Trois-Pistoles
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Trois-Pistoles clear sky chart from 2005-11-06 to 2024-01-16.

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	17% 9% 4 7% 6% 3 5% 5% 5% 7% 31%	74613
	Night	18% 12% 5% 8% 7% 4 5% 5% 5% 6% 26%	75194
Transparency	Day	54% 6% 13% 19% 8% 1	74306
	Night	60% 6% 11% 16% 7% 1	75036
Seeing	Day	27% 17% 30% 18% 7% 1	14637
	Night	26% 15% 29% 21% 7% 1	22863

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% 18% 6% 10% 10% 5% 6% 6% 5% 5% 12%	1327
	11th to 20th	Day	14% 17% 7% 12% 9% 4 8% 7% 6% 5% 12%	1480
	21st to end	Day	9% 12% 5% 10% 8% 6% 9% 8% 5% 6% 22%	1584
February	1st to 10th	Day	8% 13% 6% 10% 10% 6% 8% 7% 6% 7% 19%	1502
	11th to 20th	Day	16% 12% 6% 12% 8% 4 6% 6% 5% 5% 21%	1613
	21st to end	Day	12% 10% 5% 9% 7% 5% 8% 6% 5% 6% 25%	1480
March	1st to 10th	Day	15% 12% 5% 7% 6% 4 7% 7% 6% 7% 26%	1797
	11th to 20th	Day	17% 12% 5% 9% 7% 4 6% 4 5% 6% 25%	1959
	21st to end	Day	16% 14% 5% 7% 6% 3 4 4 4 6% 30%	2209
April	1st to 10th	Day	21% 10% 4 7% 5% 3 5% 5% 5% 7% 27%	2166
	11th to 20th	Day	19% 10% 3 5% 4 3 4 4 5% 6% 37%	2312
	21st to end	Day	22% 10% 3 6% 4 2 4 5% 5% 6% 33%	2340
May	1st to 10th	Day	23% 8% 3 6% 5% 3 4 4 5% 5% 34%	2340
	11th to 20th	Day	19% 7% 4 6% 5% 3 4 4 5% 6% 37%	2542
	21st to end	Day	21% 7% 3 5% 5% 3 5% 4 5% 8% 37%	2919
June	1st to 10th	Day	18% 8% 4 6% 5% 3 5% 5% 5% 7% 33%	2700
	11th to 20th	Day	19% 6% 2 5% 6% 3 5% 4 6% 7% 38%	2700
	21st to end	Day	20% 7% 4 7% 7% 3 5% 5% 6% 7% 30%	2700
July	1st to 10th	Day	16% 7% 3 7% 6% 3 4 5% 7% 10% 33%	2700
	11th to 20th	Day	13% 6% 3 6% 6% 4 5% 5% 7% 7% 37%	2660
	21st to end	Day	13% 7% 3 6% 5% 3 5% 5% 6% 8% 38%	2744
August	1st to 10th	Day	15% 5% 2 5% 6% 3 6% 6% 7% 10% 36%	2440
	11th to 20th	Day	14% 6% 2 6% 5% 3 4 4 6% 9% 41%	2304
	21st to end	Day	14% 6% 3 6% 6% 3 5% 5% 6% 8% 36%	2574
September	1st to 10th	Day	17% 5% 2 5% 5% 2 4 5% 6% 8% 41%	2149
	11th to 20th	Day	18% 6% 2 4 4 3 3 3 4 6% 46%	1980
	21st to end	Day	18% 5% 2 5% 6% 3 3 4 5% 6% 43%	1980
October	1st to 10th	Day	17% 8% 3 5% 5% 3 5% 5% 6% 7% 37%	1918
	11th to 20th	Day	24% 8% 3 6% 6% 5% 4 4 5% 6% 28%	1705
	21st to end	Day	27% 11% 4 6% 5% 2 5% 4 4 6% 27%	1782
November	1st to 10th	Day	20% 12% 3 8% 5% 3 4 5% 6% 5% 28%	1671
	11th to 20th	Day	20% 11% 5% 8% 6% 3 5% 5% 6% 7% 22%	1520
	21st to end	Day	20% 16% 6% 8% 6% 3 5% 3 5% 6% 22%	1387
December	1st to 10th	Day	17% 16% 7% 12% 10% 5% 5% 4 4 5% 14%	1330
	11th to 20th	Day	15% 16% 6% 12% 9% 5% 6% 4 4 5% 17%	1668
	21st to end	Day	20% 13% 4 9% 7% 4 5% 5% 6% 7% 21%	2431
January	1st to 10th	Night	16% 18% 7% 13% 11% 4 7% 5% 4 4 12%	2834
	11th to 20th	Night	15% 16% 7% 11% 9% 5% 6% 5% 5% 6% 15%	2602
	21st to end	Night	9% 13% 6% 10% 10% 5% 8% 7% 5% 6% 21%	2772
February	1st to 10th	Night	11% 13% 6% 11% 10% 6% 6% 6% 5% 6% 20%	2457
