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 2026-10-29.

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	14% 9% 3 8% 5% 5% 5% 4 6% 7% 36%	150110
	Night	14% 10% 3 8% 5% 4 4 3 5% 7% 37%	141999
Transparency	Day	46% 3 10% 24% 14% 2	153764
	Night	47% 3 10% 23% 15% 2	146417
Seeing	Day	21% 11% 27% 22% 13% 6%	17937
	Night	20% 10% 24% 28% 15% 2	27325

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% 16% 6% 10% 4 4 4 3 4 5% 26%	5258
	11th to 20th	Day	12% 14% 5% 14% 5% 5% 3 3 3 4 31%	5280
	21st to end	Day	20% 13% 5% 10% 6% 5% 5% 3 4 5% 24%	5780
February	1st to 10th	Day	19% 14% 4 9% 4 3 3 3 4 6% 32%	2006
	11th to 20th	Day	18% 11% 5% 9% 5% 4 3 3 4 5% 32%	2048
	21st to end	Day	18% 13% 5% 8% 4 3 3 3 4 6% 32%	1730
March	1st to 10th	Day	19% 14% 4 8% 4 3 3 3 4 5% 33%	4627
	11th to 20th	Day	14% 8% 3 6% 5% 4 4 4 6% 7% 39%	5090
	21st to end	Day	17% 9% 3 7% 5% 4 4 4 5% 7% 35%	5586
April	1st to 10th	Day	16% 9% 2 7% 5% 4 5% 4 5% 7% 37%	2466
	11th to 20th	Day	16% 9% 2 7% 4 3 4 3 5% 8% 39%	2550
	21st to end	Day	16% 8% 3 7% 4 5% 4 4 6% 6% 36%	2730
May	1st to 10th	Day	17% 9% 3 8% 5% 5% 5% 4 7% 8% 29%	7616
	11th to 20th	Day	17% 8% 3 7% 4 4 4 4 5% 7% 37%	7626
	21st to end	Day	17% 8% 3 9% 5% 5% 6% 5% 7% 8% 26%	8391
June	1st to 10th	Day	12% 5% 2 6% 5% 5% 5% 4 6% 8% 41%	2730
	11th to 20th	Day	9% 5% 2 7% 5% 5% 6% 4 6% 9% 41%	2873
	21st to end	Day	9% 7% 2 6% 5% 6% 6% 5% 6% 9% 39%	2940
July	1st to 10th	Day	9% 6% 3 7% 5% 5% 6% 4 7% 9% 39%	8280
	11th to 20th	Day	10% 6% 2 6% 5% 6% 6% 5% 7% 10% 37%	7824
	21st to end	Day	9% 7% 3 8% 6% 6% 7% 5% 8% 9% 32%	8340
August	1st to 10th	Day	10% 6% 2 7% 4 5% 5% 4 7% 10% 39%	6014
	11th to 20th	Day	9% 7% 3 9% 5% 5% 5% 6% 8% 10% 33%	5951
	21st to end	Day	4 4 2 4 3 4 4 4 6% 8% 57%	6110
September	1st to 10th	Day	13% 5% 2 5% 4 4 4 3 5% 6% 49%	2383
	11th to 20th	Day	8% 4 2 5% 4 4 4 4 7% 8% 49%	2310
	21st to end	Day	16% 6% 2 5% 3 3 3 3 4 6% 46%	2310
October	1st to 10th	Day	12% 4 2 5% 4 4 4 3 5% 7% 52%	2310
	11th to 20th	Day	14% 6% 2 5% 4 4 4 3 5% 7% 47%	2132
	21st to end	Day	19% 8% 3 5% 4 2 4 2 4 7% 41%	2139
November	1st to 10th	Day	10% 8% 2 5% 4 3 4 3 4 6% 52%	1852
	11th to 20th	Day	15% 11% 3 6% 4 4 4 3 4 6% 38%	1890
	21st to end	Day	18% 10% 4 8% 5% 3 3 3 4 6% 36%	1890
December	1st to 10th	Day	18% 12% 3 8% 4 3 4 2 3 4 38%	3020
	11th to 20th	Day	18% 14% 5% 8% 5% 5% 5% 3 4 5% 28%	3463
	21st to end	Day	22% 19% 5% 9% 5% 5% 4 3 4 5% 20%	4565
January	1st to 10th	Night	14% 15% 6% 12% 6% 5% 5% 3 5% 6% 23%	7635
	11th to 20th	Night	14% 15% 7% 14% 6% 4 4 3 4 5% 25%	7680
	21st to end	Night	18% 12% 4 8% 5% 4 4 3 4 5% 32%	8401
February	1st to 10th	Night	20% 13% 5% 8% 5% 4 4 3 4 5% 29%	2609
	11th to 20th	Night	20% 11% 3 10% 4 4 4 3 4 6% 31%	2458
	21st to end	Night	20% 14% 4 8% 4 3 4 3 5% 5% 31%	2076
