Point Clark
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Point Clark clear sky chart from 2005-11-06 to 2026-01-02.

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% 12% 4 10% 5% 4 4 3 5% 6% 32%	127117
	Night	16% 15% 6% 13% 6% 4 4 3 4 5% 26%	124305
Transparency	Day	51% 8% 12% 18% 10% 1	130665
	Night	59% 7% 10% 15% 8% 1	128844
Seeing	Day	19% 10% 25% 28% 15% 4	16673
	Night	23% 11% 26% 27% 12% 2	26046

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	13% 23% 11% 29% 7% 4 2 1 2 2 6%	3376
	11th to 20th	Day	10% 24% 12% 28% 13% 4 2 1 1 2 3	3654
	21st to end	Day	15% 19% 11% 23% 9% 6% 4 2 2 2 6%	4466
February	1st to 10th	Day	14% 21% 8% 18% 10% 4 3 3 4 4 13%	1800
	11th to 20th	Day	13% 17% 9% 20% 11% 4 4 2 3 4 13%	1758
	21st to end	Day	15% 17% 6% 13% 8% 4 4 3 4 4 21%	1650
March	1st to 10th	Day	16% 12% 6% 14% 8% 3 3 3 4 5% 26%	4743
	11th to 20th	Day	13% 15% 6% 10% 4 4 4 4 6% 7% 27%	4980
	21st to end	Day	19% 14% 6% 12% 5% 4 4 3 4 6% 25%	5465
April	1st to 10th	Day	17% 14% 4 8% 4 4 4 4 5% 5% 30%	2298
	11th to 20th	Day	18% 10% 3 7% 4 4 4 3 5% 7% 37%	2572
	21st to end	Day	18% 9% 4 7% 4 4 4 3 5% 7% 37%	2600
May	1st to 10th	Day	17% 9% 2 6% 4 4 4 3 5% 7% 39%	5888
	11th to 20th	Day	15% 8% 3 7% 4 4 4 3 5% 7% 40%	5924
	21st to end	Day	19% 8% 2 5% 3 3 3 3 5% 6% 42%	6949
June	1st to 10th	Day	12% 6% 2 6% 5% 5% 4 4 6% 9% 41%	2951
	11th to 20th	Day	11% 5% 2 7% 4 5% 4 4 7% 9% 43%	3000
	21st to end	Day	15% 6% 2 5% 4 4 4 3 6% 8% 44%	3000
July	1st to 10th	Day	12% 6% 2 6% 4 4 4 4 7% 8% 42%	6819
	11th to 20th	Day	12% 5% 2 4 3 4 4 3 5% 8% 51%	6462
	21st to end	Day	8% 5% 2 5% 3 3 4 3 6% 9% 51%	6429
August	1st to 10th	Day	12% 5% 2 5% 4 5% 5% 4 7% 8% 42%	4234
	11th to 20th	Day	14% 5% 3 6% 4 4 5% 4 6% 8% 41%	4174
	21st to end	Day	10% 5% 2 6% 4 4 4 4 6% 9% 46%	4675
September	1st to 10th	Day	13% 6% 2 6% 4 4 5% 4 7% 8% 41%	2327
	11th to 20th	Day	14% 5% 2 5% 3 3 4 4 6% 7% 47%	2200
	21st to end	Day	17% 9% 2 7% 5% 4 4 4 6% 7% 35%	2200
October	1st to 10th	Day	21% 8% 2 6% 4 4 4 4 5% 6% 36%	2057
	11th to 20th	Day	25% 12% 3 8% 6% 4 5% 4 5% 6% 22%	2000
	21st to end	Day	29% 17% 4 8% 4 4 4 3 4 5% 19%	2102
November	1st to 10th	Day	19% 21% 4 8% 5% 5% 4 2 4 5% 23%	1852
	11th to 20th	Day	18% 23% 5% 10% 5% 4 4 3 5% 4 18%	1706
	21st to end	Day	20% 33% 6% 10% 5% 4 3 2 3 3 10%	1680
December	1st to 10th	Day	18% 38% 12% 13% 4 3 3 2 2 2 4	2680
	11th to 20th	Day	20% 25% 9% 22% 5% 3 3 2 3 3 7%	2893
	21st to end	Day	27% 24% 8% 12% 6% 4 3 3 3 3 7%	3553
January	1st to 10th	Night	14% 21% 13% 31% 5% 3 3 1 2 2 5%	6598
	11th to 20th	Night	13% 22% 11% 28% 12% 4 2 2 2 2 3	6245
	21st to end	Night	15% 18% 9% 23% 7% 8% 5% 2 3 3 8%	6490
February	1st to 10th	Night	14% 22% 6% 19% 10% 4 3 3 5% 3 11%	2600
	11th to 20th	Night	14% 18% 8% 17% 9% 5% 4 2 4 4 14%	2525
