Levittown
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Levittown clear sky chart from 2005-11-06 to 2025-05-26.

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% 6% 2 6% 4 4 4 4 6% 7% 41%	113943
	Night	16% 7% 2 6% 4 4 4 3 5% 6% 43%	115314
Transparency	Day	40% 6% 12% 23% 17% 3	117519
	Night	39% 6% 11% 23% 17% 4	119902
Seeing	Day	21% 15% 29% 22% 10% 3	15671
	Night	19% 12% 31% 28% 9% 1	25010

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	13% 7% 2 5% 3 3 3 3 5% 6% 52%	3597
	11th to 20th	Day	14% 9% 3 8% 4 4 4 3 4 6% 42%	3598
	21st to end	Day	19% 8% 3 6% 4 4 3 3 4 5% 42%	4466
February	1st to 10th	Day	15% 8% 3 6% 5% 5% 4 3 6% 6% 39%	1800
	11th to 20th	Day	17% 8% 3 6% 4 4 4 3 5% 6% 41%	1925
	21st to end	Day	17% 9% 3 7% 4 4 3 3 6% 6% 39%	1650
March	1st to 10th	Day	21% 5% 2 5% 3 4 3 3 4 5% 45%	4476
	11th to 20th	Day	11% 6% 2 6% 4 5% 5% 4 6% 6% 45%	4924
	21st to end	Day	18% 5% 2 5% 3 4 4 4 5% 6% 43%	5832
April	1st to 10th	Day	17% 8% 3 6% 4 3 5% 3 6% 6% 39%	2400
	11th to 20th	Day	15% 7% 2 5% 4 5% 4 4 6% 7% 41%	2374
	21st to end	Day	16% 5% 2 6% 5% 4 4 4 7% 7% 40%	2400
May	1st to 10th	Day	27% 8% 3 6% 4 4 4 4 5% 7% 28%	4183
	11th to 20th	Day	23% 8% 3 7% 5% 5% 4 4 5% 6% 30%	4538
	21st to end	Day	12% 6% 2 5% 4 4 4 4 6% 9% 43%	4907
June	1st to 10th	Day	13% 5% 2 6% 5% 5% 5% 4 7% 9% 39%	2660
	11th to 20th	Day	11% 7% 2 6% 5% 5% 5% 4 7% 9% 39%	2660
	21st to end	Day	10% 6% 2 7% 4 5% 5% 4 7% 10% 41%	2660
July	1st to 10th	Day	7% 5% 2 7% 6% 6% 7% 6% 9% 10% 35%	4440
	11th to 20th	Day	11% 6% 2 6% 5% 5% 6% 5% 8% 10% 37%	4440
	21st to end	Day	11% 9% 3 8% 6% 5% 6% 5% 6% 8% 32%	4793
August	1st to 10th	Day	18% 6% 3 8% 5% 6% 5% 4 7% 8% 32%	4074
	11th to 20th	Day	13% 6% 2 5% 4 5% 5% 4 7% 9% 40%	3730
	21st to end	Day	10% 5% 2 5% 4 4 5% 4 7% 8% 45%	4180
September	1st to 10th	Day	13% 6% 2 6% 5% 5% 3 4 6% 6% 44%	2280
	11th to 20th	Day	12% 5% 2 4 3 4 4 4 4 8% 50%	2233
	21st to end	Day	18% 8% 3 7% 4 3 5% 4 5% 6% 38%	2090
October	1st to 10th	Day	17% 6% 2 6% 3 3 3 4 5% 6% 44%	1932
	11th to 20th	Day	15% 5% 2 5% 3 3 3 4 4 7% 50%	1900
	21st to end	Day	17% 6% 3 6% 3 3 3 2 5% 6% 46%	1999
November	1st to 10th	Day	12% 6% 2 5% 3 4 2 2 5% 6% 53%	1761
	11th to 20th	Day	15% 6% 2 5% 3 3 4 3 5% 6% 48%	1800
	21st to end	Day	15% 5% 2 5% 4 4 4 3 5% 7% 46%	1695
December	1st to 10th	Day	13% 7% 2 6% 4 4 3 3 6% 7% 45%	2600
	11th to 20th	Day	20% 9% 2 4 3 2 3 2 4 5% 45%	2986
	21st to end	Day	16% 5% 2 5% 4 4 5% 4 6% 7% 41%	3960
January	1st to 10th	Night	13% 6% 2 5% 3 3 4 3 4 6% 50%	6349
	11th to 20th	Night	15% 7% 2 6% 4 3 3 3 4 5% 49%	6270
	21st to end	Night	18% 8% 2 6% 4 3 4 3 5% 5% 42%	6490
February	1st to 10th	Night	16% 9% 2 6% 4 4 4 3 5% 7% 41%	2600
	11th to 20th	Night	18% 8% 2 6% 4 4 3 3 5% 6% 41%	2359
	21st to end	Night	17% 8% 3 6% 4 3 4 3 5% 5% 42%	1980
