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 2026-01-02.

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% 11% 4 8% 5% 5% 5% 4 6% 7% 31%	127368
	Night	13% 11% 4 9% 5% 5% 5% 4 6% 7% 31%	124102
Transparency	Day	50% 6% 13% 20% 8% 1	130799
	Night	51% 6% 13% 21% 9% 1	128759
Seeing	Day	26% 17% 29% 19% 7% 2	17067
	Night	24% 16% 25% 26% 9% 1	25316

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	13% 23% 7% 10% 6% 4 4 3 4 6% 21%	3309
	11th to 20th	Day	7% 12% 6% 15% 9% 6% 5% 4 6% 5% 26%	3570
	21st to end	Day	5% 6% 4 12% 7% 6% 7% 6% 7% 8% 33%	3960
February	1st to 10th	Day	6% 12% 4 11% 9% 7% 7% 5% 7% 6% 26%	1632
	11th to 20th	Day	9% 15% 5% 12% 8% 6% 5% 4 5% 6% 26%	1843
	21st to end	Day	10% 12% 4 9% 7% 6% 6% 4 6% 5% 31%	1650
March	1st to 10th	Day	13% 17% 5% 11% 5% 5% 4 3 4 6% 26%	4476
	11th to 20th	Day	10% 15% 6% 10% 6% 6% 6% 4 7% 7% 24%	4875
	21st to end	Day	13% 17% 5% 10% 4 4 4 3 4 5% 31%	5648
April	1st to 10th	Day	16% 16% 4 8% 6% 6% 4 3 5% 5% 27%	2400
	11th to 20th	Day	16% 12% 3 6% 5% 4 5% 3 4 6% 35%	2544
	21st to end	Day	20% 13% 3 7% 4 4 4 3 5% 6% 32%	2600
May	1st to 10th	Day	20% 13% 3 7% 5% 4 4 3 4 5% 32%	5968
	11th to 20th	Day	23% 9% 3 7% 4 4 4 3 5% 6% 32%	6380
	21st to end	Day	19% 9% 3 7% 4 5% 5% 4 6% 8% 30%	7451
June	1st to 10th	Day	20% 10% 2 8% 5% 5% 5% 3 6% 7% 30%	3000
	11th to 20th	Day	19% 7% 2 6% 5% 5% 4 4 7% 8% 33%	3000
	21st to end	Day	22% 9% 3 7% 5% 5% 5% 3 6% 7% 27%	3000
July	1st to 10th	Day	15% 6% 3 8% 6% 5% 6% 5% 7% 9% 29%	6820
	11th to 20th	Day	14% 7% 3 7% 6% 6% 7% 5% 8% 9% 28%	6546
	21st to end	Day	9% 5% 2 7% 4 5% 6% 5% 7% 9% 40%	6926
August	1st to 10th	Day	12% 6% 2 8% 6% 6% 7% 5% 8% 9% 31%	4499
	11th to 20th	Day	16% 6% 3 7% 5% 6% 7% 5% 8% 8% 29%	4175
	21st to end	Day	16% 7% 2 7% 5% 5% 5% 5% 6% 8% 35%	4649
September	1st to 10th	Day	14% 7% 3 7% 5% 5% 5% 4 6% 8% 38%	2379
	11th to 20th	Day	14% 6% 2 7% 4 5% 4 4 6% 7% 43%	2200
	21st to end	Day	16% 8% 2 6% 4 4 5% 4 5% 8% 37%	2200
October	1st to 10th	Day	16% 9% 3 7% 4 5% 5% 4 6% 7% 33%	2162
	11th to 20th	Day	20% 9% 4 8% 5% 5% 5% 4 6% 7% 28%	1852
	21st to end	Day	22% 12% 3 10% 4 4 4 3 4 7% 26%	1980
November	1st to 10th	Day	15% 13% 4 10% 6% 6% 5% 3 5% 5% 27%	1851
	11th to 20th	Day	16% 14% 5% 10% 6% 5% 5% 4 5% 6% 25%	1741
	21st to end	Day	18% 16% 5% 9% 6% 4 4 3 5% 7% 23%	1491
December	1st to 10th	Day	14% 17% 5% 7% 5% 5% 4 3 4 4 32%	2350
	11th to 20th	Day	14% 14% 4 8% 6% 6% 4 3 4 6% 32%	2688
	21st to end	Day	14% 14% 4 10% 5% 4 3 3 4 6% 34%	3553
January	1st to 10th	Night	12% 20% 7% 12% 6% 5% 4 3 5% 6% 20%	6668
	11th to 20th	Night	7% 13% 7% 17% 8% 5% 5% 4 5% 6% 24%	6315
	21st to end	Night	4 7% 5% 12% 7% 7% 7% 6% 7% 8% 30%	6996
February	1st to 10th	Night	7% 12% 5% 11% 7% 6% 6% 4 7% 6% 31%	2767
	11th to 20th	Night	8% 13% 6% 12% 7% 6% 4 4 6% 7% 27%	2442
