Darwin
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Darwin clear sky chart from 2005-11-06 to 2024-12-24.

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% 8% 3 8% 5% 5% 5% 4 6% 7% 38%	102499
	Night	12% 9% 3 8% 5% 4 4 4 5% 7% 40%	97624
Transparency	Day	43% 6% 14% 25% 11% 1	106125
	Night	42% 6% 13% 25% 13% 2	102138
Seeing	Day	16% 9% 31% 28% 13% 3	16178
	Night	15% 9% 33% 32% 11% 1	26141

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	10% 17% 4 16% 8% 6% 5% 3 5% 6% 20%	2379
	11th to 20th	Day	5% 10% 5% 15% 8% 8% 8% 6% 8% 6% 21%	2656
	21st to end	Day	5% 18% 8% 13% 7% 7% 5% 4 5% 7% 20%	3135
February	1st to 10th	Day	8% 11% 4 10% 7% 6% 5% 5% 6% 8% 30%	1710
	11th to 20th	Day	8% 10% 4 10% 7% 5% 6% 4 5% 6% 33%	1664
	21st to end	Day	10% 11% 3 10% 7% 5% 6% 3 7% 7% 31%	1432
March	1st to 10th	Day	11% 12% 4 9% 5% 4 5% 3 5% 7% 36%	3436
	11th to 20th	Day	10% 8% 3 8% 4 4 4 3 5% 8% 42%	3480
	21st to end	Day	23% 11% 4 11% 8% 5% 5% 3 4 5% 21%	3814
April	1st to 10th	Day	18% 9% 3 7% 4 4 3 4 6% 6% 36%	2256
	11th to 20th	Day	18% 11% 4 8% 5% 4 3 3 5% 5% 32%	2335
	21st to end	Day	23% 10% 2 6% 5% 4 3 3 5% 6% 32%	2470
May	1st to 10th	Day	17% 5% 2 6% 4 5% 5% 4 6% 7% 39%	4164
	11th to 20th	Day	13% 7% 2 6% 5% 4 4 3 5% 7% 45%	4399
	21st to end	Day	17% 6% 2 6% 5% 4 5% 4 7% 8% 35%	4824
June	1st to 10th	Day	11% 5% 2 5% 4 5% 4 5% 6% 9% 45%	2660
	11th to 20th	Day	13% 7% 3 5% 5% 5% 5% 4 6% 8% 38%	2840
	21st to end	Day	10% 5% 2 5% 4 4 5% 5% 7% 10% 43%	2850
July	1st to 10th	Day	9% 5% 2 5% 4 5% 5% 5% 8% 11% 39%	4750
	11th to 20th	Day	5% 3 1 3 3 3 3 3 5% 8% 61%	4504
	21st to end	Day	5% 4 2 6% 4 5% 5% 4 7% 9% 49%	4635
August	1st to 10th	Day	13% 6% 2 5% 4 4 4 4 6% 7% 45%	4104
	11th to 20th	Day	12% 6% 2 6% 5% 5% 5% 4 7% 9% 41%	4041
	21st to end	Day	9% 6% 2 5% 4 4 4 3 5% 7% 50%	4415
September	1st to 10th	Day	10% 4 2 6% 3 4 4 4 5% 7% 52%	2280
	11th to 20th	Day	11% 4 2 6% 4 4 6% 3 6% 7% 46%	2180
	21st to end	Day	15% 6% 2 5% 3 3 3 3 5% 7% 47%	2043
October	1st to 10th	Day	17% 7% 3 6% 4 4 3 3 5% 7% 43%	1900
	11th to 20th	Day	15% 9% 2 6% 4 4 4 3 5% 7% 41%	1900
	21st to end	Day	17% 11% 4 7% 4 3 3 3 5% 7% 37%	2090
November	1st to 10th	Day	13% 11% 3 8% 4 4 5% 3 5% 7% 37%	1610
	11th to 20th	Day	9% 12% 6% 13% 6% 5% 5% 3 5% 6% 30%	1600
	21st to end	Day	13% 10% 4 8% 6% 5% 5% 4 6% 8% 32%	1600
December	1st to 10th	Day	9% 12% 4 12% 7% 7% 5% 5% 6% 6% 26%	1600
	11th to 20th	Day	10% 13% 6% 12% 6% 5% 5% 3 5% 6% 29%	1998
	21st to end	Day	21% 14% 5% 16% 5% 3 3 3 4 6% 20%	2745
January	1st to 10th	Night	10% 13% 6% 18% 7% 4 3 3 5% 6% 27%	4530
	11th to 20th	Night	6% 11% 4 13% 9% 8% 9% 5% 8% 6% 21%	4312
	21st to end	Night	8% 19% 8% 12% 6% 5% 4 3 5% 5% 26%	4532
February	1st to 10th	Night	7% 11% 5% 8% 6% 6% 5% 5% 5% 6% 36%	2470
	11th to 20th	Night	6% 9% 3 8% 5% 5% 5% 4 6% 8% 40%	2403
