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 2025-01-07.

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% 7% 2 6% 5% 5% 5% 4 6% 8% 40%	104587
	Night	14% 7% 2 6% 4 4 4 4 5% 7% 43%	104376
Transparency	Day	40% 7% 12% 21% 17% 3	108224
	Night	39% 6% 11% 22% 18% 4	108878
Seeing	Day	18% 12% 27% 24% 14% 5%	15467
	Night	17% 10% 28% 31% 13% 2	25152

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	17% 6% 1 5% 3 2 3 3 4 5% 50%	2739
	11th to 20th	Day	13% 6% 3 5% 4 3 5% 3 4 5% 48%	2840
	21st to end	Day	14% 11% 3 8% 4 3 3 3 4 6% 41%	3124
February	1st to 10th	Day	13% 9% 2 6% 4 5% 3 4 6% 7% 41%	1710
	11th to 20th	Day	19% 6% 2 5% 5% 4 3 3 4 5% 44%	1822
	21st to end	Day	17% 8% 3 5% 4 3 4 4 7% 8% 37%	1570
March	1st to 10th	Day	24% 9% 2 5% 3 3 3 3 4 6% 36%	3326
	11th to 20th	Day	12% 6% 2 4 3 3 3 3 4 6% 54%	3480
	21st to end	Day	18% 6% 2 5% 4 3 4 3 4 7% 44%	3932
April	1st to 10th	Day	13% 6% 1 4 3 4 3 3 5% 7% 51%	2280
	11th to 20th	Day	10% 5% 1 6% 5% 5% 4 3 5% 7% 49%	2254
	21st to end	Day	12% 7% 3 6% 5% 4 5% 3 5% 7% 44%	2280
May	1st to 10th	Day	13% 7% 3 7% 6% 6% 6% 4 7% 9% 34%	3765
	11th to 20th	Day	20% 7% 3 6% 5% 5% 5% 5% 6% 6% 30%	4161
	21st to end	Day	9% 5% 2 6% 4 4 5% 4 7% 10% 44%	4823
June	1st to 10th	Day	11% 5% 2 5% 4 5% 6% 6% 7% 10% 38%	2660
	11th to 20th	Day	9% 6% 2 7% 5% 5% 6% 4 7% 10% 39%	2660
	21st to end	Day	8% 6% 2 7% 6% 6% 5% 4 8% 11% 36%	2660
July	1st to 10th	Day	8% 5% 2 7% 5% 5% 6% 6% 10% 12% 35%	4440
	11th to 20th	Day	11% 7% 3 8% 6% 6% 6% 5% 7% 9% 31%	4166
	21st to end	Day	9% 8% 3 9% 7% 7% 6% 6% 7% 10% 29%	4466
August	1st to 10th	Day	18% 8% 3 10% 5% 6% 6% 5% 7% 10% 21%	4052
	11th to 20th	Day	10% 7% 3 7% 5% 6% 6% 5% 8% 9% 34%	3730
	21st to end	Day	8% 4 1 7% 5% 6% 6% 5% 7% 10% 39%	4180
September	1st to 10th	Day	13% 6% 3 7% 5% 5% 6% 4 7% 8% 36%	2280
	11th to 20th	Day	14% 7% 3 7% 5% 5% 5% 3 5% 7% 38%	2280
	21st to end	Day	22% 8% 2 6% 4 4 4 3 5% 6% 34%	2035
October	1st to 10th	Day	17% 7% 2 5% 4 5% 4 3 3 6% 44%	1900
	11th to 20th	Day	13% 6% 2 5% 4 3 4 3 3 6% 50%	1900
	21st to end	Day	12% 5% 2 6% 4 3 3 4 4 6% 51%	2090
November	1st to 10th	Day	15% 7% 2 4 4 3 4 3 4 6% 48%	1872
	11th to 20th	Day	16% 6% 2 4 3 3 3 2 5% 7% 48%	1800
	21st to end	Day	14% 5% 2 4 5% 4 3 3 5% 6% 50%	1760
December	1st to 10th	Day	10% 6% 2 5% 4 4 3 3 4 6% 53%	2600
	11th to 20th	Day	14% 7% 3 8% 5% 3 3 3 4 6% 44%	2990
	21st to end	Day	13% 5% 2 5% 4 3 4 3 5% 7% 49%	3960
January	1st to 10th	Night	13% 7% 2 5% 4 3 4 4 5% 6% 46%	4323
	11th to 20th	Night	17% 7% 2 7% 4 3 4 4 5% 5% 42%	4120
	21st to end	Night	18% 7% 2 7% 4 4 4 3 4 6% 42%	4532
February	1st to 10th	Night	17% 8% 2 5% 4 3 4 3 5% 7% 43%	2470
	11th to 20th	Night	20% 8% 2 5% 4 4 3 3 4 6% 41%	2242
	21st to end	Night	15% 9% 1 5% 5% 4 3 4 4 6% 45%	1884
March	1st to 10th	Night	25% 8% 2 7% 4 4 4 3 5% 5% 33%	3524
