Powerpoint Lookout
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Powerpoint Lookout clear sky chart from 2005-11-06 to 2026-07-01.

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	9% 4 1 3 2 2 3 2 4 5% 64%	146727
	Night	12% 6% 2 4 2 2 3 2 4 6% 57%	143084
Transparency	Day	24% 2 7% 20% 25% 22%	141599
	Night	30% 2 7% 19% 23% 19%	139206
Seeing	Day	13% 10% 23% 28% 19% 8%	17413
	Night	13% 6% 16% 30% 28% 7%	26630

By Month

Percentage Cloud Cover SW (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	22% 9% 2 5% 3 3 4 3 5% 6% 37%	4980
	11th to 20th	Day	16% 5% 2 4 2 3 3 2 3 4 56%	5340
	21st to end	Day	18% 7% 2 5% 3 3 4 3 5% 6% 45%	5843
February	1st to 10th	Day	20% 6% 2 6% 3 3 3 3 4 6% 42%	1890
	11th to 20th	Day	16% 10% 3 6% 5% 3 3 4 4 6% 40%	1852
	21st to end	Day	19% 9% 3 5% 3 4 3 4 6% 5% 40%	1730
March	1st to 10th	Day	22% 15% 3 6% 3 2 3 2 3 4 36%	5060
	11th to 20th	Day	18% 9% 2 5% 3 3 3 2 4 6% 45%	5110
	21st to end	Day	20% 11% 3 6% 4 4 4 3 6% 8% 32%	5607
April	1st to 10th	Day	15% 9% 3 6% 4 4 3 3 5% 8% 41%	2520
	11th to 20th	Day	12% 6% 2 4 4 3 3 4 4 7% 50%	2489
	21st to end	Day	8% 5% 2 5% 3 3 4 3 6% 8% 53%	2529
May	1st to 10th	Day	5% 4 1 3 2 2 3 2 4 7% 67%	7627
	11th to 20th	Day	3 2 1 2 1 2 2 2 3 6% 79%	7781
	21st to end	Day	3 1 1 2 2 2 2 2 4 7% 74%	8992
June	1st to 10th	Day	6% 4 2 3 3 3 3 3 5% 7% 62%	2940
	11th to 20th	Day	2 2 2 1 2 2 2 4 5% 77%	2940
	21st to end	Day	2 1 2 1 1 1 2 3 3 84%	2940
July	1st to 10th	Day	1 1 1 1 1 1 2 2 91%	6320
	11th to 20th	Day	1 1 1 1 1 1 2 3 90%	5971
	21st to end	Day	1 1 1 1 1 2 4 87%	6402
August	1st to 10th	Day	1 1 1 1 1 1 2 2 4 5% 83%	5777
	11th to 20th	Day	1 1 1 1 1 2 2 91%	5712
	21st to end	Day	1 1 1 2 1 1 2 2 3 4 84%	5984
September	1st to 10th	Day	1 1 2 1 1 1 2 3 5% 83%	2400
	11th to 20th	Day	3 2 1 3 2 2 2 2 5% 6% 71%	2370
	21st to end	Day	3 2 1 2 1 2 2 2 3 5% 76%	2119
October	1st to 10th	Day	4 2 1 3 2 2 2 2 4 5% 74%	3280
	11th to 20th	Day	8% 2 1 3 2 2 2 2 5% 6% 67%	3261
	21st to end	Day	9% 4 1 4 4 4 4 3 5% 7% 54%	3558
November	1st to 10th	Day	11% 6% 2 4 3 3 3 3 5% 8% 51%	2027
	11th to 20th	Day	15% 7% 2 5% 4 4 4 3 5% 6% 45%	1796
