Auburn / Lewiston
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Auburn / Lewiston clear sky chart from 2005-11-06 to 2025-05-11.

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	17% 8% 2 6% 4 4 4 4 5% 7% 37%	112936
	Night	18% 8% 3 6% 4 4 4 4 5% 6% 37%	115981
Transparency	Day	45% 6% 12% 21% 14% 2	116491
	Night	46% 5% 12% 21% 14% 2	120590
Seeing	Day	23% 17% 31% 20% 7% 2	15537
	Night	22% 13% 32% 25% 8% 1	24612

By Month

Percentage Cloud Cover NE (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	14% 6% 3 8% 5% 5% 5% 4 6% 7% 37%	3597
	11th to 20th	Day	13% 8% 3 6% 4 4 4 4 5% 7% 43%	3570
	21st to end	Day	12% 11% 3 6% 3 3 4 3 4 5% 46%	3960
February	1st to 10th	Day	15% 10% 3 7% 5% 4 4 4 5% 6% 37%	1757
	11th to 20th	Day	13% 9% 2 7% 6% 5% 5% 4 5% 6% 39%	1948
	21st to end	Day	15% 10% 3 6% 5% 4 5% 5% 7% 5% 36%	1650
March	1st to 10th	Day	22% 11% 3 8% 5% 5% 4 3 4 4 31%	4476
	11th to 20th	Day	17% 11% 3 7% 5% 4 4 3 5% 5% 36%	4878
	21st to end	Day	26% 9% 2 5% 3 3 4 3 5% 6% 32%	5620
April	1st to 10th	Day	20% 11% 4 7% 4 4 3 3 3 6% 36%	2400
	11th to 20th	Day	19% 6% 2 6% 5% 5% 4 4 6% 7% 38%	2472
	21st to end	Day	23% 7% 3 7% 4 4 4 3 5% 5% 34%	2600
May	1st to 10th	Day	24% 11% 3 7% 5% 4 5% 4 6% 6% 27%	4236
	11th to 20th	Day	19% 8% 2 8% 5% 5% 5% 4 5% 7% 31%	4166
	21st to end	Day	15% 6% 2 6% 4 5% 5% 4 6% 9% 38%	4837
June	1st to 10th	Day	22% 8% 3 7% 5% 4 5% 4 6% 8% 29%	2660
	11th to 20th	Day	16% 7% 3 6% 5% 3 5% 4 6% 7% 38%	2660
	21st to end	Day	23% 7% 3 6% 5% 4 6% 5% 5% 6% 30%	2660
July	1st to 10th	Day	14% 6% 2 7% 5% 4 6% 5% 7% 8% 36%	4440
	11th to 20th	Day	12% 6% 2 6% 5% 5% 5% 5% 8% 10% 36%	4440
	21st to end	Day	19% 7% 2 6% 4 4 5% 4 5% 8% 36%	4814
August	1st to 10th	Day	16% 6% 3 7% 5% 5% 5% 4 7% 9% 34%	4147
	11th to 20th	Day	17% 9% 3 8% 5% 4 4 4 5% 7% 34%	4045
	21st to end	Day	10% 5% 2 6% 3 4 5% 5% 7% 8% 46%	4340
September	1st to 10th	Day	12% 5% 1 5% 4 4 3 3 6% 7% 49%	2241
	11th to 20th	Day	12% 5% 2 4 4 3 3 3 4 6% 54%	2090
	21st to end	Day	16% 5% 2 5% 3 4 4 3 5% 8% 45%	2090
October	1st to 10th	Day	18% 7% 2 7% 5% 4 3 4 5% 7% 39%	2090
	11th to 20th	Day	17% 8% 2 6% 4 4 5% 2 5% 7% 42%	1825
	21st to end	Day	23% 7% 2 6% 3 4 3 3 4 6% 38%	1881
November	1st to 10th	Day	17% 6% 2 5% 4 3 4 2 5% 6% 46%	1761
	11th to 20th	Day	19% 5% 2 4 3 4 4 4 5% 6% 44%	1800
	21st to end	Day	23% 7% 2 5% 3 2 3 3 5% 6% 42%	1800
December	1st to 10th	Day	16% 10% 2 5% 4 4 4 3 6% 7% 38%	2297
	11th to 20th	Day	19% 8% 2 4 2 4 3 2 5% 6% 45%	2728
	21st to end	Day	21% 9% 3 6% 4 4 4 3 5% 6% 35%	3960
January	1st to 10th	Night	12% 9% 3 7% 4 4 5% 3 6% 6% 41%	6349
	11th to 20th	Night	13% 11% 4 10% 5% 5% 5% 4 6% 6% 32%	6315
	21st to end	Night	14% 9% 3 7% 4 5% 5% 3 5% 5% 39%	6996
February	1st to 10th	Night	16% 9% 3 7% 5% 5% 4 4 5% 7% 34%	2636
	11th to 20th	Night	12% 11% 3 6% 5% 5% 4 4 5% 5% 40%	2338
