Mont St-Alex
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mont St-Alex clear sky chart from 2005-11-06 to 2025-01-22.

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% 4 8% 5% 5% 5% 4 6% 7% 30%	105240
	Night	19% 13% 4 9% 5% 4 4 3 5% 5% 28%	104133
Transparency	Day	53% 3 13% 22% 8% 1	108714
	Night	58% 3 10% 19% 9% 1	108748
Seeing	Day	24% 9% 27% 24% 13% 3	14806
	Night	26% 8% 26% 29% 10% 1	23866

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	19% 19% 6% 13% 6% 5% 4 3 4 4 18%	2597
	11th to 20th	Day	15% 16% 7% 15% 7% 5% 4 3 5% 5% 18%	2600
	21st to end	Day	15% 17% 6% 10% 7% 6% 5% 4 5% 6% 19%	2780
February	1st to 10th	Day	18% 15% 5% 10% 7% 6% 5% 4 4 5% 20%	1644
	11th to 20th	Day	15% 17% 6% 10% 6% 4 5% 4 5% 5% 24%	1796
	21st to end	Day	16% 16% 5% 7% 7% 5% 5% 4 5% 6% 24%	1570
March	1st to 10th	Day	19% 13% 4 9% 6% 5% 5% 3 5% 5% 25%	3116
	11th to 20th	Day	16% 18% 4 10% 5% 5% 4 3 4 6% 25%	3267
	21st to end	Day	16% 11% 4 8% 4 4 4 3 4 5% 36%	4166
April	1st to 10th	Day	23% 12% 3 7% 6% 4 4 4 4 5% 29%	2280
	11th to 20th	Day	21% 9% 3 7% 4 4 4 2 4 7% 35%	2254
	21st to end	Day	23% 10% 3 6% 5% 4 4 3 4 6% 32%	2456
May	1st to 10th	Day	23% 9% 3 7% 4 4 5% 4 5% 6% 29%	4287
	11th to 20th	Day	18% 8% 3 8% 5% 6% 5% 4 6% 7% 30%	4398
	21st to end	Day	14% 7% 3 7% 5% 5% 6% 4 7% 9% 34%	4837
June	1st to 10th	Day	23% 7% 2 7% 5% 4 5% 4 6% 7% 30%	2660
	11th to 20th	Day	16% 6% 2 6% 4 5% 5% 4 6% 8% 37%	2660
	21st to end	Day	22% 8% 3 7% 4 5% 5% 4 5% 6% 32%	2660
July	1st to 10th	Day	12% 6% 3 7% 4 5% 6% 4 7% 10% 35%	4440
	11th to 20th	Day	13% 6% 2 6% 5% 5% 5% 5% 8% 9% 35%	4440
	21st to end	Day	13% 6% 2 6% 4 4 4 5% 6% 8% 42%	4814
August	1st to 10th	Day	16% 6% 3 8% 6% 5% 6% 5% 7% 9% 30%	4423
	11th to 20th	Day	14% 7% 3 6% 5% 4 5% 4 6% 8% 38%	3975
	21st to end	Day	15% 6% 2 6% 4 4 4 3 6% 8% 40%	4180
September	1st to 10th	Day	14% 6% 3 6% 4 4 4 4 5% 8% 43%	2280
	11th to 20th	Day	16% 6% 2 5% 3 4 4 2 5% 7% 47%	2176
	21st to end	Day	16% 7% 2 6% 4 4 4 3 6% 9% 39%	2090
October	1st to 10th	Day	22% 8% 2 6% 5% 5% 5% 4 6% 6% 31%	2001
	11th to 20th	Day	20% 9% 3 7% 5% 5% 4 5% 6% 6% 29%	1835
	21st to end	Day	26% 11% 2 7% 4 5% 4 3 4 5% 28%	1881
November	1st to 10th	Day	19% 13% 2 6% 5% 4 4 4 5% 5% 32%	1761
	11th to 20th	Day	18% 13% 4 9% 6% 5% 4 4 6% 6% 26%	1770
	21st to end	Day	22% 15% 4 8% 5% 4 4 4 5% 5% 21%	1600
December	1st to 10th	Day	19% 21% 8% 12% 7% 4 4 3 4 4 15%	2600
	11th to 20th	Day	21% 14% 6% 10% 5% 4 4 4 5% 5% 23%	2986
	21st to end	Day	23% 16% 5% 10% 6% 5% 5% 5% 6% 4 15%	3960
January	1st to 10th	Night	18% 21% 7% 12% 5% 4 4 3 3 5% 19%	4569
	11th to 20th	Night	13% 17% 7% 15% 8% 6% 5% 4 5% 4 16%	4580
	21st to end	Night	20% 18% 5% 10% 7% 4 3 3 3 4 23%	4899
February	1st to 10th	Night	18% 17% 6% 13% 6% 5% 4 3 5% 5% 18%	2532
	11th to 20th	Night	15% 14% 5% 12% 8% 5% 4 3 5% 5% 23%	2270