	21st to end	Day	14% 5% 1 5% 3 3 4 2 5% 5% 53%	1680
December	1st to 10th	Day	11% 5% 2 4 2 3 3 4 6% 7% 53%	2700
	11th to 20th	Day	29% 10% 3 5% 3 4 4 4 5% 6% 26%	3108
	21st to end	Day	26% 11% 3 7% 4 4 4 4 5% 6% 26%	4092
January	1st to 10th	Night	24% 10% 2 5% 3 3 4 3 5% 7% 34%	7909
	11th to 20th	Night	14% 7% 2 4 3 3 2 2 3 4 56%	7650
	21st to end	Night	18% 9% 3 6% 3 3 3 2 4 6% 42%	8371
February	1st to 10th	Night	19% 7% 2 5% 3 3 3 3 5% 5% 44%	2730
	11th to 20th	Night	17% 10% 2 6% 4 4 3 3 5% 7% 40%	2653
	21st to end	Night	17% 9% 2 5% 3 2 3 3 5% 6% 46%	2075
March	1st to 10th	Night	18% 18% 4 6% 3 3 3 3 4 5% 33%	5052
	11th to 20th	Night	19% 11% 2 4 2 2 2 2 4 5% 46%	5110
	21st to end	Night	18% 16% 3 5% 4 3 4 3 5% 8% 31%	5597
April	1st to 10th	Night	13% 9% 2 6% 4 3 3 3 5% 7% 43%	2100
	11th to 20th	Night	10% 7% 2 6% 3 4 3 3 5% 8% 49%	2079
	21st to end	Night	7% 6% 1 4 3 3 3 3 5% 7% 57%	2087
May	1st to 10th	Night	5% 6% 3 4 2 2 2 1 3 6% 66%	5321
	11th to 20th	Night	3 3 1 4 2 2 2 1 3 6% 74%	5080
	21st to end	Night	3 2 1 2 1 1 2 2 4 6% 76%	5181
June	1st to 10th	Night	5% 4 1 5% 3 3 3 3 6% 7% 61%	1680
	11th to 20th	Night	2 2 2 2 1 2 2 3 4 80%	1680
	21st to end	Night	2 2 1 2 1 1 2 1 2 5% 79%	1680
July	1st to 10th	Night	1 1 1 1 1 1 2 92%	3640
	11th to 20th	Night	1 1 1 1 1 1 1 2 2 91%	4000
	21st to end	Night	1 1 1 1 1 3 5% 84%	4472
August	1st to 10th	Night	1 1 1 1 1 2 2 4 4 84%	4035
	11th to 20th	Night	3 1 1 1 1 2 3 86%	4139
	21st to end	Night	2 2 2 1 1 2 1 2 3 84%	5015
September	1st to 10th	Night	1 1 1 2 1 1 4 5% 85%	2000
	11th to 20th	Night	3 3 1 3 2 2 3 2 5% 6% 69%	2026
	21st to end	Night	3 2 1 3 2 1 2 1 4 5% 76%	2280
October	1st to 10th	Night	3 3 1 2 2 2 2 2 3 3 77%	3920
	11th to 20th	Night	4 4 2 4 2 3 3 2 5% 8% 64%	3897
	21st to end	Night	9% 4 2 4 3 3 4 3 5% 7% 56%	4253
November	1st to 10th	Night	13% 7% 2 4 4 3 4 4 5% 7% 48%	2491
	11th to 20th	Night	14% 6% 2 5% 4 4 4 4 7% 7% 44%	2819
	21st to end	Night	13% 6% 2 5% 3 3 3 3 5% 6% 51%	2940
December	1st to 10th	Night	13% 5% 1 3 2 3 3 3 5% 7% 54%	4700
	11th to 20th	Night	30% 10% 3 5% 3 4 4 3 6% 6% 26%	5316
	21st to end	Night	33% 9% 2 6% 3 3 3 2 3 4 30%	7106

