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 2024-11-05.

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% 3 8% 5% 5% 4 4 6% 7% 34%	100929
	Night	15% 11% 4 8% 5% 4 4 3 5% 6% 34%	98098
Transparency	Day	47% 7% 12% 21% 12% 1	104529
	Night	48% 6% 12% 21% 12% 1	102639
Seeing	Day	19% 12% 28% 22% 14% 5%	15522
	Night	20% 10% 30% 29% 11% 1	25321

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	15% 19% 7% 12% 6% 5% 4 3 5% 4 21%	2527
	11th to 20th	Day	15% 19% 7% 16% 11% 9% 4 2 3 4 9%	2530
	21st to end	Day	27% 21% 6% 11% 6% 4 3 3 3 4 13%	2946
February	1st to 10th	Day	12% 17% 4 12% 8% 5% 5% 4 5% 5% 22%	1710
	11th to 20th	Day	12% 15% 6% 12% 8% 5% 4 3 4 5% 25%	1805
	21st to end	Day	14% 17% 4 12% 7% 5% 4 4 5% 4 25%	1570
March	1st to 10th	Day	17% 14% 4 8% 5% 4 4 3 5% 6% 30%	3152
	11th to 20th	Day	12% 14% 5% 11% 6% 4 4 3 5% 6% 30%	3480
	21st to end	Day	18% 13% 4 9% 6% 4 4 3 5% 6% 28%	3815
April	1st to 10th	Day	17% 12% 4 8% 6% 4 5% 3 5% 7% 30%	2247
	11th to 20th	Day	17% 10% 4 7% 5% 4 4 4 5% 7% 36%	2394
	21st to end	Day	16% 10% 3 7% 5% 5% 4 3 5% 6% 35%	2470
May	1st to 10th	Day	17% 9% 3 6% 4 4 5% 4 5% 7% 36%	4082
	11th to 20th	Day	16% 8% 2 6% 4 4 5% 4 6% 8% 37%	4081
	21st to end	Day	10% 6% 2 7% 4 4 4 4 5% 8% 45%	4596
June	1st to 10th	Day	11% 6% 2 6% 5% 5% 5% 5% 7% 9% 41%	2707
	11th to 20th	Day	11% 6% 3 7% 4 4 4 4 6% 9% 42%	2850
	21st to end	Day	10% 7% 2 6% 4 5% 6% 5% 8% 9% 38%	2673
July	1st to 10th	Day	11% 7% 2 7% 5% 5% 6% 5% 7% 8% 37%	4440
	11th to 20th	Day	8% 4 1 4 3 4 5% 4 7% 10% 50%	4440
	21st to end	Day	8% 5% 2 6% 6% 5% 5% 4 7% 9% 42%	4656
August	1st to 10th	Day	12% 5% 2 7% 4 5% 5% 4 6% 9% 40%	4104
	11th to 20th	Day	12% 6% 2 6% 4 5% 5% 4 6% 8% 41%	4044
	21st to end	Day	9% 5% 3 7% 5% 5% 6% 4 7% 9% 41%	4448
September	1st to 10th	Day	10% 7% 3 6% 5% 5% 5% 5% 6% 8% 40%	2173
	11th to 20th	Day	12% 4 2 5% 3 4 5% 4 6% 9% 47%	2090
	21st to end	Day	14% 7% 3 7% 5% 5% 5% 4 5% 8% 37%	2090
October	1st to 10th	Day	13% 7% 2 8% 5% 5% 4 4 5% 7% 41%	2052
	11th to 20th	Day	19% 11% 3 7% 5% 4 5% 4 5% 7% 31%	1900
	21st to end	Day	21% 10% 3 7% 4 5% 4 4 6% 7% 28%	1895
November	1st to 10th	Day	12% 11% 3 8% 5% 4 4 4 5% 7% 36%	1708
	11th to 20th	Day	15% 13% 4 9% 6% 5% 4 4 5% 7% 28%	1710
	21st to end	Day	18% 14% 6% 8% 6% 4 4 3 5% 6% 26%	1620
December	1st to 10th	Day	14% 18% 6% 13% 7% 5% 3 3 6% 5% 20%	1516
	11th to 20th	Day	16% 18% 5% 10% 4 4 4 4 5% 6% 23%	1675
	21st to end	Day	24% 22% 6% 13% 5% 4 3 3 5% 5% 11%	2733
January	1st to 10th	Night	16% 16% 7% 13% 5% 5% 4 3 4 5% 21%	4428
	11th to 20th	Night	15% 17% 8% 16% 7% 9% 4 3 4 4 13%	4440
	21st to end	Night	21% 19% 8% 10% 6% 4 4 3 4 5% 16%	4714
February	1st to 10th	Night	14% 17% 5% 12% 7% 5% 4 4 4 5% 23%	2470
	11th to 20th	Night	14% 14% 6% 10% 7% 4 5% 3 5% 6% 26%	2259
	21st to end	Night	18% 12% 4 10% 6% 5% 5% 3 4 6% 27%	1884
March	1st to 10th	Night	14% 11% 5% 8% 4 4 4 3 4 6% 37%	3701
	11th to 20th	Night	10% 9% 3 7% 4 4 5% 4 6% 8% 40%	3480
