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 2024-11-03.

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% 39%	101294
	Night	18% 7% 2 6% 4 4 4 3 5% 6% 41%	97691
Transparency	Day	24% 49% 6% 12% 8% 1	101049
	Night	24% 49% 6% 12% 8% 1	97556
Seeing	Day	20% 12% 30% 24% 12% 3	14991
	Night	20% 10% 31% 28% 10% 1	24108

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% 7% 3 5% 4 3 4 3 5% 5% 48%	2517
	11th to 20th	Day	15% 10% 3 7% 5% 5% 5% 3 5% 6% 36%	2520
	21st to end	Day	22% 11% 4 7% 4 4 4 3 4 5% 33%	2996
February	1st to 10th	Day	18% 7% 2 6% 5% 3 5% 3 4 6% 40%	1722
	11th to 20th	Day	15% 7% 3 6% 4 4 4 3 4 5% 45%	1848
	21st to end	Day	20% 7% 2 6% 4 3 4 4 5% 5% 39%	1570
March	1st to 10th	Day	26% 9% 2 6% 4 3 3 3 4 4 36%	3116
	11th to 20th	Day	9% 5% 2 6% 5% 6% 5% 5% 6% 8% 43%	3320
	21st to end	Day	20% 7% 2 5% 3 3 3 3 4 6% 43%	4151
April	1st to 10th	Day	19% 7% 2 6% 4 4 3 4 5% 6% 39%	2280
	11th to 20th	Day	17% 6% 2 6% 4 4 4 3 5% 7% 41%	2254
	21st to end	Day	20% 5% 2 5% 4 4 4 3 5% 8% 40%	2309
May	1st to 10th	Day	28% 9% 2 5% 4 3 4 3 5% 7% 30%	4106
	11th to 20th	Day	23% 8% 3 7% 5% 4 4 4 5% 6% 31%	4361
	21st to end	Day	14% 5% 2 5% 3 4 4 5% 5% 8% 44%	4837
June	1st to 10th	Day	16% 6% 2 5% 4 4 5% 4 8% 9% 37%	2660
	11th to 20th	Day	15% 7% 2 6% 4 5% 5% 5% 6% 8% 37%	2660
	21st to end	Day	12% 6% 2 6% 5% 5% 5% 4 7% 9% 39%	2660
July	1st to 10th	Day	9% 5% 2 7% 6% 5% 6% 5% 7% 10% 36%	4440
	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% 6% 2 5% 3 4 2 3 5% 5% 51%	1689
	11th to 20th	Day	19% 6% 2 4 3 3 3 2 5% 6% 47%	1710
	21st to end	Day	15% 7% 2 5% 4 3 4 3 5% 7% 45%	1634
December	1st to 10th	Day	19% 8% 2 6% 5% 3 3 3 5% 7% 39%	1520
	11th to 20th	Day	23% 6% 2 4 2 2 3 3 4 6% 44%	1906
	21st to end	Day	18% 9% 3 9% 5% 5% 5% 4 6% 7% 31%	2772
January	1st to 10th	Night	17% 6% 2 5% 3 3 3 3 4 5% 47%	4429
	11th to 20th	Night	17% 8% 3 6% 3 4 4 3 4 5% 42%	4440
	21st to end	Night	25% 10% 3 5% 3 3 3 3 5% 5% 34%	4656
February	1st to 10th	Night	17% 9% 2 5% 5% 3 4 3 4 5% 42%	2456
	11th to 20th	Night	17% 8% 3 5% 5% 4 4 3 4 6% 41%	2218
	21st to end	Night	20% 7% 2 5% 5% 4 3 3 5% 5% 41%	1884
March	1st to 10th	Night	24% 10% 2 5% 3 4 3 3 4 5% 36%	3724
	11th to 20th	Night	12% 7% 2 6% 4 4 4 3 5% 6% 46%	3624
	21st to end	Night	20% 9% 3 5% 3 3 4 3 4 5% 41%	3480
April	1st to 10th	Night	19% 7% 3 6% 4 4 3 3 6% 6% 38%	1900
	11th to 20th	Night	19% 7% 2 5% 4 3 5% 3 5% 6% 40%	1875
	21st to end	Night	20% 6% 2 5% 3 4 3 4 4 6% 42%	1868
May	1st to 10th	Night	25% 10% 3 7% 4 4 3 3 4 7% 29%	2834
	11th to 20th	Night	24% 10% 3 7% 5% 3 4 3 4 6% 33%	2560
	21st to end	Night	17% 7% 2 5% 4 3 3 3 6% 9% 41%	2738
June	1st to 10th	Night	17% 6% 2 5% 5% 4 4 3 6% 8% 41%	1520
	11th to 20th	Night	13% 6% 2 6% 5% 4 5% 3 6% 9% 42%	1520
