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 2025-01-07.

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 8% 5% 5% 5% 4 6% 7% 31%	105519
	Night	15% 11% 4 9% 5% 4 4 4 5% 6% 32%	103493
Transparency	Day	50% 8% 13% 19% 10% 1	109125
	Night	49% 7% 12% 19% 11% 1	107977
Seeing	Day	18% 12% 29% 23% 13% 5%	15067
	Night	19% 11% 29% 29% 11% 1	24247

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% 12% 6% 5% 4 3 3 4 20%	2708
	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	11% 5% 2 7% 4 5% 5% 4 7% 10% 40%	4742
	11th to 20th	Day	10% 5% 2 6% 5% 5% 5% 5% 7% 10% 39%	4193
	21st to end	Day	8% 5% 2 6% 6% 6% 6% 5% 6% 8% 41%	4466
August	1st to 10th	Day	15% 6% 2 6% 5% 5% 5% 4 7% 8% 37%	4104
	11th to 20th	Day	11% 7% 3 7% 4 6% 7% 5% 6% 10% 34%	4044
	21st to end	Day	9% 6% 2 6% 6% 5% 5% 4 7% 9% 40%	4446
September	1st to 10th	Day	11% 6% 2 8% 5% 4 5% 5% 6% 8% 39%	2253
	11th to 20th	Day	11% 5% 2 6% 4 4 4 4 6% 8% 45%	2090
	21st to end	Day	15% 7% 2 8% 6% 5% 5% 4 7% 8% 34%	2090
October	1st to 10th	Day	17% 7% 3 7% 5% 4 4 4 6% 7% 36%	1924
	11th to 20th	Day	20% 9% 3 7% 4 5% 6% 3 6% 7% 30%	1900
	21st to end	Day	23% 11% 4 8% 6% 5% 5% 4 5% 6% 22%	2076
November	1st to 10th	Day	14% 12% 3 8% 4 4 5% 4 5% 7% 33%	1762
	11th to 20th	Day	16% 14% 4 9% 5% 4 5% 3 6% 8% 27%	1610
	21st to end	Day	19% 16% 7% 10% 6% 5% 5% 3 6% 6% 18%	1600
December	1st to 10th	Day	19% 19% 7% 13% 6% 5% 5% 4 5% 5% 13%	2600
	11th to 20th	Day	21% 20% 6% 11% 5% 4 4 3 5% 4 18%	2986
	21st to end	Day	27% 19% 7% 12% 6% 4 4 3 4 5% 9%	3960
January	1st to 10th	Night	17% 16% 7% 13% 6% 5% 5% 3 5% 5% 18%	4354
	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	6% 4 2 6% 3 3 4 3 7% 10% 51%	2210
	11th to 20th	Night	9% 5% 2 5% 3 3 3 4 6% 9% 52%	2761
	21st to end	Night	6% 5% 2 6% 4 4 5% 5% 7% 8% 49%	3087
August	1st to 10th	Night	11% 5% 2 6% 4 5% 5% 4 6% 7% 46%	2825
	11th to 20th	Night	11% 6% 3 5% 4 3 5% 4 6% 8% 46%	2785
	21st to end	Night	8% 5% 2 6% 4 5% 4 3 6% 8% 48%	3178
September	1st to 10th	Night	10% 6% 3 7% 5% 4 3 3 5% 6% 47%	1924
	11th to 20th	Night	10% 5% 1 4 4 3 4 3 5% 7% 54%	2090
	21st to end	Night	16% 6% 3 6% 4 5% 4 3 5% 7% 40%	2090
October	1st to 10th	Night	15% 7% 2 6% 4 4 5% 3 5% 7% 43%	2256
	11th to 20th	Night	18% 9% 3 7% 5% 4 4 4 5% 7% 35%	2280
	21st to end	Night	22% 9% 3 8% 5% 4 5% 3 6% 6% 29%	2519
November	1st to 10th	Night	15% 8% 3 6% 4 4 3 4 6% 7% 38%	2536
	11th to 20th	Night	16% 13% 3 8% 5% 5% 4 4 6% 8% 28%	2788
	21st to end	Night	20% 15% 4 8% 5% 4 5% 4 6% 6% 22%	2800
December	1st to 10th	Night	14% 17% 6% 13% 7% 6% 6% 5% 6% 5% 16%	4580
	11th to 20th	Night	14% 22% 6% 11% 5% 4 4 3 5% 5% 21%	5208
	21st to end	Night	23% 19% 6% 10% 5% 4 4 3 4 5% 16%	6996

