Schoonover Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Schoonover Observatory clear sky chart from 2005-11-06 to 2024-01-31.

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	15% 10% 4 7% 6% 3 5% 5% 5% 7% 33%	75132
	Night	15% 10% 4 7% 6% 3 4 4 5% 6% 35%	75003
Transparency	Day	49% 6% 12% 20% 12% 2	74845
	Night	49% 5% 11% 20% 13% 2	74810
Seeing	Day	18% 10% 27% 23% 15% 7%	14409
	Night	19% 9% 28% 29% 13% 1	24338

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	18% 15% 6% 12% 8% 4 5% 4 4 4 19%	1517
	11th to 20th	Day	18% 17% 8% 12% 8% 4 3 5% 3 5% 17%	1550
	21st to end	Day	17% 18% 9% 11% 9% 3 4 3 4 5% 17%	1872
February	1st to 10th	Day	19% 15% 6% 11% 9% 3 4 4 4 5% 20%	1652
	11th to 20th	Day	15% 13% 7% 13% 9% 4 5% 4 4 5% 21%	1748
	21st to end	Day	17% 15% 7% 9% 5% 3 4 3 4 7% 26%	1480
March	1st to 10th	Day	18% 13% 6% 9% 7% 3 4 4 4 6% 27%	1818
	11th to 20th	Day	18% 11% 5% 7% 7% 3 4 5% 5% 6% 29%	1980
	21st to end	Day	24% 13% 4 7% 5% 4 4 4 4 6% 25%	2178
April	1st to 10th	Day	15% 13% 5% 7% 6% 3 4 4 5% 6% 32%	2115
	11th to 20th	Day	18% 9% 3 6% 5% 3 4 4 5% 7% 35%	2222
	21st to end	Day	20% 8% 2 6% 6% 4 6% 4 4 7% 32%	2340
May	1st to 10th	Day	18% 9% 4 7% 7% 4 5% 5% 5% 7% 30%	2340
	11th to 20th	Day	18% 8% 3 5% 6% 3 5% 5% 6% 7% 34%	2301
	21st to end	Day	9% 6% 3 6% 6% 4 6% 7% 6% 9% 39%	2531
June	1st to 10th	Day	13% 6% 2 6% 5% 3 6% 5% 6% 7% 39%	2436
	11th to 20th	Day	11% 6% 2 4 6% 4 5% 5% 7% 9% 41%	2520
	21st to end	Day	11% 5% 2 5% 6% 4 6% 7% 7% 10% 37%	2520
July	1st to 10th	Day	11% 5% 2 5% 5% 4 5% 6% 7% 10% 39%	2520
	11th to 20th	Day	8% 4 2 4 5% 4 5% 5% 7% 9% 46%	2513
	21st to end	Day	9% 5% 2 5% 6% 3 5% 6% 7% 10% 41%	2547
August	1st to 10th	Day	8% 4 2 4 5% 3 5% 6% 7% 10% 46%	2327
	11th to 20th	Day	8% 5% 2 6% 6% 3 6% 7% 7% 10% 39%	2303
	21st to end	Day	10% 4 2 5% 6% 3 5% 5% 6% 10% 43%	2462
September	1st to 10th	Day	14% 5% 3 5% 5% 3 4 5% 5% 7% 46%	2048
	11th to 20th	Day	9% 5% 2 6% 6% 3 5% 5% 6% 8% 44%	1980
	21st to end	Day	16% 6% 2 5% 4 3 3 4 5% 7% 45%	1980
October	1st to 10th	Day	13% 7% 3 6% 5% 4 5% 4 5% 7% 42%	1976
	11th to 20th	Day	17% 7% 3 6% 5% 3 5% 5% 5% 6% 39%	1800
	21st to end	Day	20% 9% 3 6% 6% 4 4 5% 6% 6% 30%	1832
November	1st to 10th	Day	10% 9% 3 5% 4 2 3 4 4 7% 48%	1672
	11th to 20th	Day	17% 13% 4 6% 5% 4 4 4 5% 6% 33%	1710
	21st to end	Day	19% 15% 6% 7% 5% 2 3 4 4 6% 29%	1710
December	1st to 10th	Day	17% 18% 9% 9% 6% 3 4 5% 4 4 21%	1710
	11th to 20th	Day	15% 17% 7% 9% 7% 3 5% 4 5% 7% 21%	2139
	21st to end	Day	21% 23% 10% 10% 7% 4 5% 3 3 4 11%	2783
January	1st to 10th	Night	17% 15% 6% 11% 8% 3 4 4 4 4 23%	2648
	11th to 20th	Night	18% 17% 7% 11% 7% 4 4 4 3 5% 21%	2626
	21st to end	Night	18% 18% 7% 11% 6% 3 4 4 4 4 22%	2711
February	1st to 10th	Night	20% 14% 6% 9% 7% 4 4 4 3 5% 23%	2305
	11th to 20th	Night	15% 14% 5% 10% 6% 3 5% 4 5% 6% 27%	2098
