Corvus Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Corvus Observatory clear sky chart from 2005-11-06 to 2024-03-23.

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% 8% 3 6% 6% 3 5% 5% 5% 7% 35%	78567
	Night	18% 9% 4 7% 6% 3 5% 4 5% 6% 34%	81308
Transparency	Day	48% 6% 13% 20% 11% 1	78272
	Night	50% 6% 13% 20% 11% 1	81137
Seeing	Day	24% 16% 29% 20% 9% 3	13969
	Night	23% 15% 29% 25% 7% 1	23191

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% 11% 4 7% 7% 4 5% 5% 5% 6% 31%	2517
	11th to 20th	Day	16% 13% 5% 9% 8% 4 6% 5% 4 5% 25%	2520
	21st to end	Day	19% 13% 5% 8% 7% 4 5% 4 5% 6% 24%	2868
February	1st to 10th	Day	16% 11% 5% 8% 6% 4 6% 5% 5% 7% 27%	1710
	11th to 20th	Day	12% 12% 5% 8% 7% 4 5% 4 6% 7% 30%	1836
	21st to end	Day	19% 10% 4 8% 7% 4 5% 4 4 5% 31%	1570
March	1st to 10th	Day	16% 10% 5% 8% 6% 2 4 4 5% 7% 33%	1897
	11th to 20th	Day	16% 12% 4 6% 5% 3 4 4 5% 7% 33%	1967
	21st to end	Day	19% 11% 3 6% 6% 3 4 5% 4 5% 36%	2400
April	1st to 10th	Day	19% 9% 5% 5% 6% 3 4 5% 4 5% 35%	2160
	11th to 20th	Day	16% 7% 3 6% 6% 3 5% 4 5% 6% 38%	2134
	21st to end	Day	22% 6% 3 6% 6% 3 5% 4 5% 6% 33%	2242
May	1st to 10th	Day	21% 8% 4 6% 6% 3 6% 4 5% 6% 32%	2362
	11th to 20th	Day	17% 6% 3 4 5% 3 5% 4 6% 9% 39%	2478
	21st to end	Day	14% 5% 2 5% 5% 4 4 5% 7% 8% 40%	2725
June	1st to 10th	Day	16% 6% 3 6% 6% 4 6% 5% 7% 8% 33%	2520
	11th to 20th	Day	16% 6% 3 5% 5% 3 6% 5% 7% 10% 34%	2520
	21st to end	Day	16% 6% 3 7% 5% 3 6% 5% 5% 9% 35%	2520
July	1st to 10th	Day	11% 6% 3 6% 5% 3 6% 6% 6% 8% 39%	2520
	11th to 20th	Day	11% 5% 2 6% 5% 4 6% 6% 6% 9% 40%	2520
	21st to end	Day	12% 5% 2 6% 7% 4 6% 6% 7% 10% 36%	2744
August	1st to 10th	Day	9% 4 3 5% 7% 4 6% 7% 6% 10% 39%	2486
	11th to 20th	Day	11% 7% 2 6% 6% 5% 6% 6% 6% 9% 35%	2126
	21st to end	Day	13% 5% 2 4 5% 4 5% 4 7% 9% 42%	2376
September	1st to 10th	Day	15% 5% 2 5% 5% 3 4 5% 5% 6% 44%	2160
	11th to 20th	Day	14% 5% 2 4 4 2 4 4 5% 7% 48%	2070
	21st to end	Day	15% 6% 2 4 4 3 4 5% 6% 8% 43%	1980
October	1st to 10th	Day	21% 8% 3 7% 6% 3 4 3 4 5% 36%	1891
	11th to 20th	Day	16% 7% 3 6% 4 3 5% 4 6% 7% 39%	1800
	21st to end	Day	23% 9% 4 7% 5% 3 4 5% 5% 6% 29%	1787
November	1st to 10th	Day	15% 8% 2 5% 4 3 4 4 4 8% 43%	1671
	11th to 20th	Day	17% 8% 4 6% 5% 3 5% 5% 5% 6% 35%	1710
	21st to end	Day	18% 9% 3 6% 6% 3 5% 6% 5% 7% 32%	1582
December	1st to 10th	Day	19% 12% 5% 8% 6% 4 6% 5% 4 7% 25%	1520
	11th to 20th	Day	23% 11% 3 8% 5% 3 3 3 4 4 32%	1906
	21st to end	Day	25% 16% 5% 8% 7% 3 4 3 4 5% 22%	2772
January	1st to 10th	Night	17% 11% 4 8% 5% 3 4 3 5% 6% 34%	4429
	11th to 20th	Night	14% 14% 5% 11% 7% 3 5% 4 4 6% 27%	4440
	21st to end	Night	24% 12% 5% 8% 7% 3 4 4 4 5% 25%	4784
February	1st to 10th	Night	17% 10% 4 9% 7% 3 5% 5% 5% 6% 29%	2470
	11th to 20th	Night	14% 10% 4 9% 7% 4 7% 5% 6% 7% 28%	2228
