Visual Reconstructions Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Visual Reconstructions Observatory clear sky chart from 2005-11-06 to 2024-04-10.

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% 10% 4 7% 6% 4 5% 5% 5% 7% 32%	82948
	Night	15% 10% 4 7% 6% 3 4 5% 5% 6% 34%	85822
Transparency	Day	49% 7% 13% 19% 11% 1	82659
	Night	49% 7% 13% 20% 11% 1	85633
Seeing	Day	16% 11% 29% 24% 14% 6%	14488
	Night	18% 9% 29% 30% 12% 1	24328

By Month

Percentage Cloud Cover SE (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	16% 16% 6% 11% 7% 3 5% 4 4 6% 22%	2527
	11th to 20th	Day	15% 16% 7% 11% 9% 7% 8% 5% 5% 5% 12%	2533
	21st to end	Day	28% 17% 8% 9% 7% 3 5% 4 3 4 13%	3124
February	1st to 10th	Day	14% 14% 5% 10% 9% 5% 6% 5% 5% 5% 22%	1710
	11th to 20th	Day	13% 12% 6% 11% 8% 4 6% 5% 5% 5% 25%	1770
	21st to end	Day	14% 13% 5% 10% 7% 4 4 5% 5% 6% 26%	1570
March	1st to 10th	Day	18% 15% 5% 8% 6% 4 4 4 4 6% 27%	3230
	11th to 20th	Day	13% 12% 5% 7% 7% 4 5% 5% 4 7% 31%	3480
	21st to end	Day	20% 12% 4 8% 6% 3 5% 4 4 6% 28%	3815
April	1st to 10th	Day	15% 13% 4 7% 6% 3 4 5% 5% 7% 30%	2174
	11th to 20th	Day	16% 10% 3 6% 6% 3 5% 5% 5% 6% 33%	2298
	21st to end	Day	19% 8% 3 7% 5% 3 4 4 5% 7% 33%	2340
May	1st to 10th	Day	17% 8% 3 7% 6% 4 5% 5% 6% 7% 33%	2340
	11th to 20th	Day	18% 8% 3 6% 5% 4 5% 5% 5% 7% 35%	2301
	21st to end	Day	13% 6% 2 5% 5% 3 5% 6% 6% 9% 40%	2531
June	1st to 10th	Day	10% 6% 3 5% 7% 3 5% 5% 6% 10% 41%	2624
	11th to 20th	Day	11% 5% 2 6% 6% 3 5% 6% 5% 9% 42%	2700
	21st to end	Day	9% 5% 3 6% 6% 4 6% 7% 8% 9% 38%	2634
July	1st to 10th	Day	7% 4 2 5% 6% 3 6% 6% 7% 8% 45%	2520
	11th to 20th	Day	9% 4 3 5% 4 4 6% 6% 7% 10% 43%	2520
	21st to end	Day	7% 4 3 5% 6% 4 6% 7% 7% 10% 40%	2565
August	1st to 10th	Day	8% 5% 2 6% 6% 4 6% 7% 7% 10% 40%	2327
	11th to 20th	Day	9% 5% 2 5% 6% 5% 6% 7% 8% 9% 39%	2303
	21st to end	Day	11% 5% 2 5% 6% 3 5% 5% 6% 9% 41%	2574
September	1st to 10th	Day	12% 5% 3 6% 6% 4 5% 5% 5% 9% 40%	2026
	11th to 20th	Day	10% 5% 3 4 5% 3 4 4 7% 8% 46%	1980
	21st to end	Day	14% 6% 2 6% 5% 3 5% 6% 6% 9% 37%	1980
October	1st to 10th	Day	13% 6% 2 6% 6% 3 5% 4 6% 8% 42%	1913
	11th to 20th	Day	17% 10% 3 6% 6% 4 5% 5% 4 7% 33%	1800
	21st to end	Day	20% 11% 3 7% 6% 4 4 5% 4 6% 30%	1854
November	1st to 10th	Day	11% 10% 3 7% 5% 4 6% 5% 6% 7% 39%	1672
	11th to 20th	Day	14% 11% 3 6% 7% 5% 5% 5% 5% 7% 32%	1710
