A. J. Jolly Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the A. J. Jolly Park clear sky chart from 2005-11-06 to 2025-07-06.

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% 9% 3 7% 5% 4 4 4 5% 7% 36%	120691
	Night	15% 10% 3 7% 4 4 4 3 5% 7% 37%	118120
Transparency	Day	46% 3 10% 24% 15% 2	124387
	Night	47% 3 10% 23% 15% 2	122561
Seeing	Day	21% 11% 27% 22% 13% 6%	16121
	Night	20% 10% 24% 28% 15% 2	25620

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% 18% 7% 11% 4 4 3 2 4 4 27%	4056
	11th to 20th	Day	14% 15% 6% 13% 5% 5% 3 3 3 4 30%	4060
	21st to end	Day	22% 13% 6% 8% 4 5% 4 3 4 5% 26%	4466
February	1st to 10th	Day	19% 14% 4 9% 5% 3 3 3 4 6% 31%	1910
	11th to 20th	Day	18% 11% 5% 9% 5% 4 3 3 4 5% 32%	1948
	21st to end	Day	18% 13% 4 8% 4 3 3 3 4 6% 32%	1650
March	1st to 10th	Day	19% 14% 4 8% 4 3 3 3 4 5% 33%	4526
	11th to 20th	Day	14% 8% 3 6% 4 4 4 4 6% 7% 40%	4980
	21st to end	Day	18% 10% 3 7% 5% 4 4 4 5% 7% 35%	5465
April	1st to 10th	Day	17% 9% 2 7% 5% 4 5% 4 5% 6% 36%	2349
	11th to 20th	Day	17% 9% 2 7% 4 3 4 3 4 7% 39%	2427
	21st to end	Day	17% 8% 3 7% 4 5% 4 4 6% 6% 35%	2600
May	1st to 10th	Day	19% 9% 3 8% 5% 5% 5% 4 7% 8% 27%	5862
	11th to 20th	Day	19% 9% 3 7% 4 4 4 4 5% 7% 33%	5861
	21st to end	Day	13% 7% 3 8% 5% 6% 6% 5% 8% 9% 31%	6433
June	1st to 10th	Day	12% 5% 2 6% 5% 5% 5% 4 6% 8% 41%	2600
	11th to 20th	Day	9% 5% 2 7% 5% 5% 6% 4 6% 9% 42%	2736
	21st to end	Day	9% 6% 2 6% 5% 6% 6% 5% 6% 9% 39%	2800
July	1st to 10th	Day	12% 7% 3 6% 5% 5% 5% 4 6% 8% 39%	4511
	11th to 20th	Day	7% 4 1 5% 4 5% 5% 4 7% 11% 45%	4194
	21st to end	Day	11% 8% 3 9% 6% 6% 7% 5% 7% 8% 30%	4466
August	1st to 10th	Day	8% 5% 2 6% 4 4 5% 4 7% 11% 44%	4104
	11th to 20th	Day	7% 6% 2 7% 5% 5% 5% 6% 8% 11% 39%	4044
	21st to end	Day	5% 4 2 5% 4 4 4 4 6% 8% 54%	4196
September	1st to 10th	Day	13% 5% 2 5% 5% 4 4 3 6% 6% 47%	2157
	11th to 20th	Day	9% 4 2 5% 4 4 4 4 7% 8% 48%	2090
	21st to end	Day	17% 6% 2 5% 4 3 3 3 4 6% 46%	2090
October	1st to 10th	Day	12% 4 2 5% 4 4 4 3 5% 7% 51%	2090
	11th to 20th	Day	14% 7% 2 5% 4 4 4 3 4 7% 46%	1929
	21st to end	Day	20% 8% 2 5% 4 2 4 3 4 7% 40%	1960
November	1st to 10th	Day	10% 7% 2 5% 4 3 4 3 4 6% 52%	1762
	11th to 20th	Day	15% 11% 3 7% 4 3 4 3 5% 7% 38%	1800
	21st to end	Day	18% 10% 4 7% 5% 3 4 3 4 6% 37%	1800
December	1st to 10th	Day	19% 11% 3 7% 4 3 4 2 3 4 39%	2930
	11th to 20th	Day	18% 15% 5% 8% 5% 5% 5% 3 4 4 28%	3373
	21st to end	Day	22% 19% 5% 9% 4 5% 4 3 4 5% 20%	4466
January	1st to 10th	Night	16% 16% 6% 14% 6% 5% 5% 3 5% 5% 19%	5889
	11th to 20th	Night	16% 16% 6% 13% 6% 4 4 3 3 5% 23%	5900
	21st to end	Night	21% 12% 4 7% 4 4 4 2 4 5% 32%	6490
February	1st to 10th	Night	21% 13% 5% 8% 4 4 4 3 5% 5% 28%	2485
	11th to 20th	Night	20% 12% 3 10% 4 4 4 3 4 5% 30%	2338
	21st to end	Night	21% 14% 4 7% 4 3 4 3 5% 4 31%	1980
