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 2025-02-21.

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% 12% 4 9% 5% 5% 4 3 5% 6% 29%	108577
	Night	19% 14% 5% 10% 5% 4 4 3 4 5% 28%	110008
Transparency	Day	55% 7% 12% 18% 7% 1	112080
	Night	59% 6% 10% 16% 8% 1	114669
Seeing	Day	26% 17% 30% 18% 7% 2	14894
	Night	26% 14% 29% 22% 8% 1	23940

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% 24% 7% 18% 6% 5% 3 2 2 2 13%	3597
	11th to 20th	Day	11% 18% 8% 22% 9% 5% 4 2 3 4 14%	3570
	21st to end	Day	11% 18% 8% 13% 6% 7% 4 3 4 5% 20%	3960
February	1st to 10th	Day	17% 17% 6% 12% 7% 6% 4 3 4 4 21%	1685
	11th to 20th	Day	15% 19% 6% 14% 7% 4 4 3 4 4 20%	1918
	21st to end	Day	16% 19% 5% 9% 5% 6% 4 3 4 6% 23%	1570
March	1st to 10th	Day	21% 14% 5% 10% 6% 5% 3 3 4 5% 24%	3116
	11th to 20th	Day	17% 21% 5% 10% 5% 4 3 3 3 4 24%	3246
	21st to end	Day	17% 14% 5% 9% 4 4 3 2 4 5% 34%	4161
April	1st to 10th	Day	23% 16% 3 8% 5% 4 4 3 3 4 27%	2280
	11th to 20th	Day	21% 11% 3 6% 4 4 3 3 5% 4 35%	2277
	21st to end	Day	25% 12% 3 6% 5% 3 4 3 4 5% 30%	2470
May	1st to 10th	Day	25% 9% 3 7% 4 4 4 4 5% 6% 28%	4248
	11th to 20th	Day	19% 7% 3 7% 6% 5% 5% 4 6% 7% 30%	4398
	21st to end	Day	16% 7% 2 8% 5% 5% 5% 4 6% 8% 33%	4837
June	1st to 10th	Day	25% 8% 3 6% 4 4 5% 3 5% 7% 29%	2660
	11th to 20th	Day	18% 6% 3 6% 5% 4 4 4 6% 9% 35%	2660
	21st to end	Day	24% 7% 4 7% 5% 5% 5% 3 5% 7% 28%	2660
July	1st to 10th	Day	15% 7% 2 6% 5% 6% 6% 5% 6% 9% 33%	4440
	11th to 20th	Day	15% 7% 3 7% 5% 5% 6% 5% 6% 9% 33%	4440
	21st to end	Day	15% 6% 2 6% 4 4 4 4 6% 8% 42%	4814
August	1st to 10th	Day	18% 7% 3 8% 4 5% 6% 5% 7% 9% 28%	4423
	11th to 20th	Day	19% 6% 3 6% 4 4 5% 4 7% 8% 33%	4032
	21st to end	Day	21% 5% 2 6% 4 3 4 3 5% 7% 39%	4180
September	1st to 10th	Day	15% 7% 2 5% 4 4 5% 4 5% 8% 41%	2280
	11th to 20th	Day	19% 6% 2 5% 3 3 3 3 5% 7% 44%	2151
	21st to end	Day	20% 8% 2 5% 3 3 4 3 6% 7% 38%	2090
October	1st to 10th	Day	23% 8% 3 6% 4 4 5% 4 6% 6% 31%	2035
	11th to 20th	Day	24% 11% 3 7% 5% 4 4 3 5% 6% 28%	1801
	21st to end	Day	26% 15% 3 7% 4 4 3 2 4 5% 25%	1881
November	1st to 10th	Day	21% 14% 3 8% 4 4 4 3 4 5% 31%	1761
	11th to 20th	Day	19% 17% 6% 9% 5% 4 3 3 4 5% 25%	1790
	21st to end	Day	22% 18% 5% 9% 5% 4 4 3 5% 5% 21%	1600
December	1st to 10th	Day	20% 22% 6% 13% 7% 4 3 2 4 4 14%	2600
	11th to 20th	Day	21% 18% 7% 10% 5% 4 4 2 3 4 22%	2986
	21st to end	Day	21% 18% 5% 12% 5% 4 4 3 4 5% 20%	3960
January	1st to 10th	Night	15% 24% 8% 15% 6% 4 3 2 3 3 16%	6349
	11th to 20th	Night	11% 21% 8% 19% 8% 5% 4 3 4 4 13%	6315
	21st to end	Night	11% 18% 7% 13% 8% 5% 3 3 4 5% 23%	6996
February	1st to 10th	Night	14% 18% 5% 14% 7% 6% 3 3 4 5% 20%	2713
	11th to 20th	Night	14% 17% 5% 13% 7% 5% 4 3 4 4 23%	2368
	21st to end	Night	15% 18% 5% 10% 6% 4 3 3 4 4 28%	1885