	21st to end	Night	14% 10% 3 6% 5% 5% 5% 3 5% 7% 38%	1980
March	1st to 10th	Night	25% 11% 3 7% 4 4 4 3 4 5% 31%	5364
	11th to 20th	Night	15% 9% 3 7% 5% 5% 5% 4 6% 7% 33%	5080
	21st to end	Night	23% 8% 3 6% 4 4 5% 4 6% 6% 31%	5294
April	1st to 10th	Night	21% 10% 3 5% 5% 5% 4 3 4 6% 34%	2000
	11th to 20th	Night	18% 7% 2 7% 5% 4 4 4 4 7% 37%	1876
	21st to end	Night	23% 7% 2 7% 4 4 4 3 5% 5% 36%	1800
May	1st to 10th	Night	23% 9% 3 6% 4 4 5% 4 6% 8% 28%	2924
	11th to 20th	Night	17% 8% 3 7% 6% 5% 6% 4 8% 9% 27%	2761
	21st to end	Night	16% 8% 2 7% 5% 4 4 4 5% 7% 38%	2738
June	1st to 10th	Night	21% 8% 3 7% 4 4 5% 3 5% 6% 32%	1520
	11th to 20th	Night	17% 7% 2 5% 4 4 4 4 6% 8% 39%	1520
	21st to end	Night	22% 9% 2 6% 4 4 5% 3 6% 7% 31%	1520
July	1st to 10th	Night	12% 6% 3 6% 6% 5% 5% 5% 7% 10% 34%	2520
	11th to 20th	Night	14% 6% 3 7% 4 5% 5% 4 6% 8% 38%	2520
	21st to end	Night	15% 7% 2 5% 4 4 5% 4 6% 7% 40%	2739
August	1st to 10th	Night	21% 7% 3 7% 5% 5% 4 4 5% 7% 32%	2752
	11th to 20th	Night	16% 8% 3 8% 5% 4 5% 4 6% 9% 33%	2782
	21st to end	Night	11% 5% 2 7% 5% 3 4 4 6% 9% 44%	3312
September	1st to 10th	Night	13% 6% 2 4 3 3 4 3 5% 8% 49%	1938
	11th to 20th	Night	15% 5% 2 4 3 3 3 3 4 7% 51%	2090
	21st to end	Night	16% 6% 2 5% 3 3 3 4 4 7% 47%	2090
October	1st to 10th	Night	18% 7% 2 6% 3 5% 5% 3 5% 6% 39%	2090
	11th to 20th	Night	17% 6% 2 6% 3 4 4 4 6% 7% 42%	2351
	21st to end	Night	24% 7% 2 5% 3 3 4 2 5% 6% 37%	2717
November	1st to 10th	Night	16% 6% 2 6% 4 4 4 3 4 6% 45%	2537
	11th to 20th	Night	18% 6% 2 5% 4 4 4 3 4 6% 45%	2600
	21st to end	Night	17% 7% 2 6% 4 4 4 3 5% 6% 41%	2600
December	1st to 10th	Night	17% 10% 2 6% 4 4 4 4 6% 7% 36%	4882
	11th to 20th	Night	24% 8% 2 5% 4 3 3 3 4 5% 40%	5454
	21st to end	Night	21% 11% 3 6% 4 4 4 3 4 5% 37%	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	45% 4 11% 26% 13% 1	3598
	11th to 20th	Day	40% 4 14% 27% 12% 3	3600
	21st to end	Day	41% 4 10% 20% 18% 6%	3960
February	1st to 10th	Day	46% 5% 12% 20% 14% 3	1757
	11th to 20th	Day	46% 6% 12% 19% 14% 4	1957
	21st to end	Day	47% 5% 11% 19% 14% 4	1650
March	1st to 10th	Day	56% 4 8% 12% 13% 8%	4479
	11th to 20th	Day	48% 6% 13% 18% 11% 3	4878
	21st to end	Day	52% 3 5% 17% 17% 5%	5620
April	1st to 10th	Day	51% 4 9% 17% 16% 4	2400
	11th to 20th	Day	44% 7% 10% 22% 14% 3	2472
	21st to end	Day	51% 6% 9% 17% 14% 4	2600
May	1st to 10th	Day	54% 9% 11% 17% 8% 1	4250
	11th to 20th	Day	49% 8% 15% 16% 9% 2	4170
	21st to end	Day	39% 9% 16% 20% 14% 1	4837
June	1st to 10th	Day	51% 8% 12% 20% 9%	2660
	11th to 20th	Day	43% 7% 12% 19% 15% 3	2660
	21st to end	Day	52% 7% 11% 19% 10% 1	2660
July	1st to 10th	Day	43% 6% 13% 25% 13%	4370
	11th to 20th	Day	39% 8% 16% 26% 10%	4365
	21st to end	Day	45% 7% 13% 21% 13% 1	4661
August	1st to 10th	Day	45% 8% 16% 24% 8%	4133
	11th to 20th	Day	48% 7% 15% 22% 8%	4084
