Apple Ridge Observatory
Clear Sky Chart
History

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

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% 11% 4 9% 6% 5% 5% 4 5% 7% 32%	101167
	Night	14% 12% 5% 10% 5% 5% 4 3 5% 6% 31%	97787
Transparency	Day	52% 5% 11% 20% 12% 1	100958
	Night	54% 5% 11% 19% 10% 1	97668
Seeing	Day	19% 15% 31% 22% 10% 3	15828
	Night	19% 11% 32% 28% 10% 1	25738

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% 23% 11% 19% 8% 6% 4 3 2 4 9%	2527
	11th to 20th	Day	13% 18% 8% 19% 13% 11% 6% 3 2 3 5%	2530
	21st to end	Day	18% 21% 12% 13% 8% 4 5% 3 4 4 8%	2783
February	1st to 10th	Day	10% 16% 7% 13% 13% 7% 6% 3 4 4 16%	1671
	11th to 20th	Day	10% 15% 6% 17% 12% 6% 5% 3 5% 4 17%	1848
	21st to end	Day	10% 17% 8% 14% 8% 5% 5% 3 4 5% 21%	1570
March	1st to 10th	Day	12% 15% 5% 9% 5% 5% 5% 3 6% 5% 29%	3120
	11th to 20th	Day	10% 8% 6% 16% 6% 5% 5% 3 6% 7% 28%	3383
	21st to end	Day	18% 12% 5% 13% 6% 5% 4 3 4 4 26%	3959
April	1st to 10th	Day	18% 16% 3 8% 5% 5% 3 4 6% 5% 28%	2280
	11th to 20th	Day	20% 13% 4 7% 3 4 4 3 5% 5% 33%	2333
	21st to end	Day	16% 12% 3 8% 5% 4 4 4 5% 7% 32%	2470
May	1st to 10th	Day	15% 9% 2 7% 5% 4 4 3 5% 8% 38%	4082
	11th to 20th	Day	11% 8% 3 6% 4 4 4 4 5% 7% 42%	4167
	21st to end	Day	12% 7% 2 6% 4 4 4 4 6% 8% 42%	4824
June	1st to 10th	Day	11% 6% 2 7% 5% 5% 5% 4 6% 7% 42%	2660
	11th to 20th	Day	12% 7% 2 7% 5% 5% 4 4 6% 8% 41%	2660
	21st to end	Day	13% 7% 2 6% 5% 4 5% 4 7% 7% 40%	2660
July	1st to 10th	Day	14% 7% 3 7% 5% 5% 5% 4 6% 9% 35%	4440
	11th to 20th	Day	7% 4 2 5% 4 4 4 4 6% 11% 47%	4440
	21st to end	Day	8% 5% 2 7% 5% 5% 5% 4 6% 9% 43%	4813
August	1st to 10th	Day	11% 5% 2 7% 5% 5% 6% 5% 6% 8% 38%	4204
	11th to 20th	Day	14% 5% 2 6% 3 4 5% 3 5% 7% 45%	4044
	21st to end	Day	10% 6% 2 7% 5% 5% 5% 4 6% 8% 41%	4292
September	1st to 10th	Day	13% 6% 2 6% 5% 5% 5% 4 6% 7% 41%	2252
	11th to 20th	Day	12% 7% 2 5% 4 5% 4 4 5% 7% 46%	2090
	21st to end	Day	14% 8% 3 7% 5% 5% 5% 3 6% 8% 37%	2090
October	1st to 10th	Day	17% 8% 3 6% 4 4 4 3 5% 6% 40%	2090
	11th to 20th	Day	20% 15% 4 8% 5% 5% 4 3 5% 6% 23%	1821
	21st to end	Day	20% 14% 4 10% 6% 6% 5% 3 5% 7% 20%	1881
November	1st to 10th	Day	14% 14% 4 7% 5% 5% 5% 4 6% 7% 30%	1672
	11th to 20th	Day	13% 20% 7% 11% 5% 4 4 4 6% 6% 19%	1710
	21st to end	Day	18% 22% 8% 14% 4 3 3 3 3 6% 18%	1706
December	1st to 10th	Day	13% 19% 11% 18% 7% 4 4 3 4 3 14%	1432
	11th to 20th	Day	14% 20% 7% 15% 8% 6% 5% 4 5% 4 11%	1880
	21st to end	Day	20% 25% 8% 14% 6% 5% 4 2 3 4 9%	2783
January	1st to 10th	Night	15% 18% 11% 17% 6% 6% 3 3 3 4 14%	4428
	11th to 20th	Night	12% 16% 8% 21% 10% 12% 5% 2 3 3 8%	4440
	21st to end	Night	16% 21% 10% 18% 7% 5% 5% 3 4 4 9%	4884
February	1st to 10th	Night	10% 14% 6% 14% 12% 6% 6% 5% 4 5% 17%	2503
	11th to 20th	Night	12% 12% 6% 14% 10% 5% 5% 4 6% 6% 20%	2218