	21st to end	Night	10% 14% 4 10% 5% 5% 5% 4 5% 6% 31%	1980
March	1st to 10th	Night	15% 15% 4 10% 6% 5% 7% 5% 5% 6% 23%	5364
	11th to 20th	Night	8% 14% 4 11% 6% 6% 6% 5% 7% 7% 26%	5084
	21st to end	Night	14% 17% 5% 11% 5% 4 3 2 4 5% 31%	5269
April	1st to 10th	Night	17% 15% 5% 8% 5% 4 4 3 4 5% 30%	2000
	11th to 20th	Night	18% 9% 3 7% 4 5% 4 4 6% 7% 33%	1803
	21st to end	Night	21% 11% 3 7% 3 3 4 3 5% 6% 33%	1800
May	1st to 10th	Night	17% 10% 3 7% 4 4 4 3 6% 7% 34%	4014
	11th to 20th	Night	25% 8% 3 7% 4 3 4 3 5% 6% 33%	3515
	21st to end	Night	18% 7% 2 7% 4 4 5% 5% 5% 8% 35%	3446
June	1st to 10th	Night	17% 9% 4 9% 6% 4 4 4 6% 7% 31%	1400
	11th to 20th	Night	16% 6% 2 7% 4 4 4 4 6% 8% 38%	1400
	21st to end	Night	23% 7% 3 6% 5% 4 5% 4 5% 7% 30%	1400
July	1st to 10th	Night	12% 6% 2 6% 5% 5% 5% 5% 7% 11% 36%	3160
	11th to 20th	Night	11% 7% 3 6% 6% 5% 5% 5% 6% 9% 37%	3418
	21st to end	Night	9% 6% 2 6% 4 5% 5% 4 5% 8% 45%	3926
August	1st to 10th	Night	14% 5% 3 7% 5% 5% 5% 4 6% 8% 37%	2619
	11th to 20th	Night	12% 5% 3 10% 6% 7% 6% 5% 6% 7% 33%	2872
	21st to end	Night	15% 6% 2 6% 4 4 4 3 5% 8% 42%	3246
September	1st to 10th	Night	13% 5% 2 6% 4 4 4 4 5% 8% 45%	2020
	11th to 20th	Night	15% 7% 2 7% 4 4 4 4 5% 6% 42%	2200
	21st to end	Night	15% 8% 3 6% 4 4 4 3 4 6% 44%	2200
October	1st to 10th	Night	14% 8% 2 7% 3 3 4 3 7% 7% 41%	2237
	11th to 20th	Night	21% 8% 3 8% 4 5% 4 4 6% 7% 32%	2545
	21st to end	Night	20% 9% 3 7% 5% 4 4 3 6% 8% 30%	2860
November	1st to 10th	Night	16% 10% 4 9% 5% 5% 5% 4 5% 6% 31%	2667
	11th to 20th	Night	15% 12% 4 9% 6% 5% 4 4 6% 6% 30%	2877
	21st to end	Night	16% 14% 4 10% 6% 6% 5% 5% 5% 6% 24%	3124
December	1st to 10th	Night	11% 14% 6% 10% 5% 5% 5% 3 5% 6% 30%	5060
	11th to 20th	Night	14% 14% 4 8% 5% 4 5% 4 6% 6% 29%	5741
	21st to end	Night	12% 13% 5% 10% 5% 5% 5% 3 5% 5% 31%	7667

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	65% 3 11% 17% 4	3310
	11th to 20th	Day	58% 5% 10% 19% 7% 1	3600
	21st to end	Day	44% 8% 14% 18% 16%	3960
February	1st to 10th	Day	54% 5% 10% 17% 10% 3	1632
	11th to 20th	Day	58% 4 9% 17% 10%	1851
	21st to end	Day	53% 4 7% 21% 12% 3	1650
March	1st to 10th	Day	58% 5% 10% 11% 12% 4	4479
	11th to 20th	Day	57% 7% 13% 15% 8% 1	4875
	21st to end	Day	55% 3 7% 18% 12% 4	5648
April	1st to 10th	Day	56% 4 9% 18% 9% 3	2400
	11th to 20th	Day	49% 3 11% 25% 9% 2	2544
	21st to end	Day	54% 5% 9% 17% 14% 2	2600
May	1st to 10th	Day	53% 5% 11% 18% 11% 1	5979
	11th to 20th	Day	52% 5% 12% 22% 7% 2	6384
	21st to end	Day	50% 6% 12% 21% 10% 1	7451
June	1st to 10th	Day	52% 5% 11% 21% 10% 1	3000
	11th to 20th	Day	47% 6% 14% 21% 11% 1	3000
	21st to end	Day	54% 6% 13% 17% 9% 1	3000
July	1st to 10th	Day	48% 8% 15% 24% 6%	6745
	11th to 20th	Day	46% 11% 19% 20% 4	6466
	21st to end	Day	36% 8% 18% 30% 8%	6728
August	1st to 10th	Day	43% 9% 20% 22% 6%	4485
