Long Mountain Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Long Mountain Observatory clear sky chart from 2005-11-06 to 2024-11-06.

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	13% 8% 3 7% 5% 5% 5% 4 6% 7% 37%	100916
	Night	13% 9% 3 6% 4 4 4 4 5% 7% 41%	98119
Transparency	Day	43% 6% 11% 21% 15% 3	104683
	Night	41% 6% 10% 22% 17% 4	102490
Seeing	Day	19% 12% 23% 22% 16% 8%	14641
	Night	18% 10% 21% 28% 19% 3	24645

By Month

Percentage Cloud Cover SE (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% 13% 6% 11% 5% 4 4 4 5% 5% 28%	2836
	11th to 20th	Day	19% 12% 5% 12% 4 4 4 3 3 4 30%	2840
	21st to end	Day	23% 13% 6% 6% 4 3 3 3 4 4 31%	3315
February	1st to 10th	Day	20% 12% 4 8% 5% 4 3 2 4 4 33%	1900
	11th to 20th	Day	20% 12% 4 8% 5% 4 3 4 5% 4 32%	1848
	21st to end	Day	19% 12% 4 7% 5% 4 5% 3 4 5% 32%	1570
March	1st to 10th	Day	21% 12% 4 7% 4 3 4 3 5% 6% 31%	3120
	11th to 20th	Day	14% 9% 3 6% 4 3 3 3 4 5% 46%	3435
	21st to end	Day	15% 10% 3 6% 5% 5% 4 4 6% 6% 37%	3846
April	1st to 10th	Day	13% 7% 3 6% 5% 5% 3 4 5% 8% 41%	2280
	11th to 20th	Day	14% 9% 2 6% 4 4 4 3 5% 7% 43%	2254
	21st to end	Day	14% 8% 3 7% 4 4 5% 4 5% 7% 40%	2381
May	1st to 10th	Day	15% 8% 2 7% 5% 4 5% 4 7% 7% 35%	4082
	11th to 20th	Day	17% 9% 3 8% 6% 5% 5% 4 6% 6% 32%	4081
	21st to end	Day	11% 7% 3 7% 6% 5% 5% 5% 6% 8% 39%	4476
June	1st to 10th	Day	10% 6% 3 7% 6% 5% 6% 4 7% 8% 38%	2470
	11th to 20th	Day	5% 4 2 6% 5% 5% 5% 5% 9% 10% 44%	2470
	21st to end	Day	6% 5% 2 6% 6% 6% 6% 6% 9% 11% 37%	2470
July	1st to 10th	Day	7% 6% 2 7% 6% 6% 7% 6% 9% 12% 33%	4120
	11th to 20th	Day	10% 6% 2 7% 6% 6% 6% 5% 8% 10% 34%	4120
	21st to end	Day	15% 11% 5% 10% 8% 7% 7% 5% 6% 7% 20%	4466
August	1st to 10th	Day	6% 4 2 5% 5% 5% 6% 5% 9% 11% 43%	4053
	11th to 20th	Day	7% 5% 2 7% 5% 6% 6% 5% 8% 12% 36%	3729
	21st to end	Day	7% 5% 2 6% 5% 6% 6% 5% 7% 8% 44%	4180
September	1st to 10th	Day	12% 6% 3 7% 5% 5% 5% 5% 6% 7% 38%	2189
	11th to 20th	Day	13% 7% 2 7% 5% 5% 5% 4 6% 7% 39%	2090
	21st to end	Day	13% 5% 2 7% 4 4 5% 4 6% 6% 44%	2090
October	1st to 10th	Day	11% 5% 2 4 4 4 3 3 5% 5% 54%	2090
	11th to 20th	Day	14% 5% 2 4 3 3 3 2 5% 7% 53%	2043
	21st to end	Day	14% 7% 2 4 4 3 4 4 5% 6% 47%	1948
November	1st to 10th	Day	12% 6% 2 3 2 3 3 3 5% 6% 55%	1717
	11th to 20th	Day	11% 9% 2 5% 4 4 3 4 5% 6% 47%	1710