	21st to end	Night	11% 10% 3 8% 5% 5% 5% 4 6% 7% 36%	2036
March	1st to 10th	Night	8% 8% 3 7% 5% 4 4 4 5% 7% 48%	3421
	11th to 20th	Night	8% 7% 3 8% 5% 5% 4 4 6% 8% 42%	3480
	21st to end	Night	25% 12% 3 9% 5% 4 3 2 3 5% 28%	3817
April	1st to 10th	Night	14% 9% 3 7% 5% 4 4 4 5% 6% 39%	1923
	11th to 20th	Night	19% 11% 3 7% 4 3 3 3 6% 5% 36%	1793
	21st to end	Night	19% 10% 3 6% 4 4 3 3 5% 6% 37%	1710
May	1st to 10th	Night	15% 7% 2 6% 4 4 4 4 4 5% 45%	2741
	11th to 20th	Night	14% 5% 2 4 4 3 4 4 5% 8% 47%	2506
	21st to end	Night	16% 6% 2 6% 3 3 3 3 6% 7% 43%	2743
June	1st to 10th	Night	11% 4 1 4 4 4 4 3 6% 9% 50%	1520
	11th to 20th	Night	9% 4 2 6% 4 4 4 4 7% 9% 48%	1335
	21st to end	Night	9% 3 1 3 3 3 3 4 7% 6% 56%	1330
July	1st to 10th	Night	11% 4 2 5% 4 4 5% 4 6% 10% 45%	2220
	11th to 20th	Night	3 2 1 4 3 4 3 3 5% 8% 63%	2463
	21st to end	Night	6% 4 1 4 4 4 4 3 6% 8% 57%	2925
August	1st to 10th	Night	12% 6% 2 5% 4 3 4 3 5% 6% 50%	2836
	11th to 20th	Night	13% 5% 2 5% 3 4 4 3 6% 7% 50%	2798
	21st to end	Night	9% 4 2 6% 4 4 4 3 6% 7% 53%	3247
September	1st to 10th	Night	8% 4 1 5% 3 3 4 3 6% 8% 57%	1900
	11th to 20th	Night	9% 5% 1 5% 3 4 3 3 6% 7% 55%	1997
	21st to end	Night	10% 6% 2 5% 3 2 3 3 5% 6% 55%	2117
October	1st to 10th	Night	15% 6% 2 5% 3 3 4 3 4 6% 50%	2280
	11th to 20th	Night	15% 8% 3 5% 3 4 4 3 4 7% 44%	2280
	21st to end	Night	17% 11% 3 6% 4 3 3 3 5% 6% 39%	2508
November	1st to 10th	Night	12% 7% 2 6% 5% 4 4 4 6% 7% 43%	2685
	11th to 20th	Night	12% 11% 5% 10% 6% 4 4 3 4 5% 36%	2800
	21st to end	Night	12% 10% 3 9% 5% 4 4 3 5% 6% 39%	2800
December	1st to 10th	Night	9% 10% 5% 11% 8% 6% 4 3 5% 7% 32%	2800
	11th to 20th	Night	11% 11% 5% 11% 6% 6% 6% 5% 6% 6% 28%	3419
	21st to end	Night	20% 14% 4 13% 6% 5% 4 3 4 4 22%	4947

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	64% 7% 11% 14% 4	2380
	11th to 20th	Day	58% 7% 14% 17% 4	2656
	21st to end	Day	61% 9% 12% 13% 4	3135
February	1st to 10th	Day	51% 6% 13% 21% 8% 1	1710
	11th to 20th	Day	50% 6% 15% 20% 8% 1	1673
	21st to end	Day	50% 7% 12% 20% 11%	1432
March	1st to 10th	Day	46% 7% 13% 24% 9% 1	3436
	11th to 20th	Day	41% 6% 12% 30% 10% 2	3480
	21st to end	Day	64% 6% 9% 16% 4	3814
April	1st to 10th	Day	47% 6% 12% 23% 11% 1	2256
	11th to 20th	Day	52% 6% 12% 18% 11% 1	2335
	21st to end	Day	52% 7% 12% 19% 9% 1	2470
May	1st to 10th	Day	41% 8% 13% 24% 14% 1	4202
	11th to 20th	Day	37% 7% 11% 29% 14% 2	4403
	21st to end	Day	42% 9% 14% 25% 8% 1	4837
June	1st to 10th	Day	34% 9% 16% 28% 12% 1	2660
	11th to 20th	Day	41% 9% 14% 20% 14% 1	2840
	21st to end	Day	33% 9% 18% 27% 11% 1	2850
July	1st to 10th	Day	38% 5% 22% 23% 12%	4676
	11th to 20th	Day	22% 4 17% 37% 17% 2	4426
	21st to end	Day	31% 6% 17% 31% 15% 1	4489
August	1st to 10th	Day	38% 6% 13% 29% 12% 2	4090
	11th to 20th	Day	40% 5% 14% 33% 8%	4080
	21st to end	Day	34% 4 19% 28% 13% 1	4414
