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 2024-03-01.

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% 7% 3 5% 5% 3 5% 4 5% 7% 39%	77987
	Night	18% 8% 3 5% 5% 3 4 4 5% 7% 38%	81383
Transparency	Day	44% 6% 12% 22% 14% 2	77692
	Night	45% 6% 12% 22% 13% 2	81212
Seeing	Day	22% 17% 31% 20% 8% 2	13979
	Night	22% 13% 32% 25% 8% 1	23085

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% 6% 3 5% 5% 3 4 4 5% 7% 41%	2517
	11th to 20th	Day	17% 8% 2 5% 5% 3 5% 5% 4 7% 39%	2520
	21st to end	Day	16% 12% 3 6% 4 2 5% 5% 5% 5% 37%	2772
February	1st to 10th	Day	16% 9% 3 6% 5% 3 5% 4 5% 6% 37%	1668
	11th to 20th	Day	12% 9% 3 6% 7% 4 5% 5% 4 5% 39%	1848
	21st to end	Day	16% 9% 3 5% 5% 3 5% 5% 6% 6% 36%	1570
March	1st to 10th	Day	16% 9% 3 6% 6% 4 5% 4 6% 7% 37%	1797
	11th to 20th	Day	16% 7% 3 6% 6% 2 4 5% 5% 5% 41%	1934
	21st to end	Day	16% 9% 3 5% 6% 3 4 4 5% 5% 41%	2236
April	1st to 10th	Day	20% 9% 4 6% 4 3 4 4 3 6% 36%	2160
	11th to 20th	Day	18% 5% 2 5% 6% 3 5% 5% 6% 7% 38%	2222
	21st to end	Day	24% 7% 3 7% 6% 3 5% 4 4 5% 32%	2340
May	1st to 10th	Day	25% 7% 3 5% 5% 3 5% 4 5% 7% 32%	2340
	11th to 20th	Day	19% 6% 3 6% 6% 3 4 4 4 7% 38%	2344
	21st to end	Day	16% 7% 3 6% 5% 4 5% 4 6% 7% 38%	2725
June	1st to 10th	Day	23% 7% 3 5% 6% 3 5% 5% 6% 8% 29%	2520
	11th to 20th	Day	17% 6% 3 6% 5% 2 4 5% 5% 7% 39%	2520
	21st to end	Day	23% 7% 3 5% 5% 3 6% 6% 5% 7% 30%	2520
July	1st to 10th	Day	16% 5% 2 5% 5% 3 5% 5% 6% 8% 38%	2520
	11th to 20th	Day	13% 6% 3 6% 6% 3 6% 5% 7% 9% 35%	2520
	21st to end	Day	14% 5% 2 6% 5% 3 6% 6% 6% 10% 36%	2744
August	1st to 10th	Day	13% 5% 2 5% 5% 3 5% 5% 7% 9% 40%	2355
	11th to 20th	Day	15% 6% 2 5% 6% 3 5% 5% 5% 8% 39%	2304
	21st to end	Day	12% 4 2 5% 4 3 4 5% 7% 7% 46%	2466
September	1st to 10th	Day	13% 5% 1 5% 4 3 4 4 5% 7% 48%	2124
	11th to 20th	Day	13% 5% 2 4 4 2 3 4 4 6% 54%	1980
	21st to end	Day	16% 5% 2 4 4 3 3 4 5% 8% 46%	1980
October	1st to 10th	Day	19% 7% 3 6% 5% 2 4 4 4 6% 39%	1980
	11th to 20th	Day	17% 8% 2 5% 5% 3 5% 3 5% 7% 41%	1730
	21st to end	Day	24% 8% 2 5% 4 3 4 3 4 6% 37%	1782
November	1st to 10th	Day	18% 6% 2 5% 4 1 3 4 5% 6% 46%	1671
	11th to 20th	Day	20% 5% 2 4 4 2 4 4 6% 6% 43%	1710
	21st to end	Day	23% 7% 2 4 4 2 3 3 5% 6% 42%	1710
December	1st to 10th	Day	21% 11% 3 6% 4 2 3 4 4 6% 35%	1347
