St-Placide
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the St-Placide clear sky chart from 2005-11-06 to 2024-11-30.

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% 9% 3 8% 5% 5% 5% 4 6% 7% 33%	101753
	Night	18% 11% 4 8% 5% 4 4 3 5% 6% 32%	97848
Transparency	Day	49% 6% 13% 21% 10% 1	105203
	Night	52% 6% 12% 19% 10% 1	102475
Seeing	Day	21% 12% 29% 24% 11% 3	14613
	Night	22% 10% 30% 28% 10% 1	23622

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	16% 17% 4 13% 6% 5% 4 3 4 4 23%	2517
	11th to 20th	Day	15% 13% 6% 11% 6% 6% 5% 4 5% 7% 24%	2520
	21st to end	Day	14% 17% 5% 10% 6% 5% 5% 4 6% 6% 22%	2772
February	1st to 10th	Day	14% 17% 4 10% 6% 5% 5% 4 5% 5% 25%	1692
	11th to 20th	Day	14% 13% 5% 9% 7% 5% 4 4 6% 6% 27%	1739
	21st to end	Day	19% 14% 5% 9% 6% 5% 4 3 4 5% 27%	1570
March	1st to 10th	Day	20% 13% 4 10% 6% 4 4 3 4 5% 26%	3116
	11th to 20th	Day	11% 17% 5% 11% 6% 4 5% 3 5% 5% 27%	3320
	21st to end	Day	14% 7% 3 8% 5% 5% 4 4 5% 6% 39%	4131
April	1st to 10th	Day	21% 10% 3 7% 5% 4 4 3 5% 5% 33%	2280
	11th to 20th	Day	21% 9% 3 7% 4 4 4 3 5% 5% 35%	2254
	21st to end	Day	22% 9% 3 7% 5% 4 4 3 5% 5% 32%	2411
May	1st to 10th	Day	20% 9% 3 7% 5% 5% 5% 3 6% 7% 29%	4416
	11th to 20th	Day	17% 8% 3 8% 5% 5% 4 4 5% 7% 33%	4398
	21st to end	Day	15% 6% 2 6% 5% 5% 5% 4 7% 8% 37%	4837
June	1st to 10th	Day	20% 8% 2 7% 5% 4 5% 4 6% 7% 30%	2660
	11th to 20th	Day	14% 6% 3 7% 4 5% 5% 4 6% 8% 38%	2660
	21st to end	Day	18% 8% 3 7% 5% 5% 5% 4 7% 7% 30%	2660
July	1st to 10th	Day	11% 6% 2 8% 6% 5% 6% 4 6% 8% 36%	4440
	11th to 20th	Day	14% 5% 2 7% 4 5% 5% 4 8% 8% 37%	4440
	21st to end	Day	12% 5% 2 5% 4 4 5% 4 7% 9% 44%	4814
August	1st to 10th	Day	15% 6% 3 8% 5% 5% 6% 4 7% 9% 34%	4423
	11th to 20th	Day	14% 7% 3 7% 5% 4 4 4 6% 8% 38%	3972
	21st to end	Day	16% 4 2 6% 4 5% 5% 4 7% 8% 39%	4180
September	1st to 10th	Day	12% 6% 2 6% 5% 5% 5% 4 6% 9% 41%	2280
	11th to 20th	Day	12% 5% 2 5% 3 4 4 3 4 8% 49%	2218
	21st to end	Day	17% 5% 3 6% 4 4 3 3 6% 8% 41%	2090
October	1st to 10th	Day	20% 8% 2 7% 4 4 4 3 5% 6% 37%	1933
	11th to 20th	Day	20% 9% 3 8% 6% 5% 5% 4 5% 6% 30%	1880
	21st to end	Day	24% 10% 3 7% 4 4 4 3 6% 6% 28%	1881
November	1st to 10th	Day	16% 10% 3 7% 6% 4 5% 4 6% 7% 33%	1761
	11th to 20th	Day	18% 11% 3 8% 5% 5% 5% 4 5% 8% 29%	1692
	21st to end	Day	22% 11% 4 8% 4 6% 5% 4 6% 5% 23%	1598
December	1st to 10th	Day	24% 16% 5% 8% 4 5% 4 3 6% 5% 19%	1520
	11th to 20th	Day	21% 15% 4 8% 5% 4 5% 4 4 5% 25%	1906
	21st to end	Day	28% 17% 4 10% 5% 4 4 2 3 4 20%	2772
January	1st to 10th	Night	17% 17% 6% 10% 5% 5% 5% 3 5% 5% 22%	4429
	11th to 20th	Night	13% 14% 5% 13% 7% 6% 5% 4 6% 6% 22%	4440
	21st to end	Night	16% 18% 5% 11% 6% 5% 4 3 4 5% 23%	4884
February	1st to 10th	Night	15% 14% 5% 12% 6% 5% 5% 4 5% 6% 23%	2485
	11th to 20th	Night	14% 11% 4 10% 6% 5% 6% 4 6% 6% 28%	2326
