Chapleau
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Chapleau clear sky chart from 2005-11-06 to 2024-02-05.

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% 5% 9% 7% 4 5% 4 5% 6% 26%	77760
	Night	15% 14% 6% 10% 8% 4 5% 4 5% 5% 24%	81135
Transparency	Day	60% 3 10% 18% 8% 1	77454
	Night	63% 4 10% 16% 7% 1	80976
Seeing	Day	24% 16% 31% 20% 8% 2	14395
	Night	23% 13% 32% 24% 8% 1	23865

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	10% 23% 10% 15% 7% 4 6% 5% 4 4 12%	2208
	11th to 20th	Day	9% 13% 7% 16% 11% 5% 7% 6% 4 4 19%	2476
	21st to end	Day	9% 22% 12% 17% 8% 5% 5% 4 4 4 9%	2783
February	1st to 10th	Day	7% 13% 6% 11% 11% 8% 7% 6% 5% 7% 21%	1580
	11th to 20th	Day	10% 16% 8% 10% 8% 5% 5% 5% 4 6% 23%	1587
	21st to end	Day	8% 17% 9% 13% 10% 5% 6% 5% 5% 6% 18%	1480
March	1st to 10th	Day	11% 14% 5% 10% 9% 4 7% 4 4 4 28%	1806
	11th to 20th	Day	11% 14% 6% 10% 7% 4 5% 3 4 5% 31%	1980
	21st to end	Day	15% 14% 5% 8% 6% 3 5% 4 4 5% 30%	2178
April	1st to 10th	Day	18% 16% 7% 11% 7% 3 4 4 4 5% 22%	2182
	11th to 20th	Day	19% 14% 4 7% 5% 3 4 4 5% 6% 29%	2312
	21st to end	Day	17% 14% 4 8% 5% 3 5% 4 4 5% 31%	2340
May	1st to 10th	Day	18% 12% 5% 7% 7% 4 5% 4 4 6% 29%	2340
	11th to 20th	Day	19% 10% 3 7% 5% 4 4 4 5% 6% 34%	2502
	21st to end	Day	18% 8% 3 6% 5% 4 5% 5% 5% 7% 35%	2919
June	1st to 10th	Day	21% 8% 3 5% 6% 3 5% 4 5% 7% 33%	2700
	11th to 20th	Day	20% 6% 3 5% 5% 3 4 5% 6% 8% 36%	2700
	21st to end	Day	20% 7% 3 6% 6% 4 5% 5% 5% 8% 32%	2700
July	1st to 10th	Day	16% 6% 3 6% 6% 4 5% 5% 5% 8% 36%	2700
	11th to 20th	Day	15% 6% 2 5% 7% 4 6% 5% 6% 7% 35%	2692
	21st to end	Day	18% 6% 3 6% 6% 3 6% 5% 5% 8% 34%	2743
August	1st to 10th	Day	16% 8% 3 8% 7% 4 5% 6% 6% 8% 30%	2412
	11th to 20th	Day	17% 7% 3 6% 5% 4 4 5% 5% 7% 37%	2303
	21st to end	Day	20% 7% 3 6% 6% 3 4 5% 5% 7% 34%	2574
September	1st to 10th	Day	22% 7% 3 6% 4 3 4 5% 4 7% 35%	2153
	11th to 20th	Day	22% 9% 3 6% 5% 3 4 3 5% 7% 33%	1980
	21st to end	Day	23% 11% 3 6% 5% 3 3 3 4 5% 32%	1980
October	1st to 10th	Day	22% 17% 5% 6% 5% 3 4 4 3 4 27%	1890
	11th to 20th	Day	26% 22% 5% 7% 4 3 3 3 4 5% 17%	1746
	21st to end	Day	23% 24% 7% 8% 6% 3 3 3 3 5% 14%	1782
November	1st to 10th	Day	21% 19% 7% 9% 6% 3 4 3 4 6% 19%	1640
	11th to 20th	Day	18% 21% 8% 11% 7% 4 5% 4 2 3 15%	1520
	21st to end	Day	19% 24% 9% 12% 7% 3 4 4 3 5% 9%	1440
December	1st to 10th	Day	13% 17% 8% 15% 13% 5% 5% 4 5% 4 11%	1330
	11th to 20th	Day	12% 19% 8% 11% 10% 4 5% 5% 5% 5% 15%	1671
	21st to end	Day	20% 22% 11% 14% 11% 3 3 2 3 3 9%	2431
January	1st to 10th	Night	11% 20% 8% 16% 8% 6% 8% 5% 5% 5% 9%	4748
	11th to 20th	Night	9% 15% 7% 15% 13% 6% 6% 4 5% 4 16%	4490
	21st to end	Night	11% 18% 10% 16% 10% 4 6% 5% 5% 4 12%	4884
February	1st to 10th	Night	9% 13% 5% 10% 10% 7% 8% 7% 6% 6% 18%	2474
