Scarborough
Clear Sky Chart
History

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

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	15% 8% 3 7% 5% 5% 5% 4 6% 7% 35%	101476
	Night	16% 9% 3 7% 5% 4 5% 4 5% 7% 36%	97588
Transparency	Day	45% 8% 14% 21% 11% 1	105079
	Night	46% 8% 12% 21% 11% 1	102073
Seeing	Day	16% 6% 23% 31% 19% 5%	14454
	Night	19% 7% 27% 31% 15% 2	23820

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	17% 11% 4 8% 4 5% 4 3 4 6% 33%	2517
	11th to 20th	Day	12% 16% 7% 15% 8% 6% 4 4 4 4 20%	2722
	21st to end	Day	22% 18% 5% 10% 6% 5% 4 3 4 5% 18%	3124
February	1st to 10th	Day	15% 14% 5% 11% 6% 6% 6% 3 4 5% 24%	1710
	11th to 20th	Day	12% 13% 5% 11% 6% 5% 5% 3 5% 6% 29%	1663
	21st to end	Day	17% 12% 4 9% 6% 5% 4 4 5% 5% 28%	1464
March	1st to 10th	Day	20% 10% 3 8% 5% 4 4 4 4 6% 32%	3432
	11th to 20th	Day	11% 12% 5% 9% 6% 5% 5% 4 6% 6% 31%	3480
	21st to end	Day	16% 9% 2 7% 5% 4 4 3 5% 6% 39%	3815
April	1st to 10th	Day	17% 11% 4 7% 5% 4 5% 4 5% 6% 31%	2255
	11th to 20th	Day	19% 9% 3 6% 4 4 4 3 5% 6% 36%	2309
	21st to end	Day	19% 9% 3 7% 5% 4 4 4 6% 5% 34%	2470
May	1st to 10th	Day	17% 7% 3 8% 5% 5% 5% 4 6% 7% 34%	4108
	11th to 20th	Day	16% 8% 3 8% 5% 4 4 4 6% 8% 34%	4398
	21st to end	Day	11% 5% 2 5% 4 4 4 4 5% 8% 48%	4837
June	1st to 10th	Day	14% 6% 2 6% 6% 5% 5% 4 8% 8% 37%	2660
	11th to 20th	Day	11% 5% 2 6% 4 5% 5% 4 8% 10% 40%	2660
	21st to end	Day	13% 5% 2 6% 4 5% 5% 5% 7% 9% 40%	2660
July	1st to 10th	Day	9% 4 1 6% 5% 5% 6% 4 7% 10% 43%	4440
	11th to 20th	Day	10% 4 2 5% 4 4 5% 4 7% 8% 48%	4440
	21st to end	Day	8% 5% 2 6% 4 5% 6% 5% 7% 8% 43%	4539
August	1st to 10th	Day	16% 7% 2 6% 4 4 4 4 6% 7% 39%	4104
	11th to 20th	Day	10% 6% 3 7% 5% 5% 5% 4 7% 10% 39%	4044
	21st to end	Day	9% 6% 2 6% 4 5% 5% 4 7% 8% 45%	4340
September	1st to 10th	Day	13% 5% 2 6% 4 5% 5% 4 6% 8% 44%	2280
	11th to 20th	Day	11% 5% 2 5% 4 3 4 4 6% 8% 49%	2185
	21st to end	Day	12% 6% 3 8% 6% 5% 5% 4 5% 9% 38%	2040
October	1st to 10th	Day	17% 7% 2 7% 4 4 5% 3 6% 6% 38%	1900
	11th to 20th	Day	19% 8% 3 7% 5% 5% 4 3 5% 7% 33%	1900
	21st to end	Day	23% 9% 4 9% 5% 5% 5% 3 5% 6% 26%	2090
November	1st to 10th	Day	14% 8% 3 8% 6% 5% 5% 4 6% 8% 34%	1652
	11th to 20th	Day	16% 11% 3 8% 6% 6% 6% 4 7% 8% 26%	1520
	21st to end	Day	18% 12% 4 9% 6% 5% 3 4 7% 7% 25%	1520
