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 2026-08-15.

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% 11% 4 10% 5% 5% 4 4 5% 7% 29%	143543
	Night	16% 13% 5% 10% 5% 4 4 3 4 6% 29%	138318
Transparency	Day	53% 5% 10% 19% 11% 1	147145
	Night	55% 5% 10% 18% 11% 1	142786
Seeing	Day	24% 16% 28% 19% 9% 3	16908
	Night	24% 14% 27% 24% 10% 1	26518

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	17% 21% 7% 24% 7% 4 3 2 2 4 10%	5122
	11th to 20th	Day	10% 20% 10% 22% 9% 7% 4 2 3 3 11%	5280
	21st to end	Day	18% 17% 8% 13% 10% 8% 3 2 3 4 14%	5780
February	1st to 10th	Day	17% 19% 6% 13% 8% 5% 3 2 3 4 21%	1890
	11th to 20th	Day	16% 15% 7% 15% 8% 4 4 3 4 4 19%	1843
	21st to end	Day	19% 16% 4 12% 5% 4 4 3 4 5% 23%	1711
March	1st to 10th	Day	17% 11% 7% 11% 5% 4 3 2 4 5% 30%	5045
	11th to 20th	Day	12% 11% 5% 10% 5% 5% 4 3 4 6% 34%	5090
	21st to end	Day	19% 12% 4 9% 5% 4 4 3 5% 5% 29%	5586
April	1st to 10th	Day	17% 15% 3 8% 4 4 5% 3 5% 6% 30%	2425
	11th to 20th	Day	19% 12% 3 7% 5% 4 4 3 5% 6% 32%	2550
	21st to end	Day	21% 11% 2 7% 5% 4 3 3 5% 5% 34%	2730
May	1st to 10th	Day	21% 10% 3 8% 6% 5% 5% 4 5% 6% 26%	7616
	11th to 20th	Day	17% 9% 3 8% 5% 5% 5% 4 6% 8% 30%	7626
	21st to end	Day	20% 8% 3 7% 4 4 5% 4 6% 6% 34%	9005
June	1st to 10th	Day	15% 7% 2 8% 6% 5% 5% 4 6% 8% 34%	2940
	11th to 20th	Day	15% 8% 2 7% 5% 5% 5% 4 6% 9% 33%	2940
	21st to end	Day	15% 5% 2 6% 5% 6% 5% 5% 6% 9% 36%	2940
July	1st to 10th	Day	10% 7% 3 8% 4 5% 5% 4 6% 9% 39%	8188
	11th to 20th	Day	10% 7% 3 6% 5% 4 5% 4 7% 10% 39%	7680
	21st to end	Day	13% 7% 3 7% 4 5% 5% 5% 6% 8% 38%	8340
August	1st to 10th	Day	15% 8% 3 9% 6% 5% 5% 5% 6% 8% 31%	4364
	11th to 20th	Day	13% 7% 3 7% 6% 5% 5% 5% 7% 8% 33%	4226
	21st to end	Day	9% 5% 2 7% 5% 6% 6% 5% 6% 10% 39%	4477
September	1st to 10th	Day	16% 7% 3 6% 3 3 4 3 5% 8% 42%	2400
	11th to 20th	Day	12% 6% 2 6% 4 4 5% 4 6% 7% 44%	2210
	21st to end	Day	21% 8% 3 7% 4 4 4 4 5% 8% 33%	2196
October	1st to 10th	Day	16% 7% 2 6% 5% 4 4 4 5% 8% 39%	2000
	11th to 20th	Day	19% 9% 3 8% 5% 5% 5% 3 5% 5% 33%	2000
	21st to end	Day	23% 11% 4 7% 4 4 4 4 5% 7% 28%	2200
November	1st to 10th	Day	11% 11% 3 7% 5% 5% 5% 4 5% 7% 38%	1947
	11th to 20th	Day	17% 17% 4 9% 5% 4 4 3 5% 5% 28%	1718
	21st to end	Day	18% 20% 6% 10% 5% 4 3 4 4 5% 20%	1680
December	1st to 10th	Day	20% 20% 9% 20% 4 3 3 2 3 3 12%	2680
	11th to 20th	Day	22% 19% 6% 12% 4 3 3 3 4 5% 18%	3070
	21st to end	Day	23% 26% 7% 12% 4 4 3 2 3 4 12%	4048
January	1st to 10th	Night	14% 21% 8% 25% 6% 4 3 2 3 4 10%	7753
	11th to 20th	Night	12% 19% 10% 20% 10% 6% 5% 3 3 3 10%	7680
	21st to end	Night	18% 17% 7% 12% 8% 6% 5% 2 3 4 17%	8401
February	1st to 10th	Night	17% 16% 6% 12% 8% 5% 4 3 3 4 21%	2730
	11th to 20th	Night	18% 14% 6% 14% 7% 5% 5% 3 5% 5% 20%	2663