	21st to end	Night	22% 13% 5% 9% 5% 2 5% 4 4 5% 26%	1776
March	1st to 10th	Night	15% 11% 5% 7% 6% 3 4 4 4 5% 33%	2140
	11th to 20th	Night	13% 10% 4 5% 6% 3 4 4 5% 8% 38%	1980
	21st to end	Night	20% 10% 4 6% 6% 3 4 4 5% 5% 34%	2178
April	1st to 10th	Night	14% 10% 4 6% 5% 3 5% 5% 5% 7% 37%	1859
	11th to 20th	Night	17% 8% 3 5% 5% 4 5% 5% 6% 7% 35%	1685
	21st to end	Night	18% 8% 3 7% 6% 3 4 4 5% 7% 36%	1620
May	1st to 10th	Night	20% 9% 3 6% 6% 4 5% 4 5% 7% 31%	1620
	11th to 20th	Night	21% 7% 3 5% 4 2 3 4 5% 8% 38%	1592
	21st to end	Night	8% 5% 2 5% 5% 3 6% 6% 7% 12% 41%	1744
June	1st to 10th	Night	10% 4 3 5% 4 3 5% 5% 5% 8% 48%	1519
	11th to 20th	Night	10% 4 2 4 4 3 6% 4 7% 9% 46%	1440
	21st to end	Night	9% 5% 3 5% 6% 3 4 5% 7% 9% 45%	1440
July	1st to 10th	Night	9% 4 2 6% 6% 3 4 4 6% 9% 47%	1440
	11th to 20th	Night	7% 4 1 5% 5% 3 4 6% 7% 9% 49%	1444
	21st to end	Night	7% 4 2 5% 6% 3 5% 4 5% 8% 51%	1771
August	1st to 10th	Night	7% 4 2 4 5% 4 5% 6% 7% 10% 47%	1611
	11th to 20th	Night	9% 6% 2 5% 4 3 4 5% 7% 8% 48%	1598
	21st to end	Night	6% 4 2 6% 5% 3 4 5% 5% 7% 52%	1890
September	1st to 10th	Night	11% 6% 3 4 4 3 4 4 4 8% 49%	1894
	11th to 20th	Night	11% 5% 2 4 3 3 4 4 5% 7% 53%	1980
	21st to end	Night	11% 5% 3 6% 5% 3 4 5% 5% 5% 48%	1980
October	1st to 10th	Night	11% 5% 2 5% 4 2 5% 4 5% 7% 49%	1982
	11th to 20th	Night	19% 8% 3 6% 5% 2 4 4 5% 6% 39%	2160
	21st to end	Night	22% 8% 2 5% 6% 2 4 4 4 6% 36%	2521
November	1st to 10th	Night	13% 9% 3 5% 5% 3 4 4 5% 6% 44%	2406
	11th to 20th	Night	16% 11% 5% 7% 5% 3 4 3 5% 7% 35%	2470
	21st to end	Night	18% 13% 6% 7% 6% 3 5% 4 4 6% 27%	2470
December	1st to 10th	Night	18% 15% 7% 8% 7% 3 4 4 4 6% 24%	2470
	11th to 20th	Night	17% 16% 6% 9% 6% 3 5% 4 5% 5% 25%	3051
	21st to end	Night	24% 20% 8% 9% 6% 3 4 4 4 5% 14%	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	69% 4 8% 13% 5%	1518
	11th to 20th	Day	71% 4 12% 9% 4	1550
	21st to end	Day	71% 3 10% 11% 5%	1872
February	1st to 10th	Day	68% 4 9% 12% 6% 1	1652
	11th to 20th	Day	66% 5% 7% 14% 7%	1758
	21st to end	Day	59% 5% 11% 15% 8% 2	1480
March	1st to 10th	Day	60% 5% 10% 19% 6% 1	1818
	11th to 20th	Day	56% 6% 10% 17% 10% 1	1980
	21st to end	Day	61% 5% 10% 19% 5% 1	2178
April	1st to 10th	Day	53% 6% 12% 18% 12% 1	2115
	11th to 20th	Day	49% 5% 11% 20% 12% 2	2222
	21st to end	Day	51% 6% 11% 20% 9% 2	2340
May	1st to 10th	Day	53% 7% 11% 17% 10% 1	2340
	11th to 20th	Day	49% 7% 11% 20% 11% 1	2305
	21st to end	Day	40% 9% 14% 24% 11% 2	2531
June	1st to 10th	Day	42% 6% 12% 24% 14% 2	2436
	11th to 20th	Day	38% 7% 14% 23% 15% 2	2520
	21st to end	Day	38% 9% 15% 19% 14% 4	2520
July	1st to 10th	Day	38% 8% 13% 22% 17% 3	2451
	11th to 20th	Day	32% 8% 16% 27% 16% 1	2438
	21st to end	Day	34% 10% 14% 24% 15% 3	2405
August	1st to 10th	Day	31% 8% 15% 28% 16% 1	2314
