Edinboro University Planetarium and Observatory.
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Edinboro University Planetarium and Observatory. clear sky chart from 2005-11-06 to 2026-05-02.

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% 13% 5% 10% 5% 4 4 3 5% 6% 27%	131818
	Night	16% 15% 6% 11% 5% 4 4 3 4 5% 26%	130667
Transparency	Day	57% 4 10% 19% 10% 1	135417
	Night	60% 3 9% 17% 9% 1	135138
Seeing	Day	27% 15% 29% 18% 8% 3	16411
	Night	26% 14% 27% 22% 9% 1	26116

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	16% 22% 10% 28% 5% 3 3 2 2 3 6%	4998
	11th to 20th	Day	10% 23% 11% 23% 9% 8% 3 1 2 3 8%	5280
	21st to end	Day	17% 17% 8% 17% 10% 8% 4 3 3 3 11%	5780
February	1st to 10th	Day	15% 19% 7% 16% 10% 5% 4 2 3 3 15%	1890
	11th to 20th	Day	15% 18% 8% 17% 9% 5% 4 3 3 4 15%	1843
	21st to end	Day	16% 20% 4 14% 5% 3 4 3 4 5% 20%	1688
March	1st to 10th	Day	16% 12% 9% 12% 6% 3 4 3 4 6% 26%	5045
	11th to 20th	Day	12% 17% 7% 10% 4 4 4 3 4 5% 30%	5090
	21st to end	Day	20% 15% 6% 12% 4 3 3 2 4 5% 25%	5586
April	1st to 10th	Day	18% 15% 4 8% 5% 4 4 3 5% 6% 29%	2431
	11th to 20th	Day	20% 14% 3 7% 4 4 4 3 5% 5% 32%	2572
	21st to end	Day	20% 13% 3 7% 4 3 4 3 4 6% 33%	2730
May	1st to 10th	Day	21% 10% 3 9% 5% 5% 4 3 4 5% 29%	5875
	11th to 20th	Day	19% 10% 3 8% 5% 4 4 3 6% 7% 30%	5940
	21st to end	Day	20% 9% 3 6% 4 5% 4 4 5% 7% 34%	6934
June	1st to 10th	Day	17% 7% 2 7% 5% 4 4 4 6% 7% 37%	2800
	11th to 20th	Day	15% 7% 3 7% 5% 5% 5% 3 6% 9% 35%	2800
	21st to end	Day	15% 6% 2 6% 4 5% 4 4 7% 8% 38%	2800
July	1st to 10th	Day	10% 6% 2 7% 5% 5% 5% 4 6% 9% 41%	6360
	11th to 20th	Day	13% 6% 3 7% 5% 4 5% 5% 6% 9% 38%	5957
	21st to end	Day	13% 6% 2 6% 5% 4 5% 4 6% 7% 43%	6424
August	1st to 10th	Day	14% 7% 2 7% 5% 6% 5% 5% 6% 9% 33%	4234
	11th to 20th	Day	15% 7% 3 8% 5% 5% 6% 5% 8% 8% 30%	4174
	21st to end	Day	12% 5% 3 7% 5% 5% 5% 5% 7% 10% 38%	4492
September	1st to 10th	Day	18% 7% 2 6% 4 4 4 4 6% 8% 38%	2400
	11th to 20th	Day	12% 6% 2 6% 4 4 5% 4 6% 7% 43%	2215
	21st to end	Day	21% 9% 3 7% 5% 4 4 4 5% 6% 32%	2195
October	1st to 10th	Day	18% 8% 2 7% 4 4 4 4 6% 7% 36%	2000
	11th to 20th	Day	22% 10% 3 8% 6% 4 4 3 5% 6% 28%	2000
	21st to end	Day	25% 14% 3 8% 5% 5% 5% 3 4 6% 22%	2200
November	1st to 10th	Day	15% 15% 3 8% 5% 4 4 4 5% 6% 31%	1922
	11th to 20th	Day	17% 23% 4 10% 4 3 4 3 4 6% 22%	1685
	21st to end	Day	19% 28% 7% 9% 5% 4 4 3 4 5% 14%	1680
December	1st to 10th	Day	18% 30% 15% 13% 4 3 3 2 2 2 7%	2680
	11th to 20th	Day	22% 25% 9% 12% 6% 3 3 2 4 4 11%	3070
	21st to end	Day	23% 26% 8% 14% 5% 3 3 2 2 3 9%	4048
January	1st to 10th	Night	14% 21% 11% 31% 6% 3 2 1 2 2 7%	7891
	11th to 20th	Night	10% 21% 12% 24% 9% 6% 3 2 3 3 8%	7680
	21st to end	Night	16% 18% 8% 16% 8% 5% 5% 3 4 4 14%	8401
February	1st to 10th	Night	18% 19% 6% 14% 8% 5% 3 3 3 4 17%	2730
