The Mount Academy
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the The Mount Academy clear sky chart from 2005-11-06 to 2024-03-06.

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% 7% 3 6% 5% 3 5% 5% 5% 7% 38%	78418
	Night	17% 8% 3 6% 5% 3 4 4 5% 7% 38%	81090
Transparency	Day	44% 7% 12% 22% 13% 2	78123
	Night	44% 7% 12% 22% 14% 2	80919
Seeing	Day	21% 13% 28% 24% 11% 3	13942
	Night	20% 10% 30% 29% 9% 1	23205

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	14% 8% 3 5% 6% 3 4 5% 6% 6% 40%	2517
	11th to 20th	Day	15% 9% 4 8% 7% 3 5% 5% 6% 6% 31%	2520
	21st to end	Day	20% 11% 4 6% 6% 4 5% 4 4 5% 31%	2936
February	1st to 10th	Day	15% 9% 4 7% 6% 4 5% 5% 5% 6% 33%	1710
	11th to 20th	Day	13% 8% 4 7% 6% 3 5% 4 5% 7% 39%	1834
	21st to end	Day	19% 8% 3 4 6% 3 4 4 5% 7% 35%	1570
March	1st to 10th	Day	15% 7% 4 7% 6% 3 4 4 4 6% 39%	1847
	11th to 20th	Day	15% 9% 4 6% 5% 3 4 5% 5% 7% 38%	1885
	21st to end	Day	19% 8% 3 6% 6% 3 4 4 4 5% 38%	2362
April	1st to 10th	Day	17% 9% 4 6% 5% 2 4 4 5% 6% 37%	2160
	11th to 20th	Day	16% 7% 2 5% 6% 3 5% 4 4 6% 41%	2134
	21st to end	Day	21% 6% 2 5% 5% 3 5% 4 4 5% 39%	2212
May	1st to 10th	Day	22% 8% 3 6% 5% 2 4 5% 4 7% 34%	2357
	11th to 20th	Day	17% 6% 3 5% 4 3 5% 5% 5% 9% 39%	2478
	21st to end	Day	14% 5% 2 5% 5% 4 5% 6% 6% 8% 41%	2725
June	1st to 10th	Day	16% 5% 2 6% 5% 4 6% 5% 7% 10% 35%	2520
	11th to 20th	Day	15% 5% 3 6% 5% 3 5% 5% 7% 10% 36%	2520
	21st to end	Day	13% 6% 3 5% 6% 4 5% 5% 6% 10% 37%	2520
July	1st to 10th	Day	11% 6% 2 5% 5% 4 7% 6% 6% 9% 40%	2520
	11th to 20th	Day	10% 5% 2 5% 5% 4 6% 5% 7% 11% 40%	2520
	21st to end	Day	11% 5% 3 6% 6% 3 6% 6% 7% 9% 38%	2744
August	1st to 10th	Day	11% 5% 2 5% 5% 4 5% 7% 7% 9% 40%	2441
	11th to 20th	Day	11% 6% 2 6% 5% 3 5% 6% 9% 10% 37%	2126
	21st to end	Day	12% 5% 2 4 5% 3 5% 5% 6% 9% 43%	2376
September	1st to 10th	Day	14% 6% 3 5% 5% 4 5% 5% 5% 7% 42%	2160
	11th to 20th	Day	13% 5% 2 4 4 3 4 4 6% 6% 49%	2082
	21st to end	Day	16% 6% 1 5% 4 3 5% 5% 6% 7% 43%	1980
October	1st to 10th	Day	21% 6% 3 5% 4 3 4 4 4 6% 41%	1877
	11th to 20th	Day	15% 7% 2 6% 5% 3 4 5% 5% 7% 42%	1800
	21st to end	Day	23% 7% 2 5% 5% 3 5% 4 5% 7% 33%	1814
November	1st to 10th	Day	14% 7% 3 5% 5% 3 4 3 4 7% 47%	1671
	11th to 20th	Day	18% 7% 3 5% 5% 3 4 4 5% 6% 42%	1710
	21st to end	Day	18% 8% 3 5% 4 2 4 4 5% 6% 40%	1592
December	1st to 10th	Day	19% 9% 3 6% 6% 3 6% 5% 4 6% 31%	1520
	11th to 20th	Day	24% 6% 2 4 4 3 4 4 5% 6% 39%	1906
	21st to end	Day	20% 10% 4 9% 6% 4 4 4 4 6% 28%	2772
January	1st to 10th	Night	16% 7% 3 7% 6% 3 4 4 6% 6% 39%	4429
	11th to 20th	Night	14% 9% 5% 8% 7% 4 6% 4 5% 6% 33%	4440
	21st to end	Night	24% 12% 3 6% 4 2 4 4 4 5% 31%	4718
February	1st to 10th	Night	16% 9% 3 7% 5% 3 5% 5% 4 6% 37%	2470
	11th to 20th	Night	14% 8% 4 6% 6% 3 6% 4 6% 6% 37%	2230
	21st to end	Night	18% 8% 2 6% 6% 3 4 5% 5% 5% 38%	1884
