Presbyterian Point
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Presbyterian Point 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	12% 6% 2 6% 4 4 4 4 6% 8% 43%	126514
	Night	13% 6% 2 6% 4 4 4 4 5% 7% 44%	124824
Transparency	Day	24% 39% 8% 14% 11% 3	130119
	Night	25% 38% 7% 13% 13% 4	129289
Seeing	Day	17% 12% 26% 25% 15% 5%	16714
	Night	16% 10% 27% 30% 15% 1	26736

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	15% 5% 1 5% 3 3 3 2 4 4 56%	4065
	11th to 20th	Day	11% 7% 2 5% 3 3 2 2 3 5% 57%	4060
	21st to end	Day	15% 6% 3 6% 4 4 4 3 4 5% 46%	4466
February	1st to 10th	Day	13% 6% 2 7% 5% 4 4 4 6% 8% 42%	1800
	11th to 20th	Day	22% 6% 1 4 4 3 3 3 4 5% 44%	1787
	21st to end	Day	18% 7% 2 6% 5% 4 3 3 5% 6% 41%	1740
March	1st to 10th	Day	17% 8% 2 5% 4 4 4 3 5% 6% 40%	4935
	11th to 20th	Day	11% 5% 2 5% 3 3 4 3 5% 6% 53%	4980
	21st to end	Day	15% 5% 2 5% 4 4 4 4 5% 6% 45%	5465
April	1st to 10th	Day	10% 5% 2 5% 2 4 4 3 6% 7% 53%	2360
	11th to 20th	Day	10% 5% 2 5% 4 4 4 3 6% 7% 50%	2374
	21st to end	Day	12% 6% 2 6% 4 4 4 4 6% 7% 44%	2400
May	1st to 10th	Day	9% 6% 3 8% 5% 5% 6% 5% 7% 11% 35%	5763
	11th to 20th	Day	19% 8% 3 7% 5% 5% 5% 4 7% 9% 29%	5861
	21st to end	Day	12% 5% 2 5% 4 5% 4 4 6% 9% 44%	6450
June	1st to 10th	Day	9% 5% 2 5% 5% 5% 5% 4 7% 9% 43%	2800
	11th to 20th	Day	8% 4 2 6% 5% 4 5% 4 7% 9% 46%	2800
	21st to end	Day	7% 4 2 5% 5% 4 6% 5% 8% 12% 42%	2702
July	1st to 10th	Day	8% 5% 2 6% 5% 6% 6% 5% 8% 11% 38%	5900
	11th to 20th	Day	9% 5% 2 7% 6% 6% 6% 6% 9% 13% 32%	5900
	21st to end	Day	8% 6% 2 6% 5% 6% 6% 5% 9% 11% 37%	6424
August	1st to 10th	Day	17% 9% 3 8% 5% 5% 5% 4 8% 10% 26%	4234
	11th to 20th	Day	9% 6% 3 8% 5% 5% 6% 5% 7% 10% 36%	4014
	21st to end	Day	6% 4 2 5% 4 4 5% 4 7% 11% 49%	4312
September	1st to 10th	Day	10% 5% 1 5% 4 4 5% 3 7% 8% 46%	2400
	11th to 20th	Day	15% 6% 2 6% 4 5% 4 3 5% 8% 42%	2325
	21st to end	Day	21% 5% 3 7% 3 2 4 3 6% 7% 38%	2125
October	1st to 10th	Day	15% 6% 2 5% 3 4 3 2 4 5% 51%	2000
	11th to 20th	Day	14% 5% 2 3 3 3 2 3 5% 5% 55%	2000
	21st to end	Day	12% 4 2 5% 3 2 3 3 4 5% 57%	2200
November	1st to 10th	Day	13% 4 2 5% 3 3 4 3 5% 6% 54%	2057
	11th to 20th	Day	14% 6% 2 5% 2 3 3 3 5% 6% 52%	2025
	21st to end	Day	14% 5% 2 4 3 3 3 3 5% 6% 51%	1681
December	1st to 10th	Day	11% 6% 2 6% 3 3 4 3 4 6% 51%	2680
	11th to 20th	Day	17% 6% 2 6% 3 3 3 3 5% 6% 46%	3070
	21st to end	Day	14% 6% 2 6% 4 4 4 3 6% 8% 43%	4359
January	1st to 10th	Night	12% 6% 2 5% 3 3 3 3 4 5% 53%	5903
	11th to 20th	Night	13% 6% 2 5% 3 2 2 3 4 5% 55%	5900
	21st to end	Night	15% 7% 3 5% 3 3 3 3 4 5% 49%	6490
February	1st to 10th	Night	17% 7% 3 5% 3 4 3 4 5% 6% 44%	2600
	11th to 20th	Night	20% 7% 2 5% 4 3 4 3 5% 6% 41%	2498
	21st to end	Night	14% 7% 2 5% 4 4 3 3 5% 6% 47%	1885