	21st to end	Night	17% 10% 4 9% 5% 5% 5% 3 4 5% 33%	3817
April	1st to 10th	Night	17% 12% 4 6% 4 3 4 3 6% 6% 35%	1950
	11th to 20th	Night	19% 7% 3 6% 5% 4 3 3 5% 6% 37%	1734
	21st to end	Night	17% 8% 3 7% 4 4 4 3 6% 6% 37%	1710
May	1st to 10th	Night	13% 9% 3 7% 5% 4 4 4 6% 7% 38%	2813
	11th to 20th	Night	16% 7% 2 6% 4 4 3 3 4 7% 43%	2812
	21st to end	Night	11% 6% 2 6% 4 4 5% 4 6% 7% 48%	2958
June	1st to 10th	Night	11% 5% 2 5% 4 4 4 4 5% 8% 46%	1463
	11th to 20th	Night	11% 5% 2 6% 5% 4 4 4 5% 8% 46%	1330
	21st to end	Night	10% 4 2 6% 4 4 6% 2 6% 10% 47%	1493
July	1st to 10th	Night	7% 5% 3 5% 5% 4 5% 4 8% 9% 45%	2530
	11th to 20th	Night	9% 4 1 5% 3 3 4 3 5% 8% 54%	2530
	21st to end	Night	6% 4 2 6% 4 5% 5% 4 7% 9% 46%	2900
August	1st to 10th	Night	10% 5% 2 5% 4 4 5% 4 6% 8% 48%	2825
	11th to 20th	Night	12% 5% 2 6% 4 4 4 3 6% 7% 48%	2785
	21st to end	Night	9% 5% 2 6% 4 4 4 4 5% 7% 48%	3206
September	1st to 10th	Night	9% 7% 2 5% 4 4 5% 4 5% 7% 47%	1987
	11th to 20th	Night	11% 4 1 5% 3 4 3 4 4 7% 54%	2090
	21st to end	Night	15% 6% 3 7% 5% 4 4 3 5% 7% 43%	2090
October	1st to 10th	Night	15% 6% 2 6% 4 4 3 3 5% 6% 45%	2127
	11th to 20th	Night	20% 11% 2 7% 4 5% 4 3 5% 6% 33%	2280
	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% 41%	2470
	11th to 20th	Night	15% 13% 4 8% 5% 5% 6% 5% 6% 5% 29%	2470
	21st to end	Night	20% 13% 4 8% 5% 4 5% 4 4 7% 28%	2555
December	1st to 10th	Night	17% 17% 6% 12% 6% 5% 4 4 4 6% 19%	2660
	11th to 20th	Night	15% 14% 6% 14% 5% 5% 4 3 5% 5% 23%	3522
	21st to end	Night	25% 23% 6% 10% 5% 3 3 3 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% 19% 11%	2247
	11th to 20th	Day	48% 6% 12% 20% 13% 2	2394
	21st to end	Day	49% 7% 11% 17% 14% 1	2470
May	1st to 10th	Day	45% 7% 12% 21% 12% 2	4120
	11th to 20th	Day	42% 9% 13% 25% 9% 1	4085
	21st to end	Day	37% 6% 11% 20% 23% 4	4609
June	1st to 10th	Day	37% 8% 11% 26% 15% 2	2707
	11th to 20th	Day	38% 6% 12% 25% 16% 2	2850
	21st to end	Day	38% 9% 12% 24% 15% 1	2673
July	1st to 10th	Day	41% 8% 14% 19% 16% 2	4371
	11th to 20th	Day	27% 8% 14% 34% 16% 1	4365
	21st to end	Day	35% 9% 14% 19% 21% 2	4509
August	1st to 10th	Day	38% 8% 13% 24% 16% 1	4091
	11th to 20th	Day	37% 8% 12% 30% 12% 1	4083
	21st to end	Day	37% 8% 14% 27% 14% 1	4447
September	1st to 10th	Day	40% 8% 12% 25% 12% 2	2173
	11th to 20th	Day	33% 7% 13% 31% 15% 2	2090
	21st to end	Day	44% 6% 13% 23% 13%	2090
October	1st to 10th	Day	32% 5% 10% 32% 18% 2	3416
	11th to 20th	Day	40% 6% 11% 26% 16%	3140
	21st to end	Day	47% 6% 14% 24% 9% 1	3095
November	1st to 10th	Day	47% 7% 13% 23% 10% 1	1708
	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% 14% 2	1950
	11th to 20th	Night	46% 6% 11% 18% 17% 2	1734
	21st to end	Night	46% 5% 11% 20% 16% 3	1710
May	1st to 10th	Night	43% 8% 12% 21% 14% 4	2840
	11th to 20th	Night	40% 7% 9% 28% 13% 3	2813
	21st to end	Night	35% 7% 11% 22% 20% 6%	2966
June	1st to 10th	Night	35% 6% 9% 28% 19% 2	1463
