Observatoire Bennett
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire Bennett clear sky chart from 2005-11-06 to 2024-03-01.

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	17% 13% 5% 9% 7% 4 5% 4 5% 6% 24%	78028
	Night	15% 14% 6% 11% 9% 4 5% 4 4 5% 23%	81348
Transparency	Day	60% 7% 10% 15% 7% 1	77733
	Night	63% 7% 10% 14% 7% 1	81178
Seeing	Day	28% 21% 28% 15% 6% 1	13983
	Night	26% 19% 27% 20% 7% 1	22974

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	10% 16% 10% 15% 14% 5% 6% 4 4 4 12%	2517
	11th to 20th	Day	7% 13% 6% 19% 19% 8% 4 3 3 3 15%	2520
	21st to end	Day	9% 15% 8% 19% 9% 4 6% 4 4 5% 17%	2772
February	1st to 10th	Day	11% 17% 8% 14% 14% 5% 5% 4 3 3 16%	1585
	11th to 20th	Day	9% 18% 10% 17% 10% 5% 5% 4 4 4 15%	1848
	21st to end	Day	9% 18% 6% 13% 9% 5% 7% 4 5% 5% 18%	1570
March	1st to 10th	Day	10% 17% 9% 12% 8% 5% 4 5% 3 4 22%	1797
	11th to 20th	Day	13% 15% 7% 10% 8% 5% 4 4 4 5% 25%	1898
	21st to end	Day	16% 17% 7% 12% 7% 3 4 3 3 3 25%	2292
April	1st to 10th	Day	18% 19% 7% 11% 7% 2 2 3 3 5% 23%	2160
	11th to 20th	Day	16% 16% 6% 7% 5% 3 4 3 3 5% 32%	2208
	21st to end	Day	22% 17% 4 8% 5% 2 4 3 5% 5% 24%	2340
May	1st to 10th	Day	23% 13% 4 7% 5% 2 4 4 4 5% 29%	2340
	11th to 20th	Day	22% 10% 4 7% 5% 3 5% 4 5% 5% 31%	2459
	21st to end	Day	20% 9% 3 7% 6% 4 5% 5% 6% 8% 27%	2725
June	1st to 10th	Day	28% 10% 3 6% 5% 3 5% 5% 6% 6% 23%	2538
	11th to 20th	Day	21% 7% 3 6% 6% 3 5% 5% 6% 7% 31%	2700
	21st to end	Day	23% 8% 5% 7% 6% 4 5% 5% 5% 7% 24%	2530
July	1st to 10th	Day	19% 7% 3 6% 6% 4 5% 4 6% 8% 31%	2520
	11th to 20th	Day	18% 8% 4 7% 7% 4 7% 6% 7% 8% 27%	2520
	21st to end	Day	20% 8% 4 6% 6% 4 6% 6% 6% 8% 25%	2744
August	1st to 10th	Day	20% 7% 3 7% 6% 4 6% 6% 6% 9% 27%	2445
	11th to 20th	Day	18% 8% 3 7% 6% 3 5% 6% 7% 8% 28%	2304
	21st to end	Day	20% 8% 3 5% 6% 3 4 5% 6% 7% 33%	2446
September	1st to 10th	Day	19% 7% 3 6% 5% 4 4 4 5% 6% 37%	2160
	11th to 20th	Day	19% 9% 2 5% 5% 3 4 4 4 6% 39%	1985
	21st to end	Day	19% 10% 3 6% 4 3 5% 4 6% 7% 33%	1980
October	1st to 10th	Day	20% 13% 4 5% 4 3 5% 5% 6% 7% 27%	1980
	11th to 20th	Day	16% 17% 5% 9% 7% 3 4 5% 5% 5% 24%	1682
	21st to end	Day	21% 24% 5% 7% 6% 2 4 4 4 4 20%	1782
November	1st to 10th	Day	16% 18% 7% 8% 7% 3 4 4 4 4 25%	1671
	11th to 20th	Day	16% 15% 9% 11% 7% 3 4 5% 5% 5% 19%	1710
	21st to end	Day	14% 17% 7% 13% 8% 3 5% 4 4 7% 17%	1559
December	1st to 10th	Day	16% 20% 11% 15% 9% 3 3 3 3 3 14%	1330
	11th to 20th	Day	15% 18% 8% 11% 9% 4 5% 3 3 4 19%	1668
	21st to end	Day	18% 20% 8% 11% 11% 3 4 4 3 3 14%	2743
January	1st to 10th	Night	11% 15% 9% 18% 16% 5% 6% 4 3 3 10%	4429
	11th to 20th	Night	9% 15% 8% 16% 19% 7% 7% 4 3 3 9%	4440
	21st to end	Night	10% 15% 10% 16% 11% 6% 7% 4 4 4 13%	4884
February	1st to 10th	Night	9% 14% 9% 14% 13% 6% 7% 4 4 4 16%	2590
