Lac St-Joseph
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lac St-Joseph clear sky chart from 2005-11-06 to 2025-04-26.

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% 11% 4 8% 5% 4 4 4 5% 6% 29%	113040
	Night	19% 13% 4 9% 5% 4 4 3 5% 5% 29%	115602
Transparency	Day	54% 8% 12% 16% 9% 1	116530
	Night	56% 6% 12% 17% 8% 1	120277
Seeing	Day	26% 18% 29% 19% 7% 1	15653
	Night	25% 13% 27% 26% 8% 1	24381

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% 20% 6% 12% 6% 5% 3 3 3 4 21%	3597
	11th to 20th	Day	10% 15% 7% 19% 9% 5% 4 3 3 4 22%	3570
	21st to end	Day	8% 13% 5% 13% 6% 4 4 4 5% 6% 31%	3960
February	1st to 10th	Day	11% 16% 5% 13% 8% 6% 5% 3 4 4 25%	1603
	11th to 20th	Day	13% 18% 6% 12% 5% 5% 4 3 5% 5% 23%	1926
	21st to end	Day	13% 16% 5% 12% 6% 4 4 4 4 6% 26%	1650
March	1st to 10th	Day	23% 15% 5% 10% 5% 4 4 2 4 3 25%	4476
	11th to 20th	Day	16% 17% 4 8% 5% 4 4 3 4 6% 29%	4720
	21st to end	Day	19% 15% 3 7% 4 4 4 3 3 4 33%	5867
April	1st to 10th	Day	23% 13% 3 8% 5% 4 4 2 4 4 29%	2400
	11th to 20th	Day	23% 9% 3 7% 4 4 4 3 4 5% 35%	2457
	21st to end	Day	24% 10% 3 8% 4 4 4 3 3 6% 30%	2535
May	1st to 10th	Day	22% 8% 3 7% 4 4 4 3 4 6% 35%	4252
	11th to 20th	Day	18% 7% 2 7% 5% 5% 5% 4 6% 8% 33%	4398
	21st to end	Day	20% 7% 3 7% 5% 5% 5% 4 5% 7% 31%	4837
June	1st to 10th	Day	21% 7% 3 7% 6% 6% 5% 5% 6% 8% 26%	2845
	11th to 20th	Day	20% 8% 2 6% 4 5% 5% 4 6% 6% 34%	2850
	21st to end	Day	25% 9% 3 8% 6% 5% 4 3 5% 6% 25%	2850
July	1st to 10th	Day	17% 8% 3 9% 5% 5% 6% 4 6% 7% 30%	4445
	11th to 20th	Day	19% 7% 3 7% 5% 5% 5% 5% 8% 8% 28%	4440
	21st to end	Day	17% 6% 2 5% 5% 5% 5% 4 6% 8% 38%	4814
August	1st to 10th	Day	17% 7% 3 7% 5% 5% 6% 5% 8% 9% 28%	4423
	11th to 20th	Day	23% 6% 3 7% 5% 5% 5% 5% 6% 8% 27%	4053
	21st to end	Day	23% 7% 3 6% 4 4 4 4 5% 7% 34%	4308
September	1st to 10th	Day	21% 7% 3 5% 4 4 5% 4 5% 8% 35%	2280
	11th to 20th	Day	19% 5% 2 5% 3 4 3 3 6% 6% 44%	2124
	21st to end	Day	25% 7% 2 6% 4 3 3 3 5% 6% 36%	2090
October	1st to 10th	Day	23% 8% 3 6% 4 5% 6% 3 5% 6% 32%	2066
	11th to 20th	Day	27% 10% 4 8% 5% 5% 5% 4 5% 6% 23%	1752
	21st to end	Day	29% 10% 3 8% 5% 4 4 3 4 5% 25%	1881
November	1st to 10th	Day	22% 11% 3 8% 5% 4 4 3 4 5% 31%	1761
	11th to 20th	Day	22% 14% 5% 10% 5% 4 4 3 4 5% 26%	1780
	21st to end	Day	21% 19% 5% 9% 6% 5% 4 4 3 5% 19%	1463
December	1st to 10th	Day	20% 16% 6% 11% 5% 5% 4 3 5% 5% 19%	2280
	11th to 20th	Day	21% 15% 6% 10% 5% 4 4 2 3 4 27%	2618
	21st to end	Day	20% 18% 5% 8% 4 4 5% 3 4 5% 26%	3669
January	1st to 10th	Night	16% 22% 7% 14% 6% 4 3 2 3 3 20%	6349
	11th to 20th	Night	10% 19% 9% 16% 7% 5% 4 3 4 4 19%	6315
	21st to end	Night	7% 13% 5% 13% 7% 6% 5% 4 6% 6% 28%	6996
February	1st to 10th	Night	12% 14% 5% 11% 8% 5% 4 4 5% 5% 28%	2795
	11th to 20th	Night	13% 17% 5% 12% 6% 5% 4 3 4 5% 26%	2358
