Spodue Lookout
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Spodue Lookout clear sky chart from 2005-11-06 to 2026-09-14.

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	7% 8% 2 5% 3 3 3 3 4 6% 56%	158307
	Night	8% 9% 2 5% 3 3 3 3 4 6% 52%	150168
Transparency	Day	30% 4 8% 20% 23% 15%	153174
	Night	34% 5% 10% 21% 20% 11%	146293
Seeing	Day	14% 12% 23% 26% 19% 7%	17169
	Night	14% 7% 20% 35% 21% 3	26215

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	17% 23% 6% 9% 4 3 4 3 3 5% 23%	4722
	11th to 20th	Day	13% 11% 3 3 2 2 2 1 3 5% 55%	4740
	21st to end	Day	12% 10% 2 6% 4 4 4 3 5% 6% 43%	5783
February	1st to 10th	Day	12% 15% 3 7% 4 4 3 3 5% 8% 36%	1890
	11th to 20th	Day	11% 18% 5% 7% 4 4 4 2 4 6% 35%	1885
	21st to end	Day	11% 18% 5% 8% 5% 4 4 3 4 6% 32%	1730
March	1st to 10th	Day	11% 18% 6% 9% 4 3 3 2 4 7% 33%	4701
	11th to 20th	Day	8% 19% 4 8% 4 4 3 2 4 5% 38%	5110
	21st to end	Day	11% 19% 4 9% 5% 5% 4 3 5% 6% 28%	5845
April	1st to 10th	Day	12% 15% 4 8% 5% 4 4 3 4 7% 34%	2520
	11th to 20th	Day	11% 13% 3 7% 4 4 4 4 5% 6% 39%	2489
	21st to end	Day	7% 11% 2 6% 5% 4 3 2 5% 7% 47%	2524
May	1st to 10th	Day	6% 8% 2 4 3 3 3 3 5% 6% 57%	8041
	11th to 20th	Day	4 5% 2 5% 3 3 3 3 5% 6% 62%	8160
	21st to end	Day	6% 6% 2 5% 3 3 3 3 5% 8% 57%	8992
June	1st to 10th	Day	10% 6% 2 5% 4 4 4 4 5% 7% 49%	2940
	11th to 20th	Day	4 5% 2 4 3 3 3 3 5% 6% 63%	2940
	21st to end	Day	4 3 1 3 3 3 2 3 3 5% 71%	2940
July	1st to 10th	Day	1 1 2 2 2 2 2 3 4 81%	8219
	11th to 20th	Day	3 3 1 3 2 2 3 2 3 4 73%	8220
	21st to end	Day	2 2 1 2 2 2 2 2 3 4 78%	8907
August	1st to 10th	Day	2 2 1 3 2 3 3 2 4 5% 75%	7547
	11th to 20th	Day	2 2 1 2 2 2 2 2 3 5% 79%	7400
	21st to end	Day	3 3 1 4 2 3 3 2 4 5% 71%	7750
September	1st to 10th	Day	3 2 1 3 2 2 2 2 3 5% 75%	2520
	11th to 20th	Day	4 4 1 4 3 3 3 3 4 5% 64%	2437
	21st to end	Day	4 5% 1 5% 2 3 2 2 4 5% 67%	2144
October	1st to 10th	Day	5% 4 1 4 2 2 2 2 4 5% 70%	3280
	11th to 20th	Day	6% 6% 2 5% 3 4 4 5% 6% 8% 52%	3261
	21st to end	Day	11% 10% 3 7% 4 4 3 3 5% 7% 42%	3467
November	1st to 10th	Day	15% 11% 2 7% 4 3 3 3 6% 7% 41%	1854
	11th to 20th	Day	17% 11% 3 6% 4 4 4 5% 7% 7% 33%	1769
	21st to end	Day	10% 15% 3 7% 3 4 3 4 5% 8% 38%	1680
December	1st to 10th	Day	8% 8% 1 5% 4 4 3 3 5% 7% 51%	2700
	11th to 20th	Day	19% 20% 4 8% 4 3 3 3 6% 7% 22%	3108
	21st to end	Day	14% 19% 5% 11% 6% 5% 4 3 5% 6% 20%	4092
January	1st to 10th	Night	15% 23% 5% 9% 4 4 4 3 5% 6% 23%	8172
	11th to 20th	Night	10% 10% 2 5% 2 2 2 2 3 5% 57%	8220
	21st to end	Night	12% 11% 3 7% 5% 5% 5% 4 5% 6% 40%	8411
February	1st to 10th	Night	13% 13% 4 6% 4 4 3 3 5% 6% 37%	2730
	11th to 20th	Night	12% 15% 3 8% 4 4 3 3 4 6% 38%	2621
	21st to end	Night	11% 14% 5% 6% 4 4 4 4 4 8% 35%	2076
March	1st to 10th	Night	8% 17% 5% 9% 4 4 4 3 5% 6% 35%	5411
