Mount Nemo Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mount Nemo Observatory clear sky chart from 2005-11-06 to 2024-03-08.

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	14% 9% 4 7% 6% 4 5% 5% 6% 7% 32%	78655
	Night	15% 9% 4 7% 6% 3 5% 5% 5% 7% 34%	80846
Transparency	Day	49% 6% 13% 20% 11% 1	78372
	Night	50% 6% 12% 20% 11% 1	80663
Seeing	Day	17% 11% 26% 27% 14% 6%	13624
	Night	18% 10% 28% 29% 13% 2	23118

By Month

Percentage Cloud Cover NE (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	14% 16% 6% 10% 6% 4 4 3 5% 5% 27%	2517
	11th to 20th	Day	11% 17% 8% 14% 9% 4 5% 4 4 6% 18%	2822
	21st to end	Day	22% 17% 7% 10% 8% 4 4 4 4 4 17%	3124
February	1st to 10th	Day	14% 15% 6% 10% 9% 4 6% 5% 6% 5% 21%	1710
	11th to 20th	Day	12% 12% 7% 10% 8% 4 6% 5% 5% 7% 24%	1663
	21st to end	Day	19% 11% 4 10% 7% 3 4 6% 5% 6% 25%	1483
March	1st to 10th	Day	13% 10% 5% 9% 8% 4 5% 4 5% 6% 30%	2054
	11th to 20th	Day	13% 12% 5% 8% 7% 3 5% 5% 4 5% 33%	1980
	21st to end	Day	16% 10% 4 8% 7% 3 5% 5% 5% 6% 31%	2178
April	1st to 10th	Day	15% 10% 5% 7% 6% 3 6% 5% 5% 6% 30%	2106
	11th to 20th	Day	17% 8% 3 6% 6% 3 5% 4 4 7% 36%	2219
	21st to end	Day	19% 8% 3 7% 6% 3 5% 5% 5% 6% 33%	2340
May	1st to 10th	Day	15% 8% 3 7% 6% 4 4 5% 6% 7% 35%	2340
	11th to 20th	Day	14% 6% 3 6% 7% 4 5% 5% 5% 6% 39%	2419
	21st to end	Day	11% 5% 2 6% 6% 3 5% 5% 6% 9% 43%	2725
June	1st to 10th	Day	13% 5% 3 6% 6% 3 5% 5% 5% 8% 41%	2520
	11th to 20th	Day	11% 6% 3 5% 6% 3 5% 6% 7% 8% 41%	2520
	21st to end	Day	12% 5% 2 5% 5% 3 6% 5% 6% 8% 42%	2644
July	1st to 10th	Day	7% 4 2 4 4 4 6% 6% 8% 9% 46%	2534
	11th to 20th	Day	11% 5% 2 4 5% 3 5% 6% 8% 11% 39%	2494
	21st to end	Day	8% 5% 2 5% 6% 5% 5% 7% 7% 10% 39%	2547
August	1st to 10th	Day	8% 5% 2 6% 6% 4 6% 6% 7% 10% 40%	2327
	11th to 20th	Day	8% 4 3 6% 7% 4 6% 7% 6% 9% 40%	2303
	21st to end	Day	11% 6% 2 5% 5% 4 4 6% 7% 9% 41%	2491
September	1st to 10th	Day	13% 5% 3 5% 6% 4 6% 4 6% 8% 40%	2160
	11th to 20th	Day	11% 5% 3 5% 5% 3 5% 5% 6% 8% 46%	2026
	21st to end	Day	13% 5% 3 7% 6% 5% 6% 6% 6% 8% 35%	1961
October	1st to 10th	Day	19% 9% 2 5% 6% 3 5% 4 5% 6% 35%	1800
	11th to 20th	Day	19% 9% 4 8% 7% 4 4 5% 5% 7% 30%	1800
	21st to end	Day	23% 12% 3 7% 7% 4 5% 5% 5% 5% 24%	1980
November	1st to 10th	Day	13% 8% 3 8% 6% 4 6% 6% 6% 8% 32%	1630
	11th to 20th	Day	14% 10% 4 9% 7% 4 6% 6% 6% 8% 26%	1520
