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 2024-04-10.

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	11% 8% 4 8% 6% 4 5% 5% 6% 7% 36%	83126
	Night	9% 9% 4 8% 7% 4 5% 5% 6% 7% 37%	85660
Transparency	Day	46% 7% 14% 23% 9% 1	82838
	Night	46% 7% 14% 22% 10% 1	85528
Seeing	Day	14% 8% 29% 29% 16% 4	15355
	Night	13% 7% 31% 34% 13% 2	25063

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% 8% 14% 9% 4 6% 5% 8% 8% 17%	2283
	11th to 20th	Day	5% 8% 5% 11% 13% 7% 8% 8% 7% 8% 18%	2516
	21st to end	Day	7% 13% 6% 10% 9% 4 6% 4 5% 6% 31%	2794
February	1st to 10th	Day	8% 13% 6% 11% 8% 5% 7% 8% 5% 6% 23%	1520
	11th to 20th	Day	7% 10% 3 10% 8% 6% 10% 6% 5% 7% 28%	1645
	21st to end	Day	5% 10% 5% 11% 9% 5% 6% 7% 7% 8% 27%	1570
March	1st to 10th	Day	9% 13% 6% 11% 9% 5% 5% 4 6% 7% 25%	3130
	11th to 20th	Day	8% 10% 5% 11% 8% 4 6% 5% 5% 7% 32%	3226
	21st to end	Day	7% 8% 4 8% 7% 5% 5% 5% 5% 7% 37%	4165
April	1st to 10th	Day	8% 9% 5% 7% 6% 4 5% 5% 6% 7% 37%	2269
	11th to 20th	Day	15% 13% 5% 8% 7% 3 4 5% 5% 6% 28%	2230
	21st to end	Day	13% 8% 3 7% 6% 3 5% 5% 5% 8% 36%	2412
May	1st to 10th	Day	13% 7% 3 7% 5% 3 5% 5% 5% 7% 40%	2520
	11th to 20th	Day	11% 7% 3 5% 6% 3 5% 5% 5% 9% 40%	2499
	21st to end	Day	20% 7% 3 6% 6% 4 4 5% 5% 8% 33%	2918
June	1st to 10th	Day	16% 6% 2 5% 5% 3 5% 5% 8% 8% 37%	2700
	11th to 20th	Day	21% 7% 3 6% 5% 4 5% 5% 7% 7% 29%	2851
	21st to end	Day	14% 5% 2 4 6% 4 6% 6% 6% 9% 38%	2880
July	1st to 10th	Day	8% 3 1 5% 5% 3 5% 5% 8% 9% 48%	2856
	11th to 20th	Day	10% 5% 2 5% 4 3 6% 6% 6% 9% 44%	2613
	21st to end	Day	7% 4 2 5% 5% 3 4 6% 7% 8% 50%	2742
August	1st to 10th	Day	8% 4 3 5% 5% 4 5% 5% 7% 9% 46%	2507
	11th to 20th	Day	10% 4 2 5% 5% 3 5% 6% 6% 9% 45%	2464
	21st to end	Day	13% 5% 2 5% 4 2 5% 4 5% 7% 49%	2480
September	1st to 10th	Day	12% 4 2 5% 4 3 6% 4 5% 8% 47%	2160
	11th to 20th	Day	13% 7% 3 6% 5% 3 5% 5% 5% 7% 43%	2088
	21st to end	Day	13% 7% 3 5% 5% 3 3 3 4 6% 49%	1980
October	1st to 10th	Day	17% 12% 3 7% 5% 3 4 4 4 6% 36%	1859
	11th to 20th	Day	11% 10% 3 7% 5% 4 4 5% 5% 6% 40%	1654
	21st to end	Day	11% 11% 6% 10% 6% 4 5% 5% 5% 6% 31%	1782
November	1st to 10th	Day	18% 14% 5% 9% 6% 4 5% 4 4 6% 25%	1627
	11th to 20th	Day	9% 13% 7% 11% 9% 5% 5% 5% 5% 5% 26%	1405
	21st to end	Day	10% 16% 7% 9% 7% 4 3 5% 4 6% 29%	1330
December	1st to 10th	Day	8% 11% 6% 11% 10% 5% 6% 6% 6% 7% 23%	1330
	11th to 20th	Day	9% 13% 7% 18% 9% 4 6% 5% 5% 6% 18%	1679
	21st to end	Day	5% 8% 4 6% 5% 4 5% 3 5% 7% 49%	2442
January	1st to 10th	Night	5% 13% 6% 14% 10% 5% 5% 5% 6% 7% 23%	4670
	11th to 20th	Night	5% 8% 4 14% 14% 7% 8% 7% 7% 8% 18%	4392
	21st to end	Night	6% 12% 5% 11% 8% 4 5% 5% 6% 7% 31%	4873
February	1st to 10th	Night	9% 11% 5% 9% 9% 4 6% 5% 6% 7% 29%	2660
	11th to 20th	Night	5% 8% 4 9% 8% 5% 8% 7% 6% 7% 32%	2440
	21st to end	Night	4 9% 5% 10% 8% 5% 7% 6% 5% 7% 35%	1884
March	1st to 10th	Night	8% 11% 5% 10% 7% 4 5% 5% 6% 8% 30%	3734
