West Grand High School
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the West Grand High School clear sky chart from 2005-11-06 to 2026-10-29.

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	2 5% 2 7% 5% 5% 6% 5% 8% 9% 46%	158503
	Night	2 6% 3 7% 5% 5% 5% 5% 8% 8% 46%	151182
Transparency	Day	30% 9% 13% 23% 18% 7%	153417
	Night	31% 9% 15% 25% 16% 5%	147277
Seeing	Day	9% 15% 27% 28% 17% 4	18289
	Night	6% 8% 27% 41% 17% 1	28280

By Month

Percentage Cloud Cover SW (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	1 6% 6% 16% 8% 7% 7% 5% 8% 8% 29%	4720
	11th to 20th	Day	6% 3 11% 7% 5% 6% 5% 8% 8% 40%	5134
	21st to end	Day	6% 4 11% 6% 7% 5% 4 7% 8% 41%	5844
February	1st to 10th	Day	1 11% 4 11% 8% 5% 5% 4 6% 8% 36%	1890
	11th to 20th	Day	8% 5% 10% 7% 7% 7% 6% 8% 7% 35%	1934
	21st to end	Day	1 8% 4 11% 6% 6% 6% 5% 8% 7% 38%	1730
March	1st to 10th	Day	1 6% 4 8% 6% 5% 6% 4 8% 7% 45%	4759
	11th to 20th	Day	7% 3 8% 5% 4 5% 5% 7% 10% 44%	5110
	21st to end	Day	1 7% 3 11% 7% 7% 7% 6% 8% 9% 34%	5803
April	1st to 10th	Day	2 10% 3 7% 5% 5% 5% 4 7% 9% 43%	2520
	11th to 20th	Day	3 9% 3 10% 7% 5% 6% 4 8% 7% 38%	2491
	21st to end	Day	2 10% 3 8% 5% 6% 6% 5% 8% 8% 39%	2520
May	1st to 10th	Day	3 9% 4 8% 6% 5% 7% 6% 8% 9% 37%	7524
	11th to 20th	Day	3 5% 2 7% 5% 6% 6% 6% 8% 9% 43%	8191
	21st to end	Day	2 5% 2 6% 5% 6% 7% 6% 8% 10% 43%	9026
June	1st to 10th	Day	3 4 2 5% 4 5% 5% 4 7% 10% 52%	2940
	11th to 20th	Day	3 3 1 4 3 4 5% 4 6% 8% 59%	2940
	21st to end	Day	2 2 1 4 4 4 5% 4 7% 8% 58%	2940
July	1st to 10th	Day	2 2 1 4 3 4 6% 5% 7% 10% 57%	8249
	11th to 20th	Day	1 2 1 4 4 6% 8% 6% 9% 11% 48%	8250
	21st to end	Day	2 3 2 6% 5% 6% 7% 5% 8% 10% 45%	8489
August	1st to 10th	Day	3 3 1 4 4 5% 6% 5% 8% 10% 52%	7549
	11th to 20th	Day	2 3 1 4 4 5% 7% 5% 8% 11% 49%	7247
	21st to end	Day	3 3 2 6% 6% 7% 8% 6% 9% 11% 41%	7751
September	1st to 10th	Day	4 3 1 4 4 4 5% 4 6% 9% 57%	2520
	11th to 20th	Day	3 3 2 5% 3 4 6% 4 7% 8% 54%	2520
	21st to end	Day	5% 5% 2 5% 3 3 3 3 5% 7% 61%	2255
October	1st to 10th	Day	3 4 1 3 3 3 3 2 4 4 70%	3370
	11th to 20th	Day	3 5% 1 5% 3 4 4 5% 7% 9% 55%	3350
	21st to end	Day	4 6% 2 7% 4 4 4 4 5% 7% 53%	3628
November	1st to 10th	Day	2 7% 2 5% 4 3 4 4 6% 7% 55%	1853
	11th to 20th	Day	2 8% 3 6% 5% 3 4 4 5% 7% 52%	1878
