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 2026-05-02.

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% 11% 4 10% 5% 5% 5% 4 5% 7% 30%	132560
	Night	14% 11% 4 10% 5% 5% 4 4 5% 6% 31%	129906
Transparency	Day	51% 7% 12% 19% 10% 1	136156
	Night	50% 7% 12% 18% 12% 1	134399
Seeing	Day	18% 13% 29% 23% 12% 5%	16779
	Night	19% 11% 29% 28% 11% 1	25955

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	15% 16% 7% 21% 7% 5% 4 3 3 4 15%	4943
	11th to 20th	Day	10% 22% 10% 23% 8% 8% 3 2 3 4 8%	5246
	21st to end	Day	15% 16% 6% 17% 8% 6% 6% 3 4 5% 14%	5780
February	1st to 10th	Day	14% 17% 6% 12% 9% 7% 5% 3 4 5% 18%	1890
	11th to 20th	Day	13% 15% 7% 15% 8% 5% 5% 3 4 5% 19%	1843
	21st to end	Day	16% 17% 5% 13% 6% 5% 5% 4 5% 5% 21%	1704
March	1st to 10th	Day	17% 12% 7% 11% 7% 4 4 3 4 4 26%	4952
	11th to 20th	Day	12% 13% 4 11% 5% 4 4 4 5% 8% 30%	5090
	21st to end	Day	19% 13% 5% 10% 5% 5% 4 3 4 5% 29%	5586
April	1st to 10th	Day	16% 14% 5% 8% 5% 4 4 3 5% 7% 28%	2404
	11th to 20th	Day	17% 11% 3 8% 5% 5% 4 3 5% 7% 32%	2658
	21st to end	Day	19% 11% 3 8% 5% 4 3 2 5% 6% 34%	2730
May	1st to 10th	Day	20% 10% 3 8% 5% 4 4 3 5% 6% 32%	5901
	11th to 20th	Day	17% 10% 3 7% 5% 4 4 4 6% 9% 32%	5946
	21st to end	Day	17% 8% 2 7% 4 4 4 4 5% 7% 38%	6949
June	1st to 10th	Day	13% 6% 3 7% 5% 4 5% 4 6% 8% 39%	2800
	11th to 20th	Day	11% 6% 3 6% 5% 5% 6% 5% 7% 9% 38%	2921
	21st to end	Day	12% 5% 3 6% 5% 5% 5% 5% 6% 9% 39%	3000
July	1st to 10th	Day	10% 5% 2 7% 5% 5% 5% 4 7% 9% 41%	6801
	11th to 20th	Day	9% 5% 2 6% 5% 5% 5% 5% 7% 9% 41%	6001
	21st to end	Day	8% 5% 2 6% 5% 5% 5% 4 6% 8% 46%	6424
August	1st to 10th	Day	15% 6% 2 6% 5% 5% 5% 4 7% 8% 37%	4234
	11th to 20th	Day	11% 7% 3 7% 4 6% 6% 5% 6% 10% 35%	4174
	21st to end	Day	9% 6% 2 6% 6% 5% 5% 4 7% 9% 41%	4586
September	1st to 10th	Day	11% 6% 2 8% 5% 4 5% 5% 7% 8% 40%	2371
	11th to 20th	Day	11% 5% 2 5% 4 4 4 4 6% 8% 46%	2200
	21st to end	Day	15% 7% 2 7% 6% 5% 5% 4 7% 8% 34%	2200
October	1st to 10th	Day	17% 7% 3 7% 4 4 4 4 6% 7% 37%	2025
	11th to 20th	Day	19% 9% 3 7% 4 5% 6% 4 6% 6% 31%	2000
	21st to end	Day	22% 11% 4 8% 6% 5% 5% 4 5% 6% 23%	2185
November	1st to 10th	Day	15% 12% 3 8% 4 4 5% 4 5% 7% 32%	1852
	11th to 20th	Day	15% 15% 4 9% 5% 4 5% 3 5% 8% 27%	1690
	21st to end	Day	19% 17% 7% 10% 6% 4 5% 3 6% 6% 18%	1680
December	1st to 10th	Day	19% 19% 7% 13% 6% 5% 5% 4 5% 5% 13%	2680
	11th to 20th	Day	20% 20% 6% 11% 5% 5% 4 3 5% 4 18%	3066
	21st to end	Day	27% 19% 7% 12% 6% 4 4 3 4 4 9%	4048
January	1st to 10th	Night	14% 14% 7% 20% 7% 5% 5% 3 4 5% 15%	7935
	11th to 20th	Night	10% 18% 8% 19% 9% 7% 5% 4 4 4 11%	7639
	21st to end	Night	14% 14% 7% 15% 7% 6% 5% 3 5% 5% 20%	8401
February	1st to 10th	Night	15% 16% 5% 12% 6% 6% 4 4 5% 5% 21%	2730
	11th to 20th	Night	15% 13% 5% 10% 6% 5% 5% 4 6% 7% 23%	2663
