Observatoire Plourde
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire Plourde clear sky chart from 2005-11-06 to 2024-11-05.

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% 13% 4 10% 6% 5% 5% 4 5% 6% 26%	101868
	Night	16% 15% 5% 11% 7% 5% 5% 4 5% 5% 23%	97250
Transparency	Day	58% 6% 10% 18% 8% 1	105325
	Night	62% 6% 9% 16% 7% 1	101883
Seeing	Day	25% 16% 32% 19% 7% 2	15232
	Night	24% 12% 31% 24% 8% 1	24126

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	15% 22% 7% 13% 6% 8% 8% 4 5% 3 8%	2208
	11th to 20th	Day	8% 15% 6% 19% 11% 7% 7% 6% 6% 5% 11%	2210
	21st to end	Day	10% 24% 10% 15% 6% 6% 5% 3 5% 5% 11%	2785
February	1st to 10th	Day	8% 15% 6% 13% 9% 9% 7% 5% 7% 6% 15%	1710
	11th to 20th	Day	9% 19% 6% 13% 9% 6% 6% 5% 6% 6% 16%	1663
	21st to end	Day	9% 18% 6% 13% 7% 5% 6% 5% 6% 6% 19%	1413
March	1st to 10th	Day	17% 15% 4 10% 6% 5% 5% 3 5% 4 25%	3316
	11th to 20th	Day	11% 18% 6% 17% 6% 4 3 2 3 4 26%	3480
	21st to end	Day	10% 16% 6% 13% 7% 6% 6% 3 4 5% 23%	3841
April	1st to 10th	Day	17% 18% 6% 11% 6% 4 3 3 5% 5% 23%	2280
	11th to 20th	Day	18% 14% 5% 10% 4 3 4 3 4 5% 29%	2421
	21st to end	Day	19% 13% 5% 9% 5% 4 4 3 4 5% 30%	2470
May	1st to 10th	Day	16% 11% 4 9% 6% 5% 5% 5% 6% 6% 29%	4425
	11th to 20th	Day	16% 9% 3 8% 5% 5% 6% 4 6% 8% 30%	4398
	21st to end	Day	19% 10% 3 8% 4 4 4 4 5% 7% 33%	5045
June	1st to 10th	Day	22% 9% 2 7% 5% 5% 5% 4 6% 7% 29%	2850
	11th to 20th	Day	16% 9% 3 7% 5% 5% 5% 4 6% 7% 34%	2850
	21st to end	Day	20% 9% 2 7% 5% 4 5% 4 6% 7% 31%	2850
July	1st to 10th	Day	17% 8% 3 8% 6% 6% 6% 4 7% 8% 28%	4760
	11th to 20th	Day	15% 8% 2 7% 5% 5% 6% 4 7% 8% 33%	4760
	21st to end	Day	15% 8% 3 7% 5% 4 5% 4 7% 8% 34%	5009
August	1st to 10th	Day	15% 8% 3 7% 5% 5% 5% 5% 7% 9% 31%	4272
	11th to 20th	Day	17% 9% 3 8% 5% 5% 4 4 5% 7% 34%	4044
	21st to end	Day	13% 8% 3 7% 5% 4 4 3 5% 9% 38%	4471
September	1st to 10th	Day	21% 8% 3 7% 4 4 5% 3 5% 7% 32%	2280
	11th to 20th	Day	23% 10% 3 7% 5% 4 4 3 6% 7% 28%	2218
	21st to end	Day	23% 11% 3 9% 4 4 4 3 4 5% 30%	2024
October	1st to 10th	Day	26% 13% 3 7% 4 4 2 2 4 6% 30%	1900
	11th to 20th	Day	29% 21% 5% 8% 4 3 3 3 3 3 17%	1900
	21st to end	Day	28% 23% 6% 7% 4 4 4 3 3 3 14%	1920
November	1st to 10th	Day	22% 26% 7% 9% 5% 5% 4 2 3 5% 13%	1518
	11th to 20th	Day	23% 21% 7% 15% 7% 5% 3 2 3 3 11%	1520
	21st to end	Day	21% 25% 9% 13% 6% 5% 4 2 3 3 9%	1520
December	1st to 10th	Day	15% 27% 6% 15% 7% 5% 4 2 4 4 12%	1435
	11th to 20th	Day	12% 21% 7% 13% 6% 6% 5% 4 5% 5% 15%	1671
	21st to end	Day	15% 21% 9% 21% 9% 5% 3 2 3 3 8%	2431
January	1st to 10th	Night	13% 16% 8% 17% 9% 9% 6% 4 5% 4 10%	4748
	11th to 20th	Night	10% 16% 7% 17% 10% 7% 8% 6% 6% 5% 9%	4760
	21st to end	Night	8% 21% 11% 15% 8% 7% 7% 4 5% 4 11%	4875
February	1st to 10th	Night	8% 15% 5% 11% 10% 9% 9% 6% 7% 6% 15%	2470
