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 2026-10-29.

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	16% 6% 2 6% 4 4 4 4 6% 8% 41%	149595
	Night	16% 7% 2 6% 4 4 4 3 5% 7% 43%	142473
Transparency	Day	40% 6% 12% 23% 17% 3	153138
	Night	40% 5% 11% 23% 17% 3	147017
Seeing	Day	20% 13% 28% 23% 12% 4	17587
	Night	19% 10% 32% 29% 10% 1	26824

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 5% 4 5% 4 4 6% 6% 46%	4661
	11th to 20th	Day	16% 7% 2 6% 4 3 3 2 4 6% 46%	4844
	21st to end	Day	16% 6% 2 5% 4 4 5% 4 6% 6% 43%	5780
February	1st to 10th	Day	15% 8% 2 6% 4 4 5% 4 5% 8% 40%	1890
	11th to 20th	Day	17% 8% 3 6% 4 4 5% 4 5% 6% 40%	1997
	21st to end	Day	18% 9% 3 6% 4 4 3 3 4 7% 39%	1730
March	1st to 10th	Day	20% 4 2 4 3 3 3 3 4 6% 46%	4612
	11th to 20th	Day	12% 6% 2 5% 4 4 4 4 5% 7% 46%	5090
	21st to end	Day	18% 5% 2 5% 3 3 4 4 5% 6% 44%	5908
April	1st to 10th	Day	16% 7% 2 6% 4 4 4 3 6% 7% 41%	2520
	11th to 20th	Day	14% 6% 2 5% 4 4 5% 3 6% 7% 43%	2494
	21st to end	Day	16% 6% 2 6% 4 4 4 4 6% 8% 41%	2520
May	1st to 10th	Day	24% 7% 2 5% 4 4 4 3 5% 7% 35%	7493
	11th to 20th	Day	20% 7% 2 6% 4 4 4 4 5% 7% 38%	8221
	21st to end	Day	24% 6% 2 5% 4 4 4 3 5% 7% 36%	9060
June	1st to 10th	Day	12% 6% 2 5% 4 4 6% 5% 6% 9% 41%	2940
	11th to 20th	Day	13% 5% 2 6% 6% 5% 5% 5% 7% 9% 38%	2940
	21st to end	Day	10% 4 2 6% 4 5% 5% 4 6% 10% 43%	2940
July	1st to 10th	Day	12% 5% 2 6% 5% 5% 6% 5% 7% 9% 39%	8280
	11th to 20th	Day	10% 6% 2 7% 5% 5% 6% 5% 8% 11% 35%	8280
	21st to end	Day	11% 5% 2 6% 5% 5% 5% 4 7% 10% 39%	8781
August	1st to 10th	Day	15% 5% 3 7% 6% 6% 5% 5% 7% 10% 32%	6014
	11th to 20th	Day	12% 4 2 6% 4 4 4 4 7% 10% 42%	5493
	21st to end	Day	10% 5% 2 6% 4 4 5% 4 7% 8% 45%	6080
September	1st to 10th	Day	14% 5% 2 5% 4 4 5% 3 5% 6% 46%	2520
	11th to 20th	Day	13% 4 1 5% 3 3 4 4 5% 7% 49%	2491
	21st to end	Day	20% 8% 2 7% 4 4 5% 4 5% 6% 36%	2305
October	1st to 10th	Day	17% 5% 2 5% 3 4 3 4 5% 7% 45%	2100
	11th to 20th	Day	16% 4 2 4 3 3 4 3 5% 6% 50%	2100
	21st to end	Day	17% 5% 2 4 3 3 4 3 5% 6% 49%	2221
November	1st to 10th	Day	13% 5% 2 4 3 3 3 2 5% 6% 53%	1851
	11th to 20th	Day	16% 5% 1 4 4 4 3 4 5% 7% 47%	1890
	21st to end	Day	15% 6% 2 5% 3 3 4 3 5% 6% 47%	1755
December	1st to 10th	Day	14% 7% 2 5% 3 4 4 4 5% 6% 45%	2680
	11th to 20th	Day	20% 9% 2 4 3 3 3 2 5% 6% 44%	3066
	21st to end	Day	16% 5% 1 6% 4 4 5% 4 6% 8% 40%	4048
January	1st to 10th	Night	12% 7% 2 6% 4 4 4 3 4 6% 47%	8234
	11th to 20th	Night	16% 7% 2 5% 3 3 3 3 4 5% 50%	8038
	21st to end	Night	16% 8% 2 5% 4 3 4 3 5% 6% 45%	8401
February	1st to 10th	Night	16% 9% 2 6% 3 4 4 3 5% 6% 40%	2730
	11th to 20th	Night	19% 7% 2 6% 4 4 3 3 5% 5% 41%	2506
	21st to end	Night	17% 7% 2 6% 4 3 4 3 5% 6% 42%	2076
March	1st to 10th	Night	19% 7% 2 6% 3 3 3 2 4 6% 45%	5444
