Elliott-Astronomy Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Elliott-Astronomy Observatory clear sky chart from 2005-11-06 to 2024-08-15.

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	15% 11% 4 8% 5% 5% 5% 4 5% 7% 31%	95575
	Night	17% 12% 4 9% 5% 5% 4 4 5% 6% 30%	93144
Transparency	Day	50% 9% 13% 18% 9% 1	95302
	Night	53% 9% 13% 16% 9% 1	92970
Seeing	Day	21% 16% 29% 21% 10% 3	14201
	Night	22% 15% 29% 24% 10% 1	23580

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	17% 22% 8% 11% 7% 4 4 2 4 4 17%	2517
	11th to 20th	Day	12% 23% 7% 21% 10% 4 4 3 3 3 9%	2748
	21st to end	Day	23% 19% 9% 12% 7% 5% 5% 3 4 4 10%	3124
February	1st to 10th	Day	17% 20% 4 13% 7% 7% 4 3 5% 5% 15%	1710
	11th to 20th	Day	13% 18% 7% 16% 9% 5% 5% 3 4 4 17%	1663
	21st to end	Day	20% 15% 5% 12% 9% 4 4 4 5% 5% 18%	1478
March	1st to 10th	Day	18% 13% 5% 10% 6% 5% 4 3 4 5% 28%	3432
	11th to 20th	Day	10% 21% 4 9% 5% 6% 4 3 5% 6% 28%	3480
	21st to end	Day	17% 11% 3 9% 4 4 4 3 6% 7% 31%	3815
April	1st to 10th	Day	18% 15% 4 8% 4 4 4 3 5% 5% 30%	2266
	11th to 20th	Day	20% 10% 3 7% 5% 4 4 3 4 6% 35%	2272
	21st to end	Day	20% 10% 3 8% 5% 4 4 3 5% 5% 34%	2470
May	1st to 10th	Day	19% 9% 3 7% 5% 4 5% 3 5% 7% 33%	4108
	11th to 20th	Day	15% 10% 3 8% 5% 5% 5% 4 5% 8% 30%	4391
	21st to end	Day	11% 7% 2 5% 4 4 4 4 6% 8% 46%	4837
June	1st to 10th	Day	16% 6% 3 6% 4 4 5% 4 6% 7% 38%	2660
	11th to 20th	Day	12% 5% 3 7% 5% 5% 5% 4 7% 10% 39%	2660
	21st to end	Day	15% 5% 2 6% 4 4 4 3 7% 8% 41%	2660
July	1st to 10th	Day	8% 5% 2 6% 4 4 5% 4 6% 10% 45%	4440
	11th to 20th	Day	12% 5% 2 5% 5% 4 5% 4 7% 10% 40%	4440
	21st to end	Day	8% 5% 3 6% 5% 5% 5% 5% 7% 9% 42%	4511
August	1st to 10th	Day	10% 6% 2 6% 4 5% 5% 5% 7% 10% 41%	2457
	11th to 20th	Day	10% 5% 2 8% 4 6% 6% 4 8% 10% 37%	2357
	21st to end	Day	12% 6% 2 5% 4 5% 5% 4 5% 8% 43%	2441
September	1st to 10th	Day	14% 8% 2 6% 4 4 4 4 7% 7% 41%	2160
	11th to 20th	Day	12% 6% 2 5% 4 4 5% 4 7% 8% 43%	2089
	21st to end	Day	15% 8% 3 7% 5% 6% 5% 4 6% 8% 34%	1922
October	1st to 10th	Day	21% 7% 3 7% 5% 5% 5% 4 4 7% 33%	1800
	11th to 20th	Day	20% 10% 4 10% 5% 5% 5% 3 5% 6% 27%	1800
	21st to end	Day	26% 15% 4 9% 5% 4 4 2 4 5% 21%	1980
November	1st to 10th	Day	14% 11% 3 9% 6% 5% 5% 4 5% 5% 32%	1649
	11th to 20th	Day	15% 14% 4 10% 4 4 5% 3 5% 8% 28%	1520
	21st to end	Day	20% 18% 4 9% 6% 5% 4 3 5% 6% 20%	1520
December	1st to 10th	Day	19% 20% 6% 12% 6% 4 5% 3 4 5% 15%	1520
	11th to 20th	Day	20% 19% 6% 12% 6% 4 3 4 5% 5% 15%	1906
	21st to end	Day	27% 23% 6% 12% 4 4 3 3 3 4 11%	2772
January	1st to 10th	Night	18% 20% 6% 11% 6% 5% 4 3 4 4 18%	4429
	11th to 20th	Night	14% 20% 8% 16% 7% 6% 5% 3 4 4 13%	4209
	21st to end	Night	25% 20% 6% 13% 7% 5% 4 2 3 3 11%	4532
February	1st to 10th	Night	18% 18% 6% 12% 7% 4 4 3 4 4 19%	2470
	11th to 20th	Night	15% 16% 5% 12% 8% 6% 5% 4 5% 5% 21%	2403