	21st to end	Day	1 6% 3 9% 4 4 4 4 6% 7% 52%	1680
December	1st to 10th	Day	1 6% 3 9% 6% 4 4 4 10% 6% 47%	2700
	11th to 20th	Day	1 6% 3 7% 5% 4 5% 4 7% 9% 48%	3106
	21st to end	Day	1 7% 4 12% 7% 7% 7% 6% 8% 8% 33%	4092
January	1st to 10th	Night	1 8% 6% 12% 8% 6% 7% 7% 9% 9% 27%	8201
	11th to 20th	Night	1 7% 4 11% 10% 6% 6% 5% 10% 7% 34%	7913
	21st to end	Night	1 10% 5% 11% 6% 5% 5% 5% 10% 7% 35%	8370
February	1st to 10th	Night	1 10% 6% 12% 6% 4 6% 5% 6% 7% 37%	2730
	11th to 20th	Night	1 9% 5% 11% 6% 5% 5% 5% 8% 9% 36%	2572
	21st to end	Night	1 8% 6% 11% 7% 6% 5% 4 6% 6% 41%	2076
March	1st to 10th	Night	1 10% 4 10% 5% 4 4 5% 9% 7% 41%	5325
	11th to 20th	Night	1 7% 3 7% 5% 5% 5% 6% 8% 7% 47%	5110
	21st to end	Night	2 8% 4 9% 5% 5% 6% 5% 8% 9% 40%	5391
April	1st to 10th	Night	3 8% 3 7% 5% 4 4 4 6% 9% 47%	2100
	11th to 20th	Night	4 9% 3 8% 5% 5% 4 4 6% 9% 43%	2077
	21st to end	Night	5% 9% 3 5% 4 4 4 3 6% 8% 50%	2100
May	1st to 10th	Night	4 8% 3 7% 5% 4 6% 5% 6% 9% 44%	5418
	11th to 20th	Night	4 6% 2 6% 5% 5% 6% 4 7% 9% 46%	4701
	21st to end	Night	3 4 2 5% 5% 5% 6% 5% 6% 9% 50%	5181
June	1st to 10th	Night	3 2 1 3 3 4 4 3 7% 9% 62%	1680
	11th to 20th	Night	2 2 1 3 3 3 4 4 5% 7% 65%	1680
	21st to end	Night	2 2 1 3 3 3 5% 4 6% 9% 63%	1680
July	1st to 10th	Night	2 2 1 3 3 4 5% 4 7% 10% 58%	4740
	11th to 20th	Night	1 1 1 4 4 4 6% 5% 8% 11% 56%	4740
	21st to end	Night	2 3 2 5% 5% 6% 7% 5% 9% 10% 47%	5603
August	1st to 10th	Night	2 2 1 4 4 5% 6% 5% 7% 9% 55%	5273
	11th to 20th	Night	2 3 2 5% 5% 6% 7% 5% 7% 10% 49%	5607
	21st to end	Night	3 4 2 6% 5% 7% 8% 5% 7% 10% 42%	6465
September	1st to 10th	Night	4 3 2 4 3 4 4 4 5% 7% 60%	2100
	11th to 20th	Night	3 4 2 4 3 3 4 4 5% 7% 62%	2100
	21st to end	Night	3 4 2 5% 3 3 3 3 4 7% 62%	2361
October	1st to 10th	Night	2 3 1 3 2 2 3 3 3 5% 73%	4040
	11th to 20th	Night	3 4 2 5% 2 3 4 4 5% 9% 60%	4018
	21st to end	Night	4 6% 2 5% 3 3 3 3 5% 6% 61%	4348
November	1st to 10th	Night	3 7% 2 5% 3 3 3 3 6% 6% 58%	2643
	11th to 20th	Night	2 9% 3 6% 4 4 3 4 6% 7% 54%	2740
	21st to end	Night	2 7% 3 8% 4 4 4 4 6% 9% 49%	2940
December	1st to 10th	Night	1 6% 4 9% 5% 4 5% 8% 16% 7% 37%	4710
	11th to 20th	Night	1 7% 4 7% 5% 6% 7% 6% 10% 10% 38%	5321
	21st to end	Night	1 9% 5% 13% 8% 7% 7% 6% 10% 9% 24%	7128

