Tenafly Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Tenafly Observatory clear sky chart from 2005-11-06 to 2025-07-06.

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	17% 7% 2 6% 4 4 4 4 5% 7% 40%	119807
	Night	18% 7% 2 5% 4 4 4 3 5% 6% 42%	118964
Transparency	Day	27% 40% 7% 14% 10% 2	123366
	Night	27% 39% 7% 14% 11% 2	123566
Seeing	Day	20% 13% 30% 24% 11% 3	15813
	Night	20% 11% 31% 28% 9% 1	24965

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	13% 6% 2 4 4 3 4 3 5% 7% 49%	3597
	11th to 20th	Day	14% 9% 2 6% 5% 4 4 3 4 6% 42%	3570
	21st to end	Day	18% 9% 3 7% 4 4 3 3 4 4 40%	4282
February	1st to 10th	Day	18% 7% 2 6% 5% 3 5% 4 4 6% 40%	1813
	11th to 20th	Day	15% 8% 3 6% 4 4 4 3 4 5% 44%	1948
	21st to end	Day	20% 7% 2 6% 4 3 4 4 5% 5% 40%	1650
March	1st to 10th	Day	22% 7% 2 5% 4 3 4 3 4 5% 42%	4476
	11th to 20th	Day	12% 8% 2 6% 5% 5% 4 4 5% 7% 42%	4750
	21st to end	Day	18% 7% 2 6% 4 4 4 3 4 6% 42%	5941
April	1st to 10th	Day	19% 8% 3 6% 4 4 3 4 5% 6% 39%	2400
	11th to 20th	Day	18% 6% 2 6% 4 4 4 3 5% 7% 41%	2374
	21st to end	Day	19% 5% 2 5% 4 4 4 3 5% 8% 40%	2431
May	1st to 10th	Day	29% 8% 2 5% 4 3 4 3 6% 8% 28%	5886
	11th to 20th	Day	23% 9% 2 6% 4 3 3 3 4 6% 35%	6267
	21st to end	Day	21% 6% 2 5% 4 4 5% 4 6% 8% 35%	6949
June	1st to 10th	Day	16% 6% 2 5% 4 4 5% 4 8% 9% 37%	2800
	11th to 20th	Day	17% 7% 2 6% 4 4 5% 4 6% 8% 37%	2800
	21st to end	Day	12% 6% 2 6% 5% 5% 5% 4 7% 9% 39%	2800
July	1st to 10th	Day	9% 5% 2 7% 6% 5% 6% 5% 7% 10% 36%	4510
	11th to 20th	Day	11% 6% 2 6% 5% 5% 5% 4 8% 9% 38%	4440
	21st to end	Day	14% 8% 3 8% 6% 5% 6% 5% 6% 8% 31%	4814
August	1st to 10th	Day	21% 5% 2 7% 5% 5% 5% 4 6% 8% 32%	4185
	11th to 20th	Day	13% 5% 2 6% 4 4 4 4 6% 9% 42%	3730
	21st to end	Day	10% 5% 2 6% 5% 4 5% 4 6% 8% 46%	4180
September	1st to 10th	Day	14% 5% 2 5% 5% 5% 5% 4 5% 6% 44%	2280
	11th to 20th	Day	14% 5% 2 5% 3 3 4 4 5% 7% 49%	2195
	21st to end	Day	19% 5% 2 6% 5% 4 5% 3 5% 5% 40%	2090
October	1st to 10th	Day	21% 6% 2 5% 3 3 3 3 4 8% 41%	1990
	11th to 20th	Day	15% 5% 2 6% 4 3 3 3 4 6% 48%	1900
	21st to end	Day	21% 5% 1 4 4 4 4 2 4 6% 44%	1932
November	1st to 10th	Day	15% 5% 2 5% 3 4 2 3 5% 6% 52%	1761
	11th to 20th	Day	18% 5% 2 4 3 3 3 2 5% 6% 48%	1800
	21st to end	Day	16% 6% 2 5% 4 3 4 3 6% 7% 44%	1720
December	1st to 10th	Day	16% 7% 2 6% 4 3 3 2 5% 7% 45%	2600
	11th to 20th	Day	23% 6% 2 4 2 2 2 3 4 6% 45%	2986
	21st to end	Day	18% 7% 2 7% 4 4 4 3 5% 7% 38%	3960
January	1st to 10th	Night	13% 6% 2 5% 3 4 4 4 4 5% 49%	6349
	11th to 20th	Night	14% 8% 2 6% 4 4 4 3 4 5% 47%	6315
	21st to end	Night	18% 9% 2 5% 3 4 4 3 5% 6% 40%	6656
February	1st to 10th	Night	18% 9% 2 5% 5% 4 4 3 4 5% 42%	2585
	11th to 20th	Night	17% 8% 3 5% 5% 4 4 3 4 6% 41%	2338
	21st to end	Night	19% 7% 3 6% 5% 4 4 3 5% 5% 41%	1980
