Great Neck South High Big Blue Rebel Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Great Neck South High Big Blue Rebel Observatory clear sky chart from 2005-11-06 to 2025-02-25.

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 5% 7% 41%	108487
	Night	17% 7% 2 6% 4 4 4 3 5% 6% 42%	110156
Transparency	Day	40% 7% 13% 22% 16% 2	112062
	Night	41% 6% 11% 22% 17% 3	114732
Seeing	Day	18% 12% 31% 26% 11% 2	15330
	Night	19% 11% 31% 28% 10% 1	24590

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	14% 6% 2 4 3 3 3 3 4 6% 51%	3597
	11th to 20th	Day	14% 8% 2 6% 4 4 4 3 4 6% 43%	3570
	21st to end	Day	17% 10% 4 8% 4 4 3 3 4 5% 39%	4259
February	1st to 10th	Day	17% 8% 2 7% 4 4 4 3 5% 6% 40%	1835
	11th to 20th	Day	15% 7% 3 6% 4 4 4 3 4 6% 44%	1948
	21st to end	Day	20% 7% 2 5% 4 4 4 3 5% 6% 39%	1610
March	1st to 10th	Day	27% 9% 2 6% 3 3 3 3 4 5% 36%	3116
	11th to 20th	Day	9% 5% 2 6% 5% 5% 5% 4 7% 8% 44%	3288
	21st to end	Day	20% 7% 2 6% 4 3 3 3 5% 6% 43%	4161
April	1st to 10th	Day	18% 8% 3 6% 3 3 4 3 5% 8% 39%	2280
	11th to 20th	Day	17% 6% 2 6% 4 4 4 3 5% 8% 41%	2254
	21st to end	Day	19% 6% 1 5% 4 5% 4 3 6% 7% 40%	2322
May	1st to 10th	Day	27% 9% 3 5% 3 3 3 3 5% 8% 31%	4106
	11th to 20th	Day	23% 8% 2 7% 4 4 4 4 6% 7% 30%	4320
	21st to end	Day	15% 5% 2 5% 4 3 4 3 5% 9% 45%	4837
June	1st to 10th	Day	16% 6% 2 5% 4 4 4 4 7% 9% 38%	2660
	11th to 20th	Day	14% 7% 2 6% 4 4 5% 4 6% 8% 39%	2660
	21st to end	Day	10% 6% 2 7% 4 4 5% 4 7% 9% 41%	2660
July	1st to 10th	Day	9% 6% 2 7% 5% 6% 7% 5% 7% 10% 37%	4440
	11th to 20th	Day	11% 6% 2 5% 5% 4 5% 5% 7% 10% 39%	4440
	21st to end	Day	14% 8% 3 7% 5% 5% 6% 4 7% 8% 33%	4814
August	1st to 10th	Day	19% 6% 2 6% 4 4 5% 5% 7% 8% 33%	4163
	11th to 20th	Day	12% 6% 2 6% 4 4 5% 4 7% 8% 41%	3730
	21st to end	Day	9% 4 2 5% 4 4 4 4 6% 9% 47%	4180
September	1st to 10th	Day	13% 5% 2 5% 3 4 5% 4 5% 7% 46%	2280
	11th to 20th	Day	12% 5% 2 5% 3 4 4 3 5% 7% 50%	2180
	21st to end	Day	19% 6% 2 6% 4 3 4 4 5% 6% 40%	2090
October	1st to 10th	Day	19% 7% 2 6% 3 4 4 3 5% 6% 41%	2010
	11th to 20th	Day	15% 5% 2 6% 4 4 4 3 5% 6% 47%	1900
	21st to end	Day	20% 5% 2 6% 3 4 4 3 4 6% 43%	1920
November	1st to 10th	Day	13% 6% 2 6% 4 2 3 3 5% 5% 52%	1761
	11th to 20th	Day	16% 6% 2 4 3 3 3 3 4 6% 48%	1800
	21st to end	Day	15% 7% 2 5% 3 4 4 4 5% 7% 45%	1750
December	1st to 10th	Day	16% 7% 2 5% 4 3 3 3 5% 7% 45%	2600
	11th to 20th	Day	22% 8% 2 4 3 2 3 2 3 6% 46%	2986
	21st to end	Day	17% 9% 2 6% 4 4 4 3 5% 6% 39%	3960
January	1st to 10th	Night	14% 6% 2 5% 3 3 3 3 5% 6% 50%	6349
	11th to 20th	Night	14% 8% 2 6% 3 3 4 3 4 5% 47%	6315
	21st to end	Night	18% 9% 3 6% 4 4 4 4 5% 6% 39%	6692
February	1st to 10th	Night	18% 8% 2 6% 4 4 4 3 4 6% 41%	2563
	11th to 20th	Night	18% 8% 3 6% 4 4 3 3 5% 5% 41%	2338
	21st to end	Night	20% 8% 2 5% 4 4 4 3 5% 6% 42%	1939
