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 2025-08-05.

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	19% 9% 3 8% 5% 5% 4 4 5% 6% 33%	130701
	Night	21% 10% 3 8% 5% 4 4 4 5% 6% 31%	125868
Transparency	Day	51% 8% 14% 18% 8% 2	130418
	Night	53% 8% 14% 17% 7% 1	125728
Seeing	Day	24% 10% 20% 25% 17% 4	15966
	Night	28% 8% 17% 27% 18% 2	24223

By Month

Percentage Cloud Cover NW (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	36% 14% 4 9% 7% 6% 5% 4 4 4 8%	3522
	11th to 20th	Day	17% 11% 4 9% 5% 6% 6% 4 5% 7% 26%	3616
	21st to end	Day	30% 10% 3 7% 4 3 3 2 4 5% 28%	4142
February	1st to 10th	Day	29% 13% 3 9% 6% 4 4 3 5% 8% 17%	1800
	11th to 20th	Day	31% 13% 4 8% 5% 4 3 3 4 5% 19%	1755
	21st to end	Day	27% 14% 4 9% 6% 5% 5% 3 4 4 19%	1560
March	1st to 10th	Day	18% 14% 4 10% 6% 5% 6% 5% 6% 7% 18%	4623
	11th to 20th	Day	20% 13% 4 9% 5% 5% 5% 4 4 4 25%	5000
	21st to end	Day	24% 14% 4 10% 6% 7% 5% 5% 6% 7% 12%	5674
April	1st to 10th	Day	25% 12% 4 9% 6% 6% 6% 5% 6% 7% 16%	2400
	11th to 20th	Day	21% 10% 4 8% 6% 5% 5% 4 5% 6% 25%	2383
	21st to end	Day	19% 11% 4 10% 7% 6% 5% 4 5% 6% 23%	2640
May	1st to 10th	Day	15% 8% 2 7% 4 4 5% 5% 5% 7% 38%	6320
	11th to 20th	Day	19% 11% 4 8% 5% 5% 5% 4 5% 7% 27%	6277
	21st to end	Day	18% 10% 3 8% 5% 5% 5% 4 6% 8% 28%	6903
June	1st to 10th	Day	19% 10% 3 7% 5% 5% 5% 4 6% 8% 29%	2800
	11th to 20th	Day	20% 11% 4 9% 6% 6% 6% 4 6% 7% 21%	2996
	21st to end	Day	12% 7% 3 8% 5% 5% 5% 4 6% 7% 38%	3000
July	1st to 10th	Day	7% 5% 2 4 3 2 3 3 4 5% 62%	6780
	11th to 20th	Day	5% 4 2 4 2 3 3 2 3 5% 69%	6373
	21st to end	Day	8% 5% 2 5% 3 4 3 3 5% 6% 57%	6874
August	1st to 10th	Day	5% 3 2 5% 3 3 3 3 5% 7% 61%	4371
	11th to 20th	Day	9% 7% 3 7% 5% 5% 5% 4 6% 8% 40%	4026
	21st to end	Day	16% 8% 3 7% 4 4 3 4 5% 6% 40%	4316
September	1st to 10th	Day	9% 6% 2 6% 4 4 4 3 5% 6% 50%	2280
	11th to 20th	Day	14% 7% 3 8% 6% 4 4 3 6% 7% 37%	2280
	21st to end	Day	17% 8% 3 7% 4 4 4 3 6% 7% 38%	2010
October	1st to 10th	Day	16% 7% 2 6% 4 4 4 4 7% 10% 36%	3180
	11th to 20th	Day	27% 10% 3 7% 4 5% 4 3 5% 7% 26%	3161
	21st to end	Day	26% 10% 3 10% 6% 5% 5% 3 5% 6% 21%	3261
November	1st to 10th	Day	31% 11% 3 8% 5% 4 5% 4 5% 6% 18%	1623
	11th to 20th	Day	30% 12% 3 8% 5% 4 3 4 4 5% 21%	1600
	21st to end	Day	29% 10% 4 9% 5% 4 5% 3 6% 5% 20%	1600
