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 2024-11-04.

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% 2 6% 4 4 4 3 5% 7% 46%	100758
	Night	12% 7% 2 5% 4 3 4 3 5% 7% 49%	98302
Transparency	Day	37% 5% 12% 26% 18% 3	104408
	Night	34% 5% 11% 26% 20% 4	102792
Seeing	Day	14% 9% 26% 28% 18% 5%	15574
	Night	14% 8% 31% 33% 13% 1	25383

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 8% 4 3 4 3 4 6% 41%	2847
	11th to 20th	Day	11% 12% 4 7% 5% 4 4 2 4 6% 41%	2850
	21st to end	Day	18% 14% 3 6% 3 3 3 3 3 4 39%	3135
February	1st to 10th	Day	16% 10% 3 9% 5% 3 3 3 4 4 41%	1710
	11th to 20th	Day	13% 9% 4 8% 3 3 3 3 3 5% 45%	1668
	21st to end	Day	13% 9% 3 7% 5% 4 3 4 6% 6% 40%	1663
March	1st to 10th	Day	15% 8% 2 6% 3 2 3 2 4 5% 49%	3436
	11th to 20th	Day	13% 7% 2 4 3 2 3 3 5% 6% 51%	3480
	21st to end	Day	16% 10% 3 7% 5% 4 4 3 5% 7% 36%	3814
April	1st to 10th	Day	12% 7% 3 5% 4 5% 4 4 5% 6% 44%	2185
	11th to 20th	Day	15% 6% 2 7% 4 4 5% 4 5% 6% 42%	2254
	21st to end	Day	21% 7% 2 7% 5% 4 4 3 5% 5% 37%	2366
May	1st to 10th	Day	19% 9% 2 7% 5% 5% 4 3 5% 6% 35%	4082
	11th to 20th	Day	14% 7% 2 6% 4 4 4 4 6% 7% 41%	4082
	21st to end	Day	14% 6% 2 6% 5% 4 5% 4 6% 9% 40%	4477
June	1st to 10th	Day	6% 4 2 6% 5% 5% 5% 4 7% 9% 48%	2491
	11th to 20th	Day	7% 4 2 6% 5% 4 5% 5% 6% 9% 47%	2589
	21st to end	Day	5% 2 1 3 3 4 5% 4 6% 9% 57%	2470
July	1st to 10th	Day	11% 6% 2 7% 4 5% 5% 4 6% 8% 41%	4120
	11th to 20th	Day	6% 4 2 5% 4 4 4 4 6% 10% 52%	4120
	21st to end	Day	7% 4 2 5% 4 5% 6% 5% 8% 11% 43%	4465
August	1st to 10th	Day	5% 3 2 5% 3 4 4 4 7% 9% 54%	4104
	11th to 20th	Day	9% 6% 2 6% 5% 4 5% 4 6% 8% 46%	4041
	21st to end	Day	6% 3 2 4 3 4 4 3 5% 8% 57%	4221
September	1st to 10th	Day	11% 6% 2 5% 4 3 3 3 5% 6% 54%	2280
	11th to 20th	Day	10% 4 2 5% 4 5% 4 3 6% 7% 48%	2098
	21st to end	Day	9% 4 2 4 4 4 4 3 5% 6% 55%	2080
October	1st to 10th	Day	11% 4 2 5% 3 3 3 3 4 7% 54%	1900
	11th to 20th	Day	12% 5% 2 4 3 3 3 2 4 6% 58%	1900
	21st to end	Day	18% 6% 2 6% 2 3 2 3 4 5% 49%	2090
November	1st to 10th	Day	10% 6% 2 5% 3 2 3 2 4 5% 58%	1888
	11th to 20th	Day	14% 6% 2 5% 3 2 3 3 4 5% 53%	1763
	21st to end	Day	15% 8% 3 6% 3 2 2 2 4 5% 51%	1539
December	1st to 10th	Day	12% 8% 3 7% 4 4 3 3 4 5% 46%	1520
	11th to 20th	Day	14% 9% 3 7% 4 3 4 2 4 6% 44%	1918
	21st to end	Day	18% 16% 5% 7% 4 4 3 4 4 6% 28%	3112
January	1st to 10th	Night	12% 9% 3 9% 4 4 3 3 4 5% 45%	4108
	11th to 20th	Night	11% 7% 3 7% 6% 5% 5% 4 5% 5% 41%	4120
	21st to end	Night	21% 11% 3 7% 3 2 2 2 3 5% 40%	4532
February	1st to 10th	Night	13% 12% 3 6% 4 3 4 3 5% 5% 41%	2470
	11th to 20th	Night	14% 7% 3 6% 4 3 4 3 5% 6% 46%	2403
	21st to end	Night	15% 8% 3 6% 3 3 3 3 5% 6% 45%	1799
March	1st to 10th	Night	14% 8% 2 6% 3 3 3 3 4 5% 49%	3419
	11th to 20th	Night	11% 6% 2 4 3 3 4 3 4 6% 54%	3480
	21st to end	Night	15% 7% 3 6% 5% 4 5% 3 5% 6% 42%	3817
April	1st to 10th	Night	10% 6% 2 6% 4 3 3 4 5% 6% 50%	1995
	11th to 20th	Night	14% 8% 2 5% 3 3 3 3 4 6% 49%	1875