	21st to end	Night	14% 16% 4 10% 5% 4 4 4 4 5% 30%	1884
March	1st to 10th	Night	20% 11% 3 8% 5% 4 5% 3 4 5% 32%	3724
	11th to 20th	Night	17% 18% 5% 10% 5% 4 4 3 4 5% 26%	3622
	21st to end	Night	13% 11% 3 9% 5% 5% 4 2 4 4 39%	3500
April	1st to 10th	Night	23% 10% 3 6% 5% 5% 4 3 5% 6% 32%	1900
	11th to 20th	Night	23% 8% 3 7% 4 4 4 3 5% 6% 34%	1875
	21st to end	Night	21% 8% 3 6% 5% 4 4 3 5% 6% 34%	1767
May	1st to 10th	Night	21% 9% 3 7% 5% 5% 4 4 6% 6% 31%	2553
	11th to 20th	Night	22% 8% 2 5% 4 3 4 3 4 6% 38%	2495
	21st to end	Night	16% 8% 3 7% 4 4 4 4 5% 8% 37%	2738
June	1st to 10th	Night	20% 6% 3 6% 5% 5% 6% 5% 7% 8% 30%	1520
	11th to 20th	Night	15% 7% 3 6% 5% 4 5% 4 5% 8% 40%	1520
	21st to end	Night	19% 7% 3 7% 4 4 5% 5% 5% 7% 35%	1520
July	1st to 10th	Night	14% 7% 3 7% 5% 5% 5% 4 7% 6% 35%	2520
	11th to 20th	Night	14% 6% 2 6% 5% 4 4 4 5% 9% 41%	2520
	21st to end	Night	12% 6% 2 6% 4 4 4 4 6% 7% 44%	2739
August	1st to 10th	Night	15% 7% 3 7% 4 4 4 4 6% 8% 38%	2506
	11th to 20th	Night	16% 7% 3 7% 4 5% 4 3 5% 7% 39%	2820
	21st to end	Night	16% 6% 2 7% 4 5% 5% 4 5% 7% 39%	3476
September	1st to 10th	Night	11% 5% 3 7% 5% 5% 5% 3 6% 8% 43%	1900
	11th to 20th	Night	15% 6% 2 4 4 2 3 3 4 8% 49%	1962
	21st to end	Night	17% 5% 2 5% 4 4 4 3 5% 6% 44%	2090
October	1st to 10th	Night	19% 7% 3 6% 5% 4 4 3 5% 7% 38%	2245
	11th to 20th	Night	20% 8% 3 8% 4 4 4 4 4 6% 34%	2299
	21st to end	Night	21% 9% 3 8% 5% 5% 4 3 5% 6% 29%	2717
November	1st to 10th	Night	19% 9% 3 7% 5% 4 5% 4 4 8% 32%	2537
	11th to 20th	Night	18% 9% 4 8% 6% 5% 5% 3 5% 5% 32%	2705
	21st to end	Night	22% 13% 4 10% 5% 4 4 3 4 6% 26%	2798
December	1st to 10th	Night	21% 15% 6% 9% 6% 4 4 4 5% 5% 21%	2660
	11th to 20th	Night	23% 15% 4 10% 5% 4 4 3 4 4 25%	3288
	21st to end	Night	29% 17% 4 9% 4 3 3 2 4 4 21%	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	62% 8% 12% 12% 5% 1	2518
	11th to 20th	Day	57% 6% 14% 15% 7% 1	2520
	21st to end	Day	60% 8% 13% 12% 5%	2772
February	1st to 10th	Day	60% 5% 10% 18% 5% 2	1692
	11th to 20th	Day	56% 6% 12% 16% 9% 1	1748
	21st to end	Day	60% 4 10% 14% 10% 2	1570
March	1st to 10th	Day	59% 7% 8% 17% 8% 1	3119
	11th to 20th	Day	56% 6% 12% 13% 10% 2	3320
	21st to end	Day	45% 5% 10% 19% 18% 2	4131
April	1st to 10th	Day	54% 5% 8% 19% 12% 2	2280
	11th to 20th	Day	49% 4 9% 20% 15% 2	2254
	21st to end	Day	54% 5% 9% 16% 13% 3	2411
May	1st to 10th	Day	52% 7% 10% 21% 9% 1	4430
	11th to 20th	Day	48% 9% 14% 19% 9% 2	4402
	21st to end	Day	42% 7% 13% 23% 13% 1	4837
June	1st to 10th	Day	51% 8% 9% 19% 12% 1	2660
	11th to 20th	Day	43% 8% 11% 22% 14% 3	2660
	21st to end	Day	51% 8% 12% 18% 10% 1	2660
July	1st to 10th	Day	44% 5% 13% 26% 11% 1	4370
	11th to 20th	Day	41% 5% 15% 29% 9%	4365
	21st to end	Day	37% 6% 14% 34% 10%	4661
August	1st to 10th	Day	47% 6% 16% 23% 9%	4409
