Observatoire de Ste-Christine
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire de Ste-Christine clear sky chart from 2005-11-06 to 2024-01-31.

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	20% 11% 4 7% 6% 3 4 4 5% 6% 30%	74916
	Night	20% 12% 4 8% 6% 3 4 4 4 6% 29%	75207
Transparency	Day	56% 6% 11% 18% 8% 1	74621
	Night	57% 6% 10% 17% 8% 1	75036
Seeing	Day	26% 17% 30% 18% 7% 2	13564
	Night	26% 14% 29% 23% 8% 1	22614

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	21% 22% 6% 13% 7% 3 4 3 3 4 14%	1517
	11th to 20th	Day	19% 18% 7% 12% 7% 4 4 3 3 4 19%	1520
	21st to end	Day	11% 16% 6% 11% 8% 4 6% 4 5% 6% 23%	1664
February	1st to 10th	Day	18% 17% 6% 11% 8% 4 6% 3 4 4 20%	1516
	11th to 20th	Day	16% 18% 6% 12% 6% 3 5% 3 5% 5% 20%	1721
	21st to end	Day	16% 18% 6% 8% 7% 5% 4 4 3 6% 23%	1480
March	1st to 10th	Day	17% 15% 5% 10% 8% 4 5% 3 4 5% 25%	1797
	11th to 20th	Day	19% 13% 4 7% 6% 4 4 4 4 6% 29%	1844
	21st to end	Day	20% 13% 4 8% 5% 3 4 3 4 5% 31%	2371
April	1st to 10th	Day	24% 14% 4 7% 7% 3 4 4 3 4 27%	2160
	11th to 20th	Day	22% 11% 3 5% 5% 3 3 4 4 5% 36%	2155
	21st to end	Day	25% 11% 3 6% 5% 3 4 4 4 6% 30%	2340
May	1st to 10th	Day	24% 8% 3 6% 5% 3 4 4 5% 5% 32%	2412
	11th to 20th	Day	19% 7% 3 5% 6% 3 4 5% 5% 6% 36%	2478
	21st to end	Day	20% 6% 3 7% 5% 3 5% 5% 6% 7% 32%	2725
June	1st to 10th	Day	26% 7% 3 5% 5% 3 5% 5% 5% 7% 29%	2520
	11th to 20th	Day	19% 5% 3 6% 5% 3 5% 5% 6% 9% 36%	2520
	21st to end	Day	24% 6% 4 6% 6% 4 5% 4 5% 7% 29%	2520
July	1st to 10th	Day	17% 6% 2 6% 6% 4 6% 5% 5% 9% 36%	2520
	11th to 20th	Day	15% 6% 3 6% 5% 3 6% 6% 6% 10% 33%	2520
	21st to end	Day	17% 6% 3 5% 5% 3 5% 6% 7% 9% 33%	2744
August	1st to 10th	Day	16% 7% 3 6% 5% 4 5% 6% 6% 8% 32%	2506
	11th to 20th	Day	16% 6% 2 5% 5% 3 5% 6% 7% 9% 37%	2305
	21st to end	Day	17% 5% 2 5% 5% 3 4 4 6% 8% 39%	2376
September	1st to 10th	Day	16% 7% 2 4 5% 3 4 5% 6% 8% 40%	2160
	11th to 20th	Day	20% 5% 2 4 4 2 3 4 5% 7% 44%	2038
	21st to end	Day	20% 7% 3 4 4 2 5% 4 6% 7% 38%	1980
October	1st to 10th	Day	24% 8% 3 5% 5% 3 5% 5% 6% 6% 30%	1928
	11th to 20th	Day	25% 10% 3 6% 6% 3 4 4 5% 7% 27%	1707
	21st to end	Day	28% 15% 3 6% 4 3 3 3 4 6% 24%	1782
November	1st to 10th	Day	21% 12% 3 7% 5% 3 4 4 4 6% 31%	1671
	11th to 20th	Day	20% 15% 8% 9% 5% 3 3 4 4 6% 24%	1701
	21st to end	Day	22% 17% 5% 9% 5% 3 4 4 5% 6% 22%	1520
December	1st to 10th	Day	26% 19% 6% 9% 8% 3 4 3 4 4 15%	1520
	11th to 20th	Day	22% 17% 7% 8% 5% 3 5% 3 3 4 23%	1906
	21st to end	Day	26% 18% 5% 12% 5% 2 4 3 3 4 18%	2772
January	1st to 10th	Night	20% 19% 8% 10% 7% 3 4 4 3 4 17%	2649
	11th to 20th	Night	17% 19% 7% 12% 8% 3 4 3 3 4 20%	2660
	21st to end	Night	14% 15% 6% 10% 9% 4 4 4 4 5% 24%	2919
February	1st to 10th	Night	15% 17% 6% 13% 8% 5% 4 4 4 5% 20%	2442
	11th to 20th	Night	15% 16% 6% 11% 8% 4 5% 4 4 5% 24%	2125