	21st to end	Night	13% 15% 5% 14% 7% 6% 4 3 5% 6% 23%	1884
March	1st to 10th	Night	16% 9% 5% 9% 4 4 4 3 5% 6% 37%	3733
	11th to 20th	Night	9% 11% 5% 8% 5% 4 5% 4 5% 7% 38%	3576
	21st to end	Night	14% 12% 5% 11% 6% 5% 5% 3 5% 6% 28%	3700
April	1st to 10th	Night	15% 12% 4 9% 5% 4 4 4 5% 7% 31%	1900
	11th to 20th	Night	20% 9% 3 7% 4 5% 4 2 5% 7% 35%	1794
	21st to end	Night	17% 8% 3 8% 5% 4 4 4 5% 6% 37%	1710
May	1st to 10th	Night	14% 8% 3 6% 5% 5% 4 4 5% 7% 40%	2813
	11th to 20th	Night	15% 6% 2 6% 5% 4 4 3 7% 8% 39%	2725
	21st to end	Night	17% 7% 2 5% 4 3 3 3 5% 7% 44%	2743
June	1st to 10th	Night	12% 8% 3 5% 4 4 4 3 7% 7% 43%	1520
	11th to 20th	Night	11% 5% 2 7% 4 4 5% 3 6% 9% 44%	1520
	21st to end	Night	10% 6% 2 7% 5% 3 4 4 6% 7% 46%	1520
July	1st to 10th	Night	11% 8% 2 6% 4 4 5% 4 7% 9% 39%	2530
	11th to 20th	Night	6% 4 2 4 4 4 4 3 5% 7% 57%	2530
	21st to end	Night	7% 5% 2 5% 4 4 4 3 5% 7% 52%	2750
August	1st to 10th	Night	11% 5% 2 6% 4 4 4 5% 6% 7% 45%	2727
	11th to 20th	Night	12% 5% 2 5% 3 3 3 3 5% 7% 51%	2785
	21st to end	Night	8% 7% 2 6% 5% 4 4 3 6% 7% 48%	3348
September	1st to 10th	Night	11% 4 2 5% 4 4 4 3 4 6% 53%	1909
	11th to 20th	Night	11% 5% 2 4 3 3 4 4 6% 8% 51%	2090
	21st to end	Night	14% 9% 2 7% 3 4 4 4 5% 7% 40%	2090
October	1st to 10th	Night	16% 8% 3 6% 3 3 4 3 4 6% 44%	2090
	11th to 20th	Night	17% 13% 4 7% 5% 5% 4 4 5% 5% 32%	2355
	21st to end	Night	22% 13% 3 8% 5% 4 3 3 5% 6% 28%	2717
November	1st to 10th	Night	11% 15% 4 8% 5% 4 4 3 5% 6% 34%	2413
	11th to 20th	Night	14% 16% 5% 12% 7% 5% 5% 4 6% 6% 20%	2470
	21st to end	Night	15% 19% 7% 11% 6% 4 5% 4 4 5% 20%	2470
December	1st to 10th	Night	15% 19% 7% 15% 8% 5% 4 4 4 5% 14%	2724
	11th to 20th	Night	13% 20% 7% 18% 7% 5% 4 3 4 5% 13%	3294
	21st to end	Night	23% 25% 7% 13% 5% 3 3 2 3 3 11%	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	82% 3 7% 6% 2	2528
	11th to 20th	Day	88% 3 3 4 1	2530
	21st to end	Day	83% 4 8% 4 1	2783
February	1st to 10th	Day	71% 5% 8% 13% 3	1671
	11th to 20th	Day	70% 5% 8% 12% 5%	1858
	21st to end	Day	65% 5% 11% 13% 5%	1570
March	1st to 10th	Day	56% 4 10% 20% 9%	3120
	11th to 20th	Day	55% 4 14% 17% 8% 2	3383
	21st to end	Day	63% 4 9% 17% 7% 1	3959
April	1st to 10th	Day	57% 5% 9% 18% 11%	2280
	11th to 20th	Day	54% 4 9% 18% 14% 2	2333
	21st to end	Day	52% 5% 11% 15% 15% 2	2470
May	1st to 10th	Day	44% 5% 10% 22% 18% 2	4120
	11th to 20th	Day	39% 6% 11% 25% 17% 2	4171
	21st to end	Day	39% 5% 11% 22% 20% 3	4837
June	1st to 10th	Day	41% 5% 11% 25% 17% 2	2660
	11th to 20th	Day	41% 5% 11% 23% 18% 2	2660
	21st to end	Day	41% 7% 13% 24% 14% 1	2660
July	1st to 10th	Day	45% 6% 11% 22% 13% 2	4371
	11th to 20th	Day	29% 6% 14% 30% 18% 2	4365
	21st to end	Day	36% 8% 11% 24% 20% 2	4662
August	1st to 10th	Day	40% 6% 12% 26% 14% 1	4189
