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 2024-11-08.

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	16% 7% 2 6% 4 4 4 4 6% 7% 40%	101293
	Night	17% 8% 3 6% 4 4 4 3 5% 7% 42%	97807
Transparency	Day	41% 6% 12% 23% 16% 2	104838
	Night	42% 5% 11% 23% 16% 3	102338
Seeing	Day	18% 6% 23% 31% 18% 4	15085
	Night	19% 6% 28% 30% 14% 2	24250

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	15% 8% 2 5% 4 3 4 3 4 6% 46%	2517
	11th to 20th	Day	16% 9% 3 6% 4 3 4 4 4 6% 41%	2520
	21st to end	Day	22% 11% 4 8% 4 4 3 3 3 5% 32%	3060
February	1st to 10th	Day	15% 10% 3 5% 4 3 4 3 4 6% 41%	1738
	11th to 20th	Day	16% 8% 3 5% 4 4 4 4 5% 5% 43%	1848
	21st to end	Day	18% 8% 3 6% 4 4 4 3 5% 5% 39%	1570
March	1st to 10th	Day	28% 7% 2 4 3 3 3 3 4 6% 37%	3116
	11th to 20th	Day	9% 4 2 5% 5% 4 5% 4 6% 6% 49%	3342
	21st to end	Day	20% 8% 2 5% 4 3 3 3 4 5% 43%	4132
April	1st to 10th	Day	17% 8% 2 5% 5% 4 4 3 5% 7% 40%	2280
	11th to 20th	Day	15% 6% 2 6% 4 5% 4 3 6% 8% 42%	2254
	21st to end	Day	17% 6% 2 5% 5% 4 5% 4 6% 7% 39%	2283
May	1st to 10th	Day	25% 10% 3 7% 4 4 4 4 5% 7% 27%	4106
	11th to 20th	Day	27% 6% 2 6% 4 4 4 3 4 6% 33%	4319
	21st to end	Day	14% 6% 2 5% 4 4 4 4 6% 9% 43%	4837
June	1st to 10th	Day	14% 6% 2 5% 5% 4 5% 5% 7% 10% 38%	2660
	11th to 20th	Day	12% 6% 2 6% 5% 5% 5% 5% 6% 10% 39%	2660
	21st to end	Day	9% 5% 2 5% 5% 5% 6% 5% 7% 10% 42%	2660
July	1st to 10th	Day	8% 4 2 7% 6% 7% 8% 6% 7% 10% 35%	4440
	11th to 20th	Day	10% 6% 2 6% 5% 5% 6% 6% 7% 10% 36%	4440
	21st to end	Day	11% 8% 3 8% 5% 5% 6% 5% 7% 8% 33%	4814
August	1st to 10th	Day	17% 6% 3 7% 5% 5% 5% 4 7% 9% 32%	4070
	11th to 20th	Day	12% 6% 3 6% 4 4 5% 4 6% 9% 42%	3730
	21st to end	Day	9% 4 1 5% 3 4 4 5% 7% 10% 47%	4180
September	1st to 10th	Day	14% 5% 3 6% 4 3 3 3 5% 8% 46%	2280
	11th to 20th	Day	11% 5% 2 6% 3 3 4 3 5% 8% 49%	2195
	21st to end	Day	18% 7% 3 6% 4 3 4 4 6% 6% 39%	2090
October	1st to 10th	Day	21% 5% 2 5% 3 3 4 4 5% 7% 43%	1990
	11th to 20th	Day	14% 6% 2 5% 4 3 3 2 5% 7% 50%	1900
	21st to end	Day	18% 7% 2 5% 3 3 3 3 5% 7% 45%	1952
November	1st to 10th	Day	13% 6% 2 5% 3 3 3 2 5% 6% 51%	1734
	11th to 20th	Day	17% 5% 2 4 5% 3 4 3 5% 6% 46%	1710
	21st to end	Day	16% 6% 2 4 4 4 5% 3 5% 7% 46%	1668
December	1st to 10th	Day	17% 7% 2 7% 3 4 3 4 6% 6% 40%	1520
	11th to 20th	Day	19% 7% 2 6% 3 2 3 3 5% 6% 44%	1906
	21st to end	Day	16% 8% 3 6% 4 5% 4 4 5% 7% 37%	2772
January	1st to 10th	Night	18% 6% 2 5% 3 3 4 3 4 6% 47%	4429
	11th to 20th	Night	18% 10% 2 5% 3 3 3 3 4 4 44%	4440
	21st to end	Night	23% 10% 3 6% 4 3 3 3 4 6% 34%	4592
