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 2024-01-15.

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	10% 8% 4 7% 6% 4 5% 5% 6% 8% 37%	74628
	Night	7% 9% 4 7% 6% 4 5% 5% 6% 8% 38%	75149
Transparency	Day	43% 9% 15% 22% 10% 2	74314
	Night	41% 8% 15% 22% 11% 2	74981
Seeing	Day	13% 9% 27% 30% 16% 4	14192
	Night	11% 6% 31% 36% 14% 2	23443

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	4 9% 6% 9% 6% 2 6% 5% 7% 9% 36%	1329
	11th to 20th	Day	5% 9% 4 7% 6% 4 5% 5% 8% 10% 36%	1324
	21st to end	Day	5% 10% 4 9% 7% 5% 6% 5% 7% 9% 34%	1584
February	1st to 10th	Day	3 9% 5% 11% 8% 5% 7% 6% 7% 8% 30%	1440
	11th to 20th	Day	4 10% 6% 9% 8% 6% 7% 6% 7% 9% 29%	1558
	21st to end	Day	4 10% 6% 9% 9% 5% 6% 6% 7% 7% 31%	1448
March	1st to 10th	Day	4 10% 5% 10% 9% 5% 6% 6% 6% 8% 32%	1800
	11th to 20th	Day	4 10% 5% 6% 8% 4 6% 6% 7% 9% 36%	1947
	21st to end	Day	7% 14% 6% 10% 7% 4 7% 5% 6% 7% 26%	2217
April	1st to 10th	Day	9% 14% 5% 8% 7% 4 6% 5% 7% 8% 27%	2202
	11th to 20th	Day	12% 14% 5% 8% 6% 4 5% 5% 5% 7% 30%	2310
	21st to end	Day	11% 12% 4 7% 6% 4 5% 6% 5% 8% 29%	2340
May	1st to 10th	Day	13% 11% 4 8% 6% 4 6% 6% 6% 7% 28%	2459
	11th to 20th	Day	14% 7% 3 6% 6% 4 6% 6% 6% 8% 33%	2654
	21st to end	Day	21% 8% 3 7% 6% 4 5% 5% 7% 8% 27%	2917
June	1st to 10th	Day	18% 7% 3 7% 6% 5% 6% 6% 7% 8% 28%	2700
	11th to 20th	Day	22% 8% 3 7% 7% 4 6% 6% 6% 7% 25%	2700
	21st to end	Day	9% 4 3 5% 6% 3 5% 6% 7% 11% 41%	2700
July	1st to 10th	Day	9% 5% 2 5% 5% 4 5% 6% 7% 9% 41%	2700
	11th to 20th	Day	11% 3 2 4 5% 3 5% 6% 7% 9% 45%	2700
	21st to end	Day	5% 4 1 4 5% 3 5% 6% 6% 9% 53%	2862
August	1st to 10th	Day	10% 5% 2 4 5% 3 5% 5% 7% 9% 45%	2507
	11th to 20th	Day	9% 4 1 4 5% 2 4 5% 6% 9% 50%	2333
	21st to end	Day	10% 4 2 4 5% 3 5% 5% 7% 8% 48%	2574
September	1st to 10th	Day	11% 6% 2 5% 4 3 3 5% 4 7% 50%	2229
	11th to 20th	Day	14% 7% 3 5% 5% 2 4 4 4 8% 44%	1980
	21st to end	Day	9% 7% 4 5% 6% 3 4 4 5% 8% 44%	1980
October	1st to 10th	Day	12% 9% 3 7% 5% 4 4 5% 6% 6% 39%	1910
	11th to 20th	Day	9% 10% 3 6% 6% 3 5% 6% 5% 8% 39%	1656
	21st to end	Day	7% 10% 4 6% 6% 4 5% 6% 6% 7% 38%	1782
November	1st to 10th	Day	9% 13% 5% 7% 7% 4 4 4 6% 7% 33%	1562
	11th to 20th	Day	6% 9% 4 7% 6% 3 5% 5% 7% 7% 41%	1440
	21st to end	Day	4 10% 4 9% 5% 3 4 5% 7% 9% 39%	1330
December	1st to 10th	Day	4 8% 5% 11% 8% 5% 6% 6% 5% 8% 34%	1330
	11th to 20th	Day	3 11% 4 12% 8% 5% 6% 6% 7% 8% 31%	1682
	21st to end	Day	3 9% 3 8% 5% 4 4 5% 6% 8% 44%	2442
January	1st to 10th	Night	4 10% 5% 8% 9% 4 6% 6% 7% 9% 30%	2836
	11th to 20th	Night	4 8% 5% 9% 7% 4 6% 7% 7% 9% 33%	2740
	21st to end	Night	4 10% 4 8% 7% 3 6% 5% 8% 9% 36%	2772
February	1st to 10th	Night	4 8% 5% 9% 8% 5% 6% 5% 6% 8% 34%	2520
