Lead Parachute Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lead Parachute Observatory clear sky chart from 2005-11-06 to 2026-04-02.

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% 11% 4 9% 5% 5% 5% 4 5% 7% 30%	131664
	Night	15% 12% 4 10% 5% 5% 4 3 5% 6% 31%	130137
Transparency	Day	51% 6% 11% 19% 10% 1	135253
	Night	52% 6% 12% 18% 10% 1	134635
Seeing	Day	25% 18% 29% 17% 8% 3	16426
	Night	22% 17% 28% 23% 9% 1	25900

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	14% 17% 8% 18% 7% 4 4 3 4 4 19%	4661
	11th to 20th	Day	9% 14% 8% 21% 9% 7% 5% 3 4 5% 16%	4965
	21st to end	Day	14% 12% 7% 10% 6% 5% 5% 4 5% 6% 25%	5780
February	1st to 10th	Day	13% 16% 5% 12% 7% 5% 5% 4 5% 5% 24%	1890
	11th to 20th	Day	12% 14% 7% 13% 8% 5% 5% 4 4 5% 25%	1843
	21st to end	Day	16% 15% 4 11% 7% 3 4 3 5% 5% 28%	1727
March	1st to 10th	Day	17% 15% 6% 9% 4 3 3 2 3 5% 32%	4890
	11th to 20th	Day	12% 13% 4 8% 4 4 4 3 5% 6% 36%	5090
	21st to end	Day	12% 12% 4 11% 6% 5% 5% 4 5% 5% 31%	5715
April	1st to 10th	Day	16% 15% 4 9% 5% 4 5% 3 5% 6% 29%	2412
	11th to 20th	Day	16% 12% 3 8% 4 5% 4 4 5% 6% 32%	2374
	21st to end	Day	19% 10% 3 7% 4 4 4 3 5% 6% 35%	2464
May	1st to 10th	Day	27% 10% 3 7% 5% 4 4 3 4 6% 27%	6013
	11th to 20th	Day	23% 10% 3 8% 5% 4 4 3 5% 7% 27%	6318
	21st to end	Day	20% 9% 3 7% 5% 5% 5% 4 6% 7% 31%	6949
June	1st to 10th	Day	16% 7% 2 7% 5% 6% 5% 4 6% 8% 34%	2800
	11th to 20th	Day	16% 7% 3 8% 5% 4 4 5% 7% 7% 34%	2800
	21st to end	Day	13% 6% 2 7% 5% 6% 6% 4 7% 8% 36%	2800
July	1st to 10th	Day	8% 6% 3 8% 5% 5% 7% 5% 7% 8% 37%	6360
	11th to 20th	Day	7% 5% 3 9% 7% 7% 7% 6% 8% 11% 32%	6360
	21st to end	Day	11% 6% 3 7% 5% 5% 6% 4 6% 8% 40%	6617
August	1st to 10th	Day	19% 8% 3 7% 4 5% 5% 4 6% 8% 31%	4234
	11th to 20th	Day	15% 8% 3 7% 5% 6% 6% 5% 7% 9% 29%	4113
	21st to end	Day	12% 8% 3 7% 4 4 5% 4 6% 9% 37%	4312
September	1st to 10th	Day	17% 6% 2 6% 4 4 4 4 6% 6% 41%	2400
	11th to 20th	Day	14% 6% 2 6% 4 4 5% 3 4 7% 45%	2400
	21st to end	Day	22% 8% 3 6% 5% 4 5% 5% 4 6% 34%	2101
October	1st to 10th	Day	17% 9% 3 7% 5% 4 5% 2 5% 8% 35%	2000
	11th to 20th	Day	19% 10% 3 8% 5% 4 4 4 5% 6% 32%	2000
	21st to end	Day	20% 13% 3 8% 5% 4 4 3 5% 7% 29%	2200
November	1st to 10th	Day	12% 12% 3 8% 4 5% 4 3 4 5% 39%	1861
	11th to 20th	Day	14% 17% 4 8% 5% 4 4 3 6% 6% 28%	1741
	21st to end	Day	16% 17% 4 8% 6% 4 4 3 5% 8% 25%	1680
December	1st to 10th	Day	14% 18% 9% 15% 6% 4 5% 3 4 4 17%	2680
	11th to 20th	Day	19% 15% 7% 9% 5% 4 4 2 5% 5% 26%	3066
	21st to end	Day	17% 18% 6% 14% 6% 5% 4 3 5% 5% 17%	4048
January	1st to 10th	Night	11% 15% 7% 20% 7% 5% 4 3 4 5% 18%	8234
	11th to 20th	Night	9% 16% 7% 18% 7% 5% 5% 4 5% 6% 19%	7905
	21st to end	Night	13% 12% 6% 11% 8% 7% 6% 4 5% 5% 24%	8401
February	1st to 10th	Night	12% 14% 5% 10% 7% 6% 6% 4 5% 6% 26%	2730
	11th to 20th	Night	11% 14% 6% 12% 7% 5% 5% 4 5% 6% 24%	2663