	21st to end	Night	18% 15% 5% 12% 6% 4 4 4 4 5% 23%	2089
March	1st to 10th	Night	20% 14% 5% 8% 6% 4 3 2 3 5% 29%	5028
	11th to 20th	Night	14% 11% 6% 7% 5% 3 4 3 4 6% 37%	5090
	21st to end	Night	18% 11% 5% 9% 5% 4 4 3 3 5% 33%	5588
April	1st to 10th	Night	19% 15% 4 7% 5% 4 4 3 5% 6% 29%	2194
	11th to 20th	Night	18% 10% 3 8% 4 5% 4 4 4 6% 34%	2037
	21st to end	Night	14% 12% 3 8% 4 3 4 4 6% 6% 35%	1890
May	1st to 10th	Night	25% 11% 3 7% 4 4 4 3 4 6% 29%	5237
	11th to 20th	Night	17% 10% 3 7% 4 4 4 3 5% 8% 35%	5234
	21st to end	Night	23% 7% 2 6% 3 3 4 3 5% 8% 36%	5149
June	1st to 10th	Night	10% 5% 3 5% 6% 5% 4 4 6% 7% 44%	1680
	11th to 20th	Night	12% 6% 3 7% 5% 3 4 4 6% 7% 42%	1680
	21st to end	Night	11% 6% 2 7% 5% 4 4 4 6% 9% 40%	1680
July	1st to 10th	Night	12% 8% 3 7% 5% 5% 4 4 5% 7% 39%	4752
	11th to 20th	Night	10% 7% 2 6% 4 4 5% 4 7% 10% 41%	5277
	21st to end	Night	11% 6% 3 7% 4 4 4 4 5% 7% 45%	5736
August	1st to 10th	Night	12% 9% 4 8% 4 5% 4 4 5% 7% 38%	3005
	11th to 20th	Night	15% 8% 3 6% 4 4 4 3 5% 6% 42%	2911
	21st to end	Night	8% 5% 2 6% 5% 4 5% 5% 7% 9% 44%	3388
September	1st to 10th	Night	12% 5% 3 6% 4 4 4 3 5% 6% 48%	2000
	11th to 20th	Night	10% 4 2 5% 3 3 3 3 5% 8% 53%	2185
	21st to end	Night	18% 8% 3 7% 4 5% 4 3 5% 5% 38%	2202
October	1st to 10th	Night	15% 6% 2 5% 4 4 4 3 5% 6% 45%	2400
	11th to 20th	Night	17% 8% 2 8% 4 4 4 4 5% 7% 38%	2400
	21st to end	Night	24% 10% 2 6% 4 4 4 4 5% 6% 33%	2640
November	1st to 10th	Night	13% 11% 3 6% 4 4 4 3 5% 7% 40%	2566
	11th to 20th	Night	17% 15% 5% 9% 6% 4 4 3 5% 6% 27%	2898
	21st to end	Night	20% 16% 5% 9% 5% 4 4 3 4 6% 24%	2940
December	1st to 10th	Night	16% 19% 10% 17% 6% 4 4 3 4 4 14%	4720
	11th to 20th	Night	21% 19% 8% 11% 5% 4 3 3 3 5% 19%	5345
	21st to end	Night	23% 21% 7% 11% 5% 4 4 3 4 5% 14%	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	81% 3 6% 6% 4	5123
	11th to 20th	Day	81% 2 6% 7% 3	5280
	21st to end	Day	76% 3 7% 11% 3	5780
February	1st to 10th	Day	69% 3 8% 13% 7%	1890
	11th to 20th	Day	69% 3 8% 13% 6%	1852
	21st to end	Day	64% 5% 10% 14% 6% 1	1711
March	1st to 10th	Day	56% 4 11% 21% 7%	5045
	11th to 20th	Day	52% 4 15% 20% 7% 2	5090
	21st to end	Day	56% 4 8% 19% 12% 1	5586
April	1st to 10th	Day	54% 6% 11% 16% 12% 1	2425
	11th to 20th	Day	52% 6% 10% 17% 13% 2	2550
	21st to end	Day	52% 5% 10% 20% 12% 2	2730
May	1st to 10th	Day	56% 6% 10% 19% 7% 3	7651
	11th to 20th	Day	51% 6% 11% 22% 10% 1	7630
	21st to end	Day	48% 6% 10% 17% 16% 2	9020
June	1st to 10th	Day	46% 7% 12% 22% 13% 1	2940
	11th to 20th	Day	46% 8% 13% 20% 13% 1	2940
	21st to end	Day	42% 8% 11% 24% 13% 1	2940
July	1st to 10th	Day	41% 7% 11% 26% 14% 1	8119
	11th to 20th	Day	37% 6% 12% 31% 13%	7611
	21st to end	Day	41% 6% 11% 23% 19% 1	8156
August	1st to 10th	Day	49% 8% 12% 21% 9% 1	4351
	11th to 20th	Day	45% 8% 12% 26% 9% 1	4265