December	1st to 10th	Day	16% 15% 5% 11% 6% 6% 5% 4 6% 7% 19%	1520
	11th to 20th	Day	20% 12% 4 8% 5% 5% 4 5% 6% 6% 25%	1906
	21st to end	Day	29% 15% 5% 12% 6% 4 3 3 4 5% 14%	2772
January	1st to 10th	Night	18% 14% 4 9% 5% 5% 4 4 5% 7% 26%	4429
	11th to 20th	Night	16% 12% 5% 11% 8% 6% 6% 4 5% 6% 23%	4234
	21st to end	Night	22% 13% 5% 9% 7% 5% 5% 3 4 5% 22%	4532
February	1st to 10th	Night	14% 16% 4 8% 5% 6% 5% 4 6% 6% 26%	2470
	11th to 20th	Night	15% 12% 4 9% 7% 4 5% 4 5% 7% 28%	2403
	21st to end	Night	15% 11% 4 9% 6% 5% 5% 4 5% 6% 30%	1986
March	1st to 10th	Night	19% 9% 4 7% 5% 5% 5% 3 4 5% 34%	3408
	11th to 20th	Night	14% 10% 4 8% 5% 4 5% 3 5% 6% 37%	3479
	21st to end	Night	17% 7% 2 6% 4 4 4 3 5% 5% 44%	3817
April	1st to 10th	Night	19% 10% 2 7% 5% 4 4 3 5% 6% 34%	1924
	11th to 20th	Night	16% 7% 3 6% 5% 5% 5% 3 5% 6% 39%	1835
	21st to end	Night	17% 7% 3 6% 5% 4 5% 4 6% 7% 36%	1710
May	1st to 10th	Night	18% 7% 3 6% 4 4 4 4 5% 5% 39%	2833
	11th to 20th	Night	17% 7% 2 7% 5% 4 5% 3 6% 7% 37%	2495
	21st to end	Night	10% 4 2 5% 4 3 4 3 6% 8% 52%	2738
June	1st to 10th	Night	13% 5% 2 6% 5% 4 5% 4 6% 8% 42%	1520
	11th to 20th	Night	8% 6% 2 6% 5% 5% 5% 4 6% 8% 44%	1520
	21st to end	Night	14% 5% 2 5% 4 4 5% 4 6% 8% 44%	1520
July	1st to 10th	Night	6% 4 2 5% 5% 4 5% 4 6% 9% 50%	2520
	11th to 20th	Night	12% 4 1 5% 4 3 4 3 5% 9% 51%	2520
	21st to end	Night	8% 4 1 5% 3 3 4 4 7% 8% 52%	3012
August	1st to 10th	Night	10% 5% 2 5% 4 4 5% 4 6% 8% 47%	2825
	11th to 20th	Night	12% 5% 2 5% 3 4 3 3 5% 7% 51%	2785
	21st to end	Night	11% 5% 2 6% 4 4 5% 4 6% 7% 47%	3283
September	1st to 10th	Night	10% 5% 2 5% 4 4 6% 4 6% 6% 47%	1900
	11th to 20th	Night	11% 3 1 5% 3 3 3 3 4 6% 56%	1990
	21st to end	Night	16% 6% 2 7% 4 4 4 4 5% 7% 42%	2139
October	1st to 10th	Night	16% 7% 3 7% 4 3 5% 4 5% 6% 40%	2280
	11th to 20th	Night	19% 7% 2 7% 6% 4 4 4 5% 7% 35%	2280
	21st to end	Night	21% 9% 3 7% 4 5% 5% 3 6% 6% 31%	2508
November	1st to 10th	Night	16% 7% 2 6% 5% 4 5% 3 5% 7% 39%	2541
	11th to 20th	Night	17% 9% 3 7% 5% 5% 4 4 7% 7% 32%	2660
	21st to end	Night	20% 10% 3 6% 5% 5% 5% 4 6% 7% 27%	2660
December	1st to 10th	Night	21% 14% 3 8% 6% 5% 5% 3 5% 6% 24%	2660
	11th to 20th	Night	17% 15% 5% 8% 6% 5% 5% 4 6% 6% 24%	3288
	21st to end	Night	32% 13% 4 8% 5% 5% 5% 4 4 5% 15%	4884

