Winter Bay Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Winter Bay Observatory clear sky chart from 2005-11-06 to 2024-11-10.

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	17% 11% 4 9% 5% 4 4 4 5% 7% 29%	102359
	Night	18% 12% 4 10% 6% 4 4 3 5% 6% 27%	96862
Transparency	Day	54% 5% 13% 20% 7% 1	105905
	Night	56% 5% 13% 18% 7% 1	101409
Seeing	Day	24% 12% 30% 24% 9% 1	17559
	Night	25% 12% 30% 25% 7% 1	24610

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% 16% 8% 26% 6% 4 4 3 3 4 12%	2526
	11th to 20th	Day	12% 12% 6% 12% 9% 7% 6% 4 4 5% 23%	2530
	21st to end	Day	13% 10% 6% 17% 7% 5% 4 4 5% 7% 23%	3029
February	1st to 10th	Day	18% 14% 4 11% 6% 5% 5% 4 4 5% 25%	1710
	11th to 20th	Day	17% 14% 5% 9% 7% 5% 5% 4 4 5% 25%	1663
	21st to end	Day	10% 12% 4 10% 8% 6% 5% 4 5% 7% 30%	1460
March	1st to 10th	Day	21% 14% 5% 7% 4 5% 4 3 4 5% 28%	3302
	11th to 20th	Day	11% 18% 7% 13% 7% 5% 5% 3 5% 5% 20%	3480
	21st to end	Day	21% 17% 5% 12% 5% 4 3 3 5% 5% 20%	3879
April	1st to 10th	Day	18% 14% 4 9% 5% 4 3 3 5% 6% 30%	2280
	11th to 20th	Day	20% 11% 3 6% 4 4 4 2 5% 8% 34%	2301
	21st to end	Day	20% 12% 3 7% 3 3 4 4 5% 7% 31%	2470
May	1st to 10th	Day	24% 15% 3 6% 4 3 3 2 4 6% 29%	4380
	11th to 20th	Day	16% 8% 3 7% 5% 4 5% 3 5% 6% 38%	4398
	21st to end	Day	17% 9% 3 7% 5% 4 5% 4 6% 8% 30%	4836
June	1st to 10th	Day	24% 11% 3 8% 4 4 5% 4 5% 7% 24%	2660
	11th to 20th	Day	19% 9% 2 7% 4 4 4 3 6% 7% 35%	2840
	21st to end	Day	23% 10% 3 7% 5% 3 4 3 5% 6% 30%	2850
July	1st to 10th	Day	16% 8% 3 7% 5% 5% 5% 5% 7% 7% 33%	4744
	11th to 20th	Day	15% 6% 2 7% 5% 5% 5% 5% 7% 8% 36%	4440
	21st to end	Day	12% 7% 3 7% 5% 4 4 4 7% 9% 38%	4815
August	1st to 10th	Day	16% 10% 3 9% 5% 4 5% 4 6% 7% 31%	4183
	11th to 20th	Day	14% 7% 2 7% 4 4 5% 4 7% 8% 37%	4045
	21st to end	Day	13% 6% 2 6% 4 4 4 4 5% 8% 43%	4322
September	1st to 10th	Day	17% 7% 2 5% 3 3 4 4 6% 8% 41%	2280
	11th to 20th	Day	19% 9% 3 7% 3 3 4 3 5% 6% 39%	2272
	21st to end	Day	18% 9% 3 6% 4 4 4 3 4 6% 38%	1989
October	1st to 10th	Day	20% 8% 3 7% 4 4 4 4 5% 8% 32%	1900
	11th to 20th	Day	20% 12% 3 9% 6% 5% 4 4 5% 7% 25%	1900
	21st to end	Day	20% 15% 4 9% 5% 4 5% 4 4 7% 24%	2021
November	1st to 10th	Day	19% 18% 4 9% 6% 4 5% 3 5% 5% 22%	1605
	11th to 20th	Day	20% 21% 5% 10% 6% 5% 4 3 3 6% 16%	1520
	21st to end	Day	18% 18% 6% 11% 7% 4 5% 4 5% 7% 15%	1520
December	1st to 10th	Day	23% 23% 7% 12% 5% 3 4 4 4 6% 11%	1520
	11th to 20th	Day	20% 21% 8% 16% 7% 6% 4 3 3 3 9%	1906
	21st to end	Day	20% 17% 9% 15% 5% 4 4 3 3 4 16%	2783
January	1st to 10th	Night	13% 13% 7% 23% 8% 4 4 4 4 4 16%	4429
	11th to 20th	Night	15% 13% 5% 14% 8% 5% 5% 4 4 5% 22%	4440
	21st to end	Night	12% 13% 6% 20% 9% 5% 4 3 4 5% 18%	4628
February	1st to 10th	Night	17% 14% 3 10% 6% 4 4 4 5% 4 27%	2470
	11th to 20th	Night	17% 15% 4 11% 7% 5% 5% 4 5% 5% 22%	2403
