Grove City College
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Grove City College clear sky chart from 2005-11-06 to 2025-04-11.

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% 12% 4 10% 5% 5% 4 4 5% 6% 29%	113532
	Night	16% 13% 5% 10% 5% 4 4 3 4 6% 29%	114744
Transparency	Day	54% 6% 11% 19% 10% 1	117178
	Night	55% 5% 10% 18% 10% 1	119237
Seeing	Day	24% 16% 28% 19% 9% 3	15109
	Night	24% 14% 27% 24% 10% 1	24903

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% 8% 24% 6% 3 3 2 2 4 12%	3946
	11th to 20th	Day	11% 22% 10% 21% 8% 7% 3 2 2 3 12%	4060
	21st to end	Day	20% 19% 9% 13% 8% 5% 3 2 3 4 13%	4466
February	1st to 10th	Day	18% 19% 6% 13% 8% 4 3 2 3 4 20%	1800
	11th to 20th	Day	16% 15% 7% 15% 9% 4 4 3 5% 4 19%	1753
	21st to end	Day	19% 16% 4 13% 6% 4 4 3 4 5% 23%	1632
March	1st to 10th	Day	17% 12% 7% 11% 5% 4 3 2 4 5% 30%	4935
	11th to 20th	Day	12% 11% 5% 10% 5% 5% 4 3 4 6% 34%	4980
	21st to end	Day	20% 12% 4 9% 5% 4 3 3 5% 5% 29%	5465
April	1st to 10th	Day	17% 15% 3 8% 4 4 5% 3 4 6% 30%	2310
	11th to 20th	Day	20% 12% 3 7% 4 3 4 3 5% 6% 32%	2304
	21st to end	Day	21% 11% 2 7% 5% 3 3 3 5% 5% 33%	2470
May	1st to 10th	Day	23% 9% 3 8% 5% 5% 4 4 5% 6% 28%	4082
	11th to 20th	Day	20% 9% 3 7% 5% 5% 5% 5% 6% 7% 28%	4081
	21st to end	Day	12% 6% 3 6% 5% 5% 5% 4 6% 8% 39%	4810
June	1st to 10th	Day	16% 7% 2 8% 6% 5% 5% 5% 7% 9% 32%	2660
	11th to 20th	Day	14% 8% 2 7% 5% 5% 5% 4 6% 9% 34%	2660
	21st to end	Day	16% 5% 2 6% 5% 6% 5% 5% 6% 9% 36%	2660
July	1st to 10th	Day	9% 6% 3 7% 5% 6% 5% 5% 6% 10% 38%	4390
	11th to 20th	Day	11% 6% 2 6% 4 4 5% 4 7% 9% 42%	4120
	21st to end	Day	11% 7% 3 7% 5% 5% 6% 5% 7% 8% 37%	4466
August	1st to 10th	Day	15% 8% 3 9% 6% 5% 5% 5% 6% 8% 30%	4104
	11th to 20th	Day	13% 7% 3 7% 6% 5% 5% 5% 7% 8% 33%	4044
	21st to end	Day	9% 5% 2 7% 5% 6% 6% 5% 6% 10% 39%	4340
September	1st to 10th	Day	16% 7% 3 6% 4 3 4 3 5% 8% 42%	2280
	11th to 20th	Day	13% 7% 2 6% 4 4 5% 4 6% 7% 42%	2100
	21st to end	Day	21% 8% 3 7% 5% 4 4 4 5% 8% 33%	2086
October	1st to 10th	Day	16% 8% 2 6% 6% 4 4 4 5% 8% 37%	1900
	11th to 20th	Day	20% 9% 3 8% 5% 5% 5% 3 4 5% 32%	1900
	21st to end	Day	24% 11% 4 7% 4 3 4 4 5% 7% 28%	2090
November	1st to 10th	Day	11% 11% 3 7% 5% 4 5% 4 5% 7% 38%	1852
	11th to 20th	Day	17% 17% 4 8% 5% 4 4 3 5% 5% 28%	1636
	21st to end	Day	18% 20% 6% 10% 5% 4 3 4 4 5% 20%	1600
December	1st to 10th	Day	20% 20% 9% 20% 4 3 3 2 3 3 12%	2600
	11th to 20th	Day	23% 19% 6% 11% 4 3 3 3 4 5% 18%	2990
	21st to end	Day	23% 26% 7% 11% 4 4 3 2 3 4 12%	3960
January	1st to 10th	Night	14% 20% 9% 26% 5% 3 3 2 3 4 11%	5981
	11th to 20th	Night	12% 19% 10% 19% 9% 6% 4 3 3 3 11%	5900
	21st to end	Night	21% 18% 8% 13% 7% 4 5% 2 3 4 14%	6490
February	1st to 10th	Night	18% 16% 6% 12% 8% 5% 4 3 3 4 20%	2600
	11th to 20th	Night	18% 14% 6% 13% 7% 5% 5% 3 5% 5% 21%	2533
