Cornland Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cornland Park clear sky chart from 2005-11-06 to 2024-01-17.

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	13% 6% 3 5% 5% 3 5% 5% 6% 8% 41%	74704
	Night	14% 6% 2 5% 5% 3 4 4 5% 7% 44%	75119
Transparency	Day	40% 7% 12% 22% 16% 3	74418
	Night	39% 7% 12% 22% 17% 4	74924
Seeing	Day	18% 12% 26% 24% 14% 5%	14169
	Night	17% 9% 28% 31% 13% 2	23877

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	16% 7% 2 5% 4 2 4 5% 5% 6% 46%	1624
	11th to 20th	Day	16% 6% 3 4 5% 3 5% 5% 4 5% 43%	1674
	21st to end	Day	15% 7% 3 5% 4 2 3 4 4 6% 47%	1782
February	1st to 10th	Day	14% 8% 3 5% 5% 4 3 5% 5% 7% 40%	1620
	11th to 20th	Day	19% 6% 2 4 6% 3 4 3 4 5% 44%	1724
	21st to end	Day	17% 7% 3 5% 5% 3 4 5% 6% 8% 37%	1480
March	1st to 10th	Day	14% 6% 2 5% 4 2 4 3 4 5% 51%	1909
	11th to 20th	Day	17% 7% 2 4 5% 3 4 5% 4 7% 42%	1980
	21st to end	Day	17% 6% 3 5% 5% 3 5% 4 5% 8% 40%	2240
April	1st to 10th	Day	13% 6% 2 4 3 3 3 4 4 7% 52%	2160
	11th to 20th	Day	10% 4 2 5% 5% 3 5% 4 4 8% 49%	2134
	21st to end	Day	12% 6% 3 5% 5% 3 5% 4 5% 8% 44%	2160
May	1st to 10th	Day	14% 6% 2 4 4 3 6% 5% 6% 8% 41%	2160
	11th to 20th	Day	16% 6% 4 5% 5% 3 4 6% 5% 7% 38%	2339
	21st to end	Day	13% 6% 2 6% 4 3 5% 5% 6% 9% 40%	2725
June	1st to 10th	Day	11% 5% 2 4 5% 4 6% 7% 8% 11% 37%	2520
	11th to 20th	Day	10% 6% 3 5% 6% 4 7% 5% 7% 10% 38%	2520
	21st to end	Day	8% 5% 3 6% 7% 4 6% 6% 8% 12% 35%	2520
July	1st to 10th	Day	9% 5% 2 5% 6% 3 6% 7% 8% 10% 38%	2520
	11th to 20th	Day	8% 5% 3 6% 6% 5% 8% 6% 8% 11% 34%	2372
	21st to end	Day	7% 5% 4 6% 8% 5% 7% 7% 7% 12% 32%	2547
August	1st to 10th	Day	11% 6% 3 7% 7% 5% 7% 7% 7% 10% 31%	2302
	11th to 20th	Day	11% 8% 3 6% 7% 4 6% 6% 8% 10% 31%	2126
	21st to end	Day	12% 6% 2 7% 7% 4 7% 6% 7% 9% 33%	2376
September	1st to 10th	Day	13% 6% 3 6% 6% 4 5% 6% 7% 8% 36%	2160
	11th to 20th	Day	14% 7% 3 6% 6% 4 6% 4 5% 7% 39%	2160
	21st to end	Day	22% 8% 2 5% 5% 3 5% 4 5% 6% 35%	1929
October	1st to 10th	Day	17% 7% 2 5% 5% 3 5% 4 3 6% 44%	1800
	11th to 20th	Day	14% 6% 2 4 5% 3 4 4 3 6% 49%	1800
	21st to end	Day	12% 5% 2 5% 5% 2 3 5% 4 6% 50%	1980
November	1st to 10th	Day	16% 6% 2 4 4 2 4 4 4 6% 49%	1777
	11th to 20th	Day	16% 6% 2 4 4 2 3 3 5% 7% 49%	1710
	21st to end	Day	14% 4 2 3 5% 3 4 3 5% 6% 50%	1672
December	1st to 10th	Day	16% 7% 3 5% 5% 3 4 4 4 7% 42%	1520
	11th to 20th	Day	15% 6% 3 4 4 2 3 3 3 6% 52%	1910
	21st to end	Day	16% 6% 2 5% 4 2 3 4 5% 7% 44%	2772
January	1st to 10th	Night	15% 7% 3 5% 4 2 4 4 5% 6% 46%	2538
	11th to 20th	Night	16% 7% 3 7% 5% 3 5% 5% 5% 7% 38%	2430
	21st to end	Night	17% 5% 2 5% 4 3 4 4 4 6% 47%	2574
February	1st to 10th	Night	18% 7% 3 4 4 2 4 4 5% 7% 42%	2340
	11th to 20th	Night	20% 8% 2 5% 4 2 3 3 4 6% 41%	2120
	21st to end	Night	16% 8% 2 4 5% 3 4 4 4 6% 45%	1776