	11th to 20th	Night	7% 9% 4 6% 6% 4 5% 5% 6% 8% 41%	3728
	21st to end	Night	6% 7% 3 8% 9% 5% 7% 5% 6% 7% 39%	3477
April	1st to 10th	Night	6% 7% 4 6% 6% 4 5% 5% 6% 8% 43%	1900
	11th to 20th	Night	15% 9% 4 7% 5% 3 6% 5% 5% 6% 35%	1681
	21st to end	Night	16% 8% 4 6% 5% 4 4 5% 5% 7% 36%	1545
May	1st to 10th	Night	12% 7% 3 6% 5% 3 5% 5% 6% 7% 41%	1440
	11th to 20th	Night	13% 5% 3 5% 5% 3 4 6% 7% 7% 41%	1397
	21st to end	Night	19% 5% 3 4 5% 3 4 5% 6% 9% 37%	1358
June	1st to 10th	Night	13% 6% 3 6% 5% 3 4 5% 5% 9% 42%	1260
	11th to 20th	Night	17% 5% 3 5% 5% 2 5% 4 5% 9% 40%	1104
	21st to end	Night	11% 5% 2 5% 5% 3 4 6% 6% 9% 45%	1080
July	1st to 10th	Night	7% 4 2 4 4 2 4 4 7% 7% 54%	1102
	11th to 20th	Night	7% 3 1 4 5% 2 4 4 5% 9% 56%	1343
	21st to end	Night	6% 3 2 2 2 2 3 3 4 9% 63%	1576
August	1st to 10th	Night	5% 3 2 3 4 2 5% 6% 7% 9% 54%	1432
	11th to 20th	Night	8% 4 1 4 4 3 5% 4 6% 7% 55%	1436
	21st to end	Night	9% 5% 2 3 4 2 4 4 5% 7% 54%	1873
September	1st to 10th	Night	9% 5% 2 4 5% 3 4 4 5% 8% 50%	1800
	11th to 20th	Night	11% 6% 3 6% 5% 3 4 4 6% 7% 46%	1872
	21st to end	Night	11% 6% 3 5% 3 3 4 4 6% 7% 47%	1980
October	1st to 10th	Night	15% 9% 3 5% 5% 2 4 4 6% 8% 40%	2098
	11th to 20th	Night	9% 8% 4 6% 5% 3 4 5% 5% 6% 44%	2287
	21st to end	Night	12% 12% 5% 9% 5% 4 5% 5% 5% 6% 33%	2574
November	1st to 10th	Night	15% 12% 4 8% 9% 3 5% 4 5% 6% 29%	2447
	11th to 20th	Night	9% 12% 6% 10% 9% 4 5% 5% 5% 5% 28%	2774
	21st to end	Night	9% 11% 6% 11% 8% 4 5% 5% 5% 7% 29%	2850
December	1st to 10th	Night	7% 10% 6% 11% 9% 5% 6% 5% 6% 7% 27%	2850
	11th to 20th	Night	8% 13% 7% 12% 8% 4 7% 7% 5% 6% 23%	3518
	21st to end	Night	6% 7% 3 8% 6% 4 5% 6% 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%	2269
	11th to 20th	Day	56% 6% 13% 16% 8% 2	2230
	21st to end	Day	46% 7% 15% 23% 8%	2412
May	1st to 10th	Day	43% 6% 11% 27% 12% 1	2520
	11th to 20th	Day	42% 7% 11% 26% 14% 1	2503
	21st to end	Day	50% 7% 12% 20% 11% 1	2918
June	1st to 10th	Day	41% 8% 15% 25% 9% 1	2700
	11th to 20th	Day	51% 8% 14% 18% 8% 1	2851
	21st to end	Day	41% 9% 18% 25% 7%	2880
July	1st to 10th	Day	29% 10% 21% 32% 8%	2778
	11th to 20th	Day	35% 10% 18% 28% 9% 1	2532
	21st to end	Day	29% 9% 20% 33% 8%	2590
August	1st to 10th	Day	34% 10% 18% 27% 11% 1	2491
	11th to 20th	Day	34% 10% 19% 32% 5%	2464
	21st to end	Day	35% 7% 14% 33% 11%	2480
September	1st to 10th	Day	35% 7% 14% 31% 12% 1	2160
	11th to 20th	Day	41% 6% 15% 26% 11% 1	2088
	21st to end	Day	38% 5% 13% 31% 12% 1	1980
October	1st to 10th	Day	50% 5% 13% 24% 7% 1	1859
	11th to 20th	Day	44% 7% 11% 28% 9%	1654
	21st to end	Day	55% 6% 14% 19% 6%	1782
November	1st to 10th	Day	61% 5% 11% 16% 7% 1	1627
	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	49% 6% 11% 20% 12% 2	1681
	21st to end	Night	47% 6% 12% 21% 12% 1	1545
May	1st to 10th	Night	40% 6% 11% 26% 17% 1	1440
	11th to 20th	Night	40% 8% 9% 24% 17% 2	1397
	21st to end	Night	44% 6% 15% 22% 12% 1	1358
