Arcadia
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Arcadia clear sky chart from 2005-11-06 to 2024-04-03.

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% 7% 3 5% 5% 3 4 4 5% 7% 45%	78812
	Night	12% 7% 3 5% 4 2 4 4 5% 7% 48%	81322
Transparency	Day	39% 6% 12% 25% 16% 3	78535
	Night	37% 5% 11% 25% 19% 4	81119
Seeing	Day	14% 9% 26% 28% 18% 5%	14653
	Night	14% 8% 31% 32% 13% 1	24701

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	16% 9% 3 7% 5% 2 4 4 4 6% 41%	2847
	11th to 20th	Day	11% 11% 4 6% 6% 3 4 3 4 6% 41%	2850
	21st to end	Day	18% 14% 3 5% 4 3 3 3 3 4 39%	3135
February	1st to 10th	Day	16% 10% 3 8% 6% 2 3 3 4 4 41%	1710
	11th to 20th	Day	13% 8% 5% 7% 4 3 3 3 3 5% 45%	1668
	21st to end	Day	14% 9% 3 6% 5% 3 4 4 6% 7% 40%	1663
March	1st to 10th	Day	14% 8% 4 6% 5% 2 4 3 3 6% 45%	2090
	11th to 20th	Day	21% 9% 3 4 4 2 4 3 5% 5% 39%	2090
	21st to end	Day	20% 10% 4 7% 5% 3 5% 4 5% 6% 32%	2299
April	1st to 10th	Day	13% 7% 3 5% 4 4 5% 5% 5% 6% 44%	2092
	11th to 20th	Day	16% 7% 2 6% 5% 3 5% 5% 5% 6% 41%	2134
	21st to end	Day	21% 7% 3 6% 5% 3 4 4 5% 5% 37%	2241
May	1st to 10th	Day	19% 8% 2 5% 5% 4 4 4 5% 6% 37%	2340
	11th to 20th	Day	15% 6% 3 6% 5% 3 4 4 6% 7% 40%	2302
	21st to end	Day	13% 6% 3 7% 7% 3 5% 5% 7% 10% 35%	2531
June	1st to 10th	Day	6% 3 2 5% 5% 3 5% 5% 6% 10% 49%	2360
	11th to 20th	Day	8% 4 2 5% 5% 3 5% 6% 6% 9% 46%	2453
	21st to end	Day	5% 2 1 3 4 2 5% 5% 6% 9% 57%	2340
July	1st to 10th	Day	10% 5% 2 6% 5% 4 6% 6% 7% 10% 40%	2340
	11th to 20th	Day	4 3 2 3 4 3 4 5% 6% 10% 55%	2340
	21st to end	Day	8% 5% 2 5% 5% 3 5% 5% 8% 9% 44%	2546
August	1st to 10th	Day	7% 4 2 4 5% 4 6% 6% 7% 10% 45%	2328
	11th to 20th	Day	9% 4 2 4 5% 3 5% 6% 5% 8% 48%	2301
	21st to end	Day	7% 4 2 4 4 3 5% 4 5% 8% 54%	2403
September	1st to 10th	Day	11% 6% 2 4 4 2 3 3 4 7% 53%	2160
	11th to 20th	Day	11% 4 3 4 5% 3 5% 5% 6% 7% 48%	1988
	21st to end	Day	9% 4 2 3 4 3 4 4 5% 6% 56%	1971
October	1st to 10th	Day	12% 5% 2 5% 4 2 3 4 4 7% 52%	1800
	11th to 20th	Day	13% 5% 2 4 3 2 3 3 4 6% 55%	1800
	21st to end	Day	19% 6% 2 5% 3 2 2 3 4 4 48%	1980
November	1st to 10th	Day	10% 5% 2 4 4 2 3 3 4 5% 59%	1858
	11th to 20th	Day	14% 5% 3 4 4 2 3 4 4 5% 53%	1763
	21st to end	Day	15% 7% 3 5% 4 2 3 2 3 6% 51%	1539
December	1st to 10th	Day	13% 8% 3 6% 4 3 3 4 4 5% 47%	1520
	11th to 20th	Day	14% 9% 3 6% 5% 2 3 3 3 6% 44%	1918
	21st to end	Day	18% 16% 6% 6% 5% 3 4 4 4 6% 29%	3112
January	1st to 10th	Night	12% 9% 3 8% 5% 3 3 4 4 5% 45%	4108
	11th to 20th	Night	11% 7% 3 6% 7% 4 5% 6% 5% 6% 42%	4120
	21st to end	Night	22% 10% 4 6% 3 2 2 2 3 5% 40%	4532
February	1st to 10th	Night	13% 11% 4 5% 5% 2 4 4 5% 6% 42%	2470
	11th to 20th	Night	14% 6% 4 5% 5% 3 3 4 4 6% 46%	2403
	21st to end	Night	15% 8% 3 5% 4 2 3 4 4 7% 45%	1799