	11th to 20th	Night	9% 17% 7% 14% 8% 6% 6% 5% 5% 6% 16%	2403
	21st to end	Night	10% 18% 4 13% 8% 6% 7% 5% 7% 5% 17%	2041
March	1st to 10th	Night	15% 14% 4 10% 6% 6% 6% 4 5% 6% 24%	3523
	11th to 20th	Night	10% 18% 7% 15% 10% 6% 5% 3 4 4 18%	3479
	21st to end	Night	12% 13% 5% 13% 8% 7% 5% 3 4 4 26%	3791
April	1st to 10th	Night	18% 17% 5% 10% 4 4 3 3 3 5% 28%	1900
	11th to 20th	Night	19% 11% 4 10% 5% 5% 4 3 5% 5% 29%	1725
	21st to end	Night	20% 12% 5% 7% 5% 3 4 3 4 6% 32%	1710
May	1st to 10th	Night	18% 11% 3 7% 5% 5% 4 4 5% 6% 32%	2514
	11th to 20th	Night	16% 10% 3 6% 4 4 5% 4 6% 6% 36%	2495
	21st to end	Night	19% 8% 3 7% 6% 5% 5% 4 6% 8% 29%	2533
June	1st to 10th	Night	20% 10% 3 7% 5% 4 4 2 5% 7% 32%	1330
	11th to 20th	Night	15% 8% 3 7% 4 4 3 4 5% 6% 39%	1330
	21st to end	Night	17% 6% 2 6% 5% 5% 5% 3 6% 7% 37%	1330
July	1st to 10th	Night	16% 9% 2 6% 4 4 4 3 6% 8% 37%	2210
	11th to 20th	Night	18% 10% 4 7% 5% 4 4 4 6% 7% 33%	2210
	21st to end	Night	14% 8% 3 7% 5% 6% 5% 4 6% 7% 35%	2547
August	1st to 10th	Night	9% 7% 3 8% 6% 5% 5% 5% 6% 7% 40%	2655
	11th to 20th	Night	14% 9% 3 8% 4 4 4 3 6% 6% 39%	2785
	21st to end	Night	17% 7% 3 7% 4 4 3 3 4 5% 43%	3152
September	1st to 10th	Night	20% 9% 2 7% 5% 4 4 3 5% 6% 34%	1900
	11th to 20th	Night	19% 10% 4 7% 4 4 4 3 5% 7% 35%	1958
	21st to end	Night	22% 10% 3 6% 4 3 3 2 4 6% 37%	2156
October	1st to 10th	Night	22% 12% 3 7% 4 4 4 3 5% 6% 29%	2280
	11th to 20th	Night	27% 20% 5% 8% 5% 3 3 2 4 5% 16%	2280
	21st to end	Night	22% 23% 6% 10% 5% 4 5% 2 4 5% 15%	2674
November	1st to 10th	Night	21% 22% 6% 11% 4 4 4 3 4 4 17%	2660
	11th to 20th	Night	21% 21% 7% 12% 7% 5% 3 3 3 4 14%	2660
	21st to end	Night	20% 22% 7% 14% 8% 5% 4 3 3 3 11%	2660
December	1st to 10th	Night	14% 25% 7% 15% 9% 6% 5% 4 3 3 10%	2744
	11th to 20th	Night	15% 20% 6% 14% 10% 6% 6% 4 4 4 11%	3526
	21st to end	Night	17% 20% 10% 18% 8% 5% 4 3 3 3 8%	5236

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	78% 5% 9% 7% 1	2209
	11th to 20th	Day	73% 6% 5% 12% 4	2210
	21st to end	Day	74% 4 6% 11% 5%	2785
February	1st to 10th	Day	66% 5% 7% 14% 7%	1710
	11th to 20th	Day	66% 5% 8% 14% 6%	1672
	21st to end	Day	63% 6% 7% 16% 6% 1	1413
March	1st to 10th	Day	62% 4 7% 18% 8%	3319
	11th to 20th	Day	65% 3 6% 16% 9% 1	3480
	21st to end	Day	62% 5% 7% 15% 10% 1	3841
April	1st to 10th	Day	64% 5% 7% 13% 10% 1	2280
	11th to 20th	Day	58% 5% 8% 17% 12% 1	2421
	21st to end	Day	56% 5% 8% 15% 14% 2	2470
May	1st to 10th	Day	51% 7% 9% 21% 10% 1	4439
	11th to 20th	Day	50% 8% 10% 22% 10%	4402
	21st to end	Day	50% 7% 9% 20% 14% 1	5045
June	1st to 10th	Day	53% 6% 10% 21% 9% 1	2850
	11th to 20th	Day	48% 6% 10% 22% 13% 1	2850
	21st to end	Day	50% 7% 10% 23% 10% 1	2850
July	1st to 10th	Day	51% 8% 13% 22% 6%	4686
	11th to 20th	Day	46% 8% 16% 20% 10% 1	4679
	21st to end	Day	45% 7% 15% 26% 6%	4850
