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 2024-03-23.

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 6% 5% 3 4 5% 5% 7% 36%	79592
	Night	16% 10% 4 6% 5% 3 4 4 5% 7% 37%	80300
Transparency	Day	47% 4 11% 22% 14% 2	79308
	Night	47% 3 10% 22% 14% 2	80104
Seeing	Day	21% 11% 27% 22% 13% 6%	14325
	Night	20% 10% 24% 28% 15% 2	23988

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% 8% 5% 3 4 4 4 5% 26%	2836
	11th to 20th	Day	18% 13% 6% 11% 7% 4 3 4 4 4 26%	2840
	21st to end	Day	29% 16% 7% 6% 5% 2 3 3 3 4 21%	3124
February	1st to 10th	Day	19% 13% 4 8% 5% 2 3 4 4 6% 31%	1814
	11th to 20th	Day	18% 11% 5% 8% 6% 3 4 4 4 5% 33%	1848
	21st to end	Day	19% 13% 4 7% 5% 3 4 3 4 6% 31%	1570
March	1st to 10th	Day	20% 11% 4 6% 5% 3 3 5% 4 5% 35%	1919
	11th to 20th	Day	19% 10% 3 7% 6% 3 3 5% 5% 6% 34%	2090
	21st to end	Day	22% 11% 3 7% 6% 3 4 4 5% 6% 30%	2200
April	1st to 10th	Day	15% 8% 3 6% 6% 3 5% 5% 5% 6% 38%	2113
	11th to 20th	Day	18% 8% 2 5% 5% 2 4 4 4 7% 40%	2181
	21st to end	Day	18% 8% 3 6% 5% 4 4 5% 6% 6% 35%	2340
May	1st to 10th	Day	21% 7% 3 6% 6% 3 5% 4 5% 6% 33%	2340
	11th to 20th	Day	20% 8% 3 6% 5% 3 4 5% 4 7% 34%	2301
	21st to end	Day	8% 6% 3 7% 7% 4 7% 7% 7% 10% 35%	2531
June	1st to 10th	Day	13% 4 2 5% 5% 3 6% 5% 6% 8% 41%	2340
	11th to 20th	Day	10% 4 2 5% 5% 4 5% 6% 6% 9% 42%	2462
	21st to end	Day	10% 6% 3 5% 5% 5% 6% 7% 6% 9% 39%	2520
July	1st to 10th	Day	13% 5% 3 5% 6% 4 6% 6% 6% 8% 38%	2520
	11th to 20th	Day	8% 4 3 6% 5% 4 7% 6% 7% 11% 39%	2386
	21st to end	Day	10% 5% 3 5% 5% 4 5% 6% 6% 9% 42%	2547
August	1st to 10th	Day	9% 5% 2 5% 5% 4 6% 5% 6% 10% 43%	2327
	11th to 20th	Day	7% 5% 3 7% 6% 3 5% 7% 7% 10% 38%	2303
	21st to end	Day	7% 5% 3 5% 5% 3 4 5% 6% 9% 46%	2392
September	1st to 10th	Day	14% 5% 2 4 6% 2 5% 4 5% 6% 46%	2044
	11th to 20th	Day	9% 4 2 4 5% 3 5% 5% 7% 8% 48%	1980
	21st to end	Day	15% 5% 2 4 4 3 3 4 4 7% 48%	1980
October	1st to 10th	Day	12% 4 2 5% 5% 3 4 4 5% 7% 49%	1980
	11th to 20th	Day	15% 7% 3 4 5% 3 4 5% 4 7% 45%	1828
	21st to end	Day	21% 9% 3 4 5% 2 3 4 4 7% 39%	1857
November	1st to 10th	Day	9% 7% 3 4 4 2 4 4 4 5% 53%	1672
	11th to 20th	Day	15% 10% 4 5% 5% 2 4 4 4 6% 39%	1710
	21st to end	Day	18% 9% 4 7% 5% 2 3 4 4 6% 38%	1710
December	1st to 10th	Day	22% 13% 5% 7% 6% 3 5% 3 4 4 28%	1710
	11th to 20th	Day	16% 13% 5% 7% 6% 4 4 4 3 5% 31%	2153
	21st to end	Day	22% 19% 5% 7% 6% 4 4 4 3 5% 20%	3124
January	1st to 10th	Night	16% 18% 6% 9% 6% 3 4 5% 5% 5% 23%	4109
	11th to 20th	Night	17% 16% 6% 12% 7% 3 3 3 3 5% 24%	4120
	21st to end	Night	27% 16% 5% 7% 4 3 4 3 3 5% 24%	4532
February	1st to 10th	Night	22% 12% 5% 7% 5% 3 4 4 5% 5% 29%	2361
	11th to 20th	Night	19% 10% 4 9% 5% 3 4 4 5% 6% 32%	2218
	21st to end	Night	22% 14% 4 7% 5% 2 4 4 5% 4 30%	1884
March	1st to 10th	Night	19% 10% 4 6% 5% 3 4 3 4 5% 38%	2261
	11th to 20th	Night	18% 10% 3 6% 4 3 4 5% 5% 7% 36%	2090
	21st to end	Night	18% 10% 4 6% 6% 3 4 4 5% 6% 33%	2201
April	1st to 10th	Night	13% 8% 3 5% 5% 3 5% 6% 6% 8% 38%	1863
	11th to 20th	Night	15% 7% 3 5% 5% 3 4 4 6% 7% 42%	1728
