Yarger Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Yarger 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 9% 5% 5% 5% 4 5% 7% 33%	119757
	Night	15% 11% 4 10% 5% 4 4 3 5% 6% 31%	119528
Transparency	Day	51% 2 11% 22% 13% 1	123356
	Night	53% 2 10% 21% 13% 1	124070
Seeing	Day	17% 11% 28% 24% 15% 6%	16711
	Night	19% 8% 29% 30% 12% 1	26551

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	12% 17% 9% 22% 5% 4 5% 4 3 4 15%	3617
	11th to 20th	Day	12% 14% 7% 16% 12% 7% 10% 4 4 3 8%	3620
	21st to end	Day	20% 18% 7% 15% 5% 4 3 3 3 5% 16%	4003
February	1st to 10th	Day	14% 15% 6% 13% 10% 7% 5% 3 4 5% 18%	1903
	11th to 20th	Day	15% 12% 6% 16% 9% 5% 4 4 5% 4 21%	1948
	21st to end	Day	16% 15% 7% 13% 5% 4 5% 4 5% 6% 21%	1650
March	1st to 10th	Day	16% 11% 6% 13% 6% 5% 4 3 3 5% 29%	4480
	11th to 20th	Day	10% 10% 6% 8% 5% 5% 4 4 6% 8% 34%	4837
	21st to end	Day	17% 16% 7% 10% 6% 5% 5% 3 4 5% 22%	5677
April	1st to 10th	Day	18% 13% 4 8% 5% 5% 4 3 5% 6% 30%	2400
	11th to 20th	Day	15% 11% 2 7% 5% 4 4 4 5% 6% 36%	2409
	21st to end	Day	17% 9% 3 7% 5% 4 4 3 5% 7% 36%	2600
May	1st to 10th	Day	19% 9% 3 7% 4 4 5% 4 6% 6% 33%	5862
	11th to 20th	Day	14% 7% 2 7% 4 4 5% 4 6% 8% 39%	5861
	21st to end	Day	14% 6% 2 6% 4 4 4 4 6% 8% 42%	6816
June	1st to 10th	Day	9% 6% 2 7% 4 5% 4 4 6% 8% 44%	2800
	11th to 20th	Day	10% 5% 2 6% 4 4 5% 5% 7% 9% 43%	2800
	21st to end	Day	10% 6% 2 6% 5% 5% 5% 4 7% 9% 42%	2800
July	1st to 10th	Day	10% 7% 3 8% 5% 5% 5% 5% 6% 9% 36%	4580
	11th to 20th	Day	7% 4 2 5% 4 4 4 4 6% 11% 49%	4580
	21st to end	Day	6% 6% 3 7% 4 6% 6% 5% 7% 8% 43%	4791
August	1st to 10th	Day	10% 5% 2 6% 4 4 5% 4 6% 8% 46%	4104
	11th to 20th	Day	9% 5% 2 6% 4 5% 5% 4 6% 7% 46%	4030
	21st to end	Day	7% 5% 2 6% 4 4 5% 4 6% 9% 47%	4180
September	1st to 10th	Day	11% 6% 2 6% 4 4 4 4 5% 9% 46%	2246
	11th to 20th	Day	11% 4 2 5% 4 4 5% 3 6% 8% 48%	2090
	21st to end	Day	13% 7% 3 6% 5% 5% 4 4 6% 8% 40%	2090
October	1st to 10th	Day	13% 6% 2 8% 5% 4 4 3 5% 6% 43%	2090
	11th to 20th	Day	18% 8% 3 8% 5% 5% 4 4 5% 7% 33%	1880
	21st to end	Day	21% 11% 4 8% 6% 6% 5% 3 5% 7% 26%	1881
November	1st to 10th	Day	12% 12% 4 7% 4 4 5% 4 6% 7% 37%	1762
	11th to 20th	Day	16% 18% 5% 9% 6% 5% 4 3 5% 6% 24%	1800
	21st to end	Day	21% 15% 5% 11% 5% 4 4 3 4 5% 22%	1800
December	1st to 10th	Day	10% 18% 7% 15% 6% 4 4 4 5% 6% 20%	2780
	11th to 20th	Day	16% 21% 10% 15% 8% 4 3 3 3 4 13%	3008
	21st to end	Day	25% 20% 7% 14% 6% 4 4 2 3 3 10%	3982
January	1st to 10th	Night	13% 18% 10% 20% 6% 5% 4 3 4 4 14%	6348
	11th to 20th	Night	13% 17% 8% 19% 9% 6% 7% 5% 4 4 9%	6360
	21st to end	Night	19% 15% 7% 12% 6% 5% 5% 3 4 4 19%	6973
February	1st to 10th	Night	16% 15% 4 13% 7% 5% 4 3 5% 6% 22%	2495
	11th to 20th	Night	14% 12% 5% 13% 7% 6% 4 3 5% 6% 24%	2338
	21st to end	Night	18% 12% 5% 12% 5% 4 4 3 5% 5% 26%	1980