	11th to 20th	Night	5% 12% 5% 9% 6% 4 7% 6% 6% 9% 30%	2288
	21st to end	Night	3 9% 6% 12% 8% 5% 6% 5% 6% 6% 34%	1806
March	1st to 10th	Night	4 9% 5% 11% 9% 4 5% 5% 7% 8% 33%	2160
	11th to 20th	Night	4 10% 4 8% 7% 4 6% 6% 7% 9% 36%	2011
	21st to end	Night	6% 13% 7% 8% 6% 4 5% 6% 7% 8% 30%	2138
April	1st to 10th	Night	9% 13% 4 10% 7% 4 6% 5% 5% 8% 30%	1757
	11th to 20th	Night	12% 13% 5% 9% 6% 2 4 5% 6% 7% 31%	1601
	21st to end	Night	11% 11% 4 9% 5% 3 5% 6% 5% 8% 33%	1620
May	1st to 10th	Night	13% 9% 4 8% 7% 3 5% 5% 6% 8% 33%	1497
	11th to 20th	Night	11% 7% 3 5% 5% 3 5% 5% 6% 8% 42%	1239
	21st to end	Night	20% 5% 3 7% 6% 3 5% 5% 6% 8% 32%	1358
June	1st to 10th	Night	16% 7% 2 7% 5% 4 5% 5% 6% 8% 34%	1260
	11th to 20th	Night	19% 6% 3 7% 5% 3 6% 5% 6% 9% 32%	1260
	21st to end	Night	7% 5% 2 5% 4 5% 6% 6% 8% 10% 43%	1260
July	1st to 10th	Night	8% 4 2 4 5% 3 5% 4 6% 10% 48%	1260
	11th to 20th	Night	9% 5% 2 5% 4 4 6% 6% 6% 9% 45%	1260
	21st to end	Night	5% 4 2 4 3 2 3 5% 7% 8% 58%	1452
August	1st to 10th	Night	10% 4 2 5% 5% 3 3 5% 7% 9% 47%	1432
	11th to 20th	Night	8% 4 2 3 4 2 4 5% 6% 10% 51%	1568
	21st to end	Night	8% 4 2 4 3 2 4 5% 6% 8% 54%	1782
September	1st to 10th	Night	10% 7% 2 4 5% 2 3 4 6% 8% 48%	1728
	11th to 20th	Night	14% 7% 2 4 4 2 4 4 5% 7% 49%	1980
	21st to end	Night	10% 7% 2 4 4 3 4 4 6% 9% 46%	1980
October	1st to 10th	Night	11% 8% 3 5% 5% 3 5% 5% 6% 7% 41%	2049
	11th to 20th	Night	7% 8% 2 5% 6% 4 5% 6% 6% 8% 42%	2302
	21st to end	Night	6% 10% 4 7% 6% 3 5% 5% 7% 8% 39%	2574
November	1st to 10th	Night	8% 13% 5% 6% 5% 4 6% 5% 6% 7% 36%	2498
	11th to 20th	Night	4 9% 4 7% 6% 4 6% 5% 6% 8% 41%	2737
	21st to end	Night	4 9% 5% 7% 7% 4 5% 6% 5% 8% 40%	2850
December	1st to 10th	Night	4 10% 4 9% 8% 4 6% 6% 7% 8% 34%	2850
	11th to 20th	Night	2 8% 5% 10% 9% 5% 6% 6% 6% 10% 33%	3510
	21st to end	Night	3 8% 4 7% 6% 4 5% 6% 6% 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% 25% 8% 4	1329
	11th to 20th	Day	41% 9% 14% 23% 10% 3	1324
	21st to end	Day	46% 7% 15% 17% 13% 2	1584
February	1st to 10th	Day	48% 9% 15% 17% 8% 3	1440
	11th to 20th	Day	48% 9% 15% 19% 9% 1	1567
	21st to end	Day	49% 8% 13% 16% 12% 1	1448
March	1st to 10th	Day	47% 9% 17% 17% 8% 1	1800
	11th to 20th	Day	41% 9% 15% 22% 12% 2	1948
	21st to end	Day	53% 10% 14% 16% 6% 1	2217
April	1st to 10th	Day	51% 8% 16% 17% 7% 1	2202
	11th to 20th	Day	52% 6% 13% 19% 9% 1	2310
	21st to end	Day	50% 8% 14% 19% 8% 1	2340
May	1st to 10th	Day	51% 10% 14% 18% 7% 1	2459
	11th to 20th	Day	45% 8% 15% 22% 10% 1	2658
	21st to end	Day	52% 8% 15% 19% 6% 1	2918
June	1st to 10th	Day	51% 9% 14% 16% 8% 1	2700
	11th to 20th	Day	54% 10% 13% 16% 6% 2	2700
	21st to end	Day	35% 10% 20% 24% 9% 2	2700
