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 2024-03-01.

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	14% 11% 5% 8% 7% 4 5% 5% 5% 6% 30%	78269
	Night	14% 12% 6% 9% 7% 4 5% 4 5% 6% 29%	81140
Transparency	Day	55% 5% 11% 18% 10% 1	77970
	Night	57% 5% 11% 17% 9% 1	80960
Seeing	Day	19% 15% 31% 22% 10% 3	14800
	Night	19% 11% 31% 28% 10% 1	24924

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	12% 21% 13% 18% 8% 5% 5% 3 2 4 9%	2527
	11th to 20th	Day	13% 17% 9% 16% 15% 9% 8% 3 2 3 5%	2530
	21st to end	Day	18% 20% 13% 12% 9% 3 5% 4 4 4 8%	2783
February	1st to 10th	Day	10% 14% 8% 12% 14% 6% 7% 4 4 4 16%	1671
	11th to 20th	Day	10% 14% 7% 15% 13% 5% 5% 4 5% 4 17%	1848
	21st to end	Day	11% 16% 9% 13% 9% 4 5% 4 5% 5% 21%	1570
March	1st to 10th	Day	13% 12% 5% 9% 7% 5% 6% 4 6% 6% 27%	1800
	11th to 20th	Day	11% 11% 5% 10% 7% 4 5% 5% 6% 6% 31%	1925
	21st to end	Day	17% 11% 4 8% 8% 3 4 4 5% 6% 29%	2254
April	1st to 10th	Day	18% 14% 5% 7% 6% 3 4 5% 5% 5% 27%	2160
	11th to 20th	Day	20% 13% 4 6% 4 2 5% 4 4 5% 33%	2208
	21st to end	Day	16% 12% 3 7% 6% 3 5% 5% 5% 7% 31%	2340
May	1st to 10th	Day	16% 10% 3 6% 6% 3 4 4 5% 8% 35%	2340
	11th to 20th	Day	16% 9% 3 6% 5% 3 4 5% 5% 8% 37%	2345
	21st to end	Day	12% 6% 3 5% 5% 4 5% 6% 6% 8% 41%	2725
June	1st to 10th	Day	12% 6% 3 6% 6% 3 5% 5% 5% 7% 43%	2520
	11th to 20th	Day	12% 7% 2 6% 6% 3 5% 4 5% 8% 41%	2520
	21st to end	Day	13% 6% 3 6% 5% 3 6% 5% 7% 7% 40%	2520
July	1st to 10th	Day	7% 4 2 5% 4 3 5% 6% 6% 11% 48%	2520
	11th to 20th	Day	10% 5% 3 6% 5% 4 5% 5% 5% 9% 44%	2520
	21st to end	Day	9% 5% 2 5% 5% 4 6% 5% 6% 9% 43%	2743
August	1st to 10th	Day	9% 5% 2 6% 7% 3 6% 7% 6% 9% 40%	2386
	11th to 20th	Day	12% 5% 2 6% 5% 4 5% 5% 6% 8% 43%	2303
	21st to end	Day	12% 6% 2 5% 5% 3 5% 5% 5% 8% 42%	2446
September	1st to 10th	Day	14% 6% 2 6% 5% 4 6% 5% 6% 7% 40%	2134
	11th to 20th	Day	12% 6% 3 4 4 3 4 5% 5% 7% 45%	1980
	21st to end	Day	14% 7% 3 7% 6% 4 5% 4 6% 8% 36%	1980
October	1st to 10th	Day	18% 8% 3 6% 5% 3 5% 4 5% 6% 38%	1980
	11th to 20th	Day	22% 15% 4 8% 6% 4 5% 3 5% 6% 21%	1726
	21st to end	Day	21% 14% 5% 9% 8% 4 6% 3 5% 7% 20%	1782
November	1st to 10th	Day	15% 13% 4 7% 5% 3 6% 4 6% 8% 30%	1672
	11th to 20th	Day	13% 18% 9% 10% 6% 3 5% 5% 6% 6% 19%	1710
	21st to end	Day	18% 20% 9% 12% 6% 2 3 3 3 6% 18%	1706
December	1st to 10th	Day	14% 17% 12% 18% 8% 3 3 4 3 4 14%	1432