March	1st to 10th	Night	14% 5% 2 5% 4 3 4 3 4 5% 51%	2048
	11th to 20th	Night	17% 7% 2 5% 4 3 5% 5% 5% 7% 39%	1980
	21st to end	Night	15% 6% 3 5% 5% 3 4 4 5% 7% 42%	2114
April	1st to 10th	Night	13% 5% 2 4 5% 3 5% 5% 6% 6% 45%	1800
	11th to 20th	Night	13% 5% 2 4 5% 3 3 4 5% 7% 49%	1775
	21st to end	Night	14% 6% 2 4 4 3 4 5% 4 6% 48%	1800
May	1st to 10th	Night	14% 6% 2 6% 6% 3 5% 4 6% 8% 42%	1800
	11th to 20th	Night	15% 7% 2 5% 5% 4 5% 4 6% 8% 40%	1567
	21st to end	Night	13% 5% 2 5% 5% 3 5% 5% 7% 8% 43%	1550
June	1st to 10th	Night	11% 5% 2 4 5% 3 4 5% 7% 12% 41%	1440
	11th to 20th	Night	8% 5% 3 6% 5% 4 5% 6% 7% 13% 38%	1440
	21st to end	Night	8% 4 2 5% 6% 3 6% 6% 6% 11% 43%	1440
July	1st to 10th	Night	7% 6% 2 5% 6% 3 6% 6% 7% 11% 39%	1440
	11th to 20th	Night	8% 4 2 5% 6% 3 5% 7% 8% 10% 43%	1584
	21st to end	Night	8% 5% 3 6% 6% 3 6% 8% 8% 12% 36%	1771
August	1st to 10th	Night	9% 7% 3 6% 7% 4 6% 5% 6% 9% 38%	1619
	11th to 20th	Night	9% 7% 3 7% 6% 5% 5% 6% 7% 10% 36%	1774
	21st to end	Night	11% 7% 3 6% 6% 3 5% 5% 7% 9% 38%	1980
September	1st to 10th	Night	11% 5% 2 5% 5% 3 4 5% 7% 10% 44%	1800
	11th to 20th	Night	13% 6% 2 6% 5% 3 5% 4 5% 7% 45%	1800
	21st to end	Night	20% 6% 3 7% 6% 3 4 4 5% 7% 36%	2024
October	1st to 10th	Night	14% 5% 2 4 5% 3 5% 4 5% 5% 48%	2160
	11th to 20th	Night	15% 6% 2 4 4 2 3 4 4 6% 49%	2160
	21st to end	Night	13% 6% 2 4 4 3 4 4 5% 6% 51%	2376
November	1st to 10th	Night	16% 6% 2 4 3 2 3 4 4 5% 49%	2297
	11th to 20th	Night	15% 6% 3 4 4 2 4 4 4 6% 48%	2470
	21st to end	Night	13% 5% 2 4 4 3 5% 4 4 7% 49%	2503
December	1st to 10th	Night	16% 8% 3 6% 5% 3 3 4 5% 5% 41%	2660
	11th to 20th	Night	17% 6% 2 5% 4 3 3 4 4 6% 46%	3285
	21st to end	Night	14% 6% 2 5% 4 3 4 4 5% 7% 46%	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	39% 5% 9% 25% 17% 5%	1625
	11th to 20th	Day	43% 6% 9% 20% 19% 3	1674
	21st to end	Day	40% 4 8% 23% 20% 4	1782
February	1st to 10th	Day	42% 5% 11% 24% 14% 4	1620
	11th to 20th	Day	44% 4 7% 19% 20% 6%	1733
	21st to end	Day	43% 7% 11% 17% 16% 6%	1480
March	1st to 10th	Day	37% 4 10% 24% 21% 5%	1909
	11th to 20th	Day	43% 5% 9% 20% 17% 6%	1980
	21st to end	Day	43% 5% 12% 18% 19% 3	2240
April	1st to 10th	Day	33% 4 12% 23% 22% 6%	2160
	11th to 20th	Day	34% 5% 11% 23% 21% 6%	2134
	21st to end	Day	38% 7% 12% 21% 17% 5%	2160
May	1st to 10th	Day	39% 8% 15% 20% 14% 3	2160
	11th to 20th	Day	45% 8% 12% 23% 10% 2	2343
	21st to end	Day	40% 8% 14% 24% 13% 1	2725
June	1st to 10th	Day	38% 10% 15% 22% 14% 1	2520
	11th to 20th	Day	38% 9% 16% 21% 14% 1	2520
	21st to end	Day	39% 9% 16% 21% 13% 2	2520
July	1st to 10th	Day	36% 12% 15% 23% 12% 2	2450
	11th to 20th	Day	39% 11% 18% 22% 9% 1	2301
	21st to end	Day	40% 11% 16% 21% 10% 1	2405
August	1st to 10th	Day	45% 11% 16% 20% 8%	2289
	11th to 20th	Day	46% 10% 14% 20% 10% 1	2126
