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 2024-04-10.

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	15% 10% 4 7% 6% 4 5% 5% 5% 7% 32%	82750
	Night	16% 11% 5% 8% 6% 3 4 4 5% 6% 33%	86027
Transparency	Day	50% 7% 12% 19% 11% 1	82457
	Night	51% 6% 12% 19% 11% 1	85842
Seeing	Day	19% 12% 28% 22% 14% 5%	14642
	Night	20% 10% 30% 29% 11% 1	24647

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	16% 18% 7% 10% 7% 4 5% 4 4 4 21%	2527
	11th to 20th	Day	16% 18% 8% 14% 13% 8% 4 3 3 4 9%	2530
	21st to end	Day	27% 20% 7% 10% 7% 3 4 3 3 4 13%	2946
February	1st to 10th	Day	12% 16% 5% 11% 9% 4 5% 5% 5% 6% 22%	1710
	11th to 20th	Day	13% 13% 7% 11% 9% 4 4 4 4 5% 25%	1805
	21st to end	Day	14% 15% 6% 10% 8% 3 5% 4 4 5% 26%	1570
March	1st to 10th	Day	17% 13% 5% 7% 6% 3 3 4 5% 6% 30%	3152
	11th to 20th	Day	12% 13% 6% 10% 7% 3 4 4 5% 6% 30%	3480
	21st to end	Day	18% 13% 4 8% 7% 3 5% 4 4 6% 28%	3815
April	1st to 10th	Day	18% 12% 4 6% 7% 4 4 4 5% 7% 30%	2236
	11th to 20th	Day	17% 10% 4 6% 5% 3 4 5% 5% 7% 35%	2266
	21st to end	Day	17% 9% 4 6% 6% 4 5% 4 5% 6% 34%	2340
May	1st to 10th	Day	17% 8% 4 5% 5% 3 5% 5% 6% 8% 35%	2340
	11th to 20th	Day	19% 9% 2 6% 5% 3 4 4 5% 6% 37%	2301
	21st to end	Day	13% 6% 2 5% 5% 4 5% 5% 6% 8% 40%	2595
June	1st to 10th	Day	11% 6% 2 5% 5% 3 4 6% 6% 9% 41%	2564
	11th to 20th	Day	11% 6% 3 6% 5% 3 4 5% 5% 9% 42%	2700
	21st to end	Day	9% 6% 2 6% 5% 3 6% 6% 7% 10% 39%	2533
July	1st to 10th	Day	7% 5% 2 4 4 3 5% 6% 7% 9% 47%	2520
	11th to 20th	Day	10% 5% 2 5% 4 3 5% 5% 7% 9% 45%	2520
	21st to end	Day	8% 6% 2 4 6% 4 6% 5% 7% 9% 43%	2653
August	1st to 10th	Day	10% 5% 2 5% 5% 4 6% 6% 6% 10% 40%	2327
	11th to 20th	Day	10% 5% 2 5% 6% 4 6% 6% 6% 7% 41%	2303
	21st to end	Day	11% 5% 3 6% 5% 4 5% 5% 6% 8% 44%	2532
September	1st to 10th	Day	11% 7% 3 5% 7% 4 6% 6% 6% 8% 38%	2059
	11th to 20th	Day	12% 5% 2 5% 3 3 4 5% 6% 9% 46%	1980
	21st to end	Day	13% 6% 3 6% 6% 4 5% 5% 5% 8% 38%	1980
October	1st to 10th	Day	13% 7% 3 7% 5% 4 4 5% 5% 7% 39%	1944
	11th to 20th	Day	19% 10% 4 7% 6% 3 5% 5% 5% 7% 29%	1800
	21st to end	Day	22% 10% 3 6% 6% 4 4 4 5% 7% 28%	1796
November	1st to 10th	Day	13% 11% 4 6% 7% 3 4 4 5% 7% 37%	1672
	11th to 20th	Day	15% 12% 4 8% 7% 4 4 5% 5% 7% 29%	1710
	21st to end	Day	19% 13% 6% 7% 6% 3 5% 4 5% 6% 26%	1620
December	1st to 10th	Day	14% 17% 7% 12% 8% 4 4 4 5% 5% 20%	1516
	11th to 20th	Day	16% 17% 6% 9% 5% 3 5% 5% 5% 6% 23%	1675
	21st to end	Day	25% 21% 6% 12% 6% 3 3 3 4 5% 12%	2733
January	1st to 10th	Night	17% 16% 8% 11% 6% 4 4 4 4 5% 21%	4428
	11th to 20th	Night	15% 17% 8% 14% 9% 8% 5% 4 4 4 13%	4440
	21st to end	Night	22% 17% 9% 9% 7% 3 4 4 4 5% 16%	4714
February	1st to 10th	Night	15% 15% 6% 11% 8% 4 5% 5% 4 5% 23%	2470
	11th to 20th	Night	14% 13% 6% 8% 8% 4 5% 4 5% 6% 26%	2259
	21st to end	Night	18% 11% 4 9% 7% 4 6% 4 4 6% 27%	1884
