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 2026-09-29.

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% 8% 40%	149296
	Night	16% 7% 2 6% 4 4 4 3 5% 7% 42%	142096
Transparency	Day	40% 6% 12% 23% 17% 2	152825
	Night	40% 5% 11% 23% 17% 3	146655
Seeing	Day	21% 15% 29% 22% 10% 3	17472
	Night	19% 12% 31% 28% 9% 1	26648

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% 6% 2 6% 4 4 3 3 5% 6% 48%	4661
	11th to 20th	Day	15% 8% 2 7% 4 3 3 3 4 5% 46%	4692
	21st to end	Day	16% 6% 2 5% 3 4 5% 4 5% 6% 42%	5780
February	1st to 10th	Day	14% 8% 3 6% 5% 4 4 3 6% 6% 41%	1890
	11th to 20th	Day	17% 8% 3 6% 4 4 4 3 5% 6% 40%	2024
	21st to end	Day	17% 9% 3 6% 4 4 3 3 5% 5% 40%	1730
March	1st to 10th	Day	21% 5% 2 5% 3 4 3 3 4 5% 45%	4576
	11th to 20th	Day	11% 6% 2 6% 4 5% 5% 4 6% 6% 45%	5032
	21st to end	Day	18% 5% 2 5% 3 4 5% 4 5% 6% 43%	5961
April	1st to 10th	Day	17% 7% 3 5% 4 3 5% 3 6% 7% 40%	2520
	11th to 20th	Day	14% 6% 2 5% 4 5% 4 4 6% 8% 42%	2494
	21st to end	Day	16% 5% 2 6% 5% 4 4 4 6% 7% 40%	2520
May	1st to 10th	Day	23% 7% 3 6% 4 4 4 4 5% 7% 34%	7532
	11th to 20th	Day	19% 8% 3 6% 4 4 4 3 5% 6% 39%	8221
	21st to end	Day	24% 7% 2 6% 4 4 4 3 5% 7% 35%	9060
June	1st to 10th	Day	13% 5% 2 6% 5% 5% 4 4 7% 9% 40%	2940
	11th to 20th	Day	12% 6% 2 6% 5% 5% 5% 4 6% 9% 39%	2940
	21st to end	Day	10% 6% 2 7% 4 4 5% 4 7% 9% 41%	2940
July	1st to 10th	Day	12% 6% 2 7% 5% 5% 5% 5% 7% 9% 37%	8280
	11th to 20th	Day	10% 6% 3 7% 5% 5% 6% 5% 8% 11% 35%	8280
	21st to end	Day	10% 7% 2 7% 5% 5% 5% 4 7% 10% 39%	8958
August	1st to 10th	Day	14% 6% 3 8% 5% 6% 6% 5% 7% 10% 30%	5969
	11th to 20th	Day	12% 5% 2 5% 4 5% 5% 4 7% 10% 40%	5488
	21st to end	Day	11% 5% 2 6% 5% 4 5% 5% 7% 9% 41%	6080
September	1st to 10th	Day	13% 6% 2 6% 4 4 3 4 6% 7% 45%	2520
	11th to 20th	Day	12% 6% 2 4 3 4 4 4 4 8% 49%	2468
	21st to end	Day	18% 8% 3 7% 4 4 5% 4 5% 6% 36%	2288
October	1st to 10th	Day	17% 6% 2 5% 3 3 3 4 5% 6% 46%	2033
	11th to 20th	Day	16% 5% 2 5% 4 3 3 3 4 7% 49%	2000
	21st to end	Day	17% 6% 2 6% 3 3 3 2 5% 6% 47%	2104
November	1st to 10th	Day	12% 6% 2 5% 3 4 2 2 5% 6% 53%	1851
	11th to 20th	Day	15% 6% 2 5% 3 3 4 3 6% 6% 47%	1890
	21st to end	Day	15% 5% 2 6% 4 4 4 3 5% 7% 46%	1780
December	1st to 10th	Day	13% 7% 2 6% 4 4 3 3 6% 7% 45%	2680
	11th to 20th	Day	20% 9% 2 4 3 2 3 2 4 5% 45%	3066
	21st to end	Day	16% 6% 2 5% 4 4 5% 4 6% 7% 41%	4048
January	1st to 10th	Night	12% 7% 2 6% 4 4 4 3 4 7% 47%	8234
	11th to 20th	Night	16% 7% 3 6% 3 3 3 3 4 5% 48%	8176
	21st to end	Night	16% 8% 2 6% 3 3 4 3 5% 5% 45%	8401
February	1st to 10th	Night	16% 9% 2 6% 4 4 4 3 5% 7% 41%	2730
	11th to 20th	Night	18% 8% 2 6% 4 4 3 3 5% 6% 40%	2480
	21st to end	Night	17% 8% 3 6% 4 3 4 3 5% 5% 42%	2076
March	1st to 10th	Night	19% 8% 2 5% 3 3 3 3 4 6% 44%	5484