	21st to end	Night	18% 10% 4 8% 6% 3 5% 4 6% 6% 30%	1884
March	1st to 10th	Night	17% 10% 4 8% 6% 4 5% 4 4 6% 32%	2270
	11th to 20th	Night	16% 10% 5% 6% 7% 4 5% 5% 5% 6% 31%	2208
	21st to end	Night	18% 9% 4 7% 4 3 4 5% 5% 6% 36%	2001
April	1st to 10th	Night	19% 10% 4 7% 6% 4 4 4 5% 6% 32%	1800
	11th to 20th	Night	21% 7% 4 5% 4 3 4 4 5% 6% 36%	1775
	21st to end	Night	21% 8% 2 5% 5% 3 4 4 4 6% 36%	1716
May	1st to 10th	Night	21% 11% 3 8% 6% 3 4 3 4 6% 32%	1614
	11th to 20th	Night	18% 7% 4 5% 6% 3 5% 4 6% 7% 36%	1415
	21st to end	Night	12% 5% 3 6% 6% 3 5% 4 7% 9% 39%	1550
June	1st to 10th	Night	17% 7% 3 5% 5% 3 5% 5% 5% 7% 39%	1440
	11th to 20th	Night	16% 5% 3 5% 5% 4 5% 5% 6% 9% 38%	1440
	21st to end	Night	12% 4 3 5% 6% 3 5% 5% 6% 8% 43%	1440
July	1st to 10th	Night	12% 4 3 4 6% 3 5% 5% 7% 9% 42%	1440
	11th to 20th	Night	13% 5% 2 5% 6% 3 4 6% 8% 9% 39%	1440
	21st to end	Night	12% 4 3 5% 6% 3 6% 6% 5% 8% 43%	1574
August	1st to 10th	Night	9% 5% 3 6% 5% 3 5% 5% 5% 9% 45%	1432
	11th to 20th	Night	12% 5% 2 7% 6% 3 6% 6% 6% 9% 38%	1773
	21st to end	Night	15% 5% 3 5% 4 2 4 4 7% 8% 44%	1980
September	1st to 10th	Night	16% 6% 2 6% 5% 3 4 5% 5% 7% 41%	1800
	11th to 20th	Night	14% 6% 2 3 4 3 3 4 4 6% 52%	1890
	21st to end	Night	14% 7% 3 5% 5% 4 4 3 5% 6% 44%	1980
October	1st to 10th	Night	19% 8% 3 6% 6% 3 4 4 4 6% 36%	2065
	11th to 20th	Night	16% 6% 3 6% 5% 3 4 5% 5% 7% 40%	2160
	21st to end	Night	25% 9% 3 6% 5% 3 4 4 5% 7% 30%	2568
November	1st to 10th	Night	16% 8% 3 5% 6% 3 5% 4 4 5% 43%	2407
	11th to 20th	Night	19% 8% 4 7% 5% 3 4 5% 4 5% 36%	2470
	21st to end	Night	16% 9% 4 7% 5% 4 5% 5% 5% 7% 34%	2593
December	1st to 10th	Night	20% 11% 4 7% 6% 4 5% 5% 5% 7% 26%	2660
	11th to 20th	Night	22% 11% 4 7% 5% 3 4 4 5% 6% 28%	3288
	21st to end	Night	26% 14% 4 7% 5% 3 4 4 5% 5% 23%	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	51% 4 16% 24% 5%	2518
	11th to 20th	Day	61% 6% 13% 15% 5% 1	2520
	21st to end	Day	60% 7% 12% 15% 5% 1	2868
February	1st to 10th	Day	56% 5% 15% 15% 8% 1	1710
	11th to 20th	Day	54% 4 11% 19% 9% 1	1845
	21st to end	Day	56% 4 11% 18% 11% 1	1570
March	1st to 10th	Day	51% 5% 13% 19% 9% 2	1900
	11th to 20th	Day	50% 5% 13% 17% 12% 2	1967
	21st to end	Day	52% 4 8% 17% 16% 4	2400
April	1st to 10th	Day	52% 5% 9% 21% 11% 2	2160
	11th to 20th	Day	46% 5% 11% 21% 15% 2	2134
	21st to end	Day	51% 5% 10% 19% 12% 3	2242
May	1st to 10th	Day	53% 5% 10% 19% 12% 2	2362
	11th to 20th	Day	43% 7% 9% 23% 15% 2	2482
	21st to end	Day	40% 8% 16% 23% 12% 2	2725
June	1st to 10th	Day	47% 8% 14% 20% 10% 1	2520
	11th to 20th	Day	44% 7% 15% 20% 12% 1	2520
	21st to end	Day	46% 7% 14% 21% 11% 1	2520
July	1st to 10th	Day	42% 7% 13% 22% 14% 2	2450
	11th to 20th	Day	39% 8% 15% 26% 12%	2445
	21st to end	Day	41% 9% 15% 21% 13% 1	2591
August	1st to 10th	Day	39% 8% 16% 24% 11% 1	2472