	21st to end	Night	12% 14% 5% 9% 6% 5% 5% 4 5% 6% 30%	1994
March	1st to 10th	Night	22% 12% 4 9% 5% 5% 4 3 4 5% 27%	3534
	11th to 20th	Night	19% 18% 7% 12% 7% 4 4 3 4 4 19%	3479
	21st to end	Night	23% 15% 5% 10% 4 4 5% 4 4 4 21%	3739
April	1st to 10th	Night	22% 11% 3 9% 5% 5% 5% 4 5% 5% 26%	1900
	11th to 20th	Night	21% 12% 3 6% 4 5% 4 2 5% 5% 33%	1826
	21st to end	Night	22% 15% 3 8% 5% 4 3 2 4 5% 30%	1710
May	1st to 10th	Night	28% 14% 3 8% 4 4 4 3 4 5% 22%	2567
	11th to 20th	Night	15% 9% 2 7% 4 4 4 4 5% 7% 39%	2506
	21st to end	Night	14% 10% 3 9% 6% 5% 6% 5% 6% 9% 28%	2749
June	1st to 10th	Night	27% 8% 4 7% 5% 4 4 3 4 6% 27%	1520
	11th to 20th	Night	17% 10% 2 5% 3 4 5% 4 4 7% 39%	1352
	21st to end	Night	23% 9% 4 8% 5% 4 4 4 6% 6% 26%	1330
July	1st to 10th	Night	14% 9% 3 8% 6% 7% 5% 4 8% 7% 29%	2210
	11th to 20th	Night	14% 6% 3 7% 6% 4 6% 5% 7% 9% 33%	2498
	21st to end	Night	12% 7% 3 6% 4 4 4 3 6% 9% 43%	2750
August	1st to 10th	Night	18% 8% 4 8% 5% 5% 5% 5% 7% 8% 29%	2746
	11th to 20th	Night	10% 7% 3 8% 5% 5% 5% 4 5% 8% 40%	2782
	21st to end	Night	13% 6% 2 6% 4 4 4 4 5% 7% 44%	3334
September	1st to 10th	Night	15% 8% 2 6% 4 4 5% 2 4 7% 42%	1900
	11th to 20th	Night	18% 7% 2 6% 4 4 4 3 5% 6% 41%	1905
	21st to end	Night	19% 6% 2 6% 4 3 4 4 5% 7% 40%	2190
October	1st to 10th	Night	19% 7% 3 8% 5% 3 4 3 5% 6% 36%	2280
	11th to 20th	Night	19% 11% 4 7% 5% 5% 4 4 5% 6% 31%	2280
	21st to end	Night	24% 13% 4 8% 5% 4 3 4 6% 5% 24%	2576
November	1st to 10th	Night	20% 17% 3 9% 6% 4 4 3 4 5% 24%	2678
	11th to 20th	Night	21% 17% 5% 10% 5% 4 4 4 5% 6% 19%	2660
	21st to end	Night	25% 17% 5% 10% 5% 5% 4 3 4 5% 17%	2660
December	1st to 10th	Night	24% 18% 6% 14% 5% 4 4 4 4 5% 12%	2660
	11th to 20th	Night	22% 20% 7% 15% 6% 4 3 2 3 3 14%	3293
	21st to end	Night	26% 15% 6% 16% 5% 3 3 2 4 4 16%	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	76% 4 12% 6% 2	2527
	11th to 20th	Day	58% 5% 11% 18% 8%	2530
	21st to end	Day	57% 4 14% 16% 8% 1	3029
February	1st to 10th	Day	60% 4 10% 18% 8% 1	1710
	11th to 20th	Day	61% 4 10% 17% 7% 1	1671
	21st to end	Day	53% 6% 12% 16% 11% 2	1460
March	1st to 10th	Day	58% 3 9% 23% 6% 1	3306
	11th to 20th	Day	66% 5% 9% 15% 5% 1	3480
	21st to end	Day	68% 4 8% 13% 6% 2	3879
April	1st to 10th	Day	56% 4 9% 17% 10% 3	2280
	11th to 20th	Day	50% 4 10% 22% 12% 1	2301
	21st to end	Day	53% 5% 12% 16% 11% 2	2470
May	1st to 10th	Day	58% 4 14% 16% 7% 1	4395
	11th to 20th	Day	48% 5% 14% 26% 7%	4402
	21st to end	Day	50% 8% 13% 20% 9%	4836
June	1st to 10th	Day	58% 5% 12% 19% 5%	2660
	11th to 20th	Day	48% 6% 12% 24% 8% 1	2840
	21st to end	Day	54% 5% 13% 18% 9% 1	2850
July	1st to 10th	Day	49% 6% 17% 18% 10%	4669
	11th to 20th	Day	45% 7% 17% 24% 7%	4364
	21st to end	Day	42% 9% 19% 24% 6%	4662
August	1st to 10th	Day	53% 6% 13% 23% 4	4169