	11th to 20th	Day	22% 8% 2 5% 3 3 4 3 4 4 40%	1739
	21st to end	Day	25% 10% 3 5% 5% 3 4 4 5% 6% 30%	2772
January	1st to 10th	Night	16% 9% 3 5% 4 2 4 3 5% 6% 41%	4429
	11th to 20th	Night	14% 9% 4 8% 6% 3 4 5% 6% 7% 34%	4440
	21st to end	Night	19% 11% 3 7% 6% 3 5% 4 4 6% 32%	4884
February	1st to 10th	Night	16% 8% 4 6% 7% 4 4 5% 5% 7% 34%	2505
	11th to 20th	Night	13% 10% 4 5% 5% 4 5% 5% 4 5% 40%	2218
	21st to end	Night	15% 9% 3 5% 5% 4 5% 4 4 7% 39%	1884
March	1st to 10th	Night	14% 12% 2 6% 5% 3 4 5% 5% 6% 38%	2157
	11th to 20th	Night	17% 8% 3 7% 5% 4 4 5% 4 7% 37%	2024
	21st to end	Night	17% 8% 3 6% 4 3 4 4 4 5% 41%	2116
April	1st to 10th	Night	21% 9% 3 5% 5% 3 5% 4 4 6% 35%	1800
	11th to 20th	Night	18% 6% 2 6% 5% 3 5% 5% 4 7% 38%	1687
	21st to end	Night	24% 6% 2 5% 5% 3 5% 5% 5% 5% 34%	1620
May	1st to 10th	Night	20% 9% 3 5% 5% 3 5% 5% 5% 7% 32%	1620
	11th to 20th	Night	20% 7% 3 6% 6% 3 5% 5% 7% 8% 32%	1562
	21st to end	Night	18% 9% 4 6% 6% 3 4 4 5% 6% 34%	1550
June	1st to 10th	Night	22% 8% 3 6% 5% 4 5% 4 5% 7% 32%	1440
	11th to 20th	Night	18% 7% 2 4 5% 2 5% 5% 6% 7% 39%	1440
	21st to end	Night	22% 8% 3 5% 4 3 5% 5% 6% 8% 33%	1440
July	1st to 10th	Night	15% 5% 3 4 6% 4 6% 4 6% 8% 38%	1440
	11th to 20th	Night	16% 6% 2 6% 5% 3 4 5% 5% 9% 39%	1440
	21st to end	Night	15% 5% 2 4 5% 3 6% 6% 7% 8% 41%	1574
August	1st to 10th	Night	12% 5% 2 5% 6% 3 5% 6% 6% 9% 41%	1566
	11th to 20th	Night	14% 6% 2 5% 6% 3 5% 6% 6% 10% 37%	1596
	21st to end	Night	14% 5% 2 5% 4 2 3 4 5% 8% 47%	1886
September	1st to 10th	Night	14% 5% 2 3 4 2 4 4 5% 8% 49%	1836
	11th to 20th	Night	16% 5% 2 3 3 2 3 4 4 7% 50%	1980
	21st to end	Night	16% 5% 2 4 4 3 3 4 4 7% 47%	1980
October	1st to 10th	Night	19% 7% 2 5% 4 4 4 4 5% 6% 39%	1980
	11th to 20th	Night	17% 6% 3 6% 4 3 4 5% 6% 7% 40%	2226
	21st to end	Night	26% 7% 3 5% 4 3 3 4 4 6% 36%	2574
November	1st to 10th	Night	17% 6% 2 5% 4 3 4 4 4 6% 44%	2407
	11th to 20th	Night	18% 6% 2 4 4 3 4 4 4 6% 44%	2470
	21st to end	Night	17% 6% 3 5% 5% 3 4 4 5% 7% 42%	2470
December	1st to 10th	Night	22% 9% 3 6% 4 3 4 5% 4 6% 34%	2822
	11th to 20th	Night	23% 8% 2 4 4 3 4 3 5% 5% 39%	3436
	21st to end	Night	25% 9% 3 5% 5% 3 4 4 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	47% 5% 12% 18% 15% 4	1800
	11th to 20th	Day	43% 5% 10% 20% 16% 5%	1934
	21st to end	Day	45% 6% 8% 18% 18% 6%	2236
