Ossian Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ossian Observatory clear sky chart from 2005-11-06 to 2024-01-22.

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	15% 12% 5% 8% 7% 4 5% 5% 5% 7% 28%	74765
	Night	14% 12% 5% 9% 7% 4 5% 5% 5% 6% 28%	75170
Transparency	Day	55% 7% 11% 17% 9% 1	74477
	Night	55% 7% 12% 17% 8% 1	74992
Seeing	Day	25% 19% 29% 17% 8% 3	13512
	Night	24% 19% 26% 21% 9% 1	22996

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	9% 18% 11% 14% 9% 4 7% 4 5% 4 15%	1517
	11th to 20th	Day	12% 19% 7% 15% 10% 5% 5% 4 4 4 14%	1615
	21st to end	Day	8% 17% 10% 15% 13% 5% 6% 6% 4 5% 12%	1791
February	1st to 10th	Day	15% 17% 7% 14% 11% 4 5% 4 3 4 15%	1620
	11th to 20th	Day	12% 16% 9% 15% 9% 3 5% 4 3 5% 18%	1573
	21st to end	Day	18% 15% 5% 13% 8% 4 4 3 4 6% 20%	1443
March	1st to 10th	Day	13% 14% 8% 14% 7% 4 4 3 4 5% 24%	1931
	11th to 20th	Day	13% 17% 7% 9% 6% 3 4 4 5% 6% 27%	1980
	21st to end	Day	17% 14% 6% 8% 7% 4 5% 4 4 5% 26%	2204
April	1st to 10th	Day	14% 17% 6% 8% 5% 3 4 4 4 7% 29%	2160
	11th to 20th	Day	18% 12% 3 7% 5% 4 5% 4 4 5% 33%	2134
	21st to end	Day	19% 13% 4 7% 5% 3 4 5% 4 5% 30%	2270
May	1st to 10th	Day	17% 12% 4 7% 7% 3 5% 4 5% 7% 30%	2380
	11th to 20th	Day	17% 9% 3 7% 6% 4 6% 4 5% 7% 32%	2478
	21st to end	Day	13% 7% 3 6% 6% 4 5% 5% 6% 8% 38%	2725
June	1st to 10th	Day	17% 7% 3 6% 6% 3 5% 6% 6% 7% 35%	2520
	11th to 20th	Day	14% 7% 3 7% 6% 4 5% 5% 6% 9% 35%	2520
	21st to end	Day	14% 6% 2 6% 6% 3 6% 5% 6% 9% 37%	2520
July	1st to 10th	Day	10% 6% 3 6% 6% 4 6% 7% 6% 9% 38%	2520
	11th to 20th	Day	11% 6% 3 6% 7% 4 6% 6% 8% 10% 34%	2520
	21st to end	Day	11% 7% 3 6% 7% 4 7% 7% 7% 8% 32%	2631
August	1st to 10th	Day	11% 5% 2 6% 7% 5% 6% 6% 7% 10% 36%	2327
	11th to 20th	Day	12% 7% 3 7% 8% 4 6% 6% 8% 9% 30%	2303
	21st to end	Day	14% 7% 3 7% 7% 5% 5% 6% 6% 9% 32%	2381
September	1st to 10th	Day	18% 7% 3 6% 5% 4 5% 4 6% 7% 37%	2160
	11th to 20th	Day	15% 6% 2 5% 5% 3 4 4 5% 7% 42%	2160
	21st to end	Day	16% 8% 3 7% 7% 3 6% 5% 6% 7% 33%	1877
October	1st to 10th	Day	19% 11% 3 6% 6% 3 4 5% 5% 8% 32%	1800
	11th to 20th	Day	21% 12% 4 8% 6% 4 4 5% 4 6% 27%	1800
	21st to end	Day	25% 16% 3 8% 6% 3 4 3 4 5% 23%	1980
November	1st to 10th	Day	13% 16% 5% 7% 5% 3 5% 5% 5% 5% 32%	1687
	11th to 20th	Day	14% 18% 6% 8% 6% 3 4 5% 5% 7% 23%	1520
	21st to end	Day	16% 19% 7% 10% 6% 3 4 4 5% 5% 21%	1520
December	1st to 10th	Day	17% 19% 9% 15% 7% 2 4 4 4 5% 13%	1520
	11th to 20th	Day	15% 19% 8% 14% 7% 3 4 4 4 5% 16%	1906
	21st to end	Day	21% 22% 9% 12% 7% 3 3 4 3 4 11%	2772
January	1st to 10th	Night	12% 17% 7% 15% 9% 4 7% 5% 5% 5% 14%	2649
	11th to 20th	Night	12% 17% 8% 13% 11% 6% 5% 4 5% 5% 13%	2563
	21st to end	Night	9% 15% 9% 14% 12% 7% 7% 5% 4 4 14%	2599
February	1st to 10th	Night	14% 16% 7% 13% 12% 4 6% 4 4 4 16%	2340
