Widener University
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Widener University clear sky chart from 2005-11-06 to 2025-07-06.

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	16% 6% 2 6% 4 4 4 4 6% 7% 41%	119931
	Night	16% 7% 2 6% 4 4 4 3 5% 6% 44%	118856
Transparency	Day	40% 6% 12% 23% 17% 3	123518
	Night	40% 5% 11% 23% 18% 4	123429
Seeing	Day	19% 13% 28% 24% 12% 4	15829
	Night	19% 10% 32% 29% 10% 1	25141

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% 5% 2 4 3 5% 4 4 5% 6% 48%	3597
	11th to 20th	Day	14% 8% 2 7% 5% 4 4 3 4 6% 42%	3722
	21st to end	Day	18% 7% 2 6% 4 3 4 3 4 5% 44%	4466
February	1st to 10th	Day	15% 8% 2 6% 5% 4 4 4 5% 7% 39%	1800
	11th to 20th	Day	17% 8% 3 5% 4 4 5% 4 5% 6% 40%	1899
	21st to end	Day	18% 9% 3 6% 4 4 3 3 4 7% 39%	1650
March	1st to 10th	Day	20% 4 2 4 3 3 3 3 4 6% 47%	4512
	11th to 20th	Day	12% 6% 2 5% 4 4 4 4 5% 7% 46%	4980
	21st to end	Day	19% 6% 2 5% 3 3 4 4 5% 6% 44%	5780
April	1st to 10th	Day	17% 7% 2 6% 4 4 4 3 6% 7% 40%	2400
	11th to 20th	Day	15% 7% 2 5% 4 4 5% 3 6% 7% 42%	2374
	21st to end	Day	16% 6% 2 6% 4 4 4 4 6% 8% 41%	2400
May	1st to 10th	Day	27% 8% 2 5% 4 4 4 3 5% 7% 31%	5783
	11th to 20th	Day	25% 8% 2 6% 4 4 4 3 5% 7% 32%	6318
	21st to end	Day	19% 6% 2 5% 4 4 5% 4 6% 8% 38%	6949
June	1st to 10th	Day	13% 6% 2 5% 4 4 6% 5% 6% 9% 40%	2800
	11th to 20th	Day	14% 5% 2 6% 5% 5% 5% 5% 7% 9% 37%	2800
	21st to end	Day	10% 4 2 6% 4 5% 5% 4 6% 10% 43%	2800
July	1st to 10th	Day	7% 5% 2 6% 6% 6% 7% 6% 8% 11% 38%	4510
	11th to 20th	Day	10% 5% 2 5% 5% 5% 5% 4 8% 10% 39%	4440
	21st to end	Day	11% 7% 3 8% 6% 6% 6% 5% 7% 8% 32%	4700
August	1st to 10th	Day	19% 5% 2 6% 5% 5% 5% 5% 6% 8% 34%	4104
	11th to 20th	Day	13% 5% 2 6% 4 4 4 4 7% 9% 43%	3735
	21st to end	Day	11% 5% 2 5% 4 4 4 4 6% 7% 49%	4180
September	1st to 10th	Day	14% 5% 2 5% 5% 4 5% 3 5% 6% 45%	2280
	11th to 20th	Day	13% 4 2 5% 3 3 4 4 5% 7% 50%	2254
	21st to end	Day	20% 8% 2 7% 3 4 4 4 4 6% 38%	2085
October	1st to 10th	Day	18% 5% 2 5% 3 3 3 4 5% 6% 44%	1900
	11th to 20th	Day	16% 4 2 4 3 3 4 3 5% 7% 50%	1900
	21st to end	Day	18% 6% 2 5% 3 3 4 3 5% 6% 47%	2034
November	1st to 10th	Day	13% 5% 2 4 3 3 3 2 5% 6% 53%	1761
	11th to 20th	Day	16% 4 2 4 4 4 3 4 5% 7% 48%	1800
	21st to end	Day	15% 6% 2 5% 3 3 4 3 5% 6% 47%	1672
December	1st to 10th	Day	14% 7% 2 5% 3 4 4 4 5% 6% 46%	2600
	11th to 20th	Day	21% 9% 2 4 3 3 3 2 5% 6% 44%	2986
	21st to end	Day	16% 5% 1 6% 4 4 5% 4 6% 8% 40%	3960
January	1st to 10th	Night	13% 6% 2 5% 3 4 4 3 4 6% 50%	6349
	11th to 20th	Night	15% 7% 2 5% 3 3 3 3 4 5% 51%	6160
	21st to end	Night	18% 8% 2 5% 4 3 4 3 5% 5% 43%	6490
February	1st to 10th	Night	17% 9% 2 6% 3 4 4 3 5% 6% 40%	2600
	11th to 20th	Night	19% 7% 2 6% 4 4 3 3 5% 5% 42%	2384
	21st to end	Night	18% 7% 2 6% 5% 3 4 3 5% 6% 42%	1980
