Inlet Outlet Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Inlet Outlet Observatory clear sky chart from 2005-11-06 to 2024-01-12.

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	15% 6% 2 5% 5% 3 5% 5% 6% 8% 42%	74760
	Night	16% 6% 3 5% 5% 3 4 4 5% 7% 43%	74951
Transparency	Day	40% 7% 12% 23% 16% 2	74465
	Night	41% 5% 11% 23% 16% 3	74780
Seeing	Day	18% 6% 23% 31% 18% 4	13938
	Night	19% 6% 29% 30% 14% 2	23229

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% 7% 3 5% 5% 3 5% 5% 5% 7% 43%	1517
	11th to 20th	Day	15% 9% 3 5% 4 2 5% 5% 4 7% 41%	1454
	21st to end	Day	16% 8% 3 4 4 3 4 4 4 7% 43%	1746
February	1st to 10th	Day	16% 10% 4 4 6% 3 4 4 4 6% 40%	1647
	11th to 20th	Day	16% 7% 3 5% 4 3 4 4 5% 6% 43%	1748
	21st to end	Day	18% 7% 3 6% 5% 3 4 4 5% 5% 39%	1480
March	1st to 10th	Day	15% 6% 2 5% 4 3 5% 5% 5% 7% 46%	1797
	11th to 20th	Day	15% 6% 2 5% 5% 3 5% 5% 6% 7% 42%	1898
	21st to end	Day	20% 7% 3 5% 5% 3 4 4 4 5% 40%	2356
April	1st to 10th	Day	17% 8% 3 5% 5% 3 4 4 5% 7% 41%	2160
	11th to 20th	Day	15% 5% 2 5% 4 3 5% 4 6% 8% 42%	2134
	21st to end	Day	19% 5% 2 4 5% 3 5% 5% 6% 7% 38%	2162
May	1st to 10th	Day	20% 7% 3 5% 4 3 5% 5% 5% 8% 35%	2340
	11th to 20th	Day	21% 5% 2 5% 4 3 5% 5% 5% 7% 38%	2427
	21st to end	Day	16% 6% 2 5% 4 3 4 4 6% 9% 40%	2725
June	1st to 10th	Day	15% 5% 2 4 5% 3 6% 6% 7% 10% 37%	2520
	11th to 20th	Day	13% 6% 3 5% 5% 3 5% 6% 5% 10% 38%	2520
	21st to end	Day	9% 4 2 4 5% 4 5% 6% 7% 10% 42%	2520
July	1st to 10th	Day	10% 4 2 5% 6% 4 6% 7% 7% 10% 39%	2520
	11th to 20th	Day	8% 5% 2 5% 5% 3 6% 7% 7% 10% 43%	2520
	21st to end	Day	10% 6% 3 6% 5% 4 5% 7% 8% 8% 38%	2744
August	1st to 10th	Day	8% 5% 2 6% 5% 3 5% 6% 8% 9% 42%	2320
	11th to 20th	Day	11% 5% 3 5% 5% 3 5% 5% 6% 9% 43%	2126
	21st to end	Day	13% 5% 2 5% 4 3 4 5% 7% 9% 43%	2376
September	1st to 10th	Day	14% 6% 2 4 4 3 3 4 5% 8% 45%	2160
	11th to 20th	Day	11% 4 3 5% 4 2 4 4 5% 8% 50%	2080
	21st to end	Day	17% 6% 3 5% 4 3 4 5% 6% 7% 41%	1980
October	1st to 10th	Day	21% 5% 2 4 4 3 3 5% 5% 7% 42%	1886
	11th to 20th	Day	15% 5% 2 4 5% 2 3 3 5% 7% 48%	1800
	21st to end	Day	19% 7% 2 5% 4 2 3 4 5% 7% 43%	1850
November	1st to 10th	Day	14% 5% 2 5% 4 3 3 3 5% 6% 50%	1671
	11th to 20th	Day	17% 5% 2 3 5% 3 4 4 5% 6% 46%	1710
	21st to end	Day	16% 5% 2 4 4 2 5% 4 5% 7% 46%	1668
December	1st to 10th	Day	17% 7% 3 6% 5% 3 4 5% 5% 7% 40%	1520
	11th to 20th	Day	19% 7% 2 5% 4 2 3 4 5% 6% 45%	1906
	21st to end	Day	16% 8% 3 6% 5% 4 4 5% 5% 7% 37%	2772
January	1st to 10th	Night	17% 6% 2 4 4 2 4 4 4 6% 47%	2649
	11th to 20th	Night	20% 7% 3 4 4 3 4 4 5% 6% 40%	2546
	21st to end	Night	15% 7% 2 4 5% 3 4 3 5% 7% 44%	2606
February	1st to 10th	Night	17% 9% 3 5% 4 2 4 4 5% 6% 40%	2310
	11th to 20th	Night	18% 8% 3 4 4 2 4 4 4 5% 42%	2098
	21st to end	Night	20% 6% 2 5% 5% 2 3 4 5% 6% 44%	1776