	11th to 20th	Day	49% 9% 19% 19% 4	4214
	21st to end	Day	42% 7% 19% 22% 10% 1	4649
September	1st to 10th	Day	42% 5% 18% 25% 10%	2379
	11th to 20th	Day	39% 5% 16% 30% 9% 1	2200
	21st to end	Day	44% 5% 16% 26% 9%	2200
October	1st to 10th	Day	53% 6% 14% 21% 6%	3526
	11th to 20th	Day	51% 7% 15% 24% 2	2990
	21st to end	Day	50% 7% 17% 21% 6%	3180
November	1st to 10th	Day	56% 5% 13% 19% 5% 1	1851
	11th to 20th	Day	58% 5% 10% 21% 6%	1741
	21st to end	Day	59% 5% 13% 18% 5%	1491
December	1st to 10th	Day	54% 5% 12% 18% 10%	2350
	11th to 20th	Day	52% 6% 11% 20% 11% 1	2688
	21st to end	Day	52% 5% 13% 20% 7% 2	3553
January	1st to 10th	Night	66% 4 12% 14% 5%	6668
	11th to 20th	Night	61% 5% 12% 17% 6%	6360
	21st to end	Night	47% 7% 10% 21% 14% 1	6996
February	1st to 10th	Night	52% 5% 9% 20% 12% 1	2767
	11th to 20th	Night	57% 5% 9% 19% 9% 1	2445
	21st to end	Night	53% 4 8% 24% 10% 1	1980
March	1st to 10th	Night	59% 7% 9% 13% 12% 1	5374
	11th to 20th	Night	56% 7% 12% 16% 7% 2	5085
	21st to end	Night	56% 3 8% 19% 14% 1	5269
April	1st to 10th	Night	57% 4 6% 17% 13% 3	2000
	11th to 20th	Night	50% 4 8% 23% 14% 1	1803
	21st to end	Night	51% 4 9% 21% 13% 2	1800
May	1st to 10th	Night	48% 6% 11% 20% 14% 1	4020
	11th to 20th	Night	53% 5% 10% 22% 10% 1	3516
	21st to end	Night	45% 8% 11% 22% 12% 2	3447
June	1st to 10th	Night	51% 5% 12% 22% 9% 1	1400
	11th to 20th	Night	44% 6% 13% 20% 14% 3	1400
	21st to end	Night	54% 5% 12% 19% 10%	1400
July	1st to 10th	Night	41% 8% 19% 26% 6%	3125
	11th to 20th	Night	42% 8% 23% 23% 4	3375
	21st to end	Night	37% 7% 20% 27% 9%	3809
August	1st to 10th	Night	44% 8% 18% 23% 7%	2609
	11th to 20th	Night	49% 10% 19% 16% 6%	2899
	21st to end	Night	40% 6% 15% 30% 9%	3246
September	1st to 10th	Night	38% 6% 15% 29% 10% 1	2020
	11th to 20th	Night	43% 5% 16% 26% 10% 1	2200
	21st to end	Night	41% 5% 14% 27% 12%	2200
October	1st to 10th	Night	45% 5% 12% 29% 8% 1	3653
	11th to 20th	Night	47% 5% 15% 27% 6%	4146
	21st to end	Night	45% 8% 18% 20% 8%	4610
November	1st to 10th	Night	53% 5% 13% 21% 8%	2667
	11th to 20th	Night	53% 5% 14% 20% 8%	2877
	21st to end	Night	60% 5% 11% 17% 6%	3124
December	1st to 10th	Night	55% 5% 12% 22% 6%	5060
	11th to 20th	Night	53% 6% 9% 23% 8% 1	5742
	21st to end	Night	54% 6% 12% 19% 8% 1	7667

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	27% 18% 36% 15% 3	202
	11th to 20th	Day	25% 25% 32% 12% 5% 2	200
	21st to end	Day	18% 23% 35% 17% 5% 1	220
February	1st to 10th	Day	24% 24% 32% 14% 5% 1	232
	11th to 20th	Day	26% 24% 32% 15% 3	441
	21st to end	Day	23% 26% 34% 13% 4 1	414
March	1st to 10th	Day	29% 23% 28% 15% 4 1	500
	11th to 20th	Day	28% 22% 30% 14% 5% 1	500
	21st to end	Day	35% 21% 25% 12% 5% 1	550
April	1st to 10th	Day	36% 22% 23% 13% 4 1	500
	11th to 20th	Day	31% 18% 33% 13% 3 2	492
	21st to end	Day	35% 18% 30% 12% 4 1	500