August	1st to 10th	Day	46% 9% 16% 24% 5%	4258
	11th to 20th	Day	49% 7% 14% 23% 6% 1	4083
	21st to end	Day	44% 6% 14% 28% 8%	4471
September	1st to 10th	Day	52% 7% 14% 20% 8%	2280
	11th to 20th	Day	55% 7% 15% 18% 5%	2218
	21st to end	Day	57% 6% 9% 21% 7%	2024
October	1st to 10th	Day	63% 4 11% 16% 5%	3160
	11th to 20th	Day	66% 5% 10% 14% 4	3140
	21st to end	Day	73% 4 11% 7% 5%	3135
November	1st to 10th	Day	75% 6% 9% 6% 4	1518
	11th to 20th	Day	81% 3 6% 8% 2	1520
	21st to end	Day	83% 4 6% 6% 1	1520
December	1st to 10th	Day	76% 5% 6% 9% 3	1435
	11th to 20th	Day	70% 5% 5% 15% 4	1671
	21st to end	Day	84% 3 6% 6% 2	2431
January	1st to 10th	Night	76% 6% 9% 8% 1	4748
	11th to 20th	Night	73% 8% 5% 11% 3	4760
	21st to end	Night	74% 5% 5% 10% 5%	4875
February	1st to 10th	Night	65% 8% 9% 11% 8%	2470
	11th to 20th	Night	67% 5% 8% 14% 6%	2405
	21st to end	Night	65% 7% 7% 14% 7% 1	2041
March	1st to 10th	Night	61% 5% 8% 13% 12% 1	3533
	11th to 20th	Night	69% 6% 8% 11% 5% 1	3480
	21st to end	Night	59% 5% 7% 13% 14% 1	3791
April	1st to 10th	Night	60% 4 6% 16% 12% 2	1900
	11th to 20th	Night	56% 6% 7% 17% 12% 1	1725
	21st to end	Night	53% 4 7% 17% 16% 3	1710
May	1st to 10th	Night	50% 6% 11% 17% 14% 2	2520
	11th to 20th	Night	45% 8% 10% 25% 12%	2496
	21st to end	Night	50% 8% 10% 18% 11% 3	2534
June	1st to 10th	Night	52% 6% 9% 21% 11% 1	1330
	11th to 20th	Night	44% 5% 10% 22% 18% 1	1330
	21st to end	Night	45% 7% 12% 24% 11% 2	1330
July	1st to 10th	Night	44% 6% 12% 29% 8%	2175
	11th to 20th	Night	48% 7% 14% 19% 11% 1	2168
	21st to end	Night	47% 8% 11% 28% 6%	2466
August	1st to 10th	Night	41% 8% 16% 30% 6%	2645
	11th to 20th	Night	43% 7% 18% 27% 4	2812
	21st to end	Night	43% 6% 13% 27% 10% 1	3152
September	1st to 10th	Night	50% 7% 14% 21% 8%	1900
	11th to 20th	Night	48% 7% 16% 22% 5%	1958
	21st to end	Night	50% 6% 13% 24% 7%	2156
October	1st to 10th	Night	57% 6% 11% 20% 6%	3800
	11th to 20th	Night	64% 5% 9% 20% 2	3779
	21st to end	Night	67% 6% 12% 11% 5%	4409
November	1st to 10th	Night	72% 5% 10% 11% 2	2660
	11th to 20th	Night	76% 5% 8% 9% 3	2660
	21st to end	Night	80% 5% 7% 7% 1	2660
December	1st to 10th	Night	80% 5% 6% 6% 3	2744
	11th to 20th	Night	76% 5% 6% 10% 2	3525
	21st to end	Night	82% 4 6% 6% 3	5236

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% 19% 37% 16% 3 1	180
	11th to 20th	Day	13% 19% 39% 22% 6% 1	180
	21st to end	Day	17% 15% 38% 25% 4 1	245
February	1st to 10th	Day	16% 25% 37% 19% 2 1	270
	11th to 20th	Day	18% 19% 39% 20% 3 1	270
	21st to end	Day	24% 24% 40% 11%	225
March	1st to 10th	Day	20% 18% 42% 15% 5% 1	431
	11th to 20th	Day	24% 16% 39% 17% 4	460
	21st to end	Day	20% 25% 35% 15% 5% 1	506
April	1st to 10th	Day	23% 21% 30% 17% 7% 2	460
	11th to 20th	Day	27% 17% 31% 16% 6% 2	452
	21st to end	Day	27% 16% 31% 18% 7% 1	460
May	1st to 10th	Day	23% 14% 33% 21% 7% 2	463
