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 2026-08-15.

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	16% 13% 5% 11% 7% 6% 5% 4 5% 6% 23%	143244
	Night	14% 14% 6% 13% 8% 6% 5% 3 4 5% 22%	138634
Transparency	Day	59% 7% 11% 16% 7% 1	146714
	Night	62% 7% 10% 14% 7% 1	143254
Seeing	Day	28% 21% 28% 15% 6% 1	17213
	Night	26% 19% 27% 20% 7% 1	25960

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	9% 14% 10% 18% 12% 9% 8% 4 4 3 10%	4661
	11th to 20th	Day	5% 14% 7% 27% 17% 10% 4 2 3 2 9%	4650
	21st to end	Day	5% 12% 6% 18% 10% 14% 9% 4 5% 5% 12%	5124
February	1st to 10th	Day	10% 16% 7% 17% 14% 7% 5% 3 3 3 16%	1753
	11th to 20th	Day	9% 18% 9% 19% 8% 7% 4 3 3 4 15%	2048
	21st to end	Day	8% 18% 5% 14% 9% 8% 5% 4 5% 5% 18%	1730
March	1st to 10th	Day	13% 16% 6% 16% 8% 6% 5% 3 4 4 19%	4576
	11th to 20th	Day	11% 18% 6% 12% 6% 5% 4 4 4 6% 24%	4891
	21st to end	Day	18% 16% 7% 14% 6% 4 4 2 4 4 22%	5901
April	1st to 10th	Day	17% 22% 5% 11% 5% 3 2 3 3 4 24%	2520
	11th to 20th	Day	15% 17% 6% 9% 4 4 4 2 4 5% 30%	2581
	21st to end	Day	20% 17% 4 10% 4 3 4 3 5% 5% 26%	2730
May	1st to 10th	Day	24% 15% 4 9% 5% 6% 5% 4 5% 5% 17%	7639
	11th to 20th	Day	17% 10% 4 10% 6% 6% 6% 4 6% 7% 23%	8161
	21st to end	Day	22% 10% 3 7% 5% 5% 5% 4 6% 7% 27%	9060
June	1st to 10th	Day	26% 11% 3 7% 4 4 5% 4 6% 6% 23%	2961
	11th to 20th	Day	20% 8% 3 6% 6% 5% 5% 4 7% 7% 30%	3150
	21st to end	Day	22% 10% 4 7% 6% 5% 5% 4 6% 7% 24%	2950
July	1st to 10th	Day	14% 8% 3 9% 6% 6% 6% 5% 8% 9% 26%	8280
	11th to 20th	Day	13% 8% 3 7% 5% 6% 6% 5% 7% 9% 31%	8280
	21st to end	Day	13% 8% 3 7% 5% 6% 6% 4 6% 9% 33%	8993
August	1st to 10th	Day	18% 8% 3 9% 6% 6% 6% 5% 6% 8% 25%	4579
	11th to 20th	Day	18% 10% 4 9% 6% 5% 6% 6% 8% 7% 22%	4227
	21st to end	Day	19% 9% 3 7% 4 5% 4 4 6% 8% 32%	4428
September	1st to 10th	Day	17% 7% 2 7% 4 5% 5% 4 5% 6% 38%	2400
	11th to 20th	Day	17% 9% 2 6% 4 4 4 4 4 6% 41%	2205
	21st to end	Day	18% 11% 3 7% 4 4 5% 3 6% 7% 33%	2200
October	1st to 10th	Day	19% 13% 4 6% 4 4 4 4 6% 7% 29%	2200
	11th to 20th	Day	15% 18% 5% 10% 5% 4 4 4 5% 5% 25%	1867
	21st to end	Day	19% 24% 5% 9% 5% 3 4 3 4 4 21%	1980
November	1st to 10th	Day	15% 21% 7% 9% 6% 4 4 3 4 4 24%	1851
	11th to 20th	Day	15% 18% 9% 13% 6% 4 3 3 4 5% 20%	1890
	21st to end	Day	14% 19% 8% 16% 7% 4 4 3 4 6% 16%	1722
December	1st to 10th	Day	12% 19% 9% 23% 11% 5% 3 2 3 3 10%	2350
	11th to 20th	Day	13% 17% 9% 14% 9% 5% 3 2 4 4 19%	2688
	21st to end	Day	13% 20% 7% 14% 8% 4 6% 3 4 5% 17%	4018
January	1st to 10th	Night	8% 15% 10% 22% 12% 9% 8% 4 3 3 8%	8234
	11th to 20th	Night	7% 15% 9% 25% 16% 9% 5% 3 3 3 6%	8235
	21st to end	Night	6% 11% 7% 17% 11% 14% 9% 4 6% 4 12%	9057
February	1st to 10th	Night	8% 15% 7% 17% 11% 7% 6% 3 4 4 17%	2862
	11th to 20th	Night	8% 16% 8% 19% 10% 8% 5% 3 3 4 15%	2458
