Pickering
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Pickering clear sky chart from 2005-11-06 to 2025-02-25.

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	14% 9% 3 8% 5% 5% 5% 4 6% 7% 34%	108810
	Night	15% 9% 3 8% 5% 5% 5% 4 5% 7% 34%	109843
Transparency	Day	46% 6% 14% 21% 11% 1	112445
	Night	48% 6% 12% 21% 11% 1	114370
Seeing	Day	17% 6% 22% 31% 19% 5%	14715
	Night	19% 7% 26% 31% 15% 3	24246

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	13% 10% 3 10% 5% 5% 5% 3 5% 6% 34%	3597
	11th to 20th	Day	10% 16% 7% 17% 9% 6% 5% 4 4 5% 18%	3843
	21st to end	Day	17% 16% 7% 13% 6% 5% 4 3 5% 5% 20%	4466
February	1st to 10th	Day	15% 14% 5% 12% 6% 6% 5% 4 4 6% 23%	1800
	11th to 20th	Day	13% 12% 5% 13% 7% 5% 4 3 4 6% 27%	1753
	21st to end	Day	18% 12% 4 10% 6% 5% 4 3 5% 5% 27%	1496
March	1st to 10th	Day	20% 10% 3 8% 5% 4 4 3 5% 5% 32%	3432
	11th to 20th	Day	11% 12% 5% 9% 6% 5% 6% 4 5% 6% 30%	3480
	21st to end	Day	16% 8% 3 6% 4 4 4 3 5% 6% 39%	3815
April	1st to 10th	Day	17% 11% 3 9% 5% 4 4 3 6% 7% 30%	2261
	11th to 20th	Day	19% 9% 2 6% 4 4 5% 4 5% 6% 36%	2304
	21st to end	Day	19% 8% 3 7% 5% 4 5% 3 6% 5% 34%	2470
May	1st to 10th	Day	17% 8% 3 7% 5% 4 4 5% 6% 8% 33%	4130
	11th to 20th	Day	15% 9% 3 8% 6% 4 4 4 7% 9% 31%	4398
	21st to end	Day	11% 5% 2 6% 4 4 5% 3 6% 9% 47%	4837
June	1st to 10th	Day	13% 7% 2 7% 5% 5% 5% 4 7% 8% 36%	2660
	11th to 20th	Day	11% 5% 2 6% 4 5% 5% 4 7% 10% 40%	2660
	21st to end	Day	13% 6% 2 5% 5% 4 4 4 8% 9% 41%	2660
July	1st to 10th	Day	9% 4 2 6% 4 5% 5% 4 7% 10% 43%	4440
	11th to 20th	Day	9% 5% 2 5% 4 4 5% 5% 7% 8% 46%	4440
	21st to end	Day	7% 5% 2 6% 5% 5% 6% 5% 7% 9% 43%	4565
August	1st to 10th	Day	15% 7% 3 6% 4 4 4 4 6% 7% 40%	4104
	11th to 20th	Day	10% 5% 3 7% 5% 4 5% 4 7% 10% 39%	4044
	21st to end	Day	8% 5% 2 6% 4 4 5% 4 7% 9% 45%	4323
September	1st to 10th	Day	12% 5% 2 6% 4 4 6% 4 6% 7% 45%	2280
	11th to 20th	Day	11% 5% 2 5% 5% 4 5% 3 6% 8% 49%	2195
	21st to end	Day	13% 5% 3 7% 5% 5% 5% 4 6% 9% 39%	2034
October	1st to 10th	Day	17% 7% 2 7% 5% 4 5% 4 5% 7% 37%	1900
	11th to 20th	Day	19% 9% 3 7% 5% 4 5% 3 6% 7% 33%	1900
	21st to end	Day	22% 10% 4 8% 5% 5% 5% 3 5% 7% 26%	2090
November	1st to 10th	Day	14% 9% 3 9% 6% 5% 5% 3 6% 8% 34%	1687
	11th to 20th	Day	15% 11% 4 10% 5% 6% 6% 4 7% 7% 27%	1600
	21st to end	Day	19% 12% 4 9% 6% 5% 6% 4 5% 8% 24%	1600
December	1st to 10th	Day	18% 14% 5% 12% 6% 7% 7% 4 7% 6% 15%	2600
	11th to 20th	Day	20% 14% 4 9% 5% 4 4 4 5% 6% 25%	2986
	21st to end	Day	27% 15% 6% 12% 6% 4 3 3 4 5% 15%	3960
January	1st to 10th	Night	15% 11% 4 9% 5% 5% 5% 4 6% 6% 30%	6349
	11th to 20th	Night	13% 13% 5% 13% 8% 6% 6% 4 5% 6% 20%	6026
	21st to end	Night	16% 13% 4 10% 6% 5% 5% 4 5% 7% 25%	6490
February	1st to 10th	Night	13% 16% 4 9% 6% 6% 5% 4 5% 6% 26%	2600
	11th to 20th	Night	15% 12% 5% 10% 6% 5% 5% 4 5% 6% 27%	2533
