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 2024-01-13.

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% 10% 4 7% 6% 4 5% 5% 5% 7% 31%	74579
	Night	15% 10% 4 8% 6% 4 5% 5% 5% 7% 32%	75168
Transparency	Day	51% 5% 13% 21% 9% 1	74273
	Night	52% 5% 12% 21% 9% 1	75009
Seeing	Day	26% 16% 29% 19% 8% 2	14474
	Night	24% 16% 25% 26% 9% 1	22802

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	12% 15% 6% 9% 7% 3 6% 5% 5% 7% 24%	1384
	11th to 20th	Day	12% 11% 6% 10% 10% 5% 6% 4 4 4 29%	1462
	21st to end	Day	8% 8% 4 10% 9% 5% 5% 6% 5% 8% 32%	1584
February	1st to 10th	Day	6% 11% 6% 10% 9% 4 7% 7% 7% 7% 26%	1469
	11th to 20th	Day	9% 14% 5% 10% 9% 4 5% 5% 4 6% 26%	1654
	21st to end	Day	10% 12% 5% 8% 9% 5% 6% 5% 5% 6% 30%	1480
March	1st to 10th	Day	13% 15% 6% 7% 6% 3 5% 4 5% 6% 29%	1797
	11th to 20th	Day	13% 13% 6% 8% 6% 4 4 4 6% 7% 29%	1931
	21st to end	Day	14% 14% 5% 8% 5% 3 5% 5% 4 6% 32%	2250
April	1st to 10th	Day	18% 13% 6% 7% 7% 4 5% 4 5% 5% 26%	2160
	11th to 20th	Day	17% 12% 3 5% 5% 3 5% 4 5% 6% 36%	2286
	21st to end	Day	21% 12% 4 5% 5% 3 4 4 5% 5% 32%	2340
May	1st to 10th	Day	19% 10% 3 6% 5% 3 4 4 4 6% 36%	2366
	11th to 20th	Day	16% 8% 3 6% 6% 4 5% 5% 5% 6% 35%	2498
	21st to end	Day	19% 7% 3 5% 5% 3 5% 5% 6% 8% 34%	2919
June	1st to 10th	Day	20% 9% 3 7% 6% 3 6% 4 6% 7% 29%	2700
	11th to 20th	Day	20% 7% 3 5% 6% 4 4 4 5% 8% 34%	2700
	21st to end	Day	23% 8% 3 6% 6% 4 5% 4 6% 7% 27%	2700
July	1st to 10th	Day	16% 6% 3 6% 7% 4 6% 6% 7% 9% 30%	2700
	11th to 20th	Day	13% 6% 4 7% 7% 4 7% 7% 6% 9% 30%	2594
	21st to end	Day	13% 6% 3 8% 6% 5% 6% 6% 7% 9% 31%	2744
August	1st to 10th	Day	15% 6% 3 7% 8% 5% 7% 6% 8% 10% 25%	2471
	11th to 20th	Day	14% 6% 3 6% 6% 4 6% 6% 8% 9% 32%	2304
	21st to end	Day	12% 6% 2 6% 7% 4 5% 7% 7% 8% 35%	2563
September	1st to 10th	Day	15% 7% 3 6% 6% 3 5% 5% 6% 7% 37%	2142
	11th to 20th	Day	15% 6% 2 6% 6% 3 5% 4 5% 7% 40%	1980
	21st to end	Day	18% 7% 2 5% 5% 3 5% 5% 5% 8% 37%	1980
October	1st to 10th	Day	16% 9% 3 6% 5% 4 5% 5% 5% 7% 33%	1946
	11th to 20th	Day	21% 8% 4 7% 6% 4 6% 5% 6% 7% 26%	1668
	21st to end	Day	22% 13% 4 8% 6% 4 4 4 4 7% 26%	1782
November	1st to 10th	Day	16% 11% 5% 8% 7% 5% 5% 4 5% 5% 27%	1671
	11th to 20th	Day	17% 12% 5% 8% 7% 4 5% 5% 5% 7% 25%	1576
	21st to end	Day	16% 14% 6% 8% 7% 3 5% 4 5% 7% 25%	1349
December	1st to 10th	Day	18% 14% 5% 8% 7% 5% 5% 4 5% 5% 25%	1330
	11th to 20th	Day	17% 17% 4 6% 6% 3 4 4 4 6% 29%	1668
	21st to end	Day	18% 15% 4 7% 6% 3 3 3 3 4 34%	2431
January	1st to 10th	Night	12% 13% 6% 11% 8% 5% 6% 5% 6% 6% 22%	2777
	11th to 20th	Night	12% 11% 6% 9% 6% 5% 6% 6% 6% 6% 27%	2560
