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 2024-02-15.

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	12% 5% 2 3 3 2 3 3 4 6% 58%	78472
	Night	14% 6% 2 4 3 2 3 3 4 6% 53%	80640
Transparency	Day	29% 2 8% 20% 23% 17%	78190
	Night	33% 3 9% 19% 21% 15%	80444
Seeing	Day	13% 10% 22% 28% 20% 8%	14260
	Night	13% 5% 15% 30% 29% 7%	23606

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% 10% 2 6% 4 2 3 4 5% 6% 36%	2671
	11th to 20th	Day	30% 10% 3 6% 4 3 4 3 3 5% 31%	2860
	21st to end	Day	28% 10% 3 4 3 3 3 3 5% 6% 32%	3146
February	1st to 10th	Day	20% 6% 2 6% 4 2 4 4 4 6% 43%	1710
	11th to 20th	Day	15% 8% 2 5% 5% 3 3 4 5% 7% 45%	1617
	21st to end	Day	19% 9% 3 4 3 2 3 4 5% 5% 42%	1480
March	1st to 10th	Day	22% 12% 3 6% 4 2 4 4 4 5% 33%	1978
	11th to 20th	Day	21% 7% 3 5% 5% 4 3 4 5% 7% 36%	1980
	21st to end	Day	18% 8% 2 4 5% 3 4 5% 5% 7% 39%	2178
April	1st to 10th	Day	17% 8% 3 5% 4 3 3 4 5% 8% 39%	2160
	11th to 20th	Day	13% 6% 2 3 4 2 4 4 4 7% 50%	2129
	21st to end	Day	8% 4 2 4 3 3 3 4 6% 9% 54%	2167
May	1st to 10th	Day	7% 4 2 3 3 2 4 3 4 9% 59%	2340
	11th to 20th	Day	7% 4 2 3 3 2 4 4 5% 7% 60%	2357
	21st to end	Day	7% 3 1 3 3 2 3 4 6% 7% 60%	2723
June	1st to 10th	Day	7% 4 2 3 3 2 4 4 5% 7% 59%	2520
	11th to 20th	Day	3 2 2 2 1 3 2 3 6% 76%	2520
	21st to end	Day	3 1 1 1 1 1 1 2 3 3 83%	2520
July	1st to 10th	Day	1 1 1 1 2 1 1 2 2 4 84%	2520
	11th to 20th	Day	1 1 1 1 1 2 2 3 4 84%	2379
	21st to end	Day	1 1 1 1 1 2 2 3 4 85%	2546
August	1st to 10th	Day	1 2 1 1 2 1 2 2 3 5% 81%	2328
	11th to 20th	Day	1 1 2 1 1 1 2 3 87%	2266
	21st to end	Day	1 1 1 1 1 2 2 4 87%	2376
September	1st to 10th	Day	1 1 1 1 1 2 3 5% 84%	2160
	11th to 20th	Day	3 2 1 3 2 2 2 3 5% 6% 72%	2134
	21st to end	Day	3 2 1 2 2 1 3 3 4 5% 76%	1908
October	1st to 10th	Day	7% 3 1 3 2 1 3 2 3 4 71%	1800
	11th to 20th	Day	8% 3 1 3 3 2 3 3 4 5% 66%	1800
	21st to end	Day	12% 4 1 3 3 2 3 3 4 6% 60%	1980
November	1st to 10th	Day	12% 5% 2 4 4 2 4 4 5% 8% 50%	1831
	11th to 20th	Day	15% 5% 2 4 4 3 4 4 5% 6% 48%	1626
	21st to end	Day	14% 4 2 5% 4 3 4 4 5% 5% 52%	1520
December	1st to 10th	Day	19% 7% 3 4 4 3 3 4 4 5% 45%	1520
	11th to 20th	Day	32% 10% 3 5% 4 3 3 3 4 5% 29%	1928
	21st to end	Day	24% 9% 3 6% 4 3 4 4 5% 6% 32%	2794
January	1st to 10th	Night	19% 9% 2 5% 4 2 4 4 6% 7% 37%	4273
	11th to 20th	Night	25% 13% 3 6% 5% 3 4 3 4 5% 30%	4110
	21st to end	Night	29% 12% 3 5% 4 2 3 3 4 6% 28%	4521
February	1st to 10th	Night	19% 6% 3 4 4 2 3 4 5% 6% 44%	2470
	11th to 20th	Night	15% 7% 2 5% 5% 3 4 4 5% 7% 43%	2322
	21st to end	Night	17% 7% 2 4 4 1 3 4 4 7% 47%	1776
March	1st to 10th	Night	20% 10% 3 6% 4 2 5% 5% 4 5% 35%	1980
	11th to 20th	Night	19% 10% 2 5% 4 2 3 4 5% 7% 38%	1980
	21st to end	Night	17% 9% 3 4 3 2 3 4 5% 6% 44%	2177