	21st to end	Day	15% 8% 2 6% 4 4 4 4 5% 6% 43%	1710
December	1st to 10th	Day	19% 12% 3 8% 4 4 4 3 5% 6% 32%	1710
	11th to 20th	Day	14% 14% 3 7% 5% 5% 5% 3 5% 5% 34%	2153
	21st to end	Day	15% 13% 6% 7% 5% 4 4 4 5% 7% 29%	3124
January	1st to 10th	Night	17% 15% 5% 8% 3 3 3 3 4 5% 34%	4109
	11th to 20th	Night	18% 13% 5% 8% 5% 5% 3 2 3 3 34%	4120
	21st to end	Night	20% 16% 4 6% 4 3 3 3 3 4 33%	4340
February	1st to 10th	Night	19% 10% 4 9% 4 4 4 3 5% 6% 33%	2280
	11th to 20th	Night	23% 11% 3 7% 5% 4 3 3 4 4 33%	2218
	21st to end	Night	23% 12% 3 6% 4 3 4 3 5% 5% 31%	1884
March	1st to 10th	Night	22% 14% 3 6% 5% 4 4 3 5% 5% 31%	3733
	11th to 20th	Night	14% 7% 2 5% 3 4 4 3 5% 6% 46%	3523
	21st to end	Night	15% 8% 3 8% 5% 5% 5% 3 5% 6% 38%	3800
April	1st to 10th	Night	13% 6% 2 5% 4 5% 3 4 5% 7% 45%	1900
	11th to 20th	Night	15% 6% 3 4 3 3 3 3 5% 7% 48%	1875
	21st to end	Night	14% 6% 2 6% 4 4 4 4 6% 8% 44%	1796
May	1st to 10th	Night	12% 7% 2 6% 5% 5% 5% 4 6% 8% 40%	2813
	11th to 20th	Night	15% 9% 3 8% 5% 4 4 3 5% 7% 37%	2812
	21st to end	Night	7% 5% 2 7% 5% 5% 6% 5% 7% 12% 41%	3079
June	1st to 10th	Night	5% 7% 3 7% 6% 6% 4 5% 6% 9% 43%	1710
	11th to 20th	Night	3 4 1 4 4 4 3 4 7% 12% 53%	1710
	21st to end	Night	6% 5% 2 6% 5% 5% 5% 5% 7% 10% 45%	1710
July	1st to 10th	Night	8% 5% 2 6% 5% 5% 5% 5% 10% 11% 37%	2840
	11th to 20th	Night	8% 5% 2 6% 4 4 5% 4 8% 12% 43%	2840
	21st to end	Night	11% 10% 4 10% 7% 7% 6% 5% 7% 8% 24%	3087
August	1st to 10th	Night	5% 4 2 5% 4 5% 4 4 7% 10% 50%	2872
	11th to 20th	Night	7% 6% 2 5% 4 4 5% 4 7% 10% 46%	3100
	21st to end	Night	5% 4 1 5% 3 4 4 4 6% 9% 55%	3476
September	1st to 10th	Night	10% 7% 2 6% 4 3 5% 4 6% 7% 46%	1971
	11th to 20th	Night	10% 7% 2 6% 4 4 5% 4 6% 8% 44%	2090
	21st to end	Night	10% 5% 2 6% 4 4 4 3 5% 7% 52%	2090
October	1st to 10th	Night	10% 4 2 4 3 2 2 3 4 5% 59%	2090
	11th to 20th	Night	15% 5% 2 5% 3 4 3 2 4 5% 52%	2137
	21st to end	Night	14% 7% 2 5% 3 3 3 3 4 6% 50%	2647
November	1st to 10th	Night	12% 7% 2 5% 3 3 3 3 5% 6% 51%	2483
	11th to 20th	Night	13% 8% 2 5% 4 3 3 3 5% 7% 47%	2470
	21st to end	Night	15% 10% 3 5% 4 3 3 4 5% 6% 42%	2470
December	1st to 10th	Night	20% 12% 4 8% 4 5% 4 3 4 6% 31%	2470
	11th to 20th	Night	16% 12% 4 8% 4 3 3 3 5% 5% 38%	3042
	21st to end	Night	13% 15% 5% 9% 5% 6% 5% 4 5% 7% 26%	4532