	11th to 20th	Night	11% 15% 7% 14% 10% 4 7% 6% 4 6% 17%	2273
	21st to end	Night	15% 14% 6% 15% 9% 3 4 4 5% 5% 21%	1812
March	1st to 10th	Night	11% 14% 7% 13% 9% 4 4 5% 5% 5% 23%	2014
	11th to 20th	Night	15% 15% 6% 9% 7% 3 4 4 4 5% 29%	1979
	21st to end	Night	14% 15% 5% 9% 6% 3 5% 4 5% 5% 29%	2151
April	1st to 10th	Night	15% 14% 6% 7% 5% 3 4 5% 5% 6% 30%	1800
	11th to 20th	Night	18% 12% 3 6% 5% 3 4 5% 4 5% 34%	1775
	21st to end	Night	16% 12% 4 7% 5% 2 4 4 5% 8% 33%	1706
May	1st to 10th	Night	17% 11% 4 6% 7% 3 5% 5% 5% 7% 31%	1580
	11th to 20th	Night	13% 7% 3 6% 6% 4 6% 5% 6% 8% 36%	1415
	21st to end	Night	12% 6% 2 5% 5% 3 4 5% 4 8% 46%	1550
June	1st to 10th	Night	15% 6% 2 6% 5% 3 5% 6% 7% 8% 37%	1440
	11th to 20th	Night	12% 6% 3 6% 5% 3 4 6% 7% 9% 41%	1440
	21st to end	Night	9% 5% 3 7% 5% 4 5% 6% 6% 8% 44%	1440
July	1st to 10th	Night	8% 5% 2 6% 6% 4 4 5% 6% 9% 45%	1440
	11th to 20th	Night	9% 4 3 4 5% 4 5% 5% 6% 8% 48%	1440
	21st to end	Night	12% 4 2 5% 4 4 6% 5% 7% 8% 43%	1684
August	1st to 10th	Night	8% 6% 2 4 6% 4 6% 5% 7% 8% 45%	1611
	11th to 20th	Night	12% 6% 2 5% 5% 3 4 6% 5% 9% 41%	1598
	21st to end	Night	12% 5% 2 6% 5% 2 5% 5% 6% 8% 43%	1956
September	1st to 10th	Night	15% 6% 2 4 5% 3 4 4 5% 8% 45%	1800
	11th to 20th	Night	15% 6% 2 5% 4 2 4 4 5% 8% 46%	1800
	21st to end	Night	16% 7% 3 5% 5% 4 5% 5% 5% 7% 38%	2078
October	1st to 10th	Night	16% 8% 3 6% 6% 3 4 4 5% 8% 36%	2160
	11th to 20th	Night	19% 10% 3 7% 5% 3 4 5% 5% 7% 31%	2160
	21st to end	Night	26% 13% 4 7% 5% 3 4 4 4 6% 26%	2376
November	1st to 10th	Night	14% 13% 4 6% 4 3 4 4 5% 7% 36%	2390
	11th to 20th	Night	15% 15% 4 7% 6% 4 5% 6% 5% 7% 26%	2659
	21st to end	Night	14% 16% 6% 11% 7% 4 5% 5% 5% 5% 22%	2660
December	1st to 10th	Night	15% 20% 8% 11% 8% 4 6% 6% 4 5% 13%	2660
	11th to 20th	Night	15% 19% 8% 13% 8% 3 4 4 4 4 17%	3288
	21st to end	Night	22% 19% 10% 10% 7% 3 5% 5% 5% 5% 10%	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	70% 6% 10% 10% 5%	1518
	11th to 20th	Day	73% 6% 8% 8% 4	1615
	21st to end	Day	73% 5% 8% 8% 4	1791
February	1st to 10th	Day	73% 6% 9% 8% 3	1620
	11th to 20th	Day	69% 5% 6% 13% 6%	1582
	21st to end	Day	64% 5% 10% 14% 6% 1	1443
March	1st to 10th	Day	62% 5% 11% 16% 5% 1	1934
	11th to 20th	Day	59% 5% 11% 14% 10% 2	1980
	21st to end	Day	61% 4 6% 17% 10% 2	2204
April	1st to 10th	Day	56% 5% 10% 17% 10% 2	2160
	11th to 20th	Day	52% 6% 10% 17% 14% 1	2134
	21st to end	Day	55% 6% 9% 17% 13% 1	2270
May	1st to 10th	Day	54% 6% 9% 19% 10% 2	2380
	11th to 20th	Day	51% 7% 10% 18% 12% 1	2482
	21st to end	Day	43% 9% 14% 21% 12% 1	2725
June	1st to 10th	Day	47% 7% 12% 19% 14% 1	2520
	11th to 20th	Day	45% 7% 14% 21% 11% 1	2520
	21st to end	Day	43% 9% 13% 21% 13%	2520
July	1st to 10th	Day	41% 9% 13% 24% 11% 1	2450
	11th to 20th	Day	41% 9% 16% 22% 11%	2445
	21st to end	Day	46% 10% 13% 20% 11% 1	2484
