Whitby Ridge Observatory
Clear Sky Chart
History

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

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	21% 12% 4 8% 5% 4 4 3 5% 6% 28%	109009
	Night	20% 11% 4 9% 5% 4 4 3 5% 6% 28%	109332
Transparency	Day	32% 45% 6% 11% 6% 1	112637
	Night	32% 43% 6% 12% 6% 1	113867
Seeing	Day	27% 19% 31% 16% 5% 1	17641
	Night	27% 17% 30% 20% 6%	25322

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	14% 18% 6% 16% 9% 4 4 3 3 4 20%	3616
	11th to 20th	Day	15% 17% 7% 16% 7% 6% 5% 3 4 5% 15%	3723
	21st to end	Day	14% 11% 5% 9% 6% 7% 5% 3 5% 6% 29%	4466
February	1st to 10th	Day	20% 14% 5% 10% 7% 5% 5% 4 4 4 21%	1755
	11th to 20th	Day	17% 16% 5% 12% 5% 5% 5% 4 4 5% 23%	1663
	21st to end	Day	13% 15% 4 8% 8% 5% 3 3 3 7% 30%	1447
March	1st to 10th	Day	24% 15% 4 8% 5% 5% 3 2 3 4 26%	3416
	11th to 20th	Day	16% 19% 4 10% 5% 4 4 3 4 5% 25%	3480
	21st to end	Day	31% 15% 4 9% 5% 3 3 3 3 4 20%	3816
April	1st to 10th	Day	26% 16% 3 8% 5% 3 3 2 4 5% 25%	2276
	11th to 20th	Day	22% 12% 2 6% 4 4 4 4 5% 6% 31%	2307
	21st to end	Day	22% 12% 3 7% 5% 4 4 3 4 7% 29%	2470
May	1st to 10th	Day	24% 14% 4 9% 6% 4 4 3 5% 6% 20%	4217
	11th to 20th	Day	22% 12% 4 8% 5% 4 3 3 5% 5% 30%	4398
	21st to end	Day	20% 9% 3 7% 4 4 4 4 7% 8% 29%	4836
June	1st to 10th	Day	25% 11% 3 8% 5% 5% 4 4 5% 7% 24%	2660
	11th to 20th	Day	22% 9% 3 7% 4 4 4 3 5% 7% 32%	2673
	21st to end	Day	30% 10% 2 6% 5% 4 4 3 5% 6% 25%	2850
July	1st to 10th	Day	23% 10% 3 7% 4 4 4 3 6% 7% 29%	4504
	11th to 20th	Day	18% 15% 3 6% 4 3 3 4 6% 8% 30%	4440
	21st to end	Day	22% 9% 3 7% 4 4 4 4 6% 8% 30%	4672
August	1st to 10th	Day	26% 11% 3 7% 5% 3 4 4 5% 7% 25%	4105
	11th to 20th	Day	18% 8% 2 7% 5% 5% 5% 4 6% 8% 31%	4045
	21st to end	Day	10% 6% 2 6% 4 4 5% 4 7% 9% 45%	4340
September	1st to 10th	Day	18% 7% 2 6% 4 4 3 3 4 8% 40%	2280
	11th to 20th	Day	20% 8% 2 5% 4 3 3 3 4 6% 42%	2218
	21st to end	Day	20% 7% 3 6% 3 4 3 3 5% 6% 40%	2024
October	1st to 10th	Day	19% 7% 3 6% 4 3 4 3 6% 7% 37%	1900
	11th to 20th	Day	20% 8% 2 7% 5% 4 4 3 6% 8% 34%	1900
	21st to end	Day	21% 10% 3 7% 5% 4 4 4 5% 5% 32%	2090
November	1st to 10th	Day	22% 11% 3 9% 5% 4 3 3 4 7% 29%	1634
	11th to 20th	Day	23% 12% 4 9% 5% 5% 4 3 4 6% 25%	1600
	21st to end	Day	19% 15% 4 9% 7% 4 5% 3 5% 5% 25%	1600
December	1st to 10th	Day	22% 12% 5% 13% 5% 5% 3 4 5% 5% 21%	2610
	11th to 20th	Day	30% 11% 3 7% 4 5% 5% 3 4 4 25%	2996
	21st to end	Day	20% 14% 6% 12% 5% 3 3 3 4 7% 24%	3982
January	1st to 10th	Night	14% 16% 5% 13% 8% 5% 5% 3 5% 5% 20%	6349
	11th to 20th	Night	17% 14% 6% 19% 6% 5% 4 3 4 5% 16%	6161
	21st to end	Night	12% 11% 5% 12% 7% 5% 5% 4 7% 6% 25%	6490
February	1st to 10th	Night	20% 14% 4 10% 6% 6% 5% 4 5% 5% 22%	2536
	11th to 20th	Night	18% 12% 4 10% 6% 5% 5% 4 7% 6% 22%	2403