	21st to end	Night	19% 15% 5% 12% 6% 4 4 4 4 5% 23%	1992
March	1st to 10th	Night	20% 14% 6% 8% 6% 4 3 2 3 5% 29%	4918
	11th to 20th	Night	14% 11% 6% 7% 5% 3 4 3 4 6% 37%	4980
	21st to end	Night	18% 11% 5% 9% 5% 4 4 3 3 5% 33%	5467
April	1st to 10th	Night	19% 15% 4 7% 5% 4 4 3 5% 6% 29%	2090
	11th to 20th	Night	19% 10% 3 7% 3 5% 4 4 4 5% 35%	1848
	21st to end	Night	15% 12% 3 8% 4 3 4 4 6% 6% 35%	1710
May	1st to 10th	Night	27% 10% 3 6% 4 4 4 3 5% 6% 28%	2813
	11th to 20th	Night	17% 10% 3 6% 4 4 5% 3 6% 8% 34%	2812
	21st to end	Night	11% 6% 2 6% 4 3 4 3 6% 11% 42%	2745
June	1st to 10th	Night	10% 5% 3 5% 6% 5% 4 5% 7% 7% 43%	1520
	11th to 20th	Night	11% 5% 3 6% 5% 3 5% 4 7% 7% 43%	1520
	21st to end	Night	11% 6% 2 7% 5% 4 4 4 6% 9% 41%	1520
July	1st to 10th	Night	12% 7% 3 7% 5% 4 4 4 5% 7% 40%	2566
	11th to 20th	Night	10% 5% 2 5% 4 4 4 4 6% 9% 45%	2840
	21st to end	Night	10% 7% 3 7% 4 4 5% 5% 6% 7% 43%	3087
August	1st to 10th	Night	13% 9% 4 8% 4 5% 4 4 5% 6% 38%	2825
	11th to 20th	Night	15% 7% 2 6% 4 4 4 3 5% 7% 42%	2785
	21st to end	Night	8% 5% 2 6% 5% 4 5% 5% 7% 9% 44%	3284
September	1st to 10th	Night	13% 5% 3 6% 4 4 4 3 5% 6% 47%	1900
	11th to 20th	Night	11% 5% 2 5% 3 3 3 3 5% 8% 52%	2076
	21st to end	Night	18% 8% 3 7% 4 4 4 3 5% 5% 39%	2092
October	1st to 10th	Night	16% 6% 2 6% 4 4 4 3 5% 7% 44%	2280
	11th to 20th	Night	17% 8% 2 8% 4 4 4 4 5% 7% 37%	2280
	21st to end	Night	24% 10% 2 6% 4 4 4 4 5% 6% 32%	2508
November	1st to 10th	Night	13% 11% 3 5% 4 4 4 3 5% 7% 40%	2441
	11th to 20th	Night	17% 15% 4 9% 6% 4 4 3 5% 6% 27%	2760
	21st to end	Night	20% 16% 4 9% 5% 4 4 3 4 6% 25%	2800
December	1st to 10th	Night	17% 18% 10% 17% 6% 4 4 3 4 4 14%	4580
	11th to 20th	Night	21% 19% 8% 11% 5% 4 3 3 3 5% 18%	5205
	21st to end	Night	23% 21% 7% 11% 5% 4 4 3 4 5% 14%	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	79% 3 6% 7% 5%	3947
	11th to 20th	Day	81% 2 6% 8% 3 1	4060
	21st to end	Day	77% 3 7% 9% 4	4466
February	1st to 10th	Day	70% 3 8% 12% 6%	1800
	11th to 20th	Day	69% 4 8% 13% 6%	1762
	21st to end	Day	64% 5% 10% 14% 6% 2	1632
March	1st to 10th	Day	56% 4 11% 21% 7%	4935
	11th to 20th	Day	52% 4 15% 20% 7% 2	4980
	21st to end	Day	56% 4 8% 19% 12% 1	5465
April	1st to 10th	Day	55% 5% 11% 16% 12% 1	2310
	11th to 20th	Day	52% 5% 10% 17% 13% 2	2304
	21st to end	Day	53% 5% 9% 20% 11% 2	2470
May	1st to 10th	Day	56% 6% 9% 21% 8% 1	4120
	11th to 20th	Day	52% 7% 11% 19% 8% 1	4085
	21st to end	Day	40% 9% 13% 21% 13% 3	4824
June	1st to 10th	Day	47% 8% 12% 21% 11% 1	2660
	11th to 20th	Day	45% 8% 13% 20% 13% 1	2660
	21st to end	Day	42% 8% 10% 25% 13% 1	2660
July	1st to 10th	Day	40% 7% 12% 23% 15% 3	4321
	11th to 20th	Day	37% 7% 11% 27% 17%	4051
	21st to end	Day	41% 7% 14% 20% 17% 1	4324
August	1st to 10th	Day	50% 8% 12% 22% 9%	4091
