Làr Na Cruinne Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Làr Na Cruinne Observatory clear sky chart from 2005-11-06 to 2026-01-17.

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	8% 8% 3 8% 5% 5% 5% 4 7% 8% 38%	131627
	Night	6% 9% 4 9% 5% 5% 5% 4 6% 8% 38%	128763
Transparency	Day	40% 8% 16% 24% 11% 2	131329
	Night	41% 8% 15% 23% 12% 2	128638
Seeing	Day	13% 9% 28% 30% 16% 4	16828
	Night	11% 6% 32% 36% 14% 2	26027

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	2 8% 6% 14% 7% 7% 5% 4 7% 8% 32%	3249
	11th to 20th	Day	2 8% 4 10% 7% 5% 5% 5% 7% 7% 40%	3293
	21st to end	Day	3 6% 3 7% 5% 5% 5% 4 6% 11% 47%	4004
February	1st to 10th	Day	3 11% 4 14% 7% 7% 7% 5% 7% 8% 30%	1600
	11th to 20th	Day	3 10% 5% 10% 7% 7% 7% 5% 8% 9% 29%	1737
	21st to end	Day	3 11% 4 10% 7% 7% 6% 4 7% 8% 32%	1615
March	1st to 10th	Day	2 9% 4 10% 5% 5% 6% 3 6% 11% 38%	4518
	11th to 20th	Day	4 10% 5% 9% 4 4 4 4 6% 8% 41%	4928
	21st to end	Day	7% 21% 7% 13% 5% 4 6% 4 6% 6% 20%	5589
April	1st to 10th	Day	8% 15% 4 10% 6% 5% 5% 4 7% 8% 28%	2448
	11th to 20th	Day	11% 14% 5% 9% 5% 5% 4 4 6% 8% 30%	2570
	21st to end	Day	11% 13% 4 8% 6% 5% 5% 5% 6% 8% 29%	2600
May	1st to 10th	Day	14% 11% 3 6% 4 4 4 4 6% 7% 38%	6198
	11th to 20th	Day	13% 11% 5% 9% 6% 6% 6% 5% 7% 8% 24%	6734
	21st to end	Day	12% 8% 3 9% 6% 5% 5% 4 6% 7% 35%	7405
June	1st to 10th	Day	17% 7% 3 7% 6% 6% 5% 5% 7% 8% 30%	3000
	11th to 20th	Day	20% 8% 3 7% 6% 5% 5% 5% 6% 7% 27%	3000
	21st to end	Day	9% 5% 2 6% 5% 5% 5% 6% 8% 10% 40%	3000
July	1st to 10th	Day	7% 5% 2 5% 4 5% 5% 5% 7% 9% 47%	6780
	11th to 20th	Day	11% 3 1 4 3 4 5% 5% 7% 9% 46%	6780
	21st to end	Day	9% 5% 2 5% 4 3 4 4 6% 9% 48%	7177
August	1st to 10th	Day	9% 5% 2 6% 4 4 5% 5% 9% 9% 41%	4541
	11th to 20th	Day	7% 5% 2 5% 4 4 5% 5% 8% 10% 44%	4218
	21st to end	Day	9% 4 1 4 3 3 4 3 6% 8% 53%	4664
September	1st to 10th	Day	10% 6% 2 6% 3 4 4 3 5% 7% 51%	2475
	11th to 20th	Day	14% 7% 2 5% 4 2 5% 3 5% 8% 45%	2200
	21st to end	Day	8% 7% 3 6% 5% 4 5% 3 6% 8% 46%	2200
October	1st to 10th	Day	7% 6% 2 7% 4 5% 4 4 7% 8% 45%	3470
	11th to 20th	Day	6% 7% 2 6% 4 5% 5% 5% 7% 10% 43%	2996
	21st to end	Day	7% 7% 2 6% 5% 5% 5% 4 5% 7% 46%	3200
November	1st to 10th	Day	7% 15% 4 8% 6% 5% 4 4 6% 6% 34%	1730
	11th to 20th	Day	5% 11% 4 8% 5% 5% 5% 4 6% 7% 40%	1591
