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 2005-11-05 to 2024-10-14.

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 6% 7% 40%	101053
	Night	18% 8% 2 6% 4 4 4 3 5% 6% 41%	97481
Transparency	Day	41% 7% 13% 22% 14% 2	100809
	Night	43% 6% 12% 22% 15% 2	97350
Seeing	Day	18% 11% 30% 26% 12% 2	14961
	Night	19% 10% 31% 28% 10% 1	24054

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	16% 7% 3 5% 4 3 3 3 4 5% 48%	2517
	11th to 20th	Day	16% 9% 2 6% 4 5% 5% 3 5% 7% 37%	2520
	21st to end	Day	21% 12% 5% 7% 4 3 3 3 4 5% 32%	2973
February	1st to 10th	Day	17% 8% 3 6% 4 4 4 3 5% 6% 40%	1743
	11th to 20th	Day	15% 6% 3 6% 4 4 4 3 4 6% 45%	1848
	21st to end	Day	21% 7% 2 6% 4 4 4 4 5% 6% 38%	1570
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% 46%	1830
	21st to end	Day	21% 6% 2 6% 3 4 4 3 5% 6% 41%	1819
November	1st to 10th	Day	14% 7% 2 6% 4 2 3 3 5% 4 51%	1671
	11th to 20th	Day	17% 6% 2 4 3 3 3 3 5% 6% 47%	1710
	21st to end	Day	14% 7% 2 5% 3 4 4 4 5% 6% 45%	1663
December	1st to 10th	Day	18% 7% 2 6% 5% 3 4 3 5% 7% 39%	1520
	11th to 20th	Day	22% 7% 2 4 2 2 3 3 4 6% 45%	1906
	21st to end	Day	18% 10% 3 7% 5% 5% 5% 4 6% 6% 32%	2772
January	1st to 10th	Night	17% 7% 2 5% 3 3 3 3 5% 6% 47%	4429
	11th to 20th	Night	17% 9% 2 6% 3 3 4 3 4 5% 43%	4440
	21st to end	Night	24% 10% 3 6% 4 4 3 3 4 5% 34%	4678
February	1st to 10th	Night	17% 8% 2 6% 4 4 4 3 4 6% 41%	2435
	11th to 20th	Night	17% 8% 3 6% 4 4 3 3 5% 5% 42%	2218
	21st to end	Night	20% 8% 2 5% 4 4 3 3 5% 6% 42%	1884
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	15% 5% 2 5% 4 3 3 3 4 6% 49%	2203
	21st to end	Night	22% 7% 3 5% 4 3 3 3 4 5% 42%	2535
November	1st to 10th	Night	13% 5% 2 6% 4 4 3 3 4 5% 50%	2407
	11th to 20th	Night	20% 6% 2 4 3 3 3 2 4 5% 48%	2470
	21st to end	Night	14% 6% 2 5% 4 4 3 4 5% 6% 47%	2515
December	1st to 10th	Night	21% 7% 2 5% 4 3 4 3 5% 6% 39%	2660
	11th to 20th	Night	19% 6% 2 5% 4 3 4 3 5% 6% 43%	3288
	21st to end	Night	20% 9% 3 6% 4 4 5% 3 5% 5% 37%	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	38% 4 10% 31% 14% 3	2518
	11th to 20th	Day	44% 6% 12% 23% 13% 2	2520
	21st to end	Day	53% 7% 9% 22% 9% 2	2973
February	1st to 10th	Day	45% 5% 13% 23% 13% 1	1743
	11th to 20th	Day	41% 5% 10% 26% 16% 2	1857
	21st to end	Day	46% 5% 12% 20% 14% 3	1570
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	43% 6% 12% 20% 17% 2	2010
	11th to 20th	Day	36% 6% 13% 25% 19% 1	1831
	21st to end	Day	43% 5% 11% 22% 17% 2	1819
November	1st to 10th	Day	35% 6% 13% 23% 21% 2	1671
	11th to 20th	Day	39% 5% 10% 22% 21% 3	1710
	21st to end	Day	38% 5% 15% 29% 11% 2	1663
December	1st to 10th	Day	45% 6% 15% 19% 13% 1	1520
	11th to 20th	Day	42% 5% 14% 23% 15% 2	1906
	21st to end	Day	48% 9% 11% 23% 8%	2772
January	1st to 10th	Night	38% 5% 11% 29% 12% 4	4429
	11th to 20th	Night	44% 5% 13% 24% 13% 2	4440
	21st to end	Night	52% 5% 9% 21% 12% 2	4678
February	1st to 10th	Night	44% 5% 13% 23% 13% 2	2435
	11th to 20th	Night	45% 5% 9% 19% 17% 5%	2220
	21st to end	Night	44% 5% 8% 23% 17% 4	1884
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	44% 7% 11% 20% 15% 3	2166
	11th to 20th	Night	35% 6% 13% 29% 16% 2	2207
	21st to end	Night	44% 5% 11% 22% 17% 1	2535
November	1st to 10th	Night	36% 5% 12% 22% 21% 4	2407
	11th to 20th	Night	40% 5% 8% 23% 19% 4	2470
	21st to end	Night	37% 6% 13% 28% 15% 2	2515
December	1st to 10th	Night	45% 6% 13% 22% 13% 2	2660
	11th to 20th	Night	42% 5% 13% 20% 17% 3	3288
	21st to end	Night	46% 7% 13% 23% 11%	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	20% 26% 29% 20% 4 1	180
	11th to 20th	Day	17% 29% 36% 16% 3	180
	21st to end	Day	19% 18% 41% 15% 6% 2	256
February	1st to 10th	Day	25% 15% 39% 18% 3	303
	11th to 20th	Day	21% 19% 39% 19% 2	456
	21st to end	Day	24% 19% 35% 18% 4	382
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% 11% 30% 27% 13% 2	462
	21st to end	Day	21% 11% 36% 21% 10% 1	414
November	1st to 10th	Day	14% 11% 31% 29% 12% 3	365
	11th to 20th	Day	19% 19% 32% 24% 6% 1	370
	21st to end	Day	18% 14% 35% 26% 7% 1	323
December	1st to 10th	Day	19% 18% 38% 18% 7%	180
	11th to 20th	Day	27% 21% 34% 15% 3	180
	21st to end	Day	24% 18% 37% 12% 9% 1	198
January	1st to 10th	Night	19% 17% 41% 20% 3	760
	11th to 20th	Night	23% 17% 33% 23% 3	760
	21st to end	Night	19% 16% 42% 21% 3	836
February	1st to 10th	Night	21% 14% 39% 24% 2	760
	11th to 20th	Night	21% 17% 42% 18% 2	743
	21st to end	Night	24% 16% 37% 20% 4	628
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% 33% 11%	735
	21st to end	Night	24% 10% 34% 23% 8% 1	792
November	1st to 10th	Night	15% 10% 35% 28% 12% 1	740
	11th to 20th	Night	22% 13% 32% 24% 8%	760
	21st to end	Night	16% 15% 36% 27% 6% 1	760
December	1st to 10th	Night	25% 14% 36% 19% 5% 1	760
	11th to 20th	Night	22% 15% 35% 24% 4	760
	21st to end	Night	23% 14% 39% 22% 3	836

Page generated at 2024-10-11 10:50:02. Version ac07

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