	11th to 20th	Day	25% 18% 30% 18% 7% 2	487
	21st to end	Day	26% 16% 33% 19% 7%	646
June	1st to 10th	Day	26% 14% 32% 20% 7%	680
	11th to 20th	Day	23% 18% 31% 20% 6% 2	680
	21st to end	Day	21% 10% 34% 24% 8% 2	680
July	1st to 10th	Day	18% 15% 33% 23% 8% 2	671
	11th to 20th	Day	18% 13% 33% 25% 10% 1	668
	21st to end	Day	20% 11% 30% 27% 9% 3	649
August	1st to 10th	Day	25% 9% 28% 26% 9% 3	486
	11th to 20th	Day	20% 8% 27% 27% 13% 6%	479
	21st to end	Day	24% 12% 28% 20% 12% 4	539
September	1st to 10th	Day	26% 14% 28% 20% 10% 2	490
	11th to 20th	Day	27% 10% 31% 22% 9% 2	490
	21st to end	Day	30% 12% 29% 18% 8% 3	490
October	1st to 10th	Day	32% 14% 28% 17% 7% 1	490
	11th to 20th	Day	38% 20% 26% 12% 3 1	490
	21st to end	Day	36% 20% 29% 12% 2 1	409
November	1st to 10th	Day	39% 18% 31% 12% 1	188
	11th to 20th	Day	32% 23% 29% 12% 3 1	180
	21st to end	Day	37% 23% 28% 8% 4	180
December	1st to 10th	Day	31% 13% 31% 14% 8% 2	180
	11th to 20th	Day	24% 22% 37% 11% 7% 1	180
	21st to end	Day	28% 17% 31% 18% 5% 2	198
January	1st to 10th	Night	23% 13% 36% 21% 6% 1	950
	11th to 20th	Night	24% 11% 37% 23% 5%	950
	21st to end	Night	17% 11% 32% 28% 11% 1	926
February	1st to 10th	Night	15% 12% 38% 25% 9% 1	760
	11th to 20th	Night	20% 13% 35% 25% 8%	743
	21st to end	Night	19% 15% 39% 21% 6% 1	628
March	1st to 10th	Night	17% 16% 34% 25% 6% 1	760
	11th to 20th	Night	24% 15% 32% 23% 6%	760
	21st to end	Night	19% 15% 37% 22% 6% 1	836
April	1st to 10th	Night	28% 13% 32% 21% 5% 1	760
	11th to 20th	Night	25% 14% 30% 23% 7% 1	601
	21st to end	Night	24% 11% 32% 25% 8% 1	570
May	1st to 10th	Night	19% 10% 30% 31% 10%	380
	11th to 20th	Night	26% 11% 25% 30% 6% 1	374
	21st to end	Night	22% 11% 34% 28% 5%	411
June	1st to 10th	Night	24% 10% 31% 26% 8% 1	380
	11th to 20th	Night	17% 14% 31% 28% 9% 1	380
	21st to end	Night	19% 6% 27% 36% 11% 1	380
July	1st to 10th	Night	17% 7% 31% 33% 11% 1	370
	11th to 20th	Night	18% 7% 27% 36% 11%	368
	21st to end	Night	15% 5% 26% 39% 13% 1	416
August	1st to 10th	Night	17% 7% 27% 29% 18% 2	462
	11th to 20th	Night	20% 5% 23% 33% 18% 1	564
	21st to end	Night	23% 8% 25% 28% 14% 1	642
September	1st to 10th	Night	25% 11% 28% 23% 12% 1	760
	11th to 20th	Night	25% 10% 26% 26% 11% 2	760
	21st to end	Night	28% 8% 23% 28% 10% 2	760
October	1st to 10th	Night	29% 11% 27% 24% 8% 1	760
	11th to 20th	Night	37% 13% 26% 18% 5% 1	760
	21st to end	Night	34% 12% 29% 19% 5% 1	836
November	1st to 10th	Night	31% 15% 32% 16% 5% 1	760
	11th to 20th	Night	30% 17% 28% 19% 5%	760
	21st to end	Night	33% 13% 34% 15% 4 1	760
December	1st to 10th	Night	28% 15% 30% 20% 7%	844
	11th to 20th	Night	27% 12% 34% 20% 7% 1	950
	21st to end	Night	28% 13% 29% 21% 7% 3	1045

Page generated at 2024-11-03 02:11:24. Version ac07

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