	21st to end	Night	17% 7% 3 6% 5% 3 3 3 5% 6% 43%	1810
May	1st to 10th	Night	15% 8% 2 6% 4 4 4 3 4 6% 42%	2823
	11th to 20th	Night	14% 7% 3 6% 4 4 4 3 6% 8% 42%	2823
	21st to end	Night	11% 4 1 5% 4 3 4 3 6% 8% 51%	3090
June	1st to 10th	Night	5% 3 1 5% 4 4 4 4 6% 10% 53%	1667
	11th to 20th	Night	4 3 2 4 3 4 5% 5% 8% 11% 53%	1567
	21st to end	Night	4 3 1 4 4 3 4 3 7% 8% 59%	1710
July	1st to 10th	Night	10% 6% 2 6% 4 3 3 4 5% 8% 49%	2850
	11th to 20th	Night	3 2 1 4 3 3 4 4 6% 11% 57%	2850
	21st to end	Night	7% 4 1 4 4 3 4 4 7% 11% 50%	3098
August	1st to 10th	Night	3 2 1 3 3 3 4 3 6% 9% 63%	2836
	11th to 20th	Night	9% 4 2 6% 4 4 3 3 6% 8% 51%	2798
	21st to end	Night	3 2 1 4 3 3 4 3 5% 8% 63%	3435
September	1st to 10th	Night	10% 5% 2 4 3 3 4 3 4 6% 57%	1900
	11th to 20th	Night	9% 4 2 5% 4 3 5% 3 5% 8% 53%	2078
	21st to end	Night	7% 5% 1 4 4 4 4 3 4 6% 58%	2090
October	1st to 10th	Night	8% 4 1 4 2 3 3 2 5% 7% 61%	2270
	11th to 20th	Night	13% 5% 2 4 3 3 2 3 4 5% 58%	2280
	21st to end	Night	15% 6% 2 4 3 3 3 2 4 6% 53%	2508
November	1st to 10th	Night	11% 5% 1 3 2 2 3 2 3 5% 62%	2263
	11th to 20th	Night	11% 7% 2 6% 4 3 3 3 4 5% 54%	2413
	21st to end	Night	16% 6% 2 4 3 2 2 2 3 5% 52%	2636
December	1st to 10th	Night	13% 8% 3 6% 3 3 4 3 6% 6% 46%	2660
	11th to 20th	Night	14% 8% 3 6% 4 3 4 3 4 6% 45%	3279
	21st to end	Night	18% 15% 5% 7% 4 4 3 3 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	39% 3 8% 23% 23% 4	3436
	11th to 20th	Day	34% 5% 11% 28% 18% 4	3480
	21st to end	Day	48% 6% 16% 22% 7% 1	3814
April	1st to 10th	Day	39% 6% 12% 23% 16% 3	2185
	11th to 20th	Day	42% 6% 13% 22% 15% 2	2254
	21st to end	Day	49% 5% 11% 23% 11% 1	2366
May	1st to 10th	Day	49% 7% 10% 18% 13% 2	4120
	11th to 20th	Day	40% 8% 13% 24% 14%	4086
	21st to end	Day	40% 7% 15% 24% 13% 1	4489
June	1st to 10th	Day	31% 8% 17% 27% 17% 2	2491
	11th to 20th	Day	32% 7% 13% 31% 16% 2	2589
	21st to end	Day	22% 7% 16% 32% 19% 4	2470
July	1st to 10th	Day	39% 7% 12% 22% 17% 3	4056
	11th to 20th	Day	28% 6% 12% 36% 17% 2	4051
	21st to end	Day	30% 9% 20% 29% 11%	4325
August	1st to 10th	Day	25% 6% 17% 24% 25% 3	4090
	11th to 20th	Day	36% 7% 15% 26% 16% 1	4080
	21st to end	Day	25% 6% 12% 40% 13% 4	4220
September	1st to 10th	Day	32% 5% 10% 27% 17% 8%	2280
	11th to 20th	Day	34% 6% 8% 27% 23% 2	2098
	21st to end	Day	30% 6% 9% 25% 26% 4	2080
October	1st to 10th	Day	19% 3 6% 18% 39% 15%	3160
	11th to 20th	Day	18% 2 4 28% 37% 11%	3140
	21st to end	Day	30% 3 8% 27% 26% 4	3428
November	1st to 10th	Day	30% 4 9% 31% 22% 5%	1888
	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% 4 10% 22% 21% 5%	3419
	11th to 20th	Night	33% 4 9% 25% 26% 2	3480
	21st to end	Night	43% 6% 14% 25% 11% 1	3817
April	1st to 10th	Night	34% 5% 10% 23% 22% 6%	1995
	11th to 20th	Night	37% 5% 9% 24% 20% 5%	1875
	21st to end	Night	42% 5% 11% 24% 16% 2	1810
May	1st to 10th	Night	42% 8% 12% 20% 15% 3	2850
	11th to 20th	Night	40% 8% 12% 26% 12% 1	2824
	21st to end	Night	30% 8% 13% 29% 18% 1	3099
