Clarion University of Pennsylvania
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Clarion University of Pennsylvania clear sky chart from 2005-11-06 to 2025-11-03.

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	17% 11% 4 9% 5% 5% 4 4 5% 7% 29%	126700
	Night	17% 12% 5% 10% 5% 4 4 3 5% 6% 29%	123335
Transparency	Day	55% 4 10% 20% 10% 1	130298
	Night	56% 3 10% 19% 11% 1	127807
Seeing	Day	25% 14% 27% 20% 10% 3	15952
	Night	24% 12% 27% 26% 11% 1	25482

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	15% 21% 9% 25% 5% 4 3 1 2 3 12%	3804
	11th to 20th	Day	11% 20% 11% 22% 8% 7% 3 2 2 2 12%	4060
	21st to end	Day	21% 17% 8% 14% 8% 5% 4 3 3 4 14%	4466
February	1st to 10th	Day	18% 19% 6% 12% 7% 5% 4 2 4 4 18%	1800
	11th to 20th	Day	16% 15% 7% 14% 8% 5% 5% 3 5% 5% 19%	1753
	21st to end	Day	21% 16% 3 11% 5% 5% 5% 3 4 5% 22%	1621
March	1st to 10th	Day	17% 11% 6% 10% 6% 4 4 3 4 6% 30%	4935
	11th to 20th	Day	13% 12% 6% 9% 5% 5% 5% 3 4 6% 32%	4980
	21st to end	Day	17% 12% 4 9% 5% 5% 4 3 4 6% 30%	5465
April	1st to 10th	Day	18% 15% 3 8% 5% 4 4 3 5% 7% 28%	2345
	11th to 20th	Day	18% 13% 3 7% 5% 4 4 4 5% 5% 32%	2378
	21st to end	Day	22% 10% 3 6% 4 4 4 3 5% 6% 33%	2600
May	1st to 10th	Day	22% 10% 4 8% 5% 5% 5% 4 6% 6% 26%	5862
	11th to 20th	Day	20% 9% 3 8% 5% 5% 5% 4 6% 8% 25%	5993
	21st to end	Day	20% 7% 3 7% 5% 5% 5% 5% 7% 7% 31%	6934
June	1st to 10th	Day	16% 8% 3 6% 5% 5% 5% 4 6% 8% 33%	2800
	11th to 20th	Day	16% 7% 3 7% 5% 6% 5% 4 6% 9% 33%	2800
	21st to end	Day	16% 6% 2 6% 4 5% 5% 4 8% 10% 35%	2800
July	1st to 10th	Day	9% 7% 2 7% 5% 5% 5% 5% 7% 9% 39%	6360
	11th to 20th	Day	11% 7% 3 7% 5% 6% 5% 5% 8% 10% 33%	6021
	21st to end	Day	11% 7% 2 7% 4 5% 5% 4 6% 8% 42%	6424
August	1st to 10th	Day	17% 9% 4 9% 5% 5% 6% 4 6% 8% 29%	4234
	11th to 20th	Day	13% 7% 3 7% 5% 5% 6% 5% 7% 9% 33%	4174
	21st to end	Day	11% 6% 2 6% 5% 5% 6% 5% 7% 10% 37%	4416
September	1st to 10th	Day	17% 7% 3 6% 4 4 3 3 4 6% 43%	2400
	11th to 20th	Day	12% 7% 3 6% 4 4 4 4 6% 8% 41%	2268
	21st to end	Day	21% 8% 3 7% 5% 4 4 3 5% 7% 32%	2164
October	1st to 10th	Day	17% 8% 2 6% 4 4 4 4 6% 6% 38%	2000
	11th to 20th	Day	22% 9% 3 6% 6% 4 5% 4 5% 6% 32%	2000
	21st to end	Day	24% 12% 3 7% 4 4 4 4 5% 6% 28%	2200
November	1st to 10th	Day	12% 10% 3 7% 5% 4 4 4 5% 7% 39%	1893
	11th to 20th	Day	18% 15% 4 8% 5% 4 5% 3 5% 5% 28%	1600
	21st to end	Day	20% 20% 5% 8% 5% 4 5% 3 4 6% 21%	1600
December	1st to 10th	Day	19% 20% 10% 20% 5% 3 3 2 3 3 11%	2600
	11th to 20th	Day	21% 20% 8% 10% 4 3 3 2 3 4 22%	2990
	21st to end	Day	24% 24% 6% 11% 5% 4 4 3 3 4 13%	3960
January	1st to 10th	Night	15% 18% 9% 26% 7% 4 3 2 3 4 11%	6137
	11th to 20th	Night	12% 17% 9% 21% 9% 6% 4 3 4 4 11%	5900
	21st to end	Night	21% 16% 8% 13% 7% 5% 5% 3 3 3 16%	6490
February	1st to 10th	Night	19% 15% 5% 12% 7% 5% 4 3 3 4 21%	2600