	21st to end	Night	15% 16% 7% 14% 7% 4 4 3 4 5% 21%	1980
March	1st to 10th	Night	15% 13% 5% 12% 7% 4 4 3 4 6% 28%	5097
	11th to 20th	Night	10% 14% 6% 8% 5% 5% 4 4 6% 8% 30%	4979
	21st to end	Night	21% 12% 6% 12% 5% 3 4 2 4 4 27%	5467
April	1st to 10th	Night	21% 12% 5% 8% 5% 4 4 2 4 6% 30%	2117
	11th to 20th	Night	19% 10% 2 7% 5% 4 4 3 4 6% 36%	1777
	21st to end	Night	19% 11% 4 7% 6% 4 5% 3 4 6% 32%	1800
May	1st to 10th	Night	18% 8% 3 8% 5% 4 4 3 4 7% 36%	4053
	11th to 20th	Night	14% 9% 3 8% 5% 4 4 3 4 6% 40%	3953
	21st to end	Night	19% 7% 2 5% 4 4 4 2 4 6% 42%	3926
June	1st to 10th	Night	15% 6% 2 6% 4 5% 3 4 7% 8% 40%	1444
	11th to 20th	Night	13% 5% 3 6% 5% 5% 5% 4 8% 10% 38%	1400
	21st to end	Night	13% 6% 2 7% 4 5% 4 4 5% 9% 41%	1400
July	1st to 10th	Night	10% 7% 3 8% 5% 4 4 3 5% 8% 45%	3160
	11th to 20th	Night	11% 5% 2 5% 4 4 4 3 5% 8% 50%	3515
	21st to end	Night	10% 6% 2 5% 3 4 4 3 5% 7% 50%	4422
August	1st to 10th	Night	11% 6% 2 7% 4 4 5% 3 6% 7% 44%	2915
	11th to 20th	Night	13% 7% 3 6% 3 4 4 3 5% 8% 43%	2875
	21st to end	Night	10% 6% 2 6% 4 4 4 4 5% 7% 48%	3223
September	1st to 10th	Night	12% 6% 2 6% 4 4 5% 3 5% 7% 45%	2047
	11th to 20th	Night	13% 4 2 5% 3 3 4 3 4 8% 51%	2200
	21st to end	Night	19% 8% 2 8% 5% 4 4 4 5% 7% 36%	2200
October	1st to 10th	Night	19% 7% 2 7% 4 4 4 3 6% 6% 38%	2342
	11th to 20th	Night	27% 12% 3 10% 4 5% 4 2 4 6% 23%	2400
	21st to end	Night	28% 15% 4 8% 5% 4 4 3 4 5% 21%	2735
November	1st to 10th	Night	20% 18% 3 8% 5% 4 4 3 5% 6% 24%	2666
	11th to 20th	Night	20% 23% 5% 10% 4 5% 4 3 4 5% 15%	2911
	21st to end	Night	24% 27% 7% 10% 5% 3 4 2 2 3 12%	2940
December	1st to 10th	Night	18% 31% 13% 14% 5% 4 3 2 2 2 5%	4720
	11th to 20th	Night	14% 29% 10% 18% 6% 4 3 2 2 2 9%	5516
	21st to end	Night	23% 23% 10% 15% 6% 4 3 2 3 3 7%	7667

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	87% 5% 5% 2	3377
	11th to 20th	Day	92% 4 3 1 1	3685
	21st to end	Day	84% 7% 6% 2 1	4466
February	1st to 10th	Day	74% 8% 7% 10% 1	1800
	11th to 20th	Day	75% 8% 7% 7% 3 1	1767
	21st to end	Day	64% 8% 10% 11% 5%	1650
March	1st to 10th	Day	58% 7% 16% 12% 6%	4746
	11th to 20th	Day	52% 8% 14% 18% 6% 1	4980
	21st to end	Day	57% 9% 13% 14% 7% 1	5465
April	1st to 10th	Day	54% 7% 12% 18% 9%	2298
	11th to 20th	Day	45% 7% 11% 21% 14% 1	2572
	21st to end	Day	46% 7% 14% 19% 12% 2	2600
May	1st to 10th	Day	42% 9% 14% 17% 14% 5%	5897
	11th to 20th	Day	42% 11% 13% 18% 16% 1	5928
	21st to end	Day	41% 8% 11% 19% 16% 5%	6949
June	1st to 10th	Day	38% 9% 13% 24% 15% 1	2951
	11th to 20th	Day	35% 8% 13% 26% 16% 1	3000
	21st to end	Day	38% 9% 14% 23% 15% 1	3000
July	1st to 10th	Day	36% 9% 16% 22% 16% 1	6746
	11th to 20th	Day	30% 7% 13% 34% 15% 2	6384
	21st to end	Day	29% 8% 16% 30% 17% 1	6245
August	1st to 10th	Day	35% 9% 16% 25% 14% 1	4221