	21st to end	Day	38% 8% 13% 27% 12% 1	4477
September	1st to 10th	Day	41% 6% 11% 22% 17% 3	2400
	11th to 20th	Day	37% 7% 14% 25% 16% 1	2210
	21st to end	Day	49% 7% 11% 20% 12%	2196
October	1st to 10th	Day	34% 6% 12% 28% 19% 1	3260
	11th to 20th	Day	46% 5% 10% 21% 14% 4	3240
	21st to end	Day	42% 5% 13% 26% 14% 1	3538
November	1st to 10th	Day	45% 6% 12% 20% 15% 2	1947
	11th to 20th	Day	58% 5% 10% 17% 8% 2	1718
	21st to end	Day	67% 4 9% 14% 5% 1	1680
December	1st to 10th	Day	78% 4 9% 7% 2	2680
	11th to 20th	Day	69% 4 9% 14% 3	3066
	21st to end	Day	78% 3 8% 9% 3	4048
January	1st to 10th	Night	80% 4 6% 7% 3	7754
	11th to 20th	Night	80% 3 7% 6% 3	7680
	21st to end	Night	73% 3 8% 11% 5% 1	8401
February	1st to 10th	Night	67% 4 8% 15% 6%	2730
	11th to 20th	Night	66% 4 9% 14% 6%	2665
	21st to end	Night	64% 5% 8% 14% 9% 1	2089
March	1st to 10th	Night	59% 4 10% 19% 8%	5028
	11th to 20th	Night	49% 4 14% 22% 8% 3	5090
	21st to end	Night	55% 3 10% 17% 14% 1	5588
April	1st to 10th	Night	57% 5% 9% 17% 12% 1	2194
	11th to 20th	Night	51% 6% 10% 18% 13% 2	2037
	21st to end	Night	48% 6% 11% 22% 11% 2	1890
May	1st to 10th	Night	56% 5% 8% 16% 12% 3	5264
	11th to 20th	Night	47% 5% 10% 25% 11% 2	5235
	21st to end	Night	47% 5% 10% 22% 14% 2	5156
June	1st to 10th	Night	38% 7% 12% 25% 17% 2	1680
	11th to 20th	Night	39% 8% 13% 22% 16% 2	1680
	21st to end	Night	40% 7% 13% 23% 16%	1680
July	1st to 10th	Night	44% 6% 9% 23% 17% 1	4713
	11th to 20th	Night	37% 7% 15% 30% 12% 1	5226
	21st to end	Night	38% 6% 10% 18% 27% 1	5606
August	1st to 10th	Night	45% 7% 12% 22% 12% 1	2994
	11th to 20th	Night	41% 6% 10% 31% 11% 1	2938
	21st to end	Night	34% 7% 15% 29% 13% 2	3388
September	1st to 10th	Night	36% 5% 12% 26% 19% 3	2000
	11th to 20th	Night	30% 6% 13% 28% 22% 1	2185
	21st to end	Night	49% 5% 11% 19% 16% 1	2202
October	1st to 10th	Night	35% 5% 9% 26% 24% 1	3920
	11th to 20th	Night	41% 6% 11% 20% 14% 7%	3899
	21st to end	Night	39% 4 13% 25% 18% 1	4252
November	1st to 10th	Night	42% 5% 13% 23% 14% 3	2566
	11th to 20th	Night	58% 5% 9% 17% 8% 3	2898
	21st to end	Night	62% 6% 10% 17% 5% 1	2940
December	1st to 10th	Night	75% 5% 10% 7% 3	4720
	11th to 20th	Night	70% 3 10% 14% 3	5348
	21st to end	Night	73% 5% 9% 11% 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	33% 28% 27% 8% 3	305
	11th to 20th	Day	36% 30% 25% 6% 2 1	330
	21st to end	Day	33% 30% 27% 9% 1	363
February	1st to 10th	Day	32% 27% 33% 7% 1	330
	11th to 20th	Day	38% 28% 28% 5% 1	330
	21st to end	Day	37% 25% 32% 5%	295
March	1st to 10th	Day	32% 24% 30% 12% 2	540
	11th to 20th	Day	36% 19% 30% 11% 3 1	540
	21st to end	Day	34% 24% 26% 13% 3	594
April	1st to 10th	Day	31% 22% 27% 14% 6% 1	540
	11th to 20th	Day	29% 21% 27% 16% 5% 3	532
	21st to end	Day	31% 16% 31% 16% 4 2	540
