Point Petre
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Point Petre clear sky chart from 2005-11-06 to 2026-06-16.

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 8% 5% 4 4 3 5% 7% 35%	138148
	Night	17% 12% 4 10% 5% 4 4 3 5% 7% 29%	133853
Transparency	Day	48% 5% 13% 22% 11% 1	141691
	Night	55% 5% 11% 18% 10% 1	138397
Seeing	Day	19% 5% 18% 31% 21% 6%	16519
	Night	22% 7% 23% 28% 16% 3	25798

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	17% 17% 8% 11% 6% 5% 4 3 4 7% 17%	4661
	11th to 20th	Day	12% 22% 9% 22% 8% 4 3 2 3 4 10%	4650
	21st to end	Day	12% 15% 6% 14% 10% 5% 5% 3 5% 7% 17%	5762
February	1st to 10th	Day	14% 15% 6% 14% 6% 4 5% 4 5% 5% 21%	1890
	11th to 20th	Day	15% 12% 5% 13% 6% 5% 4 3 5% 6% 26%	1843
	21st to end	Day	20% 12% 4 11% 5% 5% 4 4 5% 6% 24%	1695
March	1st to 10th	Day	18% 10% 4 9% 5% 5% 4 3 5% 7% 31%	4804
	11th to 20th	Day	11% 11% 4 9% 5% 5% 5% 3 5% 7% 36%	5090
	21st to end	Day	19% 8% 3 7% 5% 3 4 3 5% 5% 39%	5758
April	1st to 10th	Day	18% 9% 3 7% 5% 4 4 3 5% 7% 34%	2520
	11th to 20th	Day	19% 8% 2 6% 4 4 4 3 4 5% 41%	2494
	21st to end	Day	19% 7% 3 7% 5% 4 5% 3 5% 6% 36%	2650
May	1st to 10th	Day	20% 9% 3 7% 4 5% 4 3 5% 6% 34%	8054
	11th to 20th	Day	13% 9% 3 9% 6% 5% 4 3 5% 7% 36%	8221
	21st to end	Day	18% 6% 2 6% 4 4 4 4 6% 8% 38%	9060
June	1st to 10th	Day	15% 6% 2 6% 4 4 4 4 6% 7% 40%	2940
	11th to 20th	Day	12% 5% 2 6% 4 4 4 4 6% 9% 43%	2870
	21st to end	Day	13% 7% 2 6% 4 4 4 3 5% 8% 44%	2800
July	1st to 10th	Day	10% 5% 2 6% 4 4 5% 4 6% 9% 46%	6360
	11th to 20th	Day	9% 5% 2 5% 4 4 4 4 6% 8% 50%	6360
	21st to end	Day	8% 4 2 5% 4 4 4 3 6% 8% 51%	6909
August	1st to 10th	Day	16% 6% 2 6% 4 4 3 3 5% 7% 45%	4234
	11th to 20th	Day	14% 6% 2 6% 4 3 4 4 6% 9% 43%	4174
	21st to end	Day	12% 6% 2 4 3 4 4 3 6% 8% 48%	4314
September	1st to 10th	Day	12% 6% 2 6% 4 3 5% 3 5% 8% 48%	2400
	11th to 20th	Day	10% 4 2 6% 4 3 4 4 5% 8% 51%	2400
	21st to end	Day	16% 6% 3 6% 4 5% 4 4 6% 7% 39%	2103
October	1st to 10th	Day	17% 7% 3 6% 5% 4 4 4 5% 7% 38%	2000
	11th to 20th	Day	20% 7% 2 7% 4 5% 4 4 6% 8% 33%	2000
	21st to end	Day	26% 10% 2 7% 5% 5% 5% 3 5% 5% 27%	2143
November	1st to 10th	Day	15% 11% 4 7% 4 4 4 4 5% 7% 34%	1835
	11th to 20th	Day	15% 14% 4 9% 5% 5% 5% 4 5% 6% 28%	1680
	21st to end	Day	22% 18% 4 8% 5% 4 4 4 5% 6% 21%	1680
December	1st to 10th	Day	20% 21% 5% 9% 5% 5% 5% 3 5% 6% 16%	2680
	11th to 20th	Day	20% 17% 5% 15% 5% 4 4 3 5% 6% 16%	3066
	21st to end	Day	25% 14% 5% 11% 5% 4 5% 3 5% 7% 16%	4048
January	1st to 10th	Night	17% 21% 7% 11% 5% 5% 4 3 4 7% 16%	8234
	11th to 20th	Night	14% 19% 9% 26% 7% 4 4 3 3 4 7%	8235
	21st to end	Night	15% 16% 8% 16% 8% 5% 4 3 4 6% 15%	8401
February	1st to 10th	Night	16% 16% 6% 13% 6% 5% 4 3 4 5% 21%	2730
	11th to 20th	Night	17% 16% 5% 10% 6% 5% 4 3 5% 7% 24%	2663