	21st to end	Day	44% 11% 14% 16% 12% 3	2376
September	1st to 10th	Day	42% 9% 15% 16% 15% 3	2160
	11th to 20th	Day	45% 6% 10% 20% 17% 2	2160
	21st to end	Day	50% 6% 9% 19% 15% 2	1929
October	1st to 10th	Day	43% 5% 8% 20% 21% 3	1800
	11th to 20th	Day	38% 4 7% 25% 21% 4	1800
	21st to end	Day	35% 5% 7% 21% 26% 6%	1980
November	1st to 10th	Day	37% 5% 10% 23% 20% 4	1777
	11th to 20th	Day	37% 4 11% 21% 21% 6%	1710
	21st to end	Day	37% 4 9% 25% 21% 4	1672
December	1st to 10th	Day	44% 4 12% 21% 16% 4	1520
	11th to 20th	Day	36% 4 9% 27% 17% 7%	1906
	21st to end	Day	40% 4 10% 28% 17% 2	2772
January	1st to 10th	Night	40% 4 9% 23% 19% 6%	2538
	11th to 20th	Night	46% 7% 8% 19% 16% 4	2430
	21st to end	Night	39% 4 8% 23% 20% 5%	2574
February	1st to 10th	Night	42% 5% 9% 22% 18% 4	2340
	11th to 20th	Night	46% 4 8% 20% 16% 6%	2122
	21st to end	Night	42% 4 8% 21% 18% 7%	1776
March	1st to 10th	Night	37% 4 11% 23% 20% 5%	2048
	11th to 20th	Night	45% 7% 11% 18% 16% 4	1980
	21st to end	Night	42% 6% 11% 22% 16% 4	2114
April	1st to 10th	Night	38% 6% 13% 17% 22% 5%	1800
	11th to 20th	Night	36% 4 10% 24% 20% 5%	1775
	21st to end	Night	37% 6% 11% 24% 18% 4	1800
May	1st to 10th	Night	39% 9% 12% 24% 13% 3	1800
	11th to 20th	Night	41% 8% 14% 22% 12% 2	1568
	21st to end	Night	36% 10% 16% 24% 11% 2	1551
June	1st to 10th	Night	35% 8% 16% 27% 13% 1	1440
	11th to 20th	Night	36% 11% 18% 20% 14% 1	1440
	21st to end	Night	35% 11% 16% 23% 13% 2	1440
July	1st to 10th	Night	37% 11% 18% 21% 11% 3	1400
	11th to 20th	Night	31% 12% 20% 26% 10% 1	1532
	21st to end	Night	35% 13% 17% 25% 9% 1	1672
August	1st to 10th	Night	41% 10% 21% 21% 7%	1608
	11th to 20th	Night	41% 11% 16% 21% 10%	1774
	21st to end	Night	40% 10% 16% 21% 11% 2	1980
September	1st to 10th	Night	35% 10% 18% 20% 15% 3	1800
	11th to 20th	Night	40% 7% 10% 21% 19% 3	1800
	21st to end	Night	48% 6% 11% 18% 16% 2	2024
October	1st to 10th	Night	37% 6% 8% 22% 22% 3	2160
	11th to 20th	Night	36% 6% 9% 22% 23% 4	2160
	21st to end	Night	35% 4 9% 21% 25% 7%	2376
November	1st to 10th	Night	37% 5% 9% 20% 24% 4	2297
	11th to 20th	Night	38% 5% 10% 19% 21% 8%	2470
	21st to end	Night	35% 5% 8% 25% 22% 5%	2503
December	1st to 10th	Night	45% 6% 9% 20% 17% 3	2660
	11th to 20th	Night	39% 5% 10% 21% 20% 6%	3288
	21st to end	Night	38% 5% 13% 23% 19% 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	22% 31% 31% 14% 3	231
	11th to 20th	Day	25% 25% 35% 13% 2	258
	21st to end	Day	22% 25% 38% 13% 1 1	264
February	1st to 10th	Day	23% 24% 38% 11% 4	240
	11th to 20th	Day	30% 24% 29% 13% 3	392
	21st to end	Day	26% 23% 32% 14% 5% 1	346
March	1st to 10th	Day	21% 24% 34% 15% 5% 1	420
	11th to 20th	Day	23% 22% 33% 16% 4 2	420
	21st to end	Day	21% 20% 34% 18% 5% 2	462
April	1st to 10th	Day	23% 19% 35% 16% 6% 2	420
	11th to 20th	Day	15% 17% 33% 22% 9% 3	412