	21st to end	Night	18% 16% 4 14% 6% 5% 4 3 4 6% 19%	1971
March	1st to 10th	Night	21% 13% 4 9% 5% 3 4 3 3 4 31%	3408
	11th to 20th	Night	18% 16% 3 8% 4 4 4 3 5% 6% 28%	3479
	21st to end	Night	16% 9% 2 8% 4 4 4 3 5% 6% 40%	3817
April	1st to 10th	Night	19% 13% 3 8% 6% 4 3 3 4 5% 31%	1914
	11th to 20th	Night	18% 9% 3 7% 5% 4 4 4 5% 6% 35%	1874
	21st to end	Night	17% 9% 4 7% 3 5% 6% 4 5% 6% 34%	1710
May	1st to 10th	Night	22% 10% 3 7% 4 4 3 3 5% 6% 32%	2833
	11th to 20th	Night	13% 7% 3 7% 6% 6% 5% 4 6% 9% 34%	2500
	21st to end	Night	12% 6% 3 5% 4 4 4 4 6% 9% 44%	2738
June	1st to 10th	Night	12% 6% 3 7% 6% 6% 6% 5% 7% 8% 35%	1520
	11th to 20th	Night	11% 5% 2 7% 5% 5% 5% 5% 6% 7% 42%	1520
	21st to end	Night	13% 6% 2 7% 4 6% 4 4 5% 9% 40%	1520
July	1st to 10th	Night	9% 6% 3 7% 5% 5% 4 3 6% 9% 43%	2520
	11th to 20th	Night	11% 6% 2 6% 3 4 4 4 5% 9% 46%	2520
	21st to end	Night	10% 4 2 5% 4 5% 5% 4 6% 8% 47%	3038
August	1st to 10th	Night	8% 6% 2 5% 4 4 5% 5% 7% 9% 44%	1701
	11th to 20th	Night	10% 5% 3 7% 4 4 5% 4 5% 9% 45%	1643
	21st to end	Night	10% 6% 2 6% 5% 4 4 4 6% 8% 46%	1895
September	1st to 10th	Night	13% 7% 2 6% 4 4 4 4 6% 6% 44%	1800
	11th to 20th	Night	14% 4 2 5% 3 4 4 3 5% 6% 51%	1867
	21st to end	Night	15% 8% 2 6% 5% 4 5% 4 5% 8% 38%	2038
October	1st to 10th	Night	16% 9% 3 6% 4 4 4 4 5% 7% 38%	2160
	11th to 20th	Night	22% 11% 3 8% 5% 4 5% 4 5% 6% 29%	2160
	21st to end	Night	26% 11% 3 8% 4 4 4 4 5% 6% 25%	2376
November	1st to 10th	Night	16% 10% 3 7% 4 4 4 3 4 7% 38%	2427
	11th to 20th	Night	15% 13% 4 8% 6% 5% 4 4 5% 7% 29%	2660
	21st to end	Night	18% 15% 5% 9% 5% 5% 5% 4 5% 6% 23%	2660
December	1st to 10th	Night	21% 20% 7% 10% 5% 4 4 3 4 4 17%	2660
	11th to 20th	Night	16% 22% 6% 11% 5% 4 4 3 4 5% 18%	3288
	21st to end	Night	30% 16% 6% 10% 5% 5% 5% 3 5% 5% 11%	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	69% 11% 8% 9% 3	2518
	11th to 20th	Day	78% 10% 6% 5% 1	2748
	21st to end	Day	77% 9% 10% 3 1	3124
February	1st to 10th	Day	71% 7% 11% 9% 1	1710
	11th to 20th	Day	70% 8% 9% 10% 2	1672
	21st to end	Day	67% 8% 11% 9% 4	1478
March	1st to 10th	Day	55% 8% 13% 18% 6%	3435
	11th to 20th	Day	52% 11% 17% 14% 6% 1	3480
	21st to end	Day	47% 11% 12% 21% 7% 1	3815
April	1st to 10th	Day	55% 6% 12% 17% 9% 1	2266
	11th to 20th	Day	49% 7% 12% 18% 13% 2	2272
	21st to end	Day	51% 7% 11% 17% 12% 2	2470
May	1st to 10th	Day	48% 8% 14% 17% 11% 2	4120
	11th to 20th	Day	48% 12% 14% 18% 7% 1	4395
	21st to end	Day	33% 10% 14% 25% 16% 3	4837
June	1st to 10th	Day	41% 9% 14% 19% 15% 2	2660
	11th to 20th	Day	39% 8% 16% 23% 14% 1	2660
	21st to end	Day	38% 9% 15% 23% 14% 1	2660
July	1st to 10th	Day	33% 8% 14% 27% 17% 2	4370
	11th to 20th	Day	35% 8% 16% 29% 12% 1	4365
	21st to end	Day	35% 10% 17% 22% 15% 1	4367
August	1st to 10th	Day	35% 10% 18% 24% 12% 1	2444