April	1st to 10th	Night	14% 8% 3 5% 6% 3 3 4 5% 7% 41%	1800
	11th to 20th	Night	11% 5% 2 5% 4 3 4 4 5% 8% 50%	1779
	21st to end	Night	7% 4 1 3 3 3 4 4 5% 8% 59%	1790
May	1st to 10th	Night	7% 4 1 4 3 2 3 3 4 6% 64%	1620
	11th to 20th	Night	5% 4 1 4 3 2 4 4 5% 9% 59%	1532
	21st to end	Night	5% 3 2 2 3 1 3 4 5% 8% 63%	1552
June	1st to 10th	Night	5% 4 1 5% 4 2 4 4 5% 8% 59%	1440
	11th to 20th	Night	2 2 1 2 2 1 2 2 3 5% 78%	1440
	21st to end	Night	3 2 1 2 2 1 2 2 2 5% 78%	1440
July	1st to 10th	Night	1 1 1 1 1 2 2 2 4 86%	1440
	11th to 20th	Night	1 1 1 2 1 2 1 3 4 84%	1576
	21st to end	Night	1 1 1 1 1 1 3 5% 86%	1773
August	1st to 10th	Night	1 1 1 1 1 1 2 5% 4 81%	1611
	11th to 20th	Night	1 1 1 1 1 2 3 5% 84%	1633
	21st to end	Night	1 1 1 1 1 1 2 3 4 84%	1980
September	1st to 10th	Night	1 1 1 1 1 1 1 4 5% 85%	1800
	11th to 20th	Night	3 3 1 2 3 2 3 3 5% 6% 70%	1822
	21st to end	Night	3 2 1 3 2 1 2 2 4 6% 75%	2052
October	1st to 10th	Night	4 3 1 3 3 2 2 3 3 5% 71%	2160
	11th to 20th	Night	6% 3 2 3 3 2 3 4 5% 5% 65%	2160
	21st to end	Night	11% 4 2 2 3 2 3 4 4 6% 60%	2376
November	1st to 10th	Night	13% 6% 2 4 4 3 4 5% 5% 7% 48%	2247
	11th to 20th	Night	14% 5% 2 4 4 3 4 5% 7% 7% 45%	2550
	21st to end	Night	12% 5% 2 5% 4 3 3 4 5% 6% 52%	2660
December	1st to 10th	Night	22% 7% 2 3 4 2 3 3 5% 7% 43%	2660
	11th to 20th	Night	32% 8% 2 4 3 2 3 4 5% 6% 30%	3276
	21st to end	Night	25% 9% 3 6% 5% 3 4 3 4 5% 33%	4862

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	49% 3 12% 25% 7% 4	2671
	11th to 20th	Day	59% 2 9% 13% 9% 9%	2860
	21st to end	Day	55% 3 7% 17% 13% 6%	3146
February	1st to 10th	Day	43% 3 8% 18% 19% 9%	1710
	11th to 20th	Day	40% 3 9% 20% 21% 8%	1626
	21st to end	Day	43% 3 11% 21% 15% 7%	1480
March	1st to 10th	Day	54% 4 10% 14% 14% 5%	1978
	11th to 20th	Day	48% 3 9% 21% 15% 6%	1980
	21st to end	Day	44% 4 13% 18% 16% 4	2178
April	1st to 10th	Day	43% 2 13% 23% 15% 3	2160
	11th to 20th	Day	33% 4 14% 23% 20% 6%	2132
	21st to end	Day	26% 4 16% 29% 19% 5%	2167
May	1st to 10th	Day	23% 3 12% 31% 24% 7%	2340
	11th to 20th	Day	23% 3 11% 32% 23% 8%	2360
	21st to end	Day	22% 4 15% 38% 18% 3	2724
June	1st to 10th	Day	24% 3 13% 29% 25% 6%	2520
	11th to 20th	Day	11% 2 10% 25% 34% 18%	2520
	21st to end	Day	9% 1 4 18% 38% 30%	2520
July	1st to 10th	Day	7% 2 2 14% 33% 42%	2451
	11th to 20th	Day	7% 2 5% 12% 31% 44%	2307
	21st to end	Day	6% 2 2 10% 30% 51%	2405
August	1st to 10th	Day	9% 2 3 18% 33% 35%	2312
	11th to 20th	Day	5% 1 2 15% 38% 39%	2266
	21st to end	Day	5% 1 3 16% 38% 37%	2376
September	1st to 10th	Day	6% 2 3 11% 31% 48%	2160
	11th to 20th	Day	14% 2 5% 26% 37% 16%	2134
	21st to end	Day	12% 2 5% 22% 33% 27%	1908
October	1st to 10th	Day	20% 2 4 18% 32% 24%	1800