March	1st to 10th	Night	15% 11% 5% 7% 5% 3 4 4 4 6% 37%	3701
	11th to 20th	Night	10% 9% 4 6% 5% 3 5% 5% 6% 8% 40%	3480
	21st to end	Night	17% 9% 5% 7% 6% 4 5% 4 4 5% 33%	3817
April	1st to 10th	Night	17% 10% 5% 6% 4 3 4 4 6% 6% 35%	1950
	11th to 20th	Night	19% 7% 3 5% 5% 3 4 4 5% 6% 38%	1642
	21st to end	Night	18% 7% 4 6% 5% 3 4 4 6% 7% 37%	1620
May	1st to 10th	Night	15% 8% 4 7% 6% 3 4 5% 6% 7% 35%	1620
	11th to 20th	Night	19% 7% 3 5% 3 3 3 4 4 7% 42%	1592
	21st to end	Night	11% 5% 2 5% 5% 3 5% 6% 7% 8% 45%	1675
June	1st to 10th	Night	12% 4 2 5% 5% 3 4 5% 5% 8% 47%	1386
	11th to 20th	Night	12% 5% 2 4 5% 2 4 6% 5% 9% 47%	1260
	21st to end	Night	9% 4 3 5% 4 3 6% 3 5% 10% 47%	1414
July	1st to 10th	Night	6% 3 3 4 5% 3 4 3 7% 8% 53%	1440
	11th to 20th	Night	8% 4 2 4 4 3 4 5% 6% 9% 50%	1440
	21st to end	Night	7% 4 2 5% 4 3 5% 5% 6% 9% 50%	1662
August	1st to 10th	Night	7% 4 2 4 5% 3 4 6% 7% 9% 48%	1611
	11th to 20th	Night	9% 3 1 4 5% 4 4 5% 6% 8% 50%	1598
	21st to end	Night	10% 5% 2 5% 4 3 4 5% 5% 8% 51%	1822
September	1st to 10th	Night	10% 7% 2 5% 5% 3 5% 5% 5% 8% 46%	1882
	11th to 20th	Night	12% 4 2 4 4 2 4 5% 4 7% 52%	1980
	21st to end	Night	14% 5% 3 6% 5% 2 4 4 5% 7% 44%	1980
October	1st to 10th	Night	16% 7% 2 6% 5% 3 4 4 5% 6% 44%	2015
	11th to 20th	Night	21% 11% 3 6% 6% 3 5% 4 5% 6% 32%	2160
	21st to end	Night	22% 10% 3 8% 6% 3 4 4 5% 6% 31%	2556
November	1st to 10th	Night	14% 8% 3 5% 6% 3 4 4 5% 6% 42%	2406
	11th to 20th	Night	15% 12% 4 7% 6% 4 5% 6% 6% 5% 29%	2470
	21st to end	Night	20% 12% 4 7% 6% 3 5% 4 4 7% 28%	2555
December	1st to 10th	Night	17% 16% 7% 11% 6% 3 5% 4 4 6% 19%	2660
	11th to 20th	Night	15% 13% 7% 12% 6% 4 5% 4 4 5% 24%	3522
	21st to end	Night	25% 22% 6% 9% 6% 3 3 4 3 5% 14%	4916

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	66% 7% 10% 12% 4	2528
	11th to 20th	Day	79% 6% 8% 5% 2	2530
	21st to end	Day	76% 6% 8% 7% 3	2946
February	1st to 10th	Day	61% 8% 11% 14% 7%	1710
	11th to 20th	Day	61% 5% 9% 15% 9% 1	1815
	21st to end	Day	61% 6% 11% 14% 7% 2	1570
March	1st to 10th	Day	54% 6% 12% 20% 7% 1	3152
	11th to 20th	Day	53% 7% 12% 18% 9% 1	3480
	21st to end	Day	56% 7% 11% 15% 9% 2	3815
April	1st to 10th	Day	55% 5% 11% 18% 11%	2236
	11th to 20th	Day	48% 5% 12% 19% 13% 2	2266
	21st to end	Day	50% 7% 12% 17% 13% 2	2340
May	1st to 10th	Day	47% 7% 12% 22% 10% 2	2340
	11th to 20th	Day	48% 5% 11% 21% 13% 2	2305
	21st to end	Day	41% 7% 14% 22% 14% 2	2595
June	1st to 10th	Day	37% 8% 12% 26% 15% 2	2564
	11th to 20th	Day	39% 6% 12% 25% 16% 2	2700
	21st to end	Day	37% 9% 12% 24% 16% 1	2533
July	1st to 10th	Day	31% 8% 12% 27% 18% 3	2451
	11th to 20th	Day	33% 8% 13% 26% 18% 2	2445
	21st to end	Day	35% 8% 13% 24% 17% 3	2506
August	1st to 10th	Day	36% 9% 14% 26% 13% 2	2314
	11th to 20th	Day	38% 9% 14% 24% 14% 2	2303
