Pictor Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Pictor Observatory clear sky chart from 2005-11-06 to 2024-07-31.

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% 4 4 6% 7% 30%	90430
	Night	15% 11% 4 8% 5% 4 4 4 5% 6% 32%	89381
Transparency	Day	51% 8% 12% 18% 9% 1	90158
	Night	50% 8% 13% 18% 10% 1	89208
Seeing	Day	18% 12% 29% 23% 13% 5%	14552
	Night	19% 10% 29% 29% 11% 1	23639

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	16% 19% 8% 11% 6% 5% 4 3 3 4 20%	2659
	11th to 20th	Day	12% 20% 9% 20% 6% 5% 3 3 5% 5% 11%	2840
	21st to end	Day	23% 20% 7% 12% 7% 5% 5% 3 3 4 11%	3124
February	1st to 10th	Day	15% 18% 6% 11% 9% 6% 5% 3 4 5% 18%	1710
	11th to 20th	Day	13% 16% 7% 15% 7% 5% 5% 3 4 5% 19%	1663
	21st to end	Day	17% 16% 5% 12% 6% 5% 5% 3 5% 5% 22%	1546
March	1st to 10th	Day	20% 15% 5% 9% 6% 4 4 3 5% 4 26%	3372
	11th to 20th	Day	12% 16% 5% 11% 5% 4 4 3 5% 7% 28%	3480
	21st to end	Day	17% 11% 3 10% 5% 5% 4 3 5% 5% 31%	3815
April	1st to 10th	Day	15% 14% 5% 8% 5% 4 4 3 5% 7% 28%	2175
	11th to 20th	Day	18% 11% 3 8% 5% 4 4 3 6% 7% 32%	2402
	21st to end	Day	20% 11% 3 8% 5% 4 3 2 5% 6% 33%	2470
May	1st to 10th	Day	19% 8% 3 7% 5% 4 4 4 6% 7% 33%	4108
	11th to 20th	Day	16% 9% 3 7% 5% 5% 5% 4 7% 9% 31%	4138
	21st to end	Day	12% 6% 2 6% 4 4 4 4 6% 8% 45%	4837
June	1st to 10th	Day	13% 6% 3 7% 5% 5% 5% 4 6% 8% 39%	2660
	11th to 20th	Day	11% 6% 3 6% 4 5% 6% 4 7% 9% 39%	2775
	21st to end	Day	12% 5% 3 5% 5% 5% 5% 5% 6% 9% 39%	2850
July	1st to 10th	Day	9% 5% 2 6% 4 5% 5% 4 7% 9% 44%	2845
	11th to 20th	Day	11% 6% 3 6% 5% 5% 5% 5% 8% 11% 36%	2517
	21st to end	Day	9% 6% 3 6% 6% 6% 6% 4 6% 9% 39%	2679
August	1st to 10th	Day	8% 5% 2 7% 6% 6% 6% 5% 8% 9% 38%	2327
	11th to 20th	Day	11% 7% 2 7% 4 7% 6% 6% 6% 10% 36%	2303
	21st to end	Day	12% 7% 2 5% 6% 5% 4 4 6% 9% 40%	2530
September	1st to 10th	Day	12% 7% 2 8% 5% 5% 5% 5% 7% 8% 38%	2135
	11th to 20th	Day	12% 5% 2 6% 4 4 4 4 6% 9% 43%	1980
	21st to end	Day	15% 6% 2 8% 6% 5% 4 4 7% 8% 36%	1980
October	1st to 10th	Day	18% 8% 3 7% 5% 4 4 4 6% 6% 35%	1823
	11th to 20th	Day	21% 10% 4 7% 5% 5% 6% 3 6% 7% 28%	1800
	21st to end	Day	24% 11% 4 8% 6% 5% 5% 4 5% 6% 22%	1967
November	1st to 10th	Day	14% 12% 3 8% 5% 4 5% 4 5% 7% 33%	1672
	11th to 20th	Day	15% 14% 4 9% 5% 4 5% 3 6% 8% 27%	1530
	21st to end	Day	20% 16% 6% 9% 6% 4 5% 3 6% 6% 19%	1520
December	1st to 10th	Day	16% 18% 6% 13% 5% 4 4 4 5% 6% 18%	1520
	11th to 20th	Day	17% 19% 7% 12% 7% 5% 5% 4 5% 4 15%	1906
	21st to end	Day	29% 18% 8% 12% 6% 4 3 3 4 4 9%	2772
January	1st to 10th	Night	17% 16% 7% 12% 6% 5% 5% 3 5% 6% 18%	4270
	11th to 20th	Night	15% 16% 7% 15% 7% 7% 6% 5% 5% 5% 11%	4120
	21st to end	Night	23% 17% 8% 14% 6% 4 3 3 4 4 15%	4532
February	1st to 10th	Night	16% 16% 5% 11% 7% 6% 4 4 5% 4 21%	2470
	11th to 20th	Night	15% 13% 5% 10% 6% 6% 5% 4 6% 7% 23%	2403