March	1st to 10th	Night	19% 14% 2 7% 4 3 3 3 4 5% 36%	5446
	11th to 20th	Night	13% 8% 3 6% 4 4 4 4 6% 7% 43%	5090
	21st to end	Night	16% 10% 3 9% 5% 5% 4 4 5% 6% 33%	5588
April	1st to 10th	Night	14% 10% 2 6% 5% 4 5% 4 6% 7% 37%	2172
	11th to 20th	Night	15% 7% 3 6% 4 4 3 4 7% 7% 41%	2019
	21st to end	Night	16% 8% 3 7% 4 4 3 3 7% 8% 37%	1890
May	1st to 10th	Night	19% 9% 2 7% 5% 4 5% 4 6% 8% 32%	5237
	11th to 20th	Night	14% 7% 2 7% 5% 5% 5% 4 7% 9% 35%	5234
	21st to end	Night	16% 8% 3 8% 5% 5% 5% 4 7% 8% 32%	5761
June	1st to 10th	Night	8% 5% 2 4 5% 4 4 4 5% 10% 48%	1890
	11th to 20th	Night	8% 5% 2 6% 4 4 4 4 6% 10% 47%	1739
	21st to end	Night	7% 5% 2 5% 5% 4 4 5% 7% 11% 45%	1680
July	1st to 10th	Night	7% 6% 2 7% 5% 4 4 4 6% 9% 46%	4708
	11th to 20th	Night	8% 6% 3 7% 5% 5% 5% 5% 7% 9% 42%	5123
	21st to end	Night	9% 6% 2 7% 6% 5% 6% 5% 7% 9% 38%	5736
August	1st to 10th	Night	10% 7% 3 7% 5% 5% 5% 4 6% 9% 40%	4135
	11th to 20th	Night	10% 6% 3 8% 5% 5% 5% 4 7% 8% 39%	4095
	21st to end	Night	3 2 1 4 3 3 3 4 6% 10% 61%	4999
September	1st to 10th	Night	11% 5% 2 4 3 3 3 3 6% 7% 53%	2215
	11th to 20th	Night	8% 4 2 5% 3 4 4 4 6% 8% 52%	2310
	21st to end	Night	15% 5% 2 5% 4 4 3 4 5% 6% 48%	2310
October	1st to 10th	Night	8% 4 2 6% 4 3 3 4 4 7% 55%	2310
	11th to 20th	Night	14% 6% 2 5% 4 3 4 4 5% 6% 47%	2487
	21st to end	Night	18% 8% 2 5% 4 4 4 3 4 5% 43%	2875
November	1st to 10th	Night	13% 7% 2 6% 3 3 4 3 5% 6% 48%	2666
	11th to 20th	Night	16% 9% 2 7% 4 3 3 3 5% 6% 40%	2730
	21st to end	Night	19% 13% 3 6% 5% 4 4 3 4 6% 34%	2730
December	1st to 10th	Night	18% 12% 4 8% 4 4 3 2 4 5% 37%	4380
	11th to 20th	Night	20% 14% 6% 9% 4 4 3 3 4 6% 28%	4952
	21st to end	Night	23% 19% 5% 11% 5% 5% 4 3 4 5% 18%	6633

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	62% 1 11% 19% 7%	5259
	11th to 20th	Day	58% 2 6% 18% 15% 2	5280
	21st to end	Day	63% 2 7% 19% 6% 3	5780
February	1st to 10th	Day	55% 3 8% 23% 10% 1	2006
	11th to 20th	Day	56% 2 9% 21% 11% 1	2058
	21st to end	Day	54% 2 9% 22% 10% 2	1730
March	1st to 10th	Day	54% 3 6% 19% 14% 5%	4627
	11th to 20th	Day	44% 3 8% 28% 15% 2	5090
	21st to end	Day	49% 3 12% 22% 12% 2	5586
April	1st to 10th	Day	46% 4 11% 24% 14% 2	2466
	11th to 20th	Day	45% 3 10% 23% 16% 3	2550
	21st to end	Day	47% 3 11% 24% 12% 2	2730
May	1st to 10th	Day	52% 3 11% 22% 11% 1	7651
	11th to 20th	Day	47% 3 10% 24% 14%	7630
	21st to end	Day	53% 5% 10% 19% 11% 2	8405
June	1st to 10th	Day	40% 5% 11% 24% 19% 2	2730
	11th to 20th	Day	38% 5% 14% 23% 18% 2	2873
	21st to end	Day	39% 6% 13% 23% 14% 4	2940
July	1st to 10th	Day	41% 4 12% 25% 17% 1	8211
	11th to 20th	Day	41% 5% 12% 28% 13% 1	7752
	21st to end	Day	46% 4 11% 23% 14% 1	8156
August	1st to 10th	Day	40% 4 14% 29% 11% 2	6001
	11th to 20th	Day	44% 4 12% 28% 11% 1	5990
	21st to end	Day	25% 3 16% 35% 19% 2	6109