	21st to end	Night	8% 9% 6% 11% 8% 4 5% 6% 6% 7% 30%	2772
February	1st to 10th	Night	8% 11% 6% 9% 8% 4 7% 5% 6% 6% 30%	2490
	11th to 20th	Night	8% 13% 7% 11% 7% 4 5% 5% 5% 7% 27%	2191
	21st to end	Night	10% 13% 5% 9% 6% 3 6% 5% 5% 7% 30%	1776
March	1st to 10th	Night	12% 14% 6% 9% 5% 3 5% 5% 5% 7% 30%	2150
	11th to 20th	Night	13% 13% 3 8% 6% 4 5% 5% 6% 6% 30%	2028
	21st to end	Night	13% 12% 4 6% 6% 3 5% 5% 5% 6% 35%	2105
April	1st to 10th	Night	20% 14% 4 7% 6% 3 4 5% 4 5% 28%	1800
	11th to 20th	Night	18% 9% 3 5% 6% 3 4 5% 6% 7% 35%	1621
	21st to end	Night	21% 11% 3 5% 4 2 5% 4 5% 6% 34%	1620
May	1st to 10th	Night	22% 9% 3 7% 5% 3 5% 3 4 6% 31%	1608
	11th to 20th	Night	20% 8% 3 6% 4 3 3 4 5% 6% 38%	1394
	21st to end	Night	18% 9% 3 7% 4 3 6% 6% 5% 6% 33%	1356
June	1st to 10th	Night	17% 9% 4 8% 7% 3 4 5% 5% 8% 29%	1260
	11th to 20th	Night	16% 6% 2 7% 5% 3 5% 5% 5% 8% 39%	1260
	21st to end	Night	23% 7% 3 6% 6% 3 5% 5% 5% 7% 30%	1260
July	1st to 10th	Night	19% 6% 3 5% 5% 3 5% 5% 5% 9% 36%	1260
	11th to 20th	Night	10% 6% 3 6% 7% 4 7% 6% 6% 9% 36%	1362
	21st to end	Night	13% 7% 3 5% 5% 4 6% 6% 5% 9% 36%	1574
August	1st to 10th	Night	13% 4 3 5% 6% 4 5% 5% 8% 9% 39%	1450
	11th to 20th	Night	14% 5% 3 7% 7% 4 6% 6% 6% 8% 34%	1596
	21st to end	Night	12% 5% 2 5% 6% 3 5% 5% 6% 9% 42%	1790
September	1st to 10th	Night	14% 6% 2 6% 5% 3 4 5% 5% 8% 43%	1818
	11th to 20th	Night	16% 7% 2 6% 6% 4 4 5% 4 6% 41%	1980
	21st to end	Night	16% 7% 3 5% 4 3 4 4 4 6% 44%	1980
October	1st to 10th	Night	14% 8% 2 6% 4 3 4 4 6% 7% 41%	2013
	11th to 20th	Night	22% 7% 3 7% 5% 3 4 5% 5% 8% 31%	2290
	21st to end	Night	21% 9% 4 6% 6% 2 4 4 6% 8% 30%	2574
November	1st to 10th	Night	16% 9% 4 8% 5% 3 5% 5% 5% 6% 32%	2407
	11th to 20th	Night	16% 10% 4 8% 6% 4 5% 5% 6% 7% 30%	2603
	21st to end	Night	16% 13% 4 9% 7% 4 6% 6% 5% 6% 25%	2826
December	1st to 10th	Night	15% 14% 7% 8% 6% 4 5% 4 4 6% 26%	2850
	11th to 20th	Night	14% 15% 4 8% 6% 3 5% 5% 5% 5% 28%	3531
	21st to end	Night	14% 13% 5% 9% 7% 4 4 4 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	59% 4 11% 18% 8%	1385
	11th to 20th	Day	60% 5% 9% 17% 8% 2	1462
	21st to end	Day	49% 5% 11% 19% 14% 1	1584
February	1st to 10th	Day	54% 5% 11% 17% 10% 3	1469
	11th to 20th	Day	59% 4 9% 18% 10% 1	1662
	21st to end	Day	54% 3 6% 21% 12% 3	1480
March	1st to 10th	Day	56% 4 9% 16% 13% 3	1800
	11th to 20th	Day	53% 5% 9% 20% 12% 2	1931
	21st to end	Day	54% 4 9% 20% 10% 2	2250
April	1st to 10th	Day	58% 4 10% 16% 9% 3	2160
	11th to 20th	Day	48% 3 11% 26% 9% 2	2286
	21st to end	Day	54% 4 9% 17% 13% 2	2340
May	1st to 10th	Day	49% 4 12% 19% 14% 2	2366
	11th to 20th	Day	49% 3 12% 24% 12% 1	2502