	21st to end	Day	17% 13% 5% 6% 7% 3 5% 6% 7% 7% 24%	1520
December	1st to 10th	Day	14% 16% 6% 11% 8% 3 5% 5% 6% 6% 19%	1520
	11th to 20th	Day	17% 13% 5% 9% 7% 4 6% 5% 5% 6% 22%	1906
	21st to end	Day	28% 17% 6% 11% 7% 4 5% 4 4 4 11%	2772
January	1st to 10th	Night	16% 13% 6% 9% 7% 4 5% 5% 5% 6% 23%	4429
	11th to 20th	Night	14% 11% 5% 12% 9% 5% 7% 5% 6% 7% 19%	4120
	21st to end	Night	22% 12% 6% 8% 7% 4 5% 4 4 5% 22%	4532
February	1st to 10th	Night	15% 11% 5% 8% 9% 3 6% 5% 6% 7% 25%	2470
	11th to 20th	Night	12% 10% 6% 9% 9% 4 5% 5% 5% 7% 28%	2403
	21st to end	Night	13% 11% 5% 9% 7% 3 6% 5% 6% 7% 28%	1967
March	1st to 10th	Night	13% 7% 4 7% 7% 3 6% 6% 6% 7% 35%	2054
	11th to 20th	Night	15% 10% 5% 8% 5% 3 5% 4 4 7% 34%	1979
	21st to end	Night	15% 10% 4 8% 5% 3 4 3 4 5% 39%	2178
April	1st to 10th	Night	17% 7% 4 7% 5% 4 6% 5% 5% 6% 34%	1854
	11th to 20th	Night	15% 6% 4 7% 6% 4 4 4 5% 6% 39%	1705
	21st to end	Night	16% 8% 3 6% 5% 4 4 4 5% 6% 39%	1620
May	1st to 10th	Night	16% 5% 3 6% 5% 3 5% 5% 6% 7% 39%	1620
	11th to 20th	Night	14% 6% 2 5% 5% 3 4 5% 6% 7% 43%	1471
	21st to end	Night	9% 4 2 4 4 3 4 5% 6% 8% 51%	1550
June	1st to 10th	Night	10% 5% 2 5% 5% 4 6% 5% 6% 9% 43%	1440
	11th to 20th	Night	11% 5% 3 4 5% 3 4 5% 7% 9% 44%	1440
	21st to end	Night	10% 5% 2 4 5% 4 4 5% 5% 7% 48%	1298
July	1st to 10th	Night	6% 3 2 4 4 3 4 4 4 9% 58%	1408
	11th to 20th	Night	9% 3 2 4 5% 2 4 5% 5% 10% 50%	1462
	21st to end	Night	7% 3 2 4 5% 4 4 5% 6% 9% 51%	1771
August	1st to 10th	Night	8% 4 2 4 5% 3 6% 5% 7% 8% 48%	1611
	11th to 20th	Night	7% 4 1 4 5% 3 4 5% 6% 9% 53%	1598
	21st to end	Night	10% 4 2 4 5% 3 5% 5% 5% 7% 48%	1846
September	1st to 10th	Night	11% 4 2 5% 5% 4 5% 4 6% 7% 46%	1800
	11th to 20th	Night	10% 4 2 4 4 2 3 4 5% 8% 54%	1931
	21st to end	Night	13% 6% 3 7% 5% 4 4 5% 6% 6% 42%	1998
October	1st to 10th	Night	17% 7% 2 6% 4 3 3 5% 5% 6% 41%	2160
	11th to 20th	Night	17% 8% 3 6% 6% 4 4 5% 6% 6% 35%	2160
	21st to end	Night	20% 9% 4 7% 5% 4 5% 5% 5% 6% 31%	2376
November	1st to 10th	Night	15% 6% 3 5% 6% 3 5% 5% 6% 7% 40%	2443
	11th to 20th	Night	14% 10% 4 6% 6% 3 6% 6% 6% 8% 30%	2660
	21st to end	Night	18% 9% 4 7% 6% 4 5% 6% 6% 8% 28%	2660
December	1st to 10th	Night	17% 12% 5% 8% 6% 4 5% 6% 6% 6% 24%	2660
	11th to 20th	Night	16% 14% 5% 10% 6% 4 5% 6% 6% 6% 23%	3288
	21st to end	Night	28% 17% 6% 10% 6% 3 4 4 5% 5% 12%	4884

