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 2024-11-03.

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% 37%	101709
	Night	15% 10% 3 7% 4 4 4 3 5% 7% 38%	97240
Transparency	Day	46% 4 10% 24% 14% 2	101514
	Night	46% 3 10% 24% 15% 2	97105
Seeing	Day	21% 11% 27% 23% 13% 6%	15245
	Night	20% 10% 24% 28% 16% 2	24734

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% 17% 6% 10% 4 4 4 3 4 5% 26%	2836
	11th to 20th	Day	17% 14% 6% 13% 6% 5% 3 3 4 4 26%	2840
	21st to end	Day	29% 17% 7% 7% 4 3 3 2 4 4 21%	3124
February	1st to 10th	Day	19% 14% 4 9% 5% 3 3 3 4 6% 31%	1814
	11th to 20th	Day	17% 11% 4 9% 5% 4 3 3 4 5% 32%	1848
	21st to end	Day	19% 14% 4 8% 4 3 3 3 4 6% 31%	1570
March	1st to 10th	Day	24% 15% 3 7% 4 3 3 3 4 5% 29%	3152
	11th to 20th	Day	15% 8% 2 6% 5% 4 3 4 6% 7% 42%	3480
	21st to end	Day	17% 10% 2 7% 5% 4 4 3 5% 6% 37%	3815
April	1st to 10th	Day	16% 9% 2 8% 5% 4 5% 4 5% 6% 37%	2231
	11th to 20th	Day	17% 9% 2 6% 4 3 4 3 4 8% 39%	2304
	21st to end	Day	17% 8% 3 7% 4 5% 4 4 6% 6% 35%	2470
May	1st to 10th	Day	21% 9% 3 8% 5% 4 4 4 6% 7% 29%	4082
	11th to 20th	Day	21% 8% 2 6% 4 4 4 3 5% 7% 36%	4081
	21st to end	Day	10% 6% 3 8% 5% 6% 6% 5% 8% 10% 33%	4476
June	1st to 10th	Day	13% 5% 2 6% 5% 5% 5% 4 6% 8% 40%	2470
	11th to 20th	Day	9% 5% 2 6% 5% 5% 6% 4 6% 9% 43%	2599
	21st to end	Day	9% 7% 2 6% 5% 6% 6% 5% 6% 9% 39%	2660
July	1st to 10th	Day	12% 7% 3 6% 5% 5% 5% 4 6% 8% 39%	4440
	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% 9% 2 5% 4 2 4 3 4 7% 40%	1960
November	1st to 10th	Day	9% 8% 2 5% 4 3 4 3 4 5% 54%	1690
	11th to 20th	Day	15% 12% 3 6% 4 3 4 3 5% 6% 39%	1710
	21st to end	Day	18% 10% 3 7% 5% 3 4 3 4 6% 38%	1710
December	1st to 10th	Day	22% 15% 4 8% 5% 4 5% 2 4 4 28%	1710
	11th to 20th	Day	16% 14% 5% 8% 6% 4 4 3 4 5% 31%	2153
	21st to end	Day	21% 20% 5% 9% 5% 5% 4 3 4 5% 19%	3124
January	1st to 10th	Night	16% 18% 6% 11% 5% 4 5% 3 4 5% 23%	4109
	11th to 20th	Night	17% 17% 6% 13% 6% 4 3 3 3 5% 24%	4120
	21st to end	Night	27% 17% 5% 7% 3 3 3 2 3 5% 24%	4532
February	1st to 10th	Night	22% 13% 5% 8% 4 4 4 3 5% 5% 29%	2361
	11th to 20th	Night	19% 11% 3 10% 4 4 4 3 5% 6% 32%	2218
	21st to end	Night	22% 15% 4 8% 4 3 4 3 5% 4 30%	1884
March	1st to 10th	Night	22% 14% 3 6% 4 3 4 3 4 6% 31%	3701
	11th to 20th	Night	13% 9% 2 6% 4 3 4 3 5% 7% 44%	3480
	21st to end	Night	16% 9% 3 7% 5% 5% 4 3 5% 5% 39%	3817
April	1st to 10th	Night	13% 9% 2 6% 5% 4 5% 4 6% 7% 37%	1966
	11th to 20th	Night	15% 7% 3 6% 4 4 3 3 7% 6% 42%	1825
	21st to end	Night	16% 8% 3 7% 4 4 4 3 6% 8% 37%	1710
May	1st to 10th	Night	21% 12% 3 8% 6% 4 4 3 6% 7% 27%	2813
	11th to 20th	Night	19% 6% 2 4 4 5% 4 3 6% 8% 38%	2812
	21st to end	Night	9% 6% 2 6% 4 4 4 4 7% 9% 46%	3079
June	1st to 10th	Night	8% 5% 2 4 5% 5% 4 4 5% 10% 48%	1710
	11th to 20th	Night	7% 4 2 6% 4 4 4 4 6% 10% 48%	1573
	21st to end	Night	6% 4 2 4 5% 5% 4 5% 7% 12% 46%	1520
July	1st to 10th	Night	9% 6% 2 5% 4 4 4 4 6% 8% 48%	2530
	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	13% 7% 2 6% 3 3 4 3 5% 5% 49%	2433
	11th to 20th	Night	16% 9% 3 7% 4 3 3 3 5% 6% 40%	2470
	21st to end	Night	19% 12% 3 5% 5% 5% 3 3 4 6% 36%	2470
December	1st to 10th	Night	21% 13% 4 8% 5% 4 3 3 5% 5% 29%	2470
	11th to 20th	Night	18% 12% 6% 8% 4 4 3 2 4 6% 31%	3042
	21st to end	Night	21% 20% 5% 10% 5% 5% 4 3 4 5% 18%	4532

