Whitby
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Whitby 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%	108812
	Night	15% 9% 3 8% 5% 5% 5% 4 5% 7% 34%	109839
Transparency	Day	47% 6% 14% 22% 11% 1	112447
	Night	48% 5% 13% 21% 12% 1	114368
Seeing	Day	20% 10% 29% 25% 12% 4	14717
	Night	20% 9% 28% 29% 12% 1	24233

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% 11% 3 11% 7% 5% 4 3 5% 5% 32%	3597
	11th to 20th	Day	10% 17% 6% 17% 9% 6% 5% 4 4 4 17%	3817
	21st to end	Day	16% 17% 6% 14% 6% 6% 4 3 5% 4 19%	4466
February	1st to 10th	Day	15% 15% 4 12% 6% 7% 5% 4 5% 5% 23%	1800
	11th to 20th	Day	12% 13% 6% 12% 6% 6% 4 3 5% 6% 26%	1753
	21st to end	Day	18% 13% 5% 10% 6% 4 4 4 4 4 28%	1494
March	1st to 10th	Day	20% 10% 4 9% 5% 4 4 3 4 6% 32%	3432
	11th to 20th	Day	11% 13% 5% 9% 6% 5% 6% 4 6% 6% 30%	3480
	21st to end	Day	16% 8% 3 7% 5% 4 4 3 5% 6% 39%	3815
April	1st to 10th	Day	18% 11% 4 8% 6% 4 4 4 6% 6% 30%	2266
	11th to 20th	Day	20% 9% 3 6% 4 4 4 4 5% 6% 36%	2296
	21st to end	Day	19% 8% 3 7% 5% 5% 4 3 5% 6% 34%	2470
May	1st to 10th	Day	17% 8% 3 8% 4 5% 5% 4 6% 8% 32%	4157
	11th to 20th	Day	14% 9% 3 8% 5% 4 4 4 6% 8% 32%	4398
	21st to end	Day	11% 6% 2 6% 4 3 4 3 5% 8% 47%	4837
June	1st to 10th	Day	15% 6% 3 7% 5% 5% 5% 4 7% 8% 36%	2660
	11th to 20th	Day	11% 6% 2 6% 4 4 5% 4 7% 9% 40%	2660
	21st to end	Day	13% 6% 2 5% 4 5% 5% 4 6% 9% 40%	2660
July	1st to 10th	Day	9% 4 2 6% 5% 5% 5% 5% 7% 10% 42%	4440
	11th to 20th	Day	9% 4 2 5% 4 4 5% 5% 8% 9% 45%	4440
	21st to end	Day	6% 5% 2 6% 5% 5% 6% 5% 8% 9% 43%	4579
August	1st to 10th	Day	15% 7% 2 6% 4 4 5% 3 6% 8% 38%	4104
	11th to 20th	Day	11% 6% 3 7% 5% 4 5% 5% 8% 10% 38%	4044
	21st to end	Day	8% 5% 2 6% 4 4 5% 4 7% 10% 44%	4318
September	1st to 10th	Day	13% 5% 2 5% 5% 4 5% 4 6% 7% 44%	2280
	11th to 20th	Day	11% 4 2 5% 4 4 4 4 7% 8% 48%	2204
	21st to end	Day	13% 5% 3 7% 5% 5% 5% 4 6% 7% 40%	2028
October	1st to 10th	Day	16% 9% 2 7% 5% 5% 5% 4 5% 6% 36%	1900
	11th to 20th	Day	19% 8% 3 8% 5% 4 5% 4 6% 6% 32%	1900
	21st to end	Day	22% 11% 3 9% 5% 5% 4 4 5% 6% 26%	2090
November	1st to 10th	Day	15% 8% 3 9% 5% 6% 4 4 6% 7% 33%	1681
	11th to 20th	Day	15% 11% 3 10% 7% 5% 4 4 7% 6% 27%	1600
	21st to end	Day	20% 10% 4 10% 6% 5% 5% 3 5% 7% 24%	1600
December	1st to 10th	Day	18% 15% 4 12% 7% 7% 6% 4 6% 6% 14%	2600
	11th to 20th	Day	20% 14% 4 10% 5% 5% 4 3 4 5% 25%	2986
	21st to end	Day	27% 15% 6% 12% 6% 4 4 3 3 5% 15%	3960
January	1st to 10th	Night	15% 12% 4 9% 6% 5% 5% 4 6% 6% 27%	6349
	11th to 20th	Night	13% 13% 5% 14% 8% 6% 5% 4 5% 6% 20%	6065
	21st to end	Night	16% 14% 5% 10% 5% 5% 5% 4 5% 6% 25%	6490
February	1st to 10th	Night	14% 15% 5% 10% 7% 5% 5% 4 5% 5% 25%	2600
	11th to 20th	Night	15% 13% 5% 9% 7% 5% 5% 3 5% 6% 27%	2533
	21st to end	Night	15% 11% 4 10% 6% 5% 4 5% 6% 6% 29%	2051