	11th to 20th	Day	44% 8% 15% 23% 9% 1	2126
	21st to end	Day	38% 7% 15% 26% 14% 1	2376
September	1st to 10th	Day	40% 7% 13% 25% 14% 1	2160
	11th to 20th	Day	36% 6% 11% 24% 21% 2	2070
	21st to end	Day	38% 7% 13% 25% 15% 2	1980
October	1st to 10th	Day	51% 5% 10% 20% 13% 2	1891
	11th to 20th	Day	44% 6% 15% 25% 9% 1	1800
	21st to end	Day	57% 5% 12% 15% 10% 2	1787
November	1st to 10th	Day	41% 6% 15% 25% 13% 1	1671
	11th to 20th	Day	49% 6% 12% 19% 13% 1	1710
	21st to end	Day	50% 5% 15% 22% 7% 1	1582
December	1st to 10th	Day	60% 6% 13% 14% 7% 1	1520
	11th to 20th	Day	56% 4 14% 18% 7% 1	1906
	21st to end	Day	65% 6% 9% 15% 5%	2772
January	1st to 10th	Night	52% 5% 16% 18% 8% 1	4429
	11th to 20th	Night	59% 5% 12% 16% 7% 1	4440
	21st to end	Night	62% 5% 12% 15% 6% 1	4784
February	1st to 10th	Night	56% 6% 13% 16% 8% 2	2470
	11th to 20th	Night	55% 6% 11% 17% 10% 1	2230
	21st to end	Night	54% 4 13% 18% 8% 2	1884
March	1st to 10th	Night	54% 5% 11% 19% 10% 1	2280
	11th to 20th	Night	54% 6% 11% 18% 9% 2	2209
	21st to end	Night	49% 5% 9% 18% 15% 3	2001
April	1st to 10th	Night	53% 5% 11% 19% 10% 2	1800
	11th to 20th	Night	49% 4 10% 19% 16% 1	1775
	21st to end	Night	49% 4 11% 19% 13% 4	1716
May	1st to 10th	Night	55% 5% 9% 15% 13% 3	1614
	11th to 20th	Night	48% 5% 10% 20% 13% 3	1416
	21st to end	Night	42% 9% 15% 21% 13% 1	1551
June	1st to 10th	Night	43% 6% 13% 24% 11% 2	1440
	11th to 20th	Night	44% 7% 14% 23% 12%	1440
	21st to end	Night	37% 9% 16% 25% 13% 1	1440
July	1st to 10th	Night	36% 8% 15% 25% 14% 2	1400
	11th to 20th	Night	37% 9% 16% 27% 11%	1392
	21st to end	Night	37% 8% 15% 24% 14% 2	1486
August	1st to 10th	Night	35% 8% 17% 26% 13% 1	1422
	11th to 20th	Night	41% 9% 16% 24% 10%	1773
	21st to end	Night	38% 7% 12% 27% 15% 1	1980
September	1st to 10th	Night	42% 7% 10% 26% 14% 1	1800
	11th to 20th	Night	33% 6% 11% 26% 23% 1	1890
	21st to end	Night	40% 6% 11% 24% 18% 1	1980
October	1st to 10th	Night	49% 6% 12% 19% 12% 1	2065
	11th to 20th	Night	44% 7% 14% 24% 11% 1	2160
	21st to end	Night	54% 5% 13% 17% 9% 1	2568
November	1st to 10th	Night	43% 6% 12% 21% 16% 2	2407
	11th to 20th	Night	50% 5% 12% 19% 11% 2	2470
	21st to end	Night	50% 6% 17% 20% 7% 1	2593
December	1st to 10th	Night	57% 7% 14% 16% 6%	2660
	11th to 20th	Night	57% 5% 14% 15% 9%	3288
	21st to end	Night	63% 6% 10% 16% 5%	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	31% 24% 26% 13% 6%	180
	11th to 20th	Day	33% 25% 27% 13% 2 1	180
	21st to end	Day	27% 24% 30% 15% 3 1	225
February	1st to 10th	Day	37% 27% 27% 7% 1	270
	11th to 20th	Day	33% 27% 27% 11% 2	444
	21st to end	Day	29% 27% 29% 14% 2	382
March	1st to 10th	Day	30% 20% 33% 15% 2	460
	11th to 20th	Day	30% 23% 28% 15% 3	460
	21st to end	Day	35% 19% 26% 11% 6% 2	470
April	1st to 10th	Day	33% 21% 24% 16% 5% 1	420
	11th to 20th	Day	26% 25% 27% 15% 6% 2	412