March	1st to 10th	Night	19% 7% 2 6% 3 3 3 2 4 6% 46%	5325
	11th to 20th	Night	11% 8% 3 5% 3 3 3 3 4 5% 52%	4979
	21st to end	Night	15% 8% 3 6% 4 4 4 3 4 5% 44%	5151
April	1st to 10th	Night	17% 7% 3 6% 4 4 4 4 5% 6% 40%	2000
	11th to 20th	Night	15% 6% 2 7% 4 3 4 4 4 7% 42%	1975
	21st to end	Night	18% 5% 2 5% 3 3 5% 3 5% 6% 44%	2000
May	1st to 10th	Night	23% 8% 3 7% 4 4 4 4 6% 7% 28%	4186
	11th to 20th	Night	23% 9% 3 7% 4 4 3 3 5% 7% 32%	3575
	21st to end	Night	22% 6% 2 6% 4 3 4 3 6% 8% 37%	3926
June	1st to 10th	Night	16% 5% 2 7% 4 4 4 3 5% 9% 43%	1600
	11th to 20th	Night	13% 7% 2 6% 5% 5% 5% 4 7% 9% 39%	1600
	21st to end	Night	10% 5% 2 5% 3 5% 5% 5% 8% 10% 42%	1600
July	1st to 10th	Night	8% 5% 3 7% 5% 5% 6% 5% 8% 10% 39%	2560
	11th to 20th	Night	12% 6% 2 6% 4 5% 5% 5% 7% 9% 38%	2520
	21st to end	Night	15% 6% 3 7% 5% 4 5% 5% 7% 7% 36%	2850
August	1st to 10th	Night	21% 6% 2 6% 4 4 5% 4 6% 8% 34%	2825
	11th to 20th	Night	15% 6% 2 5% 4 4 5% 3 5% 7% 43%	3062
	21st to end	Night	12% 4 2 5% 4 4 4 3 6% 7% 50%	3476
September	1st to 10th	Night	14% 6% 3 6% 4 3 4 4 5% 7% 46%	1900
	11th to 20th	Night	13% 5% 2 4 3 3 3 3 5% 7% 53%	1924
	21st to end	Night	20% 6% 2 6% 4 3 4 4 5% 7% 39%	2092
October	1st to 10th	Night	20% 6% 2 6% 3 4 3 3 4 6% 43%	2280
	11th to 20th	Night	16% 5% 2 4 4 3 3 3 4 7% 51%	2280
	21st to end	Night	17% 6% 2 5% 3 3 3 2 5% 6% 49%	2561
November	1st to 10th	Night	11% 5% 2 5% 4 3 4 3 4 5% 54%	2537
	11th to 20th	Night	17% 6% 2 5% 3 3 4 3 4 5% 48%	2600
	21st to end	Night	13% 6% 2 5% 4 4 4 4 6% 7% 46%	2725
December	1st to 10th	Night	13% 7% 2 6% 4 3 3 3 4 7% 48%	4580
	11th to 20th	Night	23% 6% 2 5% 3 3 3 3 5% 7% 41%	5208
	21st to end	Night	19% 6% 2 6% 4 4 3 4 5% 6% 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	35% 4 10% 26% 22% 3	3598
	11th to 20th	Day	43% 4 9% 22% 16% 5%	3753
	21st to end	Day	43% 5% 11% 24% 15% 2	4466
February	1st to 10th	Day	43% 5% 14% 25% 11% 2	1800
	11th to 20th	Day	43% 5% 11% 24% 15% 2	1908
	21st to end	Day	45% 4 11% 22% 13% 4	1650
March	1st to 10th	Day	39% 3 10% 24% 17% 7%	4515
	11th to 20th	Day	36% 5% 10% 29% 15% 5%	4980
	21st to end	Day	42% 4 10% 16% 23% 5%	5780
April	1st to 10th	Day	42% 6% 11% 20% 16% 5%	2400
	11th to 20th	Day	40% 6% 12% 22% 16% 4	2374
	21st to end	Day	40% 6% 11% 19% 19% 4	2400
May	1st to 10th	Day	52% 6% 13% 18% 10% 2	5792
	11th to 20th	Day	51% 6% 9% 21% 12% 1	6322
	21st to end	Day	43% 6% 11% 23% 15% 1	6949
June	1st to 10th	Day	39% 8% 13% 23% 15% 1	2800
	11th to 20th	Day	40% 9% 12% 24% 12% 3	2800
	21st to end	Day	36% 8% 14% 23% 17% 1	2800
July	1st to 10th	Day	37% 12% 16% 18% 15% 3	4440
	11th to 20th	Day	38% 8% 16% 23% 14% 2	4365
	21st to end	Day	45% 8% 12% 18% 16% 1	4550
August	1st to 10th	Day	46% 8% 14% 22% 9% 1	4091
	11th to 20th	Day	36% 6% 12% 30% 14% 1	3771
	21st to end	Day	33% 6% 11% 27% 21% 2	4180