	21st to end	Night	15% 15% 5% 9% 6% 4 5% 3 4 6% 28%	1980
March	1st to 10th	Night	22% 13% 4 11% 5% 4 5% 3 4 5% 23%	5364
	11th to 20th	Night	16% 15% 3 8% 6% 6% 6% 4 5% 7% 24%	5238
	21st to end	Night	20% 15% 4 8% 4 4 4 3 4 5% 30%	5064
April	1st to 10th	Night	22% 14% 4 6% 5% 4 4 3 5% 6% 29%	2000
	11th to 20th	Night	21% 10% 3 6% 5% 4 5% 3 5% 6% 32%	1892
	21st to end	Night	22% 11% 3 6% 4 4 3 3 3 7% 34%	1762
May	1st to 10th	Night	24% 6% 2 6% 4 4 5% 4 5% 5% 34%	2719
	11th to 20th	Night	22% 7% 3 6% 4 4 3 3 5% 6% 36%	2495
	21st to end	Night	20% 5% 2 6% 5% 4 5% 4 6% 7% 35%	2738
June	1st to 10th	Night	22% 8% 2 7% 4 4 6% 4 5% 7% 30%	1330
	11th to 20th	Night	20% 6% 3 5% 4 4 4 4 6% 7% 37%	1330
	21st to end	Night	24% 8% 3 8% 5% 4 4 4 5% 7% 30%	1330
July	1st to 10th	Night	18% 6% 2 8% 5% 5% 6% 4 6% 7% 33%	2510
	11th to 20th	Night	21% 9% 3 6% 4 4 4 3 5% 7% 34%	2520
	21st to end	Night	14% 5% 2 6% 4 3 5% 4 6% 7% 45%	2739
August	1st to 10th	Night	19% 8% 2 7% 4 4 4 3 6% 7% 35%	2506
	11th to 20th	Night	22% 6% 2 7% 4 6% 4 4 5% 6% 32%	2743
	21st to end	Night	20% 8% 3 8% 4 4 4 3 4 6% 34%	3343
September	1st to 10th	Night	19% 7% 2 6% 4 3 3 3 6% 6% 42%	1900
	11th to 20th	Night	19% 6% 2 5% 3 4 3 4 4 5% 44%	2055
	21st to end	Night	22% 7% 2 5% 4 4 3 2 4 5% 41%	2090
October	1st to 10th	Night	21% 8% 2 5% 4 4 4 3 5% 5% 37%	2111
	11th to 20th	Night	26% 9% 3 6% 5% 4 4 4 4 5% 31%	2427
	21st to end	Night	28% 10% 3 6% 4 4 4 3 5% 6% 29%	2717
November	1st to 10th	Night	20% 13% 3 7% 5% 4 4 2 5% 6% 30%	2537
	11th to 20th	Night	21% 11% 4 7% 5% 4 4 3 4 6% 31%	2619
	21st to end	Night	23% 17% 4 8% 5% 4 4 3 4 5% 23%	2934
December	1st to 10th	Night	17% 16% 7% 12% 9% 5% 4 3 4 5% 20%	4910
	11th to 20th	Night	23% 16% 5% 10% 6% 4 4 3 4 4 23%	5591
	21st to end	Night	22% 18% 5% 9% 4 3 3 2 3 3 27%	7295

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	66% 6% 8% 12% 8%	3598
	11th to 20th	Day	66% 7% 7% 13% 6% 1	3600
	21st to end	Day	50% 7% 8% 18% 17%	3960
February	1st to 10th	Day	61% 6% 8% 14% 9% 2	1603
	11th to 20th	Day	61% 6% 10% 12% 9% 1	1935
	21st to end	Day	59% 5% 9% 16% 9% 3	1650
March	1st to 10th	Day	63% 7% 6% 11% 10% 4	4479
	11th to 20th	Day	54% 8% 14% 13% 10% 1	4720
	21st to end	Day	55% 5% 6% 16% 15% 4	5867
April	1st to 10th	Day	59% 6% 10% 12% 10% 4	2400
	11th to 20th	Day	50% 7% 10% 20% 10% 3	2457
	21st to end	Day	56% 6% 9% 15% 12% 2	2535
May	1st to 10th	Day	48% 8% 13% 15% 14% 1	4266
	11th to 20th	Day	45% 12% 18% 18% 7% 1	4402
	21st to end	Day	48% 11% 10% 17% 13% 1	4837
June	1st to 10th	Day	53% 10% 11% 17% 7% 1	2845
	11th to 20th	Day	47% 9% 15% 17% 11% 1	2850
	21st to end	Day	58% 7% 11% 15% 8%	2850
July	1st to 10th	Day	51% 9% 14% 19% 7%	4375
	11th to 20th	Day	49% 10% 19% 17% 4	4365
	21st to end	Day	43% 10% 17% 23% 6%	4661
August	1st to 10th	Day	48% 11% 18% 18% 5%	4409