March	1st to 10th	Night	15% 10% 4 10% 5% 4 3 3 4 6% 34%	5373
	11th to 20th	Night	12% 7% 3 7% 5% 4 4 4 5% 7% 42%	5121
	21st to end	Night	17% 12% 4 10% 5% 4 4 3 4 5% 31%	5294
April	1st to 10th	Night	16% 10% 2 7% 5% 4 5% 4 5% 7% 35%	2000
	11th to 20th	Night	18% 8% 2 7% 4 4 4 4 4 6% 37%	1938
	21st to end	Night	17% 8% 2 8% 5% 4 4 3 5% 7% 37%	1800
May	1st to 10th	Night	18% 11% 3 8% 4 4 4 4 5% 6% 32%	4033
	11th to 20th	Night	17% 8% 3 5% 3 3 4 3 4 7% 43%	4032
	21st to end	Night	16% 6% 3 8% 4 4 4 3 5% 7% 41%	4040
June	1st to 10th	Night	10% 4 2 4 4 5% 4 4 7% 10% 46%	1600
	11th to 20th	Night	10% 5% 2 6% 4 4 5% 5% 6% 9% 43%	1600
	21st to end	Night	9% 6% 2 5% 5% 4 4 4 7% 11% 43%	1600
July	1st to 10th	Night	8% 5% 2 6% 4 4 5% 4 7% 10% 44%	2610
	11th to 20th	Night	7% 4 2 5% 4 3 3 3 6% 9% 56%	2610
	21st to end	Night	6% 5% 2 5% 5% 5% 5% 4 6% 10% 46%	2770
August	1st to 10th	Night	9% 6% 2 6% 4 4 4 4 7% 10% 45%	2825
	11th to 20th	Night	8% 4 2 6% 4 5% 4 4 6% 8% 48%	2785
	21st to end	Night	9% 5% 2 6% 4 4 4 4 5% 8% 48%	3473
September	1st to 10th	Night	10% 5% 3 5% 4 4 4 4 5% 6% 50%	1914
	11th to 20th	Night	10% 4 1 4 5% 3 4 3 4 8% 54%	2090
	21st to end	Night	14% 7% 2 6% 4 4 4 4 5% 7% 43%	2090
October	1st to 10th	Night	13% 7% 2 6% 4 3 3 3 5% 6% 47%	2090
	11th to 20th	Night	17% 9% 3 9% 5% 4 4 2 4 6% 38%	2298
	21st to end	Night	21% 11% 3 7% 4 4 4 3 4 6% 33%	2717
November	1st to 10th	Night	15% 10% 3 7% 4 4 4 3 5% 6% 39%	2536
	11th to 20th	Night	16% 14% 4 9% 6% 4 5% 4 6% 6% 26%	2600
	21st to end	Night	17% 18% 5% 10% 4 5% 3 3 5% 6% 24%	2600
December	1st to 10th	Night	12% 16% 6% 16% 7% 5% 5% 4 5% 6% 18%	4400
	11th to 20th	Night	17% 20% 9% 14% 8% 5% 4 3 4 4 13%	5199
	21st to end	Night	26% 20% 6% 12% 5% 4 4 3 4 4 11%	6996

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	74% 2 8% 14% 2	3618
	11th to 20th	Day	77% 2 7% 8% 6%	3620
	21st to end	Day	73% 2 8% 11% 6%	4003
February	1st to 10th	Day	68% 2 8% 14% 6% 1	1903
	11th to 20th	Day	65% 3 7% 15% 9% 1	1958
	21st to end	Day	63% 3 10% 15% 7% 1	1650
March	1st to 10th	Day	59% 2 10% 21% 9%	4480
	11th to 20th	Day	48% 1 13% 28% 8% 1	4837
	21st to end	Day	67% 1 9% 16% 7%	5679
April	1st to 10th	Day	56% 3 9% 20% 12%	2400
	11th to 20th	Day	49% 2 10% 23% 13% 2	2409
	21st to end	Day	49% 2 12% 21% 14% 2	2600
May	1st to 10th	Day	53% 1 9% 22% 14% 1	5897
	11th to 20th	Day	44% 2 14% 26% 13% 1	5865
	21st to end	Day	43% 2 9% 26% 19% 1	6830
June	1st to 10th	Day	38% 3 11% 27% 18% 2	2800
	11th to 20th	Day	37% 4 11% 26% 19% 3	2800
	21st to end	Day	40% 4 14% 23% 16% 3	2800
July	1st to 10th	Day	45% 2 12% 21% 17% 3	4511
	11th to 20th	Day	31% 2 13% 34% 17% 2	4505
	21st to end	Day	39% 3 14% 20% 21% 2	4640
August	1st to 10th	Day	36% 3 15% 29% 17% 1	4091
	11th to 20th	Day	37% 2 12% 32% 17% 1	4069