	21st to end	Night	17% 7% 3 6% 5% 3 4 4 5% 8% 37%	1620
May	1st to 10th	Night	17% 8% 4 6% 6% 3 3 4 6% 8% 35%	1620
	11th to 20th	Night	16% 6% 2 6% 5% 4 6% 5% 5% 8% 37%	1592
	21st to end	Night	8% 5% 2 5% 5% 3 5% 6% 9% 11% 42%	1744
June	1st to 10th	Night	7% 4 2 3 5% 4 5% 5% 5% 10% 49%	1620
	11th to 20th	Night	8% 4 3 5% 5% 3 4 4 5% 10% 49%	1491
	21st to end	Night	6% 4 2 4 5% 3 4 6% 7% 12% 46%	1440
July	1st to 10th	Night	11% 5% 2 5% 5% 3 5% 5% 7% 8% 45%	1440
	11th to 20th	Night	6% 4 2 5% 5% 3 4 5% 7% 10% 49%	1570
	21st to end	Night	9% 5% 1 5% 5% 3 4 5% 4 8% 50%	1771
August	1st to 10th	Night	7% 4 2 5% 4 3 5% 5% 8% 9% 48%	1611
	11th to 20th	Night	8% 4 2 6% 6% 4 4 5% 6% 9% 46%	1598
	21st to end	Night	6% 3 2 4 3 2 4 4 5% 10% 56%	1961
September	1st to 10th	Night	12% 5% 2 4 3 3 4 4 6% 7% 51%	1898
	11th to 20th	Night	9% 3 2 4 4 3 5% 5% 6% 8% 52%	1980
	21st to end	Night	13% 4 2 4 4 3 4 5% 5% 6% 51%	1980
October	1st to 10th	Night	8% 4 2 5% 5% 3 3 5% 4 7% 54%	1980
	11th to 20th	Night	15% 6% 2 4 5% 2 5% 5% 5% 7% 45%	2131
	21st to end	Night	19% 8% 2 5% 4 3 4 4 4 5% 41%	2496
November	1st to 10th	Night	14% 6% 2 5% 4 3 4 4 5% 5% 49%	2406
	11th to 20th	Night	16% 8% 3 7% 5% 2 4 4 5% 6% 40%	2470
	21st to end	Night	19% 11% 3 4 5% 3 4 4 4 6% 36%	2470
December	1st to 10th	Night	21% 12% 5% 7% 5% 3 4 3 5% 6% 29%	2470
	11th to 20th	Night	18% 12% 6% 7% 5% 3 4 3 4 6% 32%	3042
	21st to end	Night	21% 19% 5% 9% 6% 4 4 4 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	52% 2 9% 24% 12% 1	1919
	11th to 20th	Day	52% 4 10% 20% 13% 2	2090
	21st to end	Day	56% 3 10% 21% 9% 2	2200
April	1st to 10th	Day	45% 4 10% 25% 14% 2	2113
	11th to 20th	Day	45% 3 9% 22% 17% 4	2181
	21st to end	Day	48% 3 11% 24% 11% 2	2340
May	1st to 10th	Day	51% 4 12% 23% 9% 2	2340
	11th to 20th	Day	50% 5% 12% 20% 12% 1	2305
	21st to end	Day	42% 7% 16% 21% 13% 1	2531
June	1st to 10th	Day	39% 5% 11% 26% 17% 2	2340
	11th to 20th	Day	37% 6% 14% 24% 17% 2	2462
	21st to end	Day	39% 6% 14% 23% 14% 4	2520
July	1st to 10th	Day	42% 5% 12% 21% 18% 2	2451
	11th to 20th	Day	37% 6% 14% 24% 17% 2	2314
	21st to end	Day	38% 5% 13% 27% 14% 3	2405
August	1st to 10th	Day	35% 6% 15% 28% 15% 1	2314
	11th to 20th	Day	38% 5% 13% 27% 15% 1	2303
	21st to end	Day	34% 4 15% 23% 18% 5%	2392
September	1st to 10th	Day	39% 4 10% 23% 18% 6%	2044
	11th to 20th	Day	33% 4 12% 26% 23% 2	1980
	21st to end	Day	37% 3 9% 27% 22% 2	1980
October	1st to 10th	Day	35% 4 10% 26% 23% 3	1980
	11th to 20th	Day	40% 3 8% 26% 19% 3	1828
	21st to end	Day	47% 2 10% 24% 15% 2	1857
November	1st to 10th	Day	34% 3 8% 29% 22% 4	1672
	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	50% 3 7% 23% 16% 2	2261
	11th to 20th	Night	48% 4 10% 23% 13% 2	2090
	21st to end	Night	52% 4 10% 23% 9% 2	2201
April	1st to 10th	Night	42% 5% 11% 26% 14% 2	1863
	11th to 20th	Night	42% 2 10% 20% 19% 6%	1728
	21st to end	Night	46% 3 12% 24% 13% 3	1620
May	1st to 10th	Night	48% 5% 12% 22% 11% 3	1620
	11th to 20th	Night	45% 6% 14% 20% 13% 2	1593
	21st to end	Night	33% 6% 19% 22% 17% 3	1745
June	1st to 10th	Night	30% 5% 14% 27% 20% 3	1620
