Olmzog Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Olmzog Observatory clear sky chart from 2005-11-06 to 2024-07-31.

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	16% 8% 2 7% 5% 4 5% 4 6% 7% 37%	89833
	Night	16% 8% 3 6% 4 4 4 4 5% 7% 39%	90011
Transparency	Day	45% 6% 12% 22% 13% 2	89552
	Night	45% 5% 13% 22% 13% 2	89846
Seeing	Day	24% 16% 29% 19% 8% 3	14525
	Night	21% 15% 30% 25% 8% 1	23496

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	11% 8% 3 8% 4 6% 4 5% 6% 7% 38%	2517
	11th to 20th	Day	15% 8% 5% 10% 5% 5% 5% 4 6% 6% 31%	2520
	21st to end	Day	15% 14% 5% 11% 6% 4 4 3 4 5% 29%	2772
February	1st to 10th	Day	13% 9% 3 9% 6% 5% 5% 4 7% 7% 32%	1735
	11th to 20th	Day	11% 8% 2 9% 6% 5% 5% 3 7% 6% 37%	1848
	21st to end	Day	18% 10% 3 8% 5% 5% 4 3 4 5% 34%	1570
March	1st to 10th	Day	20% 13% 4 8% 5% 4 4 3 4 5% 30%	3116
	11th to 20th	Day	12% 8% 2 7% 5% 5% 5% 5% 7% 7% 37%	3258
	21st to end	Day	19% 10% 2 6% 4 3 4 3 5% 7% 38%	4166
April	1st to 10th	Day	16% 10% 3 8% 6% 4 4 3 5% 6% 36%	2280
	11th to 20th	Day	16% 8% 2 6% 5% 4 5% 4 7% 7% 36%	2254
	21st to end	Day	19% 7% 2 8% 5% 4 5% 4 5% 6% 34%	2423
May	1st to 10th	Day	23% 11% 3 7% 4 4 4 3 5% 6% 30%	4106
	11th to 20th	Day	23% 8% 3 7% 4 4 4 4 5% 7% 32%	4356
	21st to end	Day	13% 5% 2 5% 4 4 5% 4 7% 9% 43%	4837
June	1st to 10th	Day	17% 6% 2 7% 5% 5% 6% 4 7% 8% 34%	2660
	11th to 20th	Day	16% 6% 2 6% 5% 5% 4 4 6% 9% 38%	2660
	21st to end	Day	16% 7% 2 7% 5% 6% 5% 4 7% 8% 32%	2660
July	1st to 10th	Day	13% 5% 2 6% 6% 5% 5% 5% 6% 10% 39%	2660
	11th to 20th	Day	11% 5% 2 6% 5% 5% 5% 5% 6% 10% 40%	2660
	21st to end	Day	14% 6% 2 6% 5% 4 5% 5% 7% 7% 39%	2887
August	1st to 10th	Day	11% 5% 2 7% 5% 5% 6% 5% 8% 8% 38%	2449
	11th to 20th	Day	12% 5% 2 7% 5% 5% 5% 5% 7% 10% 37%	2197
	21st to end	Day	13% 4 1 6% 5% 5% 4 4 7% 9% 42%	2376
September	1st to 10th	Day	13% 6% 2 5% 4 5% 5% 3 6% 8% 43%	2160
	11th to 20th	Day	14% 5% 2 6% 3 3 3 3 6% 7% 48%	2034
	21st to end	Day	17% 6% 2 5% 4 4 4 4 4 8% 44%	1980
October	1st to 10th	Day	24% 5% 2 6% 4 4 4 3 5% 6% 38%	1948
	11th to 20th	Day	14% 7% 2 6% 4 5% 5% 4 5% 8% 42%	1756
	21st to end	Day	21% 8% 3 7% 4 5% 4 3 4 7% 34%	1782
November	1st to 10th	Day	12% 7% 2 6% 5% 3 3 4 4 6% 48%	1671
	11th to 20th	Day	17% 7% 3 5% 3 4 5% 5% 5% 6% 41%	1710
	21st to end	Day	17% 9% 2 6% 4 4 4 4 6% 6% 39%	1627
December	1st to 10th	Day	16% 10% 2 10% 6% 5% 6% 4 6% 6% 30%	1520
	11th to 20th	Day	20% 9% 2 6% 5% 4 4 3 5% 5% 39%	1906
	21st to end	Day	18% 11% 3 7% 5% 5% 4 3 5% 7% 31%	2772
January	1st to 10th	Night	14% 8% 4 6% 3 4 4 4 5% 5% 42%	4429
	11th to 20th	Night	12% 9% 4 10% 6% 6% 5% 4 5% 6% 31%	4440
	21st to end	Night	17% 13% 4 9% 4 4 5% 4 5% 6% 29%	4884
February	1st to 10th	Night	12% 9% 3 7% 5% 5% 6% 4 5% 6% 37%	2438
	11th to 20th	Night	9% 8% 3 6% 6% 6% 6% 5% 6% 7% 39%	2218
