Sunset Bay
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sunset Bay clear sky chart from 2005-11-06 to 2024-10-24.

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% 10% 4 9% 5% 5% 4 4 5% 7% 32%	101493
	Night	16% 11% 4 9% 5% 5% 4 4 5% 6% 31%	97279
Transparency	Day	51% 6% 11% 21% 10% 1	101251
	Night	52% 6% 12% 20% 9% 1	97141
Seeing	Day	23% 16% 31% 19% 8% 3	14413
	Night	23% 14% 31% 24% 8% 1	23518

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% 14% 6% 13% 8% 6% 5% 3 4 5% 22%	2517
	11th to 20th	Day	12% 15% 6% 15% 7% 7% 4 4 4 4 21%	2520
	21st to end	Day	14% 22% 7% 15% 6% 6% 4 3 3 3 17%	2968
February	1st to 10th	Day	12% 16% 5% 14% 8% 6% 5% 4 4 5% 22%	1710
	11th to 20th	Day	10% 15% 6% 11% 7% 6% 4 4 4 5% 28%	1663
	21st to end	Day	18% 14% 3 11% 6% 5% 5% 4 5% 5% 25%	1541
March	1st to 10th	Day	19% 15% 5% 11% 5% 4 3 3 4 5% 27%	3198
	11th to 20th	Day	10% 17% 5% 11% 8% 5% 4 3 5% 4 28%	3480
	21st to end	Day	10% 10% 4 8% 5% 4 4 3 4 6% 42%	3969
April	1st to 10th	Day	20% 14% 3 7% 5% 4 4 3 5% 6% 30%	2280
	11th to 20th	Day	21% 10% 3 7% 4 3 4 3 4 4 37%	2254
	21st to end	Day	21% 10% 4 8% 4 4 4 3 4 5% 32%	2413
May	1st to 10th	Day	19% 9% 3 8% 5% 5% 4 4 6% 6% 32%	4426
	11th to 20th	Day	15% 9% 4 8% 6% 4 5% 4 6% 8% 32%	4398
	21st to end	Day	14% 8% 2 7% 5% 5% 5% 4 5% 8% 38%	4837
June	1st to 10th	Day	20% 10% 3 7% 5% 5% 5% 4 6% 6% 30%	2660
	11th to 20th	Day	14% 7% 3 6% 4 5% 5% 5% 7% 7% 38%	2660
	21st to end	Day	17% 7% 2 7% 6% 5% 4 4 6% 7% 33%	2660
July	1st to 10th	Day	11% 7% 3 8% 5% 6% 6% 4 6% 9% 34%	4440
	11th to 20th	Day	11% 6% 2 7% 5% 5% 5% 5% 7% 9% 39%	4440
	21st to end	Day	10% 6% 2 7% 4 4 4 5% 6% 8% 44%	4814
August	1st to 10th	Day	14% 8% 3 9% 5% 5% 5% 4 6% 7% 35%	4265
	11th to 20th	Day	16% 7% 2 7% 5% 4 4 4 6% 8% 37%	4044
	21st to end	Day	12% 5% 2 6% 4 5% 5% 5% 7% 10% 40%	4185
September	1st to 10th	Day	14% 6% 2 6% 5% 5% 4 4 5% 8% 40%	2280
	11th to 20th	Day	12% 5% 1 6% 4 5% 4 4 6% 8% 45%	2280
	21st to end	Day	17% 7% 3 7% 4 5% 4 4 5% 7% 39%	2012
October	1st to 10th	Day	19% 10% 3 7% 4 4 4 3 5% 6% 34%	1900
	11th to 20th	Day	20% 12% 3 8% 5% 5% 5% 3 4 7% 28%	1900
	21st to end	Day	25% 11% 4 9% 4 4 4 3 4 5% 26%	1902
November	1st to 10th	Day	14% 11% 4 8% 5% 5% 4 4 5% 7% 35%	1639
	11th to 20th	Day	17% 12% 5% 9% 7% 5% 5% 3 5% 5% 28%	1520
	21st to end	Day	19% 15% 5% 11% 6% 6% 5% 3 4 6% 20%	1520
December	1st to 10th	Day	20% 20% 6% 12% 7% 5% 4 3 5% 4 15%	1520
	11th to 20th	Day	18% 15% 6% 10% 6% 4 4 3 4 5% 25%	1906
	21st to end	Day	26% 18% 4 16% 4 3 3 2 2 3 19%	2772
January	1st to 10th	Night	15% 15% 7% 12% 7% 5% 5% 4 5% 5% 18%	4429
	11th to 20th	Night	11% 14% 5% 14% 9% 7% 6% 4 5% 6% 21%	4440
	21st to end	Night	15% 20% 7% 11% 6% 7% 3 3 4 4 20%	4686
February	1st to 10th	Night	11% 16% 5% 12% 7% 5% 5% 4 5% 6% 22%	2470
	11th to 20th	Night	12% 14% 6% 11% 7% 5% 5% 3 4 5% 29%	2403