	11th to 20th	Night	12% 9% 3 5% 3 3 3 3 4 5% 50%	5142
	21st to end	Night	16% 8% 3 6% 4 3 4 3 5% 5% 42%	5213
April	1st to 10th	Night	17% 7% 2 7% 4 4 4 3 5% 6% 40%	2100
	11th to 20th	Night	16% 6% 2 7% 4 5% 4 3 5% 6% 42%	2075
	21st to end	Night	17% 6% 2 5% 3 3 4 3 5% 7% 45%	2100
May	1st to 10th	Night	19% 8% 3 8% 4 4 4 4 6% 8% 32%	5387
	11th to 20th	Night	19% 8% 3 7% 4 4 4 4 5% 8% 36%	4645
	21st to end	Night	25% 8% 2 7% 3 3 4 3 5% 8% 31%	5114
June	1st to 10th	Night	14% 6% 1 6% 5% 3 3 4 6% 8% 44%	1680
	11th to 20th	Night	12% 6% 3 6% 5% 5% 4 4 6% 7% 41%	1680
	21st to end	Night	9% 6% 2 5% 5% 5% 6% 5% 7% 10% 40%	1680
July	1st to 10th	Night	12% 6% 3 7% 5% 5% 6% 4 6% 10% 36%	4680
	11th to 20th	Night	10% 7% 3 8% 5% 5% 6% 5% 8% 11% 34%	4680
	21st to end	Night	13% 6% 2 7% 4 4 5% 5% 6% 8% 40%	5115
August	1st to 10th	Night	19% 6% 3 6% 5% 5% 5% 5% 7% 9% 31%	4135
	11th to 20th	Night	13% 6% 3 7% 5% 5% 5% 4 6% 8% 40%	4554
	21st to end	Night	11% 6% 2 6% 4 4 4 4 5% 7% 46%	5045
September	1st to 10th	Night	14% 6% 2 6% 5% 4 5% 3 5% 7% 44%	2100
	11th to 20th	Night	12% 5% 2 5% 3 3 3 3 5% 7% 51%	2152
	21st to end	Night	21% 7% 2 6% 4 3 2 3 6% 7% 38%	2289
October	1st to 10th	Night	18% 6% 2 5% 4 4 4 3 4 5% 45%	2364
	11th to 20th	Night	15% 5% 2 5% 3 4 3 3 4 6% 51%	2400
	21st to end	Night	17% 7% 2 5% 3 3 3 3 5% 5% 47%	2735
November	1st to 10th	Night	10% 5% 2 5% 4 3 3 3 5% 6% 53%	2667
	11th to 20th	Night	16% 6% 2 6% 3 3 4 3 4 4 48%	2730
	21st to end	Night	13% 6% 2 6% 4 4 4 4 6% 7% 45%	2835
December	1st to 10th	Night	13% 7% 2 6% 3 3 3 3 4 6% 48%	4720
	11th to 20th	Night	22% 7% 2 5% 3 3 3 3 4 6% 41%	5348
	21st to end	Night	19% 8% 3 6% 3 4 3 3 4 6% 41%	7150

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	37% 4 10% 27% 20% 2	4662
	11th to 20th	Day	40% 3 8% 23% 20% 6%	4722
	21st to end	Day	41% 4 13% 26% 14% 1	5780
February	1st to 10th	Day	43% 6% 12% 25% 12% 2	1890
	11th to 20th	Day	44% 4 10% 24% 15% 2	2033
	21st to end	Day	45% 5% 9% 24% 13% 4	1730
March	1st to 10th	Day	41% 4 9% 23% 15% 7%	4579
	11th to 20th	Day	36% 6% 11% 28% 14% 5%	5032
	21st to end	Day	42% 5% 9% 16% 22% 5%	5961
April	1st to 10th	Day	42% 6% 11% 22% 15% 5%	2520
	11th to 20th	Day	39% 6% 14% 23% 16% 3	2494
	21st to end	Day	41% 6% 10% 21% 18% 4	2520
May	1st to 10th	Day	48% 6% 12% 18% 15% 1	7543
	11th to 20th	Day	44% 6% 9% 24% 16% 1	8225
	21st to end	Day	48% 6% 9% 22% 14% 2	9061
June	1st to 10th	Day	38% 8% 13% 22% 17% 1	2940
	11th to 20th	Day	39% 9% 13% 24% 12% 3	2940
	21st to end	Day	37% 9% 14% 22% 17% 1	2940
July	1st to 10th	Day	41% 10% 13% 17% 17% 2	8210
	11th to 20th	Day	41% 8% 15% 24% 12% 1	8205
	21st to end	Day	39% 7% 10% 21% 22% 1	8760
August	1st to 10th	Day	47% 9% 16% 19% 8%	5956
	11th to 20th	Day	37% 7% 15% 28% 12% 1	5524
	21st to end	Day	36% 7% 11% 26% 18% 2	6080
September	1st to 10th	Day	38% 7% 13% 20% 20% 3	2520