	11th to 20th	Night	11% 8% 3 5% 3 3 3 3 4 5% 52%	5089
	21st to end	Night	15% 8% 3 6% 4 4 4 3 4 5% 44%	5265
April	1st to 10th	Night	17% 7% 2 6% 4 3 4 4 5% 6% 41%	2100
	11th to 20th	Night	15% 6% 2 7% 4 4 4 4 4 7% 43%	2075
	21st to end	Night	18% 5% 2 5% 3 3 4 3 5% 6% 44%	2100
May	1st to 10th	Night	21% 7% 3 7% 4 4 4 4 6% 7% 33%	5448
	11th to 20th	Night	21% 7% 2 6% 4 3 4 3 5% 7% 36%	4639
	21st to end	Night	26% 6% 2 6% 4 3 3 3 5% 6% 34%	5114
June	1st to 10th	Night	15% 4 2 7% 4 4 4 3 5% 9% 44%	1680
	11th to 20th	Night	12% 7% 2 6% 5% 5% 5% 4 7% 9% 39%	1680
	21st to end	Night	11% 5% 2 5% 3 5% 6% 5% 7% 10% 42%	1680
July	1st to 10th	Night	13% 6% 3 7% 5% 4 5% 5% 6% 9% 37%	4680
	11th to 20th	Night	12% 6% 3 7% 5% 5% 5% 5% 8% 11% 33%	4680
	21st to end	Night	12% 6% 2 6% 4 4 4 4 7% 8% 42%	5279
August	1st to 10th	Night	18% 7% 3 7% 5% 5% 5% 4 6% 9% 31%	4135
	11th to 20th	Night	15% 6% 2 6% 4 4 5% 3 6% 7% 41%	4507
	21st to end	Night	13% 5% 2 5% 4 4 4 3 6% 7% 47%	5045
September	1st to 10th	Night	14% 6% 2 6% 4 3 4 4 5% 7% 45%	2100
	11th to 20th	Night	13% 5% 2 4 3 3 3 3 4 6% 53%	2127
	21st to end	Night	21% 6% 2 6% 4 3 4 4 5% 7% 37%	2312
October	1st to 10th	Night	18% 6% 2 6% 3 4 3 3 4 6% 45%	2520
	11th to 20th	Night	17% 4 2 4 3 3 3 3 4 6% 51%	2520
	21st to end	Night	16% 5% 2 5% 3 3 3 2 5% 6% 50%	2793
November	1st to 10th	Night	11% 5% 2 5% 4 3 3 3 5% 6% 54%	2667
	11th to 20th	Night	17% 6% 2 5% 3 3 4 3 4 5% 48%	2730
	21st to end	Night	13% 6% 2 5% 4 4 4 4 6% 7% 46%	2861
December	1st to 10th	Night	13% 8% 2 6% 4 3 3 3 4 7% 48%	4720
	11th to 20th	Night	22% 6% 2 5% 3 3 3 3 5% 7% 42%	5348
	21st to end	Night	19% 6% 2 6% 4 4 3 4 5% 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	38% 4 10% 26% 19% 2	4662
	11th to 20th	Day	41% 4 8% 23% 19% 6%	4875
	21st to end	Day	41% 4 13% 26% 14% 1	5780
February	1st to 10th	Day	42% 5% 14% 25% 12% 2	1890
	11th to 20th	Day	44% 4 11% 24% 15% 2	2006
	21st to end	Day	45% 4 10% 23% 13% 4	1730
March	1st to 10th	Day	40% 3 10% 23% 17% 7%	4615
	11th to 20th	Day	36% 5% 11% 29% 15% 5%	5090
	21st to end	Day	42% 4 10% 16% 22% 5%	5908
April	1st to 10th	Day	41% 6% 12% 20% 16% 5%	2520
	11th to 20th	Day	39% 6% 13% 22% 16% 4	2494
	21st to end	Day	41% 6% 11% 20% 18% 4	2520
May	1st to 10th	Day	48% 6% 12% 18% 15% 1	7502
	11th to 20th	Day	45% 5% 10% 23% 15% 1	8225
	21st to end	Day	48% 5% 9% 22% 14% 2	9061
June	1st to 10th	Day	38% 8% 13% 23% 17% 1	2940
	11th to 20th	Day	39% 9% 12% 24% 12% 3	2940
	21st to end	Day	37% 8% 14% 23% 17% 1	2940
July	1st to 10th	Day	40% 9% 14% 18% 17% 2	8210
	11th to 20th	Day	41% 8% 14% 25% 12% 1	8205
	21st to end	Day	39% 7% 11% 22% 22% 1	8586
August	1st to 10th	Day	46% 9% 17% 20% 8% 1	6001
	11th to 20th	Day	36% 6% 15% 30% 12% 1	5529
	21st to end	Day	35% 6% 12% 26% 19% 2	6080
September	1st to 10th	Day	37% 7% 12% 20% 22% 3	2520