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	61% 2 11% 15% 10%	2837
	11th to 20th	Day	64% 1 7% 18% 9% 1	2840
	21st to end	Day	68% 2 7% 18% 4 1	3124
February	1st to 10th	Day	56% 3 8% 21% 11% 2	1814
	11th to 20th	Day	55% 2 9% 21% 11% 2	1858
	21st to end	Day	55% 3 9% 21% 10% 2	1570
March	1st to 10th	Day	58% 3 7% 20% 9% 3	3152
	11th to 20th	Day	42% 3 10% 27% 17% 1	3480
	21st to end	Day	48% 3 11% 25% 13% 1	3815
April	1st to 10th	Day	46% 4 10% 24% 14% 2	2231
	11th to 20th	Day	45% 3 9% 23% 17% 3	2304
	21st to end	Day	47% 3 12% 23% 12% 2	2470
May	1st to 10th	Day	54% 3 11% 22% 8% 1	4120
	11th to 20th	Day	48% 4 12% 23% 13% 1	4085
	21st to end	Day	43% 6% 13% 19% 17% 2	4489
June	1st to 10th	Day	40% 5% 11% 25% 17% 2	2470
	11th to 20th	Day	37% 6% 14% 24% 18% 2	2599
	21st to end	Day	39% 6% 13% 23% 14% 4	2660
July	1st to 10th	Day	42% 4 11% 22% 19% 2	4371
	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	33% 3 9% 27% 24% 3	2090
	11th to 20th	Day	39% 3 7% 27% 20% 3	1929
	21st to end	Day	45% 2 10% 24% 16% 2	1960
November	1st to 10th	Day	34% 3 8% 30% 22% 4	1690
	11th to 20th	Day	46% 3 7% 23% 18% 3	1710
	21st to end	Day	48% 3 9% 23% 15% 1	1710
December	1st to 10th	Day	62% 2 9% 19% 8%	1710
	11th to 20th	Day	57% 3 7% 20% 13% 1	2150
	21st to end	Day	69% 2 8% 12% 8% 1	3124
January	1st to 10th	Night	63% 3 8% 16% 9%	4109
	11th to 20th	Night	66% 2 8% 15% 8% 1	4120
	21st to end	Night	65% 2 7% 18% 7% 1	4532
February	1st to 10th	Night	58% 3 10% 20% 8% 1	2361
	11th to 20th	Night	54% 3 8% 22% 12% 1	2219
	21st to end	Night	58% 2 10% 17% 10% 3	1884
March	1st to 10th	Night	56% 2 6% 24% 11% 1	3701
	11th to 20th	Night	40% 4 10% 28% 17% 1	3480
	21st to end	Night	48% 3 8% 28% 12% 1	3817
April	1st to 10th	Night	43% 4 11% 25% 14% 2	1966
	11th to 20th	Night	42% 2 10% 21% 19% 6%	1825
	21st to end	Night	45% 3 12% 24% 13% 3	1710
May	1st to 10th	Night	57% 4 10% 20% 8% 2	2840
	11th to 20th	Night	44% 6% 13% 27% 9% 1	2813
	21st to end	Night	33% 5% 15% 27% 16% 4	3087
June	1st to 10th	Night	31% 5% 14% 27% 20% 3	1710
	11th to 20th	Night	31% 5% 15% 24% 21% 4	1573
	21st to end	Night	30% 5% 18% 25% 17% 5%	1520
July	1st to 10th	Night	35% 5% 12% 24% 19% 5%	2490
	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	30% 3 10% 29% 25% 4	2090
	11th to 20th	Night	37% 4 8% 26% 23% 2	2250
	21st to end	Night	44% 3 8% 23% 19% 3	2635
November	1st to 10th	Night	37% 3 9% 23% 25% 4	2433
	11th to 20th	Night	45% 3 8% 21% 20% 4	2470
	21st to end	Night	51% 2 9% 23% 13% 1	2470
December	1st to 10th	Night	57% 2 10% 20% 10% 1	2470
	11th to 20th	Night	55% 3 9% 22% 11% 1	3044
	21st to end	Night	69% 2 8% 14% 6%	4532