	11th to 20th	Day	38% 5% 13% 25% 18% 1	4083
	21st to end	Day	40% 7% 12% 27% 13% 1	4291
September	1st to 10th	Day	42% 6% 11% 25% 15% 2	2252
	11th to 20th	Day	36% 5% 13% 29% 15% 1	2090
	21st to end	Day	45% 5% 12% 26% 12%	2090
October	1st to 10th	Day	45% 5% 9% 26% 13% 1	2090
	11th to 20th	Day	62% 5% 11% 17% 5%	1821
	21st to end	Day	64% 6% 12% 13% 5%	1881
November	1st to 10th	Day	52% 6% 12% 20% 9%	1672
	11th to 20th	Day	65% 5% 12% 13% 4	1710
	21st to end	Day	71% 4 12% 10% 3	1706
December	1st to 10th	Day	77% 4 7% 9% 2	1432
	11th to 20th	Day	76% 6% 10% 7% 1	1877
	21st to end	Day	82% 3 7% 6% 2	2783
January	1st to 10th	Night	75% 5% 8% 11% 2	4428
	11th to 20th	Night	83% 4 6% 5% 2	4440
	21st to end	Night	80% 5% 7% 5% 2	4884
February	1st to 10th	Night	69% 5% 7% 13% 5% 1	2503
	11th to 20th	Night	64% 6% 9% 14% 6%	2219
	21st to end	Night	63% 4 12% 15% 5% 1	1884
March	1st to 10th	Night	49% 4 15% 23% 8% 1	3733
	11th to 20th	Night	46% 5% 15% 22% 11% 1	3576
	21st to end	Night	58% 6% 10% 20% 7% 1	3700
April	1st to 10th	Night	52% 6% 9% 18% 13% 1	1900
	11th to 20th	Night	50% 4 8% 20% 15% 2	1794
	21st to end	Night	48% 4 10% 20% 14% 3	1710
May	1st to 10th	Night	43% 6% 13% 19% 17% 3	2840
	11th to 20th	Night	41% 6% 9% 29% 14% 2	2726
	21st to end	Night	41% 4 12% 22% 16% 5%	2751
June	1st to 10th	Night	38% 6% 12% 26% 16% 2	1520
	11th to 20th	Night	37% 6% 13% 23% 20% 1	1520
	21st to end	Night	36% 7% 13% 27% 16% 2	1520
July	1st to 10th	Night	41% 6% 12% 24% 12% 6%	2490
	11th to 20th	Night	25% 5% 14% 35% 19% 1	2482
	21st to end	Night	31% 7% 15% 24% 22% 1	2662
August	1st to 10th	Night	36% 5% 16% 27% 15% 1	2718
	11th to 20th	Night	33% 5% 13% 33% 16%	2812
	21st to end	Night	35% 5% 13% 26% 19% 2	3348
September	1st to 10th	Night	32% 6% 12% 29% 19% 2	1909
	11th to 20th	Night	31% 5% 15% 34% 14% 1	2090
	21st to end	Night	43% 4 14% 28% 11% 1	2090
October	1st to 10th	Night	41% 5% 10% 29% 15% 1	2090
	11th to 20th	Night	53% 5% 12% 22% 7% 1	2355
	21st to end	Night	58% 5% 12% 18% 7%	2717
November	1st to 10th	Night	52% 5% 11% 21% 10% 1	2413
	11th to 20th	Night	63% 6% 13% 12% 6% 1	2470
	21st to end	Night	67% 5% 14% 11% 2 1	2470
December	1st to 10th	Night	74% 5% 9% 9% 3	2724
	11th to 20th	Night	75% 6% 10% 7% 2	3296
	21st to end	Night	79% 3 10% 5% 2	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	20% 19% 37% 16% 7%	270
	11th to 20th	Day	27% 18% 40% 14% 1	270
	21st to end	Day	25% 15% 38% 19% 3	297
February	1st to 10th	Day	19% 26% 34% 14% 4 1	270
	11th to 20th	Day	20% 33% 31% 15% 1	270
	21st to end	Day	29% 34% 28% 9% 1	225
March	1st to 10th	Day	25% 28% 34% 11% 2	270
	11th to 20th	Day	25% 17% 31% 17% 9% 1	402
	21st to end	Day	28% 19% 28% 18% 5% 1	506
April	1st to 10th	Day	26% 20% 35% 14% 4 1	460
	11th to 20th	Day	31% 19% 27% 13% 6% 3	452
	21st to end	Day	25% 16% 28% 22% 7% 1	460
