Flushing Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Flushing Observatory clear sky chart from 2005-11-06 to 2025-10-19.

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	14% 10% 4 8% 5% 5% 4 4 5% 7% 34%	125795
	Night	14% 11% 4 9% 5% 4 4 3 5% 6% 34%	124019
Transparency	Day	47% 7% 12% 21% 12% 1	129349
	Night	49% 6% 12% 20% 12% 1	128536
Seeing	Day	19% 12% 28% 22% 13% 5%	16823
	Night	20% 10% 30% 29% 11% 1	26586

By Month

Percentage Cloud Cover SE (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% 17% 7% 16% 6% 5% 4 3 4 4 22%	3617
	11th to 20th	Day	13% 17% 8% 19% 10% 9% 5% 3 3 4 10%	3620
	21st to end	Day	22% 18% 6% 13% 6% 4 5% 3 3 4 15%	4223
February	1st to 10th	Day	12% 17% 4 12% 8% 5% 5% 4 6% 5% 22%	1800
	11th to 20th	Day	13% 15% 7% 12% 8% 5% 4 3 5% 5% 24%	1903
	21st to end	Day	13% 16% 4 12% 7% 5% 4 3 4 5% 25%	1650
March	1st to 10th	Day	14% 11% 5% 9% 6% 4 4 3 5% 6% 33%	4526
	11th to 20th	Day	12% 13% 4 9% 5% 4 4 3 5% 8% 33%	4980
	21st to end	Day	18% 14% 5% 8% 6% 5% 4 3 4 6% 27%	5465
April	1st to 10th	Day	18% 12% 4 8% 5% 4 5% 3 5% 7% 30%	2365
	11th to 20th	Day	17% 10% 4 7% 5% 4 4 4 5% 6% 36%	2522
	21st to end	Day	15% 10% 3 7% 5% 5% 4 3 5% 7% 35%	2600
May	1st to 10th	Day	19% 9% 3 6% 4 3 4 4 5% 7% 36%	5862
	11th to 20th	Day	15% 9% 2 7% 5% 4 5% 4 6% 8% 35%	5861
	21st to end	Day	14% 7% 2 7% 4 4 4 4 5% 8% 41%	6609
June	1st to 10th	Day	11% 6% 2 6% 4 5% 5% 4 7% 8% 41%	2850
	11th to 20th	Day	11% 7% 3 7% 4 4 4 4 6% 10% 41%	3000
	21st to end	Day	9% 7% 2 6% 5% 5% 6% 5% 7% 9% 39%	2813
July	1st to 10th	Day	10% 6% 2 6% 5% 5% 6% 4 7% 10% 39%	6360
	11th to 20th	Day	9% 5% 2 5% 4 4 4 4 6% 9% 48%	6360
	21st to end	Day	8% 5% 2 5% 5% 5% 4 4 7% 9% 46%	6698
August	1st to 10th	Day	11% 5% 2 7% 4 5% 5% 4 6% 9% 41%	4234
	11th to 20th	Day	12% 6% 2 6% 4 5% 5% 4 6% 8% 41%	4174
	21st to end	Day	8% 5% 3 7% 5% 5% 6% 4 7% 9% 42%	4588
September	1st to 10th	Day	10% 7% 3 6% 5% 5% 5% 5% 6% 8% 41%	2287
	11th to 20th	Day	11% 4 2 5% 3 4 4 4 6% 9% 48%	2200
	21st to end	Day	14% 7% 3 7% 5% 5% 5% 4 5% 8% 38%	2200
October	1st to 10th	Day	12% 7% 2 7% 5% 5% 4 4 5% 7% 42%	2160
	11th to 20th	Day	18% 10% 3 7% 5% 4 5% 4 5% 7% 31%	1980
	21st to end	Day	21% 10% 3 7% 4 5% 4 4 6% 7% 28%	1895
November	1st to 10th	Day	12% 12% 3 8% 5% 4 4 4 5% 7% 36%	1762
	11th to 20th	Day	15% 13% 4 10% 6% 5% 4 4 6% 7% 27%	1800
	21st to end	Day	18% 15% 6% 8% 6% 4 4 3 4 6% 25%	1705
December	1st to 10th	Day	14% 17% 7% 11% 6% 4 4 4 7% 7% 20%	2583
	11th to 20th	Day	17% 22% 7% 11% 5% 4 4 3 4 4 19%	2625
	21st to end	Day	25% 20% 6% 13% 5% 4 3 3 4 5% 13%	3918
January	1st to 10th	Night	13% 14% 7% 15% 5% 5% 4 3 4 5% 24%	6348
	11th to 20th	Night	13% 15% 7% 16% 9% 9% 5% 4 5% 5% 13%	6360
	21st to end	Night	16% 18% 8% 10% 5% 5% 5% 3 5% 6% 19%	6742
February	1st to 10th	Night	14% 17% 5% 12% 7% 5% 4 4 4 5% 23%	2600