	11th to 20th	Night	31% 5% 15% 24% 20% 4	1491
	21st to end	Night	30% 5% 18% 25% 16% 5%	1440
July	1st to 10th	Night	37% 6% 14% 21% 18% 5%	1400
	11th to 20th	Night	30% 4 15% 28% 21% 3	1519
	21st to end	Night	32% 5% 14% 30% 16% 3	1672
August	1st to 10th	Night	31% 6% 16% 29% 16% 3	1600
	11th to 20th	Night	33% 7% 13% 29% 17% 1	1598
	21st to end	Night	25% 4 17% 28% 20% 5%	1961
September	1st to 10th	Night	32% 4 12% 27% 18% 7%	1898
	11th to 20th	Night	30% 4 11% 26% 26% 3	1980
	21st to end	Night	35% 3 8% 24% 27% 3	1980
October	1st to 10th	Night	31% 3 10% 29% 23% 4	1980
	11th to 20th	Night	38% 4 8% 25% 21% 3	2131
	21st to end	Night	46% 3 8% 23% 18% 3	2496
November	1st to 10th	Night	37% 3 9% 24% 24% 4	2406
	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% 31% 14% 5% 1	460
	21st to end	Day	34% 17% 28% 16% 5%	470
April	1st to 10th	Day	26% 16% 29% 18% 10% 1	420
	11th to 20th	Day	26% 18% 26% 19% 8% 3	412
	21st to end	Day	27% 15% 34% 14% 7% 2	420
May	1st to 10th	Day	28% 12% 33% 15% 7% 4	423
	11th to 20th	Day	23% 10% 30% 22% 10% 5%	447
	21st to end	Day	14% 7% 27% 28% 15% 9%	485
June	1st to 10th	Day	15% 7% 24% 29% 18% 7%	450
	11th to 20th	Day	12% 4 27% 35% 14% 8%	572
	21st to end	Day	13% 7% 27% 27% 17% 8%	630
July	1st to 10th	Day	15% 3 16% 27% 21% 17%	621
	11th to 20th	Day	10% 2 22% 32% 23% 12%	487
	21st to end	Day	13% 3 19% 31% 19% 15%	488
August	1st to 10th	Day	14% 2 14% 31% 26% 13%	446
	11th to 20th	Day	13% 2 19% 34% 21% 11%	439
	21st to end	Day	9% 3 16% 32% 25% 14%	495
September	1st to 10th	Day	17% 4 15% 28% 26% 9%	450
	11th to 20th	Day	11% 2 17% 26% 30% 14%	450
	21st to end	Day	21% 7% 20% 24% 22% 7%	450
October	1st to 10th	Day	14% 7% 24% 31% 16% 8%	450
	11th to 20th	Day	20% 13% 32% 22% 10% 2	450
	21st to end	Day	28% 9% 38% 18% 7%	372
November	1st to 10th	Day	17% 14% 34% 23% 8% 4	270
	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% 30% 26% 7%	801
April	1st to 10th	Night	19% 14% 30% 29% 8%	603
	11th to 20th	Night	19% 11% 30% 27% 11% 2	533
	21st to end	Night	20% 8% 35% 27% 9% 1	540
May	1st to 10th	Night	22% 8% 30% 27% 12% 1	540
	11th to 20th	Night	19% 5% 23% 33% 19% 2	531
	21st to end	Night	9% 3 20% 38% 26% 5%	584
June	1st to 10th	Night	11% 3 20% 41% 24% 2	540
	11th to 20th	Night	11% 2 15% 43% 24% 4	540
	21st to end	Night	8% 3 22% 38% 25% 3	540
July	1st to 10th	Night	14% 2 11% 29% 32% 11%	525
	11th to 20th	Night	6% 1 13% 36% 40% 4	522
	21st to end	Night	12% 1 10% 38% 35% 4	591
August	1st to 10th	Night	10% 1 8% 35% 41% 5%	537
	11th to 20th	Night	9% 2 10% 38% 35% 6%	534
	21st to end	Night	7% 1 13% 34% 37% 8%	594
September	1st to 10th	Night	15% 3 11% 32% 35% 5%	638
	11th to 20th	Night	11% 3 14% 32% 34% 6%	720
	21st to end	Night	14% 6% 19% 31% 26% 3	720
October	1st to 10th	Night	11% 4 24% 33% 24% 4	720
	11th to 20th	Night	19% 10% 24% 32% 14% 1	720
	21st to end	Night	25% 9% 28% 25% 11% 1	792
November	1st to 10th	Night	18% 9% 27% 28% 16% 2	740
	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 2024-03-19 23:31:09. Version ac07

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