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 2026-09-29.

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% 3 8% 5% 5% 5% 4 6% 7% 34%	149739
	Night	14% 9% 3 8% 5% 5% 5% 4 6% 7% 35%	141582
Transparency	Day	46% 7% 13% 21% 11% 1	153336
	Night	46% 7% 13% 20% 13% 1	146073
Seeing	Day	18% 13% 26% 25% 13% 5%	17022
	Night	18% 11% 28% 29% 12% 1	26258

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% 14% 6% 13% 6% 5% 4 3 5% 5% 24%	4661
	11th to 20th	Day	8% 19% 9% 18% 8% 7% 5% 3 4 6% 13%	5228
	21st to end	Day	14% 14% 6% 14% 8% 6% 6% 4 4 5% 19%	5780
February	1st to 10th	Day	13% 16% 5% 11% 8% 5% 5% 4 6% 5% 22%	1890
	11th to 20th	Day	13% 14% 5% 11% 8% 5% 5% 4 5% 7% 23%	1843
	21st to end	Day	18% 12% 4 11% 5% 4 5% 4 5% 6% 25%	1634
March	1st to 10th	Day	17% 9% 4 11% 6% 4 4 3 5% 5% 31%	5042
	11th to 20th	Day	11% 11% 5% 9% 6% 4 5% 4 6% 8% 31%	5090
	21st to end	Day	16% 10% 4 9% 5% 5% 5% 4 6% 5% 32%	5586
April	1st to 10th	Day	16% 12% 4 8% 5% 5% 5% 4 5% 5% 30%	2457
	11th to 20th	Day	16% 10% 2 8% 5% 4 5% 4 4 6% 35%	2594
	21st to end	Day	18% 9% 3 8% 5% 4 5% 4 5% 6% 34%	2730
May	1st to 10th	Day	18% 8% 3 8% 5% 5% 5% 4 5% 7% 34%	7642
	11th to 20th	Day	14% 8% 3 8% 5% 5% 5% 4 6% 7% 35%	8038
	21st to end	Day	16% 5% 2 5% 4 4 4 3 5% 7% 44%	9060
June	1st to 10th	Day	12% 6% 2 7% 5% 5% 5% 4 6% 7% 41%	2940
	11th to 20th	Day	11% 6% 2 7% 5% 5% 5% 5% 7% 8% 39%	2940
	21st to end	Day	12% 5% 2 6% 5% 4 5% 4 6% 8% 41%	3086
July	1st to 10th	Day	10% 5% 2 6% 4 5% 6% 5% 7% 10% 40%	8335
	11th to 20th	Day	6% 4 1 4 4 5% 5% 4 7% 11% 48%	8184
	21st to end	Day	8% 4 2 6% 5% 5% 5% 4 6% 8% 46%	8340
August	1st to 10th	Day	18% 7% 3 6% 4 4 4 4 5% 7% 38%	6014
	11th to 20th	Day	8% 6% 3 7% 5% 5% 6% 5% 7% 10% 38%	5951
	21st to end	Day	10% 6% 3 7% 5% 6% 5% 5% 7% 9% 38%	6366
September	1st to 10th	Day	12% 5% 2 6% 4 5% 5% 3 6% 9% 42%	2520
	11th to 20th	Day	10% 6% 2 6% 5% 5% 4 3 6% 8% 47%	2363
	21st to end	Day	14% 6% 3 7% 5% 6% 6% 5% 6% 8% 35%	2266
October	1st to 10th	Day	17% 9% 2 5% 5% 4 5% 3 6% 7% 37%	2000
	11th to 20th	Day	18% 9% 3 8% 6% 5% 4 4 6% 7% 31%	2000
	21st to end	Day	21% 12% 2 8% 6% 6% 5% 4 6% 6% 24%	2200
November	1st to 10th	Day	13% 9% 3 9% 5% 6% 6% 5% 6% 7% 32%	1805
	11th to 20th	Day	13% 11% 4 9% 6% 6% 6% 4 6% 7% 27%	1680
	21st to end	Day	16% 15% 5% 8% 6% 5% 5% 5% 6% 6% 22%	1680
December	1st to 10th	Day	16% 17% 5% 11% 7% 5% 5% 4 7% 7% 15%	2680
	11th to 20th	Day	21% 15% 4 9% 5% 4 4 4 5% 6% 22%	3066
	21st to end	Day	25% 17% 6% 13% 6% 5% 4 3 4 4 13%	4048
January	1st to 10th	Night	14% 12% 5% 12% 6% 5% 5% 4 5% 7% 26%	8234
	11th to 20th	Night	9% 14% 6% 14% 9% 7% 6% 4 6% 6% 18%	7639
	21st to end	Night	13% 11% 5% 11% 8% 6% 5% 4 6% 7% 25%	8401
February	1st to 10th	Night	14% 12% 4 10% 7% 5% 4 4 6% 6% 27%	2730
	11th to 20th	Night	13% 11% 5% 11% 7% 5% 5% 4 5% 6% 28%	2663