	11th to 20th	Day	22% 2 8% 18% 26% 24%	1800
	21st to end	Day	26% 2 7% 18% 27% 19%	1980
November	1st to 10th	Day	32% 3 8% 27% 17% 13%	1831
	11th to 20th	Day	37% 3 11% 21% 19% 10%	1626
	21st to end	Day	34% 3 11% 19% 19% 15%	1520
December	1st to 10th	Day	41% 4 7% 17% 19% 12%	1520
	11th to 20th	Day	60% 1 5% 12% 16% 5%	1928
	21st to end	Day	52% 3 9% 20% 10% 5%	2794
January	1st to 10th	Night	46% 2 19% 20% 10% 4	4273
	11th to 20th	Night	59% 2 8% 12% 11% 8%	4110
	21st to end	Night	59% 3 7% 12% 13% 6%	4521
February	1st to 10th	Night	40% 3 8% 19% 19% 11%	2470
	11th to 20th	Night	41% 2 8% 22% 19% 7%	2324
	21st to end	Night	37% 3 13% 23% 19% 5%	1776
March	1st to 10th	Night	51% 6% 9% 15% 17% 4	1980
	11th to 20th	Night	44% 3 10% 20% 17% 6%	1980
	21st to end	Night	41% 4 15% 21% 15% 4	2177
April	1st to 10th	Night	41% 4 16% 19% 16% 5%	1800
	11th to 20th	Night	32% 3 14% 24% 19% 7%	1779
	21st to end	Night	24% 3 15% 32% 21% 6%	1790
May	1st to 10th	Night	23% 3 7% 29% 30% 8%	1620
	11th to 20th	Night	22% 4 12% 29% 25% 9%	1533
	21st to end	Night	19% 4 17% 35% 21% 4	1552
June	1st to 10th	Night	23% 3 13% 28% 26% 6%	1440
	11th to 20th	Night	11% 2 10% 25% 35% 18%	1440
	21st to end	Night	13% 2 4 17% 35% 31%	1440
July	1st to 10th	Night	7% 2 2 16% 29% 44%	1400
	11th to 20th	Night	6% 3 6% 12% 29% 45%	1525
	21st to end	Night	5% 2 1 10% 28% 54%	1674
August	1st to 10th	Night	8% 2 2 18% 33% 36%	1602
	11th to 20th	Night	6% 2 3 13% 33% 43%	1633
	21st to end	Night	7% 2 2 17% 34% 38%	1980
September	1st to 10th	Night	5% 2 3 13% 29% 49%	1800
	11th to 20th	Night	15% 3 5% 18% 37% 22%	1822
	21st to end	Night	12% 2 4 23% 28% 31%	2052
October	1st to 10th	Night	18% 2 7% 19% 29% 26%	2160
	11th to 20th	Night	21% 4 5% 19% 27% 24%	2160
	21st to end	Night	25% 2 7% 21% 21% 23%	2376
November	1st to 10th	Night	34% 4 11% 20% 18% 13%	2247
	11th to 20th	Night	35% 3 14% 19% 19% 10%	2550
	21st to end	Night	33% 3 10% 18% 22% 14%	2660
December	1st to 10th	Night	43% 2 8% 16% 20% 12%	2660
	11th to 20th	Night	56% 3 8% 14% 15% 5%	3276
	21st to end	Night	54% 3 10% 18% 11% 4	4862

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	37% 12% 23% 13% 14% 2	260
	11th to 20th	Day	29% 11% 22% 20% 15% 4	370
	21st to end	Day	23% 9% 23% 22% 18% 5%	407
February	1st to 10th	Day	25% 11% 19% 23% 18% 4	370
	11th to 20th	Day	23% 18% 23% 21% 15% 1	351
	21st to end	Day	20% 15% 23% 25% 14% 2	346
March	1st to 10th	Day	34% 14% 24% 18% 9% 2	420
	11th to 20th	Day	26% 11% 28% 20% 11% 4	420
	21st to end	Day	20% 20% 29% 21% 9% 1	462
April	1st to 10th	Day	22% 18% 26% 21% 10% 4	420
	11th to 20th	Day	21% 17% 27% 21% 10% 4	412
	21st to end	Day	13% 16% 31% 20% 14% 5%	420
May	1st to 10th	Day	11% 18% 26% 23% 16% 5%	423
	11th to 20th	Day	11% 16% 30% 22% 15% 6%	448
