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 2026-02-16.

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	16% 10% 3 8% 5% 5% 5% 4 6% 7% 32%	130948
	Night	17% 11% 4 9% 5% 5% 4 3 5% 6% 30%	129899
Transparency	Day	51% 5% 12% 21% 10% 1	134380
	Night	55% 5% 11% 19% 10% 1	134542
Seeing	Day	21% 13% 29% 23% 11% 3	16044
	Night	22% 10% 30% 27% 9% 1	25171

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	14% 18% 5% 14% 5% 5% 4 3 5% 5% 22%	4661
	11th to 20th	Day	12% 17% 6% 12% 7% 6% 4 3 5% 6% 21%	4650
	21st to end	Day	9% 14% 5% 13% 9% 7% 6% 4 5% 5% 23%	5124
February	1st to 10th	Day	13% 16% 4 10% 6% 5% 5% 4 5% 6% 26%	1871
	11th to 20th	Day	14% 12% 5% 10% 8% 5% 4 3 6% 6% 27%	1879
	21st to end	Day	19% 14% 5% 8% 6% 5% 4 3 4 5% 27%	1650
March	1st to 10th	Day	18% 13% 5% 12% 6% 4 4 3 4 5% 25%	4476
	11th to 20th	Day	10% 13% 4 10% 6% 4 5% 4 6% 7% 31%	4750
	21st to end	Day	19% 9% 4 9% 5% 4 4 3 4 5% 35%	5921
April	1st to 10th	Day	21% 11% 3 7% 5% 4 4 3 5% 5% 33%	2400
	11th to 20th	Day	20% 9% 3 7% 4 4 4 3 5% 5% 35%	2374
	21st to end	Day	22% 9% 3 7% 5% 4 4 3 5% 6% 32%	2538
May	1st to 10th	Day	25% 10% 3 9% 5% 5% 5% 3 6% 6% 22%	6336
	11th to 20th	Day	18% 9% 3 9% 5% 5% 4 4 5% 7% 31%	6318
	21st to end	Day	21% 8% 3 7% 4 5% 4 4 6% 6% 31%	6949
June	1st to 10th	Day	20% 8% 2 7% 5% 4 5% 4 6% 7% 30%	2800
	11th to 20th	Day	14% 6% 3 6% 4 5% 6% 4 6% 8% 38%	2800
	21st to end	Day	18% 8% 3 7% 5% 5% 5% 4 7% 7% 31%	2800
July	1st to 10th	Day	12% 7% 3 8% 5% 6% 6% 4 6% 8% 34%	6360
	11th to 20th	Day	12% 5% 2 7% 4 5% 5% 4 7% 8% 42%	6360
	21st to end	Day	11% 5% 2 5% 4 4 5% 4 7% 10% 46%	6926
August	1st to 10th	Day	14% 6% 2 8% 5% 5% 6% 4 7% 9% 35%	4563
	11th to 20th	Day	14% 7% 3 7% 5% 4 4 4 6% 8% 39%	4100
	21st to end	Day	16% 4 2 6% 4 5% 5% 4 7% 9% 40%	4312
September	1st to 10th	Day	12% 6% 2 5% 5% 5% 5% 4 6% 9% 42%	2400
	11th to 20th	Day	12% 5% 2 5% 3 4 4 3 4 8% 50%	2335
	21st to end	Day	17% 5% 3 6% 4 4 3 3 6% 8% 41%	2200
October	1st to 10th	Day	19% 7% 2 7% 4 4 4 3 5% 6% 39%	2035
	11th to 20th	Day	19% 9% 3 8% 6% 5% 5% 4 5% 6% 31%	1979
	21st to end	Day	24% 10% 3 7% 4 4 4 3 6% 6% 28%	1980
November	1st to 10th	Day	16% 10% 3 7% 6% 4 4 4 6% 6% 32%	1851
	11th to 20th	Day	18% 11% 3 8% 5% 5% 5% 4 5% 7% 28%	1776
	21st to end	Day	23% 12% 4 8% 4 6% 6% 4 6% 5% 23%	1680
December	1st to 10th	Day	20% 21% 5% 9% 4 4 4 4 6% 5% 17%	2680
	11th to 20th	Day	18% 15% 5% 10% 5% 5% 5% 4 4 4 26%	3066
	21st to end	Day	23% 14% 4 10% 5% 4 5% 3 4 4 23%	4048
January	1st to 10th	Night	14% 19% 8% 13% 5% 4 4 3 4 5% 21%	8234
	11th to 20th	Night	12% 17% 7% 17% 8% 6% 4 3 5% 5% 17%	8235
	21st to end	Night	11% 14% 5% 12% 8% 6% 5% 4 5% 6% 25%	9057
February	1st to 10th	Night	14% 14% 5% 12% 6% 4 5% 5% 5% 6% 24%	2746
	11th to 20th	Night	13% 11% 4 10% 6% 5% 5% 4 6% 6% 28%	2517
