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 2026-05-02.

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% 2 6% 4 5% 5% 4 6% 8% 41%	131430
	Night	14% 7% 2 6% 4 4 4 3 5% 7% 44%	131033
Transparency	Day	39% 7% 12% 21% 17% 4	135023
	Night	39% 6% 11% 21% 18% 5%	135510
Seeing	Day	18% 13% 28% 23% 13% 4	17217
	Night	17% 10% 29% 30% 13% 2	26926

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	13% 5% 1 5% 3 3 3 3 4 5% 55%	5001
	11th to 20th	Day	14% 5% 2 5% 3 3 3 2 3 4 56%	5280
	21st to end	Day	13% 9% 3 8% 4 4 4 3 3 5% 44%	5780
February	1st to 10th	Day	13% 8% 2 6% 4 5% 3 4 6% 7% 41%	1890
	11th to 20th	Day	20% 7% 2 5% 5% 4 3 3 4 5% 42%	2020
	21st to end	Day	17% 7% 3 6% 4 3 4 4 7% 7% 39%	1730
March	1st to 10th	Day	20% 8% 2 6% 4 4 4 4 4 6% 39%	4876
	11th to 20th	Day	11% 6% 2 5% 3 3 3 3 4 6% 52%	5090
	21st to end	Day	13% 5% 2 5% 4 4 4 3 5% 7% 47%	5763
April	1st to 10th	Day	12% 6% 2 4 4 4 3 3 5% 7% 50%	2520
	11th to 20th	Day	10% 5% 1 5% 4 5% 4 3 5% 7% 50%	2494
	21st to end	Day	11% 7% 3 6% 5% 4 5% 3 5% 7% 44%	2520
May	1st to 10th	Day	13% 7% 2 7% 5% 6% 6% 4 6% 9% 34%	5417
	11th to 20th	Day	18% 7% 3 7% 5% 5% 5% 4 6% 8% 30%	5983
	21st to end	Day	14% 6% 2 7% 4 4 5% 4 6% 9% 40%	6934
June	1st to 10th	Day	11% 5% 2 5% 4 5% 6% 6% 7% 10% 38%	2800
	11th to 20th	Day	9% 6% 2 7% 5% 5% 6% 4 7% 10% 39%	2800
	21st to end	Day	7% 6% 2 6% 6% 6% 5% 4 8% 12% 37%	2800
July	1st to 10th	Day	9% 5% 2 7% 5% 5% 6% 6% 9% 12% 34%	6360
	11th to 20th	Day	10% 7% 3 8% 7% 7% 7% 5% 8% 11% 27%	5960
	21st to end	Day	8% 6% 2 8% 6% 6% 6% 6% 8% 12% 31%	6424
August	1st to 10th	Day	18% 8% 4 10% 6% 6% 6% 5% 7% 9% 21%	4180
	11th to 20th	Day	10% 7% 3 7% 5% 6% 6% 5% 8% 9% 33%	3850
	21st to end	Day	8% 4 1 7% 5% 6% 6% 5% 7% 10% 39%	4312
September	1st to 10th	Day	13% 6% 3 7% 5% 5% 6% 4 7% 8% 37%	2400
	11th to 20th	Day	15% 7% 3 7% 5% 5% 5% 3 5% 7% 37%	2400
	21st to end	Day	23% 8% 2 6% 4 4 4 3 5% 6% 34%	2142
October	1st to 10th	Day	16% 7% 2 6% 4 5% 5% 3 4 6% 44%	2000
	11th to 20th	Day	15% 6% 2 5% 4 3 4 3 3 6% 50%	2000
	21st to end	Day	13% 5% 2 6% 4 3 3 4 4 6% 51%	2200
November	1st to 10th	Day	15% 7% 2 4 3 3 4 3 4 6% 49%	1968
	11th to 20th	Day	15% 6% 2 4 4 3 3 2 5% 7% 49%	1890
	21st to end	Day	13% 5% 2 4 5% 4 3 3 5% 6% 50%	1848
December	1st to 10th	Day	11% 6% 2 5% 4 4 3 3 4 6% 52%	2680
	11th to 20th	Day	14% 7% 3 8% 4 3 3 3 4 6% 44%	3070
	21st to end	Day	13% 5% 2 6% 4 3 4 3 5% 7% 49%	4048
January	1st to 10th	Night	11% 6% 3 5% 4 3 4 3 5% 6% 50%	7876
	11th to 20th	Night	13% 6% 2 6% 4 3 3 3 4 4 53%	7680
	21st to end	Night	16% 7% 2 7% 4 4 4 3 4 6% 44%	8401
February	1st to 10th	Night	17% 7% 2 5% 4 3 4 3 5% 7% 43%	2730
	11th to 20th	Night	20% 8% 2 5% 4 4 3 3 4 6% 40%	2484
	21st to end	Night	15% 9% 1 5% 5% 4 3 4 4 5% 46%	2076
March	1st to 10th	Night	20% 7% 2 6% 4 4 3 3 4 4 42%	5180