	11th to 20th	Day	38% 10% 17% 24% 10% 1	2357
	21st to end	Day	37% 8% 16% 26% 12% 2	2441
September	1st to 10th	Day	39% 9% 16% 24% 11% 1	2160
	11th to 20th	Day	36% 9% 15% 26% 14% 1	2089
	21st to end	Day	44% 9% 15% 21% 9% 1	1922
October	1st to 10th	Day	50% 8% 14% 16% 11% 1	1800
	11th to 20th	Day	54% 9% 15% 14% 6% 1	1800
	21st to end	Day	66% 6% 11% 11% 5% 1	1980
November	1st to 10th	Day	52% 9% 13% 17% 8% 1	1649
	11th to 20th	Day	54% 9% 17% 13% 6% 1	1520
	21st to end	Day	64% 9% 13% 11% 3	1520
December	1st to 10th	Day	70% 9% 13% 7% 1	1520
	11th to 20th	Day	70% 11% 11% 7% 2	1906
	21st to end	Day	77% 9% 9% 5% 1	2772
January	1st to 10th	Night	66% 13% 12% 7% 2	4429
	11th to 20th	Night	70% 14% 9% 5% 1	4209
	21st to end	Night	76% 9% 8% 5% 1	4532
February	1st to 10th	Night	68% 9% 9% 11% 2	2470
	11th to 20th	Night	64% 9% 13% 11% 4	2405
	21st to end	Night	63% 8% 12% 12% 5%	1971
March	1st to 10th	Night	55% 7% 12% 20% 6%	3418
	11th to 20th	Night	53% 11% 15% 15% 6% 1	3480
	21st to end	Night	41% 7% 14% 24% 13% 1	3817
April	1st to 10th	Night	56% 6% 10% 18% 10% 1	1914
	11th to 20th	Night	49% 6% 11% 19% 13% 2	1874
	21st to end	Night	48% 8% 11% 17% 13% 2	1710
May	1st to 10th	Night	50% 9% 11% 17% 12% 2	2840
	11th to 20th	Night	43% 11% 18% 18% 8% 1	2501
	21st to end	Night	32% 10% 13% 23% 20% 2	2739
June	1st to 10th	Night	43% 9% 11% 20% 16% 1	1520
	11th to 20th	Night	38% 9% 12% 21% 18% 2	1520
	21st to end	Night	41% 8% 15% 19% 16% 2	1520
July	1st to 10th	Night	37% 6% 13% 23% 19% 2	2480
	11th to 20th	Night	34% 7% 16% 29% 13% 1	2472
	21st to end	Night	33% 8% 18% 23% 17% 2	2941
August	1st to 10th	Night	32% 10% 18% 27% 13% 1	1690
	11th to 20th	Night	35% 9% 16% 28% 12%	1643
	21st to end	Night	34% 9% 14% 28% 13% 2	1895
September	1st to 10th	Night	38% 8% 16% 23% 14% 1	1800
	11th to 20th	Night	33% 6% 14% 29% 17% 1	1867
	21st to end	Night	43% 9% 14% 22% 13%	2038
October	1st to 10th	Night	45% 8% 13% 19% 14% 1	2160
	11th to 20th	Night	53% 9% 14% 16% 8%	2160
	21st to end	Night	61% 7% 12% 12% 8% 1	2376
November	1st to 10th	Night	47% 8% 12% 20% 11% 2	2427
	11th to 20th	Night	53% 9% 14% 15% 7% 1	2660
	21st to end	Night	60% 11% 15% 12% 2	2660
December	1st to 10th	Night	69% 10% 13% 7% 2	2660
	11th to 20th	Night	67% 11% 10% 9% 2	3288
	21st to end	Night	74% 9% 11% 5% 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	27% 30% 23% 13% 6% 1	180
	11th to 20th	Day	28% 29% 28% 12% 3 1	245
	21st to end	Day	24% 25% 31% 16% 4	297
February	1st to 10th	Day	31% 30% 29% 9% 1	270
	11th to 20th	Day	26% 31% 34% 8% 1	270
	21st to end	Day	38% 17% 33% 10% 1	280
March	1st to 10th	Day	25% 21% 35% 15% 4	460
	11th to 20th	Day	27% 18% 35% 16% 3 1	460
	21st to end	Day	29% 17% 30% 18% 4 2	506
April	1st to 10th	Day	26% 21% 31% 16% 5% 1	460
	11th to 20th	Day	31% 20% 22% 17% 7% 2	452
	21st to end	Day	27% 16% 35% 14% 7% 2	460