April	1st to 10th	Day	50% 4 9% 17% 16% 4	2160
	11th to 20th	Day	43% 7% 10% 22% 14% 3	2222
	21st to end	Day	53% 6% 9% 16% 13% 4	2340
May	1st to 10th	Day	51% 6% 8% 20% 14% 2	2340
	11th to 20th	Day	46% 6% 10% 19% 17% 3	2348
	21st to end	Day	44% 7% 14% 20% 12% 2	2725
June	1st to 10th	Day	51% 7% 12% 19% 9%	2520
	11th to 20th	Day	43% 7% 11% 20% 16% 3	2520
	21st to end	Day	52% 8% 11% 19% 9% 1	2520
July	1st to 10th	Day	41% 7% 14% 23% 14% 1	2450
	11th to 20th	Day	42% 9% 14% 24% 10% 1	2445
	21st to end	Day	39% 9% 16% 23% 11% 1	2591
August	1st to 10th	Day	37% 10% 17% 26% 10%	2341
	11th to 20th	Day	42% 8% 15% 24% 11% 1	2304
	21st to end	Day	34% 8% 13% 25% 18% 1	2466
September	1st to 10th	Day	34% 7% 15% 27% 17% 1	2124
	11th to 20th	Day	32% 5% 10% 29% 22% 3	1980
	21st to end	Day	36% 5% 12% 28% 17% 1	1980
October	1st to 10th	Day	45% 5% 10% 22% 15% 2	1980
	11th to 20th	Day	44% 5% 13% 27% 11% 1	1730
	21st to end	Day	49% 5% 11% 20% 14% 2	1782
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	47% 5% 9% 21% 15% 3	2167
	11th to 20th	Night	47% 5% 11% 18% 14% 4	2025
	21st to end	Night	43% 5% 9% 19% 19% 5%	2116
April	1st to 10th	Night	50% 4 10% 18% 15% 4	1800
	11th to 20th	Night	44% 6% 9% 22% 17% 1	1687
	21st to end	Night	50% 7% 10% 17% 12% 4	1620
May	1st to 10th	Night	51% 7% 9% 19% 13% 2	1620
	11th to 20th	Night	48% 8% 11% 18% 12% 4	1563
	21st to end	Night	50% 6% 12% 18% 12% 1	1551
June	1st to 10th	Night	51% 7% 10% 21% 10% 1	1440
	11th to 20th	Night	42% 7% 14% 21% 14% 2	1440
	21st to end	Night	49% 8% 15% 18% 9% 1	1440
July	1st to 10th	Night	42% 9% 16% 20% 13% 1	1400
	11th to 20th	Night	42% 6% 16% 25% 10%	1392
	21st to end	Night	39% 8% 17% 25% 10% 1	1486
August	1st to 10th	Night	38% 8% 16% 27% 10% 1	1556
	11th to 20th	Night	42% 8% 16% 21% 13%	1596
	21st to end	Night	36% 7% 13% 27% 17% 1	1886
September	1st to 10th	Night	35% 6% 13% 31% 15%	1836
	11th to 20th	Night	35% 4 11% 30% 18% 2	1980
	21st to end	Night	36% 6% 12% 30% 15% 2	1980
October	1st to 10th	Night	44% 6% 11% 23% 14% 1	1980
	11th to 20th	Night	42% 6% 13% 27% 12% 1	2226
	21st to end	Night	50% 5% 12% 19% 13% 2	2574
November	1st to 10th	Night	41% 6% 11% 25% 15% 2	2407
	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% 20% 35% 17% 3	382
March	1st to 10th	Day	25% 22% 34% 16% 3	420