	11th to 20th	Day	39% 8% 18% 26% 9% 1	4213
	21st to end	Day	33% 9% 16% 29% 13%	4674
September	1st to 10th	Day	38% 9% 17% 25% 10% 2	2327
	11th to 20th	Day	35% 8% 16% 28% 13%	2200
	21st to end	Day	46% 9% 13% 22% 9% 1	2200
October	1st to 10th	Day	42% 8% 14% 26% 10% 1	3343
	11th to 20th	Day	49% 8% 11% 21% 9%	3240
	21st to end	Day	60% 8% 12% 16% 4	3378
November	1st to 10th	Day	63% 7% 8% 15% 6%	1852
	11th to 20th	Day	68% 7% 11% 8% 6%	1706
	21st to end	Day	80% 5% 7% 6% 1	1680
December	1st to 10th	Day	89% 5% 3 2 1	2680
	11th to 20th	Day	85% 5% 5% 5%	2892
	21st to end	Day	82% 6% 7% 4 1	3553
January	1st to 10th	Night	88% 5% 4 3	6598
	11th to 20th	Night	90% 5% 3 2 1	6289
	21st to end	Night	81% 7% 8% 4 1	6490
February	1st to 10th	Night	77% 7% 7% 7% 1	2600
	11th to 20th	Night	73% 7% 9% 9% 2	2527
	21st to end	Night	64% 8% 11% 11% 6%	1980
March	1st to 10th	Night	55% 7% 14% 16% 7% 1	5107
	11th to 20th	Night	48% 8% 17% 19% 7% 1	4980
	21st to end	Night	57% 9% 10% 14% 9% 1	5467
April	1st to 10th	Night	55% 5% 9% 17% 12% 1	2117
	11th to 20th	Night	48% 6% 9% 19% 17% 2	1777
	21st to end	Night	52% 7% 9% 15% 16% 2	1800
May	1st to 10th	Night	47% 7% 9% 16% 14% 7%	4060
	11th to 20th	Night	44% 8% 11% 19% 17% 1	3954
	21st to end	Night	42% 6% 10% 23% 15% 3	3927
June	1st to 10th	Night	40% 7% 10% 24% 16% 3	1444
	11th to 20th	Night	38% 8% 14% 22% 16% 2	1400
	21st to end	Night	40% 6% 13% 23% 16% 2	1400
July	1st to 10th	Night	37% 6% 12% 24% 17% 4	3125
	11th to 20th	Night	31% 7% 12% 29% 19% 1	3470
	21st to end	Night	32% 7% 11% 27% 21% 2	4292
August	1st to 10th	Night	37% 8% 12% 28% 15% 1	2904
	11th to 20th	Night	38% 8% 16% 22% 15% 1	2902
	21st to end	Night	34% 7% 13% 32% 12% 1	3223
September	1st to 10th	Night	37% 7% 13% 26% 15% 2	2047
	11th to 20th	Night	34% 6% 16% 28% 16% 1	2200
	21st to end	Night	46% 8% 12% 22% 10% 1	2200
October	1st to 10th	Night	38% 8% 11% 25% 17% 1	3836
	11th to 20th	Night	53% 5% 14% 18% 9%	3899
	21st to end	Night	54% 6% 15% 18% 7%	4409
November	1st to 10th	Night	60% 7% 11% 15% 6%	2666
	11th to 20th	Night	70% 7% 10% 8% 4 1	2911
	21st to end	Night	78% 5% 9% 7% 1	2940
December	1st to 10th	Night	86% 5% 6% 2 1	4720
	11th to 20th	Night	83% 5% 7% 5% 1	5516
	21st to end	Night	82% 7% 6% 4 1	7667

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	22% 18% 37% 16% 5% 1	249
	11th to 20th	Day	18% 21% 38% 17% 6%	300
	21st to end	Day	29% 14% 32% 22% 4	330
February	1st to 10th	Day	22% 23% 35% 17% 3	300
	11th to 20th	Day	21% 16% 43% 18% 2	300
	21st to end	Day	21% 25% 35% 17% 2	249
March	1st to 10th	Day	20% 15% 40% 19% 6%	410
	11th to 20th	Day	21% 14% 30% 27% 7% 1	500
	21st to end	Day	25% 11% 31% 26% 7% 1	550
April	1st to 10th	Day	21% 14% 32% 25% 8%	500
	11th to 20th	Day	24% 13% 24% 24% 11% 4	492
	21st to end	Day	22% 8% 29% 29% 11% 1	500
May	1st to 10th	Day	19% 8% 26% 30% 15% 2	503
