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 2026-09-29.

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 6% 7% 37%	148451
	Night	17% 8% 3 7% 4 4 4 3 5% 7% 37%	142957
Transparency	Day	45% 5% 12% 22% 14% 2	151960
	Night	46% 5% 11% 22% 14% 2	147537
Seeing	Day	23% 17% 31% 19% 7% 2	17376
	Night	22% 13% 32% 25% 8%	26259

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	12% 6% 3 8% 5% 5% 5% 4 6% 7% 37%	4661
	11th to 20th	Day	14% 11% 3 6% 4 4 4 3 4 6% 41%	4650
	21st to end	Day	10% 10% 2 6% 3 4 4 3 5% 6% 46%	5124
February	1st to 10th	Day	15% 9% 2 7% 5% 5% 4 4 6% 6% 38%	1845
	11th to 20th	Day	12% 9% 2 7% 6% 5% 5% 4 4 6% 39%	2048
	21st to end	Day	15% 10% 2 6% 5% 4 5% 4 6% 5% 37%	1730
March	1st to 10th	Day	22% 11% 3 8% 5% 5% 4 3 4 4 32%	4576
	11th to 20th	Day	17% 11% 3 7% 5% 4 4 4 5% 5% 36%	4985
	21st to end	Day	26% 9% 2 5% 3 3 4 3 5% 7% 32%	5744
April	1st to 10th	Day	19% 11% 4 7% 4 4 3 3 4 6% 36%	2520
	11th to 20th	Day	19% 6% 2 6% 5% 4 4 4 6% 7% 37%	2597
	21st to end	Day	23% 7% 3 7% 4 4 4 3 5% 5% 35%	2730
May	1st to 10th	Day	29% 10% 3 6% 4 4 4 3 5% 6% 25%	7639
	11th to 20th	Day	18% 7% 3 8% 5% 5% 5% 4 6% 7% 33%	7794
	21st to end	Day	19% 7% 2 7% 5% 5% 5% 4 6% 8% 32%	9060
June	1st to 10th	Day	22% 7% 3 7% 5% 4 5% 4 6% 8% 30%	2940
	11th to 20th	Day	16% 7% 2 6% 5% 3 5% 4 6% 8% 38%	2940
	21st to end	Day	22% 7% 3 6% 4 4 5% 4 5% 6% 32%	2940
July	1st to 10th	Day	14% 7% 3 7% 5% 5% 6% 5% 7% 8% 34%	8280
	11th to 20th	Day	11% 5% 2 5% 4 4 5% 5% 7% 10% 42%	8280
	21st to end	Day	15% 5% 2 5% 4 4 5% 3 6% 9% 43%	8993
August	1st to 10th	Day	14% 6% 3 8% 5% 5% 6% 4 7% 9% 34%	6086
	11th to 20th	Day	17% 8% 3 6% 4 4 4 4 6% 8% 36%	5953
	21st to end	Day	11% 5% 2 6% 4 4 5% 5% 7% 8% 44%	6312
September	1st to 10th	Day	12% 5% 1 5% 4 4 3 3 6% 8% 48%	2477
	11th to 20th	Day	12% 5% 2 4 3 3 3 3 4 6% 55%	2310
	21st to end	Day	17% 5% 2 5% 3 4 4 3 5% 7% 46%	2288
October	1st to 10th	Day	18% 7% 2 7% 5% 4 3 3 5% 7% 41%	2200
	11th to 20th	Day	17% 8% 2 6% 4 4 5% 2 5% 7% 41%	1921
	21st to end	Day	23% 7% 2 6% 3 4 4 3 4 6% 38%	1980
November	1st to 10th	Day	17% 7% 2 5% 4 3 4 2 5% 6% 45%	1851
	11th to 20th	Day	18% 5% 2 5% 4 4 4 3 5% 6% 44%	1890
	21st to end	Day	22% 8% 2 5% 3 2 3 3 5% 6% 41%	1890
December	1st to 10th	Day	16% 10% 2 5% 4 4 4 3 6% 7% 38%	2368
	11th to 20th	Day	19% 8% 2 4 3 3 3 2 4 6% 45%	2801
	21st to end	Day	21% 10% 3 6% 4 4 4 3 5% 6% 35%	4048
January	1st to 10th	Night	12% 9% 3 8% 5% 4 4 3 5% 6% 40%	8234
	11th to 20th	Night	14% 12% 4 9% 5% 5% 5% 4 5% 6% 30%	8235
	21st to end	Night	12% 9% 3 7% 5% 5% 5% 3 5% 6% 41%	9057
February	1st to 10th	Night	15% 9% 3 7% 5% 5% 4 4 5% 7% 35%	2767
	11th to 20th	Night	12% 11% 3 6% 5% 5% 4 4 5% 6% 40%	2458
	21st to end	Night	14% 10% 3 6% 5% 5% 4 3 5% 7% 39%	2076
March	1st to 10th	Night	25% 11% 3 7% 4 4 4 3 4 5% 31%	5484
