Lookout Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lookout Observatory clear sky chart from 2005-11-06 to 2026-09-29.

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% 7% 3 8% 5% 5% 6% 5% 7% 8% 38%	148889
	Night	10% 8% 3 8% 5% 5% 5% 4 6% 8% 39%	142513
Transparency	Day	41% 7% 14% 20% 15% 4	152600
	Night	40% 8% 14% 20% 14% 4	146874
Seeing	Day	18% 13% 22% 22% 16% 8%	17587
	Night	16% 11% 20% 30% 19% 3	27591

By Month

Percentage Cloud Cover SE (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	11% 7% 3 6% 5% 4 4 3 5% 7% 45%	5258
	11th to 20th	Day	7% 5% 3 5% 5% 5% 4 3 4 5% 54%	5280
	21st to end	Day	10% 11% 4 8% 3 3 4 4 5% 6% 40%	5780
February	1st to 10th	Day	11% 8% 3 7% 5% 5% 5% 4 6% 7% 39%	1979
	11th to 20th	Day	13% 9% 4 9% 5% 4 4 4 5% 6% 36%	2048
	21st to end	Day	12% 7% 3 9% 5% 4 6% 4 5% 6% 39%	1730
March	1st to 10th	Day	14% 9% 4 8% 5% 4 4 4 5% 6% 38%	4941
	11th to 20th	Day	10% 7% 3 7% 4 3 4 3 4 6% 49%	5090
	21st to end	Day	12% 8% 3 6% 4 4 4 4 5% 6% 44%	5586
April	1st to 10th	Day	10% 6% 3 5% 4 5% 5% 5% 6% 8% 42%	2310
	11th to 20th	Day	12% 7% 3 5% 5% 4 4 3 6% 8% 44%	2517
	21st to end	Day	11% 7% 2 6% 5% 4 5% 4 6% 7% 44%	2730
May	1st to 10th	Day	9% 8% 4 9% 6% 6% 6% 5% 6% 8% 34%	7616
	11th to 20th	Day	11% 7% 3 8% 6% 5% 6% 5% 7% 9% 34%	7626
	21st to end	Day	9% 8% 4 10% 7% 7% 6% 5% 7% 9% 28%	8391
June	1st to 10th	Day	9% 6% 3 7% 7% 8% 6% 6% 8% 10% 32%	2730
	11th to 20th	Day	5% 6% 3 8% 6% 8% 6% 6% 9% 10% 33%	2730
	21st to end	Day	7% 6% 3 6% 7% 6% 7% 6% 9% 10% 34%	2730
July	1st to 10th	Day	4 5% 3 8% 7% 7% 7% 7% 8% 11% 34%	7680
	11th to 20th	Day	8% 7% 3 9% 8% 7% 7% 6% 9% 10% 26%	7680
	21st to end	Day	10% 8% 3 10% 8% 7% 7% 5% 8% 10% 24%	8340
August	1st to 10th	Day	11% 7% 4 10% 7% 7% 7% 6% 10% 11% 20%	6014
	11th to 20th	Day	5% 4 2 6% 5% 6% 7% 5% 9% 13% 37%	5951
	21st to end	Day	5% 5% 2 5% 5% 5% 6% 5% 7% 8% 47%	6094
September	1st to 10th	Day	8% 6% 3 7% 6% 5% 6% 5% 7% 8% 38%	2310
	11th to 20th	Day	13% 7% 2 8% 6% 5% 6% 5% 7% 9% 33%	2310
	21st to end	Day	12% 7% 3 7% 5% 5% 6% 4 7% 7% 37%	2288
October	1st to 10th	Day	10% 6% 3 6% 3 4 5% 3 5% 6% 48%	2165
	11th to 20th	Day	8% 5% 2 6% 4 3 5% 3 3 6% 54%	2000
	21st to end	Day	11% 6% 3 5% 4 3 4 3 4 6% 52%	2200
November	1st to 10th	Day	7% 7% 2 6% 4 3 3 3 4 6% 54%	1957