	11th to 20th	Night	14% 6% 2 5% 4 3 3 3 4 5% 51%	3480
	21st to end	Night	18% 8% 2 5% 3 3 2 2 4 5% 48%	3698
April	1st to 10th	Night	13% 5% 2 5% 4 4 5% 4 6% 6% 45%	1900
	11th to 20th	Night	12% 6% 2 5% 4 3 4 3 5% 7% 49%	1875
	21st to end	Night	13% 7% 2 5% 4 4 3 4 4 6% 48%	1900
May	1st to 10th	Night	14% 8% 3 9% 6% 5% 5% 3 6% 8% 35%	3130
	11th to 20th	Night	20% 9% 2 6% 4 4 4 4 5% 7% 34%	2759
	21st to end	Night	10% 6% 2 7% 4 5% 5% 4 7% 9% 41%	2732
June	1st to 10th	Night	10% 6% 1 5% 5% 5% 4 4 8% 11% 40%	1520
	11th to 20th	Night	7% 6% 2 7% 4 5% 5% 4 8% 12% 39%	1520
	21st to end	Night	8% 5% 2 6% 5% 4 5% 5% 7% 10% 44%	1520
July	1st to 10th	Night	8% 6% 2 7% 5% 5% 6% 5% 8% 12% 37%	2520
	11th to 20th	Night	10% 7% 3 7% 5% 5% 5% 6% 8% 9% 36%	2776
	21st to end	Night	16% 9% 3 8% 6% 4 5% 5% 6% 8% 29%	3087
August	1st to 10th	Night	19% 8% 3 8% 6% 4 5% 4 5% 8% 29%	2847
	11th to 20th	Night	10% 7% 2 8% 5% 6% 5% 4 7% 8% 38%	3097
	21st to end	Night	9% 5% 2 6% 4 4 5% 4 8% 9% 44%	3476
September	1st to 10th	Night	11% 6% 2 5% 4 4 4 4 7% 9% 44%	1900
	11th to 20th	Night	14% 6% 2 7% 5% 4 4 3 5% 6% 44%	1900
	21st to end	Night	20% 7% 3 8% 5% 4 4 3 5% 8% 35%	2138
October	1st to 10th	Night	14% 6% 2 6% 4 4 4 3 5% 5% 48%	2280
	11th to 20th	Night	15% 6% 2 4 3 3 3 3 4 6% 51%	2280
	21st to end	Night	12% 5% 2 5% 4 3 4 3 4 6% 53%	2508
November	1st to 10th	Night	15% 6% 2 5% 3 3 3 3 5% 5% 49%	2422
	11th to 20th	Night	16% 6% 3 5% 3 3 3 3 4 6% 47%	2600
	21st to end	Night	13% 5% 2 4 4 4 4 3 4 7% 50%	2635
December	1st to 10th	Night	10% 5% 2 6% 4 4 3 3 5% 5% 53%	4580
	11th to 20th	Night	17% 7% 3 8% 5% 5% 5% 4 4 5% 38%	5205
	21st to end	Night	12% 5% 2 5% 3 3 4 3 5% 7% 50%	6996

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	36% 4 7% 29% 21% 4	2740
	11th to 20th	Day	38% 5% 7% 18% 27% 5%	2840
	21st to end	Day	45% 5% 10% 18% 19% 4	3124
February	1st to 10th	Day	41% 4 12% 25% 15% 3	1710
	11th to 20th	Day	44% 4 7% 19% 20% 6%	1831
	21st to end	Day	43% 7% 12% 17% 17% 5%	1570
March	1st to 10th	Day	49% 5% 9% 17% 14% 6%	3326
	11th to 20th	Day	32% 5% 8% 20% 25% 10%	3480
	21st to end	Day	41% 5% 14% 18% 19% 3	3932
April	1st to 10th	Day	34% 4 12% 22% 22% 6%	2280
	11th to 20th	Day	34% 5% 10% 23% 21% 6%	2254
	21st to end	Day	38% 7% 11% 22% 17% 5%	2280
May	1st to 10th	Day	45% 9% 16% 20% 9% 2	3800
	11th to 20th	Day	50% 9% 11% 20% 8% 1	4165
	21st to end	Day	33% 8% 16% 26% 16% 2	4837
June	1st to 10th	Day	38% 9% 15% 22% 14% 2	2660
	11th to 20th	Day	37% 9% 15% 23% 15% 1	2660
	21st to end	Day	38% 9% 16% 22% 13% 1	2660
July	1st to 10th	Day	36% 13% 19% 20% 10% 2	4370
	11th to 20th	Day	46% 9% 21% 17% 5% 1	4095
	21st to end	Day	48% 11% 13% 17% 11% 1	4324
August	1st to 10th	Day	56% 9% 15% 15% 4	4039
	11th to 20th	Day	42% 10% 14% 23% 11%	3766
	21st to end	Day	37% 9% 12% 25% 15% 2	4180