	11th to 20th	Night	11% 14% 4 6% 3 3 3 3 4 6% 44%	5110
	21st to end	Night	8% 19% 4 9% 5% 5% 5% 4 5% 7% 28%	5371
April	1st to 10th	Night	13% 12% 3 7% 4 4 4 3 5% 7% 38%	2100
	11th to 20th	Night	8% 11% 3 6% 5% 4 4 4 5% 6% 45%	2079
	21st to end	Night	10% 9% 2 5% 3 3 4 4 6% 7% 48%	2093
May	1st to 10th	Night	5% 6% 2 5% 3 3 4 2 3 5% 61%	4870
	11th to 20th	Night	4 4 2 5% 4 4 4 3 5% 5% 61%	4700
	21st to end	Night	6% 4 2 4 3 3 3 2 4 6% 64%	5181
June	1st to 10th	Night	10% 5% 2 5% 3 4 4 3 6% 8% 51%	1680
	11th to 20th	Night	5% 5% 2 4 3 3 2 2 4 6% 65%	1680
	21st to end	Night	4 3 1 3 2 3 2 2 4 4 72%	1680
July	1st to 10th	Night	2 2 1 3 1 2 2 2 3 4 79%	4740
	11th to 20th	Night	3 3 1 3 2 2 2 2 3 3 75%	4740
	21st to end	Night	3 2 1 3 2 2 3 2 4 5% 74%	5153
August	1st to 10th	Night	2 2 1 2 2 2 2 3 5% 5% 75%	5275
	11th to 20th	Night	2 2 1 3 2 3 2 2 3 4 75%	5462
	21st to end	Night	3 3 1 4 2 2 3 2 3 6% 70%	6499
September	1st to 10th	Night	1 2 1 2 2 2 2 2 4 5% 76%	2100
	11th to 20th	Night	4 4 1 4 2 3 3 3 5% 6% 66%	2030
	21st to end	Night	5% 4 1 3 2 2 2 2 4 5% 69%	2253
October	1st to 10th	Night	3 3 1 3 3 2 3 2 3 4 74%	3920
	11th to 20th	Night	8% 6% 2 4 3 3 3 3 4 6% 59%	3897
	21st to end	Night	7% 6% 3 5% 4 4 4 4 6% 8% 49%	4341
November	1st to 10th	Night	14% 11% 3 6% 5% 4 4 3 4 7% 39%	2665
	11th to 20th	Night	17% 11% 3 5% 4 4 4 4 6% 9% 33%	2846
	21st to end	Night	11% 12% 2 6% 4 3 4 3 5% 7% 43%	2940
December	1st to 10th	Night	9% 7% 2 4 3 3 3 3 5% 8% 54%	4700
	11th to 20th	Night	16% 19% 4 9% 5% 5% 5% 4 5% 6% 24%	5316
	21st to end	Night	20% 17% 4 8% 5% 4 4 3 4 6% 26%	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	63% 5% 11% 15% 6%	4723
	11th to 20th	Day	35% 3 6% 20% 23% 13%	4740
	21st to end	Day	41% 4 8% 16% 19% 11%	5783
February	1st to 10th	Day	47% 6% 14% 19% 12% 2	1890
	11th to 20th	Day	49% 7% 12% 17% 13% 3	1894
	21st to end	Day	51% 6% 14% 14% 11% 4	1730
March	1st to 10th	Day	51% 5% 8% 22% 10% 4	4701
	11th to 20th	Day	47% 4 12% 19% 17% 1	5110
	21st to end	Day	53% 7% 12% 21% 6% 1	5845
April	1st to 10th	Day	50% 6% 11% 19% 10% 3	2520
	11th to 20th	Day	45% 4 12% 20% 15% 3	2492
	21st to end	Day	36% 6% 14% 25% 17% 2	2524
May	1st to 10th	Day	26% 4 6% 27% 31% 6%	8041
	11th to 20th	Day	22% 3 8% 25% 34% 7%	8163
	21st to end	Day	26% 4 9% 35% 25% 2	8994
June	1st to 10th	Day	32% 6% 11% 25% 23% 2	2940
	11th to 20th	Day	22% 5% 8% 27% 28% 10%	2940
	21st to end	Day	17% 3 7% 24% 33% 17%	2940
July	1st to 10th	Day	10% 2 3 16% 28% 42%	8151
	11th to 20th	Day	16% 2 2 11% 22% 47%	8145
	21st to end	Day	11% 2 3 17% 33% 34%	8708
August	1st to 10th	Day	13% 2 3 9% 22% 51%	5976
	11th to 20th	Day	11% 2 2 24% 42% 19%	5835
	21st to end	Day	14% 1 4 23% 35% 23%	6077
September	1st to 10th	Day	13% 2 4 17% 32% 32%	2520
	11th to 20th	Day	21% 4 9% 18% 31% 17%	2437
