State College
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the State College clear sky chart from 2005-11-06 to 2026-03-03.

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	14% 10% 4 9% 5% 5% 5% 4 5% 7% 32%	131208
	Night	14% 10% 4 10% 5% 5% 4 4 5% 7% 33%	129930
Transparency	Day	50% 6% 11% 21% 12% 1	134803
	Night	49% 6% 11% 21% 12% 2	134405
Seeing	Day	22% 15% 27% 21% 11% 4	16377
	Night	21% 13% 25% 29% 11% 1	25957

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	13% 17% 5% 17% 6% 5% 4 4 4 4 21%	4661
	11th to 20th	Day	9% 14% 8% 22% 9% 6% 4 3 4 4 16%	5276
	21st to end	Day	14% 13% 7% 11% 7% 6% 5% 3 4 5% 25%	5780
February	1st to 10th	Day	14% 16% 5% 10% 7% 5% 5% 3 4 6% 25%	1890
	11th to 20th	Day	13% 12% 4 12% 7% 5% 5% 4 6% 6% 25%	1843
	21st to end	Day	16% 13% 4 11% 6% 4 4 4 4 6% 28%	1711
March	1st to 10th	Day	17% 13% 4 8% 4 4 4 3 4 5% 34%	4912
	11th to 20th	Day	12% 11% 4 9% 5% 4 5% 3 5% 7% 35%	4980
	21st to end	Day	13% 10% 4 8% 6% 5% 5% 3 5% 5% 36%	5505
April	1st to 10th	Day	17% 11% 4 8% 5% 5% 4 4 4 7% 31%	2400
	11th to 20th	Day	14% 11% 3 8% 4 5% 4 4 5% 7% 34%	2374
	21st to end	Day	19% 8% 3 8% 5% 5% 4 3 5% 6% 35%	2475
May	1st to 10th	Day	23% 9% 3 8% 6% 5% 5% 4 5% 6% 26%	5862
	11th to 20th	Day	22% 9% 3 8% 5% 5% 4 4 4 8% 28%	6226
	21st to end	Day	18% 8% 2 7% 5% 5% 6% 4 6% 8% 32%	6934
June	1st to 10th	Day	13% 7% 3 7% 5% 5% 5% 5% 7% 7% 36%	2800
	11th to 20th	Day	15% 6% 3 7% 6% 5% 5% 5% 6% 9% 34%	2800
	21st to end	Day	11% 6% 2 6% 5% 5% 5% 5% 7% 9% 39%	2800
July	1st to 10th	Day	6% 6% 3 8% 6% 6% 6% 5% 7% 8% 39%	6360
	11th to 20th	Day	7% 7% 3 9% 6% 7% 7% 6% 8% 9% 30%	6298
	21st to end	Day	10% 8% 3 8% 5% 4 5% 4 6% 8% 40%	6424
August	1st to 10th	Day	16% 9% 3 8% 5% 5% 5% 4 7% 9% 29%	4234
	11th to 20th	Day	13% 7% 3 8% 5% 6% 7% 5% 7% 7% 33%	4123
	21st to end	Day	11% 7% 2 6% 4 4 4 4 6% 9% 42%	4312
September	1st to 10th	Day	16% 6% 2 6% 4 4 4 4 4 6% 44%	2400
	11th to 20th	Day	14% 5% 2 5% 4 4 4 3 5% 8% 48%	2388
	21st to end	Day	20% 9% 3 7% 4 4 4 4 6% 6% 34%	2092
October	1st to 10th	Day	15% 7% 3 7% 4 4 6% 3 5% 6% 40%	2000
	11th to 20th	Day	17% 8% 3 7% 4 5% 5% 4 6% 7% 35%	2000
	21st to end	Day	16% 9% 3 8% 4 4 5% 4 5% 7% 35%	2200
November	1st to 10th	Day	10% 8% 2 7% 4 4 5% 5% 5% 6% 43%	1931
	11th to 20th	Day	15% 13% 4 9% 5% 5% 5% 4 5% 5% 30%	1739
	21st to end	Day	16% 12% 5% 8% 6% 5% 5% 4 6% 6% 28%	1680
December	1st to 10th	Day	14% 12% 6% 17% 7% 6% 5% 4 4 5% 20%	2680
	11th to 20th	Day	20% 15% 6% 9% 4 4 4 4 4 5% 25%	3070
	21st to end	Day	16% 17% 7% 13% 7% 5% 6% 4 5% 4 17%	4048
January	1st to 10th	Night	11% 15% 6% 20% 7% 5% 4 4 5% 5% 18%	8233
	11th to 20th	Night	10% 13% 6% 19% 7% 6% 5% 3 5% 6% 20%	7680
	21st to end	Night	14% 12% 5% 10% 8% 8% 5% 3 4 5% 26%	8401
February	1st to 10th	Night	14% 11% 4 10% 5% 5% 5% 4 5% 6% 30%	2730
	11th to 20th	Night	16% 11% 4 10% 6% 5% 5% 5% 5% 6% 28%	2663