	21st to end	Night	15% 16% 6% 10% 6% 3 4 3 3 5% 28%	1776
March	1st to 10th	Night	17% 16% 6% 9% 7% 3 4 3 4 4 27%	2150
	11th to 20th	Night	20% 14% 5% 8% 5% 4 4 3 4 4 30%	2115
	21st to end	Night	20% 13% 5% 6% 5% 2 4 3 4 5% 33%	1983
April	1st to 10th	Night	25% 12% 4 7% 5% 3 4 4 4 6% 26%	1800
	11th to 20th	Night	24% 8% 3 6% 5% 3 4 4 4 6% 34%	1753
	21st to end	Night	24% 11% 3 6% 4 3 4 4 4 5% 33%	1620
May	1st to 10th	Night	25% 10% 4 6% 4 3 4 4 5% 5% 31%	1562
	11th to 20th	Night	21% 7% 2 6% 5% 3 5% 4 4 7% 36%	1415
	21st to end	Night	21% 6% 2 5% 6% 3 4 5% 6% 8% 35%	1550
June	1st to 10th	Night	25% 7% 3 5% 5% 3 5% 5% 5% 8% 30%	1440
	11th to 20th	Night	20% 5% 2 5% 5% 3 4 4 5% 8% 37%	1440
	21st to end	Night	18% 7% 3 6% 6% 4 5% 6% 5% 7% 32%	1440
July	1st to 10th	Night	14% 6% 3 6% 6% 4 6% 5% 6% 7% 38%	1440
	11th to 20th	Night	12% 6% 3 5% 6% 4 5% 6% 7% 9% 39%	1440
	21st to end	Night	15% 6% 3 6% 5% 3 5% 5% 7% 8% 39%	1574
August	1st to 10th	Night	17% 5% 2 5% 5% 4 5% 5% 6% 8% 39%	1432
	11th to 20th	Night	15% 7% 3 5% 6% 3 5% 5% 6% 8% 37%	1572
	21st to end	Night	16% 6% 2 6% 5% 2 4 4 6% 7% 41%	1980
September	1st to 10th	Night	17% 7% 2 6% 5% 3 4 4 5% 6% 42%	1800
	11th to 20th	Night	17% 6% 1 4 4 3 3 3 4 6% 47%	1921
	21st to end	Night	19% 6% 2 4 5% 3 4 3 4 7% 43%	1980
October	1st to 10th	Night	19% 8% 3 5% 5% 3 3 4 6% 6% 36%	2029
	11th to 20th	Night	23% 10% 4 6% 5% 3 5% 4 4 6% 30%	2252
	21st to end	Night	28% 10% 3 6% 6% 3 4 4 4 5% 26%	2574
November	1st to 10th	Night	21% 13% 4 7% 5% 3 4 4 4 5% 29%	2407
	11th to 20th	Night	22% 13% 5% 7% 5% 3 3 4 4 5% 28%	2475
	21st to end	Night	22% 16% 6% 8% 5% 2 3 3 4 5% 25%	2660
December	1st to 10th	Night	25% 20% 7% 9% 7% 3 4 3 3 4 16%	2660
	11th to 20th	Night	22% 17% 7% 10% 7% 3 4 3 3 4 20%	3288
	21st to end	Night	26% 18% 5% 10% 5% 3 3 3 3 4 20%	4884

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	77% 5% 7% 9% 2	1518
	11th to 20th	Day	71% 5% 8% 11% 5%	1520
	21st to end	Day	64% 7% 10% 12% 6% 1	1664
February	1st to 10th	Day	71% 5% 8% 12% 4 1	1516
	11th to 20th	Day	69% 5% 10% 10% 5% 1	1730
	21st to end	Day	67% 5% 7% 14% 6% 2	1480
March	1st to 10th	Day	64% 5% 8% 14% 7% 2	1800
	11th to 20th	Day	58% 6% 11% 13% 11% 1	1844
	21st to end	Day	58% 4 8% 18% 10% 2	2371
April	1st to 10th	Day	63% 5% 8% 15% 8% 2	2160
	11th to 20th	Day	53% 5% 8% 19% 13% 2	2155
	21st to end	Day	58% 5% 10% 15% 9% 2	2340
May	1st to 10th	Day	54% 4 9% 19% 13% 2	2412
	11th to 20th	Day	48% 6% 12% 20% 12% 1	2482
	21st to end	Day	50% 8% 11% 18% 12% 1	2725
June	1st to 10th	Day	54% 7% 12% 18% 8% 1	2520
	11th to 20th	Day	45% 7% 13% 22% 12% 1	2520
	21st to end	Day	55% 7% 11% 18% 9%	2520
July	1st to 10th	Day	43% 8% 15% 25% 9%	2450
	11th to 20th	Day	44% 9% 15% 25% 6%	2445
	21st to end	Day	47% 9% 16% 21% 6%	2591
