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 2024-11-01.

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	18% 8% 2 6% 4 4 4 4 6% 7% 37%	100923
	Night	18% 8% 3 6% 4 4 4 4 5% 7% 37%	98010
Transparency	Day	45% 7% 12% 21% 13% 2	100681
	Night	46% 6% 12% 21% 13% 2	97872
Seeing	Day	22% 17% 31% 20% 8% 2	14938
	Night	22% 13% 31% 25% 8% 1	23856

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	16% 7% 3 6% 4 4 4 4 5% 6% 41%	2517
	11th to 20th	Day	17% 8% 2 6% 4 5% 5% 4 5% 7% 39%	2520
	21st to end	Day	16% 12% 3 7% 3 3 5% 3 5% 5% 37%	2772
February	1st to 10th	Day	16% 10% 3 7% 5% 4 4 4 5% 6% 37%	1668
	11th to 20th	Day	12% 10% 2 7% 6% 5% 5% 4 4 5% 39%	1848
	21st to end	Day	16% 10% 3 6% 5% 4 5% 5% 7% 5% 35%	1570
March	1st to 10th	Day	25% 12% 3 6% 4 4 4 3 5% 5% 29%	3116
	11th to 20th	Day	16% 8% 2 7% 5% 4 5% 4 5% 5% 37%	3406
	21st to end	Day	23% 10% 2 6% 4 3 4 3 6% 6% 34%	3928
April	1st to 10th	Day	20% 11% 4 6% 4 4 3 3 4 6% 36%	2280
	11th to 20th	Day	18% 5% 2 6% 5% 5% 4 4 6% 7% 38%	2347
	21st to end	Day	23% 7% 3 8% 4 4 4 3 5% 5% 33%	2470
May	1st to 10th	Day	23% 11% 3 7% 5% 4 5% 4 6% 6% 27%	4106
	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 5% 38%	1881
November	1st to 10th	Day	18% 6% 2 5% 4 3 3 3 5% 6% 46%	1671
	11th to 20th	Day	20% 5% 2 4 4 4 4 4 5% 6% 43%	1710
	21st to end	Day	22% 7% 2 5% 3 2 3 3 5% 6% 42%	1710
December	1st to 10th	Day	21% 12% 3 6% 4 3 3 3 4 6% 35%	1347
	11th to 20th	Day	22% 9% 2 5% 3 4 3 3 4 4 40%	1739
	21st to end	Day	25% 11% 3 6% 4 4 4 3 5% 5% 30%	2772
January	1st to 10th	Night	15% 10% 3 6% 4 3 4 3 6% 6% 41%	4429
	11th to 20th	Night	14% 9% 3 9% 5% 4 4 4 6% 7% 34%	4440
	21st to end	Night	19% 12% 3 8% 4 4 5% 3 4 6% 32%	4884
February	1st to 10th	Night	16% 9% 3 7% 5% 5% 4 4 5% 6% 34%	2505
	11th to 20th	Night	13% 11% 3 6% 5% 5% 4 4 4 5% 40%	2218
	21st to end	Night	14% 10% 3 6% 5% 5% 4 3 4 7% 39%	1884
March	1st to 10th	Night	28% 12% 2 5% 4 3 3 3 4 4 32%	3724
	11th to 20th	Night	13% 9% 3 8% 5% 6% 6% 5% 6% 7% 32%	3552
	21st to end	Night	24% 10% 3 6% 4 4 4 4 6% 6% 30%	3700
April	1st to 10th	Night	21% 10% 3 4 5% 5% 4 3 4 6% 35%	1900
	11th to 20th	Night	18% 7% 2 7% 5% 4 4 4 4 7% 37%	1781
	21st to end	Night	23% 7% 2 6% 4 4 4 3 5% 5% 35%	1710
May	1st to 10th	Night	22% 9% 3 6% 4 4 5% 4 6% 8% 29%	2834
	11th to 20th	Night	17% 8% 3 8% 6% 5% 6% 4 7% 9% 27%	2754
	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	25% 7% 2 5% 3 3 4 3 5% 6% 37%	2717
November	1st to 10th	Night	17% 6% 2 5% 4 4 4 3 4 6% 44%	2414
	11th to 20th	Night	18% 6% 2 5% 4 4 4 3 4 6% 44%	2470
	21st to end	Night	17% 7% 2 6% 4 4 4 3 5% 6% 42%	2470
December	1st to 10th	Night	22% 10% 3 7% 3 4 4 4 5% 5% 33%	2822
	11th to 20th	Night	23% 8% 2 5% 4 3 3 3 5% 5% 38%	3436
	21st to end	Night	25% 10% 3 6% 4 4 4 3 4 6% 33%	4884

