Pont Rouge Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Pont Rouge Observatory clear sky chart from 2005-11-06 to 2026-07-31.

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	19% 11% 4 8% 5% 5% 5% 4 5% 6% 29%	137833
	Night	18% 12% 4 9% 5% 4 4 3 5% 6% 28%	135209
Transparency	Day	54% 7% 13% 17% 9% 1	141277
	Night	56% 6% 11% 17% 8% 1	139855
Seeing	Day	25% 17% 29% 19% 8% 1	17310
	Night	25% 12% 28% 27% 8%	25842

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	16% 17% 5% 12% 5% 4 4 3 4 5% 24%	4661
	11th to 20th	Day	11% 18% 7% 19% 7% 6% 4 2 3 4 18%	4650
	21st to end	Day	6% 13% 6% 12% 5% 5% 5% 6% 7% 7% 29%	5124
February	1st to 10th	Day	11% 15% 6% 12% 7% 6% 5% 3 4 5% 27%	1689
	11th to 20th	Day	13% 16% 6% 12% 5% 5% 5% 3 4 5% 25%	2023
	21st to end	Day	13% 15% 6% 12% 5% 5% 4 3 5% 6% 27%	1730
March	1st to 10th	Day	23% 14% 5% 10% 5% 4 3 3 3 4 25%	4576
	11th to 20th	Day	16% 16% 5% 9% 5% 4 4 4 4 5% 29%	4808
	21st to end	Day	19% 15% 3 7% 4 4 4 3 4 4 33%	5999
April	1st to 10th	Day	23% 12% 3 9% 5% 5% 4 3 3 4 29%	2520
	11th to 20th	Day	22% 8% 3 7% 5% 4 4 3 4 6% 34%	2576
	21st to end	Day	23% 10% 3 8% 5% 4 5% 3 3 6% 30%	2730
May	1st to 10th	Day	28% 9% 3 6% 4 4 5% 3 5% 6% 26%	7895
	11th to 20th	Day	21% 7% 3 7% 4 5% 5% 4 6% 8% 31%	8221
	21st to end	Day	21% 9% 3 7% 5% 5% 5% 4 6% 6% 28%	9060
June	1st to 10th	Day	20% 7% 2 8% 6% 6% 6% 4 7% 7% 27%	3124
	11th to 20th	Day	19% 8% 3 7% 4 4 5% 5% 6% 7% 33%	3150
	21st to end	Day	24% 9% 3 8% 4 5% 5% 4 5% 6% 26%	3132
July	1st to 10th	Day	18% 7% 3 8% 5% 5% 6% 5% 7% 9% 27%	6500
	11th to 20th	Day	17% 7% 3 7% 5% 5% 5% 4 8% 8% 31%	6500
	21st to end	Day	13% 5% 2 6% 4 5% 6% 4 7% 9% 39%	7066
August	1st to 10th	Day	16% 6% 3 8% 5% 5% 6% 5% 8% 10% 29%	4563
	11th to 20th	Day	21% 7% 3 7% 5% 5% 5% 4 7% 8% 29%	4184
	21st to end	Day	22% 7% 3 6% 4 4 5% 4 6% 6% 35%	4426
September	1st to 10th	Day	19% 7% 3 6% 3 4 4 4 6% 8% 36%	2400
	11th to 20th	Day	18% 5% 2 4 3 4 4 3 5% 7% 45%	2240
	21st to end	Day	24% 7% 3 6% 4 3 3 4 4 7% 37%	2200
October	1st to 10th	Day	22% 8% 3 6% 4 5% 5% 4 5% 7% 33%	2172
	11th to 20th	Day	25% 9% 4 8% 5% 5% 5% 4 5% 6% 24%	1847
	21st to end	Day	28% 9% 3 9% 5% 4 4 2 5% 5% 25%	1980
November	1st to 10th	Day	22% 12% 3 8% 5% 5% 4 3 5% 5% 29%	1851
	11th to 20th	Day	21% 15% 4 10% 6% 4 4 3 4 4 26%	1869
	21st to end	Day	21% 19% 4 9% 6% 5% 4 3 5% 5% 19%	1551
December	1st to 10th	Day	20% 16% 5% 10% 6% 5% 4 4 5% 5% 20%	2350
	11th to 20th	Day	21% 15% 6% 10% 5% 4 3 2 3 4 27%	2688
	21st to end	Day	20% 18% 4 8% 4 4 5% 4 5% 5% 24%	3778
January	1st to 10th	Night	15% 18% 6% 14% 6% 5% 4 3 4 4 20%	8234
	11th to 20th	Night	11% 24% 8% 17% 6% 5% 4 2 3 4 16%	8235
	21st to end	Night	6% 12% 6% 14% 8% 6% 5% 4 7% 7% 25%	9057
February	1st to 10th	Night	11% 14% 5% 11% 7% 5% 3 4 4 5% 29%	2929
	11th to 20th	Night	13% 16% 6% 12% 5% 4 4 4 5% 4 26%	2481