	11th to 20th	Night	18% 15% 5% 13% 6% 5% 5% 3 4 5% 21%	2533
	21st to end	Night	20% 13% 4 12% 5% 5% 4 4 3 4 24%	2005
March	1st to 10th	Night	19% 14% 5% 8% 7% 3 3 3 4 5% 29%	4918
	11th to 20th	Night	13% 12% 6% 7% 4 3 3 3 4 6% 38%	4980
	21st to end	Night	17% 11% 4 8% 5% 5% 4 3 4 6% 33%	5467
April	1st to 10th	Night	19% 13% 4 8% 5% 4 4 3 5% 6% 30%	2055
	11th to 20th	Night	18% 10% 3 6% 4 4 4 4 6% 7% 35%	1975
	21st to end	Night	15% 10% 3 8% 5% 4 4 4 5% 8% 35%	1813
May	1st to 10th	Night	28% 11% 3 7% 4 4 4 3 4 5% 26%	4033
	11th to 20th	Night	20% 11% 3 7% 4 4 4 3 5% 6% 34%	3898
	21st to end	Night	20% 8% 3 6% 3 4 4 4 6% 9% 35%	3920
June	1st to 10th	Night	11% 6% 2 7% 5% 4 4 4 5% 9% 43%	1600
	11th to 20th	Night	13% 6% 2 7% 5% 4 4 4 6% 9% 39%	1600
	21st to end	Night	12% 7% 3 6% 5% 4 5% 4 6% 9% 41%	1600
July	1st to 10th	Night	12% 7% 3 8% 5% 4 4 3 5% 9% 40%	3598
	11th to 20th	Night	11% 6% 3 7% 5% 5% 5% 4 7% 10% 37%	3918
	21st to end	Night	10% 6% 2 6% 4 4 5% 4 5% 8% 46%	4427
August	1st to 10th	Night	14% 9% 3 9% 4 4 4 4 5% 7% 36%	2915
	11th to 20th	Night	15% 7% 3 7% 5% 4 4 4 6% 7% 39%	2875
	21st to end	Night	9% 5% 2 5% 4 4 6% 4 6% 9% 45%	3449
September	1st to 10th	Night	15% 5% 2 5% 3 4 4 4 4 6% 48%	2000
	11th to 20th	Night	10% 5% 2 5% 3 4 4 3 5% 8% 51%	2130
	21st to end	Night	19% 8% 3 6% 5% 4 4 3 6% 6% 36%	2235
October	1st to 10th	Night	16% 6% 2 7% 4 3 3 3 5% 8% 44%	2400
	11th to 20th	Night	19% 8% 3 7% 4 4 4 3 5% 7% 38%	2400
	21st to end	Night	22% 11% 2 7% 4 4 4 4 4 6% 33%	2640
November	1st to 10th	Night	14% 9% 3 6% 4 4 4 3 5% 6% 42%	2443
	11th to 20th	Night	19% 15% 3 7% 5% 5% 4 4 5% 6% 27%	2800
	21st to end	Night	20% 16% 5% 8% 5% 4 4 3 5% 6% 24%	2800
December	1st to 10th	Night	18% 17% 9% 17% 5% 5% 4 3 4 4 13%	4580
	11th to 20th	Night	23% 17% 7% 12% 5% 4 3 2 3 4 20%	5205
	21st to end	Night	22% 19% 6% 11% 5% 4 5% 3 4 5% 16%	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	81% 1 5% 8% 4	3805
	11th to 20th	Day	82% 1 6% 7% 3 1	4060
	21st to end	Day	77% 2 7% 10% 4	4466
February	1st to 10th	Day	71% 2 8% 13% 6%	1800
	11th to 20th	Day	69% 3 8% 14% 6%	1762
	21st to end	Day	66% 2 10% 15% 6% 1	1621
March	1st to 10th	Day	58% 2 10% 22% 7%	4935
	11th to 20th	Day	54% 3 16% 20% 6% 2	4980
	21st to end	Day	57% 2 7% 20% 12% 1	5465
April	1st to 10th	Day	57% 3 10% 17% 12% 1	2345
	11th to 20th	Day	55% 3 10% 19% 12% 2	2378
	21st to end	Day	53% 3 9% 21% 13% 2	2600
May	1st to 10th	Day	58% 3 8% 19% 8% 3	5897
	11th to 20th	Day	56% 4 8% 21% 9% 1	5997
	21st to end	Day	50% 4 11% 21% 12% 2	6949
June	1st to 10th	Day	48% 4 11% 24% 13% 1	2800
	11th to 20th	Day	48% 4 14% 20% 13% 1	2800
	21st to end	Day	43% 5% 12% 26% 13% 1	2800
July	1st to 10th	Day	41% 6% 11% 27% 15% 1	6290
	11th to 20th	Day	44% 5% 12% 26% 12%	5949
	21st to end	Day	40% 5% 9% 26% 20%	6240