	11th to 20th	Night	15% 17% 7% 16% 8% 6% 4 3 4 4 15%	2663
	21st to end	Night	18% 16% 6% 16% 6% 4 4 3 3 4 21%	2113
March	1st to 10th	Night	18% 17% 5% 9% 7% 3 3 2 4 5% 26%	5028
	11th to 20th	Night	13% 14% 7% 8% 4 3 3 3 4 6% 34%	5090
	21st to end	Night	17% 15% 7% 11% 4 4 3 3 3 4 30%	5588
April	1st to 10th	Night	19% 16% 5% 7% 5% 4 3 4 4 5% 27%	2189
	11th to 20th	Night	18% 12% 2 7% 5% 5% 4 3 5% 6% 31%	2014
	21st to end	Night	15% 12% 3 7% 6% 4 4 4 5% 7% 34%	1890
May	1st to 10th	Night	25% 12% 3 8% 4 4 4 3 4 5% 30%	4042
	11th to 20th	Night	16% 10% 3 7% 5% 4 4 3 5% 6% 36%	3951
	21st to end	Night	22% 7% 2 4 3 3 4 3 5% 9% 38%	3920
June	1st to 10th	Night	11% 6% 3 6% 5% 5% 5% 4 7% 8% 40%	1600
	11th to 20th	Night	11% 8% 3 7% 6% 4 4 4 6% 7% 40%	1600
	21st to end	Night	12% 7% 2 6% 4 4 5% 4 6% 9% 41%	1600
July	1st to 10th	Night	12% 8% 2 7% 5% 4 4 3 6% 9% 41%	3598
	11th to 20th	Night	12% 7% 2 6% 4 5% 4 4 6% 9% 40%	3982
	21st to end	Night	9% 5% 2 6% 4 5% 5% 4 6% 8% 47%	4427
August	1st to 10th	Night	11% 8% 3 8% 5% 5% 4 4 5% 7% 39%	2915
	11th to 20th	Night	15% 8% 3 7% 4 4 5% 4 5% 6% 39%	2875
	21st to end	Night	9% 6% 3 7% 4 5% 5% 5% 7% 9% 42%	3373
September	1st to 10th	Night	13% 6% 2 6% 4 3 4 4 5% 7% 45%	2000
	11th to 20th	Night	12% 6% 2 5% 4 4 3 3 6% 6% 50%	2181
	21st to end	Night	19% 9% 2 7% 4 4 5% 3 5% 7% 35%	2204
October	1st to 10th	Night	18% 6% 2 6% 4 3 4 3 5% 6% 42%	2400
	11th to 20th	Night	21% 9% 2 8% 4 5% 5% 4 5% 5% 31%	2400
	21st to end	Night	26% 13% 3 7% 4 4 4 2 5% 5% 28%	2640
November	1st to 10th	Night	16% 13% 3 8% 4 4 4 3 6% 6% 32%	2595
	11th to 20th	Night	19% 21% 4 9% 4 4 5% 3 5% 5% 21%	2932
	21st to end	Night	20% 23% 6% 9% 4 4 3 3 4 5% 18%	2940
December	1st to 10th	Night	16% 23% 14% 13% 4 4 3 3 3 4 13%	4720
	11th to 20th	Night	18% 26% 10% 13% 4 4 3 2 3 4 14%	5345
	21st to end	Night	21% 25% 7% 12% 7% 4 3 3 4 4 11%	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	87% 1 5% 4 2	4999
	11th to 20th	Day	85% 2 4 6% 3	5280
	21st to end	Day	80% 2 6% 8% 4	5780
February	1st to 10th	Day	76% 2 6% 11% 5%	1890
	11th to 20th	Day	75% 2 5% 12% 5%	1852
	21st to end	Day	68% 2 9% 14% 5% 2	1688
March	1st to 10th	Day	61% 2 11% 20% 5%	5045
	11th to 20th	Day	58% 2 14% 19% 6% 2	5090
	21st to end	Day	64% 2 5% 19% 9% 1	5586
April	1st to 10th	Day	57% 3 12% 17% 12%	2431
	11th to 20th	Day	55% 3 8% 20% 12% 2	2572
	21st to end	Day	53% 2 10% 21% 11% 3	2730
May	1st to 10th	Day	56% 3 7% 20% 9% 4	5910
	11th to 20th	Day	54% 3 9% 23% 10% 1	5944
	21st to end	Day	50% 4 11% 21% 12% 3	6949
June	1st to 10th	Day	46% 3 12% 25% 13% 1	2800
	11th to 20th	Day	46% 4 14% 23% 13% 1	2800
	21st to end	Day	42% 5% 11% 26% 15% 1	2800
July	1st to 10th	Day	37% 6% 12% 26% 17% 1	6290
	11th to 20th	Day	40% 6% 13% 24% 15% 1	5886
	21st to end	Day	38% 6% 10% 26% 19% 1	6240