	21st to end	Night	14% 13% 4 10% 7% 6% 5% 4 5% 6% 27%	2006
March	1st to 10th	Night	23% 11% 4 10% 7% 6% 4 3 3 5% 23%	3422
	11th to 20th	Night	19% 16% 6% 9% 4 6% 4 3 4 5% 23%	3479
	21st to end	Night	30% 13% 5% 11% 5% 3 2 2 3 3 24%	3816
April	1st to 10th	Night	25% 13% 4 7% 4 4 4 3 5% 5% 28%	1903
	11th to 20th	Night	23% 11% 3 6% 5% 4 4 3 4 6% 32%	1820
	21st to end	Night	24% 11% 3 6% 5% 3 3 2 5% 5% 31%	1710
May	1st to 10th	Night	22% 16% 5% 8% 5% 3 3 3 5% 7% 24%	2724
	11th to 20th	Night	23% 11% 3 7% 4 3 5% 3 5% 5% 30%	2506
	21st to end	Night	21% 12% 4 9% 5% 4 4 3 4 6% 28%	2749
June	1st to 10th	Night	29% 10% 3 7% 4 4 3 2 4 7% 27%	1520
	11th to 20th	Night	20% 11% 4 7% 4 3 4 3 5% 5% 34%	1513
	21st to end	Night	29% 13% 3 6% 5% 4 5% 3 4 5% 24%	1330
July	1st to 10th	Night	20% 12% 4 10% 6% 5% 5% 4 4 7% 23%	2423
	11th to 20th	Night	21% 12% 4 9% 5% 4 4 4 5% 6% 26%	2530
	21st to end	Night	21% 8% 2 7% 4 4 4 4 4 7% 35%	2885
August	1st to 10th	Night	24% 12% 3 6% 3 3 3 3 4 5% 33%	2825
	11th to 20th	Night	18% 10% 3 7% 4 4 5% 3 6% 8% 32%	2782
	21st to end	Night	12% 7% 2 5% 4 3 4 3 5% 7% 50%	3316
September	1st to 10th	Night	18% 8% 2 5% 4 3 3 3 5% 6% 43%	1900
	11th to 20th	Night	19% 7% 2 6% 3 3 3 3 4 6% 44%	1960
	21st to end	Night	20% 10% 3 7% 3 3 3 3 5% 6% 37%	2156
October	1st to 10th	Night	19% 7% 2 5% 4 3 4 3 5% 6% 41%	2280
	11th to 20th	Night	20% 6% 2 6% 4 5% 3 3 5% 7% 39%	2280
	21st to end	Night	25% 9% 2 5% 4 4 4 3 4 6% 34%	2508
November	1st to 10th	Night	21% 9% 3 7% 4 4 4 3 5% 7% 34%	2661
	11th to 20th	Night	22% 11% 3 8% 5% 5% 4 3 5% 6% 27%	2800
	21st to end	Night	21% 11% 4 8% 6% 5% 5% 4 5% 5% 27%	2800
December	1st to 10th	Night	17% 11% 4 12% 6% 5% 5% 4 6% 6% 25%	4580
	11th to 20th	Night	27% 12% 3 7% 4 4 4 3 4 5% 27%	5213
	21st to end	Night	25% 11% 4 9% 4 3 3 3 4 5% 28%	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	49% 29% 10% 8% 5%	3617
	11th to 20th	Day	48% 31% 8% 10% 2	3752
	21st to end	Day	38% 32% 5% 8% 14% 3	4466
February	1st to 10th	Day	26% 64% 2 4 4 1	1755
	11th to 20th	Day	23% 64% 3 6% 4 1	1671
	21st to end	Day	18% 65% 3 7% 6% 2	1447
March	1st to 10th	Day	37% 41% 6% 10% 5% 2	3420
	11th to 20th	Day	35% 47% 6% 9% 4	3480
	21st to end	Day	47% 40% 4 4 5% 1	3816
April	1st to 10th	Day	22% 65% 2 4 5% 2	2276
	11th to 20th	Day	20% 66% 3 8% 3	2307
	21st to end	Day	20% 66% 3 5% 5% 1	2470
May	1st to 10th	Day	37% 45% 7% 9% 2	4231
	11th to 20th	Day	36% 43% 6% 11% 3	4402
	21st to end	Day	30% 44% 12% 9% 4	4836
June	1st to 10th	Day	20% 66% 4 7% 4	2660
	11th to 20th	Day	17% 65% 5% 8% 5%	2673
	21st to end	Day	21% 63% 2 7% 5%	2850
July	1st to 10th	Day	38% 37% 6% 10% 9%	4434
	11th to 20th	Day	36% 37% 7% 14% 5%	4364
	21st to end	Day	34% 37% 8% 13% 7%	4523
August	1st to 10th	Day	39% 39% 6% 11% 5%	4092