	21st to end	Night	12% 12% 5% 11% 5% 5% 6% 4 6% 7% 27%	2167
March	1st to 10th	Night	16% 7% 4 8% 5% 4 5% 4 6% 7% 34%	5018
	11th to 20th	Night	10% 8% 4 7% 5% 4 5% 4 7% 9% 39%	5089
	21st to end	Night	18% 9% 3 7% 4 4 4 3 4 5% 39%	5588
April	1st to 10th	Night	17% 9% 4 7% 5% 5% 4 4 5% 6% 33%	2162
	11th to 20th	Night	16% 7% 3 8% 5% 5% 4 3 5% 6% 37%	1993
	21st to end	Night	15% 8% 3 6% 5% 5% 4 3 6% 6% 39%	1890
May	1st to 10th	Night	19% 7% 3 7% 5% 5% 5% 3 6% 7% 35%	5257
	11th to 20th	Night	14% 8% 3 8% 5% 5% 4 4 6% 7% 36%	4819
	21st to end	Night	18% 4 2 5% 4 3 4 3 5% 7% 45%	5114
June	1st to 10th	Night	10% 5% 2 6% 4 5% 5% 4 6% 8% 45%	1680
	11th to 20th	Night	10% 6% 2 5% 4 5% 5% 4 8% 9% 43%	1680
	21st to end	Night	10% 5% 2 5% 4 6% 4 5% 5% 7% 47%	1514
July	1st to 10th	Night	8% 4 2 6% 4 4 5% 3 6% 9% 49%	4583
	11th to 20th	Night	8% 3 2 5% 4 4 4 4 6% 9% 52%	4772
	21st to end	Night	8% 5% 2 5% 4 4 4 4 6% 8% 51%	5737
August	1st to 10th	Night	12% 7% 2 7% 5% 5% 5% 4 5% 6% 43%	4135
	11th to 20th	Night	10% 5% 2 6% 4 4 4 4 6% 8% 49%	4095
	21st to end	Night	11% 5% 2 6% 4 4 5% 4 6% 8% 46%	4712
September	1st to 10th	Night	10% 5% 2 6% 5% 5% 4 4 6% 7% 47%	2100
	11th to 20th	Night	9% 4 2 4 4 3 3 3 5% 7% 55%	2254
	21st to end	Night	15% 6% 3 7% 4 4 4 4 6% 5% 41%	2310
October	1st to 10th	Night	16% 6% 2 6% 4 4 3 4 5% 6% 44%	2400
	11th to 20th	Night	16% 9% 2 7% 5% 5% 4 4 6% 6% 36%	2400
	21st to end	Night	19% 9% 4 8% 4 5% 4 4 5% 6% 32%	2640
November	1st to 10th	Night	14% 8% 3 6% 5% 4 4 4 6% 7% 40%	2708
	11th to 20th	Night	14% 11% 3 7% 5% 5% 6% 5% 6% 8% 29%	2940
	21st to end	Night	18% 10% 4 8% 5% 5% 5% 4 6% 8% 27%	2940
December	1st to 10th	Night	12% 14% 5% 10% 6% 6% 6% 5% 8% 8% 20%	4720
	11th to 20th	Night	17% 15% 4 10% 5% 5% 5% 4 5% 6% 24%	5348
	21st to end	Night	25% 16% 6% 11% 5% 4 4 3 5% 5% 15%	7150

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	56% 11% 12% 12% 9% 1	4662
	11th to 20th	Day	69% 8% 9% 9% 4	5262
	21st to end	Day	62% 8% 13% 11% 6%	5780
February	1st to 10th	Day	62% 6% 9% 16% 5% 1	1890
	11th to 20th	Day	61% 5% 11% 15% 7% 1	1852
	21st to end	Day	60% 5% 13% 15% 7% 1	1634
March	1st to 10th	Day	54% 6% 14% 15% 9% 1	5045
	11th to 20th	Day	49% 6% 18% 18% 7% 2	5090
	21st to end	Day	49% 6% 12% 20% 11% 1	5586
April	1st to 10th	Day	54% 4 11% 18% 12% 1	2457
	11th to 20th	Day	49% 5% 12% 20% 13% 1	2594
	21st to end	Day	50% 5% 12% 19% 12% 3	2730
May	1st to 10th	Day	48% 7% 13% 18% 10% 4	7651
	11th to 20th	Day	45% 9% 12% 20% 12% 2	8042
	21st to end	Day	39% 6% 11% 25% 17% 2	9061
June	1st to 10th	Day	40% 6% 11% 23% 18% 2	2940
	11th to 20th	Day	39% 7% 14% 23% 15% 1	2940
	21st to end	Day	38% 6% 14% 25% 16%	3086
July	1st to 10th	Day	36% 8% 15% 26% 14% 2	8266
	11th to 20th	Day	28% 8% 15% 32% 16% 1	8109
	21st to end	Day	33% 7% 13% 26% 19% 1	8156
August	1st to 10th	Day	44% 7% 13% 18% 14% 4	6001
	11th to 20th	Day	37% 9% 18% 27% 8%	5990
