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 2026-04-17.

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	9% 3 1 3 2 2 2 2 3 5% 66%	140322
	Night	12% 4 1 3 2 2 3 2 4 5% 61%	139291
Transparency	Day	23% 3 7% 19% 25% 24%	135259
	Night	28% 3 7% 19% 23% 20%	135339
Seeing	Day	11% 7% 21% 32% 24% 6%	16982
	Night	13% 3 12% 37% 30% 5%	26408

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	26% 6% 2 3 2 3 3 2 4 6% 42%	4722
	11th to 20th	Day	14% 5% 2 4 3 3 2 2 3 4 59%	5178
	21st to end	Day	17% 6% 2 5% 3 4 4 3 5% 7% 45%	5843
February	1st to 10th	Day	22% 5% 2 4 2 3 3 4 5% 5% 45%	1890
	11th to 20th	Day	20% 6% 2 5% 4 4 3 3 4 5% 44%	1981
	21st to end	Day	19% 7% 2 5% 3 3 2 3 4 6% 47%	1730
March	1st to 10th	Day	19% 11% 3 7% 4 4 4 3 5% 5% 36%	4749
	11th to 20th	Day	20% 6% 1 4 3 3 3 2 4 6% 48%	5110
	21st to end	Day	19% 7% 2 6% 4 4 4 4 6% 8% 37%	5827
April	1st to 10th	Day	16% 6% 2 3 3 3 4 4 5% 6% 48%	2520
	11th to 20th	Day	13% 4 1 4 3 3 3 3 5% 6% 55%	2442
	21st to end	Day	9% 4 2 2 2 2 3 3 5% 7% 61%	2400
May	1st to 10th	Day	6% 2 1 3 1 1 2 2 2 4 76%	5568
	11th to 20th	Day	3 2 1 2 2 2 2 2 3 4 78%	6277
	21st to end	Day	3 1 1 2 1 1 2 2 3 4 80%	6902
June	1st to 10th	Day	6% 2 1 2 3 3 2 3 4 6% 68%	2800
	11th to 20th	Day	2 1 2 1 2 2 2 3 4 81%	2800
	21st to end	Day	2 1 1 1 1 1 1 1 2 3 85%	2800
July	1st to 10th	Day	1 1 1 1 1 2 94%	6319
	11th to 20th	Day	1 1 1 1 1 1 1 2 2 89%	6320
	21st to end	Day	1 1 2 1 2 2 2 3 4 83%	6449
August	1st to 10th	Day	1 1 2 1 1 1 2 2 3 85%	5777
	11th to 20th	Day	1 1 1 1 1 2 2 91%	5448
	21st to end	Day	2 1 1 1 1 1 2 1 2 3 85%	5984
September	1st to 10th	Day	2 1 1 1 1 1 1 2 3 87%	2400
	11th to 20th	Day	4 2 1 2 2 2 2 2 3 3 77%	2400
	21st to end	Day	4 2 1 2 1 1 2 2 2 4 79%	2161
October	1st to 10th	Day	3 2 1 3 2 2 1 2 4 5% 74%	3280
	11th to 20th	Day	6% 2 1 2 2 2 3 2 4 4 74%	3261
	21st to end	Day	6% 3 2 4 3 3 3 2 4 6% 64%	3558
November	1st to 10th	Day	12% 4 1 3 3 3 2 3 5% 7% 56%	1889
	11th to 20th	Day	16% 4 1 4 4 4 3 3 5% 7% 50%	1890
	21st to end	Day	13% 4 1 3 3 3 3 3 4 6% 56%	1747
December	1st to 10th	Day	10% 3 1 5% 3 3 3 3 4 7% 60%	2700
	11th to 20th	Day	30% 7% 2 5% 3 2 3 3 5% 6% 34%	3108
	21st to end	Day	29% 6% 2 5% 4 3 4 3 7% 7% 30%	4092
January	1st to 10th	Night	23% 7% 2 4 3 3 3 3 5% 7% 40%	8172
	11th to 20th	Night	13% 4 1 3 2 2 3 3 3 5% 59%	7786
	21st to end	Night	17% 6% 2 6% 4 3 3 3 4 5% 45%	8371
February	1st to 10th	Night	21% 5% 1 4 3 3 3 2 4 5% 50%	2730
	11th to 20th	Night	18% 6% 2 5% 3 3 4 3 5% 7% 44%	2525
	21st to end	Night	18% 6% 1 4 3 3 3 3 4 5% 49%	2076
March	1st to 10th	Night	22% 11% 2 6% 4 4 4 3 4 6% 37%	5361
	11th to 20th	Night	24% 7% 2 3 2 2 2 2 3 5% 48%	5110
	21st to end	Night	22% 7% 3 5% 3 4 4 3 5% 7% 37%	5388