	21st to end	Night	14% 16% 4 10% 5% 4 4 4 4 5% 30%	1980
March	1st to 10th	Night	21% 13% 4 8% 5% 3 5% 3 4 4 29%	5364
	11th to 20th	Night	14% 14% 4 8% 4 5% 5% 4 6% 7% 30%	5192
	21st to end	Night	16% 11% 4 9% 5% 5% 5% 3 4 5% 32%	5010
April	1st to 10th	Night	22% 10% 3 6% 5% 5% 4 3 5% 6% 32%	2000
	11th to 20th	Night	22% 8% 3 7% 4 4 4 3 5% 6% 33%	1975
	21st to end	Night	22% 8% 3 6% 5% 4 4 3 5% 6% 34%	1860
May	1st to 10th	Night	24% 9% 3 8% 5% 5% 5% 4 6% 6% 25%	3647
	11th to 20th	Night	22% 9% 3 7% 4 4 4 3 4 7% 34%	3575
	21st to end	Night	19% 10% 4 9% 5% 4 4 4 5% 7% 31%	3926
June	1st to 10th	Night	20% 7% 3 6% 5% 5% 6% 5% 7% 8% 30%	1600
	11th to 20th	Night	15% 7% 3 6% 5% 4 5% 4 6% 8% 39%	1600
	21st to end	Night	18% 7% 3 7% 4 4 5% 5% 5% 7% 36%	1600
July	1st to 10th	Night	14% 6% 3 7% 5% 6% 6% 5% 8% 8% 33%	3600
	11th to 20th	Night	14% 6% 2 6% 5% 4 4 3 5% 8% 41%	3600
	21st to end	Night	10% 5% 2 6% 4 4 4 4 6% 8% 46%	3926
August	1st to 10th	Night	15% 7% 3 7% 4 4 4 4 6% 8% 39%	2586
	11th to 20th	Night	16% 7% 3 7% 4 5% 4 3 5% 7% 40%	2910
	21st to end	Night	16% 6% 2 7% 4 5% 5% 4 5% 7% 39%	3586
September	1st to 10th	Night	11% 5% 3 7% 5% 5% 5% 3 6% 8% 44%	2000
	11th to 20th	Night	14% 6% 2 4 4 2 3 3 4 8% 50%	2065
	21st to end	Night	17% 6% 2 6% 4 4 4 3 5% 6% 44%	2200
October	1st to 10th	Night	18% 7% 3 5% 5% 4 4 3 5% 7% 39%	2363
	11th to 20th	Night	20% 8% 3 8% 4 4 4 4 4 6% 35%	2420
	21st to end	Night	21% 9% 3 8% 5% 5% 4 3 5% 6% 30%	2860
November	1st to 10th	Night	20% 9% 3 6% 5% 4 5% 4 4 7% 32%	2667
	11th to 20th	Night	18% 9% 4 8% 5% 5% 5% 3 5% 5% 32%	2840
	21st to end	Night	22% 13% 4 10% 5% 4 4 3 4 6% 25%	2940
December	1st to 10th	Night	18% 17% 6% 11% 6% 5% 5% 4 5% 5% 19%	4720
	11th to 20th	Night	23% 15% 4 10% 5% 4 4 3 4 6% 22%	5348
	21st to end	Night	25% 16% 4 9% 4 3 3 3 5% 4 23%	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	64% 5% 10% 17% 4	4662
	11th to 20th	Day	64% 3 8% 14% 10% 1	4680
	21st to end	Day	63% 4 9% 11% 11% 1	5124
February	1st to 10th	Day	59% 4 9% 19% 6% 2	1871
	11th to 20th	Day	57% 6% 12% 16% 9% 1	1888
	21st to end	Day	60% 4 9% 15% 10% 2	1650
March	1st to 10th	Day	62% 5% 7% 13% 11% 3	4479
	11th to 20th	Day	51% 5% 18% 14% 11% 2	4750
	21st to end	Day	52% 4 8% 16% 18% 2	5921
April	1st to 10th	Day	53% 5% 8% 19% 13% 2	2400
	11th to 20th	Day	50% 4 9% 20% 16% 2	2374
	21st to end	Day	53% 4 9% 17% 13% 3	2538
May	1st to 10th	Day	61% 5% 8% 18% 7% 1	6347
	11th to 20th	Day	52% 7% 13% 18% 9% 2	6322
	21st to end	Day	51% 5% 12% 19% 12% 1	6949
June	1st to 10th	Day	51% 8% 9% 19% 13% 1	2800
	11th to 20th	Day	42% 8% 11% 22% 14% 3	2800
	21st to end	Day	50% 8% 12% 19% 10% 1	2800
July	1st to 10th	Day	48% 4 13% 26% 9%	6290
	11th to 20th	Day	40% 4 13% 30% 13%	6285
	21st to end	Day	36% 4 14% 37% 9%	6728
August	1st to 10th	Day	46% 5% 16% 24% 9%	4549
	11th to 20th	Day	43% 5% 16% 29% 6%	4142