	11th to 20th	Night	13% 16% 7% 11% 8% 4 7% 5% 4 5% 19%	2229
	21st to end	Night	13% 15% 6% 10% 9% 4 4 4 5% 5% 26%	1776
March	1st to 10th	Night	13% 13% 5% 10% 9% 5% 6% 5% 5% 6% 24%	2150
	11th to 20th	Night	16% 17% 5% 9% 8% 4 5% 3 4 5% 25%	1998
	21st to end	Night	17% 15% 5% 8% 5% 3 4 4 4 5% 30%	2142
April	1st to 10th	Night	24% 15% 5% 8% 6% 3 4 4 4 3 25%	1793
	11th to 20th	Night	21% 10% 3 5% 6% 4 5% 4 5% 6% 32%	1598
	21st to end	Night	25% 11% 3 6% 4 2 4 4 4 5% 32%	1620
May	1st to 10th	Night	26% 8% 4 7% 5% 4 5% 4 5% 4 28%	1620
	11th to 20th	Night	23% 7% 3 6% 4 2 3 3 5% 7% 36%	1364
	21st to end	Night	23% 8% 4 6% 5% 3 5% 5% 5% 6% 30%	1356
June	1st to 10th	Night	20% 8% 4 7% 7% 3 5% 5% 6% 6% 28%	1260
	11th to 20th	Night	18% 8% 2 6% 6% 3 4 6% 6% 7% 34%	1260
	21st to end	Night	21% 8% 3 7% 6% 5% 4 5% 5% 6% 29%	1260
July	1st to 10th	Night	19% 6% 3 6% 7% 4 6% 5% 5% 8% 30%	1260
	11th to 20th	Night	13% 6% 3 8% 7% 3 6% 6% 7% 8% 33%	1298
	21st to end	Night	14% 9% 3 8% 6% 4 5% 6% 6% 9% 30%	1574
August	1st to 10th	Night	14% 6% 3 5% 7% 5% 6% 7% 7% 8% 33%	1481
	11th to 20th	Night	17% 7% 3 6% 6% 3 5% 6% 7% 8% 31%	1596
	21st to end	Night	17% 6% 3 7% 4 3 5% 6% 5% 8% 35%	1782
September	1st to 10th	Night	17% 6% 3 7% 6% 3 6% 5% 5% 7% 37%	1808
	11th to 20th	Night	21% 6% 4 6% 4 2 4 5% 4 5% 39%	1980
	21st to end	Night	19% 6% 2 6% 4 3 4 4 4 6% 42%	1980
October	1st to 10th	Night	19% 7% 2 6% 5% 3 4 3 4 6% 40%	2042
	11th to 20th	Night	25% 10% 4 7% 5% 3 5% 4 4 5% 28%	2254
	21st to end	Night	24% 11% 4 7% 5% 3 4 4 5% 6% 27%	2574
November	1st to 10th	Night	21% 12% 4 7% 6% 3 4 4 5% 5% 28%	2407
	11th to 20th	Night	20% 13% 6% 7% 6% 4 5% 4 5% 5% 25%	2658
	21st to end	Night	19% 16% 7% 10% 6% 3 4 4 4 4 20%	2792
December	1st to 10th	Night	20% 16% 7% 11% 8% 4 5% 5% 4 5% 16%	2850
	11th to 20th	Night	17% 16% 5% 11% 10% 6% 6% 5% 4 5% 14%	3531
	21st to end	Night	16% 18% 6% 10% 7% 4 5% 5% 5% 6% 20%	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	76% 6% 8% 8% 2	1328
	11th to 20th	Day	72% 6% 9% 9% 2 1	1480
	21st to end	Day	61% 6% 10% 15% 8%	1584
February	1st to 10th	Day	64% 6% 12% 11% 6% 1	1502
	11th to 20th	Day	66% 7% 10% 13% 5%	1621
	21st to end	Day	59% 5% 8% 19% 8% 1	1480
March	1st to 10th	Day	59% 6% 12% 14% 7% 1	1800
	11th to 20th	Day	62% 5% 9% 15% 8% 1	1959
	21st to end	Day	58% 5% 9% 18% 9% 1	2209
April	1st to 10th	Day	58% 4 12% 16% 8% 2	2166
	11th to 20th	Day	49% 5% 11% 22% 11% 1	2312
	21st to end	Day	54% 5% 7% 20% 12% 1	2340
May	1st to 10th	Day	53% 5% 11% 19% 11% 1	2340
	11th to 20th	Day	49% 6% 10% 23% 12% 1	2546
	21st to end	Day	49% 6% 11% 24% 10% 1	2919
June	1st to 10th	Day	51% 6% 11% 19% 11% 1	2700
	11th to 20th	Day	46% 7% 13% 21% 11% 1	2700
	21st to end	Day	54% 6% 12% 20% 8%	2700
July	1st to 10th	Day	47% 7% 18% 22% 7%	2625
	11th to 20th	Day	45% 7% 16% 23% 8% 1	2579
