Lachute
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lachute clear sky chart from 2005-11-06 to 2024-12-06.

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	18% 10% 3 8% 5% 5% 4 4 5% 6% 32%	101821
	Night	18% 11% 4 8% 5% 4 4 3 5% 6% 33%	97907
Transparency	Day	51% 3 12% 22% 10% 1	105283
	Night	53% 3 12% 21% 10% 1	102534
Seeing	Day	23% 13% 30% 21% 9% 2	14605
	Night	23% 12% 28% 26% 9% 1	23634

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	17% 18% 5% 15% 5% 5% 4 2 3 4 22%	2517
	11th to 20th	Day	15% 13% 6% 11% 7% 5% 5% 3 4 5% 24%	2520
	21st to end	Day	13% 20% 7% 8% 6% 5% 6% 4 5% 5% 22%	2772
February	1st to 10th	Day	14% 16% 5% 12% 5% 5% 4 3 5% 5% 25%	1695
	11th to 20th	Day	14% 15% 5% 10% 6% 5% 4 4 5% 6% 26%	1730
	21st to end	Day	19% 15% 4 9% 6% 5% 4 3 5% 5% 25%	1570
March	1st to 10th	Day	20% 14% 4 9% 6% 4 5% 2 4 4 26%	3116
	11th to 20th	Day	14% 17% 4 10% 6% 5% 4 4 5% 5% 26%	3340
	21st to end	Day	15% 8% 3 8% 5% 5% 4 3 5% 5% 39%	4125
April	1st to 10th	Day	21% 12% 3 7% 5% 4 4 3 4 5% 33%	2280
	11th to 20th	Day	22% 8% 3 7% 4 5% 4 3 5% 5% 35%	2254
	21st to end	Day	24% 9% 3 7% 4 5% 4 3 4 5% 32%	2412
May	1st to 10th	Day	21% 9% 3 7% 5% 5% 5% 4 6% 6% 28%	4426
	11th to 20th	Day	19% 7% 4 8% 5% 5% 4 3 5% 6% 33%	4398
	21st to end	Day	17% 6% 2 7% 5% 5% 5% 4 6% 8% 36%	4837
June	1st to 10th	Day	21% 9% 3 7% 5% 4 4 4 6% 7% 29%	2660
	11th to 20th	Day	15% 6% 3 7% 5% 6% 5% 4 6% 8% 36%	2660
	21st to end	Day	21% 8% 3 7% 6% 5% 5% 5% 5% 7% 29%	2660
July	1st to 10th	Day	12% 7% 2 7% 6% 6% 5% 5% 7% 8% 35%	4440
	11th to 20th	Day	15% 6% 2 5% 5% 5% 5% 5% 7% 8% 36%	4440
	21st to end	Day	12% 6% 2 5% 4 4 5% 4 6% 8% 46%	4814
August	1st to 10th	Day	15% 6% 2 8% 5% 5% 6% 4 7% 8% 33%	4423
	11th to 20th	Day	16% 7% 2 6% 4 4 4 5% 6% 8% 38%	3991
	21st to end	Day	16% 5% 2 6% 4 5% 5% 3 7% 8% 39%	4180
September	1st to 10th	Day	15% 5% 2 6% 4 4 5% 5% 6% 8% 41%	2280
	11th to 20th	Day	14% 4 2 5% 4 4 4 3 5% 7% 49%	2223
	21st to end	Day	19% 5% 2 5% 4 4 3 3 6% 7% 42%	2090
October	1st to 10th	Day	22% 7% 3 8% 4 3 4 3 5% 6% 36%	1924
	11th to 20th	Day	23% 9% 3 7% 6% 5% 4 4 4 6% 29%	1884
	21st to end	Day	24% 11% 3 7% 4 5% 4 3 5% 6% 28%	1881
November	1st to 10th	Day	16% 10% 3 8% 6% 5% 4 4 6% 6% 33%	1761
	11th to 20th	Day	19% 11% 3 7% 5% 6% 5% 4 6% 6% 29%	1680
	21st to end	Day	23% 14% 3 7% 5% 5% 5% 3 5% 6% 24%	1600
December	1st to 10th	Day	24% 17% 4 9% 5% 5% 4 4 4 4 19%	1560
	11th to 20th	Day	21% 14% 4 10% 5% 4 3 4 4 4 26%	1906
	21st to end	Day	27% 19% 4 9% 5% 3 3 2 3 3 21%	2772
January	1st to 10th	Night	17% 17% 6% 10% 5% 4 4 4 4 5% 23%	4429
	11th to 20th	Night	13% 15% 5% 12% 7% 5% 5% 4 5% 6% 23%	4440
	21st to end	Night	15% 18% 6% 11% 6% 5% 4 3 4 5% 24%	4884
February	1st to 10th	Night	14% 14% 5% 10% 6% 5% 5% 3 5% 6% 25%	2482
	11th to 20th	Night	13% 12% 5% 10% 6% 6% 5% 3 5% 6% 29%	2335