	11th to 20th	Night	13% 6% 2 5% 4 4 4 3 4 5% 49%	5090
	21st to end	Night	15% 7% 2 5% 3 3 4 3 4 5% 48%	5409
April	1st to 10th	Night	13% 5% 2 5% 4 4 5% 4 6% 7% 45%	2100
	11th to 20th	Night	11% 6% 2 5% 4 3 4 3 5% 8% 49%	2075
	21st to end	Night	13% 6% 2 5% 4 4 4 4 4 6% 48%	2100
May	1st to 10th	Night	12% 8% 3 9% 5% 5% 5% 4 6% 9% 33%	4501
	11th to 20th	Night	20% 9% 3 7% 5% 4 5% 4 5% 7% 32%	3951
	21st to end	Night	14% 8% 3 7% 4 5% 5% 4 6% 7% 37%	3920
June	1st to 10th	Night	10% 6% 1 5% 5% 5% 4 4 8% 11% 40%	1600
	11th to 20th	Night	8% 6% 3 7% 4 5% 5% 4 8% 12% 38%	1600
	21st to end	Night	7% 5% 2 5% 5% 5% 5% 5% 7% 10% 44%	1600
July	1st to 10th	Night	8% 5% 2 6% 5% 5% 5% 5% 10% 14% 34%	3598
	11th to 20th	Night	10% 7% 3 7% 6% 5% 5% 6% 9% 11% 30%	3965
	21st to end	Night	12% 7% 3 7% 6% 4 5% 4 6% 10% 35%	4427
August	1st to 10th	Night	19% 8% 3 8% 6% 4 5% 4 5% 8% 29%	2938
	11th to 20th	Night	10% 7% 3 8% 5% 6% 5% 4 7% 8% 37%	3197
	21st to end	Night	9% 5% 2 6% 4 4 5% 4 8% 9% 44%	3586
September	1st to 10th	Night	11% 5% 2 5% 4 4 4 3 7% 9% 45%	2000
	11th to 20th	Night	15% 7% 2 7% 5% 4 4 3 5% 6% 43%	2000
	21st to end	Night	20% 7% 2 8% 5% 4 4 3 5% 7% 35%	2251
October	1st to 10th	Night	14% 6% 2 6% 4 4 5% 3 4 5% 49%	2400
	11th to 20th	Night	16% 6% 2 4 3 3 3 3 4 6% 50%	2400
	21st to end	Night	13% 6% 2 5% 4 3 4 3 4 6% 52%	2640
November	1st to 10th	Night	15% 6% 2 5% 3 3 3 3 5% 5% 49%	2546
	11th to 20th	Night	15% 6% 3 5% 3 3 3 3 4 6% 48%	2730
	21st to end	Night	12% 5% 2 4 4 4 4 4 4 7% 50%	2767
December	1st to 10th	Night	10% 5% 2 6% 4 4 3 3 5% 5% 53%	4720
	11th to 20th	Night	17% 7% 3 8% 5% 5% 4 4 4 5% 38%	5345
	21st to end	Night	12% 5% 2 5% 3 3 4 3 5% 7% 50%	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	32% 3 11% 25% 18% 11%	5002
	11th to 20th	Day	34% 3 4 15% 36% 8%	5280
	21st to end	Day	43% 4 7% 23% 18% 4	5780
February	1st to 10th	Day	41% 4 12% 24% 15% 4	1890
	11th to 20th	Day	45% 4 7% 18% 20% 5%	2029
	21st to end	Day	43% 6% 11% 18% 18% 5%	1730
March	1st to 10th	Day	46% 4 8% 18% 16% 8%	4876
	11th to 20th	Day	33% 4 8% 19% 25% 10%	5090
	21st to end	Day	37% 5% 14% 19% 20% 5%	5763
April	1st to 10th	Day	34% 4 13% 22% 22% 5%	2520
	11th to 20th	Day	34% 5% 11% 25% 20% 5%	2494
	21st to end	Day	38% 7% 12% 23% 17% 4	2520
May	1st to 10th	Day	44% 9% 17% 18% 11% 1	5449
	11th to 20th	Day	49% 8% 14% 19% 10% 1	5987
	21st to end	Day	39% 7% 14% 25% 14% 2	6949
June	1st to 10th	Day	37% 9% 15% 22% 15% 1	2800
	11th to 20th	Day	37% 9% 16% 22% 14% 1	2800
	21st to end	Day	37% 9% 16% 23% 14% 1	2800
July	1st to 10th	Day	37% 12% 18% 22% 9% 2	6290
	11th to 20th	Day	47% 13% 22% 14% 3 1	5889
	21st to end	Day	41% 11% 14% 23% 10% 1	6240
August	1st to 10th	Day	57% 9% 15% 15% 4	4167
	11th to 20th	Day	42% 10% 14% 22% 11%	3886
	21st to end	Day	37% 9% 12% 25% 15% 2	4312
