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 2025-02-06.

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	17% 11% 4 8% 5% 5% 5% 4 6% 7% 30%	108423
	Night	18% 13% 4 9% 5% 4 4 3 5% 5% 28%	109829
Transparency	Day	52% 7% 13% 20% 8% 1	111927
	Night	57% 6% 10% 18% 9% 1	114489
Seeing	Day	23% 11% 27% 24% 12% 3	14833
	Night	25% 9% 27% 28% 10% 1	23927

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% 22% 8% 13% 5% 5% 3 2 4 3 17%	3597
	11th to 20th	Day	12% 17% 8% 16% 8% 6% 4 3 4 5% 17%	3570
	21st to end	Day	13% 16% 6% 11% 6% 5% 5% 4 5% 6% 23%	3960
February	1st to 10th	Day	18% 15% 5% 11% 6% 6% 5% 3 4 5% 21%	1690
	11th to 20th	Day	15% 16% 6% 10% 7% 4 4 3 5% 5% 25%	1793
	21st to end	Day	16% 16% 4 8% 7% 5% 5% 4 5% 6% 25%	1570
March	1st to 10th	Day	19% 13% 4 10% 6% 4 5% 3 4 6% 25%	3116
	11th to 20th	Day	15% 18% 4 11% 5% 5% 4 3 4 6% 25%	3266
	21st to end	Day	16% 11% 4 8% 4 4 4 3 5% 5% 36%	4166
April	1st to 10th	Day	23% 11% 3 7% 5% 4 4 4 5% 5% 29%	2280
	11th to 20th	Day	21% 9% 3 7% 4 4 4 2 5% 6% 36%	2254
	21st to end	Day	23% 9% 4 6% 5% 4 5% 3 4 6% 32%	2453
May	1st to 10th	Day	23% 9% 3 8% 5% 3 4 4 6% 6% 29%	4288
	11th to 20th	Day	18% 8% 3 7% 6% 5% 6% 4 7% 7% 30%	4398
	21st to end	Day	14% 7% 3 6% 5% 5% 5% 5% 7% 9% 34%	4837
June	1st to 10th	Day	22% 7% 3 7% 5% 4 5% 4 6% 7% 30%	2660
	11th to 20th	Day	16% 6% 2 6% 5% 4 5% 5% 6% 8% 37%	2660
	21st to end	Day	21% 8% 3 7% 5% 4 5% 4 6% 6% 32%	2660
July	1st to 10th	Day	12% 6% 2 6% 5% 5% 5% 4 7% 10% 36%	4440
	11th to 20th	Day	13% 5% 2 6% 5% 5% 5% 5% 8% 9% 37%	4440
	21st to end	Day	13% 6% 2 6% 4 4 4 4 6% 8% 42%	4814
August	1st to 10th	Day	15% 7% 3 8% 5% 5% 5% 5% 7% 9% 30%	4423
	11th to 20th	Day	14% 7% 3 7% 4 4 5% 4 6% 8% 38%	3973
	21st to end	Day	15% 6% 2 6% 4 4 5% 3 6% 8% 41%	4180
September	1st to 10th	Day	14% 5% 2 6% 5% 4 4 4 5% 8% 43%	2280
	11th to 20th	Day	16% 6% 2 5% 3 4 3 3 5% 7% 47%	2176
	21st to end	Day	16% 7% 2 6% 4 4 5% 4 6% 8% 40%	2090
October	1st to 10th	Day	21% 8% 3 7% 4 5% 5% 4 6% 6% 31%	1998
	11th to 20th	Day	20% 9% 3 6% 5% 5% 4 5% 7% 6% 30%	1838
	21st to end	Day	25% 11% 2 7% 5% 4 4 3 4 6% 29%	1881
November	1st to 10th	Day	19% 12% 3 6% 5% 5% 5% 3 5% 6% 32%	1761
	11th to 20th	Day	17% 12% 4 9% 6% 5% 4 4 6% 6% 27%	1765
	21st to end	Day	22% 15% 5% 8% 5% 5% 5% 4 5% 5% 22%	1600
December	1st to 10th	Day	18% 22% 7% 12% 6% 5% 4 3 4 4 15%	2600
	11th to 20th	Day	21% 13% 5% 10% 5% 4 4 4 5% 6% 24%	2986
	21st to end	Day	22% 16% 5% 11% 5% 5% 5% 5% 5% 4 17%	3960
January	1st to 10th	Night	15% 26% 8% 12% 5% 4 3 3 3 4 17%	6349
	11th to 20th	Night	11% 19% 8% 16% 8% 6% 5% 4 5% 5% 14%	6315
	21st to end	Night	15% 17% 5% 13% 7% 5% 4 3 4 5% 22%	6996
February	1st to 10th	Night	18% 17% 5% 13% 7% 5% 4 3 4 5% 20%	2598
	11th to 20th	Night	15% 14% 5% 11% 7% 5% 5% 4 4 5% 24%	2271