	21st to end	Night	14% 13% 4 13% 6% 5% 5% 3 4 5% 26%	2077
March	1st to 10th	Night	16% 13% 5% 9% 6% 5% 4 3 4 5% 29%	5166
	11th to 20th	Night	13% 14% 5% 7% 4 4 4 3 4 6% 36%	5089
	21st to end	Night	14% 13% 4 10% 5% 5% 4 3 4 5% 34%	5459
April	1st to 10th	Night	18% 13% 4 10% 5% 3 3 4 4 5% 30%	2011
	11th to 20th	Night	17% 12% 3 7% 5% 4 4 3 6% 6% 35%	1975
	21st to end	Night	16% 11% 3 7% 4 4 4 4 5% 6% 38%	1953
May	1st to 10th	Night	30% 11% 3 7% 4 4 3 2 4 5% 27%	3925
	11th to 20th	Night	25% 9% 3 7% 4 5% 4 3 5% 5% 31%	3575
	21st to end	Night	19% 9% 3 8% 4 4 4 3 5% 7% 33%	3926
June	1st to 10th	Night	14% 7% 3 7% 4 4 4 3 6% 8% 39%	1600
	11th to 20th	Night	13% 7% 2 6% 5% 4 5% 4 6% 8% 39%	1600
	21st to end	Night	12% 5% 3 6% 4 5% 5% 4 7% 8% 43%	1600
July	1st to 10th	Night	10% 9% 3 7% 5% 4 4 4 6% 9% 39%	3600
	11th to 20th	Night	9% 7% 3 7% 5% 5% 5% 5% 7% 10% 38%	3600
	21st to end	Night	10% 6% 2 7% 4 4 4 3 5% 7% 48%	4217
August	1st to 10th	Night	18% 8% 2 6% 5% 5% 5% 4 6% 7% 36%	2915
	11th to 20th	Night	17% 6% 2 6% 4 4 4 3 5% 7% 41%	2903
	21st to end	Night	12% 6% 2 6% 4 4 5% 5% 6% 7% 43%	3586
September	1st to 10th	Night	14% 6% 2 6% 5% 4 4 3 5% 6% 46%	2000
	11th to 20th	Night	13% 5% 2 5% 3 3 3 3 5% 7% 51%	2000
	21st to end	Night	18% 7% 2 7% 5% 4 3 4 5% 6% 37%	2295
October	1st to 10th	Night	17% 8% 3 6% 4 3 4 3 5% 6% 41%	2400
	11th to 20th	Night	18% 9% 2 7% 4 4 4 3 4 7% 37%	2400
	21st to end	Night	20% 12% 3 7% 4 4 4 3 5% 7% 32%	2640
November	1st to 10th	Night	11% 11% 3 7% 4 4 4 3 5% 6% 41%	2657
	11th to 20th	Night	16% 14% 4 8% 5% 5% 5% 3 5% 6% 29%	2877
	21st to end	Night	14% 15% 5% 8% 5% 5% 5% 4 6% 6% 26%	2940
December	1st to 10th	Night	11% 16% 7% 15% 7% 6% 5% 4 5% 6% 18%	4720
	11th to 20th	Night	18% 15% 6% 11% 5% 4 4 3 4 4 27%	5348
	21st to end	Night	18% 17% 8% 11% 6% 4 4 3 4 5% 20%	7150

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	68% 4 10% 13% 4 1	4662
	11th to 20th	Day	69% 4 8% 11% 7% 1	4998
	21st to end	Day	58% 5% 11% 17% 9% 1	5780
February	1st to 10th	Day	62% 5% 10% 14% 7% 1	1890
	11th to 20th	Day	61% 6% 8% 17% 8%	1852
	21st to end	Day	57% 5% 10% 19% 8% 2	1727
March	1st to 10th	Day	54% 5% 11% 18% 9% 3	4893
	11th to 20th	Day	48% 6% 17% 18% 7% 3	5090
	21st to end	Day	52% 7% 9% 17% 14% 3	5715
April	1st to 10th	Day	55% 5% 8% 20% 10% 2	2412
	11th to 20th	Day	51% 7% 10% 17% 14% 1	2374
	21st to end	Day	49% 6% 9% 19% 14% 3	2464
May	1st to 10th	Day	58% 6% 9% 16% 10% 2	6022
	11th to 20th	Day	55% 8% 9% 18% 9% 1	6322
	21st to end	Day	50% 7% 12% 20% 11% 1	6949
June	1st to 10th	Day	47% 8% 12% 20% 13% 1	2800
	11th to 20th	Day	46% 8% 14% 19% 12% 1	2800
	21st to end	Day	43% 9% 12% 24% 11% 1	2800
July	1st to 10th	Day	41% 7% 15% 25% 12% 1	6290
	11th to 20th	Day	41% 9% 16% 23% 11%	6285
	21st to end	Day	40% 7% 11% 24% 17% 1	6428
August	1st to 10th	Day	49% 8% 13% 19% 11%	4221
