Rang St-Joachim
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rang St-Joachim clear sky chart from 2005-11-06 to 2026-06-01.

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	17% 10% 4 8% 5% 5% 5% 4 5% 7% 30%	132106
	Night	18% 13% 4 10% 6% 5% 4 3 5% 5% 28%	131063
Transparency	Day	53% 6% 12% 20% 8% 1	135562
	Night	57% 5% 10% 18% 9% 1	135694
Seeing	Day	23% 11% 27% 23% 12% 3	16550
	Night	25% 9% 27% 28% 10% 1	25562

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% 7% 14% 6% 5% 4 3 4 4 17%	4661
	11th to 20th	Day	12% 18% 7% 16% 8% 6% 5% 3 4 5% 16%	4650
	21st to end	Day	11% 14% 5% 12% 8% 7% 6% 4 6% 6% 21%	5124
February	1st to 10th	Day	17% 14% 5% 12% 7% 6% 5% 3 4 5% 22%	1822
	11th to 20th	Day	15% 15% 6% 10% 7% 4 4 3 5% 6% 25%	1988
	21st to end	Day	16% 16% 4 8% 7% 5% 5% 4 5% 6% 24%	1730
March	1st to 10th	Day	18% 13% 5% 11% 6% 5% 6% 3 4 6% 24%	4576
	11th to 20th	Day	14% 14% 3 9% 5% 5% 4 3 5% 7% 30%	4771
	21st to end	Day	19% 12% 4 8% 4 5% 4 3 4 5% 31%	6102
April	1st to 10th	Day	22% 12% 3 7% 5% 4 4 4 5% 5% 29%	2520
	11th to 20th	Day	21% 9% 3 8% 4 4 4 2 4 6% 35%	2494
	21st to end	Day	22% 9% 4 6% 5% 4 5% 3 4 6% 32%	2711
May	1st to 10th	Day	28% 11% 3 9% 5% 4 4 4 5% 5% 22%	6288
	11th to 20th	Day	20% 7% 3 7% 5% 5% 5% 3 6% 7% 30%	6458
	21st to end	Day	21% 9% 3 7% 4 4 5% 4 6% 7% 30%	7103
June	1st to 10th	Day	22% 7% 3 7% 5% 4 5% 4 6% 7% 30%	2800
	11th to 20th	Day	15% 6% 2 7% 5% 4 5% 5% 6% 8% 38%	2800
	21st to end	Day	21% 8% 3 6% 4 4 5% 4 6% 7% 32%	2800
July	1st to 10th	Day	13% 7% 3 8% 6% 6% 6% 5% 7% 9% 32%	6360
	11th to 20th	Day	11% 5% 2 6% 5% 5% 6% 5% 7% 9% 40%	6360
	21st to end	Day	12% 6% 2 5% 3 4 4 4 6% 9% 43%	6926
August	1st to 10th	Day	15% 7% 3 8% 5% 5% 5% 5% 7% 9% 32%	4563
	11th to 20th	Day	14% 7% 3 7% 4 4 5% 4 6% 8% 39%	4101
	21st to end	Day	15% 6% 2 6% 4 4 5% 3 6% 8% 41%	4312
September	1st to 10th	Day	13% 5% 2 6% 4 4 4 4 5% 8% 44%	2400
	11th to 20th	Day	15% 6% 2 4 3 4 3 3 5% 7% 48%	2290
	21st to end	Day	16% 7% 2 6% 4 4 5% 4 6% 8% 40%	2200
October	1st to 10th	Day	20% 8% 3 7% 4 5% 5% 4 6% 6% 33%	2103
	11th to 20th	Day	19% 9% 3 7% 6% 5% 4 5% 6% 6% 30%	1935
	21st to end	Day	25% 11% 3 8% 5% 4 4 3 4 5% 28%	1980
November	1st to 10th	Day	19% 13% 3 6% 5% 5% 5% 4 5% 6% 30%	1851
	11th to 20th	Day	17% 13% 4 9% 6% 5% 4 4 6% 6% 27%	1853
	21st to end	Day	22% 15% 4 8% 5% 5% 4 4 5% 5% 22%	1680
December	1st to 10th	Day	18% 22% 6% 12% 7% 5% 4 3 4 4 15%	2680
	11th to 20th	Day	21% 13% 5% 10% 5% 4 4 4 5% 6% 23%	3066
	21st to end	Day	22% 16% 5% 11% 5% 5% 5% 6% 5% 4 17%	4048
January	1st to 10th	Night	15% 24% 7% 12% 5% 4 3 3 3 4 19%	8234
	11th to 20th	Night	12% 19% 7% 17% 8% 6% 5% 4 5% 5% 13%	8235
	21st to end	Night	12% 14% 5% 14% 9% 6% 5% 3 4 5% 22%	9057
February	1st to 10th	Night	17% 16% 5% 13% 7% 5% 4 3 5% 5% 21%	2795
	11th to 20th	Night	14% 14% 5% 12% 7% 5% 5% 4 4 5% 24%	2516