September	1st to 10th	Day	39% 7% 11% 19% 22% 3	2280
	11th to 20th	Day	32% 4 12% 24% 24% 4	2254
	21st to end	Day	47% 5% 8% 18% 19% 2	2085
October	1st to 10th	Day	36% 4 9% 18% 28% 5%	3160
	11th to 20th	Day	24% 3 12% 23% 30% 7%	3140
	21st to end	Day	25% 3 11% 28% 28% 5%	3336
November	1st to 10th	Day	33% 3 14% 25% 21% 4	1761
	11th to 20th	Day	36% 5% 10% 25% 21% 3	1800
	21st to end	Day	38% 3 13% 31% 12% 2	1672
December	1st to 10th	Day	39% 4 16% 25% 13% 3	2600
	11th to 20th	Day	44% 3 11% 29% 11% 2	2986
	21st to end	Day	40% 7% 12% 22% 17% 2	3960
January	1st to 10th	Night	36% 4 8% 25% 21% 6%	6349
	11th to 20th	Night	38% 3 10% 24% 18% 7%	6204
	21st to end	Night	43% 4 9% 23% 18% 3	6490
February	1st to 10th	Night	44% 5% 13% 24% 13% 2	2600
	11th to 20th	Night	44% 4 9% 20% 18% 4	2386
	21st to end	Night	42% 5% 9% 22% 17% 6%	1980
March	1st to 10th	Night	41% 4 9% 23% 13% 10%	5335
	11th to 20th	Night	35% 6% 13% 26% 15% 5%	4980
	21st to end	Night	43% 4 7% 16% 25% 5%	5151
April	1st to 10th	Night	43% 5% 11% 20% 18% 4	2000
	11th to 20th	Night	41% 6% 10% 19% 20% 4	1975
	21st to end	Night	39% 5% 10% 20% 20% 5%	2000
May	1st to 10th	Night	53% 7% 11% 16% 11% 2	4193
	11th to 20th	Night	51% 7% 10% 18% 13% 1	3576
	21st to end	Night	44% 7% 12% 20% 14% 2	3927
June	1st to 10th	Night	39% 6% 12% 21% 21% 2	1600
	11th to 20th	Night	40% 9% 12% 24% 14% 1	1600
	21st to end	Night	34% 9% 16% 24% 16% 2	1600
July	1st to 10th	Night	39% 10% 20% 17% 12% 2	2520
	11th to 20th	Night	39% 9% 17% 23% 11% 1	2472
	21st to end	Night	43% 7% 15% 19% 14% 1	2759
August	1st to 10th	Night	47% 8% 18% 18% 9% 1	2814
	11th to 20th	Night	40% 6% 12% 26% 15% 1	3092
	21st to end	Night	33% 5% 11% 28% 20% 2	3476
September	1st to 10th	Night	38% 7% 11% 19% 22% 3	1900
	11th to 20th	Night	32% 5% 9% 23% 27% 4	1924
	21st to end	Night	43% 6% 8% 20% 21% 2	2092
October	1st to 10th	Night	41% 4 10% 21% 21% 3	3800
	11th to 20th	Night	24% 3 10% 28% 29% 5%	3779
	21st to end	Night	26% 3 12% 31% 24% 4	4209
November	1st to 10th	Night	32% 4 12% 25% 20% 6%	2537
	11th to 20th	Night	39% 5% 8% 22% 21% 5%	2600
	21st to end	Night	37% 5% 12% 27% 17% 2	2725
December	1st to 10th	Night	38% 4 12% 30% 14% 2	4580
	11th to 20th	Night	44% 4 11% 23% 14% 4	5208
	21st to end	Night	43% 5% 11% 20% 18% 2	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	27% 24% 32% 14% 3 2	200
	11th to 20th	Day	24% 34% 26% 13% 3	232
	21st to end	Day	23% 24% 31% 17% 5%	330
February	1st to 10th	Day	24% 24% 35% 13% 4	300
	11th to 20th	Day	30% 20% 36% 12% 2	447
	21st to end	Day	24% 20% 36% 16% 3	414
March	1st to 10th	Day	23% 21% 32% 19% 4 1	500
	11th to 20th	Day	21% 22% 32% 19% 4 1	500
	21st to end	Day	25% 20% 31% 18% 4 1	550
April	1st to 10th	Day	25% 18% 37% 13% 6% 1	500
	11th to 20th	Day	21% 19% 32% 19% 7% 2	492
	21st to end	Day	23% 15% 32% 23% 6% 1	500