April	1st to 10th	Night	14% 5% 2 4 4 3 3 3 4 6% 49%	2100
	11th to 20th	Night	13% 4 1 5% 3 3 3 3 4 6% 54%	2039
	21st to end	Night	8% 3 2 3 2 2 4 2 5% 6% 63%	2000
May	1st to 10th	Night	4 3 1 3 2 2 2 2 3 4 74%	4422
	11th to 20th	Night	4 1 1 2 2 2 3 2 3 4 76%	3616
	21st to end	Night	2 1 2 1 1 2 2 3 4 82%	3972
June	1st to 10th	Night	6% 3 1 3 3 3 2 4 4 6% 67%	1600
	11th to 20th	Night	1 1 1 2 2 2 2 2 2 6% 81%	1600
	21st to end	Night	2 1 1 1 1 2 2 2 2 3 83%	1600
July	1st to 10th	Night	1 1 1 1 1 1 93%	3640
	11th to 20th	Night	2 1 1 1 1 1 1 2 2 88%	3640
	21st to end	Night	1 1 1 2 1 2 2 2 4 5% 79%	4418
August	1st to 10th	Night	2 1 1 1 1 1 1 2 3 4 82%	4035
	11th to 20th	Night	1 1 1 1 2 3 91%	4418
	21st to end	Night	3 1 1 2 1 1 2 1 2 3 83%	5015
September	1st to 10th	Night	1 1 1 1 1 1 1 2 4 88%	2000
	11th to 20th	Night	3 3 1 2 1 2 2 2 3 5% 78%	2000
	21st to end	Night	3 1 1 1 2 2 2 2 3 3 80%	2235
October	1st to 10th	Night	3 2 1 3 2 2 2 1 3 3 78%	3920
	11th to 20th	Night	4 1 1 2 1 1 2 2 2 4 79%	3897
	21st to end	Night	8% 2 1 3 3 3 3 3 4 6% 64%	4253
November	1st to 10th	Night	14% 4 1 3 2 3 3 3 5% 7% 56%	2630
	11th to 20th	Night	13% 5% 1 3 3 3 3 3 5% 7% 54%	2730
	21st to end	Night	14% 4 1 3 3 3 3 2 4 6% 57%	2870
December	1st to 10th	Night	11% 3 1 3 2 3 3 3 4 6% 62%	4700
	11th to 20th	Night	29% 6% 2 4 3 3 4 3 6% 9% 30%	5316
	21st to end	Night	29% 6% 3 7% 4 5% 4 3 4 5% 30%	7106

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% 4 14% 22% 11% 5%	4723
	11th to 20th	Day	32% 2 5% 13% 26% 21%	5178
	21st to end	Day	40% 3 8% 18% 20% 11%	5843
February	1st to 10th	Day	40% 4 9% 19% 17% 10%	1890
	11th to 20th	Day	41% 4 10% 20% 18% 7%	1990
	21st to end	Day	40% 3 10% 22% 17% 7%	1730
March	1st to 10th	Day	49% 4 8% 18% 19% 2	4749
	11th to 20th	Day	38% 4 11% 28% 11% 8%	5110
	21st to end	Day	43% 6% 14% 24% 11% 2	5827
April	1st to 10th	Day	36% 5% 11% 25% 18% 5%	2520
	11th to 20th	Day	29% 5% 13% 26% 21% 6%	2445
	21st to end	Day	23% 4 13% 30% 26% 4	2400
May	1st to 10th	Day	14% 3 7% 27% 33% 16%	5568
	11th to 20th	Day	12% 3 5% 29% 41% 10%	6280
	21st to end	Day	10% 3 8% 30% 42% 8%	6904
June	1st to 10th	Day	18% 3 10% 27% 31% 12%	2800
	11th to 20th	Day	9% 2 7% 19% 36% 27%	2800
	21st to end	Day	8% 1 2 13% 36% 40%	2800
July	1st to 10th	Day	3 1 1 6% 19% 71%	6251
	11th to 20th	Day	5% 1 2 5% 11% 76%	6245
	21st to end	Day	7% 3 3 14% 26% 48%	6262
August	1st to 10th	Day	9% 2 2 7% 23% 57%	4206
	11th to 20th	Day	4 1 1 7% 35% 51%	3941
	21st to end	Day	6% 1 2 8% 38% 45%	4311
September	1st to 10th	Day	5% 1 2 9% 28% 55%	2400
	11th to 20th	Day	13% 3 4 21% 36% 23%	2400
	21st to end	Day	12% 2 4 18% 34% 30%	2161
October	1st to 10th	Day	13% 2 4 12% 24% 44%	3280
	11th to 20th	Day	15% 3 4 20% 39% 18%	3261