	21st to end	Night	16% 13% 5% 12% 6% 5% 5% 4 5% 6% 22%	1905
March	1st to 10th	Night	16% 11% 4 8% 6% 4 4 3 5% 6% 33%	3468
	11th to 20th	Night	11% 10% 4 8% 6% 5% 5% 4 6% 8% 36%	3479
	21st to end	Night	17% 11% 3 7% 4 3 4 3 5% 4 38%	3817
April	1st to 10th	Night	18% 10% 3 7% 5% 5% 4 4 5% 6% 33%	2005
	11th to 20th	Night	18% 9% 2 7% 5% 4 4 3 5% 6% 36%	1743
	21st to end	Night	15% 8% 2 8% 5% 4 5% 6% 7% 7% 33%	1710
May	1st to 10th	Night	18% 8% 3 6% 4 3 4 4 5% 7% 38%	2833
	11th to 20th	Night	11% 9% 3 8% 5% 5% 5% 4 6% 8% 36%	2754
	21st to end	Night	10% 6% 2 4 3 3 4 4 6% 7% 51%	2738
June	1st to 10th	Night	12% 6% 2 5% 4 4 5% 3 7% 8% 44%	1520
	11th to 20th	Night	9% 5% 2 5% 4 4 6% 5% 7% 10% 42%	1399
	21st to end	Night	10% 6% 2 5% 4 4 4 4 6% 8% 46%	1330
July	1st to 10th	Night	5% 4 2 6% 4 3 3 3 7% 9% 55%	1330
	11th to 20th	Night	9% 5% 1 5% 4 3 3 4 6% 8% 50%	1657
	21st to end	Night	7% 5% 1 6% 3 4 5% 5% 7% 8% 48%	1870
August	1st to 10th	Night	7% 4 2 6% 4 5% 5% 4 6% 8% 48%	1611
	11th to 20th	Night	8% 4 2 5% 4 3 6% 4 7% 9% 49%	1598
	21st to end	Night	9% 5% 2 6% 4 4 4 3 6% 8% 49%	1808
September	1st to 10th	Night	11% 6% 3 7% 5% 4 3 4 5% 6% 46%	1822
	11th to 20th	Night	10% 5% 1 4 4 3 4 3 5% 7% 53%	1980
	21st to end	Night	15% 6% 3 6% 4 5% 4 3 5% 7% 41%	1980
October	1st to 10th	Night	15% 7% 2 6% 4 4 5% 3 5% 7% 41%	2137
	11th to 20th	Night	18% 9% 3 7% 5% 4 4 4 5% 7% 34%	2160
	21st to end	Night	23% 10% 4 8% 5% 5% 5% 3 6% 6% 27%	2386
November	1st to 10th	Night	15% 8% 3 6% 4 4 3 4 6% 7% 38%	2406
	11th to 20th	Night	16% 13% 3 8% 5% 4 4 4 6% 8% 28%	2648
	21st to end	Night	20% 15% 4 8% 5% 4 5% 4 6% 6% 23%	2660
December	1st to 10th	Night	19% 16% 5% 10% 6% 5% 5% 4 5% 5% 18%	2660
	11th to 20th	Night	14% 19% 5% 12% 5% 4 4 4 5% 6% 21%	3288
	21st to end	Night	26% 21% 7% 11% 5% 4 4 3 4 4 12%	4884

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	66% 8% 11% 10% 5%	2660
	11th to 20th	Day	74% 7% 9% 6% 3	2840
	21st to end	Day	76% 9% 7% 6% 3	3124
February	1st to 10th	Day	68% 6% 9% 12% 4 1	1710
	11th to 20th	Day	65% 7% 8% 14% 6%	1672
	21st to end	Day	63% 7% 10% 13% 6% 1	1546
March	1st to 10th	Day	60% 6% 9% 19% 4 1	3375
	11th to 20th	Day	53% 7% 15% 17% 6% 1	3480
	21st to end	Day	52% 7% 11% 18% 11% 1	3815
April	1st to 10th	Day	55% 6% 11% 17% 10% 1	2175
	11th to 20th	Day	50% 6% 12% 20% 12% 1	2402
	21st to end	Day	53% 5% 11% 19% 11% 2	2470
May	1st to 10th	Day	47% 8% 14% 19% 10% 3	4120
	11th to 20th	Day	45% 11% 16% 20% 7% 1	4142
	21st to end	Day	35% 9% 12% 20% 20% 4	4837
June	1st to 10th	Day	40% 8% 14% 24% 12% 2	2660
	11th to 20th	Day	39% 9% 13% 22% 16% 2	2775
	21st to end	Day	39% 9% 13% 25% 15%	2850
July	1st to 10th	Day	34% 8% 13% 26% 16% 3	2771
	11th to 20th	Day	39% 9% 14% 25% 12% 1	2445
	21st to end	Day	38% 10% 14% 22% 14% 2	2537
August	1st to 10th	Day	37% 11% 16% 25% 11% 1	2314
	11th to 20th	Day	40% 10% 16% 22% 10% 1	2303
