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 2024-11-25.

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% 9% 3 8% 5% 5% 5% 4 7% 8% 38%	105795
	Night	7% 9% 3 9% 5% 5% 5% 4 6% 8% 39%	102271
Transparency	Day	40% 8% 16% 24% 11% 2	105542
	Night	40% 8% 15% 23% 12% 2	102170
Seeing	Day	13% 9% 28% 30% 16% 4	15406
	Night	11% 6% 31% 36% 14% 2	24479

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	3 8% 6% 13% 6% 4 4 4 8% 9% 35%	2219
	11th to 20th	Day	3 9% 4 11% 6% 6% 5% 5% 8% 8% 35%	2263
	21st to end	Day	4 8% 3 8% 6% 6% 6% 4 6% 10% 40%	2794
February	1st to 10th	Day	4 11% 4 13% 7% 7% 7% 5% 7% 8% 30%	1520
	11th to 20th	Day	4 11% 5% 10% 7% 7% 6% 5% 8% 8% 30%	1647
	21st to end	Day	3 12% 5% 11% 8% 7% 6% 4 7% 7% 31%	1536
March	1st to 10th	Day	2 10% 4 12% 7% 6% 8% 4 6% 7% 32%	3138
	11th to 20th	Day	6% 9% 3 6% 5% 4 4 4 6% 9% 45%	3444
	21st to end	Day	8% 21% 7% 13% 6% 4 5% 3 5% 6% 22%	3902
April	1st to 10th	Day	8% 16% 4 10% 6% 5% 5% 4 7% 8% 27%	2325
	11th to 20th	Day	11% 14% 5% 8% 5% 5% 4 4 6% 7% 30%	2440
	21st to end	Day	11% 13% 4 8% 6% 5% 5% 5% 6% 8% 29%	2470
May	1st to 10th	Day	18% 14% 4 7% 5% 4 5% 4 5% 6% 28%	4335
	11th to 20th	Day	11% 8% 4 8% 6% 6% 6% 6% 8% 8% 29%	4694
	21st to end	Day	17% 10% 4 11% 7% 6% 6% 4 7% 7% 23%	5161
June	1st to 10th	Day	17% 8% 3 7% 6% 6% 6% 5% 7% 8% 28%	2850
	11th to 20th	Day	20% 9% 3 7% 6% 5% 5% 5% 6% 7% 26%	2850
	21st to end	Day	9% 5% 2 6% 5% 5% 5% 5% 8% 10% 40%	2850
July	1st to 10th	Day	7% 5% 2 6% 4 5% 5% 4 7% 7% 48%	4740
	11th to 20th	Day	7% 3 1 4 3 4 5% 5% 8% 10% 50%	4740
	21st to end	Day	4 3 1 4 4 3 4 5% 6% 9% 57%	4995
August	1st to 10th	Day	9% 5% 2 6% 4 4 5% 5% 9% 9% 42%	4401
	11th to 20th	Day	7% 5% 2 5% 4 4 5% 5% 8% 10% 44%	4086
	21st to end	Day	9% 4 2 4 3 3 4 3 6% 8% 52%	4521
September	1st to 10th	Day	10% 6% 2 6% 3 3 4 3 5% 7% 50%	2352
	11th to 20th	Day	14% 7% 3 5% 4 2 5% 3 5% 7% 44%	2090
	21st to end	Day	8% 8% 3 6% 4 4 5% 3 6% 8% 44%	2090
October	1st to 10th	Day	7% 6% 2 7% 4 5% 4 4 7% 8% 44%	3364
	11th to 20th	Day	5% 7% 2 6% 4 5% 5% 5% 7% 10% 42%	2904
	21st to end	Day	7% 7% 3 7% 5% 5% 5% 4 5% 7% 46%	3101
November	1st to 10th	Day	8% 15% 4 8% 7% 5% 4 4 6% 7% 33%	1646
	11th to 20th	Day	5% 11% 4 8% 5% 5% 5% 4 7% 7% 40%	1515
	21st to end	Day	4 12% 4 10% 5% 5% 4 3 8% 9% 38%	1358
December	1st to 10th	Day	4 10% 5% 12% 7% 6% 5% 5% 6% 8% 34%	1330
	11th to 20th	Day	3 11% 5% 13% 7% 6% 6% 5% 7% 8% 30%	1682
	21st to end	Day	3 10% 3 9% 4 5% 4 4 6% 8% 44%	2442
January	1st to 10th	Night	4 11% 5% 12% 7% 6% 6% 5% 7% 8% 27%	4726
	11th to 20th	Night	3 7% 5% 13% 6% 5% 7% 6% 6% 8% 33%	4664
	21st to end	Night	4 10% 4 10% 6% 5% 5% 4 7% 8% 38%	4862
February	1st to 10th	Night	4 11% 4 11% 6% 7% 6% 4 6% 8% 33%	2660
	11th to 20th	Night	4 13% 5% 10% 5% 5% 6% 5% 7% 9% 31%	2419
	21st to end	Night	2 10% 4 13% 7% 6% 5% 4 7% 6% 35%	1916