	21st to end	Day	33% 7% 15% 25% 18% 1	4340
September	1st to 10th	Day	33% 7% 14% 27% 19% 1	2241
	11th to 20th	Day	32% 5% 10% 30% 21% 3	2090
	21st to end	Day	37% 5% 12% 27% 17% 1	2090
October	1st to 10th	Day	47% 5% 12% 22% 14% 1	3480
	11th to 20th	Day	35% 4 11% 28% 22% 1	3002
	21st to end	Day	36% 3 12% 24% 21% 3	3081
November	1st to 10th	Day	39% 5% 14% 24% 16% 3	1761
	11th to 20th	Day	39% 6% 10% 21% 20% 4	1800
	21st to end	Day	43% 4 17% 23% 12% 1	1800
December	1st to 10th	Day	45% 4 14% 25% 11% 1	2297
	11th to 20th	Day	41% 4 12% 19% 17% 8%	2728
	21st to end	Day	50% 5% 10% 17% 13% 5%	3960
January	1st to 10th	Night	43% 4 12% 30% 11% 2	6349
	11th to 20th	Night	50% 5% 13% 19% 11% 2	6360
	21st to end	Night	46% 4 8% 19% 17% 6%	6996
February	1st to 10th	Night	48% 6% 13% 17% 13% 3	2636
	11th to 20th	Night	44% 5% 12% 20% 16% 3	2340
	21st to end	Night	46% 4 10% 22% 14% 4	1980
March	1st to 10th	Night	56% 3 8% 13% 13% 6%	5374
	11th to 20th	Night	47% 7% 17% 18% 9% 2	5081
	21st to end	Night	52% 4 6% 15% 18% 5%	5294
April	1st to 10th	Night	51% 4 10% 18% 15% 4	2000
	11th to 20th	Night	46% 6% 10% 20% 17% 1	1876
	21st to end	Night	49% 6% 10% 17% 14% 4	1800
May	1st to 10th	Night	52% 10% 13% 18% 8% 1	2930
	11th to 20th	Night	49% 11% 14% 17% 7% 2	2762
	21st to end	Night	42% 7% 17% 19% 13% 1	2739
June	1st to 10th	Night	51% 8% 11% 20% 10% 1	1520
	11th to 20th	Night	41% 7% 15% 21% 14% 2	1520
	21st to end	Night	50% 7% 15% 18% 9% 2	1520
July	1st to 10th	Night	42% 8% 16% 20% 13%	2480
	11th to 20th	Night	43% 6% 15% 24% 11%	2472
	21st to end	Night	41% 7% 14% 26% 12%	2651
August	1st to 10th	Night	51% 7% 14% 20% 7%	2742
	11th to 20th	Night	47% 7% 15% 20% 11%	2809
	21st to end	Night	35% 7% 16% 25% 16% 1	3312
September	1st to 10th	Night	34% 6% 13% 31% 16%	1938
	11th to 20th	Night	34% 4 11% 30% 18% 2	2090
	21st to end	Night	37% 5% 12% 30% 15% 2	2090
October	1st to 10th	Night	45% 5% 13% 22% 14% 1	3480
	11th to 20th	Night	34% 4 11% 27% 23% 1	3913
	21st to end	Night	40% 3 11% 27% 18% 3	4467
November	1st to 10th	Night	40% 5% 11% 26% 15% 2	2537
	11th to 20th	Night	41% 5% 11% 24% 17% 3	2600
	21st to end	Night	43% 5% 15% 21% 14% 1	2600
December	1st to 10th	Night	47% 4 10% 29% 10%	4882
	11th to 20th	Night	47% 4 11% 16% 19% 3	5454
	21st to end	Night	50% 5% 9% 19% 16% 1	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	31% 21% 29% 16% 4	200
	11th to 20th	Day	24% 24% 30% 19% 3 2	200
	21st to end	Day	20% 24% 36% 15% 5%	220
February	1st to 10th	Day	27% 21% 33% 16% 3	355
	11th to 20th	Day	26% 27% 33% 12% 2	496
	21st to end	Day	25% 20% 36% 17% 3	414
March	1st to 10th	Day	27% 23% 33% 15% 3	500
	11th to 20th	Day	24% 28% 31% 14% 3 1	500
	21st to end	Day	29% 22% 31% 11% 5% 2	550
April	1st to 10th	Day	31% 25% 25% 14% 4 1	500
	11th to 20th	Day	29% 22% 30% 14% 4 1	492