	11th to 20th	Day	32% 39% 8% 17% 3	4084
	21st to end	Day	21% 38% 7% 20% 13%	4340
September	1st to 10th	Day	17% 60% 6% 10% 5% 1	2280
	11th to 20th	Day	20% 60% 5% 9% 5%	2218
	21st to end	Day	16% 60% 4 13% 7%	2024
October	1st to 10th	Day	31% 39% 6% 15% 9%	3160
	11th to 20th	Day	23% 38% 5% 18% 15% 1	3140
	21st to end	Day	26% 37% 10% 16% 10% 1	3428
November	1st to 10th	Day	27% 57% 4 8% 3 1	1634
	11th to 20th	Day	27% 58% 5% 6% 3 1	1600
	21st to end	Day	29% 58% 5% 6% 3	1600
December	1st to 10th	Day	39% 38% 6% 15% 2	2610
	11th to 20th	Day	40% 33% 6% 9% 11%	2995
	21st to end	Day	44% 27% 10% 12% 7%	3982
January	1st to 10th	Night	43% 32% 7% 15% 3	6349
	11th to 20th	Night	49% 32% 7% 9% 3	6206
	21st to end	Night	39% 32% 6% 11% 11% 1	6490
February	1st to 10th	Night	26% 63% 3 3 4 1	2536
	11th to 20th	Night	21% 64% 3 7% 5%	2406
	21st to end	Night	19% 65% 3 7% 5% 1	2006
March	1st to 10th	Night	39% 42% 4 9% 5% 1	3431
	11th to 20th	Night	39% 44% 4 8% 6%	3480
	21st to end	Night	47% 40% 3 6% 3	3816
April	1st to 10th	Night	22% 65% 2 4 5% 2	1903
	11th to 20th	Night	19% 66% 3 9% 4 1	1820
	21st to end	Night	20% 65% 2 7% 5% 2	1710
May	1st to 10th	Night	36% 44% 10% 6% 4	2730
	11th to 20th	Night	34% 43% 7% 12% 4	2507
	21st to end	Night	37% 42% 8% 10% 3	2750
June	1st to 10th	Night	20% 64% 3 9% 3	1520
	11th to 20th	Night	17% 65% 4 10% 5%	1513
	21st to end	Night	22% 63% 4 7% 4	1330
July	1st to 10th	Night	43% 37% 5% 8% 6% 1	2384
	11th to 20th	Night	38% 38% 9% 9% 6%	2482
	21st to end	Night	32% 36% 6% 15% 10% 1	2794
August	1st to 10th	Night	36% 38% 7% 15% 3	2813
	11th to 20th	Night	30% 40% 10% 16% 3	2809
	21st to end	Night	18% 38% 9% 20% 15%	3315
September	1st to 10th	Night	15% 60% 4 12% 7% 1	1900
	11th to 20th	Night	18% 59% 4 12% 6%	1960
	21st to end	Night	17% 60% 4 14% 5%	2156
October	1st to 10th	Night	32% 37% 7% 15% 7%	3800
	11th to 20th	Night	18% 39% 6% 19% 17%	3779
	21st to end	Night	24% 37% 8% 17% 13%	4120
November	1st to 10th	Night	24% 57% 7% 8% 4	2661
	11th to 20th	Night	26% 58% 4 7% 5%	2800
	21st to end	Night	26% 58% 5% 6% 4	2800
December	1st to 10th	Night	32% 38% 6% 19% 5%	4580
	11th to 20th	Night	39% 32% 6% 12% 10% 1	5215
	21st to end	Night	41% 29% 7% 14% 9%	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	31% 25% 30% 13% 2	400
	11th to 20th	Day	32% 20% 30% 13% 4	400
	21st to end	Day	24% 23% 37% 13% 3	440
February	1st to 10th	Day	32% 24% 27% 14% 2	385
	11th to 20th	Day	32% 29% 28% 10% 1	366
	21st to end	Day	24% 25% 35% 12% 4	307
March	1st to 10th	Day	28% 28% 32% 10% 2	454
	11th to 20th	Day	29% 27% 29% 11% 3	460
	21st to end	Day	32% 26% 28% 11% 3 1	506
April	1st to 10th	Day	36% 28% 27% 7% 2	460
	11th to 20th	Day	29% 29% 30% 10% 2	452
	21st to end	Day	27% 24% 31% 13% 5%	460
May	1st to 10th	Day	31% 24% 31% 11% 2 1	522