	21st to end	Night	17% 12% 4 9% 5% 5% 6% 5% 6% 7% 24%	2109
March	1st to 10th	Night	18% 9% 4 10% 6% 5% 4 4 6% 7% 28%	5254
	11th to 20th	Night	15% 12% 3 8% 4 3 4 4 5% 7% 34%	5089
	21st to end	Night	21% 7% 3 7% 4 4 4 3 4 6% 37%	5414
April	1st to 10th	Night	20% 9% 2 7% 5% 4 5% 3 5% 7% 32%	2100
	11th to 20th	Night	19% 8% 4 7% 4 3 4 4 5% 6% 37%	2075
	21st to end	Night	19% 8% 2 7% 4 3 4 4 5% 6% 37%	1989
May	1st to 10th	Night	27% 9% 3 7% 5% 4 4 3 5% 6% 27%	4845
	11th to 20th	Night	15% 7% 3 8% 5% 5% 5% 4 6% 8% 34%	4639
	21st to end	Night	19% 6% 2 7% 4 5% 4 4 6% 8% 36%	5114
June	1st to 10th	Night	15% 6% 2 7% 6% 4 5% 5% 7% 9% 36%	1680
	11th to 20th	Night	9% 6% 3 7% 5% 4 6% 4 6% 9% 43%	1640
	21st to end	Night	11% 8% 3 7% 5% 5% 3 5% 6% 7% 40%	1600
July	1st to 10th	Night	11% 6% 3 6% 4 5% 5% 5% 7% 9% 41%	3600
	11th to 20th	Night	10% 5% 2 6% 5% 4 4 4 6% 8% 45%	3600
	21st to end	Night	10% 5% 2 5% 4 4 4 3 5% 8% 50%	3939
August	1st to 10th	Night	11% 6% 2 7% 4 4 4 4 6% 8% 45%	2915
	11th to 20th	Night	12% 6% 2 6% 4 4 5% 4 5% 9% 42%	2875
	21st to end	Night	8% 4 2 6% 4 4 5% 4 7% 10% 48%	3549
September	1st to 10th	Night	11% 6% 3 6% 4 4 3 3 5% 8% 47%	2000
	11th to 20th	Night	11% 5% 2 5% 4 3 4 3 5% 6% 52%	2000
	21st to end	Night	17% 6% 2 7% 4 5% 4 4 5% 6% 40%	2293
October	1st to 10th	Night	17% 7% 3 8% 5% 4 5% 4 5% 6% 37%	2400
	11th to 20th	Night	20% 9% 3 8% 5% 4 5% 3 5% 6% 30%	2400
	21st to end	Night	24% 9% 4 8% 4 4 4 3 5% 6% 28%	2695
November	1st to 10th	Night	18% 11% 3 6% 4 4 5% 3 5% 6% 34%	2678
	11th to 20th	Night	17% 13% 4 7% 4 4 5% 4 5% 7% 28%	2940
	21st to end	Night	23% 17% 4 8% 5% 4 4 4 5% 7% 19%	2940
December	1st to 10th	Night	22% 24% 5% 8% 5% 4 4 3 4 6% 16%	4720
	11th to 20th	Night	23% 18% 6% 12% 4 4 4 3 4 6% 16%	5348
	21st to end	Night	28% 14% 5% 10% 4 4 4 3 5% 6% 16%	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% 7% 12% 8% 5%	4662
	11th to 20th	Day	81% 3 7% 6% 2	4680
	21st to end	Day	67% 6% 14% 9% 4	5762
February	1st to 10th	Day	66% 3 11% 15% 3 1	1890
	11th to 20th	Day	61% 4 10% 17% 8% 1	1852
	21st to end	Day	62% 3 11% 16% 8%	1695
March	1st to 10th	Day	52% 5% 13% 17% 12% 1	4807
	11th to 20th	Day	47% 4 20% 17% 11% 2	5090
	21st to end	Day	47% 3 8% 24% 16% 2	5758
April	1st to 10th	Day	49% 4 9% 23% 14% 2	2520
	11th to 20th	Day	46% 4 8% 24% 16% 2	2494
	21st to end	Day	48% 4 10% 21% 15% 3	2650
May	1st to 10th	Day	50% 5% 10% 21% 13% 2	8064
	11th to 20th	Day	48% 5% 11% 22% 13% 1	8225
	21st to end	Day	44% 4 13% 25% 13% 1	9061
June	1st to 10th	Day	41% 5% 12% 24% 17% 2	2940
	11th to 20th	Day	36% 5% 13% 30% 14% 2	2870
	21st to end	Day	38% 5% 15% 26% 15% 1	2800
July	1st to 10th	Day	34% 6% 13% 31% 16% 1	6290
	11th to 20th	Day	31% 6% 15% 32% 15% 2	6285
	21st to end	Day	31% 6% 15% 34% 14%	6711
August	1st to 10th	Day	40% 5% 14% 26% 15% 1	4221
	11th to 20th	Day	37% 5% 19% 28% 10%	4213