September	1st to 10th	Day	42% 8% 15% 17% 15% 3	2400
	11th to 20th	Day	47% 6% 10% 20% 16% 2	2400
	21st to end	Day	50% 6% 10% 18% 14% 2	2142
October	1st to 10th	Day	34% 5% 9% 23% 27% 3	3260
	11th to 20th	Day	28% 3 6% 20% 34% 10%	3240
	21st to end	Day	23% 4 7% 27% 29% 9%	3538
November	1st to 10th	Day	36% 5% 10% 24% 21% 4	1968
	11th to 20th	Day	36% 4 11% 22% 21% 6%	1890
	21st to end	Day	36% 4 9% 25% 22% 4	1848
December	1st to 10th	Day	35% 3 8% 27% 22% 4	2680
	11th to 20th	Day	42% 5% 12% 20% 15% 5%	3066
	21st to end	Day	35% 4 12% 29% 18% 1	4048
January	1st to 10th	Night	35% 3 11% 22% 22% 7%	7877
	11th to 20th	Night	35% 4 5% 18% 30% 9%	7680
	21st to end	Night	42% 4 7% 23% 18% 6%	8401
February	1st to 10th	Night	42% 5% 10% 22% 18% 4	2730
	11th to 20th	Night	46% 3 8% 20% 17% 5%	2486
	21st to end	Night	42% 4 8% 21% 18% 7%	2076
March	1st to 10th	Night	45% 4 9% 17% 17% 8%	5180
	11th to 20th	Night	38% 5% 8% 16% 22% 11%	5090
	21st to end	Night	39% 5% 10% 24% 16% 6%	5409
April	1st to 10th	Night	37% 6% 13% 17% 22% 4	2100
	11th to 20th	Night	34% 4 11% 26% 19% 5%	2075
	21st to end	Night	37% 6% 11% 25% 18% 3	2100
May	1st to 10th	Night	45% 10% 16% 19% 9% 1	4531
	11th to 20th	Night	51% 8% 12% 21% 8% 1	3952
	21st to end	Night	43% 9% 16% 21% 11% 1	3927
June	1st to 10th	Night	36% 9% 16% 25% 14% 1	1600
	11th to 20th	Night	36% 11% 17% 21% 14% 1	1600
	21st to end	Night	33% 10% 15% 27% 13% 2	1600
July	1st to 10th	Night	36% 12% 21% 21% 9% 2	3560
	11th to 20th	Night	43% 15% 22% 16% 4	3916
	21st to end	Night	43% 10% 13% 21% 13%	4297
August	1st to 10th	Night	52% 8% 18% 18% 4	2927
	11th to 20th	Night	42% 10% 14% 22% 12%	3227
	21st to end	Night	35% 8% 12% 26% 18% 2	3586
September	1st to 10th	Night	34% 9% 18% 20% 16% 3	2000
	11th to 20th	Night	42% 7% 10% 20% 19% 2	2000
	21st to end	Night	49% 6% 11% 18% 15% 2	2251
October	1st to 10th	Night	37% 5% 8% 23% 25% 2	3920
	11th to 20th	Night	28% 4 6% 19% 32% 11%	3899
	21st to end	Night	22% 3 7% 28% 27% 13%	4252
November	1st to 10th	Night	37% 5% 8% 20% 25% 4	2546
	11th to 20th	Night	38% 5% 10% 19% 20% 8%	2730
	21st to end	Night	35% 5% 8% 25% 22% 5%	2767
December	1st to 10th	Night	34% 4 7% 23% 25% 6%	4720
	11th to 20th	Night	48% 6% 9% 16% 15% 6%	5348
	21st to end	Night	34% 5% 15% 27% 17% 1	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	23% 30% 32% 12% 2	283
	11th to 20th	Day	26% 25% 37% 10% 2	330
	21st to end	Day	21% 28% 38% 11% 1 1	363
February	1st to 10th	Day	23% 25% 35% 12% 4	330
	11th to 20th	Day	31% 25% 29% 12% 3	508
	21st to end	Day	26% 21% 34% 14% 4	446
March	1st to 10th	Day	22% 23% 33% 16% 5% 1	540
	11th to 20th	Day	22% 23% 33% 15% 5% 1	540
	21st to end	Day	20% 22% 37% 15% 4 1	594
April	1st to 10th	Day	21% 19% 36% 15% 6% 2	540
	11th to 20th	Day	15% 17% 36% 21% 8% 3	532
	21st to end	Day	18% 16% 30% 27% 8% 1	540
