390
	11th to 20th	Night	6% 4 24% 52% 14% 1	388
	21st to end	Night	6% 3 25% 48% 17% 1	588
August	1st to 10th	Night	7% 2 23% 47% 20% 2	597
	11th to 20th	Night	7% 4 20% 46% 21% 3	594
	21st to end	Night	9% 7% 23% 39% 20% 2	660
September	1st to 10th	Night	10% 4 23% 46% 17% 2	600
	11th to 20th	Night	10% 6% 26% 38% 16% 3	743
	21st to end	Night	12% 11% 30% 31% 13% 4	800
October	1st to 10th	Night	15% 12% 27% 31% 14% 2	800
	11th to 20th	Night	12% 21% 30% 25% 10% 2	800
	21st to end	Night	11% 27% 31% 21% 8% 1	880
November	1st to 10th	Night	13% 29% 34% 19% 5% 1	980
	11th to 20th	Night	14% 34% 33% 15% 3	1050
	21st to end	Night	8% 32% 35% 21% 4 1	1050
December	1st to 10th	Night	12% 30% 31% 19% 7% 1	1050
	11th to 20th	Night	11% 35% 32% 16% 5% 1	1050
	21st to end	Night	12% 34% 30% 17% 6% 1	1155

Page generated at 2026-02-27 23:40:24. Version ac07

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