Observatoire St-gabriel Lalemant
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire St-gabriel Lalemant clear sky chart from 2005-11-06 to 2024-04-10.

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 6% 6% 3 5% 5% 5% 7% 33%	82622
	Night	17% 12% 4 7% 6% 3 5% 5% 5% 6% 29%	86165
Transparency	Day	51% 8% 14% 18% 8% 1	82319
	Night	55% 9% 13% 16% 7% 1	86004
Seeing	Day	23% 15% 32% 21% 8% 2	14754
	Night	23% 13% 31% 25% 8% 1	23186

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% 15% 5% 8% 7% 5% 6% 6% 6% 7% 22%	2362
	11th to 20th	Day	11% 12% 6% 8% 7% 4 6% 5% 5% 6% 29%	2520
	21st to end	Day	10% 9% 4 9% 8% 3 4 6% 6% 6% 35%	2772
February	1st to 10th	Day	8% 13% 6% 9% 9% 4 5% 5% 6% 7% 27%	1569
	11th to 20th	Day	13% 15% 6% 9% 7% 4 6% 4 5% 6% 25%	1757
	21st to end	Day	12% 10% 3 9% 7% 5% 6% 6% 4 6% 32%	1570
March	1st to 10th	Day	17% 13% 4 7% 7% 3 5% 5% 6% 6% 28%	3116
	11th to 20th	Day	16% 18% 5% 8% 7% 3 5% 4 4 5% 24%	3406
	21st to end	Day	15% 16% 5% 6% 5% 2 3 4 4 6% 34%	3935
April	1st to 10th	Day	21% 12% 4 7% 5% 3 5% 4 5% 6% 29%	2270
	11th to 20th	Day	19% 8% 3 5% 5% 3 4 4 4 6% 39%	2280
	21st to end	Day	23% 10% 3 4 5% 3 4 4 5% 7% 33%	2340
May	1st to 10th	Day	20% 8% 4 5% 5% 3 5% 5% 4 6% 35%	2340
	11th to 20th	Day	18% 8% 3 6% 6% 3 5% 4 6% 6% 36%	2478
	21st to end	Day	20% 6% 3 5% 5% 3 6% 5% 5% 7% 36%	2909
June	1st to 10th	Day	19% 7% 3 5% 6% 3 6% 5% 6% 8% 32%	2700
	11th to 20th	Day	18% 6% 2 5% 4 3 5% 5% 7% 8% 37%	2700
	21st to end	Day	20% 7% 3 6% 6% 4 5% 6% 5% 7% 31%	2700
July	1st to 10th	Day	14% 6% 3 5% 5% 3 5% 6% 7% 10% 36%	2700
	11th to 20th	Day	12% 6% 3 6% 6% 3 6% 6% 8% 9% 36%	2555
	21st to end	Day	13% 7% 3 5% 5% 3 5% 6% 6% 9% 38%	2744
August	1st to 10th	Day	14% 5% 2 5% 6% 4 6% 6% 8% 9% 34%	2451
	11th to 20th	Day	11% 6% 2 6% 5% 3 5% 5% 6% 8% 43%	2304
	21st to end	Day	14% 6% 2 6% 5% 3 4 5% 6% 8% 41%	2555
September	1st to 10th	Day	15% 6% 3 5% 4 3 4 5% 5% 8% 44%	2136
	11th to 20th	Day	17% 5% 2 4 4 2 3 4 4 6% 50%	1980
	21st to end	Day	18% 5% 3 4 4 2 4 5% 6% 7% 42%	1980
October	1st to 10th	Day	16% 6% 3 6% 6% 4 4 5% 6% 7% 38%	1950
	11th to 20th	Day	21% 8% 3 7% 5% 4 5% 4 6% 6% 30%	1679
	21st to end	Day	26% 11% 4 7% 5% 3 5% 4 5% 6% 26%	1782
November	1st to 10th	Day	18% 8% 4 7% 6% 3 4 5% 5% 7% 31%	1671
	11th to 20th	Day	18% 11% 5% 8% 8% 4 4 5% 4 7% 27%	1601
	21st to end	Day	19% 13% 5% 8% 6% 3 5% 4 6% 5% 25%	1381
December	1st to 10th	Day	19% 13% 6% 10% 10% 4 4 3 5% 5% 20%	1330
	11th to 20th	Day	19% 14% 7% 8% 5% 3 5% 5% 4 4 27%	1668
	21st to end	Day	21% 14% 5% 7% 6% 3 3 4 4 5% 29%	2431
January	1st to 10th	Night	12% 17% 6% 10% 9% 4 5% 6% 6% 5% 21%	4587
	11th to 20th	Night	11% 14% 5% 9% 9% 5% 7% 6% 6% 7% 21%	4440
	21st to end	Night	9% 12% 5% 9% 7% 4 5% 5% 6% 7% 30%	4884
February	1st to 10th	Night	10% 12% 5% 9% 8% 4 6% 5% 5% 6% 29%	2609
	11th to 20th	Night	12% 15% 6% 10% 9% 4 5% 4 4 5% 26%	2305