March	1st to 10th	Night	16% 6% 3 4 5% 2 3 3 5% 7% 47%	2150
	11th to 20th	Night	18% 6% 3 5% 5% 2 4 4 4 6% 42%	2059
	21st to end	Night	19% 7% 3 5% 5% 2 4 4 4 6% 42%	1999
April	1st to 10th	Night	17% 8% 3 6% 5% 2 3 5% 5% 5% 41%	1800
	11th to 20th	Night	16% 7% 3 5% 5% 3 4 3 5% 6% 42%	1775
	21st to end	Night	19% 6% 3 4 4 2 4 4 4 7% 41%	1796
May	1st to 10th	Night	20% 9% 3 5% 5% 3 4 4 5% 6% 34%	1620
	11th to 20th	Night	20% 7% 3 5% 5% 2 4 4 6% 7% 36%	1481
	21st to end	Night	17% 8% 2 5% 5% 2 5% 4 5% 8% 37%	1550
June	1st to 10th	Night	15% 7% 3 5% 5% 3 4 5% 4 8% 40%	1440
	11th to 20th	Night	16% 6% 2 5% 5% 3 5% 5% 6% 8% 39%	1440
	21st to end	Night	8% 5% 3 5% 6% 3 6% 6% 7% 10% 42%	1440
July	1st to 10th	Night	9% 6% 3 5% 7% 4 5% 5% 6% 9% 40%	1440
	11th to 20th	Night	8% 6% 2 5% 6% 3 5% 6% 6% 10% 42%	1440
	21st to end	Night	9% 5% 2 6% 6% 4 5% 5% 8% 9% 41%	1574
August	1st to 10th	Night	8% 6% 3 6% 5% 3 5% 6% 7% 9% 42%	1598
	11th to 20th	Night	10% 6% 3 6% 5% 3 5% 5% 6% 9% 41%	1774
	21st to end	Night	12% 6% 2 5% 5% 2 4 5% 6% 8% 43%	1980
September	1st to 10th	Night	15% 6% 2 4 6% 3 5% 4 5% 7% 43%	1800
	11th to 20th	Night	13% 5% 3 4 4 2 4 4 5% 7% 51%	1879
	21st to end	Night	19% 7% 3 4 4 2 4 3 5% 7% 42%	1980
October	1st to 10th	Night	21% 5% 3 5% 4 3 4 4 4 5% 42%	2070
	11th to 20th	Night	16% 4 2 5% 4 2 3 4 5% 6% 49%	2160
	21st to end	Night	20% 7% 3 5% 3 3 3 3 4 5% 44%	2504
November	1st to 10th	Night	13% 4 2 4 5% 2 4 3 4 6% 51%	2407
	11th to 20th	Night	17% 6% 3 5% 4 2 3 3 3 5% 47%	2470
	21st to end	Night	14% 5% 2 4 4 2 4 5% 5% 7% 48%	2508
December	1st to 10th	Night	20% 6% 3 5% 5% 2 3 4 5% 6% 41%	2660
	11th to 20th	Night	18% 5% 2 5% 4 2 3 4 5% 7% 44%	3288
	21st to end	Night	17% 9% 3 5% 4 3 4 4 5% 6% 39%	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	41% 5% 12% 24% 14% 4	1518
	11th to 20th	Day	42% 6% 13% 24% 12% 3	1454
	21st to end	Day	42% 4 12% 26% 14% 3	1746
February	1st to 10th	Day	45% 5% 13% 22% 13% 2	1647
	11th to 20th	Day	43% 5% 9% 25% 16% 2	1757
	21st to end	Day	46% 5% 10% 21% 13% 5%	1480
March	1st to 10th	Day	38% 6% 13% 25% 15% 3	1800
	11th to 20th	Day	40% 6% 12% 23% 15% 3	1898
	21st to end	Day	46% 5% 8% 20% 17% 4	2356
April	1st to 10th	Day	43% 5% 11% 19% 17% 5%	2160
	11th to 20th	Day	39% 7% 11% 23% 17% 3	2134
	21st to end	Day	43% 6% 11% 18% 18% 4	2162
May	1st to 10th	Day	46% 8% 10% 19% 15% 2	2340
	11th to 20th	Day	45% 7% 11% 19% 16% 2	2431
	21st to end	Day	40% 8% 14% 22% 13% 2	2725
June	1st to 10th	Day	40% 9% 14% 21% 14% 2	2520
	11th to 20th	Day	40% 11% 13% 22% 12% 2	2520
	21st to end	Day	35% 10% 15% 24% 16% 1	2520
July	1st to 10th	Day	38% 10% 13% 22% 15% 1	2450
	11th to 20th	Day	33% 9% 15% 27% 13% 2	2445
	21st to end	Day	37% 10% 12% 24% 15% 2	2591
August	1st to 10th	Day	33% 10% 15% 27% 14% 1	2306
	11th to 20th	Day	36% 10% 15% 23% 15% 1	2126
