Bench Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bench Observatory clear sky chart from 2005-11-06 to 2024-01-13.

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	5% 6% 3 6% 6% 4 6% 6% 7% 9% 44%	75053
	Night	5% 6% 3 6% 6% 3 5% 6% 7% 9% 45%	74709
Transparency	Day	33% 9% 17% 24% 14% 4	74759
	Night	33% 9% 18% 24% 13% 4	74525
Seeing	Day	8% 10% 34% 31% 14% 2	14691
	Night	8% 7% 31% 39% 14% 1	24566

By Month

Percentage Cloud Cover SW (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	3 7% 4 9% 8% 5% 6% 8% 7% 12% 30%	1518
	11th to 20th	Day	3 8% 3 7% 8% 4 7% 8% 10% 10% 32%	1500
	21st to end	Day	3 8% 4 7% 7% 4 6% 7% 9% 11% 35%	1782
February	1st to 10th	Day	5% 9% 5% 10% 7% 5% 7% 7% 8% 10% 28%	1620
	11th to 20th	Day	2 7% 4 10% 10% 5% 8% 7% 9% 8% 30%	1575
	21st to end	Day	4 8% 5% 7% 9% 5% 8% 7% 9% 10% 30%	1367
March	1st to 10th	Day	3 6% 3 7% 7% 4 6% 7% 8% 10% 40%	1944
	11th to 20th	Day	3 5% 4 6% 6% 4 6% 6% 7% 10% 41%	1980
	21st to end	Day	6% 8% 4 7% 7% 5% 6% 6% 7% 9% 35%	2182
April	1st to 10th	Day	6% 8% 4 6% 5% 4 6% 5% 8% 10% 38%	2160
	11th to 20th	Day	7% 7% 3 7% 7% 4 6% 6% 7% 10% 36%	2167
	21st to end	Day	9% 9% 3 7% 6% 3 5% 6% 6% 9% 36%	2340
May	1st to 10th	Day	8% 8% 3 7% 6% 4 5% 6% 6% 8% 38%	2412
	11th to 20th	Day	9% 7% 3 5% 5% 4 6% 6% 8% 9% 39%	2478
	21st to end	Day	13% 8% 3 6% 5% 3 6% 6% 8% 10% 31%	2724
June	1st to 10th	Day	8% 5% 2 5% 5% 3 6% 7% 8% 10% 40%	2520
	11th to 20th	Day	6% 6% 3 5% 6% 4 6% 6% 7% 10% 42%	2565
	21st to end	Day	3 3 1 3 4 3 5% 6% 6% 8% 57%	2700
July	1st to 10th	Day	3 2 1 3 3 3 6% 7% 7% 10% 55%	2620
	11th to 20th	Day	2 2 1 3 4 3 4 6% 7% 9% 61%	2520
	21st to end	Day	4 2 1 4 4 3 4 5% 6% 8% 60%	2681
August	1st to 10th	Day	6% 4 2 4 4 2 4 5% 7% 9% 53%	2328
	11th to 20th	Day	4 3 1 3 5% 3 4 6% 6% 8% 58%	2299
	21st to end	Day	4 3 1 4 5% 2 4 4 5% 8% 59%	2484
September	1st to 10th	Day	6% 3 1 3 3 3 4 3 4 7% 64%	2160
	11th to 20th	Day	6% 3 2 4 4 2 4 4 6% 8% 57%	2104
	21st to end	Day	8% 4 2 4 4 3 3 4 5% 7% 56%	1929
October	1st to 10th	Day	11% 9% 2 6% 6% 3 4 4 5% 7% 44%	1800
	11th to 20th	Day	8% 5% 2 5% 5% 3 5% 4 5% 6% 52%	1800
	21st to end	Day	6% 7% 2 5% 6% 3 4 5% 7% 8% 46%	1980
November	1st to 10th	Day	5% 8% 3 6% 6% 5% 6% 6% 6% 8% 42%	1534
	11th to 20th	Day	3 6% 2 5% 7% 4 6% 6% 8% 9% 43%	1520
