Spring Hill School Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Spring Hill School Observatory clear sky chart from 2005-11-06 to 2024-11-30.

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% 3 8% 5% 5% 5% 4 6% 7% 32%	102085
	Night	15% 10% 4 8% 5% 4 4 4 5% 7% 34%	97495
Transparency	Day	48% 7% 13% 20% 11% 1	105690
	Night	47% 7% 13% 20% 12% 1	101980
Seeing	Day	18% 12% 28% 23% 13% 5%	14919
	Night	19% 11% 29% 28% 11% 1	24052

By Month

Percentage Cloud Cover NE (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	16% 17% 7% 12% 6% 5% 4 3 4 6% 22%	2610
	11th to 20th	Day	11% 20% 7% 18% 8% 5% 3 3 4 6% 15%	2840
	21st to end	Day	23% 19% 6% 13% 6% 5% 4 3 4 4 12%	3124
February	1st to 10th	Day	14% 18% 5% 11% 7% 6% 6% 4 5% 5% 18%	1710
	11th to 20th	Day	13% 15% 7% 13% 7% 5% 5% 3 5% 5% 22%	1663
	21st to end	Day	17% 14% 4 12% 6% 4 5% 3 5% 5% 24%	1522
March	1st to 10th	Day	20% 15% 5% 8% 5% 5% 4 3 4 6% 26%	3396
	11th to 20th	Day	12% 14% 5% 10% 6% 4 5% 4 6% 6% 29%	3480
	21st to end	Day	16% 11% 4 10% 6% 5% 4 3 5% 6% 31%	3815
April	1st to 10th	Day	16% 13% 5% 8% 6% 5% 4 3 5% 7% 28%	2193
	11th to 20th	Day	18% 11% 3 7% 5% 5% 4 4 4 7% 34%	2383
	21st to end	Day	20% 11% 3 8% 5% 4 4 3 4 5% 33%	2470
May	1st to 10th	Day	18% 8% 3 7% 5% 5% 5% 4 5% 8% 33%	4108
	11th to 20th	Day	16% 10% 3 7% 5% 4 5% 4 6% 9% 31%	4200
	21st to end	Day	11% 5% 2 6% 4 5% 4 4 5% 8% 46%	4837
June	1st to 10th	Day	13% 7% 2 7% 5% 5% 5% 5% 6% 8% 37%	2660
	11th to 20th	Day	11% 6% 2 7% 5% 4 5% 4 8% 10% 38%	2740
	21st to end	Day	12% 6% 2 7% 5% 4 5% 5% 7% 9% 40%	2850
July	1st to 10th	Day	10% 5% 2 6% 5% 5% 5% 5% 8% 10% 39%	4696
	11th to 20th	Day	10% 5% 2 5% 5% 4 5% 4 7% 10% 42%	4262
	21st to end	Day	8% 5% 2 6% 5% 5% 6% 5% 7% 9% 41%	4466
August	1st to 10th	Day	16% 6% 2 6% 5% 5% 5% 5% 6% 8% 36%	4104
	11th to 20th	Day	11% 6% 3 7% 5% 5% 6% 5% 7% 9% 36%	4044
	21st to end	Day	8% 5% 2 7% 5% 4 6% 5% 7% 9% 41%	4418
September	1st to 10th	Day	11% 6% 3 7% 5% 5% 4 4 6% 9% 39%	2279
	11th to 20th	Day	10% 7% 2 5% 4 4 4 4 7% 8% 45%	2090
	21st to end	Day	15% 6% 3 7% 5% 5% 5% 5% 6% 8% 35%	2090
October	1st to 10th	Day	17% 9% 3 8% 5% 5% 4 3 4 7% 36%	1910
	11th to 20th	Day	19% 9% 3 8% 5% 5% 4 4 5% 8% 30%	1900
	21st to end	Day	22% 11% 3 9% 5% 5% 5% 4 6% 7% 23%	2090
November	1st to 10th	Day	13% 10% 4 10% 6% 4 4 4 6% 6% 33%	1739
	11th to 20th	Day	15% 14% 4 9% 6% 5% 5% 3 7% 8% 25%	1600