	21st to end	Night	14% 13% 4 9% 7% 5% 5% 4 5% 5% 28%	1913
March	1st to 10th	Night	19% 12% 4 10% 6% 4 3 3 3 4 31%	3639
	11th to 20th	Night	14% 16% 5% 10% 6% 4 5% 3 6% 6% 25%	3479
	21st to end	Night	13% 10% 3 8% 6% 4 4 4 5% 7% 37%	3661
April	1st to 10th	Night	20% 12% 4 7% 5% 4 3 3 4 6% 33%	1900
	11th to 20th	Night	19% 9% 3 7% 4 4 4 3 4 6% 36%	1875
	21st to end	Night	20% 10% 3 7% 5% 5% 4 3 4 6% 33%	1782
May	1st to 10th	Night	19% 10% 4 7% 5% 4 5% 4 6% 5% 33%	2514
	11th to 20th	Night	17% 9% 3 7% 4 4 4 4 6% 7% 36%	2495
	21st to end	Night	12% 6% 3 7% 5% 5% 5% 4 6% 8% 40%	2738
June	1st to 10th	Night	15% 7% 3 8% 5% 5% 4 5% 7% 8% 33%	1520
	11th to 20th	Night	13% 6% 3 7% 3 4 4 4 5% 7% 43%	1520
	21st to end	Night	17% 7% 2 7% 4 4 5% 3 5% 9% 36%	1520
July	1st to 10th	Night	9% 8% 3 9% 6% 6% 6% 4 6% 7% 36%	2520
	11th to 20th	Night	12% 5% 2 6% 5% 4 4 5% 6% 8% 43%	2520
	21st to end	Night	9% 6% 2 6% 5% 5% 5% 3 7% 7% 45%	2739
August	1st to 10th	Night	11% 6% 2 7% 5% 5% 4 4 7% 8% 41%	2660
	11th to 20th	Night	13% 6% 3 7% 4 4 4 3 6% 7% 43%	2785
	21st to end	Night	12% 6% 2 6% 4 5% 5% 4 6% 8% 44%	3438
September	1st to 10th	Night	11% 6% 2 6% 4 4 4 5% 5% 6% 47%	1900
	11th to 20th	Night	14% 5% 1 4 4 4 4 3 5% 6% 50%	1900
	21st to end	Night	16% 6% 2 6% 4 4 4 3 5% 6% 43%	2165
October	1st to 10th	Night	17% 9% 2 6% 4 3 4 4 5% 6% 39%	2280
	11th to 20th	Night	19% 11% 3 8% 5% 4 4 3 5% 6% 31%	2280
	21st to end	Night	21% 11% 3 9% 5% 4 5% 4 5% 6% 27%	2521
November	1st to 10th	Night	16% 13% 3 7% 4 4 5% 3 5% 6% 34%	2435
	11th to 20th	Night	16% 12% 4 9% 6% 5% 5% 4 5% 6% 28%	2660
	21st to end	Night	20% 14% 5% 10% 6% 4 4 3 5% 6% 23%	2660
December	1st to 10th	Night	18% 19% 5% 12% 6% 5% 5% 4 4 4 18%	2660
	11th to 20th	Night	19% 17% 5% 11% 6% 4 4 3 3 4 25%	3288
	21st to end	Night	27% 18% 5% 13% 5% 4 4 3 3 3 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	63% 8% 13% 10% 7%	2518
	11th to 20th	Day	66% 5% 10% 11% 7% 1	2520
	21st to end	Day	73% 4 7% 10% 6% 1	2968
February	1st to 10th	Day	63% 5% 9% 17% 4 1	1710
	11th to 20th	Day	58% 5% 11% 16% 9% 1	1672
	21st to end	Day	61% 5% 11% 12% 11% 1	1541
March	1st to 10th	Day	60% 4 9% 17% 9% 1	3201
	11th to 20th	Day	56% 7% 10% 15% 9% 2	3480
	21st to end	Day	42% 4 8% 24% 18% 4	3969
April	1st to 10th	Day	54% 5% 7% 19% 13% 3	2280
	11th to 20th	Day	51% 4 7% 21% 15% 2	2254
	21st to end	Day	54% 5% 8% 15% 15% 3	2413
May	1st to 10th	Day	50% 7% 8% 21% 12% 2	4440
	11th to 20th	Day	48% 7% 13% 20% 10% 1	4402
	21st to end	Day	42% 7% 12% 21% 15% 2	4837
June	1st to 10th	Day	52% 6% 10% 19% 11% 1	2660
	11th to 20th	Day	42% 7% 12% 24% 13% 2	2660
	21st to end	Day	48% 6% 13% 21% 11% 1	2660
July	1st to 10th	Day	44% 6% 13% 25% 11% 1	4370
	11th to 20th	Day	38% 8% 14% 30% 10%	4365
	21st to end	Day	37% 7% 12% 33% 12%	4661
August	1st to 10th	Day	47% 6% 14% 23% 10%	4251