	11th to 20th	Day	9% 6% 2 6% 5% 3 4 4 5% 7% 49%	1890
	21st to end	Day	10% 8% 4 6% 4 4 3 3 5% 7% 46%	1890
December	1st to 10th	Day	10% 6% 3 7% 4 5% 5% 4 5% 6% 46%	3020
	11th to 20th	Day	11% 7% 3 8% 5% 4 5% 4 7% 8% 37%	3463
	21st to end	Day	11% 8% 3 8% 6% 5% 5% 3 5% 8% 38%	4565
January	1st to 10th	Night	11% 8% 3 9% 6% 5% 4 3 5% 7% 39%	7635
	11th to 20th	Night	9% 7% 3 8% 5% 4 4 4 5% 6% 47%	7680
	21st to end	Night	10% 10% 4 8% 4 4 4 3 5% 6% 42%	8401
February	1st to 10th	Night	10% 8% 3 8% 4 5% 4 4 7% 7% 39%	2635
	11th to 20th	Night	15% 9% 3 7% 5% 5% 4 4 5% 6% 36%	2458
	21st to end	Night	12% 8% 4 10% 5% 5% 5% 4 5% 5% 36%	2076
March	1st to 10th	Night	15% 10% 4 9% 5% 4 5% 3 5% 6% 34%	5130
	11th to 20th	Night	8% 6% 3 6% 4 3 4 4 6% 8% 48%	5090
	21st to end	Night	12% 8% 3 6% 5% 4 4 3 4 7% 43%	5588
April	1st to 10th	Night	10% 7% 3 5% 5% 4 4 4 6% 8% 44%	2310
	11th to 20th	Night	7% 8% 3 7% 4 4 4 4 6% 8% 46%	2067
	21st to end	Night	9% 6% 3 6% 6% 4 3 3 5% 7% 46%	1890
May	1st to 10th	Night	10% 8% 3 7% 4 5% 5% 4 8% 11% 34%	5237
	11th to 20th	Night	11% 9% 4 9% 5% 5% 5% 5% 6% 7% 35%	5234
	21st to end	Night	12% 9% 4 10% 6% 6% 5% 5% 6% 9% 27%	5761
June	1st to 10th	Night	7% 6% 2 8% 4 6% 6% 5% 9% 13% 34%	1890
	11th to 20th	Night	5% 7% 2 5% 5% 5% 5% 5% 10% 11% 39%	1890
	21st to end	Night	5% 6% 2 6% 5% 6% 5% 4 8% 12% 42%	1890
July	1st to 10th	Night	5% 6% 2 8% 6% 7% 7% 5% 9% 12% 34%	5278
	11th to 20th	Night	7% 6% 3 9% 7% 6% 7% 5% 9% 11% 30%	5277
	21st to end	Night	11% 9% 4 10% 6% 6% 6% 5% 7% 10% 26%	5736
August	1st to 10th	Night	9% 8% 3 9% 7% 7% 8% 6% 9% 11% 24%	4135
	11th to 20th	Night	6% 5% 3 8% 5% 5% 5% 5% 8% 11% 38%	4095
	21st to end	Night	6% 5% 2 7% 5% 5% 5% 5% 7% 10% 42%	4966
September	1st to 10th	Night	9% 5% 2 7% 5% 6% 6% 4 6% 8% 41%	2310
	11th to 20th	Night	11% 9% 3 8% 6% 5% 5% 4 6% 7% 36%	2310
	21st to end	Night	10% 6% 3 8% 4 3 5% 4 4 7% 44%	2289
October	1st to 10th	Night	12% 6% 3 6% 4 4 4 4 5% 6% 47%	2234
	11th to 20th	Night	8% 6% 2 7% 4 4 4 3 6% 6% 49%	2400
	21st to end	Night	9% 7% 3 7% 3 3 3 3 5% 5% 52%	2640
November	1st to 10th	Night	10% 6% 2 5% 4 4 4 5% 5% 6% 49%	2556
	11th to 20th	Night	10% 7% 3 7% 4 4 3 4 5% 6% 48%	2730
	21st to end	Night	10% 7% 3 7% 5% 5% 4 4 5% 6% 45%	2730
December	1st to 10th	Night	10% 6% 3 8% 5% 4 4 4 5% 6% 44%	4380
	11th to 20th	Night	14% 10% 4 9% 5% 5% 5% 4 6% 6% 34%	4952
