Port-Aux-Quilles Astronomical Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Port-Aux-Quilles Astronomical Observatory clear sky chart from 2005-11-06 to 2024-11-12.

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	15% 10% 3 8% 6% 5% 5% 4 6% 7% 31%	101743
	Night	14% 11% 4 9% 5% 5% 5% 4 5% 7% 31%	97487
Transparency	Day	50% 6% 14% 21% 8% 1	105192
	Night	51% 5% 13% 21% 9% 1	102128
Seeing	Day	26% 17% 29% 19% 8% 2	15648
	Night	24% 16% 25% 26% 9% 1	23782

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	11% 16% 7% 10% 6% 5% 5% 4 5% 6% 24%	2300
	11th to 20th	Day	9% 11% 5% 13% 10% 7% 5% 3 5% 4 28%	2520
	21st to end	Day	7% 8% 6% 12% 8% 6% 6% 4 6% 6% 32%	2772
February	1st to 10th	Day	6% 12% 5% 11% 9% 6% 7% 5% 7% 7% 27%	1550
	11th to 20th	Day	9% 14% 5% 12% 8% 6% 4 4 5% 6% 26%	1748
	21st to end	Day	10% 12% 5% 9% 7% 6% 6% 4 6% 5% 30%	1570
March	1st to 10th	Day	12% 16% 4 10% 5% 5% 4 3 5% 7% 28%	3116
	11th to 20th	Day	12% 19% 6% 9% 5% 5% 4 4 6% 6% 23%	3403
	21st to end	Day	12% 16% 5% 9% 4 4 4 3 4 5% 34%	3942
April	1st to 10th	Day	17% 16% 4 8% 6% 5% 4 3 5% 5% 27%	2280
	11th to 20th	Day	16% 12% 3 6% 5% 4 5% 3 5% 6% 35%	2415
	21st to end	Day	20% 13% 3 7% 4 4 4 3 5% 6% 32%	2470
May	1st to 10th	Day	15% 13% 3 8% 5% 4 4 4 4 6% 34%	4160
	11th to 20th	Day	15% 8% 3 7% 5% 5% 4 4 6% 8% 35%	4446
	21st to end	Day	16% 8% 3 7% 5% 6% 6% 5% 7% 8% 30%	5185
June	1st to 10th	Day	20% 10% 2 8% 5% 5% 5% 3 6% 7% 30%	2850
	11th to 20th	Day	19% 7% 2 6% 5% 5% 4 4 6% 8% 34%	2850
	21st to end	Day	22% 9% 3 7% 5% 5% 5% 3 6% 7% 27%	2850
July	1st to 10th	Day	14% 6% 3 8% 6% 5% 6% 5% 7% 9% 31%	4760
	11th to 20th	Day	12% 7% 3 8% 7% 7% 7% 6% 7% 9% 28%	4570
	21st to end	Day	10% 6% 2 7% 5% 6% 5% 5% 7% 9% 37%	4814
August	1st to 10th	Day	12% 6% 3 9% 6% 6% 7% 5% 8% 9% 30%	4361
	11th to 20th	Day	17% 7% 3 7% 6% 6% 7% 5% 8% 8% 28%	4045
	21st to end	Day	16% 6% 2 6% 5% 5% 5% 4 6% 8% 36%	4507
September	1st to 10th	Day	15% 7% 3 7% 5% 5% 4 4 6% 8% 37%	2260
	11th to 20th	Day	14% 6% 2 7% 4 5% 4 4 6% 7% 41%	2090
	21st to end	Day	17% 8% 2 7% 4 4 5% 3 5% 7% 37%	2090
October	1st to 10th	Day	17% 9% 3 8% 4 5% 5% 4 6% 7% 32%	2054
	11th to 20th	Day	20% 9% 4 8% 5% 5% 5% 4 6% 7% 26%	1760
	21st to end	Day	21% 12% 4 10% 4 4 4 3 4 6% 27%	1881
November	1st to 10th	Day	16% 13% 4 10% 6% 6% 5% 3 5% 5% 27%	1761
	11th to 20th	Day	16% 13% 5% 9% 6% 5% 5% 4 5% 6% 25%	1585
	21st to end	Day	16% 15% 5% 9% 6% 4 4 3 5% 7% 25%	1349
December	1st to 10th	Day	17% 15% 4 9% 6% 6% 5% 3 5% 5% 25%	1330
	11th to 20th	Day	17% 18% 3 7% 5% 5% 3 3 4 6% 29%	1668
	21st to end	Day	18% 15% 4 8% 5% 4 3 3 3 4 33%	2431
January	1st to 10th	Night	10% 16% 8% 13% 8% 6% 5% 4 5% 5% 21%	4648
	11th to 20th	Night	9% 12% 6% 12% 7% 6% 6% 4 6% 6% 26%	4440
	21st to end	Night	6% 10% 7% 14% 7% 7% 5% 5% 6% 7% 27%	4884
February	1st to 10th	Night	7% 12% 5% 10% 6% 6% 6% 4 7% 6% 30%	2629
