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 2024-01-13.

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 6% 5% 3 5% 5% 5% 7% 41%	74769
	Night	11% 7% 3 6% 5% 3 4 4 5% 7% 44%	74990
Transparency	Day	41% 7% 14% 24% 12% 1	74474
	Night	39% 7% 14% 24% 14% 2	74805
Seeing	Day	15% 10% 32% 29% 13% 2	14769
	Night	13% 9% 34% 33% 10% 1	24800

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	7% 10% 5% 10% 8% 5% 8% 6% 5% 7% 29%	1427
	11th to 20th	Day	7% 12% 7% 11% 6% 4 7% 5% 6% 7% 26%	1538
	21st to end	Day	10% 13% 6% 12% 8% 4 7% 6% 5% 7% 22%	1782
February	1st to 10th	Day	9% 9% 4 10% 9% 6% 6% 7% 5% 7% 26%	1620
	11th to 20th	Day	8% 10% 5% 8% 8% 4 6% 5% 6% 6% 33%	1577
	21st to end	Day	11% 10% 5% 7% 6% 4 5% 5% 6% 7% 35%	1480
March	1st to 10th	Day	14% 10% 5% 7% 5% 2 4 4 4 8% 35%	1908
	11th to 20th	Day	14% 10% 4 8% 6% 3 4 5% 5% 6% 34%	1980
	21st to end	Day	18% 12% 4 8% 6% 3 4 4 6% 7% 28%	2178
April	1st to 10th	Day	17% 7% 3 6% 5% 2 5% 5% 6% 8% 36%	2039
	11th to 20th	Day	19% 10% 3 5% 4 3 4 4 5% 6% 37%	2312
	21st to end	Day	21% 8% 3 5% 4 2 4 4 5% 7% 37%	2340
May	1st to 10th	Day	18% 7% 3 6% 6% 4 4 5% 5% 7% 35%	2340
	11th to 20th	Day	18% 7% 3 6% 5% 4 5% 5% 6% 6% 36%	2318
	21st to end	Day	18% 6% 2 6% 6% 3 4 4 6% 8% 37%	2725
June	1st to 10th	Day	12% 5% 2 5% 4 3 4 5% 5% 9% 47%	2610
	11th to 20th	Day	13% 5% 2 5% 5% 3 4 5% 6% 8% 44%	2700
	21st to end	Day	9% 4 1 4 5% 3 5% 6% 6% 8% 48%	2700
July	1st to 10th	Day	6% 4 2 3 4 3 5% 5% 6% 10% 53%	2700
	11th to 20th	Day	7% 3 2 4 4 3 3 4 5% 10% 57%	2515
	21st to end	Day	6% 3 1 3 4 3 5% 5% 7% 10% 53%	2546
August	1st to 10th	Day	9% 5% 2 6% 6% 4 5% 6% 7% 8% 42%	2328
	11th to 20th	Day	10% 5% 2 5% 4 3 4 5% 6% 9% 46%	2301
	21st to end	Day	7% 3 2 4 4 3 4 4 5% 7% 57%	2574
September	1st to 10th	Day	13% 6% 2 4 4 2 3 4 4 7% 51%	2108
	11th to 20th	Day	12% 5% 2 4 4 2 3 3 4 7% 53%	1980
	21st to end	Day	12% 4 2 5% 3 3 4 4 4 8% 51%	1980
October	1st to 10th	Day	15% 7% 3 5% 5% 3 3 4 4 6% 46%	1846
	11th to 20th	Day	14% 7% 2 4 3 3 4 4 4 6% 51%	1800
	21st to end	Day	16% 8% 2 6% 5% 2 3 3 4 6% 46%	1909
November	1st to 10th	Day	11% 6% 3 6% 5% 2 4 4 6% 8% 46%	1673
	11th to 20th	Day	9% 8% 5% 10% 6% 4 5% 5% 4 7% 38%	1549
	21st to end	Day	12% 8% 3 6% 4 3 5% 5% 6% 7% 40%	1520
December	1st to 10th	Day	8% 8% 4 10% 8% 4 5% 5% 5% 9% 33%	1520
	11th to 20th	Day	9% 10% 5% 10% 9% 5% 6% 5% 6% 7% 28%	1904
	21st to end	Day	18% 8% 5% 14% 7% 4 4 5% 6% 7% 25%	2442
January	1st to 10th	Night	8% 7% 3 8% 9% 4 7% 5% 6% 8% 35%	2734
	11th to 20th	Night	7% 9% 6% 10% 9% 4 6% 6% 5% 8% 31%	2480
	21st to end	Night	10% 12% 5% 9% 6% 4 5% 5% 5% 8% 32%	2574
February	1st to 10th	Night	8% 10% 4 9% 8% 4 4 4 4 7% 37%	2340
	11th to 20th	Night	8% 9% 4 8% 6% 4 5% 5% 6% 7% 39%	2273
	21st to end	Night	10% 9% 4 6% 7% 3 5% 5% 5% 8% 38%	1790
