Predator Bay
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Predator Bay clear sky chart from 2005-11-06 to 2025-04-11.

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	8% 9% 3 8% 5% 5% 5% 4 6% 8% 39%	116863
	Night	6% 9% 4 9% 5% 5% 5% 4 6% 8% 38%	120135
Transparency	Day	41% 6% 15% 25% 12% 2	116609
	Night	42% 6% 14% 23% 12% 2	120036
Seeing	Day	12% 8% 26% 31% 17% 5%	15799
	Night	11% 6% 29% 37% 15% 2	25106

By Month

Percentage Cloud Cover NW (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	2 10% 7% 13% 8% 8% 4 4 6% 7% 31%	3179
	11th to 20th	Day	3 8% 3 11% 6% 5% 5% 5% 7% 7% 39%	3250
	21st to end	Day	3 7% 2 8% 5% 4 5% 4 6% 11% 45%	4004
February	1st to 10th	Day	3 11% 5% 12% 7% 7% 6% 5% 7% 7% 30%	1600
	11th to 20th	Day	4 12% 5% 11% 6% 6% 6% 5% 7% 9% 28%	1754
	21st to end	Day	3 12% 6% 10% 7% 6% 6% 4 6% 9% 32%	1608
March	1st to 10th	Day	3 9% 4 11% 6% 5% 5% 3 5% 11% 38%	4518
	11th to 20th	Day	4 10% 4 8% 5% 4 4 5% 6% 9% 41%	4950
	21st to end	Day	7% 20% 7% 12% 5% 4 5% 4 6% 7% 22%	5563
April	1st to 10th	Day	8% 15% 5% 10% 6% 5% 5% 4 6% 8% 30%	2455
	11th to 20th	Day	11% 13% 4 9% 5% 5% 5% 5% 6% 8% 30%	2442
	21st to end	Day	12% 12% 4 8% 6% 4 6% 4 6% 8% 31%	2470
May	1st to 10th	Day	18% 14% 4 8% 5% 4 4 4 6% 6% 29%	4306
	11th to 20th	Day	10% 7% 3 9% 6% 6% 6% 5% 8% 9% 30%	4694
	21st to end	Day	16% 8% 3 10% 7% 6% 7% 5% 6% 7% 25%	5161
June	1st to 10th	Day	16% 7% 3 8% 6% 5% 5% 5% 7% 9% 30%	2850
	11th to 20th	Day	20% 9% 2 7% 5% 5% 6% 5% 6% 8% 27%	2850
	21st to end	Day	9% 4 2 5% 5% 4 6% 5% 8% 9% 42%	2850
July	1st to 10th	Day	7% 4 2 5% 4 4 5% 4 6% 8% 50%	4740
	11th to 20th	Day	6% 3 1 4 3 4 4 4 7% 11% 53%	4740
	21st to end	Day	3 3 1 3 3 3 4 4 6% 9% 60%	4998
August	1st to 10th	Day	9% 6% 2 6% 3 4 5% 5% 8% 10% 42%	4401
	11th to 20th	Day	7% 5% 2 5% 4 5% 4 4 8% 11% 46%	4059
	21st to end	Day	9% 4 2 4 3 3 4 4 6% 8% 53%	4521
September	1st to 10th	Day	10% 6% 2 6% 3 3 4 3 5% 6% 52%	2351
	11th to 20th	Day	14% 7% 2 5% 5% 3 3 4 5% 7% 44%	2090
	21st to end	Day	8% 7% 3 6% 4 4 4 4 6% 8% 45%	2090
October	1st to 10th	Day	7% 7% 2 7% 4 4 5% 4 7% 9% 44%	3344
	11th to 20th	Day	6% 7% 3 6% 4 4 5% 5% 8% 10% 43%	2918
	21st to end	Day	6% 8% 3 7% 5% 4 5% 4 6% 7% 45%	3101
November	1st to 10th	Day	8% 15% 4 9% 5% 4 5% 4 5% 8% 33%	1641
	11th to 20th	Day	6% 12% 3 8% 5% 5% 4 4 7% 8% 40%	1535
	21st to end	Day	4 12% 4 10% 4 6% 4 5% 6% 10% 35%	1400
December	1st to 10th	Day	3 12% 4 11% 6% 5% 6% 4 6% 8% 35%	2290
	11th to 20th	Day	2 10% 5% 10% 7% 8% 6% 5% 6% 8% 33%	2642
	21st to end	Day	3 10% 4 9% 5% 4 5% 4 6% 8% 42%	3498