May	1st to 10th	Day	25% 13% 30% 19% 9% 3	463
	11th to 20th	Day	19% 11% 30% 25% 11% 3	487
	21st to end	Day	15% 12% 29% 26% 13% 5%	529
June	1st to 10th	Day	18% 16% 31% 25% 8% 2	490
	11th to 20th	Day	15% 14% 27% 30% 12% 3	490
	21st to end	Day	17% 10% 32% 29% 9% 2	490
July	1st to 10th	Day	10% 7% 26% 33% 21% 4	485
	11th to 20th	Day	14% 9% 27% 28% 16% 5%	484
	21st to end	Day	11% 7% 32% 31% 14% 5%	532
August	1st to 10th	Day	14% 7% 23% 30% 17% 8%	486
	11th to 20th	Day	11% 6% 25% 30% 20% 8%	456
	21st to end	Day	12% 8% 29% 27% 15% 9%	495
September	1st to 10th	Day	14% 10% 25% 29% 14% 8%	450
	11th to 20th	Day	12% 8% 22% 25% 22% 10%	450
	21st to end	Day	18% 14% 29% 21% 12% 7%	450
October	1st to 10th	Day	22% 15% 25% 18% 15% 5%	450
	11th to 20th	Day	24% 22% 30% 18% 5% 1	450
	21st to end	Day	37% 18% 24% 15% 5%	495
November	1st to 10th	Day	24% 21% 31% 15% 7% 2	311
	11th to 20th	Day	29% 28% 23% 14% 3 2	180
	21st to end	Day	30% 27% 29% 13% 1	180
December	1st to 10th	Day	31% 24% 31% 8% 5% 1	180
	11th to 20th	Day	31% 28% 27% 12% 2	180
	21st to end	Day	29% 37% 24% 9% 1 1	198
January	1st to 10th	Night	29% 23% 31% 13% 4	760
	11th to 20th	Night	31% 23% 29% 15% 2	760
	21st to end	Night	25% 19% 33% 18% 4	836
February	1st to 10th	Night	26% 26% 30% 15% 2	760
	11th to 20th	Night	24% 24% 33% 17% 3	743
	21st to end	Night	29% 21% 31% 18% 2	628
March	1st to 10th	Night	23% 18% 34% 21% 5%	760
	11th to 20th	Night	26% 18% 31% 20% 5% 1	760
	21st to end	Night	22% 14% 33% 22% 8% 1	836
April	1st to 10th	Night	25% 17% 33% 22% 3	760
	11th to 20th	Night	23% 15% 32% 22% 7% 1	750
	21st to end	Night	21% 9% 32% 27% 9%	570
May	1st to 10th	Night	20% 9% 27% 29% 13% 2	570
	11th to 20th	Night	15% 7% 30% 40% 8% 1	379
	21st to end	Night	11% 9% 27% 36% 14% 1	411
June	1st to 10th	Night	13% 7% 35% 33% 12%	380
	11th to 20th	Night	13% 7% 31% 34% 14% 1	380
	21st to end	Night	14% 7% 30% 39% 9%	380
July	1st to 10th	Night	8% 6% 25% 41% 19% 1	370
	11th to 20th	Night	10% 6% 29% 36% 17% 1	368
	21st to end	Night	11% 3 26% 39% 19% 2	588
August	1st to 10th	Night	9% 6% 18% 42% 22% 2	567
	11th to 20th	Night	9% 5% 22% 34% 28% 2	549
	21st to end	Night	12% 5% 23% 35% 21% 3	707
September	1st to 10th	Night	15% 7% 22% 34% 20% 3	720
	11th to 20th	Night	14% 5% 21% 30% 25% 5%	720
	21st to end	Night	17% 10% 24% 29% 16% 4	720
October	1st to 10th	Night	20% 10% 29% 23% 16% 2	720
	11th to 20th	Night	27% 18% 26% 22% 7% 1	720
	21st to end	Night	33% 15% 26% 22% 4	792
November	1st to 10th	Night	24% 15% 29% 22% 10% 1	740
	11th to 20th	Night	22% 21% 32% 16% 8% 1	760
	21st to end	Night	27% 21% 31% 16% 6%	760
December	1st to 10th	Night	34% 22% 24% 16% 3	760
	11th to 20th	Night	26% 24% 32% 15% 3	760
	21st to end	Night	33% 19% 32% 13% 2	836

Page generated at 2024-08-12 09:52:54. Version ac07

Copyright © 2024 Attilla Danko.