Melville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Melville clear sky chart from 2005-11-06 to 2024-11-05.

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	10% 8% 3 8% 5% 5% 5% 4 6% 8% 37%	106121
	Night	8% 9% 3 9% 6% 5% 5% 4 6% 7% 38%	101539
Transparency	Day	44% 7% 15% 25% 8% 1	105875
	Night	44% 6% 15% 24% 10% 1	101431
Seeing	Day	14% 8% 29% 29% 16% 4	16274
	Night	13% 7% 31% 34% 13% 2	25720

By Month

Percentage Cloud Cover NW (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	6% 15% 7% 15% 8% 6% 5% 4 8% 8% 17%	2283
	11th to 20th	Day	5% 9% 5% 13% 11% 9% 8% 7% 8% 8% 18%	2516
	21st to end	Day	7% 14% 5% 12% 7% 5% 6% 3 5% 6% 31%	2794
February	1st to 10th	Day	8% 14% 6% 12% 7% 7% 7% 6% 5% 6% 23%	1520
	11th to 20th	Day	6% 11% 3 11% 7% 9% 9% 4 5% 7% 28%	1645
	21st to end	Day	5% 11% 4 12% 8% 7% 6% 5% 7% 8% 27%	1570
March	1st to 10th	Day	9% 14% 5% 13% 7% 7% 5% 3 6% 7% 25%	3130
	11th to 20th	Day	7% 11% 4 12% 7% 5% 5% 4 5% 7% 32%	3226
	21st to end	Day	7% 9% 4 10% 6% 6% 5% 4 5% 7% 37%	4165
April	1st to 10th	Day	8% 10% 4 8% 5% 5% 5% 4 6% 7% 37%	2280
	11th to 20th	Day	15% 15% 5% 8% 6% 4 4 4 5% 6% 28%	2356
	21st to end	Day	13% 9% 3 8% 5% 5% 5% 4 6% 8% 36%	2546
May	1st to 10th	Day	19% 10% 2 6% 4 4 4 3 4 6% 37%	4430
	11th to 20th	Day	13% 9% 3 7% 5% 5% 5% 4 5% 8% 35%	4437
	21st to end	Day	14% 7% 3 8% 6% 6% 5% 5% 7% 8% 34%	5173
June	1st to 10th	Day	16% 7% 2 5% 5% 4 5% 4 8% 8% 37%	2850
	11th to 20th	Day	20% 8% 3 7% 5% 5% 5% 4 7% 7% 29%	3010
	21st to end	Day	14% 6% 2 5% 5% 5% 5% 5% 6% 9% 38%	3040
July	1st to 10th	Day	7% 3 2 7% 5% 6% 6% 5% 9% 9% 40%	5010
	11th to 20th	Day	7% 4 2 4 3 4 5% 4 6% 10% 52%	4593
	21st to end	Day	4 4 1 5% 4 4 4 4 6% 8% 56%	4802
August	1st to 10th	Day	8% 5% 2 5% 5% 5% 5% 5% 7% 9% 44%	4412
	11th to 20th	Day	7% 3 2 5% 4 4 6% 5% 8% 11% 46%	4317
	21st to end	Day	12% 5% 2 6% 3 4 4 3 5% 8% 48%	4354
September	1st to 10th	Day	12% 4 2 6% 3 5% 5% 4 5% 8% 48%	2280
	11th to 20th	Day	13% 8% 2 7% 4 4 4 3 5% 7% 42%	2204
	21st to end	Day	13% 8% 2 6% 4 3 3 3 4 6% 49%	2090
October	1st to 10th	Day	11% 9% 2 7% 4 4 4 3 4 7% 45%	3268
	11th to 20th	Day	8% 7% 2 6% 3 4 4 4 7% 9% 48%	2880
	21st to end	Day	8% 11% 5% 10% 5% 5% 5% 4 6% 6% 37%	3091
November	1st to 10th	Day	18% 14% 5% 10% 5% 5% 5% 3 5% 5% 26%	1663
	11th to 20th	Day	9% 14% 6% 12% 8% 6% 4 4 5% 5% 26%	1405