March	1st to 10th	Night	22% 13% 4 8% 5% 4 3 3 3 4 32%	3724
	11th to 20th	Night	19% 21% 5% 9% 4 4 3 2 3 4 25%	3713
	21st to end	Night	16% 16% 6% 10% 4 3 3 3 3 4 31%	3469
April	1st to 10th	Night	24% 13% 4 7% 5% 4 4 3 4 6% 27%	1900
	11th to 20th	Night	24% 9% 3 7% 4 4 4 3 4 6% 32%	1851
	21st to end	Night	23% 11% 3 7% 3 4 4 3 4 5% 33%	1710
May	1st to 10th	Night	26% 10% 3 7% 4 4 4 3 5% 6% 28%	2720
	11th to 20th	Night	23% 7% 2 7% 4 4 4 3 5% 7% 34%	2495
	21st to end	Night	19% 6% 2 6% 5% 5% 5% 3 6% 8% 35%	2738
June	1st to 10th	Night	25% 7% 2 5% 4 4 5% 4 5% 8% 30%	1520
	11th to 20th	Night	20% 6% 1 6% 4 4 5% 3 6% 8% 38%	1520
	21st to end	Night	19% 8% 3 7% 5% 4 5% 5% 5% 7% 32%	1520
July	1st to 10th	Night	14% 8% 3 8% 6% 5% 6% 4 7% 7% 33%	2520
	11th to 20th	Night	16% 7% 2 6% 5% 4 4 5% 5% 7% 39%	2520
	21st to end	Night	16% 6% 2 6% 4 4 4 4 6% 8% 40%	2739
August	1st to 10th	Night	23% 8% 3 7% 4 5% 4 4 5% 6% 33%	2506
	11th to 20th	Night	18% 8% 3 7% 6% 5% 4 4 6% 7% 34%	2759
	21st to end	Night	20% 6% 2 6% 4 3 4 3 5% 6% 41%	3476
September	1st to 10th	Night	17% 7% 2 7% 5% 4 3 3 5% 6% 42%	1900
	11th to 20th	Night	16% 6% 1 5% 3 4 3 3 4 6% 48%	2028
	21st to end	Night	19% 6% 2 5% 5% 4 4 2 4 7% 42%	2090
October	1st to 10th	Night	19% 8% 2 6% 5% 4 4 4 6% 6% 36%	2142
	11th to 20th	Night	23% 11% 4 7% 4 4 4 3 4 6% 30%	2378
	21st to end	Night	27% 11% 3 7% 4 5% 4 3 4 5% 27%	2717
November	1st to 10th	Night	21% 13% 3 8% 4 4 4 4 4 5% 29%	2537
	11th to 20th	Night	21% 14% 5% 8% 4 3 3 3 4 5% 28%	2606
	21st to end	Night	22% 18% 5% 9% 4 3 3 2 4 5% 25%	2800
December	1st to 10th	Night	19% 25% 8% 13% 6% 4 3 2 3 3 13%	4580
	11th to 20th	Night	22% 18% 6% 11% 5% 5% 3 2 3 3 21%	5208
	21st to end	Night	22% 18% 5% 10% 4 4 3 2 4 6% 22%	6996

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	79% 5% 6% 9% 1	3598
	11th to 20th	Day	74% 8% 6% 9% 3	3600
	21st to end	Day	67% 8% 7% 10% 8%	3960
February	1st to 10th	Day	70% 5% 8% 12% 5% 1	1685
	11th to 20th	Day	70% 5% 9% 10% 5% 1	1927
	21st to end	Day	65% 5% 8% 14% 6% 2	1570
March	1st to 10th	Day	63% 7% 8% 13% 8% 1	3119
	11th to 20th	Day	64% 6% 10% 10% 10% 1	3246
	21st to end	Day	54% 5% 8% 17% 15% 1	4161
April	1st to 10th	Day	63% 5% 8% 16% 8% 1	2280
	11th to 20th	Day	53% 5% 8% 19% 13% 1	2277
	21st to end	Day	57% 5% 10% 16% 10% 2	2470
May	1st to 10th	Day	54% 7% 12% 18% 8% 1	4262
	11th to 20th	Day	50% 9% 19% 15% 7% 1	4402
	21st to end	Day	45% 9% 12% 22% 11% 1	4837
June	1st to 10th	Day	53% 7% 12% 18% 8% 1	2660
	11th to 20th	Day	45% 7% 14% 22% 12% 1	2660
	21st to end	Day	55% 7% 11% 18% 9%	2660
July	1st to 10th	Day	46% 7% 14% 26% 7%	4370
	11th to 20th	Day	45% 8% 16% 27% 4	4365
	21st to end	Day	42% 8% 14% 30% 7%	4661
August	1st to 10th	Day	50% 8% 16% 20% 6%	4409
	11th to 20th	Day	47% 8% 20% 19% 6%	4071