August	1st to 10th	Day	40% 9% 16% 23% 11% 1	2314
	11th to 20th	Day	47% 10% 14% 21% 7% 1	2303
	21st to end	Day	47% 8% 13% 22% 9% 2	2381
September	1st to 10th	Day	45% 7% 12% 23% 11% 2	2160
	11th to 20th	Day	41% 7% 12% 26% 14% 1	2160
	21st to end	Day	48% 8% 11% 21% 11% 1	1877
October	1st to 10th	Day	50% 6% 13% 17% 12% 1	1800
	11th to 20th	Day	56% 7% 12% 16% 8% 1	1800
	21st to end	Day	63% 5% 10% 13% 6% 2	1980
November	1st to 10th	Day	52% 7% 12% 16% 11% 2	1687
	11th to 20th	Day	60% 6% 12% 15% 5% 2	1520
	21st to end	Day	65% 6% 11% 13% 4	1520
December	1st to 10th	Day	72% 6% 9% 9% 3	1520
	11th to 20th	Day	70% 6% 13% 9% 3 1	1906
	21st to end	Day	77% 5% 8% 8% 1	2772
January	1st to 10th	Night	71% 6% 8% 10% 4	2649
	11th to 20th	Night	72% 7% 10% 7% 4	2563
	21st to end	Night	72% 6% 8% 9% 5% 1	2599
February	1st to 10th	Night	70% 7% 9% 9% 5%	2340
	11th to 20th	Night	67% 6% 10% 12% 5%	2275
	21st to end	Night	64% 6% 10% 12% 8% 1	1812
March	1st to 10th	Night	63% 5% 10% 16% 5% 1	2024
	11th to 20th	Night	58% 5% 10% 16% 9% 1	1980
	21st to end	Night	57% 6% 8% 15% 12% 2	2151
April	1st to 10th	Night	55% 6% 11% 18% 10% 1	1800
	11th to 20th	Night	52% 6% 11% 17% 13% 1	1775
	21st to end	Night	49% 7% 11% 19% 12% 2	1706
May	1st to 10th	Night	53% 7% 10% 18% 11% 1	1580
	11th to 20th	Night	44% 9% 13% 21% 13% 1	1416
	21st to end	Night	37% 9% 16% 21% 15% 2	1551
June	1st to 10th	Night	41% 8% 13% 23% 14% 1	1440
	11th to 20th	Night	38% 9% 15% 23% 13% 2	1440
	21st to end	Night	36% 10% 15% 25% 13% 2	1440
July	1st to 10th	Night	35% 9% 14% 25% 15% 2	1400
	11th to 20th	Night	34% 8% 13% 28% 16% 1	1392
	21st to end	Night	36% 8% 17% 24% 14% 1	1590
August	1st to 10th	Night	35% 8% 17% 29% 10% 1	1600
	11th to 20th	Night	38% 9% 17% 28% 8%	1598
	21st to end	Night	37% 9% 14% 27% 11% 2	1956
September	1st to 10th	Night	37% 8% 16% 26% 11% 2	1800
	11th to 20th	Night	36% 7% 13% 28% 15% 1	1800
	21st to end	Night	43% 9% 13% 22% 13% 1	2078
October	1st to 10th	Night	46% 8% 13% 19% 13% 1	2160
	11th to 20th	Night	50% 7% 15% 17% 9% 1	2160
	21st to end	Night	60% 6% 12% 15% 6% 1	2376
November	1st to 10th	Night	48% 7% 11% 21% 10% 3	2390
	11th to 20th	Night	57% 7% 12% 15% 6% 2	2659
	21st to end	Night	62% 7% 14% 13% 4	2660
December	1st to 10th	Night	71% 8% 10% 9% 2	2660
	11th to 20th	Night	70% 6% 10% 11% 2	3288
	21st to end	Night	74% 7% 9% 8% 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	36% 26% 25% 10% 3 1	180
	11th to 20th	Day	32% 39% 23% 4 1	225
	21st to end	Day	24% 37% 29% 7% 3	267
February	1st to 10th	Day	40% 33% 23% 4	240
	11th to 20th	Day	40% 31% 27% 2	240
	21st to end	Day	41% 26% 26% 7% 1	309
March	1st to 10th	Day	32% 28% 28% 10% 3	420
	11th to 20th	Day	32% 25% 30% 9% 4	420
	21st to end	Day	36% 20% 28% 11% 3 2	462
April	1st to 10th	Day	33% 23% 27% 10% 6% 1	420
	11th to 20th	Day	33% 20% 25% 13% 6% 3	412