	21st to end	Day	5% 8% 4 7% 6% 4 6% 6% 6% 9% 40%	1520
December	1st to 10th	Day	3 7% 3 8% 8% 5% 9% 6% 7% 9% 36%	1520
	11th to 20th	Day	2 4 2 7% 7% 4 8% 8% 7% 13% 37%	1926
	21st to end	Day	3 6% 3 7% 7% 4 6% 7% 7% 9% 40%	2794
January	1st to 10th	Night	3 7% 4 7% 8% 5% 6% 6% 7% 10% 37%	2647
	11th to 20th	Night	3 9% 4 6% 7% 5% 7% 7% 7% 10% 37%	2537
	21st to end	Night	4 8% 3 7% 7% 4 5% 5% 8% 12% 37%	2574
February	1st to 10th	Night	4 8% 6% 10% 7% 4 6% 6% 6% 9% 33%	2340
	11th to 20th	Night	3 8% 6% 10% 8% 4 7% 6% 8% 9% 30%	2272
	21st to end	Night	2 7% 5% 8% 8% 4 6% 7% 7% 10% 36%	1888
March	1st to 10th	Night	3 8% 4 7% 6% 3 5% 5% 7% 10% 42%	2016
	11th to 20th	Night	3 8% 2 6% 5% 4 5% 6% 7% 12% 42%	1980
	21st to end	Night	6% 10% 5% 7% 6% 4 7% 6% 5% 9% 34%	2174
April	1st to 10th	Night	8% 8% 4 7% 6% 3 6% 5% 6% 7% 41%	1800
	11th to 20th	Night	6% 10% 4 8% 7% 4 5% 6% 6% 8% 36%	1739
	21st to end	Night	9% 8% 3 6% 6% 3 4 6% 6% 8% 40%	1620
May	1st to 10th	Night	9% 7% 3 5% 6% 3 5% 5% 6% 7% 43%	1548
	11th to 20th	Night	8% 6% 2 5% 7% 3 6% 6% 7% 11% 40%	1417
	21st to end	Night	12% 7% 3 6% 5% 3 5% 6% 7% 11% 34%	1552
June	1st to 10th	Night	9% 5% 2 4 5% 4 6% 7% 8% 9% 42%	1440
	11th to 20th	Night	8% 5% 2 5% 6% 3 6% 6% 7% 9% 44%	1386
	21st to end	Night	3 3 2 3 3 2 5% 4 6% 8% 60%	1260
July	1st to 10th	Night	3 1 1 3 3 4 6% 6% 10% 62%	1336
	11th to 20th	Night	2 2 1 3 4 1 4 4 6% 9% 64%	1440
	21st to end	Night	3 2 1 3 4 2 4 4 7% 7% 63%	1634
August	1st to 10th	Night	4 4 2 4 5% 2 5% 5% 8% 9% 52%	1611
	11th to 20th	Night	5% 2 1 3 4 2 3 5% 5% 8% 61%	1602
	21st to end	Night	4 4 2 5% 4 2 4 5% 4 7% 59%	1872
September	1st to 10th	Night	6% 4 2 3 3 2 3 3 5% 7% 63%	1800
	11th to 20th	Night	7% 4 2 3 3 3 3 4 5% 7% 59%	1854
	21st to end	Night	8% 5% 2 5% 3 2 3 4 5% 7% 57%	2030
October	1st to 10th	Night	10% 7% 2 5% 5% 4 4 5% 6% 9% 44%	2160
	11th to 20th	Night	8% 6% 3 4 5% 3 4 4 5% 5% 53%	2160
	21st to end	Night	5% 6% 2 5% 5% 3 5% 5% 7% 8% 50%	2376
November	1st to 10th	Night	5% 8% 3 5% 6% 4 5% 5% 6% 9% 44%	2520
	11th to 20th	Night	3 6% 3 6% 6% 4 6% 6% 7% 9% 44%	2660
	21st to end	Night	3 8% 3 6% 6% 4 6% 7% 6% 8% 43%	2660
December	1st to 10th	Night	2 7% 4 8% 7% 4 6% 8% 8% 9% 37%	2660
	11th to 20th	Night	2 6% 3 7% 6% 4 6% 6% 7% 10% 43%	3271
	21st to end	Night	3 7% 3 6% 6% 3 6% 6% 9% 10% 42%	4873