	11th to 20th	Night	9% 15% 7% 12% 10% 5% 6% 5% 5% 6% 20%	2258
	21st to end	Night	8% 19% 8% 11% 7% 5% 7% 5% 5% 5% 21%	1776
March	1st to 10th	Night	9% 11% 6% 11% 10% 4 5% 4 5% 6% 30%	2141
	11th to 20th	Night	12% 13% 6% 10% 7% 3 6% 4 5% 6% 28%	1979
	21st to end	Night	11% 12% 6% 10% 6% 4 5% 4 5% 6% 32%	2178
April	1st to 10th	Night	18% 14% 4 8% 6% 4 4 5% 6% 6% 25%	1792
	11th to 20th	Night	17% 13% 5% 8% 5% 2 4 4 5% 6% 30%	1597
	21st to end	Night	17% 12% 4 6% 5% 3 3 4 5% 6% 36%	1620
May	1st to 10th	Night	17% 10% 3 5% 6% 4 4 5% 5% 7% 34%	1620
	11th to 20th	Night	19% 9% 4 7% 5% 4 5% 4 6% 4 34%	1389
	21st to end	Night	17% 9% 3 3 5% 3 4 4 6% 7% 39%	1357
June	1st to 10th	Night	19% 8% 3 4 5% 3 4 5% 6% 7% 37%	1260
	11th to 20th	Night	18% 7% 3 7% 6% 2 4 5% 5% 7% 36%	1260
	21st to end	Night	16% 5% 2 6% 6% 4 5% 4 5% 8% 40%	1260
July	1st to 10th	Night	14% 5% 2 4 4 3 4 5% 5% 9% 45%	1260
	11th to 20th	Night	14% 6% 3 5% 4 3 4 5% 6% 8% 43%	1265
	21st to end	Night	13% 6% 3 5% 5% 4 5% 4 6% 9% 41%	1575
August	1st to 10th	Night	12% 8% 3 6% 5% 4 4 4 5% 8% 41%	1525
	11th to 20th	Night	14% 6% 3 5% 5% 3 5% 4 4 6% 46%	1598
	21st to end	Night	17% 7% 4 6% 5% 3 4 4 4 6% 39%	1782
September	1st to 10th	Night	18% 8% 3 6% 5% 3 4 4 4 6% 39%	1786
	11th to 20th	Night	19% 8% 2 6% 5% 3 4 4 5% 7% 38%	1980
	21st to end	Night	22% 12% 4 5% 5% 3 4 3 3 7% 32%	1980
October	1st to 10th	Night	22% 14% 3 6% 6% 3 4 4 4 5% 31%	2070
	11th to 20th	Night	23% 17% 5% 8% 6% 3 4 4 3 5% 23%	2213
	21st to end	Night	23% 20% 7% 8% 6% 2 4 4 4 4 18%	2574
November	1st to 10th	Night	18% 17% 6% 9% 7% 3 4 4 4 5% 22%	2436
	11th to 20th	Night	19% 17% 6% 11% 8% 4 5% 4 4 5% 16%	2660
	21st to end	Night	18% 19% 9% 13% 8% 4 5% 5% 3 4 12%	2736
December	1st to 10th	Night	13% 19% 7% 15% 12% 5% 5% 4 4 5% 11%	2850
	11th to 20th	Night	13% 19% 9% 11% 10% 4 5% 4 4 4 16%	3526
	21st to end	Night	20% 20% 8% 14% 13% 4 4 3 3 4 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	77% 2 7% 12% 2	2209
	11th to 20th	Day	71% 2 8% 14% 5% 1	2476
	21st to end	Day	80% 2 5% 7% 6% 1	2783
February	1st to 10th	Day	64% 4 8% 14% 9% 1	1580
	11th to 20th	Day	62% 3 9% 15% 10% 1	1596
	21st to end	Day	68% 3 5% 13% 10% 1	1480
March	1st to 10th	Day	60% 3 9% 14% 13% 2	1808
	11th to 20th	Day	57% 3 9% 18% 11% 2	1980
	21st to end	Day	58% 3 7% 18% 12% 2	2178
April	1st to 10th	Day	67% 2 6% 15% 9% 1	2182
	11th to 20th	Day	57% 2 7% 23% 9% 1	2312
	21st to end	Day	56% 3 8% 16% 14% 3	2340
May	1st to 10th	Day	57% 3 9% 19% 11% 2	2340
	11th to 20th	Day	52% 4 7% 22% 14% 1	2506
	21st to end	Day	48% 5% 11% 24% 9% 2	2919
June	1st to 10th	Day	52% 3 10% 20% 14% 1	2700
	11th to 20th	Day	47% 4 10% 25% 13% 1	2700
	21st to end	Day	51% 4 12% 21% 11% 1	2700
July	1st to 10th	Day	45% 5% 13% 26% 11%	2626
	11th to 20th	Day	46% 5% 12% 27% 9% 1	2611
	21st to end	Day	49% 4 14% 24% 9%	2591