	11th to 20th	Day	37% 9% 15% 26% 12% 2	2303
	21st to end	Day	35% 8% 14% 22% 17% 4	2462
September	1st to 10th	Day	37% 6% 13% 22% 18% 4	2048
	11th to 20th	Day	36% 7% 10% 25% 20% 2	1980
	21st to end	Day	38% 7% 10% 23% 21% 1	1980
October	1st to 10th	Day	41% 6% 10% 25% 16% 2	1976
	11th to 20th	Day	45% 5% 11% 22% 16% 2	1800
	21st to end	Day	53% 7% 11% 18% 10% 1	1832
November	1st to 10th	Day	37% 5% 12% 25% 19% 1	1672
	11th to 20th	Day	53% 3 10% 21% 11% 2	1710
	21st to end	Day	57% 4 11% 18% 9% 1	1710
December	1st to 10th	Day	68% 5% 9% 14% 4	1710
	11th to 20th	Day	62% 5% 11% 17% 5%	2136
	21st to end	Day	79% 4 6% 7% 4	2783
January	1st to 10th	Night	65% 5% 8% 15% 8%	2648
	11th to 20th	Night	68% 4 10% 13% 5%	2626
	21st to end	Night	67% 3 10% 14% 6% 1	2711
February	1st to 10th	Night	65% 5% 10% 14% 6% 1	2305
	11th to 20th	Night	58% 5% 11% 15% 9% 1	2099
	21st to end	Night	61% 4 9% 15% 10% 2	1776
March	1st to 10th	Night	54% 4 11% 19% 11% 1	2140
	11th to 20th	Night	45% 5% 13% 22% 13% 3	1980
	21st to end	Night	54% 4 8% 22% 10% 1	2178
April	1st to 10th	Night	47% 5% 12% 21% 13% 1	1859
	11th to 20th	Night	47% 6% 11% 17% 17% 3	1685
	21st to end	Night	48% 6% 12% 19% 14% 3	1620
May	1st to 10th	Night	53% 7% 10% 17% 10% 3	1620
	11th to 20th	Night	45% 6% 11% 21% 15% 2	1593
	21st to end	Night	33% 8% 17% 25% 14% 3	1745
June	1st to 10th	Night	34% 7% 12% 24% 19% 3	1519
	11th to 20th	Night	33% 8% 14% 25% 17% 3	1440
	21st to end	Night	35% 7% 16% 23% 17% 3	1440
July	1st to 10th	Night	35% 8% 11% 24% 18% 4	1400
	11th to 20th	Night	30% 8% 12% 29% 19% 1	1396
	21st to end	Night	30% 7% 16% 27% 17% 3	1672
August	1st to 10th	Night	31% 8% 15% 28% 18% 1	1600
	11th to 20th	Night	33% 7% 14% 28% 18% 1	1598
	21st to end	Night	30% 8% 14% 22% 21% 5%	1890
September	1st to 10th	Night	34% 6% 14% 24% 16% 6%	1894
	11th to 20th	Night	30% 6% 11% 27% 24% 2	1980
	21st to end	Night	37% 5% 11% 23% 21% 3	1980
October	1st to 10th	Night	34% 6% 12% 25% 22% 1	1982
	11th to 20th	Night	46% 5% 9% 24% 15% 1	2160
	21st to end	Night	48% 6% 9% 22% 13% 2	2521
November	1st to 10th	Night	41% 4 11% 24% 18% 2	2406
	11th to 20th	Night	50% 3 11% 20% 14% 2	2470
	21st to end	Night	58% 5% 10% 19% 8%	2470
December	1st to 10th	Night	62% 5% 11% 15% 7%	2470
	11th to 20th	Night	61% 5% 12% 16% 6% 1	3053
	21st to end	Night	74% 5% 9% 9% 3	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% 19% 34% 17% 5% 1	270
	11th to 20th	Day	27% 16% 39% 12% 4 1	270
	21st to end	Day	31% 15% 34% 15% 5% 1	294
February	1st to 10th	Day	33% 17% 36% 13% 1	240
	11th to 20th	Day	25% 19% 38% 14% 4	240
	21st to end	Day	26% 20% 43% 9% 2	198
March	1st to 10th	Day	22% 19% 40% 14% 4	258
	11th to 20th	Day	28% 11% 32% 20% 7% 2	420
	21st to end	Day	31% 13% 33% 17% 6%	462
April	1st to 10th	Day	22% 13% 30% 25% 7% 3	420
	11th to 20th	Day	22% 17% 28% 17% 11% 4	412