	11th to 20th	Night	34% 7% 12% 23% 20% 2	1330
	21st to end	Night	33% 6% 13% 27% 19% 2	1493
July	1st to 10th	Night	33% 7% 12% 27% 15% 6%	2490
	11th to 20th	Night	28% 6% 13% 30% 21% 1	2482
	21st to end	Night	31% 9% 18% 19% 21% 2	2808
August	1st to 10th	Night	33% 8% 13% 30% 17% 1	2814
	11th to 20th	Night	33% 8% 12% 33% 12% 2	2812
	21st to end	Night	33% 8% 12% 31% 15% 1	3206
September	1st to 10th	Night	35% 7% 11% 28% 17% 2	1987
	11th to 20th	Night	30% 6% 12% 30% 20% 2	2090
	21st to end	Night	40% 7% 12% 27% 14% 1	2090
October	1st to 10th	Night	26% 5% 11% 33% 25% 1	3543
	11th to 20th	Night	45% 5% 10% 22% 17% 1	3779
	21st to end	Night	41% 5% 12% 30% 12%	4449
November	1st to 10th	Night	43% 5% 13% 25% 14% 1	2470
	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	25% 15% 32% 21% 7% 1	460
	11th to 20th	Day	29% 17% 29% 13% 7% 5%	452
	21st to end	Day	23% 14% 28% 22% 10% 1	460
May	1st to 10th	Day	23% 15% 28% 21% 11% 2	463
	11th to 20th	Day	20% 9% 30% 22% 14% 5%	487
	21st to end	Day	16% 7% 24% 26% 20% 7%	597
June	1st to 10th	Day	11% 13% 27% 29% 15% 4	680
	11th to 20th	Day	15% 9% 30% 25% 16% 5%	680
	21st to end	Day	12% 9% 28% 29% 17% 5%	680
July	1st to 10th	Day	9% 7% 22% 28% 22% 12%	671
	11th to 20th	Day	11% 7% 29% 26% 19% 8%	668
	21st to end	Day	9% 5% 25% 30% 23% 8%	644
August	1st to 10th	Day	11% 4 22% 25% 22% 16%	486
	11th to 20th	Day	14% 5% 20% 25% 26% 11%	479
	21st to end	Day	12% 5% 22% 27% 23% 11%	539
September	1st to 10th	Day	12% 7% 26% 25% 20% 10%	490
	11th to 20th	Day	11% 4 20% 21% 29% 14%	490
	21st to end	Day	19% 10% 22% 24% 17% 8%	490
October	1st to 10th	Day	17% 10% 30% 21% 17% 5%	490
	11th to 20th	Day	23% 16% 25% 26% 9% 1	490
	21st to end	Day	30% 15% 34% 15% 6%	344
November	1st to 10th	Day	19% 20% 34% 19% 6% 2	282
	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% 11% 34% 23% 8% 1	563
	21st to end	Night	22% 10% 32% 30% 6% 1	570
May	1st to 10th	Night	18% 7% 33% 33% 8% 1	570
	11th to 20th	Night	22% 5% 32% 32% 9% 1	561
	21st to end	Night	13% 4 28% 36% 16% 2	617
June	1st to 10th	Night	12% 6% 26% 43% 12% 1	513
	11th to 20th	Night	13% 4 30% 42% 11%	380
	21st to end	Night	11% 6% 25% 41% 16% 2	543
July	1st to 10th	Night	8% 3 17% 41% 28% 2	555
	11th to 20th	Night	12% 1 24% 41% 20% 3	552
	21st to end	Night	8% 3 19% 47% 21% 1	624
August	1st to 10th	Night	8% 2 18% 42% 28% 2	567
	11th to 20th	Night	10% 2 17% 40% 27% 3	564
	21st to end	Night	12% 4 18% 36% 26% 3	627
September	1st to 10th	Night	12% 4 23% 34% 23% 5%	657
	11th to 20th	Night	13% 4 18% 33% 28% 4	760
	21st to end	Night	17% 7% 21% 31% 20% 4	760
October	1st to 10th	Night	19% 7% 24% 32% 17% 1	760
	11th to 20th	Night	25% 12% 26% 28% 8% 1	760
	21st to end	Night	25% 10% 34% 25% 5%	836
November	1st to 10th	Night	20% 13% 30% 27% 9% 1	760
	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 2024-11-03 02:11:20. Version ac07

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