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 2025-02-25.

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	10% 5% 1 3 2 2 3 2 4 5% 62%	112792
	Night	12% 6% 2 4 3 3 3 2 4 5% 56%	114703
Transparency	Day	26% 2 7% 19% 23% 22%	112550
	Night	30% 2 8% 18% 22% 19%	114535
Seeing	Day	13% 10% 22% 28% 20% 8%	15604
	Night	13% 6% 15% 30% 29% 7%	24942

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	18% 9% 2 6% 3 3 4 3 5% 7% 40%	3841
	11th to 20th	Day	21% 7% 2 4 2 3 2 1 2 4 51%	4100
	21st to end	Day	22% 7% 2 3 2 2 2 2 4 5% 47%	4510
February	1st to 10th	Day	21% 7% 2 6% 3 3 3 3 4 6% 42%	1800
	11th to 20th	Day	17% 9% 3 6% 5% 3 3 4 4 6% 41%	1761
	21st to end	Day	19% 9% 3 5% 3 4 3 4 6% 5% 40%	1611
March	1st to 10th	Day	27% 19% 3 6% 3 2 3 2 3 3 28%	3440
	11th to 20th	Day	13% 6% 2 4 3 3 3 3 4 6% 54%	3490
	21st to end	Day	21% 12% 3 6% 4 4 4 4 5% 7% 32%	3825
April	1st to 10th	Day	16% 9% 3 6% 3 4 3 3 6% 8% 40%	2280
	11th to 20th	Day	12% 7% 2 4 4 3 3 4 4 7% 49%	2249
	21st to end	Day	8% 4 2 5% 3 3 3 4 7% 8% 54%	2288
May	1st to 10th	Day	6% 4 1 2 2 2 3 2 4 6% 68%	4110
	11th to 20th	Day	4 2 1 2 1 2 2 2 3 5% 76%	4179
	21st to end	Day	4 2 1 2 2 2 2 2 5% 7% 72%	4813
June	1st to 10th	Day	7% 4 2 4 3 3 3 3 5% 7% 60%	2660
	11th to 20th	Day	2 2 2 1 2 3 2 4 6% 76%	2660
	21st to end	Day	3 1 2 1 1 2 2 3 3 83%	2660
July	1st to 10th	Day	1 1 1 1 1 1 2 2 91%	4420
	11th to 20th	Day	1 1 1 1 1 1 2 2 3 86%	4175
	21st to end	Day	1 1 1 1 1 2 3 89%	4455
August	1st to 10th	Day	1 2 1 2 1 1 2 2 5% 6% 77%	4091
	11th to 20th	Day	1 1 1 1 1 1 2 3 90%	3968
	21st to end	Day	1 1 1 2 1 1 2 1 2 3 86%	4180
September	1st to 10th	Day	1 1 1 1 1 2 3 5% 85%	2280
	11th to 20th	Day	3 2 1 3 2 2 2 2 5% 6% 72%	2252
	21st to end	Day	3 1 1 2 1 2 3 2 3 5% 77%	2013
October	1st to 10th	Day	4 2 1 3 2 2 2 2 4 5% 74%	3180
	11th to 20th	Day	8% 2 1 2 2 2 2 2 5% 6% 68%	3161
	21st to end	Day	9% 4 2 4 4 4 4 3 5% 7% 54%	3448
November	1st to 10th	Day	11% 6% 2 4 3 3 3 3 5% 8% 51%	1929
	11th to 20th	Day	15% 6% 2 5% 3 4 4 3 5% 6% 46%	1711
	21st to end	Day	15% 5% 2 5% 3 3 4 3 5% 5% 51%	1600
December	1st to 10th	Day	11% 5% 2 4 2 3 4 4 6% 7% 53%	2620
	11th to 20th	Day	29% 10% 3 5% 3 4 4 4 5% 6% 26%	3028
	21st to end	Day	25% 11% 3 7% 4 4 4 4 5% 6% 26%	4004
January	1st to 10th	Night	16% 10% 2 5% 4 4 4 3 6% 8% 38%	6108
	11th to 20th	Night	18% 9% 2 5% 3 3 2 2 3 4 50%	5880
	21st to end	Night	21% 9% 2 5% 3 3 3 2 3 5% 45%	6468
February	1st to 10th	Night	20% 7% 2 5% 3 3 3 3 5% 5% 44%	2600
	11th to 20th	Night	16% 9% 2 6% 4 4 3 3 5% 6% 41%	2524
	21st to end	Night	16% 8% 2 5% 3 2 4 3 4 6% 47%	1936
March	1st to 10th	Night	23% 21% 4 6% 3 3 3 3 4 4 27%	3432
	11th to 20th	Night	15% 6% 1 5% 2 2 2 2 5% 5% 54%	3490
	21st to end	Night	16% 18% 3 5% 4 3 4 3 5% 6% 33%	3815