	21st to end	Night	12% 8% 4 9% 5% 5% 5% 4 6% 7% 36%	6633

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	36% 5% 12% 25% 20% 1	5259
	11th to 20th	Day	31% 6% 6% 12% 37% 7%	5280
	21st to end	Day	42% 5% 9% 19% 18% 6%	5780
February	1st to 10th	Day	43% 6% 11% 20% 18% 3	1979
	11th to 20th	Day	45% 7% 9% 18% 17% 3	2058
	21st to end	Day	45% 6% 10% 16% 18% 6%	1730
March	1st to 10th	Day	43% 7% 8% 14% 19% 9%	4941
	11th to 20th	Day	35% 6% 7% 17% 22% 14%	5090
	21st to end	Day	40% 5% 10% 26% 16% 3	5586
April	1st to 10th	Day	36% 7% 14% 23% 17% 4	2310
	11th to 20th	Day	38% 5% 10% 21% 20% 5%	2517
	21st to end	Day	37% 7% 14% 25% 15% 2	2730
May	1st to 10th	Day	46% 7% 14% 21% 12% 1	7651
	11th to 20th	Day	44% 8% 16% 21% 10% 1	7630
	21st to end	Day	49% 9% 13% 16% 11% 2	8405
June	1st to 10th	Day	43% 11% 19% 17% 9% 1	2730
	11th to 20th	Day	41% 10% 19% 18% 11% 1	2730
	21st to end	Day	41% 10% 18% 18% 11% 2	2730
July	1st to 10th	Day	42% 9% 22% 20% 7%	7615
	11th to 20th	Day	50% 9% 23% 14% 3	7611
	21st to end	Day	53% 7% 17% 14% 7% 1	8156
August	1st to 10th	Day	54% 10% 19% 15% 2	6001
	11th to 20th	Day	35% 7% 30% 20% 7% 1	5990
	21st to end	Day	32% 7% 16% 33% 11% 1	6094
September	1st to 10th	Day	40% 9% 14% 18% 15% 3	2310
	11th to 20th	Day	43% 8% 14% 20% 13% 2	2310
	21st to end	Day	43% 6% 14% 16% 15% 5%	2288
October	1st to 10th	Day	29% 6% 7% 20% 26% 12%	3529
	11th to 20th	Day	23% 5% 6% 24% 23% 19%	3240
	21st to end	Day	27% 3 8% 26% 22% 13%	3538
November	1st to 10th	Day	31% 4 10% 21% 26% 8%	1957
	11th to 20th	Day	33% 5% 8% 23% 25% 6%	1890
	21st to end	Day	37% 5% 9% 24% 21% 4	1890
December	1st to 10th	Day	39% 4 6% 20% 26% 4	3020
	11th to 20th	Day	41% 5% 15% 17% 19% 3	3460
	21st to end	Day	41% 6% 14% 23% 13% 3	4565
January	1st to 10th	Night	39% 7% 14% 24% 15% 1	7636
	11th to 20th	Night	34% 7% 7% 18% 28% 6%	7680
	21st to end	Night	42% 4 9% 19% 19% 6%	8401
February	1st to 10th	Night	41% 5% 13% 21% 17% 3	2635
	11th to 20th	Night	47% 7% 9% 18% 15% 4	2459
	21st to end	Night	47% 6% 10% 16% 17% 4	2076
March	1st to 10th	Night	45% 11% 7% 14% 18% 5%	5130
	11th to 20th	Night	31% 6% 10% 19% 22% 12%	5090
	21st to end	Night	42% 4 13% 26% 13% 3	5588
April	1st to 10th	Night	35% 7% 15% 22% 17% 2	2310
	11th to 20th	Night	34% 6% 12% 24% 20% 4	2067