	21st to end	Day	37% 8% 16% 29% 9%	6366
September	1st to 10th	Day	38% 7% 15% 27% 11% 1	2520
	11th to 20th	Day	33% 6% 15% 30% 16%	2363
	21st to end	Day	44% 7% 14% 24% 11% 1	2266
October	1st to 10th	Day	36% 6% 17% 25% 14% 1	3260
	11th to 20th	Day	40% 6% 14% 24% 16%	3240
	21st to end	Day	49% 7% 15% 22% 8%	3538
November	1st to 10th	Day	47% 7% 14% 23% 9% 1	1805
	11th to 20th	Day	53% 7% 15% 14% 10% 1	1680
	21st to end	Day	58% 7% 15% 15% 5% 1	1680
December	1st to 10th	Day	64% 9% 14% 10% 3	2680
	11th to 20th	Day	60% 6% 13% 10% 10%	3066
	21st to end	Day	71% 9% 9% 7% 5%	4048
January	1st to 10th	Night	54% 9% 13% 17% 7%	8234
	11th to 20th	Night	59% 9% 12% 12% 7% 1	7680
	21st to end	Night	57% 7% 11% 15% 10%	8401
February	1st to 10th	Night	57% 6% 12% 18% 6% 1	2730
	11th to 20th	Night	55% 6% 13% 17% 9% 1	2665
	21st to end	Night	56% 5% 13% 18% 8% 1	2167
March	1st to 10th	Night	47% 7% 15% 18% 11% 2	5028
	11th to 20th	Night	41% 5% 20% 21% 12% 1	5090
	21st to end	Night	47% 4 10% 19% 17% 2	5588
April	1st to 10th	Night	52% 5% 11% 18% 12% 2	2162
	11th to 20th	Night	48% 5% 9% 20% 15% 3	1993
	21st to end	Night	46% 5% 10% 20% 16% 3	1890
May	1st to 10th	Night	48% 6% 12% 14% 14% 5%	5264
	11th to 20th	Night	46% 10% 12% 19% 11% 1	4820
	21st to end	Night	39% 5% 11% 25% 18% 2	5115
June	1st to 10th	Night	37% 7% 10% 24% 20% 2	1680
	11th to 20th	Night	35% 6% 13% 24% 19% 2	1680
	21st to end	Night	35% 7% 14% 24% 18% 1	1514
July	1st to 10th	Night	33% 6% 15% 24% 19% 2	4543
	11th to 20th	Night	27% 7% 14% 28% 21% 3	4724
	21st to end	Night	30% 7% 14% 23% 24% 2	5606
August	1st to 10th	Night	41% 6% 11% 21% 16% 4	4124
	11th to 20th	Night	33% 7% 20% 29% 10% 1	4122
	21st to end	Night	33% 7% 18% 28% 13% 1	4712
September	1st to 10th	Night	36% 6% 13% 29% 14% 2	2100
	11th to 20th	Night	29% 5% 12% 34% 19% 1	2254
	21st to end	Night	42% 6% 12% 25% 13% 1	2310
October	1st to 10th	Night	31% 5% 11% 29% 23% 1	3920
	11th to 20th	Night	43% 5% 12% 25% 15%	3899
	21st to end	Night	39% 6% 15% 27% 13% 1	4252
November	1st to 10th	Night	42% 6% 12% 25% 13% 1	2708
	11th to 20th	Night	49% 8% 14% 19% 10% 1	2940
	21st to end	Night	54% 8% 16% 17% 5%	2940
December	1st to 10th	Night	56% 8% 18% 14% 4	4720
	11th to 20th	Night	56% 7% 11% 14% 10% 1	5348
	21st to end	Night	67% 8% 10% 9% 4	7150

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% 19% 34% 19% 7% 1	220
	11th to 20th	Day	27% 20% 35% 14% 4 1	327
	21st to end	Day	26% 20% 29% 20% 4	363
February	1st to 10th	Day	25% 17% 37% 15% 5%	330
	11th to 20th	Day	23% 22% 35% 18% 2	330
	21st to end	Day	27% 27% 30% 15% 1	277
March	1st to 10th	Day	22% 16% 33% 23% 6%	540
	11th to 20th	Day	24% 18% 31% 19% 6% 1	540
	21st to end	Day	26% 14% 30% 21% 7% 1	594
April	1st to 10th	Day	21% 17% 28% 25% 7% 1	540
	11th to 20th	Day	25% 17% 25% 21% 8% 3	532
	21st to end	Day	23% 13% 32% 21% 8% 3	540