	21st to end	Night	14% 13% 5% 8% 7% 3 5% 4 5% 6% 31%	1884
March	1st to 10th	Night	18% 13% 4 7% 7% 3 7% 5% 5% 5% 26%	3724
	11th to 20th	Night	15% 20% 5% 10% 7% 4 5% 5% 4 5% 20%	3553
	21st to end	Night	20% 16% 4 6% 5% 2 4 4 4 5% 29%	3695
April	1st to 10th	Night	23% 14% 4 7% 5% 2 4 4 5% 4 28%	1900
	11th to 20th	Night	21% 8% 3 6% 6% 3 5% 4 5% 6% 32%	1628
	21st to end	Night	28% 9% 3 6% 4 2 4 2 3 6% 32%	1620
May	1st to 10th	Night	24% 10% 3 7% 4 3 4 5% 5% 5% 30%	1620
	11th to 20th	Night	23% 7% 4 5% 5% 3 3 4 5% 5% 36%	1429
	21st to end	Night	22% 8% 3 6% 5% 3 4 4 5% 6% 35%	1365
June	1st to 10th	Night	21% 9% 4 6% 7% 3 5% 5% 5% 7% 29%	1260
	11th to 20th	Night	17% 7% 3 5% 5% 2 4 6% 6% 7% 38%	1260
	21st to end	Night	21% 8% 2 7% 6% 3 5% 5% 6% 6% 31%	1260
July	1st to 10th	Night	17% 7% 4 7% 5% 3 4 4 6% 7% 35%	1260
	11th to 20th	Night	14% 5% 3 6% 5% 4 7% 5% 8% 7% 36%	1402
	21st to end	Night	13% 7% 3 5% 6% 5% 6% 6% 7% 9% 35%	1574
August	1st to 10th	Night	13% 6% 2 5% 6% 2 7% 5% 6% 8% 39%	1468
	11th to 20th	Night	16% 6% 3 6% 6% 4 5% 6% 7% 8% 34%	1596
	21st to end	Night	16% 7% 2 4 6% 3 4 5% 5% 7% 41%	1800
September	1st to 10th	Night	16% 5% 2 5% 5% 3 4 5% 6% 7% 39%	1823
	11th to 20th	Night	18% 7% 3 6% 5% 3 4 4 4 6% 41%	1980
	21st to end	Night	17% 7% 3 4 4 3 3 4 5% 7% 43%	1980
October	1st to 10th	Night	19% 9% 3 6% 4 3 4 4 4 5% 40%	2009
	11th to 20th	Night	24% 11% 3 5% 5% 4 5% 4 4 6% 29%	2279
	21st to end	Night	24% 10% 4 6% 5% 3 4 4 5% 6% 29%	2574
November	1st to 10th	Night	20% 11% 3 6% 6% 4 4 4 5% 6% 31%	2407
	11th to 20th	Night	19% 10% 5% 8% 7% 3 4 5% 5% 6% 27%	2576
	21st to end	Night	17% 14% 5% 10% 7% 3 4 5% 5% 5% 25%	2797
December	1st to 10th	Night	19% 17% 6% 9% 7% 4 4 4 4 5% 20%	2850
	11th to 20th	Night	18% 14% 5% 9% 7% 4 6% 5% 4 6% 21%	3531
	21st to end	Night	19% 16% 5% 9% 6% 3 4 5% 4 5% 24%	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	56% 13% 17% 11% 3	2363
	11th to 20th	Day	52% 11% 14% 18% 4 1	2520
	21st to end	Day	48% 12% 13% 17% 10%	2772
February	1st to 10th	Day	57% 8% 12% 14% 8% 1	1569
	11th to 20th	Day	60% 6% 12% 14% 7% 1	1765
	21st to end	Day	52% 7% 12% 20% 8% 2	1570
March	1st to 10th	Day	54% 12% 12% 12% 8% 2	3119
	11th to 20th	Day	59% 11% 13% 11% 5% 1	3406
	21st to end	Day	52% 5% 10% 18% 11% 4	3935
April	1st to 10th	Day	59% 4 11% 14% 9% 2	2270
	11th to 20th	Day	50% 5% 13% 20% 11% 2	2280
	21st to end	Day	53% 5% 11% 17% 12% 3	2340
May	1st to 10th	Day	51% 6% 13% 16% 13% 2	2340
	11th to 20th	Day	49% 7% 11% 21% 12% 1	2482
	21st to end	Day	49% 8% 12% 20% 10% 1	2909
June	1st to 10th	Day	50% 9% 13% 18% 9% 1	2700
	11th to 20th	Day	45% 8% 15% 20% 10% 1	2700
	21st to end	Day	53% 8% 14% 16% 8% 1	2700
July	1st to 10th	Day	43% 10% 19% 21% 7%	2625
	11th to 20th	Day	43% 10% 17% 23% 7% 1	2478
	21st to end	Day	44% 10% 19% 19% 7% 1	2591