March	1st to 10th	Night	19% 8% 2 5% 3 3 3 3 4 6% 44%	5364
	11th to 20th	Night	12% 9% 3 5% 3 3 3 3 4 5% 50%	5031
	21st to end	Night	16% 8% 3 6% 4 3 4 3 5% 5% 42%	5100
April	1st to 10th	Night	17% 7% 3 7% 4 4 4 3 5% 6% 40%	2000
	11th to 20th	Night	16% 6% 2 7% 4 5% 4 3 5% 6% 42%	1975
	21st to end	Night	17% 5% 2 5% 3 4 4 3 5% 7% 45%	2000
May	1st to 10th	Night	22% 10% 3 8% 3 4 4 4 5% 8% 30%	2998
	11th to 20th	Night	22% 9% 3 8% 4 4 3 4 5% 7% 31%	2581
	21st to end	Night	14% 7% 2 6% 3 3 4 4 6% 11% 41%	2784
June	1st to 10th	Night	14% 6% 1 6% 5% 3 3 4 7% 8% 43%	1520
	11th to 20th	Night	11% 6% 3 6% 5% 5% 4 4 6% 7% 43%	1520
	21st to end	Night	8% 5% 2 5% 5% 5% 6% 5% 7% 10% 41%	1520
July	1st to 10th	Night	8% 6% 3 7% 5% 6% 6% 5% 8% 11% 36%	2520
	11th to 20th	Night	11% 6% 2 6% 4 4 6% 5% 8% 10% 38%	2520
	21st to end	Night	15% 7% 2 7% 5% 5% 5% 5% 6% 7% 35%	2756
August	1st to 10th	Night	22% 6% 2 6% 5% 4 4 5% 6% 8% 32%	2825
	11th to 20th	Night	13% 6% 2 6% 5% 5% 5% 4 6% 8% 41%	3094
	21st to end	Night	9% 6% 2 5% 4 4 4 4 5% 8% 49%	3476
September	1st to 10th	Night	14% 6% 2 6% 4 4 5% 4 5% 7% 45%	1900
	11th to 20th	Night	12% 5% 2 5% 3 3 3 3 5% 7% 52%	1947
	21st to end	Night	19% 6% 2 6% 4 3 3 4 6% 7% 41%	2090
October	1st to 10th	Night	18% 7% 2 5% 4 4 4 3 4 6% 44%	2246
	11th to 20th	Night	14% 5% 2 5% 3 4 3 3 4 6% 51%	2280
	21st to end	Night	17% 7% 2 5% 3 3 3 3 5% 5% 47%	2598
November	1st to 10th	Night	11% 5% 2 5% 4 3 3 3 4 6% 53%	2537
	11th to 20th	Night	16% 6% 2 6% 4 3 4 3 4 4 49%	2600
	21st to end	Night	13% 6% 2 5% 4 5% 4 4 6% 7% 45%	2700
December	1st to 10th	Night	14% 7% 2 5% 3 3 3 3 4 6% 48%	4580
	11th to 20th	Night	23% 7% 2 5% 3 3 3 3 4 6% 41%	5208
	21st to end	Night	19% 8% 3 6% 3 4 3 3 4 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 10% 27% 23% 3	3598
	11th to 20th	Day	42% 4 9% 23% 16% 5%	3628
	21st to end	Day	44% 5% 12% 23% 14% 1	4466
February	1st to 10th	Day	44% 6% 12% 25% 11% 2	1800
	11th to 20th	Day	44% 5% 10% 24% 15% 2	1934
	21st to end	Day	45% 5% 10% 24% 13% 4	1650
March	1st to 10th	Day	41% 4 9% 23% 15% 7%	4479
	11th to 20th	Day	36% 6% 11% 28% 15% 5%	4924
	21st to end	Day	42% 5% 9% 16% 23% 5%	5832
April	1st to 10th	Day	43% 6% 11% 21% 15% 5%	2400
	11th to 20th	Day	40% 6% 13% 22% 16% 4	2374
	21st to end	Day	40% 7% 11% 20% 19% 4	2400
May	1st to 10th	Day	53% 8% 11% 17% 10% 2	4197
	11th to 20th	Day	52% 8% 13% 18% 8% 1	4542
	21st to end	Day	34% 8% 13% 26% 16% 2	4907
June	1st to 10th	Day	39% 8% 13% 23% 15% 1	2660
	11th to 20th	Day	39% 10% 13% 24% 12% 3	2660
	21st to end	Day	37% 9% 14% 23% 16% 1	2660
July	1st to 10th	Day	39% 12% 15% 18% 14% 3	4370
	11th to 20th	Day	38% 9% 16% 21% 14% 1	4365
	21st to end	Day	46% 8% 11% 18% 16% 1	4640
August	1st to 10th	Day	48% 8% 14% 21% 9% 1	4061
	11th to 20th	Day	37% 7% 13% 28% 14% 1	3766
	21st to end	Day	33% 7% 11% 27% 20% 2	4180