March	1st to 10th	Night	20% 8% 2 5% 3 3 3 3 4 5% 43%	5364
	11th to 20th	Night	15% 9% 2 6% 3 3 4 3 4 6% 44%	5194
	21st to end	Night	19% 8% 3 6% 4 4 4 3 4 5% 40%	4990
April	1st to 10th	Night	20% 7% 3 6% 4 4 4 3 6% 6% 37%	2000
	11th to 20th	Night	19% 8% 2 5% 4 4 5% 3 5% 6% 40%	1975
	21st to end	Night	19% 6% 2 5% 3 4 3 4 4 6% 43%	1966
May	1st to 10th	Night	28% 9% 3 7% 4 4 3 3 5% 7% 27%	4054
	11th to 20th	Night	23% 10% 3 6% 4 3 4 3 4 6% 35%	3668
	21st to end	Night	22% 7% 3 6% 4 3 4 3 5% 8% 35%	3926
June	1st to 10th	Night	17% 6% 2 5% 5% 4 5% 3 6% 8% 41%	1600
	11th to 20th	Night	14% 6% 2 6% 5% 4 5% 4 5% 9% 40%	1600
	21st to end	Night	11% 4 2 6% 5% 4 5% 4 7% 8% 43%	1600
July	1st to 10th	Night	10% 6% 3 8% 6% 5% 6% 4 7% 9% 37%	2560
	11th to 20th	Night	14% 6% 2 6% 5% 4 6% 4 8% 9% 36%	2520
	21st to end	Night	19% 7% 2 5% 4 4 5% 4 6% 7% 36%	2739
August	1st to 10th	Night	23% 6% 3 6% 4 4 6% 4 5% 7% 32%	2710
	11th to 20th	Night	14% 7% 2 7% 4 5% 4 5% 6% 7% 39%	3097
	21st to end	Night	10% 5% 2 4 3 4 4 3 6% 8% 51%	3476
September	1st to 10th	Night	15% 6% 3 6% 4 4 4 3 5% 7% 44%	1900
	11th to 20th	Night	14% 5% 2 4 3 3 3 2 4 7% 52%	1985
	21st to end	Night	18% 7% 3 5% 4 3 3 3 4 6% 44%	2090
October	1st to 10th	Night	19% 7% 2 6% 4 4 4 2 4 7% 41%	2186
	11th to 20th	Night	15% 5% 1 5% 4 3 3 3 4 6% 50%	2280
	21st to end	Night	20% 7% 3 5% 2 3 3 3 5% 5% 44%	2665
November	1st to 10th	Night	13% 5% 2 4 4 3 3 4 5% 6% 52%	2537
	11th to 20th	Night	19% 6% 2 4 3 3 3 3 4 5% 48%	2600
	21st to end	Night	15% 6% 2 5% 4 3 4 4 5% 6% 47%	2675
December	1st to 10th	Night	16% 7% 2 5% 3 3 3 3 5% 5% 48%	4580
	11th to 20th	Night	26% 7% 2 4 2 3 3 3 3 4 42%	5208
	21st to end	Night	19% 9% 3 6% 4 3 4 3 5% 5% 40%	6996

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	26% 26% 4 26% 16% 2	3598
	11th to 20th	Day	31% 27% 7% 18% 13% 5%	3600
	21st to end	Day	37% 29% 6% 17% 10% 1	4282
February	1st to 10th	Day	19% 63% 6% 8% 3 1	1813
	11th to 20th	Day	18% 60% 2 10% 9% 1	1957
	21st to end	Day	17% 62% 5% 9% 5% 1	1650
March	1st to 10th	Day	33% 29% 8% 12% 10% 8%	4479
	11th to 20th	Day	26% 32% 10% 23% 6% 3	4750
	21st to end	Day	33% 29% 7% 7% 19% 5%	5941
April	1st to 10th	Day	21% 62% 4 7% 6% 1	2400
	11th to 20th	Day	16% 62% 5% 8% 8% 1	2374
	21st to end	Day	17% 62% 3 10% 6% 1	2431
May	1st to 10th	Day	42% 31% 12% 9% 6%	5897
	11th to 20th	Day	37% 30% 8% 15% 10% 1	6271
	21st to end	Day	35% 30% 7% 17% 11%	6949
June	1st to 10th	Day	17% 63% 4 9% 7%	2800
	11th to 20th	Day	17% 62% 4 9% 7%	2800
	21st to end	Day	15% 62% 5% 9% 9% 1	2800
July	1st to 10th	Day	28% 38% 8% 14% 11% 1	4440
	11th to 20th	Day	28% 37% 12% 14% 8% 1	4365
	21st to end	Day	35% 37% 8% 10% 9% 1	4661
August	1st to 10th	Day	36% 37% 9% 14% 4	4171
	11th to 20th	Day	25% 37% 8% 23% 6%	3766
	21st to end	Day	20% 37% 6% 22% 14% 1	4180