March	1st to 10th	Night	23% 11% 3 6% 4 3 3 2 4 6% 36%	3724
	11th to 20th	Night	11% 6% 2 7% 4 5% 4 4 5% 7% 45%	3653
	21st to end	Night	21% 9% 2 6% 4 3 3 2 5% 5% 41%	3470
April	1st to 10th	Night	19% 7% 3 6% 4 4 5% 4 5% 7% 37%	1900
	11th to 20th	Night	19% 8% 2 5% 3 4 5% 4 4 6% 39%	1875
	21st to end	Night	18% 7% 3 6% 4 3 4 4 5% 6% 42%	1857
May	1st to 10th	Night	23% 10% 4 8% 5% 3 4 2 5% 6% 30%	2834
	11th to 20th	Night	25% 10% 2 7% 4 4 3 3 4 5% 33%	2601
	21st to end	Night	17% 8% 2 5% 3 4 4 3 5% 8% 41%	2738
June	1st to 10th	Night	18% 7% 2 4 4 4 4 4 5% 8% 41%	1520
	11th to 20th	Night	13% 7% 2 6% 4 4 4 4 6% 10% 40%	1520
	21st to end	Night	10% 5% 2 6% 4 5% 5% 4 8% 11% 40%	1520
July	1st to 10th	Night	10% 7% 4 8% 6% 6% 6% 6% 6% 9% 34%	2520
	11th to 20th	Night	13% 7% 2 6% 5% 5% 5% 5% 7% 8% 36%	2520
	21st to end	Night	18% 8% 3 6% 4 3 4 4 6% 7% 36%	2739
August	1st to 10th	Night	23% 7% 2 6% 5% 4 4 4 6% 7% 32%	2717
	11th to 20th	Night	14% 8% 2 7% 4 5% 5% 4 6% 7% 38%	3097
	21st to end	Night	8% 6% 2 5% 3 4 5% 3 6% 7% 52%	3476
September	1st to 10th	Night	14% 5% 2 7% 4 5% 5% 4 5% 6% 44%	1900
	11th to 20th	Night	12% 6% 2 6% 3 3 3 3 5% 6% 52%	1998
	21st to end	Night	17% 6% 2 7% 4 4 4 3 5% 7% 42%	2090
October	1st to 10th	Night	19% 7% 3 6% 5% 3 4 3 4 6% 42%	2166
	11th to 20th	Night	14% 5% 2 5% 4 3 3 3 3 6% 51%	2280
	21st to end	Night	21% 7% 3 5% 4 3 3 3 4 6% 43%	2676
November	1st to 10th	Night	12% 5% 2 6% 4 4 3 3 4 6% 51%	2537
	11th to 20th	Night	19% 6% 2 4 3 3 3 2 4 5% 48%	2600
	21st to end	Night	15% 6% 2 5% 4 4 3 4 5% 6% 46%	2648
December	1st to 10th	Night	17% 7% 2 4 3 3 4 3 4 5% 48%	4580
	11th to 20th	Night	25% 7% 2 4 3 3 3 3 4 4 43%	5208
	21st to end	Night	19% 8% 3 6% 4 3 4 3 5% 5% 41%	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	33% 4 8% 33% 20% 2	3598
	11th to 20th	Day	40% 5% 11% 23% 17% 5%	3600
	21st to end	Day	48% 5% 9% 23% 13% 1	4259
February	1st to 10th	Day	45% 5% 14% 23% 13% 1	1835
	11th to 20th	Day	42% 5% 9% 25% 16% 2	1957
	21st to end	Day	45% 5% 12% 21% 14% 3	1610
March	1st to 10th	Day	48% 6% 12% 23% 9% 2	3119
	11th to 20th	Day	30% 9% 16% 31% 13% 1	3288
	21st to end	Day	43% 5% 8% 17% 22% 5%	4161
April	1st to 10th	Day	43% 6% 11% 20% 16% 4	2280
	11th to 20th	Day	41% 5% 13% 22% 16% 3	2254
	21st to end	Day	41% 7% 11% 20% 16% 4	2322
May	1st to 10th	Day	52% 9% 13% 14% 11% 1	4120
	11th to 20th	Day	49% 9% 14% 18% 8% 1	4324
	21st to end	Day	34% 9% 15% 24% 17% 2	4837
June	1st to 10th	Day	40% 9% 14% 21% 15% 2	2660
	11th to 20th	Day	40% 9% 14% 24% 12% 2	2660
	21st to end	Day	36% 10% 16% 22% 16% 1	2660
July	1st to 10th	Day	41% 11% 13% 20% 15% 1	4370
	11th to 20th	Day	38% 9% 17% 22% 13% 1	4365
	21st to end	Day	46% 9% 13% 16% 15% 1	4661
August	1st to 10th	Day	45% 9% 16% 22% 8%	4149
	11th to 20th	Day	37% 8% 14% 30% 10% 1	3766
	21st to end	Day	31% 8% 12% 28% 19% 2	4180