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	55% 5% 8% 16% 14% 2	2837
	11th to 20th	Day	58% 4 5% 13% 18% 2	2840
	21st to end	Day	55% 4 7% 20% 13% 1	3315
February	1st to 10th	Day	55% 3 7% 15% 18% 2	1900
	11th to 20th	Day	53% 5% 7% 17% 15% 4	1858
	21st to end	Day	53% 5% 6% 14% 16% 5%	1570
March	1st to 10th	Day	53% 5% 8% 15% 12% 7%	3120
	11th to 20th	Day	41% 4 8% 23% 18% 6%	3435
	21st to end	Day	47% 5% 9% 24% 14% 1	3846
April	1st to 10th	Day	42% 6% 11% 21% 17% 3	2280
	11th to 20th	Day	42% 5% 8% 19% 24% 3	2254
	21st to end	Day	43% 5% 9% 27% 14% 1	2381
May	1st to 10th	Day	45% 9% 10% 23% 11% 1	4120
	11th to 20th	Day	50% 8% 11% 22% 9%	4085
	21st to end	Day	41% 8% 10% 21% 17% 1	4489
June	1st to 10th	Day	41% 7% 14% 23% 12% 2	2470
	11th to 20th	Day	32% 9% 20% 23% 15% 2	2470
	21st to end	Day	37% 9% 19% 19% 13% 3	2470
July	1st to 10th	Day	38% 12% 21% 20% 7% 1	4055
	11th to 20th	Day	42% 9% 18% 23% 6% 2	4051
	21st to end	Day	61% 9% 10% 15% 4 1	4324
August	1st to 10th	Day	31% 9% 17% 32% 11% 1	4040
	11th to 20th	Day	36% 9% 19% 23% 13% 1	3765
	21st to end	Day	34% 8% 13% 31% 13% 1	4179
September	1st to 10th	Day	43% 6% 13% 17% 16% 5%	2189
	11th to 20th	Day	43% 7% 10% 20% 18% 2	2090
	21st to end	Day	39% 6% 11% 22% 18% 5%	2090
October	1st to 10th	Day	24% 4 7% 18% 34% 12%	3480
	11th to 20th	Day	23% 3 6% 24% 29% 15%	3374
	21st to end	Day	27% 4 9% 24% 26% 10%	3185
November	1st to 10th	Day	31% 4 9% 24% 27% 5%	1717
	11th to 20th	Day	39% 3 6% 23% 23% 6%	1710
	21st to end	Day	42% 4 7% 22% 21% 4	1710
December	1st to 10th	Day	54% 4 6% 20% 14% 3	1710
	11th to 20th	Day	52% 4 8% 16% 18% 3	2150
	21st to end	Day	52% 6% 10% 18% 12% 3	3124
January	1st to 10th	Night	53% 5% 6% 18% 16% 2	4109
	11th to 20th	Night	55% 3 5% 13% 17% 6%	4120
	21st to end	Night	56% 3 6% 14% 19% 2	4340
February	1st to 10th	Night	51% 4 9% 17% 17% 2	2280
	11th to 20th	Night	56% 3 5% 17% 14% 5%	2219
	21st to end	Night	54% 5% 8% 15% 13% 5%	1884
March	1st to 10th	Night	56% 5% 8% 12% 15% 4	3733
	11th to 20th	Night	38% 5% 7% 24% 15% 10%	3523
	21st to end	Night	47% 4 9% 23% 16% 1	3800
April	1st to 10th	Night	39% 4 11% 23% 21% 3	1900
	11th to 20th	Night	36% 5% 9% 22% 22% 6%	1875
	21st to end	Night	38% 6% 11% 28% 15% 1	1796
May	1st to 10th	Night	40% 9% 13% 24% 13% 1	2840
	11th to 20th	Night	46% 6% 13% 21% 13% 1	2813
	21st to end	Night	33% 10% 15% 25% 15% 2	3087
June	1st to 10th	Night	37% 8% 15% 25% 12% 2	1710
	11th to 20th	Night	22% 7% 22% 32% 15% 2	1710
	21st to end	Night	32% 9% 17% 27% 12% 4	1710
July	1st to 10th	Night	35% 12% 21% 23% 8% 1	2795
	11th to 20th	Night	31% 9% 21% 29% 7% 3	2786
	21st to end	Night	54% 10% 13% 15% 7% 1	2988
August	1st to 10th	Night	26% 7% 14% 37% 14% 1	2861
	11th to 20th	Night	31% 9% 24% 23% 14% 1	3130
	21st to end	Night	24% 7% 14% 36% 17% 1	3476
September	1st to 10th	Night	35% 7% 14% 22% 17% 5%	1971
	11th to 20th	Night	36% 8% 11% 22% 21% 1	2090
	21st to end	Night	33% 5% 10% 24% 23% 5%	2090
October	1st to 10th	Night	22% 3 7% 24% 30% 15%	3480
	11th to 20th	Night	24% 3 5% 23% 28% 18%	3545
	21st to end	Night	24% 3 6% 26% 28% 12%	4360
November	1st to 10th	Night	35% 3 7% 22% 24% 8%	2483
	11th to 20th	Night	37% 4 7% 20% 25% 8%	2470
	21st to end	Night	44% 3 6% 22% 21% 5%	2470
December	1st to 10th	Night	54% 5% 7% 18% 14% 3	2470
	11th to 20th	Night	49% 4 7% 16% 21% 4	3044
	21st to end	Night	55% 6% 8% 17% 12% 2	4532