March	1st to 10th	Night	18% 10% 3 7% 5% 5% 5% 3 4 6% 33%	3408
	11th to 20th	Night	14% 10% 4 8% 6% 5% 4 4 6% 6% 34%	3479
	21st to end	Night	17% 6% 2 5% 4 4 5% 4 4 6% 43%	3817
April	1st to 10th	Night	19% 10% 3 6% 5% 4 4 4 5% 6% 34%	1913
	11th to 20th	Night	16% 7% 3 7% 5% 4 5% 4 5% 6% 39%	1848
	21st to end	Night	17% 9% 3 7% 5% 4 5% 4 6% 7% 35%	1710
May	1st to 10th	Night	19% 7% 3 5% 5% 4 4 4 5% 5% 39%	2783
	11th to 20th	Night	15% 7% 2 7% 5% 4 5% 5% 7% 7% 35%	2495
	21st to end	Night	10% 4 2 5% 4 4 3 4 5% 9% 50%	2738
June	1st to 10th	Night	12% 5% 2 6% 5% 5% 5% 4 7% 8% 41%	1520
	11th to 20th	Night	8% 4 3 7% 4 5% 4 5% 6% 8% 44%	1520
	21st to end	Night	12% 6% 2 6% 4 4 5% 5% 6% 9% 42%	1520
July	1st to 10th	Night	6% 5% 2 5% 4 5% 5% 4 6% 9% 50%	2520
	11th to 20th	Night	11% 4 2 4 3 3 4 3 7% 8% 49%	2520
	21st to end	Night	8% 4 1 5% 3 3 4 4 6% 9% 52%	2958
August	1st to 10th	Night	10% 5% 2 5% 4 4 4 4 6% 8% 47%	2825
	11th to 20th	Night	11% 5% 2 6% 3 3 3 3 5% 8% 50%	2785
	21st to end	Night	9% 5% 2 6% 4 4 4 4 6% 9% 47%	3305
September	1st to 10th	Night	10% 5% 3 5% 4 4 5% 4 6% 7% 47%	1900
	11th to 20th	Night	10% 5% 2 4 4 4 3 3 5% 7% 55%	1972
	21st to end	Night	16% 6% 2 7% 4 3 4 4 4 6% 43%	2152
October	1st to 10th	Night	15% 6% 3 7% 5% 4 4 4 5% 6% 40%	2280
	11th to 20th	Night	19% 9% 3 7% 5% 5% 5% 4 5% 6% 33%	2280
	21st to end	Night	21% 9% 3 6% 5% 5% 5% 5% 5% 6% 31%	2508
November	1st to 10th	Night	17% 8% 2 7% 5% 4 4 3 5% 7% 38%	2611
	11th to 20th	Night	16% 10% 3 7% 6% 6% 4 4 6% 7% 30%	2800
	21st to end	Night	20% 11% 3 7% 5% 5% 6% 4 7% 7% 25%	2800
December	1st to 10th	Night	18% 13% 5% 10% 6% 6% 6% 4 6% 7% 19%	4580
	11th to 20th	Night	17% 16% 4 9% 6% 5% 5% 4 5% 6% 24%	5208
	21st to end	Night	25% 14% 7% 11% 5% 5% 5% 3 5% 5% 16%	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	54% 4 15% 15% 11% 1	3598
	11th to 20th	Day	71% 4 10% 10% 5% 1	3850
	21st to end	Day	67% 4 10% 11% 8%	4466
February	1st to 10th	Day	63% 4 11% 17% 5% 1	1800
	11th to 20th	Day	59% 6% 9% 17% 8% 1	1762
	21st to end	Day	58% 5% 12% 18% 7% 1	1494
March	1st to 10th	Day	53% 5% 14% 18% 10%	3435
	11th to 20th	Day	51% 7% 14% 16% 10% 2	3480
	21st to end	Day	44% 5% 11% 22% 16% 2	3815
April	1st to 10th	Day	53% 5% 12% 18% 11% 2	2266
	11th to 20th	Day	48% 5% 10% 22% 14% 1	2296
	21st to end	Day	50% 5% 11% 20% 12% 3	2470
May	1st to 10th	Day	47% 6% 13% 19% 13% 2	4169
	11th to 20th	Day	48% 6% 17% 18% 9% 1	4402
	21st to end	Day	34% 5% 16% 26% 14% 3	4837
June	1st to 10th	Day	43% 7% 13% 22% 14% 1	2660
	11th to 20th	Day	38% 6% 14% 26% 15% 2	2660
	21st to end	Day	39% 7% 15% 25% 13% 1	2660
July	1st to 10th	Day	36% 5% 15% 27% 15% 2	4370
	11th to 20th	Day	32% 7% 14% 36% 10% 1	4365
	21st to end	Day	34% 8% 17% 24% 16% 1	4433
August	1st to 10th	Day	43% 6% 14% 23% 12% 1	4091
	11th to 20th	Day	39% 6% 16% 29% 10%	4083