	21st to end	Night	17% 14% 5% 10% 5% 5% 3 3 4 5% 29%	2076
March	1st to 10th	Night	21% 13% 4 8% 6% 4 4 3 4 5% 28%	5484
	11th to 20th	Night	16% 15% 4 8% 5% 5% 4 3 5% 6% 28%	5403
	21st to end	Night	16% 15% 4 10% 6% 5% 4 3 4 4 29%	5072
April	1st to 10th	Night	23% 11% 4 7% 5% 4 5% 3 5% 5% 28%	2100
	11th to 20th	Night	23% 12% 3 8% 4 3 4 3 4 5% 31%	2075
	21st to end	Night	21% 10% 3 7% 4 4 3 3 5% 5% 36%	1908
May	1st to 10th	Night	26% 10% 4 8% 5% 4 4 4 5% 6% 24%	3914
	11th to 20th	Night	23% 10% 3 8% 5% 4 4 3 5% 7% 29%	3655
	21st to end	Night	18% 10% 3 8% 5% 5% 4 4 5% 7% 32%	4014
June	1st to 10th	Night	24% 8% 2 5% 5% 5% 4 4 6% 7% 31%	1600
	11th to 20th	Night	17% 6% 2 6% 5% 4 5% 4 6% 8% 37%	1600
	21st to end	Night	19% 8% 2 7% 5% 4 5% 4 5% 7% 34%	1600
July	1st to 10th	Night	13% 7% 3 8% 5% 5% 6% 4 7% 9% 33%	3600
	11th to 20th	Night	15% 6% 3 6% 5% 4 5% 4 5% 7% 40%	3600
	21st to end	Night	10% 6% 2 7% 6% 6% 5% 4 7% 7% 41%	3926
August	1st to 10th	Night	17% 8% 2 7% 5% 4 4 3 6% 7% 36%	2586
	11th to 20th	Night	15% 7% 3 7% 5% 4 5% 4 6% 7% 37%	2911
	21st to end	Night	17% 6% 2 6% 4 4 4 4 5% 7% 40%	3586
September	1st to 10th	Night	14% 6% 3 6% 4 4 5% 4 5% 7% 43%	2000
	11th to 20th	Night	14% 5% 2 5% 4 3 4 3 5% 6% 49%	2110
	21st to end	Night	18% 7% 2 6% 4 3 4 4 5% 5% 41%	2200
October	1st to 10th	Night	19% 7% 3 6% 4 4 4 4 5% 6% 38%	2294
	11th to 20th	Night	21% 9% 3 7% 5% 4 4 3 5% 6% 33%	2465
	21st to end	Night	25% 10% 3 9% 5% 3 5% 3 4 5% 28%	2860
November	1st to 10th	Night	21% 12% 3 7% 3 4 5% 4 5% 5% 30%	2667
	11th to 20th	Night	20% 11% 4 9% 5% 5% 4 4 4 5% 30%	2762
	21st to end	Night	22% 14% 4 9% 5% 5% 5% 3 4 5% 24%	2940
December	1st to 10th	Night	18% 22% 7% 12% 7% 5% 4 3 4 4 14%	4720
	11th to 20th	Night	23% 15% 5% 11% 5% 4 4 3 4 3 23%	5348
	21st to end	Night	24% 16% 5% 10% 5% 4 4 4 6% 4 19%	7150

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	71% 7% 9% 12% 1	4662
	11th to 20th	Day	72% 5% 8% 9% 5%	4680
	21st to end	Day	63% 6% 11% 11% 9%	5124
February	1st to 10th	Day	64% 5% 9% 15% 5% 1	1822
	11th to 20th	Day	62% 5% 11% 17% 5% 1	1997
	21st to end	Day	60% 5% 12% 15% 7% 1	1730
March	1st to 10th	Day	61% 6% 9% 14% 8% 2	4579
	11th to 20th	Day	53% 6% 16% 15% 9% 1	4771
	21st to end	Day	55% 6% 6% 17% 14% 1	6102
April	1st to 10th	Day	57% 6% 7% 19% 9% 1	2520
	11th to 20th	Day	52% 5% 8% 20% 13% 1	2494
	21st to end	Day	54% 5% 10% 18% 11% 2	2711
May	1st to 10th	Day	62% 6% 8% 17% 7% 1	6299
	11th to 20th	Day	51% 8% 14% 18% 8% 1	6462
	21st to end	Day	51% 6% 11% 21% 10% 1	7103
June	1st to 10th	Day	51% 7% 12% 19% 10% 1	2800
	11th to 20th	Day	43% 7% 11% 24% 13% 2	2800
	21st to end	Day	51% 7% 11% 21% 9% 1	2800
July	1st to 10th	Day	46% 7% 15% 24% 8%	6290
	11th to 20th	Day	38% 8% 14% 30% 10%	6285
	21st to end	Day	36% 7% 14% 35% 8%	6728
August	1st to 10th	Day	47% 8% 17% 21% 7%	4549