	11th to 20th	Night	8% 15% 9% 17% 12% 6% 7% 4 3 4 15%	2218
	21st to end	Night	10% 14% 7% 13% 9% 5% 7% 4 4 5% 22%	1884
March	1st to 10th	Night	11% 17% 8% 11% 9% 5% 6% 4 3 4 22%	2157
	11th to 20th	Night	13% 14% 5% 11% 8% 4 6% 4 4 5% 25%	2061
	21st to end	Night	16% 15% 7% 11% 6% 3 4 3 4 4 27%	2062
April	1st to 10th	Night	19% 18% 6% 9% 5% 3 4 4 3 4 25%	1800
	11th to 20th	Night	19% 14% 5% 6% 4 3 4 4 4 6% 31%	1701
	21st to end	Night	21% 15% 4 6% 6% 2 5% 4 4 6% 27%	1620
May	1st to 10th	Night	21% 13% 4 7% 5% 3 4 4 6% 6% 27%	1620
	11th to 20th	Night	18% 9% 4 8% 8% 3 5% 4 4 5% 32%	1450
	21st to end	Night	21% 8% 3 6% 5% 3 5% 4 6% 7% 32%	1550
June	1st to 10th	Night	27% 9% 3 8% 5% 2 4 4 5% 7% 27%	1411
	11th to 20th	Night	19% 8% 3 6% 5% 2 5% 4 6% 7% 34%	1260
	21st to end	Night	19% 7% 4 7% 7% 4 5% 5% 5% 7% 30%	1418
July	1st to 10th	Night	16% 8% 3 6% 6% 3 6% 5% 5% 8% 34%	1440
	11th to 20th	Night	14% 7% 3 5% 6% 5% 5% 7% 6% 9% 33%	1440
	21st to end	Night	16% 7% 3 6% 6% 3 6% 5% 6% 8% 34%	1574
August	1st to 10th	Night	16% 5% 3 5% 5% 3 5% 6% 6% 8% 37%	1476
	11th to 20th	Night	16% 8% 3 7% 6% 3 4 4 6% 8% 35%	1596
	21st to end	Night	16% 7% 3 5% 5% 3 4 4 5% 8% 40%	1908
September	1st to 10th	Night	16% 9% 3 6% 5% 3 4 4 5% 6% 39%	1800
	11th to 20th	Night	18% 9% 2 4 4 3 3 5% 5% 6% 41%	1975
	21st to end	Night	20% 8% 2 5% 5% 3 4 4 4 7% 40%	1980
October	1st to 10th	Night	18% 10% 3 7% 6% 4 4 5% 5% 5% 33%	1980
	11th to 20th	Night	20% 16% 3 7% 7% 4 4 4 4 6% 25%	2273
	21st to end	Night	23% 18% 4 8% 5% 3 5% 5% 4 4 21%	2574
November	1st to 10th	Night	19% 17% 6% 8% 7% 3 4 3 3 5% 23%	2407
	11th to 20th	Night	14% 14% 9% 13% 7% 3 3 4 4 5% 24%	2470
	21st to end	Night	14% 16% 9% 14% 11% 4 4 3 3 5% 18%	2612
December	1st to 10th	Night	16% 19% 10% 15% 9% 4 4 4 4 4 12%	2850
	11th to 20th	Night	13% 21% 9% 17% 10% 4 5% 3 3 3 12%	3531
	21st to end	Night	18% 18% 7% 13% 9% 4 4 3 3 4 17%	4907

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	74% 7% 10% 7% 2	2518
	11th to 20th	Day	75% 5% 4 11% 3 1	2520
	21st to end	Day	70% 5% 9% 7% 6% 2	2772
February	1st to 10th	Day	74% 3 5% 10% 6% 1	1585
	11th to 20th	Day	74% 4 7% 9% 5% 1	1857
	21st to end	Day	67% 5% 8% 12% 6% 2	1570
March	1st to 10th	Day	66% 6% 7% 13% 5% 3	1800
	11th to 20th	Day	62% 5% 10% 11% 10% 2	1898
	21st to end	Day	66% 4 6% 13% 9% 2	2292
April	1st to 10th	Day	65% 4 9% 12% 8% 2	2160
	11th to 20th	Day	56% 4 8% 19% 12% 1	2208
	21st to end	Day	61% 6% 8% 13% 9% 3	2340
May	1st to 10th	Day	58% 5% 7% 17% 11% 1	2340
	11th to 20th	Day	55% 7% 11% 17% 9% 1	2463
	21st to end	Day	53% 10% 13% 15% 9%	2725
June	1st to 10th	Day	60% 8% 10% 17% 5%	2538
	11th to 20th	Day	51% 8% 13% 20% 8% 1	2700
	21st to end	Day	58% 9% 11% 16% 5%	2530
July	1st to 10th	Day	50% 8% 16% 20% 7%	2450
	11th to 20th	Day	52% 9% 14% 19% 6%	2445
	21st to end	Day	55% 9% 13% 17% 5%	2591