	21st to end	Day	31% 21% 29% 13% 5% 1	420
May	1st to 10th	Day	30% 20% 26% 14% 7% 3	423
	11th to 20th	Day	23% 17% 31% 19% 8% 2	447
	21st to end	Day	18% 15% 30% 22% 11% 4	485
June	1st to 10th	Day	21% 18% 32% 19% 8% 2	450
	11th to 20th	Day	18% 13% 34% 20% 12% 3	450
	21st to end	Day	16% 14% 38% 22% 7% 3	450
July	1st to 10th	Day	13% 10% 27% 31% 15% 4	445
	11th to 20th	Day	12% 9% 32% 28% 13% 5%	444
	21st to end	Day	14% 11% 39% 24% 9% 4	488
August	1st to 10th	Day	11% 11% 29% 26% 17% 6%	446
	11th to 20th	Day	14% 8% 34% 22% 15% 7%	439
	21st to end	Day	13% 14% 29% 22% 14% 7%	495
September	1st to 10th	Day	19% 12% 26% 23% 13% 7%	450
	11th to 20th	Day	15% 11% 26% 22% 18% 9%	450
	21st to end	Day	18% 17% 29% 19% 13% 4	450
October	1st to 10th	Day	24% 14% 26% 20% 12% 4	450
	11th to 20th	Day	25% 26% 28% 16% 5% 1	450
	21st to end	Day	38% 21% 25% 15% 3	495
November	1st to 10th	Day	28% 20% 25% 17% 8% 2	372
	11th to 20th	Day	38% 23% 24% 12% 1 1	180
	21st to end	Day	35% 25% 32% 8%	180
December	1st to 10th	Day	41% 19% 29% 7% 3 1	180
	11th to 20th	Day	43% 22% 26% 8% 1	180
	21st to end	Day	32% 32% 29% 6% 1	198
January	1st to 10th	Night	29% 27% 29% 12% 3	760
	11th to 20th	Night	28% 27% 28% 13% 3	760
	21st to end	Night	23% 29% 31% 15% 2	800
February	1st to 10th	Night	30% 29% 28% 12%	720
	11th to 20th	Night	30% 29% 28% 11% 2	703
	21st to end	Night	32% 27% 27% 13% 2	592
March	1st to 10th	Night	26% 26% 30% 15% 2	720
	11th to 20th	Night	31% 23% 23% 18% 4	720
	21st to end	Night	24% 23% 30% 17% 5% 1	792
April	1st to 10th	Night	27% 20% 30% 21% 3	720
	11th to 20th	Night	28% 18% 28% 19% 6% 2	711
	21st to end	Night	24% 14% 28% 24% 9%	626
May	1st to 10th	Night	22% 14% 20% 31% 11% 1	500
	11th to 20th	Night	16% 10% 31% 33% 9% 1	354
	21st to end	Night	15% 10% 25% 31% 18% 1	389
June	1st to 10th	Night	19% 7% 28% 31% 15% 1	360
	11th to 20th	Night	14% 11% 23% 37% 14%	360
	21st to end	Night	10% 8% 30% 41% 12%	360
July	1st to 10th	Night	9% 4 22% 42% 19% 3	350
	11th to 20th	Night	9% 5% 27% 35% 23% 1	348
	21st to end	Night	12% 3 26% 36% 22% 2	504
August	1st to 10th	Night	10% 5% 25% 34% 23% 2	537
	11th to 20th	Night	13% 6% 20% 30% 27% 4	534
	21st to end	Night	13% 7% 23% 34% 21% 2	768
September	1st to 10th	Night	18% 9% 23% 28% 20% 3	720
	11th to 20th	Night	18% 8% 20% 25% 25% 4	720
	21st to end	Night	19% 14% 22% 25% 17% 3	720
October	1st to 10th	Night	20% 13% 27% 21% 17% 2	720
	11th to 20th	Night	26% 18% 27% 22% 6% 1	720
	21st to end	Night	35% 17% 28% 17% 3	792
November	1st to 10th	Night	25% 18% 27% 22% 8% 1	740
	11th to 20th	Night	28% 24% 26% 15% 5% 2	760
	21st to end	Night	26% 25% 28% 16% 5%	760
December	1st to 10th	Night	33% 28% 25% 10% 4	760
	11th to 20th	Night	29% 28% 26% 13% 3	760
	21st to end	Night	29% 28% 30% 11% 2	836

Page generated at 2024-01-19 09:28:30. Version ac07

Copyright 2024 Attilla Danko