May	1st to 10th	Day	31% 20% 27% 15% 5% 2	543
	11th to 20th	Day	25% 13% 33% 17% 9% 3	567
	21st to end	Day	21% 12% 28% 23% 11% 6%	617
June	1st to 10th	Day	18% 13% 34% 24% 9% 3	570
	11th to 20th	Day	22% 15% 25% 24% 11% 2	570
	21st to end	Day	15% 14% 31% 25% 11% 3	570
July	1st to 10th	Day	11% 8% 23% 29% 21% 8%	565
	11th to 20th	Day	13% 7% 28% 29% 18% 6%	564
	21st to end	Day	14% 6% 29% 28% 16% 7%	620
August	1st to 10th	Day	14% 7% 26% 28% 19% 7%	566
	11th to 20th	Day	17% 7% 24% 28% 16% 8%	535
	21st to end	Day	10% 6% 27% 32% 17% 8%	583
September	1st to 10th	Day	17% 8% 24% 25% 19% 7%	530
	11th to 20th	Day	12% 6% 22% 28% 23% 10%	530
	21st to end	Day	25% 12% 25% 22% 12% 4	530
October	1st to 10th	Day	17% 11% 27% 23% 17% 4	530
	11th to 20th	Day	25% 17% 33% 16% 8% 2	530
	21st to end	Day	32% 16% 31% 16% 6%	583
November	1st to 10th	Day	22% 22% 33% 14% 7% 2	425
	11th to 20th	Day	34% 22% 29% 10% 4 2	239
	21st to end	Day	30% 25% 34% 10% 1	220
December	1st to 10th	Day	37% 30% 25% 5% 2 2	220
	11th to 20th	Day	38% 23% 29% 9% 1	220
	21st to end	Day	37% 25% 29% 9% 1	242
January	1st to 10th	Night	32% 22% 31% 12% 2	840
	11th to 20th	Night	34% 23% 29% 13% 2	840
	21st to end	Night	29% 24% 30% 15% 2	924
February	1st to 10th	Night	31% 19% 28% 20% 2	840
	11th to 20th	Night	29% 22% 34% 13% 1	823
	21st to end	Night	31% 22% 31% 15% 2	692
March	1st to 10th	Night	28% 19% 32% 18% 3	840
	11th to 20th	Night	31% 18% 27% 18% 6%	840
	21st to end	Night	27% 18% 34% 17% 4	924
April	1st to 10th	Night	30% 15% 30% 19% 6%	840
	11th to 20th	Night	24% 16% 32% 19% 8% 1	793
	21st to end	Night	21% 13% 32% 28% 5% 1	630
May	1st to 10th	Night	24% 11% 24% 31% 10%	630
	11th to 20th	Night	21% 8% 28% 33% 9% 1	621
	21st to end	Night	13% 6% 28% 32% 18% 2	471
June	1st to 10th	Night	11% 4 30% 38% 16%	420
	11th to 20th	Night	15% 7% 28% 37% 13%	420
	21st to end	Night	12% 6% 26% 35% 19%	420
July	1st to 10th	Night	9% 3 19% 42% 22% 4	431
	11th to 20th	Night	10% 5% 19% 37% 26% 4	612
	21st to end	Night	12% 3 14% 43% 26% 1	690
August	1st to 10th	Night	12% 3 18% 40% 25% 3	627
	11th to 20th	Night	15% 3 14% 39% 25% 3	606
	21st to end	Night	12% 4 21% 34% 25% 5%	760
September	1st to 10th	Night	15% 5% 23% 32% 24% 3	800
	11th to 20th	Night	12% 4 18% 35% 26% 4	800
	21st to end	Night	21% 10% 23% 25% 18% 3	800
October	1st to 10th	Night	18% 8% 24% 29% 18% 3	800
	11th to 20th	Night	21% 13% 33% 24% 8% 1	800
	21st to end	Night	29% 13% 30% 23% 5%	880
November	1st to 10th	Night	20% 13% 31% 27% 9%	820
	11th to 20th	Night	30% 18% 27% 19% 5% 1	840
	21st to end	Night	33% 15% 30% 17% 4	840
December	1st to 10th	Night	32% 23% 26% 15% 3	840
	11th to 20th	Night	30% 24% 27% 16% 3	840
	21st to end	Night	33% 21% 28% 17% 1	924

Page generated at 2026-08-12 03:37:20. Version ac07

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