	21st to end	Day	4 12% 4 11% 5% 5% 4 3 7% 9% 36%	1470
December	1st to 10th	Day	3 10% 5% 12% 6% 6% 6% 5% 6% 8% 33%	2360
	11th to 20th	Day	2 9% 4 12% 7% 6% 8% 5% 8% 8% 30%	2712
	21st to end	Day	3 10% 4 10% 5% 5% 4 4 6% 7% 42%	3575
January	1st to 10th	Night	4 12% 6% 13% 9% 7% 6% 5% 6% 7% 26%	6916
	11th to 20th	Night	2 7% 4 13% 7% 5% 7% 6% 6% 8% 35%	6767
	21st to end	Night	3 8% 4 9% 5% 5% 5% 4 6% 9% 42%	6952
February	1st to 10th	Night	4 10% 4 11% 7% 7% 6% 4 7% 8% 33%	2800
	11th to 20th	Night	4 12% 5% 10% 6% 6% 6% 5% 7% 9% 31%	2549
	21st to end	Night	2 10% 4 13% 7% 6% 5% 4 7% 7% 35%	2013
March	1st to 10th	Night	2 8% 3 13% 7% 6% 6% 4 7% 10% 34%	5376
	11th to 20th	Night	4 8% 4 10% 5% 5% 6% 5% 6% 8% 38%	5070
	21st to end	Night	9% 18% 7% 13% 6% 4 4 4 5% 6% 23%	5372
April	1st to 10th	Night	9% 14% 3 11% 5% 5% 5% 4 5% 7% 31%	1951
	11th to 20th	Night	11% 12% 4 10% 5% 4 4 4 6% 7% 31%	1781
	21st to end	Night	10% 11% 4 10% 5% 4 5% 4 5% 8% 33%	1800
May	1st to 10th	Night	14% 11% 3 8% 5% 4 3 3 4 6% 38%	3767
	11th to 20th	Night	14% 11% 3 8% 6% 4 5% 4 7% 9% 30%	3159
	21st to end	Night	11% 7% 3 9% 5% 5% 5% 5% 6% 6% 38%	3470
June	1st to 10th	Night	15% 8% 2 8% 5% 5% 5% 3 6% 7% 34%	1400
	11th to 20th	Night	18% 7% 3 7% 4 4 6% 4 6% 8% 32%	1400
	21st to end	Night	8% 5% 2 6% 4 7% 5% 5% 8% 9% 42%	1400
July	1st to 10th	Night	7% 5% 3 7% 5% 5% 5% 3 5% 8% 48%	3180
	11th to 20th	Night	10% 5% 2 5% 4 4 5% 4 6% 9% 46%	3180
	21st to end	Night	11% 4 2 4 3 3 3 3 6% 9% 52%	3663
August	1st to 10th	Night	10% 6% 2 7% 4 4 4 5% 8% 10% 42%	2609
	11th to 20th	Night	6% 4 2 6% 5% 4 5% 5% 7% 10% 46%	2839
	21st to end	Night	8% 4 1 4 3 3 4 4 6% 8% 55%	3245
September	1st to 10th	Night	9% 7% 2 4 4 3 4 3 6% 8% 50%	1922
	11th to 20th	Night	13% 7% 2 4 3 2 4 3 5% 7% 49%	2200
	21st to end	Night	9% 6% 2 5% 3 4 4 3 6% 9% 48%	2200
October	1st to 10th	Night	8% 6% 2 5% 3 4 5% 4 6% 8% 49%	3725
	11th to 20th	Night	5% 7% 2 5% 4 5% 4 4 6% 8% 49%	4150
	21st to end	Night	5% 9% 3 6% 4 5% 5% 4 6% 7% 46%	4600
November	1st to 10th	Night	7% 14% 4 8% 5% 5% 5% 5% 6% 7% 36%	2768
	11th to 20th	Night	4 10% 4 9% 5% 6% 5% 4 7% 8% 39%	3026
	21st to end	Night	4 11% 3 9% 6% 6% 5% 4 5% 8% 39%	3150
December	1st to 10th	Night	3 10% 4 9% 6% 6% 6% 5% 8% 9% 33%	5040
	11th to 20th	Night	2 10% 5% 14% 8% 7% 5% 4 6% 9% 30%	5700
