Walkerton
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Walkerton clear sky chart from 2005-11-06 to 2024-01-12.

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% 11% 5% 8% 6% 3 5% 4 5% 7% 30%	74751
	Night	16% 13% 5% 9% 7% 4 5% 4 5% 6% 27%	74958
Transparency	Day	54% 7% 11% 17% 9% 1	74458
	Night	58% 7% 11% 15% 8% 1	74786
Seeing	Day	19% 12% 29% 24% 12% 4	13959
	Night	21% 11% 29% 28% 10% 1	23339

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% 17% 10% 16% 11% 5% 5% 4 4 5% 10%	1370
	11th to 20th	Day	15% 20% 11% 17% 10% 3 5% 4 3 4 9%	1543
	21st to end	Day	12% 18% 9% 16% 11% 5% 5% 4 3 4 11%	1782
February	1st to 10th	Day	14% 18% 8% 17% 11% 4 5% 3 4 4 12%	1620
	11th to 20th	Day	13% 15% 9% 17% 12% 3 6% 4 5% 4 13%	1573
	21st to end	Day	16% 18% 8% 12% 8% 3 4 4 4 4 17%	1452
March	1st to 10th	Day	14% 13% 6% 12% 9% 3 4 4 4 6% 26%	1918
	11th to 20th	Day	13% 13% 8% 9% 7% 2 5% 5% 4 5% 29%	1980
	21st to end	Day	18% 11% 5% 7% 6% 3 4 5% 5% 6% 30%	2178
April	1st to 10th	Day	17% 15% 6% 8% 6% 3 4 4 5% 6% 27%	2060
	11th to 20th	Day	18% 12% 3 5% 5% 2 3 4 5% 6% 36%	2311
	21st to end	Day	20% 11% 4 6% 5% 3 4 4 5% 7% 32%	2340
May	1st to 10th	Day	19% 8% 4 6% 5% 3 4 4 6% 6% 35%	2340
	11th to 20th	Day	17% 9% 3 5% 5% 3 4 4 4 6% 40%	2369
	21st to end	Day	14% 6% 3 4 5% 3 5% 4 5% 8% 43%	2725
June	1st to 10th	Day	15% 7% 3 5% 5% 3 5% 5% 6% 7% 40%	2603
	11th to 20th	Day	13% 5% 2 4 5% 3 5% 5% 6% 8% 43%	2700
	21st to end	Day	16% 6% 2 5% 5% 3 4 4 5% 8% 41%	2700
July	1st to 10th	Day	9% 5% 2 4 4 2 5% 5% 6% 8% 48%	2700
	11th to 20th	Day	12% 6% 3 6% 4 3 6% 6% 7% 9% 39%	2575
	21st to end	Day	11% 6% 3 5% 5% 3 5% 6% 7% 9% 41%	2547
August	1st to 10th	Day	11% 5% 3 6% 6% 4 5% 5% 7% 10% 38%	2327
	11th to 20th	Day	12% 6% 2 6% 7% 4 5% 6% 7% 9% 36%	2303
	21st to end	Day	13% 6% 3 6% 5% 3 5% 5% 7% 8% 39%	2553
September	1st to 10th	Day	13% 8% 2 7% 5% 3 5% 5% 6% 8% 38%	2131
	11th to 20th	Day	14% 5% 3 5% 5% 3 4 5% 7% 7% 42%	1980
	21st to end	Day	17% 7% 3 7% 6% 3 4 6% 6% 8% 34%	1980
October	1st to 10th	Day	20% 8% 3 7% 6% 3 4 5% 5% 7% 32%	1828
	11th to 20th	Day	24% 14% 4 9% 7% 3 5% 4 5% 7% 19%	1800
	21st to end	Day	28% 15% 4 8% 7% 4 6% 4 4 4 17%	1922
November	1st to 10th	Day	15% 19% 5% 9% 6% 4 4 4 4 6% 25%	1653
	11th to 20th	Day	17% 16% 6% 10% 6% 4 6% 6% 4 6% 17%	1520
	21st to end	Day	19% 21% 9% 10% 6% 4 5% 4 4 5% 13%	1520
December	1st to 10th	Day	14% 25% 12% 15% 10% 3 5% 3 3 4 6%	1520
	11th to 20th	Day	18% 19% 9% 15% 7% 4 5% 3 4 5% 10%	1897
	21st to end	Day	25% 23% 8% 12% 8% 3 3 3 3 4 8%	2431
January	1st to 10th	Night	17% 17% 9% 15% 10% 4 5% 5% 5% 5% 10%	2792
	11th to 20th	Night	17% 20% 9% 14% 10% 4 5% 4 4 4 10%	2454
	21st to end	Night	12% 14% 9% 16% 11% 6% 6% 5% 4 5% 11%	2574
February	1st to 10th	Night	13% 20% 8% 14% 11% 5% 5% 4 3 4 12%	2340
	11th to 20th	Night	13% 15% 9% 15% 9% 4 5% 4 4 5% 17%	2273