	21st to end	Night	15% 13% 3 11% 6% 6% 4 3 4 5% 31%	2094
March	1st to 10th	Night	17% 11% 5% 9% 5% 4 4 3 4 5% 33%	4970
	11th to 20th	Night	9% 9% 5% 8% 4 4 4 3 5% 7% 41%	4980
	21st to end	Night	13% 10% 3 8% 5% 4 4 3 5% 6% 39%	5427
April	1st to 10th	Night	18% 13% 4 9% 5% 4 3 4 4 5% 32%	2000
	11th to 20th	Night	16% 9% 3 6% 5% 4 4 4 5% 7% 37%	1975
	21st to end	Night	16% 7% 2 8% 5% 4 4 4 5% 8% 37%	1941
May	1st to 10th	Night	26% 10% 3 7% 4 4 4 3 5% 6% 27%	4033
	11th to 20th	Night	23% 11% 3 6% 4 4 3 3 4 6% 32%	3650
	21st to end	Night	18% 9% 3 7% 4 4 4 3 5% 8% 34%	3920
June	1st to 10th	Night	13% 7% 2 6% 4 3 4 4 5% 9% 43%	1600
	11th to 20th	Night	13% 6% 2 7% 5% 4 5% 4 7% 8% 38%	1600
	21st to end	Night	11% 5% 2 5% 4 4 4 4 7% 12% 41%	1600
July	1st to 10th	Night	8% 8% 3 7% 5% 5% 5% 4 6% 10% 39%	3598
	11th to 20th	Night	8% 7% 3 8% 6% 6% 6% 4 8% 11% 34%	3642
	21st to end	Night	9% 6% 2 6% 5% 4 4 3 6% 9% 45%	4427
August	1st to 10th	Night	15% 8% 3 7% 4 4 5% 4 6% 8% 36%	2915
	11th to 20th	Night	13% 8% 3 7% 4 4 4 3 6% 7% 40%	2893
	21st to end	Night	11% 7% 2 6% 4 3 4 4 6% 8% 46%	3586
September	1st to 10th	Night	15% 5% 2 5% 4 4 5% 3 4 7% 46%	2000
	11th to 20th	Night	10% 6% 2 4 3 3 4 3 6% 8% 50%	2009
	21st to end	Night	18% 7% 2 7% 5% 4 4 3 5% 6% 39%	2306
October	1st to 10th	Night	16% 6% 2 6% 4 3 4 3 5% 8% 45%	2400
	11th to 20th	Night	15% 8% 2 7% 4 3 4 3 5% 6% 42%	2400
	21st to end	Night	18% 9% 3 6% 3 4 3 3 5% 6% 39%	2640
November	1st to 10th	Night	10% 8% 2 7% 5% 3 4 3 4 7% 48%	2585
	11th to 20th	Night	16% 11% 3 7% 5% 5% 4 3 5% 7% 34%	2877
	21st to end	Night	16% 11% 4 9% 4 4 5% 4 5% 6% 32%	2940
December	1st to 10th	Night	12% 10% 7% 14% 6% 6% 5% 4 5% 7% 24%	4720
	11th to 20th	Night	19% 12% 5% 11% 5% 4 4 3 5% 6% 27%	5345
	21st to end	Night	17% 15% 5% 12% 6% 5% 5% 4 5% 5% 22%	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	64% 7% 11% 12% 6% 1	4662
	11th to 20th	Day	71% 4 7% 11% 7% 1	5276
	21st to end	Day	60% 5% 10% 18% 6%	5780
February	1st to 10th	Day	59% 5% 11% 18% 7% 1	1890
	11th to 20th	Day	57% 5% 9% 21% 7% 1	1852
	21st to end	Day	56% 4 10% 19% 8% 2	1711
March	1st to 10th	Day	52% 4 11% 21% 10% 2	4912
	11th to 20th	Day	47% 6% 14% 22% 9% 2	4980
	21st to end	Day	48% 5% 10% 19% 15% 3	5505
April	1st to 10th	Day	52% 5% 9% 19% 12% 2	2400
	11th to 20th	Day	48% 6% 9% 19% 15% 2	2374
	21st to end	Day	49% 5% 8% 21% 14% 2	2475
May	1st to 10th	Day	56% 7% 9% 16% 10% 2	5897
	11th to 20th	Day	54% 7% 10% 19% 9% 1	6230
	21st to end	Day	47% 7% 11% 22% 11% 2	6949
June	1st to 10th	Day	44% 7% 11% 22% 14% 1	2800
	11th to 20th	Day	45% 7% 13% 21% 13% 2	2800
	21st to end	Day	39% 8% 13% 26% 14% 1	2800
July	1st to 10th	Day	40% 8% 12% 25% 14% 1	6290
	11th to 20th	Day	44% 9% 15% 21% 11%	6223
	21st to end	Day	40% 6% 9% 24% 20%	6240
August	1st to 10th	Day	49% 8% 13% 20% 10%	4221
	11th to 20th	Day	45% 8% 9% 27% 10% 1	4162