	11th to 20th	Day	33% 4 12% 25% 22% 4	2491
	21st to end	Day	49% 5% 8% 17% 18% 2	2305
October	1st to 10th	Day	35% 4 9% 19% 28% 5%	3360
	11th to 20th	Day	25% 3 11% 23% 30% 7%	3340
	21st to end	Day	24% 3 11% 28% 29% 6%	3523
November	1st to 10th	Day	32% 3 14% 25% 21% 4	1851
	11th to 20th	Day	37% 5% 10% 24% 21% 3	1890
	21st to end	Day	38% 3 13% 31% 12% 2	1755
December	1st to 10th	Day	39% 4 16% 25% 13% 2	2680
	11th to 20th	Day	44% 3 11% 29% 11% 2	3066
	21st to end	Day	40% 7% 12% 22% 17% 2	4048
January	1st to 10th	Night	39% 4 11% 24% 17% 5%	8234
	11th to 20th	Night	39% 3 9% 22% 19% 8%	8082
	21st to end	Night	40% 4 8% 25% 20% 3	8401
February	1st to 10th	Night	44% 5% 12% 24% 13% 2	2730
	11th to 20th	Night	45% 4 9% 20% 18% 4	2508
	21st to end	Night	42% 5% 9% 23% 16% 5%	2076
March	1st to 10th	Night	41% 4 9% 23% 13% 10%	5454
	11th to 20th	Night	35% 6% 13% 26% 15% 5%	5090
	21st to end	Night	43% 4 8% 16% 24% 4	5265
April	1st to 10th	Night	43% 5% 11% 19% 17% 4	2100
	11th to 20th	Night	41% 6% 11% 20% 20% 4	2075
	21st to end	Night	40% 5% 10% 21% 19% 5%	2100
May	1st to 10th	Night	49% 6% 11% 19% 13% 2	5455
	11th to 20th	Night	46% 6% 11% 23% 12% 1	4640
	21st to end	Night	51% 6% 10% 19% 13% 2	5115
June	1st to 10th	Night	38% 6% 11% 22% 21% 2	1680
	11th to 20th	Night	40% 8% 13% 24% 14% 1	1680
	21st to end	Night	35% 9% 16% 24% 15% 2	1680
July	1st to 10th	Night	42% 8% 15% 21% 13% 1	4640
	11th to 20th	Night	43% 8% 16% 22% 10% 1	4632
	21st to end	Night	38% 7% 13% 22% 18% 1	5159
August	1st to 10th	Night	49% 8% 16% 18% 9%	4124
	11th to 20th	Night	41% 7% 14% 26% 12% 1	4537
	21st to end	Night	36% 6% 11% 28% 19% 1	5045
September	1st to 10th	Night	38% 7% 11% 20% 21% 3	2100
	11th to 20th	Night	33% 5% 9% 23% 26% 4	2127
	21st to end	Night	46% 6% 8% 19% 19% 2	2312
October	1st to 10th	Night	40% 4 10% 22% 22% 3	4040
	11th to 20th	Night	25% 3 10% 27% 29% 5%	4019
	21st to end	Night	25% 3 12% 30% 25% 5%	4441
November	1st to 10th	Night	32% 4 12% 25% 20% 6%	2667
	11th to 20th	Night	39% 4 9% 21% 21% 5%	2730
	21st to end	Night	38% 5% 12% 27% 17% 2	2861
December	1st to 10th	Night	38% 4 12% 30% 14% 2	4720
	11th to 20th	Night	44% 4 11% 23% 15% 4	5348
	21st to end	Night	43% 5% 12% 20% 18% 2	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	26% 23% 34% 14% 2 1	220
	11th to 20th	Day	25% 34% 25% 13% 2	255
	21st to end	Day	23% 25% 31% 16% 5%	363
February	1st to 10th	Day	23% 23% 34% 15% 4	330
	11th to 20th	Day	30% 19% 36% 14% 2	485
	21st to end	Day	24% 20% 35% 17% 3	446
March	1st to 10th	Day	24% 20% 31% 19% 5% 1	540
	11th to 20th	Day	23% 21% 32% 19% 4 1	540
	21st to end	Day	25% 22% 30% 18% 4 1	594
April	1st to 10th	Day	26% 18% 36% 13% 7% 1	540
	11th to 20th	Day	20% 20% 32% 19% 7% 2	532
	21st to end	Day	23% 15% 32% 23% 6% 1	540