	11th to 20th	Day	16% 5% 24% 30% 20% 5%	527
	21st to end	Day	16% 5% 21% 28% 25% 5%	573
June	1st to 10th	Day	11% 3 27% 34% 22% 2	681
	11th to 20th	Day	11% 4 23% 38% 20% 4	730
	21st to end	Day	16% 5% 19% 39% 18% 3	730
July	1st to 10th	Day	9% 3 18% 37% 27% 6%	721
	11th to 20th	Day	13% 4 18% 36% 23% 7%	718
	21st to end	Day	9% 3 15% 39% 26% 6%	581
August	1st to 10th	Day	11% 3 15% 36% 25% 10%	526
	11th to 20th	Day	13% 3 13% 34% 25% 12%	519
	21st to end	Day	12% 4 18% 34% 26% 6%	583
September	1st to 10th	Day	14% 7% 19% 29% 22% 9%	530
	11th to 20th	Day	10% 4 16% 28% 31% 12%	530
	21st to end	Day	18% 8% 22% 26% 19% 8%	530
October	1st to 10th	Day	21% 10% 22% 23% 18% 6%	530
	11th to 20th	Day	26% 14% 32% 22% 6% 1	530
	21st to end	Day	32% 16% 27% 19% 5% 1	485
November	1st to 10th	Day	28% 16% 28% 20% 8%	330
	11th to 20th	Day	29% 21% 29% 14% 5% 2	234
	21st to end	Day	35% 20% 30% 15% 1	220
December	1st to 10th	Day	37% 19% 25% 15% 2 1	220
	11th to 20th	Day	29% 25% 30% 14% 3	220
	21st to end	Day	37% 19% 31% 11% 2	242
January	1st to 10th	Night	26% 18% 33% 16% 6% 1	1006
	11th to 20th	Night	28% 17% 32% 18% 4 1	968
	21st to end	Night	22% 13% 35% 24% 6%	880
February	1st to 10th	Night	26% 14% 32% 23% 4	800
	11th to 20th	Night	25% 15% 33% 22% 5%	783
	21st to end	Night	22% 14% 37% 23% 4	660
March	1st to 10th	Night	20% 13% 35% 23% 8%	800
	11th to 20th	Night	19% 14% 34% 26% 6% 2	800
	21st to end	Night	24% 10% 26% 28% 11% 2	880
April	1st to 10th	Night	25% 12% 27% 31% 6% 1	780
	11th to 20th	Night	22% 10% 25% 30% 12% 2	593
	21st to end	Night	21% 10% 25% 31% 13% 1	600
May	1st to 10th	Night	18% 5% 23% 38% 15% 2	600
	11th to 20th	Night	19% 3 23% 35% 20% 1	564
	21st to end	Night	14% 2 20% 38% 25% 2	433
June	1st to 10th	Night	16% 4 19% 40% 20% 2	400
	11th to 20th	Night	13% 5% 20% 38% 23% 1	400
	21st to end	Night	13% 4 19% 39% 24% 2	400
July	1st to 10th	Night	10% 1 14% 43% 28% 4	390
	11th to 20th	Night	10% 1 17% 39% 27% 6%	532
	21st to end	Night	11% 3 13% 43% 28% 2	657
August	1st to 10th	Night	11% 2 13% 40% 29% 4	597
	11th to 20th	Night	10% 4 16% 31% 32% 6%	594
	21st to end	Night	12% 3 18% 36% 27% 4	660
September	1st to 10th	Night	14% 5% 19% 34% 21% 8%	775
	11th to 20th	Night	13% 3 15% 35% 30% 5%	800
	21st to end	Night	19% 6% 20% 30% 19% 5%	800
October	1st to 10th	Night	21% 6% 25% 28% 17% 2	800
	11th to 20th	Night	31% 11% 25% 24% 8% 1	800
	21st to end	Night	35% 12% 26% 22% 4	880
November	1st to 10th	Night	30% 14% 24% 23% 8%	820
	11th to 20th	Night	31% 18% 28% 18% 6%	840
	21st to end	Night	36% 17% 26% 18% 3	840
December	1st to 10th	Night	36% 19% 27% 14% 4	840
	11th to 20th	Night	27% 23% 34% 14% 2	919
	21st to end	Night	34% 16% 33% 15% 2	1155

Page generated at 2025-12-30 01:14:11. Version ac07

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