	21st to end	Day	38% 6% 10% 29% 15% 2	4312
September	1st to 10th	Day	41% 6% 9% 24% 18% 3	2400
	11th to 20th	Day	35% 5% 11% 28% 20% 2	2388
	21st to end	Day	48% 6% 10% 18% 16% 1	2092
October	1st to 10th	Day	39% 5% 8% 26% 18% 4	3260
	11th to 20th	Day	43% 5% 9% 23% 17% 4	3240
	21st to end	Day	32% 5% 14% 30% 18% 1	3538
November	1st to 10th	Day	39% 6% 13% 22% 17% 3	1931
	11th to 20th	Day	54% 5% 10% 20% 9% 2	1739
	21st to end	Day	55% 7% 11% 20% 7%	1680
December	1st to 10th	Day	66% 6% 10% 13% 5% 1	2680
	11th to 20th	Day	60% 5% 12% 18% 5%	3066
	21st to end	Day	68% 5% 11% 10% 5% 1	4048
January	1st to 10th	Night	64% 7% 9% 14% 6%	8234
	11th to 20th	Night	64% 5% 10% 11% 9% 1	7680
	21st to end	Night	59% 5% 9% 19% 7% 1	8401
February	1st to 10th	Night	53% 5% 11% 21% 9% 1	2730
	11th to 20th	Night	54% 5% 10% 19% 10% 1	2665
	21st to end	Night	54% 5% 9% 20% 11% 1	2094
March	1st to 10th	Night	53% 4 11% 20% 10% 2	4970
	11th to 20th	Night	40% 6% 15% 26% 9% 4	4980
	21st to end	Night	47% 4 8% 19% 20% 2	5427
April	1st to 10th	Night	54% 4 8% 19% 14% 2	2000
	11th to 20th	Night	46% 6% 10% 21% 15% 2	1975
	21st to end	Night	45% 5% 9% 24% 14% 3	1941
May	1st to 10th	Night	58% 6% 8% 15% 10% 3	4060
	11th to 20th	Night	52% 7% 11% 19% 11% 1	3651
	21st to end	Night	46% 7% 12% 20% 13% 3	3927
June	1st to 10th	Night	39% 6% 13% 25% 15% 2	1600
	11th to 20th	Night	40% 8% 14% 22% 15% 2	1600
	21st to end	Night	35% 8% 13% 27% 16% 1	1600
July	1st to 10th	Night	40% 7% 13% 23% 15% 2	3560
	11th to 20th	Night	40% 10% 16% 22% 12% 1	3597
	21st to end	Night	35% 6% 11% 23% 23% 1	4297
August	1st to 10th	Night	45% 8% 14% 22% 10%	2904
	11th to 20th	Night	42% 6% 12% 27% 13% 1	2920
	21st to end	Night	35% 6% 12% 32% 13% 2	3586
September	1st to 10th	Night	37% 6% 11% 25% 18% 3	2000
	11th to 20th	Night	31% 6% 11% 30% 20% 2	2009
	21st to end	Night	45% 5% 10% 21% 17% 1	2306
October	1st to 10th	Night	37% 5% 10% 25% 21% 1	3920
	11th to 20th	Night	35% 5% 10% 26% 20% 4	3899
	21st to end	Night	33% 4 13% 28% 20% 2	4252
November	1st to 10th	Night	36% 5% 14% 25% 18% 2	2585
	11th to 20th	Night	49% 5% 10% 22% 12% 3	2877
	21st to end	Night	51% 5% 12% 22% 8% 1	2940
December	1st to 10th	Night	57% 7% 13% 18% 5%	4720
	11th to 20th	Night	58% 4 13% 18% 6%	5348
	21st to end	Night	61% 6% 9% 16% 7%	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	28% 29% 27% 10% 4 1	220
	11th to 20th	Day	33% 27% 29% 10% 1 1	328
	21st to end	Day	26% 24% 36% 11% 4 1	363
February	1st to 10th	Day	25% 26% 32% 13% 4	330
	11th to 20th	Day	35% 24% 33% 8% 1	330
	21st to end	Day	32% 19% 33% 15% 2	427
March	1st to 10th	Day	29% 22% 27% 19% 3	508
	11th to 20th	Day	30% 22% 28% 15% 4 1	500
	21st to end	Day	26% 22% 31% 14% 5% 2	550
April	1st to 10th	Day	30% 21% 26% 18% 5% 1	500
	11th to 20th	Day	23% 24% 23% 18% 9% 3	492
	21st to end	Day	27% 17% 33% 13% 9% 2	500