March	1st to 10th	Night	16% 6% 2 6% 5% 4 4 3 5% 5% 43%	4918
	11th to 20th	Night	11% 4 2 5% 4 3 4 3 5% 6% 54%	4980
	21st to end	Night	13% 5% 2 5% 4 4 3 3 5% 7% 50%	5467
April	1st to 10th	Night	13% 6% 2 6% 3 3 4 3 5% 7% 46%	2040
	11th to 20th	Night	11% 5% 2 5% 4 4 4 4 5% 7% 50%	1975
	21st to end	Night	13% 4 2 5% 4 4 4 4 5% 7% 47%	2000
May	1st to 10th	Night	11% 8% 3 8% 5% 5% 5% 4 7% 10% 35%	4173
	11th to 20th	Night	21% 8% 3 7% 4 4 4 3 5% 8% 33%	4032
	21st to end	Night	15% 5% 2 6% 4 4 4 3 6% 8% 42%	4386
June	1st to 10th	Night	10% 5% 2 6% 5% 5% 5% 4 7% 9% 43%	1600
	11th to 20th	Night	10% 5% 2 6% 6% 5% 4 4 7% 10% 41%	1600
	21st to end	Night	7% 5% 2 4 5% 5% 6% 5% 7% 11% 42%	1688
July	1st to 10th	Night	10% 5% 3 7% 5% 6% 6% 5% 8% 11% 34%	4058
	11th to 20th	Night	11% 8% 3 8% 6% 6% 7% 6% 8% 10% 27%	4057
	21st to end	Night	11% 7% 3 8% 6% 5% 6% 5% 7% 10% 33%	4427
August	1st to 10th	Night	19% 8% 3 7% 5% 5% 6% 5% 7% 10% 27%	2915
	11th to 20th	Night	7% 5% 2 7% 5% 6% 7% 5% 8% 10% 39%	3002
	21st to end	Night	7% 5% 2 6% 5% 4 5% 5% 7% 9% 45%	3586
September	1st to 10th	Night	12% 5% 2 5% 4 3 3 4 5% 9% 48%	2000
	11th to 20th	Night	15% 6% 3 7% 4 3 4 3 5% 8% 41%	2070
	21st to end	Night	21% 7% 3 7% 5% 4 4 3 5% 6% 35%	2275
October	1st to 10th	Night	14% 5% 2 6% 5% 3 4 3 5% 5% 47%	2400
	11th to 20th	Night	14% 6% 2 4 3 3 3 3 4 6% 53%	2400
	21st to end	Night	12% 4 2 5% 3 3 4 3 5% 6% 53%	2640
November	1st to 10th	Night	13% 6% 2 5% 3 3 3 3 4 6% 51%	2461
	11th to 20th	Night	13% 6% 1 4 4 3 4 3 5% 5% 51%	2591
	21st to end	Night	13% 4 2 5% 4 3 3 3 5% 5% 52%	2935
December	1st to 10th	Night	11% 5% 2 5% 4 4 4 3 4 5% 52%	4720
	11th to 20th	Night	18% 7% 3 7% 4 4 4 3 4 5% 40%	5345
	21st to end	Night	13% 6% 2 6% 3 3 4 3 5% 6% 47%	6807

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	24% 25% 2 15% 26% 8%	4066
	11th to 20th	Day	22% 26% 3 13% 27% 9%	4060
	21st to end	Day	30% 29% 5% 18% 14% 4	4466
February	1st to 10th	Day	16% 62% 4 10% 6% 2	1800
	11th to 20th	Day	20% 61% 3 7% 7% 2	1796
	21st to end	Day	17% 62% 4 6% 9% 2	1740
March	1st to 10th	Day	36% 30% 5% 11% 10% 9%	4935
	11th to 20th	Day	21% 29% 5% 14% 20% 11%	4980
	21st to end	Day	27% 30% 7% 14% 16% 5%	5465
April	1st to 10th	Day	13% 63% 5% 8% 8% 2	2360
	11th to 20th	Day	13% 63% 6% 10% 6% 2	2374
	21st to end	Day	15% 63% 6% 10% 6% 1	2400
May	1st to 10th	Day	31% 33% 14% 15% 6% 1	5797
	11th to 20th	Day	38% 31% 9% 15% 7%	5865
	21st to end	Day	26% 31% 11% 16% 14% 2	6465
June	1st to 10th	Day	13% 64% 6% 10% 6% 1	2800
	11th to 20th	Day	11% 65% 8% 9% 7%	2800
	21st to end	Day	11% 63% 8% 10% 7%	2702
July	1st to 10th	Day	28% 32% 15% 15% 8% 2	5835
	11th to 20th	Day	32% 33% 21% 11% 2	5831
	21st to end	Day	28% 31% 12% 19% 10%	6240
August	1st to 10th	Day	38% 38% 12% 10% 2	4221
	11th to 20th	Day	24% 40% 14% 15% 6%	4053
	21st to end	Day	14% 38% 12% 24% 11% 1	4312