	21st to end	Day	33% 5% 14% 38% 9% 1	4314
September	1st to 10th	Day	35% 5% 14% 33% 12% 1	2400
	11th to 20th	Day	33% 3 13% 34% 15% 1	2400
	21st to end	Day	44% 5% 14% 28% 10%	2103
October	1st to 10th	Day	38% 7% 14% 29% 13%	3260
	11th to 20th	Day	42% 5% 16% 27% 10%	3240
	21st to end	Day	47% 7% 13% 24% 9%	3445
November	1st to 10th	Day	49% 5% 13% 21% 11%	1835
	11th to 20th	Day	56% 5% 14% 15% 8% 1	1680
	21st to end	Day	66% 3 13% 12% 5%	1680
December	1st to 10th	Day	70% 6% 14% 8% 2	2680
	11th to 20th	Day	70% 7% 13% 8% 2	3066
	21st to end	Day	69% 8% 10% 10% 3	4048
January	1st to 10th	Night	71% 6% 9% 10% 4	8234
	11th to 20th	Night	83% 4 5% 5% 3	8280
	21st to end	Night	72% 4 10% 8% 7%	8401
February	1st to 10th	Night	68% 4 10% 14% 4	2730
	11th to 20th	Night	62% 3 9% 18% 7%	2665
	21st to end	Night	59% 4 13% 17% 6% 1	2109
March	1st to 10th	Night	55% 4 11% 17% 10% 3	5264
	11th to 20th	Night	50% 4 16% 19% 9% 3	5090
	21st to end	Night	48% 4 7% 23% 16% 2	5414
April	1st to 10th	Night	52% 4 9% 22% 12% 2	2100
	11th to 20th	Night	48% 4 10% 19% 17% 1	2075
	21st to end	Night	47% 4 10% 20% 16% 3	1989
May	1st to 10th	Night	58% 4 8% 15% 12% 2	4851
	11th to 20th	Night	47% 6% 13% 21% 13% 1	4640
	21st to end	Night	46% 5% 11% 22% 15% 2	5115
June	1st to 10th	Night	42% 6% 10% 25% 14% 3	1680
	11th to 20th	Night	38% 4 12% 22% 21% 3	1640
	21st to end	Night	41% 7% 11% 23% 16% 2	1600
July	1st to 10th	Night	38% 6% 14% 22% 19% 1	3560
	11th to 20th	Night	35% 7% 12% 28% 18% 1	3552
	21st to end	Night	32% 6% 12% 31% 18% 1	3822
August	1st to 10th	Night	36% 5% 15% 28% 15% 1	2904
	11th to 20th	Night	39% 5% 17% 26% 11% 1	2902
	21st to end	Night	31% 6% 14% 37% 11% 1	3549
September	1st to 10th	Night	37% 4 13% 32% 12% 2	2000
	11th to 20th	Night	33% 4 12% 33% 17% 1	2000
	21st to end	Night	43% 5% 11% 26% 13% 1	2293
October	1st to 10th	Night	39% 5% 10% 28% 18% 1	3920
	11th to 20th	Night	45% 5% 15% 25% 10%	3899
	21st to end	Night	46% 5% 12% 27% 10% 1	4343
November	1st to 10th	Night	52% 4 11% 20% 11% 2	2678
	11th to 20th	Night	57% 4 11% 18% 9% 1	2940
	21st to end	Night	67% 3 13% 13% 3	2940
December	1st to 10th	Night	72% 5% 9% 12% 2	4720
	11th to 20th	Night	72% 5% 10% 9% 3	5348
	21st to end	Night	71% 6% 11% 8% 4	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	22% 15% 27% 26% 7% 3	220
	11th to 20th	Day	27% 14% 30% 22% 7%	220
	21st to end	Day	23% 12% 26% 28% 11% 2	360
February	1st to 10th	Day	23% 11% 28% 28% 9% 1	330
	11th to 20th	Day	20% 11% 28% 33% 6% 1	330
	21st to end	Day	27% 10% 28% 29% 6%	411
March	1st to 10th	Day	20% 9% 27% 34% 9% 1	540
	11th to 20th	Day	21% 9% 29% 30% 10% 1	540
	21st to end	Day	27% 5% 25% 30% 11% 2	594
April	1st to 10th	Day	22% 7% 23% 35% 11% 2	540
	11th to 20th	Day	24% 5% 23% 28% 15% 5%	532
	21st to end	Day	24% 4 19% 34% 17% 2	540
May	1st to 10th	Day	22% 3 14% 36% 20% 4	543