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	42% 6% 13% 27% 11% 1	2518
	11th to 20th	Day	44% 6% 14% 23% 11% 2	2520
	21st to end	Day	48% 6% 12% 21% 12% 1	2772
February	1st to 10th	Day	47% 5% 12% 20% 14% 3	1668
	11th to 20th	Day	46% 6% 12% 19% 14% 4	1857
	21st to end	Day	47% 5% 11% 19% 13% 4	1570
March	1st to 10th	Day	58% 5% 8% 12% 14% 3	3119
	11th to 20th	Day	44% 8% 11% 19% 14% 4	3406
	21st to end	Day	49% 4 6% 16% 19% 5%	3928
April	1st to 10th	Day	51% 4 9% 17% 15% 4	2280
	11th to 20th	Day	43% 7% 10% 22% 14% 3	2347
	21st to end	Day	51% 6% 9% 16% 14% 4	2470
May	1st to 10th	Day	54% 9% 11% 17% 8% 1	4120
	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	45% 5% 11% 22% 15% 2	2090
	11th to 20th	Day	42% 5% 12% 27% 12% 1	1825
	21st to end	Day	48% 5% 11% 20% 15% 2	1881
November	1st to 10th	Day	39% 5% 14% 24% 15% 3	1671
	11th to 20th	Day	40% 6% 10% 21% 18% 3	1710
	21st to end	Day	43% 4 18% 22% 12% 1	1710
December	1st to 10th	Day	51% 5% 10% 21% 12% 2	1347
	11th to 20th	Day	46% 5% 10% 20% 14% 4	1739
	21st to end	Day	55% 6% 11% 17% 9% 3	2772
January	1st to 10th	Night	43% 5% 13% 28% 10% 2	4429
	11th to 20th	Night	46% 6% 14% 19% 12% 2	4440
	21st to end	Night	52% 6% 9% 20% 11% 2	4884
February	1st to 10th	Night	48% 6% 13% 18% 12% 3	2505
	11th to 20th	Night	45% 5% 11% 21% 16% 3	2220
	21st to end	Night	46% 4 11% 22% 14% 5%	1884
March	1st to 10th	Night	55% 4 10% 17% 10% 4	3734
	11th to 20th	Night	46% 8% 12% 20% 11% 3	3553
	21st to end	Night	52% 5% 7% 16% 16% 5%	3700
April	1st to 10th	Night	49% 4 10% 18% 15% 4	1900
	11th to 20th	Night	45% 6% 9% 21% 17% 1	1781
	21st to end	Night	49% 7% 11% 17% 14% 4	1710
May	1st to 10th	Night	51% 10% 13% 18% 8% 1	2840
	11th to 20th	Night	49% 11% 14% 17% 7% 2	2755
	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	44% 7% 12% 23% 14% 1	2090
	11th to 20th	Night	40% 6% 13% 26% 13% 1	2351
	21st to end	Night	49% 5% 11% 20% 14% 2	2717
November	1st to 10th	Night	41% 6% 11% 25% 15% 2	2414
	11th to 20th	Night	42% 5% 11% 24% 16% 3	2470
	21st to end	Night	42% 6% 15% 21% 15% 1	2470
December	1st to 10th	Night	52% 5% 10% 21% 11% 1	2822
	11th to 20th	Night	46% 5% 11% 18% 18% 1	3436
	21st to end	Night	53% 6% 10% 20% 11% 1	4884

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	29% 19% 29% 18% 4	180
	11th to 20th	Day	26% 23% 28% 18% 2 2	180
	21st to end	Day	20% 23% 35% 17% 5%	198
February	1st to 10th	Day	28% 20% 33% 17% 2	326
	11th to 20th	Day	24% 28% 33% 13% 2	456
	21st to end	Day	25% 19% 35% 17% 3	382
March	1st to 10th	Day	26% 22% 33% 16% 3	460
	11th to 20th	Day	23% 27% 32% 14% 3 1	460
	21st to end	Day	28% 23% 31% 11% 5% 2	506
April	1st to 10th	Day	30% 25% 25% 14% 4 1	460
	11th to 20th	Day	26% 22% 31% 15% 5% 2	452
	21st to end	Day	31% 21% 28% 13% 5% 2	460
May	1st to 10th	Day	31% 21% 25% 18% 4 1	463
	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% 17% 24% 20% 7%	429
November	1st to 10th	Day	23% 17% 30% 21% 8% 2	365
	11th to 20th	Day	30% 15% 30% 20% 5% 1	370
	21st to end	Day	29% 19% 25% 19% 7% 1	370
December	1st to 10th	Day	26% 18% 35% 14% 7%	195
	11th to 20th	Day	30% 23% 34% 9% 3	180
	21st to end	Day	30% 22% 27% 16% 5% 1	198
January	1st to 10th	Night	23% 18% 34% 21% 3	760
	11th to 20th	Night	26% 20% 31% 20% 3	760
	21st to end	Night	19% 19% 40% 19% 3	836
February	1st to 10th	Night	22% 18% 33% 23% 3	760
	11th to 20th	Night	21% 19% 39% 17% 2	743
	21st to end	Night	23% 17% 35% 21% 4	628
March	1st to 10th	Night	25% 17% 37% 19% 2	760
	11th to 20th	Night	21% 18% 36% 20% 6%	760
	21st to end	Night	24% 17% 33% 21% 4 1	836
April	1st to 10th	Night	27% 17% 31% 21% 4	760
	11th to 20th	Night	21% 15% 37% 23% 4	657
	21st to end	Night	28% 14% 30% 23% 4	570
May	1st to 10th	Night	25% 11% 32% 26% 5% 1	570
	11th to 20th	Night	22% 13% 32% 27% 6%	529
	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% 11% 34% 26% 7% 1	743
	11th to 20th	Night	24% 13% 32% 23% 7% 1	760
	21st to end	Night	22% 19% 32% 22% 4 1	760
December	1st to 10th	Night	26% 14% 36% 18% 5%	845
	11th to 20th	Night	25% 19% 31% 21% 3	823
	21st to end	Night	28% 17% 32% 20% 3	836

Page generated at 2024-10-29 11:20:48. Version ac07

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