March	1st to 10th	Night	16% 9% 3 5% 5% 3 5% 4 4 6% 40%	2217
	11th to 20th	Night	16% 8% 4 6% 5% 3 5% 5% 5% 6% 38%	2069
	21st to end	Night	17% 7% 4 5% 6% 3 3 5% 5% 5% 40%	1994
April	1st to 10th	Night	18% 11% 3 7% 6% 3 4 4 5% 8% 33%	1800
	11th to 20th	Night	18% 6% 3 5% 5% 3 4 4 4 8% 38%	1775
	21st to end	Night	21% 8% 3 5% 5% 2 4 3 4 6% 39%	1746
May	1st to 10th	Night	22% 9% 3 6% 5% 3 4 4 4 6% 33%	1619
	11th to 20th	Night	17% 6% 3 6% 6% 2 6% 4 5% 7% 39%	1415
	21st to end	Night	14% 6% 2 5% 5% 3 5% 5% 6% 8% 41%	1550
June	1st to 10th	Night	16% 5% 2 5% 5% 3 5% 4 5% 9% 41%	1440
	11th to 20th	Night	15% 7% 2 5% 4 3 4 4 6% 10% 39%	1440
	21st to end	Night	12% 4 2 4 4 4 4 5% 8% 10% 43%	1440
July	1st to 10th	Night	13% 4 3 5% 4 3 4 6% 8% 8% 43%	1440
	11th to 20th	Night	12% 5% 1 6% 5% 3 5% 6% 8% 9% 39%	1440
	21st to end	Night	10% 6% 3 5% 5% 4 5% 5% 6% 9% 44%	1574
August	1st to 10th	Night	9% 5% 2 5% 6% 3 4 5% 7% 10% 43%	1476
	11th to 20th	Night	11% 6% 3 6% 6% 4 5% 6% 7% 10% 36%	1774
	21st to end	Night	15% 5% 3 5% 4 3 4 4 5% 8% 44%	1980
September	1st to 10th	Night	14% 6% 2 6% 4 3 4 4 5% 6% 46%	1800
	11th to 20th	Night	13% 5% 2 4 4 2 3 3 5% 7% 53%	1877
	21st to end	Night	16% 5% 3 4 4 3 4 4 5% 6% 47%	1980
October	1st to 10th	Night	22% 5% 2 5% 5% 2 4 4 4 5% 41%	2078
	11th to 20th	Night	15% 7% 2 5% 6% 3 4 4 4 6% 43%	2160
	21st to end	Night	24% 7% 3 5% 5% 3 3 4 4 5% 36%	2542
November	1st to 10th	Night	14% 6% 3 5% 4 3 3 5% 5% 7% 45%	2407
	11th to 20th	Night	20% 7% 3 5% 4 2 4 4 4 6% 41%	2470
	21st to end	Night	15% 7% 2 5% 5% 3 4 4 6% 7% 42%	2584
December	1st to 10th	Night	21% 8% 2 6% 5% 3 4 4 5% 8% 35%	2660
	11th to 20th	Night	22% 8% 4 6% 4 3 4 4 4 6% 34%	3288
	21st to end	Night	24% 12% 3 6% 5% 3 4 4 5% 6% 30%	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	40% 6% 13% 31% 8% 2	2518
	11th to 20th	Day	50% 7% 12% 22% 8% 2	2520
	21st to end	Day	54% 7% 10% 20% 9% 1	2936
February	1st to 10th	Day	50% 6% 12% 18% 12% 1	1710
	11th to 20th	Day	44% 6% 10% 22% 15% 3	1843
	21st to end	Day	49% 5% 11% 21% 12% 2	1570
March	1st to 10th	Day	45% 5% 12% 21% 13% 3	1850
	11th to 20th	Day	46% 6% 11% 22% 14% 2	1885
	21st to end	Day	49% 5% 8% 17% 17% 5%	2362
April	1st to 10th	Day	47% 6% 9% 21% 13% 4	2160
	11th to 20th	Day	43% 5% 11% 22% 16% 3	2134
	21st to end	Day	46% 6% 9% 20% 15% 4	2212
May	1st to 10th	Day	50% 6% 10% 18% 14% 3	2357
	11th to 20th	Day	43% 7% 10% 22% 16% 2	2482
	21st to end	Day	40% 9% 15% 21% 12% 2	2725
June	1st to 10th	Day	43% 9% 14% 20% 13% 1	2520
	11th to 20th	Day	42% 8% 14% 24% 10% 2	2520
	21st to end	Day	41% 9% 12% 25% 12% 1	2520
July	1st to 10th	Day	40% 9% 13% 20% 16% 2	2450
	11th to 20th	Day	36% 10% 15% 25% 14% 1	2445
	21st to end	Day	40% 9% 14% 20% 15% 2	2591
August	1st to 10th	Day	36% 12% 14% 25% 12% 1	2427
	11th to 20th	Day	38% 10% 17% 24% 11%	2126