	11th to 20th	Day	25% 18% 32% 20% 5% 1	674
	21st to end	Day	28% 17% 35% 17% 3 1	735
June	1st to 10th	Day	31% 16% 31% 17% 5%	680
	11th to 20th	Day	25% 16% 33% 19% 6% 1	680
	21st to end	Day	35% 11% 28% 19% 6% 1	680
July	1st to 10th	Day	23% 11% 34% 24% 8% 1	670
	11th to 20th	Day	22% 10% 35% 22% 10% 1	668
	21st to end	Day	29% 10% 31% 23% 7% 1	659
August	1st to 10th	Day	21% 9% 34% 28% 7% 1	486
	11th to 20th	Day	22% 12% 31% 23% 10% 2	479
	21st to end	Day	18% 11% 35% 24% 9% 4	539
September	1st to 10th	Day	18% 13% 37% 23% 7% 1	490
	11th to 20th	Day	26% 16% 30% 17% 9% 3	490
	21st to end	Day	22% 15% 31% 24% 8% 2	455
October	1st to 10th	Day	22% 13% 34% 19% 10% 2	390
	11th to 20th	Day	21% 21% 32% 16% 7% 2	390
	21st to end	Day	26% 23% 32% 13% 5% 1	429
November	1st to 10th	Day	26% 21% 30% 15% 7% 1	395
	11th to 20th	Day	35% 22% 26% 13% 5% 1	400
	21st to end	Day	31% 26% 28% 13% 2 1	400
December	1st to 10th	Day	34% 20% 31% 13% 2 1	400
	11th to 20th	Day	36% 26% 27% 10% 1	400
	21st to end	Day	29% 27% 30% 11% 3 1	440
January	1st to 10th	Night	29% 22% 34% 13% 2	900
	11th to 20th	Night	29% 22% 29% 16% 3	867
	21st to end	Night	23% 25% 34% 16% 2	880
February	1st to 10th	Night	29% 22% 30% 17% 2	781
	11th to 20th	Night	28% 26% 31% 12% 1	743
	21st to end	Night	20% 24% 34% 19% 4	628
March	1st to 10th	Night	24% 24% 34% 15% 2	760
	11th to 20th	Night	24% 20% 30% 20% 5%	760
	21st to end	Night	27% 23% 29% 17% 4	836
April	1st to 10th	Night	32% 19% 29% 17% 3	573
	11th to 20th	Night	27% 20% 33% 16% 3	564
	21st to end	Night	29% 15% 33% 19% 4 1	570
May	1st to 10th	Night	31% 13% 33% 18% 5% 1	570
	11th to 20th	Night	27% 13% 29% 22% 7% 1	562
	21st to end	Night	25% 14% 35% 23% 4	616
June	1st to 10th	Night	34% 11% 29% 23% 4	570
	11th to 20th	Night	24% 10% 36% 23% 6% 1	563
	21st to end	Night	33% 7% 23% 28% 9%	380
July	1st to 10th	Night	23% 8% 30% 32% 8%	488
	11th to 20th	Night	25% 6% 29% 31% 10%	552
	21st to end	Night	22% 7% 28% 33% 10%	623
August	1st to 10th	Night	21% 4 29% 32% 14% 1	568
	11th to 20th	Night	24% 5% 24% 33% 13% 1	562
	21st to end	Night	19% 7% 26% 31% 14% 1	627
September	1st to 10th	Night	21% 8% 32% 29% 11% 1	570
	11th to 20th	Night	22% 11% 26% 28% 13% 1	630
	21st to end	Night	25% 13% 27% 25% 9% 1	760
October	1st to 10th	Night	22% 13% 29% 27% 9% 1	760
	11th to 20th	Night	21% 17% 31% 21% 9% 1	760
	21st to end	Night	31% 16% 31% 18% 4	836
November	1st to 10th	Night	29% 14% 31% 20% 4 1	873
	11th to 20th	Night	29% 21% 27% 18% 5%	900
	21st to end	Night	31% 22% 27% 16% 4	900
December	1st to 10th	Night	32% 18% 32% 14% 4	900
	11th to 20th	Night	33% 23% 30% 12% 2	900
	21st to end	Night	29% 22% 30% 16% 3	990

Page generated at 2025-02-03 04:05:52. Version ac07

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