March	1st to 10th	Night	11% 8% 4 6% 5% 3 4 4 5% 7% 42%	2051
	11th to 20th	Night	12% 10% 4 7% 5% 3 4 5% 5% 6% 40%	1980
	21st to end	Night	15% 9% 4 6% 6% 3 4 5% 6% 6% 35%	2178
April	1st to 10th	Night	15% 8% 2 5% 5% 3 4 5% 5% 7% 40%	1918
	11th to 20th	Night	17% 8% 4 6% 5% 3 4 3 4 6% 43%	1599
	21st to end	Night	17% 7% 3 5% 4 2 4 4 6% 7% 40%	1620
May	1st to 10th	Night	15% 5% 2 4 5% 3 5% 4 6% 7% 43%	1620
	11th to 20th	Night	14% 7% 3 5% 4 2 4 3 5% 7% 46%	1576
	21st to end	Night	15% 5% 2 5% 5% 3 4 5% 6% 8% 41%	1551
June	1st to 10th	Night	9% 4 2 4 4 3 5% 4 4 8% 53%	1346
	11th to 20th	Night	7% 4 2 3 4 3 4 4 6% 10% 53%	1260
	21st to end	Night	7% 3 2 3 4 1 3 5% 6% 8% 58%	1260
July	1st to 10th	Night	4 4 2 3 4 2 3 4 5% 8% 61%	1260
	11th to 20th	Night	4 1 1 2 3 2 3 5% 5% 8% 66%	1440
	21st to end	Night	5% 3 1 2 3 1 4 5% 7% 10% 60%	1772
August	1st to 10th	Night	6% 4 2 4 5% 3 6% 6% 6% 10% 48%	1611
	11th to 20th	Night	7% 3 2 3 3 3 4 4 5% 7% 60%	1600
	21st to end	Night	6% 2 1 3 3 2 3 4 5% 8% 63%	1782
September	1st to 10th	Night	8% 4 2 5% 3 2 3 4 4 6% 58%	1849
	11th to 20th	Night	9% 4 2 4 3 2 4 4 5% 7% 55%	1980
	21st to end	Night	10% 5% 2 3 3 2 3 3 5% 7% 56%	1980
October	1st to 10th	Night	15% 5% 2 4 4 2 3 3 4 6% 52%	2095
	11th to 20th	Night	13% 6% 3 4 4 2 3 4 4 6% 51%	2160
	21st to end	Night	14% 7% 2 6% 4 2 4 3 4 6% 48%	2443
November	1st to 10th	Night	10% 5% 2 5% 4 3 5% 4 4 6% 52%	2405
	11th to 20th	Night	9% 7% 3 7% 6% 3 4 5% 5% 7% 44%	2630
	21st to end	Night	10% 7% 3 6% 5% 3 4 4 5% 7% 47%	2660
December	1st to 10th	Night	7% 9% 3 10% 7% 4 5% 5% 5% 8% 37%	2660
	11th to 20th	Night	10% 8% 5% 7% 6% 3 5% 5% 5% 8% 36%	3288
	21st to end	Night	17% 10% 5% 13% 7% 3 4 4 5% 5% 27%	5225

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	53% 7% 16% 15% 8% 1	1428
	11th to 20th	Day	56% 7% 12% 17% 8%	1538
	21st to end	Day	60% 7% 15% 13% 5%	1782
February	1st to 10th	Day	55% 7% 12% 16% 9%	1620
	11th to 20th	Day	50% 7% 13% 20% 8% 2	1586
	21st to end	Day	48% 9% 13% 18% 11% 1	1480
March	1st to 10th	Day	48% 7% 15% 22% 7% 1	1908
	11th to 20th	Day	50% 7% 12% 23% 8%	1980
	21st to end	Day	55% 7% 14% 18% 5% 1	2178
April	1st to 10th	Day	45% 6% 14% 23% 10% 1	2039
	11th to 20th	Day	48% 6% 11% 23% 11% 2	2312
	21st to end	Day	48% 6% 12% 25% 9%	2340
May	1st to 10th	Day	48% 8% 13% 19% 12%	2340
	11th to 20th	Day	46% 8% 15% 21% 10%	2322
	21st to end	Day	45% 9% 13% 22% 12% 1	2725
June	1st to 10th	Day	34% 8% 17% 27% 13% 1	2610
	11th to 20th	Day	37% 8% 14% 24% 14% 3	2700
	21st to end	Day	30% 9% 16% 28% 14% 2	2700
July	1st to 10th	Day	25% 8% 19% 32% 14% 1	2626
	11th to 20th	Day	24% 6% 15% 28% 22% 5%	2438
	21st to end	Day	24% 8% 19% 28% 18% 2	2405
August	1st to 10th	Day	36% 9% 17% 24% 12% 2	2314
	11th to 20th	Day	33% 8% 17% 30% 11% 1	2301
	21st to end	Day	27% 6% 14% 31% 18% 4	2574