March	1st to 10th	Night	13% 6% 2 6% 5% 2 4 4 4 6% 48%	2090
	11th to 20th	Night	17% 7% 3 5% 4 3 4 4 4 6% 45%	2090
	21st to end	Night	20% 7% 4 6% 5% 3 4 4 5% 7% 37%	2299
April	1st to 10th	Night	10% 6% 2 5% 4 2 4 4 5% 7% 50%	1912
	11th to 20th	Night	14% 8% 3 4 3 2 3 4 4 6% 48%	1775
	21st to end	Night	17% 6% 3 5% 5% 2 4 4 5% 6% 43%	1715
May	1st to 10th	Night	15% 6% 3 5% 6% 3 5% 4 4 7% 41%	1620
	11th to 20th	Night	13% 5% 2 5% 4 3 4 4 5% 8% 48%	1593
	21st to end	Night	12% 5% 2 5% 5% 3 5% 5% 7% 9% 43%	1745
June	1st to 10th	Night	5% 3 1 5% 4 2 5% 5% 6% 9% 54%	1580
	11th to 20th	Night	4 3 2 3 4 3 5% 6% 7% 11% 52%	1484
	21st to end	Night	4 2 1 3 4 2 4 3 6% 8% 61%	1620
July	1st to 10th	Night	7% 4 2 5% 4 2 4 5% 6% 10% 50%	1620
	11th to 20th	Night	3 2 1 3 3 3 4 5% 6% 10% 59%	1620
	21st to end	Night	7% 3 2 4 4 2 4 5% 7% 10% 51%	1772
August	1st to 10th	Night	5% 3 2 4 5% 2 5% 4 6% 10% 53%	1611
	11th to 20th	Night	6% 4 1 4 4 2 3 3 6% 8% 58%	1600
	21st to end	Night	5% 2 2 4 5% 2 4 3 5% 8% 60%	1952
September	1st to 10th	Night	10% 5% 2 4 3 2 4 4 4 6% 56%	1800
	11th to 20th	Night	10% 4 2 4 5% 2 4 4 5% 8% 52%	1968
	21st to end	Night	7% 5% 1 3 4 3 4 4 4 7% 59%	1980
October	1st to 10th	Night	9% 4 2 3 3 2 3 3 5% 7% 59%	2150
	11th to 20th	Night	13% 5% 2 4 3 2 3 3 4 5% 56%	2160
	21st to end	Night	15% 6% 2 4 3 2 3 3 4 5% 52%	2376
November	1st to 10th	Night	11% 4 1 3 3 1 3 3 3 5% 62%	2220
	11th to 20th	Night	11% 6% 2 5% 4 2 3 3 4 5% 54%	2413
	21st to end	Night	16% 6% 3 4 3 2 3 3 3 6% 52%	2636
December	1st to 10th	Night	13% 8% 3 5% 4 2 4 3 5% 7% 46%	2660
	11th to 20th	Night	14% 8% 3 5% 5% 2 4 4 4 6% 45%	3279
	21st to end	Night	18% 14% 5% 6% 5% 3 3 4 4 5% 33%	4550

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	45% 4 9% 26% 16% 1	2848
	11th to 20th	Day	45% 3 13% 25% 11% 2	2850
	21st to end	Day	51% 3 10% 19% 17% 1	3135
February	1st to 10th	Day	48% 4 10% 24% 11% 3	1710
	11th to 20th	Day	44% 3 12% 22% 15% 4	1677
	21st to end	Day	44% 4 7% 23% 15% 7%	1663
March	1st to 10th	Day	42% 3 10% 22% 18% 5%	2090
	11th to 20th	Day	48% 5% 10% 22% 13% 3	2090
	21st to end	Day	53% 6% 12% 20% 8% 1	2299
April	1st to 10th	Day	40% 6% 12% 23% 16% 2	2092
	11th to 20th	Day	43% 7% 13% 22% 14% 2	2134
	21st to end	Day	49% 5% 11% 23% 11% 1	2241
May	1st to 10th	Day	48% 6% 12% 20% 12% 1	2340
	11th to 20th	Day	43% 6% 13% 25% 12% 1	2306
	21st to end	Day	45% 8% 16% 22% 9%	2531
June	1st to 10th	Day	30% 8% 17% 27% 17% 2	2360
	11th to 20th	Day	33% 7% 13% 29% 16% 2	2453
	21st to end	Day	22% 7% 16% 33% 19% 4	2340
July	1st to 10th	Day	36% 8% 14% 25% 14% 3	2276
	11th to 20th	Day	24% 7% 15% 31% 19% 4	2271
	21st to end	Day	33% 8% 15% 30% 14% 1	2405
August	1st to 10th	Day	31% 9% 18% 25% 16% 1	2314
	11th to 20th	Day	32% 8% 11% 29% 18% 1	2301
	21st to end	Day	28% 7% 13% 26% 20% 7%	2403