August	1st to 10th	Day	52% 5% 12% 22% 8%	4221
	11th to 20th	Day	45% 5% 13% 28% 9% 1	4213
	21st to end	Day	40% 6% 12% 29% 12% 1	4416
September	1st to 10th	Day	44% 4 9% 25% 17% 2	2400
	11th to 20th	Day	40% 4 12% 27% 16% 1	2268
	21st to end	Day	53% 3 10% 21% 13%	2164
October	1st to 10th	Day	39% 3 10% 28% 19% 1	3260
	11th to 20th	Day	47% 3 12% 21% 14% 4	3240
	21st to end	Day	44% 3 12% 27% 13% 1	3538
November	1st to 10th	Day	46% 3 12% 21% 15% 2	1893
	11th to 20th	Day	58% 3 10% 18% 9% 2	1600
	21st to end	Day	66% 3 11% 15% 5% 1	1600
December	1st to 10th	Day	81% 2 8% 7% 2	2600
	11th to 20th	Day	69% 2 10% 14% 4	2986
	21st to end	Day	77% 2 7% 9% 3	3960
January	1st to 10th	Night	81% 1 5% 10% 2	6137
	11th to 20th	Night	79% 2 8% 9% 2	5900
	21st to end	Night	75% 2 8% 10% 5% 1	6490
February	1st to 10th	Night	69% 2 8% 15% 6%	2600
	11th to 20th	Night	68% 3 8% 15% 6%	2535
	21st to end	Night	65% 2 8% 15% 9% 1	2005
March	1st to 10th	Night	60% 2 9% 21% 7% 1	4918
	11th to 20th	Night	49% 2 14% 24% 8% 3	4980
	21st to end	Night	54% 2 7% 19% 16% 1	5467
April	1st to 10th	Night	57% 3 8% 19% 13% 1	2055
	11th to 20th	Night	49% 4 10% 21% 14% 2	1975
	21st to end	Night	49% 3 9% 25% 12% 2	1813
May	1st to 10th	Night	61% 3 7% 15% 10% 3	4060
	11th to 20th	Night	53% 3 9% 23% 11% 1	3899
	21st to end	Night	48% 3 10% 22% 13% 3	3927
June	1st to 10th	Night	40% 4 14% 25% 15% 2	1600
	11th to 20th	Night	42% 5% 13% 24% 14% 2	1600
	21st to end	Night	41% 4 14% 24% 17% 1	1600
July	1st to 10th	Night	42% 4 9% 26% 17% 1	3560
	11th to 20th	Night	40% 5% 16% 25% 12% 1	3871
	21st to end	Night	36% 5% 10% 22% 26% 1	4297
August	1st to 10th	Night	47% 5% 13% 23% 11% 1	2904
	11th to 20th	Night	43% 4 12% 30% 11% 1	2902
	21st to end	Night	34% 6% 14% 32% 13% 2	3449
September	1st to 10th	Night	38% 4 10% 26% 18% 4	2000
	11th to 20th	Night	32% 4 12% 29% 22% 1	2130
	21st to end	Night	50% 4 11% 19% 15% 1	2235
October	1st to 10th	Night	39% 3 9% 25% 23% 1	3920
	11th to 20th	Night	42% 3 11% 21% 16% 6%	3899
	21st to end	Night	40% 2 13% 23% 19% 1	4252
November	1st to 10th	Night	44% 3 12% 24% 14% 3	2443
	11th to 20th	Night	59% 2 9% 18% 9% 3	2800
	21st to end	Night	62% 3 10% 19% 5% 1	2800
December	1st to 10th	Night	76% 3 10% 8% 2	4580
	11th to 20th	Night	70% 2 10% 14% 3	5208
	21st to end	Night	72% 3 9% 13% 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	34% 30% 24% 9% 3	245
	11th to 20th	Day	36% 29% 27% 6% 1 2	300
	21st to end	Day	32% 25% 34% 8% 2	330
February	1st to 10th	Day	33% 27% 32% 8% 1	300
	11th to 20th	Day	42% 23% 28% 7% 1	300
	21st to end	Day	39% 23% 30% 8% 1	306
March	1st to 10th	Day	30% 21% 32% 15% 2	500
	11th to 20th	Day	34% 17% 33% 11% 3 1	500
	21st to end	Day	33% 21% 28% 13% 4 1	550
April	1st to 10th	Day	33% 20% 25% 16% 5% 1	500
	11th to 20th	Day	28% 21% 27% 15% 8% 2	492
	21st to end	Day	28% 17% 32% 15% 6% 1	500