September	1st to 10th	Day	34% 7% 11% 28% 18% 2	2108
	11th to 20th	Day	32% 6% 16% 31% 14% 1	1980
	21st to end	Day	32% 7% 11% 31% 18% 1	1980
October	1st to 10th	Day	39% 7% 13% 27% 15% 1	1846
	11th to 20th	Day	34% 5% 13% 28% 18% 3	1800
	21st to end	Day	42% 5% 13% 25% 15% 1	1909
November	1st to 10th	Day	36% 6% 16% 25% 14% 3	1673
	11th to 20th	Day	45% 7% 14% 21% 12%	1549
	21st to end	Day	42% 6% 15% 23% 12% 1	1520
December	1st to 10th	Day	48% 6% 18% 18% 9% 2	1520
	11th to 20th	Day	53% 6% 17% 19% 5%	1901
	21st to end	Day	57% 6% 13% 15% 7% 1	2442
January	1st to 10th	Night	47% 7% 13% 21% 11%	2734
	11th to 20th	Night	50% 8% 16% 18% 7% 1	2480
	21st to end	Night	51% 7% 14% 17% 10% 1	2574
February	1st to 10th	Night	47% 6% 13% 23% 11% 1	2340
	11th to 20th	Night	43% 7% 12% 22% 12% 3	2274
	21st to end	Night	43% 8% 12% 20% 13% 3	1790
March	1st to 10th	Night	41% 6% 19% 23% 8% 2	2051
	11th to 20th	Night	44% 6% 11% 26% 12% 1	1980
	21st to end	Night	48% 8% 15% 20% 7% 1	2178
April	1st to 10th	Night	42% 7% 14% 23% 12% 1	1918
	11th to 20th	Night	43% 6% 11% 23% 15% 2	1599
	21st to end	Night	42% 7% 11% 26% 12% 2	1620
May	1st to 10th	Night	38% 7% 15% 25% 14% 1	1620
	11th to 20th	Night	37% 7% 14% 24% 16% 2	1577
	21st to end	Night	39% 9% 16% 20% 14% 2	1552
June	1st to 10th	Night	28% 8% 16% 28% 17% 2	1346
	11th to 20th	Night	27% 7% 17% 25% 20% 4	1260
	21st to end	Night	23% 7% 18% 28% 22% 2	1260
July	1st to 10th	Night	21% 7% 16% 34% 20% 2	1225
	11th to 20th	Night	16% 7% 15% 32% 24% 6%	1394
	21st to end	Night	18% 8% 16% 33% 20% 5%	1673
August	1st to 10th	Night	30% 9% 16% 27% 15% 3	1601
	11th to 20th	Night	24% 8% 14% 36% 17% 2	1600
	21st to end	Night	20% 6% 16% 28% 24% 5%	1782
September	1st to 10th	Night	27% 6% 15% 27% 22% 3	1849
	11th to 20th	Night	27% 7% 14% 33% 17% 2	1980
	21st to end	Night	27% 7% 12% 32% 22% 2	1980
October	1st to 10th	Night	33% 6% 12% 28% 20% 1	2095
	11th to 20th	Night	35% 5% 11% 27% 19% 3	2160
	21st to end	Night	38% 5% 13% 24% 18% 2	2443
November	1st to 10th	Night	33% 5% 15% 23% 19% 4	2405
	11th to 20th	Night	38% 7% 14% 25% 14% 2	2630
	21st to end	Night	37% 5% 16% 27% 14% 1	2660
December	1st to 10th	Night	44% 8% 17% 23% 8%	2660
	11th to 20th	Night	43% 7% 23% 20% 6%	3290
	21st to end	Night	57% 7% 10% 18% 7% 1	5225

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% 10% 35% 26% 11% 2	270
	11th to 20th	Day	20% 10% 38% 25% 8%	248
	21st to end	Day	16% 12% 41% 24% 7%	264
February	1st to 10th	Day	12% 20% 39% 26% 3	240
	11th to 20th	Day	12% 18% 41% 22% 7% 1	240
	21st to end	Day	18% 15% 42% 22% 3 1	198
March	1st to 10th	Day	22% 14% 38% 22% 4 1	240
	11th to 20th	Day	22% 11% 36% 22% 8% 1	240
	21st to end	Day	25% 13% 33% 20% 8% 1	264
April	1st to 10th	Day	25% 16% 36% 19% 4	299
	11th to 20th	Day	25% 16% 30% 23% 5% 1	590