August	1st to 10th	Day	51% 5% 16% 21% 7% 1	2397
	11th to 20th	Day	46% 5% 13% 26% 10%	2303
	21st to end	Day	51% 5% 13% 22% 9% 1	2574
September	1st to 10th	Day	50% 3 14% 22% 11% 1	2153
	11th to 20th	Day	52% 4 16% 22% 6%	1980
	21st to end	Day	55% 3 12% 22% 7%	1980
October	1st to 10th	Day	61% 3 12% 19% 6%	1890
	11th to 20th	Day	72% 3 8% 14% 3	1746
	21st to end	Day	75% 3 8% 9% 5%	1782
November	1st to 10th	Day	70% 2 10% 13% 4	1640
	11th to 20th	Day	75% 2 9% 10% 3 1	1520
	21st to end	Day	80% 3 8% 7% 1	1440
December	1st to 10th	Day	78% 4 6% 8% 5%	1330
	11th to 20th	Day	71% 3 8% 14% 4	1671
	21st to end	Day	84% 1 4 8% 3	2431
January	1st to 10th	Night	80% 2 7% 9% 2	4748
	11th to 20th	Night	72% 2 7% 15% 4	4490
	21st to end	Night	76% 3 6% 11% 4	4884
February	1st to 10th	Night	64% 6% 9% 12% 8% 1	2474
	11th to 20th	Night	65% 3 10% 16% 7%	2260
	21st to end	Night	65% 4 8% 16% 6% 1	1776
March	1st to 10th	Night	55% 4 9% 17% 13% 1	2152
	11th to 20th	Night	58% 4 8% 18% 11% 1	1980
	21st to end	Night	53% 4 10% 18% 13% 3	2178
April	1st to 10th	Night	59% 4 8% 16% 12%	1792
	11th to 20th	Night	56% 2 7% 20% 13% 1	1597
	21st to end	Night	50% 4 10% 21% 13% 3	1620
May	1st to 10th	Night	50% 4 10% 23% 11% 2	1620
	11th to 20th	Night	52% 4 8% 24% 11% 1	1390
	21st to end	Night	44% 5% 14% 23% 12% 2	1358
June	1st to 10th	Night	46% 3 12% 24% 14% 1	1260
	11th to 20th	Night	48% 4 11% 22% 15% 2	1260
	21st to end	Night	42% 5% 16% 25% 11% 1	1260
July	1st to 10th	Night	37% 5% 15% 30% 12% 1	1225
	11th to 20th	Night	39% 4 14% 32% 10% 1	1223
	21st to end	Night	41% 4 17% 30% 8%	1487
August	1st to 10th	Night	42% 5% 19% 25% 8%	1516
	11th to 20th	Night	40% 4 20% 28% 8%	1598
	21st to end	Night	46% 4 14% 25% 10% 1	1782
September	1st to 10th	Night	48% 4 13% 24% 10% 1	1786
	11th to 20th	Night	47% 4 18% 24% 6%	1980
	21st to end	Night	54% 4 15% 22% 5%	1980
October	1st to 10th	Night	57% 4 12% 21% 7%	2070
	11th to 20th	Night	65% 3 10% 17% 4	2213
	21st to end	Night	72% 3 8% 12% 5%	2574
November	1st to 10th	Night	64% 4 11% 15% 5%	2436
	11th to 20th	Night	72% 3 10% 11% 4	2660
	21st to end	Night	77% 4 9% 7% 3	2736
December	1st to 10th	Night	77% 4 6% 10% 3	2850
	11th to 20th	Night	72% 4 7% 11% 5% 1	3525
	21st to end	Night	82% 2 5% 7% 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	23% 20% 36% 11% 8% 2	180
	11th to 20th	Day	19% 16% 34% 26% 5%	257
	21st to end	Day	19% 16% 33% 27% 5%	297
February	1st to 10th	Day	18% 25% 37% 14% 5% 2	252
	11th to 20th	Day	25% 21% 36% 13% 3 3	240
	21st to end	Day	18% 39% 34% 8% 1 1	198
March	1st to 10th	Day	21% 23% 38% 15% 3	248
	11th to 20th	Day	22% 20% 36% 15% 6% 1	420
	21st to end	Day	28% 15% 35% 15% 6%	462
April	1st to 10th	Day	25% 16% 36% 17% 5%	420
	11th to 20th	Day	28% 19% 27% 15% 7% 4	412
	21st to end	Day	27% 19% 24% 18% 10% 2	420
May	1st to 10th	Day	24% 14% 35% 16% 9% 2	423