June	1st to 10th	Night	26% 8% 17% 28% 18% 3	1667
	11th to 20th	Night	24% 7% 16% 31% 21% 2	1567
	21st to end	Night	22% 5% 14% 33% 21% 4	1710
July	1st to 10th	Night	34% 6% 13% 24% 19% 4	2805
	11th to 20th	Night	22% 5% 10% 39% 22% 3	2796
	21st to end	Night	25% 7% 22% 31% 14%	2999
August	1st to 10th	Night	19% 4 17% 33% 21% 6%	2826
	11th to 20th	Night	32% 5% 14% 29% 19% 2	2825
	21st to end	Night	20% 5% 12% 40% 19% 4	3435
September	1st to 10th	Night	29% 4 11% 26% 22% 9%	1900
	11th to 20th	Night	30% 5% 8% 24% 26% 5%	2078
	21st to end	Night	28% 4 8% 26% 28% 5%	2090
October	1st to 10th	Night	15% 3 6% 18% 43% 16%	3790
	11th to 20th	Night	21% 3 6% 20% 33% 17%	3779
	21st to end	Night	30% 3 6% 30% 25% 5%	4120
November	1st to 10th	Night	27% 4 10% 29% 24% 6%	2263
	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	28% 16% 37% 13% 4 1	297
April	1st to 10th	Day	16% 19% 39% 20% 6% 1	365
	11th to 20th	Day	17% 15% 37% 24% 7%	452
	21st to end	Day	24% 15% 30% 22% 9% 1	546
May	1st to 10th	Day	19% 11% 36% 24% 10% 1	653
	11th to 20th	Day	16% 11% 29% 28% 14% 2	675
	21st to end	Day	14% 8% 29% 25% 18% 6%	734
June	1st to 10th	Day	6% 4 18% 34% 28% 10%	680
	11th to 20th	Day	8% 2 21% 41% 21% 6%	680
	21st to end	Day	5% 4 30% 36% 21% 4	680
July	1st to 10th	Day	11% 3 16% 28% 31% 12%	671
	11th to 20th	Day	4 2 15% 38% 32% 9%	668
	21st to end	Day	7% 1 12% 33% 35% 12%	739
August	1st to 10th	Day	8% 2 12% 39% 33% 6%	676
	11th to 20th	Day	8% 2 16% 34% 33% 7%	665
	21st to end	Day	10% 2 9% 27% 40% 12%	567
September	1st to 10th	Day	11% 1 14% 31% 32% 10%	490
	11th to 20th	Day	6% 2 14% 39% 27% 11%	308
	21st to end	Day	13% 5% 18% 34% 22% 8%	300
October	1st to 10th	Day	12% 7% 24% 30% 18% 9%	300
	11th to 20th	Day	11% 14% 37% 27% 8% 2	300
	21st to end	Day	27% 12% 33% 21% 7% 1	330
November	1st to 10th	Day	16% 12% 35% 24% 11% 3	279
	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% 39% 28% 7%	570
	11th to 20th	Night	18% 13% 34% 29% 5%	563
	21st to end	Night	19% 9% 38% 26% 8%	570
May	1st to 10th	Night	16% 6% 37% 33% 8%	570
	11th to 20th	Night	15% 4 29% 36% 16% 1	561
	21st to end	Night	12% 5% 27% 35% 18% 3	617
June	1st to 10th	Night	7% 2 18% 42% 29% 2	570
	11th to 20th	Night	5% 1 24% 48% 21% 1	570
	21st to end	Night	5% 2 24% 50% 19% 1	570
July	1st to 10th	Night	10% 1 12% 43% 31% 3	555
	11th to 20th	Night	4 1 11% 48% 33% 3	552
	21st to end	Night	8% 1 11% 41% 38% 2	624
August	1st to 10th	Night	5% 2 15% 43% 34% 2	567
	11th to 20th	Night	8% 1 13% 47% 28% 2	564
	21st to end	Night	5% 1 10% 38% 43% 3	627
September	1st to 10th	Night	11% 2 13% 42% 30% 2	570
	11th to 20th	Night	10% 2 17% 39% 28% 4	570
	21st to end	Night	8% 2 22% 43% 22% 3	570
October	1st to 10th	Night	9% 3 27% 36% 22% 2	750
	11th to 20th	Night	14% 7% 37% 33% 9%	760
	21st to end	Night	18% 10% 32% 30% 9% 1	836
November	1st to 10th	Night	13% 7% 38% 31% 10% 1	755
	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 2024-11-01 21:47:46. Version ac07

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