September	1st to 10th	Day	39% 7% 11% 19% 21% 3	2280
	11th to 20th	Day	32% 5% 12% 24% 24% 4	2233
	21st to end	Day	46% 7% 8% 17% 20% 2	2090
October	1st to 10th	Day	36% 5% 10% 17% 28% 5%	3205
	11th to 20th	Day	24% 3 10% 24% 31% 7%	3140
	21st to end	Day	25% 4 12% 26% 28% 5%	3276
November	1st to 10th	Day	33% 4 13% 25% 22% 3	1761
	11th to 20th	Day	38% 5% 9% 24% 21% 3	1800
	21st to end	Day	37% 5% 13% 31% 12% 2	1695
December	1st to 10th	Day	38% 4 15% 27% 13% 2	2600
	11th to 20th	Day	43% 4 11% 29% 11% 2	2986
	21st to end	Day	40% 7% 12% 22% 17% 2	3960
January	1st to 10th	Night	35% 4 8% 25% 21% 6%	6349
	11th to 20th	Night	39% 4 10% 24% 17% 7%	6315
	21st to end	Night	43% 4 9% 23% 19% 3	6490
February	1st to 10th	Night	44% 4 14% 24% 12% 2	2600
	11th to 20th	Night	44% 5% 9% 20% 17% 5%	2361
	21st to end	Night	43% 4 9% 22% 17% 5%	1980
March	1st to 10th	Night	41% 4 9% 23% 13% 10%	5374
	11th to 20th	Night	36% 6% 14% 26% 14% 4	5032
	21st to end	Night	43% 5% 7% 16% 24% 5%	5100
April	1st to 10th	Night	44% 6% 10% 19% 17% 4	2000
	11th to 20th	Night	42% 5% 10% 19% 20% 3	1975
	21st to end	Night	38% 6% 10% 20% 20% 5%	2000
May	1st to 10th	Night	51% 9% 10% 18% 11% 1	3004
	11th to 20th	Night	53% 8% 13% 14% 10% 2	2582
	21st to end	Night	36% 10% 16% 21% 15% 2	2785
June	1st to 10th	Night	38% 7% 12% 22% 19% 2	1520
	11th to 20th	Night	39% 9% 12% 26% 13% 1	1520
	21st to end	Night	34% 9% 16% 24% 15% 2	1520
July	1st to 10th	Night	39% 11% 20% 17% 11% 2	2480
	11th to 20th	Night	37% 9% 18% 23% 11% 1	2472
	21st to end	Night	45% 7% 15% 17% 14% 1	2668
August	1st to 10th	Night	47% 8% 19% 16% 9% 1	2814
	11th to 20th	Night	40% 7% 12% 27% 14% 1	3124
	21st to end	Night	32% 7% 10% 27% 22% 2	3476
September	1st to 10th	Night	38% 8% 12% 19% 21% 3	1900
	11th to 20th	Night	31% 6% 12% 21% 27% 4	1947
	21st to end	Night	43% 6% 9% 19% 21% 2	2090
October	1st to 10th	Night	38% 5% 10% 23% 21% 2	3753
	11th to 20th	Night	24% 4 10% 28% 29% 5%	3779
	21st to end	Night	27% 4 11% 30% 24% 4	4271
November	1st to 10th	Night	32% 5% 13% 23% 22% 5%	2537
	11th to 20th	Night	39% 5% 9% 22% 20% 5%	2600
	21st to end	Night	37% 6% 13% 26% 17% 2	2700
December	1st to 10th	Night	37% 4 12% 31% 14% 2	4580
	11th to 20th	Night	45% 4 11% 24% 14% 4	5208
	21st to end	Night	44% 5% 11% 20% 17% 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	26% 29% 31% 11% 3 1	200
	11th to 20th	Day	35% 28% 26% 10% 1	207
	21st to end	Day	28% 24% 30% 13% 5%	330
February	1st to 10th	Day	28% 25% 34% 10% 2	300
	11th to 20th	Day	31% 25% 33% 10% 2	473
	21st to end	Day	29% 21% 34% 13% 2	414
March	1st to 10th	Day	27% 22% 30% 17% 3	500
	11th to 20th	Day	24% 24% 33% 13% 4 1	500
	21st to end	Day	27% 22% 31% 16% 4 1	550
April	1st to 10th	Day	28% 24% 30% 13% 5% 1	500
	11th to 20th	Day	23% 22% 32% 17% 6% 1	492
	21st to end	Day	26% 16% 32% 19% 5% 1	500