	21st to end	Day	9% 18% 5% 11% 7% 5% 3 4 5% 5% 29%	1330
December	1st to 10th	Day	7% 13% 5% 13% 9% 7% 6% 4 6% 6% 23%	1330
	11th to 20th	Day	9% 14% 6% 19% 7% 5% 6% 4 5% 6% 18%	1679
	21st to end	Day	4 8% 3 7% 4 5% 4 3 5% 7% 49%	2442
January	1st to 10th	Night	5% 14% 6% 16% 7% 7% 5% 4 7% 7% 23%	4670
	11th to 20th	Night	5% 9% 4 17% 11% 9% 8% 5% 7% 8% 18%	4392
	21st to end	Night	6% 13% 5% 13% 7% 5% 5% 4 6% 6% 31%	4873
February	1st to 10th	Night	9% 12% 4 11% 8% 6% 5% 5% 6% 7% 29%	2660
	11th to 20th	Night	5% 9% 3 10% 7% 7% 8% 5% 6% 7% 32%	2440
	21st to end	Night	4 11% 4 11% 8% 6% 6% 4 5% 7% 35%	1884
March	1st to 10th	Night	8% 12% 5% 11% 6% 6% 5% 4 6% 8% 30%	3734
	11th to 20th	Night	6% 10% 3 7% 4 5% 4 4 7% 8% 41%	3728
	21st to end	Night	6% 7% 3 9% 8% 6% 6% 4 6% 7% 39%	3477
April	1st to 10th	Night	6% 8% 2 7% 5% 5% 5% 4 6% 7% 43%	1900
	11th to 20th	Night	14% 11% 4 8% 4 5% 5% 3 5% 5% 35%	1775
	21st to end	Night	15% 8% 3 6% 5% 4 4 4 6% 7% 37%	1630
May	1st to 10th	Night	18% 9% 2 6% 5% 5% 4 4 5% 6% 35%	2540
	11th to 20th	Night	11% 7% 4 6% 5% 5% 6% 5% 6% 7% 37%	2469
	21st to end	Night	15% 6% 3 6% 5% 4 4 4 6% 8% 39%	2414
June	1st to 10th	Night	13% 6% 2 6% 5% 4 4 4 5% 9% 42%	1330
	11th to 20th	Night	17% 6% 2 6% 4 3 5% 3 6% 8% 39%	1165
	21st to end	Night	11% 5% 2 6% 5% 4 4 5% 6% 8% 45%	1140
July	1st to 10th	Night	6% 4 2 6% 4 4 5% 4 9% 9% 46%	1950
	11th to 20th	Night	5% 3 1 5% 3 3 3 3 5% 8% 61%	2373
	21st to end	Night	4 2 1 3 2 3 3 3 5% 9% 65%	2762
August	1st to 10th	Night	6% 5% 2 5% 4 4 5% 4 6% 9% 51%	2528
	11th to 20th	Night	6% 3 2 5% 4 6% 4 4 7% 8% 52%	2521
	21st to end	Night	8% 5% 2 5% 4 3 4 4 5% 8% 52%	3310
September	1st to 10th	Night	8% 5% 2 5% 4 4 4 3 6% 7% 51%	1900
	11th to 20th	Night	11% 6% 3 7% 4 3 3 3 6% 8% 46%	1976
	21st to end	Night	11% 6% 3 6% 3 4 4 3 6% 7% 48%	2090
October	1st to 10th	Night	11% 6% 2 6% 4 4 4 3 5% 8% 47%	3696
	11th to 20th	Night	6% 6% 3 6% 4 5% 5% 5% 7% 10% 43%	4016
	21st to end	Night	9% 9% 4 7% 4 4 4 4 5% 8% 43%	4467
November	1st to 10th	Night	15% 13% 4 9% 8% 4 4 4 5% 6% 29%	2512
	11th to 20th	Night	9% 14% 5% 12% 8% 5% 5% 4 5% 5% 28%	2774
	21st to end	Night	9% 12% 5% 12% 7% 5% 5% 4 5% 7% 29%	2850
December	1st to 10th	Night	6% 12% 5% 13% 8% 7% 5% 4 6% 7% 27%	2850
	11th to 20th	Night	8% 14% 6% 14% 7% 6% 7% 5% 5% 6% 23%	3518
	21st to end	Night	6% 8% 3 8% 5% 5% 5% 4 5% 5% 46%	5225

