Wild Apple Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Wild Apple Observatory clear sky chart from 2005-11-06 to 2024-01-16.

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	13% 9% 4 7% 6% 3 5% 5% 5% 7% 37%	74804
	Night	14% 9% 4 6% 5% 3 4 4 5% 7% 39%	75028
Transparency	Day	46% 6% 13% 22% 12% 1	74504
	Night	45% 5% 12% 23% 14% 2	74848
Seeing	Day	16% 11% 29% 25% 14% 5%	14726
	Night	17% 10% 31% 30% 11% 1	24724

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% 10% 6% 10% 6% 3 6% 5% 5% 6% 33%	1517
	11th to 20th	Day	12% 14% 7% 13% 8% 3 4 4 6% 6% 23%	1485
	21st to end	Day	12% 14% 6% 13% 8% 3 5% 5% 5% 7% 23%	1688
February	1st to 10th	Day	13% 12% 6% 8% 6% 3 5% 5% 5% 7% 30%	1620
	11th to 20th	Day	14% 12% 5% 6% 6% 3 5% 4 5% 7% 35%	1670
	21st to end	Day	13% 15% 4 9% 8% 3 4 4 4 6% 32%	1480
March	1st to 10th	Day	14% 10% 6% 8% 6% 3 5% 5% 5% 6% 34%	1800
	11th to 20th	Day	13% 10% 3 7% 6% 3 4 4 5% 7% 39%	1934
	21st to end	Day	20% 10% 4 7% 5% 3 5% 5% 4 6% 30%	2327
April	1st to 10th	Day	18% 11% 4 7% 7% 3 4 4 4 7% 31%	2160
	11th to 20th	Day	18% 10% 3 7% 6% 3 4 4 5% 6% 33%	2134
	21st to end	Day	19% 9% 3 7% 6% 3 5% 3 5% 5% 33%	2196
May	1st to 10th	Day	17% 9% 3 6% 7% 4 6% 5% 6% 7% 30%	2438
	11th to 20th	Day	18% 7% 3 7% 7% 3 4 4 5% 7% 35%	2479
	21st to end	Day	14% 7% 3 6% 6% 4 5% 5% 6% 8% 36%	2725
June	1st to 10th	Day	11% 5% 3 5% 5% 3 6% 5% 6% 9% 44%	2520
	11th to 20th	Day	12% 4 2 4 5% 3 5% 5% 7% 9% 43%	2520
	21st to end	Day	12% 6% 3 5% 7% 4 5% 5% 7% 8% 40%	2520
July	1st to 10th	Day	6% 4 2 5% 5% 4 5% 6% 7% 10% 46%	2520
	11th to 20th	Day	7% 4 2 5% 5% 4 5% 6% 7% 9% 45%	2520
	21st to end	Day	7% 4 2 5% 6% 4 5% 5% 7% 10% 45%	2743
August	1st to 10th	Day	7% 4 2 5% 5% 4 6% 7% 8% 10% 41%	2441
	11th to 20th	Day	11% 5% 3 6% 6% 3 6% 5% 5% 7% 43%	2194
	21st to end	Day	10% 5% 3 5% 5% 3 4 4 6% 8% 46%	2376
September	1st to 10th	Day	14% 6% 2 5% 5% 4 5% 4 6% 7% 43%	2160
	11th to 20th	Day	13% 5% 2 3 4 2 4 4 5% 8% 50%	2120
	21st to end	Day	13% 7% 3 6% 5% 3 4 4 5% 7% 44%	1980
October	1st to 10th	Day	13% 7% 3 5% 5% 3 4 4 3 6% 47%	1811
	11th to 20th	Day	20% 9% 3 6% 5% 3 4 3 5% 5% 37%	1800
	21st to end	Day	18% 11% 3 6% 5% 3 3 3 3 5% 40%	1836
November	1st to 10th	Day	11% 7% 3 7% 5% 4 4 4 5% 5% 45%	1672
	11th to 20th	Day	15% 11% 4 7% 6% 4 5% 4 4 6% 35%	1677
	21st to end	Day	14% 11% 4 8% 6% 3 4 3 4 7% 37%	1520
December	1st to 10th	Day	14% 14% 5% 8% 6% 3 4 5% 5% 6% 31%	1520
	11th to 20th	Day	13% 13% 6% 8% 6% 3 5% 5% 5% 8% 28%	1918
	21st to end	Day	18% 20% 10% 10% 5% 3 4 4 4 4 16%	2783
January	1st to 10th	Night	12% 11% 5% 8% 7% 3 4 3 5% 5% 35%	2648
	11th to 20th	Night	14% 12% 6% 11% 8% 3 4 4 5% 5% 28%	2603
	21st to end	Night	12% 13% 7% 10% 8% 4 5% 4 5% 6% 26%	2664
February	1st to 10th	Night	11% 13% 5% 8% 7% 4 5% 4 4 5% 32%	2340
	11th to 20th	Night	12% 9% 4 7% 6% 4 5% 5% 4 6% 38%	2176