	11th to 20th	Day	23% 14% 34% 17% 9% 3	543
	21st to end	Day	23% 16% 33% 19% 6% 2	679
June	1st to 10th	Day	22% 18% 35% 18% 6% 2	630
	11th to 20th	Day	24% 17% 29% 21% 7% 2	630
	21st to end	Day	23% 11% 30% 23% 10% 3	630
July	1st to 10th	Day	14% 14% 36% 25% 8% 3	621
	11th to 20th	Day	19% 13% 29% 26% 9% 4	618
	21st to end	Day	17% 12% 30% 27% 10% 4	684
August	1st to 10th	Day	17% 12% 27% 27% 12% 4	531
	11th to 20th	Day	20% 7% 24% 27% 15% 7%	439
	21st to end	Day	24% 10% 27% 20% 14% 4	495
September	1st to 10th	Day	25% 11% 30% 18% 13% 4	450
	11th to 20th	Day	26% 10% 32% 22% 8% 2	450
	21st to end	Day	28% 13% 26% 22% 8% 2	450
October	1st to 10th	Day	30% 17% 25% 19% 8% 1	450
	11th to 20th	Day	34% 18% 29% 14% 4 1	396
	21st to end	Day	32% 23% 29% 14% 2	297
November	1st to 10th	Day	34% 19% 31% 13% 3	255
	11th to 20th	Day	37% 19% 29% 12% 3 1	180
	21st to end	Day	29% 24% 33% 13% 1	180
December	1st to 10th	Day	20% 18% 37% 16% 7% 2	180
	11th to 20th	Day	25% 19% 36% 16% 2 1	180
	21st to end	Day	31% 17% 30% 15% 7% 2	198
January	1st to 10th	Night	22% 15% 39% 19% 5% 1	950
	11th to 20th	Night	22% 15% 33% 23% 7% 1	950
	21st to end	Night	20% 12% 31% 27% 9% 1	1045
February	1st to 10th	Night	17% 14% 39% 24% 6% 1	814
	11th to 20th	Night	19% 17% 35% 22% 7% 1	703
	21st to end	Night	19% 17% 38% 21% 5%	592
March	1st to 10th	Night	16% 18% 37% 23% 6%	720
	11th to 20th	Night	19% 19% 37% 17% 7% 1	720
	21st to end	Night	16% 14% 38% 23% 8% 1	792
April	1st to 10th	Night	26% 12% 32% 23% 6% 1	563
	11th to 20th	Night	25% 15% 26% 26% 7% 1	533
	21st to end	Night	22% 12% 29% 25% 11% 1	540
May	1st to 10th	Night	20% 8% 33% 31% 7%	540
	11th to 20th	Night	21% 12% 31% 28% 7% 1	424
	21st to end	Night	22% 8% 36% 29% 5%	389
June	1st to 10th	Night	23% 10% 28% 34% 4	360
	11th to 20th	Night	23% 9% 30% 29% 9%	360
	21st to end	Night	16% 10% 27% 33% 13% 1	360
July	1st to 10th	Night	15% 7% 38% 32% 7% 1	350
	11th to 20th	Night	18% 8% 30% 31% 12% 1	353
	21st to end	Night	14% 8% 29% 30% 17% 2	591
August	1st to 10th	Night	17% 7% 25% 33% 16% 1	537
	11th to 20th	Night	18% 5% 23% 34% 18% 2	534
	21st to end	Night	22% 7% 29% 24% 15% 2	594
September	1st to 10th	Night	22% 8% 28% 27% 12% 2	598
	11th to 20th	Night	24% 11% 26% 25% 12% 2	720
	21st to end	Night	28% 9% 27% 24% 11% 2	720
October	1st to 10th	Night	30% 10% 27% 24% 8%	720
	11th to 20th	Night	32% 13% 29% 20% 5% 1	720
	21st to end	Night	36% 13% 26% 20% 4	792
November	1st to 10th	Night	28% 15% 34% 17% 5% 1	740
	11th to 20th	Night	30% 17% 29% 19% 6%	760
	21st to end	Night	28% 16% 31% 19% 5% 1	836
December	1st to 10th	Night	24% 14% 34% 21% 6% 1	950
	11th to 20th	Night	23% 17% 35% 16% 7% 1	950
	21st to end	Night	27% 17% 28% 20% 7% 1	1045

Page generated at 2024-02-02 05:20:29. Version ac07

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