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 2026-10-29.

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% 6% 2 6% 4 4 4 4 5% 7% 40%	149544
	Night	17% 7% 2 6% 4 4 4 3 5% 6% 42%	142521
Transparency	Day	30% 33% 8% 16% 12% 2	153060
	Night	30% 33% 7% 16% 12% 2	147094
Seeing	Day	20% 13% 30% 23% 11% 3	17559
	Night	20% 11% 31% 28% 9% 1	26633

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	12% 6% 2 5% 4 4 4 3 5% 6% 48%	4661
	11th to 20th	Day	16% 9% 2 5% 4 4 4 3 4 5% 45%	4650
	21st to end	Day	16% 8% 3 6% 4 4 4 3 5% 6% 42%	5541
February	1st to 10th	Day	17% 7% 2 6% 5% 3 5% 3 4 6% 41%	1904
	11th to 20th	Day	15% 8% 3 6% 4 4 5% 3 4 6% 43%	2048
	21st to end	Day	19% 7% 2 5% 4 3 4 4 5% 6% 40%	1730
March	1st to 10th	Day	22% 7% 2 5% 4 3 4 3 4 5% 42%	4576
	11th to 20th	Day	12% 8% 2 6% 5% 5% 4 4 5% 7% 42%	4855
	21st to end	Day	18% 7% 2 6% 4 4 4 3 5% 6% 42%	6072
April	1st to 10th	Day	19% 7% 3 6% 4 4 3 3 5% 6% 39%	2520
	11th to 20th	Day	17% 6% 2 6% 4 4 4 3 5% 7% 41%	2494
	21st to end	Day	19% 5% 2 5% 4 4 4 3 5% 8% 40%	2553
May	1st to 10th	Day	26% 7% 2 5% 4 3 4 3 5% 7% 33%	7639
	11th to 20th	Day	20% 9% 2 6% 4 4 4 3 5% 6% 38%	8157
	21st to end	Day	24% 6% 2 6% 4 4 5% 4 6% 7% 33%	9060
June	1st to 10th	Day	16% 6% 2 5% 4 4 5% 4 8% 9% 38%	2940
	11th to 20th	Day	16% 7% 2 6% 4 4 5% 4 6% 8% 38%	2940
	21st to end	Day	12% 6% 2 6% 5% 5% 5% 4 7% 9% 39%	2940
July	1st to 10th	Day	13% 6% 2 7% 5% 5% 5% 5% 6% 9% 37%	8280
	11th to 20th	Day	10% 6% 2 7% 5% 5% 5% 5% 8% 11% 38%	8280
	21st to end	Day	13% 7% 2 6% 5% 4 5% 4 6% 8% 39%	8993
August	1st to 10th	Day	16% 5% 2 8% 5% 6% 6% 5% 8% 10% 29%	6139
	11th to 20th	Day	12% 5% 2 5% 4 4 4 4 6% 10% 44%	5488
	21st to end	Day	11% 5% 2 6% 4 4 5% 4 6% 8% 43%	6080
September	1st to 10th	Day	14% 5% 2 5% 5% 5% 4 4 5% 7% 44%	2520
	11th to 20th	Day	14% 5% 2 5% 3 3 4 4 5% 7% 49%	2425
	21st to end	Day	18% 6% 2 7% 5% 5% 5% 4 5% 5% 38%	2310
October	1st to 10th	Day	20% 6% 2 5% 3 3 3 3 5% 7% 44%	2200
	11th to 20th	Day	16% 5% 2 5% 4 3 3 3 4 7% 48%	2100
	21st to end	Day	20% 5% 1 4 4 4 4 3 4 6% 46%	2108
November	1st to 10th	Day	14% 5% 2 5% 3 4 2 3 5% 6% 51%	1851
	11th to 20th	Day	18% 5% 2 4 3 4 3 3 5% 6% 47%	1890
	21st to end	Day	17% 6% 2 5% 4 3 4 3 5% 7% 44%	1806
December	1st to 10th	Day	16% 7% 2 5% 4 3 3 2 5% 7% 45%	2680
	11th to 20th	Day	23% 6% 2 4 2 2 2 3 4 6% 45%	3066
	21st to end	Day	18% 7% 2 7% 4 4 4 3 5% 7% 38%	4048
January	1st to 10th	Night	13% 8% 3 6% 4 4 4 4 4 6% 46%	8234
	11th to 20th	Night	16% 8% 2 6% 4 3 4 3 4 5% 45%	8235
	21st to end	Night	16% 8% 2 5% 3 4 4 3 5% 6% 43%	8622
February	1st to 10th	Night	17% 9% 2 5% 5% 4 4 3 4 6% 42%	2714
	11th to 20th	Night	17% 8% 3 5% 5% 4 4 3 4 6% 40%	2458
	21st to end	Night	18% 7% 3 6% 5% 4 4 3 5% 5% 40%	2076
March	1st to 10th	Night	21% 9% 2 5% 3 3 3 3 4 5% 43%	5484