	21st to end	Day	36% 8% 13% 25% 17% 1	2376
September	1st to 10th	Day	40% 7% 12% 23% 16% 2	2160
	11th to 20th	Day	35% 6% 10% 24% 23% 2	2082
	21st to end	Day	38% 7% 12% 22% 18% 3	1980
October	1st to 10th	Day	43% 6% 10% 23% 15% 2	1877
	11th to 20th	Day	40% 8% 13% 26% 13% 1	1800
	21st to end	Day	51% 5% 11% 18% 12% 2	1814
November	1st to 10th	Day	37% 6% 13% 26% 16% 2	1671
	11th to 20th	Day	42% 6% 11% 21% 17% 2	1710
	21st to end	Day	44% 5% 14% 26% 9% 2	1592
December	1st to 10th	Day	53% 6% 13% 17% 10% 1	1520
	11th to 20th	Day	45% 5% 16% 22% 9% 2	1906
	21st to end	Day	54% 8% 10% 20% 7%	2772
January	1st to 10th	Night	42% 6% 13% 25% 11% 2	4429
	11th to 20th	Night	49% 6% 13% 20% 9% 3	4440
	21st to end	Night	54% 6% 10% 19% 9% 2	4718
February	1st to 10th	Night	47% 6% 14% 21% 11% 2	2470
	11th to 20th	Night	46% 7% 10% 17% 17% 3	2232
	21st to end	Night	46% 6% 9% 22% 13% 4	1884
March	1st to 10th	Night	43% 7% 11% 22% 14% 3	2227
	11th to 20th	Night	45% 6% 10% 21% 14% 3	2070
	21st to end	Night	46% 5% 10% 18% 18% 4	1994
April	1st to 10th	Night	49% 6% 9% 20% 14% 2	1800
	11th to 20th	Night	45% 7% 10% 18% 19% 1	1775
	21st to end	Night	46% 7% 8% 21% 15% 4	1746
May	1st to 10th	Night	51% 7% 9% 16% 15% 2	1619
	11th to 20th	Night	45% 6% 10% 20% 17% 3	1416
	21st to end	Night	39% 9% 15% 22% 13% 2	1551
June	1st to 10th	Night	42% 7% 11% 23% 15% 2	1440
	11th to 20th	Night	39% 10% 14% 26% 10% 1	1440
	21st to end	Night	33% 11% 13% 27% 14% 1	1440
July	1st to 10th	Night	35% 10% 13% 24% 15% 3	1400
	11th to 20th	Night	37% 9% 14% 28% 11% 1	1392
	21st to end	Night	34% 9% 15% 23% 15% 3	1486
August	1st to 10th	Night	34% 10% 14% 26% 15% 1	1466
	11th to 20th	Night	41% 10% 15% 23% 11%	1774
	21st to end	Night	38% 8% 11% 23% 19% 1	1980
September	1st to 10th	Night	39% 7% 12% 26% 16% 1	1800
	11th to 20th	Night	33% 6% 10% 25% 25% 2	1877
	21st to end	Night	37% 7% 9% 23% 23% 1	1980
October	1st to 10th	Night	45% 7% 10% 22% 15% 2	2078
	11th to 20th	Night	40% 8% 11% 27% 13% 1	2160
	21st to end	Night	49% 6% 11% 21% 12% 1	2542
November	1st to 10th	Night	38% 7% 10% 22% 20% 3	2407
	11th to 20th	Night	45% 4 10% 22% 16% 4	2470
	21st to end	Night	41% 6% 15% 28% 10% 1	2584
December	1st to 10th	Night	48% 6% 14% 21% 11% 1	2660
	11th to 20th	Night	50% 6% 14% 16% 13% 2	3288
	21st to end	Night	53% 8% 11% 20% 9%	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	25% 19% 28% 19% 9%	180
	11th to 20th	Day	24% 23% 34% 13% 4 1	180
	21st to end	Day	20% 18% 40% 16% 5% 2	245
February	1st to 10th	Day	29% 21% 33% 14% 3	270
	11th to 20th	Day	24% 20% 37% 18% 1	442
	21st to end	Day	27% 19% 34% 17% 3	382
March	1st to 10th	Day	24% 18% 32% 22% 4	440
	11th to 20th	Day	22% 23% 32% 18% 4 1	420
	21st to end	Day	29% 18% 29% 18% 4 3	462
April	1st to 10th	Day	28% 18% 28% 17% 7% 3	420
	11th to 20th	Day	24% 22% 28% 16% 8% 2	412