	21st to end	Night	14% 12% 3 10% 5% 5% 5% 5% 5% 6% 30%	2049
March	1st to 10th	Night	18% 10% 3 8% 5% 4 5% 3 5% 6% 33%	3408
	11th to 20th	Night	14% 10% 3 8% 6% 4 5% 3 5% 6% 35%	3479
	21st to end	Night	17% 6% 2 5% 4 4 4 3 5% 5% 43%	3817
April	1st to 10th	Night	18% 10% 3 7% 5% 4 4 3 5% 6% 34%	1919
	11th to 20th	Night	16% 6% 3 7% 5% 5% 5% 3 5% 6% 39%	1841
	21st to end	Night	16% 8% 3 7% 5% 5% 5% 4 6% 7% 35%	1710
May	1st to 10th	Night	19% 6% 2 6% 4 4 4 3 5% 6% 39%	2809
	11th to 20th	Night	16% 7% 3 7% 5% 4 6% 4 6% 8% 34%	2495
	21st to end	Night	9% 4 2 5% 3 4 4 3 6% 8% 51%	2738
June	1st to 10th	Night	12% 5% 2 6% 5% 5% 5% 4 6% 7% 43%	1520
	11th to 20th	Night	8% 5% 2 7% 6% 4 4 4 7% 8% 44%	1520
	21st to end	Night	12% 6% 2 5% 5% 4 4 4 6% 9% 43%	1520
July	1st to 10th	Night	6% 5% 2 6% 4 4 4 4 6% 9% 50%	2520
	11th to 20th	Night	11% 4 2 5% 4 4 3 3 5% 9% 50%	2520
	21st to end	Night	8% 4 2 4 3 4 4 4 6% 8% 52%	2984
August	1st to 10th	Night	10% 5% 2 6% 4 4 4 4 6% 8% 47%	2825
	11th to 20th	Night	12% 5% 1 6% 3 3 3 3 5% 7% 51%	2785
	21st to end	Night	10% 5% 2 6% 4 4 4 4 6% 8% 47%	3299
September	1st to 10th	Night	10% 5% 2 6% 4 5% 4 5% 5% 7% 47%	1900
	11th to 20th	Night	11% 4 2 4 3 4 3 3 5% 7% 55%	1982
	21st to end	Night	16% 6% 3 7% 4 4 4 3 5% 7% 42%	2144
October	1st to 10th	Night	16% 7% 3 7% 4 4 4 3 5% 7% 40%	2280
	11th to 20th	Night	19% 8% 3 7% 5% 4 4 4 6% 6% 34%	2280
	21st to end	Night	21% 8% 4 7% 4 5% 5% 4 5% 6% 31%	2508
November	1st to 10th	Night	17% 7% 2 6% 5% 4 4 4 5% 7% 38%	2609
	11th to 20th	Night	17% 9% 3 7% 6% 5% 4 5% 6% 7% 31%	2800
	21st to end	Night	20% 11% 3 8% 5% 5% 5% 5% 6% 8% 26%	2800
December	1st to 10th	Night	18% 13% 4 10% 6% 6% 5% 4 5% 7% 21%	4580
	11th to 20th	Night	18% 15% 4 9% 5% 5% 4 4 5% 6% 25%	5208
	21st to end	Night	26% 13% 7% 10% 6% 5% 4 4 5% 5% 15%	6996

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	50% 8% 16% 15% 11% 1	3598
	11th to 20th	Day	70% 7% 10% 9% 4	3876
	21st to end	Day	65% 6% 11% 10% 7%	4466
February	1st to 10th	Day	62% 6% 11% 16% 4 1	1800
	11th to 20th	Day	57% 7% 12% 17% 7% 1	1762
	21st to end	Day	57% 5% 13% 17% 6%	1496
March	1st to 10th	Day	53% 7% 12% 19% 9%	3435
	11th to 20th	Day	51% 6% 14% 19% 9% 1	3480
	21st to end	Day	43% 5% 13% 23% 14% 2	3815
April	1st to 10th	Day	50% 6% 13% 18% 11% 2	2261
	11th to 20th	Day	47% 6% 10% 21% 14% 2	2304
	21st to end	Day	49% 6% 11% 19% 12% 3	2470
May	1st to 10th	Day	46% 7% 14% 18% 14% 2	4142
	11th to 20th	Day	47% 12% 13% 18% 9% 1	4402
	21st to end	Day	34% 6% 15% 26% 16% 3	4837
June	1st to 10th	Day	41% 8% 14% 22% 14% 1	2660
	11th to 20th	Day	36% 7% 14% 25% 16% 2	2660
	21st to end	Day	36% 6% 18% 25% 14% 1	2660
July	1st to 10th	Day	32% 5% 17% 28% 16% 2	4370
	11th to 20th	Day	32% 5% 15% 36% 11% 1	4365
	21st to end	Day	35% 7% 16% 24% 17% 1	4419
August	1st to 10th	Day	42% 5% 15% 23% 14% 1	4091
