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 2025-03-27.

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%	108426
	Night	19% 12% 4 9% 5% 4 4 3 5% 6% 29%	110923
Transparency	Day	53% 7% 13% 17% 8% 1	111916
	Night	56% 6% 12% 17% 8% 1	115598
Seeing	Day	25% 17% 29% 20% 8% 1	15494
	Night	25% 12% 28% 27% 8%	24265

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	18% 20% 6% 12% 6% 4 4 3 4 4 21%	3597
	11th to 20th	Day	10% 15% 7% 20% 7% 5% 4 3 3 4 21%	3570
	21st to end	Day	8% 13% 6% 13% 5% 5% 4 4 5% 7% 31%	3960
February	1st to 10th	Day	11% 15% 6% 12% 8% 6% 5% 3 4 4 25%	1608
	11th to 20th	Day	14% 16% 6% 12% 6% 5% 5% 3 4 5% 24%	1924
	21st to end	Day	13% 15% 6% 12% 5% 5% 4 3 5% 6% 27%	1650
March	1st to 10th	Day	22% 12% 4 8% 5% 5% 4 3 4 4 29%	3216
	11th to 20th	Day	16% 19% 5% 9% 5% 4 4 3 4 4 26%	3392
	21st to end	Day	15% 14% 3 8% 5% 4 5% 3 4 4 35%	4163
April	1st to 10th	Day	23% 12% 3 9% 5% 5% 4 3 3 4 29%	2280
	11th to 20th	Day	22% 8% 3 7% 5% 4 4 3 4 5% 35%	2328
	21st to end	Day	24% 10% 3 9% 4 4 5% 3 3 6% 30%	2470
May	1st to 10th	Day	22% 8% 3 6% 4 4 5% 3 5% 6% 35%	4252
	11th to 20th	Day	17% 7% 3 8% 5% 5% 5% 4 6% 9% 32%	4398
	21st to end	Day	19% 8% 2 8% 5% 5% 5% 4 5% 6% 31%	4837
June	1st to 10th	Day	20% 8% 3 8% 6% 6% 5% 4 7% 7% 26%	2826
	11th to 20th	Day	19% 8% 3 6% 4 4 5% 5% 6% 7% 34%	2850
	21st to end	Day	24% 9% 3 9% 4 5% 5% 4 5% 6% 26%	2834
July	1st to 10th	Day	16% 8% 3 8% 6% 5% 6% 4 7% 7% 30%	4440
	11th to 20th	Day	18% 7% 3 7% 5% 5% 6% 5% 8% 8% 28%	4440
	21st to end	Day	16% 6% 2 6% 4 5% 5% 4 6% 8% 38%	4814
August	1st to 10th	Day	16% 6% 3 8% 5% 5% 7% 5% 8% 10% 28%	4423
	11th to 20th	Day	21% 7% 3 7% 5% 5% 5% 5% 7% 8% 27%	4054
	21st to end	Day	22% 7% 3 6% 4 4 4 3 6% 6% 35%	4290
September	1st to 10th	Day	19% 7% 3 6% 3 4 4 4 6% 8% 36%	2280
	11th to 20th	Day	19% 5% 2 4 3 4 4 3 5% 7% 44%	2128
	21st to end	Day	24% 7% 2 6% 4 2 3 4 4 7% 36%	2090
October	1st to 10th	Day	23% 8% 3 6% 4 5% 5% 4 5% 6% 31%	2064
	11th to 20th	Day	26% 10% 4 8% 5% 5% 5% 4 5% 6% 24%	1755
	21st to end	Day	29% 10% 3 8% 5% 4 4 2 5% 5% 25%	1881
November	1st to 10th	Day	21% 12% 3 8% 5% 5% 4 3 5% 5% 31%	1761
	11th to 20th	Day	22% 14% 4 10% 6% 4 4 3 4 4 26%	1780
	21st to end	Day	21% 19% 4 9% 6% 5% 4 3 5% 5% 20%	1477
December	1st to 10th	Day	20% 16% 5% 10% 6% 5% 4 4 5% 5% 20%	2280
	11th to 20th	Day	21% 15% 6% 10% 5% 4 3 2 3 4 27%	2618
	21st to end	Day	20% 18% 4 8% 4 3 5% 4 5% 5% 24%	3696
January	1st to 10th	Night	16% 22% 6% 14% 6% 5% 3 2 4 4 19%	6349
	11th to 20th	Night	11% 20% 8% 17% 6% 5% 4 3 4 4 19%	6315
	21st to end	Night	8% 13% 5% 13% 7% 5% 5% 4 6% 6% 27%	6996
February	1st to 10th	Night	12% 15% 5% 11% 8% 6% 4 4 5% 5% 27%	2790
	11th to 20th	Night	14% 16% 6% 12% 5% 4 4 4 5% 4 25%	2360
	21st to end	Night	15% 14% 5% 9% 5% 4 5% 3 5% 5% 28%	1980