	21st to end	Night	18% 14% 4 10% 5% 5% 3 3 4 5% 29%	1884
March	1st to 10th	Night	22% 12% 3 8% 5% 4 4 3 4 5% 31%	3724
	11th to 20th	Night	19% 19% 4 9% 5% 4 3 2 4 4 26%	3688
	21st to end	Night	14% 13% 4 9% 5% 4 4 3 4 4 35%	3466
April	1st to 10th	Night	23% 11% 3 7% 5% 4 5% 3 5% 5% 28%	1900
	11th to 20th	Night	23% 11% 2 8% 4 3 4 3 4 6% 32%	1875
	21st to end	Night	22% 11% 3 7% 4 4 3 3 4 5% 35%	1726
May	1st to 10th	Night	24% 9% 4 7% 5% 4 4 4 5% 7% 29%	2679
	11th to 20th	Night	21% 10% 3 8% 4 3 4 2 5% 7% 33%	2495
	21st to end	Night	16% 7% 2 7% 4 5% 4 4 5% 8% 37%	2738
June	1st to 10th	Night	24% 8% 2 5% 5% 5% 4 4 6% 7% 31%	1520
	11th to 20th	Night	17% 6% 2 7% 5% 4 4 4 6% 8% 37%	1520
	21st to end	Night	19% 8% 2 7% 5% 4 4 4 5% 7% 34%	1520
July	1st to 10th	Night	13% 7% 3 9% 5% 5% 5% 4 6% 8% 34%	2520
	11th to 20th	Night	14% 6% 3 6% 5% 5% 5% 4 6% 8% 41%	2520
	21st to end	Night	13% 7% 2 7% 6% 6% 4 4 6% 6% 40%	2739
August	1st to 10th	Night	18% 8% 2 8% 5% 4 4 3 5% 7% 34%	2506
	11th to 20th	Night	16% 7% 3 7% 5% 4 4 4 6% 7% 36%	2821
	21st to end	Night	17% 6% 2 6% 4 4 4 4 5% 7% 40%	3476
September	1st to 10th	Night	14% 6% 3 6% 4 4 4 5% 6% 7% 42%	1900
	11th to 20th	Night	15% 5% 2 5% 4 3 4 3 4 6% 48%	2004
	21st to end	Night	18% 7% 2 6% 4 3 4 4 5% 5% 41%	2090
October	1st to 10th	Night	19% 7% 3 7% 4 4 4 4 5% 6% 36%	2179
	11th to 20th	Night	22% 9% 3 8% 5% 4 4 3 5% 5% 32%	2342
	21st to end	Night	25% 10% 3 9% 5% 3 5% 3 4 5% 28%	2717
November	1st to 10th	Night	20% 12% 3 7% 4 4 5% 4 6% 5% 30%	2537
	11th to 20th	Night	20% 11% 3 9% 5% 5% 4 4 4 5% 30%	2630
	21st to end	Night	23% 14% 4 9% 5% 5% 4 3 4 5% 25%	2800
December	1st to 10th	Night	19% 22% 7% 13% 7% 5% 4 2 4 4 13%	4580
	11th to 20th	Night	24% 15% 5% 11% 5% 4 4 2 4 3 23%	5208
	21st to end	Night	24% 16% 5% 10% 5% 4 4 5% 6% 4 19%	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	72% 8% 8% 11% 1	3598
	11th to 20th	Day	71% 6% 9% 9% 5%	3600
	21st to end	Day	62% 7% 12% 12% 7%	3960
February	1st to 10th	Day	66% 5% 9% 15% 4 1	1690
	11th to 20th	Day	62% 5% 11% 16% 5% 1	1802
	21st to end	Day	60% 5% 12% 15% 7% 1	1570
March	1st to 10th	Day	59% 7% 9% 18% 6% 1	3119
	11th to 20th	Day	60% 6% 12% 12% 9% 1	3266
	21st to end	Day	48% 7% 7% 21% 15% 1	4166
April	1st to 10th	Day	57% 6% 7% 19% 9% 1	2280
	11th to 20th	Day	50% 5% 9% 21% 13% 2	2254
	21st to end	Day	54% 5% 11% 17% 10% 3	2453
May	1st to 10th	Day	54% 6% 10% 20% 9% 1	4302
	11th to 20th	Day	49% 9% 15% 18% 8% 1	4402
	21st to end	Day	44% 8% 13% 24% 11% 1	4837
June	1st to 10th	Day	51% 7% 12% 20% 10% 1	2660
	11th to 20th	Day	43% 7% 12% 24% 13% 2	2660
	21st to end	Day	52% 7% 11% 21% 9% 1	2660
July	1st to 10th	Day	41% 7% 15% 28% 9%	4370
	11th to 20th	Day	41% 8% 16% 31% 5%	4365
	21st to end	Day	39% 8% 14% 31% 8%	4661
August	1st to 10th	Day	48% 8% 16% 20% 7%	4409
	11th to 20th	Day	42% 8% 19% 25% 6%	4013