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	41% 11% 22% 21% 5% 1	1519
	11th to 20th	Day	38% 12% 21% 23% 5% 1	1500
	21st to end	Day	37% 11% 20% 24% 8%	1782
February	1st to 10th	Day	47% 9% 18% 21% 5%	1620
	11th to 20th	Day	46% 11% 19% 17% 7% 1	1584
	21st to end	Day	42% 10% 16% 20% 11% 1	1367
March	1st to 10th	Day	32% 11% 23% 26% 8%	1944
	11th to 20th	Day	34% 11% 20% 24% 10% 1	1980
	21st to end	Day	41% 11% 23% 19% 5% 1	2182
April	1st to 10th	Day	38% 11% 19% 22% 9% 1	2160
	11th to 20th	Day	40% 9% 19% 25% 7%	2170
	21st to end	Day	42% 10% 16% 24% 8%	2340
May	1st to 10th	Day	41% 9% 15% 25% 10% 1	2412
	11th to 20th	Day	37% 11% 20% 23% 9%	2482
	21st to end	Day	45% 12% 20% 18% 5% 1	2724
June	1st to 10th	Day	34% 10% 21% 22% 10% 2	2520
	11th to 20th	Day	33% 10% 16% 21% 15% 4	2565
	21st to end	Day	20% 8% 14% 26% 21% 10%	2700
July	1st to 10th	Day	22% 8% 13% 26% 24% 7%	2550
	11th to 20th	Day	18% 5% 9% 25% 27% 16%	2445
	21st to end	Day	20% 6% 10% 19% 27% 18%	2532
August	1st to 10th	Day	25% 7% 12% 25% 20% 11%	2313
	11th to 20th	Day	21% 6% 10% 27% 25% 10%	2299
	21st to end	Day	21% 5% 11% 24% 26% 13%	2484
September	1st to 10th	Day	19% 6% 10% 23% 29% 12%	2160
	11th to 20th	Day	24% 6% 12% 27% 25% 6%	2104
	21st to end	Day	28% 4 12% 30% 23% 4	1929
October	1st to 10th	Day	39% 7% 14% 23% 15% 3	1800
	11th to 20th	Day	31% 6% 18% 30% 11% 4	1800
	21st to end	Day	31% 9% 21% 26% 13% 1	1980
November	1st to 10th	Day	37% 9% 16% 26% 11% 1	1534
	11th to 20th	Day	31% 11% 22% 23% 11% 2	1520
	21st to end	Day	36% 9% 21% 24% 10% 1	1520
December	1st to 10th	Day	42% 10% 19% 20% 8% 1	1520
	11th to 20th	Day	31% 13% 30% 21% 5%	1924
	21st to end	Day	35% 9% 14% 26% 12% 3	2794
January	1st to 10th	Night	36% 11% 23% 21% 7% 1	2647
	11th to 20th	Night	37% 11% 22% 20% 8% 2	2537
	21st to end	Night	38% 9% 21% 25% 7% 1	2574
February	1st to 10th	Night	44% 9% 19% 21% 7%	2340
	11th to 20th	Night	45% 11% 20% 17% 6% 1	2273
	21st to end	Night	39% 10% 16% 21% 13% 1	1888
March	1st to 10th	Night	34% 9% 23% 23% 10% 1	2016
	11th to 20th	Night	31% 11% 21% 25% 11% 1	1980
	21st to end	Night	44% 11% 16% 22% 7% 1	2174
April	1st to 10th	Night	40% 9% 18% 21% 9% 2	1800
	11th to 20th	Night	42% 9% 16% 26% 6%	1739
	21st to end	Night	40% 8% 17% 25% 10%	1620
May	1st to 10th	Night	35% 10% 17% 26% 11% 1	1548
	11th to 20th	Night	34% 14% 18% 24% 9% 1	1418
	21st to end	Night	41% 11% 22% 21% 5%	1552
June	1st to 10th	Night	34% 10% 18% 23% 11% 2	1440
	11th to 20th	Night	32% 9% 19% 21% 14% 5%	1386
	21st to end	Night	20% 7% 13% 30% 22% 8%	1260
July	1st to 10th	Night	15% 7% 15% 31% 26% 6%	1297
	11th to 20th	Night	15% 5% 10% 29% 25% 15%	1392
	21st to end	Night	16% 6% 10% 22% 27% 18%	1543
August	1st to 10th	Night	23% 7% 15% 26% 19% 10%	1602
	11th to 20th	Night	19% 7% 11% 23% 26% 14%	1602
	21st to end	Night	23% 5% 10% 23% 25% 14%	1872
September	1st to 10th	Night	20% 7% 9% 21% 28% 15%	1800
	11th to 20th	Night	24% 7% 11% 24% 26% 8%	1854
	21st to end	Night	27% 5% 10% 27% 26% 5%	2030
October	1st to 10th	Night	35% 8% 15% 25% 13% 4	2160
	11th to 20th	Night	33% 6% 14% 30% 14% 4	2160
	21st to end	Night	30% 9% 17% 28% 14% 2	2376
November	1st to 10th	Night	33% 10% 18% 24% 12% 3	2520
	11th to 20th	Night	33% 9% 19% 27% 9% 2	2660
	21st to end	Night	34% 9% 21% 22% 14% 1	2660
December	1st to 10th	Night	37% 11% 22% 20% 8% 2	2660
	11th to 20th	Night	31% 11% 26% 27% 5%	3272
	21st to end	Night	31% 10% 19% 26% 12% 2	4873