December	1st to 10th	Day	22% 8% 3 6% 5% 6% 6% 5% 7% 8% 24%	2620
	11th to 20th	Day	31% 13% 4 9% 6% 5% 5% 5% 6% 5% 11%	3025
	21st to end	Day	31% 14% 4 11% 6% 5% 4 3 4 5% 12%	3910
January	1st to 10th	Night	34% 15% 5% 10% 6% 6% 5% 3 4 3 9%	6312
	11th to 20th	Night	19% 9% 4 7% 5% 5% 5% 4 5% 7% 30%	6282
	21st to end	Night	27% 9% 3 7% 4 4 4 3 4 5% 29%	6806
February	1st to 10th	Night	29% 13% 3 9% 6% 5% 4 3 3 6% 18%	2600
	11th to 20th	Night	27% 12% 3 7% 6% 5% 4 4 4 5% 23%	2532
	21st to end	Night	28% 12% 3 7% 6% 4 5% 4 5% 5% 21%	2070
March	1st to 10th	Night	18% 14% 4 9% 6% 5% 5% 5% 7% 8% 20%	5255
	11th to 20th	Night	23% 11% 3 7% 5% 4 4 4 6% 6% 28%	4999
	21st to end	Night	30% 14% 4 9% 5% 5% 5% 4 5% 5% 13%	5300
April	1st to 10th	Night	22% 11% 4 9% 5% 5% 6% 6% 6% 6% 20%	2000
	11th to 20th	Night	17% 10% 3 8% 5% 5% 5% 4 6% 6% 30%	1964
	21st to end	Night	19% 10% 4 7% 6% 6% 5% 3 6% 7% 25%	1760
May	1st to 10th	Night	16% 8% 3 7% 4 4 4 3 4 5% 40%	3640
	11th to 20th	Night	16% 9% 4 9% 6% 5% 6% 4 6% 8% 27%	3616
	21st to end	Night	13% 11% 3 10% 6% 6% 5% 5% 6% 7% 28%	3972
June	1st to 10th	Night	15% 8% 3 7% 7% 6% 5% 4 4 6% 34%	1599
	11th to 20th	Night	16% 10% 3 8% 6% 4 5% 6% 7% 7% 29%	1400
	21st to end	Night	11% 7% 3 8% 4 4 3 4 6% 6% 45%	1400
July	1st to 10th	Night	5% 5% 2 4 4 3 3 2 5% 5% 62%	3180
	11th to 20th	Night	2 3 1 3 2 2 3 2 3 4 75%	3584
	21st to end	Night	7% 4 1 4 2 3 3 3 5% 7% 62%	3969
August	1st to 10th	Night	3 3 1 4 3 3 3 2 4 5% 68%	2647
	11th to 20th	Night	10% 6% 3 6% 4 4 4 3 4 7% 49%	2812
	21st to end	Night	15% 7% 2 6% 4 3 3 3 5% 6% 47%	3357
September	1st to 10th	Night	8% 6% 2 5% 3 3 3 5% 5% 6% 55%	1900
	11th to 20th	Night	15% 7% 2 6% 5% 5% 5% 3 5% 5% 43%	1900
	21st to end	Night	16% 6% 3 7% 4 4 3 3 5% 7% 42%	2167
October	1st to 10th	Night	15% 6% 2 7% 4 4 5% 4 5% 8% 40%	3800
	11th to 20th	Night	26% 9% 2 6% 4 4 5% 4 5% 5% 29%	3777
	21st to end	Night	26% 11% 3 8% 5% 4 5% 3 5% 6% 24%	4301
November	1st to 10th	Night	32% 9% 3 8% 5% 4 5% 3 5% 5% 21%	2673
	11th to 20th	Night	30% 11% 3 8% 5% 4 4 3 4 5% 22%	2800
	21st to end	Night	28% 12% 3 8% 5% 4 4 3 5% 7% 21%	2800
December	1st to 10th	Night	21% 9% 3 6% 5% 5% 5% 5% 7% 6% 26%	4560
	11th to 20th	Night	32% 15% 4 9% 6% 5% 4 3 5% 5% 12%	5180
	21st to end	Night	30% 15% 5% 11% 6% 5% 4 3 4 5% 12%	6954