	21st to end	Day	20% 4 9% 22% 25% 19%	2144
October	1st to 10th	Day	19% 3 8% 16% 31% 24%	3280
	11th to 20th	Day	27% 5% 13% 31% 20% 6%	3261
	21st to end	Day	40% 4 9% 23% 20% 4	3467
November	1st to 10th	Day	42% 6% 13% 20% 16% 3	1854
	11th to 20th	Day	47% 7% 17% 14% 12% 3	1769
	21st to end	Day	44% 6% 12% 17% 16% 5%	1680
December	1st to 10th	Day	33% 5% 9% 24% 24% 4	2700
	11th to 20th	Day	61% 5% 13% 13% 7% 1	3108
	21st to end	Day	62% 7% 10% 15% 5% 1	4092
January	1st to 10th	Night	60% 6% 13% 15% 5%	8172
	11th to 20th	Night	33% 5% 7% 20% 24% 12%	8220
	21st to end	Night	45% 4 8% 14% 18% 11%	8411
February	1st to 10th	Night	45% 7% 14% 18% 14% 3	2730
	11th to 20th	Night	46% 6% 13% 19% 12% 3	2623
	21st to end	Night	46% 8% 15% 18% 11% 2	2076
March	1st to 10th	Night	47% 6% 10% 23% 10% 4	5411
	11th to 20th	Night	41% 5% 11% 25% 18% 1	5110
	21st to end	Night	50% 11% 13% 18% 7% 1	5371
April	1st to 10th	Night	44% 7% 16% 20% 11% 1	2100
	11th to 20th	Night	39% 6% 15% 21% 15% 4	2079
	21st to end	Night	34% 7% 18% 25% 14% 2	2093
May	1st to 10th	Night	24% 5% 8% 27% 33% 3	4868
	11th to 20th	Night	23% 3 14% 30% 29% 2	4700
	21st to end	Night	21% 4 11% 42% 20% 1	5182
June	1st to 10th	Night	31% 6% 14% 28% 20% 2	1680
	11th to 20th	Night	21% 5% 8% 32% 25% 8%	1680
	21st to end	Night	16% 3 8% 30% 33% 11%	1680
July	1st to 10th	Night	11% 2 4 18% 32% 33%	4700
	11th to 20th	Night	15% 2 2 11% 24% 46%	4692
	21st to end	Night	14% 2 4 20% 29% 31%	5040
August	1st to 10th	Night	11% 2 4 11% 27% 45%	4169
	11th to 20th	Night	13% 2 4 30% 34% 17%	4300
	21st to end	Night	14% 1 5% 25% 34% 20%	5092
September	1st to 10th	Night	12% 2 5% 18% 31% 33%	2100
	11th to 20th	Night	19% 4 9% 22% 30% 18%	2030
	21st to end	Night	19% 2 8% 24% 25% 21%	2253
October	1st to 10th	Night	16% 3 7% 18% 32% 24%	3920
	11th to 20th	Night	26% 3 13% 33% 19% 6%	3897
	21st to end	Night	31% 4 11% 30% 17% 6%	4341
November	1st to 10th	Night	44% 6% 13% 19% 15% 4	2665
	11th to 20th	Night	47% 8% 13% 17% 12% 3	2846
	21st to end	Night	40% 6% 13% 18% 16% 7%	2940
December	1st to 10th	Night	30% 5% 10% 24% 30% 2	4700
	11th to 20th	Night	61% 5% 11% 14% 8% 1	5316
	21st to end	Night	58% 7% 11% 14% 8% 1	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	32% 19% 22% 14% 9% 4	220
	11th to 20th	Day	27% 11% 16% 20% 17% 9%	220
	21st to end	Day	18% 13% 21% 23% 18% 6%	452
February	1st to 10th	Day	21% 15% 23% 22% 15% 4	430
	11th to 20th	Day	23% 17% 26% 19% 12% 2	447
	21st to end	Day	22% 17% 24% 27% 9% 2	446
March	1st to 10th	Day	25% 18% 27% 21% 8% 1	540
	11th to 20th	Day	22% 15% 26% 21% 13% 3	540
	21st to end	Day	23% 21% 24% 23% 7% 2	594
April	1st to 10th	Day	20% 18% 23% 24% 11% 4	540
	11th to 20th	Day	19% 21% 25% 18% 11% 4	532
	21st to end	Day	13% 18% 26% 23% 15% 5%	540
May	1st to 10th	Day	12% 16% 27% 26% 15% 4	543
	11th to 20th	Day	20% 16% 23% 20% 15% 6%	568