	21st to end	Day	44% 6% 16% 20% 13% 1	4180
September	1st to 10th	Day	41% 7% 15% 26% 10% 1	2280
	11th to 20th	Day	40% 6% 13% 29% 12%	2151
	21st to end	Day	45% 6% 14% 25% 9%	2090
October	1st to 10th	Day	47% 7% 15% 26% 6%	3386
	11th to 20th	Day	52% 5% 14% 24% 4	2965
	21st to end	Day	52% 4 17% 20% 7% 1	3081
November	1st to 10th	Day	57% 5% 12% 19% 7%	1761
	11th to 20th	Day	62% 6% 9% 14% 8% 1	1790
	21st to end	Day	67% 7% 11% 13% 2	1600
December	1st to 10th	Day	76% 5% 7% 10% 2	2600
	11th to 20th	Day	68% 4 7% 16% 5%	2986
	21st to end	Day	69% 4 7% 12% 8%	3960
January	1st to 10th	Night	75% 5% 9% 8% 3	6349
	11th to 20th	Night	75% 7% 8% 8% 2	6360
	21st to end	Night	67% 4 8% 10% 11%	6996
February	1st to 10th	Night	68% 4 9% 13% 6% 1	2713
	11th to 20th	Night	66% 6% 8% 14% 6%	2370
	21st to end	Night	61% 5% 9% 13% 11% 1	1885
March	1st to 10th	Night	57% 5% 10% 17% 8% 3	3734
	11th to 20th	Night	64% 5% 8% 12% 9% 1	3714
	21st to end	Night	56% 7% 6% 18% 10% 2	3469
April	1st to 10th	Night	60% 5% 7% 16% 11% 1	1900
	11th to 20th	Night	54% 5% 8% 20% 12% 1	1851
	21st to end	Night	53% 6% 8% 18% 12% 2	1710
May	1st to 10th	Night	57% 7% 11% 16% 8% 1	2726
	11th to 20th	Night	48% 8% 16% 18% 9% 1	2496
	21st to end	Night	44% 9% 12% 18% 16% 1	2739
June	1st to 10th	Night	52% 7% 11% 21% 9% 1	1520
	11th to 20th	Night	45% 7% 11% 22% 12% 3	1520
	21st to end	Night	51% 7% 12% 19% 9% 1	1520
July	1st to 10th	Night	48% 7% 14% 20% 11%	2480
	11th to 20th	Night	43% 7% 16% 25% 8%	2472
	21st to end	Night	42% 7% 18% 24% 9%	2651
August	1st to 10th	Night	51% 6% 14% 24% 5%	2496
	11th to 20th	Night	48% 9% 17% 20% 6%	2786
	21st to end	Night	43% 6% 12% 25% 14% 1	3476
September	1st to 10th	Night	42% 7% 13% 25% 13%	1900
	11th to 20th	Night	38% 5% 15% 30% 11% 1	2028
	21st to end	Night	42% 6% 13% 25% 13% 1	2090
October	1st to 10th	Night	51% 5% 11% 24% 9%	3571
	11th to 20th	Night	51% 6% 10% 26% 7%	3953
	21st to end	Night	52% 5% 14% 18% 10% 2	4467
November	1st to 10th	Night	58% 6% 11% 18% 6% 1	2537
	11th to 20th	Night	57% 7% 10% 15% 9% 2	2606
	21st to end	Night	65% 5% 11% 15% 4	2800
December	1st to 10th	Night	79% 4 8% 7% 2	4580
	11th to 20th	Night	70% 5% 6% 12% 7%	5208
	21st to end	Night	66% 5% 7% 13% 8%	6996

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	36% 15% 33% 14% 3 1	200
	11th to 20th	Day	32% 22% 35% 11% 2	200
	21st to end	Day	22% 27% 32% 12% 6%	220
February	1st to 10th	Day	35% 28% 25% 10% 1 1	243
	11th to 20th	Day	29% 25% 36% 9% 2	466
	21st to end	Day	27% 27% 27% 16% 2	382
March	1st to 10th	Day	29% 21% 30% 17% 3	460
	11th to 20th	Day	28% 23% 32% 13% 3 1	460
	21st to end	Day	29% 25% 25% 14% 5% 1	506
April	1st to 10th	Day	33% 17% 28% 14% 5% 2	460
	11th to 20th	Day	32% 21% 25% 13% 5% 3	452
	21st to end	Day	32% 20% 32% 10% 4 2	460
May	1st to 10th	Day	33% 17% 29% 14% 6% 1	463