	11th to 20th	Day	43% 6% 16% 29% 6%	4014
	21st to end	Day	41% 5% 18% 22% 14% 1	4180
September	1st to 10th	Day	37% 7% 15% 27% 13%	2280
	11th to 20th	Day	34% 7% 13% 31% 14% 1	2218
	21st to end	Day	42% 6% 14% 26% 11% 1	2090
October	1st to 10th	Day	48% 4 12% 28% 9%	3206
	11th to 20th	Day	45% 4 17% 27% 7%	3096
	21st to end	Day	46% 4 20% 22% 8% 1	3081
November	1st to 10th	Day	48% 7% 15% 21% 8% 1	1761
	11th to 20th	Day	53% 6% 12% 18% 11%	1692
	21st to end	Day	61% 8% 14% 13% 4 1	1598
December	1st to 10th	Day	67% 7% 11% 12% 4	1520
	11th to 20th	Day	60% 7% 13% 15% 5%	1906
	21st to end	Day	69% 6% 9% 11% 5%	2772
January	1st to 10th	Night	62% 8% 14% 11% 4	4429
	11th to 20th	Night	59% 8% 15% 13% 4 1	4440
	21st to end	Night	62% 7% 12% 11% 7% 1	4884
February	1st to 10th	Night	60% 8% 10% 16% 6% 1	2485
	11th to 20th	Night	53% 7% 13% 18% 8% 1	2328
	21st to end	Night	55% 5% 9% 17% 13% 1	1884
March	1st to 10th	Night	53% 6% 10% 18% 9% 3	3734
	11th to 20th	Night	59% 6% 10% 13% 10% 2	3623
	21st to end	Night	47% 3 8% 22% 16% 3	3500
April	1st to 10th	Night	53% 5% 9% 17% 14% 2	1900
	11th to 20th	Night	51% 5% 8% 20% 14% 2	1875
	21st to end	Night	51% 5% 8% 17% 14% 4	1767
May	1st to 10th	Night	52% 7% 11% 19% 9% 3	2559
	11th to 20th	Night	46% 8% 11% 20% 12% 2	2496
	21st to end	Night	44% 7% 10% 19% 18% 1	2739
June	1st to 10th	Night	49% 8% 11% 19% 12% 1	1520
	11th to 20th	Night	42% 7% 11% 21% 16% 2	1520
	21st to end	Night	48% 8% 12% 19% 13% 1	1520
July	1st to 10th	Night	47% 5% 14% 21% 13%	2480
	11th to 20th	Night	41% 5% 17% 29% 9%	2472
	21st to end	Night	39% 5% 17% 25% 13%	2651
August	1st to 10th	Night	45% 5% 14% 27% 9%	2496
	11th to 20th	Night	45% 5% 17% 25% 8%	2844
	21st to end	Night	45% 5% 15% 21% 13% 1	3476
September	1st to 10th	Night	38% 8% 12% 25% 16% 1	1900
	11th to 20th	Night	35% 6% 13% 33% 13% 1	1962
	21st to end	Night	40% 7% 12% 27% 14%	2090
October	1st to 10th	Night	45% 4 13% 28% 9% 1	3752
	11th to 20th	Night	46% 4 13% 29% 8%	3810
	21st to end	Night	48% 4 18% 18% 12% 1	4467
November	1st to 10th	Night	51% 6% 13% 20% 9% 1	2537
	11th to 20th	Night	52% 6% 13% 17% 10% 2	2705
	21st to end	Night	60% 7% 11% 16% 6%	2798
December	1st to 10th	Night	64% 7% 11% 13% 4	2660
	11th to 20th	Night	62% 6% 8% 16% 6%	3288
	21st to end	Night	67% 5% 9% 14% 4	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	23% 14% 29% 27% 6% 1	180
	11th to 20th	Day	26% 19% 29% 20% 6% 1	180
	21st to end	Day	20% 16% 32% 24% 8% 1	198
February	1st to 10th	Day	30% 19% 33% 14% 3	262
	11th to 20th	Day	21% 16% 40% 21% 2	346
	21st to end	Day	29% 13% 31% 25% 2	382
March	1st to 10th	Day	24% 13% 33% 24% 6%	460
	11th to 20th	Day	19% 20% 34% 20% 5% 1	460
	21st to end	Day	25% 15% 31% 18% 11% 1	506
April	1st to 10th	Day	27% 15% 28% 20% 8% 2	460
	11th to 20th	Day	26% 17% 27% 17% 10% 2	452
	21st to end	Day	27% 16% 29% 19% 8% 2	460
