Wilcox Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Wilcox Park clear sky chart from 2005-11-06 to 2025-09-04.

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	17% 8% 3 7% 5% 4 4 4 5% 7% 37%	126144
	Night	18% 9% 3 7% 4 4 4 3 5% 6% 37%	122579
Transparency	Day	45% 5% 12% 23% 13% 2	129658
	Night	46% 5% 12% 21% 14% 2	127152
Seeing	Day	24% 15% 30% 20% 9% 2	15960
	Night	22% 14% 31% 24% 8% 1	24987

By Month

Percentage Cloud Cover NE (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	12% 9% 4 11% 5% 5% 4 3 5% 6% 36%	3597
	11th to 20th	Day	14% 9% 4 12% 5% 5% 4 3 5% 4 35%	3570
	21st to end	Day	17% 10% 3 7% 5% 4 5% 4 4 5% 36%	4162
February	1st to 10th	Day	16% 10% 3 8% 6% 5% 4 4 6% 6% 32%	1800
	11th to 20th	Day	14% 10% 3 8% 6% 5% 5% 4 4 6% 36%	1946
	21st to end	Day	19% 9% 3 7% 6% 4 4 3 4 6% 36%	1650
March	1st to 10th	Day	22% 11% 4 7% 4 3 3 3 3 5% 35%	4476
	11th to 20th	Day	13% 10% 3 7% 4 5% 5% 3 5% 6% 40%	4704
	21st to end	Day	20% 9% 3 7% 5% 4 4 3 4 5% 35%	5965
April	1st to 10th	Day	20% 10% 3 6% 4 3 4 3 5% 5% 35%	2400
	11th to 20th	Day	17% 8% 2 6% 6% 4 4 4 5% 7% 38%	2374
	21st to end	Day	20% 7% 3 6% 4 5% 4 3 4 6% 38%	2474
May	1st to 10th	Day	30% 9% 2 6% 4 4 4 3 5% 7% 27%	5919
	11th to 20th	Day	19% 8% 3 8% 5% 4 4 3 5% 7% 35%	6318
	21st to end	Day	20% 7% 2 6% 4 4 4 4 6% 8% 34%	6949
June	1st to 10th	Day	17% 6% 2 6% 5% 5% 5% 5% 6% 10% 34%	2800
	11th to 20th	Day	17% 6% 2 6% 4 5% 5% 4 7% 10% 34%	2800
	21st to end	Day	14% 7% 2 7% 6% 4 4 4 7% 9% 36%	2800
July	1st to 10th	Day	12% 7% 3 7% 6% 5% 6% 4 6% 9% 36%	6360
	11th to 20th	Day	10% 6% 2 7% 5% 5% 5% 5% 8% 12% 35%	6360
	21st to end	Day	13% 7% 3 6% 4 4 4 3 6% 8% 42%	6926
August	1st to 10th	Day	18% 6% 3 8% 5% 5% 5% 4 5% 8% 32%	4452
	11th to 20th	Day	13% 6% 2 6% 4 4 4 4 6% 10% 41%	3850
	21st to end	Day	12% 4 2 5% 5% 4 4 4 6% 9% 44%	4312
September	1st to 10th	Day	14% 7% 3 6% 4 4 4 4 6% 7% 43%	2316
	11th to 20th	Day	12% 5% 2 6% 3 3 4 4 5% 6% 50%	2187
	21st to end	Day	17% 6% 2 5% 4 4 5% 4 7% 7% 40%	2090
October	1st to 10th	Day	20% 7% 2 6% 4 4 4 3 5% 6% 40%	1995
	11th to 20th	Day	15% 7% 2 7% 3 4 4 3 5% 6% 43%	1900
	21st to end	Day	23% 8% 2 5% 4 4 5% 4 5% 6% 34%	1900
November	1st to 10th	Day	13% 7% 2 6% 4 3 3 3 4 7% 47%	1761
	11th to 20th	Day	16% 8% 2 6% 4 4 4 3 5% 6% 41%	1800
	21st to end	Day	19% 8% 3 5% 5% 4 4 4 5% 7% 37%	1685
December	1st to 10th	Day	16% 10% 3 7% 4 4 5% 3 5% 6% 36%	2600
	11th to 20th	Day	22% 9% 3 5% 3 3 3 3 4 6% 38%	2986
	21st to end	Day	20% 10% 4 9% 5% 4 4 3 4 6% 32%	3960
January	1st to 10th	Night	13% 7% 4 13% 5% 5% 4 3 5% 5% 35%	6349
	11th to 20th	Night	13% 9% 3 11% 6% 5% 5% 4 5% 6% 32%	6315
	21st to end	Night	19% 9% 3 8% 6% 4 4 3 5% 6% 34%	6789
February	1st to 10th	Night	16% 11% 4 7% 5% 4 5% 4 5% 6% 34%	2600
	11th to 20th	Night	15% 10% 4 8% 5% 5% 4 4 6% 6% 33%	2338