March	1st to 10th	Night	24% 12% 3 8% 4 4 6% 3 4 5% 27%	3844
	11th to 20th	Night	17% 17% 4 10% 5% 6% 4 4 5% 5% 23%	3787
	21st to end	Night	17% 14% 4 9% 4 4 4 3 4 5% 33%	3604
April	1st to 10th	Night	23% 14% 3 7% 5% 3 3 3 5% 6% 28%	1900
	11th to 20th	Night	21% 9% 3 6% 6% 4 4 4 5% 6% 33%	1800
	21st to end	Night	22% 10% 3 7% 4 4 4 3 4 7% 34%	1710
May	1st to 10th	Night	24% 7% 3 7% 4 4 5% 4 4 6% 33%	2718
	11th to 20th	Night	22% 7% 2 7% 4 4 4 3 5% 7% 36%	2495
	21st to end	Night	19% 6% 3 6% 5% 5% 5% 4 5% 8% 35%	2738
June	1st to 10th	Night	21% 8% 3 6% 5% 5% 5% 4 5% 8% 29%	1349
	11th to 20th	Night	20% 6% 2 5% 5% 4 4 4 7% 7% 36%	1330
	21st to end	Night	24% 8% 3 7% 6% 4 4 4 5% 7% 30%	1339
July	1st to 10th	Night	16% 6% 2 8% 5% 5% 6% 5% 7% 8% 31%	2520
	11th to 20th	Night	20% 8% 3 6% 4 4 4 4 5% 7% 34%	2520
	21st to end	Night	14% 5% 2 5% 4 4 4 4 6% 8% 44%	2739
August	1st to 10th	Night	19% 8% 3 7% 4 4 4 3 6% 8% 34%	2506
	11th to 20th	Night	21% 6% 3 7% 5% 6% 5% 3 6% 7% 31%	2743
	21st to end	Night	19% 8% 3 9% 5% 5% 4 4 4 6% 33%	3363
September	1st to 10th	Night	19% 6% 2 6% 4 3 4 3 5% 6% 41%	1900
	11th to 20th	Night	18% 5% 2 5% 4 3 4 3 4 5% 45%	2052
	21st to end	Night	21% 7% 2 5% 4 4 3 2 4 6% 40%	2090
October	1st to 10th	Night	21% 8% 3 5% 4 4 4 4 5% 6% 37%	2114
	11th to 20th	Night	25% 9% 3 6% 4 4 4 4 4 5% 30%	2424
	21st to end	Night	28% 10% 2 6% 3 4 3 3 5% 6% 29%	2717
November	1st to 10th	Night	20% 13% 3 7% 5% 4 4 3 4 7% 30%	2537
	11th to 20th	Night	21% 12% 3 8% 4 4 5% 3 4 5% 32%	2619
	21st to end	Night	24% 16% 4 8% 5% 4 4 3 4 4 24%	2920
December	1st to 10th	Night	18% 16% 7% 11% 9% 5% 4 3 3 5% 19%	4910
	11th to 20th	Night	24% 15% 4 10% 6% 4 4 3 4 5% 22%	5591
	21st to end	Night	22% 18% 5% 9% 4 3 4 2 3 4 26%	7254

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	67% 6% 8% 12% 7%	3598
	11th to 20th	Day	66% 5% 8% 13% 6% 1	3600
	21st to end	Day	51% 6% 8% 19% 15%	3960
February	1st to 10th	Day	61% 6% 10% 13% 9% 2	1608
	11th to 20th	Day	62% 6% 11% 12% 9% 1	1933
	21st to end	Day	58% 5% 9% 16% 9% 2	1650
March	1st to 10th	Day	57% 7% 10% 15% 9% 2	3219
	11th to 20th	Day	58% 9% 10% 15% 7% 1	3392
	21st to end	Day	52% 5% 8% 17% 13% 5%	4163
April	1st to 10th	Day	59% 6% 10% 12% 9% 4	2280
	11th to 20th	Day	49% 6% 11% 21% 10% 3	2328
	21st to end	Day	56% 5% 10% 15% 12% 2	2470
May	1st to 10th	Day	48% 7% 13% 17% 14% 1	4266
	11th to 20th	Day	45% 10% 20% 17% 7% 1	4402
	21st to end	Day	49% 9% 10% 17% 14% 1	4837
June	1st to 10th	Day	53% 9% 12% 18% 7% 2	2826
	11th to 20th	Day	46% 8% 16% 17% 11% 1	2850
	21st to end	Day	58% 7% 12% 15% 9%	2834
July	1st to 10th	Day	50% 8% 15% 20% 7%	4370
	11th to 20th	Day	49% 9% 21% 17% 4	4365
	21st to end	Day	43% 8% 20% 23% 6%	4661
August	1st to 10th	Day	48% 9% 20% 18% 5%	4409
	11th to 20th	Day	51% 10% 19% 16% 4	4093