	21st to end	Night	15% 15% 5% 9% 5% 4 4 3 4 5% 31%	1884
March	1st to 10th	Night	19% 12% 4 7% 6% 4 4 3 4 5% 32%	3724
	11th to 20th	Night	17% 20% 4 8% 5% 4 4 3 4 5% 27%	3617
	21st to end	Night	13% 10% 4 8% 5% 4 4 3 4 4 39%	3506
April	1st to 10th	Night	23% 9% 3 7% 4 4 4 3 5% 6% 33%	1900
	11th to 20th	Night	21% 8% 3 5% 5% 5% 4 3 4 6% 36%	1875
	21st to end	Night	22% 9% 2 6% 5% 4 4 3 5% 5% 35%	1772
May	1st to 10th	Night	21% 8% 3 7% 5% 5% 4 3 6% 6% 32%	2528
	11th to 20th	Night	22% 8% 2 5% 4 3 4 3 5% 6% 39%	2495
	21st to end	Night	18% 7% 3 6% 4 5% 4 4 6% 7% 36%	2738
June	1st to 10th	Night	20% 7% 2 6% 4 5% 4 5% 6% 8% 32%	1520
	11th to 20th	Night	17% 7% 3 6% 4 4 4 4 5% 7% 40%	1520
	21st to end	Night	20% 6% 2 6% 5% 5% 4 4 5% 6% 37%	1520
July	1st to 10th	Night	14% 7% 3 8% 5% 5% 5% 5% 6% 8% 35%	2520
	11th to 20th	Night	15% 6% 3 5% 4 4 4 4 5% 9% 42%	2520
	21st to end	Night	12% 6% 2 6% 4 4 5% 4 6% 8% 45%	2739
August	1st to 10th	Night	15% 7% 3 7% 4 4 5% 4 5% 8% 39%	2506
	11th to 20th	Night	17% 7% 2 6% 4 4 4 4 6% 6% 41%	2803
	21st to end	Night	17% 6% 2 7% 4 4 4 3 5% 8% 41%	3476
September	1st to 10th	Night	12% 5% 2 6% 5% 4 4 3 6% 7% 45%	1900
	11th to 20th	Night	14% 6% 2 5% 3 3 3 3 3 7% 50%	1956
	21st to end	Night	17% 5% 2 5% 4 4 3 3 4 7% 45%	2090
October	1st to 10th	Night	19% 7% 3 6% 3 4 4 3 5% 6% 39%	2252
	11th to 20th	Night	21% 8% 3 6% 5% 4 5% 3 4 5% 35%	2295
	21st to end	Night	23% 9% 3 8% 5% 5% 4 3 4 5% 30%	2717
November	1st to 10th	Night	19% 11% 3 7% 4 4 4 3 5% 6% 33%	2537
	11th to 20th	Night	18% 11% 3 8% 5% 5% 4 4 4 5% 33%	2718
	21st to end	Night	21% 14% 4 8% 5% 4 4 3 4 5% 27%	2800
December	1st to 10th	Night	20% 16% 6% 9% 6% 5% 4 3 6% 4 21%	2737
	11th to 20th	Night	22% 15% 4 9% 5% 4 4 3 4 4 26%	3288
	21st to end	Night	28% 17% 5% 8% 4 3 3 2 3 5% 22%	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	68% 2 11% 14% 6% 1	2518
	11th to 20th	Day	61% 2 12% 17% 8% 1	2520
	21st to end	Day	64% 3 12% 14% 6% 1	2772
February	1st to 10th	Day	61% 2 8% 20% 6% 2	1695
	11th to 20th	Day	59% 2 11% 17% 10% 1	1739
	21st to end	Day	62% 1 9% 14% 11% 2	1570
March	1st to 10th	Day	62% 1 8% 18% 9% 1	3119
	11th to 20th	Day	61% 1 10% 14% 11% 2	3340
	21st to end	Day	49% 1 7% 21% 20% 3	4125
April	1st to 10th	Day	55% 2 7% 20% 13% 3	2280
	11th to 20th	Day	52% 2 6% 22% 16% 2	2254
	21st to end	Day	56% 2 8% 17% 13% 4	2412
May	1st to 10th	Day	56% 2 8% 23% 11% 2	4440
	11th to 20th	Day	53% 2 14% 21% 9% 2	4402
	21st to end	Day	46% 2 11% 25% 15% 1	4837
June	1st to 10th	Day	53% 4 9% 20% 12% 1	2660
	11th to 20th	Day	44% 3 12% 23% 14% 3	2660
	21st to end	Day	54% 3 13% 19% 10% 1	2660
July	1st to 10th	Day	44% 5% 15% 26% 11%	4370
	11th to 20th	Day	42% 5% 16% 29% 8%	4365
	21st to end	Day	36% 5% 15% 33% 11%	4661
August	1st to 10th	Day	47% 5% 17% 22% 9%	4409