	21st to end	Night	17% 15% 4 10% 6% 4 4 3 4 5% 29%	1884
March	1st to 10th	Night	23% 12% 3 8% 5% 4 4 3 4 4 30%	3724
	11th to 20th	Night	20% 19% 4 9% 5% 3 4 2 3 4 26%	3689
	21st to end	Night	15% 13% 4 9% 5% 4 4 3 4 4 34%	3466
April	1st to 10th	Night	23% 11% 3 7% 6% 4 4 3 5% 5% 28%	1900
	11th to 20th	Night	23% 11% 3 7% 5% 3 3 3 4 5% 32%	1875
	21st to end	Night	22% 10% 4 7% 4 3 4 3 4 5% 35%	1724
May	1st to 10th	Night	24% 9% 3 8% 4 5% 4 4 5% 7% 28%	2683
	11th to 20th	Night	22% 10% 3 8% 4 4 4 3 4 7% 33%	2495
	21st to end	Night	17% 7% 3 7% 4 5% 4 4 5% 8% 37%	2738
June	1st to 10th	Night	25% 7% 2 6% 4 4 5% 4 5% 7% 31%	1520
	11th to 20th	Night	17% 6% 2 6% 5% 4 4 3 7% 8% 37%	1520
	21st to end	Night	19% 9% 3 6% 5% 4 4 4 5% 8% 33%	1520
July	1st to 10th	Night	13% 8% 3 9% 5% 5% 5% 4 6% 8% 34%	2520
	11th to 20th	Night	14% 6% 2 6% 4 5% 5% 4 6% 8% 40%	2520
	21st to end	Night	13% 6% 2 7% 6% 6% 5% 4 5% 7% 39%	2739
August	1st to 10th	Night	19% 8% 3 8% 4 5% 4 3 5% 7% 34%	2506
	11th to 20th	Night	16% 7% 3 7% 5% 4 5% 4 6% 7% 35%	2805
	21st to end	Night	17% 6% 3 6% 4 4 4 4 5% 7% 41%	3476
September	1st to 10th	Night	14% 7% 2 6% 5% 4 4 4 5% 7% 42%	1900
	11th to 20th	Night	15% 6% 2 6% 3 3 3 3 5% 6% 48%	2004
	21st to end	Night	18% 6% 3 6% 4 4 4 3 5% 6% 41%	2090
October	1st to 10th	Night	20% 7% 3 7% 5% 4 4 3 6% 6% 35%	2175
	11th to 20th	Night	22% 10% 3 8% 4 4 3 3 5% 5% 32%	2343
	21st to end	Night	26% 11% 3 8% 4 4 4 3 4 5% 28%	2717
November	1st to 10th	Night	20% 12% 4 7% 4 4 6% 4 5% 6% 30%	2537
	11th to 20th	Night	20% 11% 3 10% 4 4 4 4 4 5% 30%	2629
	21st to end	Night	23% 15% 4 9% 5% 5% 4 3 4 5% 24%	2800
December	1st to 10th	Night	19% 24% 7% 13% 6% 4 4 3 3 4 13%	4580
	11th to 20th	Night	24% 16% 5% 12% 5% 4 4 2 4 3 22%	5208
	21st to end	Night	23% 17% 5% 10% 5% 4 4 4 7% 4 18%	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% 1 11% 14% 1	2598
	11th to 20th	Day	70% 1 13% 12% 4	2600
	21st to end	Day	67% 3 15% 12% 3	2780
February	1st to 10th	Day	67% 3 10% 16% 4 1	1644
	11th to 20th	Day	64% 2 12% 17% 5% 1	1805
	21st to end	Day	61% 2 12% 16% 8% 1	1570
March	1st to 10th	Day	62% 2 9% 20% 6% 1	3119
	11th to 20th	Day	63% 2 11% 14% 9% 1	3267
	21st to end	Day	53% 2 7% 23% 15% 1	4166
April	1st to 10th	Day	59% 3 8% 20% 9% 1	2280
	11th to 20th	Day	52% 2 8% 23% 12% 2	2254
	21st to end	Day	56% 3 11% 18% 10% 3	2456
May	1st to 10th	Day	57% 2 10% 21% 9% 1	4301
	11th to 20th	Day	54% 3 16% 18% 8% 1	4402
	21st to end	Day	46% 4 13% 25% 11% 1	4837
June	1st to 10th	Day	53% 3 11% 21% 10% 1	2660
	11th to 20th	Day	44% 5% 12% 25% 13% 2	2660
	21st to end	Day	53% 4 12% 22% 9% 1	2660
July	1st to 10th	Day	42% 5% 15% 29% 9%	4370
	11th to 20th	Day	42% 6% 16% 31% 5%	4365
	21st to end	Day	40% 5% 15% 32% 8%	4661
August	1st to 10th	Day	50% 5% 17% 21% 7%	4409