March	1st to 10th	Night	2 8% 4 15% 8% 8% 7% 5% 7% 8% 29%	3736
	11th to 20th	Night	5% 8% 2 6% 4 4 5% 4 6% 9% 46%	3534
	21st to end	Night	10% 20% 7% 13% 6% 4 4 3 5% 5% 21%	3750
April	1st to 10th	Night	9% 14% 3 11% 5% 6% 5% 4 5% 7% 30%	1854
	11th to 20th	Night	11% 13% 4 10% 5% 4 4 4 6% 7% 31%	1691
	21st to end	Night	11% 12% 4 9% 5% 4 5% 5% 5% 8% 33%	1710
May	1st to 10th	Night	19% 13% 3 9% 5% 4 4 3 5% 6% 31%	2625
	11th to 20th	Night	11% 9% 3 7% 6% 4 5% 4 8% 9% 35%	2199
	21st to end	Night	15% 9% 3 10% 5% 6% 6% 5% 7% 7% 27%	2414
June	1st to 10th	Night	16% 8% 2 8% 5% 5% 5% 3 6% 8% 34%	1330
	11th to 20th	Night	18% 7% 3 7% 5% 4 6% 3 6% 9% 32%	1330
	21st to end	Night	7% 5% 2 6% 4 7% 5% 5% 8% 9% 42%	1330
July	1st to 10th	Night	7% 4 2 7% 6% 5% 4 3 5% 7% 49%	2220
	11th to 20th	Night	6% 3 1 4 3 4 5% 4 7% 11% 50%	2220
	21st to end	Night	4 4 2 4 3 3 4 3 5% 7% 60%	2554
August	1st to 10th	Night	10% 6% 2 7% 4 4 4 5% 8% 9% 42%	2529
	11th to 20th	Night	6% 4 2 5% 5% 4 5% 5% 7% 10% 46%	2751
	21st to end	Night	9% 4 1 4 3 3 4 4 6% 8% 54%	3146
September	1st to 10th	Night	10% 7% 2 4 4 3 4 3 6% 8% 49%	1825
	11th to 20th	Night	14% 7% 2 4 3 2 4 3 5% 7% 49%	2090
	21st to end	Night	10% 7% 2 5% 3 4 4 3 7% 9% 47%	2090
October	1st to 10th	Night	8% 6% 2 5% 3 4 5% 4 6% 8% 49%	3611
	11th to 20th	Night	5% 7% 2 5% 4 5% 5% 4 6% 8% 49%	4022
	21st to end	Night	5% 9% 3 7% 4 5% 5% 4 6% 7% 46%	4457
November	1st to 10th	Night	7% 14% 4 7% 5% 5% 5% 4 6% 6% 36%	2633
	11th to 20th	Night	4 10% 4 9% 5% 6% 5% 4 6% 8% 39%	2882
	21st to end	Night	4 11% 3 9% 6% 5% 5% 4 5% 8% 39%	2917
December	1st to 10th	Night	4 11% 4 10% 7% 5% 5% 5% 6% 8% 34%	2850
	11th to 20th	Night	2 9% 4 12% 7% 7% 5% 5% 7% 9% 33%	3510
	21st to end	Night	3 8% 4 9% 5% 5% 5% 4 7% 7% 43%	5214

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% 7% 14% 24% 10% 3	2219
	11th to 20th	Day	43% 7% 11% 17% 18% 4	2284
	21st to end	Day	36% 9% 16% 29% 9% 1	2794
February	1st to 10th	Day	49% 8% 15% 17% 9% 3	1520
	11th to 20th	Day	47% 8% 15% 18% 10% 2	1656
	21st to end	Day	48% 8% 13% 17% 12% 1	1536
March	1st to 10th	Day	47% 8% 16% 16% 13% 1	3138
	11th to 20th	Day	34% 7% 19% 26% 13% 1	3445
	21st to end	Day	59% 10% 12% 14% 5%	3902
April	1st to 10th	Day	51% 8% 16% 17% 7% 1	2325
	11th to 20th	Day	51% 6% 14% 19% 9% 1	2440
	21st to end	Day	50% 8% 14% 19% 8% 1	2470
May	1st to 10th	Day	55% 8% 10% 23% 4	4335
	11th to 20th	Day	44% 9% 15% 22% 9%	4698
	21st to end	Day	55% 8% 16% 14% 7% 1	5162
June	1st to 10th	Day	50% 9% 15% 16% 8% 1	2850
	11th to 20th	Day	53% 10% 13% 16% 7% 2	2850
	21st to end	Day	35% 9% 20% 23% 10% 2	2850
July	1st to 10th	Day	30% 9% 14% 26% 16% 4	4666
	11th to 20th	Day	25% 9% 19% 33% 12% 2	4659
	21st to end	Day	21% 8% 12% 29% 24% 7%	4837
August	1st to 10th	Day	33% 10% 16% 35% 6% 1	4384
	11th to 20th	Day	30% 10% 25% 27% 6% 1	4126
	21st to end	Day	28% 7% 18% 33% 12% 1	4520