	11th to 20th	Night	8% 13% 6% 13% 7% 6% 4 4 6% 7% 27%	2317
	21st to end	Night	10% 14% 4 10% 5% 5% 5% 4 5% 7% 31%	1884
March	1st to 10th	Night	14% 14% 5% 11% 5% 4 6% 4 5% 6% 25%	3724
	11th to 20th	Night	10% 16% 4 11% 6% 6% 5% 4 6% 6% 25%	3556
	21st to end	Night	14% 15% 4 12% 5% 4 4 3 4 5% 30%	3675
April	1st to 10th	Night	18% 15% 4 8% 5% 4 4 3 4 5% 30%	1900
	11th to 20th	Night	18% 9% 3 7% 4 5% 4 4 6% 6% 34%	1712
	21st to end	Night	20% 11% 3 7% 3 3 4 3 5% 6% 34%	1710
May	1st to 10th	Night	18% 9% 3 7% 4 4 4 3 6% 7% 33%	2808
	11th to 20th	Night	17% 9% 3 7% 4 3 4 3 5% 6% 38%	2448
	21st to end	Night	16% 8% 2 7% 4 4 5% 5% 6% 8% 34%	2401
June	1st to 10th	Night	17% 9% 4 9% 6% 4 4 4 6% 7% 30%	1330
	11th to 20th	Night	16% 6% 2 7% 4 4 4 4 6% 8% 39%	1330
	21st to end	Night	23% 7% 3 6% 5% 4 5% 4 5% 7% 29%	1330
July	1st to 10th	Night	14% 6% 2 6% 4 5% 5% 5% 6% 10% 37%	2210
	11th to 20th	Night	12% 6% 3 6% 6% 5% 6% 5% 6% 9% 37%	2390
	21st to end	Night	10% 6% 2 5% 4 5% 5% 4 6% 9% 44%	2739
August	1st to 10th	Night	15% 5% 3 7% 6% 5% 5% 4 7% 8% 36%	2538
	11th to 20th	Night	12% 5% 3 10% 6% 7% 6% 5% 6% 7% 32%	2782
	21st to end	Night	15% 6% 2 6% 4 4 4 3 5% 8% 43%	3146
September	1st to 10th	Night	14% 6% 2 6% 4 4 5% 4 5% 8% 43%	1919
	11th to 20th	Night	15% 7% 2 7% 4 4 4 4 4 6% 42%	2090
	21st to end	Night	15% 8% 3 6% 4 4 4 3 4 6% 43%	2090
October	1st to 10th	Night	15% 8% 2 7% 3 3 4 3 7% 7% 40%	2125
	11th to 20th	Night	22% 8% 3 8% 4 4 4 4 6% 7% 31%	2418
	21st to end	Night	20% 9% 3 7% 5% 4 4 3 6% 8% 30%	2717
November	1st to 10th	Night	16% 10% 4 9% 5% 5% 5% 4 5% 6% 32%	2537
	11th to 20th	Night	16% 11% 3 9% 6% 5% 4 4 6% 7% 29%	2617
	21st to end	Night	15% 13% 4 9% 6% 5% 5% 5% 5% 6% 25%	2826
December	1st to 10th	Night	15% 16% 6% 8% 6% 5% 4 3 5% 6% 26%	2850
	11th to 20th	Night	14% 16% 3 9% 5% 5% 5% 4 5% 5% 28%	3531
	21st to end	Night	14% 14% 5% 10% 6% 5% 4 3 5% 5% 29%	5236

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	58% 4 15% 18% 5%	2301
	11th to 20th	Day	59% 4 8% 21% 6% 1	2520
	21st to end	Day	50% 6% 12% 18% 13%	2772
February	1st to 10th	Day	54% 5% 10% 18% 10% 3	1550
	11th to 20th	Day	59% 4 9% 18% 10% 1	1756
	21st to end	Day	54% 4 7% 21% 12% 3	1570
March	1st to 10th	Day	55% 5% 14% 14% 9% 4	3119
	11th to 20th	Day	60% 5% 11% 16% 7% 1	3403
	21st to end	Day	53% 3 8% 21% 11% 4	3942
April	1st to 10th	Day	57% 4 9% 17% 9% 3	2280
	11th to 20th	Day	49% 3 11% 25% 9% 2	2415
	21st to end	Day	53% 4 9% 17% 14% 2	2470
May	1st to 10th	Day	50% 4 13% 19% 12% 1	4174
	11th to 20th	Day	47% 5% 14% 26% 8%	4450
	21st to end	Day	48% 7% 11% 24% 9% 1	5185
June	1st to 10th	Day	52% 5% 11% 20% 11% 1	2850
	11th to 20th	Day	47% 6% 14% 21% 11% 1	2850
	21st to end	Day	55% 6% 13% 18% 8% 1	2850
July	1st to 10th	Day	45% 7% 16% 26% 6%	4685
	11th to 20th	Day	46% 11% 18% 20% 4	4490
	21st to end	Day	39% 8% 20% 26% 7%	4661