	11th to 20th	Day	14% 19% 8% 14% 10% 4 5% 5% 5% 4 12%	1880
	21st to end	Day	21% 24% 9% 13% 7% 4 5% 3 2 4 9%	2783
January	1st to 10th	Night	15% 17% 11% 15% 8% 5% 4 4 3 4 14%	4428
	11th to 20th	Night	12% 15% 8% 18% 13% 9% 7% 3 3 3 8%	4440
	21st to end	Night	16% 20% 11% 16% 8% 4 5% 4 4 4 9%	4884
February	1st to 10th	Night	10% 13% 8% 12% 13% 5% 7% 6% 4 5% 17%	2503
	11th to 20th	Night	12% 10% 6% 13% 11% 4 5% 5% 6% 6% 20%	2218
	21st to end	Night	13% 14% 6% 11% 10% 5% 5% 4 4 6% 23%	1884
March	1st to 10th	Night	13% 10% 5% 7% 6% 4 5% 5% 5% 6% 33%	2167
	11th to 20th	Night	12% 10% 6% 8% 6% 2 5% 4 5% 7% 35%	2034
	21st to end	Night	17% 8% 4 8% 6% 4 5% 4 5% 6% 33%	2116
April	1st to 10th	Night	15% 11% 5% 8% 6% 3 4 5% 5% 8% 31%	1800
	11th to 20th	Night	20% 8% 4 6% 5% 3 5% 3 5% 7% 35%	1699
	21st to end	Night	17% 8% 3 7% 6% 3 3 5% 5% 6% 38%	1620
May	1st to 10th	Night	14% 8% 3 6% 6% 4 6% 5% 6% 8% 35%	1620
	11th to 20th	Night	15% 6% 3 6% 6% 4 5% 5% 5% 9% 37%	1544
	21st to end	Night	13% 5% 2 5% 4 2 3 4 6% 9% 45%	1551
June	1st to 10th	Night	13% 6% 3 5% 4 3 4 4 7% 8% 44%	1440
	11th to 20th	Night	12% 5% 2 6% 5% 3 4 4 5% 9% 44%	1440
	21st to end	Night	10% 6% 2 6% 5% 3 4 5% 6% 7% 47%	1440
July	1st to 10th	Night	6% 4 1 3 4 2 4 5% 6% 11% 53%	1440
	11th to 20th	Night	6% 4 2 4 5% 2 5% 5% 5% 8% 53%	1440
	21st to end	Night	7% 5% 3 4 6% 3 5% 5% 6% 7% 50%	1575
August	1st to 10th	Night	7% 4 3 5% 4 3 4 6% 7% 9% 48%	1551
	11th to 20th	Night	8% 4 2 5% 5% 3 5% 4 5% 8% 52%	1598
	21st to end	Night	10% 7% 2 4 5% 3 4 4 6% 7% 48%	1908
September	1st to 10th	Night	11% 4 2 4 4 3 5% 4 4 6% 52%	1808
	11th to 20th	Night	12% 5% 2 4 3 2 4 5% 6% 8% 50%	1980
	21st to end	Night	14% 8% 3 6% 5% 3 4 5% 5% 7% 40%	1980
October	1st to 10th	Night	17% 8% 2 5% 4 3 4 4 4 6% 43%	1980
	11th to 20th	Night	19% 12% 4 6% 6% 3 5% 5% 5% 5% 30%	2230
	21st to end	Night	23% 13% 4 7% 5% 3 3 4 5% 6% 27%	2574
November	1st to 10th	Night	11% 14% 5% 7% 6% 3 5% 4 5% 6% 34%	2406
	11th to 20th	Night	15% 15% 6% 11% 7% 4 5% 5% 6% 7% 20%	2470
	21st to end	Night	16% 17% 8% 9% 7% 3 5% 4 4 5% 20%	2470
December	1st to 10th	Night	15% 16% 9% 14% 9% 4 5% 4 4 5% 15%	2724
	11th to 20th	Night	13% 19% 8% 17% 8% 4 5% 5% 4 5% 13%	3294
	21st to end	Night	24% 24% 8% 12% 7% 3 3 3 3 4 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	57% 5% 11% 17% 9% 1	1800
	11th to 20th	Day	52% 5% 12% 18% 10% 3	1925