	21st to end	Day	47% 6% 12% 24% 11% 1	2919
June	1st to 10th	Day	53% 5% 11% 19% 11% 1	2700
	11th to 20th	Day	48% 5% 13% 22% 11% 1	2700
	21st to end	Day	55% 5% 13% 18% 8% 1	2700
July	1st to 10th	Day	47% 6% 17% 24% 6%	2625
	11th to 20th	Day	47% 6% 16% 23% 7%	2514
	21st to end	Day	46% 7% 18% 22% 7%	2591
August	1st to 10th	Day	49% 7% 21% 19% 4	2457
	11th to 20th	Day	44% 6% 20% 23% 5%	2304
	21st to end	Day	41% 6% 19% 27% 7%	2563
September	1st to 10th	Day	44% 4 17% 25% 10%	2142
	11th to 20th	Day	41% 5% 16% 28% 9% 1	1980
	21st to end	Day	44% 5% 16% 25% 9%	1980
October	1st to 10th	Day	49% 3 15% 22% 10%	1946
	11th to 20th	Day	56% 6% 15% 21% 3	1668
	21st to end	Day	60% 4 12% 17% 6%	1782
November	1st to 10th	Day	57% 5% 13% 20% 5% 1	1671
	11th to 20th	Day	58% 5% 10% 20% 6%	1576
	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% 5% 9% 16% 7%	2777
	11th to 20th	Night	58% 6% 10% 18% 8% 1	2560
	21st to end	Night	52% 5% 8% 22% 12% 1	2772
February	1st to 10th	Night	53% 4 9% 20% 12% 1	2490
	11th to 20th	Night	58% 5% 9% 18% 10% 1	2194
	21st to end	Night	54% 4 7% 24% 10% 1	1776
March	1st to 10th	Night	55% 4 8% 22% 10% 1	2160
	11th to 20th	Night	54% 4 10% 20% 11% 1	2029
	21st to end	Night	50% 3 10% 22% 13% 2	2105
April	1st to 10th	Night	58% 4 7% 16% 13% 2	1800
	11th to 20th	Night	49% 4 8% 23% 15% 1	1621
	21st to end	Night	51% 4 9% 21% 13% 2	1620
May	1st to 10th	Night	55% 4 9% 17% 13% 2	1608
	11th to 20th	Night	48% 3 10% 23% 13% 2	1395
	21st to end	Night	51% 6% 10% 18% 14% 1	1357
June	1st to 10th	Night	53% 5% 12% 20% 9% 1	1260
	11th to 20th	Night	45% 5% 11% 22% 14% 3	1260
	21st to end	Night	54% 5% 12% 19% 10%	1260
July	1st to 10th	Night	45% 6% 17% 26% 6%	1225
	11th to 20th	Night	43% 6% 19% 24% 8% 1	1319
	21st to end	Night	46% 8% 17% 22% 8%	1486
August	1st to 10th	Night	41% 9% 19% 26% 5%	1440
	11th to 20th	Night	47% 7% 18% 21% 7%	1596
	21st to end	Night	39% 5% 20% 28% 8%	1790
September	1st to 10th	Night	40% 6% 15% 28% 10% 1	1818
	11th to 20th	Night	46% 4 16% 24% 10% 1	1980
	21st to end	Night	41% 5% 15% 27% 12%	1980
October	1st to 10th	Night	42% 4 15% 26% 12% 2	2013
	11th to 20th	Night	52% 4 14% 24% 5%	2290
	21st to end	Night	52% 5% 15% 20% 7%	2574
November	1st to 10th	Night	52% 4 14% 21% 8%	2407
	11th to 20th	Night	53% 5% 14% 20% 8%	2603
	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	23% 25% 33% 13% 4 2	166
	21st to end	Day	19% 23% 35% 16% 6% 1	176
February	1st to 10th	Day	26% 22% 31% 16% 4 1	189
	11th to 20th	Day	24% 24% 32% 16% 3	372
	21st to end	Day	24% 25% 33% 13% 4 1	346
March	1st to 10th	Day	29% 22% 29% 15% 4 1	420
	11th to 20th	Day	28% 22% 29% 14% 6% 1	420
	21st to end	Day	32% 21% 26% 13% 6% 1	462