May	1st to 10th	Day	29% 17% 28% 14% 9% 3	503
	11th to 20th	Day	24% 17% 28% 16% 12% 3	527
	21st to end	Day	21% 11% 26% 22% 15% 5%	573
June	1st to 10th	Day	20% 13% 27% 25% 12% 3	530
	11th to 20th	Day	20% 10% 25% 28% 13% 4	530
	21st to end	Day	14% 11% 30% 29% 13% 4	530
July	1st to 10th	Day	12% 8% 23% 29% 18% 9%	525
	11th to 20th	Day	9% 6% 28% 30% 20% 7%	524
	21st to end	Day	13% 7% 27% 30% 16% 7%	576
August	1st to 10th	Day	11% 7% 25% 27% 22% 8%	526
	11th to 20th	Day	14% 5% 24% 27% 20% 10%	519
	21st to end	Day	14% 8% 23% 29% 15% 12%	583
September	1st to 10th	Day	16% 8% 20% 27% 20% 9%	530
	11th to 20th	Day	15% 4 19% 28% 23% 11%	530
	21st to end	Day	26% 12% 22% 22% 15% 5%	530
October	1st to 10th	Day	20% 10% 18% 25% 20% 6%	530
	11th to 20th	Day	20% 16% 29% 22% 10% 2	530
	21st to end	Day	23% 14% 32% 22% 7% 1	583
November	1st to 10th	Day	17% 17% 30% 25% 10% 2	469
	11th to 20th	Day	26% 22% 28% 17% 6% 1	279
	21st to end	Day	25% 24% 34% 15% 2 1	220
December	1st to 10th	Day	27% 27% 33% 9% 3 1	220
	11th to 20th	Day	28% 24% 29% 18% 2	220
	21st to end	Day	27% 24% 29% 15% 5%	242
January	1st to 10th	Night	22% 23% 34% 18% 3	840
	11th to 20th	Night	27% 18% 31% 22% 3	840
	21st to end	Night	22% 20% 34% 22% 2	924
February	1st to 10th	Night	25% 17% 29% 27% 2	840
	11th to 20th	Night	27% 24% 32% 17% 1	823
	21st to end	Night	27% 19% 31% 21% 2	692
March	1st to 10th	Night	25% 16% 32% 24% 3	809
	11th to 20th	Night	25% 18% 30% 22% 5%	800
	21st to end	Night	24% 16% 32% 22% 6% 1	880
April	1st to 10th	Night	27% 18% 29% 22% 5%	800
	11th to 20th	Night	22% 14% 32% 24% 7% 1	791
	21st to end	Night	23% 12% 28% 30% 7%	741
May	1st to 10th	Night	24% 9% 24% 31% 11% 1	600
	11th to 20th	Night	19% 10% 27% 34% 9%	430
	21st to end	Night	16% 6% 21% 34% 21% 1	433
June	1st to 10th	Night	16% 6% 21% 38% 19% 1	400
	11th to 20th	Night	15% 6% 20% 42% 17%	400
	21st to end	Night	11% 6% 22% 43% 18% 1	400
July	1st to 10th	Night	12% 5% 17% 42% 22% 3	390
	11th to 20th	Night	7% 2 18% 43% 29% 1	407
	21st to end	Night	11% 3 17% 44% 23% 1	657
August	1st to 10th	Night	10% 2 14% 43% 28% 2	597
	11th to 20th	Night	14% 5% 12% 37% 27% 4	599
	21st to end	Night	14% 4 17% 34% 29% 3	880
September	1st to 10th	Night	17% 4 17% 35% 24% 3	800
	11th to 20th	Night	13% 5% 16% 31% 30% 5%	800
	21st to end	Night	22% 8% 19% 29% 20% 3	800
October	1st to 10th	Night	20% 7% 20% 29% 22% 3	800
	11th to 20th	Night	20% 13% 23% 32% 11% 1	800
	21st to end	Night	23% 14% 24% 32% 7%	880
November	1st to 10th	Night	16% 12% 27% 34% 11% 1	820
	11th to 20th	Night	25% 18% 23% 25% 7% 1	840
	21st to end	Night	24% 17% 28% 26% 4 1	840
December	1st to 10th	Night	26% 17% 31% 21% 5%	840
	11th to 20th	Night	26% 18% 28% 25% 4	840
	21st to end	Night	25% 16% 29% 27% 3	924

Page generated at 2026-02-28 01:40:19. Version ac07

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