	21st to end	Day	47% 8% 15% 16% 14%	4290
September	1st to 10th	Day	44% 8% 16% 22% 10%	2280
	11th to 20th	Day	40% 6% 17% 27% 10%	2128
	21st to end	Day	48% 6% 15% 23% 8%	2090
October	1st to 10th	Day	55% 8% 11% 21% 5%	3428
	11th to 20th	Day	56% 8% 17% 18% 2	2893
	21st to end	Day	55% 7% 17% 14% 6%	3081
November	1st to 10th	Day	55% 6% 12% 18% 7%	1761
	11th to 20th	Day	62% 5% 9% 17% 7% 1	1780
	21st to end	Day	66% 6% 12% 11% 4 1	1477
December	1st to 10th	Day	66% 6% 10% 13% 6%	2280
	11th to 20th	Day	62% 4 9% 16% 10%	2618
	21st to end	Day	62% 5% 10% 12% 10% 1	3696
January	1st to 10th	Night	70% 5% 9% 11% 5%	6349
	11th to 20th	Night	68% 5% 10% 13% 3	6360
	21st to end	Night	55% 6% 10% 17% 12%	6996
February	1st to 10th	Night	59% 6% 8% 17% 9% 1	2790
	11th to 20th	Night	60% 6% 10% 14% 9% 1	2362
	21st to end	Night	57% 6% 8% 16% 12% 2	1980
March	1st to 10th	Night	59% 6% 12% 14% 8% 2	3854
	11th to 20th	Night	61% 7% 10% 13% 7% 1	3788
	21st to end	Night	54% 5% 9% 20% 10% 3	3604
April	1st to 10th	Night	56% 5% 10% 14% 12% 2	1900
	11th to 20th	Night	50% 7% 8% 22% 12% 2	1800
	21st to end	Night	51% 7% 9% 17% 14% 2	1710
May	1st to 10th	Night	50% 7% 12% 20% 10% 1	2724
	11th to 20th	Night	45% 9% 16% 18% 12% 1	2496
	21st to end	Night	45% 8% 12% 18% 16% 1	2739
June	1st to 10th	Night	51% 8% 13% 19% 9% 1	1349
	11th to 20th	Night	45% 7% 14% 19% 12% 3	1330
	21st to end	Night	54% 7% 12% 16% 10%	1339
July	1st to 10th	Night	48% 9% 19% 19% 6%	2480
	11th to 20th	Night	48% 7% 20% 20% 4	2472
	21st to end	Night	38% 8% 23% 23% 8%	2651
August	1st to 10th	Night	48% 7% 16% 22% 6%	2496
	11th to 20th	Night	51% 10% 19% 16% 5%	2770
	21st to end	Night	51% 6% 12% 20% 10%	3363
September	1st to 10th	Night	42% 7% 15% 24% 11% 1	1900
	11th to 20th	Night	40% 8% 17% 27% 8%	2052
	21st to end	Night	45% 5% 13% 25% 11%	2090
October	1st to 10th	Night	51% 5% 13% 24% 7%	3530
	11th to 20th	Night	51% 8% 14% 24% 3	4025
	21st to end	Night	50% 6% 18% 16% 10%	4467
November	1st to 10th	Night	53% 6% 14% 19% 7% 1	2537
	11th to 20th	Night	54% 6% 13% 17% 9%	2619
	21st to end	Night	64% 5% 10% 14% 6%	2920
December	1st to 10th	Night	68% 5% 12% 12% 3	4910
	11th to 20th	Night	65% 4 6% 18% 6%	5592
	21st to end	Night	63% 4 7% 15% 9% 1	7254

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	29% 22% 30% 17% 3	200
	11th to 20th	Day	25% 21% 31% 18% 6% 1	200
	21st to end	Day	18% 21% 40% 14% 6%	220
February	1st to 10th	Day	25% 27% 34% 12% 1	205
	11th to 20th	Day	24% 25% 34% 15% 2	472
	21st to end	Day	24% 27% 29% 17% 3	414
March	1st to 10th	Day	28% 20% 30% 18% 4	500
	11th to 20th	Day	26% 23% 30% 15% 5% 1	500
	21st to end	Day	25% 23% 28% 15% 8% 1	530
April	1st to 10th	Day	30% 18% 29% 17% 5%	460
	11th to 20th	Day	29% 18% 27% 19% 5% 2	452
	21st to end	Day	31% 20% 30% 12% 5% 1	460
May	1st to 10th	Day	29% 19% 32% 15% 5%	463