	11th to 20th	Night	14% 15% 6% 10% 7% 4 5% 3 5% 6% 25%	2381
	21st to end	Night	17% 12% 4 10% 6% 5% 5% 3 4 6% 27%	1980
March	1st to 10th	Night	14% 10% 4 8% 4 4 4 3 5% 6% 37%	5327
	11th to 20th	Night	11% 9% 3 7% 4 4 5% 4 6% 9% 39%	4980
	21st to end	Night	17% 10% 4 8% 5% 4 4 3 4 5% 35%	5467
April	1st to 10th	Night	17% 11% 4 6% 4 3 4 3 6% 6% 35%	2052
	11th to 20th	Night	19% 7% 3 7% 5% 4 3 3 5% 6% 38%	1826
	21st to end	Night	17% 8% 3 7% 4 4 4 3 6% 6% 37%	1800
May	1st to 10th	Night	18% 9% 4 8% 5% 4 4 3 5% 6% 35%	4033
	11th to 20th	Night	17% 9% 3 7% 4 4 4 3 4 6% 40%	4032
	21st to end	Night	15% 6% 2 5% 4 4 4 4 5% 6% 45%	4248
June	1st to 10th	Night	12% 5% 2 5% 4 4 4 4 5% 9% 46%	1540
	11th to 20th	Night	11% 5% 2 6% 5% 4 4 4 6% 8% 45%	1400
	21st to end	Night	9% 4 2 6% 4 4 5% 2 6% 10% 47%	1572
July	1st to 10th	Night	8% 5% 3 6% 5% 4 5% 4 7% 9% 45%	3618
	11th to 20th	Night	9% 5% 2 5% 3 4 4 4 6% 9% 50%	3617
	21st to end	Night	9% 5% 2 6% 4 5% 4 4 6% 7% 48%	4162
August	1st to 10th	Night	10% 4 2 5% 4 4 5% 4 6% 8% 48%	2915
	11th to 20th	Night	12% 5% 2 6% 4 4 4 3 6% 7% 48%	2875
	21st to end	Night	9% 5% 2 6% 4 4 4 4 5% 7% 49%	3307
September	1st to 10th	Night	9% 7% 2 5% 4 4 5% 4 5% 7% 48%	2092
	11th to 20th	Night	11% 4 1 5% 3 3 3 4 4 7% 55%	2200
	21st to end	Night	15% 6% 3 7% 5% 4 4 3 5% 7% 43%	2200
October	1st to 10th	Night	15% 6% 2 6% 4 4 3 3 5% 6% 46%	2239
	11th to 20th	Night	20% 11% 2 7% 4 5% 4 3 5% 6% 34%	2377
	21st to end	Night	21% 10% 3 8% 4 4 4 3 5% 6% 32%	2699
November	1st to 10th	Night	14% 9% 3 7% 5% 4 3 3 5% 6% 42%	2536
	11th to 20th	Night	15% 13% 4 8% 5% 5% 5% 5% 6% 5% 28%	2600
	21st to end	Night	19% 14% 4 8% 5% 4 5% 3 4 7% 27%	2690
December	1st to 10th	Night	13% 17% 7% 12% 5% 5% 4 4 5% 7% 22%	4580
	11th to 20th	Night	15% 20% 6% 13% 6% 5% 4 2 4 4 20%	5582
	21st to end	Night	23% 22% 7% 10% 5% 3 3 3 3 5% 16%	7042

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	65% 6% 11% 13% 5%	3618
	11th to 20th	Day	77% 6% 8% 5% 4	3620
	21st to end	Day	72% 5% 10% 8% 4	4223
February	1st to 10th	Day	60% 8% 11% 14% 7%	1800
	11th to 20th	Day	62% 5% 9% 15% 8% 1	1913
	21st to end	Day	61% 6% 11% 14% 7% 2	1650
March	1st to 10th	Day	50% 5% 14% 19% 9% 2	4526
	11th to 20th	Day	49% 6% 14% 20% 9% 1	4980
	21st to end	Day	57% 6% 10% 16% 9% 2	5465
April	1st to 10th	Day	55% 4 11% 19% 10% 1	2365
	11th to 20th	Day	48% 5% 11% 21% 13% 2	2522
	21st to end	Day	48% 7% 12% 19% 13% 1	2600
May	1st to 10th	Day	47% 7% 11% 18% 14% 3	5897
	11th to 20th	Day	45% 8% 11% 21% 13% 2	5865
	21st to end	Day	41% 6% 9% 21% 19% 3	6623
June	1st to 10th	Day	37% 8% 11% 27% 15% 2	2850
	11th to 20th	Day	39% 7% 12% 26% 16% 2	3000
	21st to end	Day	38% 9% 12% 24% 16% 1	2813
July	1st to 10th	Day	37% 8% 14% 24% 15% 1	6291
	11th to 20th	Day	30% 8% 13% 31% 18% 1	6285
	21st to end	Day	32% 8% 14% 24% 21% 1	6507
August	1st to 10th	Day	37% 8% 13% 25% 16% 1	4221