February	1st to 10th	Night	17% 9% 2 6% 4 3 3 3 6% 6% 41%	2439
	11th to 20th	Night	18% 9% 3 5% 4 3 4 3 4 5% 42%	2218
	21st to end	Night	20% 7% 2 5% 3 3 3 3 5% 6% 43%	1884
March	1st to 10th	Night	22% 11% 4 6% 3 3 2 2 3 5% 38%	3724
	11th to 20th	Night	13% 6% 2 6% 4 4 4 3 4 7% 47%	3615
	21st to end	Night	21% 9% 2 6% 4 3 2 2 4 5% 41%	3499
April	1st to 10th	Night	17% 9% 3 6% 4 4 3 4 5% 5% 40%	1900
	11th to 20th	Night	16% 8% 3 6% 4 4 3 3 5% 6% 42%	1875
	21st to end	Night	19% 6% 3 5% 3 3 4 4 4 7% 42%	1895
May	1st to 10th	Night	23% 11% 4 7% 3 5% 3 3 5% 7% 28%	2834
	11th to 20th	Night	27% 8% 3 6% 4 3 3 3 5% 6% 32%	2603
	21st to end	Night	15% 9% 2 6% 3 3 4 3 6% 9% 40%	2738
June	1st to 10th	Night	15% 8% 2 6% 4 4 4 4 5% 9% 40%	1520
	11th to 20th	Night	15% 6% 2 6% 4 4 5% 4 6% 8% 41%	1520
	21st to end	Night	8% 5% 2 6% 5% 5% 6% 5% 7% 10% 41%	1520
July	1st to 10th	Night	7% 8% 3 8% 7% 6% 6% 5% 6% 8% 36%	2520
	11th to 20th	Night	9% 8% 2 7% 4 5% 5% 4 7% 10% 37%	2520
	21st to end	Night	16% 8% 3 8% 5% 4 4 4 7% 8% 34%	2739
August	1st to 10th	Night	21% 8% 3 7% 5% 4 4 4 6% 8% 31%	2812
	11th to 20th	Night	11% 7% 3 7% 4 4 5% 4 6% 8% 42%	3097
	21st to end	Night	8% 5% 2 5% 4 3 4 4 5% 8% 53%	3476
September	1st to 10th	Night	14% 6% 2 5% 4 4 4 4 5% 7% 44%	1900
	11th to 20th	Night	12% 5% 2 5% 3 3 3 3 5% 7% 50%	1984
	21st to end	Night	20% 7% 3 5% 4 3 4 3 5% 6% 40%	2090
October	1st to 10th	Night	20% 6% 3 5% 4 4 4 3 4 5% 43%	2185
	11th to 20th	Night	15% 4 2 5% 3 3 3 3 5% 7% 51%	2280
	21st to end	Night	19% 7% 2 5% 3 3 3 3 4 6% 45%	2644
November	1st to 10th	Night	13% 5% 2 5% 4 3 3 3 4 6% 52%	2505
	11th to 20th	Night	17% 7% 3 5% 4 3 3 3 4 5% 47%	2470
	21st to end	Night	13% 6% 2 4 4 3 5% 4 6% 7% 47%	2508
December	1st to 10th	Night	19% 7% 2 6% 4 3 4 3 5% 6% 41%	2660
	11th to 20th	Night	18% 5% 2 5% 4 3 3 4 5% 7% 44%	3288
	21st to end	Night	17% 9% 3 6% 4 4 4 3 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	40% 4 10% 27% 16% 3	2518
	11th to 20th	Day	45% 5% 10% 23% 14% 2	2520
	21st to end	Day	55% 5% 8% 21% 10% 2	3060
February	1st to 10th	Day	44% 5% 13% 22% 14% 2	1738
	11th to 20th	Day	42% 5% 9% 24% 17% 3	1857
	21st to end	Day	46% 5% 10% 21% 13% 5%	1570
March	1st to 10th	Day	48% 5% 10% 25% 10% 2	3119
	11th to 20th	Day	33% 6% 11% 32% 16% 3	3342
	21st to end	Day	44% 4 9% 17% 21% 5%	4132
April	1st to 10th	Day	43% 6% 10% 19% 17% 5%	2280
	11th to 20th	Day	39% 7% 12% 22% 17% 3	2254
	21st to end	Day	42% 6% 11% 18% 19% 4	2283
May	1st to 10th	Day	54% 9% 11% 15% 10% 1	4120
	11th to 20th	Day	52% 7% 12% 19% 9% 1	4323
	21st to end	Day	36% 8% 11% 25% 17% 2	4837