	21st to end	Day	30% 15% 28% 18% 5% 3	420
May	1st to 10th	Day	31% 15% 27% 17% 8% 2	423
	11th to 20th	Day	19% 11% 37% 22% 8% 2	447
	21st to end	Day	19% 10% 22% 30% 14% 5%	485
June	1st to 10th	Day	19% 12% 27% 25% 14% 2	450
	11th to 20th	Day	14% 12% 30% 26% 14% 2	450
	21st to end	Day	15% 10% 29% 26% 16% 4	450
July	1st to 10th	Day	16% 4 24% 32% 19% 5%	445
	11th to 20th	Day	13% 5% 23% 34% 20% 5%	444
	21st to end	Day	12% 6% 27% 34% 17% 4	488
August	1st to 10th	Day	12% 7% 20% 36% 17% 8%	446
	11th to 20th	Day	14% 5% 23% 28% 21% 8%	439
	21st to end	Day	11% 7% 25% 30% 18% 9%	495
September	1st to 10th	Day	18% 11% 19% 25% 19% 8%	450
	11th to 20th	Day	15% 8% 30% 19% 17% 11%	450
	21st to end	Day	17% 10% 27% 27% 13% 6%	450
October	1st to 10th	Day	29% 8% 20% 22% 15% 6%	450
	11th to 20th	Day	17% 12% 32% 26% 10% 2	450
	21st to end	Day	27% 13% 28% 23% 8% 1	412
November	1st to 10th	Day	18% 14% 25% 30% 10% 2	365
	11th to 20th	Day	23% 15% 30% 24% 7% 1	370
	21st to end	Day	21% 15% 30% 26% 7% 1	252
December	1st to 10th	Day	23% 22% 33% 14% 8%	180
	11th to 20th	Day	27% 21% 33% 17% 2	180
	21st to end	Day	21% 14% 37% 23% 4 1	198
January	1st to 10th	Night	19% 13% 37% 28% 3	760
	11th to 20th	Night	23% 13% 35% 26% 3	760
	21st to end	Night	18% 14% 39% 25% 3	836
February	1st to 10th	Night	22% 14% 37% 26% 2	760
	11th to 20th	Night	20% 15% 43% 22% 1	743
	21st to end	Night	24% 14% 37% 22% 3	628
March	1st to 10th	Night	22% 17% 34% 24% 4	743
	11th to 20th	Night	22% 14% 38% 21% 5%	720
	21st to end	Night	22% 16% 36% 20% 6% 1	792
April	1st to 10th	Night	26% 14% 34% 22% 4	720
	11th to 20th	Night	22% 12% 35% 23% 7%	711
	21st to end	Night	25% 15% 29% 25% 6%	666
May	1st to 10th	Night	24% 13% 32% 24% 7%	539
	11th to 20th	Night	18% 6% 36% 34% 5%	354
	21st to end	Night	17% 6% 21% 41% 15% 1	389
June	1st to 10th	Night	17% 4 26% 38% 15% 1	360
	11th to 20th	Night	17% 5% 23% 38% 16% 1	360
	21st to end	Night	14% 1 24% 44% 17%	360
July	1st to 10th	Night	13% 2 18% 44% 22% 1	350
	11th to 20th	Night	13% 5% 17% 45% 18% 1	348
	21st to end	Night	12% 4 20% 44% 19% 2	394
August	1st to 10th	Night	12% 1 16% 48% 21% 2	402
	11th to 20th	Night	12% 4 16% 41% 24% 3	710
	21st to end	Night	16% 3 18% 37% 24% 3	792
September	1st to 10th	Night	18% 2 24% 36% 18% 2	720
	11th to 20th	Night	16% 4 24% 30% 21% 5%	720
	21st to end	Night	17% 6% 25% 35% 15% 2	720
October	1st to 10th	Night	25% 6% 24% 30% 13% 2	720
	11th to 20th	Night	19% 8% 29% 35% 9%	720
	21st to end	Night	28% 10% 29% 27% 6%	792
November	1st to 10th	Night	16% 9% 33% 31% 10% 1	740
	11th to 20th	Night	25% 9% 32% 25% 7% 1	760
	21st to end	Night	20% 11% 33% 29% 6% 1	760
December	1st to 10th	Night	25% 12% 34% 23% 5%	760
	11th to 20th	Night	25% 10% 34% 27% 4	760
	21st to end	Night	25% 11% 38% 23% 3	836

Page generated at 2024-03-03 06:28:56. Version ac07

Copyright © 2024 Attilla Danko.