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	46% 5% 11% 21% 12% 5%	4981
	11th to 20th	Day	34% 1 5% 9% 22% 28%	5340
	21st to end	Day	41% 2 7% 17% 14% 19%	5843
February	1st to 10th	Day	43% 3 8% 18% 18% 10%	1890
	11th to 20th	Day	44% 3 9% 19% 19% 7%	1861
	21st to end	Day	44% 3 11% 20% 15% 7%	1730
March	1st to 10th	Day	52% 2 7% 18% 17% 4	5060
	11th to 20th	Day	41% 2 12% 23% 13% 9%	5110
	21st to end	Day	49% 4 11% 23% 10% 2	5607
April	1st to 10th	Day	41% 3 13% 24% 16% 3	2520
	11th to 20th	Day	34% 3 14% 22% 20% 6%	2492
	21st to end	Day	27% 3 16% 30% 20% 5%	2529
May	1st to 10th	Day	17% 2 11% 26% 28% 16%	7627
	11th to 20th	Day	10% 1 6% 28% 39% 16%	7784
	21st to end	Day	11% 2 7% 37% 38% 4	8994
June	1st to 10th	Day	22% 3 12% 28% 28% 7%	2940
	11th to 20th	Day	10% 2 9% 23% 35% 21%	2940
	21st to end	Day	8% 1 4 18% 37% 32%	2940
July	1st to 10th	Day	4 1 1 7% 25% 61%	6252
	11th to 20th	Day	4 1 3 5% 17% 70%	5899
	21st to end	Day	4 2 5% 16% 31% 43%	6217
August	1st to 10th	Day	9% 1 2 11% 26% 50%	4206
	11th to 20th	Day	4 1 1 13% 43% 38%	4135
	21st to end	Day	7% 1 3 14% 37% 38%	4311
September	1st to 10th	Day	6% 2 3 12% 30% 48%	2400
	11th to 20th	Day	14% 2 5% 27% 37% 15%	2370
	21st to end	Day	11% 2 5% 20% 34% 27%	2119
October	1st to 10th	Day	15% 1 4 13% 24% 43%	3280
	11th to 20th	Day	19% 2 6% 25% 31% 17%	3261
	21st to end	Day	27% 3 9% 19% 29% 13%	3558
November	1st to 10th	Day	31% 3 8% 27% 18% 13%	2027
	11th to 20th	Day	39% 3 11% 20% 19% 9%	1796
	21st to end	Day	33% 3 10% 18% 20% 16%	1680
December	1st to 10th	Day	29% 3 6% 23% 28% 11%	2700
	11th to 20th	Day	58% 2 8% 15% 14% 4	3108
	21st to end	Day	57% 3 9% 18% 9% 4	4092
January	1st to 10th	Night	49% 4 14% 17% 13% 4	7909
	11th to 20th	Night	34% 1 5% 13% 23% 23%	7650
	21st to end	Night	44% 2 6% 12% 18% 18%	8371
February	1st to 10th	Night	41% 3 8% 19% 18% 12%	2730
	11th to 20th	Night	44% 2 9% 21% 17% 6%	2655
	21st to end	Night	39% 3 12% 23% 18% 5%	2075
March	1st to 10th	Night	52% 3 8% 18% 15% 4	5052
	11th to 20th	Night	41% 2 8% 23% 18% 8%	5110
	21st to end	Night	51% 4 11% 20% 11% 2	5597
April	1st to 10th	Night	39% 4 15% 21% 17% 4	2100
	11th to 20th	Night	33% 3 14% 26% 18% 7%	2079
	21st to end	Night	25% 3 14% 32% 21% 5%	2087
May	1st to 10th	Night	21% 3 6% 22% 32% 16%	5319
	11th to 20th	Night	13% 1 6% 26% 37% 16%	5081
	21st to end	Night	11% 2 8% 39% 34% 6%	5182
June	1st to 10th	Night	22% 3 12% 27% 30% 6%	1680
	11th to 20th	Night	10% 2 9% 23% 36% 20%	1680
	21st to end	Night	12% 2 3 16% 36% 31%	1680
July	1st to 10th	Night	3 1 1 9% 25% 60%	3600
	11th to 20th	Night	4 1 4 5% 18% 67%	3949
	21st to end	Night	5% 2 5% 17% 28% 42%	4345
August	1st to 10th	Night	10% 1 2 11% 28% 48%	2929
	11th to 20th	Night	4 1 3 10% 45% 38%	2990
	21st to end	Night	9% 1 2 15% 36% 36%	3608
September	1st to 10th	Night	6% 1 3 13% 28% 49%	2000
	11th to 20th	Night	16% 3 5% 20% 36% 20%	2026
	21st to end	Night	12% 1 4 23% 29% 30%	2280
October	1st to 10th	Night	14% 1 4 13% 21% 46%	3920
	11th to 20th	Night	19% 3 6% 26% 28% 18%	3897
	21st to end	Night	26% 2 8% 22% 25% 17%	4253
November	1st to 10th	Night	34% 4 11% 21% 19% 12%	2491
	11th to 20th	Night	37% 3 14% 18% 19% 9%	2819
	21st to end	Night	33% 3 9% 18% 22% 15%	2940
December	1st to 10th	Night	29% 2 6% 25% 24% 14%	4700
	11th to 20th	Night	56% 3 8% 13% 15% 4	5316
	21st to end	Night	59% 3 9% 16% 10% 3	7106