May	1st to 10th	Day	18% 15% 36% 21% 8% 2	507
	11th to 20th	Day	20% 10% 31% 27% 10% 2	527
	21st to end	Day	22% 7% 25% 25% 17% 4	573
June	1st to 10th	Day	13% 7% 27% 32% 19% 3	530
	11th to 20th	Day	13% 8% 23% 30% 20% 6%	530
	21st to end	Day	9% 6% 22% 37% 21% 6%	530
July	1st to 10th	Day	10% 3 18% 38% 25% 6%	525
	11th to 20th	Day	8% 3 14% 36% 31% 8%	524
	21st to end	Day	9% 4 21% 35% 23% 8%	576
August	1st to 10th	Day	17% 5% 19% 31% 21% 7%	526
	11th to 20th	Day	12% 4 16% 27% 28% 13%	519
	21st to end	Day	12% 4 20% 30% 23% 11%	583
September	1st to 10th	Day	16% 4 23% 25% 17% 15%	530
	11th to 20th	Day	19% 6% 20% 27% 18% 10%	530
	21st to end	Day	27% 8% 22% 23% 15% 6%	530
October	1st to 10th	Day	21% 8% 21% 24% 17% 9%	530
	11th to 20th	Day	20% 12% 26% 23% 16% 3	530
	21st to end	Day	17% 12% 31% 22% 13% 5%	583
November	1st to 10th	Day	19% 12% 30% 24% 12% 4	488
	11th to 20th	Day	21% 18% 30% 23% 8% 2	430
	21st to end	Day	19% 17% 27% 22% 13% 1	388
December	1st to 10th	Day	24% 19% 38% 15% 4 1	220
	11th to 20th	Day	18% 19% 36% 19% 8%	220
	21st to end	Day	23% 22% 29% 17% 6% 2	242
January	1st to 10th	Night	19% 19% 34% 23% 4	840
	11th to 20th	Night	22% 17% 32% 24% 5%	840
	21st to end	Night	20% 15% 40% 23% 2	924
February	1st to 10th	Night	22% 13% 39% 22% 4	840
	11th to 20th	Night	27% 19% 37% 16% 1	823
	21st to end	Night	21% 19% 37% 21% 3	692
March	1st to 10th	Night	20% 14% 36% 25% 5%	840
	11th to 20th	Night	22% 14% 38% 21% 5%	840
	21st to end	Night	19% 16% 37% 24% 4	924
April	1st to 10th	Night	19% 14% 40% 21% 5%	840
	11th to 20th	Night	14% 13% 39% 26% 8%	831
	21st to end	Night	18% 9% 37% 31% 6%	840
May	1st to 10th	Night	16% 12% 36% 30% 6%	805
	11th to 20th	Night	17% 7% 28% 39% 9% 1	562
	21st to end	Night	16% 2 19% 45% 16% 2	433
June	1st to 10th	Night	10% 4 23% 46% 17% 1	400
	11th to 20th	Night	8% 4 22% 45% 19% 3	400
	21st to end	Night	8% 2 19% 50% 20% 1	400
July	1st to 10th	Night	9% 2 17% 49% 22% 2	390
	11th to 20th	Night	9% 1 12% 40% 32% 5%	544
	21st to end	Night	9% 2 16% 44% 26% 3	657
August	1st to 10th	Night	11% 2 15% 43% 26% 3	607
	11th to 20th	Night	12% 3 14% 40% 27% 4	790
	21st to end	Night	13% 3 14% 34% 32% 5%	880
September	1st to 10th	Night	14% 2 15% 38% 26% 6%	800
	11th to 20th	Night	17% 5% 16% 33% 26% 3	800
	21st to end	Night	22% 5% 21% 30% 21% 1	800
October	1st to 10th	Night	15% 6% 19% 30% 24% 5%	800
	11th to 20th	Night	20% 7% 27% 29% 16% 2	800
	21st to end	Night	16% 9% 26% 30% 16% 3	880
November	1st to 10th	Night	18% 8% 28% 30% 14% 3	820
	11th to 20th	Night	18% 12% 34% 28% 9% 1	840
	21st to end	Night	14% 11% 30% 32% 11% 1	840
December	1st to 10th	Night	21% 12% 32% 26% 8%	840
	11th to 20th	Night	19% 12% 34% 29% 7%	840
	21st to end	Night	18% 14% 32% 30% 6%	924

Page generated at 2026-04-29 02:21:47. Version ac07

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