	21st to end	Night	15% 14% 5% 13% 6% 5% 5% 4 5% 6% 22%	2099
March	1st to 10th	Night	14% 11% 5% 8% 6% 4 5% 4 6% 6% 32%	5108
	11th to 20th	Night	10% 9% 3 8% 5% 4 5% 4 6% 9% 36%	5089
	21st to end	Night	18% 11% 4 8% 4 4 4 3 4 4 37%	5588
April	1st to 10th	Night	18% 10% 3 8% 5% 5% 4 4 5% 6% 31%	2215
	11th to 20th	Night	17% 9% 3 7% 5% 4 4 4 5% 6% 35%	1929
	21st to end	Night	14% 8% 2 8% 5% 4 5% 6% 6% 7% 34%	1890
May	1st to 10th	Night	19% 9% 3 8% 4 4 4 3 5% 6% 35%	4062
	11th to 20th	Night	13% 9% 3 9% 5% 5% 5% 3 5% 6% 36%	3946
	21st to end	Night	17% 7% 2 4 3 3 4 3 5% 6% 45%	3926
June	1st to 10th	Night	12% 6% 2 5% 4 4 5% 4 7% 8% 45%	1600
	11th to 20th	Night	9% 5% 2 6% 4 4 6% 5% 7% 10% 42%	1472
	21st to end	Night	10% 6% 2 5% 4 4 4 4 6% 8% 47%	1400
July	1st to 10th	Night	7% 5% 2 6% 4 4 4 4 7% 10% 49%	3160
	11th to 20th	Night	9% 6% 2 6% 4 3 4 4 6% 9% 49%	3953
	21st to end	Night	7% 5% 2 6% 3 4 5% 4 6% 7% 51%	4428
August	1st to 10th	Night	11% 5% 2 6% 4 5% 5% 4 6% 8% 46%	2915
	11th to 20th	Night	11% 6% 3 5% 4 3 5% 4 6% 8% 46%	2875
	21st to end	Night	8% 5% 2 6% 4 5% 4 3 6% 8% 49%	3279
September	1st to 10th	Night	10% 6% 3 7% 5% 4 4 3 5% 6% 48%	2025
	11th to 20th	Night	9% 5% 1 4 4 3 4 3 5% 7% 55%	2200
	21st to end	Night	16% 7% 3 6% 4 5% 4 3 5% 7% 40%	2200
October	1st to 10th	Night	14% 7% 2 6% 4 4 5% 2 4 7% 45%	2375
	11th to 20th	Night	17% 9% 3 7% 5% 4 4 4 5% 7% 36%	2400
	21st to end	Night	21% 9% 3 8% 5% 4 5% 3 6% 6% 30%	2652
November	1st to 10th	Night	14% 9% 3 6% 4 4 4 4 6% 7% 38%	2666
	11th to 20th	Night	16% 13% 3 8% 5% 5% 4 5% 7% 8% 28%	2928
	21st to end	Night	20% 16% 4 8% 5% 4 4 4 5% 6% 22%	2940
December	1st to 10th	Night	14% 17% 6% 13% 7% 6% 6% 5% 6% 5% 16%	4720
	11th to 20th	Night	14% 21% 6% 11% 5% 4 4 3 5% 5% 21%	5348
	21st to end	Night	23% 19% 6% 11% 5% 4 4 3 4 5% 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	73% 6% 8% 9% 4	4944
	11th to 20th	Day	81% 5% 6% 5% 3	5280
	21st to end	Day	72% 6% 9% 7% 5%	5780
February	1st to 10th	Day	68% 6% 9% 13% 4 1	1890
	11th to 20th	Day	65% 7% 8% 14% 6%	1852
	21st to end	Day	64% 6% 10% 13% 6% 1	1704
March	1st to 10th	Day	60% 5% 13% 16% 5% 1	4955
	11th to 20th	Day	51% 6% 16% 18% 6% 2	5090
	21st to end	Day	57% 6% 10% 17% 9% 1	5586
April	1st to 10th	Day	56% 5% 11% 17% 10% 1	2404
	11th to 20th	Day	51% 6% 11% 20% 12% 1	2658
	21st to end	Day	52% 5% 11% 20% 11% 2	2730
May	1st to 10th	Day	50% 7% 11% 18% 9% 5%	5910
	11th to 20th	Day	47% 9% 12% 20% 11% 1	5950
	21st to end	Day	44% 7% 10% 18% 17% 3	6949
June	1st to 10th	Day	41% 8% 13% 23% 13% 2	2800
	11th to 20th	Day	40% 9% 13% 22% 15% 2	2921
	21st to end	Day	38% 9% 13% 24% 15%	3000
July	1st to 10th	Day	37% 7% 13% 25% 16% 2	6728
	11th to 20th	Day	36% 8% 13% 28% 14% 1	5929
	21st to end	Day	34% 8% 12% 25% 20% 1	6240
August	1st to 10th	Day	42% 9% 14% 22% 13% 1	4221
	11th to 20th	Day	41% 8% 16% 26% 8% 1	4213