	21st to end	Night	16% 13% 7% 11% 9% 4 5% 4 4 5% 20%	1803
March	1st to 10th	Night	13% 12% 6% 13% 9% 3 5% 4 5% 5% 27%	2028
	11th to 20th	Night	12% 14% 6% 9% 7% 3 5% 5% 4 5% 29%	1979
	21st to end	Night	17% 12% 4 8% 5% 3 5% 4 4 5% 33%	2178
April	1st to 10th	Night	19% 13% 5% 6% 6% 3 4 4 5% 6% 29%	1900
	11th to 20th	Night	17% 9% 3 6% 4 4 4 5% 5% 6% 37%	1614
	21st to end	Night	17% 11% 4 7% 7% 4 4 4 5% 6% 31%	1620
May	1st to 10th	Night	16% 7% 4 6% 5% 3 5% 4 5% 7% 37%	1620
	11th to 20th	Night	16% 7% 3 6% 5% 3 4 4 5% 7% 41%	1522
	21st to end	Night	9% 5% 2 4 5% 3 5% 5% 6% 7% 49%	1550
June	1st to 10th	Night	13% 6% 3 6% 6% 3 4 4 5% 9% 41%	1351
	11th to 20th	Night	11% 6% 1 6% 5% 3 5% 6% 5% 9% 42%	1260
	21st to end	Night	13% 5% 2 6% 4 3 5% 6% 4 8% 43%	1260
July	1st to 10th	Night	7% 4 2 4 4 3 3 3 6% 9% 55%	1260
	11th to 20th	Night	9% 5% 2 5% 5% 3 4 6% 6% 7% 48%	1378
	21st to end	Night	9% 4 2 6% 5% 3 4 7% 5% 8% 47%	1771
August	1st to 10th	Night	9% 5% 2 5% 6% 3 5% 4 6% 7% 48%	1611
	11th to 20th	Night	9% 5% 2 4 5% 3 5% 5% 5% 10% 47%	1598
	21st to end	Night	12% 6% 2 4 6% 3 5% 5% 5% 6% 45%	1783
September	1st to 10th	Night	10% 5% 3 6% 5% 4 4 4 7% 8% 45%	1826
	11th to 20th	Night	13% 5% 2 4 4 2 5% 4 5% 7% 48%	1980
	21st to end	Night	14% 7% 3 6% 6% 4 4 4 5% 7% 39%	1980
October	1st to 10th	Night	18% 9% 3 6% 6% 3 4 4 6% 6% 36%	2131
	11th to 20th	Night	24% 11% 4 7% 6% 3 4 5% 6% 7% 23%	2160
	21st to end	Night	24% 15% 5% 7% 7% 3 5% 4 5% 5% 20%	2430
November	1st to 10th	Night	18% 13% 3 7% 7% 4 5% 5% 5% 6% 27%	2424
	11th to 20th	Night	18% 16% 6% 10% 6% 4 5% 5% 6% 6% 19%	2660
	21st to end	Night	21% 18% 8% 10% 7% 3 4 3 4 6% 15%	2660
December	1st to 10th	Night	19% 23% 10% 13% 7% 3 5% 4 4 4 8%	2660
	11th to 20th	Night	14% 20% 10% 14% 8% 4 4 5% 5% 5% 12%	3292
	21st to end	Night	24% 21% 9% 14% 7% 3 4 4 3 3 7%	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	80% 5% 7% 6% 2	1371
	11th to 20th	Day	81% 6% 5% 5% 3	1543
	21st to end	Day	77% 5% 7% 7% 3	1782
February	1st to 10th	Day	77% 5% 7% 9% 1	1620
	11th to 20th	Day	74% 7% 7% 8% 4	1582
	21st to end	Day	70% 6% 8% 11% 4	1452
March	1st to 10th	Day	61% 6% 12% 14% 7% 1	1921
	11th to 20th	Day	57% 6% 10% 15% 9% 2	1980
	21st to end	Day	54% 6% 12% 16% 10% 2	2178
April	1st to 10th	Day	58% 6% 10% 16% 8%	2060
	11th to 20th	Day	49% 6% 10% 21% 14% 1	2311
	21st to end	Day	52% 6% 11% 17% 11% 2	2340
May	1st to 10th	Day	48% 6% 9% 22% 14% 1	2340
	11th to 20th	Day	45% 7% 10% 23% 14% 2	2373
	21st to end	Day	39% 7% 14% 22% 14% 3	2725
June	1st to 10th	Day	42% 7% 12% 23% 15% 1	2603
	11th to 20th	Day	38% 7% 12% 25% 17% 1	2700
	21st to end	Day	41% 6% 13% 25% 14% 1	2700
July	1st to 10th	Day	32% 8% 14% 24% 20% 3	2626
	11th to 20th	Day	36% 10% 14% 26% 12% 2	2494
	21st to end	Day	38% 9% 14% 24% 14% 2	2405