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	6% 13% 41% 31% 9%	270
	11th to 20th	Day	6% 12% 46% 25% 9% 2	248
	21st to end	Day	6% 11% 52% 25% 5% 2	264
February	1st to 10th	Day	6% 15% 54% 24% 1	240
	11th to 20th	Day	6% 12% 54% 23% 5% 1	240
	21st to end	Day	3 11% 51% 28% 6% 1	198
March	1st to 10th	Day	5% 11% 46% 32% 4 1	384
	11th to 20th	Day	7% 10% 39% 36% 8% 1	420
	21st to end	Day	10% 16% 35% 26% 10% 2	462
April	1st to 10th	Day	13% 13% 45% 25% 4	420
	11th to 20th	Day	11% 19% 44% 22% 4	412
	21st to end	Day	18% 13% 29% 27% 12% 1	420
May	1st to 10th	Day	13% 13% 28% 27% 16% 3	495
	11th to 20th	Day	12% 10% 27% 31% 16% 4	625
	21st to end	Day	16% 10% 21% 27% 21% 5%	679
June	1st to 10th	Day	8% 8% 25% 34% 22% 4	630
	11th to 20th	Day	11% 14% 30% 32% 12% 1	630
	21st to end	Day	4 7% 25% 42% 20% 2	630
July	1st to 10th	Day	5% 4 21% 44% 24% 2	621
	11th to 20th	Day	3 4 26% 44% 21% 2	618
	21st to end	Day	3 4 19% 43% 27% 4	623
August	1st to 10th	Day	7% 5% 24% 37% 22% 5%	447
	11th to 20th	Day	6% 5% 22% 36% 27% 3	437
	21st to end	Day	5% 6% 26% 36% 20% 7%	495
September	1st to 10th	Day	7% 6% 31% 33% 21% 3	450
	11th to 20th	Day	10% 7% 26% 34% 18% 5%	450
	21st to end	Day	13% 9% 29% 32% 15% 2	399
October	1st to 10th	Day	11% 6% 35% 30% 15% 3	270
	11th to 20th	Day	8% 15% 39% 25% 11% 2	270
	21st to end	Day	10% 16% 42% 23% 8% 1	297
November	1st to 10th	Day	10% 11% 49% 23% 7% 1	270
	11th to 20th	Day	7% 15% 51% 23% 3 1	270
	21st to end	Day	10% 11% 51% 23% 4	270
December	1st to 10th	Day	7% 10% 55% 22% 6% 1	270
	11th to 20th	Day	8% 12% 54% 22% 4	270
	21st to end	Day	7% 11% 49% 26% 7%	297
January	1st to 10th	Night	5% 9% 41% 36% 8% 1	950
	11th to 20th	Night	8% 10% 42% 31% 8% 1	890
	21st to end	Night	7% 7% 41% 36% 8% 1	792
February	1st to 10th	Night	7% 9% 42% 33% 7% 1	720
	11th to 20th	Night	8% 7% 41% 35% 8% 1	704
	21st to end	Night	5% 7% 38% 36% 11% 3	592
March	1st to 10th	Night	6% 6% 36% 40% 11% 1	720
	11th to 20th	Night	6% 7% 34% 38% 13% 2	720
	21st to end	Night	11% 9% 26% 39% 14% 2	788
April	1st to 10th	Night	11% 10% 29% 41% 9% 1	540
	11th to 20th	Night	10% 10% 35% 38% 7% 1	533
	21st to end	Night	11% 7% 27% 40% 12% 2	540
May	1st to 10th	Night	14% 10% 21% 35% 19% 2	540
	11th to 20th	Night	10% 7% 21% 39% 22% 2	531
	21st to end	Night	13% 7% 21% 37% 19% 2	584
June	1st to 10th	Night	10% 7% 22% 36% 23% 2	540
	11th to 20th	Night	10% 8% 28% 39% 15%	486
	21st to end	Night	4 5% 14% 54% 23% 1	360
July	1st to 10th	Night	3 2 16% 46% 32% 1	422
	11th to 20th	Night	3 3 20% 53% 20% 1	522
	21st to end	Night	3 2 15% 52% 25% 2	591
August	1st to 10th	Night	5% 3 14% 50% 27% 2	537
	11th to 20th	Night	4 4 14% 48% 28% 2	534
	21st to end	Night	5% 5% 17% 47% 24% 2	594
September	1st to 10th	Night	7% 4 16% 45% 24% 4	540
	11th to 20th	Night	7% 4 22% 42% 22% 3	594
	21st to end	Night	11% 5% 22% 40% 20% 3	720
October	1st to 10th	Night	13% 4 25% 38% 17% 3	720
	11th to 20th	Night	10% 8% 31% 35% 15% 2	720
	21st to end	Night	9% 8% 34% 36% 11% 2	792
November	1st to 10th	Night	9% 8% 37% 35% 9% 1	905
	11th to 20th	Night	6% 11% 41% 36% 5%	950
	21st to end	Night	7% 8% 42% 36% 7%	950
December	1st to 10th	Night	5% 8% 40% 37% 8% 1	950
	11th to 20th	Night	6% 7% 44% 34% 8% 1	950
	21st to end	Night	7% 10% 42% 33% 7% 1	1045

Page generated at 2024-01-10 17:35:20. Version ac07

Copyright 2024 Attilla Danko