	21st to end	Day	34% 3 13% 30% 18% 3	4179
September	1st to 10th	Day	37% 3 14% 25% 19% 3	2246
	11th to 20th	Day	35% 3 9% 30% 21% 2	2090
	21st to end	Day	42% 3 9% 26% 19% 1	2090
October	1st to 10th	Day	30% 2 9% 39% 18% 1	3480
	11th to 20th	Day	42% 1 10% 23% 23%	3096
	21st to end	Day	49% 2 10% 26% 11% 2	3081
November	1st to 10th	Day	45% 3 11% 25% 15% 1	1762
	11th to 20th	Day	61% 1 10% 19% 8% 1	1800
	21st to end	Day	65% 2 11% 17% 5%	1800
December	1st to 10th	Day	64% 2 15% 17% 3	2780
	11th to 20th	Day	76% 2 9% 11% 2	3005
	21st to end	Day	82% 2 6% 8% 3	3982
January	1st to 10th	Night	74% 1 6% 14% 4 1	6348
	11th to 20th	Night	78% 2 8% 8% 4	6360
	21st to end	Night	69% 1 12% 10% 7%	6973
February	1st to 10th	Night	65% 2 10% 15% 7% 1	2495
	11th to 20th	Night	62% 2 8% 19% 9%	2339
	21st to end	Night	60% 2 11% 18% 7% 2	1980
March	1st to 10th	Night	53% 1 11% 26% 9% 1	5373
	11th to 20th	Night	44% 2 11% 30% 13% 2	5121
	21st to end	Night	57% 1 9% 20% 12% 1	5294
April	1st to 10th	Night	49% 2 11% 23% 14% 1	2000
	11th to 20th	Night	49% 2 8% 20% 19% 2	1938
	21st to end	Night	49% 2 9% 23% 15% 2	1800
May	1st to 10th	Night	53% 2 9% 20% 14% 2	4060
	11th to 20th	Night	44% 2 10% 25% 16% 1	4033
	21st to end	Night	45% 2 10% 22% 20% 2	4048
June	1st to 10th	Night	34% 3 11% 30% 19% 3	1600
	11th to 20th	Night	37% 4 13% 25% 19% 2	1600
	21st to end	Night	35% 3 17% 25% 17% 3	1600
July	1st to 10th	Night	36% 2 15% 26% 14% 6%	2570
	11th to 20th	Night	28% 2 14% 28% 25% 3	2562
	21st to end	Night	35% 3 15% 18% 26% 3	2682
August	1st to 10th	Night	36% 3 13% 30% 17% 1	2814
	11th to 20th	Night	33% 3 12% 33% 18% 1	2812
	21st to end	Night	35% 3 9% 31% 19% 3	3473
September	1st to 10th	Night	35% 3 11% 25% 22% 4	1914
	11th to 20th	Night	30% 2 7% 34% 26% 2	2090
	21st to end	Night	41% 3 8% 29% 18% 1	2090
October	1st to 10th	Night	28% 2 8% 34% 27% 1	3480
	11th to 20th	Night	41% 1 8% 26% 23% 1	3821
	21st to end	Night	42% 2 7% 30% 18% 1	4467
November	1st to 10th	Night	47% 2 9% 25% 16% 1	2536
	11th to 20th	Night	56% 3 11% 19% 9% 2	2600
	21st to end	Night	62% 2 12% 19% 6%	2600
December	1st to 10th	Night	67% 2 14% 14% 3	4400
	11th to 20th	Night	76% 2 9% 10% 3	5201
	21st to end	Night	78% 1 9% 9% 3	6996

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	20% 17% 34% 19% 9% 1	300
	11th to 20th	Day	20% 16% 41% 16% 6% 1	300
	21st to end	Day	24% 18% 30% 23% 5%	330
February	1st to 10th	Day	22% 20% 32% 18% 6% 1	300
	11th to 20th	Day	24% 20% 33% 19% 4	300
	21st to end	Day	24% 20% 41% 11% 4	249
March	1st to 10th	Day	20% 19% 43% 13% 5%	300
	11th to 20th	Day	23% 16% 30% 23% 8% 1	435
	21st to end	Day	30% 14% 29% 19% 6% 1	550
April	1st to 10th	Day	25% 13% 31% 23% 7% 1	500
	11th to 20th	Day	23% 17% 29% 18% 10% 3	492
	21st to end	Day	23% 12% 31% 21% 11% 2	500
May	1st to 10th	Day	24% 11% 28% 22% 11% 3	503