	21st to end	Night	18% 10% 2 7% 5% 4 4 3 5% 6% 36%	1980
March	1st to 10th	Night	20% 8% 3 7% 5% 4 4 3 4 6% 36%	5364
	11th to 20th	Night	17% 10% 4 7% 4 4 4 3 4 5% 37%	5239
	21st to end	Night	20% 10% 4 9% 4 4 3 3 5% 4 35%	4967
April	1st to 10th	Night	20% 10% 3 7% 5% 5% 5% 4 6% 7% 29%	2000
	11th to 20th	Night	20% 8% 2 6% 4 4 4 3 5% 7% 36%	1975
	21st to end	Night	21% 8% 3 6% 4 3 3 3 5% 6% 39%	1925
May	1st to 10th	Night	33% 9% 3 6% 3 4 4 2 4 6% 27%	4054
	11th to 20th	Night	19% 10% 3 7% 5% 5% 4 3 5% 6% 32%	3585
	21st to end	Night	20% 8% 3 8% 4 4 5% 3 5% 7% 33%	3926
June	1st to 10th	Night	16% 7% 3 6% 4 3 5% 5% 6% 6% 40%	1600
	11th to 20th	Night	16% 7% 3 5% 5% 3 5% 4 7% 8% 38%	1600
	21st to end	Night	12% 5% 2 5% 4 5% 4 4 6% 10% 41%	1600
July	1st to 10th	Night	14% 7% 2 6% 4 4 4 4 6% 8% 41%	3600
	11th to 20th	Night	15% 7% 2 7% 5% 4 5% 5% 7% 9% 35%	3600
	21st to end	Night	12% 7% 2 6% 4 3 4 4 4 6% 48%	3926
August	1st to 10th	Night	22% 6% 2 6% 4 5% 5% 4 6% 7% 33%	2663
	11th to 20th	Night	13% 8% 2 7% 4 4 4 4 5% 8% 41%	3197
	21st to end	Night	11% 4 2 5% 3 3 4 3 4 7% 51%	3586
September	1st to 10th	Night	15% 6% 2 6% 4 4 4 3 5% 6% 46%	1931
	11th to 20th	Night	12% 5% 2 4 3 3 3 2 5% 7% 53%	1991
	21st to end	Night	16% 7% 2 6% 3 4 4 3 5% 6% 44%	2090
October	1st to 10th	Night	20% 7% 2 6% 5% 4 4 3 4 5% 41%	2180
	11th to 20th	Night	15% 6% 2 6% 4 4 4 3 4 7% 44%	2280
	21st to end	Night	22% 9% 3 6% 4 4 4 3 4 7% 36%	2698
November	1st to 10th	Night	15% 8% 2 5% 3 3 4 4 4 6% 46%	2537
	11th to 20th	Night	18% 9% 2 6% 4 4 3 3 5% 6% 40%	2600
	21st to end	Night	15% 9% 3 6% 5% 4 5% 3 5% 7% 39%	2710
December	1st to 10th	Night	19% 11% 3 7% 4 4 3 3 4 6% 36%	4580
	11th to 20th	Night	25% 9% 3 6% 4 3 3 3 4 4 36%	5208
	21st to end	Night	21% 12% 4 8% 4 4 4 3 4 5% 32%	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	48% 4 10% 26% 11% 2	3598
	11th to 20th	Day	50% 5% 9% 21% 11% 4	3600
	21st to end	Day	51% 4 8% 23% 14% 1	4162
February	1st to 10th	Day	53% 4 12% 18% 11% 1	1800
	11th to 20th	Day	49% 5% 8% 22% 13% 2	1955
	21st to end	Day	50% 3 11% 21% 13% 2	1650
March	1st to 10th	Day	52% 4 10% 16% 11% 7%	4479
	11th to 20th	Day	43% 7% 14% 25% 8% 4	4704
	21st to end	Day	50% 5% 6% 14% 21% 5%	5965
April	1st to 10th	Day	51% 4 8% 20% 14% 3	2400
	11th to 20th	Day	46% 4 10% 22% 17% 2	2374
	21st to end	Day	47% 4 9% 21% 15% 3	2474
May	1st to 10th	Day	57% 5% 13% 15% 9% 1	5930
	11th to 20th	Day	49% 5% 13% 21% 12% 1	6322
	21st to end	Day	46% 6% 11% 25% 11% 1	6949
June	1st to 10th	Day	44% 6% 13% 23% 12% 1	2800
	11th to 20th	Day	44% 6% 14% 24% 11% 1	2800
	21st to end	Day	43% 7% 12% 25% 12% 1	2800
July	1st to 10th	Day	46% 6% 13% 21% 14% 1	6290
	11th to 20th	Day	39% 8% 16% 25% 11% 1	6285
	21st to end	Day	41% 5% 12% 25% 17% 1	6728
August	1st to 10th	Day	50% 5% 14% 22% 8% 1	4438
	11th to 20th	Day	38% 5% 17% 30% 8%	3886