	11th to 20th	Day	44% 5% 20% 25% 6%	4015
	21st to end	Day	41% 4 18% 22% 14%	4180
September	1st to 10th	Day	41% 4 14% 29% 11% 1	2280
	11th to 20th	Day	38% 3 12% 34% 13%	2176
	21st to end	Day	43% 5% 15% 27% 10% 1	2090
October	1st to 10th	Day	45% 4 13% 31% 7%	3326
	11th to 20th	Day	48% 4 17% 26% 5%	3025
	21st to end	Day	50% 3 18% 23% 6% 1	3081
November	1st to 10th	Day	55% 3 12% 22% 7% 1	1761
	11th to 20th	Day	59% 3 12% 16% 10%	1770
	21st to end	Day	65% 4 14% 14% 3	1600
December	1st to 10th	Day	75% 4 9% 11% 2	2600
	11th to 20th	Day	64% 3 10% 17% 6%	2986
	21st to end	Day	70% 3 10% 12% 5%	3960
January	1st to 10th	Night	70% 1 14% 12% 2	4569
	11th to 20th	Night	71% 2 10% 13% 3	4580
	21st to end	Night	69% 2 11% 12% 5%	4899
February	1st to 10th	Night	69% 2 8% 15% 5% 1	2532
	11th to 20th	Night	64% 3 9% 18% 6%	2272
	21st to end	Night	61% 2 9% 16% 10% 2	1884
March	1st to 10th	Night	58% 2 9% 20% 9% 3	3734
	11th to 20th	Night	64% 2 7% 16% 10% 1	3690
	21st to end	Night	56% 1 5% 24% 11% 2	3466
April	1st to 10th	Night	60% 2 7% 19% 11% 1	1900
	11th to 20th	Night	56% 2 6% 22% 13% 1	1875
	21st to end	Night	53% 3 8% 19% 14% 3	1724
May	1st to 10th	Night	57% 2 10% 20% 9% 2	2689
	11th to 20th	Night	53% 2 11% 22% 10% 2	2496
	21st to end	Night	46% 4 10% 21% 18% 1	2739
June	1st to 10th	Night	53% 3 10% 22% 10% 1	1520
	11th to 20th	Night	45% 4 12% 22% 14% 3	1520
	21st to end	Night	49% 5% 12% 21% 11% 1	1520
July	1st to 10th	Night	48% 5% 12% 22% 12%	2480
	11th to 20th	Night	42% 5% 15% 29% 9%	2472
	21st to end	Night	45% 5% 15% 22% 13%	2651
August	1st to 10th	Night	50% 5% 13% 24% 8%	2496
	11th to 20th	Night	48% 6% 17% 21% 8%	2831
	21st to end	Night	43% 5% 12% 24% 15% 1	3476
September	1st to 10th	Night	42% 4 12% 28% 14% 1	1900
	11th to 20th	Night	37% 3 14% 32% 13% 1	2004
	21st to end	Night	44% 4 11% 26% 14% 1	2090
October	1st to 10th	Night	48% 4 12% 26% 9%	3630
	11th to 20th	Night	49% 2 10% 29% 9%	3892
	21st to end	Night	53% 3 13% 20% 11% 1	4467
November	1st to 10th	Night	55% 3 12% 22% 7% 1	2537
	11th to 20th	Night	57% 3 10% 19% 9% 2	2629
	21st to end	Night	65% 2 12% 17% 5%	2800
December	1st to 10th	Night	77% 3 9% 9% 2	4580
	11th to 20th	Night	70% 2 6% 15% 7%	5208
	21st to end	Night	67% 2 9% 14% 8%	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	31% 12% 26% 22% 9% 2	200
	11th to 20th	Day	30% 13% 35% 17% 6% 1	200
	21st to end	Day	21% 11% 36% 21% 10% 2	200
February	1st to 10th	Day	33% 18% 31% 14% 5%	239
	11th to 20th	Day	26% 15% 34% 19% 6%	404
	21st to end	Day	27% 13% 30% 26% 5%	382
March	1st to 10th	Day	30% 8% 26% 28% 7%	460
	11th to 20th	Day	28% 9% 35% 21% 6% 2	460
	21st to end	Day	30% 14% 24% 22% 9% 1	506
April	1st to 10th	Day	31% 11% 26% 20% 10% 2	460
	11th to 20th	Day	32% 14% 26% 16% 8% 5%	452
	21st to end	Day	31% 9% 30% 17% 11% 2	460
May	1st to 10th	Day	28% 10% 29% 19% 13% 2	463