	21st to end	Day	39% 9% 14% 25% 12% 2	2530
September	1st to 10th	Day	41% 8% 15% 22% 12% 1	2135
	11th to 20th	Day	35% 8% 14% 28% 14%	1980
	21st to end	Day	43% 9% 14% 23% 10% 1	1980
October	1st to 10th	Day	48% 7% 12% 20% 12% 1	1823
	11th to 20th	Day	54% 7% 14% 16% 8% 1	1800
	21st to end	Day	62% 7% 12% 13% 6%	1967
November	1st to 10th	Day	49% 8% 11% 23% 7% 2	1672
	11th to 20th	Day	53% 8% 16% 14% 8% 1	1530
	21st to end	Day	63% 8% 14% 12% 3	1520
December	1st to 10th	Day	65% 10% 11% 11% 3	1520
	11th to 20th	Day	69% 8% 10% 10% 3	1906
	21st to end	Day	78% 8% 8% 6% 1	2772
January	1st to 10th	Night	64% 10% 12% 10% 4	4270
	11th to 20th	Night	71% 10% 9% 8% 3	4120
	21st to end	Night	72% 7% 9% 9% 3 1	4532
February	1st to 10th	Night	63% 8% 11% 14% 5%	2470
	11th to 20th	Night	58% 7% 13% 15% 6%	2405
	21st to end	Night	59% 8% 12% 15% 7%	1905
March	1st to 10th	Night	50% 7% 14% 22% 6% 1	3478
	11th to 20th	Night	43% 8% 19% 19% 11% 1	3480
	21st to end	Night	46% 5% 11% 22% 14% 2	3817
April	1st to 10th	Night	50% 6% 10% 19% 13% 1	2005
	11th to 20th	Night	47% 5% 10% 19% 16% 2	1743
	21st to end	Night	46% 7% 12% 18% 14% 3	1710
May	1st to 10th	Night	44% 6% 12% 18% 15% 5%	2840
	11th to 20th	Night	42% 9% 15% 23% 8% 2	2755
	21st to end	Night	29% 8% 14% 23% 23% 3	2739
June	1st to 10th	Night	36% 7% 13% 26% 15% 3	1520
	11th to 20th	Night	33% 9% 13% 25% 18% 2	1399
	21st to end	Night	35% 8% 14% 24% 19% 1	1330
July	1st to 10th	Night	26% 7% 11% 28% 23% 4	1295
	11th to 20th	Night	30% 7% 13% 29% 17% 3	1607
	21st to end	Night	29% 10% 17% 24% 17% 3	1771
August	1st to 10th	Night	31% 9% 15% 31% 13% 1	1600
	11th to 20th	Night	29% 9% 16% 30% 14% 2	1598
	21st to end	Night	32% 7% 14% 29% 16% 2	1808
September	1st to 10th	Night	38% 7% 13% 25% 15% 2	1822
	11th to 20th	Night	29% 7% 13% 32% 17% 1	1980
	21st to end	Night	41% 8% 12% 26% 12% 1	1980
October	1st to 10th	Night	42% 7% 11% 23% 15% 1	2137
	11th to 20th	Night	48% 7% 13% 21% 10%	2160
	21st to end	Night	56% 7% 10% 17% 9% 1	2386
November	1st to 10th	Night	42% 7% 14% 23% 12% 1	2406
	11th to 20th	Night	51% 9% 14% 17% 8% 1	2648
	21st to end	Night	60% 7% 17% 12% 4 1	2660
December	1st to 10th	Night	65% 9% 11% 11% 4	2660
	11th to 20th	Night	61% 7% 14% 13% 4	3288
	21st to end	Night	75% 7% 10% 6% 2	4884

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	23% 19% 33% 19% 5% 1	222
	11th to 20th	Day	20% 21% 41% 13% 3 1	270
	21st to end	Day	28% 14% 35% 19% 3 1	297
February	1st to 10th	Day	26% 17% 40% 13% 3 1	270
	11th to 20th	Day	24% 21% 39% 13% 3	270
	21st to end	Day	26% 28% 33% 12% 1	225
March	1st to 10th	Day	23% 15% 36% 19% 5% 1	422
	11th to 20th	Day	23% 14% 37% 19% 5% 1	460
	21st to end	Day	28% 15% 30% 21% 7% 1	506
April	1st to 10th	Day	19% 19% 33% 22% 6% 2	460
	11th to 20th	Day	27% 15% 25% 18% 10% 4	452
	21st to end	Day	25% 12% 32% 22% 7% 2	460