	21st to end	Day	35% 7% 14% 23% 18% 3	2376
September	1st to 10th	Day	36% 7% 14% 21% 19% 3	2160
	11th to 20th	Day	32% 7% 11% 24% 24% 2	2080
	21st to end	Day	42% 6% 10% 19% 21% 2	1980
October	1st to 10th	Day	42% 6% 11% 20% 19% 2	1886
	11th to 20th	Day	37% 4 10% 24% 23% 1	1800
	21st to end	Day	40% 6% 10% 22% 20% 2	1850
November	1st to 10th	Day	36% 3 13% 27% 19% 2	1671
	11th to 20th	Day	40% 4 10% 22% 23% 2	1710
	21st to end	Day	39% 4 12% 29% 12% 2	1668
December	1st to 10th	Day	44% 4 16% 22% 14% 1	1520
	11th to 20th	Day	42% 3 12% 25% 15% 2	1906
	21st to end	Day	46% 6% 12% 24% 11% 1	2772
January	1st to 10th	Night	40% 3 11% 26% 17% 3	2649
	11th to 20th	Night	44% 5% 14% 24% 11% 2	2546
	21st to end	Night	40% 3 9% 26% 19% 2	2606
February	1st to 10th	Night	44% 5% 14% 23% 12% 2	2310
	11th to 20th	Night	45% 4 9% 20% 17% 4	2100
	21st to end	Night	42% 3 8% 25% 17% 4	1776
March	1st to 10th	Night	39% 3 11% 25% 17% 5%	2160
	11th to 20th	Night	44% 5% 9% 20% 17% 5%	2060
	21st to end	Night	44% 4 8% 19% 19% 6%	1999
April	1st to 10th	Night	45% 4 9% 20% 18% 4	1800
	11th to 20th	Night	43% 5% 10% 19% 21% 2	1775
	21st to end	Night	43% 5% 8% 20% 19% 5%	1796
May	1st to 10th	Night	51% 6% 7% 19% 15% 2	1620
	11th to 20th	Night	47% 6% 11% 18% 16% 3	1482
	21st to end	Night	44% 7% 14% 19% 13% 2	1551
June	1st to 10th	Night	43% 8% 9% 20% 19% 1	1440
	11th to 20th	Night	40% 9% 13% 24% 13% 1	1440
	21st to end	Night	36% 8% 15% 24% 15% 2	1440
July	1st to 10th	Night	41% 8% 14% 22% 13% 2	1400
	11th to 20th	Night	36% 8% 13% 27% 14% 2	1392
	21st to end	Night	35% 8% 15% 26% 13% 2	1486
August	1st to 10th	Night	35% 10% 17% 23% 14% 1	1588
	11th to 20th	Night	39% 8% 15% 24% 13% 1	1774
	21st to end	Night	37% 8% 13% 21% 18% 3	1980
September	1st to 10th	Night	41% 7% 11% 22% 17% 2	1800
	11th to 20th	Night	34% 5% 11% 24% 24% 3	1879
	21st to end	Night	44% 5% 6% 23% 20% 2	1980
October	1st to 10th	Night	45% 5% 10% 21% 16% 2	2070
	11th to 20th	Night	36% 4 12% 28% 17% 2	2160
	21st to end	Night	44% 3 10% 23% 19% 1	2504
November	1st to 10th	Night	35% 4 12% 25% 21% 4	2407
	11th to 20th	Night	41% 4 9% 23% 19% 4	2470
	21st to end	Night	36% 5% 13% 28% 17% 1	2508
December	1st to 10th	Night	45% 4 13% 22% 14% 1	2660
	11th to 20th	Night	41% 4 13% 21% 18% 4	3288
	21st to end	Night	46% 5% 13% 24% 12% 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	17% 11% 42% 23% 7% 1	180
	11th to 20th	Day	18% 19% 36% 23% 3 1	164
	21st to end	Day	22% 9% 38% 23% 8% 1	248
February	1st to 10th	Day	24% 7% 34% 29% 4 1	267
	11th to 20th	Day	23% 12% 37% 28% 2	416
	21st to end	Day	22% 13% 36% 25% 3	346
March	1st to 10th	Day	16% 9% 41% 27% 6%	420
	11th to 20th	Day	18% 7% 39% 29% 5% 1	420
	21st to end	Day	24% 9% 32% 26% 8% 1	462
April	1st to 10th	Day	18% 7% 37% 27% 9% 1	420
	11th to 20th	Day	17% 6% 29% 34% 13% 1	412