	21st to end	Day	41% 5% 18% 22% 14% 1	4312
September	1st to 10th	Day	37% 7% 15% 29% 13%	2400
	11th to 20th	Day	34% 7% 12% 32% 15% 1	2335
	21st to end	Day	42% 6% 14% 26% 12% 1	2200
October	1st to 10th	Day	47% 4 11% 28% 10%	3308
	11th to 20th	Day	45% 4 16% 27% 7%	3195
	21st to end	Day	46% 4 19% 22% 8% 1	3180
November	1st to 10th	Day	49% 6% 15% 21% 8% 1	1851
	11th to 20th	Day	55% 6% 12% 17% 10%	1776
	21st to end	Day	61% 7% 13% 13% 5% 1	1680
December	1st to 10th	Day	70% 4 10% 14% 3	2680
	11th to 20th	Day	62% 5% 9% 16% 8%	3066
	21st to end	Day	65% 4 9% 15% 7%	4048
January	1st to 10th	Night	66% 4 10% 14% 5%	8234
	11th to 20th	Night	70% 4 9% 11% 6%	8280
	21st to end	Night	60% 4 8% 14% 13% 1	9057
February	1st to 10th	Night	59% 7% 10% 16% 7% 1	2746
	11th to 20th	Night	54% 7% 13% 19% 8% 1	2519
	21st to end	Night	55% 5% 8% 18% 12% 1	1980
March	1st to 10th	Night	58% 5% 7% 14% 12% 4	5374
	11th to 20th	Night	53% 4 14% 15% 11% 3	5193
	21st to end	Night	55% 2 7% 21% 13% 2	5010
April	1st to 10th	Night	54% 4 9% 17% 14% 2	2000
	11th to 20th	Night	52% 5% 7% 19% 14% 2	1975
	21st to end	Night	51% 4 8% 18% 14% 4	1860
May	1st to 10th	Night	59% 5% 9% 17% 7% 2	3653
	11th to 20th	Night	52% 6% 10% 20% 11% 2	3576
	21st to end	Night	53% 5% 10% 17% 14% 1	3927
June	1st to 10th	Night	50% 7% 11% 19% 12% 1	1600
	11th to 20th	Night	42% 7% 11% 22% 16% 2	1600
	21st to end	Night	47% 8% 11% 19% 14% 1	1600
July	1st to 10th	Night	48% 3 16% 22% 10%	3560
	11th to 20th	Night	42% 3 15% 29% 10%	3552
	21st to end	Night	38% 4 15% 31% 13%	3809
August	1st to 10th	Night	44% 5% 15% 27% 9%	2576
	11th to 20th	Night	44% 5% 17% 25% 9%	2934
	21st to end	Night	45% 5% 15% 21% 13% 1	3586
September	1st to 10th	Night	38% 8% 12% 27% 16% 1	2000
	11th to 20th	Night	34% 6% 13% 34% 13% 1	2065
	21st to end	Night	40% 7% 12% 26% 15%	2200
October	1st to 10th	Night	45% 3 13% 28% 10% 1	3870
	11th to 20th	Night	46% 4 12% 29% 9%	3931
	21st to end	Night	48% 4 18% 19% 12% 1	4610
November	1st to 10th	Night	52% 5% 13% 21% 8% 1	2667
	11th to 20th	Night	53% 6% 13% 18% 10% 1	2840
	21st to end	Night	61% 6% 11% 16% 6%	2940
December	1st to 10th	Night	68% 4 12% 13% 4	4720
	11th to 20th	Night	64% 4 6% 15% 10%	5348
	21st to end	Night	64% 3 8% 13% 11%	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	24% 15% 31% 23% 6%	220
	11th to 20th	Day	30% 20% 28% 16% 5%	220
	21st to end	Day	22% 17% 31% 23% 7% 1	242
February	1st to 10th	Day	28% 21% 32% 16% 3	321
	11th to 20th	Day	23% 17% 38% 20% 2	396
	21st to end	Day	29% 14% 31% 24% 2	414
March	1st to 10th	Day	25% 14% 33% 23% 5%	500
	11th to 20th	Day	19% 20% 35% 19% 5% 1	500
	21st to end	Day	27% 16% 30% 17% 10% 1	550
April	1st to 10th	Day	29% 17% 26% 19% 8% 2	500
	11th to 20th	Day	27% 16% 28% 17% 10% 2	492
	21st to end	Day	28% 17% 29% 18% 7% 2	500