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	52% 11% 19% 10% 7% 1	2518
	11th to 20th	Day	69% 8% 10% 9% 4	2722
	21st to end	Day	68% 9% 11% 8% 4	3124
February	1st to 10th	Day	62% 8% 12% 15% 3 1	1710
	11th to 20th	Day	56% 7% 13% 16% 7% 1	1672
	21st to end	Day	56% 7% 14% 15% 7% 1	1464
March	1st to 10th	Day	53% 7% 13% 18% 9% 1	3435
	11th to 20th	Day	51% 7% 14% 18% 9% 1	3480
	21st to end	Day	43% 6% 14% 21% 14% 2	3815
April	1st to 10th	Day	52% 6% 13% 17% 11% 1	2255
	11th to 20th	Day	47% 6% 11% 20% 14% 2	2309
	21st to end	Day	50% 7% 10% 18% 12% 3	2470
May	1st to 10th	Day	46% 9% 13% 17% 14% 2	4120
	11th to 20th	Day	46% 15% 11% 18% 9% 1	4402
	21st to end	Day	32% 9% 14% 25% 17% 3	4837
June	1st to 10th	Day	41% 9% 13% 21% 15% 1	2660
	11th to 20th	Day	36% 9% 13% 24% 17% 2	2660
	21st to end	Day	37% 9% 16% 24% 15%	2660
July	1st to 10th	Day	32% 8% 16% 26% 15% 2	4370
	11th to 20th	Day	30% 8% 14% 36% 11% 1	4365
	21st to end	Day	34% 10% 15% 22% 18% 1	4394
August	1st to 10th	Day	42% 8% 14% 21% 15% 1	4091
	11th to 20th	Day	38% 8% 16% 26% 11% 1	4083
	21st to end	Day	34% 7% 14% 34% 10% 1	4340
September	1st to 10th	Day	36% 9% 14% 28% 11% 1	2280
	11th to 20th	Day	33% 9% 14% 29% 15% 1	2185
	21st to end	Day	41% 9% 13% 26% 9%	2040
October	1st to 10th	Day	35% 7% 16% 27% 15% 1	3160
	11th to 20th	Day	37% 6% 18% 24% 15% 1	3140
	21st to end	Day	49% 7% 15% 22% 6%	3428
November	1st to 10th	Day	46% 8% 16% 20% 9% 1	1652
	11th to 20th	Day	54% 9% 15% 14% 8% 1	1520
	21st to end	Day	57% 9% 15% 15% 3	1520
December	1st to 10th	Day	64% 9% 12% 12% 3	1520
	11th to 20th	Day	58% 11% 14% 11% 6%	1906
	21st to end	Day	73% 8% 9% 8% 2	2772
January	1st to 10th	Night	58% 9% 15% 13% 4 1	4429
	11th to 20th	Night	64% 13% 10% 9% 3 1	4234
	21st to end	Night	65% 9% 12% 9% 4 1	4532
February	1st to 10th	Night	58% 9% 11% 17% 4 1	2470
	11th to 20th	Night	56% 8% 11% 16% 8% 1	2405
	21st to end	Night	54% 5% 14% 19% 8%	1986
March	1st to 10th	Night	52% 6% 11% 23% 7% 1	3418
	11th to 20th	Night	46% 7% 14% 20% 11% 1	3480
	21st to end	Night	40% 5% 10% 24% 19% 2	3817
April	1st to 10th	Night	50% 5% 11% 19% 14% 1	1924
	11th to 20th	Night	47% 6% 9% 21% 15% 2	1835
	21st to end	Night	45% 8% 10% 20% 15% 2	1710
May	1st to 10th	Night	44% 8% 12% 18% 16% 2	2840
	11th to 20th	Night	43% 14% 12% 18% 10% 2	2496
	21st to end	Night	30% 7% 13% 26% 21% 3	2739
June	1st to 10th	Night	38% 8% 11% 24% 16% 3	1520
	11th to 20th	Night	36% 7% 12% 22% 21% 2	1520
	21st to end	Night	38% 8% 11% 24% 18% 1	1520
July	1st to 10th	Night	30% 7% 14% 25% 21% 3	2480
	11th to 20th	Night	31% 7% 13% 33% 15% 1	2472
	21st to end	Night	29% 9% 15% 29% 17% 2	2916
August	1st to 10th	Night	35% 7% 13% 28% 15% 2	2814
	11th to 20th	Night	32% 7% 15% 33% 12% 1	2812
	21st to end	Night	34% 7% 12% 31% 14% 1	3283
September	1st to 10th	Night	33% 9% 14% 28% 14% 1	1900
	11th to 20th	Night	28% 8% 10% 35% 18%	1990
	21st to end	Night	41% 8% 12% 27% 12%	2139
October	1st to 10th	Night	34% 6% 9% 26% 23% 1	3800
	11th to 20th	Night	42% 7% 14% 27% 10%	3779
	21st to end	Night	40% 7% 15% 27% 10% 1	4120
November	1st to 10th	Night	44% 7% 13% 23% 12% 1	2541
	11th to 20th	Night	51% 8% 14% 17% 10% 1	2660
	21st to end	Night	55% 10% 16% 15% 4	2660
December	1st to 10th	Night	61% 8% 12% 14% 5%	2660
	11th to 20th	Night	60% 9% 13% 14% 4	3288
	21st to end	Night	71% 9% 11% 7% 2	4884