	21st to end	Day	45% 7% 17% 23% 8%	2591
August	1st to 10th	Day	46% 8% 19% 22% 5%	2426
	11th to 20th	Day	41% 8% 19% 26% 6%	2304
	21st to end	Day	46% 7% 16% 23% 8%	2574
September	1st to 10th	Day	42% 6% 16% 25% 10%	2149
	11th to 20th	Day	41% 5% 17% 25% 11% 1	1980
	21st to end	Day	45% 5% 15% 25% 10%	1980
October	1st to 10th	Day	47% 6% 14% 20% 11% 1	1918
	11th to 20th	Day	59% 5% 15% 16% 5%	1705
	21st to end	Day	61% 5% 13% 15% 6%	1782
November	1st to 10th	Day	58% 7% 12% 17% 5%	1671
	11th to 20th	Day	63% 7% 11% 14% 4	1520
	21st to end	Day	66% 6% 12% 12% 3	1387
December	1st to 10th	Day	76% 5% 9% 8% 2	1330
	11th to 20th	Day	72% 6% 8% 11% 3	1668
	21st to end	Day	66% 8% 12% 10% 4 1	2431
January	1st to 10th	Night	76% 5% 9% 8% 2	2834
	11th to 20th	Night	69% 6% 10% 11% 3	2602
	21st to end	Night	63% 6% 9% 15% 6%	2772
February	1st to 10th	Night	64% 5% 10% 13% 8%	2457
	11th to 20th	Night	68% 5% 10% 12% 5%	2232
	21st to end	Night	61% 4 9% 18% 7%	1776
March	1st to 10th	Night	60% 5% 10% 17% 7%	2160
	11th to 20th	Night	64% 4 8% 15% 9% 1	1999
	21st to end	Night	60% 5% 8% 18% 8% 1	2142
April	1st to 10th	Night	65% 4 7% 11% 10% 2	1793
	11th to 20th	Night	52% 6% 10% 17% 14% 1	1598
	21st to end	Night	55% 5% 7% 20% 12% 2	1620
May	1st to 10th	Night	58% 5% 8% 16% 12% 1	1620
	11th to 20th	Night	50% 4 10% 22% 12% 2	1365
	21st to end	Night	55% 7% 8% 16% 13% 2	1357
June	1st to 10th	Night	54% 8% 10% 18% 9% 2	1260
	11th to 20th	Night	48% 6% 11% 18% 14% 3	1260
	21st to end	Night	55% 7% 12% 16% 10%	1260
July	1st to 10th	Night	49% 9% 16% 21% 6%	1225
	11th to 20th	Night	45% 9% 16% 21% 8% 1	1256
	21st to end	Night	51% 9% 15% 19% 7%	1486
August	1st to 10th	Night	46% 10% 18% 22% 4	1471
	11th to 20th	Night	47% 11% 17% 18% 7%	1596
	21st to end	Night	45% 7% 17% 23% 8%	1782
September	1st to 10th	Night	45% 7% 13% 24% 10% 1	1808
	11th to 20th	Night	48% 6% 16% 21% 9% 1	1980
	21st to end	Night	44% 6% 12% 25% 12% 1	1980
October	1st to 10th	Night	46% 6% 13% 23% 12% 1	2042
	11th to 20th	Night	59% 6% 12% 19% 4	2254
	21st to end	Night	59% 6% 13% 16% 5%	2574
November	1st to 10th	Night	59% 7% 11% 16% 6%	2407
	11th to 20th	Night	64% 5% 12% 14% 6%	2658
	21st to end	Night	70% 6% 12% 9% 3	2792
December	1st to 10th	Night	73% 7% 9% 8% 2	2850
	11th to 20th	Night	72% 8% 9% 9% 2	3532
	21st to end	Night	69% 6% 11% 11% 4	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	28% 28% 29% 11% 4 1	180
	11th to 20th	Day	29% 25% 31% 12% 4	170
	21st to end	Day	20% 26% 30% 20% 5%	176
February	1st to 10th	Day	27% 22% 36% 12% 3	222
	11th to 20th	Day	26% 24% 34% 14% 2 1	354
	21st to end	Day	26% 26% 28% 13% 5% 2	346
March	1st to 10th	Day	26% 22% 29% 19% 2 1	420
	11th to 20th	Day	30% 20% 28% 14% 7% 1	420
	21st to end	Day	30% 20% 30% 13% 5% 1	462
April	1st to 10th	Day	34% 19% 27% 14% 5% 1	420
	11th to 20th	Day	30% 16% 31% 16% 7% 1	412
