Wally's Corner
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Wally's Corner clear sky chart from 2005-11-06 to 2026-01-02.

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% 7% 3 8% 4 4 5% 4 6% 7% 41%	127306
	Night	10% 7% 3 7% 5% 4 4 4 5% 7% 43%	124295
Transparency	Day	40% 6% 14% 24% 13% 2	130881
	Night	38% 6% 14% 25% 15% 2	128787
Seeing	Day	15% 10% 32% 28% 12% 2	17519
	Night	13% 9% 35% 33% 10% 1	27471

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	10% 13% 4 15% 9% 7% 7% 4 5% 5% 20%	3433
	11th to 20th	Day	5% 11% 5% 10% 7% 7% 8% 4 10% 8% 25%	3835
	21st to end	Day	4 9% 7% 13% 6% 6% 6% 4 5% 6% 33%	4488
February	1st to 10th	Day	9% 11% 4 12% 8% 7% 6% 5% 5% 7% 26%	1800
	11th to 20th	Day	7% 11% 5% 10% 7% 6% 5% 4 6% 6% 34%	1758
	21st to end	Day	10% 11% 4 8% 4 5% 4 4 7% 7% 37%	1650
March	1st to 10th	Day	11% 7% 3 7% 4 3 3 3 4 7% 46%	4764
	11th to 20th	Day	8% 8% 3 7% 4 3 3 3 5% 8% 49%	4980
	21st to end	Day	23% 11% 4 10% 4 4 4 3 6% 6% 24%	5462
April	1st to 10th	Day	17% 8% 3 6% 4 3 5% 4 7% 7% 37%	2267
	11th to 20th	Day	18% 10% 3 6% 4 4 4 3 5% 5% 38%	2572
	21st to end	Day	21% 9% 2 6% 4 3 4 3 5% 6% 36%	2600
May	1st to 10th	Day	12% 5% 2 5% 3 4 4 4 6% 8% 48%	5862
	11th to 20th	Day	18% 7% 2 5% 3 3 3 3 4 5% 47%	5906
	21st to end	Day	19% 8% 3 6% 5% 4 4 4 6% 7% 35%	6935
June	1st to 10th	Day	12% 5% 2 5% 3 4 4 4 6% 8% 47%	2900
	11th to 20th	Day	14% 5% 2 6% 4 4 5% 4 6% 8% 43%	3000
	21st to end	Day	9% 4 1 5% 4 4 5% 5% 7% 9% 47%	3000
July	1st to 10th	Day	8% 4 2 6% 4 5% 5% 5% 8% 10% 43%	6800
	11th to 20th	Day	8% 4 2 5% 4 4 4 3 5% 8% 53%	6312
	21st to end	Day	6% 4 2 6% 4 5% 5% 4 7% 10% 46%	6422
August	1st to 10th	Day	9% 6% 2 6% 5% 5% 6% 5% 7% 8% 42%	4234
	11th to 20th	Day	15% 8% 2 7% 4 4 5% 4 7% 9% 36%	4171
	21st to end	Day	8% 5% 2 6% 4 4 4 3 5% 7% 52%	4675
September	1st to 10th	Day	12% 6% 1 5% 4 3 4 3 5% 7% 52%	2340
	11th to 20th	Day	11% 6% 2 4 3 3 3 3 5% 8% 53%	2200
	21st to end	Day	11% 4 2 5% 3 4 4 3 4 8% 54%	2200
October	1st to 10th	Day	14% 7% 2 5% 4 3 3 3 4 6% 48%	2050
	11th to 20th	Day	14% 7% 2 4 2 4 4 3 5% 6% 50%	2000
	21st to end	Day	15% 8% 2 7% 3 3 4 3 4 6% 45%	2121
November	1st to 10th	Day	11% 7% 3 7% 4 4 3 4 6% 8% 44%	1853
	11th to 20th	Day	9% 10% 4 11% 5% 5% 4 4 4 7% 38%	1711
	21st to end	Day	10% 10% 3 8% 4 5% 4 3 6% 7% 39%	1680
December	1st to 10th	Day	4 8% 5% 12% 7% 6% 4 4 5% 8% 37%	2690
	11th to 20th	Day	8% 13% 5% 13% 7% 7% 6% 4 5% 7% 26%	3060
	21st to end	Day	16% 9% 4 15% 5% 4 4 4 6% 7% 25%	3575
January	1st to 10th	Night	8% 10% 4 14% 10% 7% 6% 5% 6% 7% 24%	6551
	11th to 20th	Night	3 7% 4 11% 7% 6% 8% 5% 9% 8% 31%	6141
	21st to end	Night	5% 9% 6% 11% 4 5% 5% 4 6% 5% 40%	6490
February	1st to 10th	Night	7% 11% 4 10% 7% 5% 4 4 5% 7% 36%	2600
	11th to 20th	Night	7% 10% 4 9% 5% 4 5% 4 6% 7% 39%	2533