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	57% 9% 13% 12% 9% 1	2518
	11th to 20th	Day	68% 4 12% 11% 4	2822
	21st to end	Day	72% 6% 10% 9% 4	3124
February	1st to 10th	Day	64% 6% 10% 15% 4 1	1710
	11th to 20th	Day	61% 5% 11% 15% 7% 1	1672
	21st to end	Day	60% 5% 12% 15% 7% 1	1483
March	1st to 10th	Day	56% 5% 14% 17% 7% 1	2057
	11th to 20th	Day	54% 4 10% 19% 11% 2	1980
	21st to end	Day	52% 5% 10% 20% 11% 2	2178
April	1st to 10th	Day	54% 4 11% 18% 12% 1	2106
	11th to 20th	Day	48% 4 13% 20% 14% 1	2219
	21st to end	Day	51% 4 12% 18% 12% 3	2340
May	1st to 10th	Day	47% 5% 12% 22% 13% 1	2340
	11th to 20th	Day	46% 6% 11% 22% 13% 2	2423
	21st to end	Day	37% 7% 15% 24% 14% 2	2725
June	1st to 10th	Day	40% 6% 12% 24% 16% 2	2520
	11th to 20th	Day	39% 7% 14% 23% 16% 1	2520
	21st to end	Day	38% 6% 14% 25% 17%	2644
July	1st to 10th	Day	31% 7% 14% 27% 18% 3	2464
	11th to 20th	Day	37% 7% 17% 26% 12% 1	2419
	21st to end	Day	38% 8% 15% 22% 15% 2	2405
August	1st to 10th	Day	35% 9% 16% 25% 13% 2	2314
	11th to 20th	Day	37% 9% 18% 24% 11% 1	2303
	21st to end	Day	37% 6% 14% 28% 14% 1	2491
September	1st to 10th	Day	41% 7% 14% 26% 11% 1	2160
	11th to 20th	Day	34% 6% 14% 30% 15%	2026
	21st to end	Day	43% 7% 15% 25% 10% 1	1961
October	1st to 10th	Day	49% 5% 14% 20% 11% 1	1800
	11th to 20th	Day	52% 6% 13% 21% 8% 1	1800
	21st to end	Day	59% 6% 13% 16% 6% 1	1980
November	1st to 10th	Day	46% 7% 14% 23% 9% 1	1630
	11th to 20th	Day	53% 7% 16% 14% 9% 1	1520
	21st to end	Day	58% 6% 16% 15% 5% 1	1520
December	1st to 10th	Day	63% 7% 14% 12% 4	1520
	11th to 20th	Day	61% 8% 15% 10% 7%	1906
	21st to end	Day	76% 7% 8% 7% 2	2772
January	1st to 10th	Night	59% 8% 14% 13% 5% 1	4429
	11th to 20th	Night	61% 8% 16% 12% 3	4120
	21st to end	Night	65% 6% 11% 14% 4	4532
February	1st to 10th	Night	59% 6% 12% 18% 5% 1	2470
	11th to 20th	Night	55% 6% 12% 17% 9% 1	2405
	21st to end	Night	56% 5% 13% 18% 8% 1	1967
March	1st to 10th	Night	49% 6% 13% 21% 9% 2	2064
	11th to 20th	Night	52% 4 9% 21% 12% 2	1980
	21st to end	Night	50% 4 7% 21% 15% 3	2178
April	1st to 10th	Night	50% 5% 11% 20% 13% 1	1854
	11th to 20th	Night	46% 5% 9% 21% 16% 3	1705
	21st to end	Night	47% 5% 9% 20% 16% 3	1620
May	1st to 10th	Night	45% 5% 9% 22% 16% 3	1620
	11th to 20th	Night	41% 5% 11% 25% 14% 4	1472
	21st to end	Night	32% 6% 15% 25% 19% 4	1551
June	1st to 10th	Night	38% 7% 11% 25% 19% 1	1440
	11th to 20th	Night	36% 6% 12% 24% 20% 2	1440
	21st to end	Night	35% 7% 14% 25% 18% 1	1298
July	1st to 10th	Night	27% 5% 11% 26% 27% 4	1368
	11th to 20th	Night	31% 7% 12% 28% 19% 3	1414
	21st to end	Night	30% 7% 16% 26% 18% 3	1672
August	1st to 10th	Night	32% 8% 14% 31% 13% 2	1600
	11th to 20th	Night	28% 7% 18% 31% 14% 2	1598
	21st to end	Night	33% 8% 13% 28% 16% 2	1846
September	1st to 10th	Night	39% 6% 13% 26% 14% 2	1800
	11th to 20th	Night	30% 5% 12% 34% 18% 1	1931
	21st to end	Night	41% 6% 12% 27% 13% 1	1998
October	1st to 10th	Night	43% 5% 11% 25% 16% 1	2160
	11th to 20th	Night	48% 6% 13% 23% 10%	2160
	21st to end	Night	55% 6% 11% 17% 11% 1	2376
November	1st to 10th	Night	42% 6% 12% 24% 14% 1	2443
	11th to 20th	Night	49% 7% 14% 20% 10% 1	2660
	21st to end	Night	53% 7% 17% 17% 5%	2660
December	1st to 10th	Night	60% 8% 13% 14% 5%	2660
	11th to 20th	Night	59% 8% 14% 15% 5%	3288
	21st to end	Night	73% 8% 9% 7% 2	4884

