Auburn
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Auburn clear sky chart from 2005-11-06 to 2025-09-04.

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	13% 9% 4 8% 5% 5% 5% 4 6% 7% 34%	125800
	Night	15% 10% 4 8% 5% 4 4 4 5% 7% 34%	123096
Transparency	Day	48% 6% 11% 22% 13% 1	129371
	Night	48% 5% 11% 21% 13% 1	127597
Seeing	Day	17% 10% 28% 24% 15% 6%	16810
	Night	18% 9% 29% 29% 13% 1	26583

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% 14% 9% 21% 7% 5% 4 3 4 4 17%	3617
	11th to 20th	Day	13% 16% 7% 14% 8% 7% 6% 5% 5% 4 15%	3620
	21st to end	Day	21% 18% 9% 13% 5% 3 3 3 3 4 17%	4199
February	1st to 10th	Day	15% 14% 6% 12% 7% 6% 5% 3 5% 6% 21%	1878
	11th to 20th	Day	14% 13% 5% 13% 8% 6% 4 4 5% 6% 23%	1948
	21st to end	Day	15% 14% 6% 10% 5% 4 4 4 5% 7% 25%	1650
March	1st to 10th	Day	17% 13% 5% 11% 6% 5% 4 3 4 4 28%	4480
	11th to 20th	Day	11% 10% 3 7% 5% 4 5% 3 6% 8% 38%	4925
	21st to end	Day	18% 14% 5% 10% 6% 5% 5% 4 5% 6% 22%	5544
April	1st to 10th	Day	16% 12% 4 9% 5% 5% 5% 4 6% 6% 29%	2400
	11th to 20th	Day	17% 9% 3 7% 5% 5% 4 4 6% 6% 35%	2434
	21st to end	Day	17% 9% 3 7% 5% 5% 4 3 6% 8% 34%	2600
May	1st to 10th	Day	20% 10% 3 8% 5% 5% 5% 4 5% 7% 30%	5862
	11th to 20th	Day	16% 7% 2 6% 5% 5% 5% 4 6% 8% 37%	5861
	21st to end	Day	14% 6% 2 7% 5% 5% 5% 4 6% 8% 39%	6587
June	1st to 10th	Day	10% 6% 3 7% 5% 6% 5% 4 6% 7% 41%	2800
	11th to 20th	Day	10% 5% 2 6% 5% 5% 5% 4 6% 9% 43%	2800
	21st to end	Day	10% 5% 3 5% 6% 5% 5% 5% 7% 10% 39%	2800
July	1st to 10th	Day	9% 5% 2 7% 4 5% 5% 4 7% 10% 41%	6360
	11th to 20th	Day	7% 5% 2 6% 5% 5% 5% 5% 7% 11% 42%	6360
	21st to end	Day	9% 6% 3 7% 5% 5% 5% 5% 7% 9% 40%	6703
August	1st to 10th	Day	8% 5% 2 6% 5% 5% 5% 4 6% 9% 45%	4234
	11th to 20th	Day	9% 5% 2 6% 4 5% 5% 4 7% 8% 45%	4174
	21st to end	Day	7% 5% 2 6% 4 4 4 4 6% 10% 48%	4360
September	1st to 10th	Day	11% 6% 2 6% 5% 4 5% 4 5% 7% 45%	2247
	11th to 20th	Day	9% 4 2 4 4 4 5% 4 7% 9% 47%	2090
	21st to end	Day	14% 7% 2 6% 4 4 4 3 6% 7% 42%	2090
October	1st to 10th	Day	12% 6% 2 7% 5% 4 4 4 5% 7% 44%	2090
	11th to 20th	Day	16% 6% 2 7% 4 5% 5% 4 5% 7% 38%	1909
	21st to end	Day	18% 9% 3 7% 6% 6% 5% 4 7% 6% 29%	1881
November	1st to 10th	Day	11% 9% 3 6% 4 4 4 4 6% 7% 43%	1762
	11th to 20th	Day	16% 14% 4 8% 5% 5% 4 3 5% 7% 30%	1800
	21st to end	Day	20% 14% 4 10% 5% 4 4 3 5% 6% 25%	1800
December	1st to 10th	Day	11% 14% 6% 12% 6% 5% 5% 3 5% 6% 26%	2930
	11th to 20th	Day	18% 15% 7% 11% 6% 5% 4 4 5% 5% 21%	3023
	21st to end	Day	26% 20% 7% 12% 5% 4 4 3 3 5% 12%	3982
January	1st to 10th	Night	15% 14% 6% 17% 6% 5% 4 3 4 5% 21%	6348
	11th to 20th	Night	12% 16% 8% 15% 7% 6% 6% 4 4 5% 15%	6360
	21st to end	Night	20% 14% 7% 10% 5% 5% 5% 3 4 5% 23%	6766
February	1st to 10th	Night	17% 14% 5% 10% 6% 5% 5% 3 4 6% 25%	2520
	11th to 20th	Night	14% 13% 4 10% 7% 5% 5% 3 5% 6% 28%	2338