	21st to end	Night	16% 13% 4 8% 5% 2 4 4 5% 6% 35%	1776
March	1st to 10th	Night	17% 9% 4 6% 6% 3 4 4 5% 6% 35%	2160
	11th to 20th	Night	13% 7% 3 5% 5% 4 5% 4 6% 8% 41%	2039
	21st to end	Night	19% 10% 4 7% 6% 3 4 5% 5% 6% 31%	2028
April	1st to 10th	Night	18% 8% 4 6% 5% 3 4 5% 5% 6% 37%	1800
	11th to 20th	Night	19% 9% 4 6% 5% 3 4 4 5% 6% 37%	1775
	21st to end	Night	18% 7% 2 5% 5% 3 5% 5% 6% 8% 37%	1764
May	1st to 10th	Night	16% 8% 3 6% 5% 4 3 6% 6% 8% 35%	1517
	11th to 20th	Night	16% 8% 4 6% 5% 3 4 5% 5% 8% 37%	1416
	21st to end	Night	12% 6% 3 4 5% 3 4 4 7% 8% 44%	1551
June	1st to 10th	Night	9% 5% 2 5% 4 3 5% 5% 7% 9% 46%	1440
	11th to 20th	Night	13% 5% 2 4 4 3 5% 4 6% 10% 46%	1440
	21st to end	Night	9% 5% 2 4 4 3 4 4 5% 8% 51%	1440
July	1st to 10th	Night	7% 3 1 4 4 2 4 4 7% 10% 54%	1440
	11th to 20th	Night	6% 4 2 5% 4 3 4 4 4 9% 55%	1440
	21st to end	Night	6% 3 2 3 4 3 5% 5% 7% 10% 52%	1575
August	1st to 10th	Night	5% 4 2 6% 5% 4 5% 6% 7% 8% 50%	1494
	11th to 20th	Night	10% 4 2 4 4 3 3 4 6% 9% 51%	1707
	21st to end	Night	9% 4 2 4 4 3 5% 4 4 7% 54%	1980
September	1st to 10th	Night	9% 5% 2 4 4 3 4 4 5% 7% 54%	1800
	11th to 20th	Night	11% 5% 2 3 5% 3 4 4 5% 7% 53%	1822
	21st to end	Night	10% 5% 2 5% 5% 3 4 5% 5% 7% 51%	1980
October	1st to 10th	Night	12% 6% 2 5% 4 3 4 4 4 6% 50%	2146
	11th to 20th	Night	17% 7% 3 5% 5% 2 3 4 5% 6% 42%	2160
	21st to end	Night	18% 8% 4 5% 5% 2 4 5% 5% 7% 37%	2520
November	1st to 10th	Night	12% 7% 3 5% 4 3 4 4 4 6% 48%	2406
	11th to 20th	Night	14% 10% 4 8% 6% 3 4 4 5% 6% 35%	2498
	21st to end	Night	17% 9% 4 6% 5% 3 3 4 5% 5% 39%	2660
December	1st to 10th	Night	14% 11% 4 9% 6% 3 6% 5% 5% 7% 31%	2660
	11th to 20th	Night	15% 13% 5% 9% 7% 3 5% 5% 5% 5% 29%	3279
	21st to end	Night	20% 16% 6% 9% 7% 4 5% 4 5% 4 20%	4884

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	52% 5% 14% 18% 11%	1518
	11th to 20th	Day	61% 5% 11% 15% 8%	1485
	21st to end	Day	61% 6% 11% 14% 8% 1	1688
February	1st to 10th	Day	54% 4 12% 19% 9% 1	1620
	11th to 20th	Day	50% 5% 12% 22% 10% 2	1679
	21st to end	Day	55% 5% 8% 19% 11% 2	1480
March	1st to 10th	Day	51% 5% 13% 21% 8% 1	1800
	11th to 20th	Day	45% 4 13% 23% 14% 1	1934
	21st to end	Day	55% 5% 10% 21% 8% 1	2327
April	1st to 10th	Day	54% 5% 10% 19% 11% 1	2160
	11th to 20th	Day	51% 4 10% 20% 12% 2	2134
	21st to end	Day	53% 6% 10% 18% 12% 2	2196
May	1st to 10th	Day	51% 6% 14% 21% 7% 1	2438
	11th to 20th	Day	48% 7% 12% 21% 12%	2483
	21st to end	Day	45% 7% 11% 20% 14% 2	2725
June	1st to 10th	Day	36% 7% 15% 27% 15% 1	2520
	11th to 20th	Day	37% 7% 14% 23% 18% 2	2520
	21st to end	Day	40% 8% 14% 23% 13% 1	2520
July	1st to 10th	Day	31% 8% 16% 29% 14% 2	2451
	11th to 20th	Day	34% 8% 16% 26% 15% 2	2445
	21st to end	Day	33% 6% 16% 28% 14% 3	2591
August	1st to 10th	Day	34% 9% 17% 28% 11% 1	2426