	11th to 20th	Day	47% 8% 15% 23% 7%	4152
	21st to end	Day	40% 7% 12% 31% 8% 1	4312
September	1st to 10th	Day	42% 6% 12% 25% 13% 2	2400
	11th to 20th	Day	39% 6% 11% 26% 17% 1	2400
	21st to end	Day	49% 6% 11% 18% 14% 1	2101
October	1st to 10th	Day	42% 5% 13% 21% 18% 1	3260
	11th to 20th	Day	45% 5% 11% 19% 17% 2	3240
	21st to end	Day	40% 5% 15% 26% 13% 1	3538
November	1st to 10th	Day	47% 6% 11% 20% 13% 3	1861
	11th to 20th	Day	55% 6% 11% 19% 7% 2	1741
	21st to end	Day	58% 6% 13% 17% 6% 1	1680
December	1st to 10th	Day	68% 6% 9% 13% 4 1	2680
	11th to 20th	Day	61% 4 13% 14% 7%	3066
	21st to end	Day	68% 5% 10% 12% 5%	4048
January	1st to 10th	Night	66% 6% 10% 12% 5% 1	8234
	11th to 20th	Night	64% 5% 11% 11% 9% 1	7947
	21st to end	Night	60% 4 9% 14% 11% 1	8401
February	1st to 10th	Night	58% 6% 11% 17% 8%	2730
	11th to 20th	Night	59% 7% 9% 16% 8% 1	2665
	21st to end	Night	59% 5% 9% 15% 10% 2	2077
March	1st to 10th	Night	56% 5% 14% 14% 9% 1	5176
	11th to 20th	Night	47% 8% 16% 19% 6% 4	5090
	21st to end	Night	51% 7% 8% 16% 15% 2	5459
April	1st to 10th	Night	56% 6% 9% 16% 11% 1	2011
	11th to 20th	Night	49% 6% 12% 18% 13% 1	1975
	21st to end	Night	46% 5% 12% 21% 15% 2	1953
May	1st to 10th	Night	60% 5% 8% 18% 6% 2	3932
	11th to 20th	Night	53% 9% 12% 16% 10% 1	3576
	21st to end	Night	48% 10% 11% 17% 11% 2	3927
June	1st to 10th	Night	42% 6% 12% 24% 15% 1	1600
	11th to 20th	Night	40% 9% 14% 23% 13% 2	1600
	21st to end	Night	37% 8% 14% 26% 14% 1	1600
July	1st to 10th	Night	41% 7% 13% 26% 13% 1	3560
	11th to 20th	Night	37% 9% 19% 24% 11%	3552
	21st to end	Night	35% 6% 13% 24% 22% 1	4092
August	1st to 10th	Night	46% 9% 15% 21% 9% 1	2904
	11th to 20th	Night	41% 7% 16% 26% 10%	2930
	21st to end	Night	38% 7% 14% 30% 10% 1	3586
September	1st to 10th	Night	39% 6% 12% 27% 14% 2	2000
	11th to 20th	Night	32% 6% 13% 29% 17% 2	2000
	21st to end	Night	46% 6% 11% 22% 14% 1	2295
October	1st to 10th	Night	45% 6% 12% 20% 17% 1	3920
	11th to 20th	Night	40% 5% 12% 22% 16% 5%	3899
	21st to end	Night	39% 5% 16% 26% 12% 1	4252
November	1st to 10th	Night	43% 6% 12% 22% 14% 2	2657
	11th to 20th	Night	55% 6% 11% 17% 9% 2	2877
	21st to end	Night	56% 7% 13% 18% 5% 1	2940
December	1st to 10th	Night	64% 7% 12% 14% 3	4720
	11th to 20th	Night	61% 5% 11% 14% 9%	5348
	21st to end	Night	65% 6% 9% 12% 8%	7150

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	37% 22% 29% 8% 3	220
	11th to 20th	Day	38% 30% 25% 6% 1	278
	21st to end	Day	33% 30% 29% 6% 2	363
February	1st to 10th	Day	34% 30% 29% 5% 2	330
	11th to 20th	Day	39% 28% 31% 2 1	330
	21st to end	Day	36% 25% 30% 7% 2	443
March	1st to 10th	Day	34% 24% 28% 11% 2	540
	11th to 20th	Day	34% 26% 25% 11% 3	540
	21st to end	Day	35% 26% 25% 9% 3 2	594
April	1st to 10th	Day	35% 22% 27% 12% 4 1	504
	11th to 20th	Day	30% 26% 25% 10% 5% 3	492