	11th to 20th	Night	15% 9% 2 6% 4 3 4 3 4 6% 44%	5309
	21st to end	Night	19% 8% 3 6% 4 4 4 3 4 5% 40%	5101
April	1st to 10th	Night	20% 7% 3 6% 4 4 4 3 6% 6% 37%	2100
	11th to 20th	Night	19% 8% 2 5% 4 4 5% 3 5% 6% 40%	2075
	21st to end	Night	19% 6% 2 5% 3 4 3 3 4 6% 42%	2064
May	1st to 10th	Night	25% 8% 3 7% 4 4 4 3 5% 7% 31%	5259
	11th to 20th	Night	20% 9% 3 6% 4 4 4 3 5% 7% 36%	4758
	21st to end	Night	24% 8% 3 7% 4 4 4 3 5% 7% 32%	5114
June	1st to 10th	Night	17% 5% 2 5% 5% 4 4 3 6% 8% 42%	1680
	11th to 20th	Night	14% 6% 2 6% 5% 5% 5% 4 6% 9% 40%	1680
	21st to end	Night	11% 4 2 7% 5% 4 5% 4 7% 8% 42%	1680
July	1st to 10th	Night	13% 7% 3 8% 5% 4 5% 4 6% 9% 37%	4680
	11th to 20th	Night	13% 8% 3 7% 4 4 5% 4 7% 9% 36%	4680
	21st to end	Night	15% 6% 2 6% 4 4 4 4 6% 8% 42%	5084
August	1st to 10th	Night	20% 7% 3 7% 5% 4 5% 4 5% 8% 32%	3961
	11th to 20th	Night	13% 6% 2 7% 4 5% 4 4 7% 8% 39%	4557
	21st to end	Night	12% 5% 2 5% 4 4 4 3 5% 7% 48%	5045
September	1st to 10th	Night	15% 6% 3 6% 4 4 4 3 5% 7% 43%	2100
	11th to 20th	Night	13% 6% 2 5% 3 3 4 2 5% 7% 50%	2194
	21st to end	Night	19% 7% 3 6% 4 3 3 3 4 6% 42%	2310
October	1st to 10th	Night	18% 7% 2 5% 4 4 4 2 4 7% 43%	2416
	11th to 20th	Night	15% 6% 2 5% 4 3 3 3 4 6% 50%	2520
	21st to end	Night	19% 6% 2 5% 2 3 3 2 5% 6% 45%	2907
November	1st to 10th	Night	13% 5% 2 4 4 3 3 4 5% 6% 51%	2667
	11th to 20th	Night	19% 6% 2 4 3 3 3 3 4 5% 48%	2730
	21st to end	Night	15% 6% 2 5% 4 3 3 4 5% 6% 47%	2809
December	1st to 10th	Night	16% 7% 2 5% 3 3 3 3 5% 5% 48%	4720
	11th to 20th	Night	26% 7% 2 4 2 3 3 3 3 4 43%	5348
	21st to end	Night	19% 9% 3 6% 4 3 4 3 5% 5% 40%	7150

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	30% 21% 6% 26% 15% 2	4662
	11th to 20th	Day	33% 21% 7% 19% 15% 6%	4680
	21st to end	Day	36% 22% 8% 20% 13% 1	5541
February	1st to 10th	Day	19% 60% 6% 10% 4 1	1904
	11th to 20th	Day	19% 57% 3 11% 9% 1	2057
	21st to end	Day	18% 59% 6% 10% 6% 1	1730
March	1st to 10th	Day	34% 28% 8% 12% 10% 7%	4579
	11th to 20th	Day	26% 31% 10% 23% 6% 3	4855
	21st to end	Day	33% 29% 7% 7% 19% 5%	6072
April	1st to 10th	Day	22% 59% 4 8% 6% 1	2520
	11th to 20th	Day	17% 59% 6% 9% 9% 1	2494
	21st to end	Day	19% 59% 4 10% 7% 1	2553
May	1st to 10th	Day	42% 24% 11% 13% 10%	7651
	11th to 20th	Day	37% 23% 8% 19% 12% 1	8161
	21st to end	Day	41% 23% 8% 16% 10%	9061
June	1st to 10th	Day	17% 60% 4 9% 10%	2940
	11th to 20th	Day	18% 59% 4 10% 8%	2940
	21st to end	Day	16% 59% 6% 9% 9% 1	2940
July	1st to 10th	Day	37% 23% 10% 16% 14%	8210
	11th to 20th	Day	34% 20% 14% 22% 10%	8205
	21st to end	Day	36% 20% 8% 19% 16% 1	8795
August	1st to 10th	Day	40% 27% 13% 13% 6%	6125
	11th to 20th	Day	28% 25% 13% 28% 6%	5524
	21st to end	Day	29% 26% 8% 23% 13% 2	6080
September	1st to 10th	Day	17% 55% 6% 12% 9% 1	2520