	21st to end	Day	35% 5% 13% 33% 13% 1	4312
September	1st to 10th	Day	40% 5% 12% 25% 16% 2	2316
	11th to 20th	Day	35% 4 11% 26% 23% 2	2187
	21st to end	Day	42% 5% 11% 23% 16% 2	2090
October	1st to 10th	Day	40% 5% 9% 20% 25% 2	3320
	11th to 20th	Day	33% 3 9% 27% 24% 4	3140
	21st to end	Day	34% 5% 14% 27% 17% 3	3112
November	1st to 10th	Day	38% 4 14% 25% 16% 2	1761
	11th to 20th	Day	43% 5% 10% 22% 18% 2	1800
	21st to end	Day	47% 4 13% 25% 10% 2	1685
December	1st to 10th	Day	48% 4 15% 25% 7%	2600
	11th to 20th	Day	47% 4 15% 20% 12% 2	2986
	21st to end	Day	54% 4 7% 18% 13% 3	3960
January	1st to 10th	Night	50% 4 11% 20% 13% 1	6349
	11th to 20th	Night	50% 6% 13% 17% 10% 3	6360
	21st to end	Night	51% 3 11% 16% 15% 3	6789
February	1st to 10th	Night	51% 4 13% 20% 10% 2	2600
	11th to 20th	Night	50% 5% 10% 16% 16% 2	2340
	21st to end	Night	50% 3 9% 21% 12% 3	1980
March	1st to 10th	Night	48% 4 12% 18% 14% 3	5374
	11th to 20th	Night	48% 5% 16% 20% 8% 3	5240
	21st to end	Night	51% 5% 6% 14% 21% 3	4967
April	1st to 10th	Night	54% 4 9% 19% 12% 2	2000
	11th to 20th	Night	48% 5% 10% 19% 17% 1	1975
	21st to end	Night	46% 4 9% 22% 16% 3	1925
May	1st to 10th	Night	60% 4 13% 13% 9% 1	4060
	11th to 20th	Night	53% 5% 12% 17% 11% 2	3586
	21st to end	Night	50% 5% 13% 20% 10% 1	3927
June	1st to 10th	Night	43% 6% 10% 25% 14% 1	1600
	11th to 20th	Night	42% 6% 17% 26% 9%	1600
	21st to end	Night	37% 5% 16% 26% 14% 1	1600
July	1st to 10th	Night	40% 6% 16% 21% 15% 1	3560
	11th to 20th	Night	44% 8% 15% 21% 11% 1	3552
	21st to end	Night	36% 4 13% 28% 17% 1	3809
August	1st to 10th	Night	49% 7% 14% 19% 9% 1	2653
	11th to 20th	Night	42% 5% 15% 30% 9%	3227
	21st to end	Night	32% 5% 13% 36% 13% 1	3586
September	1st to 10th	Night	39% 4 11% 28% 16% 1	1931
	11th to 20th	Night	31% 4 11% 28% 25% 1	1991
	21st to end	Night	40% 5% 10% 25% 20% 1	2090
October	1st to 10th	Night	44% 4 12% 22% 18% 1	3635
	11th to 20th	Night	31% 3 11% 28% 26% 1	3779
	21st to end	Night	36% 4 13% 30% 16% 1	4436
November	1st to 10th	Night	39% 5% 10% 24% 19% 3	2537
	11th to 20th	Night	45% 4 10% 20% 17% 3	2600
	21st to end	Night	44% 5% 15% 27% 9% 1	2710
December	1st to 10th	Night	49% 4 13% 27% 6%	4580
	11th to 20th	Night	52% 4 12% 15% 15% 1	5208
	21st to end	Night	54% 4 10% 16% 13% 3	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	29% 29% 25% 11% 6%	200
	11th to 20th	Day	32% 28% 27% 11% 3	200
	21st to end	Day	26% 29% 30% 10% 3 1	263
February	1st to 10th	Day	35% 27% 30% 6% 1	300
	11th to 20th	Day	31% 27% 30% 12% 1	494
	21st to end	Day	31% 22% 34% 11% 3	414
March	1st to 10th	Day	30% 21% 31% 16% 1	500
	11th to 20th	Day	29% 24% 32% 11% 3 1	500
	21st to end	Day	35% 20% 28% 10% 5% 1	550
April	1st to 10th	Day	35% 21% 26% 11% 6%	500
	11th to 20th	Day	29% 26% 26% 13% 5% 1	492
	21st to end	Day	28% 18% 34% 14% 4 1	500