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	17% 17% 34% 22% 8% 2	180
	11th to 20th	Day	23% 17% 37% 16% 5% 1	267
	21st to end	Day	23% 18% 31% 23% 5%	297
February	1st to 10th	Day	21% 18% 39% 17% 5%	270
	11th to 20th	Day	18% 23% 38% 19% 2	270
	21st to end	Day	24% 27% 31% 17% 1	229
March	1st to 10th	Day	19% 14% 34% 25% 7%	448
	11th to 20th	Day	19% 17% 34% 21% 8% 1	420
	21st to end	Day	24% 13% 29% 23% 9% 1	462
April	1st to 10th	Day	16% 16% 30% 28% 9% 1	420
	11th to 20th	Day	23% 15% 25% 23% 11% 4	412
	21st to end	Day	21% 12% 31% 24% 9% 3	420
May	1st to 10th	Day	20% 10% 27% 25% 13% 5%	423
	11th to 20th	Day	17% 8% 25% 29% 16% 6%	447
	21st to end	Day	13% 5% 23% 32% 18% 9%	485
June	1st to 10th	Day	14% 7% 27% 34% 15% 3	450
	11th to 20th	Day	12% 7% 22% 31% 22% 5%	450
	21st to end	Day	13% 9% 22% 34% 16% 5%	574
July	1st to 10th	Day	8% 3 17% 35% 25% 12%	459
	11th to 20th	Day	14% 4 17% 31% 23% 11%	444
	21st to end	Day	9% 4 19% 39% 20% 8%	488
August	1st to 10th	Day	7% 5% 17% 33% 24% 14%	446
	11th to 20th	Day	9% 5% 15% 32% 26% 13%	439
	21st to end	Day	11% 5% 20% 32% 20% 12%	495
September	1st to 10th	Day	12% 7% 18% 30% 21% 12%	450
	11th to 20th	Day	11% 4 16% 28% 26% 15%	450
	21st to end	Day	14% 11% 24% 27% 17% 8%	450
October	1st to 10th	Day	23% 12% 19% 21% 16% 9%	450
	11th to 20th	Day	19% 16% 28% 25% 10% 1	450
	21st to end	Day	29% 11% 28% 21% 9% 1	495
November	1st to 10th	Day	17% 21% 27% 22% 11% 2	266
	11th to 20th	Day	21% 21% 28% 21% 7% 2	180
	21st to end	Day	22% 16% 37% 19% 6% 1	180
December	1st to 10th	Day	17% 23% 33% 21% 5% 1	180
	11th to 20th	Day	23% 26% 29% 19% 3	180
	21st to end	Day	27% 18% 39% 13% 3 1	198
January	1st to 10th	Night	19% 18% 35% 21% 7% 1	760
	11th to 20th	Night	24% 18% 33% 21% 4	760
	21st to end	Night	18% 13% 38% 25% 7%	836
February	1st to 10th	Night	21% 16% 38% 22% 3	760
	11th to 20th	Night	19% 16% 36% 26% 3	743
	21st to end	Night	19% 17% 36% 24% 4	628
March	1st to 10th	Night	17% 12% 35% 29% 7%	751
	11th to 20th	Night	19% 14% 35% 24% 7%	720
	21st to end	Night	20% 10% 29% 30% 10% 1	792
April	1st to 10th	Night	19% 11% 32% 31% 6%	720
	11th to 20th	Night	18% 11% 32% 27% 11% 2	641
	21st to end	Night	19% 6% 27% 36% 11%	540
May	1st to 10th	Night	17% 4 25% 35% 16% 3	540
	11th to 20th	Night	15% 4 25% 39% 14% 2	410
	21st to end	Night	12% 4 22% 34% 26% 2	389
June	1st to 10th	Night	12% 4 27% 39% 16% 2	360
	11th to 20th	Night	12% 6% 24% 39% 18% 1	360
	21st to end	Night	10% 4 21% 43% 22%	360
July	1st to 10th	Night	6% 2 19% 47% 24% 2	350
	11th to 20th	Night	9% 2 20% 43% 22% 3	370
	21st to end	Night	8% 2 17% 46% 24% 3	591
August	1st to 10th	Night	9% 3 14% 42% 29% 4	537
	11th to 20th	Night	7% 2 13% 37% 36% 4	534
	21st to end	Night	12% 3 19% 35% 28% 4	658
September	1st to 10th	Night	12% 6% 17% 35% 25% 6%	720
	11th to 20th	Night	11% 4 18% 33% 27% 6%	720
	21st to end	Night	15% 6% 20% 29% 25% 5%	720
October	1st to 10th	Night	19% 8% 23% 27% 20% 3	720
	11th to 20th	Night	20% 12% 30% 28% 10% 2	720
	21st to end	Night	26% 12% 27% 29% 6%	792
November	1st to 10th	Night	18% 12% 29% 29% 11% 2	740
	11th to 20th	Night	18% 15% 33% 24% 8% 2	760
	21st to end	Night	22% 13% 34% 23% 7%	760
December	1st to 10th	Night	24% 17% 32% 20% 6% 1	760
	11th to 20th	Night	22% 18% 36% 19% 5%	760
	21st to end	Night	28% 16% 32% 21% 3	836

Page generated at 2024-03-05 07:24:00. Version ac07

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