	21st to end	Day	18% 16% 6% 9% 6% 4 4 4 7% 6% 19%	1598
December	1st to 10th	Day	15% 18% 5% 12% 7% 6% 6% 4 6% 5% 17%	1520
	11th to 20th	Day	17% 17% 6% 13% 6% 5% 5% 4 5% 5% 16%	1906
	21st to end	Day	28% 19% 7% 12% 6% 4 4 3 4 5% 9%	2772
January	1st to 10th	Night	16% 16% 5% 14% 7% 5% 5% 3 6% 6% 18%	4333
	11th to 20th	Night	14% 14% 7% 14% 7% 6% 7% 5% 6% 5% 15%	4120
	21st to end	Night	22% 15% 8% 13% 5% 4 4 3 4 4 18%	4532
February	1st to 10th	Night	15% 16% 4 11% 6% 6% 5% 4 5% 6% 21%	2470
	11th to 20th	Night	13% 13% 5% 10% 6% 5% 5% 4 6% 7% 25%	2403
	21st to end	Night	15% 14% 4 11% 7% 5% 5% 4 6% 6% 24%	1928
March	1st to 10th	Night	16% 10% 3 9% 5% 4 4 4 5% 6% 33%	3443
	11th to 20th	Night	12% 10% 3 8% 5% 4 4 4 6% 8% 37%	3479
	21st to end	Night	16% 10% 3 7% 4 4 4 3 5% 5% 40%	3817
April	1st to 10th	Night	18% 10% 3 7% 5% 4 4 4 5% 6% 33%	1986
	11th to 20th	Night	17% 9% 3 7% 5% 4 5% 3 5% 7% 36%	1762
	21st to end	Night	13% 9% 2 7% 6% 4 5% 4 6% 8% 35%	1710
May	1st to 10th	Night	18% 7% 2 7% 4 3 4 3 5% 7% 40%	2833
	11th to 20th	Night	12% 8% 3 8% 5% 5% 5% 5% 5% 8% 35%	2690
	21st to end	Night	10% 4 2 5% 3 3 4 3 5% 9% 51%	2738
June	1st to 10th	Night	11% 6% 2 5% 5% 4 5% 4 7% 8% 44%	1520
	11th to 20th	Night	10% 5% 2 5% 5% 4 5% 5% 7% 9% 44%	1433
	21st to end	Night	10% 6% 2 5% 4 4 4 5% 7% 7% 46%	1330
July	1st to 10th	Night	6% 4 2 5% 5% 3 3 3 7% 10% 52%	2267
	11th to 20th	Night	10% 4 2 5% 3 3 4 3 5% 8% 53%	2680
	21st to end	Night	6% 4 2 6% 5% 4 5% 4 6% 8% 49%	3087
August	1st to 10th	Night	11% 5% 3 6% 4 4 4 4 6% 7% 46%	2825
	11th to 20th	Night	11% 5% 2 5% 3 4 4 4 6% 8% 47%	2785
	21st to end	Night	8% 5% 2 5% 4 4 4 4 6% 9% 49%	3206
September	1st to 10th	Night	10% 6% 2 6% 4 4 5% 4 5% 6% 49%	1900
	11th to 20th	Night	9% 4 2 4 5% 3 3 3 6% 7% 54%	2088
	21st to end	Night	16% 6% 2 7% 5% 4 5% 4 5% 7% 40%	2090
October	1st to 10th	Night	16% 7% 2 6% 4 3 4 3 5% 7% 42%	2270
	11th to 20th	Night	17% 9% 2 8% 4 5% 4 3 5% 7% 35%	2280
	21st to end	Night	21% 8% 3 8% 5% 5% 4 4 5% 7% 29%	2508
November	1st to 10th	Night	14% 9% 2 7% 5% 4 5% 4 7% 7% 38%	2552
	11th to 20th	Night	15% 12% 3 9% 7% 4 5% 4 6% 7% 27%	2800
	21st to end	Night	19% 12% 4 9% 6% 5% 5% 4 6% 7% 24%	2798
December	1st to 10th	Night	18% 16% 5% 11% 6% 5% 5% 5% 5% 5% 18%	2660
	11th to 20th	Night	14% 19% 5% 10% 6% 5% 4 4 5% 7% 22%	3288
	21st to end	Night	27% 20% 6% 11% 6% 4 4 3 3 4 12%	4884