September	1st to 10th	Day	15% 61% 5% 10% 8%	2280
	11th to 20th	Day	16% 61% 4 9% 10% 1	2195
	21st to end	Day	21% 60% 4 8% 6% 1	2090
October	1st to 10th	Day	24% 36% 6% 10% 18% 6%	3302
	11th to 20th	Day	13% 36% 6% 14% 27% 4	3140
	21st to end	Day	13% 36% 10% 18% 20% 3	3157
November	1st to 10th	Day	17% 56% 6% 9% 10% 1	1761
	11th to 20th	Day	14% 56% 3 11% 13% 2	1800
	21st to end	Day	16% 57% 8% 14% 4 2	1720
December	1st to 10th	Day	26% 35% 10% 20% 7% 1	2600
	11th to 20th	Day	30% 31% 8% 16% 13% 2	2986
	21st to end	Day	34% 29% 4 17% 13% 3	3960
January	1st to 10th	Night	27% 26% 5% 19% 19% 4	6349
	11th to 20th	Night	28% 27% 11% 16% 14% 5%	6360
	21st to end	Night	36% 29% 6% 13% 12% 4	6656
February	1st to 10th	Night	18% 62% 5% 11% 3 1	2585
	11th to 20th	Night	18% 60% 3 8% 9% 2	2340
	21st to end	Night	18% 62% 3 8% 7% 2	1980
March	1st to 10th	Night	34% 30% 6% 13% 9% 8%	5374
	11th to 20th	Night	27% 30% 13% 18% 8% 3	5195
	21st to end	Night	36% 29% 4 9% 19% 3	4990
April	1st to 10th	Night	20% 62% 4 8% 5% 2	2000
	11th to 20th	Night	15% 63% 5% 9% 8% 1	1975
	21st to end	Night	17% 62% 3 10% 7% 1	1966
May	1st to 10th	Night	44% 31% 10% 9% 6% 1	4060
	11th to 20th	Night	40% 30% 11% 9% 10% 1	3669
	21st to end	Night	38% 29% 8% 17% 7% 1	3927
June	1st to 10th	Night	17% 62% 3 9% 9% 1	1600
	11th to 20th	Night	17% 62% 5% 11% 5%	1600
	21st to end	Night	15% 61% 5% 11% 8% 1	1600
July	1st to 10th	Night	29% 38% 10% 12% 10% 1	2520
	11th to 20th	Night	31% 37% 10% 15% 7%	2472
	21st to end	Night	34% 35% 10% 8% 12% 1	2651
August	1st to 10th	Night	39% 38% 9% 9% 4 1	2700
	11th to 20th	Night	28% 38% 8% 20% 6%	3127
	21st to end	Night	17% 36% 7% 26% 12% 1	3476
September	1st to 10th	Night	15% 61% 5% 12% 7% 1	1900
	11th to 20th	Night	14% 60% 5% 8% 10% 2	1985
	21st to end	Night	20% 60% 4 8% 7% 1	2090
October	1st to 10th	Night	25% 36% 8% 15% 15% 1	3654
	11th to 20th	Night	10% 37% 5% 19% 25% 3	3779
	21st to end	Night	17% 36% 8% 22% 16% 2	4390
November	1st to 10th	Night	16% 57% 6% 10% 9% 1	2537
	11th to 20th	Night	16% 57% 3 10% 12% 3	2600
	21st to end	Night	15% 57% 6% 13% 7% 1	2675
December	1st to 10th	Night	26% 36% 7% 23% 7% 1	4580
	11th to 20th	Night	33% 31% 6% 15% 12% 3	5208
	21st to end	Night	35% 29% 7% 13% 13% 4	6996

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	22% 28% 31% 16% 4 1	200
	11th to 20th	Day	25% 25% 38% 11% 2 1	200
	21st to end	Day	20% 20% 41% 12% 5% 2	290
February	1st to 10th	Day	27% 17% 39% 16% 2	313
	11th to 20th	Day	25% 20% 36% 17% 2	496
	21st to end	Day	24% 18% 36% 18% 4	414
March	1st to 10th	Day	21% 22% 33% 20% 4	500
	11th to 20th	Day	19% 20% 37% 18% 5% 1	500
	21st to end	Day	26% 20% 31% 17% 5% 1	550
April	1st to 10th	Day	26% 20% 31% 16% 6% 1	500
	11th to 20th	Day	23% 16% 34% 17% 9% 1	492
	21st to end	Day	25% 16% 33% 19% 6% 1	500
May	1st to 10th	Day	32% 13% 29% 18% 7% 2	503