	21st to end	Night	15% 14% 5% 9% 5% 4 5% 3 5% 5% 29%	2076
March	1st to 10th	Night	22% 13% 4 11% 5% 4 5% 3 4 5% 24%	5484
	11th to 20th	Night	16% 14% 4 9% 6% 6% 5% 4 5% 7% 23%	5371
	21st to end	Night	19% 15% 4 8% 4 3 4 3 4 5% 30%	5171
April	1st to 10th	Night	23% 14% 3 7% 5% 3 3 3 5% 6% 28%	2100
	11th to 20th	Night	21% 10% 3 6% 5% 4 4 4 5% 6% 32%	1992
	21st to end	Night	21% 10% 3 7% 4 4 4 3 4 6% 33%	1890
May	1st to 10th	Night	26% 8% 3 6% 4 4 4 4 4 6% 30%	5046
	11th to 20th	Night	24% 7% 2 7% 4 4 5% 3 5% 7% 32%	4639
	21st to end	Night	20% 9% 3 6% 4 4 5% 4 5% 7% 32%	5114
June	1st to 10th	Night	21% 8% 3 5% 5% 5% 5% 4 6% 8% 31%	1491
	11th to 20th	Night	21% 6% 2 5% 5% 4 4 4 7% 7% 34%	1470
	21st to end	Night	23% 8% 2 7% 5% 4 4 4 5% 7% 31%	1481
July	1st to 10th	Night	16% 7% 2 8% 5% 5% 6% 5% 7% 8% 30%	3680
	11th to 20th	Night	21% 7% 3 6% 4 4 4 3 6% 7% 35%	3680
	21st to end	Night	13% 5% 3 6% 4 4 5% 4 6% 8% 42%	4006
August	1st to 10th	Night	18% 7% 3 7% 4 4 4 3 6% 8% 35%	2586
	11th to 20th	Night	20% 6% 3 7% 5% 6% 5% 3 5% 7% 32%	2832
	21st to end	Night	20% 8% 3 9% 5% 5% 4 4 4 6% 33%	3469
September	1st to 10th	Night	18% 6% 2 6% 4 3 4 3 5% 6% 42%	2000
	11th to 20th	Night	17% 5% 2 6% 4 3 4 4 4 5% 45%	2160
	21st to end	Night	21% 6% 2 5% 4 4 3 2 4 6% 41%	2200
October	1st to 10th	Night	20% 7% 3 5% 4 4 3 4 5% 6% 39%	2225
	11th to 20th	Night	24% 9% 3 6% 4 5% 4 3 4 5% 31%	2552
	21st to end	Night	27% 11% 2 6% 4 4 3 3 5% 6% 28%	2860
November	1st to 10th	Night	21% 13% 3 7% 5% 4 4 3 4 6% 30%	2667
	11th to 20th	Night	21% 12% 3 8% 5% 4 5% 3 4 5% 30%	2750
	21st to end	Night	23% 17% 4 9% 5% 4 4 3 4 4 23%	3066
December	1st to 10th	Night	17% 16% 7% 11% 9% 5% 4 3 3 5% 20%	5060
	11th to 20th	Night	23% 15% 4 10% 6% 4 4 3 4 4 22%	5741
	21st to end	Night	22% 18% 5% 9% 4 3 4 2 3 4 26%	7414

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	61% 5% 9% 16% 9%	4662
	11th to 20th	Day	70% 5% 7% 11% 6% 1	4680
	21st to end	Day	50% 6% 10% 21% 14%	5124
February	1st to 10th	Day	59% 5% 9% 15% 9% 2	1689
	11th to 20th	Day	61% 6% 11% 13% 9% 1	2032
	21st to end	Day	58% 5% 9% 17% 9% 2	1730
March	1st to 10th	Day	63% 6% 8% 11% 10% 3	4579
	11th to 20th	Day	55% 7% 14% 14% 9% 1	4808
	21st to end	Day	55% 4 7% 16% 15% 4	5999
April	1st to 10th	Day	59% 6% 10% 13% 9% 3	2520
	11th to 20th	Day	51% 6% 11% 20% 10% 2	2576
	21st to end	Day	56% 5% 10% 16% 12% 2	2730
May	1st to 10th	Day	57% 6% 10% 17% 11% 1	7907
	11th to 20th	Day	49% 8% 16% 19% 6% 2	8225
	21st to end	Day	53% 7% 10% 16% 12% 2	9061
June	1st to 10th	Day	53% 9% 11% 19% 7% 1	3124
	11th to 20th	Day	46% 8% 15% 18% 11% 1	3150
	21st to end	Day	57% 7% 12% 15% 8% 1	3132
July	1st to 10th	Day	51% 8% 14% 20% 6%	6430
	11th to 20th	Day	46% 8% 20% 21% 4	6425
	21st to end	Day	40% 7% 19% 26% 7%	6868
August	1st to 10th	Day	47% 9% 21% 18% 6%	4549