	21st to end	Night	4 10% 4 9% 5% 5% 5% 4 7% 7% 40%	7623

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	48% 6% 11% 22% 11% 3	3249
	11th to 20th	Day	40% 6% 14% 18% 20% 3	3314
	21st to end	Day	30% 7% 16% 31% 15% 1	4004
February	1st to 10th	Day	50% 8% 15% 16% 9% 2	1600
	11th to 20th	Day	47% 8% 15% 19% 9% 1	1746
	21st to end	Day	46% 8% 13% 18% 13% 1	1615
March	1st to 10th	Day	39% 6% 16% 22% 16% 1	4518
	11th to 20th	Day	38% 6% 16% 24% 15% 1	4929
	21st to end	Day	59% 10% 12% 12% 6% 1	5589
April	1st to 10th	Day	50% 8% 16% 18% 8% 1	2448
	11th to 20th	Day	51% 6% 14% 19% 9% 1	2570
	21st to end	Day	49% 8% 14% 19% 8% 1	2600
May	1st to 10th	Day	44% 6% 9% 23% 15% 3	6198
	11th to 20th	Day	51% 10% 14% 19% 7%	6738
	21st to end	Day	43% 8% 17% 22% 10% 1	7406
June	1st to 10th	Day	49% 9% 14% 17% 9% 1	3000
	11th to 20th	Day	52% 9% 13% 17% 7% 2	3000
	21st to end	Day	35% 10% 20% 24% 10% 2	3000
July	1st to 10th	Day	29% 9% 17% 26% 15% 3	6706
	11th to 20th	Day	31% 9% 20% 30% 10% 1	6699
	21st to end	Day	31% 7% 16% 25% 17% 5%	6974
August	1st to 10th	Day	33% 10% 16% 34% 6% 1	4524
	11th to 20th	Day	30% 10% 25% 27% 6% 1	4258
	21st to end	Day	27% 7% 18% 34% 13% 1	4663
September	1st to 10th	Day	32% 6% 17% 26% 15% 4	2475
	11th to 20th	Day	37% 7% 15% 26% 14% 2	2200
	21st to end	Day	36% 7% 15% 27% 12% 3	2200
October	1st to 10th	Day	34% 8% 17% 34% 7% 1	3470
	11th to 20th	Day	33% 8% 20% 23% 13% 3	2996
	21st to end	Day	35% 6% 13% 32% 13% 1	3200
November	1st to 10th	Day	48% 8% 12% 20% 11% 2	1730
	11th to 20th	Day	41% 7% 16% 25% 10% 2	1591
	21st to end	Day	43% 8% 17% 22% 9% 2	1470
December	1st to 10th	Day	47% 7% 14% 22% 8% 2	2360
	11th to 20th	Day	45% 12% 16% 18% 7% 1	2714
	21st to end	Day	38% 6% 11% 24% 17% 4	3575
January	1st to 10th	Night	53% 9% 11% 20% 6% 2	6916
	11th to 20th	Night	44% 7% 13% 18% 13% 4	6808
	21st to end	Night	36% 7% 15% 26% 15% 1	6952
February	1st to 10th	Night	47% 8% 12% 19% 12% 3	2800
	11th to 20th	Night	47% 8% 13% 18% 12% 1	2550
	21st to end	Night	47% 6% 12% 22% 12% 2	2013
March	1st to 10th	Night	41% 7% 18% 20% 11% 2	5376
	11th to 20th	Night	39% 8% 16% 22% 14% 1	5070
	21st to end	Night	59% 7% 11% 13% 8% 1	5372
April	1st to 10th	Night	50% 6% 13% 19% 11% 1	1951
	11th to 20th	Night	50% 7% 13% 20% 9% 1	1781