	21st to end	Day	33% 6% 14% 36% 10% 1	4318
September	1st to 10th	Day	37% 7% 14% 30% 11% 1	2280
	11th to 20th	Day	32% 5% 16% 30% 15% 1	2204
	21st to end	Day	42% 7% 15% 27% 10%	2028
October	1st to 10th	Day	37% 5% 15% 28% 15% 1	3160
	11th to 20th	Day	38% 5% 17% 25% 14% 1	3140
	21st to end	Day	50% 6% 15% 22% 6%	3428
November	1st to 10th	Day	49% 6% 14% 21% 9% 1	1681
	11th to 20th	Day	55% 6% 14% 16% 9% 1	1600
	21st to end	Day	59% 4 15% 17% 4	1600
December	1st to 10th	Day	68% 6% 14% 9% 3	2600
	11th to 20th	Day	61% 6% 12% 12% 9%	2986
	21st to end	Day	71% 5% 7% 10% 6% 1	3960
January	1st to 10th	Night	55% 6% 12% 19% 7%	6349
	11th to 20th	Night	63% 6% 13% 12% 5% 1	6107
	21st to end	Night	59% 4 13% 12% 10% 1	6490
February	1st to 10th	Night	59% 5% 11% 19% 5% 1	2600
	11th to 20th	Night	56% 5% 10% 18% 10% 1	2535
	21st to end	Night	53% 5% 13% 20% 8% 1	2051
March	1st to 10th	Night	53% 4 12% 23% 8% 1	3418
	11th to 20th	Night	49% 5% 13% 21% 10% 2	3480
	21st to end	Night	40% 6% 10% 24% 19% 2	3817
April	1st to 10th	Night	51% 4 9% 21% 13% 1	1913
	11th to 20th	Night	46% 5% 10% 19% 17% 2	1848
	21st to end	Night	47% 5% 11% 20% 15% 2	1710
May	1st to 10th	Night	46% 4 13% 18% 16% 3	2790
	11th to 20th	Night	45% 5% 18% 18% 11% 2	2496
	21st to end	Night	31% 6% 14% 26% 21% 2	2739
June	1st to 10th	Night	39% 7% 11% 25% 16% 2	1520
	11th to 20th	Night	36% 5% 12% 22% 22% 2	1520
	21st to end	Night	38% 6% 14% 25% 16% 1	1520
July	1st to 10th	Night	32% 5% 14% 27% 21% 3	2480
	11th to 20th	Night	31% 5% 13% 34% 15% 1	2472
	21st to end	Night	29% 7% 16% 30% 18% 1	2864
August	1st to 10th	Night	35% 4 14% 29% 16% 2	2814
	11th to 20th	Night	33% 4 17% 32% 13% 1	2812
	21st to end	Night	33% 6% 12% 33% 15% 1	3305
September	1st to 10th	Night	35% 6% 15% 29% 14% 1	1900
	11th to 20th	Night	30% 4 13% 34% 19%	1972
	21st to end	Night	42% 5% 12% 28% 13% 1	2152
October	1st to 10th	Night	33% 4 9% 29% 24% 1	3800
	11th to 20th	Night	41% 5% 14% 30% 10%	3779
	21st to end	Night	40% 6% 15% 28% 10% 1	4120
November	1st to 10th	Night	45% 5% 13% 24% 13% 1	2611
	11th to 20th	Night	52% 4 15% 18% 10% 1	2800
	21st to end	Night	55% 7% 18% 16% 4	2800
December	1st to 10th	Night	62% 5% 15% 14% 3	4580
	11th to 20th	Night	61% 7% 10% 12% 9%	5208
	21st to end	Night	70% 5% 12% 8% 5%	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	24% 18% 32% 20% 7% 1	200
	11th to 20th	Day	27% 21% 30% 16% 5% 1	255
	21st to end	Day	30% 17% 34% 15% 3 1	330
February	1st to 10th	Day	28% 24% 32% 12% 4	300
	11th to 20th	Day	27% 24% 36% 11% 2	300
	21st to end	Day	32% 19% 35% 13% 1	277
March	1st to 10th	Day	25% 15% 35% 20% 5%	460
	11th to 20th	Day	25% 16% 33% 20% 5%	460
	21st to end	Day	30% 11% 31% 20% 7% 1	506
April	1st to 10th	Day	22% 13% 38% 21% 5% 1	460
	11th to 20th	Day	30% 12% 26% 20% 9% 3	452
	21st to end	Day	27% 12% 35% 16% 8% 2	460