May	1st to 10th	Day	30% 15% 28% 17% 8% 2	503
	11th to 20th	Day	28% 12% 27% 21% 9% 4	527
	21st to end	Day	20% 11% 26% 24% 15% 5%	573
June	1st to 10th	Day	21% 14% 28% 23% 12% 2	530
	11th to 20th	Day	22% 13% 25% 26% 12% 3	530
	21st to end	Day	18% 12% 29% 27% 12% 2	530
July	1st to 10th	Day	14% 7% 23% 28% 21% 7%	525
	11th to 20th	Day	13% 6% 29% 27% 19% 6%	524
	21st to end	Day	13% 5% 29% 28% 17% 7%	576
August	1st to 10th	Day	15% 7% 23% 27% 21% 7%	526
	11th to 20th	Day	17% 5% 23% 29% 15% 10%	519
	21st to end	Day	14% 6% 24% 29% 19% 8%	583
September	1st to 10th	Day	20% 8% 19% 25% 20% 8%	530
	11th to 20th	Day	13% 3 20% 31% 22% 10%	530
	21st to end	Day	28% 10% 24% 23% 12% 3	530
October	1st to 10th	Day	20% 9% 26% 23% 17% 5%	530
	11th to 20th	Day	24% 15% 33% 19% 7% 2	530
	21st to end	Day	34% 13% 29% 18% 6%	583
November	1st to 10th	Day	21% 18% 31% 19% 9% 2	430
	11th to 20th	Day	34% 20% 30% 13% 4 1	200
	21st to end	Day	31% 25% 33% 11% 1	200
December	1st to 10th	Day	39% 21% 30% 8% 2 2	200
	11th to 20th	Day	38% 18% 35% 6% 3 1	200
	21st to end	Day	35% 22% 30% 11% 3	220
January	1st to 10th	Night	29% 22% 34% 12% 3	800
	11th to 20th	Night	32% 21% 30% 15% 2	800
	21st to end	Night	27% 21% 32% 18% 2	880
February	1st to 10th	Night	32% 18% 29% 21% 1	800
	11th to 20th	Night	31% 19% 35% 14% 1	783
	21st to end	Night	29% 20% 32% 17% 2	660
March	1st to 10th	Night	26% 18% 35% 20% 3	800
	11th to 20th	Night	29% 18% 28% 20% 5%	800
	21st to end	Night	26% 15% 35% 19% 4	880
April	1st to 10th	Night	29% 14% 32% 20% 6%	800
	11th to 20th	Night	25% 15% 30% 22% 7% 1	791
	21st to end	Night	21% 10% 35% 28% 6%	613
May	1st to 10th	Night	25% 9% 23% 33% 9% 1	600
	11th to 20th	Night	22% 10% 28% 32% 9%	535
	21st to end	Night	14% 5% 26% 35% 18% 2	433
June	1st to 10th	Night	12% 5% 29% 39% 16% 1	400
	11th to 20th	Night	15% 6% 23% 42% 15%	400
	21st to end	Night	15% 4 28% 37% 16% 1	400
July	1st to 10th	Night	12% 2 19% 43% 21% 3	390
	11th to 20th	Night	12% 2 17% 40% 26% 3	525
	21st to end	Night	12% 4 13% 42% 27% 1	657
August	1st to 10th	Night	12% 2 15% 42% 27% 2	597
	11th to 20th	Night	14% 4 11% 38% 29% 4	594
	21st to end	Night	13% 4 18% 35% 27% 4	795
September	1st to 10th	Night	17% 5% 20% 32% 24% 3	800
	11th to 20th	Night	14% 4 16% 35% 28% 4	800
	21st to end	Night	23% 8% 21% 28% 16% 4	800
October	1st to 10th	Night	20% 6% 23% 29% 20% 3	800
	11th to 20th	Night	25% 10% 29% 26% 9% 1	800
	21st to end	Night	29% 11% 28% 26% 5%	880
November	1st to 10th	Night	22% 10% 31% 28% 9%	789
	11th to 20th	Night	29% 17% 28% 20% 6% 1	800
	21st to end	Night	32% 15% 29% 19% 5%	800
December	1st to 10th	Night	33% 20% 28% 15% 4	800
	11th to 20th	Night	31% 21% 28% 16% 4	800
	21st to end	Night	30% 18% 30% 19% 2	880

Page generated at 2025-10-31 02:02:41. Version ac07

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