April	1st to 10th	Night	13% 9% 2 6% 5% 3 3 3 6% 7% 43%	1900
	11th to 20th	Night	10% 6% 2 6% 3 4 3 3 5% 8% 49%	1879
	21st to end	Night	7% 5% 1 4 3 4 3 3 5% 8% 58%	1889
May	1st to 10th	Night	6% 5% 2 3 2 1 2 2 3 4 70%	2860
	11th to 20th	Night	3 2 1 3 2 2 2 2 3 5% 76%	2716
	21st to end	Night	3 2 1 2 2 1 2 2 4 5% 77%	2762
June	1st to 10th	Night	5% 4 1 5% 4 3 3 3 6% 8% 59%	1520
	11th to 20th	Night	2 2 2 2 1 2 2 3 4 79%	1520
	21st to end	Night	2 2 1 2 1 1 2 1 2 5% 79%	1520
July	1st to 10th	Night	1 1 1 1 1 1 1 2 92%	2540
	11th to 20th	Night	1 1 1 2 1 1 1 2 2 87%	2788
	21st to end	Night	1 1 1 1 1 1 3 4 88%	3109
August	1st to 10th	Night	2 1 2 1 1 2 2 5% 5% 78%	2848
	11th to 20th	Night	1 1 1 1 1 2 4 88%	2871
	21st to end	Night	2 2 1 2 1 1 1 1 2 3 83%	3498
September	1st to 10th	Night	1 1 1 2 1 1 4 5% 85%	1900
	11th to 20th	Night	3 3 1 2 2 2 3 2 5% 6% 70%	1924
	21st to end	Night	3 2 1 3 2 1 2 2 4 6% 76%	2166
October	1st to 10th	Night	3 3 1 2 2 2 2 2 3 3 78%	3800
	11th to 20th	Night	4 4 2 3 2 3 3 2 5% 8% 64%	3777
	21st to end	Night	9% 4 2 4 3 3 4 3 5% 7% 56%	4121
November	1st to 10th	Night	12% 6% 2 4 4 3 4 4 5% 7% 48%	2369
	11th to 20th	Night	14% 6% 2 5% 4 4 4 4 7% 7% 45%	2685
	21st to end	Night	13% 6% 2 5% 3 3 3 3 5% 6% 51%	2800
December	1st to 10th	Night	13% 5% 1 3 2 3 3 3 5% 7% 54%	4560
	11th to 20th	Night	30% 10% 3 5% 4 4 4 4 6% 6% 25%	5176
	21st to end	Night	33% 9% 2 6% 4 3 3 2 3 4 30%	6952

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	43% 5% 13% 21% 12% 7%	3841
	11th to 20th	Day	41% 1 6% 11% 22% 18%	4100
	21st to end	Day	41% 2 5% 14% 15% 22%	4510
February	1st to 10th	Day	44% 3 8% 18% 18% 10%	1800
	11th to 20th	Day	43% 3 9% 19% 19% 7%	1770
	21st to end	Day	44% 3 11% 22% 15% 6%	1611
March	1st to 10th	Day	62% 2 7% 14% 12% 3	3440
	11th to 20th	Day	33% 2 10% 26% 17% 12%	3490
	21st to end	Day	52% 3 12% 22% 10% 2	3825
April	1st to 10th	Day	42% 2 13% 24% 15% 3	2280
	11th to 20th	Day	34% 4 14% 23% 20% 5%	2252
	21st to end	Day	26% 3 17% 29% 20% 5%	2288
May	1st to 10th	Day	18% 2 15% 31% 18% 16%	4110
	11th to 20th	Day	13% 2 6% 24% 39% 16%	4182
	21st to end	Day	13% 3 10% 47% 24% 4	4814
June	1st to 10th	Day	24% 3 13% 29% 25% 6%	2660
	11th to 20th	Day	11% 2 10% 24% 35% 18%	2660
	21st to end	Day	9% 1 4 17% 37% 32%	2660
July	1st to 10th	Day	4 1 1 8% 19% 67%	4351
	11th to 20th	Day	6% 1 3 7% 20% 62%	4103
	21st to end	Day	4 1 1 7% 28% 59%	4315
August	1st to 10th	Day	9% 1 3 11% 25% 51%	4076
	11th to 20th	Day	4 1 1 13% 43% 38%	4007
	21st to end	Day	7% 1 3 14% 37% 37%	4179
September	1st to 10th	Day	5% 1 3 10% 30% 50%	2280
	11th to 20th	Day	14% 2 5% 27% 37% 15%	2252
	21st to end	Day	11% 2 5% 20% 34% 28%	2013
October	1st to 10th	Day	14% 1 3 13% 24% 44%	3180