	11th to 20th	Day	43% 6% 15% 26% 10% 1	4084
	21st to end	Day	38% 5% 15% 29% 12%	4322
September	1st to 10th	Day	42% 6% 15% 27% 10%	2280
	11th to 20th	Day	47% 5% 13% 24% 11%	2272
	21st to end	Day	46% 5% 11% 26% 11% 1	1989
October	1st to 10th	Day	51% 6% 13% 24% 6%	3160
	11th to 20th	Day	50% 5% 15% 24% 6%	3140
	21st to end	Day	52% 5% 16% 20% 6%	3315
November	1st to 10th	Day	63% 4 11% 17% 5%	1605
	11th to 20th	Day	66% 5% 13% 13% 3	1520
	21st to end	Day	65% 5% 16% 12% 2	1520
December	1st to 10th	Day	73% 4 13% 8% 2	1520
	11th to 20th	Day	77% 4 7% 9% 2	1905
	21st to end	Day	72% 3 12% 9% 3	2783
January	1st to 10th	Night	62% 6% 17% 13% 3	4429
	11th to 20th	Night	58% 5% 11% 17% 7%	4440
	21st to end	Night	62% 6% 11% 14% 6%	4628
February	1st to 10th	Night	58% 4 11% 15% 11% 2	2470
	11th to 20th	Night	62% 4 10% 16% 9% 1	2406
	21st to end	Night	55% 4 9% 20% 10% 2	1994
March	1st to 10th	Night	60% 3 7% 19% 8% 2	3543
	11th to 20th	Night	69% 3 8% 13% 5% 1	3480
	21st to end	Night	67% 3 6% 15% 7% 1	3739
April	1st to 10th	Night	59% 4 10% 14% 11% 1	1900
	11th to 20th	Night	54% 3 8% 21% 11% 2	1826
	21st to end	Night	58% 4 8% 16% 13% 2	1710
May	1st to 10th	Night	64% 4 10% 14% 7% 1	2572
	11th to 20th	Night	44% 5% 17% 24% 9% 1	2507
	21st to end	Night	52% 7% 18% 17% 6% 1	2750
June	1st to 10th	Night	59% 5% 12% 18% 6%	1520
	11th to 20th	Night	45% 6% 13% 24% 12%	1352
	21st to end	Night	57% 7% 13% 14% 9% 1	1330
July	1st to 10th	Night	51% 7% 15% 18% 6% 2	2175
	11th to 20th	Night	45% 8% 20% 21% 6%	2451
	21st to end	Night	38% 8% 22% 21% 11%	2663
August	1st to 10th	Night	52% 7% 16% 21% 4	2735
	11th to 20th	Night	42% 8% 19% 23% 9% 1	2809
	21st to end	Night	38% 5% 18% 28% 11%	3333
September	1st to 10th	Night	42% 5% 12% 30% 11%	1900
	11th to 20th	Night	43% 4 13% 28% 12%	1905
	21st to end	Night	43% 5% 13% 28% 10%	2190
October	1st to 10th	Night	49% 5% 16% 22% 7%	3800
	11th to 20th	Night	44% 4 17% 25% 10%	3779
	21st to end	Night	53% 4 13% 20% 9%	4236
November	1st to 10th	Night	61% 4 13% 15% 6%	2678
	11th to 20th	Night	62% 5% 14% 14% 5%	2660
	21st to end	Night	66% 5% 15% 11% 2	2660
December	1st to 10th	Night	70% 4 13% 10% 2	2660
	11th to 20th	Night	73% 3 8% 13% 3	3295
	21st to end	Night	71% 4 12% 10% 3	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	25% 20% 36% 14% 5%	370
	11th to 20th	Day	26% 21% 29% 18% 5% 1	370
	21st to end	Day	17% 16% 37% 25% 4	407
February	1st to 10th	Day	30% 16% 32% 16% 5% 1	370
	11th to 20th	Day	22% 23% 33% 16% 5%	366
	21st to end	Day	17% 17% 34% 25% 6% 1	307
March	1st to 10th	Day	23% 16% 33% 24% 4	423
	11th to 20th	Day	18% 17% 34% 24% 6% 1	460
	21st to end	Day	28% 15% 32% 17% 7% 1	506
April	1st to 10th	Day	26% 16% 37% 17% 5%	460
	11th to 20th	Day	23% 16% 35% 18% 8% 1	452
	21st to end	Day	24% 13% 30% 24% 8% 1	460