March	1st to 10th	Night	19% 14% 2 7% 4 3 3 3 4 6% 36%	5327
	11th to 20th	Night	13% 8% 3 6% 4 4 4 4 5% 7% 43%	4980
	21st to end	Night	16% 10% 3 9% 5% 5% 4 4 5% 6% 33%	5467
April	1st to 10th	Night	14% 10% 2 6% 5% 4 5% 4 6% 7% 36%	2069
	11th to 20th	Night	15% 7% 3 6% 4 4 3 3 6% 6% 42%	1922
	21st to end	Night	16% 8% 3 7% 4 4 4 3 7% 8% 37%	1800
May	1st to 10th	Night	20% 11% 2 8% 5% 4 4 3 6% 7% 28%	4033
	11th to 20th	Night	16% 7% 2 6% 4 6% 5% 4 7% 9% 32%	4032
	21st to end	Night	13% 7% 2 7% 5% 5% 5% 4 7% 8% 38%	4421
June	1st to 10th	Night	8% 5% 2 4 5% 4 4 4 5% 10% 49%	1800
	11th to 20th	Night	8% 5% 2 6% 4 4 4 4 6% 10% 47%	1656
	21st to end	Night	6% 5% 2 5% 5% 4 4 5% 7% 12% 46%	1600
July	1st to 10th	Night	9% 6% 2 5% 4 4 4 4 6% 8% 49%	2570
	11th to 20th	Night	6% 5% 2 5% 4 4 4 3 7% 9% 51%	2764
	21st to end	Night	11% 7% 2 7% 6% 5% 5% 5% 6% 9% 37%	3087
August	1st to 10th	Night	7% 5% 3 7% 4 4 4 3 7% 9% 46%	2825
	11th to 20th	Night	8% 5% 3 8% 4 4 4 3 7% 8% 45%	2785
	21st to end	Night	4 2 1 4 3 3 3 4 6% 10% 61%	3443
September	1st to 10th	Night	12% 5% 2 4 3 4 3 3 6% 7% 51%	2004
	11th to 20th	Night	9% 4 2 5% 3 4 4 4 6% 8% 52%	2090
	21st to end	Night	14% 5% 2 5% 4 4 3 4 5% 5% 49%	2090
October	1st to 10th	Night	8% 4 2 6% 4 3 3 4 4 7% 54%	2090
	11th to 20th	Night	14% 6% 2 5% 4 3 4 4 5% 7% 46%	2250
	21st to end	Night	18% 8% 2 5% 4 4 4 3 4 5% 42%	2635
November	1st to 10th	Night	14% 7% 2 6% 3 3 4 3 5% 6% 48%	2536
	11th to 20th	Night	16% 9% 3 7% 4 3 3 3 5% 6% 40%	2600
	21st to end	Night	19% 13% 3 5% 5% 4 4 3 4 6% 34%	2600
December	1st to 10th	Night	18% 12% 4 7% 4 4 3 2 4 5% 37%	4250
	11th to 20th	Night	20% 14% 6% 9% 4 4 3 3 4 6% 28%	4822
	21st to end	Night	23% 19% 5% 10% 5% 5% 4 3 4 5% 17%	6490

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	63% 1 9% 19% 8%	4057
	11th to 20th	Day	60% 2 5% 18% 13% 2	4060
	21st to end	Day	62% 2 7% 21% 6% 3	4466
February	1st to 10th	Day	56% 3 8% 21% 10% 2	1910
	11th to 20th	Day	56% 2 8% 20% 12% 1	1958
	21st to end	Day	54% 3 9% 22% 11% 2	1650
March	1st to 10th	Day	54% 3 6% 19% 14% 5%	4526
	11th to 20th	Day	43% 3 8% 28% 16% 2	4980
	21st to end	Day	49% 3 11% 22% 12% 2	5465
April	1st to 10th	Day	47% 4 10% 24% 14% 2	2349
	11th to 20th	Day	45% 3 9% 24% 16% 3	2427
	21st to end	Day	48% 3 11% 23% 12% 2	2600
May	1st to 10th	Day	54% 3 11% 19% 11% 1	5897
	11th to 20th	Day	51% 3 11% 24% 11%	5865
	21st to end	Day	46% 5% 12% 22% 13% 1	6447
June	1st to 10th	Day	40% 5% 11% 25% 18% 2	2600
	11th to 20th	Day	38% 6% 14% 24% 18% 2	2736
	21st to end	Day	39% 6% 13% 23% 15% 4	2800
July	1st to 10th	Day	42% 4 10% 23% 20% 2	4442
	11th to 20th	Day	32% 4 11% 33% 18% 1	4122
	21st to end	Day	50% 5% 11% 19% 12% 2	4324
August	1st to 10th	Day	34% 4 14% 35% 12% 1	4091
	11th to 20th	Day	37% 4 10% 33% 15% 1	4083