July	1st to 10th	Day	35% 11% 18% 23% 11% 2	2626
	11th to 20th	Day	34% 10% 18% 26% 11% 1	2619
	21st to end	Day	26% 10% 16% 32% 15% 2	2703
August	1st to 10th	Day	34% 9% 17% 28% 9% 2	2490
	11th to 20th	Day	29% 9% 22% 28% 9% 2	2333
	21st to end	Day	31% 9% 16% 29% 13% 2	2574
September	1st to 10th	Day	34% 6% 17% 26% 14% 4	2229
	11th to 20th	Day	39% 7% 15% 25% 13% 2	1980
	21st to end	Day	37% 7% 15% 26% 12% 3	1980
October	1st to 10th	Day	44% 8% 13% 23% 10% 2	1910
	11th to 20th	Day	42% 8% 14% 24% 10% 3	1656
	21st to end	Day	42% 7% 16% 22% 11% 1	1782
November	1st to 10th	Day	49% 8% 11% 20% 11% 1	1562
	11th to 20th	Day	40% 8% 16% 25% 10% 1	1440
	21st to end	Day	39% 8% 18% 23% 10% 3	1330
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% 9% 13% 18% 10% 3	2836
	11th to 20th	Night	42% 10% 15% 22% 8% 4	2740
	21st to end	Night	42% 8% 14% 20% 14% 2	2772
February	1st to 10th	Night	45% 8% 13% 20% 11% 3	2520
	11th to 20th	Night	47% 9% 14% 19% 11% 1	2289
	21st to end	Night	48% 6% 11% 20% 12% 2	1806
March	1st to 10th	Night	45% 9% 14% 23% 7% 1	2160
	11th to 20th	Night	41% 8% 15% 22% 13% 1	2011
	21st to end	Night	49% 8% 16% 18% 8% 1	2138
April	1st to 10th	Night	51% 6% 13% 19% 10% 1	1757
	11th to 20th	Night	51% 7% 13% 19% 8% 1	1601
	21st to end	Night	47% 9% 14% 20% 9% 2	1620
May	1st to 10th	Night	48% 8% 13% 20% 11% 1	1497
	11th to 20th	Night	38% 9% 14% 29% 9% 2	1239
	21st to end	Night	48% 8% 15% 21% 7% 1	1358
June	1st to 10th	Night	47% 8% 14% 20% 10%	1260
	11th to 20th	Night	47% 10% 16% 18% 8% 2	1260
	21st to end	Night	34% 9% 20% 27% 9% 1	1260
July	1st to 10th	Night	31% 8% 21% 26% 12% 1	1225
	11th to 20th	Night	33% 10% 19% 24% 11% 2	1218
	21st to end	Night	24% 7% 16% 33% 18% 2	1371
August	1st to 10th	Night	32% 10% 16% 29% 10% 2	1424
	11th to 20th	Night	26% 9% 22% 30% 12% 1	1568
	21st to end	Night	26% 8% 16% 31% 16% 3	1782
September	1st to 10th	Night	33% 7% 17% 24% 16% 3	1728
	11th to 20th	Night	34% 7% 15% 27% 13% 4	1980
	21st to end	Night	33% 7% 18% 24% 14% 4	1980
October	1st to 10th	Night	39% 8% 15% 23% 13% 2	2049
	11th to 20th	Night	37% 8% 16% 25% 12% 3	2302
	21st to end	Night	42% 8% 15% 24% 11% 1	2574
November	1st to 10th	Night	45% 9% 12% 20% 12% 2	2498
	11th to 20th	Night	40% 8% 15% 21% 15% 1	2737
	21st to end	Night	40% 8% 17% 21% 11% 4	2850
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	8% 7% 25% 36% 22% 2	168
	21st to end	Day	8% 9% 22% 40% 18% 3	176
February	1st to 10th	Day	9% 13% 33% 35% 5% 6%	160
	11th to 20th	Day	9% 9% 34% 36% 11% 1	233
	21st to end	Day	5% 9% 30% 37% 17% 2	314
March	1st to 10th	Day	8% 12% 39% 26% 12% 4	420
	11th to 20th	Day	8% 13% 31% 32% 13% 3	420
	21st to end	Day	13% 16% 32% 24% 11% 4	462