	21st to end	Night	15% 9% 3 8% 5% 3 5% 3 5% 6% 39%	1884
March	1st to 10th	Night	22% 12% 2 5% 4 4 4 4 5% 6% 32%	3724
	11th to 20th	Night	11% 9% 3 6% 5% 5% 5% 4 6% 7% 39%	3696
	21st to end	Night	18% 9% 3 7% 4 3 3 4 6% 6% 36%	3466
April	1st to 10th	Night	16% 8% 2 5% 4 5% 5% 4 6% 6% 38%	1900
	11th to 20th	Night	16% 7% 2 6% 4 4 4 3 5% 7% 40%	1875
	21st to end	Night	20% 8% 3 6% 4 4 3 3 5% 6% 39%	1755
May	1st to 10th	Night	24% 11% 3 5% 4 3 4 4 6% 6% 30%	2834
	11th to 20th	Night	17% 9% 3 8% 6% 5% 6% 4 6% 6% 30%	2566
	21st to end	Night	14% 5% 2 6% 4 4 4 4 6% 10% 42%	2738
June	1st to 10th	Night	17% 6% 2 5% 5% 4 5% 3 5% 7% 41%	1520
	11th to 20th	Night	17% 6% 2 4 4 4 5% 4 6% 9% 41%	1520
	21st to end	Night	15% 6% 2 5% 3 4 5% 5% 6% 8% 42%	1520
July	1st to 10th	Night	12% 6% 2 5% 4 4 5% 4 5% 8% 45%	1520
	11th to 20th	Night	13% 5% 1 5% 4 5% 4 5% 7% 9% 42%	1520
	21st to end	Night	11% 5% 2 4 4 4 5% 3 6% 8% 48%	1662
August	1st to 10th	Night	10% 4 2 6% 3 5% 4 3 5% 9% 49%	1472
	11th to 20th	Night	12% 5% 2 7% 5% 5% 5% 3 6% 7% 42%	1699
	21st to end	Night	16% 4 1 4 4 2 3 3 6% 7% 49%	1980
September	1st to 10th	Night	13% 4 2 5% 3 4 4 4 6% 8% 48%	1800
	11th to 20th	Night	14% 4 2 5% 3 3 4 3 4 6% 53%	1926
	21st to end	Night	15% 5% 2 5% 5% 4 4 3 4 6% 48%	1980
October	1st to 10th	Night	23% 6% 1 5% 3 4 4 3 5% 5% 41%	2009
	11th to 20th	Night	14% 5% 2 6% 4 5% 4 3 6% 6% 44%	2203
	21st to end	Night	23% 7% 2 6% 4 4 4 4 4 6% 37%	2574
November	1st to 10th	Night	14% 6% 2 6% 4 4 3 3 5% 5% 47%	2407
	11th to 20th	Night	17% 6% 3 5% 4 4 4 4 5% 6% 42%	2470
	21st to end	Night	13% 8% 3 6% 4 4 3 4 5% 6% 45%	2550
December	1st to 10th	Night	16% 9% 3 6% 5% 5% 4 4 6% 7% 35%	2660
	11th to 20th	Night	18% 8% 2 6% 5% 4 4 4 5% 7% 38%	3288
	21st to end	Night	21% 10% 5% 9% 4 3 4 3 5% 5% 31%	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	42% 6% 10% 32% 9% 1	2518
	11th to 20th	Day	52% 6% 10% 22% 8% 2	2520
	21st to end	Day	57% 4 9% 20% 8% 2	2772
February	1st to 10th	Day	49% 6% 13% 19% 11% 2	1735
	11th to 20th	Day	46% 6% 10% 21% 14% 3	1857
	21st to end	Day	52% 4 10% 19% 14% 2	1570
March	1st to 10th	Day	57% 4 13% 13% 11% 2	3119
	11th to 20th	Day	41% 6% 17% 22% 12% 3	3258
	21st to end	Day	47% 3 6% 18% 22% 4	4166
April	1st to 10th	Day	49% 4 9% 21% 14% 3	2280
	11th to 20th	Day	44% 6% 12% 20% 16% 2	2254
	21st to end	Day	49% 6% 9% 19% 15% 3	2423
May	1st to 10th	Day	56% 5% 11% 17% 11% 1	4120
	11th to 20th	Day	51% 5% 15% 17% 10% 2	4360
	21st to end	Day	35% 7% 15% 27% 15% 1	4837
June	1st to 10th	Day	46% 7% 13% 21% 12% 1	2660
	11th to 20th	Day	43% 6% 14% 20% 14% 2	2660
	21st to end	Day	46% 8% 13% 21% 11% 1	2660
July	1st to 10th	Day	40% 7% 13% 23% 16% 1	2590
	11th to 20th	Day	38% 6% 17% 27% 11% 1	2585
	21st to end	Day	40% 7% 14% 24% 14% 1	2734
August	1st to 10th	Day	39% 8% 16% 24% 12% 1	2435
	11th to 20th	Day	40% 6% 16% 26% 11% 1	2197