May	1st to 10th	Day	24% 22% 30% 17% 6% 3	463
	11th to 20th	Day	18% 14% 32% 24% 8% 4	534
	21st to end	Day	16% 13% 30% 27% 11% 2	734
June	1st to 10th	Day	13% 16% 35% 24% 11% 2	680
	11th to 20th	Day	18% 13% 32% 25% 9% 3	680
	21st to end	Day	17% 12% 31% 27% 9% 4	680
July	1st to 10th	Day	9% 9% 30% 31% 16% 6%	671
	11th to 20th	Day	9% 9% 30% 30% 16% 5%	668
	21st to end	Day	10% 7% 34% 27% 15% 6%	739
August	1st to 10th	Day	12% 7% 25% 28% 20% 8%	548
	11th to 20th	Day	13% 5% 21% 32% 18% 12%	479
	21st to end	Day	16% 8% 24% 30% 18% 6%	539
September	1st to 10th	Day	16% 10% 24% 26% 18% 7%	490
	11th to 20th	Day	11% 7% 24% 30% 21% 8%	490
	21st to end	Day	19% 13% 23% 26% 14% 5%	490
October	1st to 10th	Day	20% 15% 31% 20% 12% 2	490
	11th to 20th	Day	30% 15% 34% 18% 4 1	384
	21st to end	Day	29% 24% 29% 12% 4 1	330
November	1st to 10th	Day	24% 19% 36% 16% 7%	270
	11th to 20th	Day	22% 24% 40% 10% 3 1	270
	21st to end	Day	26% 25% 36% 9% 3	270
December	1st to 10th	Day	29% 22% 29% 15% 4 1	228
	11th to 20th	Day	23% 27% 35% 12% 2 1	252
	21st to end	Day	27% 26% 34% 10% 2 1	297
January	1st to 10th	Night	21% 17% 34% 21% 5% 1	950
	11th to 20th	Night	22% 16% 34% 21% 6%	950
	21st to end	Night	20% 10% 40% 26% 5% 1	1045
February	1st to 10th	Night	17% 17% 38% 24% 4	819
	11th to 20th	Night	18% 17% 36% 25% 3	743
	21st to end	Night	22% 18% 37% 19% 3	628
March	1st to 10th	Night	19% 13% 38% 22% 8%	760
	11th to 20th	Night	18% 16% 36% 24% 7%	760
	21st to end	Night	21% 12% 32% 27% 6% 1	770
April	1st to 10th	Night	19% 14% 38% 25% 3 1	570
	11th to 20th	Night	25% 13% 31% 24% 7%	563
	21st to end	Night	21% 11% 33% 27% 8% 1	570
May	1st to 10th	Night	17% 10% 37% 29% 7%	570
	11th to 20th	Night	18% 9% 35% 29% 10%	561
	21st to end	Night	15% 6% 31% 33% 14% 1	617
June	1st to 10th	Night	15% 6% 32% 36% 11% 1	570
	11th to 20th	Night	13% 6% 33% 35% 12% 1	570
	21st to end	Night	14% 4 27% 40% 15% 1	570
July	1st to 10th	Night	10% 2 21% 43% 23% 2	555
	11th to 20th	Night	9% 3 23% 42% 21% 2	552
	21st to end	Night	9% 4 23% 42% 22% 1	624
August	1st to 10th	Night	10% 3 23% 43% 21% 2	567
	11th to 20th	Night	9% 4 18% 40% 25% 5%	564
	21st to end	Night	11% 4 22% 41% 20% 2	627
September	1st to 10th	Night	13% 4 22% 37% 20% 3	579
	11th to 20th	Night	13% 5% 22% 36% 21% 3	760
	21st to end	Night	17% 8% 28% 30% 14% 3	760
October	1st to 10th	Night	21% 8% 27% 31% 12% 2	760
	11th to 20th	Night	25% 11% 28% 27% 7% 1	760
	21st to end	Night	30% 11% 30% 22% 7%	836
November	1st to 10th	Night	20% 15% 30% 27% 7% 1	743
	11th to 20th	Night	22% 17% 36% 20% 4	760
	21st to end	Night	24% 16% 32% 24% 4	760
December	1st to 10th	Night	23% 17% 35% 21% 4	950
	11th to 20th	Night	22% 18% 40% 16% 4 1	950
	21st to end	Night	30% 14% 34% 20% 2	1045

Page generated at 2024-10-29 11:20:45. Version ac07

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