June	1st to 10th	Day	39% 9% 14% 21% 15% 2	2660
	11th to 20th	Day	38% 10% 13% 24% 12% 2	2660
	21st to end	Day	34% 10% 15% 24% 16% 1	2660
July	1st to 10th	Day	43% 11% 11% 18% 16% 1	4370
	11th to 20th	Day	40% 7% 18% 21% 12% 1	4365
	21st to end	Day	44% 8% 13% 20% 14% 1	4661
August	1st to 10th	Day	45% 8% 16% 22% 9%	4056
	11th to 20th	Day	38% 6% 14% 30% 11% 1	3766
	21st to end	Day	29% 6% 15% 30% 18% 1	4180
September	1st to 10th	Day	36% 6% 14% 21% 20% 3	2280
	11th to 20th	Day	32% 7% 10% 25% 24% 2	2195
	21st to end	Day	44% 6% 10% 18% 20% 2	2090
October	1st to 10th	Day	34% 5% 13% 21% 22% 5%	3302
	11th to 20th	Day	25% 3 10% 24% 33% 5%	3140
	21st to end	Day	27% 4 15% 27% 24% 3	3190
November	1st to 10th	Day	36% 3 13% 27% 20% 2	1734
	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	39% 3 11% 31% 13% 3	4429
	11th to 20th	Night	44% 4 11% 25% 13% 3	4440
	21st to end	Night	52% 3 8% 23% 13% 1	4592
February	1st to 10th	Night	43% 5% 14% 23% 13% 2	2439
	11th to 20th	Night	45% 4 9% 20% 19% 4	2220
	21st to end	Night	42% 3 9% 25% 17% 4	1884
March	1st to 10th	Night	50% 3 8% 24% 12% 3	3734
	11th to 20th	Night	38% 5% 11% 26% 17% 3	3616
	21st to end	Night	47% 3 5% 16% 23% 5%	3499
April	1st to 10th	Night	45% 5% 9% 19% 18% 4	1900
	11th to 20th	Night	43% 5% 9% 19% 21% 2	1875
	21st to end	Night	42% 5% 8% 20% 20% 5%	1895
May	1st to 10th	Night	55% 6% 10% 18% 9% 1	2840
	11th to 20th	Night	54% 5% 13% 17% 9% 2	2604
	21st to end	Night	41% 7% 14% 20% 16% 2	2739
June	1st to 10th	Night	42% 7% 9% 20% 19% 1	1520
	11th to 20th	Night	38% 8% 13% 27% 13% 1	1520
	21st to end	Night	37% 7% 15% 24% 15% 2	1520
July	1st to 10th	Night	46% 7% 14% 19% 12% 2	2480
	11th to 20th	Night	40% 6% 17% 25% 10% 1	2472
	21st to end	Night	47% 6% 15% 17% 14% 1	2651
August	1st to 10th	Night	51% 7% 18% 16% 8% 1	2802
	11th to 20th	Night	40% 6% 13% 30% 11% 1	3127
	21st to end	Night	30% 5% 11% 32% 21% 1	3476
September	1st to 10th	Night	40% 6% 11% 22% 18% 2	1900
	11th to 20th	Night	33% 5% 11% 24% 24% 3	1984
	21st to end	Night	45% 5% 7% 22% 19% 2	2090
October	1st to 10th	Night	39% 4 10% 23% 21% 3	3640
	11th to 20th	Night	25% 3 10% 27% 31% 5%	3779
	21st to end	Night	28% 3 11% 30% 24% 4	4356
November	1st to 10th	Night	35% 4 11% 25% 21% 4	2505
	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	19% 21% 35% 21% 3 1	180
	21st to end	Day	23% 9% 35% 25% 8% 1	279
February	1st to 10th	Day	23% 7% 34% 31% 5% 1	298
	11th to 20th	Day	22% 13% 37% 27% 2	456
	21st to end	Day	21% 14% 35% 25% 5% 1	382
March	1st to 10th	Day	19% 9% 38% 27% 6%	460
	11th to 20th	Day	17% 8% 40% 29% 6% 1	460