	11th to 20th	Day	22% 16% 32% 22% 7% 1	487
	21st to end	Day	24% 22% 31% 18% 6%	529
June	1st to 10th	Day	23% 14% 34% 22% 8%	656
	11th to 20th	Day	21% 13% 30% 24% 11% 1	680
	21st to end	Day	27% 12% 28% 22% 10% 1	664
July	1st to 10th	Day	20% 12% 33% 23% 10% 1	485
	11th to 20th	Day	20% 12% 33% 25% 9% 1	484
	21st to end	Day	19% 13% 30% 27% 11% 2	532
August	1st to 10th	Day	20% 11% 28% 28% 11% 2	486
	11th to 20th	Day	23% 9% 23% 29% 14% 3	479
	21st to end	Day	24% 14% 25% 18% 14% 5%	539
September	1st to 10th	Day	22% 12% 28% 22% 13% 2	490
	11th to 20th	Day	20% 12% 24% 25% 15% 5%	490
	21st to end	Day	24% 15% 23% 21% 13% 4	490
October	1st to 10th	Day	25% 17% 26% 20% 11% 1	490
	11th to 20th	Day	31% 15% 27% 17% 8% 1	413
	21st to end	Day	34% 15% 28% 17% 5%	429
November	1st to 10th	Day	33% 16% 23% 21% 6% 1	395
	11th to 20th	Day	28% 18% 27% 17% 9% 1	380
	21st to end	Day	32% 27% 26% 15% 2 1	200
December	1st to 10th	Day	32% 14% 32% 16% 8% 1	200
	11th to 20th	Day	31% 22% 28% 16% 3 2	200
	21st to end	Day	31% 19% 32% 12% 5% 1	220
January	1st to 10th	Night	28% 14% 33% 22% 4	800
	11th to 20th	Night	26% 17% 28% 23% 6%	800
	21st to end	Night	15% 12% 34% 31% 6%	880
February	1st to 10th	Night	19% 14% 36% 26% 5%	800
	11th to 20th	Night	23% 17% 36% 19% 5%	783
	21st to end	Night	23% 16% 31% 26% 5%	660
March	1st to 10th	Night	22% 14% 36% 23% 5%	800
	11th to 20th	Night	24% 16% 34% 20% 5% 1	800
	21st to end	Night	23% 16% 29% 24% 7% 1	863
April	1st to 10th	Night	30% 14% 27% 24% 5%	760
	11th to 20th	Night	27% 13% 29% 26% 5%	676
	21st to end	Night	28% 17% 29% 20% 6%	570
May	1st to 10th	Night	27% 13% 32% 23% 6%	506
	11th to 20th	Night	25% 8% 30% 29% 7% 1	374
	21st to end	Night	27% 7% 31% 27% 8%	411
June	1st to 10th	Night	25% 7% 26% 36% 6%	380
	11th to 20th	Night	23% 5% 25% 34% 13%	380
	21st to end	Night	26% 4 22% 37% 11%	380
July	1st to 10th	Night	18% 5% 25% 40% 11% 1	370
	11th to 20th	Night	21% 4 18% 41% 15% 1	368
	21st to end	Night	18% 6% 19% 42% 17%	416
August	1st to 10th	Night	19% 2 14% 44% 21%	378
	11th to 20th	Night	18% 5% 22% 37% 18%	535
	21st to end	Night	20% 7% 23% 32% 17% 1	762
September	1st to 10th	Night	22% 4 26% 32% 15% 1	760
	11th to 20th	Night	21% 7% 21% 32% 19% 2	760
	21st to end	Night	24% 8% 24% 29% 15% 1	760
October	1st to 10th	Night	24% 11% 25% 30% 10% 1	760
	11th to 20th	Night	29% 11% 24% 25% 10%	760
	21st to end	Night	33% 11% 28% 24% 4	836
November	1st to 10th	Night	29% 12% 26% 25% 7% 1	780
	11th to 20th	Night	27% 15% 26% 23% 8% 1	800
	21st to end	Night	32% 17% 25% 20% 6% 1	860
December	1st to 10th	Night	32% 11% 26% 24% 7%	900
	11th to 20th	Night	28% 19% 24% 22% 6% 1	900
	21st to end	Night	34% 14% 27% 19% 4 1	937

Page generated at 2025-03-24 09:04:28. Version ac07

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