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	75% 8% 8% 6% 2	3522
	11th to 20th	Day	54% 10% 13% 16% 7% 1	3640
	21st to end	Day	59% 6% 8% 16% 11%	4142
February	1st to 10th	Day	67% 9% 10% 9% 4 1	1800
	11th to 20th	Day	68% 8% 8% 10% 6% 1	1764
	21st to end	Day	68% 6% 11% 11% 4	1560
March	1st to 10th	Day	62% 7% 16% 11% 4	4623
	11th to 20th	Day	60% 7% 12% 18% 2	5000
	21st to end	Day	70% 8% 13% 9%	5674
April	1st to 10th	Day	66% 8% 17% 8% 1	2400
	11th to 20th	Day	59% 7% 13% 14% 6% 1	2383
	21st to end	Day	62% 8% 14% 11% 4 1	2640
May	1st to 10th	Day	44% 7% 17% 23% 9%	6320
	11th to 20th	Day	54% 10% 19% 14% 3	6280
	21st to end	Day	52% 9% 22% 14% 2	6904
June	1st to 10th	Day	54% 9% 18% 13% 6%	2800
	11th to 20th	Day	61% 9% 15% 11% 4	2996
	21st to end	Day	44% 10% 18% 19% 7% 1	3000
July	1st to 10th	Day	24% 6% 17% 22% 17% 13%	6706
	11th to 20th	Day	20% 4 12% 29% 30% 5%	6296
	21st to end	Day	27% 7% 20% 33% 12% 2	6681
August	1st to 10th	Day	24% 6% 12% 36% 20% 3	4354
	11th to 20th	Day	40% 9% 18% 23% 8% 2	4065
	21st to end	Day	44% 6% 12% 26% 11% 1	4315
September	1st to 10th	Day	33% 8% 16% 25% 13% 5%	2280
	11th to 20th	Day	44% 11% 13% 17% 13% 2	2280
	21st to end	Day	45% 8% 18% 16% 10% 2	2010
October	1st to 10th	Day	41% 8% 14% 29% 7%	3180
	11th to 20th	Day	57% 8% 12% 15% 7% 1	3161
	21st to end	Day	63% 7% 13% 9% 7% 1	3261
November	1st to 10th	Day	66% 7% 12% 10% 4	1623
	11th to 20th	Day	67% 8% 9% 9% 7% 1	1600
	21st to end	Day	65% 9% 8% 10% 7% 1	1600
December	1st to 10th	Day	53% 8% 10% 18% 11% 1	2620
	11th to 20th	Day	71% 9% 10% 8% 1	3028
	21st to end	Day	73% 8% 11% 6% 2	3910
January	1st to 10th	Night	76% 8% 8% 5% 2 1	6312
	11th to 20th	Night	49% 9% 14% 20% 7% 1	6320
	21st to end	Night	57% 6% 9% 17% 9% 1	6806
February	1st to 10th	Night	68% 6% 11% 8% 6% 1	2600
	11th to 20th	Night	62% 10% 10% 10% 7% 2	2534
	21st to end	Night	64% 8% 12% 11% 5%	2070
March	1st to 10th	Night	58% 8% 15% 14% 5%	5255
	11th to 20th	Night	54% 7% 16% 20% 2 1	5000
	21st to end	Night	69% 11% 12% 8%	5300
April	1st to 10th	Night	63% 11% 15% 10% 1	2000
	11th to 20th	Night	54% 8% 15% 14% 7% 1	1964
	21st to end	Night	59% 9% 15% 12% 4 1	1760
May	1st to 10th	Night	45% 6% 15% 27% 7% 1	3637
	11th to 20th	Night	52% 10% 20% 14% 3	3616
	21st to end	Night	54% 13% 19% 13% 1	3972
June	1st to 10th	Night	51% 9% 18% 16% 6%	1599
	11th to 20th	Night	54% 10% 20% 13% 3	1400
	21st to end	Night	41% 7% 22% 20% 8% 2	1400
July	1st to 10th	Night	25% 8% 16% 22% 16% 13%	3145
	11th to 20th	Night	16% 4 13% 30% 35% 3	3538
	21st to end	Night	23% 6% 22% 33% 14% 2	3857
August	1st to 10th	Night	19% 5% 12% 38% 23% 2	2639
	11th to 20th	Night	35% 10% 22% 22% 9% 2	2839
	21st to end	Night	39% 7% 14% 29% 10% 1	3357
September	1st to 10th	Night	30% 8% 16% 26% 15% 5%	1900
	11th to 20th	Night	44% 8% 12% 18% 13% 5%	1900
	21st to end	Night	43% 8% 15% 21% 11% 2	2167
October	1st to 10th	Night	40% 7% 19% 28% 4 1	3800
	11th to 20th	Night	55% 7% 12% 19% 6%	3777
	21st to end	Night	60% 7% 12% 13% 8%	4301
November	1st to 10th	Night	64% 8% 12% 11% 4	2673
	11th to 20th	Night	66% 6% 10% 9% 6% 3	2800
	21st to end	Night	63% 9% 10% 9% 8% 1	2800
December	1st to 10th	Night	51% 8% 12% 19% 9% 1	4560
	11th to 20th	Night	73% 8% 9% 7% 2	5176
	21st to end	Night	72% 9% 11% 7% 2	6954