August	1st to 10th	Day	52% 10% 16% 19% 4	2431
	11th to 20th	Day	49% 11% 17% 17% 7%	2304
	21st to end	Day	48% 9% 14% 18% 11%	2446
September	1st to 10th	Day	47% 7% 14% 21% 9%	2160
	11th to 20th	Day	45% 6% 12% 25% 12% 1	1985
	21st to end	Day	49% 8% 11% 21% 10% 1	1980
October	1st to 10th	Day	54% 7% 13% 17% 9%	1980
	11th to 20th	Day	60% 8% 12% 15% 5%	1682
	21st to end	Day	68% 5% 9% 10% 7% 1	1782
November	1st to 10th	Day	61% 6% 10% 15% 7% 1	1671
	11th to 20th	Day	65% 7% 8% 11% 6% 2	1710
	21st to end	Day	67% 7% 11% 12% 3	1559
December	1st to 10th	Day	78% 4 6% 7% 5%	1330
	11th to 20th	Day	69% 5% 7% 10% 8% 1	1668
	21st to end	Day	74% 6% 5% 8% 6%	2743
January	1st to 10th	Night	78% 6% 8% 6% 2	4429
	11th to 20th	Night	80% 6% 5% 6% 2	4440
	21st to end	Night	74% 6% 8% 7% 5% 1	4884
February	1st to 10th	Night	71% 6% 7% 10% 5% 1	2590
	11th to 20th	Night	73% 6% 7% 9% 5% 1	2220
	21st to end	Night	65% 6% 6% 13% 8% 1	1884
March	1st to 10th	Night	67% 5% 6% 14% 6% 2	2167
	11th to 20th	Night	61% 8% 9% 11% 10% 2	2062
	21st to end	Night	61% 5% 7% 16% 8% 3	2062
April	1st to 10th	Night	63% 5% 8% 13% 10% 1	1800
	11th to 20th	Night	53% 7% 9% 18% 11% 1	1701
	21st to end	Night	58% 7% 11% 14% 9% 2	1620
May	1st to 10th	Night	55% 7% 9% 17% 11% 1	1620
	11th to 20th	Night	54% 7% 11% 17% 9% 1	1451
	21st to end	Night	51% 7% 13% 19% 9% 1	1551
June	1st to 10th	Night	56% 7% 11% 19% 6%	1411
	11th to 20th	Night	47% 8% 12% 22% 9% 2	1260
	21st to end	Night	52% 10% 12% 19% 6%	1418
July	1st to 10th	Night	46% 10% 16% 19% 9%	1400
	11th to 20th	Night	44% 11% 16% 23% 6%	1392
	21st to end	Night	48% 9% 14% 21% 7%	1486
August	1st to 10th	Night	42% 10% 21% 22% 4	1466
	11th to 20th	Night	46% 11% 16% 20% 7%	1596
	21st to end	Night	43% 7% 16% 24% 9%	1908
September	1st to 10th	Night	45% 8% 14% 24% 9%	1800
	11th to 20th	Night	43% 7% 14% 25% 10% 1	1975
	21st to end	Night	44% 8% 13% 23% 11% 1	1980
October	1st to 10th	Night	51% 7% 11% 19% 11% 1	1980
	11th to 20th	Night	59% 8% 12% 15% 5%	2273
	21st to end	Night	65% 7% 9% 11% 7% 1	2574
November	1st to 10th	Night	63% 6% 10% 14% 6% 1	2407
	11th to 20th	Night	64% 6% 10% 11% 7% 2	2470
	21st to end	Night	70% 6% 10% 10% 4	2612
December	1st to 10th	Night	77% 6% 7% 8% 3	2850
	11th to 20th	Night	77% 5% 5% 7% 6%	3532
	21st to end	Night	71% 7% 8% 9% 5%	4907

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	28% 31% 31% 11%	180
	11th to 20th	Day	34% 28% 26% 11% 1 1	180
	21st to end	Day	24% 25% 35% 13% 2 1	198
February	1st to 10th	Day	37% 31% 25% 6% 1	237
	11th to 20th	Day	31% 31% 29% 7% 2	456
	21st to end	Day	31% 30% 24% 13% 1	382
March	1st to 10th	Day	28% 29% 30% 10% 4	420
	11th to 20th	Day	29% 30% 23% 14% 4	420
	21st to end	Day	32% 23% 24% 14% 7%	462
April	1st to 10th	Day	39% 20% 25% 10% 6%	420
	11th to 20th	Day	31% 25% 25% 12% 6% 1	412
	21st to end	Day	38% 21% 25% 10% 4 2	420