August	1st to 10th	Day	37% 10% 16% 24% 11% 2	2314
	11th to 20th	Day	42% 9% 16% 22% 11%	2303
	21st to end	Day	40% 9% 16% 23% 12% 1	2553
September	1st to 10th	Day	43% 8% 15% 22% 11% 2	2131
	11th to 20th	Day	39% 8% 15% 27% 11%	1980
	21st to end	Day	46% 9% 14% 23% 7% 1	1980
October	1st to 10th	Day	52% 7% 11% 18% 11% 2	1828
	11th to 20th	Day	64% 7% 12% 13% 4 1	1800
	21st to end	Day	70% 7% 8% 10% 4	1922
November	1st to 10th	Day	61% 7% 10% 15% 7%	1653
	11th to 20th	Day	66% 9% 11% 8% 5% 1	1520
	21st to end	Day	75% 7% 9% 8% 1	1520
December	1st to 10th	Day	84% 6% 6% 4 1	1520
	11th to 20th	Day	77% 8% 8% 6% 1	1897
	21st to end	Day	82% 6% 8% 3	2431
January	1st to 10th	Night	76% 7% 9% 6% 1	2792
	11th to 20th	Night	79% 6% 8% 4 3	2454
	21st to end	Night	75% 6% 9% 6% 3 1	2574
February	1st to 10th	Night	78% 5% 8% 8% 1	2340
	11th to 20th	Night	71% 5% 10% 10% 3	2275
	21st to end	Night	65% 6% 10% 12% 6%	1803
March	1st to 10th	Night	59% 6% 11% 16% 8% 1	2038
	11th to 20th	Night	56% 7% 8% 16% 10% 2	1980
	21st to end	Night	54% 5% 9% 18% 11% 2	2178
April	1st to 10th	Night	55% 6% 10% 17% 11% 1	1900
	11th to 20th	Night	47% 7% 8% 20% 17% 1	1614
	21st to end	Night	52% 7% 9% 16% 13% 2	1620
May	1st to 10th	Night	46% 6% 10% 21% 15% 2	1620
	11th to 20th	Night	42% 7% 8% 23% 17% 3	1523
	21st to end	Night	34% 8% 15% 25% 16% 3	1551
June	1st to 10th	Night	41% 7% 10% 23% 18% 2	1351
	11th to 20th	Night	37% 8% 14% 24% 16% 2	1260
	21st to end	Night	38% 7% 12% 24% 17% 1	1260
July	1st to 10th	Night	26% 7% 12% 26% 25% 3	1225
	11th to 20th	Night	32% 8% 13% 28% 17% 1	1336
	21st to end	Night	33% 9% 16% 24% 16% 2	1672
August	1st to 10th	Night	34% 8% 14% 29% 14% 1	1600
	11th to 20th	Night	31% 9% 16% 27% 15% 1	1598
	21st to end	Night	39% 8% 12% 27% 13% 1	1783
September	1st to 10th	Night	36% 8% 13% 28% 13% 2	1826
	11th to 20th	Night	35% 7% 14% 29% 15%	1980
	21st to end	Night	44% 8% 13% 24% 10%	1980
October	1st to 10th	Night	49% 7% 11% 20% 13% 1	2131
	11th to 20th	Night	58% 8% 12% 16% 5%	2160
	21st to end	Night	66% 7% 11% 11% 5%	2430
November	1st to 10th	Night	56% 8% 12% 18% 6%	2424
	11th to 20th	Night	64% 9% 11% 11% 4 1	2660
	21st to end	Night	72% 7% 11% 8% 2	2660
December	1st to 10th	Night	80% 8% 6% 4 1	2660
	11th to 20th	Night	74% 9% 11% 5% 1	3292
	21st to end	Night	82% 7% 7% 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	20% 20% 36% 18% 6% 1	200
	11th to 20th	Day	22% 17% 41% 13% 6% 1	245
	21st to end	Day	25% 17% 33% 21% 3 1	264
February	1st to 10th	Day	24% 25% 37% 10% 4	240
	11th to 20th	Day	25% 21% 42% 11% 1	240
	21st to end	Day	28% 30% 28% 12% 1	198
March	1st to 10th	Day	23% 16% 37% 16% 7% 1	361
	11th to 20th	Day	21% 15% 35% 20% 7% 1	420
	21st to end	Day	29% 13% 31% 21% 6% 1	462
April	1st to 10th	Day	22% 16% 31% 22% 8% 1	420
	11th to 20th	Day	28% 15% 26% 16% 9% 6%	412