	11th to 20th	Day	43% 5% 17% 28% 7%	4033
	21st to end	Day	41% 5% 17% 22% 14% 1	4180
September	1st to 10th	Day	41% 4 13% 29% 13%	2280
	11th to 20th	Day	36% 3 14% 32% 15% 1	2223
	21st to end	Day	42% 3 14% 28% 12%	2090
October	1st to 10th	Day	47% 4 13% 26% 10%	3197
	11th to 20th	Day	46% 4 16% 26% 7%	3112
	21st to end	Day	46% 3 21% 21% 8%	3081
November	1st to 10th	Day	51% 3 14% 23% 8% 1	1761
	11th to 20th	Day	56% 3 11% 19% 11% 1	1680
	21st to end	Day	62% 5% 13% 15% 5% 1	1600
December	1st to 10th	Day	69% 3 12% 11% 4	1560
	11th to 20th	Day	63% 3 12% 16% 6%	1906
	21st to end	Day	71% 2 9% 13% 5%	2772
January	1st to 10th	Night	66% 2 15% 13% 4	4429
	11th to 20th	Night	64% 2 12% 16% 5% 1	4440
	21st to end	Night	65% 3 12% 13% 7% 1	4884
February	1st to 10th	Night	59% 4 9% 19% 8% 1	2482
	11th to 20th	Night	57% 3 10% 20% 9% 1	2337
	21st to end	Night	56% 2 9% 17% 13% 1	1884
March	1st to 10th	Night	56% 2 9% 20% 10% 3	3734
	11th to 20th	Night	63% 2 8% 15% 11% 2	3618
	21st to end	Night	51% 1 5% 22% 17% 4	3506
April	1st to 10th	Night	55% 2 7% 19% 15% 2	1900
	11th to 20th	Night	52% 3 6% 22% 16% 2	1875
	21st to end	Night	52% 3 7% 19% 15% 4	1772
May	1st to 10th	Night	54% 2 10% 21% 10% 3	2534
	11th to 20th	Night	49% 2 11% 22% 13% 2	2496
	21st to end	Night	48% 2 9% 21% 18% 2	2739
June	1st to 10th	Night	50% 3 11% 23% 12% 1	1520
	11th to 20th	Night	44% 3 10% 24% 16% 2	1520
	21st to end	Night	48% 4 13% 20% 14% 1	1520
July	1st to 10th	Night	46% 5% 16% 20% 12% 1	2480
	11th to 20th	Night	40% 5% 18% 30% 8%	2472
	21st to end	Night	38% 5% 18% 25% 14%	2651
August	1st to 10th	Night	44% 4 15% 27% 9%	2496
	11th to 20th	Night	43% 5% 17% 28% 7%	2827
	21st to end	Night	43% 5% 16% 22% 13% 1	3476
September	1st to 10th	Night	39% 4 12% 28% 16% 1	1900
	11th to 20th	Night	36% 3 13% 35% 12% 1	1956
	21st to end	Night	40% 3 12% 30% 14%	2090
October	1st to 10th	Night	43% 4 15% 26% 11% 1	3759
	11th to 20th	Night	45% 4 14% 28% 9%	3806
	21st to end	Night	47% 3 18% 19% 11% 1	4467
November	1st to 10th	Night	52% 3 13% 22% 9% 1	2537
	11th to 20th	Night	54% 3 12% 19% 10% 2	2718
	21st to end	Night	60% 4 12% 18% 6%	2800
December	1st to 10th	Night	67% 3 10% 15% 5%	2737
	11th to 20th	Night	64% 3 7% 19% 7% 1	3288
	21st to end	Night	69% 2 8% 15% 5%	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	26% 17% 28% 23% 5% 1	180
	11th to 20th	Day	27% 19% 33% 14% 6%	180
	21st to end	Day	21% 15% 38% 19% 7% 1	198
February	1st to 10th	Day	33% 19% 33% 11% 3	263
	11th to 20th	Day	23% 24% 40% 13% 1	337
	21st to end	Day	31% 20% 26% 19% 3	382
March	1st to 10th	Day	26% 17% 31% 20% 5%	460
	11th to 20th	Day	26% 20% 34% 14% 5% 1	460
	21st to end	Day	27% 18% 30% 16% 8% 1	506
April	1st to 10th	Day	31% 12% 31% 18% 6% 2	460
	11th to 20th	Day	30% 18% 27% 16% 6% 2	452
	21st to end	Day	30% 17% 29% 15% 7% 1	460