	21st to end	Night	19% 12% 4 9% 5% 4 4 4 4 5% 30%	1980
March	1st to 10th	Night	16% 11% 4 7% 4 4 4 3 5% 6% 36%	5373
	11th to 20th	Night	11% 6% 2 6% 5% 5% 5% 4 5% 8% 43%	5035
	21st to end	Night	16% 9% 4 9% 4 4 4 3 5% 7% 33%	5427
April	1st to 10th	Night	17% 9% 3 7% 4 4 5% 4 6% 7% 37%	2000
	11th to 20th	Night	17% 7% 4 7% 4 5% 4 4 5% 6% 37%	1914
	21st to end	Night	16% 9% 2 7% 6% 4 4 4 4 6% 37%	1800
May	1st to 10th	Night	19% 11% 3 8% 5% 5% 5% 4 5% 6% 30%	4033
	11th to 20th	Night	17% 8% 3 6% 4 4 3 3 5% 6% 41%	4032
	21st to end	Night	15% 6% 2 6% 4 5% 4 4 5% 7% 42%	4257
June	1st to 10th	Night	10% 6% 1 4 5% 4 4 4 7% 9% 47%	1600
	11th to 20th	Night	8% 6% 2 6% 4 5% 5% 5% 6% 8% 45%	1600
	21st to end	Night	8% 5% 2 5% 6% 5% 4 4 6% 10% 45%	1600
July	1st to 10th	Night	8% 4 2 6% 4 4 5% 4 6% 10% 47%	3618
	11th to 20th	Night	7% 5% 2 6% 4 4 4 3 7% 10% 48%	3617
	21st to end	Night	9% 5% 2 6% 5% 4 4 4 6% 11% 44%	4158
August	1st to 10th	Night	10% 6% 2 6% 4 4 5% 4 6% 10% 43%	2915
	11th to 20th	Night	7% 5% 2 6% 5% 4 5% 4 6% 9% 47%	2875
	21st to end	Night	8% 4 2 6% 4 4 4 3 6% 8% 50%	3534
September	1st to 10th	Night	10% 4 2 5% 4 4 4 3 4 6% 53%	1979
	11th to 20th	Night	10% 5% 1 4 4 3 4 2 4 7% 56%	2090
	21st to end	Night	13% 6% 3 6% 4 3 4 4 5% 6% 46%	2090
October	1st to 10th	Night	10% 6% 3 6% 4 3 4 3 6% 7% 50%	2090
	11th to 20th	Night	18% 9% 3 7% 4 4 4 3 5% 5% 39%	2267
	21st to end	Night	20% 9% 3 6% 4 3 4 3 5% 7% 37%	2717
November	1st to 10th	Night	13% 8% 3 6% 4 4 4 3 5% 6% 44%	2536
	11th to 20th	Night	16% 11% 4 8% 4 5% 5% 4 6% 7% 32%	2600
	21st to end	Night	19% 12% 4 9% 5% 4 4 4 5% 6% 27%	2600
December	1st to 10th	Night	13% 11% 5% 10% 6% 6% 5% 4 6% 8% 26%	4250
	11th to 20th	Night	18% 16% 8% 12% 5% 4 4 3 4 5% 21%	5181
	21st to end	Night	26% 19% 6% 10% 5% 4 4 3 4 5% 13%	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	70% 5% 8% 13% 3	3618
	11th to 20th	Day	70% 4 9% 7% 9% 1	3620
	21st to end	Day	72% 3 7% 12% 6%	4199
February	1st to 10th	Day	64% 5% 10% 12% 7% 1	1878
	11th to 20th	Day	62% 5% 8% 17% 8% 1	1958
	21st to end	Day	58% 5% 13% 16% 6% 2	1650
March	1st to 10th	Day	60% 4 7% 21% 7% 1	4480
	11th to 20th	Day	44% 4 13% 30% 8% 1	4925
	21st to end	Day	62% 6% 11% 15% 6% 1	5546
April	1st to 10th	Day	54% 6% 10% 18% 11%	2400
	11th to 20th	Day	49% 6% 10% 22% 11% 2	2434
	21st to end	Day	48% 6% 13% 19% 12% 2	2600
May	1st to 10th	Day	53% 6% 10% 16% 14%	5897
	11th to 20th	Day	43% 7% 14% 22% 12% 1	5865
	21st to end	Day	41% 7% 10% 23% 18% 2	6601
June	1st to 10th	Day	40% 7% 11% 24% 17% 2	2800
	11th to 20th	Day	37% 7% 12% 25% 17% 2	2800
	21st to end	Day	38% 8% 13% 22% 16% 3	2800
July	1st to 10th	Day	36% 6% 11% 28% 17% 2	6291
	11th to 20th	Day	34% 7% 14% 28% 16% 1	6285
	21st to end	Day	38% 7% 13% 22% 18% 2	6511
August	1st to 10th	Day	34% 8% 15% 26% 16% 1	4221
	11th to 20th	Day	34% 7% 12% 29% 17% 1	4213