	21st to end	Day	56% 6% 9% 19% 9% 1	2254
April	1st to 10th	Day	58% 5% 9% 18% 10%	2160
	11th to 20th	Day	54% 4 9% 17% 14% 2	2208
	21st to end	Day	52% 5% 12% 14% 15% 2	2340
May	1st to 10th	Day	47% 5% 10% 24% 12% 2	2340
	11th to 20th	Day	46% 5% 12% 21% 14% 2	2349
	21st to end	Day	40% 7% 13% 26% 14% 1	2725
June	1st to 10th	Day	40% 5% 11% 25% 17% 2	2520
	11th to 20th	Day	41% 5% 12% 23% 18% 1	2520
	21st to end	Day	41% 7% 14% 23% 15% 1	2520
July	1st to 10th	Day	30% 7% 13% 30% 17% 3	2451
	11th to 20th	Day	36% 6% 12% 26% 18% 2	2445
	21st to end	Day	36% 7% 12% 25% 18% 3	2591
August	1st to 10th	Day	38% 7% 15% 27% 12% 2	2371
	11th to 20th	Day	39% 6% 13% 26% 15% 2	2303
	21st to end	Day	39% 6% 13% 25% 15% 2	2446
September	1st to 10th	Day	43% 6% 11% 23% 15% 2	2134
	11th to 20th	Day	38% 5% 14% 30% 12% 1	1980
	21st to end	Day	46% 5% 12% 26% 10%	1980
October	1st to 10th	Day	47% 6% 9% 25% 12% 1	1980
	11th to 20th	Day	63% 5% 11% 16% 4	1726
	21st to end	Day	65% 6% 12% 13% 5%	1782
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 11% 15% 5% 1	1884
March	1st to 10th	Night	52% 5% 12% 21% 9% 1	2167
	11th to 20th	Night	49% 5% 13% 19% 12% 2	2034
	21st to end	Night	52% 5% 10% 22% 9% 1	2116
April	1st to 10th	Night	52% 6% 10% 18% 13% 1	1800
	11th to 20th	Night	49% 4 8% 20% 15% 2	1699
	21st to end	Night	47% 5% 11% 20% 14% 3	1620
May	1st to 10th	Night	46% 6% 12% 22% 12% 2	1620
	11th to 20th	Night	44% 6% 10% 21% 15% 3	1545
	21st to end	Night	37% 4 13% 28% 15% 2	1552
June	1st to 10th	Night	37% 6% 12% 26% 17% 2	1440
	11th to 20th	Night	37% 6% 14% 23% 19% 1	1440
	21st to end	Night	35% 7% 13% 27% 16% 2	1440
July	1st to 10th	Night	25% 7% 14% 31% 20% 3	1400
	11th to 20th	Night	27% 6% 15% 31% 18% 2	1392
	21st to end	Night	32% 7% 15% 27% 18% 2	1487
August	1st to 10th	Night	31% 6% 18% 31% 12% 1	1542
	11th to 20th	Night	30% 6% 15% 33% 16% 1	1598
	21st to end	Night	36% 5% 13% 26% 19% 2	1908
September	1st to 10th	Night	33% 6% 12% 28% 19% 2	1808
	11th to 20th	Night	32% 5% 16% 34% 12% 1	1980
	21st to end	Night	43% 5% 14% 28% 9% 1	1980
October	1st to 10th	Night	42% 5% 10% 27% 15% 1	1980
	11th to 20th	Night	55% 5% 12% 21% 6% 1	2230
	21st to end	Night	59% 5% 12% 17% 7%	2574
November	1st to 10th	Night	52% 5% 11% 21% 10% 1	2406
	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	30% 32% 29% 9% 1	225
March	1st to 10th	Day	26% 30% 30% 12% 3	240