August	1st to 10th	Day	48% 9% 17% 22% 4	2492
	11th to 20th	Day	43% 8% 18% 20% 10%	2305
	21st to end	Day	44% 7% 15% 24% 11%	2376
September	1st to 10th	Day	42% 8% 15% 25% 10% 1	2160
	11th to 20th	Day	41% 6% 12% 29% 12%	2038
	21st to end	Day	45% 6% 15% 25% 9% 1	1980
October	1st to 10th	Day	54% 7% 13% 19% 8%	1928
	11th to 20th	Day	55% 7% 15% 17% 5%	1707
	21st to end	Day	65% 5% 9% 14% 6% 1	1782
November	1st to 10th	Day	57% 6% 12% 18% 7%	1671
	11th to 20th	Day	63% 6% 9% 13% 7% 1	1701
	21st to end	Day	66% 7% 12% 13% 2	1520
December	1st to 10th	Day	75% 6% 8% 8% 2	1520
	11th to 20th	Day	68% 4 9% 14% 5%	1906
	21st to end	Day	74% 5% 7% 10% 4	2772
January	1st to 10th	Night	73% 5% 8% 10% 3	2649
	11th to 20th	Night	71% 5% 8% 11% 5% 1	2660
	21st to end	Night	65% 5% 9% 13% 7% 1	2919
February	1st to 10th	Night	69% 4 8% 12% 6% 1	2442
	11th to 20th	Night	65% 6% 8% 15% 6%	2127
	21st to end	Night	62% 4 9% 13% 11% 1	1776
March	1st to 10th	Night	62% 4 8% 17% 8% 2	2160
	11th to 20th	Night	59% 4 9% 14% 11% 2	2116
	21st to end	Night	55% 5% 7% 19% 11% 3	1983
April	1st to 10th	Night	61% 5% 7% 15% 11% 1	1800
	11th to 20th	Night	53% 5% 8% 20% 12% 1	1753
	21st to end	Night	54% 6% 8% 18% 12% 2	1620
May	1st to 10th	Night	55% 4 7% 17% 14% 2	1562
	11th to 20th	Night	49% 6% 11% 17% 15% 2	1416
	21st to end	Night	46% 8% 11% 19% 14% 2	1551
June	1st to 10th	Night	52% 6% 11% 22% 8% 1	1440
	11th to 20th	Night	45% 7% 11% 22% 12% 3	1440
	21st to end	Night	49% 8% 13% 20% 10% 1	1440
July	1st to 10th	Night	42% 8% 13% 23% 12% 1	1400
	11th to 20th	Night	40% 9% 16% 26% 10%	1392
	21st to end	Night	41% 8% 17% 25% 8%	1486
August	1st to 10th	Night	40% 9% 18% 25% 8%	1422
	11th to 20th	Night	43% 9% 17% 22% 9%	1572
	21st to end	Night	42% 7% 15% 26% 10% 1	1980
September	1st to 10th	Night	43% 7% 13% 24% 13%	1800
	11th to 20th	Night	39% 5% 15% 29% 11% 1	1921
	21st to end	Night	42% 6% 13% 26% 13% 1	1980
October	1st to 10th	Night	49% 7% 11% 21% 11%	2029
	11th to 20th	Night	56% 7% 11% 20% 5%	2252
	21st to end	Night	60% 6% 10% 15% 8% 1	2574
November	1st to 10th	Night	57% 6% 11% 18% 6% 1	2407
	11th to 20th	Night	58% 7% 11% 14% 8% 2	2475
	21st to end	Night	64% 5% 11% 15% 4	2660
December	1st to 10th	Night	75% 4 9% 9% 3	2660
	11th to 20th	Night	71% 6% 7% 11% 5%	3288
	21st to end	Night	70% 6% 8% 13% 3	4884

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	33% 16% 33% 15% 3 1	180
	11th to 20th	Day	33% 21% 34% 11% 2	180
	21st to end	Day	20% 27% 31% 15% 6% 1	196
February	1st to 10th	Day	38% 30% 22% 8% 1 1	194
	11th to 20th	Day	29% 23% 39% 7% 2	389
	21st to end	Day	28% 26% 28% 16% 2	346
March	1st to 10th	Day	29% 21% 31% 17% 3	420
	11th to 20th	Day	28% 23% 31% 14% 3 1	420
	21st to end	Day	29% 24% 25% 15% 6% 1	462
April	1st to 10th	Day	33% 16% 29% 14% 5% 2	420
	11th to 20th	Day	33% 20% 25% 14% 6% 3	412