	21st to end	Day	18% 10% 5% 9% 6% 3 5% 4 5% 6% 30%	1555
December	1st to 10th	Day	14% 13% 8% 11% 7% 4 6% 5% 4 6% 22%	1520
	11th to 20th	Day	17% 15% 5% 8% 6% 3 5% 5% 6% 6% 24%	1792
	21st to end	Day	26% 19% 7% 9% 7% 3 4 4 4 5% 11%	2636
January	1st to 10th	Night	16% 16% 6% 9% 6% 4 5% 3 4 5% 25%	4428
	11th to 20th	Night	13% 18% 7% 12% 8% 4 6% 6% 5% 5% 16%	4434
	21st to end	Night	23% 18% 8% 9% 5% 3 3 4 3 4 19%	4532
February	1st to 10th	Night	15% 15% 5% 10% 8% 4 5% 5% 5% 5% 23%	2470
	11th to 20th	Night	13% 12% 5% 9% 8% 3 6% 5% 5% 6% 27%	2291
	21st to end	Night	18% 11% 4 8% 6% 3 4 5% 5% 7% 29%	1884
March	1st to 10th	Night	16% 14% 4 7% 5% 3 4 4 4 6% 35%	3622
	11th to 20th	Night	10% 8% 3 5% 6% 4 5% 6% 6% 7% 41%	3480
	21st to end	Night	16% 8% 3 8% 6% 3 4 4 4 5% 37%	3817
April	1st to 10th	Night	17% 9% 3 6% 5% 3 5% 4 6% 7% 35%	2010
	11th to 20th	Night	18% 8% 4 4 5% 3 4 4 6% 6% 38%	1611
	21st to end	Night	17% 7% 2 6% 5% 3 4 5% 5% 7% 40%	1620
May	1st to 10th	Night	16% 8% 3 7% 6% 3 4 6% 5% 8% 34%	1620
	11th to 20th	Night	18% 6% 3 5% 4 3 4 4 5% 8% 40%	1592
	21st to end	Night	9% 4 2 5% 5% 3 5% 5% 6% 9% 46%	1744
June	1st to 10th	Night	11% 5% 2 6% 4 3 5% 5% 6% 7% 47%	1328
	11th to 20th	Night	9% 5% 2 5% 5% 4 4 5% 6% 8% 46%	1260
	21st to end	Night	9% 5% 2 5% 5% 3 4 4 6% 8% 49%	1319
July	1st to 10th	Night	7% 4 2 4 5% 3 4 5% 6% 8% 53%	1440
	11th to 20th	Night	8% 4 1 4 4 2 5% 4 6% 8% 53%	1440
	21st to end	Night	6% 4 3 4 4 3 5% 6% 7% 9% 50%	1750
August	1st to 10th	Night	7% 4 2 4 5% 3 4 4 6% 9% 52%	1611
	11th to 20th	Night	7% 3 3 5% 5% 3 5% 5% 6% 8% 50%	1598
	21st to end	Night	9% 4 2 4 5% 2 4 4 6% 7% 52%	1782
September	1st to 10th	Night	10% 5% 3 5% 5% 3 4 4 5% 7% 47%	1912
	11th to 20th	Night	10% 5% 2 4 4 2 3 4 5% 7% 54%	1980
	21st to end	Night	15% 5% 2 5% 5% 3 4 4 5% 7% 45%	1980
October	1st to 10th	Night	14% 7% 3 5% 4 2 4 4 5% 7% 45%	2045
	11th to 20th	Night	19% 8% 3 6% 5% 3 5% 5% 4 6% 36%	2160
	21st to end	Night	22% 9% 2 6% 6% 3 4 5% 5% 6% 31%	2499
November	1st to 10th	Night	12% 7% 3 6% 4 3 4 4 5% 7% 43%	2406
	11th to 20th	Night	15% 10% 3 7% 7% 4 5% 5% 6% 6% 32%	2470
	21st to end	Night	20% 11% 4 7% 6% 2 4 5% 5% 6% 29%	2622
December	1st to 10th	Night	18% 13% 7% 8% 7% 3 6% 5% 5% 5% 23%	2660
	11th to 20th	Night	14% 14% 6% 8% 7% 4 5% 4 5% 7% 25%	3393
	21st to end	Night	28% 20% 6% 10% 5% 3 3 4 4 4 13%	5012