May	1st to 10th	Day	21% 13% 27% 24% 11% 4	543
	11th to 20th	Day	17% 10% 25% 27% 16% 5%	567
	21st to end	Day	14% 8% 25% 29% 16% 7%	617
June	1st to 10th	Day	14% 11% 28% 31% 14% 3	570
	11th to 20th	Day	14% 10% 25% 28% 19% 4	570
	21st to end	Day	14% 10% 26% 32% 13% 4	716
July	1st to 10th	Day	9% 5% 21% 33% 21% 10%	582
	11th to 20th	Day	13% 6% 21% 29% 22% 10%	564
	21st to end	Day	9% 5% 23% 36% 20% 7%	620
August	1st to 10th	Day	11% 6% 19% 31% 21% 12%	566
	11th to 20th	Day	9% 8% 19% 30% 23% 12%	559
	21st to end	Day	12% 6% 22% 31% 19% 10%	627
September	1st to 10th	Day	11% 10% 20% 28% 21% 11%	570
	11th to 20th	Day	11% 4 16% 29% 26% 14%	570
	21st to end	Day	15% 11% 24% 27% 16% 7%	562
October	1st to 10th	Day	20% 12% 21% 23% 16% 8%	530
	11th to 20th	Day	19% 16% 29% 24% 10% 2	530
	21st to end	Day	29% 13% 28% 21% 8% 1	583
November	1st to 10th	Day	20% 21% 29% 19% 9% 2	321
	11th to 20th	Day	23% 21% 29% 19% 6% 1	220
	21st to end	Day	25% 18% 34% 17% 5%	220
December	1st to 10th	Day	22% 21% 33% 19% 4	220
	11th to 20th	Day	27% 25% 29% 16% 2	220
	21st to end	Day	30% 17% 36% 13% 2 1	242
January	1st to 10th	Night	19% 19% 36% 20% 6%	840
	11th to 20th	Night	25% 19% 33% 19% 4	840
	21st to end	Night	19% 14% 37% 23% 6%	924
February	1st to 10th	Night	21% 17% 38% 22% 3	840
	11th to 20th	Night	20% 17% 35% 25% 3	823
	21st to end	Night	20% 17% 37% 23% 4	692
March	1st to 10th	Night	19% 13% 33% 28% 7%	840
	11th to 20th	Night	21% 14% 35% 23% 6%	840
	21st to end	Night	22% 11% 31% 28% 8% 1	924
April	1st to 10th	Night	21% 12% 31% 30% 5%	840
	11th to 20th	Night	20% 11% 31% 27% 10% 1	749
	21st to end	Night	19% 7% 26% 38% 10%	630
May	1st to 10th	Night	17% 6% 25% 34% 15% 2	630
	11th to 20th	Night	16% 6% 24% 37% 14% 2	479
	21st to end	Night	14% 5% 23% 32% 24% 2	455
June	1st to 10th	Night	13% 4 28% 39% 15% 2	420
	11th to 20th	Night	12% 7% 26% 38% 16% 1	420
	21st to end	Night	11% 5% 22% 42% 20%	420
July	1st to 10th	Night	6% 3 21% 47% 21% 2	410
	11th to 20th	Night	8% 3 22% 42% 22% 3	435
	21st to end	Night	8% 3 17% 45% 24% 2	690
August	1st to 10th	Night	9% 3 15% 42% 28% 4	627
	11th to 20th	Night	8% 3 15% 38% 33% 3	624
	21st to end	Night	12% 3 20% 36% 26% 3	769
September	1st to 10th	Night	11% 6% 18% 35% 24% 5%	840
	11th to 20th	Night	11% 4 18% 33% 29% 6%	840
	21st to end	Night	16% 6% 21% 29% 24% 4	833
October	1st to 10th	Night	18% 8% 24% 27% 21% 3	800
	11th to 20th	Night	19% 13% 29% 28% 9% 2	800
	21st to end	Night	25% 13% 28% 28% 6%	880
November	1st to 10th	Night	19% 13% 28% 28% 10% 1	820
	11th to 20th	Night	20% 16% 32% 23% 7% 2	840
	21st to end	Night	23% 14% 34% 22% 6%	840
December	1st to 10th	Night	24% 17% 32% 21% 5% 1	840
	11th to 20th	Night	23% 20% 35% 18% 5%	840
	21st to end	Night	28% 16% 31% 21% 3	924

Page generated at 2026-09-26 04:18:38. Version ac07

Copyright © 2026 Attilla Danko.