	21st to end	Day	24% 9% 32% 27% 7% 1	506
April	1st to 10th	Day	19% 7% 36% 28% 8% 1	460
	11th to 20th	Day	17% 6% 29% 34% 12% 1	452
	21st to end	Day	22% 7% 27% 32% 10% 2	460
May	1st to 10th	Day	25% 5% 26% 30% 11% 3	463
	11th to 20th	Day	23% 2 21% 38% 14% 2	487
	21st to end	Day	20% 2 12% 32% 27% 7%	529
June	1st to 10th	Day	16% 3 17% 34% 26% 4	490
	11th to 20th	Day	13% 2 19% 37% 23% 5%	490
	21st to end	Day	12% 3 13% 40% 28% 4	490
July	1st to 10th	Day	11% 3 9% 34% 34% 9%	485
	11th to 20th	Day	10% 1 8% 35% 35% 11%	484
	21st to end	Day	12% 2 14% 36% 31% 5%	532
August	1st to 10th	Day	11% 1 8% 40% 31% 8%	486
	11th to 20th	Day	11% 1 9% 33% 36% 9%	479
	21st to end	Day	12% 2 10% 35% 30% 11%	539
September	1st to 10th	Day	18% 2 16% 29% 24% 11%	490
	11th to 20th	Day	14% 1 12% 34% 29% 10%	490
	21st to end	Day	24% 4 17% 31% 19% 4	490
October	1st to 10th	Day	25% 4 15% 27% 22% 7%	490
	11th to 20th	Day	15% 6% 25% 28% 22% 4	490
	21st to end	Day	20% 7% 28% 27% 14% 3	466
November	1st to 10th	Day	15% 6% 25% 34% 17% 3	386
	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% 12% 35% 25% 5%	760
	21st to end	Night	20% 11% 43% 24% 3	836
February	1st to 10th	Night	21% 10% 39% 27% 3	760
	11th to 20th	Night	23% 12% 43% 20% 2	743
	21st to end	Night	23% 12% 35% 25% 4	628
March	1st to 10th	Night	19% 10% 40% 25% 6% 1	760
	11th to 20th	Night	20% 8% 38% 27% 6% 1	760
	21st to end	Night	21% 6% 35% 30% 7% 1	836
April	1st to 10th	Night	20% 8% 34% 31% 7% 1	760
	11th to 20th	Night	19% 6% 27% 38% 10%	751
	21st to end	Night	21% 4 30% 36% 9% 1	755
May	1st to 10th	Night	25% 5% 24% 32% 13% 1	570
	11th to 20th	Night	26% 2 25% 35% 11% 1	443
	21st to end	Night	19% 2 10% 35% 28% 4	411
June	1st to 10th	Night	19% 2 18% 35% 23% 2	380
	11th to 20th	Night	16% 1 14% 43% 24% 1	380
	21st to end	Night	9% 2 12% 48% 27% 2	380
July	1st to 10th	Night	12% 3 13% 38% 31% 4	370
	11th to 20th	Night	11% 2 10% 37% 36% 4	368
	21st to end	Night	12% 1 13% 41% 31% 1	416
August	1st to 10th	Night	12% 2 9% 42% 31% 4	554
	11th to 20th	Night	13% 2 11% 34% 35% 6%	750
	21st to end	Night	14% 2 12% 36% 30% 7%	836
September	1st to 10th	Night	16% 2 17% 34% 25% 6%	760
	11th to 20th	Night	16% 2 14% 31% 29% 7%	760
	21st to end	Night	24% 3 18% 31% 21% 3	760
October	1st to 10th	Night	23% 3 23% 25% 20% 6%	760
	11th to 20th	Night	17% 6% 26% 35% 14% 2	760
	21st to end	Night	22% 5% 33% 27% 12% 1	836
November	1st to 10th	Night	15% 6% 32% 32% 14% 2	771
	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

Page generated at 2024-11-05 08:15:52. Version ac07

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