	21st to end	Night	11% 4 2 6% 5% 4 5% 4 7% 9% 43%	1520
July	1st to 10th	Night	10% 6% 3 8% 6% 5% 6% 4 7% 9% 37%	2520
	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	14% 5% 2 5% 4 3 3 4 5% 5% 51%	2434
	11th to 20th	Night	20% 6% 2 4 3 3 3 3 4 5% 48%	2470
	21st to end	Night	15% 6% 2 5% 4 3 4 4 5% 6% 47%	2541
December	1st to 10th	Night	20% 7% 3 5% 4 3 4 3 5% 6% 40%	2660
	11th to 20th	Night	20% 7% 2 5% 3 4 4 3 4 6% 42%	3288
	21st to end	Night	20% 10% 3 6% 5% 4 4 3 5% 5% 36%	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	23% 37% 6% 22% 8% 3	2518
	11th to 20th	Day	30% 38% 7% 17% 7% 1	2520
	21st to end	Day	39% 41% 4 11% 4 1	2996
February	1st to 10th	Day	17% 66% 6% 7% 3 1	1722
	11th to 20th	Day	16% 63% 2 9% 9% 1	1857
	21st to end	Day	16% 65% 5% 8% 4 1	1570
March	1st to 10th	Day	34% 41% 7% 12% 4 1	3119
	11th to 20th	Day	15% 46% 9% 22% 7% 1	3320
	21st to end	Day	26% 41% 5% 8% 16% 4	4151
April	1st to 10th	Day	18% 65% 4 6% 5% 1	2280
	11th to 20th	Day	14% 66% 5% 8% 7%	2254
	21st to end	Day	16% 65% 3 9% 6% 1	2309
May	1st to 10th	Day	34% 43% 10% 7% 5%	4120
	11th to 20th	Day	33% 43% 10% 11% 3	4365
	21st to end	Day	20% 43% 7% 17% 12% 1	4837
June	1st to 10th	Day	15% 66% 4 8% 7%	2660
	11th to 20th	Day	15% 65% 4 9% 7%	2660
	21st to end	Day	13% 65% 5% 9% 8%	2660
July	1st to 10th	Day	28% 39% 8% 13% 11% 1	4370
	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	18% 60% 5% 8% 7% 3	1990
	11th to 20th	Day	13% 60% 5% 10% 12% 1	1900
	21st to end	Day	16% 59% 4 11% 9% 1	1932
November	1st to 10th	Day	18% 58% 5% 9% 8% 1	1689
	11th to 20th	Day	14% 59% 3 10% 12% 2	1710
	21st to end	Day	14% 60% 7% 13% 5% 2	1634
December	1st to 10th	Day	20% 60% 7% 6% 6%	1520
	11th to 20th	Day	22% 48% 6% 14% 8% 2	1906
	21st to end	Day	34% 41% 5% 15% 5%	2772
January	1st to 10th	Night	25% 37% 7% 21% 7% 4	4429
	11th to 20th	Night	27% 38% 8% 17% 9% 1	4440
	21st to end	Night	37% 41% 4 11% 5% 1	4656
February	1st to 10th	Night	16% 65% 5% 11% 3 1	2456
	11th to 20th	Night	16% 64% 3 7% 9% 2	2220
	21st to end	Night	16% 65% 3 8% 6% 2	1884
March	1st to 10th	Night	36% 42% 5% 10% 6% 1	3734
	11th to 20th	Night	17% 43% 11% 17% 11% 1	3625
	21st to end	Night	29% 41% 4 7% 15% 4	3480
April	1st to 10th	Night	17% 65% 4 8% 5% 1	1900
	11th to 20th	Night	13% 66% 4 9% 7%	1875
	21st to end	Night	16% 65% 3 9% 6% 1	1868
May	1st to 10th	Night	35% 44% 7% 10% 4	2840
	11th to 20th	Night	36% 42% 11% 8% 3	2561
	21st to end	Night	25% 42% 8% 16% 8% 1	2739
June	1st to 10th	Night	15% 65% 3 8% 8% 1	1520
	11th to 20th	Night	14% 65% 5% 11% 5%	1520
	21st to end	Night	13% 64% 4 11% 7% 1	1520
July	1st to 10th	Night	29% 39% 10% 12% 10% 1	2480
	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	19% 60% 5% 8% 6% 2	2186
	11th to 20th	Night	11% 60% 6% 13% 9% 1	2280