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	27% 29% 30% 10% 4	270
	11th to 20th	Day	35% 29% 22% 10% 3 1	270
	21st to end	Day	27% 30% 33% 7% 3	297
February	1st to 10th	Day	29% 29% 29% 11% 3	270
	11th to 20th	Day	42% 24% 27% 5% 2	270
	21st to end	Day	40% 26% 28% 5%	225
March	1st to 10th	Day	29% 26% 31% 11% 2	270
	11th to 20th	Day	27% 25% 28% 15% 5% 1	428
	21st to end	Day	26% 19% 34% 15% 6% 1	506
April	1st to 10th	Day	22% 22% 28% 18% 11%	460
	11th to 20th	Day	23% 16% 32% 20% 8% 2	452
	21st to end	Day	22% 15% 30% 21% 10% 2	460
May	1st to 10th	Day	19% 13% 33% 19% 12% 4	463
	11th to 20th	Day	15% 9% 30% 25% 14% 8%	487
	21st to end	Day	15% 7% 22% 28% 16% 13%	529
June	1st to 10th	Day	14% 5% 22% 27% 21% 12%	490
	11th to 20th	Day	6% 6% 16% 32% 24% 16%	490
	21st to end	Day	8% 6% 21% 30% 20% 16%	490
July	1st to 10th	Day	12% 4 14% 28% 25% 19%	485
	11th to 20th	Day	12% 3 11% 24% 28% 22%	484
	21st to end	Day	13% 4 11% 26% 28% 18%	532
August	1st to 10th	Day	13% 3 13% 28% 24% 18%	486
	11th to 20th	Day	11% 5% 13% 35% 28% 9%	479
	21st to end	Day	15% 4 8% 24% 31% 19%	539
September	1st to 10th	Day	12% 4 12% 27% 31% 13%	490
	11th to 20th	Day	15% 5% 13% 28% 27% 12%	490
	21st to end	Day	16% 7% 17% 29% 24% 7%	490
October	1st to 10th	Day	15% 5% 21% 30% 22% 7%	490
	11th to 20th	Day	16% 10% 29% 27% 15% 3	490
	21st to end	Day	21% 10% 31% 24% 10% 3	397
November	1st to 10th	Day	20% 11% 34% 25% 8% 2	285
	11th to 20th	Day	17% 21% 39% 20% 3	270
	21st to end	Day	21% 16% 37% 17% 8% 1	270
December	1st to 10th	Day	31% 17% 32% 14% 5% 1	270
	11th to 20th	Day	29% 20% 28% 17% 6%	270
	21st to end	Day	27% 25% 30% 14% 3	297
January	1st to 10th	Night	25% 20% 29% 21% 5%	760
	11th to 20th	Night	29% 23% 27% 18% 4	760
	21st to end	Night	23% 20% 33% 20% 3	836
February	1st to 10th	Night	25% 18% 30% 25% 3	760
	11th to 20th	Night	30% 19% 29% 20% 2	743
	21st to end	Night	33% 20% 27% 19% 2	628
March	1st to 10th	Night	25% 15% 29% 26% 4	760
	11th to 20th	Night	24% 16% 30% 22% 8%	760
	21st to end	Night	22% 16% 27% 26% 9%	831
April	1st to 10th	Night	18% 15% 27% 28% 11% 1	570
	11th to 20th	Night	21% 11% 30% 27% 9% 2	563
	21st to end	Night	17% 8% 27% 35% 12% 1	570
May	1st to 10th	Night	15% 7% 28% 30% 18% 1	570
	11th to 20th	Night	15% 5% 20% 35% 20% 4	561
	21st to end	Night	9% 2 16% 35% 32% 5%	617
June	1st to 10th	Night	8% 2 15% 36% 33% 5%	570
	11th to 20th	Night	4 1 12% 36% 36% 11%	570
	21st to end	Night	8% 2 13% 33% 37% 8%	570
July	1st to 10th	Night	11% 2 6% 29% 42% 11%	555
	11th to 20th	Night	10% 2 7% 27% 42% 13%	552
	21st to end	Night	10% 2 5% 32% 40% 11%	624
August	1st to 10th	Night	8% 2 5% 29% 46% 9%	567
	11th to 20th	Night	8% 2 6% 36% 41% 6%	564
	21st to end	Night	11% 1 7% 27% 45% 9%	627
September	1st to 10th	Night	14% 2 7% 31% 37% 9%	641
	11th to 20th	Night	15% 4 13% 27% 36% 6%	760
	21st to end	Night	12% 3 14% 34% 32% 5%	760
October	1st to 10th	Night	13% 5% 16% 32% 26% 8%	760
	11th to 20th	Night	19% 9% 23% 29% 20% 2	760
	21st to end	Night	18% 9% 24% 32% 14% 3	836
November	1st to 10th	Night	16% 10% 20% 33% 17% 2	764
	11th to 20th	Night	17% 15% 28% 27% 12% 1	760
	21st to end	Night	21% 14% 26% 28% 10% 1	760
December	1st to 10th	Night	29% 14% 25% 25% 6%	760
	11th to 20th	Night	23% 15% 27% 28% 6% 1	760
	21st to end	Night	27% 18% 25% 24% 5%	836

Page generated at 2024-11-03 12:19:04. Version ac07

Copyright © 2024 Attilla Danko.