	21st to end	Night	9% 16% 7% 14% 9% 8% 5% 3 3 5% 22%	2076
March	1st to 10th	Night	14% 18% 7% 16% 7% 6% 7% 2 3 3 18%	5484
	11th to 20th	Night	11% 18% 7% 13% 7% 6% 5% 3 5% 5% 22%	5288
	21st to end	Night	15% 17% 6% 13% 7% 5% 4 3 4 4 24%	5271
April	1st to 10th	Night	18% 19% 6% 10% 4 4 4 3 4 5% 25%	2100
	11th to 20th	Night	19% 16% 4 8% 4 4 3 4 4 5% 29%	1988
	21st to end	Night	19% 16% 3 8% 5% 4 4 3 4 6% 28%	1890
May	1st to 10th	Night	24% 13% 4 9% 4 4 4 3 5% 7% 23%	5259
	11th to 20th	Night	19% 10% 3 9% 6% 5% 5% 4 5% 6% 29%	4742
	21st to end	Night	21% 11% 3 7% 4 4 4 3 5% 6% 31%	5114
June	1st to 10th	Night	25% 10% 3 8% 4 3 4 3 5% 7% 28%	1646
	11th to 20th	Night	18% 9% 3 8% 4 4 4 4 6% 7% 33%	1470
	21st to end	Night	19% 10% 3 8% 6% 5% 5% 4 6% 6% 29%	1655
July	1st to 10th	Night	19% 10% 3 8% 5% 5% 5% 4 5% 8% 28%	4680
	11th to 20th	Night	17% 8% 3 7% 4 4 4 4 6% 7% 35%	4680
	21st to end	Night	13% 8% 3 7% 5% 5% 6% 4 6% 7% 33%	5084
August	1st to 10th	Night	22% 9% 4 8% 5% 4 5% 3 5% 6% 30%	2757
	11th to 20th	Night	16% 9% 3 8% 6% 5% 6% 5% 6% 7% 29%	2909
	21st to end	Night	17% 9% 3 6% 4 4 4 3 5% 7% 39%	3454
September	1st to 10th	Night	16% 9% 3 7% 4 4 3 3 5% 6% 40%	2000
	11th to 20th	Night	16% 8% 2 5% 4 4 4 4 5% 5% 44%	2195
	21st to end	Night	18% 8% 3 6% 4 3 4 3 4 7% 39%	2200
October	1st to 10th	Night	17% 11% 3 8% 5% 4 4 4 5% 5% 35%	2200
	11th to 20th	Night	19% 17% 3 8% 5% 5% 4 3 5% 5% 26%	2527
	21st to end	Night	22% 18% 4 10% 4 4 4 3 4 4 22%	2860
November	1st to 10th	Night	18% 19% 6% 10% 6% 4 4 2 3 5% 22%	2667
	11th to 20th	Night	13% 17% 8% 16% 6% 3 3 3 3 5% 23%	2730
	21st to end	Night	14% 17% 8% 17% 9% 5% 3 2 4 4 17%	2888
December	1st to 10th	Night	12% 18% 10% 24% 12% 5% 3 2 2 3 8%	5060
	11th to 20th	Night	12% 20% 7% 17% 11% 6% 5% 3 3 3 13%	5741
	21st to end	Night	14% 19% 7% 13% 7% 6% 5% 3 4 4 19%	7173

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	78% 6% 8% 6% 2	4662
	11th to 20th	Day	80% 4 4 8% 3 1	4680
	21st to end	Day	72% 5% 8% 6% 8% 1	5124
February	1st to 10th	Day	74% 3 5% 11% 7% 1	1753
	11th to 20th	Day	73% 4 7% 10% 5% 1	2057
	21st to end	Day	67% 5% 8% 12% 7% 2	1730
March	1st to 10th	Day	68% 6% 7% 8% 7% 4	4579
	11th to 20th	Day	61% 5% 13% 12% 8% 1	4891
	21st to end	Day	65% 5% 6% 12% 12% 1	5901
April	1st to 10th	Day	65% 4 8% 13% 8% 2	2520
	11th to 20th	Day	57% 4 8% 18% 11% 1	2581
	21st to end	Day	60% 6% 8% 15% 9% 2	2730
May	1st to 10th	Day	65% 8% 8% 13% 5%	7651
	11th to 20th	Day	56% 10% 13% 15% 4 1	8165
	21st to end	Day	53% 9% 10% 21% 7%	9061
June	1st to 10th	Day	57% 8% 11% 18% 5%	2961
	11th to 20th	Day	50% 7% 14% 20% 8% 1	3150
	21st to end	Day	57% 8% 11% 17% 6%	2950
July	1st to 10th	Day	51% 7% 15% 20% 7%	8210
	11th to 20th	Day	45% 8% 14% 26% 6%	8205
	21st to end	Day	45% 8% 16% 24% 6%	8795