September	1st to 10th	Day	42% 9% 15% 16% 16% 3	2280
	11th to 20th	Day	46% 6% 10% 19% 17% 2	2280
	21st to end	Day	50% 6% 10% 18% 14% 2	2035
October	1st to 10th	Day	34% 5% 9% 23% 26% 3	3160
	11th to 20th	Day	27% 3 6% 20% 34% 10%	3140
	21st to end	Day	22% 4 7% 28% 29% 9%	3428
November	1st to 10th	Day	37% 5% 10% 24% 20% 4	1872
	11th to 20th	Day	37% 4 11% 21% 21% 6%	1800
	21st to end	Day	36% 4 9% 24% 22% 4	1760
December	1st to 10th	Day	35% 3 8% 27% 23% 4	2600
	11th to 20th	Day	43% 5% 12% 20% 15% 5%	2986
	21st to end	Day	35% 4 12% 29% 18% 1	3960
January	1st to 10th	Night	38% 4 8% 24% 21% 5%	4323
	11th to 20th	Night	44% 5% 6% 20% 21% 4	4120
	21st to end	Night	44% 5% 8% 18% 18% 6%	4532
February	1st to 10th	Night	41% 5% 10% 23% 18% 4	2470
	11th to 20th	Night	46% 4 8% 20% 17% 6%	2244
	21st to end	Night	42% 4 8% 21% 18% 7%	1884
March	1st to 10th	Night	53% 5% 10% 16% 13% 3	3524
	11th to 20th	Night	36% 5% 8% 17% 23% 10%	3480
	21st to end	Night	41% 4 8% 26% 16% 4	3698
April	1st to 10th	Night	38% 6% 13% 16% 23% 4	1900
	11th to 20th	Night	35% 5% 10% 24% 20% 5%	1875
	21st to end	Night	37% 6% 12% 24% 18% 4	1900
May	1st to 10th	Night	45% 10% 14% 21% 9% 1	3160
	11th to 20th	Night	48% 9% 12% 23% 7% 1	2760
	21st to end	Night	36% 10% 19% 22% 12% 1	2739
June	1st to 10th	Night	36% 9% 16% 26% 13% 1	1520
	11th to 20th	Night	35% 11% 18% 22% 14% 1	1520
	21st to end	Night	34% 10% 15% 25% 13% 2	1520
July	1st to 10th	Night	38% 13% 19% 20% 9% 2	2480
	11th to 20th	Night	40% 12% 23% 19% 5% 1	2724
	21st to end	Night	51% 10% 11% 16% 11%	2988
August	1st to 10th	Night	52% 8% 18% 18% 4	2836
	11th to 20th	Night	41% 10% 15% 23% 12%	3127
	21st to end	Night	34% 7% 13% 26% 18% 1	3476
September	1st to 10th	Night	34% 9% 18% 19% 16% 3	1900
	11th to 20th	Night	41% 7% 10% 21% 19% 2	1900
	21st to end	Night	48% 6% 11% 18% 15% 2	2138
October	1st to 10th	Night	37% 5% 8% 23% 24% 2	3800
	11th to 20th	Night	27% 4 6% 19% 33% 11%	3779
	21st to end	Night	21% 3 8% 28% 27% 13%	4120
November	1st to 10th	Night	37% 5% 8% 20% 24% 4	2422
	11th to 20th	Night	39% 5% 10% 19% 20% 8%	2600
	21st to end	Night	35% 5% 9% 25% 22% 4	2635
December	1st to 10th	Night	33% 4 7% 24% 26% 6%	4580
	11th to 20th	Night	48% 6% 9% 16% 15% 6%	5208
	21st to end	Night	34% 5% 15% 27% 17% 1	6996

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% 31% 31% 13% 2	245
	11th to 20th	Day	26% 24% 36% 12% 2	270
	21st to end	Day	21% 25% 40% 12% 1 1	297
February	1st to 10th	Day	21% 24% 37% 13% 4	270
	11th to 20th	Day	29% 25% 30% 13% 3	430
	21st to end	Day	26% 22% 34% 14% 5% 1	382
March	1st to 10th	Day	23% 23% 33% 15% 5% 1	460
	11th to 20th	Day	22% 23% 32% 17% 4 2	460
	21st to end	Day	21% 21% 35% 17% 5% 2	506
April	1st to 10th	Day	23% 20% 35% 15% 6% 2	460
	11th to 20th	Day	15% 18% 34% 21% 9% 3	452