	11th to 20th	Day	33% 5% 11% 25% 22% 4	2468
	21st to end	Day	48% 7% 8% 16% 19% 2	2288
October	1st to 10th	Day	35% 5% 10% 18% 28% 5%	3306
	11th to 20th	Day	25% 3 10% 25% 30% 7%	3240
	21st to end	Day	25% 4 12% 26% 28% 5%	3381
November	1st to 10th	Day	32% 4 13% 25% 22% 3	1851
	11th to 20th	Day	38% 5% 9% 24% 21% 3	1890
	21st to end	Day	38% 5% 12% 30% 12% 2	1780
December	1st to 10th	Day	38% 4 15% 27% 13% 2	2680
	11th to 20th	Day	43% 4 11% 29% 11% 2	3066
	21st to end	Day	41% 7% 11% 23% 17% 2	4048
January	1st to 10th	Night	38% 4 12% 24% 17% 5%	8234
	11th to 20th	Night	39% 3 10% 22% 18% 7%	8221
	21st to end	Night	40% 3 8% 24% 21% 3	8401
February	1st to 10th	Night	44% 4 13% 24% 13% 2	2730
	11th to 20th	Night	44% 5% 10% 20% 17% 5%	2482
	21st to end	Night	42% 4 9% 23% 17% 5%	2076
March	1st to 10th	Night	42% 4 9% 23% 13% 9%	5494
	11th to 20th	Night	36% 6% 14% 26% 14% 4	5143
	21st to end	Night	43% 5% 7% 16% 24% 5%	5213
April	1st to 10th	Night	44% 6% 10% 19% 17% 4	2100
	11th to 20th	Night	42% 5% 11% 19% 20% 3	2075
	21st to end	Night	39% 6% 10% 20% 19% 5%	2100
May	1st to 10th	Night	48% 7% 11% 19% 13% 2	5393
	11th to 20th	Night	47% 6% 12% 22% 12% 1	4646
	21st to end	Night	51% 7% 10% 19% 12% 1	5115
June	1st to 10th	Night	38% 7% 12% 23% 20% 2	1680
	11th to 20th	Night	40% 9% 12% 24% 13% 2	1680
	21st to end	Night	36% 9% 16% 23% 15% 2	1680
July	1st to 10th	Night	43% 8% 15% 21% 13% 1	4640
	11th to 20th	Night	42% 8% 16% 22% 10% 1	4632
	21st to end	Night	40% 6% 14% 21% 19% 1	4998
August	1st to 10th	Night	48% 9% 16% 18% 9% 1	4124
	11th to 20th	Night	41% 7% 14% 28% 10% 1	4584
	21st to end	Night	36% 6% 10% 26% 20% 1	5045
September	1st to 10th	Night	39% 7% 11% 20% 20% 3	2100
	11th to 20th	Night	32% 6% 11% 22% 25% 4	2152
	21st to end	Night	45% 6% 9% 19% 20% 2	2289
October	1st to 10th	Night	38% 5% 10% 23% 22% 3	3871
	11th to 20th	Night	25% 3 10% 28% 29% 5%	3899
	21st to end	Night	27% 4 11% 30% 24% 4	4408
November	1st to 10th	Night	32% 5% 13% 23% 22% 5%	2667
	11th to 20th	Night	39% 5% 9% 22% 20% 5%	2730
	21st to end	Night	38% 5% 13% 25% 17% 2	2835
December	1st to 10th	Night	37% 4 12% 31% 14% 2	4720
	11th to 20th	Night	44% 4 11% 24% 14% 4	5348
	21st to end	Night	44% 5% 11% 20% 17% 3	7150

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	25% 28% 32% 11% 3 1	220
	11th to 20th	Day	35% 28% 26% 10% 1	228
	21st to end	Day	26% 26% 31% 12% 4	363
February	1st to 10th	Day	27% 24% 35% 11% 3	330
	11th to 20th	Day	30% 24% 33% 11% 2	512
	21st to end	Day	28% 22% 34% 14% 3	446
March	1st to 10th	Day	27% 21% 30% 17% 4	540
	11th to 20th	Day	25% 23% 33% 14% 4 1	540
	21st to end	Day	26% 23% 31% 15% 4 1	594
April	1st to 10th	Day	28% 23% 30% 14% 5% 1	540
	11th to 20th	Day	22% 22% 32% 17% 6% 1	532
	21st to end	Day	26% 16% 32% 19% 5% 1	540