September	1st to 10th	Day	16% 60% 8% 8% 7% 1	2400
	11th to 20th	Day	19% 58% 5% 8% 8% 2	2325
	21st to end	Day	24% 58% 6% 9% 3	2125
October	1st to 10th	Day	21% 37% 6% 13% 19% 5%	3260
	11th to 20th	Day	10% 35% 3 13% 21% 17%	3240
	21st to end	Day	11% 35% 5% 19% 18% 11%	3538
November	1st to 10th	Day	18% 54% 4 12% 10% 3	2057
	11th to 20th	Day	16% 54% 4 11% 13% 3	2025
	21st to end	Day	16% 54% 4 11% 13% 2	1681
December	1st to 10th	Day	23% 34% 4 19% 13% 6%	2680
	11th to 20th	Day	28% 32% 8% 12% 15% 5%	3066
	21st to end	Day	29% 27% 10% 19% 14% 1	4359
January	1st to 10th	Night	24% 25% 4 13% 22% 11%	5903
	11th to 20th	Night	23% 26% 3 13% 30% 6%	5900
	21st to end	Night	28% 28% 4 18% 18% 4	6490
February	1st to 10th	Night	16% 63% 5% 8% 7% 1	2600
	11th to 20th	Night	19% 61% 4 7% 8% 2	2500
	21st to end	Night	13% 62% 4 10% 7% 4	1885
March	1st to 10th	Night	35% 29% 5% 8% 15% 8%	4918
	11th to 20th	Night	20% 29% 5% 9% 22% 14%	4980
	21st to end	Night	24% 29% 7% 18% 18% 5%	5467
April	1st to 10th	Night	14% 63% 5% 7% 9% 2	2040
	11th to 20th	Night	14% 63% 5% 11% 5% 2	1975
	21st to end	Night	13% 63% 5% 11% 7% 1	2000
May	1st to 10th	Night	34% 32% 13% 13% 7% 1	4202
	11th to 20th	Night	38% 30% 9% 14% 8% 1	4033
	21st to end	Night	29% 31% 11% 18% 11% 1	4393
June	1st to 10th	Night	15% 64% 5% 9% 6% 1	1600
	11th to 20th	Night	12% 64% 8% 8% 7%	1600
	21st to end	Night	13% 62% 7% 11% 6% 1	1688
July	1st to 10th	Night	33% 32% 13% 14% 7% 1	4015
	11th to 20th	Night	41% 34% 15% 8% 1	4006
	21st to end	Night	36% 29% 12% 14% 9%	4297
August	1st to 10th	Night	37% 39% 13% 10% 2	2904
	11th to 20th	Night	22% 41% 15% 17% 5%	3029
	21st to end	Night	19% 38% 7% 20% 16% 1	3586
September	1st to 10th	Night	15% 59% 9% 10% 7% 1	2000
	11th to 20th	Night	19% 59% 5% 8% 7% 1	2070
	21st to end	Night	26% 59% 5% 7% 3	2275
October	1st to 10th	Night	26% 37% 7% 11% 17% 2	3920
	11th to 20th	Night	13% 35% 4 13% 22% 13%	3899
	21st to end	Night	12% 35% 4 21% 15% 12%	4252
November	1st to 10th	Night	20% 54% 4 9% 11% 2	2461
	11th to 20th	Night	15% 54% 4 9% 13% 6%	2591
	21st to end	Night	15% 55% 4 11% 14% 2	2935
December	1st to 10th	Night	22% 35% 3 17% 18% 4	4720
	11th to 20th	Night	34% 31% 6% 12% 11% 6%	5348
	21st to end	Night	27% 27% 10% 20% 15% 1	6807

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	27% 28% 31% 11% 4	303
	11th to 20th	Day	26% 28% 35% 9% 2	300
	21st to end	Day	22% 21% 41% 14% 2	330
February	1st to 10th	Day	21% 25% 39% 12% 3	300
	11th to 20th	Day	39% 25% 28% 7%	334
	21st to end	Day	27% 19% 34% 18% 2	414
March	1st to 10th	Day	24% 20% 33% 17% 6%	500
	11th to 20th	Day	23% 22% 34% 15% 5% 1	500
	21st to end	Day	21% 19% 39% 16% 4 1	550
April	1st to 10th	Day	20% 20% 34% 20% 6% 1	500
	11th to 20th	Day	18% 14% 36% 19% 9% 3	492
	21st to end	Day	19% 12% 33% 26% 10% 1	500