April	1st to 10th	Day	14% 14% 37% 25% 8% 1	420
	11th to 20th	Day	20% 12% 27% 25% 12% 3	412
	21st to end	Day	18% 16% 27% 26% 11% 2	420
May	1st to 10th	Day	19% 12% 26% 25% 14% 4	450
	11th to 20th	Day	17% 6% 25% 26% 22% 4	625
	21st to end	Day	21% 5% 22% 28% 20% 5%	679
June	1st to 10th	Day	18% 9% 26% 31% 13% 3	630
	11th to 20th	Day	23% 10% 25% 28% 13% 3	630
	21st to end	Day	11% 4 27% 30% 22% 5%	630
July	1st to 10th	Day	10% 5% 24% 31% 24% 5%	621
	11th to 20th	Day	13% 4 27% 33% 20% 4	618
	21st to end	Day	6% 5% 26% 36% 21% 7%	608
August	1st to 10th	Day	13% 4 27% 30% 21% 5%	447
	11th to 20th	Day	11% 3 23% 36% 22% 6%	437
	21st to end	Day	11% 8% 24% 30% 19% 9%	495
September	1st to 10th	Day	14% 7% 30% 28% 17% 4	450
	11th to 20th	Day	18% 7% 22% 33% 16% 4	450
	21st to end	Day	16% 14% 26% 30% 11% 3	450
October	1st to 10th	Day	16% 7% 26% 29% 16% 5%	380
	11th to 20th	Day	16% 10% 25% 31% 13% 4	270
	21st to end	Day	13% 16% 33% 23% 12% 3	297
November	1st to 10th	Day	16% 11% 30% 31% 9% 3	270
	11th to 20th	Day	13% 12% 31% 33% 9% 2	232
	21st to end	Day	4 8% 35% 30% 14% 9%	180
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% 10% 1	900
	21st to end	Night	9% 12% 33% 36% 9% 1	792
February	1st to 10th	Night	8% 9% 34% 31% 15% 4	720
	11th to 20th	Night	10% 7% 35% 37% 11% 1	704
	21st to end	Night	6% 5% 32% 32% 20% 4	592
March	1st to 10th	Night	7% 6% 34% 37% 13% 3	720
	11th to 20th	Night	8% 8% 36% 36% 11% 2	720
	21st to end	Night	13% 5% 32% 35% 12% 3	792
April	1st to 10th	Night	13% 6% 30% 34% 15% 1	677
	11th to 20th	Night	20% 4 34% 31% 11%	533
	21st to end	Night	16% 7% 32% 32% 12%	540
May	1st to 10th	Night	16% 7% 27% 33% 17%	446
	11th to 20th	Night	14% 7% 26% 35% 18%	354
	21st to end	Night	22% 3 24% 34% 17% 1	389
June	1st to 10th	Night	19% 5% 27% 34% 14% 1	360
	11th to 20th	Night	20% 4 25% 35% 15% 1	360
	21st to end	Night	10% 3 19% 40% 26% 2	360
July	1st to 10th	Night	10% 2 17% 45% 25% 1	350
	11th to 20th	Night	12% 2 21% 45% 18% 3	348
	21st to end	Night	8% 2 18% 45% 24% 3	394
August	1st to 10th	Night	12% 2 13% 41% 29% 3	358
	11th to 20th	Night	9% 3 19% 43% 25% 2	500
	21st to end	Night	9% 4 21% 43% 23% 1	594
September	1st to 10th	Night	14% 3 24% 37% 20% 3	640
	11th to 20th	Night	18% 4 18% 38% 21% 2	720
	21st to end	Night	14% 4 29% 34% 15% 3	720
October	1st to 10th	Night	17% 3 27% 34% 17% 3	720
	11th to 20th	Night	12% 5% 32% 34% 15% 2	720
	21st to end	Night	12% 7% 34% 35% 11% 1	792
November	1st to 10th	Night	15% 6% 38% 30% 9% 1	833
	11th to 20th	Night	9% 10% 41% 32% 7% 1	950
	21st to end	Night	7% 6% 42% 33% 10% 2	950
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 2024-01-11 20:33:47. Version ac07

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