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	35% 11% 23% 14% 15% 2	309
	11th to 20th	Day	25% 9% 21% 20% 19% 6%	430
	21st to end	Day	21% 8% 24% 25% 18% 5%	473
February	1st to 10th	Day	26% 11% 20% 22% 17% 4	430
	11th to 20th	Day	26% 19% 22% 18% 13% 1	430
	21st to end	Day	21% 15% 22% 26% 13% 2	446
March	1st to 10th	Day	33% 15% 25% 17% 8% 1	540
	11th to 20th	Day	25% 13% 26% 20% 12% 4	540
	21st to end	Day	21% 19% 29% 20% 9% 2	594
April	1st to 10th	Day	20% 16% 26% 23% 11% 4	540
	11th to 20th	Day	19% 18% 26% 21% 11% 5%	532
	21st to end	Day	13% 16% 30% 22% 13% 6%	540
May	1st to 10th	Day	10% 17% 28% 24% 15% 6%	543
	11th to 20th	Day	11% 16% 30% 22% 15% 7%	568
	21st to end	Day	9% 12% 23% 30% 18% 8%	617
June	1st to 10th	Day	7% 14% 27% 28% 16% 7%	570
	11th to 20th	Day	6% 12% 33% 30% 16% 5%	570
	21st to end	Day	3 6% 26% 34% 21% 10%	570
July	1st to 10th	Day	3 3 21% 41% 23% 9%	527
	11th to 20th	Day	1 1 19% 40% 27% 12%	524
	21st to end	Day	1 13% 43% 27% 15%	575
August	1st to 10th	Day	2 2 23% 37% 26% 11%	527
	11th to 20th	Day	2 3 22% 36% 24% 13%	517
	21st to end	Day	1 4 17% 38% 28% 13%	583
September	1st to 10th	Day	2 3 21% 37% 28% 9%	530
	11th to 20th	Day	5% 8% 19% 33% 26% 8%	530
	21st to end	Day	4 7% 20% 33% 25% 11%	530
October	1st to 10th	Day	7% 7% 23% 27% 25% 11%	530
	11th to 20th	Day	9% 9% 18% 24% 27% 13%	530
	21st to end	Day	13% 9% 20% 27% 24% 8%	583
November	1st to 10th	Day	14% 10% 18% 24% 24% 10%	503
	11th to 20th	Day	16% 11% 13% 24% 21% 15%	280
	21st to end	Day	16% 8% 18% 24% 22% 12%	220
December	1st to 10th	Day	22% 7% 14% 24% 19% 15%	220
	11th to 20th	Day	27% 11% 17% 20% 15% 10%	220
	21st to end	Day	26% 12% 20% 19% 18% 5%	242
January	1st to 10th	Night	26% 6% 15% 28% 20% 4	840
	11th to 20th	Night	22% 5% 14% 31% 22% 5%	840
	21st to end	Night	20% 6% 16% 31% 22% 6%	924
February	1st to 10th	Night	22% 5% 15% 33% 21% 3	840
	11th to 20th	Night	21% 8% 18% 30% 18% 4	824
	21st to end	Night	21% 9% 19% 32% 18% 2	692
March	1st to 10th	Night	24% 11% 19% 28% 16% 3	840
	11th to 20th	Night	23% 7% 16% 30% 20% 4	840
	21st to end	Night	20% 10% 23% 29% 16% 2	924
April	1st to 10th	Night	16% 9% 25% 28% 18% 4	840
	11th to 20th	Night	13% 12% 22% 30% 19% 5%	831
	21st to end	Night	8% 11% 27% 27% 22% 5%	827
May	1st to 10th	Night	8% 7% 23% 31% 25% 6%	630
	11th to 20th	Night	6% 5% 23% 30% 32% 5%	549
	21st to end	Night	7% 7% 21% 29% 32% 5%	455
June	1st to 10th	Night	7% 9% 19% 34% 29% 3	420
	11th to 20th	Night	3 6% 23% 34% 31% 2	420
	21st to end	Night	3 3 14% 39% 38% 4	420
July	1st to 10th	Night	1 1 14% 35% 43% 6%	390
	11th to 20th	Night	1 1 8% 29% 48% 14%	537
	21st to end	Night	1 6% 26% 53% 14%	657
August	1st to 10th	Night	2 1 8% 29% 46% 14%	597
	11th to 20th	Night	1 1 10% 31% 44% 13%	629
	21st to end	Night	1 2 6% 31% 50% 10%	880
September	1st to 10th	Night	1 2 9% 32% 45% 10%	800
	11th to 20th	Night	5% 4 11% 35% 35% 11%	800
	21st to end	Night	4 4 14% 29% 37% 12%	800
October	1st to 10th	Night	5% 4 13% 33% 35% 9%	800
	11th to 20th	Night	7% 5% 13% 27% 40% 9%	800
	21st to end	Night	11% 5% 12% 29% 31% 12%	880
November	1st to 10th	Night	13% 7% 15% 26% 30% 8%	820
	11th to 20th	Night	17% 5% 15% 33% 25% 5%	840
	21st to end	Night	15% 6% 15% 35% 22% 7%	840
December	1st to 10th	Night	22% 5% 14% 28% 23% 8%	840
	11th to 20th	Night	28% 7% 12% 30% 19% 4	840
	21st to end	Night	29% 8% 17% 28% 16% 3	924

Page generated at 2026-06-27 23:10:48. Version ac07

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