	21st to end	Day	10% 13% 20% 29% 20% 8%	485
June	1st to 10th	Day	8% 14% 24% 29% 18% 8%	450
	11th to 20th	Day	6% 11% 31% 30% 17% 4	450
	21st to end	Day	1 6% 25% 36% 23% 9%	450
July	1st to 10th	Day	3 3 19% 44% 23% 8%	446
	11th to 20th	Day	1 1 18% 38% 30% 12%	444
	21st to end	Day	1 11% 44% 29% 15%	487
August	1st to 10th	Day	2 2 21% 37% 26% 12%	447
	11th to 20th	Day	2 2 19% 37% 27% 14%	437
	21st to end	Day	1 3 16% 38% 30% 12%	495
September	1st to 10th	Day	2 3 19% 37% 30% 10%	450
	11th to 20th	Day	4 7% 19% 35% 26% 8%	450
	21st to end	Day	4 7% 20% 34% 25% 10%	450
October	1st to 10th	Day	7% 8% 22% 28% 25% 11%	450
	11th to 20th	Day	8% 8% 17% 25% 27% 15%	450
	21st to end	Day	13% 8% 18% 27% 25% 9%	495
November	1st to 10th	Day	15% 10% 17% 24% 25% 11%	427
	11th to 20th	Day	12% 8% 13% 24% 25% 18%	230
	21st to end	Day	15% 8% 19% 24% 22% 12%	180
December	1st to 10th	Day	27% 8% 13% 23% 15% 13%	180
	11th to 20th	Day	26% 12% 17% 21% 14% 10%	180
	21st to end	Day	23% 11% 20% 21% 21% 5%	198
January	1st to 10th	Night	24% 6% 14% 29% 21% 5%	760
	11th to 20th	Night	24% 6% 15% 30% 20% 6%	760
	21st to end	Night	21% 6% 16% 29% 22% 6%	836
February	1st to 10th	Night	22% 5% 15% 33% 22% 4	760
	11th to 20th	Night	19% 7% 18% 31% 20% 5%	722
	21st to end	Night	20% 9% 20% 29% 19% 2	592
March	1st to 10th	Night	25% 9% 18% 27% 18% 3	720
	11th to 20th	Night	23% 6% 16% 31% 20% 4	720
	21st to end	Night	21% 9% 22% 29% 16% 3	792
April	1st to 10th	Night	18% 8% 25% 27% 18% 4	720
	11th to 20th	Night	13% 11% 22% 30% 18% 6%	711
	21st to end	Night	8% 10% 26% 27% 24% 5%	710
May	1st to 10th	Night	9% 6% 23% 29% 27% 6%	540
	11th to 20th	Night	6% 3 22% 32% 31% 5%	470
	21st to end	Night	7% 7% 19% 29% 33% 5%	389
June	1st to 10th	Night	8% 8% 17% 34% 29% 4	360
	11th to 20th	Night	3 4 21% 36% 33% 3	360
	21st to end	Night	3 1 12% 39% 39% 5%	360
July	1st to 10th	Night	1 1 13% 33% 45% 7%	350
	11th to 20th	Night	1 7% 28% 49% 15%	481
	21st to end	Night	1 5% 25% 54% 16%	591
August	1st to 10th	Night	1 7% 29% 48% 15%	537
	11th to 20th	Night	1 6% 31% 47% 15%	565
	21st to end	Night	1 2 5% 31% 50% 11%	792
September	1st to 10th	Night	1 2 8% 31% 47% 11%	720
	11th to 20th	Night	5% 2 10% 36% 35% 12%	720
	21st to end	Night	4 4 13% 29% 37% 13%	720
October	1st to 10th	Night	5% 4 14% 32% 36% 9%	720
	11th to 20th	Night	7% 4 11% 27% 41% 10%	720
	21st to end	Night	12% 4 11% 28% 32% 14%	792
November	1st to 10th	Night	14% 6% 15% 25% 31% 9%	740
	11th to 20th	Night	16% 4 14% 34% 28% 5%	760
	21st to end	Night	14% 6% 15% 34% 23% 8%	760
December	1st to 10th	Night	25% 5% 14% 26% 22% 8%	760
	11th to 20th	Night	29% 7% 12% 30% 19% 4	760
	21st to end	Night	26% 8% 17% 30% 17% 3	836

Page generated at 2024-02-12 03:35:37. Version ac07

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