	11th to 20th	Day	18% 55% 4 11% 11% 1	2425
	21st to end	Day	26% 55% 5% 8% 6% 1	2310
October	1st to 10th	Day	24% 34% 6% 12% 18% 6%	3512
	11th to 20th	Day	15% 34% 6% 15% 26% 4	3340
	21st to end	Day	14% 34% 10% 18% 20% 3	3333
November	1st to 10th	Day	18% 53% 6% 10% 10% 2	1851
	11th to 20th	Day	16% 54% 3 12% 13% 2	1890
	21st to end	Day	18% 54% 7% 14% 5% 2	1806
December	1st to 10th	Day	26% 34% 10% 20% 8% 1	2680
	11th to 20th	Day	30% 30% 8% 17% 13% 2	3066
	21st to end	Day	35% 29% 4 17% 13% 2	4048
January	1st to 10th	Night	33% 21% 9% 19% 16% 3	8234
	11th to 20th	Night	34% 21% 9% 16% 15% 6%	8280
	21st to end	Night	35% 22% 6% 16% 17% 4	8622
February	1st to 10th	Night	18% 59% 5% 12% 5% 1	2714
	11th to 20th	Night	20% 57% 3 9% 9% 2	2460
	21st to end	Night	19% 59% 3 9% 7% 2	2076
March	1st to 10th	Night	34% 29% 6% 13% 10% 7%	5494
	11th to 20th	Night	28% 30% 12% 19% 9% 3	5310
	21st to end	Night	37% 29% 4 9% 19% 3	5101
April	1st to 10th	Night	21% 59% 4 8% 6% 2	2100
	11th to 20th	Night	16% 60% 5% 9% 8% 1	2075
	21st to end	Night	19% 59% 3 10% 8% 1	2064
May	1st to 10th	Night	44% 24% 9% 14% 10% 1	5265
	11th to 20th	Night	40% 23% 11% 17% 9% 1	4759
	21st to end	Night	45% 22% 7% 17% 7% 1	5115
June	1st to 10th	Night	17% 59% 3 11% 10% 1	1680
	11th to 20th	Night	18% 59% 5% 11% 6% 1	1680
	21st to end	Night	16% 58% 5% 12% 7% 1	1680
July	1st to 10th	Night	38% 22% 9% 17% 12% 1	4640
	11th to 20th	Night	38% 20% 11% 20% 10%	4632
	21st to end	Night	34% 20% 11% 20% 15% 1	4967
August	1st to 10th	Night	43% 27% 10% 13% 7% 1	3951
	11th to 20th	Night	32% 26% 12% 24% 5%	4587
	21st to end	Night	27% 25% 9% 26% 13% 1	5045
September	1st to 10th	Night	18% 55% 5% 13% 8% 1	2100
	11th to 20th	Night	17% 55% 6% 8% 12% 2	2194
	21st to end	Night	25% 54% 5% 8% 7% 1	2310
October	1st to 10th	Night	25% 34% 7% 16% 16% 2	3884
	11th to 20th	Night	12% 35% 6% 19% 25% 3	4019
	21st to end	Night	17% 34% 8% 22% 17% 2	4632
November	1st to 10th	Night	17% 54% 6% 11% 10% 2	2667
	11th to 20th	Night	16% 54% 3 10% 13% 3	2730
	21st to end	Night	16% 55% 6% 14% 8% 1	2809
December	1st to 10th	Night	26% 35% 7% 23% 8% 1	4720
	11th to 20th	Night	33% 30% 6% 15% 12% 3	5348
	21st to end	Night	35% 28% 7% 13% 13% 4	7150

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	23% 25% 33% 15% 4	220
	11th to 20th	Day	27% 26% 35% 10% 1	220
	21st to end	Day	19% 23% 40% 12% 4 2	319
February	1st to 10th	Day	26% 15% 40% 16% 2	344
	11th to 20th	Day	25% 19% 38% 17% 2	536
	21st to end	Day	24% 18% 37% 18% 3	446
March	1st to 10th	Day	23% 21% 33% 19% 4	540
	11th to 20th	Day	21% 19% 37% 18% 4 1	540
	21st to end	Day	26% 22% 29% 16% 5% 1	594
April	1st to 10th	Day	26% 20% 31% 15% 6% 1	540
	11th to 20th	Day	22% 18% 34% 17% 8% 1	532
	21st to end	Day	26% 15% 33% 18% 6% 1	540