	21st to end	Day	32% 19% 33% 10% 5% 2	420
May	1st to 10th	Day	34% 16% 30% 14% 5% 1	423
	11th to 20th	Day	23% 16% 32% 21% 8% 1	447
	21st to end	Day	21% 22% 31% 17% 7% 1	485
June	1st to 10th	Day	27% 16% 34% 16% 6% 1	450
	11th to 20th	Day	21% 15% 32% 20% 10% 1	450
	21st to end	Day	24% 14% 32% 19% 9% 2	450
July	1st to 10th	Day	19% 9% 33% 25% 12% 2	445
	11th to 20th	Day	15% 10% 37% 28% 8% 2	444
	21st to end	Day	19% 9% 35% 27% 9% 1	488
August	1st to 10th	Day	19% 11% 25% 28% 14% 2	446
	11th to 20th	Day	18% 8% 30% 26% 17% 2	439
	21st to end	Day	19% 13% 27% 22% 12% 7%	495
September	1st to 10th	Day	18% 12% 34% 21% 12% 5%	450
	11th to 20th	Day	21% 10% 26% 22% 14% 7%	450
	21st to end	Day	19% 15% 28% 21% 12% 5%	450
October	1st to 10th	Day	25% 15% 26% 20% 10% 4	450
	11th to 20th	Day	29% 18% 24% 20% 8% 1	403
	21st to end	Day	37% 19% 23% 16% 4	396
November	1st to 10th	Day	33% 16% 28% 20% 3 1	365
	11th to 20th	Day	32% 20% 26% 14% 6% 1	361
	21st to end	Day	31% 23% 31% 10% 4	180
December	1st to 10th	Day	37% 18% 25% 15% 4 2	180
	11th to 20th	Day	29% 29% 28% 11% 2 1	180
	21st to end	Day	35% 25% 25% 10% 4 1	198
January	1st to 10th	Night	34% 17% 30% 16% 4	760
	11th to 20th	Night	28% 20% 31% 18% 4	760
	21st to end	Night	22% 17% 34% 22% 4	835
February	1st to 10th	Night	25% 21% 34% 16% 4	720
	11th to 20th	Night	23% 22% 33% 18% 3 1	703
	21st to end	Night	25% 17% 35% 20% 3	592
March	1st to 10th	Night	27% 18% 31% 21% 3	720
	11th to 20th	Night	29% 17% 30% 18% 5%	720
	21st to end	Night	27% 15% 27% 24% 6% 1	792
April	1st to 10th	Night	31% 15% 28% 22% 4	720
	11th to 20th	Night	27% 16% 28% 22% 6%	689
	21st to end	Night	31% 15% 28% 19% 7%	540
May	1st to 10th	Night	29% 12% 29% 22% 7% 1	482
	11th to 20th	Night	24% 11% 30% 26% 8% 1	354
	21st to end	Night	23% 11% 35% 24% 7%	389
June	1st to 10th	Night	28% 8% 32% 23% 8%	360
	11th to 20th	Night	23% 7% 28% 30% 11%	360
	21st to end	Night	18% 8% 32% 30% 12% 1	360
July	1st to 10th	Night	17% 7% 31% 33% 12% 1	350
	11th to 20th	Night	14% 5% 28% 36% 16% 1	348
	21st to end	Night	15% 6% 30% 38% 11%	394
August	1st to 10th	Night	19% 5% 23% 33% 20% 1	358
	11th to 20th	Night	18% 6% 23% 34% 19% 1	508
	21st to end	Night	17% 7% 25% 34% 15% 2	792
September	1st to 10th	Night	19% 8% 27% 31% 12% 2	720
	11th to 20th	Night	21% 6% 26% 28% 18% 2	720
	21st to end	Night	21% 9% 29% 26% 14% 2	720
October	1st to 10th	Night	23% 13% 27% 26% 9% 1	720
	11th to 20th	Night	28% 14% 25% 23% 8% 1	720
	21st to end	Night	33% 14% 30% 19% 4	792
November	1st to 10th	Night	30% 16% 30% 18% 6% 1	740
	11th to 20th	Night	28% 20% 27% 16% 8% 1	760
	21st to end	Night	32% 20% 24% 17% 6% 1	760
December	1st to 10th	Night	37% 17% 25% 17% 4	760
	11th to 20th	Night	30% 19% 30% 15% 5% 1	760
	21st to end	Night	36% 19% 25% 16% 3	836

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