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	62% 8% 12% 12% 5% 1	2528
	11th to 20th	Day	71% 7% 12% 7% 3	2533
	21st to end	Day	73% 8% 8% 6% 3 1	3124
February	1st to 10th	Day	62% 8% 9% 14% 6%	1710
	11th to 20th	Day	60% 5% 10% 17% 8% 1	1779
	21st to end	Day	57% 7% 12% 17% 7% 1	1570
March	1st to 10th	Day	58% 6% 12% 18% 5% 1	3230
	11th to 20th	Day	51% 6% 14% 19% 7% 1	3480
	21st to end	Day	56% 7% 13% 14% 9% 2	3815
April	1st to 10th	Day	51% 6% 13% 18% 11% 1	2174
	11th to 20th	Day	49% 6% 12% 18% 13% 2	2298
	21st to end	Day	50% 6% 14% 16% 13% 2	2340
May	1st to 10th	Day	49% 7% 11% 20% 10% 2	2340
	11th to 20th	Day	48% 7% 12% 18% 14% 2	2305
	21st to end	Day	39% 8% 14% 22% 15% 2	2531
June	1st to 10th	Day	39% 6% 13% 26% 13% 2	2624
	11th to 20th	Day	37% 9% 13% 23% 15% 3	2700
	21st to end	Day	38% 9% 14% 22% 16% 2	2634
July	1st to 10th	Day	34% 8% 11% 25% 19% 3	2451
	11th to 20th	Day	32% 8% 16% 25% 17% 2	2445
	21st to end	Day	35% 10% 14% 21% 17% 2	2423
August	1st to 10th	Day	34% 11% 15% 26% 12% 1	2314
	11th to 20th	Day	37% 10% 15% 24% 12% 2	2303
	21st to end	Day	38% 7% 12% 24% 17% 2	2574
September	1st to 10th	Day	40% 8% 15% 23% 13% 2	2026
	11th to 20th	Day	33% 7% 13% 33% 13%	1980
	21st to end	Day	41% 8% 14% 24% 12% 1	1980
October	1st to 10th	Day	39% 8% 13% 26% 13% 2	1913
	11th to 20th	Day	50% 6% 14% 19% 10%	1800
	21st to end	Day	54% 6% 13% 18% 8%	1854
November	1st to 10th	Day	43% 8% 13% 24% 12% 1	1672
	11th to 20th	Day	50% 6% 15% 18% 10% 1	1710
	21st to end	Day	56% 6% 13% 18% 7% 1	1555
December	1st to 10th	Day	63% 6% 11% 15% 4	1520
	11th to 20th	Day	59% 7% 14% 14% 5%	1788
	21st to end	Day	75% 6% 10% 6% 3	2636
January	1st to 10th	Night	59% 6% 13% 15% 5% 1	4428
	11th to 20th	Night	67% 8% 12% 10% 3	4434
	21st to end	Night	69% 5% 10% 13% 3	4532
February	1st to 10th	Night	60% 8% 11% 14% 7% 1	2470
	11th to 20th	Night	55% 7% 11% 17% 9% 1	2293
	21st to end	Night	54% 6% 13% 18% 8% 1	1884
March	1st to 10th	Night	51% 5% 14% 23% 7%	3622
	11th to 20th	Night	38% 7% 17% 18% 18% 1	3480
	21st to end	Night	47% 6% 12% 22% 12% 1	3817
April	1st to 10th	Night	48% 6% 12% 20% 13% 2	2010
	11th to 20th	Night	44% 7% 11% 18% 18% 2	1611
	21st to end	Night	44% 5% 11% 20% 16% 4	1620
May	1st to 10th	Night	47% 7% 12% 19% 12% 2	1620
	11th to 20th	Night	43% 6% 10% 19% 18% 3	1593
	21st to end	Night	34% 7% 15% 24% 17% 3	1745
June	1st to 10th	Night	35% 6% 12% 28% 16% 3	1328
	11th to 20th	Night	34% 8% 13% 25% 18% 2	1260
	21st to end	Night	32% 7% 12% 26% 21% 1	1319
July	1st to 10th	Night	28% 7% 12% 29% 21% 3	1400
	11th to 20th	Night	28% 7% 14% 32% 17% 2	1392
	21st to end	Night	26% 10% 19% 23% 19% 4	1653
August	1st to 10th	Night	29% 7% 17% 31% 15% 2	1600
	11th to 20th	Night	29% 9% 14% 32% 13% 3	1598
	21st to end	Night	30% 7% 14% 29% 18% 1	1782
September	1st to 10th	Night	36% 7% 14% 26% 15% 2	1912
	11th to 20th	Night	30% 6% 13% 31% 19% 1	1980
	21st to end	Night	38% 6% 12% 30% 12% 1	1980
October	1st to 10th	Night	39% 5% 12% 25% 18% 1	2045
	11th to 20th	Night	47% 7% 14% 19% 12% 1	2160
	21st to end	Night	52% 6% 12% 20% 9% 1	2499
November	1st to 10th	Night	41% 6% 13% 26% 14% 1	2406
	11th to 20th	Night	49% 6% 15% 20% 9% 1	2470
	21st to end	Night	55% 7% 13% 19% 6%	2622
December	1st to 10th	Night	61% 8% 11% 14% 5%	2660
	11th to 20th	Night	56% 7% 15% 14% 6% 1	3396
	21st to end	Night	75% 5% 10% 7% 2	5012