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% 10% 11% 7%	2611
	11th to 20th	Day	71% 5% 10% 9% 4	2840
	21st to end	Day	76% 7% 7% 7% 4	3124
February	1st to 10th	Day	65% 7% 11% 13% 4	1710
	11th to 20th	Day	63% 6% 10% 14% 7%	1672
	21st to end	Day	62% 5% 11% 14% 6% 1	1522
March	1st to 10th	Day	59% 6% 10% 20% 5% 1	3399
	11th to 20th	Day	53% 7% 15% 17% 7% 1	3480
	21st to end	Day	53% 6% 11% 19% 11% 1	3815
April	1st to 10th	Day	55% 6% 12% 16% 11% 1	2193
	11th to 20th	Day	50% 5% 12% 20% 12% 1	2383
	21st to end	Day	53% 6% 10% 18% 11% 2	2470
May	1st to 10th	Day	49% 6% 12% 19% 11% 3	4120
	11th to 20th	Day	48% 9% 15% 20% 7% 1	4204
	21st to end	Day	36% 7% 13% 20% 20% 4	4837
June	1st to 10th	Day	41% 8% 12% 23% 14% 2	2660
	11th to 20th	Day	39% 8% 13% 22% 16% 1	2740
	21st to end	Day	39% 8% 14% 24% 15%	2850
July	1st to 10th	Day	36% 8% 15% 25% 14% 2	4624
	11th to 20th	Day	34% 7% 14% 32% 12% 1	4188
	21st to end	Day	36% 9% 15% 21% 19% 1	4324
August	1st to 10th	Day	43% 8% 13% 21% 13% 1	4091
	11th to 20th	Day	40% 9% 17% 25% 9% 1	4083
	21st to end	Day	35% 8% 14% 30% 11% 1	4418
September	1st to 10th	Day	41% 8% 13% 25% 12% 1	2279
	11th to 20th	Day	34% 8% 14% 29% 15%	2090
	21st to end	Day	44% 8% 13% 25% 9% 1	2090
October	1st to 10th	Day	38% 7% 14% 23% 17% 1	3170
	11th to 20th	Day	39% 6% 15% 21% 18%	3140
	21st to end	Day	49% 8% 15% 21% 7%	3428
November	1st to 10th	Day	48% 7% 13% 22% 8% 1	1739
	11th to 20th	Day	54% 8% 15% 14% 9% 1	1600
	21st to end	Day	62% 8% 13% 13% 3	1598
December	1st to 10th	Day	65% 9% 11% 10% 4	1520
	11th to 20th	Day	66% 9% 11% 10% 4	1906
	21st to end	Day	78% 6% 8% 6% 1	2772
January	1st to 10th	Night	63% 10% 12% 11% 5% 1	4333
	11th to 20th	Night	67% 9% 12% 10% 3	4120
	21st to end	Night	70% 6% 9% 11% 4 1	4532
February	1st to 10th	Night	63% 7% 9% 16% 5%	2470
	11th to 20th	Night	56% 8% 12% 15% 8%	2405
	21st to end	Night	58% 8% 10% 16% 7%	1928
March	1st to 10th	Night	51% 6% 13% 23% 6% 1	3453
	11th to 20th	Night	42% 8% 17% 19% 12% 1	3480
	21st to end	Night	45% 5% 11% 22% 16% 2	3817
April	1st to 10th	Night	51% 5% 11% 18% 13% 1	1986
	11th to 20th	Night	47% 6% 10% 19% 16% 2	1762
	21st to end	Night	45% 7% 11% 19% 15% 3	1710
May	1st to 10th	Night	43% 6% 11% 19% 16% 4	2840
	11th to 20th	Night	45% 8% 16% 22% 7% 2	2691
	21st to end	Night	30% 7% 13% 23% 23% 3	2739
June	1st to 10th	Night	37% 7% 11% 26% 17% 2	1520
	11th to 20th	Night	34% 8% 13% 24% 18% 2	1433
	21st to end	Night	36% 7% 14% 24% 18% 1	1330
July	1st to 10th	Night	28% 6% 13% 27% 21% 6%	2231
	11th to 20th	Night	30% 6% 14% 31% 17% 2	2631
	21st to end	Night	30% 8% 16% 25% 18% 3	2988
August	1st to 10th	Night	36% 8% 13% 25% 16% 2	2814
	11th to 20th	Night	34% 8% 17% 27% 13% 1	2812
	21st to end	Night	30% 8% 13% 31% 17% 1	3206
September	1st to 10th	Night	37% 6% 13% 26% 17% 2	1900
	11th to 20th	Night	29% 7% 12% 33% 19% 1	2088
	21st to end	Night	43% 6% 12% 25% 12%	2090
October	1st to 10th	Night	32% 5% 9% 28% 24% 1	3790
	11th to 20th	Night	41% 5% 13% 24% 16%	3779
	21st to end	Night	40% 6% 15% 26% 12%	4120
November	1st to 10th	Night	43% 6% 14% 23% 13% 1	2552
	11th to 20th	Night	52% 8% 13% 17% 8% 1	2800
	21st to end	Night	57% 8% 16% 14% 5%	2798
December	1st to 10th	Night	64% 9% 12% 11% 4	2660
	11th to 20th	Night	61% 7% 13% 15% 4	3288
	21st to end	Night	76% 7% 9% 6% 2	4884