	21st to end	Night	8% 8% 3 7% 6% 5% 5% 4 6% 8% 41%	1995
March	1st to 10th	Night	10% 8% 2 5% 3 3 3 3 5% 6% 52%	5083
	11th to 20th	Night	10% 6% 2 5% 3 3 3 4 6% 8% 50%	4980
	21st to end	Night	20% 10% 3 7% 6% 4 4 4 5% 6% 32%	5467
April	1st to 10th	Night	15% 9% 2 6% 5% 4 4 4 5% 6% 39%	2129
	11th to 20th	Night	16% 8% 3 6% 4 3 3 3 4 6% 45%	1779
	21st to end	Night	18% 8% 3 6% 4 3 4 3 6% 6% 40%	1800
May	1st to 10th	Night	13% 4 1 4 2 3 3 3 5% 6% 56%	4053
	11th to 20th	Night	12% 7% 2 5% 3 3 4 2 4 6% 51%	4008
	21st to end	Night	19% 6% 3 5% 4 3 4 3 5% 7% 42%	3942
June	1st to 10th	Night	8% 4 2 5% 3 4 4 3 5% 7% 53%	1495
	11th to 20th	Night	8% 5% 2 4 4 4 4 4 6% 9% 52%	1400
	21st to end	Night	9% 4 1 4 3 3 3 4 6% 9% 56%	1400
July	1st to 10th	Night	7% 5% 2 5% 4 4 3 4 7% 8% 50%	3178
	11th to 20th	Night	7% 4 2 4 3 3 4 3 5% 7% 57%	3633
	21st to end	Night	7% 4 2 5% 3 3 4 4 6% 10% 53%	4449
August	1st to 10th	Night	6% 6% 3 7% 4 4 5% 4 6% 8% 47%	2926
	11th to 20th	Night	11% 4 2 5% 3 4 4 3 5% 8% 50%	2888
	21st to end	Night	8% 4 1 5% 3 3 4 3 6% 8% 55%	3234
September	1st to 10th	Night	8% 4 1 5% 3 3 3 3 4 6% 59%	2057
	11th to 20th	Night	9% 5% 2 4 4 3 4 3 5% 8% 54%	2200
	21st to end	Night	9% 5% 2 3 3 3 3 2 5% 7% 58%	2200
October	1st to 10th	Night	14% 5% 2 4 3 2 3 2 4 6% 55%	2329
	11th to 20th	Night	13% 7% 3 4 4 3 3 3 4 6% 51%	2400
	21st to end	Night	14% 8% 2 6% 3 4 3 3 4 6% 47%	2715
November	1st to 10th	Night	10% 6% 2 6% 4 4 4 3 4 6% 50%	2665
	11th to 20th	Night	9% 8% 3 8% 4 4 4 4 5% 6% 45%	2908
	21st to end	Night	9% 8% 3 7% 5% 5% 4 4 5% 7% 45%	2940
December	1st to 10th	Night	4 8% 3 12% 6% 5% 4 4 5% 7% 41%	4720
	11th to 20th	Night	10% 9% 4 9% 6% 6% 6% 4 6% 8% 32%	5362
	21st to end	Night	15% 14% 4 13% 6% 4 4 4 5% 6% 25%	7645

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% 6% 14% 12% 5%	3434
	11th to 20th	Day	53% 4 10% 18% 14%	3835
	21st to end	Day	49% 7% 16% 18% 10%	4488
February	1st to 10th	Day	56% 7% 12% 15% 9%	1800
	11th to 20th	Day	50% 7% 13% 20% 9% 2	1767
	21st to end	Day	45% 9% 14% 20% 11% 1	1650
March	1st to 10th	Day	37% 6% 13% 31% 11% 2	4764
	11th to 20th	Day	33% 5% 10% 32% 17% 2	4980
	21st to end	Day	59% 7% 11% 17% 5% 1	5464
April	1st to 10th	Day	45% 7% 14% 23% 10% 1	2267
	11th to 20th	Day	47% 6% 10% 23% 12% 2	2572
	21st to end	Day	48% 6% 12% 24% 10%	2600
May	1st to 10th	Day	31% 7% 12% 26% 23%	5900
	11th to 20th	Day	38% 6% 10% 21% 15% 9%	5910
	21st to end	Day	46% 7% 11% 22% 13% 1	6949
June	1st to 10th	Day	33% 9% 16% 28% 12% 2	2900
	11th to 20th	Day	38% 8% 15% 23% 13% 2	3000
	21st to end	Day	31% 9% 16% 27% 15% 3	3000
July	1st to 10th	Day	33% 8% 19% 28% 11% 1	6726
	11th to 20th	Day	30% 5% 13% 32% 18% 2	6235
	21st to end	Day	31% 7% 19% 25% 16% 1	6240
August	1st to 10th	Day	36% 8% 15% 26% 13% 2	4220
	11th to 20th	Day	43% 8% 15% 25% 8% 1	4210