January	1st to 10th	Night	3 14% 6% 13% 9% 7% 6% 4 6% 7% 26%	6766
	11th to 20th	Night	3 8% 5% 13% 6% 5% 6% 5% 6% 8% 35%	6693
	21st to end	Night	3 9% 4 9% 6% 4 4 4 6% 8% 43%	6952
February	1st to 10th	Night	4 11% 5% 11% 6% 6% 7% 4 6% 8% 31%	2800
	11th to 20th	Night	5% 12% 5% 11% 6% 5% 6% 5% 6% 8% 30%	2532
	21st to end	Night	2 10% 4 13% 8% 6% 5% 4 6% 7% 34%	2020
March	1st to 10th	Night	3 8% 4 11% 7% 6% 6% 5% 6% 10% 34%	5376
	11th to 20th	Night	4 9% 4 10% 6% 5% 5% 5% 6% 8% 39%	5049
	21st to end	Night	8% 20% 6% 12% 6% 5% 4 4 6% 7% 22%	5410
April	1st to 10th	Night	9% 14% 5% 9% 5% 4 6% 3 6% 7% 31%	1945
	11th to 20th	Night	11% 12% 5% 10% 6% 5% 4 4 5% 7% 32%	1695
	21st to end	Night	11% 11% 3 8% 5% 5% 5% 4 6% 8% 33%	1710
May	1st to 10th	Night	17% 14% 4 8% 4 4 4 4 4 6% 30%	2655
	11th to 20th	Night	9% 8% 3 9% 5% 4 5% 5% 7% 10% 34%	2199
	21st to end	Night	15% 9% 3 8% 6% 5% 6% 5% 8% 8% 27%	2414
June	1st to 10th	Night	14% 8% 3 7% 6% 4 6% 4 7% 7% 33%	1330
	11th to 20th	Night	18% 7% 2 7% 4 4 5% 5% 6% 8% 31%	1330
	21st to end	Night	8% 4 1 5% 4 5% 6% 4 8% 10% 44%	1330
July	1st to 10th	Night	6% 5% 3 7% 5% 4 4 4 5% 7% 49%	2220
	11th to 20th	Night	4 4 1 4 3 4 5% 5% 8% 11% 51%	2220
	21st to end	Night	4 3 2 5% 3 4 3 3 5% 7% 60%	2538
August	1st to 10th	Night	10% 6% 2 6% 5% 4 5% 5% 7% 8% 43%	2529
	11th to 20th	Night	5% 5% 2 6% 4 4 5% 5% 8% 10% 44%	2778
	21st to end	Night	8% 4 1 5% 2 3 4 3 6% 10% 54%	3146
September	1st to 10th	Night	10% 7% 2 6% 3 3 4 2 6% 8% 50%	1827
	11th to 20th	Night	14% 7% 2 5% 3 3 3 3 5% 7% 49%	2090
	21st to end	Night	9% 7% 2 5% 3 4 4 3 6% 8% 48%	2090
October	1st to 10th	Night	7% 6% 1 6% 4 4 4 3 6% 8% 51%	3631
	11th to 20th	Night	6% 6% 2 5% 4 4 5% 4 6% 9% 49%	4008
	21st to end	Night	5% 8% 3 7% 5% 5% 5% 4 7% 7% 45%	4457
November	1st to 10th	Night	7% 14% 4 8% 5% 5% 5% 4 6% 6% 36%	2637
	11th to 20th	Night	4 10% 4 9% 6% 5% 5% 5% 6% 8% 39%	2860
	21st to end	Night	4 11% 4 9% 5% 5% 5% 4 6% 9% 38%	3000
December	1st to 10th	Night	3 10% 4 9% 6% 6% 7% 6% 7% 9% 33%	4890
	11th to 20th	Night	2 10% 4 13% 8% 7% 6% 5% 7% 9% 30%	5550
	21st to end	Night	4 10% 5% 8% 5% 4 5% 4 6% 8% 40%	7458

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% 4 10% 22% 9% 2	3179
	11th to 20th	Day	42% 5% 13% 18% 19% 3	3271
	21st to end	Day	33% 6% 14% 32% 14% 1	4004
February	1st to 10th	Day	51% 8% 14% 15% 10% 2	1600
	11th to 20th	Day	50% 6% 14% 20% 9% 2	1763
	21st to end	Day	47% 6% 14% 19% 12% 1	1608
March	1st to 10th	Day	41% 4 15% 22% 16% 1	4518
	11th to 20th	Day	39% 5% 13% 26% 16% 1	4951
	21st to end	Day	60% 6% 12% 15% 6%	5563