	11th to 20th	Day	22% 16% 31% 22% 9% 1	487
	21st to end	Day	22% 22% 31% 18% 6% 1	529
June	1st to 10th	Day	26% 16% 34% 16% 7% 1	490
	11th to 20th	Day	20% 15% 33% 21% 10% 1	490
	21st to end	Day	26% 14% 32% 18% 8% 2	490
July	1st to 10th	Day	18% 11% 33% 24% 11% 2	485
	11th to 20th	Day	16% 11% 37% 27% 7% 2	484
	21st to end	Day	18% 9% 35% 27% 9% 1	532
August	1st to 10th	Day	20% 11% 26% 29% 13% 2	486
	11th to 20th	Day	18% 8% 29% 27% 16% 2	479
	21st to end	Day	19% 12% 27% 24% 12% 6%	539
September	1st to 10th	Day	18% 12% 33% 21% 11% 4	490
	11th to 20th	Day	20% 9% 24% 23% 16% 7%	490
	21st to end	Day	19% 14% 28% 22% 12% 5%	490
October	1st to 10th	Day	24% 15% 27% 21% 10% 3	490
	11th to 20th	Day	30% 18% 23% 20% 8% 1	437
	21st to end	Day	36% 20% 24% 16% 4	429
November	1st to 10th	Day	34% 16% 28% 19% 3 1	395
	11th to 20th	Day	33% 19% 26% 15% 6% 1	390
	21st to end	Day	33% 24% 30% 9% 4	200
December	1st to 10th	Day	35% 18% 28% 15% 4 2	200
	11th to 20th	Day	29% 30% 27% 12% 2 1	200
	21st to end	Day	33% 24% 26% 12% 5% 1	220
January	1st to 10th	Night	33% 18% 31% 15% 4	800
	11th to 20th	Night	28% 20% 30% 18% 4	800
	21st to end	Night	22% 16% 36% 21% 4	880
February	1st to 10th	Night	25% 21% 34% 17% 4	800
	11th to 20th	Night	24% 22% 34% 17% 3 1	783
	21st to end	Night	25% 17% 35% 19% 3	629
March	1st to 10th	Night	27% 18% 31% 21% 3	760
	11th to 20th	Night	29% 18% 29% 19% 5%	760
	21st to end	Night	27% 16% 27% 23% 6% 1	836
April	1st to 10th	Night	31% 15% 28% 22% 4	760
	11th to 20th	Night	28% 16% 29% 21% 6%	727
	21st to end	Night	31% 15% 28% 19% 7%	570
May	1st to 10th	Night	29% 12% 30% 22% 7% 1	508
	11th to 20th	Night	24% 11% 30% 26% 8% 1	374
	21st to end	Night	23% 11% 36% 24% 7%	411
June	1st to 10th	Night	28% 9% 31% 24% 8%	380
	11th to 20th	Night	23% 7% 28% 30% 12%	380
	21st to end	Night	20% 7% 31% 29% 12% 1	380
July	1st to 10th	Night	17% 7% 31% 33% 12% 1	370
	11th to 20th	Night	15% 5% 27% 36% 15% 1	368
	21st to end	Night	16% 6% 28% 38% 12%	416
August	1st to 10th	Night	20% 5% 22% 33% 19% 1	378
	11th to 20th	Night	18% 5% 23% 34% 19% 1	538
	21st to end	Night	17% 6% 25% 34% 15% 2	836
September	1st to 10th	Night	20% 8% 28% 31% 12% 2	760
	11th to 20th	Night	20% 5% 25% 28% 20% 2	760
	21st to end	Night	21% 9% 29% 26% 14% 2	760
October	1st to 10th	Night	23% 13% 27% 26% 10% 1	760
	11th to 20th	Night	29% 14% 25% 23% 8% 1	760
	21st to end	Night	33% 15% 29% 19% 4	836
November	1st to 10th	Night	30% 17% 30% 17% 5% 1	780
	11th to 20th	Night	28% 19% 28% 17% 8% 1	800
	21st to end	Night	33% 21% 24% 16% 6% 1	800
December	1st to 10th	Night	37% 18% 26% 17% 4	800
	11th to 20th	Night	30% 19% 30% 15% 5% 1	800
	21st to end	Night	36% 19% 25% 16% 4	880

Page generated at 2025-02-18 03:26:31. Version ac07

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