	11th to 20th	Day	24% 9% 25% 23% 14% 5%	527
	21st to end	Day	13% 8% 27% 26% 18% 8%	735
June	1st to 10th	Day	12% 7% 27% 31% 17% 5%	730
	11th to 20th	Day	12% 6% 29% 29% 18% 6%	730
	21st to end	Day	12% 8% 27% 30% 18% 6%	730
July	1st to 10th	Day	8% 3 22% 29% 23% 14%	721
	11th to 20th	Day	10% 4 24% 27% 23% 11%	718
	21st to end	Day	6% 4 21% 34% 24% 10%	729
August	1st to 10th	Day	8% 4 16% 28% 25% 19%	486
	11th to 20th	Day	10% 4 18% 28% 28% 11%	479
	21st to end	Day	10% 3 19% 29% 28% 12%	539
September	1st to 10th	Day	14% 6% 19% 27% 24% 11%	490
	11th to 20th	Day	9% 3 19% 21% 31% 17%	490
	21st to end	Day	16% 10% 23% 24% 19% 9%	490
October	1st to 10th	Day	14% 8% 27% 26% 18% 6%	490
	11th to 20th	Day	21% 18% 24% 27% 9% 1	408
	21st to end	Day	25% 16% 38% 15% 4 2	330
November	1st to 10th	Day	16% 15% 33% 24% 8% 4	300
	11th to 20th	Day	23% 21% 31% 16% 8% 1	300
	21st to end	Day	28% 13% 39% 16% 4	300
December	1st to 10th	Day	22% 24% 32% 13% 8% 1	300
	11th to 20th	Day	22% 17% 39% 17% 4	300
	21st to end	Day	24% 21% 34% 18% 3	330
January	1st to 10th	Night	22% 15% 34% 23% 6%	1000
	11th to 20th	Night	24% 13% 36% 22% 4 1	1000
	21st to end	Night	21% 11% 38% 26% 4	1090
February	1st to 10th	Night	25% 10% 36% 25% 4	800
	11th to 20th	Night	21% 14% 34% 27% 4	783
	21st to end	Night	25% 11% 37% 24% 3	660
March	1st to 10th	Night	21% 12% 35% 25% 7% 1	800
	11th to 20th	Night	18% 11% 37% 27% 7% 1	800
	21st to end	Night	23% 11% 29% 30% 6% 1	810
April	1st to 10th	Night	19% 12% 33% 29% 6% 1	600
	11th to 20th	Night	22% 10% 33% 28% 6% 1	593
	21st to end	Night	21% 7% 36% 27% 10%	600
May	1st to 10th	Night	19% 7% 32% 34% 8% 1	600
	11th to 20th	Night	23% 5% 26% 31% 15%	591
	21st to end	Night	14% 3 24% 37% 20% 1	650
June	1st to 10th	Night	11% 3 25% 44% 17% 1	600
	11th to 20th	Night	13% 4 25% 40% 17% 1	600
	21st to end	Night	10% 2 22% 41% 24% 1	600
July	1st to 10th	Night	8% 2 17% 41% 27% 5%	585
	11th to 20th	Night	9% 3 15% 42% 27% 4	582
	21st to end	Night	7% 2 14% 42% 33% 2	624
August	1st to 10th	Night	9% 2 10% 46% 29% 4	567
	11th to 20th	Night	8% 2 16% 41% 29% 5%	564
	21st to end	Night	11% 1 15% 35% 33% 5%	627
September	1st to 10th	Night	11% 3 16% 38% 29% 4	584
	11th to 20th	Night	11% 3 15% 36% 30% 5%	760
	21st to end	Night	18% 6% 23% 28% 21% 5%	760
October	1st to 10th	Night	16% 5% 24% 34% 18% 2	760
	11th to 20th	Night	22% 11% 28% 29% 10% 1	760
	21st to end	Night	27% 12% 31% 23% 7%	836
November	1st to 10th	Night	21% 9% 33% 26% 11% 1	780
	11th to 20th	Night	24% 13% 33% 23% 6% 1	800
	21st to end	Night	24% 11% 33% 27% 5%	800
December	1st to 10th	Night	25% 14% 35% 21% 5%	885
	11th to 20th	Night	25% 12% 36% 23% 4	1000
	21st to end	Night	32% 12% 31% 22% 3	1100

Page generated at 2025-07-18 01:10:00. Version ac07

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