August	1st to 10th	Day	46% 11% 22% 19% 3	2437
	11th to 20th	Day	40% 10% 21% 22% 7%	2304
	21st to end	Day	40% 9% 18% 24% 9%	2555
September	1st to 10th	Day	39% 8% 18% 24% 10% 1	2136
	11th to 20th	Day	38% 7% 16% 26% 12% 1	1980
	21st to end	Day	43% 7% 16% 22% 11%	1980
October	1st to 10th	Day	47% 7% 13% 24% 9%	1950
	11th to 20th	Day	57% 8% 16% 16% 3	1679
	21st to end	Day	61% 8% 11% 14% 5%	1782
November	1st to 10th	Day	53% 8% 15% 18% 5%	1671
	11th to 20th	Day	58% 8% 14% 15% 5%	1601
	21st to end	Day	61% 8% 14% 14% 3	1381
December	1st to 10th	Day	67% 7% 11% 11% 4	1330
	11th to 20th	Day	61% 7% 10% 15% 7%	1668
	21st to end	Day	58% 8% 15% 15% 4	2431
January	1st to 10th	Night	60% 12% 12% 10% 5%	4587
	11th to 20th	Night	57% 13% 13% 12% 5%	4440
	21st to end	Night	52% 9% 13% 15% 11%	4884
February	1st to 10th	Night	56% 6% 12% 17% 8% 1	2609
	11th to 20th	Night	61% 6% 11% 14% 7%	2308
	21st to end	Night	55% 6% 10% 18% 10% 1	1884
March	1st to 10th	Night	57% 9% 11% 16% 7%	3734
	11th to 20th	Night	63% 9% 11% 11% 5% 1	3554
	21st to end	Night	57% 6% 9% 19% 8% 1	3695
April	1st to 10th	Night	59% 5% 8% 14% 12% 3	1900
	11th to 20th	Night	51% 7% 10% 18% 12% 1	1628
	21st to end	Night	56% 5% 8% 18% 12% 2	1620
May	1st to 10th	Night	55% 6% 10% 15% 12% 2	1620
	11th to 20th	Night	49% 6% 12% 19% 13% 1	1430
	21st to end	Night	51% 8% 9% 18% 13% 1	1366
June	1st to 10th	Night	54% 8% 12% 20% 6% 1	1260
	11th to 20th	Night	43% 8% 14% 20% 12% 3	1260
	21st to end	Night	54% 8% 13% 16% 8%	1260
July	1st to 10th	Night	46% 8% 19% 21% 6%	1225
	11th to 20th	Night	45% 10% 17% 22% 6% 1	1357
	21st to end	Night	42% 13% 19% 19% 7%	1486
August	1st to 10th	Night	41% 12% 21% 24% 4	1458
	11th to 20th	Night	45% 13% 18% 17% 7%	1596
	21st to end	Night	43% 8% 17% 25% 8%	1800
September	1st to 10th	Night	42% 9% 16% 22% 10% 1	1823
	11th to 20th	Night	45% 7% 16% 21% 9% 1	1980
	21st to end	Night	42% 8% 12% 26% 11% 1	1980
October	1st to 10th	Night	48% 6% 11% 25% 9% 1	2009
	11th to 20th	Night	57% 7% 15% 17% 4	2279
	21st to end	Night	57% 7% 14% 15% 6%	2574
November	1st to 10th	Night	55% 7% 15% 17% 5%	2407
	11th to 20th	Night	56% 10% 13% 15% 7%	2576
	21st to end	Night	63% 8% 12% 12% 5%	2797
December	1st to 10th	Night	68% 7% 11% 11% 3	2850
	11th to 20th	Night	61% 9% 12% 12% 6%	3532
	21st to end	Night	59% 10% 12% 13% 5%	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	22% 25% 38% 12% 1 2	180
	11th to 20th	Day	24% 23% 36% 12% 4	180
	21st to end	Day	16% 23% 36% 17% 8% 1	198
February	1st to 10th	Day	21% 27% 33% 15% 3	229
	11th to 20th	Day	20% 21% 39% 18% 3	411
	21st to end	Day	20% 22% 35% 17% 6%	382
March	1st to 10th	Day	26% 19% 30% 20% 5%	460
	11th to 20th	Day	23% 16% 33% 18% 8% 2	460
	21st to end	Day	24% 19% 31% 18% 7% 2	506
April	1st to 10th	Day	30% 19% 30% 17% 4 1	457
	11th to 20th	Day	28% 18% 27% 20% 4 2	412
	21st to end	Day	29% 16% 31% 18% 4 2	420