	11th to 20th	Night	15% 9% 3 7% 5% 5% 5% 4 6% 7% 33%	5192
	21st to end	Night	23% 9% 3 7% 4 4 5% 3 6% 6% 31%	5412
April	1st to 10th	Night	21% 10% 3 5% 4 4 4 3 4 6% 34%	2100
	11th to 20th	Night	19% 8% 2 7% 5% 4 4 4 4 7% 36%	1971
	21st to end	Night	23% 7% 2 7% 4 4 4 3 5% 5% 36%	1890
May	1st to 10th	Night	29% 9% 3 6% 4 3 4 3 5% 7% 28%	5259
	11th to 20th	Night	18% 8% 3 7% 5% 5% 5% 4 6% 8% 32%	5120
	21st to end	Night	18% 8% 3 7% 5% 4 4 4 5% 8% 33%	5114
June	1st to 10th	Night	20% 9% 3 6% 4 4 5% 3 5% 7% 33%	1680
	11th to 20th	Night	16% 7% 2 5% 4 4 4 4 6% 8% 40%	1680
	21st to end	Night	21% 9% 2 6% 4 4 5% 3 6% 7% 33%	1680
July	1st to 10th	Night	13% 7% 3 8% 5% 5% 5% 5% 7% 9% 34%	4680
	11th to 20th	Night	13% 6% 2 7% 4 4 4 4 5% 8% 41%	4680
	21st to end	Night	15% 5% 1 4 3 3 4 4 6% 8% 46%	5084
August	1st to 10th	Night	16% 7% 3 8% 6% 5% 5% 4 6% 7% 33%	4018
	11th to 20th	Night	15% 8% 2 7% 4 4 4 4 6% 8% 38%	4092
	21st to end	Night	13% 5% 2 7% 5% 4 5% 4 7% 8% 40%	4809
September	1st to 10th	Night	13% 6% 2 4 3 3 4 3 5% 8% 49%	2142
	11th to 20th	Night	15% 5% 2 4 3 3 3 3 5% 7% 52%	2310
	21st to end	Night	17% 6% 2 5% 3 3 3 3 4 7% 46%	2289
October	1st to 10th	Night	17% 7% 2 6% 3 5% 5% 3 5% 6% 41%	2200
	11th to 20th	Night	17% 6% 2 6% 3 4 4 4 5% 7% 42%	2475
	21st to end	Night	24% 7% 2 5% 3 3 4 3 5% 6% 37%	2860
November	1st to 10th	Night	17% 7% 2 6% 4 4 4 3 4 6% 45%	2667
	11th to 20th	Night	17% 7% 2 5% 4 4 4 3 4 6% 45%	2730
	21st to end	Night	17% 7% 2 6% 4 5% 4 3 5% 7% 40%	2730
December	1st to 10th	Night	17% 10% 2 7% 4 4 4 3 6% 7% 36%	5031
	11th to 20th	Night	24% 8% 2 5% 4 3 3 3 4 5% 40%	5601
	21st to end	Night	21% 11% 3 6% 4 4 4 3 4 5% 36%	7150

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 13% 23% 14% 1	4662
	11th to 20th	Day	45% 4 11% 24% 14% 3	4680
	21st to end	Day	39% 4 10% 23% 19% 5%	5124
February	1st to 10th	Day	46% 5% 11% 21% 14% 3	1845
	11th to 20th	Day	45% 6% 12% 19% 14% 4	2057
	21st to end	Day	46% 5% 11% 19% 15% 4	1730
March	1st to 10th	Day	56% 4 8% 12% 14% 7%	4579
	11th to 20th	Day	48% 6% 13% 18% 11% 3	4985
	21st to end	Day	52% 3 5% 17% 17% 5%	5744
April	1st to 10th	Day	51% 4 9% 17% 16% 4	2520
	11th to 20th	Day	44% 7% 10% 21% 14% 3	2597
	21st to end	Day	51% 5% 8% 17% 15% 4	2730
May	1st to 10th	Day	58% 6% 12% 15% 8% 1	7651
	11th to 20th	Day	49% 6% 15% 18% 10% 2	7798
	21st to end	Day	48% 7% 12% 21% 12% 1	9061
June	1st to 10th	Day	50% 7% 12% 21% 10%	2940
	11th to 20th	Day	43% 7% 12% 20% 16% 2	2940
	21st to end	Day	51% 7% 11% 20% 10% 1	2940
July	1st to 10th	Day	46% 6% 13% 24% 11%	8210
	11th to 20th	Day	37% 6% 14% 27% 15% 1	8205
	21st to end	Day	38% 6% 13% 27% 15%	8795
August	1st to 10th	Day	45% 7% 17% 21% 8% 1	6072
	11th to 20th	Day	45% 6% 16% 22% 10% 1	5992
	21st to end	Day	35% 6% 15% 24% 18% 1	6312