May	1st to 10th	Day	23% 11% 27% 23% 12% 3	463
	11th to 20th	Day	16% 10% 30% 21% 18% 5%	487
	21st to end	Day	14% 7% 26% 28% 18% 7%	529
June	1st to 10th	Day	14% 8% 31% 31% 12% 4	490
	11th to 20th	Day	11% 9% 29% 32% 15% 4	605
	21st to end	Day	14% 8% 32% 30% 14% 3	680
July	1st to 10th	Day	9% 6% 24% 29% 25% 7%	666
	11th to 20th	Day	13% 5% 24% 27% 20% 11%	484
	21st to end	Day	9% 4 24% 33% 22% 8%	529
August	1st to 10th	Day	8% 4 21% 29% 24% 14%	446
	11th to 20th	Day	13% 5% 17% 28% 22% 14%	439
	21st to end	Day	12% 6% 22% 25% 23% 12%	495
September	1st to 10th	Day	13% 7% 22% 27% 20% 11%	450
	11th to 20th	Day	9% 5% 19% 27% 28% 12%	450
	21st to end	Day	15% 10% 26% 26% 14% 8%	450
October	1st to 10th	Day	19% 9% 26% 23% 19% 5%	450
	11th to 20th	Day	20% 18% 32% 20% 7% 2	450
	21st to end	Day	29% 13% 33% 20% 5% 1	482
November	1st to 10th	Day	20% 22% 33% 16% 7% 2	270
	11th to 20th	Day	25% 19% 33% 14% 6% 3	185
	21st to end	Day	26% 16% 41% 16% 3	180
December	1st to 10th	Day	28% 22% 32% 13% 5% 1	180
	11th to 20th	Day	26% 26% 32% 13% 3	180
	21st to end	Day	31% 20% 34% 12% 3	198
January	1st to 10th	Night	21% 18% 37% 17% 5% 1	760
	11th to 20th	Night	28% 16% 34% 20% 3	760
	21st to end	Night	20% 11% 36% 27% 6%	836
February	1st to 10th	Night	23% 16% 37% 23% 2	760
	11th to 20th	Night	22% 16% 34% 24% 5%	743
	21st to end	Night	24% 16% 35% 22% 3	628
March	1st to 10th	Night	18% 14% 36% 26% 6%	760
	11th to 20th	Night	19% 15% 36% 23% 6% 1	760
	21st to end	Night	21% 12% 32% 25% 9%	836
April	1st to 10th	Night	23% 13% 32% 28% 5%	760
	11th to 20th	Night	22% 12% 31% 26% 9% 1	619
	21st to end	Night	18% 9% 34% 32% 7%	570
May	1st to 10th	Night	20% 7% 28% 30% 14% 1	570
	11th to 20th	Night	16% 5% 27% 37% 15% 1	529
	21st to end	Night	11% 5% 26% 39% 18% 1	411
June	1st to 10th	Night	15% 4 28% 43% 10% 1	380
	11th to 20th	Night	10% 5% 31% 42% 12%	380
	21st to end	Night	13% 5% 25% 43% 14% 1	380
July	1st to 10th	Night	5% 3 22% 46% 21% 2	370
	11th to 20th	Night	10% 3 20% 41% 25% 2	504
	21st to end	Night	9% 3 17% 47% 23% 2	624
August	1st to 10th	Night	9% 3 15% 42% 30% 2	537
	11th to 20th	Night	8% 2 16% 38% 31% 5%	534
	21st to end	Night	10% 3 20% 38% 26% 3	620
September	1st to 10th	Night	12% 6% 22% 32% 23% 5%	720
	11th to 20th	Night	11% 4 16% 38% 27% 4	720
	21st to end	Night	17% 6% 20% 32% 19% 5%	720
October	1st to 10th	Night	18% 8% 26% 30% 17% 2	720
	11th to 20th	Night	21% 13% 30% 26% 10% 1	720
	21st to end	Night	27% 10% 33% 25% 5%	792
November	1st to 10th	Night	19% 11% 28% 29% 11% 1	740
	11th to 20th	Night	21% 15% 34% 21% 8% 1	760
	21st to end	Night	27% 13% 32% 22% 7%	760
December	1st to 10th	Night	27% 17% 33% 18% 4	760
	11th to 20th	Night	24% 18% 37% 17% 4	760
	21st to end	Night	29% 14% 35% 20% 2	836

Page generated at 2024-07-28 09:52:14. Version ac07

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