	21st to end	Day	40% 7% 18% 21% 14%	4180
September	1st to 10th	Day	39% 7% 13% 29% 11% 1	2280
	11th to 20th	Day	38% 4 13% 33% 12%	2176
	21st to end	Day	42% 7% 15% 26% 10% 1	2090
October	1st to 10th	Day	44% 5% 14% 29% 7%	3323
	11th to 20th	Day	45% 7% 17% 25% 5%	3028
	21st to end	Day	48% 5% 18% 22% 6%	3081
November	1st to 10th	Day	53% 6% 12% 21% 7% 1	1761
	11th to 20th	Day	57% 6% 11% 16% 9%	1765
	21st to end	Day	63% 8% 13% 13% 3	1600
December	1st to 10th	Day	73% 5% 9% 11% 1	2600
	11th to 20th	Day	62% 5% 11% 15% 6%	2986
	21st to end	Day	68% 6% 10% 12% 4	3960
January	1st to 10th	Night	73% 5% 9% 11% 2	6349
	11th to 20th	Night	72% 6% 9% 10% 3	6360
	21st to end	Night	66% 4 9% 10% 10%	6996
February	1st to 10th	Night	68% 4 8% 14% 5% 1	2598
	11th to 20th	Night	62% 5% 10% 16% 6%	2273
	21st to end	Night	59% 4 8% 16% 10% 2	1884
March	1st to 10th	Night	56% 5% 9% 18% 8% 2	3734
	11th to 20th	Night	62% 5% 7% 14% 10% 1	3689
	21st to end	Night	53% 5% 6% 22% 12% 2	3466
April	1st to 10th	Night	58% 5% 8% 18% 11% 1	1900
	11th to 20th	Night	55% 4 8% 20% 12% 1	1875
	21st to end	Night	53% 5% 8% 18% 14% 3	1726
May	1st to 10th	Night	54% 8% 9% 18% 8% 2	2685
	11th to 20th	Night	50% 6% 11% 21% 10% 2	2496
	21st to end	Night	44% 7% 10% 21% 17% 1	2739
June	1st to 10th	Night	51% 6% 11% 21% 10% 1	1520
	11th to 20th	Night	44% 5% 13% 21% 14% 3	1520
	21st to end	Night	48% 7% 13% 20% 11% 1	1520
July	1st to 10th	Night	47% 7% 12% 22% 12% 1	2480
	11th to 20th	Night	40% 8% 14% 29% 9%	2472
	21st to end	Night	44% 7% 15% 21% 13%	2651
August	1st to 10th	Night	49% 7% 13% 23% 8%	2496
	11th to 20th	Night	46% 8% 17% 20% 8%	2847
	21st to end	Night	42% 6% 13% 23% 14% 1	3476
September	1st to 10th	Night	40% 7% 12% 27% 13% 1	1900
	11th to 20th	Night	37% 4 14% 32% 12% 1	2004
	21st to end	Night	43% 6% 11% 25% 14% 1	2090
October	1st to 10th	Night	47% 6% 13% 26% 9%	3634
	11th to 20th	Night	48% 5% 10% 28% 9%	3891
	21st to end	Night	51% 5% 13% 20% 11% 1	4467
November	1st to 10th	Night	55% 5% 12% 20% 7% 1	2537
	11th to 20th	Night	56% 6% 10% 17% 9% 2	2630
	21st to end	Night	63% 5% 12% 16% 4	2800
December	1st to 10th	Night	77% 4 9% 8% 2	4580
	11th to 20th	Night	68% 5% 7% 13% 7%	5208
	21st to end	Night	66% 4 10% 13% 7%	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	30% 13% 26% 22% 8% 2	200
	11th to 20th	Day	31% 16% 31% 16% 6% 1	200
	21st to end	Day	20% 15% 36% 19% 9% 1	220
February	1st to 10th	Day	31% 19% 32% 15% 3	252
	11th to 20th	Day	27% 17% 34% 19% 3	401
	21st to end	Day	28% 14% 30% 23% 4	382
March	1st to 10th	Day	29% 9% 29% 26% 7%	460
	11th to 20th	Day	27% 11% 35% 19% 6% 2	460
	21st to end	Day	31% 16% 23% 20% 8% 1	506
April	1st to 10th	Day	31% 14% 25% 20% 9% 1	460
	11th to 20th	Day	30% 16% 27% 15% 9% 4	452
	21st to end	Day	30% 11% 32% 14% 12% 2	460
May	1st to 10th	Day	29% 10% 29% 17% 13% 2	463