September	1st to 10th	Day	37% 7% 13% 21% 19% 2	2280
	11th to 20th	Day	32% 7% 12% 24% 24% 2	2180
	21st to end	Day	44% 7% 10% 18% 19% 3	2090
October	1st to 10th	Day	36% 7% 11% 18% 23% 5%	3335
	11th to 20th	Day	25% 5% 11% 22% 32% 5%	3140
	21st to end	Day	28% 4 15% 25% 25% 3	3145
November	1st to 10th	Day	34% 5% 13% 23% 22% 3	1761
	11th to 20th	Day	38% 4 10% 22% 22% 3	1800
	21st to end	Day	39% 5% 15% 29% 11% 2	1750
December	1st to 10th	Day	39% 4 16% 27% 13% 1	2600
	11th to 20th	Day	42% 3 12% 23% 17% 2	2986
	21st to end	Day	44% 7% 9% 22% 16% 2	3960
January	1st to 10th	Night	34% 5% 9% 25% 23% 4	6349
	11th to 20th	Night	39% 4 13% 22% 17% 5%	6360
	21st to end	Night	46% 5% 9% 20% 17% 4	6692
February	1st to 10th	Night	44% 5% 13% 23% 12% 2	2563
	11th to 20th	Night	45% 5% 9% 20% 17% 5%	2340
	21st to end	Night	43% 5% 9% 24% 17% 3	1939
March	1st to 10th	Night	50% 5% 11% 21% 11% 3	3734
	11th to 20th	Night	36% 7% 14% 25% 14% 3	3654
	21st to end	Night	46% 5% 7% 15% 22% 6%	3470
April	1st to 10th	Night	45% 7% 10% 19% 16% 4	1900
	11th to 20th	Night	44% 7% 10% 18% 20% 1	1875
	21st to end	Night	42% 7% 9% 20% 18% 4	1857
May	1st to 10th	Night	55% 7% 11% 16% 10% 1	2840
	11th to 20th	Night	53% 8% 14% 14% 10% 1	2602
	21st to end	Night	40% 8% 14% 22% 13% 2	2739
June	1st to 10th	Night	42% 7% 9% 21% 20% 1	1520
	11th to 20th	Night	38% 9% 14% 27% 11% 1	1520
	21st to end	Night	37% 10% 15% 24% 14% 1	1520
July	1st to 10th	Night	46% 10% 13% 18% 12% 1	2480
	11th to 20th	Night	42% 9% 14% 24% 10% 1	2472
	21st to end	Night	45% 7% 15% 14% 17% 2	2651
August	1st to 10th	Night	51% 7% 17% 16% 9% 1	2707
	11th to 20th	Night	41% 9% 13% 27% 10% 1	3127
	21st to end	Night	30% 7% 13% 32% 18% 1	3476
September	1st to 10th	Night	39% 9% 11% 21% 19% 1	1900
	11th to 20th	Night	33% 6% 12% 24% 22% 3	1998
	21st to end	Night	42% 7% 9% 20% 20% 2	2090
October	1st to 10th	Night	38% 6% 12% 22% 19% 3	3608
	11th to 20th	Night	23% 4 10% 28% 31% 4	3779
	21st to end	Night	30% 5% 12% 29% 22% 2	4401
November	1st to 10th	Night	35% 5% 12% 22% 21% 4	2537
	11th to 20th	Night	39% 5% 8% 23% 21% 4	2600
	21st to end	Night	37% 6% 13% 28% 15% 1	2648
December	1st to 10th	Night	39% 4 12% 29% 13% 2	4580
	11th to 20th	Night	46% 4 10% 23% 15% 3	5208
	21st to end	Night	44% 5% 11% 20% 16% 3	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	24% 26% 29% 18% 4 1	200
	11th to 20th	Day	18% 31% 35% 14% 3	200
	21st to end	Day	19% 19% 41% 13% 5% 1	285
February	1st to 10th	Day	24% 18% 39% 16% 3	335
	11th to 20th	Day	25% 19% 36% 18% 2	496
	21st to end	Day	23% 19% 36% 17% 4	398
March	1st to 10th	Day	18% 21% 35% 20% 5%	460
	11th to 20th	Day	16% 18% 42% 18% 6% 1	460
	21st to end	Day	23% 18% 35% 18% 6% 1	506
April	1st to 10th	Day	22% 18% 36% 16% 7% 1	460
	11th to 20th	Day	21% 15% 33% 21% 9% 1	452
	21st to end	Day	25% 14% 34% 20% 6% 1	460