August	1st to 10th	Day	44% 9% 20% 21% 6%	4347
	11th to 20th	Day	50% 9% 19% 18% 3	4084
	21st to end	Day	42% 7% 19% 22% 10% 1	4507
September	1st to 10th	Day	43% 5% 17% 25% 10%	2260
	11th to 20th	Day	40% 5% 16% 29% 9%	2090
	21st to end	Day	45% 5% 16% 25% 9%	2090
October	1st to 10th	Day	54% 6% 14% 20% 6%	3418
	11th to 20th	Day	51% 7% 15% 24% 2	2898
	21st to end	Day	49% 7% 18% 20% 6%	3081
November	1st to 10th	Day	57% 5% 13% 19% 5% 1	1761
	11th to 20th	Day	58% 5% 10% 20% 6%	1585
	21st to end	Day	57% 5% 13% 18% 5%	1349
December	1st to 10th	Day	61% 5% 11% 17% 6%	1330
	11th to 20th	Day	57% 4 8% 19% 10%	1668
	21st to end	Day	56% 3 12% 19% 7% 4	2431
January	1st to 10th	Night	63% 4 10% 16% 7%	4648
	11th to 20th	Night	58% 5% 9% 20% 7%	4440
	21st to end	Night	55% 6% 9% 19% 9% 1	4884
February	1st to 10th	Night	53% 4 9% 20% 12% 1	2629
	11th to 20th	Night	58% 5% 9% 19% 9% 1	2320
	21st to end	Night	54% 4 8% 23% 10% 1	1884
March	1st to 10th	Night	58% 6% 11% 16% 8% 1	3734
	11th to 20th	Night	60% 5% 11% 17% 7% 1	3557
	21st to end	Night	56% 3 10% 19% 11% 1	3675
April	1st to 10th	Night	57% 4 6% 17% 13% 3	1900
	11th to 20th	Night	50% 4 8% 23% 14% 1	1712
	21st to end	Night	51% 4 9% 21% 13% 2	1710
May	1st to 10th	Night	49% 5% 13% 19% 13% 1	2814
	11th to 20th	Night	47% 5% 12% 23% 11% 1	2449
	21st to end	Night	46% 7% 10% 25% 12% 1	2402
June	1st to 10th	Night	52% 5% 12% 21% 8% 1	1330
	11th to 20th	Night	43% 6% 13% 21% 14% 3	1330
	21st to end	Night	55% 5% 11% 18% 10%	1330
July	1st to 10th	Night	41% 8% 19% 27% 6%	2175
	11th to 20th	Night	41% 6% 22% 25% 5%	2347
	21st to end	Night	37% 7% 22% 23% 10%	2651
August	1st to 10th	Night	45% 8% 18% 23% 7%	2528
	11th to 20th	Night	50% 10% 19% 15% 6%	2809
	21st to end	Night	40% 6% 15% 30% 9%	3146
September	1st to 10th	Night	40% 6% 15% 29% 10% 1	1919
	11th to 20th	Night	44% 4 16% 25% 10% 1	2090
	21st to end	Night	42% 5% 15% 27% 11%	2090
October	1st to 10th	Night	46% 5% 12% 29% 7% 1	3541
	11th to 20th	Night	47% 5% 15% 26% 6%	4019
	21st to end	Night	44% 8% 19% 20% 9%	4467
November	1st to 10th	Night	52% 5% 14% 21% 8%	2537
	11th to 20th	Night	53% 5% 14% 20% 8%	2617
	21st to end	Night	58% 5% 12% 18% 7%	2826
December	1st to 10th	Night	60% 4 11% 18% 6%	2850
	11th to 20th	Night	56% 5% 10% 21% 8%	3532
	21st to end	Night	57% 4 13% 17% 8% 1	5236

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	26% 18% 36% 16% 3 1	180
	11th to 20th	Day	24% 26% 34% 11% 3 2	180
	21st to end	Day	18% 23% 35% 18% 6% 1	198
February	1st to 10th	Day	25% 21% 33% 15% 5% 1	210
	11th to 20th	Day	24% 24% 33% 16% 3	406
	21st to end	Day	23% 26% 34% 12% 4 1	382
March	1st to 10th	Day	28% 22% 30% 15% 4 1	460
	11th to 20th	Day	28% 22% 29% 15% 5% 1	460
	21st to end	Day	34% 20% 26% 12% 6% 1	506
April	1st to 10th	Day	34% 22% 24% 15% 4 1	460
	11th to 20th	Day	31% 18% 32% 14% 3 2	452