	21st to end	Day	29% 17% 30% 18% 5% 2	420
May	1st to 10th	Day	32% 17% 28% 14% 7% 1	423
	11th to 20th	Day	22% 14% 35% 20% 7% 1	447
	21st to end	Day	19% 11% 30% 26% 10% 4	485
June	1st to 10th	Day	18% 13% 32% 22% 13% 2	450
	11th to 20th	Day	20% 10% 30% 25% 12% 2	450
	21st to end	Day	18% 12% 32% 22% 13% 3	450
July	1st to 10th	Day	15% 7% 28% 29% 17% 4	445
	11th to 20th	Day	14% 6% 27% 32% 18% 3	444
	21st to end	Day	11% 8% 33% 32% 14% 2	488
August	1st to 10th	Day	11% 7% 27% 33% 17% 5%	446
	11th to 20th	Day	14% 6% 30% 28% 16% 7%	439
	21st to end	Day	13% 9% 31% 26% 16% 6%	495
September	1st to 10th	Day	19% 9% 22% 29% 15% 7%	450
	11th to 20th	Day	17% 11% 25% 20% 17% 10%	450
	21st to end	Day	19% 10% 29% 24% 13% 6%	450
October	1st to 10th	Day	26% 12% 22% 22% 11% 5%	450
	11th to 20th	Day	21% 16% 30% 21% 10% 2	450
	21st to end	Day	32% 14% 29% 18% 7% 1	399
November	1st to 10th	Day	25% 16% 27% 20% 10% 2	365
	11th to 20th	Day	27% 21% 29% 17% 5% 1	370
	21st to end	Day	30% 22% 26% 18% 3 1	242
December	1st to 10th	Day	27% 27% 28% 13% 5%	180
	11th to 20th	Day	31% 24% 32% 9% 3	180
	21st to end	Day	28% 22% 32% 16% 2 1	198
January	1st to 10th	Night	24% 20% 37% 17% 2	760
	11th to 20th	Night	28% 22% 30% 19% 2	760
	21st to end	Night	22% 22% 34% 20% 2	836
February	1st to 10th	Night	25% 21% 33% 18% 2	760
	11th to 20th	Night	25% 23% 35% 16% 1	743
	21st to end	Night	29% 23% 30% 15% 3	628
March	1st to 10th	Night	27% 23% 32% 16% 2	760
	11th to 20th	Night	25% 24% 33% 16% 2	760
	21st to end	Night	26% 21% 29% 18% 5%	801
April	1st to 10th	Night	26% 20% 30% 21% 3	720
	11th to 20th	Night	27% 17% 29% 19% 7%	711
	21st to end	Night	28% 14% 31% 23% 4	636
May	1st to 10th	Night	27% 15% 30% 20% 8%	534
	11th to 20th	Night	22% 12% 33% 27% 5% 1	354
	21st to end	Night	14% 10% 29% 37% 10% 1	389
June	1st to 10th	Night	20% 5% 31% 31% 12%	360
	11th to 20th	Night	18% 7% 28% 35% 12% 1	360
	21st to end	Night	13% 5% 28% 42% 13% 1	360
July	1st to 10th	Night	14% 5% 20% 44% 17% 1	350
	11th to 20th	Night	15% 3 20% 43% 16% 1	348
	21st to end	Night	16% 3 20% 48% 12% 1	394
August	1st to 10th	Night	12% 3 23% 44% 18% 1	358
	11th to 20th	Night	15% 3 21% 38% 20% 3	709
	21st to end	Night	16% 6% 22% 33% 20% 2	792
September	1st to 10th	Night	17% 6% 28% 33% 14% 2	720
	11th to 20th	Night	17% 7% 26% 29% 17% 4	720
	21st to end	Night	18% 8% 28% 29% 14% 2	720
October	1st to 10th	Night	26% 8% 23% 28% 12% 2	720
	11th to 20th	Night	21% 13% 30% 27% 9%	720
	21st to end	Night	32% 12% 30% 21% 4	792
November	1st to 10th	Night	22% 14% 33% 24% 8%	740
	11th to 20th	Night	25% 15% 33% 18% 7% 1	760
	21st to end	Night	23% 20% 30% 22% 5%	760
December	1st to 10th	Night	26% 21% 32% 17% 4	760
	11th to 20th	Night	29% 17% 29% 22% 2	760
	21st to end	Night	31% 19% 32% 16% 2	836

Page generated at 2024-03-19 23:31:07. Version ac07

Copyright © 2024 Attilla Danko.