May	1st to 10th	Day	29% 11% 35% 17% 6% 1	423
	11th to 20th	Day	23% 14% 32% 25% 6% 1	447
	21st to end	Day	23% 14% 36% 17% 8% 1	669
June	1st to 10th	Day	24% 13% 34% 20% 8% 1	630
	11th to 20th	Day	21% 11% 31% 23% 11% 1	630
	21st to end	Day	21% 11% 28% 30% 9%	630
July	1st to 10th	Day	19% 10% 34% 25% 11% 1	620
	11th to 20th	Day	16% 11% 34% 29% 10% 2	477
	21st to end	Day	16% 9% 32% 31% 11% 1	488
August	1st to 10th	Day	16% 12% 30% 28% 11% 2	446
	11th to 20th	Day	16% 6% 33% 28% 14% 2	439
	21st to end	Day	19% 13% 28% 22% 13% 5%	495
September	1st to 10th	Day	18% 14% 29% 24% 12% 3	450
	11th to 20th	Day	21% 14% 29% 24% 10% 3	450
	21st to end	Day	20% 13% 30% 23% 10% 4	450
October	1st to 10th	Day	19% 15% 33% 21% 9% 3	435
	11th to 20th	Day	28% 18% 25% 20% 8% 2	360
	21st to end	Day	33% 17% 28% 16% 4 1	396
November	1st to 10th	Day	30% 18% 32% 18% 2 1	365
	11th to 20th	Day	26% 19% 28% 19% 6% 1	370
	21st to end	Day	30% 23% 31% 14% 2	231
December	1st to 10th	Day	28% 19% 27% 19% 6% 1	180
	11th to 20th	Day	31% 21% 34% 9% 4 1	180
	21st to end	Day	29% 26% 25% 16% 4	198
January	1st to 10th	Night	24% 17% 35% 19% 4	804
	11th to 20th	Night	21% 16% 38% 22% 3	760
	21st to end	Night	14% 14% 36% 29% 7% 1	836
February	1st to 10th	Night	17% 16% 39% 22% 5% 1	760
	11th to 20th	Night	20% 15% 38% 21% 5% 1	743
	21st to end	Night	21% 17% 33% 25% 5%	628
March	1st to 10th	Night	21% 12% 37% 24% 6%	760
	11th to 20th	Night	23% 15% 35% 20% 7% 1	760
	21st to end	Night	23% 13% 35% 22% 7%	836
April	1st to 10th	Night	30% 11% 30% 22% 6%	760
	11th to 20th	Night	27% 10% 30% 26% 7%	564
	21st to end	Night	33% 10% 26% 23% 7% 1	540
May	1st to 10th	Night	27% 9% 29% 28% 7%	540
	11th to 20th	Night	24% 12% 25% 28% 11%	368
	21st to end	Night	28% 10% 30% 24% 8%	389
June	1st to 10th	Night	23% 10% 26% 35% 6% 1	360
	11th to 20th	Night	19% 6% 27% 35% 14% 1	360
	21st to end	Night	23% 6% 33% 28% 9% 1	360
July	1st to 10th	Night	17% 9% 35% 29% 10% 1	350
	11th to 20th	Night	15% 6% 28% 38% 13%	348
	21st to end	Night	16% 4 23% 43% 12% 1	394
August	1st to 10th	Night	14% 5% 23% 41% 15% 1	394
	11th to 20th	Night	17% 5% 26% 36% 16% 1	532
	21st to end	Night	18% 8% 26% 34% 13% 1	612
September	1st to 10th	Night	18% 7% 32% 30% 12% 1	720
	11th to 20th	Night	22% 9% 29% 27% 11% 2	720
	21st to end	Night	18% 8% 33% 29% 11% 1	720
October	1st to 10th	Night	23% 11% 31% 26% 8% 1	720
	11th to 20th	Night	29% 10% 30% 20% 9% 1	720
	21st to end	Night	29% 12% 32% 21% 6%	792
November	1st to 10th	Night	27% 16% 29% 21% 5%	740
	11th to 20th	Night	24% 20% 29% 20% 6% 1	811
	21st to end	Night	25% 17% 32% 21% 4 1	850
December	1st to 10th	Night	28% 17% 29% 20% 5% 1	850
	11th to 20th	Night	24% 18% 34% 20% 4	850
	21st to end	Night	27% 18% 29% 18% 7% 1	935

Page generated at 2024-04-07 09:28:12. Version ac07

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