August	1st to 10th	Day	45% 6% 14% 24% 11%	4221
	11th to 20th	Day	46% 6% 14% 26% 7% 1	4213
	21st to end	Day	39% 6% 12% 29% 12% 1	4492
September	1st to 10th	Day	44% 4 12% 24% 14% 2	2400
	11th to 20th	Day	40% 4 12% 28% 16%	2215
	21st to end	Day	52% 3 10% 22% 11% 1	2195
October	1st to 10th	Day	39% 5% 13% 25% 17% 1	3260
	11th to 20th	Day	48% 4 12% 20% 13% 4	3240
	21st to end	Day	49% 4 14% 23% 9% 1	3538
November	1st to 10th	Day	55% 3 9% 20% 11% 2	1922
	11th to 20th	Day	65% 3 9% 14% 7% 2	1685
	21st to end	Day	75% 3 8% 9% 4 1	1680
December	1st to 10th	Day	85% 3 5% 5% 1	2680
	11th to 20th	Day	80% 2 6% 11% 1	3066
	21st to end	Day	84% 2 7% 7% 1	4048
January	1st to 10th	Night	87% 1 4 5% 1	7892
	11th to 20th	Night	84% 2 5% 6% 2	7680
	21st to end	Night	75% 3 8% 11% 3	8401
February	1st to 10th	Night	73% 2 7% 13% 5%	2730
	11th to 20th	Night	74% 2 7% 13% 4	2665
	21st to end	Night	69% 2 9% 12% 7% 1	2113
March	1st to 10th	Night	62% 3 10% 19% 7%	5028
	11th to 20th	Night	53% 2 12% 22% 9% 1	5090
	21st to end	Night	60% 3 7% 16% 13% 1	5588
April	1st to 10th	Night	60% 3 9% 16% 11% 1	2189
	11th to 20th	Night	53% 4 10% 18% 13% 2	2014
	21st to end	Night	51% 3 11% 22% 11% 3	1890
May	1st to 10th	Night	58% 3 7% 15% 12% 5%	4069
	11th to 20th	Night	50% 3 10% 24% 11% 1	3952
	21st to end	Night	45% 3 11% 25% 13% 2	3927
June	1st to 10th	Night	41% 5% 11% 25% 15% 3	1600
	11th to 20th	Night	42% 4 13% 24% 16% 2	1600
	21st to end	Night	40% 5% 13% 25% 17% 1	1600
July	1st to 10th	Night	40% 5% 11% 25% 17% 2	3560
	11th to 20th	Night	38% 6% 13% 26% 15% 2	3933
	21st to end	Night	34% 6% 11% 22% 25% 1	4297
August	1st to 10th	Night	43% 5% 11% 28% 12% 1	2904
	11th to 20th	Night	44% 6% 13% 29% 8% 1	2902
	21st to end	Night	36% 6% 15% 28% 12% 1	3373
September	1st to 10th	Night	37% 5% 13% 28% 15% 2	2000
	11th to 20th	Night	35% 4 13% 29% 20% 1	2181
	21st to end	Night	49% 2 12% 21% 14% 1	2204
October	1st to 10th	Night	39% 5% 8% 24% 22% 1	3920
	11th to 20th	Night	48% 5% 11% 17% 16% 4	3899
	21st to end	Night	45% 3 14% 23% 14% 1	4252
November	1st to 10th	Night	53% 3 10% 22% 10% 2	2595
	11th to 20th	Night	66% 3 8% 14% 6% 3	2932
	21st to end	Night	70% 2 10% 14% 3 1	2940
December	1st to 10th	Night	77% 4 9% 8% 2	4720
	11th to 20th	Night	78% 2 8% 11% 2	5348
	21st to end	Night	78% 3 8% 10% 1	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	36% 26% 28% 8% 2	281
	11th to 20th	Day	37% 31% 24% 5% 2 1	330
	21st to end	Day	36% 29% 26% 7% 1	363
February	1st to 10th	Day	37% 23% 34% 6% 1	330
	11th to 20th	Day	40% 25% 28% 6% 1	330
	21st to end	Day	40% 26% 29% 5%	283
March	1st to 10th	Day	33% 23% 32% 9% 3	540
	11th to 20th	Day	35% 21% 31% 10% 2 1	540
	21st to end	Day	38% 22% 26% 12% 2	594
April	1st to 10th	Day	34% 21% 30% 11% 5% 1	540
	11th to 20th	Day	36% 18% 26% 12% 7% 2	532
	21st to end	Day	29% 19% 31% 15% 4 1	540