	11th to 20th	Day	51% 11% 18% 16% 4	4092
	21st to end	Day	48% 9% 14% 16% 13%	4308
September	1st to 10th	Day	45% 9% 15% 21% 10%	2280
	11th to 20th	Day	40% 7% 17% 26% 10%	2124
	21st to end	Day	48% 8% 12% 23% 8%	2090
October	1st to 10th	Day	56% 8% 10% 20% 5%	3430
	11th to 20th	Day	56% 8% 15% 19% 2	2890
	21st to end	Day	56% 8% 16% 14% 6%	3081
November	1st to 10th	Day	56% 7% 11% 18% 7%	1761
	11th to 20th	Day	61% 6% 9% 16% 7% 1	1780
	21st to end	Day	66% 6% 12% 11% 4 1	1463
December	1st to 10th	Day	66% 6% 11% 11% 6%	2280
	11th to 20th	Day	62% 4 7% 17% 10%	2618
	21st to end	Day	61% 5% 9% 12% 11% 1	3669
January	1st to 10th	Night	69% 4 9% 12% 6%	6349
	11th to 20th	Night	67% 6% 9% 14% 4 1	6360
	21st to end	Night	53% 7% 9% 17% 13%	6996
February	1st to 10th	Night	58% 5% 9% 17% 10% 1	2795
	11th to 20th	Night	61% 5% 10% 13% 10% 1	2360
	21st to end	Night	57% 6% 8% 15% 13% 2	1980
March	1st to 10th	Night	63% 5% 9% 11% 11% 1	5374
	11th to 20th	Night	58% 8% 13% 12% 8% 2	5239
	21st to end	Night	56% 5% 6% 21% 10% 2	5064
April	1st to 10th	Night	56% 6% 8% 15% 13% 2	2000
	11th to 20th	Night	50% 7% 9% 20% 12% 2	1892
	21st to end	Night	52% 6% 9% 17% 14% 2	1762
May	1st to 10th	Night	49% 6% 12% 21% 10% 1	2725
	11th to 20th	Night	44% 10% 16% 18% 11% 1	2496
	21st to end	Night	44% 9% 12% 19% 15% 1	2739
June	1st to 10th	Night	51% 8% 13% 18% 8% 1	1330
	11th to 20th	Night	43% 8% 15% 19% 12% 2	1330
	21st to end	Night	53% 8% 12% 16% 10%	1330
July	1st to 10th	Night	47% 10% 19% 19% 6%	2470
	11th to 20th	Night	49% 8% 20% 19% 4	2472
	21st to end	Night	37% 8% 23% 24% 8%	2651
August	1st to 10th	Night	47% 7% 17% 22% 7%	2496
	11th to 20th	Night	50% 10% 19% 16% 5%	2770
	21st to end	Night	50% 8% 12% 21% 9%	3343
September	1st to 10th	Night	42% 7% 15% 23% 12% 1	1900
	11th to 20th	Night	41% 8% 16% 27% 7% 1	2055
	21st to end	Night	45% 5% 13% 25% 11%	2090
October	1st to 10th	Night	50% 7% 12% 23% 8%	3527
	11th to 20th	Night	52% 7% 14% 23% 3	4028
	21st to end	Night	51% 6% 18% 16% 9%	4467
November	1st to 10th	Night	54% 7% 13% 20% 6% 1	2537
	11th to 20th	Night	55% 6% 12% 17% 10%	2619
	21st to end	Night	64% 6% 10% 14% 6%	2934
December	1st to 10th	Night	67% 5% 13% 12% 3	4910
	11th to 20th	Night	64% 4 9% 17% 6%	5592
	21st to end	Night	62% 4 7% 15% 10% 1	7295

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	28% 20% 33% 17% 3	200
	11th to 20th	Day	25% 21% 33% 17% 6% 1	200
	21st to end	Day	18% 19% 45% 13% 5%	220
February	1st to 10th	Day	25% 28% 36% 9% 1 1	203
	11th to 20th	Day	23% 27% 33% 14% 2	474
	21st to end	Day	26% 26% 28% 17% 3	414
March	1st to 10th	Day	28% 21% 30% 17% 4	500
	11th to 20th	Day	25% 24% 29% 16% 5% 1	500
	21st to end	Day	26% 23% 28% 15% 7% 1	550
April	1st to 10th	Day	32% 20% 27% 16% 5%	500
	11th to 20th	Day	31% 19% 27% 16% 5% 2	492
	21st to end	Day	29% 21% 32% 13% 3 2	480