	21st to end	Day	31% 7% 13% 32% 15% 3	4359
September	1st to 10th	Day	37% 7% 13% 22% 17% 3	2247
	11th to 20th	Day	32% 6% 12% 27% 21% 1	2090
	21st to end	Day	40% 5% 11% 24% 18% 1	2090
October	1st to 10th	Day	29% 4 10% 36% 19% 1	3480
	11th to 20th	Day	37% 5% 11% 23% 24%	3138
	21st to end	Day	44% 5% 12% 26% 12% 1	3081
November	1st to 10th	Day	39% 6% 12% 26% 17% 1	1762
	11th to 20th	Day	55% 5% 10% 18% 10% 1	1800
	21st to end	Day	60% 5% 11% 17% 7%	1800
December	1st to 10th	Day	58% 4 16% 18% 3	2930
	11th to 20th	Day	65% 5% 10% 15% 4	3020
	21st to end	Day	77% 4 6% 8% 5%	3982
January	1st to 10th	Night	66% 5% 7% 15% 6%	6348
	11th to 20th	Night	71% 4 8% 9% 8%	6360
	21st to end	Night	64% 4 12% 12% 7%	6766
February	1st to 10th	Night	61% 5% 11% 14% 7% 2	2520
	11th to 20th	Night	56% 5% 9% 20% 9% 1	2339
	21st to end	Night	57% 4 11% 17% 10% 1	1980
March	1st to 10th	Night	49% 4 10% 25% 11% 1	5373
	11th to 20th	Night	38% 6% 11% 30% 14% 2	5035
	21st to end	Night	50% 5% 11% 22% 12% 1	5427
April	1st to 10th	Night	46% 6% 10% 21% 15% 1	2000
	11th to 20th	Night	47% 6% 10% 17% 18% 2	1914
	21st to end	Night	46% 7% 10% 20% 15% 3	1800
May	1st to 10th	Night	54% 6% 8% 16% 13% 2	4060
	11th to 20th	Night	44% 6% 10% 25% 15% 1	4033
	21st to end	Night	39% 6% 12% 22% 18% 2	4265
June	1st to 10th	Night	32% 6% 12% 27% 20% 3	1600
	11th to 20th	Night	36% 7% 12% 24% 19% 3	1600
	21st to end	Night	34% 7% 17% 23% 16% 3	1600
July	1st to 10th	Night	32% 6% 11% 26% 20% 4	3580
	11th to 20th	Night	31% 6% 17% 25% 20% 2	3572
	21st to end	Night	34% 6% 14% 23% 19% 4	4037
August	1st to 10th	Night	36% 6% 14% 28% 14% 2	2904
	11th to 20th	Night	32% 7% 12% 30% 16% 1	2902
	21st to end	Night	32% 6% 11% 30% 18% 2	3534
September	1st to 10th	Night	32% 7% 12% 24% 21% 5%	1979
	11th to 20th	Night	29% 5% 9% 30% 26% 2	2090
	21st to end	Night	37% 6% 11% 27% 18% 2	2090
October	1st to 10th	Night	22% 4 8% 32% 32% 1	3480
	11th to 20th	Night	38% 4 9% 23% 25% 1	3777
	21st to end	Night	36% 4 9% 32% 18% 1	4467
November	1st to 10th	Night	40% 5% 11% 27% 16% 1	2536
	11th to 20th	Night	51% 5% 12% 20% 11% 2	2600
	21st to end	Night	56% 6% 12% 19% 7%	2600
December	1st to 10th	Night	55% 5% 14% 20% 5% 1	4250
	11th to 20th	Night	66% 4 11% 10% 7% 1	5183
	21st to end	Night	74% 5% 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	21% 18% 37% 18% 5% 1	300
	11th to 20th	Day	25% 14% 43% 13% 4 1	300
	21st to end	Day	26% 17% 33% 19% 5%	330
February	1st to 10th	Day	23% 17% 38% 18% 4 1	300
	11th to 20th	Day	23% 20% 34% 18% 5%	300
	21st to end	Day	25% 21% 40% 12% 2	249
March	1st to 10th	Day	23% 18% 39% 17% 3	300
	11th to 20th	Day	23% 14% 32% 23% 7% 1	471
	21st to end	Day	28% 14% 32% 19% 5% 1	550
April	1st to 10th	Day	22% 16% 32% 19% 9% 2	500
	11th to 20th	Day	23% 15% 32% 18% 10% 2	492
	21st to end	Day	21% 15% 30% 19% 12% 2	500