	11th to 20th	Day	45% 8% 12% 26% 8% 1	4083
	21st to end	Day	39% 8% 13% 26% 12% 1	4340
September	1st to 10th	Day	41% 6% 12% 21% 17% 3	2280
	11th to 20th	Day	38% 7% 13% 24% 16% 1	2100
	21st to end	Day	49% 8% 11% 21% 12%	2086
October	1st to 10th	Day	35% 6% 12% 28% 19% 1	3160
	11th to 20th	Day	46% 5% 10% 21% 14% 4	3140
	21st to end	Day	42% 5% 13% 27% 14%	3428
November	1st to 10th	Day	45% 6% 12% 20% 16% 2	1852
	11th to 20th	Day	57% 5% 10% 17% 8% 2	1636
	21st to end	Day	66% 5% 9% 14% 5% 1	1600
December	1st to 10th	Day	78% 4 9% 7% 2	2600
	11th to 20th	Day	70% 4 9% 14% 3	2986
	21st to end	Day	78% 3 8% 9% 3	3960
January	1st to 10th	Night	79% 4 6% 8% 3	5981
	11th to 20th	Night	79% 4 7% 7% 2	5900
	21st to end	Night	76% 3 7% 9% 4 1	6490
February	1st to 10th	Night	68% 4 8% 15% 5%	2600
	11th to 20th	Night	66% 4 9% 14% 6%	2535
	21st to end	Night	64% 5% 8% 14% 9% 1	1992
March	1st to 10th	Night	59% 4 10% 19% 8%	4918
	11th to 20th	Night	48% 4 13% 23% 8% 3	4980
	21st to end	Night	54% 3 10% 17% 14% 1	5467
April	1st to 10th	Night	57% 4 9% 17% 12% 1	2090
	11th to 20th	Night	50% 6% 10% 17% 14% 3	1848
	21st to end	Night	48% 6% 10% 21% 11% 3	1710
May	1st to 10th	Night	55% 6% 8% 18% 10% 2	2840
	11th to 20th	Night	47% 7% 11% 23% 10% 1	2813
	21st to end	Night	34% 7% 15% 25% 15% 4	2752
June	1st to 10th	Night	38% 8% 13% 26% 15% 1	1520
	11th to 20th	Night	38% 8% 13% 22% 16% 2	1520
	21st to end	Night	39% 7% 13% 24% 17%	1520
July	1st to 10th	Night	43% 6% 10% 21% 18% 2	2525
	11th to 20th	Night	33% 7% 14% 28% 16% 1	2786
	21st to end	Night	40% 7% 10% 17% 24% 1	2988
August	1st to 10th	Night	45% 7% 12% 23% 12% 1	2814
	11th to 20th	Night	41% 6% 10% 31% 10% 1	2812
	21st to end	Night	34% 8% 15% 29% 13% 2	3284
September	1st to 10th	Night	36% 5% 12% 25% 19% 3	1900
	11th to 20th	Night	31% 6% 13% 27% 23% 1	2076
	21st to end	Night	48% 5% 11% 19% 16% 1	2092
October	1st to 10th	Night	36% 5% 9% 26% 22% 1	3800
	11th to 20th	Night	41% 6% 11% 21% 14% 7%	3779
	21st to end	Night	39% 4 13% 25% 18% 1	4120
November	1st to 10th	Night	42% 5% 13% 22% 14% 3	2441
	11th to 20th	Night	58% 5% 9% 17% 8% 3	2760
	21st to end	Night	61% 6% 10% 17% 5% 1	2800
December	1st to 10th	Night	75% 5% 10% 8% 3	4580
	11th to 20th	Night	70% 3 10% 13% 2	5208
	21st to end	Night	73% 5% 9% 11% 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	33% 30% 25% 9% 3	277
	11th to 20th	Day	34% 30% 27% 7% 2 1	300
	21st to end	Day	32% 30% 28% 8% 2	330
February	1st to 10th	Day	34% 28% 32% 6%	300
	11th to 20th	Day	38% 28% 28% 5% 1	300
	21st to end	Day	40% 24% 30% 6%	270
March	1st to 10th	Day	31% 23% 30% 13% 3	500
	11th to 20th	Day	34% 19% 31% 11% 3 1	500
	21st to end	Day	35% 23% 26% 14% 3	550
April	1st to 10th	Day	31% 22% 26% 14% 6% 1	500
	11th to 20th	Day	29% 20% 26% 17% 6% 3	452
	21st to end	Day	31% 18% 31% 14% 5% 2	460