	21st to end	Day	37% 7% 14% 27% 14% 2	2376
September	1st to 10th	Day	38% 6% 14% 26% 16% 1	2160
	11th to 20th	Day	36% 5% 10% 24% 22% 2	2034
	21st to end	Day	39% 5% 10% 25% 17% 3	1980
October	1st to 10th	Day	49% 4 10% 21% 13% 3	1948
	11th to 20th	Day	40% 6% 14% 27% 11% 2	1756
	21st to end	Day	52% 4 12% 18% 11% 3	1782
November	1st to 10th	Day	38% 4 15% 26% 15% 2	1671
	11th to 20th	Day	42% 6% 10% 21% 17% 2	1710
	21st to end	Day	44% 5% 17% 22% 10% 2	1627
December	1st to 10th	Day	53% 6% 13% 15% 12% 1	1520
	11th to 20th	Day	49% 4 11% 21% 14% 1	1906
	21st to end	Day	53% 5% 14% 17% 11% 1	2772
January	1st to 10th	Night	43% 5% 13% 25% 11% 2	4429
	11th to 20th	Night	52% 6% 12% 18% 10% 2	4440
	21st to end	Night	57% 4 10% 17% 10% 1	4884
February	1st to 10th	Night	47% 5% 15% 21% 10% 2	2438
	11th to 20th	Night	43% 7% 11% 22% 15% 2	2220
	21st to end	Night	46% 3 13% 24% 11% 4	1884
March	1st to 10th	Night	53% 4 10% 21% 11% 1	3734
	11th to 20th	Night	43% 5% 15% 23% 12% 2	3697
	21st to end	Night	48% 3 7% 15% 22% 5%	3466
April	1st to 10th	Night	45% 4 12% 21% 16% 2	1900
	11th to 20th	Night	44% 5% 10% 24% 16% 2	1875
	21st to end	Night	46% 5% 10% 20% 16% 4	1755
May	1st to 10th	Night	53% 5% 13% 19% 10% 1	2840
	11th to 20th	Night	54% 6% 15% 15% 9% 2	2567
	21st to end	Night	39% 7% 15% 24% 14% 2	2739
June	1st to 10th	Night	43% 6% 13% 26% 11% 1	1520
	11th to 20th	Night	41% 6% 18% 23% 12% 1	1520
	21st to end	Night	39% 8% 16% 23% 14% 1	1520
July	1st to 10th	Night	35% 9% 15% 25% 14% 2	1480
	11th to 20th	Night	36% 7% 16% 29% 12%	1472
	21st to end	Night	33% 6% 17% 28% 14% 2	1574
August	1st to 10th	Night	32% 6% 17% 29% 14% 1	1462
	11th to 20th	Night	41% 6% 18% 24% 11%	1699
	21st to end	Night	36% 4 13% 29% 17% 1	1980
September	1st to 10th	Night	34% 6% 15% 27% 17% 1	1800
	11th to 20th	Night	33% 4 11% 27% 23% 2	1926
	21st to end	Night	38% 4 11% 27% 17% 2	1980
October	1st to 10th	Night	45% 5% 13% 22% 12% 3	2009
	11th to 20th	Night	39% 5% 15% 27% 12% 1	2203
	21st to end	Night	49% 4 13% 20% 11% 1	2574
November	1st to 10th	Night	38% 5% 12% 24% 17% 3	2407
	11th to 20th	Night	44% 4 11% 23% 15% 3	2470
	21st to end	Night	40% 4 18% 25% 12% 1	2550
December	1st to 10th	Night	48% 5% 14% 21% 11% 1	2660
	11th to 20th	Night	47% 4 14% 18% 14% 3	3288
	21st to end	Night	55% 4 11% 21% 9% 1	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	31% 19% 30% 15% 4 1	180
	11th to 20th	Day	32% 18% 36% 8% 4 2	180
	21st to end	Day	22% 27% 33% 13% 5% 1	198
February	1st to 10th	Day	32% 28% 27% 12% 1	300
	11th to 20th	Day	31% 24% 31% 12% 1	456
	21st to end	Day	31% 21% 30% 15% 3	382
March	1st to 10th	Day	30% 19% 33% 16% 2	460
	11th to 20th	Day	31% 23% 29% 13% 3 2	460
	21st to end	Day	30% 22% 30% 10% 5% 2	506
April	1st to 10th	Day	35% 18% 29% 11% 6% 2	460
	11th to 20th	Day	33% 21% 28% 11% 7% 1	452
	21st to end	Day	32% 17% 31% 14% 5% 2	460