	21st to end	Day	37% 7% 12% 26% 16% 2	2532
September	1st to 10th	Day	42% 8% 13% 23% 11% 2	2059
	11th to 20th	Day	34% 7% 13% 32% 13% 1	1980
	21st to end	Day	43% 7% 13% 24% 12%	1980
October	1st to 10th	Day	43% 6% 11% 24% 13% 1	1944
	11th to 20th	Day	53% 6% 13% 19% 8%	1800
	21st to end	Day	55% 6% 14% 18% 7% 1	1796
November	1st to 10th	Day	47% 7% 13% 23% 10% 1	1672
	11th to 20th	Day	54% 6% 13% 18% 8% 1	1710
	21st to end	Day	58% 6% 14% 15% 6% 1	1620
December	1st to 10th	Day	65% 6% 11% 14% 3	1516
	11th to 20th	Day	61% 6% 14% 15% 4	1671
	21st to end	Day	77% 5% 9% 7% 3	2733
January	1st to 10th	Night	64% 6% 11% 12% 5% 1	4428
	11th to 20th	Night	72% 7% 9% 8% 3	4440
	21st to end	Night	71% 5% 10% 11% 3	4714
February	1st to 10th	Night	63% 6% 10% 13% 7% 1	2470
	11th to 20th	Night	59% 5% 10% 17% 8% 1	2260
	21st to end	Night	57% 5% 12% 16% 8% 1	1884
March	1st to 10th	Night	48% 7% 12% 26% 7% 1	3701
	11th to 20th	Night	38% 8% 15% 21% 15% 1	3480
	21st to end	Night	51% 6% 12% 20% 10% 1	3817
April	1st to 10th	Night	49% 5% 11% 20% 13% 2	1950
	11th to 20th	Night	46% 5% 11% 18% 17% 2	1642
	21st to end	Night	45% 5% 11% 20% 15% 3	1620
May	1st to 10th	Night	47% 6% 11% 21% 12% 3	1620
	11th to 20th	Night	43% 5% 8% 22% 17% 4	1593
	21st to end	Night	36% 8% 13% 25% 15% 3	1676
June	1st to 10th	Night	35% 6% 10% 28% 19% 2	1386
	11th to 20th	Night	34% 7% 13% 24% 20% 2	1260
	21st to end	Night	33% 7% 13% 27% 19% 2	1414
July	1st to 10th	Night	28% 7% 10% 30% 21% 4	1400
	11th to 20th	Night	30% 7% 14% 26% 21% 2	1392
	21st to end	Night	28% 8% 17% 23% 21% 2	1570
August	1st to 10th	Night	29% 10% 14% 31% 15% 1	1600
	11th to 20th	Night	30% 9% 14% 30% 13% 3	1598
	21st to end	Night	32% 7% 13% 28% 19% 1	1822
September	1st to 10th	Night	36% 8% 11% 28% 16% 2	1882
	11th to 20th	Night	31% 7% 12% 30% 19% 1	1980
	21st to end	Night	39% 7% 12% 27% 13% 1	1980
October	1st to 10th	Night	41% 6% 9% 26% 16% 1	2015
	11th to 20th	Night	53% 7% 11% 18% 10% 1	2160
	21st to end	Night	55% 5% 12% 19% 9% 1	2556
November	1st to 10th	Night	42% 5% 13% 25% 14% 1	2406
	11th to 20th	Night	54% 6% 13% 19% 8% 1	2470
	21st to end	Night	57% 5% 14% 18% 6%	2555
December	1st to 10th	Night	67% 6% 10% 13% 4	2660
	11th to 20th	Night	62% 6% 13% 13% 6% 1	3525
	21st to end	Night	74% 6% 11% 7% 2	4916

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	22% 16% 37% 17% 6% 1	270
	11th to 20th	Day	21% 17% 40% 18% 4 1	270
	21st to end	Day	29% 15% 30% 21% 5%	297
February	1st to 10th	Day	26% 21% 34% 15% 3 1	270
	11th to 20th	Day	23% 20% 38% 17% 1	270
	21st to end	Day	28% 26% 35% 8% 3	225
March	1st to 10th	Day	27% 19% 37% 12% 4 1	289
	11th to 20th	Day	23% 14% 32% 22% 8%	460
	21st to end	Day	29% 14% 31% 20% 6% 1	506
April	1st to 10th	Day	24% 15% 32% 21% 7% 1	457
	11th to 20th	Day	29% 17% 28% 14% 7% 5%	412
	21st to end	Day	24% 13% 29% 22% 11% 1	420