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	62% 8% 14% 12% 5%	2283
	11th to 20th	Day	60% 8% 12% 16% 4	2540
	21st to end	Day	54% 6% 9% 24% 7%	2794
February	1st to 10th	Day	60% 6% 14% 14% 6%	1520
	11th to 20th	Day	53% 7% 9% 19% 12%	1654
	21st to end	Day	52% 8% 12% 18% 10%	1570
March	1st to 10th	Day	58% 6% 13% 20% 4	3130
	11th to 20th	Day	52% 9% 16% 18% 5%	3227
	21st to end	Day	45% 6% 13% 21% 14% 1	4165
April	1st to 10th	Day	45% 7% 15% 22% 11%	2280
	11th to 20th	Day	56% 5% 13% 16% 8% 2	2356
	21st to end	Day	45% 7% 15% 24% 9%	2546
May	1st to 10th	Day	47% 5% 13% 26% 9%	4430
	11th to 20th	Day	45% 7% 12% 21% 14% 1	4441
	21st to end	Day	44% 9% 14% 26% 8%	5173
June	1st to 10th	Day	41% 8% 15% 25% 9% 1	2850
	11th to 20th	Day	51% 8% 14% 18% 8% 1	3010
	21st to end	Day	41% 9% 17% 25% 8%	3040
July	1st to 10th	Day	35% 10% 23% 27% 5%	4932
	11th to 20th	Day	27% 7% 17% 42% 7%	4512
	21st to end	Day	24% 6% 21% 36% 11% 1	4651
August	1st to 10th	Day	34% 8% 18% 29% 10% 1	4396
	11th to 20th	Day	29% 8% 21% 35% 6%	4359
	21st to end	Day	34% 6% 17% 35% 7%	4353
September	1st to 10th	Day	33% 7% 14% 32% 12% 1	2280
	11th to 20th	Day	41% 6% 16% 26% 10% 1	2204
	21st to end	Day	37% 5% 13% 31% 13% 1	2090
October	1st to 10th	Day	40% 4 17% 31% 8% 1	3268
	11th to 20th	Day	33% 5% 17% 35% 8% 1	2880
	21st to end	Day	48% 5% 15% 24% 7%	3091
November	1st to 10th	Day	61% 5% 11% 16% 7% 1	1663
	11th to 20th	Day	61% 6% 13% 13% 6% 1	1405
	21st to end	Day	58% 6% 13% 19% 5%	1330
December	1st to 10th	Day	59% 8% 12% 15% 6%	1330
	11th to 20th	Day	66% 7% 14% 10% 3	1680
	21st to end	Day	36% 7% 12% 25% 14% 6%	2442
January	1st to 10th	Night	60% 6% 13% 15% 5%	4670
	11th to 20th	Night	62% 7% 14% 12% 4	4430
	21st to end	Night	52% 7% 15% 19% 6%	4873
February	1st to 10th	Night	54% 5% 12% 19% 9% 1	2660
	11th to 20th	Night	47% 8% 13% 21% 11% 1	2441
	21st to end	Night	48% 6% 11% 24% 11%	1884
March	1st to 10th	Night	51% 6% 19% 19% 6%	3734
	11th to 20th	Night	40% 7% 16% 27% 9% 1	3728
	21st to end	Night	43% 6% 11% 24% 14% 1	3477
April	1st to 10th	Night	37% 7% 13% 24% 18% 1	1900
	11th to 20th	Night	50% 6% 11% 20% 12% 2	1775
	21st to end	Night	45% 7% 13% 22% 13%	1630
May	1st to 10th	Night	46% 6% 14% 20% 13% 1	2540
	11th to 20th	Night	42% 9% 10% 21% 16% 2	2469
	21st to end	Night	41% 7% 14% 28% 9% 1	2414
June	1st to 10th	Night	40% 6% 16% 23% 13% 2	1330
	11th to 20th	Night	41% 9% 17% 19% 14% 1	1165
	21st to end	Night	36% 9% 18% 28% 8% 1	1140
July	1st to 10th	Night	32% 9% 27% 25% 7%	1919
	11th to 20th	Night	22% 5% 17% 46% 10% 1	2331
	21st to end	Night	18% 5% 24% 34% 16% 2	2674
August	1st to 10th	Night	29% 8% 20% 31% 12%	2520
	11th to 20th	Night	28% 7% 19% 37% 9% 1	2545
	21st to end	Night	31% 5% 17% 36% 10%	3310
September	1st to 10th	Night	31% 7% 13% 32% 15% 2	1900
	11th to 20th	Night	36% 8% 16% 27% 12% 1	1976
	21st to end	Night	34% 5% 13% 31% 14% 2	2090
October	1st to 10th	Night	37% 5% 15% 32% 10% 3	3696
	11th to 20th	Night	35% 5% 15% 33% 11% 1	4016
	21st to end	Night	41% 5% 14% 31% 10%	4467
November	1st to 10th	Night	57% 6% 12% 16% 8% 1	2512
	11th to 20th	Night	59% 7% 14% 15% 5%	2774
	21st to end	Night	55% 7% 16% 17% 5%	2850
December	1st to 10th	Night	56% 7% 13% 17% 6% 1	2850
	11th to 20th	Night	61% 7% 12% 13% 6%	3516
	21st to end	Night	39% 6% 11% 22% 17% 5%	5225