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%	2709
	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	37% 7% 14% 25% 13% 3	4668
	11th to 20th	Day	36% 8% 13% 30% 12% 1	4121
	21st to end	Day	37% 10% 13% 20% 18% 1	4324
August	1st to 10th	Day	42% 8% 14% 22% 13% 1	4091
	11th to 20th	Day	42% 9% 16% 25% 8% 1	4083
	21st to end	Day	38% 7% 14% 29% 11% 1	4446
September	1st to 10th	Day	40% 8% 15% 23% 12% 1	2253
	11th to 20th	Day	35% 8% 14% 28% 15%	2090
	21st to end	Day	45% 9% 14% 23% 10% 1	2090
October	1st to 10th	Day	39% 7% 14% 22% 17% 1	3197
	11th to 20th	Day	40% 5% 15% 22% 18%	3140
	21st to end	Day	50% 6% 16% 22% 6%	3402
November	1st to 10th	Day	49% 7% 11% 23% 8% 2	1762
	11th to 20th	Day	54% 8% 15% 14% 8% 1	1610
	21st to end	Day	64% 7% 14% 12% 3	1600
December	1st to 10th	Day	71% 8% 11% 8% 2	2600
	11th to 20th	Day	68% 6% 10% 8% 7%	2986
	21st to end	Day	76% 7% 7% 7% 2	3960
January	1st to 10th	Night	64% 10% 12% 10% 4	4354
	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	28% 6% 12% 27% 20% 6%	2175
	11th to 20th	Night	30% 6% 14% 31% 17% 2	2711
	21st to end	Night	30% 9% 17% 23% 18% 3	2988
August	1st to 10th	Night	36% 7% 14% 25% 17% 1	2814
	11th to 20th	Night	34% 8% 16% 29% 12% 1	2812
	21st to end	Night	32% 7% 12% 31% 17% 1	3178
September	1st to 10th	Night	36% 7% 13% 26% 16% 2	1924
	11th to 20th	Night	28% 7% 13% 32% 18% 1	2090
	21st to end	Night	43% 8% 12% 25% 12%	2090
October	1st to 10th	Night	32% 5% 9% 29% 25% 1	3763
	11th to 20th	Night	41% 5% 14% 23% 16%	3779
	21st to end	Night	42% 6% 14% 25% 13%	4143
November	1st to 10th	Night	43% 7% 14% 23% 13% 1	2536
	11th to 20th	Night	52% 8% 14% 17% 8% 1	2788
	21st to end	Night	60% 7% 16% 13% 3 1	2800
December	1st to 10th	Night	67% 9% 11% 10% 3	4580
	11th to 20th	Night	64% 6% 10% 11% 8% 1	5208
	21st to end	Night	70% 7% 10% 9% 5%	6996

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% 20% 34% 18% 5% 1	235
	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% 23% 8%	532
August	1st to 10th	Day	9% 6% 21% 29% 22% 13%	486
	11th to 20th	Day	13% 5% 20% 27% 22% 14%	479
	21st to end	Day	11% 6% 22% 26% 24% 12%	539
September	1st to 10th	Day	13% 8% 23% 25% 19% 12%	490
	11th to 20th	Day	8% 5% 18% 27% 28% 15%	490
	21st to end	Day	16% 11% 26% 27% 13% 8%	490
October	1st to 10th	Day	18% 9% 26% 24% 18% 5%	490
	11th to 20th	Day	19% 18% 32% 21% 8% 2	490
	21st to end	Day	27% 14% 31% 21% 5% 1	525
November	1st to 10th	Day	19% 24% 32% 16% 7% 2	300
	11th to 20th	Day	25% 19% 33% 14% 6% 3	205
	21st to end	Day	25% 17% 40% 16% 3	200
December	1st to 10th	Day	29% 22% 31% 14% 5% 1	200
	11th to 20th	Day	30% 24% 31% 13% 3	200
	21st to end	Day	31% 19% 34% 12% 4	220
January	1st to 10th	Night	21% 19% 37% 17% 5% 1	785
	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 16% 41% 29% 2	567
	11th to 20th	Night	9% 2 16% 38% 31% 5%	564
	21st to end	Night	9% 3 20% 38% 26% 3	655
September	1st to 10th	Night	12% 6% 23% 31% 24% 5%	760
	11th to 20th	Night	11% 4 15% 38% 28% 4	760
	21st to end	Night	18% 6% 19% 33% 18% 5%	760
October	1st to 10th	Night	17% 7% 26% 30% 18% 2	760
	11th to 20th	Night	20% 13% 29% 26% 10% 1	760
	21st to end	Night	26% 10% 33% 26% 6%	836
November	1st to 10th	Night	20% 12% 29% 28% 10% 1	780
	11th to 20th	Night	21% 16% 34% 21% 7% 1	800
	21st to end	Night	27% 13% 32% 22% 6%	800
December	1st to 10th	Night	27% 17% 34% 18% 4	800
	11th to 20th	Night	24% 18% 37% 17% 4	800
	21st to end	Night	29% 14% 35% 20% 2	880

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