May	1st to 10th	Day	23% 14% 29% 21% 11% 3	423
	11th to 20th	Day	21% 10% 29% 21% 14% 5%	447
	21st to end	Day	16% 7% 24% 26% 21% 7%	549
June	1st to 10th	Day	11% 11% 28% 30% 16% 4	630
	11th to 20th	Day	16% 9% 30% 24% 16% 5%	630
	21st to end	Day	11% 8% 28% 30% 18% 5%	630
July	1st to 10th	Day	8% 7% 21% 28% 24% 12%	621
	11th to 20th	Day	12% 6% 29% 26% 19% 8%	618
	21st to end	Day	10% 4 25% 30% 22% 8%	594
August	1st to 10th	Day	11% 4 21% 25% 22% 17%	446
	11th to 20th	Day	13% 5% 20% 25% 26% 11%	439
	21st to end	Day	13% 5% 23% 25% 23% 12%	495
September	1st to 10th	Day	13% 7% 24% 26% 20% 10%	450
	11th to 20th	Day	12% 5% 22% 21% 28% 13%	450
	21st to end	Day	18% 11% 22% 23% 18% 9%	450
October	1st to 10th	Day	17% 10% 29% 20% 17% 6%	450
	11th to 20th	Day	24% 17% 26% 25% 8% 1	450
	21st to end	Day	32% 15% 34% 15% 5%	311
November	1st to 10th	Day	20% 18% 35% 19% 6% 2	270
	11th to 20th	Day	23% 20% 32% 18% 6% 1	270
	21st to end	Day	29% 18% 34% 16% 3	228
December	1st to 10th	Day	26% 22% 31% 13% 8% 1	180
	11th to 20th	Day	27% 25% 35% 10% 3 1	180
	21st to end	Day	29% 21% 33% 14% 2	285
January	1st to 10th	Night	24% 14% 34% 22% 6% 1	950
	11th to 20th	Night	26% 15% 31% 24% 4 1	950
	21st to end	Night	21% 11% 35% 27% 6%	940
February	1st to 10th	Night	24% 11% 39% 23% 3	760
	11th to 20th	Night	22% 14% 35% 23% 5%	743
	21st to end	Night	26% 16% 35% 21% 2	628
March	1st to 10th	Night	21% 14% 34% 24% 7%	760
	11th to 20th	Night	19% 14% 34% 26% 6% 1	760
	21st to end	Night	24% 11% 30% 27% 7% 1	836
April	1st to 10th	Night	21% 15% 35% 24% 5%	620
	11th to 20th	Night	23% 9% 34% 24% 9% 1	533
	21st to end	Night	22% 8% 32% 30% 7% 1	540
May	1st to 10th	Night	19% 6% 33% 33% 8% 1	540
	11th to 20th	Night	22% 5% 31% 32% 10% 1	531
	21st to end	Night	13% 3 28% 36% 17% 3	584
June	1st to 10th	Night	13% 5% 25% 44% 12% 1	486
	11th to 20th	Night	13% 3 29% 43% 12%	360
	21st to end	Night	11% 6% 25% 41% 17% 2	514
July	1st to 10th	Night	8% 3 17% 40% 30% 2	525
	11th to 20th	Night	12% 2 23% 41% 20% 3	522
	21st to end	Night	8% 3 20% 47% 21% 1	591
August	1st to 10th	Night	9% 2 17% 42% 28% 2	537
	11th to 20th	Night	10% 3 17% 39% 28% 4	534
	21st to end	Night	12% 4 19% 36% 26% 4	594
September	1st to 10th	Night	12% 4 22% 35% 22% 5%	622
	11th to 20th	Night	14% 4 19% 33% 26% 4	720
	21st to end	Night	16% 7% 21% 31% 21% 4	720
October	1st to 10th	Night	20% 7% 23% 32% 16% 1	720
	11th to 20th	Night	26% 11% 27% 28% 7% 1	720
	21st to end	Night	27% 10% 33% 25% 5%	792
November	1st to 10th	Night	20% 13% 31% 27% 10% 1	740
	11th to 20th	Night	22% 16% 34% 21% 7% 1	760
	21st to end	Night	26% 13% 36% 20% 6%	760
December	1st to 10th	Night	25% 14% 36% 19% 6% 1	760
	11th to 20th	Night	23% 15% 36% 23% 3	950
	21st to end	Night	33% 12% 34% 19% 1	1045

Page generated at 2024-04-07 09:28:16. Version ac07

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