	11th to 20th	Day	37% 8% 12% 30% 11% 1	4213
	21st to end	Day	36% 8% 14% 27% 13% 1	4587
September	1st to 10th	Day	39% 8% 12% 27% 12% 2	2287
	11th to 20th	Day	32% 7% 13% 32% 15% 2	2200
	21st to end	Day	44% 6% 12% 24% 13%	2200
October	1st to 10th	Day	32% 5% 10% 33% 18% 2	3524
	11th to 20th	Day	40% 6% 11% 27% 16%	3220
	21st to end	Day	47% 6% 14% 24% 9% 1	3095
November	1st to 10th	Day	47% 6% 13% 23% 10% 1	1762
	11th to 20th	Day	55% 6% 12% 18% 8% 1	1800
	21st to end	Day	59% 6% 14% 15% 5% 1	1705
December	1st to 10th	Day	62% 8% 17% 10% 2	2583
	11th to 20th	Day	69% 4 10% 13% 4	2621
	21st to end	Day	75% 4 8% 9% 4	3918
January	1st to 10th	Night	61% 6% 10% 15% 6% 2	6348
	11th to 20th	Night	69% 8% 10% 8% 5% 1	6360
	21st to end	Night	65% 5% 11% 13% 6%	6742
February	1st to 10th	Night	63% 6% 10% 13% 7% 1	2600
	11th to 20th	Night	59% 6% 10% 17% 8% 1	2382
	21st to end	Night	57% 5% 13% 16% 8% 1	1980
March	1st to 10th	Night	47% 6% 13% 23% 9% 1	5327
	11th to 20th	Night	39% 7% 16% 25% 13% 1	4980
	21st to end	Night	50% 6% 12% 19% 12% 1	5467
April	1st to 10th	Night	49% 5% 10% 20% 13% 2	2052
	11th to 20th	Night	46% 6% 11% 18% 17% 2	1826
	21st to end	Night	45% 6% 11% 19% 16% 3	1800
May	1st to 10th	Night	49% 7% 11% 15% 14% 4	4060
	11th to 20th	Night	44% 6% 9% 25% 11% 4	4033
	21st to end	Night	39% 6% 9% 24% 17% 5%	4256
June	1st to 10th	Night	35% 6% 9% 28% 20% 2	1540
	11th to 20th	Night	35% 7% 12% 24% 19% 2	1400
	21st to end	Night	33% 6% 13% 27% 19% 2	1572
July	1st to 10th	Night	32% 7% 13% 26% 17% 4	3580
	11th to 20th	Night	30% 6% 14% 28% 21% 1	3572
	21st to end	Night	33% 8% 14% 22% 22% 1	4041
August	1st to 10th	Night	32% 8% 13% 29% 17% 1	2904
	11th to 20th	Night	33% 8% 12% 33% 12% 2	2902
	21st to end	Night	33% 8% 12% 32% 15% 1	3307
September	1st to 10th	Night	34% 7% 11% 30% 16% 2	2092
	11th to 20th	Night	29% 6% 12% 31% 20% 2	2200
	21st to end	Night	40% 7% 12% 26% 14% 1	2200
October	1st to 10th	Night	26% 5% 11% 33% 25% 1	3655
	11th to 20th	Night	45% 5% 10% 22% 17% 1	3876
	21st to end	Night	41% 5% 12% 30% 12%	4449
November	1st to 10th	Night	43% 5% 13% 25% 14% 1	2536
	11th to 20th	Night	54% 6% 13% 18% 8% 1	2600
	21st to end	Night	58% 5% 14% 17% 6%	2690
December	1st to 10th	Night	62% 7% 16% 12% 2	4580
	11th to 20th	Night	66% 6% 10% 12% 6% 1	5585
	21st to end	Night	72% 5% 9% 8% 6%	7042

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% 18% 37% 18% 6% 1	300
	11th to 20th	Day	20% 18% 42% 16% 3 1	300
	21st to end	Day	28% 17% 31% 19% 5%	330
February	1st to 10th	Day	26% 22% 33% 15% 2 1	300
	11th to 20th	Day	24% 20% 38% 17% 1	300
	21st to end	Day	29% 26% 35% 9% 2	249
March	1st to 10th	Day	28% 18% 38% 12% 3 1	320
	11th to 20th	Day	23% 14% 32% 22% 8%	500
	21st to end	Day	29% 15% 30% 19% 5% 1	550
April	1st to 10th	Day	26% 15% 31% 20% 7% 1	500
	11th to 20th	Day	29% 17% 29% 14% 6% 4	492