	11th to 20th	Day	24% 16% 32% 18% 9% 1	365
	21st to end	Day	28% 19% 27% 19% 6% 2	462
April	1st to 10th	Day	26% 18% 35% 15% 4 1	420
	11th to 20th	Day	30% 18% 27% 14% 7% 3	412
	21st to end	Day	25% 16% 29% 22% 7% 1	420
May	1st to 10th	Day	23% 22% 29% 17% 6% 3	423
	11th to 20th	Day	19% 14% 31% 23% 8% 4	491
	21st to end	Day	15% 13% 31% 27% 12% 2	679
June	1st to 10th	Day	12% 14% 35% 25% 12% 2	630
	11th to 20th	Day	18% 13% 32% 25% 9% 3	630
	21st to end	Day	16% 11% 32% 27% 10% 4	630
July	1st to 10th	Day	8% 8% 29% 33% 17% 6%	621
	11th to 20th	Day	10% 9% 31% 30% 16% 5%	618
	21st to end	Day	10% 8% 36% 26% 14% 6%	684
August	1st to 10th	Day	12% 7% 24% 28% 21% 8%	505
	11th to 20th	Day	13% 4 21% 32% 18% 12%	439
	21st to end	Day	16% 7% 23% 29% 18% 6%	495
September	1st to 10th	Day	17% 8% 24% 26% 17% 7%	450
	11th to 20th	Day	11% 7% 25% 30% 19% 8%	450
	21st to end	Day	20% 14% 22% 24% 15% 5%	450
October	1st to 10th	Day	21% 14% 30% 20% 13% 2	450
	11th to 20th	Day	31% 15% 32% 18% 3 1	350
	21st to end	Day	31% 23% 30% 11% 5% 1	297
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% 38% 19% 3	628
March	1st to 10th	Night	18% 12% 38% 22% 9%	723
	11th to 20th	Night	18% 15% 36% 23% 7%	720
	21st to end	Night	21% 12% 32% 28% 6% 1	730
April	1st to 10th	Night	20% 14% 36% 25% 4 1	540
	11th to 20th	Night	25% 11% 31% 25% 7%	533
	21st to end	Night	21% 10% 32% 28% 9% 1	540
May	1st to 10th	Night	18% 10% 37% 29% 7%	540
	11th to 20th	Night	18% 9% 35% 28% 10%	531
	21st to end	Night	15% 5% 32% 32% 15% 1	584
June	1st to 10th	Night	15% 6% 31% 37% 11% 1	540
	11th to 20th	Night	14% 5% 31% 36% 13% 1	540
	21st to end	Night	13% 4 27% 41% 15% 1	540
July	1st to 10th	Night	9% 2 20% 43% 24% 2	525
	11th to 20th	Night	9% 2 23% 42% 21% 2	522
	21st to end	Night	9% 4 24% 42% 21% 1	591
August	1st to 10th	Night	9% 3 22% 43% 21% 2	537
	11th to 20th	Night	9% 4 17% 40% 25% 5%	534
	21st to end	Night	11% 4 22% 40% 21% 2	594
September	1st to 10th	Night	13% 4 22% 38% 20% 4	548
	11th to 20th	Night	13% 5% 22% 35% 21% 3	720
	21st to end	Night	17% 9% 27% 29% 15% 4	720
October	1st to 10th	Night	22% 7% 27% 30% 13% 2	720
	11th to 20th	Night	26% 12% 28% 27% 7% 1	720
	21st to end	Night	31% 11% 30% 21% 7% 1	792
November	1st to 10th	Night	20% 15% 30% 27% 7% 1	740
	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 2024-02-27 06:30:17. Version ac07

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