	21st to end	Day	31% 21% 28% 13% 5% 2	500
May	1st to 10th	Day	34% 19% 24% 17% 4 1	503
	11th to 20th	Day	19% 20% 36% 16% 7% 1	487
	21st to end	Day	20% 16% 35% 22% 6%	529
June	1st to 10th	Day	20% 17% 36% 17% 8% 2	490
	11th to 20th	Day	18% 18% 32% 22% 8% 3	490
	21st to end	Day	25% 14% 31% 21% 7% 2	490
July	1st to 10th	Day	18% 7% 38% 26% 9% 2	485
	11th to 20th	Day	14% 7% 38% 27% 11% 4	484
	21st to end	Day	15% 8% 38% 26% 11% 3	532
August	1st to 10th	Day	13% 10% 29% 33% 13% 2	486
	11th to 20th	Day	18% 11% 27% 26% 13% 5%	479
	21st to end	Day	12% 12% 29% 29% 13% 5%	539
September	1st to 10th	Day	16% 9% 31% 24% 17% 3	490
	11th to 20th	Day	16% 13% 29% 20% 12% 9%	490
	21st to end	Day	16% 13% 31% 24% 10% 6%	490
October	1st to 10th	Day	21% 17% 24% 21% 13% 3	490
	11th to 20th	Day	21% 17% 29% 21% 11% 2	397
	21st to end	Day	32% 18% 24% 19% 7%	429
November	1st to 10th	Day	23% 18% 29% 20% 8% 2	395
	11th to 20th	Day	29% 17% 31% 19% 4 1	400
	21st to end	Day	30% 20% 24% 19% 7% 1	400
December	1st to 10th	Day	25% 18% 36% 15% 7%	215
	11th to 20th	Day	31% 23% 33% 11% 3	200
	21st to end	Day	28% 21% 26% 20% 5%	220
January	1st to 10th	Night	22% 18% 35% 21% 3	800
	11th to 20th	Night	25% 19% 32% 21% 4	800
	21st to end	Night	18% 19% 40% 19% 3	880
February	1st to 10th	Night	23% 18% 33% 22% 3	800
	11th to 20th	Night	22% 19% 40% 17% 2	783
	21st to end	Night	22% 17% 35% 21% 4	660
March	1st to 10th	Night	26% 17% 36% 18% 2	800
	11th to 20th	Night	21% 17% 36% 20% 6%	800
	21st to end	Night	25% 17% 33% 21% 3 1	880
April	1st to 10th	Night	28% 17% 31% 20% 4	800
	11th to 20th	Night	22% 15% 37% 22% 4	692
	21st to end	Night	28% 15% 30% 23% 4	600
May	1st to 10th	Night	27% 11% 31% 26% 5% 1	600
	11th to 20th	Night	22% 13% 33% 27% 6%	532
	21st to end	Night	23% 8% 28% 34% 6%	411
June	1st to 10th	Night	25% 7% 30% 29% 9%	380
	11th to 20th	Night	20% 5% 27% 34% 14%	380
	21st to end	Night	26% 4 27% 34% 8%	380
July	1st to 10th	Night	18% 4 25% 39% 14%	370
	11th to 20th	Night	17% 4 25% 35% 19% 1	368
	21st to end	Night	16% 2 23% 43% 16% 1	416
August	1st to 10th	Night	16% 4 22% 43% 15%	520
	11th to 20th	Night	15% 5% 28% 34% 16% 1	562
	21st to end	Night	15% 5% 27% 34% 17% 2	737
September	1st to 10th	Night	14% 4 33% 32% 16% 1	760
	11th to 20th	Night	18% 7% 27% 27% 18% 3	760
	21st to end	Night	19% 8% 28% 29% 16% 1	760
October	1st to 10th	Night	21% 10% 24% 30% 14% 1	760
	11th to 20th	Night	20% 11% 31% 26% 10% 1	760
	21st to end	Night	28% 14% 30% 22% 6%	836
November	1st to 10th	Night	21% 12% 34% 26% 7% 1	780
	11th to 20th	Night	24% 13% 33% 23% 6% 1	800
	21st to end	Night	23% 20% 31% 22% 4 1	800
December	1st to 10th	Night	26% 13% 36% 19% 5%	895
	11th to 20th	Night	26% 19% 31% 20% 3	870
	21st to end	Night	27% 17% 32% 21% 3	880

Page generated at 2025-05-08 09:33:59. Version ac07

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