	11th to 20th	Day	14% 3 13% 36% 25% 8%	567
	21st to end	Day	16% 1 9% 37% 26% 10%	617
June	1st to 10th	Day	16% 2 11% 35% 29% 7%	570
	11th to 20th	Day	13% 2 12% 32% 35% 7%	550
	21st to end	Day	18% 1 11% 34% 29% 6%	530
July	1st to 10th	Day	11% 1 5% 32% 39% 11%	525
	11th to 20th	Day	12% 1 9% 30% 38% 9%	524
	21st to end	Day	11% 1 8% 40% 33% 8%	576
August	1st to 10th	Day	14% 2 7% 26% 40% 10%	526
	11th to 20th	Day	12% 2 9% 28% 37% 13%	519
	21st to end	Day	13% 3 11% 31% 34% 9%	583
September	1st to 10th	Day	13% 3 12% 30% 29% 13%	530
	11th to 20th	Day	10% 10% 30% 29% 21%	530
	21st to end	Day	17% 3 13% 32% 27% 8%	530
October	1st to 10th	Day	22% 3 16% 25% 23% 10%	530
	11th to 20th	Day	23% 7% 26% 27% 13% 4	530
	21st to end	Day	30% 5% 23% 28% 13% 1	551
November	1st to 10th	Day	22% 14% 23% 25% 15% 1	409
	11th to 20th	Day	22% 11% 28% 27% 10% 2	220
	21st to end	Day	30% 10% 30% 22% 6% 1	220
December	1st to 10th	Day	32% 10% 24% 24% 8% 1	220
	11th to 20th	Day	26% 16% 35% 18% 4 1	220
	21st to end	Day	36% 9% 30% 21% 5%	242
January	1st to 10th	Night	32% 13% 32% 16% 7%	840
	11th to 20th	Night	30% 13% 29% 21% 7%	840
	21st to end	Night	23% 13% 29% 26% 8% 1	924
February	1st to 10th	Night	25% 13% 31% 26% 6%	840
	11th to 20th	Night	25% 12% 33% 24% 7%	823
	21st to end	Night	23% 9% 36% 26% 6%	692
March	1st to 10th	Night	22% 8% 31% 30% 9%	840
	11th to 20th	Night	24% 10% 27% 30% 8% 1	840
	21st to end	Night	23% 5% 29% 29% 12% 2	924
April	1st to 10th	Night	24% 5% 24% 35% 11% 1	840
	11th to 20th	Night	23% 4 23% 34% 13% 3	831
	21st to end	Night	23% 3 20% 35% 16% 3	729
May	1st to 10th	Night	27% 1 15% 31% 22% 5%	488
	11th to 20th	Night	16% 2 13% 43% 23% 3	414
	21st to end	Night	13% 2 13% 38% 26% 7%	455
June	1st to 10th	Night	15% 2 11% 40% 27% 5%	420
	11th to 20th	Night	11% 2 14% 36% 31% 6%	410
	21st to end	Night	16% 2 13% 35% 30% 5%	400
July	1st to 10th	Night	7% 2 9% 36% 37% 8%	390
	11th to 20th	Night	11% 1 11% 35% 35% 8%	388
	21st to end	Night	11% 2 9% 41% 32% 5%	439
August	1st to 10th	Night	11% 1 10% 36% 35% 8%	597
	11th to 20th	Night	13% 2 11% 33% 32% 9%	594
	21st to end	Night	12% 2 13% 34% 33% 6%	856
September	1st to 10th	Night	15% 3 14% 30% 31% 8%	800
	11th to 20th	Night	14% 2 12% 27% 31% 13%	800
	21st to end	Night	19% 4 17% 29% 23% 9%	800
October	1st to 10th	Night	22% 5% 21% 24% 19% 8%	800
	11th to 20th	Night	23% 8% 27% 28% 12% 2	800
	21st to end	Night	30% 6% 27% 27% 10% 1	880
November	1st to 10th	Night	24% 8% 27% 28% 12% 2	820
	11th to 20th	Night	24% 11% 30% 23% 8% 2	840
	21st to end	Night	33% 11% 27% 22% 6% 1	840
December	1st to 10th	Night	36% 14% 27% 18% 5%	840
	11th to 20th	Night	28% 15% 34% 18% 5% 1	840
	21st to end	Night	36% 11% 29% 18% 5%	924

Page generated at 2026-06-13 02:31:38. Version ac07

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