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	28% 21% 34% 15% 2	270
	11th to 20th	Day	34% 21% 33% 11% 1	270
	21st to end	Day	35% 19% 32% 12% 2	297
February	1st to 10th	Day	31% 24% 33% 10% 3	270
	11th to 20th	Day	37% 24% 29% 8% 1 1	270
	21st to end	Day	37% 17% 37% 8% 1	225
March	1st to 10th	Day	30% 25% 30% 12% 1	289
	11th to 20th	Day	30% 20% 30% 14% 5% 1	460
	21st to end	Day	34% 16% 30% 15% 5%	506
April	1st to 10th	Day	28% 16% 29% 17% 9% 1	460
	11th to 20th	Day	26% 18% 28% 18% 8% 3	452
	21st to end	Day	25% 16% 35% 15% 7% 2	460
May	1st to 10th	Day	27% 12% 34% 15% 8% 4	463
	11th to 20th	Day	23% 10% 29% 22% 10% 6%	487
	21st to end	Day	14% 8% 28% 27% 15% 8%	529
June	1st to 10th	Day	16% 8% 24% 29% 17% 7%	490
	11th to 20th	Day	12% 4 26% 35% 15% 8%	619
	21st to end	Day	13% 7% 27% 28% 18% 8%	680
July	1st to 10th	Day	15% 3 18% 27% 20% 16%	671
	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% 8% 37% 20% 8% 1	409
November	1st to 10th	Day	17% 13% 34% 24% 8% 4	276
	11th to 20th	Day	26% 16% 31% 20% 6% 1	270
	21st to end	Day	27% 14% 34% 19% 4 1	270
December	1st to 10th	Day	32% 15% 33% 13% 6%	270
	11th to 20th	Day	24% 21% 36% 14% 5%	270
	21st to end	Day	34% 15% 37% 9% 5%	297
January	1st to 10th	Night	25% 20% 30% 20% 4	760
	11th to 20th	Night	31% 19% 30% 17% 3	760
	21st to end	Night	29% 16% 30% 23% 2	836
February	1st to 10th	Night	30% 14% 31% 22% 2	760
	11th to 20th	Night	30% 17% 31% 21% 1	743
	21st to end	Night	32% 15% 32% 19% 1	628
March	1st to 10th	Night	26% 16% 29% 24% 4	760
	11th to 20th	Night	24% 17% 32% 21% 6% 1	760
	21st to end	Night	25% 12% 31% 25% 6%	836
April	1st to 10th	Night	20% 14% 31% 28% 7%	636
	11th to 20th	Night	19% 12% 31% 27% 10% 1	563
	21st to end	Night	20% 8% 36% 27% 8% 1	570
May	1st to 10th	Night	22% 8% 29% 27% 13% 1	570
	11th to 20th	Night	19% 5% 22% 33% 19% 2	561
	21st to end	Night	9% 3 20% 38% 25% 4	617
June	1st to 10th	Night	12% 2 20% 41% 23% 2	570
	11th to 20th	Night	11% 2 15% 43% 25% 4	570
	21st to end	Night	8% 3 23% 38% 25% 3	570
July	1st to 10th	Night	14% 3 12% 30% 31% 11%	555
	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% 9% 27% 28% 16% 2	749
	11th to 20th	Night	22% 14% 28% 24% 11% 1	760
	21st to end	Night	27% 11% 25% 28% 8% 1	760
December	1st to 10th	Night	31% 13% 29% 22% 6%	760
	11th to 20th	Night	26% 13% 29% 24% 6% 1	760
	21st to end	Night	31% 15% 28% 23% 3	836

Page generated at 2024-10-31 03:39:22. Version ac07

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