May	1st to 10th	Day	33% 17% 27% 14% 6% 2	463
	11th to 20th	Day	24% 15% 35% 18% 6% 2	487
	21st to end	Day	20% 14% 31% 22% 10% 3	529
June	1st to 10th	Day	19% 15% 32% 23% 8% 2	490
	11th to 20th	Day	17% 13% 33% 23% 11% 1	490
	21st to end	Day	20% 15% 35% 18% 9% 3	490
July	1st to 10th	Day	15% 11% 31% 26% 14% 3	485
	11th to 20th	Day	14% 7% 34% 29% 14% 2	484
	21st to end	Day	15% 10% 36% 26% 11% 3	529
August	1st to 10th	Day	10% 9% 27% 32% 16% 6%	446
	11th to 20th	Day	15% 9% 28% 26% 15% 7%	439
	21st to end	Day	14% 12% 27% 27% 14% 7%	495
September	1st to 10th	Day	19% 10% 22% 24% 18% 7%	450
	11th to 20th	Day	17% 12% 26% 21% 16% 9%	450
	21st to end	Day	20% 12% 28% 23% 10% 7%	450
October	1st to 10th	Day	28% 13% 22% 19% 12% 6%	450
	11th to 20th	Day	20% 19% 25% 24% 11% 2	428
	21st to end	Day	34% 13% 25% 21% 7% 1	396
November	1st to 10th	Day	23% 16% 26% 24% 9% 2	365
	11th to 20th	Day	29% 21% 25% 20% 4 1	370
	21st to end	Day	31% 16% 28% 21% 5% 1	287
December	1st to 10th	Day	29% 22% 27% 18% 4 1	180
	11th to 20th	Day	39% 17% 34% 8% 3	180
	21st to end	Day	31% 19% 29% 17% 3 1	198
January	1st to 10th	Night	21% 21% 33% 20% 3	760
	11th to 20th	Night	26% 18% 32% 22% 2 1	760
	21st to end	Night	20% 19% 35% 22% 4	836
February	1st to 10th	Night	22% 19% 38% 19% 3	760
	11th to 20th	Night	22% 22% 37% 17% 1	743
	21st to end	Night	26% 21% 31% 19% 3	628
March	1st to 10th	Night	24% 21% 34% 19% 3	760
	11th to 20th	Night	24% 21% 32% 20% 4	760
	21st to end	Night	24% 17% 32% 21% 6%	836
April	1st to 10th	Night	25% 17% 33% 20% 4	760
	11th to 20th	Night	23% 19% 31% 21% 6%	751
	21st to end	Night	27% 19% 27% 22% 5%	615
May	1st to 10th	Night	29% 12% 29% 22% 7% 1	570
	11th to 20th	Night	20% 13% 34% 28% 5%	419
	21st to end	Night	19% 7% 29% 32% 12% 1	411
June	1st to 10th	Night	20% 9% 30% 29% 12%	380
	11th to 20th	Night	17% 7% 32% 32% 11%	380
	21st to end	Night	17% 7% 28% 37% 11% 1	380
July	1st to 10th	Night	13% 6% 26% 43% 12%	370
	11th to 20th	Night	14% 4 25% 41% 15% 2	368
	21st to end	Night	12% 6% 25% 41% 16%	416
August	1st to 10th	Night	13% 4 23% 37% 22% 2	398
	11th to 20th	Night	14% 6% 23% 37% 18% 3	635
	21st to end	Night	16% 6% 20% 35% 20% 2	792
September	1st to 10th	Night	15% 6% 24% 35% 18% 2	720
	11th to 20th	Night	16% 8% 23% 31% 18% 5%	720
	21st to end	Night	19% 7% 25% 31% 16% 2	720
October	1st to 10th	Night	26% 12% 21% 27% 12% 3	720
	11th to 20th	Night	19% 11% 32% 26% 11% 1	720
	21st to end	Night	27% 16% 28% 22% 6%	792
November	1st to 10th	Night	20% 17% 28% 25% 8% 1	740
	11th to 20th	Night	22% 17% 31% 22% 7% 1	760
	21st to end	Night	21% 18% 31% 24% 6% 1	760
December	1st to 10th	Night	25% 18% 33% 18% 5%	760
	11th to 20th	Night	26% 18% 32% 21% 4	760
	21st to end	Night	26% 21% 31% 19% 3	836

Page generated at 2024-07-28 09:52:09. Version ac07

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