May	1st to 10th	Day	39% 17% 27% 12% 3 1	423
	11th to 20th	Day	29% 20% 29% 16% 5% 1	447
	21st to end	Day	24% 22% 33% 15% 5% 1	485
June	1st to 10th	Day	36% 18% 29% 13% 4 1	468
	11th to 20th	Day	23% 17% 27% 23% 10%	630
	21st to end	Day	27% 17% 33% 14% 8% 1	460
July	1st to 10th	Day	21% 14% 35% 22% 7% 1	445
	11th to 20th	Day	20% 15% 38% 18% 7% 2	444
	21st to end	Day	23% 14% 33% 24% 5% 1	488
August	1st to 10th	Day	21% 15% 30% 23% 11% 1	446
	11th to 20th	Day	19% 14% 30% 23% 11% 3	439
	21st to end	Day	23% 18% 24% 20% 10% 5%	495
September	1st to 10th	Day	22% 17% 26% 20% 11% 3	450
	11th to 20th	Day	22% 14% 25% 19% 12% 7%	450
	21st to end	Day	22% 16% 26% 22% 11% 4	450
October	1st to 10th	Day	27% 20% 23% 16% 11% 4	450
	11th to 20th	Day	28% 23% 25% 14% 8% 1	376
	21st to end	Day	37% 24% 21% 15% 3	396
November	1st to 10th	Day	33% 22% 26% 15% 4	365
	11th to 20th	Day	29% 24% 30% 10% 5% 2	370
	21st to end	Day	31% 26% 28% 10% 3 2	261
December	1st to 10th	Day	28% 31% 27% 12% 3	180
	11th to 20th	Day	36% 28% 27% 7% 3 1	180
	21st to end	Day	35% 32% 24% 7% 2	198
January	1st to 10th	Night	24% 30% 33% 12% 2	760
	11th to 20th	Night	24% 30% 28% 15% 3	760
	21st to end	Night	18% 27% 36% 15% 4 1	836
February	1st to 10th	Night	19% 31% 33% 14% 2	760
	11th to 20th	Night	22% 30% 32% 14% 2	743
	21st to end	Night	25% 26% 31% 17% 2	628
March	1st to 10th	Night	27% 22% 32% 17% 2	723
	11th to 20th	Night	27% 26% 26% 16% 5% 1	720
	21st to end	Night	27% 21% 24% 20% 6% 1	792
April	1st to 10th	Night	33% 22% 24% 16% 4	720
	11th to 20th	Night	28% 19% 25% 21% 6% 1	637
	21st to end	Night	31% 21% 25% 18% 5% 1	540
May	1st to 10th	Night	29% 15% 30% 19% 7% 1	540
	11th to 20th	Night	23% 14% 30% 27% 5% 1	389
	21st to end	Night	25% 12% 29% 25% 8%	389
June	1st to 10th	Night	30% 7% 30% 23% 8% 1	360
	11th to 20th	Night	23% 9% 22% 32% 14%	360
	21st to end	Night	20% 9% 28% 33% 10% 1	360
July	1st to 10th	Night	18% 7% 30% 32% 12% 1	350
	11th to 20th	Night	16% 9% 27% 32% 15% 1	348
	21st to end	Night	19% 6% 22% 39% 14%	394
August	1st to 10th	Night	18% 5% 19% 37% 20%	402
	11th to 20th	Night	18% 8% 22% 34% 17% 1	532
	21st to end	Night	20% 9% 24% 30% 15% 2	720
September	1st to 10th	Night	20% 9% 24% 33% 13% 1	720
	11th to 20th	Night	23% 9% 20% 27% 18% 2	720
	21st to end	Night	24% 12% 24% 23% 15% 2	720
October	1st to 10th	Night	26% 12% 23% 26% 12% 1	720
	11th to 20th	Night	30% 17% 22% 21% 9% 2	720
	21st to end	Night	37% 18% 25% 16% 4	792
November	1st to 10th	Night	32% 19% 25% 18% 5% 1	740
	11th to 20th	Night	25% 23% 30% 13% 8% 2	760
	21st to end	Night	29% 23% 28% 15% 4 1	778
December	1st to 10th	Night	30% 27% 26% 14% 4	850
	11th to 20th	Night	29% 28% 24% 14% 5%	850
	21st to end	Night	33% 26% 25% 13% 2	841

Page generated at 2024-02-27 06:30:12. Version ac07

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