	21st to end	Day	23% 15% 28% 23% 11% 1	500
May	1st to 10th	Day	22% 17% 28% 21% 11% 2	503
	11th to 20th	Day	20% 10% 29% 22% 13% 5%	527
	21st to end	Day	17% 7% 26% 24% 19% 6%	645
June	1st to 10th	Day	11% 12% 29% 29% 14% 4	730
	11th to 20th	Day	15% 9% 30% 26% 15% 5%	730
	21st to end	Day	12% 9% 28% 30% 17% 5%	730
July	1st to 10th	Day	8% 7% 22% 29% 22% 11%	721
	11th to 20th	Day	11% 7% 29% 26% 19% 8%	718
	21st to end	Day	9% 5% 24% 30% 23% 8%	694
August	1st to 10th	Day	10% 4 21% 26% 23% 16%	526
	11th to 20th	Day	14% 5% 19% 25% 25% 11%	519
	21st to end	Day	12% 5% 21% 27% 23% 12%	583
September	1st to 10th	Day	12% 7% 25% 25% 20% 12%	530
	11th to 20th	Day	10% 4 19% 21% 29% 17%	530
	21st to end	Day	18% 10% 20% 25% 18% 9%	530
October	1st to 10th	Day	16% 9% 30% 21% 18% 6%	530
	11th to 20th	Day	22% 16% 26% 27% 8% 1	522
	21st to end	Day	30% 15% 34% 15% 6%	344
November	1st to 10th	Day	20% 19% 34% 19% 6% 2	300
	11th to 20th	Day	25% 20% 31% 18% 5% 1	300
	21st to end	Day	31% 17% 32% 15% 4	253
December	1st to 10th	Day	25% 22% 32% 13% 9% 1	200
	11th to 20th	Day	27% 26% 34% 11% 3 1	200
	21st to end	Day	31% 21% 32% 14% 2	317
January	1st to 10th	Night	23% 15% 34% 23% 6% 1	1000
	11th to 20th	Night	26% 15% 32% 23% 4 1	1000
	21st to end	Night	21% 11% 36% 26% 6%	989
February	1st to 10th	Night	24% 12% 39% 22% 3	800
	11th to 20th	Night	23% 14% 36% 22% 5%	783
	21st to end	Night	25% 16% 36% 21% 2	660
March	1st to 10th	Night	20% 15% 35% 24% 7%	800
	11th to 20th	Night	19% 15% 34% 26% 6% 1	800
	21st to end	Night	24% 11% 30% 27% 7% 1	880
April	1st to 10th	Night	21% 15% 35% 23% 4	652
	11th to 20th	Night	23% 12% 33% 23% 9% 1	593
	21st to end	Night	21% 11% 31% 30% 6% 1	600
May	1st to 10th	Night	19% 8% 33% 32% 8% 1	600
	11th to 20th	Night	22% 6% 31% 31% 9% 1	591
	21st to end	Night	14% 4 29% 35% 15% 2	650
June	1st to 10th	Night	12% 7% 26% 43% 11% 1	540
	11th to 20th	Night	13% 4 31% 41% 11%	400
	21st to end	Night	10% 6% 25% 41% 16% 2	572
July	1st to 10th	Night	8% 3 18% 41% 28% 2	585
	11th to 20th	Night	12% 1 23% 41% 20% 3	582
	21st to end	Night	8% 3 19% 48% 21% 1	657
August	1st to 10th	Night	8% 2 18% 42% 29% 2	597
	11th to 20th	Night	10% 3 17% 40% 27% 3	594
	21st to end	Night	12% 4 18% 37% 26% 3	660
September	1st to 10th	Night	12% 4 23% 33% 24% 5%	692
	11th to 20th	Night	13% 4 17% 33% 29% 4	800
	21st to end	Night	17% 7% 21% 32% 20% 4	800
October	1st to 10th	Night	18% 7% 24% 33% 17% 1	800
	11th to 20th	Night	25% 12% 26% 29% 8% 1	793
	21st to end	Night	25% 10% 34% 25% 5%	836
November	1st to 10th	Night	20% 13% 30% 26% 9% 1	780
	11th to 20th	Night	22% 16% 34% 21% 7% 1	800
	21st to end	Night	25% 13% 37% 19% 6%	800
December	1st to 10th	Night	25% 14% 35% 19% 6% 1	800
	11th to 20th	Night	24% 15% 36% 22% 3	1000
	21st to end	Night	33% 12% 34% 19% 2	1100

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