May	1st to 10th	Day	26% 20% 27% 15% 9% 1	543
	11th to 20th	Day	22% 10% 32% 23% 10% 2	567
	21st to end	Day	25% 7% 21% 27% 16% 5%	617
June	1st to 10th	Day	13% 11% 29% 28% 16% 3	570
	11th to 20th	Day	17% 11% 27% 27% 16% 3	570
	21st to end	Day	13% 7% 29% 30% 15% 5%	570
July	1st to 10th	Day	12% 4 19% 33% 25% 8%	565
	11th to 20th	Day	8% 4 22% 32% 27% 7%	564
	21st to end	Day	11% 6% 24% 34% 19% 6%	620
August	1st to 10th	Day	13% 4 24% 30% 21% 8%	566
	11th to 20th	Day	14% 4 18% 35% 21% 8%	559
	21st to end	Day	11% 6% 27% 28% 19% 9%	627
September	1st to 10th	Day	16% 9% 23% 27% 18% 6%	570
	11th to 20th	Day	16% 4 24% 31% 16% 10%	570
	21st to end	Day	25% 12% 21% 26% 12% 5%	570
October	1st to 10th	Day	22% 7% 26% 22% 15% 7%	570
	11th to 20th	Day	18% 14% 29% 23% 12% 3	570
	21st to end	Day	19% 11% 34% 20% 12% 3	582
November	1st to 10th	Day	16% 12% 34% 24% 12% 2	425
	11th to 20th	Day	21% 15% 33% 25% 6%	430
	21st to end	Day	20% 19% 33% 21% 5% 1	295
December	1st to 10th	Day	25% 23% 36% 10% 6%	220
	11th to 20th	Day	29% 22% 34% 11% 4	220
	21st to end	Day	26% 20% 31% 14% 8%	242
January	1st to 10th	Night	19% 15% 41% 22% 4	840
	11th to 20th	Night	24% 15% 33% 24% 3	840
	21st to end	Night	20% 14% 41% 24% 2	924
February	1st to 10th	Night	22% 14% 37% 26% 2	840
	11th to 20th	Night	24% 17% 39% 18% 1	823
	21st to end	Night	22% 16% 40% 19% 3	692
March	1st to 10th	Night	21% 15% 36% 24% 4	840
	11th to 20th	Night	20% 15% 39% 20% 5%	840
	21st to end	Night	21% 12% 40% 22% 5%	924
April	1st to 10th	Night	20% 19% 37% 18% 5%	840
	11th to 20th	Night	18% 13% 36% 27% 5%	831
	21st to end	Night	20% 10% 34% 30% 5%	840
May	1st to 10th	Night	22% 10% 34% 28% 6%	702
	11th to 20th	Night	19% 9% 36% 31% 6%	414
	21st to end	Night	20% 4 22% 38% 14% 1	455
June	1st to 10th	Night	17% 4 30% 38% 11% 1	420
	11th to 20th	Night	14% 6% 27% 42% 10% 1	420
	21st to end	Night	9% 4 26% 47% 14%	420
July	1st to 10th	Night	11% 4 24% 39% 20% 1	410
	11th to 20th	Night	7% 4 20% 44% 24% 1	408
	21st to end	Night	10% 4 24% 39% 21% 2	528
August	1st to 10th	Night	12% 2 16% 43% 24% 2	627
	11th to 20th	Night	14% 3 18% 39% 25% 2	805
	21st to end	Night	14% 4 20% 38% 22% 2	924
September	1st to 10th	Night	16% 4 25% 34% 20% 2	840
	11th to 20th	Night	16% 2 21% 35% 23% 4	840
	21st to end	Night	24% 5% 22% 30% 19% 1	840
October	1st to 10th	Night	21% 7% 25% 26% 18% 4	840
	11th to 20th	Night	19% 9% 27% 31% 13%	840
	21st to end	Night	20% 8% 33% 28% 11%	913
November	1st to 10th	Night	15% 7% 35% 31% 10% 1	820
	11th to 20th	Night	20% 12% 34% 25% 8% 1	840
	21st to end	Night	16% 14% 34% 28% 7% 1	840
December	1st to 10th	Night	24% 12% 35% 23% 6% 1	840
	11th to 20th	Night	21% 12% 36% 26% 6%	840
	21st to end	Night	22% 12% 35% 29% 3	924

Page generated at 2026-10-26 04:37:50. Version ac07

Copyright © 2026 Attilla Danko.