	11th to 20th	Day	19% 9% 28% 28% 11% 4	487
	21st to end	Day	19% 7% 33% 26% 13% 2	529
June	1st to 10th	Day	25% 8% 24% 30% 11% 2	490
	11th to 20th	Day	19% 8% 25% 30% 16% 3	490
	21st to end	Day	23% 8% 30% 23% 13% 3	490
July	1st to 10th	Day	15% 4 24% 36% 17% 5%	485
	11th to 20th	Day	18% 4 27% 30% 16% 5%	484
	21st to end	Day	19% 5% 20% 33% 19% 3	532
August	1st to 10th	Day	17% 4 23% 30% 21% 5%	486
	11th to 20th	Day	18% 4 20% 32% 20% 7%	479
	21st to end	Day	18% 7% 23% 25% 19% 9%	539
September	1st to 10th	Day	16% 7% 25% 26% 17% 8%	490
	11th to 20th	Day	16% 6% 19% 24% 22% 13%	490
	21st to end	Day	18% 6% 26% 23% 20% 7%	490
October	1st to 10th	Day	22% 7% 29% 19% 17% 5%	490
	11th to 20th	Day	29% 12% 26% 20% 12% 2	455
	21st to end	Day	36% 11% 22% 23% 8%	429
November	1st to 10th	Day	31% 14% 27% 21% 7%	395
	11th to 20th	Day	29% 14% 26% 18% 10% 2	370
	21st to end	Day	33% 17% 24% 20% 6% 1	200
December	1st to 10th	Day	38% 10% 23% 20% 8% 2	200
	11th to 20th	Day	27% 17% 36% 15% 6%	200
	21st to end	Day	34% 14% 26% 19% 5% 3	220
January	1st to 10th	Night	30% 11% 30% 23% 5% 1	800
	11th to 20th	Night	27% 11% 32% 23% 7%	800
	21st to end	Night	24% 8% 29% 30% 8% 1	841
February	1st to 10th	Night	27% 8% 32% 27% 5%	760
	11th to 20th	Night	23% 11% 33% 28% 4 1	743
	21st to end	Night	26% 10% 31% 28% 5%	628
March	1st to 10th	Night	27% 10% 27% 30% 6%	760
	11th to 20th	Night	30% 10% 27% 25% 8%	760
	21st to end	Night	28% 10% 27% 25% 8% 1	836
April	1st to 10th	Night	30% 9% 27% 28% 7%	760
	11th to 20th	Night	29% 11% 27% 23% 8%	751
	21st to end	Night	28% 10% 27% 27% 7% 1	584
May	1st to 10th	Night	26% 5% 31% 25% 11% 1	484
	11th to 20th	Night	24% 5% 28% 32% 10% 1	374
	21st to end	Night	19% 5% 29% 36% 9%	411
June	1st to 10th	Night	29% 5% 23% 32% 11% 1	380
	11th to 20th	Night	21% 3 27% 34% 16% 1	380
	21st to end	Night	22% 4 24% 37% 13% 1	380
July	1st to 10th	Night	14% 3 25% 43% 14% 1	370
	11th to 20th	Night	13% 1 18% 49% 17% 1	368
	21st to end	Night	15% 2 19% 48% 15%	416
August	1st to 10th	Night	16% 2 16% 40% 23% 2	378
	11th to 20th	Night	18% 3 17% 38% 23% 2	570
	21st to end	Night	19% 3 16% 38% 22% 2	836
September	1st to 10th	Night	17% 6% 19% 40% 16% 2	760
	11th to 20th	Night	17% 5% 17% 33% 24% 4	760
	21st to end	Night	22% 5% 26% 28% 18% 3	760
October	1st to 10th	Night	24% 4 25% 29% 16% 1	760
	11th to 20th	Night	29% 6% 26% 29% 9% 1	760
	21st to end	Night	33% 6% 29% 24% 7%	836
November	1st to 10th	Night	28% 12% 28% 24% 7% 1	780
	11th to 20th	Night	27% 12% 27% 25% 9% 1	800
	21st to end	Night	33% 10% 30% 20% 6%	800
December	1st to 10th	Night	35% 11% 27% 21% 6% 1	800
	11th to 20th	Night	33% 10% 28% 21% 6% 1	800
	21st to end	Night	35% 9% 29% 21% 5%	880

Page generated at 2025-01-19 03:06:45. Version ac07

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