	21st to end	Day	20% 15% 30% 25% 8% 2	420
May	1st to 10th	Day	20% 15% 35% 21% 8% 2	423
	11th to 20th	Day	20% 9% 29% 29% 11% 2	447
	21st to end	Day	22% 5% 22% 27% 19% 4	485
June	1st to 10th	Day	14% 6% 25% 31% 20% 3	450
	11th to 20th	Day	14% 8% 20% 31% 20% 7%	450
	21st to end	Day	10% 6% 23% 36% 19% 5%	450
July	1st to 10th	Day	11% 2 18% 36% 26% 7%	445
	11th to 20th	Day	8% 2 14% 34% 34% 8%	444
	21st to end	Day	9% 3 21% 35% 24% 7%	488
August	1st to 10th	Day	14% 3 19% 32% 24% 8%	446
	11th to 20th	Day	13% 3 14% 27% 31% 13%	439
	21st to end	Day	13% 4 16% 30% 25% 13%	495
September	1st to 10th	Day	15% 3 22% 26% 18% 17%	450
	11th to 20th	Day	16% 5% 19% 30% 19% 12%	450
	21st to end	Day	27% 7% 20% 23% 15% 7%	450
October	1st to 10th	Day	22% 8% 20% 24% 18% 9%	450
	11th to 20th	Day	18% 11% 27% 23% 18% 3	450
	21st to end	Day	17% 11% 32% 22% 13% 5%	495
November	1st to 10th	Day	20% 11% 29% 24% 12% 4	417
	11th to 20th	Day	20% 17% 28% 24% 9% 2	370
	21st to end	Day	20% 14% 27% 22% 15% 2	332
December	1st to 10th	Day	23% 19% 38% 14% 4 1	180
	11th to 20th	Day	17% 21% 34% 18% 9% 1	180
	21st to end	Day	25% 19% 27% 19% 8% 3	198
January	1st to 10th	Night	19% 18% 33% 24% 4	760
	11th to 20th	Night	22% 16% 31% 26% 5%	748
	21st to end	Night	20% 15% 39% 24% 3	792
February	1st to 10th	Night	23% 13% 39% 22% 4	720
	11th to 20th	Night	26% 20% 36% 17% 2	703
	21st to end	Night	21% 18% 36% 21% 4	592
March	1st to 10th	Night	19% 14% 38% 24% 5%	720
	11th to 20th	Night	22% 14% 38% 21% 5%	720
	21st to end	Night	20% 15% 35% 26% 4	792
April	1st to 10th	Night	20% 13% 40% 22% 4	720
	11th to 20th	Night	14% 13% 37% 27% 8%	711
	21st to end	Night	19% 9% 37% 30% 6%	720
May	1st to 10th	Night	17% 11% 36% 29% 7%	720
	11th to 20th	Night	16% 6% 27% 40% 9% 1	506
	21st to end	Night	17% 1 17% 47% 16% 2	389
June	1st to 10th	Night	10% 4 21% 46% 18% 1	360
	11th to 20th	Night	8% 3 22% 46% 19% 3	360
	21st to end	Night	9% 2 20% 50% 19% 1	360
July	1st to 10th	Night	9% 1 17% 47% 22% 3	350
	11th to 20th	Night	9% 1 11% 41% 34% 5%	488
	21st to end	Night	9% 1 16% 46% 25% 3	591
August	1st to 10th	Night	10% 1 14% 44% 27% 3	545
	11th to 20th	Night	12% 2 13% 40% 28% 4	710
	21st to end	Night	14% 2 13% 33% 33% 5%	792
September	1st to 10th	Night	14% 2 14% 37% 27% 7%	720
	11th to 20th	Night	16% 4 16% 35% 26% 4	720
	21st to end	Night	22% 5% 21% 30% 21% 2	720
October	1st to 10th	Night	16% 6% 20% 31% 24% 4	720
	11th to 20th	Night	18% 7% 27% 29% 17% 2	720
	21st to end	Night	16% 9% 27% 30% 15% 3	792
November	1st to 10th	Night	18% 7% 27% 30% 15% 3	740
	11th to 20th	Night	18% 11% 32% 28% 9% 1	760
	21st to end	Night	15% 11% 29% 32% 12% 1	760
December	1st to 10th	Night	21% 12% 32% 27% 8% 1	760
	11th to 20th	Night	18% 11% 34% 29% 7%	760
	21st to end	Night	19% 14% 30% 30% 6%	836

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