	21st to end	Day	22% 3 7% 19% 34% 16%	3558
November	1st to 10th	Day	27% 5% 10% 22% 24% 13%	1889
	11th to 20th	Day	35% 4 11% 22% 21% 7%	1890
	21st to end	Day	30% 4 10% 20% 23% 12%	1747
December	1st to 10th	Day	26% 3 8% 26% 26% 10%	2700
	11th to 20th	Day	51% 4 9% 17% 14% 6%	3108
	21st to end	Day	52% 4 16% 17% 8% 3	4092
January	1st to 10th	Night	44% 4 16% 19% 10% 6%	8172
	11th to 20th	Night	29% 2 7% 14% 28% 19%	7786
	21st to end	Night	41% 3 7% 16% 21% 13%	8371
February	1st to 10th	Night	39% 3 7% 20% 20% 11%	2730
	11th to 20th	Night	39% 4 8% 21% 20% 8%	2527
	21st to end	Night	36% 5% 9% 24% 20% 7%	2076
March	1st to 10th	Night	49% 5% 7% 19% 14% 6%	5361
	11th to 20th	Night	41% 4 8% 24% 15% 8%	5110
	21st to end	Night	45% 6% 11% 24% 12% 3	5388
April	1st to 10th	Night	36% 5% 12% 20% 21% 6%	2100
	11th to 20th	Night	31% 5% 13% 25% 16% 11%	2039
	21st to end	Night	22% 5% 12% 32% 23% 6%	2000
May	1st to 10th	Night	15% 4 11% 25% 27% 18%	4419
	11th to 20th	Night	13% 3 7% 29% 38% 10%	3616
	21st to end	Night	9% 2 9% 31% 41% 8%	3972
June	1st to 10th	Night	18% 5% 10% 28% 28% 11%	1600
	11th to 20th	Night	9% 3 6% 20% 33% 29%	1600
	21st to end	Night	9% 2 3 12% 34% 40%	1600
July	1st to 10th	Night	3 1 1 6% 23% 66%	3600
	11th to 20th	Night	6% 1 1 5% 11% 76%	3592
	21st to end	Night	9% 2 3 14% 27% 45%	4293
August	1st to 10th	Night	12% 2 1 8% 25% 52%	2929
	11th to 20th	Night	5% 1 1 8% 37% 47%	3193
	21st to end	Night	8% 1 2 9% 34% 46%	3608
September	1st to 10th	Night	6% 2 1 8% 29% 54%	2000
	11th to 20th	Night	13% 2 5% 19% 38% 23%	2000
	21st to end	Night	11% 2 4 18% 30% 34%	2235
October	1st to 10th	Night	14% 2 3 11% 19% 50%	3920
	11th to 20th	Night	12% 2 5% 26% 32% 23%	3897
	21st to end	Night	21% 3 5% 18% 32% 20%	4253
November	1st to 10th	Night	28% 4 10% 22% 19% 16%	2630
	11th to 20th	Night	30% 4 10% 26% 21% 9%	2730
	21st to end	Night	30% 3 8% 23% 22% 14%	2870
December	1st to 10th	Night	24% 3 8% 26% 25% 13%	4700
	11th to 20th	Night	51% 5% 7% 16% 17% 5%	5316
	21st to end	Night	57% 4 12% 15% 9% 3	7106

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	39% 7% 20% 18% 14% 3	220
	11th to 20th	Day	20% 6% 18% 29% 20% 6%	372
	21st to end	Day	20% 8% 22% 25% 20% 5%	473
February	1st to 10th	Day	25% 7% 21% 24% 20% 3	430
	11th to 20th	Day	23% 13% 24% 23% 14% 2	499
	21st to end	Day	19% 11% 25% 30% 13% 2	446
March	1st to 10th	Day	25% 13% 28% 21% 11% 1	540
	11th to 20th	Day	22% 13% 23% 23% 15% 4	540
	21st to end	Day	19% 12% 31% 23% 13% 2	594
April	1st to 10th	Day	19% 11% 26% 25% 15% 4	540
	11th to 20th	Day	15% 11% 30% 26% 15% 3	517
	21st to end	Day	9% 10% 23% 30% 22% 6%	500
May	1st to 10th	Day	9% 9% 30% 29% 18% 5%	503
	11th to 20th	Day	7% 10% 25% 28% 23% 7%	528