	11th to 20th	Day	19% 2 6% 24% 32% 18%	3161
	21st to end	Day	27% 3 9% 19% 29% 13%	3448
November	1st to 10th	Day	31% 3 8% 27% 18% 13%	1929
	11th to 20th	Day	38% 3 11% 21% 19% 9%	1711
	21st to end	Day	34% 3 11% 18% 18% 16%	1600
December	1st to 10th	Day	30% 3 6% 23% 28% 11%	2620
	11th to 20th	Day	58% 2 8% 15% 14% 3	3028
	21st to end	Day	56% 3 9% 18% 9% 4	4004
January	1st to 10th	Night	43% 4 18% 17% 15% 5%	6108
	11th to 20th	Night	42% 1 6% 16% 21% 14%	5880
	21st to end	Night	45% 2 6% 8% 19% 21%	6468
February	1st to 10th	Night	41% 3 8% 18% 19% 11%	2600
	11th to 20th	Night	43% 2 9% 22% 17% 7%	2526
	21st to end	Night	38% 3 12% 24% 18% 4	1936
March	1st to 10th	Night	60% 4 8% 12% 13% 2	3432
	11th to 20th	Night	32% 2 8% 28% 21% 10%	3490
	21st to end	Night	52% 3 11% 22% 9% 2	3815
April	1st to 10th	Night	39% 4 16% 21% 16% 4	1900
	11th to 20th	Night	32% 3 14% 25% 19% 7%	1879
	21st to end	Night	24% 3 15% 32% 21% 5%	1889
May	1st to 10th	Night	20% 2 7% 30% 27% 14%	2860
	11th to 20th	Night	12% 2 7% 19% 40% 20%	2717
	21st to end	Night	11% 3 10% 46% 23% 7%	2762
June	1st to 10th	Night	23% 3 13% 28% 26% 6%	1520
	11th to 20th	Night	10% 2 10% 24% 36% 18%	1520
	21st to end	Night	12% 2 3 16% 35% 32%	1520
July	1st to 10th	Night	4 1 1 9% 16% 69%	2500
	11th to 20th	Night	6% 1 4 7% 20% 61%	2737
	21st to end	Night	4 1 1 8% 27% 59%	3011
August	1st to 10th	Night	10% 1 2 10% 27% 49%	2839
	11th to 20th	Night	4 1 2 10% 46% 37%	2898
	21st to end	Night	10% 1 2 16% 36% 35%	3498
September	1st to 10th	Night	5% 1 3 13% 28% 51%	1900
	11th to 20th	Night	15% 2 5% 19% 37% 21%	1924
	21st to end	Night	11% 1 4 23% 29% 31%	2166
October	1st to 10th	Night	14% 1 4 12% 21% 48%	3800
	11th to 20th	Night	19% 3 6% 26% 28% 18%	3777
	21st to end	Night	26% 2 8% 22% 24% 18%	4121
November	1st to 10th	Night	33% 4 12% 21% 18% 13%	2369
	11th to 20th	Night	35% 3 15% 18% 19% 9%	2685
	21st to end	Night	34% 3 9% 17% 22% 15%	2800
December	1st to 10th	Night	30% 2 6% 24% 24% 14%	4560
	11th to 20th	Night	56% 3 8% 14% 15% 3	5176
	21st to end	Night	59% 3 9% 16% 10% 3	6952

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	34% 11% 23% 15% 15% 2	285
	11th to 20th	Day	27% 10% 22% 21% 15% 5%	400
	21st to end	Day	22% 8% 24% 23% 17% 6%	440
February	1st to 10th	Day	27% 11% 20% 22% 17% 4	400
	11th to 20th	Day	26% 19% 22% 19% 14% 1	399
	21st to end	Day	20% 15% 23% 26% 14% 3	399
March	1st to 10th	Day	35% 14% 24% 17% 8% 2	460
	11th to 20th	Day	25% 12% 27% 20% 12% 4	460
	21st to end	Day	21% 20% 29% 21% 8% 1	506
April	1st to 10th	Day	22% 16% 26% 22% 10% 4	460
	11th to 20th	Day	20% 17% 26% 21% 12% 4	452
	21st to end	Day	13% 17% 31% 21% 13% 6%	460
May	1st to 10th	Day	11% 18% 27% 24% 15% 5%	463
	11th to 20th	Day	10% 15% 29% 23% 16% 8%	488
	21st to end	Day	9% 12% 21% 30% 19% 8%	529