	21st to end	Day	38% 7% 14% 30% 11% 1	4586
September	1st to 10th	Day	40% 8% 15% 24% 12% 1	2371
	11th to 20th	Day	34% 8% 14% 29% 15%	2200
	21st to end	Day	44% 9% 13% 23% 10% 1	2200
October	1st to 10th	Day	38% 7% 13% 24% 17% 1	3298
	11th to 20th	Day	39% 5% 15% 22% 18%	3240
	21st to end	Day	50% 6% 16% 21% 7%	3511
November	1st to 10th	Day	50% 7% 11% 23% 8% 2	1852
	11th to 20th	Day	54% 8% 14% 14% 8% 1	1690
	21st to end	Day	64% 8% 14% 11% 3	1680
December	1st to 10th	Day	71% 8% 10% 8% 2	2680
	11th to 20th	Day	68% 6% 10% 8% 7%	3066
	21st to end	Day	76% 7% 7% 7% 2	4048
January	1st to 10th	Night	67% 9% 9% 11% 4	7935
	11th to 20th	Night	73% 7% 8% 8% 5%	7680
	21st to end	Night	65% 5% 9% 12% 8%	8401
February	1st to 10th	Night	62% 8% 10% 15% 5%	2730
	11th to 20th	Night	58% 7% 14% 15% 6%	2665
	21st to end	Night	59% 7% 12% 15% 7%	2099
March	1st to 10th	Night	50% 6% 15% 18% 10% 2	5118
	11th to 20th	Night	42% 6% 20% 21% 11% 1	5090
	21st to end	Night	50% 5% 10% 19% 15% 2	5588
April	1st to 10th	Night	52% 7% 10% 18% 13% 1	2215
	11th to 20th	Night	48% 5% 10% 19% 16% 2	1929
	21st to end	Night	45% 7% 12% 19% 14% 3	1890
May	1st to 10th	Night	48% 6% 11% 14% 12% 8%	4069
	11th to 20th	Night	46% 8% 12% 22% 10% 3	3947
	21st to end	Night	38% 6% 13% 22% 18% 2	3927
June	1st to 10th	Night	36% 6% 13% 26% 15% 4	1600
	11th to 20th	Night	34% 9% 13% 25% 17% 2	1472
	21st to end	Night	35% 8% 14% 23% 20% 1	1400
July	1st to 10th	Night	30% 6% 13% 27% 19% 4	3125
	11th to 20th	Night	33% 6% 12% 27% 19% 3	3903
	21st to end	Night	30% 8% 13% 22% 23% 4	4297
August	1st to 10th	Night	35% 7% 14% 24% 18% 1	2904
	11th to 20th	Night	34% 8% 16% 29% 12% 1	2902
	21st to end	Night	31% 7% 12% 32% 17% 1	3279
September	1st to 10th	Night	36% 7% 12% 27% 16% 2	2025
	11th to 20th	Night	27% 7% 13% 33% 19% 1	2200
	21st to end	Night	43% 8% 11% 25% 12% 1	2200
October	1st to 10th	Night	31% 5% 8% 29% 25% 1	3882
	11th to 20th	Night	41% 5% 14% 23% 17%	3899
	21st to end	Night	42% 6% 14% 25% 13% 1	4276
November	1st to 10th	Night	43% 7% 13% 23% 13% 1	2666
	11th to 20th	Night	51% 9% 14% 17% 8% 1	2928
	21st to end	Night	61% 7% 16% 13% 4 1	2940
December	1st to 10th	Night	66% 9% 11% 10% 3	4720
	11th to 20th	Night	63% 6% 10% 12% 8% 1	5348
	21st to end	Night	70% 6% 9% 9% 5%	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	23% 19% 36% 17% 4 1	272
	11th to 20th	Day	22% 25% 39% 11% 3 1	330
	21st to end	Day	28% 19% 33% 17% 2 1	363
February	1st to 10th	Day	23% 20% 39% 14% 3 1	330
	11th to 20th	Day	26% 22% 38% 13% 2	330
	21st to end	Day	25% 28% 35% 11% 1	273
March	1st to 10th	Day	24% 15% 37% 18% 5% 1	498
	11th to 20th	Day	25% 17% 34% 18% 5% 1	540
	21st to end	Day	28% 17% 29% 20% 6% 1	594
April	1st to 10th	Day	23% 19% 32% 20% 5% 1	540
	11th to 20th	Day	27% 17% 26% 17% 10% 3	532
	21st to end	Day	25% 11% 34% 21% 6% 2	540