May	1st to 10th	Day	27% 18% 27% 16% 10% 2	503
	11th to 20th	Day	23% 10% 30% 24% 10% 2	527
	21st to end	Day	22% 6% 21% 28% 17% 5%	573
June	1st to 10th	Day	14% 10% 29% 28% 16% 3	530
	11th to 20th	Day	16% 9% 27% 27% 17% 3	530
	21st to end	Day	13% 6% 30% 30% 16% 5%	530
July	1st to 10th	Day	11% 4 20% 32% 24% 9%	505
	11th to 20th	Day	8% 3 20% 35% 27% 8%	484
	21st to end	Day	12% 6% 23% 34% 19% 6%	532
August	1st to 10th	Day	13% 4 22% 30% 22% 9%	486
	11th to 20th	Day	14% 3 17% 35% 22% 9%	479
	21st to end	Day	12% 6% 25% 28% 20% 10%	539
September	1st to 10th	Day	17% 8% 20% 28% 19% 7%	490
	11th to 20th	Day	15% 3 24% 29% 18% 11%	490
	21st to end	Day	23% 13% 20% 27% 12% 5%	490
October	1st to 10th	Day	25% 6% 24% 22% 16% 7%	490
	11th to 20th	Day	16% 14% 29% 25% 13% 3	490
	21st to end	Day	20% 10% 36% 20% 12% 3	509
November	1st to 10th	Day	16% 10% 35% 24% 12% 3	395
	11th to 20th	Day	19% 15% 34% 26% 6%	400
	21st to end	Day	19% 19% 33% 22% 6% 1	272
December	1st to 10th	Day	25% 22% 37% 10% 7%	200
	11th to 20th	Day	29% 22% 33% 12% 4 1	200
	21st to end	Day	26% 19% 31% 15% 9%	220
January	1st to 10th	Night	19% 15% 40% 22% 3	800
	11th to 20th	Night	24% 14% 33% 25% 3	800
	21st to end	Night	19% 13% 41% 24% 2	880
February	1st to 10th	Night	22% 13% 37% 25% 2	800
	11th to 20th	Night	25% 17% 40% 17% 1	783
	21st to end	Night	22% 16% 40% 19% 3	660
March	1st to 10th	Night	20% 16% 37% 24% 4	800
	11th to 20th	Night	20% 15% 40% 20% 5% 1	800
	21st to end	Night	21% 12% 40% 23% 5%	880
April	1st to 10th	Night	21% 18% 38% 19% 5%	800
	11th to 20th	Night	19% 13% 36% 27% 5%	791
	21st to end	Night	20% 10% 34% 30% 6%	800
May	1st to 10th	Night	22% 9% 34% 29% 6%	668
	11th to 20th	Night	19% 9% 35% 31% 6%	394
	21st to end	Night	19% 3 23% 39% 14% 1	433
June	1st to 10th	Night	18% 3 30% 38% 11% 1	400
	11th to 20th	Night	14% 5% 26% 44% 11% 1	400
	21st to end	Night	9% 3 27% 47% 15%	400
July	1st to 10th	Night	11% 5% 24% 39% 20% 1	380
	11th to 20th	Night	7% 4 20% 44% 24% 2	368
	21st to end	Night	10% 4 23% 40% 21% 2	478
August	1st to 10th	Night	11% 2 16% 44% 23% 2	567
	11th to 20th	Night	14% 3 17% 39% 25% 2	727
	21st to end	Night	14% 3 18% 38% 23% 3	836
September	1st to 10th	Night	16% 4 24% 35% 20% 2	760
	11th to 20th	Night	16% 2 20% 36% 23% 4	760
	21st to end	Night	22% 5% 22% 30% 19% 1	760
October	1st to 10th	Night	22% 7% 24% 26% 17% 4	760
	11th to 20th	Night	18% 8% 28% 33% 14% 1	760
	21st to end	Night	21% 7% 33% 28% 10%	836
November	1st to 10th	Night	15% 7% 36% 31% 11% 1	780
	11th to 20th	Night	21% 11% 34% 26% 8% 1	800
	21st to end	Night	16% 14% 35% 28% 7% 1	800
December	1st to 10th	Night	24% 12% 35% 23% 6% 1	800
	11th to 20th	Night	20% 11% 36% 27% 6%	800
	21st to end	Night	21% 12% 35% 29% 3	880

Page generated at 2025-07-03 01:30:14. Version ac07

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