	21st to end	Day	16% 9% 22% 26% 18% 9%	617
June	1st to 10th	Day	10% 13% 24% 24% 21% 8%	570
	11th to 20th	Day	9% 16% 25% 26% 20% 5%	570
	21st to end	Day	4 8% 20% 31% 25% 12%	570
July	1st to 10th	Day	3 5% 23% 37% 23% 10%	566
	11th to 20th	Day	3 4 24% 35% 27% 7%	564
	21st to end	Day	2 3 20% 37% 27% 11%	619
August	1st to 10th	Day	2 2 22% 32% 29% 14%	567
	11th to 20th	Day	3 6% 16% 32% 27% 15%	557
	21st to end	Day	4 6% 19% 31% 29% 11%	627
September	1st to 10th	Day	5% 6% 20% 34% 23% 12%	570
	11th to 20th	Day	8% 8% 20% 31% 24% 10%	543
	21st to end	Day	6% 12% 23% 27% 25% 8%	530
October	1st to 10th	Day	12% 11% 24% 25% 20% 8%	530
	11th to 20th	Day	15% 10% 22% 23% 24% 7%	530
	21st to end	Day	17% 11% 25% 21% 18% 7%	528
November	1st to 10th	Day	21% 10% 23% 26% 13% 7%	330
	11th to 20th	Day	21% 10% 21% 26% 14% 7%	267
	21st to end	Day	20% 9% 20% 25% 20% 6%	220
December	1st to 10th	Day	21% 8% 21% 25% 10% 15%	220
	11th to 20th	Day	29% 14% 22% 16% 15% 5%	220
	21st to end	Day	25% 16% 21% 21% 14% 2	242
January	1st to 10th	Night	24% 10% 24% 25% 13% 4	840
	11th to 20th	Night	20% 11% 20% 26% 20% 4	840
	21st to end	Night	19% 9% 18% 32% 18% 4	924
February	1st to 10th	Night	19% 7% 23% 33% 15% 2	840
	11th to 20th	Night	19% 10% 23% 33% 13% 2	824
	21st to end	Night	18% 11% 21% 36% 13% 1	692
March	1st to 10th	Night	20% 13% 25% 28% 13% 2	840
	11th to 20th	Night	18% 10% 21% 30% 18% 2	840
	21st to end	Night	20% 13% 25% 30% 11% 1	924
April	1st to 10th	Night	18% 10% 24% 32% 14% 2	840
	11th to 20th	Night	13% 11% 30% 27% 15% 3	831
	21st to end	Night	13% 11% 23% 33% 18% 2	833
May	1st to 10th	Night	10% 4 29% 35% 21% 1	476
	11th to 20th	Night	9% 8% 20% 39% 22% 2	414
	21st to end	Night	11% 6% 24% 36% 22% 2	455
June	1st to 10th	Night	10% 6% 20% 41% 22%	420
	11th to 20th	Night	6% 5% 28% 45% 15% 1	420
	21st to end	Night	4 2 18% 51% 24%	420
July	1st to 10th	Night	3 1 16% 53% 27% 1	410
	11th to 20th	Night	2 1 18% 55% 23%	408
	21st to end	Night	3 1 12% 55% 29% 1	460
August	1st to 10th	Night	2 1 8% 48% 38% 3	627
	11th to 20th	Night	2 1 11% 43% 38% 4	677
	21st to end	Night	3 2 14% 46% 33% 2	924
September	1st to 10th	Night	2 3 15% 43% 34% 3	840
	11th to 20th	Night	5% 4 14% 36% 35% 6%	812
	21st to end	Night	8% 4 16% 36% 30% 7%	800
October	1st to 10th	Night	6% 5% 20% 38% 27% 4	800
	11th to 20th	Night	11% 8% 14% 36% 27% 5%	800
	21st to end	Night	13% 7% 18% 35% 21% 7%	880
November	1st to 10th	Night	20% 8% 19% 34% 15% 4	820
	11th to 20th	Night	24% 9% 19% 32% 14% 3	840
	21st to end	Night	17% 9% 19% 33% 19% 4	840
December	1st to 10th	Night	20% 7% 17% 34% 17% 4	840
	11th to 20th	Night	26% 7% 18% 32% 15% 3	840
	21st to end	Night	27% 15% 21% 26% 9% 1	924

Page generated at 2026-09-11 01:11:56. Version ac07

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