May	1st to 10th	Day	25% 12% 31% 24% 7% 2	503
	11th to 20th	Day	19% 10% 32% 25% 12% 2	527
	21st to end	Day	20% 12% 29% 27% 10% 3	573
June	1st to 10th	Day	22% 12% 26% 28% 10% 2	530
	11th to 20th	Day	16% 13% 27% 28% 14% 2	530
	21st to end	Day	24% 9% 29% 23% 12% 3	530
July	1st to 10th	Day	12% 11% 27% 28% 17% 5%	525
	11th to 20th	Day	15% 7% 28% 31% 15% 3	524
	21st to end	Day	14% 7% 27% 32% 16% 3	576
August	1st to 10th	Day	14% 5% 26% 31% 19% 5%	526
	11th to 20th	Day	13% 5% 24% 31% 19% 8%	519
	21st to end	Day	15% 7% 28% 26% 16% 8%	583
September	1st to 10th	Day	15% 8% 27% 26% 17% 8%	530
	11th to 20th	Day	11% 8% 22% 26% 23% 10%	530
	21st to end	Day	19% 10% 27% 22% 17% 5%	530
October	1st to 10th	Day	20% 11% 30% 22% 14% 4	530
	11th to 20th	Day	20% 18% 29% 22% 10% 1	518
	21st to end	Day	29% 15% 27% 23% 7%	462
November	1st to 10th	Day	30% 16% 23% 22% 8% 1	425
	11th to 20th	Day	24% 19% 33% 19% 5%	316
	21st to end	Day	30% 20% 26% 19% 5%	220
December	1st to 10th	Day	32% 13% 28% 19% 8%	220
	11th to 20th	Day	28% 15% 37% 15% 3 1	220
	21st to end	Day	32% 17% 31% 14% 5% 2	242
January	1st to 10th	Night	25% 13% 34% 24% 4	840
	11th to 20th	Night	29% 14% 30% 23% 5%	840
	21st to end	Night	19% 12% 37% 26% 7% 1	924
February	1st to 10th	Night	20% 13% 36% 26% 5%	840
	11th to 20th	Night	20% 13% 40% 23% 4	804
	21st to end	Night	23% 10% 36% 27% 4	660
March	1st to 10th	Night	24% 14% 30% 27% 5%	800
	11th to 20th	Night	24% 14% 32% 24% 5% 1	800
	21st to end	Night	23% 11% 31% 27% 8%	880
April	1st to 10th	Night	28% 12% 28% 27% 5%	800
	11th to 20th	Night	25% 13% 30% 26% 6% 1	791
	21st to end	Night	26% 10% 30% 25% 9%	660
May	1st to 10th	Night	25% 6% 35% 25% 7% 2	427
	11th to 20th	Night	23% 6% 29% 33% 9% 1	394
	21st to end	Night	15% 7% 35% 33% 9%	433
June	1st to 10th	Night	24% 5% 30% 31% 10% 1	400
	11th to 20th	Night	18% 6% 29% 34% 13% 1	400
	21st to end	Night	20% 6% 28% 31% 15% 1	400
July	1st to 10th	Night	12% 5% 28% 37% 17% 1	390
	11th to 20th	Night	13% 3 25% 42% 17%	388
	21st to end	Night	13% 3 24% 43% 16% 1	438
August	1st to 10th	Night	14% 3 18% 44% 19% 1	398
	11th to 20th	Night	14% 3 22% 33% 25% 3	600
	21st to end	Night	15% 4 25% 35% 19% 2	880
September	1st to 10th	Night	13% 6% 25% 39% 16% 1	800
	11th to 20th	Night	17% 5% 20% 34% 23% 2	800
	21st to end	Night	19% 6% 26% 30% 17% 2	800
October	1st to 10th	Night	21% 7% 29% 29% 14%	800
	11th to 20th	Night	23% 10% 31% 27% 9% 1	800
	21st to end	Night	27% 11% 31% 26% 5%	880
November	1st to 10th	Night	27% 13% 27% 25% 8%	820
	11th to 20th	Night	23% 15% 33% 21% 8%	840
	21st to end	Night	29% 15% 31% 18% 6%	840
December	1st to 10th	Night	30% 13% 31% 21% 4	840
	11th to 20th	Night	29% 16% 32% 18% 4 1	840
	21st to end	Night	34% 13% 30% 18% 5%	924

Page generated at 2026-02-13 01:42:15. Version ac07

Copyright © 2026 Attilla Danko.