September	1st to 10th	Day	32% 6% 14% 35% 13%	2280
	11th to 20th	Day	36% 7% 17% 30% 10% 1	2180
	21st to end	Day	37% 6% 12% 33% 12% 1	2043
October	1st to 10th	Day	33% 3 9% 33% 23%	3160
	11th to 20th	Day	37% 4 12% 24% 21% 1	3140
	21st to end	Day	45% 2 16% 28% 9%	3428
November	1st to 10th	Day	46% 6% 14% 20% 12% 2	1610
	11th to 20th	Day	53% 6% 12% 17% 10% 1	1600
	21st to end	Day	49% 6% 15% 22% 7% 2	1600
December	1st to 10th	Day	56% 8% 14% 15% 6%	1600
	11th to 20th	Day	56% 5% 17% 17% 5%	1995
	21st to end	Day	66% 5% 10% 13% 5%	2745
January	1st to 10th	Night	58% 5% 12% 18% 5%	4530
	11th to 20th	Night	60% 8% 12% 16% 5%	4312
	21st to end	Night	60% 5% 10% 19% 6% 1	4532
February	1st to 10th	Night	47% 5% 14% 21% 11% 1	2470
	11th to 20th	Night	41% 7% 17% 24% 10% 2	2404
	21st to end	Night	45% 6% 13% 20% 13% 2	2036
March	1st to 10th	Night	35% 6% 14% 28% 15% 2	3421
	11th to 20th	Night	36% 7% 12% 30% 14% 1	3480
	21st to end	Night	60% 4 9% 20% 6% 1	3817
April	1st to 10th	Night	45% 6% 12% 25% 11% 1	1923
	11th to 20th	Night	47% 6% 8% 21% 15% 2	1793
	21st to end	Night	48% 6% 10% 20% 14% 2	1710
May	1st to 10th	Night	39% 7% 12% 23% 16% 3	2768
	11th to 20th	Night	33% 7% 12% 24% 20% 4	2507
	21st to end	Night	38% 6% 15% 25% 14% 1	2751
June	1st to 10th	Night	29% 7% 16% 30% 15% 2	1520
	11th to 20th	Night	32% 7% 16% 25% 17% 3	1335
	21st to end	Night	25% 8% 15% 31% 17% 3	1330
July	1st to 10th	Night	35% 5% 22% 22% 14% 1	2185
	11th to 20th	Night	20% 3 15% 40% 19% 2	2418
	21st to end	Night	25% 6% 17% 35% 16% 3	2832
August	1st to 10th	Night	36% 4 13% 27% 14% 5%	2826
	11th to 20th	Night	35% 5% 15% 33% 12% 1	2825
	21st to end	Night	32% 5% 18% 30% 13% 2	3247
September	1st to 10th	Night	26% 7% 15% 33% 18% 1	1900
	11th to 20th	Night	29% 6% 17% 31% 17% 1	1997
	21st to end	Night	31% 5% 12% 33% 17% 1	2117
October	1st to 10th	Night	23% 3 6% 37% 26% 4	3800
	11th to 20th	Night	32% 3 12% 28% 22% 3	3779
	21st to end	Night	42% 4 12% 29% 12% 1	4120
November	1st to 10th	Night	39% 6% 15% 24% 13% 2	2685
	11th to 20th	Night	50% 6% 12% 19% 13% 1	2800
	21st to end	Night	46% 6% 17% 23% 7% 1	2800
December	1st to 10th	Night	51% 6% 16% 20% 7%	2800
	11th to 20th	Night	54% 9% 12% 18% 6% 1	3421
	21st to end	Night	64% 7% 10% 15% 4	4947

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	14% 10% 35% 25% 14% 2	270
	11th to 20th	Day	16% 9% 38% 33% 4 1	270
	21st to end	Day	15% 10% 39% 25% 10% 2	297
February	1st to 10th	Day	13% 13% 42% 28% 4	270
	11th to 20th	Day	14% 18% 35% 27% 6% 1	270
	21st to end	Day	17% 9% 43% 25% 5%	225
March	1st to 10th	Day	19% 12% 40% 23% 4 1	270
	11th to 20th	Day	16% 10% 42% 22% 8% 1	270
	21st to end	Day	29% 11% 25% 24% 10% 2	297
April	1st to 10th	Day	25% 14% 33% 23% 5%	436
	11th to 20th	Day	26% 14% 28% 21% 10% 2	533
	21st to end	Day	26% 11% 34% 18% 10% 1	650