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	24% 24% 27% 17% 7%	206
	11th to 20th	Day	26% 20% 37% 13% 3 1	270
	21st to end	Day	27% 18% 34% 16% 5%	297
February	1st to 10th	Day	24% 20% 40% 11% 5%	270
	11th to 20th	Day	26% 23% 35% 15% 1	270
	21st to end	Day	35% 24% 29% 12%	225
March	1st to 10th	Day	24% 14% 36% 20% 5% 1	435
	11th to 20th	Day	24% 15% 36% 19% 6% 1	460
	21st to end	Day	28% 15% 29% 20% 7%	506
April	1st to 10th	Day	22% 20% 30% 20% 7% 2	460
	11th to 20th	Day	28% 14% 26% 18% 10% 3	452
	21st to end	Day	26% 12% 33% 19% 8% 3	460
May	1st to 10th	Day	24% 14% 25% 22% 11% 5%	463
	11th to 20th	Day	16% 10% 29% 24% 17% 4	487
	21st to end	Day	13% 7% 27% 28% 16% 8%	529
June	1st to 10th	Day	14% 12% 30% 29% 12% 4	490
	11th to 20th	Day	13% 9% 29% 28% 16% 5%	570
	21st to end	Day	13% 10% 29% 31% 13% 3	680
July	1st to 10th	Day	8% 6% 22% 30% 25% 8%	635
	11th to 20th	Day	14% 6% 21% 28% 19% 12%	484
	21st to end	Day	8% 4 24% 33% 22% 8%	532
August	1st to 10th	Day	10% 5% 21% 27% 23% 13%	486
	11th to 20th	Day	12% 5% 22% 23% 23% 14%	479
	21st to end	Day	12% 5% 24% 27% 22% 11%	539
September	1st to 10th	Day	12% 7% 23% 25% 18% 14%	490
	11th to 20th	Day	9% 4 19% 24% 27% 17%	490
	21st to end	Day	15% 10% 27% 25% 14% 8%	490
October	1st to 10th	Day	19% 11% 26% 26% 13% 7%	490
	11th to 20th	Day	19% 16% 33% 21% 8% 3	490
	21st to end	Day	25% 15% 31% 21% 7% 1	539
November	1st to 10th	Day	20% 24% 32% 16% 7% 2	287
	11th to 20th	Day	27% 21% 31% 15% 7% 2	200
	21st to end	Day	26% 22% 33% 18% 2 1	200
December	1st to 10th	Day	28% 21% 35% 11% 5% 1	180
	11th to 20th	Day	25% 29% 30% 12% 4	180
	21st to end	Day	29% 21% 37% 12% 2	198
January	1st to 10th	Night	21% 18% 36% 17% 6% 1	760
	11th to 20th	Night	29% 15% 33% 21% 3	760
	21st to end	Night	20% 13% 35% 26% 5%	836
February	1st to 10th	Night	23% 17% 36% 22% 2	760
	11th to 20th	Night	23% 15% 34% 24% 4	743
	21st to end	Night	23% 16% 35% 22% 3	628
March	1st to 10th	Night	19% 13% 36% 25% 6%	760
	11th to 20th	Night	20% 15% 35% 24% 6% 1	760
	21st to end	Night	20% 11% 34% 26% 8%	836
April	1st to 10th	Night	23% 13% 32% 27% 5%	760
	11th to 20th	Night	21% 13% 31% 25% 9% 1	638
	21st to end	Night	18% 9% 33% 32% 8%	570
May	1st to 10th	Night	17% 7% 30% 30% 14% 1	570
	11th to 20th	Night	16% 5% 29% 37% 12% 1	491
	21st to end	Night	11% 5% 29% 36% 18% 1	411
June	1st to 10th	Night	13% 6% 31% 38% 12% 1	380
	11th to 20th	Night	12% 6% 27% 41% 13% 1	380
	21st to end	Night	12% 5% 28% 40% 15% 1	380
July	1st to 10th	Night	5% 2 24% 45% 22% 2	370
	11th to 20th	Night	9% 3 23% 40% 22% 3	462
	21st to end	Night	9% 3 18% 47% 21% 2	624
August	1st to 10th	Night	8% 3 17% 43% 26% 3	567
	11th to 20th	Night	8% 2 15% 39% 33% 2	564
	21st to end	Night	10% 2 21% 37% 27% 3	670
September	1st to 10th	Night	12% 5% 22% 34% 23% 5%	760
	11th to 20th	Night	10% 5% 17% 34% 30% 4	760
	21st to end	Night	18% 7% 21% 30% 19% 5%	760
October	1st to 10th	Night	17% 7% 26% 29% 18% 3	760
	11th to 20th	Night	20% 11% 30% 27% 10% 2	760
	21st to end	Night	24% 11% 32% 28% 5%	836
November	1st to 10th	Night	18% 12% 29% 28% 10% 2	780
	11th to 20th	Night	20% 18% 32% 22% 7% 1	800
	21st to end	Night	25% 13% 33% 21% 7%	800
December	1st to 10th	Night	28% 17% 29% 19% 5%	760
	11th to 20th	Night	21% 19% 38% 18% 5%	760
	21st to end	Night	31% 13% 33% 19% 3	836

Page generated at 2024-11-27 17:30:50. Version ac07

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