	21st to end	Day	31% 6% 19% 26% 15% 2	4674
September	1st to 10th	Day	32% 7% 12% 30% 17% 1	2340
	11th to 20th	Day	32% 6% 17% 31% 14% 1	2200
	21st to end	Day	30% 6% 11% 31% 21% 2	2200
October	1st to 10th	Day	25% 4 8% 30% 30% 3	3336
	11th to 20th	Day	32% 5% 14% 24% 22% 3	3240
	21st to end	Day	41% 4 13% 24% 17% 1	3414
November	1st to 10th	Day	38% 6% 15% 24% 14% 3	1853
	11th to 20th	Day	45% 6% 14% 22% 12% 1	1711
	21st to end	Day	44% 6% 15% 23% 11% 1	1680
December	1st to 10th	Day	45% 5% 16% 24% 8% 1	2690
	11th to 20th	Day	57% 6% 16% 17% 5%	3057
	21st to end	Day	57% 5% 14% 17% 7% 1	3575
January	1st to 10th	Night	57% 6% 12% 17% 8%	6551
	11th to 20th	Night	44% 7% 16% 16% 16% 1	6141
	21st to end	Night	42% 8% 14% 22% 14%	6490
February	1st to 10th	Night	47% 6% 13% 22% 11% 2	2600
	11th to 20th	Night	43% 6% 12% 23% 13% 3	2534
	21st to end	Night	40% 7% 13% 22% 14% 3	1995
March	1st to 10th	Night	32% 5% 11% 33% 16% 2	5083
	11th to 20th	Night	31% 5% 12% 33% 18% 2	4980
	21st to end	Night	52% 7% 13% 21% 6% 1	5467
April	1st to 10th	Night	43% 8% 14% 23% 12% 1	2129
	11th to 20th	Night	41% 6% 11% 24% 17% 2	1779
	21st to end	Night	43% 7% 11% 25% 13% 2	1800
May	1st to 10th	Night	29% 6% 12% 29% 23% 2	4080
	11th to 20th	Night	33% 7% 10% 22% 20% 9%	4009
	21st to end	Night	41% 7% 11% 28% 12% 1	3950
June	1st to 10th	Night	28% 8% 16% 29% 16% 3	1495
	11th to 20th	Night	28% 7% 17% 25% 19% 4	1400
	21st to end	Night	24% 7% 18% 28% 21% 2	1400
July	1st to 10th	Night	30% 6% 19% 30% 14% 1	3145
	11th to 20th	Night	26% 6% 13% 35% 17% 2	3590
	21st to end	Night	26% 8% 20% 29% 14% 2	4320
August	1st to 10th	Night	34% 7% 15% 26% 15% 2	2916
	11th to 20th	Night	33% 7% 17% 29% 13% 1	2915
	21st to end	Night	26% 7% 19% 25% 19% 3	3234
September	1st to 10th	Night	26% 6% 15% 28% 22% 3	2057
	11th to 20th	Night	27% 8% 15% 32% 17% 2	2200
	21st to end	Night	25% 6% 11% 31% 24% 2	2200
October	1st to 10th	Night	20% 3 7% 26% 40% 3	3810
	11th to 20th	Night	27% 3 14% 29% 24% 3	3899
	21st to end	Night	39% 4 12% 29% 15% 1	4376
November	1st to 10th	Night	34% 5% 15% 24% 18% 4	2665
	11th to 20th	Night	38% 6% 15% 25% 14% 2	2908
	21st to end	Night	39% 5% 15% 27% 13% 1	2940
December	1st to 10th	Night	42% 6% 16% 28% 8%	4720
	11th to 20th	Night	48% 7% 19% 20% 5%	5364
	21st to end	Night	58% 6% 11% 18% 6%	7645

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	16% 9% 37% 25% 11% 3	303
	11th to 20th	Day	17% 11% 40% 24% 7% 1	300
	21st to end	Day	13% 13% 39% 25% 10% 1	330
February	1st to 10th	Day	14% 19% 39% 25% 3	300
	11th to 20th	Day	10% 18% 40% 23% 8% 1	300
	21st to end	Day	16% 14% 45% 22% 2	249
March	1st to 10th	Day	20% 14% 41% 22% 3 1	300
	11th to 20th	Day	20% 13% 36% 21% 8% 1	300
	21st to end	Day	25% 15% 33% 19% 7% 1	330
April	1st to 10th	Day	25% 16% 37% 19% 3	367
	11th to 20th	Day	24% 18% 31% 22% 4 1	690