	11th to 20th	Day	44% 6% 13% 28% 8% 1	4083
	21st to end	Day	37% 7% 15% 30% 11% 1	4185
September	1st to 10th	Day	40% 7% 14% 28% 11%	2280
	11th to 20th	Day	36% 6% 14% 29% 15%	2280
	21st to end	Day	46% 5% 14% 26% 9%	2012
October	1st to 10th	Day	51% 6% 10% 23% 10% 1	1900
	11th to 20th	Day	55% 5% 13% 17% 8% 1	1900
	21st to end	Day	61% 5% 10% 17% 6% 1	1902
November	1st to 10th	Day	49% 5% 16% 22% 7% 1	1639
	11th to 20th	Day	57% 6% 12% 14% 10% 1	1520
	21st to end	Day	65% 5% 12% 10% 7% 1	1520
December	1st to 10th	Day	71% 6% 10% 10% 4 1	1520
	11th to 20th	Day	61% 6% 13% 14% 6%	1906
	21st to end	Day	73% 3 7% 14% 4	2772
January	1st to 10th	Night	65% 8% 12% 11% 3	4429
	11th to 20th	Night	63% 6% 14% 11% 4 1	4440
	21st to end	Night	70% 5% 9% 10% 6%	4686
February	1st to 10th	Night	61% 5% 10% 16% 6% 1	2470
	11th to 20th	Night	57% 5% 10% 20% 8% 1	2405
	21st to end	Night	56% 6% 10% 19% 10% 1	1913
March	1st to 10th	Night	57% 4 9% 20% 8% 1	3649
	11th to 20th	Night	57% 7% 14% 15% 7% 1	3480
	21st to end	Night	43% 6% 9% 22% 15% 3	3661
April	1st to 10th	Night	53% 4 7% 19% 14% 2	1900
	11th to 20th	Night	50% 4 8% 22% 15% 1	1875
	21st to end	Night	53% 5% 7% 18% 16% 2	1782
May	1st to 10th	Night	50% 7% 10% 21% 10% 3	2520
	11th to 20th	Night	44% 8% 13% 23% 10% 2	2496
	21st to end	Night	39% 8% 14% 20% 17% 2	2739
June	1st to 10th	Night	45% 7% 12% 24% 11% 1	1520
	11th to 20th	Night	39% 7% 12% 24% 18% 2	1520
	21st to end	Night	45% 8% 14% 19% 13% 1	1520
July	1st to 10th	Night	44% 7% 14% 20% 14% 2	2480
	11th to 20th	Night	38% 5% 13% 34% 10%	2472
	21st to end	Night	36% 7% 14% 28% 14%	2651
August	1st to 10th	Night	39% 6% 15% 26% 13% 1	2650
	11th to 20th	Night	39% 5% 16% 31% 8%	2812
	21st to end	Night	37% 7% 15% 28% 12% 2	3438
September	1st to 10th	Night	35% 8% 13% 29% 15% 1	1900
	11th to 20th	Night	35% 5% 13% 35% 11% 1	1900
	21st to end	Night	41% 5% 13% 30% 10%	2165
October	1st to 10th	Night	46% 5% 11% 23% 15%	2280
	11th to 20th	Night	52% 6% 13% 19% 9%	2280
	21st to end	Night	56% 6% 13% 16% 8%	2521
November	1st to 10th	Night	50% 5% 14% 21% 10% 1	2435
	11th to 20th	Night	54% 6% 12% 18% 9% 1	2660
	21st to end	Night	61% 6% 12% 16% 5%	2660
December	1st to 10th	Night	69% 6% 9% 13% 3	2660
	11th to 20th	Night	64% 4 9% 15% 7% 1	3288
	21st to end	Night	74% 4 7% 12% 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	24% 19% 35% 17% 5%	180
	11th to 20th	Day	32% 18% 35% 11% 4	180
	21st to end	Day	23% 21% 36% 14% 6% 1	254
February	1st to 10th	Day	30% 26% 30% 11% 3	270
	11th to 20th	Day	30% 25% 39% 4 1	270
	21st to end	Day	31% 25% 33% 10% 1	353
March	1st to 10th	Day	28% 19% 36% 13% 3	460
	11th to 20th	Day	28% 19% 32% 17% 2 1	460
	21st to end	Day	32% 22% 28% 13% 4	506
April	1st to 10th	Day	32% 20% 29% 13% 5%	460
	11th to 20th	Day	36% 18% 21% 16% 8% 2	452
	21st to end	Day	31% 17% 32% 12% 7% 1	460