June	1st to 10th	Day	8% 14% 25% 29% 17% 7%	490
	11th to 20th	Day	6% 12% 32% 29% 16% 4	490
	21st to end	Day	1 6% 27% 35% 22% 10%	490
July	1st to 10th	Day	3 3 18% 43% 24% 9%	486
	11th to 20th	Day	1 1 19% 39% 28% 12%	484
	21st to end	Day	1 12% 44% 27% 15%	531
August	1st to 10th	Day	2 2 22% 38% 25% 11%	487
	11th to 20th	Day	2 3 22% 35% 25% 13%	477
	21st to end	Day	1 4 17% 37% 29% 12%	539
September	1st to 10th	Day	1 3 21% 37% 29% 9%	490
	11th to 20th	Day	4 8% 20% 33% 26% 8%	490
	21st to end	Day	4 7% 20% 34% 25% 10%	490
October	1st to 10th	Day	6% 7% 22% 28% 25% 11%	490
	11th to 20th	Day	8% 9% 18% 25% 27% 14%	490
	21st to end	Day	13% 9% 20% 26% 24% 8%	539
November	1st to 10th	Day	14% 11% 18% 24% 24% 10%	465
	11th to 20th	Day	15% 10% 12% 24% 23% 16%	255
	21st to end	Day	18% 9% 18% 23% 21% 13%	200
December	1st to 10th	Day	24% 8% 14% 23% 17% 15%	200
	11th to 20th	Day	27% 12% 18% 20% 15% 9%	200
	21st to end	Day	25% 11% 20% 20% 19% 5%	220
January	1st to 10th	Night	24% 6% 16% 30% 21% 5%	800
	11th to 20th	Night	23% 6% 15% 31% 20% 6%	800
	21st to end	Night	20% 6% 16% 30% 22% 6%	880
February	1st to 10th	Night	23% 5% 15% 32% 21% 4	800
	11th to 20th	Night	20% 8% 18% 30% 19% 5%	784
	21st to end	Night	19% 9% 20% 31% 19% 2	646
March	1st to 10th	Night	26% 9% 17% 27% 17% 3	760
	11th to 20th	Night	22% 6% 16% 30% 21% 4	760
	21st to end	Night	20% 10% 22% 29% 16% 3	836
April	1st to 10th	Night	17% 8% 26% 27% 18% 4	760
	11th to 20th	Night	13% 11% 22% 30% 19% 6%	751
	21st to end	Night	8% 11% 27% 26% 23% 5%	749
May	1st to 10th	Night	9% 7% 23% 30% 26% 6%	570
	11th to 20th	Night	6% 3 22% 31% 34% 5%	496
	21st to end	Night	6% 7% 19% 30% 33% 5%	411
June	1st to 10th	Night	8% 9% 17% 34% 29% 3	380
	11th to 20th	Night	3 6% 22% 36% 32% 2	380
	21st to end	Night	3 2 13% 40% 38% 4	380
July	1st to 10th	Night	1 1 13% 34% 45% 6%	370
	11th to 20th	Night	1 1 9% 28% 47% 14%	509
	21st to end	Night	1 5% 26% 53% 15%	624
August	1st to 10th	Night	2 1 7% 29% 47% 14%	567
	11th to 20th	Night	1 1 9% 31% 45% 14%	597
	21st to end	Night	1 2 6% 31% 49% 11%	836
September	1st to 10th	Night	1 2 9% 32% 46% 11%	760
	11th to 20th	Night	5% 3 11% 36% 34% 12%	760
	21st to end	Night	4 4 13% 29% 38% 13%	760
October	1st to 10th	Night	5% 4 14% 33% 36% 9%	760
	11th to 20th	Night	7% 4 12% 27% 40% 9%	760
	21st to end	Night	12% 4 11% 29% 31% 13%	836
November	1st to 10th	Night	13% 7% 15% 26% 30% 8%	780
	11th to 20th	Night	16% 5% 15% 33% 27% 5%	800
	21st to end	Night	16% 6% 15% 34% 22% 8%	800
December	1st to 10th	Night	24% 5% 14% 27% 22% 8%	800
	11th to 20th	Night	29% 7% 12% 30% 18% 4	800
	21st to end	Night	27% 8% 17% 29% 16% 3	880

Page generated at 2025-02-22 03:51:34. Version ac07

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