	21st to end	Day	24% 7% 27% 31% 10% 1	420
May	1st to 10th	Day	25% 5% 26% 30% 11% 4	423
	11th to 20th	Day	23% 1 22% 38% 14% 2	447
	21st to end	Day	21% 2 12% 29% 27% 8%	485
June	1st to 10th	Day	17% 3 16% 33% 26% 5%	450
	11th to 20th	Day	14% 2 20% 37% 22% 4	450
	21st to end	Day	12% 3 13% 40% 28% 5%	450
July	1st to 10th	Day	12% 3 9% 33% 33% 9%	445
	11th to 20th	Day	9% 1 8% 35% 35% 12%	444
	21st to end	Day	12% 2 14% 36% 31% 5%	488
August	1st to 10th	Day	10% 1 8% 41% 32% 9%	446
	11th to 20th	Day	13% 1 9% 32% 36% 9%	439
	21st to end	Day	12% 2 11% 36% 28% 11%	495
September	1st to 10th	Day	18% 1 16% 28% 24% 12%	450
	11th to 20th	Day	14% 1 13% 35% 27% 10%	450
	21st to end	Day	23% 4 18% 32% 20% 4	450
October	1st to 10th	Day	27% 4 16% 25% 22% 7%	450
	11th to 20th	Day	16% 6% 25% 28% 22% 4	450
	21st to end	Day	21% 8% 30% 26% 12% 3	430
November	1st to 10th	Day	15% 7% 26% 32% 17% 4	365
	11th to 20th	Day	17% 11% 34% 26% 12%	370
	21st to end	Day	18% 9% 31% 30% 11% 1	328
December	1st to 10th	Day	21% 10% 40% 19% 9% 1	180
	11th to 20th	Day	26% 13% 31% 22% 8%	180
	21st to end	Day	21% 13% 29% 26% 11%	198
January	1st to 10th	Night	20% 10% 41% 23% 5%	760
	11th to 20th	Night	23% 9% 36% 26% 5%	728
	21st to end	Night	20% 11% 44% 23% 3	792
February	1st to 10th	Night	22% 10% 39% 26% 3	720
	11th to 20th	Night	23% 11% 44% 20% 2	703
	21st to end	Night	24% 12% 36% 25% 3	592
March	1st to 10th	Night	18% 10% 40% 25% 6%	720
	11th to 20th	Night	20% 7% 38% 28% 6% 1	720
	21st to end	Night	21% 6% 34% 31% 7% 1	792
April	1st to 10th	Night	20% 8% 34% 31% 7% 1	720
	11th to 20th	Night	19% 6% 26% 39% 10%	711
	21st to end	Night	21% 4 29% 36% 9% 1	716
May	1st to 10th	Night	26% 4 24% 32% 13% 1	540
	11th to 20th	Night	25% 2 26% 35% 11% 1	420
	21st to end	Night	21% 2 10% 34% 29% 5%	389
June	1st to 10th	Night	19% 3 18% 33% 24% 3	360
	11th to 20th	Night	17% 1 14% 43% 24% 1	360
	21st to end	Night	9% 2 12% 48% 27% 2	360
July	1st to 10th	Night	12% 3 13% 38% 31% 4	350
	11th to 20th	Night	11% 1 10% 37% 36% 4	348
	21st to end	Night	11% 1 13% 41% 32% 2	394
August	1st to 10th	Night	11% 2 10% 42% 32% 4	524
	11th to 20th	Night	13% 2 11% 33% 35% 5%	710
	21st to end	Night	14% 2 12% 36% 29% 7%	792
September	1st to 10th	Night	16% 2 17% 34% 25% 6%	720
	11th to 20th	Night	17% 2 15% 31% 28% 7%	720
	21st to end	Night	22% 3 19% 31% 22% 3	720
October	1st to 10th	Night	24% 3 23% 24% 19% 6%	720
	11th to 20th	Night	18% 6% 25% 35% 14% 2	720
	21st to end	Night	23% 6% 34% 26% 10% 1	792
November	1st to 10th	Night	16% 6% 33% 30% 13% 2	740
	11th to 20th	Night	21% 9% 32% 27% 11% 1	760
	21st to end	Night	14% 11% 37% 26% 10% 1	760
December	1st to 10th	Night	24% 12% 34% 22% 7% 1	760
	11th to 20th	Night	21% 9% 38% 27% 4 1	760
	21st to end	Night	21% 8% 42% 26% 3	836

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