August	1st to 10th	Day	53% 9% 15% 18% 4	4565
	11th to 20th	Day	54% 11% 15% 16% 4	4266
	21st to end	Day	48% 8% 14% 18% 11% 3	4428
September	1st to 10th	Day	45% 7% 14% 24% 10%	2400
	11th to 20th	Day	43% 6% 12% 26% 12% 1	2205
	21st to end	Day	49% 8% 11% 21% 11% 1	2200
October	1st to 10th	Day	52% 6% 14% 20% 9%	3590
	11th to 20th	Day	57% 5% 10% 21% 7%	3005
	21st to end	Day	55% 5% 14% 17% 8%	3180
November	1st to 10th	Day	63% 5% 10% 14% 7% 1	1851
	11th to 20th	Day	66% 7% 8% 10% 7% 2	1890
	21st to end	Day	69% 7% 10% 11% 3	1722
December	1st to 10th	Day	81% 4 6% 6% 4	2350
	11th to 20th	Day	67% 5% 8% 9% 11% 1	2688
	21st to end	Day	69% 5% 6% 9% 8% 3	4018
January	1st to 10th	Night	80% 5% 7% 6% 2	8234
	11th to 20th	Night	82% 5% 5% 5% 3	8280
	21st to end	Night	71% 6% 7% 8% 8% 1	9057
February	1st to 10th	Night	70% 6% 6% 12% 6% 1	2862
	11th to 20th	Night	72% 6% 7% 9% 5% 1	2460
	21st to end	Night	65% 6% 6% 13% 9% 1	2076
March	1st to 10th	Night	70% 5% 7% 10% 6% 2	5494
	11th to 20th	Night	63% 7% 12% 11% 7% 1	5289
	21st to end	Night	64% 5% 5% 12% 13% 1	5271
April	1st to 10th	Night	62% 5% 8% 15% 10% 1	2100
	11th to 20th	Night	56% 7% 9% 17% 10% 1	1988
	21st to end	Night	57% 6% 10% 15% 10% 2	1890
May	1st to 10th	Night	57% 9% 13% 13% 7%	5265
	11th to 20th	Night	52% 10% 12% 21% 4	4743
	21st to end	Night	51% 7% 12% 18% 12%	5115
June	1st to 10th	Night	54% 7% 11% 20% 7%	1646
	11th to 20th	Night	48% 9% 12% 21% 9% 1	1470
	21st to end	Night	53% 10% 11% 19% 7%	1655
July	1st to 10th	Night	53% 7% 14% 19% 7%	4640
	11th to 20th	Night	45% 7% 15% 27% 6%	4632
	21st to end	Night	47% 8% 16% 25% 5%	4967
August	1st to 10th	Night	53% 7% 15% 21% 4	2747
	11th to 20th	Night	51% 10% 17% 16% 5%	2936
	21st to end	Night	45% 6% 15% 21% 13% 1	3454
September	1st to 10th	Night	44% 7% 14% 25% 10%	2000
	11th to 20th	Night	41% 6% 14% 27% 11% 1	2195
	21st to end	Night	45% 8% 12% 23% 11% 1	2200
October	1st to 10th	Night	48% 9% 12% 20% 12%	3590
	11th to 20th	Night	57% 6% 9% 19% 9%	4128
	21st to end	Night	56% 6% 13% 15% 8% 2	4610
November	1st to 10th	Night	64% 6% 10% 14% 6%	2667
	11th to 20th	Night	65% 5% 9% 11% 8% 2	2730
	21st to end	Night	71% 6% 10% 9% 3	2888
December	1st to 10th	Night	82% 6% 5% 6% 2	5060
	11th to 20th	Night	75% 5% 5% 7% 7%	5742
	21st to end	Night	68% 6% 7% 10% 7% 2	7173

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% 10%	220
	11th to 20th	Day	35% 27% 26% 10% 1	220
	21st to end	Day	29% 25% 33% 12% 2	242
February	1st to 10th	Day	33% 31% 26% 8% 1 1	285
	11th to 20th	Day	30% 29% 32% 7% 1	536
	21st to end	Day	30% 31% 26% 12% 1	446
March	1st to 10th	Day	32% 28% 28% 9% 3	540
	11th to 20th	Day	31% 31% 22% 12% 3	540
	21st to end	Day	37% 23% 23% 11% 5%	594
April	1st to 10th	Day	40% 21% 26% 9% 5%	540
	11th to 20th	Day	33% 26% 24% 11% 4 1	532
	21st to end	Day	36% 23% 26% 10% 4 2	540