	11th to 20th	Day	39% 6% 13% 26% 13% 1	2194
	21st to end	Day	33% 6% 13% 27% 18% 2	2376
September	1st to 10th	Day	40% 6% 11% 24% 17% 2	2160
	11th to 20th	Day	33% 5% 12% 32% 16% 2	2120
	21st to end	Day	40% 5% 10% 29% 15% 1	1980
October	1st to 10th	Day	41% 4 10% 30% 15%	1811
	11th to 20th	Day	49% 4 11% 23% 12% 1	1800
	21st to end	Day	48% 4 12% 23% 13% 1	1836
November	1st to 10th	Day	42% 4 13% 25% 14% 2	1672
	11th to 20th	Day	51% 5% 13% 21% 10% 1	1677
	21st to end	Day	49% 4 16% 23% 8% 1	1520
December	1st to 10th	Day	53% 5% 15% 17% 8% 1	1520
	11th to 20th	Day	54% 4 15% 15% 8% 3	1915
	21st to end	Day	71% 5% 8% 10% 5%	2783
January	1st to 10th	Night	51% 4 10% 21% 13% 1	2648
	11th to 20th	Night	59% 5% 12% 15% 8%	2603
	21st to end	Night	59% 4 11% 16% 9% 1	2664
February	1st to 10th	Night	54% 4 11% 18% 12% 1	2340
	11th to 20th	Night	47% 5% 11% 22% 13% 1	2177
	21st to end	Night	51% 4 10% 21% 10% 3	1776
March	1st to 10th	Night	50% 5% 12% 21% 10% 2	2160
	11th to 20th	Night	41% 5% 13% 23% 16% 2	2039
	21st to end	Night	55% 5% 9% 20% 10% 2	2028
April	1st to 10th	Night	46% 7% 10% 22% 14% 2	1800
	11th to 20th	Night	49% 5% 6% 19% 18% 3	1775
	21st to end	Night	45% 6% 12% 22% 12% 2	1764
May	1st to 10th	Night	46% 7% 13% 19% 14%	1517
	11th to 20th	Night	46% 5% 11% 22% 14% 1	1417
	21st to end	Night	37% 6% 14% 24% 16% 2	1552
June	1st to 10th	Night	33% 6% 14% 27% 19% 1	1440
	11th to 20th	Night	35% 5% 11% 24% 23% 2	1440
	21st to end	Night	33% 6% 16% 24% 19% 3	1440
July	1st to 10th	Night	25% 6% 14% 34% 18% 4	1400
	11th to 20th	Night	28% 7% 11% 30% 21% 3	1392
	21st to end	Night	25% 7% 18% 29% 17% 4	1487
August	1st to 10th	Night	30% 6% 14% 31% 16% 2	1485
	11th to 20th	Night	30% 6% 15% 30% 18% 1	1707
	21st to end	Night	31% 6% 11% 28% 20% 5%	1980
September	1st to 10th	Night	30% 6% 12% 27% 23% 2	1800
	11th to 20th	Night	31% 5% 11% 32% 18% 2	1822
	21st to end	Night	33% 5% 11% 30% 20% 1	1980
October	1st to 10th	Night	35% 6% 8% 29% 21% 2	2146
	11th to 20th	Night	42% 4 12% 23% 18% 1	2160
	21st to end	Night	47% 5% 11% 23% 13% 1	2520
November	1st to 10th	Night	38% 4 11% 27% 17% 3	2406
	11th to 20th	Night	50% 4 13% 20% 11% 1	2498
	21st to end	Night	47% 4 13% 24% 10% 1	2660
December	1st to 10th	Night	54% 5% 13% 20% 8% 1	2660
	11th to 20th	Night	57% 4 12% 18% 8% 1	3281
	21st to end	Night	67% 4 8% 15% 4	4884

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	17% 16% 30% 27% 9% 2	270
	11th to 20th	Day	21% 16% 37% 20% 5% 1	257
	21st to end	Day	20% 15% 38% 22% 5%	264
February	1st to 10th	Day	15% 20% 43% 15% 5%	240
	11th to 20th	Day	23% 24% 30% 20% 4	240
	21st to end	Day	25% 18% 42% 14% 2	198
March	1st to 10th	Day	16% 21% 42% 18% 4	240
	11th to 20th	Day	18% 21% 37% 15% 6% 3	240
	21st to end	Day	27% 14% 31% 18% 8% 2	413
April	1st to 10th	Day	24% 15% 34% 22% 5%	420
	11th to 20th	Day	25% 16% 28% 19% 11% 1	412