May	1st to 10th	Day	28% 20% 31% 12% 7% 1	543
	11th to 20th	Day	21% 15% 33% 22% 8% 2	567
	21st to end	Day	23% 10% 24% 25% 14% 3	617
June	1st to 10th	Day	16% 13% 27% 28% 13% 3	570
	11th to 20th	Day	18% 12% 31% 27% 9% 3	570
	21st to end	Day	13% 9% 31% 31% 12% 3	570
July	1st to 10th	Day	11% 6% 22% 34% 22% 5%	565
	11th to 20th	Day	8% 4 26% 34% 23% 5%	564
	21st to end	Day	11% 6% 29% 33% 16% 5%	620
August	1st to 10th	Day	11% 5% 28% 33% 17% 6%	566
	11th to 20th	Day	14% 4 22% 35% 19% 6%	559
	21st to end	Day	13% 8% 28% 28% 16% 8%	627
September	1st to 10th	Day	15% 10% 29% 25% 16% 6%	570
	11th to 20th	Day	15% 6% 25% 29% 16% 8%	570
	21st to end	Day	26% 13% 23% 23% 9% 5%	562
October	1st to 10th	Day	22% 7% 26% 23% 13% 8%	530
	11th to 20th	Day	19% 16% 29% 22% 11% 3	530
	21st to end	Day	18% 18% 32% 19% 11% 2	530
November	1st to 10th	Day	19% 14% 31% 22% 11% 2	425
	11th to 20th	Day	23% 20% 32% 20% 6%	430
	21st to end	Day	23% 19% 35% 18% 5% 1	320
December	1st to 10th	Day	25% 26% 34% 10% 6%	220
	11th to 20th	Day	32% 19% 33% 11% 4	220
	21st to end	Day	27% 21% 31% 13% 6% 1	242
January	1st to 10th	Night	20% 19% 37% 20% 4	840
	11th to 20th	Night	25% 18% 32% 22% 3	840
	21st to end	Night	18% 19% 40% 22% 2	924
February	1st to 10th	Night	20% 17% 38% 23% 2	840
	11th to 20th	Night	25% 22% 35% 18% 1	823
	21st to end	Night	23% 18% 38% 19% 2	692
March	1st to 10th	Night	22% 18% 34% 21% 4	840
	11th to 20th	Night	21% 19% 36% 18% 5%	840
	21st to end	Night	22% 15% 41% 18% 5%	924
April	1st to 10th	Night	21% 20% 37% 17% 5%	840
	11th to 20th	Night	20% 14% 38% 23% 4	831
	21st to end	Night	20% 13% 34% 28% 5%	840
May	1st to 10th	Night	21% 14% 35% 24% 6%	680
	11th to 20th	Night	18% 11% 37% 27% 5%	420
	21st to end	Night	20% 6% 26% 36% 10% 1	455
June	1st to 10th	Night	16% 6% 31% 38% 9%	420
	11th to 20th	Night	13% 9% 29% 41% 9%	420
	21st to end	Night	10% 5% 27% 47% 11%	420
July	1st to 10th	Night	11% 4 25% 42% 17% 1	410
	11th to 20th	Night	7% 3 25% 45% 19% 1	408
	21st to end	Night	10% 4 27% 41% 19%	466
August	1st to 10th	Night	12% 3 19% 43% 22% 2	627
	11th to 20th	Night	14% 4 19% 39% 22% 2	827
	21st to end	Night	14% 4 20% 39% 21% 2	924
September	1st to 10th	Night	16% 5% 27% 35% 16% 2	840
	11th to 20th	Night	14% 4 22% 35% 20% 4	840
	21st to end	Night	25% 5% 21% 31% 17% 1	833
October	1st to 10th	Night	21% 7% 24% 28% 17% 3	800
	11th to 20th	Night	18% 10% 27% 33% 12% 1	800
	21st to end	Night	20% 12% 33% 26% 9% 1	880
November	1st to 10th	Night	15% 11% 35% 29% 11% 1	820
	11th to 20th	Night	20% 17% 30% 25% 8%	840
	21st to end	Night	17% 16% 35% 25% 6%	840
December	1st to 10th	Night	24% 16% 34% 20% 5% 1	840
	11th to 20th	Night	21% 16% 35% 24% 5%	840
	21st to end	Night	21% 16% 34% 27% 2	924

Page generated at 2026-09-26 04:18:38. Version ac07

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