April	1st to 10th	Day	35% 23% 23% 15% 4 1	420
	11th to 20th	Day	31% 17% 32% 15% 4 2	412
	21st to end	Day	35% 16% 30% 13% 5% 1	420
May	1st to 10th	Day	33% 16% 30% 16% 4 1	423
	11th to 20th	Day	23% 19% 31% 19% 6% 1	467
	21st to end	Day	28% 17% 30% 16% 7% 1	680
June	1st to 10th	Day	29% 15% 25% 22% 7% 2	630
	11th to 20th	Day	28% 12% 26% 20% 12% 2	630
	21st to end	Day	23% 11% 28% 23% 13% 1	630
July	1st to 10th	Day	23% 10% 32% 21% 12% 1	620
	11th to 20th	Day	15% 13% 34% 26% 10% 2	513
	21st to end	Day	17% 9% 32% 29% 11% 1	488
August	1st to 10th	Day	19% 11% 30% 26% 13% 2	446
	11th to 20th	Day	20% 8% 34% 25% 10% 4	439
	21st to end	Day	19% 15% 28% 22% 12% 4	495
September	1st to 10th	Day	20% 14% 31% 21% 10% 4	450
	11th to 20th	Day	24% 13% 29% 21% 9% 4	450
	21st to end	Day	23% 14% 30% 18% 10% 5%	450
October	1st to 10th	Day	21% 20% 23% 24% 10% 2	432
	11th to 20th	Day	35% 13% 25% 15% 9% 2	360
	21st to end	Day	34% 18% 27% 14% 7% 1	396
November	1st to 10th	Day	32% 17% 24% 21% 4 1	365
	11th to 20th	Day	30% 16% 27% 18% 9% 1	370
	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	22% 21% 29% 22% 6%	732
	21st to end	Night	16% 20% 34% 24% 6% 1	792
February	1st to 10th	Night	19% 21% 30% 23% 6% 1	720
	11th to 20th	Night	21% 25% 29% 19% 6%	703
	21st to end	Night	22% 19% 28% 24% 6% 1	592
March	1st to 10th	Night	25% 19% 26% 25% 4 1	720
	11th to 20th	Night	25% 19% 28% 19% 8%	720
	21st to end	Night	26% 20% 22% 25% 6%	792
April	1st to 10th	Night	31% 15% 26% 20% 7% 1	720
	11th to 20th	Night	25% 15% 28% 22% 9% 1	557
	21st to end	Night	34% 13% 23% 22% 8% 1	540
May	1st to 10th	Night	30% 12% 22% 27% 9%	528
	11th to 20th	Night	25% 12% 20% 31% 11% 1	354
	21st to end	Night	26% 16% 23% 24% 10% 1	389
June	1st to 10th	Night	23% 7% 24% 36% 9% 1	360
	11th to 20th	Night	21% 9% 19% 32% 18% 2	360
	21st to end	Night	27% 6% 21% 33% 11% 1	360
July	1st to 10th	Night	21% 6% 25% 34% 13% 1	350
	11th to 20th	Night	12% 9% 20% 42% 16% 1	348
	21st to end	Night	18% 7% 21% 36% 17% 2	394
August	1st to 10th	Night	16% 5% 20% 40% 18% 1	376
	11th to 20th	Night	17% 6% 22% 35% 20% 1	532
	21st to end	Night	15% 10% 23% 34% 16% 2	602
September	1st to 10th	Night	17% 10% 26% 32% 14% 2	720
	11th to 20th	Night	23% 10% 21% 29% 13% 3	720
	21st to end	Night	23% 11% 23% 29% 13% 1	720
October	1st to 10th	Night	20% 16% 22% 30% 11% 1	720
	11th to 20th	Night	28% 13% 22% 23% 12% 1	720
	21st to end	Night	28% 15% 23% 25% 8%	792
November	1st to 10th	Night	25% 18% 24% 24% 8%	740
	11th to 20th	Night	29% 17% 26% 21% 7% 1	823
	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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