	21st to end	Day	27% 13% 29% 20% 9% 2	700
May	1st to 10th	Day	20% 12% 31% 25% 11% 2	703
	11th to 20th	Day	22% 11% 28% 25% 11% 3	725
	21st to end	Day	20% 8% 29% 29% 13% 1	789
June	1st to 10th	Day	9% 10% 24% 32% 21% 3	730
	11th to 20th	Day	14% 8% 36% 28% 12% 3	730
	21st to end	Day	11% 7% 35% 32% 14% 2	730
July	1st to 10th	Day	7% 4 23% 38% 23% 5%	721
	11th to 20th	Day	7% 6% 30% 36% 18% 4	718
	21st to end	Day	6% 3 27% 41% 19% 4	794
August	1st to 10th	Day	9% 4 24% 40% 19% 4	726
	11th to 20th	Day	11% 4 26% 32% 23% 3	715
	21st to end	Day	7% 5% 28% 36% 20% 4	803
September	1st to 10th	Day	14% 9% 27% 31% 16% 4	470
	11th to 20th	Day	12% 5% 35% 32% 13% 3	330
	21st to end	Day	13% 13% 31% 25% 14% 4	330
October	1st to 10th	Day	18% 12% 31% 25% 12% 4	330
	11th to 20th	Day	16% 18% 36% 22% 7%	330
	21st to end	Day	22% 17% 34% 20% 6% 1	363
November	1st to 10th	Day	20% 9% 40% 22% 6% 2	330
	11th to 20th	Day	14% 18% 43% 18% 7%	330
	21st to end	Day	18% 18% 34% 21% 9% 1	330
December	1st to 10th	Day	11% 12% 43% 24% 10% 1	330
	11th to 20th	Day	16% 15% 42% 24% 3	330
	21st to end	Day	22% 12% 39% 24% 3	363
January	1st to 10th	Night	11% 10% 38% 30% 9% 1	1006
	11th to 20th	Night	11% 12% 39% 32% 6% 1	1000
	21st to end	Night	14% 11% 40% 29% 6%	1100
February	1st to 10th	Night	13% 12% 41% 28% 6% 1	1000
	11th to 20th	Night	12% 11% 41% 31% 5% 1	979
	21st to end	Night	12% 9% 40% 29% 8% 1	675
March	1st to 10th	Night	14% 10% 42% 28% 6% 1	678
	11th to 20th	Night	16% 12% 38% 31% 3	600
	21st to end	Night	18% 11% 36% 25% 9% 1	660
April	1st to 10th	Night	19% 13% 38% 27% 4	600
	11th to 20th	Night	21% 15% 32% 27% 5% 1	593
	21st to end	Night	21% 13% 33% 25% 8% 1	600
May	1st to 10th	Night	18% 7% 36% 31% 9%	600
	11th to 20th	Night	17% 8% 32% 32% 10% 1	591
	21st to end	Night	18% 6% 31% 33% 12%	650
June	1st to 10th	Night	9% 6% 28% 39% 18%	600
	11th to 20th	Night	8% 6% 35% 41% 10%	600
	21st to end	Night	10% 4 26% 47% 13%	600
July	1st to 10th	Night	7% 2 22% 43% 25% 1	585
	11th to 20th	Night	5% 1 27% 49% 17%	582
	21st to end	Night	5% 2 24% 51% 18% 1	657
August	1st to 10th	Night	6% 3 23% 47% 20% 1	597
	11th to 20th	Night	9% 3 23% 40% 25% 1	594
	21st to end	Night	6% 4 28% 43% 18% 2	660
September	1st to 10th	Night	8% 4 28% 43% 15% 3	600
	11th to 20th	Night	10% 6% 32% 36% 15% 2	600
	21st to end	Night	11% 7% 33% 36% 13% 1	600
October	1st to 10th	Night	15% 9% 35% 30% 11% 1	729
	11th to 20th	Night	16% 12% 36% 30% 6%	800
	21st to end	Night	18% 12% 35% 26% 8%	955
November	1st to 10th	Night	12% 10% 38% 31% 8%	1025
	11th to 20th	Night	13% 12% 39% 28% 8%	1050
	21st to end	Night	13% 11% 37% 32% 8%	1050
December	1st to 10th	Night	12% 11% 38% 32% 6%	1050
	11th to 20th	Night	16% 10% 39% 28% 6% 1	1050
	21st to end	Night	20% 11% 36% 26% 6% 1	1155

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