May	1st to 10th	Day	15% 16% 38% 21% 9% 2	503
	11th to 20th	Day	19% 9% 26% 31% 12% 3	527
	21st to end	Day	19% 8% 22% 27% 20% 5%	573
June	1st to 10th	Day	10% 5% 29% 30% 19% 6%	530
	11th to 20th	Day	9% 7% 20% 32% 24% 8%	530
	21st to end	Day	8% 5% 19% 36% 25% 8%	530
July	1st to 10th	Day	10% 2 14% 33% 30% 11%	525
	11th to 20th	Day	6% 1 12% 34% 35% 11%	524
	21st to end	Day	9% 2 16% 36% 27% 11%	576
August	1st to 10th	Day	15% 5% 18% 27% 26% 9%	526
	11th to 20th	Day	10% 2 14% 32% 33% 9%	519
	21st to end	Day	8% 2 15% 30% 29% 16%	583
September	1st to 10th	Day	12% 4 16% 29% 24% 15%	530
	11th to 20th	Day	16% 4 14% 33% 21% 11%	530
	21st to end	Day	26% 6% 22% 27% 14% 5%	530
October	1st to 10th	Day	18% 7% 21% 25% 22% 7%	530
	11th to 20th	Day	15% 11% 29% 25% 17% 3	530
	21st to end	Day	14% 13% 29% 26% 14% 4	583
November	1st to 10th	Day	16% 10% 35% 24% 12% 3	535
	11th to 20th	Day	19% 16% 30% 24% 10% 1	500
	21st to end	Day	20% 19% 26% 24% 9% 2	221
December	1st to 10th	Day	23% 18% 41% 12% 5% 1	220
	11th to 20th	Day	25% 15% 33% 24% 3 1	220
	21st to end	Day	21% 22% 34% 15% 6% 2	316
January	1st to 10th	Night	19% 21% 34% 22% 3	805
	11th to 20th	Night	22% 18% 32% 24% 4	800
	21st to end	Night	19% 17% 37% 25% 2	880
February	1st to 10th	Night	21% 16% 36% 23% 4	800
	11th to 20th	Night	26% 20% 38% 15% 1	783
	21st to end	Night	18% 16% 40% 23% 3	660
March	1st to 10th	Night	18% 17% 36% 25% 4	800
	11th to 20th	Night	19% 17% 36% 22% 6%	800
	21st to end	Night	19% 13% 43% 21% 4	880
April	1st to 10th	Night	18% 17% 37% 23% 5%	800
	11th to 20th	Night	14% 14% 36% 27% 9% 1	791
	21st to end	Night	14% 9% 36% 34% 7%	800
May	1st to 10th	Night	16% 11% 32% 30% 11%	664
	11th to 20th	Night	18% 8% 27% 33% 14%	591
	21st to end	Night	15% 3 18% 38% 24% 1	640
June	1st to 10th	Night	13% 2 20% 44% 21% 1	400
	11th to 20th	Night	10% 2 20% 42% 24% 2	400
	21st to end	Night	7% 2 14% 50% 25% 2	488
July	1st to 10th	Night	10% 1 12% 39% 34% 3	585
	11th to 20th	Night	6% 1 11% 37% 39% 5%	582
	21st to end	Night	8% 2 15% 38% 34% 3	657
August	1st to 10th	Night	13% 2 14% 40% 27% 4	597
	11th to 20th	Night	12% 2 11% 39% 32% 4	669
	21st to end	Night	10% 3 13% 34% 35% 6%	880
September	1st to 10th	Night	13% 3 13% 37% 30% 5%	800
	11th to 20th	Night	16% 4 17% 30% 30% 4	800
	21st to end	Night	23% 4 21% 33% 18% 1	800
October	1st to 10th	Night	16% 5% 19% 30% 25% 5%	800
	11th to 20th	Night	17% 9% 25% 31% 17% 1	800
	21st to end	Night	15% 10% 26% 30% 17% 2	880
November	1st to 10th	Night	17% 8% 28% 30% 15% 2	820
	11th to 20th	Night	16% 12% 30% 32% 9%	840
	21st to end	Night	16% 14% 27% 31% 11% 1	840
December	1st to 10th	Night	23% 13% 34% 23% 7%	840
	11th to 20th	Night	19% 11% 34% 30% 5%	840
	21st to end	Night	21% 15% 29% 30% 5%	924

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