	21st to end	Day	28% 4 14% 30% 21% 3	4195
September	1st to 10th	Day	38% 3 10% 23% 20% 6%	2157
	11th to 20th	Day	32% 4 12% 26% 23% 3	2090
	21st to end	Day	39% 3 9% 26% 20% 2	2090
October	1st to 10th	Day	23% 2 7% 32% 33% 2	3480
	11th to 20th	Day	30% 3 7% 30% 28% 2	3182
	21st to end	Day	35% 2 10% 28% 23% 3	3210
November	1st to 10th	Day	34% 3 8% 30% 21% 3	1762
	11th to 20th	Day	47% 3 6% 23% 17% 3	1800
	21st to end	Day	49% 3 9% 23% 15% 1	1800
December	1st to 10th	Day	51% 2 8% 25% 13%	2930
	11th to 20th	Day	61% 3 7% 20% 9% 1	3370
	21st to end	Day	68% 2 9% 14% 6% 1	4466
January	1st to 10th	Night	67% 3 7% 16% 8%	5889
	11th to 20th	Night	66% 2 7% 14% 9% 3	5900
	21st to end	Night	56% 2 6% 23% 11% 1	6490
February	1st to 10th	Night	59% 2 10% 20% 8% 1	2485
	11th to 20th	Night	56% 3 8% 21% 12% 1	2339
	21st to end	Night	57% 2 10% 18% 12% 2	1980
March	1st to 10th	Night	52% 2 5% 27% 12% 3	5327
	11th to 20th	Night	40% 3 9% 29% 18% 1	4980
	21st to end	Night	53% 3 6% 25% 11% 1	5467
April	1st to 10th	Night	45% 4 11% 24% 14% 2	2069
	11th to 20th	Night	42% 2 10% 22% 18% 6%	1922
	21st to end	Night	45% 3 12% 25% 13% 3	1800
May	1st to 10th	Night	55% 4 10% 20% 8% 2	4060
	11th to 20th	Night	47% 6% 13% 24% 9% 1	4033
	21st to end	Night	42% 4 16% 23% 12% 3	4429
June	1st to 10th	Night	31% 5% 14% 27% 21% 3	1800
	11th to 20th	Night	32% 5% 15% 24% 21% 4	1656
	21st to end	Night	30% 5% 18% 25% 17% 5%	1600
July	1st to 10th	Night	34% 5% 12% 24% 20% 5%	2530
	11th to 20th	Night	30% 3 12% 33% 20% 2	2713
	21st to end	Night	44% 4 12% 22% 13% 4	2988
August	1st to 10th	Night	33% 4 14% 34% 12% 2	2814
	11th to 20th	Night	35% 5% 11% 30% 18% 1	2812
	21st to end	Night	20% 3 16% 36% 22% 4	3443
September	1st to 10th	Night	31% 4 11% 26% 20% 7%	2004
	11th to 20th	Night	30% 4 11% 26% 27% 3	2090
	21st to end	Night	37% 3 8% 23% 25% 3	2090
October	1st to 10th	Night	23% 2 6% 26% 39% 3	3480
	11th to 20th	Night	27% 3 8% 27% 33% 2	3736
	21st to end	Night	33% 2 7% 23% 29% 5%	4335
November	1st to 10th	Night	38% 3 9% 24% 23% 4	2536
	11th to 20th	Night	46% 3 8% 21% 20% 4	2600
	21st to end	Night	52% 3 9% 22% 13% 1	2600
December	1st to 10th	Night	51% 2 11% 24% 12%	4250
	11th to 20th	Night	59% 2 11% 19% 9% 1	4824
	21st to end	Night	71% 2 8% 14% 4	6490

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	30% 21% 32% 15% 2	300
	11th to 20th	Day	33% 24% 31% 10% 1	300
	21st to end	Day	33% 20% 33% 12% 2	330
February	1st to 10th	Day	32% 23% 34% 9% 2	300
	11th to 20th	Day	38% 25% 28% 7% 1 1	300
	21st to end	Day	34% 18% 39% 8% 1	249
March	1st to 10th	Day	31% 25% 30% 12% 2	320
	11th to 20th	Day	31% 20% 30% 14% 5% 1	500
	21st to end	Day	35% 17% 29% 15% 4	550
April	1st to 10th	Day	29% 16% 29% 16% 9% 1	500
	11th to 20th	Day	26% 18% 28% 18% 7% 3	492
	21st to end	Day	25% 15% 35% 16% 7% 2	500
May	1st to 10th	Day	27% 12% 34% 16% 8% 4	503