	11th to 20th	Day	37% 5% 18% 27% 11% 1	4083
	21st to end	Day	33% 5% 15% 36% 10% 1	4323
September	1st to 10th	Day	36% 8% 14% 29% 12% 1	2280
	11th to 20th	Day	31% 7% 16% 30% 15% 1	2195
	21st to end	Day	41% 7% 16% 27% 10%	2034
October	1st to 10th	Day	36% 5% 17% 27% 15% 1	3160
	11th to 20th	Day	37% 5% 18% 25% 14% 1	3140
	21st to end	Day	49% 4 18% 23% 6%	3428
November	1st to 10th	Day	47% 6% 16% 21% 9% 1	1687
	11th to 20th	Day	54% 8% 14% 15% 8% 1	1600
	21st to end	Day	58% 7% 15% 17% 3	1600
December	1st to 10th	Day	67% 4 17% 8% 3	2600
	11th to 20th	Day	61% 7% 13% 10% 9%	2986
	21st to end	Day	72% 8% 7% 9% 4	3960
January	1st to 10th	Night	53% 7% 14% 20% 6%	6349
	11th to 20th	Night	65% 10% 9% 11% 4	6067
	21st to end	Night	60% 9% 11% 11% 9% 1	6490
February	1st to 10th	Night	59% 7% 12% 17% 5% 1	2600
	11th to 20th	Night	58% 6% 11% 16% 8% 1	2535
	21st to end	Night	55% 4 13% 19% 8%	2049
March	1st to 10th	Night	53% 5% 11% 23% 7% 1	3418
	11th to 20th	Night	49% 5% 14% 20% 11% 1	3480
	21st to end	Night	40% 6% 9% 25% 18% 2	3817
April	1st to 10th	Night	51% 4 10% 20% 14% 1	1919
	11th to 20th	Night	47% 5% 10% 20% 16% 2	1841
	21st to end	Night	46% 7% 11% 19% 15% 2	1710
May	1st to 10th	Night	46% 6% 12% 18% 16% 2	2816
	11th to 20th	Night	45% 11% 13% 19% 10% 3	2496
	21st to end	Night	31% 6% 13% 26% 21% 3	2739
June	1st to 10th	Night	39% 6% 12% 24% 16% 2	1520
	11th to 20th	Night	37% 5% 12% 23% 21% 2	1520
	21st to end	Night	38% 6% 13% 24% 17% 1	1520
July	1st to 10th	Night	31% 5% 15% 25% 21% 3	2480
	11th to 20th	Night	32% 5% 13% 34% 15% 1	2472
	21st to end	Night	31% 6% 15% 29% 17% 2	2889
August	1st to 10th	Night	35% 5% 14% 29% 15% 2	2814
	11th to 20th	Night	34% 5% 15% 33% 12% 1	2812
	21st to end	Night	35% 6% 12% 32% 15% 1	3299
September	1st to 10th	Night	35% 7% 14% 28% 15% 1	1900
	11th to 20th	Night	29% 6% 12% 34% 18%	1982
	21st to end	Night	42% 6% 13% 27% 12%	2144
October	1st to 10th	Night	35% 5% 10% 26% 24% 1	3800
	11th to 20th	Night	43% 5% 15% 28% 9%	3779
	21st to end	Night	41% 5% 16% 28% 10% 1	4120
November	1st to 10th	Night	44% 6% 13% 23% 13% 1	2609
	11th to 20th	Night	51% 7% 15% 17% 9% 1	2800
	21st to end	Night	56% 8% 17% 15% 4	2800
December	1st to 10th	Night	62% 5% 15% 15% 4	4580
	11th to 20th	Night	60% 7% 11% 13% 9%	5208
	21st to end	Night	70% 7% 11% 8% 4	6996

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	21% 15% 29% 27% 9% 1	200
	11th to 20th	Day	22% 15% 35% 18% 10% 1	260
	21st to end	Day	24% 10% 34% 27% 5% 1	330
February	1st to 10th	Day	20% 13% 39% 22% 6%	300
	11th to 20th	Day	19% 15% 38% 23% 5%	300
	21st to end	Day	22% 19% 29% 25% 5%	270
March	1st to 10th	Day	21% 8% 33% 30% 8%	460
	11th to 20th	Day	17% 13% 30% 29% 9% 1	460
	21st to end	Day	24% 7% 31% 29% 8% 1	506
April	1st to 10th	Day	17% 10% 27% 37% 8% 1	460
	11th to 20th	Day	25% 6% 29% 25% 12% 3	452
	21st to end	Day	21% 6% 27% 32% 12% 2	460