	21st to end	Night	36% 8% 15% 26% 15% 1	1890
May	1st to 10th	Night	42% 8% 15% 26% 8% 1	5264
	11th to 20th	Night	44% 10% 16% 22% 8%	5235
	21st to end	Night	50% 11% 14% 17% 7% 1	5771
June	1st to 10th	Night	38% 13% 21% 20% 8% 1	1890
	11th to 20th	Night	33% 11% 25% 21% 9%	1890
	21st to end	Night	34% 10% 21% 21% 12% 2	1890
July	1st to 10th	Night	40% 11% 23% 20% 5%	5235
	11th to 20th	Night	45% 13% 25% 14% 2 1	5226
	21st to end	Night	52% 9% 19% 12% 7% 1	5606
August	1st to 10th	Night	50% 14% 21% 12% 3	4124
	11th to 20th	Night	37% 9% 29% 19% 6%	4122
	21st to end	Night	34% 8% 19% 31% 7% 1	4966
September	1st to 10th	Night	38% 11% 14% 21% 12% 3	2310
	11th to 20th	Night	44% 10% 13% 19% 14% 1	2310
	21st to end	Night	38% 9% 12% 22% 17% 2	2289
October	1st to 10th	Night	33% 6% 8% 19% 25% 9%	3650
	11th to 20th	Night	25% 4 7% 22% 24% 17%	3899
	21st to end	Night	30% 4 6% 24% 24% 12%	4252
November	1st to 10th	Night	33% 7% 11% 21% 21% 6%	2556
	11th to 20th	Night	35% 5% 7% 22% 24% 7%	2730
	21st to end	Night	38% 5% 9% 24% 19% 5%	2730
December	1st to 10th	Night	40% 6% 10% 22% 21% 3	4380
	11th to 20th	Night	47% 6% 11% 18% 15% 2	4954
	21st to end	Night	43% 7% 14% 21% 14% 1	6633

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	33% 25% 29% 10% 2 1	330
	11th to 20th	Day	37% 23% 19% 17% 3	330
	21st to end	Day	28% 32% 25% 11% 3	363
February	1st to 10th	Day	26% 27% 30% 14% 3	330
	11th to 20th	Day	39% 29% 21% 9% 1	330
	21st to end	Day	35% 25% 27% 10% 2	273
March	1st to 10th	Day	28% 19% 26% 20% 7% 1	484
	11th to 20th	Day	29% 21% 25% 20% 5% 1	540
	21st to end	Day	27% 21% 27% 19% 6%	594
April	1st to 10th	Day	24% 19% 25% 20% 10% 2	540
	11th to 20th	Day	19% 20% 26% 20% 12% 4	532
	21st to end	Day	20% 15% 27% 19% 15% 5%	540
May	1st to 10th	Day	18% 20% 24% 22% 12% 5%	543
	11th to 20th	Day	18% 12% 20% 26% 16% 8%	567
	21st to end	Day	14% 8% 23% 26% 18% 12%	617
June	1st to 10th	Day	11% 7% 24% 27% 20% 12%	570
	11th to 20th	Day	8% 7% 21% 25% 24% 15%	570
	21st to end	Day	10% 6% 25% 24% 20% 15%	570
July	1st to 10th	Day	8% 3 13% 25% 31% 21%	565
	11th to 20th	Day	9% 3 9% 27% 28% 24%	564
	21st to end	Day	8% 3 15% 25% 29% 20%	620
August	1st to 10th	Day	17% 5% 14% 24% 19% 21%	566
	11th to 20th	Day	8% 5% 13% 30% 26% 18%	559
	21st to end	Day	10% 4 15% 26% 26% 19%	627