May	1st to 10th	Day	29% 19% 30% 13% 8% 1	503
	11th to 20th	Day	22% 15% 31% 22% 8% 2	527
	21st to end	Day	19% 11% 24% 27% 16% 3	549
June	1st to 10th	Day	15% 13% 28% 27% 14% 3	490
	11th to 20th	Day	15% 11% 31% 28% 11% 3	490
	21st to end	Day	13% 10% 31% 31% 12% 3	490
July	1st to 10th	Day	10% 6% 23% 34% 21% 6%	485
	11th to 20th	Day	8% 3 25% 36% 23% 5%	484
	21st to end	Day	12% 7% 29% 32% 16% 4	532
August	1st to 10th	Day	12% 5% 27% 33% 17% 7%	486
	11th to 20th	Day	13% 4 22% 36% 19% 6%	479
	21st to end	Day	14% 8% 25% 28% 17% 9%	539
September	1st to 10th	Day	16% 10% 25% 26% 17% 7%	490
	11th to 20th	Day	15% 6% 26% 29% 17% 9%	490
	21st to end	Day	25% 13% 23% 23% 9% 6%	490
October	1st to 10th	Day	24% 8% 27% 22% 13% 7%	490
	11th to 20th	Day	17% 15% 30% 23% 11% 3	490
	21st to end	Day	19% 16% 33% 19% 11% 2	491
November	1st to 10th	Day	19% 13% 32% 23% 12% 2	395
	11th to 20th	Day	22% 19% 33% 20% 6%	400
	21st to end	Day	22% 19% 34% 18% 5% 1	295
December	1st to 10th	Day	24% 26% 34% 10% 7%	200
	11th to 20th	Day	33% 19% 33% 11% 4 1	200
	21st to end	Day	26% 20% 33% 14% 7% 1	220
January	1st to 10th	Night	21% 20% 36% 20% 4	800
	11th to 20th	Night	24% 17% 32% 23% 3	800
	21st to end	Night	17% 19% 40% 22% 2	880
February	1st to 10th	Night	21% 17% 38% 23% 1	800
	11th to 20th	Night	25% 23% 35% 17% 1	783
	21st to end	Night	23% 19% 38% 18% 2	660
March	1st to 10th	Night	22% 19% 35% 21% 4	800
	11th to 20th	Night	21% 20% 36% 18% 5%	800
	21st to end	Night	21% 15% 40% 18% 5%	880
April	1st to 10th	Night	21% 20% 37% 17% 4	800
	11th to 20th	Night	20% 15% 37% 24% 4	791
	21st to end	Night	20% 13% 34% 27% 5%	800
May	1st to 10th	Night	21% 13% 34% 25% 6%	648
	11th to 20th	Night	19% 12% 37% 27% 5% 1	400
	21st to end	Night	17% 5% 26% 39% 11% 1	423
June	1st to 10th	Night	17% 6% 30% 38% 9% 1	380
	11th to 20th	Night	12% 7% 29% 42% 10%	380
	21st to end	Night	9% 4 28% 48% 11%	380
July	1st to 10th	Night	10% 4 26% 41% 16% 2	370
	11th to 20th	Night	7% 3 24% 45% 19% 2	368
	21st to end	Night	10% 5% 27% 41% 17%	421
August	1st to 10th	Night	12% 2 20% 43% 21% 2	567
	11th to 20th	Night	13% 5% 20% 38% 22% 2	747
	21st to end	Night	14% 4 19% 39% 22% 2	836
September	1st to 10th	Night	15% 4 27% 35% 16% 2	760
	11th to 20th	Night	14% 4 22% 35% 21% 4	760
	21st to end	Night	23% 6% 22% 31% 18% 1	760
October	1st to 10th	Night	22% 7% 24% 27% 16% 3	760
	11th to 20th	Night	17% 9% 28% 33% 12% 1	760
	21st to end	Night	21% 11% 32% 26% 9% 1	836
November	1st to 10th	Night	14% 10% 35% 29% 11% 1	780
	11th to 20th	Night	20% 16% 30% 26% 8% 1	800
	21st to end	Night	17% 16% 35% 25% 6% 1	800
December	1st to 10th	Night	24% 16% 33% 20% 5% 1	800
	11th to 20th	Night	20% 15% 35% 24% 5%	800
	21st to end	Night	21% 15% 34% 28% 2	880

Page generated at 2025-05-23 09:20:58. Version ac07

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