	11th to 20th	Day	22% 12% 32% 22% 10% 2	527
	21st to end	Day	21% 9% 24% 27% 15% 4	573
June	1st to 10th	Day	18% 9% 27% 28% 14% 4	530
	11th to 20th	Day	18% 10% 28% 31% 11% 2	530
	21st to end	Day	15% 8% 29% 27% 17% 3	530
July	1st to 10th	Day	13% 3 25% 34% 19% 6%	505
	11th to 20th	Day	11% 4 23% 35% 23% 4	484
	21st to end	Day	15% 6% 23% 34% 19% 2	532
August	1st to 10th	Day	13% 5% 20% 36% 18% 8%	486
	11th to 20th	Day	15% 4 21% 34% 21% 4	479
	21st to end	Day	12% 5% 25% 32% 17% 8%	539
September	1st to 10th	Day	18% 6% 27% 23% 19% 7%	490
	11th to 20th	Day	15% 5% 27% 26% 16% 11%	490
	21st to end	Day	21% 9% 28% 26% 12% 4	490
October	1st to 10th	Day	26% 8% 24% 21% 16% 4	490
	11th to 20th	Day	18% 13% 29% 24% 13% 2	490
	21st to end	Day	23% 13% 30% 22% 9% 2	455
November	1st to 10th	Day	17% 14% 31% 26% 11% 3	395
	11th to 20th	Day	21% 17% 35% 22% 5% 1	400
	21st to end	Day	19% 20% 32% 23% 5% 1	320
December	1st to 10th	Day	24% 21% 33% 18% 4 2	200
	11th to 20th	Day	30% 22% 34% 12% 3	200
	21st to end	Day	27% 13% 36% 15% 8%	220
January	1st to 10th	Night	20% 15% 42% 19% 3	800
	11th to 20th	Night	23% 16% 34% 23% 4	800
	21st to end	Night	20% 15% 41% 22% 2	880
February	1st to 10th	Night	23% 12% 38% 25% 2	800
	11th to 20th	Night	23% 16% 40% 20% 1	783
	21st to end	Night	24% 14% 36% 21% 4	660
March	1st to 10th	Night	22% 15% 36% 22% 4	800
	11th to 20th	Night	23% 13% 38% 22% 4 1	800
	21st to end	Night	23% 15% 36% 22% 5%	880
April	1st to 10th	Night	22% 15% 35% 22% 5%	800
	11th to 20th	Night	22% 13% 33% 25% 6%	791
	21st to end	Night	21% 11% 34% 27% 6% 1	766
May	1st to 10th	Night	25% 11% 33% 24% 7% 1	600
	11th to 20th	Night	22% 11% 32% 27% 8%	435
	21st to end	Night	21% 5% 18% 40% 14% 1	433
June	1st to 10th	Night	19% 5% 27% 36% 13% 1	400
	11th to 20th	Night	16% 4 26% 38% 16%	400
	21st to end	Night	11% 3 24% 49% 13% 1	400
July	1st to 10th	Night	12% 3 23% 43% 20%	380
	11th to 20th	Night	12% 4 19% 43% 21% 2	368
	21st to end	Night	15% 4 18% 45% 17% 1	416
August	1st to 10th	Night	14% 2 19% 43% 20% 2	491
	11th to 20th	Night	15% 4 17% 36% 25% 2	750
	21st to end	Night	15% 4 17% 37% 24% 2	836
September	1st to 10th	Night	16% 4 24% 34% 19% 2	760
	11th to 20th	Night	17% 4 22% 33% 19% 4	760
	21st to end	Night	21% 5% 23% 33% 16% 2	760
October	1st to 10th	Night	23% 9% 27% 24% 14% 2	760
	11th to 20th	Night	17% 11% 29% 31% 11% 1	760
	21st to end	Night	25% 11% 32% 24% 8%	836
November	1st to 10th	Night	15% 10% 35% 27% 12% 1	780
	11th to 20th	Night	23% 14% 32% 24% 7% 1	800
	21st to end	Night	20% 14% 35% 24% 7% 1	800
December	1st to 10th	Night	24% 14% 35% 21% 6% 1	800
	11th to 20th	Night	24% 14% 35% 24% 4	800
	21st to end	Night	25% 12% 35% 25% 3	880

Page generated at 2025-07-03 01:30:11. Version ac07

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