May	1st to 10th	Day	22% 12% 31% 25% 8% 2	463
	11th to 20th	Day	18% 9% 33% 26% 12% 2	487
	21st to end	Day	18% 12% 30% 27% 10% 3	529
June	1st to 10th	Day	22% 11% 25% 29% 10% 2	490
	11th to 20th	Day	16% 13% 27% 29% 15% 2	490
	21st to end	Day	24% 8% 28% 23% 13% 4	490
July	1st to 10th	Day	12% 10% 27% 30% 18% 5%	485
	11th to 20th	Day	16% 6% 28% 31% 15% 4	484
	21st to end	Day	14% 6% 26% 33% 17% 3	532
August	1st to 10th	Day	16% 5% 25% 31% 19% 4	486
	11th to 20th	Day	13% 5% 23% 31% 19% 9%	479
	21st to end	Day	14% 7% 29% 26% 17% 8%	539
September	1st to 10th	Day	15% 8% 28% 26% 17% 7%	490
	11th to 20th	Day	12% 8% 23% 25% 22% 11%	490
	21st to end	Day	18% 10% 27% 22% 18% 5%	490
October	1st to 10th	Day	21% 11% 28% 22% 13% 4	490
	11th to 20th	Day	21% 17% 28% 22% 11% 1	479
	21st to end	Day	29% 14% 27% 23% 7%	429
November	1st to 10th	Day	28% 15% 24% 23% 9% 1	395
	11th to 20th	Day	22% 21% 34% 19% 4	292
	21st to end	Day	27% 20% 29% 20% 5%	200
December	1st to 10th	Day	32% 12% 27% 21% 8% 1	180
	11th to 20th	Day	27% 13% 38% 17% 3 1	180
	21st to end	Day	34% 18% 29% 14% 5% 2	198
January	1st to 10th	Night	25% 12% 33% 25% 4	760
	11th to 20th	Night	27% 13% 31% 23% 5%	760
	21st to end	Night	18% 11% 37% 26% 7% 1	836
February	1st to 10th	Night	21% 12% 37% 25% 5%	760
	11th to 20th	Night	19% 13% 40% 24% 4	743
	21st to end	Night	23% 10% 35% 28% 4	628
March	1st to 10th	Night	24% 13% 31% 28% 5%	760
	11th to 20th	Night	24% 14% 31% 24% 5% 1	760
	21st to end	Night	22% 11% 32% 28% 8%	836
April	1st to 10th	Night	27% 11% 28% 28% 6%	760
	11th to 20th	Night	24% 13% 30% 27% 6% 1	751
	21st to end	Night	26% 10% 30% 25% 9%	627
May	1st to 10th	Night	24% 6% 35% 25% 8% 2	406
	11th to 20th	Night	22% 5% 30% 33% 9% 1	374
	21st to end	Night	14% 7% 36% 34% 9%	411
June	1st to 10th	Night	24% 4 29% 31% 10% 1	380
	11th to 20th	Night	18% 5% 29% 34% 13% 1	380
	21st to end	Night	20% 5% 28% 31% 16% 1	380
July	1st to 10th	Night	12% 4 28% 38% 17% 1	370
	11th to 20th	Night	12% 3 25% 43% 17%	368
	21st to end	Night	13% 2 24% 42% 17% 1	416
August	1st to 10th	Night	15% 3 18% 44% 20% 1	378
	11th to 20th	Night	15% 3 21% 33% 25% 3	570
	21st to end	Night	15% 4 24% 35% 20% 2	836
September	1st to 10th	Night	13% 6% 26% 39% 16% 1	760
	11th to 20th	Night	17% 5% 20% 33% 23% 2	760
	21st to end	Night	19% 6% 26% 30% 18% 2	760
October	1st to 10th	Night	21% 7% 28% 30% 13%	760
	11th to 20th	Night	23% 10% 29% 27% 10% 1	760
	21st to end	Night	27% 11% 30% 27% 5%	836
November	1st to 10th	Night	26% 13% 28% 25% 8%	780
	11th to 20th	Night	23% 15% 33% 21% 9%	800
	21st to end	Night	29% 16% 30% 18% 7% 1	800
December	1st to 10th	Night	31% 12% 31% 21% 5%	760
	11th to 20th	Night	29% 15% 32% 19% 5% 1	760
	21st to end	Night	34% 13% 30% 17% 5%	836

Page generated at 2024-11-27 17:30:53. Version ac07

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