	21st to end	Day	26% 13% 28% 20% 10% 2	600
May	1st to 10th	Day	22% 11% 31% 26% 9% 1	603
	11th to 20th	Day	23% 10% 30% 24% 10% 3	625
	21st to end	Day	20% 7% 29% 30% 13% 1	679
June	1st to 10th	Day	9% 8% 23% 34% 22% 3	630
	11th to 20th	Day	13% 8% 35% 28% 13% 3	630
	21st to end	Day	9% 6% 33% 34% 16% 2	630
July	1st to 10th	Day	6% 3 22% 39% 24% 5%	621
	11th to 20th	Day	6% 6% 30% 35% 18% 4	618
	21st to end	Day	6% 3 27% 41% 20% 4	684
August	1st to 10th	Day	9% 3 22% 41% 20% 4	626
	11th to 20th	Day	10% 4 25% 33% 25% 3	615
	21st to end	Day	7% 6% 29% 35% 20% 4	693
September	1st to 10th	Day	16% 9% 27% 29% 16% 4	398
	11th to 20th	Day	11% 4 34% 33% 15% 3	270
	21st to end	Day	16% 14% 34% 26% 9% 2	270
October	1st to 10th	Day	21% 11% 30% 24% 10% 4	270
	11th to 20th	Day	15% 19% 36% 22% 9%	270
	21st to end	Day	23% 18% 34% 19% 6% 1	297
November	1st to 10th	Day	20% 9% 38% 25% 7% 2	270
	11th to 20th	Day	13% 20% 43% 18% 7%	270
	21st to end	Day	20% 17% 31% 23% 9%	270
December	1st to 10th	Day	11% 11% 44% 22% 11% 1	270
	11th to 20th	Day	15% 12% 44% 26% 3	270
	21st to end	Day	23% 14% 38% 22% 2	297
January	1st to 10th	Night	12% 10% 39% 29% 9% 1	950
	11th to 20th	Night	11% 11% 37% 33% 6% 1	915
	21st to end	Night	15% 11% 39% 29% 5%	990
February	1st to 10th	Night	13% 11% 41% 29% 6% 1	900
	11th to 20th	Night	12% 11% 39% 31% 6% 1	879
	21st to end	Night	14% 10% 38% 29% 9% 1	606
March	1st to 10th	Night	13% 10% 41% 28% 7% 1	611
	11th to 20th	Night	17% 10% 37% 32% 3	540
	21st to end	Night	18% 11% 35% 26% 10% 1	594
April	1st to 10th	Night	19% 11% 39% 27% 4	540
	11th to 20th	Night	22% 14% 30% 27% 5% 1	533
	21st to end	Night	20% 11% 34% 24% 9% 1	540
May	1st to 10th	Night	17% 7% 36% 31% 8%	540
	11th to 20th	Night	18% 8% 32% 31% 10% 1	531
	21st to end	Night	18% 5% 31% 34% 11%	584
June	1st to 10th	Night	9% 6% 26% 38% 20%	540
	11th to 20th	Night	8% 5% 34% 41% 11%	540
	21st to end	Night	9% 4 24% 49% 14%	540
July	1st to 10th	Night	7% 2 22% 43% 25% 1	525
	11th to 20th	Night	4 1 28% 49% 17%	522
	21st to end	Night	5% 2 24% 51% 18%	591
August	1st to 10th	Night	7% 2 23% 47% 21% 1	537
	11th to 20th	Night	8% 3 24% 39% 25% 1	534
	21st to end	Night	5% 4 28% 43% 18% 2	594
September	1st to 10th	Night	9% 3 28% 43% 14% 3	540
	11th to 20th	Night	10% 6% 30% 36% 15% 2	540
	21st to end	Night	12% 6% 35% 35% 10% 1	540
October	1st to 10th	Night	16% 9% 35% 29% 11%	655
	11th to 20th	Night	15% 12% 36% 30% 7%	720
	21st to end	Night	19% 11% 34% 28% 8%	859
November	1st to 10th	Night	12% 10% 37% 32% 9% 1	925
	11th to 20th	Night	13% 11% 39% 28% 8%	950
	21st to end	Night	13% 11% 37% 31% 8%	950
December	1st to 10th	Night	12% 11% 38% 32% 6% 1	950
	11th to 20th	Night	16% 9% 39% 29% 7% 1	950
	21st to end	Night	21% 11% 35% 26% 6%	1045

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