	11th to 20th	Day	50% 9% 19% 17% 4	4223
	21st to end	Day	47% 8% 15% 16% 13%	4426
September	1st to 10th	Day	43% 8% 17% 22% 9%	2400
	11th to 20th	Day	39% 6% 17% 28% 10%	2240
	21st to end	Day	48% 6% 14% 23% 9%	2200
October	1st to 10th	Day	54% 8% 11% 21% 6%	3536
	11th to 20th	Day	55% 8% 17% 18% 2	2985
	21st to end	Day	55% 7% 17% 15% 6%	3180
November	1st to 10th	Day	56% 6% 12% 18% 7%	1851
	11th to 20th	Day	63% 5% 9% 16% 6% 1	1869
	21st to end	Day	67% 6% 12% 11% 4 1	1551
December	1st to 10th	Day	65% 6% 10% 13% 6%	2350
	11th to 20th	Day	62% 4 8% 15% 10%	2688
	21st to end	Day	61% 5% 10% 12% 10% 1	3778
January	1st to 10th	Night	66% 5% 9% 13% 6%	8234
	11th to 20th	Night	72% 4 8% 11% 3	8280
	21st to end	Night	56% 6% 10% 16% 12%	9057
February	1st to 10th	Night	57% 5% 8% 19% 9% 1	2929
	11th to 20th	Night	60% 6% 9% 15% 10% 1	2483
	21st to end	Night	56% 6% 8% 17% 12% 2	2076
March	1st to 10th	Night	63% 5% 9% 11% 10% 1	5494
	11th to 20th	Night	59% 8% 12% 12% 8% 1	5372
	21st to end	Night	57% 4 6% 20% 10% 2	5171
April	1st to 10th	Night	56% 5% 9% 15% 13% 2	2100
	11th to 20th	Night	51% 6% 8% 21% 11% 2	1992
	21st to end	Night	51% 6% 9% 18% 14% 2	1890
May	1st to 10th	Night	54% 6% 11% 18% 11% 1	5052
	11th to 20th	Night	49% 7% 13% 19% 10% 1	4640
	21st to end	Night	50% 6% 10% 17% 16% 2	5115
June	1st to 10th	Night	49% 7% 12% 20% 9% 1	1491
	11th to 20th	Night	47% 7% 13% 19% 12% 2	1470
	21st to end	Night	52% 7% 13% 17% 10%	1481
July	1st to 10th	Night	48% 8% 20% 19% 5%	3640
	11th to 20th	Night	48% 7% 19% 22% 4	3632
	21st to end	Night	39% 7% 19% 27% 8%	3889
August	1st to 10th	Night	47% 7% 16% 22% 7%	2576
	11th to 20th	Night	50% 10% 18% 16% 5% 1	2859
	21st to end	Night	51% 7% 13% 20% 9%	3469
September	1st to 10th	Night	41% 6% 15% 25% 11% 1	2000
	11th to 20th	Night	40% 7% 17% 28% 8%	2160
	21st to end	Night	45% 5% 13% 25% 12%	2200
October	1st to 10th	Night	50% 5% 13% 24% 7%	3641
	11th to 20th	Night	50% 8% 14% 24% 3	4153
	21st to end	Night	51% 6% 18% 16% 10%	4610
November	1st to 10th	Night	54% 6% 13% 19% 6% 1	2667
	11th to 20th	Night	55% 6% 12% 17% 9%	2750
	21st to end	Night	65% 5% 10% 14% 6%	3066
December	1st to 10th	Night	68% 4 12% 12% 3	5060
	11th to 20th	Night	66% 4 6% 18% 6%	5742
	21st to end	Night	63% 4 7% 15% 10% 1	7414

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% 21% 31% 17% 3	220
	11th to 20th	Day	26% 21% 30% 16% 5%	220
	21st to end	Day	19% 22% 39% 14% 6%	242
February	1st to 10th	Day	23% 26% 35% 13% 4	226
	11th to 20th	Day	23% 24% 33% 17% 2	511
	21st to end	Day	24% 26% 31% 17% 3	446
March	1st to 10th	Day	29% 21% 29% 17% 4	540
	11th to 20th	Day	28% 22% 30% 14% 5% 1	540
	21st to end	Day	27% 23% 27% 14% 8% 1	594
April	1st to 10th	Day	32% 19% 30% 16% 4	540
	11th to 20th	Day	31% 18% 27% 18% 4 2	532
	21st to end	Day	30% 20% 30% 13% 5% 1	540