	21st to end	Night	47% 9% 13% 20% 9% 2	1800
May	1st to 10th	Night	46% 6% 9% 21% 16% 1	3764
	11th to 20th	Night	46% 9% 14% 25% 5% 1	3159
	21st to end	Night	39% 10% 16% 26% 9% 1	3470
June	1st to 10th	Night	46% 8% 14% 21% 10% 1	1400
	11th to 20th	Night	46% 9% 15% 18% 8% 2	1400
	21st to end	Night	34% 9% 20% 27% 9% 1	1400
July	1st to 10th	Night	33% 7% 15% 27% 15% 2	3145
	11th to 20th	Night	32% 9% 21% 29% 7% 3	3138
	21st to end	Night	30% 6% 18% 26% 16% 4	3561
August	1st to 10th	Night	35% 8% 16% 29% 12% 1	2601
	11th to 20th	Night	29% 9% 27% 26% 8% 1	2865
	21st to end	Night	25% 7% 21% 33% 13% 2	3245
September	1st to 10th	Night	31% 7% 17% 26% 15% 4	1922
	11th to 20th	Night	34% 6% 15% 27% 13% 4	2200
	21st to end	Night	32% 7% 18% 26% 14% 4	2200
October	1st to 10th	Night	31% 7% 17% 25% 19% 1	3725
	11th to 20th	Night	31% 7% 19% 26% 16% 2	4150
	21st to end	Night	36% 6% 12% 33% 13% 1	4600
November	1st to 10th	Night	45% 9% 12% 20% 12% 2	2768
	11th to 20th	Night	40% 8% 15% 21% 14% 1	3026
	21st to end	Night	41% 8% 17% 22% 10% 3	3150
December	1st to 10th	Night	43% 9% 19% 20% 7% 2	5040
	11th to 20th	Night	48% 10% 17% 17% 8%	5697
	21st to end	Night	39% 6% 11% 24% 15% 4	7623

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	4 8% 27% 41% 11% 9%	220
	11th to 20th	Day	7% 10% 30% 33% 18% 2	212
	21st to end	Day	8% 9% 25% 39% 17% 3	220
February	1st to 10th	Day	9% 11% 32% 35% 9% 6%	200
	11th to 20th	Day	7% 7% 33% 38% 13% 2	292
	21st to end	Day	6% 12% 32% 34% 15% 2	379
March	1st to 10th	Day	8% 11% 38% 27% 12% 3	500
	11th to 20th	Day	8% 11% 33% 32% 12% 3	500
	21st to end	Day	14% 17% 31% 24% 10% 4	550
April	1st to 10th	Day	13% 15% 37% 25% 8% 2	500
	11th to 20th	Day	18% 14% 29% 24% 12% 3	492
	21st to end	Day	17% 15% 28% 26% 11% 3	500
May	1st to 10th	Day	17% 12% 27% 26% 14% 4	534
	11th to 20th	Day	16% 8% 25% 27% 20% 4	725
	21st to end	Day	19% 6% 21% 30% 19% 5%	789
June	1st to 10th	Day	16% 11% 27% 30% 13% 3	730
	11th to 20th	Day	21% 11% 25% 28% 13% 3	730
	21st to end	Day	11% 5% 26% 31% 22% 5%	730
July	1st to 10th	Day	10% 5% 26% 30% 24% 5%	721
	11th to 20th	Day	13% 3 26% 34% 21% 4	718
	21st to end	Day	7% 6% 25% 36% 20% 7%	709
August	1st to 10th	Day	12% 5% 26% 31% 21% 6%	527
	11th to 20th	Day	10% 4 24% 35% 21% 6%	517
	21st to end	Day	11% 8% 23% 30% 19% 9%	583