September	1st to 10th	Day	33% 6% 14% 27% 19% 1	2477
	11th to 20th	Day	31% 4 10% 29% 22% 3	2310
	21st to end	Day	37% 5% 12% 27% 17% 2	2288
October	1st to 10th	Day	46% 5% 11% 23% 14% 1	3590
	11th to 20th	Day	35% 4 11% 28% 21% 1	3098
	21st to end	Day	36% 3 12% 25% 21% 3	3180
November	1st to 10th	Day	39% 5% 14% 23% 16% 3	1851
	11th to 20th	Day	39% 6% 10% 21% 20% 3	1890
	21st to end	Day	44% 4 17% 23% 11% 1	1890
December	1st to 10th	Day	45% 4 14% 24% 12% 1	2368
	11th to 20th	Day	40% 4 12% 19% 16% 8%	2801
	21st to end	Day	50% 5% 10% 18% 13% 5%	4048
January	1st to 10th	Night	44% 3 11% 27% 12% 1	8234
	11th to 20th	Night	54% 4 11% 15% 12% 3	8280
	21st to end	Night	44% 4 7% 22% 18% 6%	9057
February	1st to 10th	Night	47% 5% 12% 19% 14% 3	2767
	11th to 20th	Night	44% 4 12% 21% 16% 3	2460
	21st to end	Night	45% 3 10% 23% 14% 4	2076
March	1st to 10th	Night	56% 3 8% 13% 13% 6%	5494
	11th to 20th	Night	47% 7% 17% 18% 9% 2	5193
	21st to end	Night	52% 4 6% 15% 18% 5%	5412
April	1st to 10th	Night	51% 4 10% 17% 15% 3	2100
	11th to 20th	Night	47% 6% 9% 20% 17% 1	1971
	21st to end	Night	49% 6% 10% 17% 15% 4	1890
May	1st to 10th	Night	57% 6% 11% 15% 11% 1	5265
	11th to 20th	Night	49% 7% 11% 25% 8% 1	5121
	21st to end	Night	47% 6% 13% 23% 10% 1	5115
June	1st to 10th	Night	50% 7% 10% 22% 10% 1	1680
	11th to 20th	Night	42% 7% 15% 21% 14% 2	1680
	21st to end	Night	49% 7% 15% 19% 9% 1	1680
July	1st to 10th	Night	45% 7% 15% 22% 10%	4640
	11th to 20th	Night	42% 5% 12% 27% 14%	4632
	21st to end	Night	35% 5% 14% 32% 13% 1	4967
August	1st to 10th	Night	50% 7% 14% 19% 8% 2	4008
	11th to 20th	Night	44% 6% 16% 24% 10%	4119
	21st to end	Night	40% 6% 16% 23% 13% 1	4809
September	1st to 10th	Night	35% 5% 13% 31% 15%	2142
	11th to 20th	Night	33% 4 11% 30% 20% 2	2310
	21st to end	Night	37% 5% 11% 28% 15% 3	2289
October	1st to 10th	Night	44% 5% 13% 22% 15% 1	3590
	11th to 20th	Night	34% 4 11% 28% 22% 1	4037
	21st to end	Night	40% 3 11% 27% 17% 3	4610
November	1st to 10th	Night	41% 5% 11% 26% 16% 2	2667
	11th to 20th	Night	41% 4 11% 24% 17% 3	2730
	21st to end	Night	43% 5% 15% 21% 14% 1	2730
December	1st to 10th	Night	46% 4 9% 29% 11% 1	5031
	11th to 20th	Night	47% 4 11% 17% 18% 3	5601
	21st to end	Night	50% 5% 9% 18% 17% 1	7150

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	30% 20% 30% 17% 4	220
	11th to 20th	Day	25% 25% 29% 17% 3 1	220
	21st to end	Day	20% 26% 35% 14% 4	242
February	1st to 10th	Day	26% 20% 34% 17% 3	383
	11th to 20th	Day	24% 26% 34% 14% 2	536
	21st to end	Day	25% 20% 36% 16% 3	446
March	1st to 10th	Day	27% 23% 33% 15% 2	540
	11th to 20th	Day	25% 27% 31% 13% 3 1	540
	21st to end	Day	31% 22% 30% 10% 4 2	594
April	1st to 10th	Day	31% 25% 26% 13% 4 1	540
	11th to 20th	Day	30% 21% 30% 14% 4 1	532
	21st to end	Day	32% 20% 28% 13% 5% 2	540