	21st to end	Day	29% 16% 35% 14% 5% 2	420
May	1st to 10th	Day	35% 14% 28% 15% 6% 1	423
	11th to 20th	Day	28% 16% 30% 19% 6% 2	521
	21st to end	Day	30% 15% 32% 16% 6% 1	680
June	1st to 10th	Day	27% 15% 31% 21% 6% 1	630
	11th to 20th	Day	26% 13% 28% 22% 10% 1	630
	21st to end	Day	24% 11% 31% 24% 8% 1	630
July	1st to 10th	Day	21% 13% 31% 25% 9%	620
	11th to 20th	Day	15% 12% 35% 26% 10% 2	578
	21st to end	Day	20% 11% 35% 25% 8% 1	488
August	1st to 10th	Day	19% 12% 31% 26% 9% 2	446
	11th to 20th	Day	19% 8% 32% 31% 9% 1	439
	21st to end	Day	22% 13% 31% 20% 12% 2	495
September	1st to 10th	Day	24% 13% 29% 20% 10% 3	450
	11th to 20th	Day	26% 13% 32% 18% 10% 2	450
	21st to end	Day	26% 15% 29% 18% 8% 3	450
October	1st to 10th	Day	24% 17% 29% 20% 8% 3	419
	11th to 20th	Day	36% 17% 24% 13% 8% 1	360
	21st to end	Day	36% 19% 25% 11% 7% 1	396
November	1st to 10th	Day	36% 21% 26% 15% 2 1	365
	11th to 20th	Day	34% 19% 26% 14% 6% 1	370
	21st to end	Day	32% 24% 28% 11% 3	237
December	1st to 10th	Day	32% 21% 28% 13% 4 2	180
	11th to 20th	Day	31% 26% 34% 7% 2	180
	21st to end	Day	33% 28% 25% 11% 3	198
January	1st to 10th	Night	26% 22% 33% 15% 4	848
	11th to 20th	Night	28% 23% 28% 17% 3 1	744
	21st to end	Night	17% 19% 38% 20% 6% 1	792
February	1st to 10th	Night	19% 26% 35% 14% 5% 1	720
	11th to 20th	Night	26% 24% 29% 17% 4	703
	21st to end	Night	23% 18% 34% 18% 6% 1	592
March	1st to 10th	Night	24% 17% 34% 19% 5% 1	720
	11th to 20th	Night	27% 18% 32% 14% 9% 1	720
	21st to end	Night	27% 18% 29% 20% 5% 1	792
April	1st to 10th	Night	33% 14% 29% 16% 7% 1	713
	11th to 20th	Night	28% 12% 29% 22% 8%	534
	21st to end	Night	31% 12% 29% 21% 8% 1	540
May	1st to 10th	Night	30% 8% 27% 26% 7% 1	540
	11th to 20th	Night	27% 10% 29% 24% 10%	380
	21st to end	Night	29% 12% 27% 24% 7% 1	389
June	1st to 10th	Night	21% 7% 30% 34% 8% 1	360
	11th to 20th	Night	23% 8% 24% 33% 11% 3	360
	21st to end	Night	23% 7% 31% 28% 11% 1	360
July	1st to 10th	Night	19% 9% 32% 30% 9% 2	350
	11th to 20th	Night	14% 11% 28% 36% 11% 1	348
	21st to end	Night	19% 4 27% 36% 13% 1	394
August	1st to 10th	Night	17% 6% 28% 32% 16%	407
	11th to 20th	Night	19% 6% 29% 32% 13% 1	532
	21st to end	Night	20% 9% 28% 30% 12% 2	594
September	1st to 10th	Night	21% 10% 29% 29% 11% 1	684
	11th to 20th	Night	26% 8% 31% 24% 9% 2	720
	21st to end	Night	23% 10% 32% 26% 9% 1	720
October	1st to 10th	Night	26% 14% 28% 24% 7% 1	720
	11th to 20th	Night	33% 14% 25% 19% 7% 1	720
	21st to end	Night	33% 15% 26% 19% 6% 1	792
November	1st to 10th	Night	32% 17% 29% 17% 4	740
	11th to 20th	Night	32% 21% 25% 16% 5% 1	850
	21st to end	Night	31% 17% 33% 15% 5%	850
December	1st to 10th	Night	30% 20% 28% 15% 5% 1	850
	11th to 20th	Night	30% 23% 28% 15% 4	850
	21st to end	Night	30% 23% 26% 16% 5% 1	935

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