May	1st to 10th	Day	29% 13% 30% 19% 7% 1	463
	11th to 20th	Day	21% 9% 33% 29% 8% 1	487
	21st to end	Day	18% 4 26% 30% 18% 3	529
June	1st to 10th	Day	16% 8% 29% 30% 14% 2	490
	11th to 20th	Day	13% 9% 30% 34% 12% 2	490
	21st to end	Day	14% 6% 31% 30% 17% 2	490
July	1st to 10th	Day	13% 3 23% 37% 20% 5%	485
	11th to 20th	Day	9% 4 24% 36% 24% 4	484
	21st to end	Day	13% 5% 25% 37% 18% 2	532
August	1st to 10th	Day	13% 3 23% 36% 19% 6%	486
	11th to 20th	Day	14% 5% 18% 37% 23% 3	479
	21st to end	Day	11% 5% 25% 36% 16% 7%	539
September	1st to 10th	Day	18% 5% 27% 26% 19% 5%	490
	11th to 20th	Day	14% 4 26% 30% 16% 10%	490
	21st to end	Day	22% 9% 26% 26% 13% 4	490
October	1st to 10th	Day	23% 10% 24% 24% 15% 5%	490
	11th to 20th	Day	17% 12% 30% 27% 12% 2	490
	21st to end	Day	20% 11% 36% 22% 10% 2	449
November	1st to 10th	Day	14% 13% 32% 27% 11% 3	395
	11th to 20th	Day	19% 18% 34% 24% 6% 1	400
	21st to end	Day	19% 15% 34% 24% 7% 1	350
December	1st to 10th	Day	21% 18% 38% 18% 7%	200
	11th to 20th	Day	28% 22% 33% 14% 4	200
	21st to end	Day	23% 17% 39% 11% 10%	220
January	1st to 10th	Night	19% 19% 40% 19% 3	800
	11th to 20th	Night	23% 18% 33% 23% 3	800
	21st to end	Night	19% 16% 42% 20% 2	880
February	1st to 10th	Night	22% 15% 38% 23% 2	800
	11th to 20th	Night	23% 17% 41% 17% 2	783
	21st to end	Night	23% 16% 37% 20% 3	647
March	1st to 10th	Night	22% 14% 38% 21% 5%	760
	11th to 20th	Night	21% 14% 39% 21% 4 1	760
	21st to end	Night	21% 12% 39% 24% 4	836
April	1st to 10th	Night	22% 14% 36% 24% 5%	760
	11th to 20th	Night	20% 11% 35% 27% 6%	751
	21st to end	Night	21% 9% 35% 29% 5% 1	717
May	1st to 10th	Night	23% 10% 32% 26% 8%	570
	11th to 20th	Night	22% 8% 34% 29% 6%	441
	21st to end	Night	20% 5% 17% 38% 18% 2	411
June	1st to 10th	Night	19% 4 26% 35% 14% 1	380
	11th to 20th	Night	13% 3 24% 44% 16%	380
	21st to end	Night	11% 4 21% 50% 14% 1	380
July	1st to 10th	Night	11% 4 21% 43% 19% 1	370
	11th to 20th	Night	14% 2 16% 45% 20% 2	368
	21st to end	Night	12% 4 21% 43% 19% 1	416
August	1st to 10th	Night	13% 3 19% 43% 21% 1	498
	11th to 20th	Night	15% 3 18% 36% 26% 2	750
	21st to end	Night	14% 4 18% 38% 24% 3	836
September	1st to 10th	Night	15% 4 24% 35% 18% 3	760
	11th to 20th	Night	15% 4 21% 34% 21% 4	760
	21st to end	Night	20% 5% 26% 31% 17% 2	760
October	1st to 10th	Night	22% 10% 25% 25% 16% 3	760
	11th to 20th	Night	17% 10% 29% 32% 12% 1	760
	21st to end	Night	23% 11% 33% 24% 9%	836
November	1st to 10th	Night	14% 10% 36% 28% 11% 1	780
	11th to 20th	Night	22% 14% 33% 24% 8%	800
	21st to end	Night	17% 16% 35% 26% 6% 1	800
December	1st to 10th	Night	25% 15% 35% 20% 5% 1	800
	11th to 20th	Night	24% 15% 34% 24% 4	800
	21st to end	Night	23% 14% 38% 22% 4	880

Page generated at 2025-02-22 06:51:35. Version ac07

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