	11th to 20th	Day	19% 10% 28% 28% 11% 3	487
	21st to end	Day	18% 9% 33% 26% 11% 2	529
June	1st to 10th	Day	24% 10% 25% 30% 9% 2	490
	11th to 20th	Day	18% 8% 26% 30% 14% 3	490
	21st to end	Day	23% 10% 29% 24% 11% 3	490
July	1st to 10th	Day	13% 5% 26% 35% 16% 5%	485
	11th to 20th	Day	16% 6% 28% 30% 16% 5%	484
	21st to end	Day	18% 5% 21% 36% 18% 2	532
August	1st to 10th	Day	15% 5% 24% 31% 21% 4	486
	11th to 20th	Day	16% 5% 22% 32% 19% 7%	479
	21st to end	Day	16% 10% 22% 25% 19% 8%	539
September	1st to 10th	Day	15% 9% 26% 26% 17% 8%	490
	11th to 20th	Day	15% 7% 20% 22% 22% 13%	490
	21st to end	Day	16% 8% 26% 23% 20% 7%	490
October	1st to 10th	Day	22% 10% 27% 20% 15% 5%	490
	11th to 20th	Day	27% 14% 25% 21% 11% 2	457
	21st to end	Day	35% 13% 22% 24% 6%	429
November	1st to 10th	Day	30% 14% 29% 20% 6% 1	395
	11th to 20th	Day	27% 17% 25% 18% 11% 1	365
	21st to end	Day	34% 17% 24% 21% 5% 1	200
December	1st to 10th	Day	35% 14% 22% 21% 8% 2	200
	11th to 20th	Day	25% 19% 39% 13% 6%	200
	21st to end	Day	33% 14% 28% 19% 4 3	220
January	1st to 10th	Night	29% 12% 31% 23% 4 1	800
	11th to 20th	Night	27% 13% 32% 22% 6%	800
	21st to end	Night	23% 10% 31% 28% 7% 1	880
February	1st to 10th	Night	27% 10% 33% 26% 5%	781
	11th to 20th	Night	22% 12% 36% 27% 3 1	743
	21st to end	Night	26% 11% 31% 28% 5%	628
March	1st to 10th	Night	27% 11% 28% 29% 5%	760
	11th to 20th	Night	30% 12% 26% 25% 8%	760
	21st to end	Night	28% 12% 27% 25% 7% 1	836
April	1st to 10th	Night	29% 10% 28% 28% 6%	760
	11th to 20th	Night	30% 11% 28% 22% 8%	751
	21st to end	Night	28% 12% 27% 26% 7% 1	586
May	1st to 10th	Night	27% 6% 30% 26% 10% 1	480
	11th to 20th	Night	23% 7% 29% 31% 9% 1	374
	21st to end	Night	18% 7% 30% 35% 9% 1	411
June	1st to 10th	Night	28% 6% 24% 30% 11% 1	380
	11th to 20th	Night	20% 4 26% 33% 16%	380
	21st to end	Night	22% 5% 23% 36% 13% 1	380
July	1st to 10th	Night	12% 5% 25% 43% 14% 1	370
	11th to 20th	Night	10% 3 21% 49% 16% 1	368
	21st to end	Night	13% 4 19% 48% 16%	416
August	1st to 10th	Night	15% 4 16% 41% 24% 1	378
	11th to 20th	Night	18% 3 17% 37% 24% 1	573
	21st to end	Night	17% 5% 17% 37% 20% 2	836
September	1st to 10th	Night	16% 6% 20% 40% 16% 2	760
	11th to 20th	Night	18% 5% 17% 33% 24% 4	760
	21st to end	Night	21% 6% 26% 26% 18% 3	760
October	1st to 10th	Night	24% 6% 25% 29% 15% 1	760
	11th to 20th	Night	29% 7% 26% 28% 9% 1	760
	21st to end	Night	31% 9% 29% 24% 6%	836
November	1st to 10th	Night	26% 13% 31% 22% 7% 1	780
	11th to 20th	Night	27% 13% 27% 23% 10% 1	800
	21st to end	Night	32% 11% 31% 20% 7%	800
December	1st to 10th	Night	33% 14% 28% 20% 6%	800
	11th to 20th	Night	31% 13% 29% 21% 6% 1	800
	21st to end	Night	34% 12% 30% 20% 5%	880

Page generated at 2025-02-03 03:05:51. Version ac07

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