May	1st to 10th	Day	23% 12% 29% 22% 11% 3	507
	11th to 20th	Day	17% 10% 31% 21% 17% 5%	527
	21st to end	Day	16% 7% 27% 27% 17% 7%	573
June	1st to 10th	Day	14% 8% 32% 30% 12% 4	530
	11th to 20th	Day	11% 9% 31% 31% 14% 4	651
	21st to end	Day	13% 8% 32% 31% 14% 3	730
July	1st to 10th	Day	9% 6% 25% 28% 24% 7%	716
	11th to 20th	Day	12% 6% 25% 27% 19% 10%	524
	21st to end	Day	9% 4 24% 33% 22% 8%	576
August	1st to 10th	Day	9% 6% 20% 30% 23% 13%	526
	11th to 20th	Day	13% 5% 20% 27% 22% 14%	519
	21st to end	Day	11% 6% 23% 26% 24% 11%	583
September	1st to 10th	Day	13% 8% 23% 24% 19% 13%	530
	11th to 20th	Day	8% 5% 17% 27% 29% 15%	530
	21st to end	Day	16% 10% 25% 27% 14% 8%	530
October	1st to 10th	Day	18% 9% 25% 25% 18% 5%	530
	11th to 20th	Day	19% 17% 33% 21% 8% 2	530
	21st to end	Day	26% 17% 30% 20% 5% 1	568
November	1st to 10th	Day	21% 24% 32% 15% 6% 2	330
	11th to 20th	Day	26% 20% 31% 15% 6% 3	225
	21st to end	Day	26% 17% 40% 15% 3	220
December	1st to 10th	Day	28% 21% 30% 15% 5%	220
	11th to 20th	Day	30% 25% 30% 12% 3	220
	21st to end	Day	32% 20% 33% 11% 3	242
January	1st to 10th	Night	21% 19% 37% 17% 5% 1	840
	11th to 20th	Night	26% 19% 33% 19% 3	840
	21st to end	Night	19% 14% 36% 25% 5%	924
February	1st to 10th	Night	22% 16% 36% 23% 2	840
	11th to 20th	Night	22% 17% 34% 23% 4	823
	21st to end	Night	23% 17% 35% 22% 3	692
March	1st to 10th	Night	18% 16% 35% 25% 6%	840
	11th to 20th	Night	20% 15% 37% 22% 6% 1	840
	21st to end	Night	22% 13% 32% 24% 9%	924
April	1st to 10th	Night	23% 15% 31% 27% 4	840
	11th to 20th	Night	22% 13% 31% 26% 8% 1	685
	21st to end	Night	17% 10% 34% 32% 7%	630
May	1st to 10th	Night	20% 7% 29% 30% 14% 1	603
	11th to 20th	Night	16% 6% 27% 36% 15% 1	557
	21st to end	Night	12% 6% 27% 37% 17% 1	433
June	1st to 10th	Night	15% 4 29% 43% 10% 1	400
	11th to 20th	Night	10% 5% 32% 42% 12%	400
	21st to end	Night	13% 5% 25% 42% 15% 1	400
July	1st to 10th	Night	5% 3 22% 47% 20% 2	390
	11th to 20th	Night	9% 3 20% 41% 25% 2	532
	21st to end	Night	9% 3 17% 47% 23% 2	657
August	1st to 10th	Night	8% 3 15% 41% 30% 2	597
	11th to 20th	Night	9% 2 16% 38% 31% 4	594
	21st to end	Night	9% 3 20% 39% 26% 3	690
September	1st to 10th	Night	11% 6% 23% 31% 25% 5%	800
	11th to 20th	Night	10% 4 15% 38% 29% 4	800
	21st to end	Night	18% 6% 20% 33% 18% 5%	800
October	1st to 10th	Night	17% 7% 25% 31% 18% 2	800
	11th to 20th	Night	20% 13% 30% 26% 10% 1	800
	21st to end	Night	25% 10% 33% 27% 5%	880
November	1st to 10th	Night	20% 12% 29% 29% 10% 1	820
	11th to 20th	Night	21% 16% 34% 21% 7% 1	840
	21st to end	Night	27% 14% 31% 22% 6%	840
December	1st to 10th	Night	26% 16% 34% 19% 4	840
	11th to 20th	Night	24% 18% 37% 17% 4	840
	21st to end	Night	29% 14% 35% 19% 2	924

Page generated at 2026-04-29 02:21:45. Version ac07

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