	11th to 20th	Day	23% 11% 29% 21% 10% 5%	527
	21st to end	Day	16% 8% 29% 26% 14% 8%	573
June	1st to 10th	Day	16% 8% 24% 29% 17% 6%	530
	11th to 20th	Day	12% 4 26% 35% 15% 7%	666
	21st to end	Day	12% 7% 26% 27% 19% 8%	730
July	1st to 10th	Day	15% 3 18% 28% 21% 16%	697
	11th to 20th	Day	9% 3 23% 31% 22% 11%	529
	21st to end	Day	14% 3 20% 32% 18% 14%	532
August	1st to 10th	Day	14% 3 15% 32% 24% 13%	486
	11th to 20th	Day	12% 3 20% 34% 20% 10%	479
	21st to end	Day	9% 4 16% 32% 26% 14%	539
September	1st to 10th	Day	16% 4 15% 30% 26% 9%	490
	11th to 20th	Day	11% 2 18% 27% 29% 13%	490
	21st to end	Day	23% 7% 19% 24% 21% 7%	490
October	1st to 10th	Day	13% 7% 23% 32% 18% 8%	490
	11th to 20th	Day	20% 12% 31% 21% 11% 4	490
	21st to end	Day	26% 9% 37% 20% 8% 1	409
November	1st to 10th	Day	18% 14% 36% 22% 8% 3	300
	11th to 20th	Day	26% 15% 34% 18% 6% 1	300
	21st to end	Day	28% 15% 34% 18% 4 1	300
December	1st to 10th	Day	32% 16% 34% 13% 6%	300
	11th to 20th	Day	26% 20% 36% 14% 4	300
	21st to end	Day	34% 15% 37% 10% 4	330
January	1st to 10th	Night	25% 20% 30% 20% 4	800
	11th to 20th	Night	31% 20% 30% 17% 3	800
	21st to end	Night	29% 16% 31% 23% 2	880
February	1st to 10th	Night	30% 14% 33% 21% 2	800
	11th to 20th	Night	31% 18% 30% 20% 1	783
	21st to end	Night	31% 16% 32% 20% 1	660
March	1st to 10th	Night	27% 16% 29% 25% 4	800
	11th to 20th	Night	25% 16% 32% 21% 6% 1	800
	21st to end	Night	25% 13% 31% 25% 6%	880
April	1st to 10th	Night	21% 13% 32% 27% 7%	669
	11th to 20th	Night	19% 12% 31% 27% 10% 1	593
	21st to end	Night	20% 8% 36% 27% 9% 1	600
May	1st to 10th	Night	23% 8% 29% 28% 13% 1	600
	11th to 20th	Night	19% 5% 21% 34% 18% 2	591
	21st to end	Night	10% 4 21% 37% 24% 4	650
June	1st to 10th	Night	12% 3 20% 41% 23% 2	600
	11th to 20th	Night	12% 3 14% 43% 25% 4	600
	21st to end	Night	8% 3 22% 38% 27% 4	600
July	1st to 10th	Night	14% 2 11% 30% 32% 11%	570
	11th to 20th	Night	6% 2 13% 36% 39% 4	552
	21st to end	Night	13% 1 10% 39% 33% 4	624
August	1st to 10th	Night	10% 1 9% 35% 40% 5%	567
	11th to 20th	Night	9% 2 10% 40% 33% 5%	564
	21st to end	Night	6% 1 13% 33% 38% 8%	627
September	1st to 10th	Night	14% 3 11% 33% 34% 5%	674
	11th to 20th	Night	11% 3 14% 33% 35% 6%	760
	21st to end	Night	16% 7% 19% 30% 25% 3	760
October	1st to 10th	Night	11% 4 23% 33% 24% 4	760
	11th to 20th	Night	18% 10% 24% 31% 15% 1	760
	21st to end	Night	24% 9% 28% 26% 12% 1	836
November	1st to 10th	Night	18% 10% 27% 28% 16% 2	780
	11th to 20th	Night	22% 14% 28% 24% 11% 1	800
	21st to end	Night	28% 12% 25% 28% 8% 1	800
December	1st to 10th	Night	31% 12% 29% 22% 6%	800
	11th to 20th	Night	27% 14% 29% 24% 6% 1	800
	21st to end	Night	31% 15% 27% 23% 3	880

Page generated at 2025-07-03 01:30:13. Version ac07

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