May	1st to 10th	Day	25% 14% 32% 21% 7% 1	463
	11th to 20th	Day	22% 13% 30% 23% 10% 2	487
	21st to end	Day	22% 14% 33% 23% 7% 2	529
June	1st to 10th	Day	25% 13% 30% 23% 9% 1	490
	11th to 20th	Day	18% 14% 32% 24% 11% 2	490
	21st to end	Day	26% 10% 29% 24% 8% 3	490
July	1st to 10th	Day	13% 8% 34% 27% 14% 3	485
	11th to 20th	Day	16% 8% 33% 30% 11% 2	484
	21st to end	Day	16% 7% 33% 28% 14% 2	532
August	1st to 10th	Day	17% 7% 26% 32% 15% 3	486
	11th to 20th	Day	13% 8% 27% 30% 15% 7%	479
	21st to end	Day	16% 8% 29% 25% 15% 6%	539
September	1st to 10th	Day	16% 7% 32% 25% 14% 6%	490
	11th to 20th	Day	13% 8% 25% 24% 20% 11%	490
	21st to end	Day	20% 11% 27% 21% 16% 4	490
October	1st to 10th	Day	24% 12% 27% 21% 13% 3	490
	11th to 20th	Day	24% 17% 28% 19% 10% 2	481
	21st to end	Day	32% 11% 30% 21% 6%	429
November	1st to 10th	Day	29% 14% 27% 22% 7% 1	395
	11th to 20th	Day	28% 17% 36% 15% 4	280
	21st to end	Day	29% 17% 31% 19% 4 1	200
December	1st to 10th	Day	29% 16% 27% 19% 7% 2	190
	11th to 20th	Day	29% 21% 32% 13% 4 1	180
	21st to end	Day	36% 16% 30% 14% 3 2	198
January	1st to 10th	Night	27% 15% 30% 24% 4	760
	11th to 20th	Night	28% 17% 28% 21% 5%	760
	21st to end	Night	19% 15% 34% 25% 6%	836
February	1st to 10th	Night	22% 16% 34% 24% 4	760
	11th to 20th	Night	21% 17% 36% 21% 4	743
	21st to end	Night	23% 16% 31% 26% 3	628
March	1st to 10th	Night	23% 15% 33% 25% 3	760
	11th to 20th	Night	27% 16% 30% 22% 5%	760
	21st to end	Night	24% 13% 30% 26% 6%	836
April	1st to 10th	Night	28% 14% 27% 26% 5%	760
	11th to 20th	Night	27% 13% 32% 23% 5% 1	751
	21st to end	Night	28% 10% 33% 20% 9%	632
May	1st to 10th	Night	24% 10% 31% 25% 7% 3	394
	11th to 20th	Night	23% 9% 30% 29% 10% 1	374
	21st to end	Night	16% 9% 35% 30% 9%	411
June	1st to 10th	Night	24% 9% 27% 29% 11% 1	380
	11th to 20th	Night	19% 7% 26% 36% 12% 1	380
	21st to end	Night	22% 5% 27% 30% 15% 1	380
July	1st to 10th	Night	12% 7% 29% 36% 16% 1	370
	11th to 20th	Night	15% 4 21% 42% 17%	368
	21st to end	Night	14% 5% 24% 40% 16% 1	416
August	1st to 10th	Night	15% 4 17% 44% 19% 1	378
	11th to 20th	Night	14% 4 22% 34% 23% 3	566
	21st to end	Night	16% 5% 24% 33% 19% 3	836
September	1st to 10th	Night	14% 5% 27% 38% 15% 2	760
	11th to 20th	Night	17% 6% 19% 33% 23% 3	760
	21st to end	Night	20% 7% 26% 28% 18% 3	760
October	1st to 10th	Night	23% 9% 25% 29% 12% 1	760
	11th to 20th	Night	25% 12% 25% 28% 9% 1	760
	21st to end	Night	28% 12% 28% 26% 5%	836
November	1st to 10th	Night	26% 15% 24% 26% 8% 1	780
	11th to 20th	Night	24% 17% 30% 21% 9%	800
	21st to end	Night	31% 16% 27% 19% 7%	800
December	1st to 10th	Night	30% 14% 31% 20% 4 1	783
	11th to 20th	Night	30% 18% 29% 18% 4 1	760
	21st to end	Night	35% 16% 28% 15% 5%	836

Page generated at 2024-12-03 06:45:10. Version ac07

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