May	1st to 10th	Day	26% 16% 32% 17% 7% 2	463
	11th to 20th	Day	21% 16% 31% 22% 8% 2	487
	21st to end	Day	20% 16% 33% 19% 9% 3	529
June	1st to 10th	Day	25% 13% 31% 21% 10%	490
	11th to 20th	Day	17% 15% 31% 22% 12% 2	490
	21st to end	Day	22% 12% 32% 21% 11% 1	490
July	1st to 10th	Day	12% 8% 31% 33% 13% 3	485
	11th to 20th	Day	14% 10% 33% 27% 13% 4	484
	21st to end	Day	15% 8% 35% 29% 11% 3	532
August	1st to 10th	Day	17% 6% 30% 30% 13% 5%	486
	11th to 20th	Day	14% 7% 29% 29% 16% 5%	479
	21st to end	Day	15% 11% 30% 24% 14% 6%	539
September	1st to 10th	Day	16% 12% 30% 22% 13% 7%	490
	11th to 20th	Day	13% 9% 26% 24% 17% 11%	490
	21st to end	Day	20% 13% 29% 19% 13% 6%	490
October	1st to 10th	Day	25% 17% 25% 20% 8% 4	490
	11th to 20th	Day	27% 21% 30% 15% 6% 1	490
	21st to end	Day	33% 18% 27% 17% 5%	453
November	1st to 10th	Day	26% 17% 32% 17% 6% 1	333
	11th to 20th	Day	29% 21% 33% 11% 2 4	180
	21st to end	Day	29% 24% 34% 8% 4 1	180
December	1st to 10th	Day	34% 16% 39% 9% 2	180
	11th to 20th	Day	31% 27% 31% 8% 3 1	180
	21st to end	Day	31% 21% 32% 13% 3 1	198
January	1st to 10th	Night	26% 20% 34% 17% 3	760
	11th to 20th	Night	27% 19% 30% 18% 5% 1	760
	21st to end	Night	20% 15% 37% 24% 5%	836
February	1st to 10th	Night	23% 18% 37% 19% 3	760
	11th to 20th	Night	21% 19% 41% 15% 3	743
	21st to end	Night	23% 21% 31% 21% 4	628
March	1st to 10th	Night	26% 18% 32% 20% 4	760
	11th to 20th	Night	25% 21% 31% 18% 5% 1	760
	21st to end	Night	23% 16% 32% 22% 7%	836
April	1st to 10th	Night	27% 16% 31% 21% 4	760
	11th to 20th	Night	25% 20% 29% 20% 7%	751
	21st to end	Night	25% 15% 29% 24% 7% 1	642
May	1st to 10th	Night	21% 10% 30% 27% 10% 1	380
	11th to 20th	Night	21% 10% 34% 27% 8% 1	374
	21st to end	Night	13% 9% 37% 30% 12%	411
June	1st to 10th	Night	16% 10% 30% 35% 8%	380
	11th to 20th	Night	14% 12% 31% 31% 10% 1	380
	21st to end	Night	23% 8% 26% 31% 12%	380
July	1st to 10th	Night	9% 7% 31% 38% 14% 1	370
	11th to 20th	Night	12% 6% 29% 40% 13% 1	368
	21st to end	Night	10% 4 30% 43% 13% 1	416
August	1st to 10th	Night	12% 5% 26% 37% 20%	467
	11th to 20th	Night	12% 4 24% 37% 20% 3	564
	21st to end	Night	13% 7% 29% 32% 17% 2	811
September	1st to 10th	Night	15% 8% 30% 30% 16% 1	760
	11th to 20th	Night	17% 6% 23% 30% 21% 4	760
	21st to end	Night	20% 10% 24% 24% 20% 2	760
October	1st to 10th	Night	24% 11% 26% 25% 13% 2	760
	11th to 20th	Night	27% 13% 31% 20% 8% 1	760
	21st to end	Night	28% 16% 28% 22% 6%	805
November	1st to 10th	Night	27% 13% 31% 22% 6% 1	740
	11th to 20th	Night	25% 19% 32% 15% 8% 1	760
	21st to end	Night	32% 17% 27% 19% 5%	760
December	1st to 10th	Night	31% 16% 34% 16% 3	760
	11th to 20th	Night	28% 19% 30% 19% 3 1	760
	21st to end	Night	35% 16% 30% 16% 3	836

Page generated at 2024-10-21 02:20:04. Version ac07

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