	11th to 20th	Day	42% 8% 19% 25% 6%	4141
	21st to end	Day	40% 7% 18% 22% 13%	4312
September	1st to 10th	Day	38% 7% 13% 31% 11% 1	2400
	11th to 20th	Day	37% 4 12% 34% 13%	2290
	21st to end	Day	42% 7% 14% 26% 11% 1	2200
October	1st to 10th	Day	43% 5% 14% 29% 8%	3428
	11th to 20th	Day	45% 7% 17% 25% 5%	3125
	21st to end	Day	49% 5% 18% 22% 6%	3180
November	1st to 10th	Day	54% 6% 12% 20% 7% 1	1851
	11th to 20th	Day	58% 6% 11% 16% 9%	1853
	21st to end	Day	63% 8% 13% 13% 3	1680
December	1st to 10th	Day	72% 5% 9% 12% 1	2680
	11th to 20th	Day	62% 5% 11% 15% 6%	3066
	21st to end	Day	68% 6% 10% 11% 5%	4048
January	1st to 10th	Night	71% 5% 10% 12% 3	8234
	11th to 20th	Night	73% 6% 8% 9% 4	8280
	21st to end	Night	65% 4 8% 12% 10%	9057
February	1st to 10th	Night	67% 4 8% 15% 6%	2795
	11th to 20th	Night	63% 5% 10% 17% 6%	2518
	21st to end	Night	59% 5% 8% 16% 10% 1	2076
March	1st to 10th	Night	59% 4 8% 14% 11% 3	5494
	11th to 20th	Night	56% 5% 13% 16% 10% 1	5404
	21st to end	Night	59% 5% 6% 20% 10% 1	5072
April	1st to 10th	Night	58% 5% 8% 18% 11% 1	2100
	11th to 20th	Night	56% 4 7% 19% 12% 1	2075
	21st to end	Night	51% 4 8% 19% 14% 3	1908
May	1st to 10th	Night	60% 7% 9% 16% 6% 2	3920
	11th to 20th	Night	54% 6% 10% 20% 8% 1	3656
	21st to end	Night	52% 6% 8% 19% 14% 1	4015
June	1st to 10th	Night	51% 6% 10% 21% 10% 1	1600
	11th to 20th	Night	44% 6% 13% 20% 14% 3	1600
	21st to end	Night	47% 8% 13% 20% 12% 1	1600
July	1st to 10th	Night	46% 7% 16% 22% 9%	3560
	11th to 20th	Night	41% 8% 13% 28% 10%	3552
	21st to end	Night	41% 6% 15% 26% 12%	3809
August	1st to 10th	Night	48% 6% 13% 24% 8%	2576
	11th to 20th	Night	46% 8% 17% 21% 8% 1	2937
	21st to end	Night	42% 6% 13% 24% 14% 1	3586
September	1st to 10th	Night	40% 6% 12% 29% 13% 1	2000
	11th to 20th	Night	37% 4 13% 32% 13% 1	2110
	21st to end	Night	43% 6% 11% 25% 14% 1	2200
October	1st to 10th	Night	46% 5% 13% 26% 10%	3749
	11th to 20th	Night	47% 5% 10% 28% 9%	4014
	21st to end	Night	51% 5% 13% 20% 11% 1	4610
November	1st to 10th	Night	55% 5% 11% 20% 7% 1	2667
	11th to 20th	Night	56% 6% 10% 17% 9% 1	2762
	21st to end	Night	63% 5% 12% 15% 4	2940
December	1st to 10th	Night	76% 4 9% 9% 2	4720
	11th to 20th	Night	68% 5% 7% 13% 7%	5348
	21st to end	Night	66% 4 10% 13% 7%	7150

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	30% 13% 26% 22% 8% 1	220
	11th to 20th	Day	29% 18% 33% 15% 5% 1	220
	21st to end	Day	19% 16% 37% 19% 9% 1	242
February	1st to 10th	Day	28% 18% 33% 16% 4	294
	11th to 20th	Day	26% 16% 34% 19% 4	476
	21st to end	Day	27% 14% 33% 21% 4	446
March	1st to 10th	Day	28% 12% 31% 24% 6%	540
	11th to 20th	Day	29% 12% 33% 18% 6% 1	540
	21st to end	Day	31% 17% 24% 19% 7% 1	594
April	1st to 10th	Day	31% 16% 25% 19% 8% 1	540
	11th to 20th	Day	31% 16% 26% 16% 8% 3	532
	21st to end	Day	28% 13% 33% 14% 11% 2	540