	21st to end	Day	6% 7% 21% 31% 26% 9%	573
June	1st to 10th	Day	5% 6% 20% 36% 25% 8%	530
	11th to 20th	Day	4 6% 25% 38% 22% 5%	530
	21st to end	Day	1 4 18% 40% 27% 9%	530
July	1st to 10th	Day	1 1 15% 45% 31% 7%	526
	11th to 20th	Day	1 10% 44% 38% 7%	524
	21st to end	Day	1 12% 44% 33% 10%	575
August	1st to 10th	Day	3 2 14% 42% 33% 7%	527
	11th to 20th	Day	1 2 18% 39% 30% 10%	517
	21st to end	Day	1 1 11% 41% 37% 9%	583
September	1st to 10th	Day	2 2 17% 44% 28% 7%	530
	11th to 20th	Day	5% 5% 20% 37% 28% 6%	530
	21st to end	Day	4 4 21% 38% 27% 6%	530
October	1st to 10th	Day	4 7% 22% 31% 28% 7%	530
	11th to 20th	Day	8% 5% 17% 31% 31% 8%	530
	21st to end	Day	11% 7% 19% 30% 27% 7%	583
November	1st to 10th	Day	16% 5% 15% 28% 28% 8%	365
	11th to 20th	Day	16% 4 20% 28% 23% 9%	330
	21st to end	Day	13% 5% 18% 31% 24% 9%	255
December	1st to 10th	Day	17% 6% 16% 27% 23% 10%	220
	11th to 20th	Day	20% 9% 21% 23% 18% 10%	220
	21st to end	Day	25% 8% 21% 24% 18% 4	242
January	1st to 10th	Night	26% 3 15% 29% 20% 7%	840
	11th to 20th	Night	16% 3 13% 40% 23% 5%	840
	21st to end	Night	21% 3 14% 36% 21% 6%	924
February	1st to 10th	Night	23% 3 14% 35% 21% 4	840
	11th to 20th	Night	20% 5% 16% 35% 19% 4	824
	21st to end	Night	20% 4 17% 41% 15% 3	692
March	1st to 10th	Night	24% 7% 15% 32% 18% 4	840
	11th to 20th	Night	22% 4 14% 31% 25% 4	840
	21st to end	Night	20% 5% 16% 37% 19% 2	924
April	1st to 10th	Night	16% 4 13% 41% 24% 2	840
	11th to 20th	Night	13% 5% 16% 36% 25% 6%	815
	21st to end	Night	9% 5% 13% 40% 29% 6%	800
May	1st to 10th	Night	9% 4 17% 39% 27% 4	740
	11th to 20th	Night	7% 2 12% 39% 36% 3	394
	21st to end	Night	7% 2 12% 40% 37% 2	433
June	1st to 10th	Night	6% 3 12% 39% 36% 5%	400
	11th to 20th	Night	3 1 14% 44% 37% 3	400
	21st to end	Night	2 1 7% 45% 42% 4	400
July	1st to 10th	Night	1 5% 42% 50% 2	390
	11th to 20th	Night	1 4 44% 47% 3	388
	21st to end	Night	1 4 34% 54% 7%	629
August	1st to 10th	Night	3 1 4 39% 48% 5%	597
	11th to 20th	Night	1 5% 44% 43% 7%	754
	21st to end	Night	2 4 37% 53% 5%	880
September	1st to 10th	Night	2 6% 38% 48% 6%	800
	11th to 20th	Night	4 1 9% 37% 42% 8%	800
	21st to end	Night	3 2 10% 41% 35% 10%	800
October	1st to 10th	Night	6% 2 10% 41% 33% 8%	800
	11th to 20th	Night	8% 3 9% 36% 38% 6%	800
	21st to end	Night	8% 2 13% 36% 29% 12%	880
November	1st to 10th	Night	14% 3 10% 33% 30% 8%	820
	11th to 20th	Night	15% 3 13% 38% 25% 7%	840
	21st to end	Night	15% 2 14% 38% 24% 7%	840
December	1st to 10th	Night	18% 3 13% 37% 23% 7%	840
	11th to 20th	Night	29% 3 11% 33% 21% 4	840
	21st to end	Night	29% 3 16% 31% 17% 3	924

Page generated at 2026-04-13 23:44:24. Version ac07

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