	21st to end	Day	22% 14% 28% 24% 10% 2	420
May	1st to 10th	Day	20% 12% 33% 26% 8% 1	521
	11th to 20th	Day	20% 12% 29% 24% 11% 4	625
	21st to end	Day	18% 9% 25% 23% 18% 7%	679
June	1st to 10th	Day	9% 6% 29% 30% 21% 5%	630
	11th to 20th	Day	14% 6% 28% 30% 17% 5%	630
	21st to end	Day	13% 8% 27% 30% 17% 5%	630
July	1st to 10th	Day	7% 4 19% 29% 28% 14%	621
	11th to 20th	Day	9% 5% 26% 31% 21% 8%	618
	21st to end	Day	7% 3 28% 33% 21% 7%	684
August	1st to 10th	Day	7% 2 19% 36% 25% 11%	626
	11th to 20th	Day	12% 5% 21% 24% 25% 13%	508
	21st to end	Day	11% 6% 20% 31% 22% 9%	495
September	1st to 10th	Day	16% 7% 23% 29% 19% 8%	450
	11th to 20th	Day	12% 4 23% 30% 23% 9%	450
	21st to end	Day	14% 12% 27% 25% 17% 4	450
October	1st to 10th	Day	17% 11% 26% 28% 14% 4	281
	11th to 20th	Day	24% 16% 36% 16% 7%	270
	21st to end	Day	25% 19% 30% 21% 5% 2	297
November	1st to 10th	Day	14% 16% 39% 21% 10% 1	270
	11th to 20th	Day	19% 19% 37% 17% 8%	270
	21st to end	Day	21% 14% 40% 21% 5%	270
December	1st to 10th	Day	18% 17% 40% 16% 8% 1	270
	11th to 20th	Day	21% 13% 37% 21% 9%	270
	21st to end	Day	27% 19% 35% 18% 2	297
January	1st to 10th	Night	16% 15% 38% 23% 7% 1	950
	11th to 20th	Night	21% 12% 38% 24% 5% 1	930
	21st to end	Night	19% 13% 36% 26% 5% 1	990
February	1st to 10th	Night	19% 12% 38% 24% 6%	900
	11th to 20th	Night	18% 14% 39% 24% 5%	781
	21st to end	Night	23% 16% 37% 20% 4 1	592
March	1st to 10th	Night	21% 14% 37% 22% 6%	720
	11th to 20th	Night	17% 11% 36% 28% 8%	599
	21st to end	Night	22% 10% 35% 26% 6% 1	594
April	1st to 10th	Night	21% 13% 36% 24% 5%	540
	11th to 20th	Night	22% 12% 29% 29% 7%	533
	21st to end	Night	19% 10% 32% 28% 9% 1	540
May	1st to 10th	Night	19% 7% 34% 30% 8% 1	540
	11th to 20th	Night	19% 6% 31% 33% 11%	531
	21st to end	Night	13% 3 28% 38% 16% 1	584
June	1st to 10th	Night	11% 4 24% 44% 16% 1	540
	11th to 20th	Night	15% 4 29% 38% 14%	540
	21st to end	Night	10% 5% 25% 43% 17% 1	540
July	1st to 10th	Night	8% 2 13% 39% 34% 4	525
	11th to 20th	Night	7% 3 22% 42% 23% 2	522
	21st to end	Night	7% 2 19% 46% 25% 2	591
August	1st to 10th	Night	6% 2 17% 44% 28% 3	537
	11th to 20th	Night	11% 3 13% 41% 27% 5%	534
	21st to end	Night	11% 2 16% 46% 23% 3	594
September	1st to 10th	Night	9% 3 24% 36% 22% 6%	540
	11th to 20th	Night	13% 3 22% 34% 23% 4	562
	21st to end	Night	12% 8% 25% 34% 19% 2	720
October	1st to 10th	Night	17% 6% 26% 33% 18% 1	720
	11th to 20th	Night	19% 13% 31% 29% 8%	720
	21st to end	Night	22% 12% 33% 26% 6% 1	792
November	1st to 10th	Night	15% 10% 39% 25% 10% 1	740
	11th to 20th	Night	19% 15% 37% 22% 6% 1	788
	21st to end	Night	21% 13% 36% 23% 7%	950
December	1st to 10th	Night	20% 13% 39% 24% 5%	950
	11th to 20th	Night	24% 11% 35% 24% 6% 1	950
	21st to end	Night	28% 14% 33% 22% 3	1045

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