May	1st to 10th	Day	30% 18% 27% 17% 6% 2	463
	11th to 20th	Day	24% 13% 33% 17% 10% 3	487
	21st to end	Day	17% 11% 28% 25% 12% 6%	529
June	1st to 10th	Day	18% 12% 33% 25% 9% 3	490
	11th to 20th	Day	20% 12% 25% 27% 13% 3	490
	21st to end	Day	16% 15% 32% 24% 10% 3	490
July	1st to 10th	Day	11% 8% 24% 28% 20% 9%	485
	11th to 20th	Day	13% 8% 28% 28% 17% 7%	484
	21st to end	Day	14% 6% 29% 27% 17% 7%	532
August	1st to 10th	Day	13% 7% 25% 28% 20% 7%	486
	11th to 20th	Day	16% 7% 25% 27% 16% 9%	479
	21st to end	Day	10% 6% 26% 32% 17% 9%	539
September	1st to 10th	Day	17% 7% 26% 26% 18% 7%	490
	11th to 20th	Day	13% 6% 23% 28% 21% 10%	490
	21st to end	Day	24% 13% 25% 22% 12% 4	490
October	1st to 10th	Day	18% 11% 29% 22% 16% 4	490
	11th to 20th	Day	25% 17% 31% 16% 8% 2	490
	21st to end	Day	32% 15% 30% 17% 6%	539
November	1st to 10th	Day	22% 22% 32% 15% 8% 2	390
	11th to 20th	Day	31% 23% 30% 10% 4 2	217
	21st to end	Day	28% 26% 36% 10% 1	200
December	1st to 10th	Day	37% 30% 24% 6% 2 2	200
	11th to 20th	Day	38% 22% 29% 10% 2	200
	21st to end	Day	35% 26% 30% 9% 1	220
January	1st to 10th	Night	32% 22% 31% 12% 2	800
	11th to 20th	Night	33% 22% 29% 13% 2	800
	21st to end	Night	29% 23% 31% 15% 2	880
February	1st to 10th	Night	33% 20% 27% 19% 2	800
	11th to 20th	Night	30% 22% 34% 13% 1	783
	21st to end	Night	31% 21% 31% 15% 2	660
March	1st to 10th	Night	28% 19% 32% 19% 3	800
	11th to 20th	Night	31% 18% 27% 19% 6%	800
	21st to end	Night	27% 17% 34% 18% 4	880
April	1st to 10th	Night	30% 15% 30% 20% 6%	800
	11th to 20th	Night	25% 15% 32% 19% 8% 1	720
	21st to end	Night	22% 12% 34% 27% 5% 1	570
May	1st to 10th	Night	23% 11% 24% 32% 10% 1	570
	11th to 20th	Night	21% 8% 27% 34% 9% 1	561
	21st to end	Night	10% 5% 28% 34% 20% 2	425
June	1st to 10th	Night	11% 3 31% 38% 17%	380
	11th to 20th	Night	14% 6% 26% 39% 14%	380
	21st to end	Night	12% 6% 27% 36% 19% 1	380
July	1st to 10th	Night	9% 3 21% 41% 22% 4	389
	11th to 20th	Night	11% 4 19% 37% 25% 4	552
	21st to end	Night	13% 3 13% 43% 27% 1	624
August	1st to 10th	Night	13% 3 16% 40% 25% 3	567
	11th to 20th	Night	14% 4 14% 40% 24% 4	564
	21st to end	Night	11% 4 20% 34% 25% 5%	722
September	1st to 10th	Night	15% 5% 22% 31% 24% 3	760
	11th to 20th	Night	13% 4 19% 34% 26% 4	760
	21st to end	Night	21% 10% 23% 24% 17% 4	760
October	1st to 10th	Night	18% 9% 25% 28% 18% 3	760
	11th to 20th	Night	22% 13% 31% 25% 8% 1	760
	21st to end	Night	29% 13% 30% 23% 5%	836
November	1st to 10th	Night	19% 13% 31% 27% 9% 1	780
	11th to 20th	Night	30% 18% 27% 18% 5% 1	800
	21st to end	Night	33% 16% 30% 18% 4 1	800
December	1st to 10th	Night	33% 23% 26% 15% 4	800
	11th to 20th	Night	30% 24% 27% 17% 3	800
	21st to end	Night	32% 21% 28% 17% 1	880

Page generated at 2025-04-08 09:17:26. Version ac07

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