May	1st to 10th	Day	31% 11% 28% 16% 12% 2	543
	11th to 20th	Day	20% 12% 27% 28% 10% 3	567
	21st to end	Day	20% 9% 33% 25% 11% 2	617
June	1st to 10th	Day	23% 10% 26% 29% 9% 2	530
	11th to 20th	Day	18% 9% 28% 30% 14% 2	530
	21st to end	Day	22% 9% 31% 24% 11% 3	530
July	1st to 10th	Day	13% 5% 27% 34% 16% 4	525
	11th to 20th	Day	15% 6% 29% 30% 16% 5%	524
	21st to end	Day	18% 5% 22% 36% 17% 2	576
August	1st to 10th	Day	14% 5% 23% 32% 22% 5%	526
	11th to 20th	Day	16% 6% 21% 32% 19% 7%	519
	21st to end	Day	16% 11% 23% 24% 19% 7%	583
September	1st to 10th	Day	14% 8% 26% 26% 18% 8%	530
	11th to 20th	Day	14% 7% 20% 22% 24% 13%	530
	21st to end	Day	16% 8% 27% 22% 20% 7%	530
October	1st to 10th	Day	21% 10% 27% 22% 15% 5%	530
	11th to 20th	Day	26% 14% 26% 22% 11% 2	494
	21st to end	Day	35% 13% 22% 24% 6%	462
November	1st to 10th	Day	31% 15% 29% 19% 6%	425
	11th to 20th	Day	28% 17% 24% 19% 11% 1	393
	21st to end	Day	34% 17% 25% 19% 5%	220
December	1st to 10th	Day	33% 15% 23% 21% 7% 2	220
	11th to 20th	Day	25% 18% 39% 12% 5%	220
	21st to end	Day	32% 15% 28% 19% 4 2	242
January	1st to 10th	Night	29% 12% 31% 23% 4	840
	11th to 20th	Night	27% 13% 31% 21% 6%	840
	21st to end	Night	22% 11% 31% 28% 7% 1	924
February	1st to 10th	Night	25% 10% 32% 28% 5%	840
	11th to 20th	Night	22% 12% 36% 26% 4	823
	21st to end	Night	25% 11% 30% 29% 4	692
March	1st to 10th	Night	26% 13% 29% 28% 5%	840
	11th to 20th	Night	30% 12% 27% 24% 7%	840
	21st to end	Night	29% 12% 27% 25% 6% 1	924
April	1st to 10th	Night	29% 12% 28% 26% 5%	840
	11th to 20th	Night	31% 12% 28% 22% 7%	831
	21st to end	Night	27% 11% 28% 26% 7%	648
May	1st to 10th	Night	26% 8% 29% 27% 9% 1	530
	11th to 20th	Night	23% 7% 30% 30% 9% 1	414
	21st to end	Night	19% 8% 30% 34% 8% 1	455
June	1st to 10th	Night	28% 6% 26% 30% 10% 1	400
	11th to 20th	Night	20% 4 27% 33% 16%	400
	21st to end	Night	22% 5% 24% 36% 13% 1	400
July	1st to 10th	Night	12% 4 26% 43% 14% 1	390
	11th to 20th	Night	10% 3 20% 50% 15% 1	388
	21st to end	Night	13% 4 19% 49% 15%	438
August	1st to 10th	Night	15% 4 15% 42% 24% 1	398
	11th to 20th	Night	17% 2 17% 37% 25% 1	603
	21st to end	Night	18% 6% 17% 38% 20% 2	880
September	1st to 10th	Night	16% 7% 21% 40% 16% 2	800
	11th to 20th	Night	17% 5% 17% 33% 24% 4	800
	21st to end	Night	21% 6% 26% 27% 18% 3	800
October	1st to 10th	Night	23% 5% 25% 31% 15% 1	800
	11th to 20th	Night	28% 8% 27% 28% 9% 1	800
	21st to end	Night	31% 9% 29% 25% 7%	880
November	1st to 10th	Night	27% 12% 31% 22% 7% 1	820
	11th to 20th	Night	28% 13% 27% 23% 9% 1	840
	21st to end	Night	32% 11% 32% 19% 6%	840
December	1st to 10th	Night	32% 14% 28% 21% 5%	840
	11th to 20th	Night	31% 13% 29% 20% 5% 1	840
	21st to end	Night	34% 12% 30% 19% 5%	924

Page generated at 2026-05-29 01:53:28. Version ac07

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