	21st to end	Day	26% 13% 28% 23% 7% 3	420
May	1st to 10th	Day	25% 13% 28% 24% 8% 3	423
	11th to 20th	Day	23% 9% 26% 24% 13% 6%	447
	21st to end	Day	11% 7% 27% 26% 21% 9%	485
June	1st to 10th	Day	12% 8% 24% 31% 18% 6%	546
	11th to 20th	Day	14% 5% 26% 26% 23% 6%	630
	21st to end	Day	12% 8% 26% 30% 18% 7%	630
July	1st to 10th	Day	12% 2 18% 29% 22% 17%	621
	11th to 20th	Day	8% 3 23% 30% 23% 13%	611
	21st to end	Day	10% 3 17% 27% 27% 15%	488
August	1st to 10th	Day	11% 2 13% 29% 28% 18%	446
	11th to 20th	Day	11% 4 19% 30% 25% 12%	439
	21st to end	Day	11% 3 16% 26% 29% 15%	495
September	1st to 10th	Day	17% 2 15% 26% 27% 13%	450
	11th to 20th	Day	10% 3 16% 22% 33% 16%	450
	21st to end	Day	17% 10% 19% 24% 20% 10%	450
October	1st to 10th	Day	11% 7% 25% 30% 18% 10%	450
	11th to 20th	Day	17% 15% 32% 24% 11% 1	450
	21st to end	Day	26% 12% 36% 21% 4 1	347
November	1st to 10th	Day	16% 12% 36% 21% 11% 4	270
	11th to 20th	Day	26% 18% 28% 17% 11%	270
	21st to end	Day	26% 17% 36% 20% 2	270
December	1st to 10th	Day	22% 20% 35% 16% 6% 1	270
	11th to 20th	Day	24% 15% 38% 18% 5%	270
	21st to end	Day	28% 20% 34% 16% 3	297
January	1st to 10th	Night	24% 15% 36% 20% 5%	950
	11th to 20th	Night	27% 15% 36% 17% 4 1	916
	21st to end	Night	26% 15% 34% 22% 4	835
February	1st to 10th	Night	28% 11% 36% 23% 3	720
	11th to 20th	Night	23% 14% 36% 24% 2	703
	21st to end	Night	28% 13% 38% 19% 3	592
March	1st to 10th	Night	20% 13% 34% 26% 6% 1	720
	11th to 20th	Night	19% 13% 35% 27% 6%	720
	21st to end	Night	24% 11% 30% 26% 8% 1	792
April	1st to 10th	Night	18% 13% 36% 27% 5% 1	599
	11th to 20th	Night	20% 12% 33% 25% 9% 2	533
	21st to end	Night	20% 7% 37% 25% 10% 1	540
May	1st to 10th	Night	25% 6% 31% 29% 8% 1	540
	11th to 20th	Night	24% 5% 27% 30% 13% 1	531
	21st to end	Night	11% 2 26% 35% 23% 3	584
June	1st to 10th	Night	11% 2 24% 45% 18%	540
	11th to 20th	Night	11% 3 22% 43% 19% 1	540
	21st to end	Night	11% 2 22% 38% 25% 1	540
July	1st to 10th	Night	10% 2 14% 41% 30% 4	525
	11th to 20th	Night	7% 2 16% 40% 29% 4	522
	21st to end	Night	9% 2 13% 44% 30% 2	591
August	1st to 10th	Night	10% 1 12% 42% 30% 5%	537
	11th to 20th	Night	10% 3 11% 41% 31% 4	534
	21st to end	Night	8% 2 13% 37% 35% 4	594
September	1st to 10th	Night	13% 3 16% 35% 29% 5%	634
	11th to 20th	Night	11% 2 15% 36% 31% 5%	720
	21st to end	Night	13% 5% 22% 34% 23% 2	720
October	1st to 10th	Night	14% 5% 24% 34% 20% 4	720
	11th to 20th	Night	22% 11% 29% 28% 9% 1	720
	21st to end	Night	26% 11% 30% 26% 7%	792
November	1st to 10th	Night	18% 8% 34% 26% 13% 1	740
	11th to 20th	Night	22% 15% 31% 24% 7% 1	760
	21st to end	Night	24% 13% 33% 25% 6%	760
December	1st to 10th	Night	23% 14% 36% 21% 5%	760
	11th to 20th	Night	26% 11% 36% 22% 4	769
	21st to end	Night	30% 15% 33% 19% 3	1045

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