September	1st to 10th	Day	33% 6% 16% 25% 15% 5%	2352
	11th to 20th	Day	39% 7% 16% 24% 13% 2	2090
	21st to end	Day	36% 7% 15% 26% 12% 3	2090
October	1st to 10th	Day	34% 8% 17% 34% 7% 1	3364
	11th to 20th	Day	33% 8% 21% 23% 12% 3	2904
	21st to end	Day	36% 6% 13% 32% 12% 1	3101
November	1st to 10th	Day	49% 8% 12% 20% 11% 1	1646
	11th to 20th	Day	41% 8% 16% 24% 10% 2	1515
	21st to end	Day	40% 8% 18% 22% 9% 3	1358
December	1st to 10th	Day	46% 8% 13% 17% 12% 3	1330
	11th to 20th	Day	47% 11% 15% 18% 8% 1	1684
	21st to end	Day	34% 7% 12% 23% 18% 5%	2442
January	1st to 10th	Night	47% 11% 12% 20% 7% 2	4726
	11th to 20th	Night	46% 8% 12% 16% 14% 5%	4705
	21st to end	Night	40% 9% 14% 24% 11% 1	4862
February	1st to 10th	Night	47% 8% 12% 19% 11% 3	2660
	11th to 20th	Night	46% 8% 14% 19% 12% 1	2420
	21st to end	Night	47% 6% 11% 22% 12% 2	1916
March	1st to 10th	Night	46% 9% 13% 21% 9% 1	3736
	11th to 20th	Night	32% 9% 20% 23% 15% 1	3534
	21st to end	Night	62% 7% 11% 14% 5% 1	3750
April	1st to 10th	Night	51% 6% 13% 19% 10% 1	1854
	11th to 20th	Night	50% 7% 13% 20% 9% 1	1691
	21st to end	Night	47% 9% 13% 20% 9% 2	1710
May	1st to 10th	Night	53% 7% 10% 23% 6%	2625
	11th to 20th	Night	40% 9% 13% 29% 8% 1	2199
	21st to end	Night	48% 12% 14% 17% 8% 1	2414
June	1st to 10th	Night	47% 8% 14% 20% 10% 1	1330
	11th to 20th	Night	47% 10% 16% 17% 8% 2	1330
	21st to end	Night	34% 9% 20% 27% 9% 1	1330
July	1st to 10th	Night	33% 8% 15% 25% 17% 3	2185
	11th to 20th	Night	24% 9% 22% 31% 9% 4	2178
	21st to end	Night	23% 6% 10% 32% 23% 5%	2473
August	1st to 10th	Night	35% 8% 15% 29% 12% 1	2521
	11th to 20th	Night	29% 9% 27% 25% 8% 1	2777
	21st to end	Night	25% 7% 21% 32% 12% 2	3146
September	1st to 10th	Night	32% 7% 17% 24% 16% 4	1825
	11th to 20th	Night	34% 7% 15% 27% 12% 4	2090
	21st to end	Night	32% 7% 18% 25% 14% 4	2090
October	1st to 10th	Night	31% 7% 17% 25% 19% 1	3611
	11th to 20th	Night	31% 7% 19% 26% 15% 2	4022
	21st to end	Night	36% 6% 12% 32% 13%	4457
November	1st to 10th	Night	45% 9% 12% 20% 12% 2	2633
	11th to 20th	Night	41% 8% 15% 21% 14% 1	2882
	21st to end	Night	41% 8% 17% 21% 10% 3	2917
December	1st to 10th	Night	45% 7% 14% 20% 10% 4	2850
	11th to 20th	Night	43% 12% 17% 21% 7% 1	3507
	21st to end	Night	36% 7% 13% 24% 14% 5%	5214

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% 21% 43% 12% 11%	180
	11th to 20th	Day	7% 8% 27% 34% 21% 2	180
	21st to end	Day	7% 8% 22% 41% 19% 3	198
February	1st to 10th	Day	9% 12% 31% 34% 8% 6%	180
	11th to 20th	Day	8% 8% 32% 37% 13% 2	262
	21st to end	Day	5% 11% 30% 36% 16% 2	348
March	1st to 10th	Day	8% 12% 39% 27% 11% 3	460
	11th to 20th	Day	8% 12% 31% 33% 13% 3	460
	21st to end	Day	13% 17% 31% 24% 11% 4	506
April	1st to 10th	Day	14% 15% 38% 24% 8% 1	460
	11th to 20th	Day	19% 12% 28% 26% 12% 3	452
	21st to end	Day	17% 16% 28% 26% 10% 3	460