May	1st to 10th	Day	24% 8% 30% 24% 9% 5%	463
	11th to 20th	Day	17% 8% 27% 30% 15% 4	487
	21st to end	Day	14% 7% 25% 31% 18% 5%	529
June	1st to 10th	Day	17% 7% 31% 29% 13% 2	490
	11th to 20th	Day	13% 7% 27% 31% 19% 2	490
	21st to end	Day	18% 6% 27% 31% 13% 5%	490
July	1st to 10th	Day	10% 4 22% 35% 22% 7%	485
	11th to 20th	Day	14% 4 23% 32% 19% 8%	484
	21st to end	Day	8% 3 29% 37% 17% 7%	532
August	1st to 10th	Day	13% 4 22% 32% 19% 11%	486
	11th to 20th	Day	13% 3 21% 28% 27% 8%	479
	21st to end	Day	12% 6% 22% 32% 18% 10%	539
September	1st to 10th	Day	14% 7% 23% 29% 17% 10%	490
	11th to 20th	Day	11% 4 20% 28% 22% 15%	490
	21st to end	Day	16% 8% 29% 25% 15% 7%	490
October	1st to 10th	Day	20% 10% 26% 25% 14% 5%	490
	11th to 20th	Day	21% 14% 33% 22% 8% 1	490
	21st to end	Day	29% 12% 29% 22% 7% 1	539
November	1st to 10th	Day	24% 16% 27% 25% 8% 1	294
	11th to 20th	Day	23% 18% 35% 19% 5% 1	200
	21st to end	Day	28% 17% 36% 15% 4 1	200
December	1st to 10th	Day	26% 15% 33% 19% 5% 3	200
	11th to 20th	Day	30% 19% 29% 17% 5%	200
	21st to end	Day	30% 18% 34% 15% 3	220
January	1st to 10th	Night	24% 16% 38% 17% 5% 1	800
	11th to 20th	Night	28% 14% 32% 22% 4 1	800
	21st to end	Night	21% 12% 34% 27% 6%	880
February	1st to 10th	Night	21% 15% 38% 23% 3	800
	11th to 20th	Night	22% 15% 36% 22% 5%	783
	21st to end	Night	22% 13% 38% 22% 4	647
March	1st to 10th	Night	21% 12% 36% 27% 4 1	760
	11th to 20th	Night	23% 12% 34% 25% 5% 1	760
	21st to end	Night	21% 11% 30% 28% 9%	836
April	1st to 10th	Night	25% 11% 31% 28% 5%	760
	11th to 20th	Night	18% 11% 33% 27% 9% 1	724
	21st to end	Night	22% 6% 29% 32% 10%	570
May	1st to 10th	Night	22% 4 26% 29% 17% 2	546
	11th to 20th	Night	17% 5% 26% 37% 14%	374
	21st to end	Night	11% 3 23% 40% 22% 1	411
June	1st to 10th	Night	15% 4 24% 38% 17% 1	380
	11th to 20th	Night	11% 6% 24% 39% 20% 1	380
	21st to end	Night	12% 5% 23% 42% 18% 1	380
July	1st to 10th	Night	6% 3 19% 46% 24% 1	370
	11th to 20th	Night	13% 2 18% 40% 26% 1	368
	21st to end	Night	11% 1 16% 46% 23% 2	547
August	1st to 10th	Night	10% 3 13% 42% 29% 3	567
	11th to 20th	Night	9% 1 14% 41% 30% 5%	564
	21st to end	Night	12% 3 19% 38% 25% 3	730
September	1st to 10th	Night	12% 6% 19% 37% 22% 5%	760
	11th to 20th	Night	13% 4 18% 32% 27% 6%	760
	21st to end	Night	19% 6% 19% 32% 21% 4	760
October	1st to 10th	Night	19% 5% 26% 29% 19% 2	760
	11th to 20th	Night	24% 9% 28% 29% 10% 1	760
	21st to end	Night	27% 7% 29% 31% 6%	836
November	1st to 10th	Night	23% 9% 26% 30% 11% 1	780
	11th to 20th	Night	22% 13% 30% 27% 7% 2	800
	21st to end	Night	25% 12% 31% 25% 7%	800
December	1st to 10th	Night	29% 13% 32% 22% 5%	800
	11th to 20th	Night	24% 13% 36% 23% 4	800
	21st to end	Night	30% 11% 35% 21% 3	880

Page generated at 2025-02-22 06:51:33. Version ac07

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