May	1st to 10th	Day	21% 11% 36% 25% 7% 2	653
	11th to 20th	Day	19% 10% 29% 26% 13% 3	675
	21st to end	Day	19% 8% 31% 28% 12% 3	734
June	1st to 10th	Day	10% 8% 27% 30% 21% 4	680
	11th to 20th	Day	16% 7% 34% 31% 10% 2	680
	21st to end	Day	12% 7% 33% 29% 16% 4	680
July	1st to 10th	Day	8% 4 23% 35% 22% 9%	671
	11th to 20th	Day	9% 6% 27% 30% 22% 7%	668
	21st to end	Day	6% 4 24% 37% 24% 5%	739
August	1st to 10th	Day	12% 3 23% 34% 25% 3	676
	11th to 20th	Day	13% 5% 21% 33% 23% 5%	665
	21st to end	Day	8% 5% 29% 33% 21% 4	683
September	1st to 10th	Day	11% 8% 29% 34% 13% 5%	490
	11th to 20th	Day	12% 5% 28% 32% 17% 5%	390
	21st to end	Day	19% 11% 30% 22% 13% 6%	300
October	1st to 10th	Day	19% 11% 31% 21% 14% 5%	300
	11th to 20th	Day	14% 18% 38% 21% 8% 1	300
	21st to end	Day	25% 13% 37% 17% 8% 1	330
November	1st to 10th	Day	18% 14% 33% 25% 8% 2	300
	11th to 20th	Day	16% 16% 42% 22% 4	300
	21st to end	Day	20% 14% 41% 21% 4	300
December	1st to 10th	Day	14% 9% 44% 23% 9%	300
	11th to 20th	Day	17% 14% 38% 27% 4	300
	21st to end	Day	27% 11% 38% 20% 3	306
January	1st to 10th	Night	11% 12% 38% 29% 9% 1	950
	11th to 20th	Night	14% 11% 37% 31% 6% 1	950
	21st to end	Night	16% 11% 36% 29% 7%	1045
February	1st to 10th	Night	12% 10% 40% 29% 8% 1	950
	11th to 20th	Night	11% 12% 42% 29% 6% 1	929
	21st to end	Night	15% 11% 36% 29% 8% 1	780
March	1st to 10th	Night	16% 10% 39% 25% 10% 1	572
	11th to 20th	Night	17% 11% 37% 30% 5% 1	570
	21st to end	Night	22% 10% 30% 26% 10% 2	627
April	1st to 10th	Night	20% 8% 38% 27% 6%	570
	11th to 20th	Night	21% 14% 28% 28% 8% 1	563
	21st to end	Night	23% 10% 31% 27% 8% 1	570
May	1st to 10th	Night	19% 10% 33% 31% 7% 1	570
	11th to 20th	Night	16% 8% 34% 30% 9% 1	561
	21st to end	Night	17% 7% 27% 36% 11% 1	617
June	1st to 10th	Night	12% 5% 29% 36% 16%	570
	11th to 20th	Night	11% 4 35% 41% 10%	570
	21st to end	Night	9% 3 27% 45% 17%	570
July	1st to 10th	Night	6% 2 24% 41% 25% 2	555
	11th to 20th	Night	5% 2 26% 49% 17% 1	552
	21st to end	Night	5% 2 22% 47% 22% 2	624
August	1st to 10th	Night	9% 4 17% 47% 21% 2	567
	11th to 20th	Night	10% 3 18% 41% 24% 3	564
	21st to end	Night	8% 4 26% 38% 22% 2	627
September	1st to 10th	Night	9% 4 26% 40% 18% 2	570
	11th to 20th	Night	11% 6% 31% 33% 18% 2	570
	21st to end	Night	12% 9% 34% 31% 13% 2	597
October	1st to 10th	Night	18% 7% 32% 30% 12% 1	760
	11th to 20th	Night	19% 11% 36% 26% 8% 1	760
	21st to end	Night	22% 13% 30% 28% 6%	836
November	1st to 10th	Night	16% 9% 35% 31% 9%	962
	11th to 20th	Night	17% 13% 37% 26% 7% 1	1000
	21st to end	Night	17% 13% 37% 26% 7%	1000
December	1st to 10th	Night	14% 11% 38% 29% 8% 1	1000
	11th to 20th	Night	19% 10% 38% 26% 7% 1	1000
	21st to end	Night	24% 11% 33% 27% 5% 1	1063

Page generated at 2024-12-21 03:13:49. Version ac07

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