May	1st to 10th	Day	19% 12% 26% 25% 14% 4	492
	11th to 20th	Day	16% 7% 25% 27% 21% 4	675
	21st to end	Day	20% 6% 21% 29% 19% 5%	734
June	1st to 10th	Day	17% 10% 27% 30% 13% 3	680
	11th to 20th	Day	22% 11% 25% 27% 13% 3	680
	21st to end	Day	11% 5% 27% 30% 21% 5%	680
July	1st to 10th	Day	10% 5% 25% 30% 24% 5%	671
	11th to 20th	Day	12% 3 26% 33% 21% 4	668
	21st to end	Day	5% 5% 26% 35% 21% 7%	658
August	1st to 10th	Day	13% 4 26% 32% 20% 5%	487
	11th to 20th	Day	10% 3 23% 36% 22% 6%	477
	21st to end	Day	12% 8% 24% 29% 19% 8%	539
September	1st to 10th	Day	13% 7% 29% 28% 18% 5%	490
	11th to 20th	Day	19% 7% 23% 32% 16% 4	490
	21st to end	Day	15% 15% 27% 30% 10% 3	490
October	1st to 10th	Day	15% 7% 28% 31% 15% 4	416
	11th to 20th	Day	15% 10% 26% 31% 14% 4	300
	21st to end	Day	14% 15% 34% 23% 11% 4	330
November	1st to 10th	Day	15% 12% 29% 32% 10% 3	300
	11th to 20th	Day	12% 12% 32% 32% 9% 2	257
	21st to end	Day	5% 7% 35% 30% 14% 9%	188
December	1st to 10th	Day	6% 5% 29% 41% 15% 4	180
	11th to 20th	Day	5% 8% 37% 36% 10% 5%	180
	21st to end	Day	7% 5% 25% 38% 20% 5%	198
January	1st to 10th	Night	8% 9% 35% 36% 10% 2	950
	11th to 20th	Night	7% 7% 37% 38% 9% 1	928
	21st to end	Night	9% 11% 33% 37% 9% 1	836
February	1st to 10th	Night	8% 9% 33% 31% 15% 4	760
	11th to 20th	Night	9% 7% 34% 37% 12% 1	744
	21st to end	Night	6% 5% 34% 32% 19% 4	628
March	1st to 10th	Night	6% 6% 35% 36% 13% 3	760
	11th to 20th	Night	8% 7% 36% 37% 11% 2	760
	21st to end	Night	14% 5% 31% 35% 12% 3	836
April	1st to 10th	Night	14% 7% 31% 33% 14% 1	714
	11th to 20th	Night	19% 5% 34% 32% 11%	563
	21st to end	Night	16% 8% 32% 32% 12%	570
May	1st to 10th	Night	17% 7% 27% 33% 16%	470
	11th to 20th	Night	14% 7% 26% 35% 18%	374
	21st to end	Night	21% 4 24% 33% 18% 1	411
June	1st to 10th	Night	18% 6% 28% 33% 13% 1	380
	11th to 20th	Night	19% 4 27% 34% 15% 1	380
	21st to end	Night	10% 3 20% 40% 25% 2	380
July	1st to 10th	Night	10% 2 18% 45% 24% 1	370
	11th to 20th	Night	11% 2 21% 44% 20% 2	368
	21st to end	Night	8% 2 19% 45% 24% 2	416
August	1st to 10th	Night	12% 2 13% 41% 29% 3	378
	11th to 20th	Night	8% 2 19% 43% 25% 2	528
	21st to end	Night	9% 4 21% 43% 22% 1	627
September	1st to 10th	Night	13% 3 23% 38% 20% 3	676
	11th to 20th	Night	18% 4 17% 38% 21% 2	760
	21st to end	Night	14% 5% 30% 34% 14% 3	760
October	1st to 10th	Night	16% 3 28% 34% 16% 2	760
	11th to 20th	Night	12% 5% 32% 35% 15% 2	760
	21st to end	Night	11% 7% 34% 35% 12% 1	836
November	1st to 10th	Night	15% 7% 38% 30% 9% 1	878
	11th to 20th	Night	9% 10% 41% 31% 7% 2	1000
	21st to end	Night	7% 6% 42% 33% 10% 2	973
December	1st to 10th	Night	10% 7% 36% 33% 13% 2	950
	11th to 20th	Night	5% 7% 38% 40% 10% 1	950
	21st to end	Night	9% 5% 36% 37% 11% 2	1045

Page generated at 2024-11-22 06:02:26. Version ac07

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