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	43% 9% 16% 22% 8% 1	4723
	11th to 20th	Day	34% 9% 15% 26% 13% 2	5134
	21st to end	Day	36% 8% 13% 25% 15% 3	5844
February	1st to 10th	Day	45% 9% 15% 17% 11% 2	1890
	11th to 20th	Day	44% 10% 11% 22% 11% 2	1943
	21st to end	Day	42% 8% 15% 17% 15% 3	1730
March	1st to 10th	Day	33% 7% 10% 26% 18% 6%	4759
	11th to 20th	Day	31% 8% 12% 36% 13% 1	5110
	21st to end	Day	39% 13% 16% 24% 7% 1	5803
April	1st to 10th	Day	35% 9% 14% 23% 14% 5%	2520
	11th to 20th	Day	42% 7% 14% 17% 18% 2	2494
	21st to end	Day	39% 10% 11% 26% 12% 2	2520
May	1st to 10th	Day	37% 10% 14% 20% 15% 4	7524
	11th to 20th	Day	28% 9% 12% 27% 20% 4	8195
	21st to end	Day	28% 9% 15% 24% 23% 2	9027
June	1st to 10th	Day	24% 9% 13% 23% 23% 8%	2940
	11th to 20th	Day	20% 7% 9% 18% 26% 19%	2940
	21st to end	Day	20% 6% 9% 21% 26% 18%	2940
July	1st to 10th	Day	17% 8% 6% 13% 29% 27%	8181
	11th to 20th	Day	21% 11% 10% 24% 22% 12%	8175
	21st to end	Day	29% 9% 14% 18% 16% 13%	8301
August	1st to 10th	Day	25% 9% 14% 17% 17% 18%	5978
	11th to 20th	Day	29% 10% 19% 21% 16% 5%	5718
	21st to end	Day	28% 9% 20% 19% 17% 7%	6078
September	1st to 10th	Day	23% 7% 9% 21% 26% 14%	2520
	11th to 20th	Day	24% 8% 12% 23% 24% 9%	2520
	21st to end	Day	24% 5% 8% 30% 26% 7%	2255
October	1st to 10th	Day	18% 5% 5% 27% 32% 12%	3370
	11th to 20th	Day	24% 5% 12% 34% 22% 3	3350
	21st to end	Day	29% 7% 10% 37% 16% 2	3628
November	1st to 10th	Day	27% 5% 15% 28% 24% 1	1853
	11th to 20th	Day	30% 7% 17% 28% 16% 2	1878
	21st to end	Day	32% 5% 15% 33% 13% 2	1680
December	1st to 10th	Day	34% 8% 16% 32% 9% 1	2700
	11th to 20th	Day	29% 8% 22% 29% 13%	3104
	21st to end	Day	42% 7% 16% 22% 12% 2	4092
January	1st to 10th	Night	43% 10% 19% 20% 8% 1	8202
	11th to 20th	Night	40% 13% 14% 20% 11% 2	7913
	21st to end	Night	39% 10% 13% 20% 16% 2	8370
February	1st to 10th	Night	42% 10% 16% 19% 10% 2	2730
	11th to 20th	Night	41% 9% 13% 24% 11% 2	2573
	21st to end	Night	43% 6% 12% 20% 17% 2	2076
March	1st to 10th	Night	36% 9% 8% 27% 18% 2	5325
	11th to 20th	Night	28% 6% 13% 33% 18% 2	5110
	21st to end	Night	35% 11% 18% 30% 6% 1	5391
April	1st to 10th	Night	32% 9% 16% 24% 16% 3	2100
	11th to 20th	Night	37% 7% 14% 23% 18% 2	2077
	21st to end	Night	33% 8% 13% 28% 19%	2100
May	1st to 10th	Night	34% 8% 16% 31% 10% 1	5416
	11th to 20th	Night	29% 9% 15% 29% 15% 3	4702
	21st to end	Night	26% 8% 17% 27% 19% 2	5182
June	1st to 10th	Night	18% 7% 16% 29% 22% 7%	1680
	11th to 20th	Night	17% 7% 11% 18% 25% 21%	1680
	21st to end	Night	15% 6% 9% 24% 26% 19%	1680
July	1st to 10th	Night	18% 7% 9% 17% 27% 23%	4700
	11th to 20th	Night	17% 9% 21% 27% 17% 9%	4692
	21st to end	Night	26% 10% 21% 20% 12% 11%	5479
August	1st to 10th	Night	21% 9% 15% 18% 21% 15%	4168
	11th to 20th	Night	30% 14% 20% 17% 12% 7%	4412
	21st to end	Night	30% 10% 21% 15% 18% 6%	5069
September	1st to 10th	Night	23% 6% 11% 20% 25% 15%	2100
	11th to 20th	Night	20% 6% 14% 24% 24% 12%	2100
	21st to end	Night	23% 6% 8% 28% 28% 7%	2361
October	1st to 10th	Night	15% 4 7% 30% 34% 10%	4040
	11th to 20th	Night	21% 4 16% 37% 19% 3	4018
	21st to end	Night	23% 5% 11% 39% 19% 2	4348
November	1st to 10th	Night	26% 5% 12% 30% 24% 3	2643
	11th to 20th	Night	29% 7% 16% 30% 16% 2	2740
	21st to end	Night	31% 7% 14% 31% 15% 2	2940
December	1st to 10th	Night	36% 17% 14% 25% 8% 1	4710
	11th to 20th	Night	29% 10% 22% 30% 9%	5322
	21st to end	Night	44% 11% 15% 17% 13% 1	7128