September	1st to 10th	Day	36% 3 10% 25% 20% 5%	2383
	11th to 20th	Day	32% 4 12% 26% 24% 3	2310
	21st to end	Day	40% 3 8% 25% 22% 3	2310
October	1st to 10th	Day	23% 2 7% 32% 34% 2	3700
	11th to 20th	Day	30% 3 7% 30% 28% 3	3385
	21st to end	Day	35% 2 9% 28% 23% 4	3389
November	1st to 10th	Day	35% 3 8% 30% 21% 3	1852
	11th to 20th	Day	47% 3 6% 24% 17% 3	1890
	21st to end	Day	50% 3 9% 23% 14% 1	1890
December	1st to 10th	Day	52% 2 8% 25% 13%	3020
	11th to 20th	Day	60% 3 7% 20% 9% 1	3460
	21st to end	Day	68% 2 9% 14% 6% 1	4565
January	1st to 10th	Night	63% 3 9% 18% 8%	7636
	11th to 20th	Night	63% 2 6% 15% 11% 3	7680
	21st to end	Night	56% 2 9% 22% 10% 1	8401
February	1st to 10th	Night	58% 2 10% 20% 8% 1	2609
	11th to 20th	Night	55% 3 8% 22% 11% 1	2459
	21st to end	Night	56% 2 10% 18% 11% 2	2076
March	1st to 10th	Night	52% 2 5% 26% 12% 3	5446
	11th to 20th	Night	40% 3 9% 29% 18% 1	5090
	21st to end	Night	53% 3 7% 25% 11% 1	5588
April	1st to 10th	Night	45% 4 11% 24% 14% 2	2172
	11th to 20th	Night	43% 3 11% 22% 17% 6%	2019
	21st to end	Night	44% 3 11% 25% 13% 3	1890
May	1st to 10th	Night	51% 3 11% 23% 10% 2	5264
	11th to 20th	Night	46% 5% 13% 23% 13% 1	5235
	21st to end	Night	49% 4 14% 20% 11% 3	5771
June	1st to 10th	Night	31% 5% 14% 26% 21% 3	1890
	11th to 20th	Night	33% 5% 14% 24% 20% 4	1739
	21st to end	Night	31% 5% 18% 25% 17% 5%	1680
July	1st to 10th	Night	37% 5% 12% 26% 18% 3	4670
	11th to 20th	Night	39% 4 12% 28% 15% 1	5075
	21st to end	Night	41% 4 13% 25% 15% 3	5606
August	1st to 10th	Night	41% 4 13% 27% 13% 2	4124
	11th to 20th	Night	41% 5% 14% 26% 13% 1	4122
	21st to end	Night	20% 3 17% 39% 20% 2	4999
September	1st to 10th	Night	30% 4 11% 26% 22% 6%	2215
	11th to 20th	Night	30% 4 10% 27% 26% 3	2310
	21st to end	Night	38% 3 8% 22% 25% 3	2310
October	1st to 10th	Night	24% 2 6% 26% 39% 3	3700
	11th to 20th	Night	27% 3 8% 26% 33% 3	3973
	21st to end	Night	34% 2 7% 23% 29% 6%	4575
November	1st to 10th	Night	37% 3 9% 24% 23% 4	2666
	11th to 20th	Night	45% 3 8% 22% 19% 3	2730
	21st to end	Night	53% 3 9% 22% 12% 1	2730
December	1st to 10th	Night	52% 2 11% 24% 12%	4380
	11th to 20th	Night	59% 2 11% 20% 8% 1	4954
	21st to end	Night	71% 2 8% 14% 5%	6633

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% 19% 34% 14% 2	330
	11th to 20th	Day	35% 25% 30% 9% 1	330
	21st to end	Day	34% 20% 33% 12% 1	363
February	1st to 10th	Day	31% 23% 34% 10% 3	330
	11th to 20th	Day	38% 25% 28% 8% 1 1	330
	21st to end	Day	33% 18% 39% 8% 1	273
March	1st to 10th	Day	32% 25% 30% 11% 2	351
	11th to 20th	Day	32% 19% 30% 14% 4 1	540
	21st to end	Day	34% 17% 30% 15% 4	594
April	1st to 10th	Day	29% 16% 30% 16% 8% 1	540
	11th to 20th	Day	25% 19% 29% 17% 7% 2	532
	21st to end	Day	24% 15% 36% 17% 7% 2	540
May	1st to 10th	Day	26% 15% 33% 15% 7% 3	543