September	1st to 10th	Day	9% 4 14% 28% 30% 16%	570
	11th to 20th	Day	15% 6% 16% 21% 29% 15%	570
	21st to end	Day	16% 6% 19% 29% 23% 7%	562
October	1st to 10th	Day	15% 9% 19% 27% 22% 8%	530
	11th to 20th	Day	13% 13% 24% 26% 19% 5%	530
	21st to end	Day	20% 15% 22% 25% 16% 3	583
November	1st to 10th	Day	17% 13% 28% 26% 13% 4	435
	11th to 20th	Day	21% 22% 32% 16% 8% 1	330
	21st to end	Day	22% 23% 29% 17% 8% 1	330
December	1st to 10th	Day	28% 26% 28% 13% 4	330
	11th to 20th	Day	24% 19% 30% 19% 7% 1	330
	21st to end	Day	25% 22% 31% 15% 6% 2	363
January	1st to 10th	Night	26% 17% 28% 24% 5%	840
	11th to 20th	Night	23% 18% 28% 27% 5%	840
	21st to end	Night	22% 20% 28% 27% 3	924
February	1st to 10th	Night	20% 16% 31% 29% 4	840
	11th to 20th	Night	27% 22% 28% 22% 1	823
	21st to end	Night	24% 22% 31% 21% 3	692
March	1st to 10th	Night	19% 18% 29% 30% 4	840
	11th to 20th	Night	22% 15% 30% 25% 8% 1	840
	21st to end	Night	18% 18% 31% 25% 7%	924
April	1st to 10th	Night	20% 17% 25% 29% 9%	840
	11th to 20th	Night	17% 13% 25% 32% 12% 1	723
	21st to end	Night	13% 10% 22% 39% 15% 1	630
May	1st to 10th	Night	14% 9% 23% 37% 16% 1	630
	11th to 20th	Night	13% 6% 19% 36% 23% 3	621
	21st to end	Night	11% 4 13% 34% 33% 5%	683
June	1st to 10th	Night	9% 2 15% 37% 31% 7%	630
	11th to 20th	Night	7% 2 12% 35% 35% 10%	630
	21st to end	Night	6% 3 8% 35% 42% 6%	630
July	1st to 10th	Night	8% 3 6% 26% 47% 9%	615
	11th to 20th	Night	9% 3 4 23% 48% 14%	612
	21st to end	Night	10% 2 3 26% 46% 13%	690
August	1st to 10th	Night	10% 2 7% 30% 42% 10%	627
	11th to 20th	Night	10% 4 7% 29% 41% 10%	624
	21st to end	Night	10% 2 5% 29% 43% 10%	746
September	1st to 10th	Night	9% 4 10% 31% 40% 7%	840
	11th to 20th	Night	13% 5% 11% 29% 35% 7%	840
	21st to end	Night	15% 5% 15% 33% 28% 4	833
October	1st to 10th	Night	15% 9% 16% 28% 26% 6%	800
	11th to 20th	Night	15% 9% 21% 35% 18% 2	800
	21st to end	Night	16% 13% 19% 35% 16% 2	880
November	1st to 10th	Night	16% 8% 19% 38% 17% 3	820
	11th to 20th	Night	19% 12% 21% 36% 12% 1	840
	21st to end	Night	20% 15% 21% 32% 12% 1	840
December	1st to 10th	Night	22% 17% 25% 29% 6%	840
	11th to 20th	Night	19% 14% 27% 32% 8% 1	840
	21st to end	Night	22% 16% 26% 30% 5%	924

Page generated at 2026-09-26 04:18:44. Version ac07

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