	21st to end	Day	30% 22% 29% 13% 5% 2	500
May	1st to 10th	Day	32% 19% 28% 12% 6% 3	503
	11th to 20th	Day	27% 17% 30% 15% 9% 3	527
	21st to end	Day	21% 13% 30% 21% 11% 4	573
June	1st to 10th	Day	18% 18% 32% 21% 9% 1	530
	11th to 20th	Day	21% 14% 30% 25% 10% 1	530
	21st to end	Day	15% 13% 37% 24% 9% 2	530
July	1st to 10th	Day	10% 10% 32% 29% 14% 4	525
	11th to 20th	Day	8% 11% 33% 28% 14% 6%	524
	21st to end	Day	12% 9% 36% 27% 11% 4	576
August	1st to 10th	Day	12% 8% 29% 29% 16% 7%	526
	11th to 20th	Day	15% 11% 26% 27% 14% 8%	519
	21st to end	Day	15% 11% 29% 23% 14% 9%	583
September	1st to 10th	Day	18% 11% 25% 24% 14% 8%	530
	11th to 20th	Day	13% 8% 26% 21% 22% 10%	530
	21st to end	Day	26% 14% 27% 18% 13% 3	530
October	1st to 10th	Day	24% 12% 24% 21% 15% 5%	530
	11th to 20th	Day	28% 17% 32% 15% 6% 2	530
	21st to end	Day	30% 21% 28% 17% 4	583
November	1st to 10th	Day	25% 24% 25% 16% 10% 1	430
	11th to 20th	Day	36% 21% 27% 11% 4 1	281
	21st to end	Day	32% 31% 30% 5% 1	220
December	1st to 10th	Day	34% 28% 29% 5% 3 1	220
	11th to 20th	Day	37% 27% 27% 7% 1	220
	21st to end	Day	35% 29% 30% 6%	242
January	1st to 10th	Night	23% 28% 34% 12% 3	840
	11th to 20th	Night	27% 25% 30% 15% 3	840
	21st to end	Night	24% 28% 30% 17% 2	924
February	1st to 10th	Night	25% 25% 31% 17% 1	840
	11th to 20th	Night	29% 25% 33% 12% 1	823
	21st to end	Night	30% 22% 31% 15% 2	692
March	1st to 10th	Night	27% 26% 30% 15% 2	840
	11th to 20th	Night	30% 23% 27% 17% 3	840
	21st to end	Night	25% 24% 30% 16% 4 1	924
April	1st to 10th	Night	27% 23% 29% 18% 3	805
	11th to 20th	Night	25% 21% 30% 18% 7% 1	791
	21st to end	Night	23% 16% 31% 24% 6%	753
May	1st to 10th	Night	28% 12% 22% 27% 10%	550
	11th to 20th	Night	19% 14% 30% 28% 9% 1	394
	21st to end	Night	13% 11% 29% 32% 15% 1	433
June	1st to 10th	Night	16% 9% 26% 35% 13% 1	400
	11th to 20th	Night	17% 9% 24% 37% 14%	400
	21st to end	Night	12% 6% 30% 40% 13%	400
July	1st to 10th	Night	9% 7% 26% 38% 18% 2	390
	11th to 20th	Night	9% 4 23% 41% 21% 2	388
	21st to end	Night	12% 6% 18% 41% 21% 2	563
August	1st to 10th	Night	10% 4 24% 38% 23% 2	597
	11th to 20th	Night	14% 5% 18% 34% 25% 3	609
	21st to end	Night	12% 7% 21% 35% 23% 3	880
September	1st to 10th	Night	17% 9% 23% 31% 18% 3	800
	11th to 20th	Night	14% 6% 20% 29% 26% 5%	800
	21st to end	Night	21% 11% 25% 26% 14% 3	800
October	1st to 10th	Night	21% 11% 24% 26% 17% 2	800
	11th to 20th	Night	23% 17% 29% 23% 8% 1	800
	21st to end	Night	28% 14% 30% 22% 5%	880
November	1st to 10th	Night	20% 19% 31% 23% 7%	820
	11th to 20th	Night	28% 21% 28% 16% 6% 1	840
	21st to end	Night	26% 21% 31% 19% 3 1	840
December	1st to 10th	Night	28% 25% 29% 13% 4	840
	11th to 20th	Night	28% 22% 30% 17% 3	840
	21st to end	Night	29% 23% 32% 14% 2	924

Page generated at 2026-03-30 02:18:41. Version ac07

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