September	1st to 10th	Day	33% 6% 11% 28% 16% 7%	2160
	11th to 20th	Day	34% 6% 8% 26% 23% 2	1988
	21st to end	Day	28% 6% 10% 26% 26% 5%	1971
October	1st to 10th	Day	33% 5% 11% 25% 22% 4	1800
	11th to 20th	Day	32% 3 7% 29% 23% 6%	1800
	21st to end	Day	40% 4 9% 23% 18% 6%	1980
November	1st to 10th	Day	29% 4 9% 31% 22% 5%	1858
	11th to 20th	Day	35% 3 7% 26% 24% 5%	1763
	21st to end	Day	38% 3 10% 27% 21% 2	1539
December	1st to 10th	Day	40% 4 9% 32% 14% 1	1520
	11th to 20th	Day	43% 4 8% 23% 18% 3	1915
	21st to end	Day	57% 4 9% 19% 9% 1	3112
January	1st to 10th	Night	42% 3 12% 27% 14% 2	4108
	11th to 20th	Night	44% 4 12% 25% 14% 1	4120
	21st to end	Night	49% 2 12% 20% 14% 2	4532
February	1st to 10th	Night	44% 4 12% 24% 14% 2	2470
	11th to 20th	Night	40% 4 10% 26% 17% 3	2404
	21st to end	Night	40% 3 9% 22% 19% 7%	1799
March	1st to 10th	Night	38% 3 10% 22% 20% 7%	2090
	11th to 20th	Night	42% 5% 10% 21% 19% 3	2090
	21st to end	Night	47% 5% 10% 24% 12% 2	2299
April	1st to 10th	Night	34% 6% 11% 23% 22% 4	1912
	11th to 20th	Night	37% 6% 9% 24% 19% 4	1775
	21st to end	Night	42% 5% 11% 23% 16% 2	1715
May	1st to 10th	Night	43% 6% 11% 23% 16% 2	1620
	11th to 20th	Night	36% 7% 13% 26% 16% 2	1594
	21st to end	Night	36% 9% 16% 26% 11% 1	1746
June	1st to 10th	Night	25% 8% 17% 29% 17% 3	1580
	11th to 20th	Night	25% 7% 16% 30% 20% 2	1484
	21st to end	Night	21% 5% 13% 34% 22% 4	1620
July	1st to 10th	Night	28% 7% 15% 29% 17% 4	1575
	11th to 20th	Night	20% 6% 11% 33% 25% 4	1566
	21st to end	Night	26% 7% 16% 31% 20% 1	1673
August	1st to 10th	Night	27% 6% 16% 34% 14% 3	1601
	11th to 20th	Night	25% 5% 12% 31% 26% 3	1600
	21st to end	Night	24% 5% 13% 27% 24% 7%	1952
September	1st to 10th	Night	29% 5% 11% 27% 21% 7%	1800
	11th to 20th	Night	31% 6% 8% 23% 27% 6%	1968
	21st to end	Night	27% 5% 8% 27% 28% 5%	1980
October	1st to 10th	Night	25% 5% 9% 26% 27% 7%	2150
	11th to 20th	Night	31% 3 8% 25% 25% 7%	2160
	21st to end	Night	36% 4 8% 22% 25% 6%	2376
November	1st to 10th	Night	26% 4 10% 29% 24% 7%	2220
	11th to 20th	Night	34% 3 8% 24% 27% 4	2413
	21st to end	Night	36% 3 8% 25% 23% 4	2636
December	1st to 10th	Night	38% 4 13% 26% 18% 1	2660
	11th to 20th	Night	41% 4 9% 24% 20% 2	3281
	21st to end	Night	55% 4 9% 19% 10% 2	4550

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	21% 14% 33% 25% 7%	270
	11th to 20th	Day	24% 18% 38% 19% 1	270
	21st to end	Day	15% 14% 44% 19% 7%	297
February	1st to 10th	Day	24% 19% 33% 20% 5%	270
	11th to 20th	Day	19% 19% 41% 17% 3 1	270
	21st to end	Day	22% 20% 40% 15% 3	225
March	1st to 10th	Day	19% 19% 36% 23% 3	270
	11th to 20th	Day	26% 13% 32% 23% 5%	270
	21st to end	Day	29% 16% 37% 13% 4 1	297
April	1st to 10th	Day	16% 17% 39% 20% 7% 1	336
	11th to 20th	Day	17% 15% 35% 25% 7%	412
	21st to end	Day	24% 14% 31% 22% 9% 1	501