	21st to end	Day	19% 17% 30% 26% 7% 2	460
May	1st to 10th	Day	19% 15% 35% 22% 8% 2	463
	11th to 20th	Day	20% 9% 30% 28% 10% 2	487
	21st to end	Day	21% 6% 24% 27% 19% 4	529
June	1st to 10th	Day	13% 7% 26% 32% 19% 3	490
	11th to 20th	Day	13% 8% 22% 30% 20% 7%	490
	21st to end	Day	10% 6% 24% 36% 18% 6%	490
July	1st to 10th	Day	10% 2 18% 36% 26% 7%	485
	11th to 20th	Day	9% 3 14% 36% 32% 7%	484
	21st to end	Day	9% 4 22% 34% 23% 7%	532
August	1st to 10th	Day	16% 3 19% 31% 22% 8%	486
	11th to 20th	Day	12% 3 16% 27% 29% 12%	479
	21st to end	Day	12% 4 17% 30% 25% 12%	539
September	1st to 10th	Day	15% 3 22% 26% 18% 16%	490
	11th to 20th	Day	18% 6% 20% 28% 18% 11%	490
	21st to end	Day	27% 8% 21% 23% 15% 6%	490
October	1st to 10th	Day	21% 8% 20% 24% 18% 8%	490
	11th to 20th	Day	18% 12% 27% 24% 17% 3	490
	21st to end	Day	16% 10% 32% 23% 14% 6%	539
November	1st to 10th	Day	19% 11% 30% 24% 12% 4	452
	11th to 20th	Day	20% 17% 30% 23% 8% 2	400
	21st to end	Day	21% 15% 27% 21% 14% 1	360
December	1st to 10th	Day	22% 21% 38% 15% 4 1	200
	11th to 20th	Day	18% 20% 36% 18% 9% 1	200
	21st to end	Day	24% 20% 29% 19% 7% 2	220
January	1st to 10th	Night	19% 19% 33% 24% 4	785
	11th to 20th	Night	22% 16% 31% 26% 5%	760
	21st to end	Night	20% 15% 38% 24% 2	836
February	1st to 10th	Night	21% 13% 39% 23% 4	760
	11th to 20th	Night	26% 20% 37% 16% 1	743
	21st to end	Night	21% 18% 36% 21% 4	628
March	1st to 10th	Night	20% 14% 37% 25% 5%	760
	11th to 20th	Night	22% 14% 38% 20% 5%	760
	21st to end	Night	20% 16% 36% 25% 4	836
April	1st to 10th	Night	20% 14% 41% 21% 4	760
	11th to 20th	Night	15% 13% 38% 26% 8%	751
	21st to end	Night	18% 9% 37% 30% 6%	760
May	1st to 10th	Night	17% 11% 36% 30% 6%	760
	11th to 20th	Night	17% 7% 27% 40% 9% 1	534
	21st to end	Night	16% 2 18% 46% 17% 2	411
June	1st to 10th	Night	10% 4 22% 46% 18% 1	380
	11th to 20th	Night	7% 3 21% 47% 19% 3	380
	21st to end	Night	8% 2 20% 50% 19% 1	380
July	1st to 10th	Night	9% 1 17% 48% 22% 2	370
	11th to 20th	Night	9% 1 11% 41% 33% 4	516
	21st to end	Night	10% 2 17% 45% 24% 3	624
August	1st to 10th	Night	11% 2 15% 43% 26% 3	576
	11th to 20th	Night	12% 2 14% 41% 28% 4	750
	21st to end	Night	13% 2 14% 33% 33% 5%	836
September	1st to 10th	Night	13% 2 14% 38% 26% 6%	760
	11th to 20th	Night	17% 5% 16% 33% 26% 3	760
	21st to end	Night	22% 5% 21% 30% 21% 1	760
October	1st to 10th	Night	16% 6% 19% 31% 24% 4	760
	11th to 20th	Night	18% 7% 27% 30% 16% 2	760
	21st to end	Night	15% 8% 26% 31% 16% 3	836
November	1st to 10th	Night	18% 7% 27% 31% 15% 3	780
	11th to 20th	Night	18% 11% 33% 28% 9% 1	800
	21st to end	Night	15% 11% 30% 31% 12% 1	800
December	1st to 10th	Night	20% 12% 33% 26% 8% 1	800
	11th to 20th	Night	19% 12% 34% 29% 7%	800
	21st to end	Night	19% 14% 31% 30% 6%	880

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