September	1st to 10th	Day	12% 7% 27% 28% 19% 6%	530
	11th to 20th	Day	17% 6% 21% 33% 17% 5%	530
	21st to end	Day	14% 15% 28% 31% 10% 3	530
October	1st to 10th	Day	14% 6% 29% 32% 15% 4	452
	11th to 20th	Day	15% 10% 27% 30% 14% 3	330
	21st to end	Day	13% 15% 34% 24% 10% 3	363
November	1st to 10th	Day	16% 13% 28% 31% 9% 3	330
	11th to 20th	Day	12% 12% 31% 33% 9% 3	283
	21st to end	Day	5% 9% 35% 30% 14% 8%	220
December	1st to 10th	Day	5% 7% 32% 38% 14% 3	220
	11th to 20th	Day	5% 8% 37% 35% 10% 5%	220
	21st to end	Day	6% 5% 28% 39% 18% 4	242
January	1st to 10th	Night	9% 9% 36% 35% 10% 2	1050
	11th to 20th	Night	7% 7% 40% 36% 9% 1	1007
	21st to end	Night	9% 12% 35% 35% 9% 1	880
February	1st to 10th	Night	8% 9% 33% 33% 15% 4	800
	11th to 20th	Night	9% 6% 34% 37% 12% 1	784
	21st to end	Night	6% 6% 35% 31% 18% 3	660
March	1st to 10th	Night	6% 6% 35% 37% 13% 3	800
	11th to 20th	Night	7% 7% 36% 37% 11% 2	800
	21st to end	Night	14% 5% 32% 34% 12% 3	880
April	1st to 10th	Night	13% 7% 32% 33% 14% 1	751
	11th to 20th	Night	18% 6% 35% 31% 10%	593
	21st to end	Night	16% 8% 32% 32% 12%	600
May	1st to 10th	Night	16% 7% 27% 34% 15%	495
	11th to 20th	Night	15% 7% 27% 33% 18%	394
	21st to end	Night	20% 4 24% 33% 18% 1	433
June	1st to 10th	Night	18% 7% 27% 34% 13% 1	400
	11th to 20th	Night	19% 4 27% 35% 15% 1	400
	21st to end	Night	11% 3 20% 41% 25% 2	400
July	1st to 10th	Night	9% 2 18% 45% 24% 1	390
	11th to 20th	Night	13% 2 20% 44% 19% 2	388
	21st to end	Night	9% 2 18% 44% 24% 2	438
August	1st to 10th	Night	12% 2 12% 42% 29% 3	398
	11th to 20th	Night	8% 3 19% 44% 24% 2	556
	21st to end	Night	8% 4 21% 44% 22% 1	660
September	1st to 10th	Night	13% 3 23% 38% 21% 3	712
	11th to 20th	Night	18% 4 17% 38% 22% 2	800
	21st to end	Night	14% 5% 30% 35% 13% 3	800
October	1st to 10th	Night	16% 4 29% 34% 16% 2	800
	11th to 20th	Night	12% 5% 33% 35% 14% 2	800
	21st to end	Night	11% 7% 35% 34% 11% 1	880
November	1st to 10th	Night	14% 7% 39% 30% 9% 1	923
	11th to 20th	Night	9% 10% 41% 32% 7% 2	1050
	21st to end	Night	7% 6% 41% 35% 10% 2	1050
December	1st to 10th	Night	10% 7% 37% 32% 12% 2	1050
	11th to 20th	Night	5% 7% 38% 39% 9% 1	1050
	21st to end	Night	9% 5% 36% 37% 11% 2	1155

Page generated at 2026-01-13 23:14:24. Version ac07

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