	11th to 20th	Day	22% 12% 30% 22% 10% 5%	567
	21st to end	Day	18% 8% 28% 26% 13% 7%	617
June	1st to 10th	Day	16% 8% 24% 28% 17% 6%	570
	11th to 20th	Day	13% 5% 28% 33% 15% 7%	713
	21st to end	Day	13% 7% 26% 28% 19% 8%	780
July	1st to 10th	Day	14% 3 17% 28% 21% 16%	771
	11th to 20th	Day	9% 3 22% 31% 23% 12%	614
	21st to end	Day	12% 3 20% 32% 19% 13%	620
August	1st to 10th	Day	13% 3 16% 31% 24% 12%	566
	11th to 20th	Day	12% 3 20% 35% 20% 10%	559
	21st to end	Day	8% 4 16% 32% 27% 13%	627
September	1st to 10th	Day	15% 4 16% 29% 27% 9%	570
	11th to 20th	Day	10% 2 16% 28% 30% 13%	570
	21st to end	Day	22% 7% 19% 24% 21% 7%	570
October	1st to 10th	Day	13% 6% 24% 32% 19% 8%	570
	11th to 20th	Day	20% 11% 31% 22% 12% 5%	570
	21st to end	Day	26% 10% 34% 20% 8% 2	474
November	1st to 10th	Day	19% 15% 35% 21% 7% 3	330
	11th to 20th	Day	28% 15% 32% 18% 5% 1	330
	21st to end	Day	30% 14% 35% 17% 4 1	330
December	1st to 10th	Day	31% 17% 35% 12% 5%	330
	11th to 20th	Day	26% 21% 35% 13% 4	330
	21st to end	Day	34% 15% 37% 10% 4	363
January	1st to 10th	Night	25% 20% 30% 21% 4	840
	11th to 20th	Night	31% 20% 30% 17% 2	840
	21st to end	Night	28% 16% 31% 22% 2	924
February	1st to 10th	Night	29% 14% 32% 23% 2	840
	11th to 20th	Night	31% 17% 31% 20% 1	823
	21st to end	Night	31% 16% 33% 20% 1	692
March	1st to 10th	Night	28% 16% 29% 24% 4	840
	11th to 20th	Night	25% 16% 32% 21% 5%	840
	21st to end	Night	24% 13% 32% 25% 6%	924
April	1st to 10th	Night	21% 13% 32% 27% 7%	702
	11th to 20th	Night	19% 12% 32% 26% 10% 1	623
	21st to end	Night	20% 8% 36% 27% 9% 1	630
May	1st to 10th	Night	23% 7% 29% 28% 12% 1	630
	11th to 20th	Night	19% 5% 22% 34% 18% 2	621
	21st to end	Night	11% 4 21% 37% 23% 4	683
June	1st to 10th	Night	12% 3 20% 40% 23% 2	630
	11th to 20th	Night	12% 3 16% 43% 23% 4	630
	21st to end	Night	8% 3 21% 38% 26% 3	630
July	1st to 10th	Night	14% 3 11% 29% 33% 10%	615
	11th to 20th	Night	7% 2 12% 37% 39% 4	612
	21st to end	Night	12% 1 10% 39% 33% 4	690
August	1st to 10th	Night	10% 1 9% 36% 39% 5%	627
	11th to 20th	Night	10% 2 9% 40% 33% 5%	624
	21st to end	Night	6% 1 12% 36% 37% 8%	693
September	1st to 10th	Night	13% 3 12% 34% 34% 5%	745
	11th to 20th	Night	10% 3 13% 33% 35% 6%	840
	21st to end	Night	17% 6% 19% 31% 25% 3	840
October	1st to 10th	Night	10% 4 23% 35% 24% 4	840
	11th to 20th	Night	18% 9% 23% 33% 16% 1	840
	21st to end	Night	23% 9% 27% 26% 13% 1	913
November	1st to 10th	Night	18% 9% 27% 28% 15% 2	820
	11th to 20th	Night	23% 15% 28% 24% 10% 1	840
	21st to end	Night	28% 12% 24% 27% 8% 1	840
December	1st to 10th	Night	30% 12% 30% 22% 5%	840
	11th to 20th	Night	27% 13% 30% 24% 6% 1	840
	21st to end	Night	32% 15% 28% 23% 3	924

Page generated at 2026-10-26 04:37:46. Version ac07

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