	21st to end	Night	17% 59% 4 11% 8% 1	2665
November	1st to 10th	Night	17% 59% 5% 9% 8% 1	2434
	11th to 20th	Night	15% 60% 3 10% 10% 3	2470
	21st to end	Night	13% 60% 6% 13% 6% 1	2541
December	1st to 10th	Night	20% 61% 5% 9% 5%	2660
	11th to 20th	Night	22% 49% 6% 9% 11% 3	3288
	21st to end	Night	31% 40% 8% 14% 6%	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	21% 25% 32% 17% 4 1	180
	11th to 20th	Day	24% 24% 37% 12% 2 1	180
	21st to end	Day	19% 19% 41% 13% 5% 2	261
February	1st to 10th	Day	27% 16% 38% 17% 2	282
	11th to 20th	Day	23% 19% 38% 18% 2	456
	21st to end	Day	25% 18% 34% 19% 4	382
March	1st to 10th	Day	20% 21% 33% 21% 4	460
	11th to 20th	Day	18% 20% 37% 19% 5% 1	460
	21st to end	Day	25% 20% 31% 18% 5% 1	506
April	1st to 10th	Day	24% 19% 32% 17% 7% 1	460
	11th to 20th	Day	21% 16% 34% 18% 9% 2	452
	21st to end	Day	25% 15% 34% 18% 7% 1	460
May	1st to 10th	Day	30% 13% 29% 18% 7% 2	463
	11th to 20th	Day	21% 10% 33% 23% 11% 2	487
	21st to end	Day	18% 9% 24% 29% 16% 4	529
June	1st to 10th	Day	17% 9% 27% 29% 15% 4	490
	11th to 20th	Day	16% 10% 28% 32% 12% 2	490
	21st to end	Day	16% 8% 29% 26% 18% 3	490
July	1st to 10th	Day	14% 3 24% 35% 19% 6%	485
	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% 31% 22% 9% 2	455
November	1st to 10th	Day	16% 14% 29% 27% 11% 3	371
	11th to 20th	Day	21% 16% 34% 22% 6% 1	370
	21st to end	Day	17% 19% 33% 25% 5% 1	294
December	1st to 10th	Day	22% 22% 33% 17% 4 2	180
	11th to 20th	Day	28% 21% 36% 12% 3	180
	21st to end	Day	28% 14% 36% 14% 8% 1	198
January	1st to 10th	Night	20% 14% 43% 20% 4	760
	11th to 20th	Night	23% 16% 34% 23% 4	760
	21st to end	Night	20% 15% 40% 22% 2	836
February	1st to 10th	Night	23% 12% 37% 26% 2	760
	11th to 20th	Night	22% 17% 40% 20% 1	743
	21st to end	Night	25% 15% 35% 21% 4	628
March	1st to 10th	Night	23% 15% 36% 22% 5%	760
	11th to 20th	Night	22% 14% 38% 21% 4 1	760
	21st to end	Night	22% 15% 36% 22% 5%	836
April	1st to 10th	Night	21% 15% 35% 23% 5%	760
	11th to 20th	Night	21% 13% 33% 26% 6%	751
	21st to end	Night	22% 11% 33% 27% 6% 1	728
May	1st to 10th	Night	24% 11% 33% 25% 7% 1	570
	11th to 20th	Night	21% 11% 33% 28% 8%	413
	21st to end	Night	20% 6% 18% 41% 14% 1	411
June	1st to 10th	Night	19% 5% 26% 35% 13% 1	380
	11th to 20th	Night	14% 4 26% 39% 17%	380
	21st to end	Night	10% 3 24% 49% 13% 1	380
July	1st to 10th	Night	11% 3 23% 43% 20%	370
	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	16% 10% 35% 26% 12% 1	749
	11th to 20th	Night	23% 13% 32% 24% 8% 1	760
	21st to end	Night	19% 13% 35% 25% 7% 1	760
December	1st to 10th	Night	24% 14% 36% 20% 5% 1	760
	11th to 20th	Night	23% 14% 35% 24% 4	760
	21st to end	Night	25% 13% 36% 24% 3	836

Page generated at 2024-10-31 03:39:21. Version ac07

Copyright © 2024 Attilla Danko.