May	1st to 10th	Day	31% 14% 30% 16% 7% 2	543
	11th to 20th	Day	21% 13% 33% 23% 10% 2	567
	21st to end	Day	23% 10% 24% 25% 14% 3	617
June	1st to 10th	Day	17% 10% 27% 30% 13% 4	570
	11th to 20th	Day	19% 11% 28% 30% 10% 2	570
	21st to end	Day	16% 8% 29% 26% 17% 3	570
July	1st to 10th	Day	14% 3 24% 36% 17% 5%	565
	11th to 20th	Day	12% 4 25% 33% 22% 4	564
	21st to end	Day	14% 6% 24% 36% 18% 2	620
August	1st to 10th	Day	13% 5% 22% 35% 17% 8%	566
	11th to 20th	Day	14% 4 23% 34% 19% 5%	559
	21st to end	Day	12% 7% 27% 31% 15% 7%	627
September	1st to 10th	Day	18% 6% 29% 22% 17% 6%	570
	11th to 20th	Day	15% 5% 28% 27% 15% 10%	570
	21st to end	Day	22% 9% 28% 25% 12% 4	570
October	1st to 10th	Day	24% 9% 26% 21% 15% 5%	570
	11th to 20th	Day	20% 14% 29% 23% 12% 2	570
	21st to end	Day	22% 13% 32% 22% 10% 2	517
November	1st to 10th	Day	18% 14% 31% 25% 10% 2	425
	11th to 20th	Day	21% 17% 34% 21% 5% 1	430
	21st to end	Day	21% 21% 31% 22% 5% 1	346
December	1st to 10th	Day	25% 20% 33% 17% 4 1	220
	11th to 20th	Day	30% 21% 33% 13% 3	220
	21st to end	Day	29% 14% 35% 14% 7%	242
January	1st to 10th	Night	20% 15% 42% 20% 3	840
	11th to 20th	Night	24% 16% 34% 23% 3	840
	21st to end	Night	19% 15% 41% 22% 2	924
February	1st to 10th	Night	23% 12% 38% 25% 2	840
	11th to 20th	Night	23% 16% 39% 21% 1	823
	21st to end	Night	24% 14% 37% 22% 4	692
March	1st to 10th	Night	23% 15% 36% 22% 5%	840
	11th to 20th	Night	23% 13% 38% 21% 4 1	840
	21st to end	Night	23% 15% 36% 21% 4	924
April	1st to 10th	Night	23% 16% 35% 22% 5%	840
	11th to 20th	Night	22% 13% 34% 25% 6%	831
	21st to end	Night	22% 11% 34% 27% 6%	804
May	1st to 10th	Night	24% 11% 34% 24% 7% 1	630
	11th to 20th	Night	21% 11% 32% 28% 8%	457
	21st to end	Night	22% 5% 18% 39% 13% 1	455
June	1st to 10th	Night	18% 5% 27% 36% 13% 1	420
	11th to 20th	Night	16% 5% 27% 37% 15%	420
	21st to end	Night	11% 3 24% 48% 13% 1	420
July	1st to 10th	Night	12% 2 23% 43% 19%	410
	11th to 20th	Night	13% 3 19% 43% 20% 1	408
	21st to end	Night	14% 5% 18% 46% 17% 1	460
August	1st to 10th	Night	15% 1 18% 44% 20% 2	544
	11th to 20th	Night	15% 4 17% 37% 24% 2	830
	21st to end	Night	15% 4 19% 38% 22% 2	924
September	1st to 10th	Night	17% 4 24% 34% 18% 2	840
	11th to 20th	Night	16% 4 23% 34% 19% 4	840
	21st to end	Night	22% 5% 23% 32% 16% 2	840
October	1st to 10th	Night	22% 9% 27% 24% 15% 3	840
	11th to 20th	Night	18% 11% 29% 31% 11% 1	840
	21st to end	Night	23% 11% 33% 24% 8%	913
November	1st to 10th	Night	16% 10% 34% 27% 11% 1	820
	11th to 20th	Night	22% 14% 32% 24% 7%	840
	21st to end	Night	19% 15% 34% 25% 7% 1	840
December	1st to 10th	Night	24% 14% 35% 20% 5% 1	840
	11th to 20th	Night	24% 14% 34% 24% 3	840
	21st to end	Night	25% 12% 35% 24% 3	924

Page generated at 2026-10-26 04:37:51. Version ac07

Copyright © 2026 Attilla Danko.