May	1st to 10th	Day	19% 11% 35% 24% 10% 1	603
	11th to 20th	Day	17% 11% 28% 28% 13% 3	625
	21st to end	Day	14% 8% 28% 25% 19% 7%	679
June	1st to 10th	Day	6% 3 17% 33% 30% 10%	630
	11th to 20th	Day	9% 2 21% 41% 21% 7%	630
	21st to end	Day	5% 4 30% 35% 22% 4	630
July	1st to 10th	Day	10% 3 14% 28% 32% 13%	621
	11th to 20th	Day	4 2 15% 37% 34% 9%	618
	21st to end	Day	7% 1 11% 34% 35% 12%	684
August	1st to 10th	Day	9% 2 12% 39% 34% 5%	626
	11th to 20th	Day	8% 2 15% 33% 34% 7%	615
	21st to end	Day	10% 2 9% 26% 40% 12%	522
September	1st to 10th	Day	12% 1 14% 31% 32% 10%	450
	11th to 20th	Day	6% 2 14% 37% 29% 13%	278
	21st to end	Day	13% 4 18% 34% 23% 7%	270
October	1st to 10th	Day	13% 7% 26% 29% 16% 9%	270
	11th to 20th	Day	12% 15% 40% 26% 6% 1	270
	21st to end	Day	30% 11% 31% 21% 7% 1	297
November	1st to 10th	Day	15% 12% 36% 23% 11% 3	270
	11th to 20th	Day	14% 17% 34% 23% 10% 1	270
	21st to end	Day	20% 17% 33% 21% 8% 1	270
December	1st to 10th	Day	16% 11% 42% 19% 9% 3	270
	11th to 20th	Day	16% 14% 39% 24% 6% 1	270
	21st to end	Day	21% 22% 40% 16% 2	297
January	1st to 10th	Night	15% 13% 38% 27% 6%	950
	11th to 20th	Night	17% 14% 41% 24% 4	950
	21st to end	Night	15% 12% 39% 29% 4	1045
February	1st to 10th	Night	19% 12% 41% 25% 3	950
	11th to 20th	Night	17% 15% 40% 26% 3	929
	21st to end	Night	22% 14% 38% 24% 3	543
March	1st to 10th	Night	17% 11% 39% 28% 5%	570
	11th to 20th	Night	20% 11% 34% 29% 5%	570
	21st to end	Night	22% 13% 37% 23% 4	627
April	1st to 10th	Night	14% 12% 38% 28% 7%	546
	11th to 20th	Night	19% 12% 33% 30% 6%	533
	21st to end	Night	19% 8% 39% 26% 8%	540
May	1st to 10th	Night	16% 6% 36% 34% 9%	540
	11th to 20th	Night	16% 4 29% 35% 15% 1	531
	21st to end	Night	12% 5% 26% 35% 19% 3	584
June	1st to 10th	Night	6% 2 17% 42% 31% 2	540
	11th to 20th	Night	6% 1 24% 48% 21% 1	540
	21st to end	Night	4 2 24% 50% 19% 1	540
July	1st to 10th	Night	9% 1 11% 43% 33% 3	525
	11th to 20th	Night	4 1 11% 47% 34% 3	522
	21st to end	Night	8% 1 11% 41% 37% 2	591
August	1st to 10th	Night	5% 2 14% 43% 34% 2	537
	11th to 20th	Night	7% 1 12% 48% 29% 3	534
	21st to end	Night	5% 1 10% 37% 43% 3	594
September	1st to 10th	Night	11% 2 14% 42% 30% 2	540
	11th to 20th	Night	10% 3 17% 38% 29% 4	540
	21st to end	Night	8% 2 22% 43% 22% 3	540
October	1st to 10th	Night	9% 3 28% 35% 21% 3	710
	11th to 20th	Night	14% 7% 38% 32% 8%	720
	21st to end	Night	18% 10% 32% 29% 10% 1	792
November	1st to 10th	Night	13% 7% 39% 31% 10% 1	740
	11th to 20th	Night	15% 12% 36% 29% 8%	893
	21st to end	Night	20% 10% 37% 27% 6%	950
December	1st to 10th	Night	18% 11% 38% 28% 6%	950
	11th to 20th	Night	21% 10% 36% 30% 4	950
	21st to end	Night	19% 14% 38% 26% 3	1045

Page generated at 2024-03-31 05:08:53. Version ac07

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