May	1st to 10th	Day	29% 21% 31% 13% 5% 1	463
	11th to 20th	Day	23% 19% 30% 20% 7% 1	487
	21st to end	Day	26% 23% 30% 16% 4 1	529
June	1st to 10th	Day	23% 16% 30% 23% 8%	675
	11th to 20th	Day	23% 14% 30% 21% 11% 1	680
	21st to end	Day	27% 14% 26% 23% 9% 1	680
July	1st to 10th	Day	19% 15% 34% 23% 9% 1	490
	11th to 20th	Day	20% 14% 35% 20% 9% 1	484
	21st to end	Day	21% 14% 30% 24% 9% 2	532
August	1st to 10th	Day	20% 13% 30% 24% 12% 2	486
	11th to 20th	Day	24% 10% 22% 29% 13% 3	479
	21st to end	Day	22% 18% 22% 19% 14% 5%	539
September	1st to 10th	Day	22% 14% 27% 23% 12% 2	490
	11th to 20th	Day	21% 11% 25% 26% 13% 4	490
	21st to end	Day	23% 16% 26% 18% 13% 4	490
October	1st to 10th	Day	25% 17% 27% 20% 10% 1	490
	11th to 20th	Day	31% 18% 25% 17% 8% 1	412
	21st to end	Day	35% 18% 25% 17% 5%	429
November	1st to 10th	Day	34% 17% 23% 20% 5% 1	395
	11th to 20th	Day	27% 21% 27% 18% 8% 1	380
	21st to end	Day	33% 25% 30% 13% 1 1	200
December	1st to 10th	Day	30% 16% 33% 15% 7% 1	200
	11th to 20th	Day	33% 23% 28% 12% 4 1	200
	21st to end	Day	33% 17% 30% 15% 4 1	220
January	1st to 10th	Night	27% 14% 34% 20% 4	800
	11th to 20th	Night	25% 18% 27% 23% 6%	800
	21st to end	Night	15% 13% 35% 30% 6%	880
February	1st to 10th	Night	18% 15% 36% 26% 5%	800
	11th to 20th	Night	22% 19% 36% 19% 4	783
	21st to end	Night	23% 17% 29% 26% 4	660
March	1st to 10th	Night	21% 16% 33% 25% 4	800
	11th to 20th	Night	25% 17% 33% 21% 5% 1	800
	21st to end	Night	23% 15% 31% 23% 6% 1	880
April	1st to 10th	Night	29% 15% 28% 23% 5%	800
	11th to 20th	Night	27% 13% 31% 24% 6%	708
	21st to end	Night	29% 17% 29% 19% 6%	588
May	1st to 10th	Night	27% 13% 31% 23% 5%	507
	11th to 20th	Night	24% 11% 26% 31% 7% 1	374
	21st to end	Night	27% 8% 32% 24% 9%	411
June	1st to 10th	Night	24% 8% 25% 36% 7%	380
	11th to 20th	Night	22% 6% 24% 36% 13%	380
	21st to end	Night	24% 6% 20% 38% 11%	380
July	1st to 10th	Night	18% 6% 23% 41% 11% 1	370
	11th to 20th	Night	19% 6% 20% 41% 15%	368
	21st to end	Night	19% 6% 19% 39% 17%	416
August	1st to 10th	Night	20% 2 13% 43% 21% 1	378
	11th to 20th	Night	19% 6% 19% 36% 20%	535
	21st to end	Night	19% 9% 22% 31% 18% 2	755
September	1st to 10th	Night	21% 5% 26% 32% 15% 1	760
	11th to 20th	Night	21% 7% 20% 32% 17% 2	760
	21st to end	Night	24% 8% 24% 28% 16% 1	760
October	1st to 10th	Night	23% 12% 25% 28% 11% 1	760
	11th to 20th	Night	30% 11% 23% 26% 10%	760
	21st to end	Night	33% 13% 26% 23% 5%	836
November	1st to 10th	Night	28% 14% 25% 25% 7% 1	780
	11th to 20th	Night	27% 16% 23% 24% 8% 1	800
	21st to end	Night	31% 18% 26% 20% 6% 1	867
December	1st to 10th	Night	31% 12% 25% 25% 7%	900
	11th to 20th	Night	27% 20% 25% 22% 5% 1	900
	21st to end	Night	33% 15% 28% 19% 4 1	945

Page generated at 2025-04-23 09:25:02. Version ac07

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