May	1st to 10th	Day	41% 18% 27% 11% 3 1	543
	11th to 20th	Day	29% 21% 27% 16% 6% 1	567
	21st to end	Day	26% 23% 32% 14% 4 1	617
June	1st to 10th	Day	33% 18% 30% 15% 4 1	591
	11th to 20th	Day	24% 17% 28% 21% 9%	780
	21st to end	Day	27% 18% 34% 13% 6% 1	580
July	1st to 10th	Day	19% 18% 36% 21% 6% 1	565
	11th to 20th	Day	21% 16% 38% 18% 6% 1	564
	21st to end	Day	23% 16% 32% 22% 6% 2	620
August	1st to 10th	Day	19% 15% 30% 23% 10% 1	566
	11th to 20th	Day	19% 14% 29% 23% 12% 3	535
	21st to end	Day	22% 18% 26% 20% 10% 4	583
September	1st to 10th	Day	22% 17% 26% 21% 12% 3	530
	11th to 20th	Day	20% 13% 25% 21% 14% 7%	530
	21st to end	Day	22% 16% 25% 22% 11% 4	530
October	1st to 10th	Day	25% 19% 25% 16% 11% 4	530
	11th to 20th	Day	28% 22% 25% 15% 8% 1	439
	21st to end	Day	35% 26% 22% 15% 3	462
November	1st to 10th	Day	35% 24% 25% 13% 3	425
	11th to 20th	Day	29% 23% 31% 10% 5% 1	430
	21st to end	Day	34% 26% 27% 9% 3 1	309
December	1st to 10th	Day	27% 28% 31% 12% 2	220
	11th to 20th	Day	36% 27% 27% 6% 2	220
	21st to end	Day	33% 30% 26% 7% 4	242
January	1st to 10th	Night	23% 30% 33% 11% 2	840
	11th to 20th	Night	24% 29% 29% 16% 3	840
	21st to end	Night	19% 27% 35% 15% 4 1	924
February	1st to 10th	Night	19% 31% 32% 15% 3	840
	11th to 20th	Night	23% 28% 33% 14% 2	823
	21st to end	Night	24% 25% 32% 16% 2	692
March	1st to 10th	Night	28% 23% 32% 15% 2	840
	11th to 20th	Night	28% 26% 25% 16% 4	840
	21st to end	Night	28% 22% 25% 18% 5% 1	924
April	1st to 10th	Night	34% 22% 25% 15% 4	840
	11th to 20th	Night	30% 20% 25% 19% 5% 1	744
	21st to end	Night	31% 20% 26% 17% 5% 1	630
May	1st to 10th	Night	29% 15% 30% 19% 6% 1	630
	11th to 20th	Night	23% 14% 30% 26% 6% 1	454
	21st to end	Night	26% 12% 29% 25% 8%	455
June	1st to 10th	Night	29% 7% 30% 26% 8%	420
	11th to 20th	Night	24% 10% 22% 30% 13%	420
	21st to end	Night	20% 10% 29% 32% 9%	420
July	1st to 10th	Night	18% 8% 31% 32% 10% 1	410
	11th to 20th	Night	17% 11% 25% 33% 13% 1	408
	21st to end	Night	18% 7% 22% 38% 14%	460
August	1st to 10th	Night	18% 6% 19% 38% 19%	470
	11th to 20th	Night	18% 9% 21% 34% 18%	605
	21st to end	Night	20% 9% 24% 30% 15% 2	800
September	1st to 10th	Night	20% 10% 24% 32% 13% 1	800
	11th to 20th	Night	21% 9% 19% 28% 21% 2	800
	21st to end	Night	23% 12% 24% 25% 15% 2	800
October	1st to 10th	Night	24% 12% 24% 27% 12% 1	800
	11th to 20th	Night	30% 16% 22% 22% 8% 2	800
	21st to end	Night	36% 19% 26% 16% 4	880
November	1st to 10th	Night	34% 20% 24% 18% 5%	820
	11th to 20th	Night	25% 23% 29% 14% 7% 2	840
	21st to end	Night	29% 24% 27% 15% 4 1	862
December	1st to 10th	Night	29% 27% 27% 13% 3	950
	11th to 20th	Night	30% 28% 23% 14% 4	950
	21st to end	Night	33% 26% 25% 14% 2	929

Page generated at 2026-08-12 03:37:14. Version ac07

Copyright © 2026 Attilla Danko.