May	1st to 10th	Day	34% 15% 27% 16% 7% 1	503
	11th to 20th	Day	26% 15% 34% 18% 7% 2	527
	21st to end	Day	22% 12% 30% 25% 10% 2	573
June	1st to 10th	Day	21% 10% 34% 22% 11% 1	530
	11th to 20th	Day	19% 13% 29% 27% 10% 2	530
	21st to end	Day	18% 10% 33% 24% 12% 3	530
July	1st to 10th	Day	14% 7% 34% 28% 13% 4	525
	11th to 20th	Day	13% 7% 29% 32% 17% 2	524
	21st to end	Day	13% 8% 36% 29% 13% 2	576
August	1st to 10th	Day	15% 5% 29% 33% 12% 5%	526
	11th to 20th	Day	17% 5% 27% 28% 17% 7%	519
	21st to end	Day	13% 8% 31% 28% 15% 6%	583
September	1st to 10th	Day	19% 9% 23% 28% 14% 7%	502
	11th to 20th	Day	16% 8% 27% 21% 16% 11%	490
	21st to end	Day	21% 9% 32% 24% 10% 4	490
October	1st to 10th	Day	25% 11% 24% 22% 13% 4	490
	11th to 20th	Day	21% 13% 35% 22% 8% 2	490
	21st to end	Day	26% 15% 30% 21% 7% 1	439
November	1st to 10th	Day	19% 19% 29% 21% 9% 2	395
	11th to 20th	Day	26% 23% 25% 20% 6% 1	400
	21st to end	Day	28% 21% 30% 18% 2 1	285
December	1st to 10th	Day	26% 26% 31% 14% 5%	200
	11th to 20th	Day	34% 25% 28% 12% 3	200
	21st to end	Day	29% 21% 32% 13% 5%	220
January	1st to 10th	Night	22% 22% 38% 16% 2	800
	11th to 20th	Night	25% 21% 33% 18% 3	800
	21st to end	Night	20% 22% 38% 18% 2	880
February	1st to 10th	Night	24% 19% 35% 21% 1	800
	11th to 20th	Night	25% 23% 36% 15% 1	783
	21st to end	Night	28% 19% 36% 15% 2	660
March	1st to 10th	Night	24% 23% 34% 16% 3	800
	11th to 20th	Night	25% 22% 35% 15% 4	800
	21st to end	Night	25% 23% 31% 17% 4	880
April	1st to 10th	Night	27% 21% 32% 18% 2	800
	11th to 20th	Night	26% 18% 32% 17% 6%	791
	21st to end	Night	26% 17% 33% 19% 5% 1	725
May	1st to 10th	Night	27% 16% 31% 20% 6%	600
	11th to 20th	Night	20% 12% 36% 27% 4	404
	21st to end	Night	19% 7% 31% 32% 11%	433
June	1st to 10th	Night	18% 7% 31% 32% 11%	400
	11th to 20th	Night	17% 7% 32% 32% 11% 1	400
	21st to end	Night	14% 6% 28% 40% 12% 1	400
July	1st to 10th	Night	15% 3 23% 42% 17% 1	390
	11th to 20th	Night	16% 4 22% 43% 15% 1	388
	21st to end	Night	13% 3 26% 44% 13% 1	438
August	1st to 10th	Night	13% 2 23% 42% 19% 1	436
	11th to 20th	Night	14% 3 19% 42% 20% 2	790
	21st to end	Night	15% 3 25% 36% 18% 2	880
September	1st to 10th	Night	18% 5% 29% 31% 15% 2	773
	11th to 20th	Night	16% 5% 28% 27% 21% 4	760
	21st to end	Night	20% 7% 26% 33% 13% 2	760
October	1st to 10th	Night	24% 8% 26% 30% 11% 1	760
	11th to 20th	Night	19% 11% 33% 27% 9%	760
	21st to end	Night	27% 13% 31% 23% 6%	836
November	1st to 10th	Night	21% 14% 33% 23% 8%	780
	11th to 20th	Night	24% 16% 32% 21% 6% 1	800
	21st to end	Night	19% 19% 35% 21% 5% 1	800
December	1st to 10th	Night	28% 19% 31% 18% 5%	800
	11th to 20th	Night	26% 19% 31% 21% 3	800
	21st to end	Night	27% 16% 38% 17% 2	880

Page generated at 2025-09-01 01:51:03. Version ac07

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