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	22% 19% 34% 17% 7%	270
	11th to 20th	Day	20% 18% 41% 16% 4 1	270
	21st to end	Day	27% 11% 37% 18% 6%	297
February	1st to 10th	Day	22% 18% 40% 17% 3 1	270
	11th to 20th	Day	20% 20% 38% 20% 2	270
	21st to end	Day	18% 24% 43% 12% 4	225
March	1st to 10th	Day	23% 19% 35% 17% 5%	328
	11th to 20th	Day	20% 15% 33% 25% 6% 1	460
	21st to end	Day	26% 14% 32% 21% 5% 1	506
April	1st to 10th	Day	15% 17% 37% 20% 9% 1	457
	11th to 20th	Day	24% 15% 29% 15% 10% 6%	412
	21st to end	Day	24% 12% 29% 23% 10% 3	420
May	1st to 10th	Day	22% 11% 29% 24% 11% 3	423
	11th to 20th	Day	18% 10% 27% 26% 12% 6%	447
	21st to end	Day	14% 7% 21% 29% 21% 9%	485
June	1st to 10th	Day	13% 7% 31% 31% 15% 3	590
	11th to 20th	Day	11% 6% 31% 31% 17% 3	630
	21st to end	Day	11% 7% 29% 32% 17% 5%	630
July	1st to 10th	Day	7% 5% 21% 31% 24% 12%	621
	11th to 20th	Day	10% 5% 24% 33% 20% 8%	618
	21st to end	Day	8% 4 23% 30% 24% 11%	506
August	1st to 10th	Day	9% 2 21% 26% 27% 15%	446
	11th to 20th	Day	10% 3 19% 30% 23% 15%	439
	21st to end	Day	13% 4 20% 29% 23% 12%	495
September	1st to 10th	Day	13% 4 24% 25% 24% 11%	450
	11th to 20th	Day	10% 5% 20% 24% 28% 14%	450
	21st to end	Day	16% 8% 24% 23% 20% 8%	450
October	1st to 10th	Day	15% 10% 27% 20% 18% 10%	450
	11th to 20th	Day	22% 16% 30% 24% 7% 2	450
	21st to end	Day	25% 15% 36% 19% 5% 1	369
November	1st to 10th	Day	14% 19% 33% 23% 9% 2	270
	11th to 20th	Day	20% 21% 34% 18% 7% 1	270
	21st to end	Day	22% 18% 38% 18% 4	196
December	1st to 10th	Day	22% 17% 41% 13% 7% 1	180
	11th to 20th	Day	27% 17% 39% 14% 3 1	180
	21st to end	Day	26% 21% 33% 17% 3	258
January	1st to 10th	Night	22% 14% 36% 22% 5% 1	950
	11th to 20th	Night	24% 14% 33% 24% 4 1	944
	21st to end	Night	20% 11% 34% 29% 6%	836
February	1st to 10th	Night	22% 12% 39% 24% 4	760
	11th to 20th	Night	20% 14% 35% 26% 5%	743
	21st to end	Night	24% 13% 40% 21% 2	628
March	1st to 10th	Night	20% 11% 36% 28% 5%	760
	11th to 20th	Night	16% 14% 38% 26% 5% 1	760
	21st to end	Night	22% 10% 32% 27% 8% 1	836
April	1st to 10th	Night	21% 14% 31% 29% 4 1	680
	11th to 20th	Night	21% 9% 32% 28% 9% 2	533
	21st to end	Night	19% 7% 32% 31% 10%	540
May	1st to 10th	Night	18% 6% 29% 35% 10% 1	540
	11th to 20th	Night	21% 4 26% 32% 16% 1	531
	21st to end	Night	11% 2 23% 41% 22% 2	584
June	1st to 10th	Night	12% 4 26% 42% 16%	392
	11th to 20th	Night	10% 4 24% 47% 15%	360
	21st to end	Night	10% 5% 20% 45% 20% 1	419
July	1st to 10th	Night	7% 3 17% 39% 29% 4	525
	11th to 20th	Night	9% 3 18% 41% 25% 4	522
	21st to end	Night	5% 3 19% 48% 23% 2	591
August	1st to 10th	Night	9% 3 17% 36% 33% 3	537
	11th to 20th	Night	7% 2 18% 37% 31% 5%	534
	21st to end	Night	9% 3 18% 36% 31% 3	594
September	1st to 10th	Night	12% 5% 18% 35% 24% 6%	661
	11th to 20th	Night	11% 3 18% 34% 28% 5%	720
	21st to end	Night	17% 6% 20% 31% 21% 5%	720
October	1st to 10th	Night	16% 8% 26% 30% 18% 3	720
	11th to 20th	Night	23% 12% 28% 27% 8% 2	720
	21st to end	Night	26% 11% 31% 27% 5%	792
November	1st to 10th	Night	17% 10% 32% 26% 14% 1	740
	11th to 20th	Night	20% 16% 32% 24% 7% 1	760
	21st to end	Night	24% 13% 34% 22% 6%	760
December	1st to 10th	Night	25% 12% 37% 20% 6%	760
	11th to 20th	Night	22% 14% 37% 23% 3	831
	21st to end	Night	28% 12% 34% 22% 3	1045

Page generated at 2024-04-07 09:28:13. Version ac07

Copyright © 2024 Attilla Danko.