June	1st to 10th	Night	40% 6% 16% 24% 13% 2	1260
	11th to 20th	Night	40% 9% 18% 18% 14% 1	1104
	21st to end	Night	36% 9% 18% 28% 8% 1	1080
July	1st to 10th	Night	27% 8% 20% 32% 13%	1071
	11th to 20th	Night	26% 7% 19% 35% 11% 1	1301
	21st to end	Night	21% 5% 20% 39% 13% 2	1488
August	1st to 10th	Night	24% 9% 21% 34% 12%	1424
	11th to 20th	Night	28% 7% 19% 34% 11% 1	1436
	21st to end	Night	30% 6% 12% 38% 14% 1	1873
September	1st to 10th	Night	32% 7% 14% 31% 14% 2	1800
	11th to 20th	Night	36% 8% 15% 27% 13% 1	1872
	21st to end	Night	35% 5% 13% 31% 14% 2	1980
October	1st to 10th	Night	43% 7% 17% 24% 8% 1	2098
	11th to 20th	Night	41% 6% 13% 28% 11% 1	2287
	21st to end	Night	51% 6% 13% 23% 6%	2574
November	1st to 10th	Night	57% 6% 12% 15% 8% 1	2447
	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	457
	11th to 20th	Day	21% 11% 27% 26% 13% 2	508
	21st to end	Day	16% 10% 28% 28% 16% 2	600
May	1st to 10th	Day	14% 8% 28% 33% 15% 3	603
	11th to 20th	Day	15% 8% 24% 29% 18% 6%	625
	21st to end	Day	19% 6% 23% 29% 16% 6%	679
June	1st to 10th	Day	17% 8% 28% 28% 13% 5%	630
	11th to 20th	Day	21% 8% 28% 26% 13% 3	630
	21st to end	Day	14% 7% 25% 30% 18% 6%	630
July	1st to 10th	Day	9% 3 24% 32% 25% 7%	621
	11th to 20th	Day	12% 6% 26% 28% 23% 5%	618
	21st to end	Day	7% 6% 26% 31% 22% 8%	684
August	1st to 10th	Day	10% 4 23% 35% 21% 8%	626
	11th to 20th	Day	10% 6% 20% 33% 23% 8%	615
	21st to end	Day	14% 6% 21% 37% 18% 4	599
September	1st to 10th	Day	13% 10% 34% 26% 14% 3	450
	11th to 20th	Day	19% 8% 26% 30% 13% 4	378
	21st to end	Day	18% 12% 27% 28% 14% 1	270
October	1st to 10th	Day	22% 6% 29% 21% 18% 3	270
	11th to 20th	Day	13% 13% 33% 24% 11% 6%	270
	21st to end	Day	14% 11% 37% 26% 8% 4	297
November	1st to 10th	Day	27% 5% 29% 25% 10% 4	270
	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% 38% 12% 1	570
	11th to 20th	Night	17% 6% 32% 33% 11%	533
	21st to end	Night	20% 6% 32% 32% 9% 1	540
May	1st to 10th	Night	15% 6% 26% 37% 14% 2	540
	11th to 20th	Night	14% 6% 29% 33% 17%	531
	21st to end	Night	19% 6% 27% 30% 16% 1	584
June	1st to 10th	Night	16% 5% 31% 34% 13% 1	540
	11th to 20th	Night	21% 4 30% 32% 13% 1	384
	21st to end	Night	15% 4 23% 39% 19% 1	360
July	1st to 10th	Night	9% 3 22% 42% 23% 1	371
	11th to 20th	Night	9% 4 29% 37% 20% 2	522
	21st to end	Night	8% 3 20% 47% 19% 4	591
August	1st to 10th	Night	6% 4 23% 45% 20% 2	537
	11th to 20th	Night	10% 4 18% 40% 25% 4	534
	21st to end	Night	11% 4 25% 41% 18% 1	594
September	1st to 10th	Night	12% 4 26% 37% 19% 2	540
	11th to 20th	Night	15% 5% 26% 40% 13% 1	540
	21st to end	Night	12% 7% 29% 36% 13% 2	540
October	1st to 10th	Night	21% 4 25% 35% 14% 2	658
	11th to 20th	Night	13% 7% 30% 36% 13% 1	847
	21st to end	Night	17% 10% 31% 33% 8% 2	990
November	1st to 10th	Night	21% 9% 32% 27% 10% 1	925
	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 2024-04-07 07:28:15. Version ac07

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