	11th to 20th	Day	22% 28% 33% 15% 2 1	420
	21st to end	Day	25% 23% 32% 12% 6% 2	462
April	1st to 10th	Day	30% 24% 26% 14% 4 1	420
	11th to 20th	Day	26% 22% 31% 15% 5% 2	412
	21st to end	Day	32% 20% 28% 13% 5% 2	420
May	1st to 10th	Day	32% 21% 25% 17% 4 1	423
	11th to 20th	Day	20% 21% 36% 15% 7% 1	447
	21st to end	Day	21% 17% 34% 22% 6%	485
June	1st to 10th	Day	20% 18% 36% 17% 7% 2	450
	11th to 20th	Day	19% 17% 33% 21% 8% 2	450
	21st to end	Day	24% 14% 30% 22% 8% 2	450
July	1st to 10th	Day	19% 7% 37% 26% 9% 2	445
	11th to 20th	Day	14% 7% 38% 26% 12% 4	444
	21st to end	Day	14% 7% 39% 28% 11% 3	488
August	1st to 10th	Day	12% 10% 29% 33% 13% 2	446
	11th to 20th	Day	17% 10% 27% 26% 13% 6%	439
	21st to end	Day	12% 12% 29% 29% 12% 5%	495
September	1st to 10th	Day	16% 8% 30% 24% 17% 4	450
	11th to 20th	Day	16% 15% 30% 19% 12% 8%	450
	21st to end	Day	15% 14% 31% 24% 10% 6%	450
October	1st to 10th	Day	22% 17% 24% 22% 13% 3	450
	11th to 20th	Day	21% 17% 30% 20% 11% 1	367
	21st to end	Day	33% 17% 23% 19% 7%	396
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	24% 18% 38% 19% 2	723
	11th to 20th	Night	22% 17% 36% 19% 6%	720
	21st to end	Night	23% 17% 33% 22% 4 1	792
April	1st to 10th	Night	28% 17% 31% 20% 4	720
	11th to 20th	Night	21% 15% 37% 23% 4	623
	21st to end	Night	29% 14% 29% 23% 5%	540
May	1st to 10th	Night	25% 11% 32% 25% 6% 1	540
	11th to 20th	Night	23% 14% 33% 25% 5%	501
	21st to end	Night	24% 8% 27% 34% 6% 1	389
June	1st to 10th	Night	26% 7% 29% 28% 9%	360
	11th to 20th	Night	21% 5% 27% 34% 14%	360
	21st to end	Night	26% 3 28% 35% 9%	360
July	1st to 10th	Night	18% 3 26% 39% 14%	350
	11th to 20th	Night	17% 3 25% 34% 20% 1	348
	21st to end	Night	15% 3 23% 42% 16% 1	394
August	1st to 10th	Night	14% 4 22% 44% 15%	492
	11th to 20th	Night	15% 5% 29% 34% 16% 1	532
	21st to end	Night	15% 6% 27% 34% 17% 2	698
September	1st to 10th	Night	15% 4 32% 32% 16% 1	720
	11th to 20th	Night	18% 8% 28% 27% 16% 3	720
	21st to end	Night	19% 8% 28% 28% 16% 1	720
October	1st to 10th	Night	22% 11% 23% 30% 13% 1	720
	11th to 20th	Night	21% 11% 31% 27% 10% 1	720
	21st to end	Night	28% 14% 31% 21% 5%	792
November	1st to 10th	Night	21% 11% 34% 26% 7% 1	740
	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 2024-02-27 06:30:14. Version ac07

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