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% 13% 27% 31% 7% 2	180
	11th to 20th	Day	20% 16% 35% 18% 10% 1	239
	21st to end	Day	22% 9% 33% 30% 6% 1	297
February	1st to 10th	Day	20% 13% 39% 23% 6%	270
	11th to 20th	Day	19% 13% 38% 25% 6%	270
	21st to end	Day	23% 20% 26% 27% 4	254
March	1st to 10th	Day	20% 9% 32% 31% 8%	460
	11th to 20th	Day	17% 12% 31% 29% 9% 1	460
	21st to end	Day	24% 6% 30% 30% 9% 1	506
April	1st to 10th	Day	19% 8% 27% 35% 9% 1	460
	11th to 20th	Day	25% 6% 28% 25% 12% 3	452
	21st to end	Day	22% 5% 26% 34% 12% 2	460
May	1st to 10th	Day	19% 5% 21% 31% 19% 5%	463
	11th to 20th	Day	14% 2 17% 35% 26% 5%	487
	21st to end	Day	13% 1 15% 35% 28% 8%	529
June	1st to 10th	Day	13% 3 18% 38% 24% 3	490
	11th to 20th	Day	13% 3 18% 35% 28% 3	490
	21st to end	Day	14% 3 16% 36% 26% 5%	490
July	1st to 10th	Day	8% 2 12% 33% 36% 9%	485
	11th to 20th	Day	15% 1 12% 31% 32% 10%	484
	21st to end	Day	8% 2 10% 42% 29% 8%	532
August	1st to 10th	Day	11% 3 10% 33% 31% 12%	486
	11th to 20th	Day	8% 4 13% 30% 30% 15%	479
	21st to end	Day	11% 2 16% 31% 29% 11%	539
September	1st to 10th	Day	10% 3 17% 31% 27% 11%	490
	11th to 20th	Day	9% 2 12% 32% 27% 18%	490
	21st to end	Day	14% 5% 21% 31% 18% 10%	490
October	1st to 10th	Day	21% 5% 24% 26% 17% 8%	490
	11th to 20th	Day	19% 7% 31% 29% 10% 3	490
	21st to end	Day	25% 9% 27% 27% 10% 1	539
November	1st to 10th	Day	19% 11% 26% 29% 14% 2	285
	11th to 20th	Day	18% 12% 27% 32% 9% 2	180
	21st to end	Day	22% 11% 34% 26% 7% 1	180
December	1st to 10th	Day	21% 10% 38% 24% 7% 1	180
	11th to 20th	Day	20% 15% 38% 20% 6% 1	180
	21st to end	Day	28% 10% 40% 18% 5%	198
January	1st to 10th	Night	23% 12% 37% 20% 8%	760
	11th to 20th	Night	26% 11% 31% 26% 5%	760
	21st to end	Night	19% 9% 36% 28% 7%	836
February	1st to 10th	Night	21% 12% 38% 24% 5%	760
	11th to 20th	Night	20% 11% 37% 25% 6%	743
	21st to end	Night	20% 10% 39% 25% 5%	628
March	1st to 10th	Night	19% 8% 34% 31% 8%	760
	11th to 20th	Night	20% 9% 36% 26% 8% 1	760
	21st to end	Night	19% 7% 29% 32% 11% 1	836
April	1st to 10th	Night	24% 6% 27% 34% 8% 1	760
	11th to 20th	Night	18% 7% 28% 34% 11% 3	711
	21st to end	Night	20% 4 24% 36% 14% 1	570
May	1st to 10th	Night	18% 3 18% 38% 21% 2	570
	11th to 20th	Night	16% 1 19% 40% 22% 2	374
	21st to end	Night	10% 3 16% 38% 30% 4	411
June	1st to 10th	Night	14% 2 16% 41% 24% 3	380
	11th to 20th	Night	11% 3 17% 39% 29% 2	380
	21st to end	Night	14% 2 14% 42% 25% 3	380
July	1st to 10th	Night	6% 2 9% 47% 31% 5%	370
	11th to 20th	Night	12% 3 12% 36% 32% 4	368
	21st to end	Night	8% 2 10% 44% 32% 4	575
August	1st to 10th	Night	10% 2 10% 36% 36% 6%	567
	11th to 20th	Night	7% 2 12% 35% 36% 7%	564
	21st to end	Night	11% 2 18% 33% 31% 5%	721
September	1st to 10th	Night	11% 3 19% 34% 26% 8%	760
	11th to 20th	Night	12% 3 14% 29% 32% 9%	760
	21st to end	Night	18% 4 19% 29% 25% 6%	760
October	1st to 10th	Night	19% 4 26% 25% 21% 5%	760
	11th to 20th	Night	20% 9% 27% 31% 12% 2	760
	21st to end	Night	26% 7% 27% 32% 8% 1	836
November	1st to 10th	Night	21% 8% 26% 32% 12% 2	764
	11th to 20th	Night	21% 9% 34% 27% 9% 2	760
	21st to end	Night	23% 10% 31% 29% 7% 1	760
December	1st to 10th	Night	27% 9% 35% 22% 6% 1	760
	11th to 20th	Night	21% 10% 41% 22% 6%	760
	21st to end	Night	31% 9% 34% 22% 4	836

Page generated at 2024-11-03 13:19:04. Version ac07

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