May	1st to 10th	Day	30% 15% 33% 16% 4 2	507
	11th to 20th	Day	26% 14% 27% 21% 10% 2	527
	21st to end	Day	21% 9% 32% 22% 11% 4	573
June	1st to 10th	Day	20% 13% 32% 24% 8% 3	530
	11th to 20th	Day	22% 10% 27% 27% 12% 2	530
	21st to end	Day	18% 10% 34% 25% 12% 2	530
July	1st to 10th	Day	12% 7% 28% 30% 16% 7%	525
	11th to 20th	Day	17% 8% 31% 27% 13% 5%	524
	21st to end	Day	11% 8% 34% 27% 16% 3	576
August	1st to 10th	Day	13% 8% 26% 30% 16% 6%	526
	11th to 20th	Day	17% 5% 27% 32% 13% 8%	519
	21st to end	Day	14% 8% 28% 28% 16% 5%	583
September	1st to 10th	Day	21% 8% 25% 25% 18% 5%	530
	11th to 20th	Day	11% 4 26% 30% 21% 7%	530
	21st to end	Day	25% 12% 28% 21% 11% 4	530
October	1st to 10th	Day	20% 14% 27% 22% 14% 3	530
	11th to 20th	Day	29% 18% 32% 15% 5% 2	530
	21st to end	Day	37% 17% 31% 14% 2	583
November	1st to 10th	Day	33% 19% 28% 15% 5% 1	400
	11th to 20th	Day	40% 19% 30% 9% 3	223
	21st to end	Day	39% 20% 35% 6%	220
December	1st to 10th	Day	41% 26% 27% 3 3	220
	11th to 20th	Day	44% 21% 26% 8% 1	220
	21st to end	Day	40% 21% 31% 7%	242
January	1st to 10th	Night	35% 25% 28% 10% 3	840
	11th to 20th	Night	38% 23% 26% 12% 1	840
	21st to end	Night	30% 24% 30% 14% 2	924
February	1st to 10th	Night	35% 20% 29% 15% 1	840
	11th to 20th	Night	30% 25% 30% 12% 2	823
	21st to end	Night	32% 22% 31% 14% 2	692
March	1st to 10th	Night	28% 20% 31% 16% 4	840
	11th to 20th	Night	30% 19% 30% 17% 4	840
	21st to end	Night	28% 17% 31% 19% 4	924
April	1st to 10th	Night	31% 16% 30% 18% 5%	840
	11th to 20th	Night	29% 13% 31% 20% 6% 1	770
	21st to end	Night	24% 12% 32% 28% 5%	630
May	1st to 10th	Night	26% 9% 27% 28% 9% 1	603
	11th to 20th	Night	20% 9% 30% 32% 7% 1	562
	21st to end	Night	15% 6% 30% 29% 18% 2	433
June	1st to 10th	Night	14% 5% 32% 36% 14%	400
	11th to 20th	Night	14% 8% 27% 40% 12%	400
	21st to end	Night	14% 6% 29% 34% 18% 1	400
July	1st to 10th	Night	13% 3 19% 40% 20% 5%	390
	11th to 20th	Night	13% 3 20% 36% 23% 4	548
	21st to end	Night	13% 3 19% 38% 27% 1	657
August	1st to 10th	Night	11% 3 20% 40% 24% 3	597
	11th to 20th	Night	13% 4 15% 35% 28% 4	594
	21st to end	Night	15% 3 23% 32% 24% 3	745
September	1st to 10th	Night	17% 6% 19% 33% 22% 4	800
	11th to 20th	Night	13% 5% 20% 33% 25% 5%	800
	21st to end	Night	23% 9% 22% 28% 14% 4	800
October	1st to 10th	Night	20% 7% 28% 27% 17% 2	800
	11th to 20th	Night	29% 13% 28% 22% 8% 1	800
	21st to end	Night	35% 14% 28% 19% 3	880
November	1st to 10th	Night	27% 14% 29% 22% 7%	820
	11th to 20th	Night	35% 19% 27% 13% 5% 1	840
	21st to end	Night	36% 19% 30% 11% 4	840
December	1st to 10th	Night	36% 23% 27% 11% 3	840
	11th to 20th	Night	34% 27% 25% 12% 2	840
	21st to end	Night	37% 19% 30% 12% 1	924

Page generated at 2026-04-29 02:21:43. Version ac07

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