May	1st to 10th	Day	33% 17% 30% 16% 4 1	503
	11th to 20th	Day	24% 18% 29% 21% 6% 1	550
	21st to end	Day	28% 17% 30% 16% 7% 1	790
June	1st to 10th	Day	29% 14% 26% 23% 7% 2	730
	11th to 20th	Day	27% 15% 26% 19% 11% 2	730
	21st to end	Day	25% 12% 28% 22% 11% 1	730
July	1st to 10th	Day	22% 12% 33% 22% 11% 1	720
	11th to 20th	Day	15% 14% 34% 26% 9% 2	601
	21st to end	Day	17% 11% 33% 27% 11% 1	576
August	1st to 10th	Day	17% 12% 29% 26% 13% 2	526
	11th to 20th	Day	19% 9% 33% 26% 10% 4	519
	21st to end	Day	19% 16% 27% 22% 12% 4	583
September	1st to 10th	Day	19% 15% 32% 21% 9% 5%	530
	11th to 20th	Day	23% 12% 27% 23% 10% 5%	530
	21st to end	Day	22% 15% 28% 19% 11% 5%	530
October	1st to 10th	Day	22% 20% 22% 24% 10% 2	508
	11th to 20th	Day	33% 16% 23% 16% 10% 2	420
	21st to end	Day	35% 18% 25% 14% 6% 1	462
November	1st to 10th	Day	32% 19% 25% 18% 4 1	425
	11th to 20th	Day	30% 18% 26% 17% 8%	430
	21st to end	Day	41% 19% 23% 15% 2	241
December	1st to 10th	Day	28% 23% 28% 15% 5% 1	220
	11th to 20th	Day	33% 22% 27% 13% 4 1	220
	21st to end	Day	31% 20% 27% 16% 5% 1	242
January	1st to 10th	Night	22% 20% 29% 23% 5%	873
	11th to 20th	Night	23% 21% 28% 21% 7%	800
	21st to end	Night	15% 19% 35% 25% 5% 1	880
February	1st to 10th	Night	18% 21% 31% 23% 6% 1	800
	11th to 20th	Night	22% 25% 29% 18% 5%	783
	21st to end	Night	23% 19% 27% 23% 6% 1	660
March	1st to 10th	Night	25% 18% 27% 25% 4 1	800
	11th to 20th	Night	24% 19% 30% 19% 8%	800
	21st to end	Night	27% 21% 23% 23% 6%	880
April	1st to 10th	Night	31% 16% 26% 20% 7% 1	800
	11th to 20th	Night	25% 15% 27% 23% 8% 1	619
	21st to end	Night	34% 13% 24% 21% 7% 1	600
May	1st to 10th	Night	29% 13% 23% 26% 9%	586
	11th to 20th	Night	25% 11% 19% 31% 12% 1	394
	21st to end	Night	25% 15% 23% 26% 10% 1	433
June	1st to 10th	Night	22% 7% 24% 36% 10% 1	400
	11th to 20th	Night	21% 10% 20% 31% 18% 2	400
	21st to end	Night	28% 7% 23% 32% 10% 1	400
July	1st to 10th	Night	21% 6% 25% 36% 11% 1	390
	11th to 20th	Night	12% 10% 19% 43% 15% 1	388
	21st to end	Night	16% 8% 24% 35% 16% 1	438
August	1st to 10th	Night	16% 5% 20% 41% 18% 1	418
	11th to 20th	Night	16% 7% 22% 36% 19% 1	592
	21st to end	Night	15% 10% 23% 35% 15% 2	670
September	1st to 10th	Night	16% 10% 26% 33% 13% 2	800
	11th to 20th	Night	21% 10% 20% 31% 15% 3	800
	21st to end	Night	22% 11% 22% 30% 14% 1	800
October	1st to 10th	Night	20% 16% 22% 30% 11% 1	800
	11th to 20th	Night	28% 14% 22% 24% 12% 1	800
	21st to end	Night	28% 16% 24% 24% 8%	880
November	1st to 10th	Night	27% 18% 24% 23% 7%	820
	11th to 20th	Night	29% 17% 26% 20% 7% 1	917
	21st to end	Night	30% 18% 24% 23% 5% 1	950
December	1st to 10th	Night	25% 19% 27% 21% 6% 1	950
	11th to 20th	Night	27% 22% 25% 19% 6%	950
	21st to end	Night	26% 19% 27% 21% 6% 1	1045

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