May	1st to 10th	Day	32% 19% 30% 14% 4	543
	11th to 20th	Day	24% 17% 30% 21% 7% 1	567
	21st to end	Day	25% 22% 30% 17% 6%	617
June	1st to 10th	Day	22% 13% 34% 23% 8%	754
	11th to 20th	Day	23% 13% 30% 23% 10% 1	780
	21st to end	Day	26% 12% 29% 22% 10% 2	762
July	1st to 10th	Day	21% 13% 33% 21% 11% 1	565
	11th to 20th	Day	20% 13% 34% 23% 9% 1	564
	21st to end	Day	18% 14% 30% 26% 10% 2	616
August	1st to 10th	Day	18% 10% 28% 29% 12% 2	526
	11th to 20th	Day	21% 9% 23% 29% 15% 3	519
	21st to end	Day	24% 13% 25% 20% 14% 5%	583
September	1st to 10th	Day	21% 13% 28% 22% 13% 3	530
	11th to 20th	Day	18% 12% 25% 24% 15% 5%	530
	21st to end	Day	23% 15% 24% 21% 13% 4	530
October	1st to 10th	Day	24% 16% 27% 21% 11% 1	530
	11th to 20th	Day	29% 16% 28% 18% 8% 1	445
	21st to end	Day	33% 15% 27% 18% 6%	462
November	1st to 10th	Day	35% 16% 22% 20% 5%	425
	11th to 20th	Day	28% 18% 28% 16% 8% 1	409
	21st to end	Day	31% 27% 26% 14% 1	220
December	1st to 10th	Day	30% 15% 32% 16% 7%	220
	11th to 20th	Day	30% 22% 28% 16% 3 1	220
	21st to end	Day	29% 21% 32% 13% 4 1	242
January	1st to 10th	Night	27% 14% 33% 22% 4	840
	11th to 20th	Night	27% 16% 28% 22% 6%	840
	21st to end	Night	15% 13% 34% 30% 7%	924
February	1st to 10th	Night	18% 14% 35% 27% 6%	840
	11th to 20th	Night	22% 17% 36% 19% 5%	823
	21st to end	Night	22% 16% 30% 27% 4	692
March	1st to 10th	Night	23% 14% 36% 22% 5%	840
	11th to 20th	Night	25% 16% 33% 20% 5% 1	840
	21st to end	Night	23% 16% 30% 24% 7% 1	924
April	1st to 10th	Night	30% 15% 29% 22% 5%	840
	11th to 20th	Night	27% 12% 31% 25% 5%	748
	21st to end	Night	28% 17% 30% 20% 6%	630
May	1st to 10th	Night	27% 13% 32% 23% 5%	559
	11th to 20th	Night	25% 8% 30% 29% 7%	414
	21st to end	Night	27% 7% 30% 28% 8%	455
June	1st to 10th	Night	24% 7% 25% 38% 6%	420
	11th to 20th	Night	25% 5% 24% 34% 12%	420
	21st to end	Night	25% 4 22% 38% 10%	420
July	1st to 10th	Night	18% 5% 25% 41% 10%	410
	11th to 20th	Night	20% 5% 18% 42% 14% 1	408
	21st to end	Night	17% 6% 18% 42% 17%	458
August	1st to 10th	Night	18% 2 14% 44% 22%	398
	11th to 20th	Night	17% 5% 22% 37% 19%	564
	21st to end	Night	20% 8% 22% 32% 17% 1	802
September	1st to 10th	Night	22% 5% 26% 32% 15% 1	800
	11th to 20th	Night	20% 6% 21% 32% 20% 2	800
	21st to end	Night	24% 8% 24% 29% 15% 1	800
October	1st to 10th	Night	23% 10% 25% 31% 10% 1	800
	11th to 20th	Night	28% 10% 25% 26% 10%	800
	21st to end	Night	33% 11% 27% 24% 5%	880
November	1st to 10th	Night	30% 12% 26% 25% 7% 1	820
	11th to 20th	Night	27% 15% 27% 23% 8% 1	840
	21st to end	Night	31% 17% 25% 20% 6% 1	906
December	1st to 10th	Night	31% 12% 26% 24% 7%	950
	11th to 20th	Night	28% 20% 25% 21% 5% 1	950
	21st to end	Night	33% 15% 28% 19% 4 1	987

Page generated at 2026-07-28 03:25:20. Version ac07

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