May	1st to 10th	Day	23% 12% 30% 21% 11% 3	503
	11th to 20th	Day	21% 9% 27% 23% 15% 6%	527
	21st to end	Day	12% 7% 28% 26% 17% 9%	636
June	1st to 10th	Day	12% 9% 28% 29% 16% 5%	730
	11th to 20th	Day	12% 6% 32% 26% 19% 6%	730
	21st to end	Day	12% 6% 27% 31% 18% 7%	730
July	1st to 10th	Day	11% 3 19% 31% 22% 14%	721
	11th to 20th	Day	8% 4 24% 30% 23% 11%	718
	21st to end	Day	9% 3 21% 29% 27% 12%	699
August	1st to 10th	Day	8% 2 16% 29% 27% 17%	526
	11th to 20th	Day	10% 4 19% 29% 26% 13%	519
	21st to end	Day	9% 3 16% 25% 31% 15%	583
September	1st to 10th	Day	11% 6% 19% 25% 25% 14%	502
	11th to 20th	Day	9% 3 13% 25% 32% 18%	490
	21st to end	Day	18% 9% 19% 25% 22% 7%	490
October	1st to 10th	Day	13% 8% 24% 30% 17% 9%	490
	11th to 20th	Day	18% 15% 28% 29% 8% 2	464
	21st to end	Day	26% 14% 36% 19% 5% 1	330
November	1st to 10th	Day	14% 15% 33% 24% 12% 2	300
	11th to 20th	Day	25% 16% 31% 18% 9%	300
	21st to end	Day	28% 14% 38% 17% 4	300
December	1st to 10th	Day	21% 22% 32% 16% 9%	300
	11th to 20th	Day	23% 16% 39% 16% 5%	300
	21st to end	Day	26% 22% 34% 16% 2	330
January	1st to 10th	Night	22% 15% 36% 21% 6%	1000
	11th to 20th	Night	25% 13% 37% 21% 4 1	1000
	21st to end	Night	22% 13% 37% 23% 4	1000
February	1st to 10th	Night	25% 12% 37% 23% 3	800
	11th to 20th	Night	20% 14% 38% 25% 2	783
	21st to end	Night	27% 14% 36% 20% 3	660
March	1st to 10th	Night	20% 12% 36% 25% 6% 1	800
	11th to 20th	Night	17% 13% 38% 27% 5% 1	800
	21st to end	Night	23% 12% 32% 26% 7%	865
April	1st to 10th	Night	20% 12% 34% 27% 7% 1	600
	11th to 20th	Night	20% 10% 34% 27% 7% 1	593
	21st to end	Night	19% 9% 36% 26% 10% 1	600
May	1st to 10th	Night	19% 7% 34% 31% 8% 1	600
	11th to 20th	Night	22% 5% 27% 31% 15% 1	591
	21st to end	Night	13% 4 25% 38% 18% 2	650
June	1st to 10th	Night	11% 4 26% 44% 14% 1	600
	11th to 20th	Night	11% 4 26% 40% 19% 1	600
	21st to end	Night	9% 4 26% 36% 24% 2	600
July	1st to 10th	Night	9% 3 15% 41% 27% 4	585
	11th to 20th	Night	9% 3 18% 38% 29% 3	582
	21st to end	Night	7% 1 16% 42% 32% 2	657
August	1st to 10th	Night	6% 2 14% 46% 28% 4	597
	11th to 20th	Night	8% 2 12% 43% 31% 4	594
	21st to end	Night	9% 1 16% 34% 37% 3	660
September	1st to 10th	Night	12% 3 16% 34% 32% 3	628
	11th to 20th	Night	11% 4 14% 35% 33% 3	760
	21st to end	Night	16% 5% 22% 34% 19% 3	760
October	1st to 10th	Night	13% 6% 25% 33% 20% 3	760
	11th to 20th	Night	20% 14% 26% 28% 11% 1	760
	21st to end	Night	23% 13% 32% 25% 7%	836
November	1st to 10th	Night	16% 12% 32% 27% 11% 1	780
	11th to 20th	Night	23% 15% 32% 25% 6% 1	800
	21st to end	Night	24% 12% 32% 26% 6%	800
December	1st to 10th	Night	26% 14% 34% 21% 5%	800
	11th to 20th	Night	26% 12% 35% 22% 4	982
	21st to end	Night	31% 13% 30% 23% 3	1100

Page generated at 2025-09-01 01:51:02. Version ac07

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