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	38% 13% 18% 15% 13% 4	200
	11th to 20th	Day	31% 13% 21% 21% 11% 4	200
	21st to end	Day	36% 14% 16% 16% 13% 5%	280
February	1st to 10th	Day	38% 13% 20% 16% 11% 3	400
	11th to 20th	Day	43% 14% 21% 12% 10% 1	395
	21st to end	Day	35% 16% 21% 20% 7% 1	369
March	1st to 10th	Day	30% 17% 24% 20% 9% 1	500
	11th to 20th	Day	29% 16% 20% 22% 11% 3	500
	21st to end	Day	34% 14% 24% 19% 8% 2	550
April	1st to 10th	Day	31% 18% 19% 20% 10% 2	500
	11th to 20th	Day	25% 17% 27% 19% 8% 5%	492
	21st to end	Day	22% 15% 25% 24% 12% 3	500
May	1st to 10th	Day	19% 12% 24% 28% 14% 3	503
	11th to 20th	Day	27% 9% 21% 26% 13% 4	528
	21st to end	Day	25% 10% 21% 25% 16% 3	573
June	1st to 10th	Day	24% 7% 23% 24% 17% 5%	530
	11th to 20th	Day	21% 12% 25% 27% 13% 2	726
	21st to end	Day	14% 7% 20% 31% 24% 4	730
July	1st to 10th	Day	13% 5% 17% 34% 26% 5%	721
	11th to 20th	Day	9% 4 20% 36% 25% 7%	549
	21st to end	Day	8% 3 14% 35% 33% 7%	575
August	1st to 10th	Day	11% 4 13% 32% 29% 12%	504
	11th to 20th	Day	7% 4 11% 34% 34% 10%	477
	21st to end	Day	15% 7% 21% 30% 20% 7%	539
September	1st to 10th	Day	13% 5% 23% 34% 18% 6%	490
	11th to 20th	Day	18% 7% 18% 30% 20% 7%	490
	21st to end	Day	18% 10% 23% 27% 20% 3	490
October	1st to 10th	Day	24% 10% 19% 22% 19% 6%	490
	11th to 20th	Day	31% 11% 14% 25% 14% 5%	490
	21st to end	Day	33% 14% 20% 19% 10% 5%	427
November	1st to 10th	Day	37% 14% 15% 20% 12% 2	228
	11th to 20th	Day	39% 15% 19% 9% 14% 6%	200
	21st to end	Day	34% 12% 20% 17% 11% 8%	200
December	1st to 10th	Day	43% 11% 11% 14% 14% 9%	200
	11th to 20th	Day	43% 9% 19% 21% 8% 2	200
	21st to end	Day	42% 10% 15% 19% 13% 1	220
January	1st to 10th	Night	42% 14% 17% 18% 9% 1	800
	11th to 20th	Night	37% 8% 15% 27% 12% 1	800
	21st to end	Night	35% 7% 17% 28% 12% 1	880
February	1st to 10th	Night	36% 10% 18% 25% 9% 2	800
	11th to 20th	Night	34% 13% 16% 25% 11% 1	784
	21st to end	Night	37% 11% 19% 23% 9% 1	660
March	1st to 10th	Night	30% 11% 20% 24% 13% 1	800
	11th to 20th	Night	32% 11% 19% 25% 12% 1	800
	21st to end	Night	35% 12% 19% 24% 10% 1	880
April	1st to 10th	Night	29% 9% 21% 25% 13% 2	800
	11th to 20th	Night	24% 12% 21% 27% 14% 2	776
	21st to end	Night	26% 9% 21% 29% 13% 2	560
May	1st to 10th	Night	20% 11% 16% 33% 19% 1	400
	11th to 20th	Night	18% 7% 18% 31% 24% 3	394
	21st to end	Night	20% 6% 18% 27% 26% 3	433
June	1st to 10th	Night	18% 6% 22% 28% 24% 2	400
	11th to 20th	Night	22% 6% 24% 28% 20% 1	400
	21st to end	Night	15% 5% 16% 34% 28% 2	400
July	1st to 10th	Night	10% 3 15% 34% 34% 4	390
	11th to 20th	Night	9% 1 11% 40% 35% 3	388
	21st to end	Night	6% 4 10% 32% 44% 5%	438
August	1st to 10th	Night	9% 2 11% 29% 41% 9%	433
	11th to 20th	Night	9% 2 9% 28% 44% 9%	564
	21st to end	Night	14% 3 13% 31% 35% 4	747
September	1st to 10th	Night	13% 4 13% 33% 34% 4	760
	11th to 20th	Night	19% 4 12% 24% 34% 7%	760
	21st to end	Night	20% 5% 17% 30% 26% 3	760
October	1st to 10th	Night	23% 5% 13% 29% 27% 3	760
	11th to 20th	Night	28% 7% 14% 27% 20% 4	760
	21st to end	Night	31% 8% 18% 26% 14% 3	836
November	1st to 10th	Night	37% 9% 20% 26% 8%	780
	11th to 20th	Night	37% 12% 18% 23% 10% 1	800
	21st to end	Night	35% 9% 18% 26% 13% 1	800
December	1st to 10th	Night	31% 8% 20% 25% 14% 1	800
	11th to 20th	Night	40% 9% 19% 23% 8% 1	800
	21st to end	Night	45% 11% 18% 19% 7%	880

Page generated at 2025-08-01 22:32:22. Version ac07

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