	21st to end	Day	25% 13% 27% 26% 7% 3	420
May	1st to 10th	Day	23% 13% 28% 25% 10% 3	423
	11th to 20th	Day	19% 10% 27% 25% 15% 4	447
	21st to end	Day	16% 8% 26% 27% 15% 8%	485
June	1st to 10th	Day	15% 10% 28% 29% 16% 3	533
	11th to 20th	Day	14% 10% 29% 29% 14% 3	630
	21st to end	Day	17% 8% 32% 28% 13% 2	630
July	1st to 10th	Day	9% 5% 26% 31% 23% 6%	621
	11th to 20th	Day	12% 7% 30% 29% 16% 7%	574
	21st to end	Day	10% 5% 28% 34% 16% 7%	488
August	1st to 10th	Day	11% 5% 24% 31% 17% 12%	446
	11th to 20th	Day	14% 5% 17% 29% 22% 13%	439
	21st to end	Day	14% 7% 20% 30% 19% 9%	495
September	1st to 10th	Day	14% 8% 23% 28% 18% 9%	450
	11th to 20th	Day	10% 6% 22% 27% 22% 12%	450
	21st to end	Day	16% 10% 28% 24% 14% 8%	450
October	1st to 10th	Day	22% 11% 26% 21% 14% 6%	450
	11th to 20th	Day	26% 20% 29% 20% 4 1	450
	21st to end	Day	33% 20% 26% 17% 4	437
November	1st to 10th	Day	25% 18% 30% 18% 8%	261
	11th to 20th	Day	28% 17% 32% 16% 3 3	180
	21st to end	Day	29% 24% 32% 14% 2	180
December	1st to 10th	Day	27% 29% 29% 12% 3	180
	11th to 20th	Day	29% 22% 32% 12% 3 1	180
	21st to end	Day	37% 17% 33% 11% 2 1	198
January	1st to 10th	Night	23% 18% 33% 19% 6% 1	950
	11th to 20th	Night	26% 16% 33% 20% 4 1	817
	21st to end	Night	19% 11% 36% 27% 6% 1	792
February	1st to 10th	Night	23% 18% 36% 21% 3	720
	11th to 20th	Night	22% 15% 35% 24% 5%	703
	21st to end	Night	23% 17% 35% 21% 3	592
March	1st to 10th	Night	18% 15% 35% 24% 7% 1	720
	11th to 20th	Night	18% 16% 34% 25% 5% 1	720
	21st to end	Night	24% 10% 30% 27% 9% 1	792
April	1st to 10th	Night	25% 14% 29% 27% 5%	720
	11th to 20th	Night	21% 13% 27% 28% 10% 1	550
	21st to end	Night	22% 10% 26% 31% 10%	540
May	1st to 10th	Night	19% 5% 29% 34% 11% 1	540
	11th to 20th	Night	20% 6% 23% 38% 12% 1	461
	21st to end	Night	12% 4 26% 42% 16%	389
June	1st to 10th	Night	15% 5% 25% 42% 12% 1	360
	11th to 20th	Night	13% 7% 26% 41% 13%	360
	21st to end	Night	17% 4 23% 41% 14% 1	360
July	1st to 10th	Night	7% 4 19% 49% 20% 1	350
	11th to 20th	Night	11% 4 22% 38% 24% 1	425
	21st to end	Night	11% 4 19% 45% 21% 1	591
August	1st to 10th	Night	11% 3 16% 40% 29% 1	537
	11th to 20th	Night	11% 2 15% 39% 29% 4	534
	21st to end	Night	14% 4 22% 32% 26% 2	595
September	1st to 10th	Night	11% 5% 23% 36% 19% 5%	720
	11th to 20th	Night	14% 4 20% 37% 21% 4	720
	21st to end	Night	16% 8% 23% 32% 18% 4	720
October	1st to 10th	Night	21% 9% 26% 28% 14% 1	720
	11th to 20th	Night	27% 13% 25% 26% 7% 1	720
	21st to end	Night	31% 13% 30% 22% 3 1	792
November	1st to 10th	Night	26% 11% 29% 24% 8% 1	740
	11th to 20th	Night	26% 19% 30% 19% 7%	760
	21st to end	Night	29% 15% 31% 22% 3	760
December	1st to 10th	Night	32% 16% 31% 18% 4	760
	11th to 20th	Night	24% 18% 38% 16% 3	764
	21st to end	Night	32% 14% 35% 17% 2	1045

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