	21st to end	Day	34% 18% 30% 13% 5% 1	460
May	1st to 10th	Day	33% 16% 29% 16% 5% 1	463
	11th to 20th	Day	22% 18% 30% 21% 6% 2	509
	21st to end	Day	28% 17% 31% 16% 7% 1	735
June	1st to 10th	Day	29% 14% 25% 23% 8% 2	680
	11th to 20th	Day	27% 14% 26% 20% 12% 2	680
	21st to end	Day	25% 11% 28% 23% 12% 1	680
July	1st to 10th	Day	22% 11% 33% 21% 11% 1	670
	11th to 20th	Day	15% 13% 34% 27% 10% 2	557
	21st to end	Day	16% 10% 33% 28% 11% 1	532
August	1st to 10th	Day	19% 12% 29% 26% 13% 2	486
	11th to 20th	Day	20% 8% 33% 26% 10% 4	479
	21st to end	Day	19% 15% 27% 23% 13% 4	539
September	1st to 10th	Day	19% 15% 32% 21% 9% 4	490
	11th to 20th	Day	23% 12% 28% 22% 10% 4	490
	21st to end	Day	23% 13% 29% 19% 11% 5%	490
October	1st to 10th	Day	22% 20% 22% 23% 10% 2	470
	11th to 20th	Day	35% 15% 24% 16% 9% 2	390
	21st to end	Day	34% 19% 26% 14% 6% 1	429
November	1st to 10th	Day	33% 18% 25% 19% 4 1	395
	11th to 20th	Day	31% 16% 27% 18% 9% 1	373
	21st to end	Day	38% 19% 26% 16% 2	199
December	1st to 10th	Day	27% 19% 31% 17% 6% 1	180
	11th to 20th	Day	34% 24% 26% 12% 3 1	180
	21st to end	Day	34% 21% 25% 16% 4 1	198
January	1st to 10th	Night	21% 20% 30% 24% 5%	821
	11th to 20th	Night	23% 21% 29% 21% 6%	760
	21st to end	Night	15% 19% 34% 25% 6% 1	836
February	1st to 10th	Night	18% 20% 31% 24% 7% 1	760
	11th to 20th	Night	21% 25% 29% 19% 6%	743
	21st to end	Night	23% 19% 28% 23% 6% 1	628
March	1st to 10th	Night	25% 18% 27% 25% 4 1	760
	11th to 20th	Night	25% 18% 29% 20% 8%	760
	21st to end	Night	27% 20% 23% 24% 6%	836
April	1st to 10th	Night	30% 15% 27% 21% 7% 1	760
	11th to 20th	Night	26% 14% 28% 22% 9% 1	588
	21st to end	Night	33% 13% 24% 22% 7% 1	570
May	1st to 10th	Night	29% 12% 22% 27% 9%	557
	11th to 20th	Night	25% 11% 19% 31% 13% 1	374
	21st to end	Night	26% 16% 23% 25% 10% 1	411
June	1st to 10th	Night	23% 6% 23% 36% 11% 1	380
	11th to 20th	Night	20% 10% 19% 31% 18% 2	380
	21st to end	Night	27% 7% 22% 32% 11% 1	380
July	1st to 10th	Night	21% 6% 25% 35% 12% 1	370
	11th to 20th	Night	13% 9% 19% 43% 15% 1	368
	21st to end	Night	17% 7% 22% 36% 17% 1	416
August	1st to 10th	Night	16% 5% 21% 40% 17% 1	397
	11th to 20th	Night	17% 6% 22% 35% 19% 1	562
	21st to end	Night	15% 10% 23% 34% 16% 2	636
September	1st to 10th	Night	17% 10% 26% 33% 13% 2	760
	11th to 20th	Night	22% 10% 21% 31% 14% 3	760
	21st to end	Night	22% 11% 22% 29% 14% 1	760
October	1st to 10th	Night	21% 16% 21% 29% 12% 1	760
	11th to 20th	Night	29% 13% 22% 24% 11% 1	760
	21st to end	Night	28% 16% 24% 24% 8%	836
November	1st to 10th	Night	26% 18% 24% 24% 8%	780
	11th to 20th	Night	28% 17% 26% 21% 7% 1	828
	21st to end	Night	29% 18% 24% 23% 5% 1	850
December	1st to 10th	Night	26% 19% 27% 21% 6% 1	850
	11th to 20th	Night	26% 22% 26% 19% 7%	850
	21st to end	Night	26% 20% 27% 21% 6% 1	935

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