May	1st to 10th	Day	33% 12% 27% 19% 7% 2	621
	11th to 20th	Day	22% 8% 27% 26% 16% 1	674
	21st to end	Day	22% 10% 32% 26% 8% 1	735
June	1st to 10th	Day	31% 6% 28% 24% 9% 1	680
	11th to 20th	Day	22% 6% 29% 32% 10% 1	680
	21st to end	Day	26% 6% 24% 30% 11% 3	680
July	1st to 10th	Day	19% 4 30% 32% 13% 2	670
	11th to 20th	Day	15% 4 29% 32% 18% 1	668
	21st to end	Day	19% 5% 24% 36% 14% 2	740
August	1st to 10th	Day	15% 2 24% 40% 15% 4	538
	11th to 20th	Day	19% 5% 22% 33% 16% 4	479
	21st to end	Day	18% 7% 22% 34% 15% 4	539
September	1st to 10th	Day	17% 7% 32% 31% 11% 2	490
	11th to 20th	Day	24% 10% 27% 26% 11% 2	490
	21st to end	Day	22% 9% 30% 25% 11% 3	436
October	1st to 10th	Day	22% 11% 25% 26% 14% 3	390
	11th to 20th	Day	24% 15% 30% 19% 10% 2	390
	21st to end	Day	27% 17% 32% 17% 6% 1	429
November	1st to 10th	Day	26% 18% 33% 15% 6% 1	392
	11th to 20th	Day	33% 20% 27% 14% 4 1	370
	21st to end	Day	31% 19% 31% 17% 2	370
December	1st to 10th	Day	33% 16% 31% 16% 3	370
	11th to 20th	Day	33% 24% 30% 12% 1	370
	21st to end	Day	26% 24% 32% 16% 2 1	407
January	1st to 10th	Night	27% 17% 34% 18% 4	850
	11th to 20th	Night	26% 17% 33% 20% 4	850
	21st to end	Night	21% 19% 31% 23% 5% 1	863
February	1st to 10th	Night	27% 14% 33% 21% 5%	760
	11th to 20th	Night	24% 17% 37% 17% 3	743
	21st to end	Night	19% 14% 35% 22% 9% 1	628
March	1st to 10th	Night	24% 12% 38% 23% 3	760
	11th to 20th	Night	21% 14% 31% 25% 8% 1	760
	21st to end	Night	28% 14% 27% 21% 9% 1	797
April	1st to 10th	Night	28% 12% 30% 24% 6%	570
	11th to 20th	Night	27% 11% 32% 22% 9% 1	564
	21st to end	Night	28% 9% 31% 23% 8% 1	570
May	1st to 10th	Night	31% 8% 25% 25% 10% 2	570
	11th to 20th	Night	23% 5% 27% 33% 10% 2	562
	21st to end	Night	21% 7% 38% 27% 6% 1	616
June	1st to 10th	Night	29% 7% 26% 30% 8% 1	570
	11th to 20th	Night	22% 5% 30% 34% 9%	402
	21st to end	Night	24% 4 31% 33% 7% 1	380
July	1st to 10th	Night	19% 6% 27% 35% 12%	370
	11th to 20th	Night	17% 2 29% 39% 12%	534
	21st to end	Night	19% 5% 27% 37% 12% 1	623
August	1st to 10th	Night	17% 4 25% 39% 14% 1	568
	11th to 20th	Night	17% 5% 23% 37% 16% 2	562
	21st to end	Night	15% 5% 23% 37% 19% 1	627
September	1st to 10th	Night	17% 5% 34% 33% 10% 1	570
	11th to 20th	Night	20% 7% 23% 38% 11% 1	575
	21st to end	Night	21% 9% 31% 28% 9% 1	760
October	1st to 10th	Night	24% 8% 26% 29% 12%	760
	11th to 20th	Night	26% 11% 29% 23% 10% 1	760
	21st to end	Night	32% 16% 29% 19% 4	873
November	1st to 10th	Night	30% 16% 31% 17% 4 1	878
	11th to 20th	Night	30% 18% 29% 18% 4 1	850
	21st to end	Night	33% 18% 28% 18% 2	850
December	1st to 10th	Night	32% 17% 30% 17% 4	850
	11th to 20th	Night	30% 22% 32% 14% 2	850
	21st to end	Night	32% 17% 31% 15% 3 1	935

Page generated at 2024-11-07 07:55:49. Version ac07

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