May	1st to 10th	Day	20% 4 20% 34% 18% 5%	463
	11th to 20th	Day	15% 2 17% 37% 25% 5%	487
	21st to end	Day	12% 2 15% 36% 29% 7%	529
June	1st to 10th	Day	13% 4 17% 39% 22% 3	490
	11th to 20th	Day	12% 3 14% 36% 31% 4	490
	21st to end	Day	15% 3 12% 41% 25% 4	490
July	1st to 10th	Day	8% 1 10% 34% 38% 9%	485
	11th to 20th	Day	14% 1 9% 32% 34% 10%	484
	21st to end	Day	8% 3 10% 39% 31% 8%	532
August	1st to 10th	Day	12% 2 9% 33% 31% 12%	486
	11th to 20th	Day	9% 1 11% 34% 31% 13%	479
	21st to end	Day	11% 2 14% 31% 32% 11%	539
September	1st to 10th	Day	10% 3 15% 33% 28% 11%	490
	11th to 20th	Day	9% 2 12% 31% 26% 20%	490
	21st to end	Day	14% 4 20% 32% 20% 10%	490
October	1st to 10th	Day	20% 5% 23% 26% 19% 7%	490
	11th to 20th	Day	19% 8% 31% 29% 11% 3	490
	21st to end	Day	26% 8% 26% 27% 12% 1	539
November	1st to 10th	Day	21% 9% 26% 28% 15% 2	294
	11th to 20th	Day	20% 13% 27% 31% 10% 1	200
	21st to end	Day	24% 9% 36% 24% 7% 1	200
December	1st to 10th	Day	23% 9% 34% 24% 8% 3	200
	11th to 20th	Day	25% 15% 37% 17% 7% 1	200
	21st to end	Day	28% 11% 37% 18% 5% 1	220
January	1st to 10th	Night	24% 11% 39% 19% 7%	800
	11th to 20th	Night	27% 12% 32% 24% 5%	800
	21st to end	Night	19% 10% 36% 27% 7% 1	880
February	1st to 10th	Night	21% 13% 39% 23% 4	800
	11th to 20th	Night	21% 12% 36% 25% 5%	783
	21st to end	Night	20% 10% 40% 24% 5%	647
March	1st to 10th	Night	19% 8% 34% 33% 7% 1	760
	11th to 20th	Night	20% 9% 36% 26% 8% 1	760
	21st to end	Night	19% 7% 29% 32% 12% 1	836
April	1st to 10th	Night	23% 6% 28% 34% 8% 1	760
	11th to 20th	Night	18% 6% 28% 34% 12% 2	717
	21st to end	Night	21% 5% 22% 37% 13% 1	570
May	1st to 10th	Night	18% 3 18% 38% 21% 2	559
	11th to 20th	Night	17% 1 19% 39% 23% 2	374
	21st to end	Night	9% 3 13% 40% 30% 4	411
June	1st to 10th	Night	13% 2 15% 42% 24% 3	380
	11th to 20th	Night	10% 3 15% 41% 28% 3	380
	21st to end	Night	12% 2 14% 41% 28% 3	380
July	1st to 10th	Night	6% 2 8% 44% 33% 6%	370
	11th to 20th	Night	13% 3 10% 37% 33% 5%	368
	21st to end	Night	9% 3 8% 43% 33% 4	560
August	1st to 10th	Night	11% 2 10% 35% 36% 7%	567
	11th to 20th	Night	8% 2 10% 36% 35% 8%	564
	21st to end	Night	11% 3 15% 35% 31% 5%	724
September	1st to 10th	Night	11% 3 16% 35% 27% 8%	760
	11th to 20th	Night	13% 3 14% 29% 30% 11%	760
	21st to end	Night	17% 5% 17% 30% 25% 6%	760
October	1st to 10th	Night	19% 4 25% 28% 20% 5%	760
	11th to 20th	Night	23% 7% 26% 31% 12% 2	760
	21st to end	Night	26% 7% 26% 31% 9% 1	836
November	1st to 10th	Night	21% 6% 25% 34% 12% 2	780
	11th to 20th	Night	21% 9% 32% 27% 8% 2	800
	21st to end	Night	25% 9% 31% 28% 7% 1	800
December	1st to 10th	Night	28% 10% 34% 23% 5% 1	800
	11th to 20th	Night	21% 11% 40% 23% 5% 1	800
	21st to end	Night	30% 9% 33% 23% 4	880

Page generated at 2025-02-22 06:51:40. Version ac07

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