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% 8% 29% 30% 16% 3	270
	11th to 20th	Day	6% 7% 38% 37% 9% 3	270
	21st to end	Day	15% 8% 27% 32% 15% 2	297
February	1st to 10th	Day	15% 8% 38% 27% 11% 1	270
	11th to 20th	Day	9% 8% 32% 34% 14% 4	270
	21st to end	Day	9% 5% 28% 38% 16% 4	225
March	1st to 10th	Day	13% 9% 30% 32% 13% 3	270
	11th to 20th	Day	13% 11% 31% 27% 15% 3	270
	21st to end	Day	15% 9% 32% 25% 17% 2	506
April	1st to 10th	Day	10% 14% 40% 25% 10% 1	460
	11th to 20th	Day	21% 12% 29% 25% 12% 2	554
	21st to end	Day	16% 10% 28% 29% 15% 2	650
May	1st to 10th	Day	16% 8% 27% 32% 15% 3	653
	11th to 20th	Day	15% 7% 26% 29% 17% 5%	675
	21st to end	Day	18% 6% 24% 29% 16% 6%	734
June	1st to 10th	Day	17% 9% 28% 27% 13% 5%	680
	11th to 20th	Day	21% 9% 28% 26% 12% 3	680
	21st to end	Day	14% 8% 24% 30% 18% 6%	680
July	1st to 10th	Day	8% 3 23% 32% 25% 8%	671
	11th to 20th	Day	11% 6% 24% 28% 24% 7%	668
	21st to end	Day	7% 6% 26% 31% 22% 8%	739
August	1st to 10th	Day	10% 5% 23% 35% 20% 8%	676
	11th to 20th	Day	9% 6% 21% 33% 23% 8%	665
	21st to end	Day	14% 7% 21% 36% 17% 4	648
September	1st to 10th	Day	12% 10% 32% 27% 15% 4	490
	11th to 20th	Day	19% 10% 26% 30% 12% 3	414
	21st to end	Day	18% 12% 29% 26% 14% 1	300
October	1st to 10th	Day	21% 7% 30% 22% 17% 3	300
	11th to 20th	Day	12% 14% 33% 24% 11% 5%	300
	21st to end	Day	14% 11% 38% 26% 8% 4	330
November	1st to 10th	Day	26% 5% 30% 25% 10% 4	282
	11th to 20th	Day	18% 10% 33% 30% 9%	270
	21st to end	Day	16% 10% 37% 29% 7% 1	270
December	1st to 10th	Day	9% 5% 40% 29% 15% 3	270
	11th to 20th	Day	14% 7% 46% 24% 7% 1	270
	21st to end	Day	11% 4 34% 31% 17% 4	297
January	1st to 10th	Night	11% 9% 36% 32% 11% 1	950
	11th to 20th	Night	15% 9% 33% 32% 9% 1	950
	21st to end	Night	13% 9% 38% 29% 9% 1	1045
February	1st to 10th	Night	13% 9% 30% 33% 14% 1	950
	11th to 20th	Night	10% 7% 35% 35% 11% 2	810
	21st to end	Night	8% 6% 29% 36% 18% 3	628
March	1st to 10th	Night	14% 7% 29% 34% 14% 2	760
	11th to 20th	Night	11% 7% 34% 32% 15% 1	727
	21st to end	Night	12% 4 30% 36% 15% 3	627
April	1st to 10th	Night	9% 7% 33% 37% 13% 1	570
	11th to 20th	Night	18% 7% 32% 32% 10%	563
	21st to end	Night	19% 6% 33% 33% 9% 1	570
May	1st to 10th	Night	16% 6% 26% 36% 14% 2	570
	11th to 20th	Night	14% 6% 30% 34% 16%	561
	21st to end	Night	19% 6% 27% 32% 16% 1	617
June	1st to 10th	Night	16% 6% 30% 34% 13% 1	570
	11th to 20th	Night	20% 5% 31% 32% 12%	405
	21st to end	Night	14% 4 23% 39% 18% 1	380
July	1st to 10th	Night	9% 3 21% 40% 25% 1	393
	11th to 20th	Night	9% 4 28% 37% 21% 2	552
	21st to end	Night	7% 3 21% 46% 19% 4	624
August	1st to 10th	Night	6% 4 23% 45% 20% 2	567
	11th to 20th	Night	9% 4 18% 39% 25% 4	564
	21st to end	Night	10% 5% 27% 40% 17% 1	627
September	1st to 10th	Night	12% 4 26% 37% 19% 2	570
	11th to 20th	Night	15% 5% 27% 38% 13% 1	570
	21st to end	Night	12% 7% 30% 36% 12% 2	570
October	1st to 10th	Night	20% 5% 25% 35% 13% 1	695
	11th to 20th	Night	13% 7% 32% 36% 12% 1	895
	21st to end	Night	16% 10% 32% 32% 8% 1	1045
November	1st to 10th	Night	21% 9% 32% 27% 10% 1	950
	11th to 20th	Night	15% 9% 37% 27% 10% 2	950
	21st to end	Night	15% 10% 38% 30% 6% 1	950
December	1st to 10th	Night	11% 7% 37% 29% 12% 4	950
	11th to 20th	Night	12% 11% 34% 31% 11% 1	950
	21st to end	Night	13% 5% 31% 33% 15% 2	1045

Page generated at 2024-11-03 00:11:08. Version ac07

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