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	9% 17% 24% 33% 13% 4	330
	11th to 20th	Day	9% 16% 29% 34% 10% 2	330
	21st to end	Day	4 12% 35% 33% 13% 2	363
February	1st to 10th	Day	12% 23% 33% 24% 6% 2	330
	11th to 20th	Day	12% 24% 31% 28% 4 1	330
	21st to end	Day	16% 22% 27% 27% 7%	273
March	1st to 10th	Day	12% 24% 30% 23% 10% 2	398
	11th to 20th	Day	12% 24% 31% 23% 9% 1	540
	21st to end	Day	12% 33% 30% 17% 7% 1	594
April	1st to 10th	Day	15% 24% 32% 17% 9% 3	540
	11th to 20th	Day	15% 34% 27% 17% 5% 1	532
	21st to end	Day	14% 26% 33% 17% 8% 2	540
May	1st to 10th	Day	15% 22% 30% 21% 9% 3	589
	11th to 20th	Day	12% 13% 28% 29% 15% 2	775
	21st to end	Day	9% 15% 28% 29% 17% 4	844
June	1st to 10th	Day	6% 13% 24% 30% 21% 6%	780
	11th to 20th	Day	6% 14% 29% 33% 17% 2	780
	21st to end	Day	5% 12% 25% 33% 22% 3	780
July	1st to 10th	Day	4 6% 19% 33% 32% 6%	771
	11th to 20th	Day	4 4 19% 32% 32% 9%	768
	21st to end	Day	7% 4 19% 33% 29% 9%	689
August	1st to 10th	Day	8% 7% 25% 33% 20% 7%	567
	11th to 20th	Day	4 6% 25% 34% 21% 10%	557
	21st to end	Day	4 8% 26% 33% 21% 8%	627
September	1st to 10th	Day	6% 11% 23% 28% 22% 10%	570
	11th to 20th	Day	5% 12% 33% 28% 17% 5%	570
	21st to end	Day	7% 9% 23% 26% 24% 10%	402
October	1st to 10th	Day	9% 9% 20% 24% 25% 13%	360
	11th to 20th	Day	8% 19% 20% 29% 17% 7%	360
	21st to end	Day	11% 18% 25% 28% 16% 2	387
November	1st to 10th	Day	11% 17% 26% 30% 14% 2	330
	11th to 20th	Day	10% 14% 27% 31% 15% 3	330
	21st to end	Day	5% 12% 33% 33% 15% 2	330
December	1st to 10th	Day	10% 18% 26% 29% 13% 3	330
	11th to 20th	Day	7% 15% 28% 39% 10% 1	330
	21st to end	Day	10% 17% 36% 29% 7% 2	363
January	1st to 10th	Night	6% 15% 27% 38% 13% 1	1050
	11th to 20th	Night	7% 13% 34% 36% 10% 1	934
	21st to end	Night	4 10% 34% 41% 10% 1	924
February	1st to 10th	Night	6% 11% 41% 35% 7% 1	840
	11th to 20th	Night	5% 12% 41% 34% 7%	824
	21st to end	Night	5% 11% 42% 39% 3	692
March	1st to 10th	Night	5% 10% 35% 40% 9%	840
	11th to 20th	Night	4 9% 31% 43% 12%	840
	21st to end	Night	5% 8% 37% 42% 9%	834
April	1st to 10th	Night	8% 11% 36% 39% 6%	630
	11th to 20th	Night	7% 12% 34% 39% 8% 1	623
	21st to end	Night	8% 12% 28% 41% 11%	630
May	1st to 10th	Night	7% 10% 29% 43% 11% 1	630
	11th to 20th	Night	10% 4 21% 46% 19% 1	621
	21st to end	Night	6% 7% 24% 41% 21% 1	683
June	1st to 10th	Night	4 5% 18% 46% 26% 1	630
	11th to 20th	Night	3 5% 25% 51% 15% 1	630
	21st to end	Night	2 3 19% 49% 26%	630
July	1st to 10th	Night	3 2 10% 41% 42% 1	615
	11th to 20th	Night	1 1 6% 47% 43% 2	612
	21st to end	Night	4 1 6% 43% 44% 3	690
August	1st to 10th	Night	5% 2 9% 44% 40% 1	627
	11th to 20th	Night	4 2 9% 51% 32% 2	624
	21st to end	Night	5% 1 8% 45% 40% 3	693
September	1st to 10th	Night	4 2 11% 52% 28% 2	630
	11th to 20th	Night	4 2 13% 54% 26% 2	630
	21st to end	Night	5% 4 17% 45% 27% 2	724
October	1st to 10th	Night	5% 5% 21% 43% 23% 2	840
	11th to 20th	Night	6% 7% 28% 43% 15% 1	840
	21st to end	Night	10% 8% 25% 41% 14% 2	912
November	1st to 10th	Night	6% 9% 33% 40% 12% 1	1003
	11th to 20th	Night	8% 11% 34% 37% 9% 1	1050
	21st to end	Night	5% 9% 32% 42% 12%	1050
December	1st to 10th	Night	6% 12% 35% 36% 10% 1	1050
	11th to 20th	Night	6% 12% 36% 36% 9%	1050
	21st to end	Night	6% 15% 36% 34% 8% 1	1155

Page generated at 2026-10-26 02:37:48. Version ac07

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