May	1st to 10th	Day	34% 21% 24% 16% 3 1	543
	11th to 20th	Day	21% 20% 35% 16% 6% 1	567
	21st to end	Day	21% 17% 35% 21% 6%	617
June	1st to 10th	Day	20% 16% 35% 18% 9% 2	570
	11th to 20th	Day	19% 19% 31% 21% 8% 2	570
	21st to end	Day	24% 15% 30% 22% 7% 2	570
July	1st to 10th	Day	17% 9% 38% 26% 8% 2	565
	11th to 20th	Day	15% 9% 38% 25% 10% 3	564
	21st to end	Day	15% 9% 36% 26% 11% 3	620
August	1st to 10th	Day	12% 10% 30% 33% 12% 3	566
	11th to 20th	Day	18% 11% 28% 25% 12% 6%	559
	21st to end	Day	12% 11% 31% 29% 12% 5%	627
September	1st to 10th	Day	16% 10% 31% 24% 15% 3	570
	11th to 20th	Day	15% 14% 29% 21% 12% 9%	570
	21st to end	Day	17% 14% 32% 23% 10% 5%	562
October	1st to 10th	Day	21% 17% 24% 22% 13% 4	530
	11th to 20th	Day	22% 17% 29% 21% 10% 1	428
	21st to end	Day	31% 18% 25% 18% 8%	462
November	1st to 10th	Day	25% 18% 28% 20% 8% 2	425
	11th to 20th	Day	28% 17% 31% 18% 5% 1	430
	21st to end	Day	30% 20% 25% 19% 6%	430
December	1st to 10th	Day	26% 17% 36% 15% 6%	236
	11th to 20th	Day	33% 22% 31% 11% 3	220
	21st to end	Day	29% 21% 26% 19% 4	242
January	1st to 10th	Night	22% 18% 35% 21% 3	840
	11th to 20th	Night	26% 19% 31% 20% 3	840
	21st to end	Night	18% 19% 40% 19% 3	924
February	1st to 10th	Night	22% 19% 33% 23% 4	840
	11th to 20th	Night	21% 19% 40% 18% 3	823
	21st to end	Night	22% 16% 36% 21% 4	692
March	1st to 10th	Night	26% 18% 37% 18% 2	840
	11th to 20th	Night	22% 17% 35% 20% 5%	840
	21st to end	Night	25% 17% 33% 21% 3 1	924
April	1st to 10th	Night	28% 17% 31% 20% 4	840
	11th to 20th	Night	22% 16% 36% 22% 4	727
	21st to end	Night	28% 15% 30% 22% 5%	630
May	1st to 10th	Night	26% 11% 32% 25% 5%	630
	11th to 20th	Night	22% 13% 33% 26% 5%	585
	21st to end	Night	23% 8% 29% 33% 6%	455
June	1st to 10th	Night	25% 7% 30% 29% 10%	420
	11th to 20th	Night	19% 7% 27% 34% 13%	420
	21st to end	Night	25% 5% 27% 36% 8%	420
July	1st to 10th	Night	17% 4 25% 40% 13%	410
	11th to 20th	Night	17% 4 25% 36% 18% 1	408
	21st to end	Night	15% 3 23% 43% 16% 1	460
August	1st to 10th	Night	15% 5% 21% 43% 16%	575
	11th to 20th	Night	14% 5% 28% 35% 16% 1	622
	21st to end	Night	15% 5% 27% 35% 16% 2	815
September	1st to 10th	Night	15% 4 32% 33% 15% 1	840
	11th to 20th	Night	17% 7% 27% 29% 18% 3	840
	21st to end	Night	20% 7% 28% 29% 15% 1	833
October	1st to 10th	Night	21% 11% 24% 30% 14% 1	800
	11th to 20th	Night	21% 11% 31% 26% 10% 1	800
	21st to end	Night	27% 13% 30% 23% 6%	880
November	1st to 10th	Night	22% 12% 34% 25% 7% 1	820
	11th to 20th	Night	24% 14% 33% 23% 7% 1	840
	21st to end	Night	22% 19% 32% 22% 4	840
December	1st to 10th	Night	26% 13% 36% 20% 5%	945
	11th to 20th	Night	26% 20% 31% 20% 3	917
	21st to end	Night	27% 17% 32% 21% 3	924

Page generated at 2026-09-26 04:18:41. Version ac07

Copyright © 2026 Attilla Danko.