April	1st to 10th	Day	51% 5% 15% 20% 8% 1	2455
	11th to 20th	Day	50% 6% 13% 20% 10% 1	2442
	21st to end	Day	49% 7% 14% 20% 9% 1	2470
May	1st to 10th	Day	54% 7% 10% 24% 5%	4306
	11th to 20th	Day	43% 9% 15% 24% 9%	4698
	21st to end	Day	53% 7% 15% 16% 7% 1	5162
June	1st to 10th	Day	48% 8% 15% 20% 8% 2	2850
	11th to 20th	Day	52% 8% 14% 17% 7% 2	2850
	21st to end	Day	33% 9% 19% 26% 11% 2	2850
July	1st to 10th	Day	29% 7% 14% 27% 18% 5%	4666
	11th to 20th	Day	24% 7% 18% 35% 14% 2	4659
	21st to end	Day	19% 6% 12% 29% 24% 10%	4840
August	1st to 10th	Day	33% 8% 14% 37% 7% 1	4384
	11th to 20th	Day	30% 7% 25% 30% 7% 1	4098
	21st to end	Day	27% 6% 17% 35% 13% 1	4520
September	1st to 10th	Day	32% 7% 14% 26% 16% 5%	2351
	11th to 20th	Day	39% 6% 14% 27% 13% 2	2090
	21st to end	Day	36% 6% 14% 29% 12% 3	2090
October	1st to 10th	Day	36% 5% 16% 34% 8% 1	3344
	11th to 20th	Day	33% 6% 19% 26% 13% 3	2918
	21st to end	Day	37% 5% 10% 33% 13% 1	3101
November	1st to 10th	Day	50% 7% 12% 20% 11% 1	1641
	11th to 20th	Day	42% 5% 16% 25% 10% 1	1535
	21st to end	Day	43% 7% 16% 24% 9% 2	1400
December	1st to 10th	Day	48% 5% 14% 24% 8% 2	2290
	11th to 20th	Day	48% 6% 19% 20% 6% 1	2644
	21st to end	Day	39% 5% 11% 24% 18% 4	3498
January	1st to 10th	Night	57% 5% 11% 20% 5% 1	6766
	11th to 20th	Night	47% 5% 12% 18% 13% 4	6734
	21st to end	Night	38% 5% 14% 28% 15% 1	6952
February	1st to 10th	Night	49% 6% 12% 19% 11% 2	2800
	11th to 20th	Night	49% 6% 13% 20% 11% 1	2533
	21st to end	Night	48% 5% 12% 22% 11% 2	2020
March	1st to 10th	Night	43% 6% 18% 20% 11% 2	5376
	11th to 20th	Night	42% 6% 14% 23% 14% 1	5049
	21st to end	Night	60% 6% 11% 13% 9% 1	5410
April	1st to 10th	Night	50% 6% 12% 20% 12% 1	1945
	11th to 20th	Night	51% 6% 12% 21% 9% 1	1695
	21st to end	Night	46% 8% 14% 21% 9% 2	1710
May	1st to 10th	Night	53% 7% 11% 22% 7%	2655
	11th to 20th	Night	40% 9% 12% 29% 8% 1	2199
	21st to end	Night	50% 9% 15% 18% 7% 1	2414
June	1st to 10th	Night	47% 7% 14% 20% 11% 1	1330
	11th to 20th	Night	46% 9% 15% 19% 8% 2	1330
	21st to end	Night	32% 10% 20% 26% 11% 1	1330
July	1st to 10th	Night	35% 6% 15% 25% 18% 2	2185
	11th to 20th	Night	23% 9% 20% 35% 10% 4	2178
	21st to end	Night	23% 5% 10% 31% 22% 9%	2458
August	1st to 10th	Night	37% 7% 13% 29% 13% 1	2521
	11th to 20th	Night	30% 10% 24% 26% 9% 1	2805
	21st to end	Night	26% 5% 19% 35% 13% 2	3146
September	1st to 10th	Night	33% 6% 15% 25% 16% 6%	1827
	11th to 20th	Night	34% 6% 15% 28% 13% 4	2090
	21st to end	Night	32% 6% 18% 26% 14% 4	2090
October	1st to 10th	Night	31% 5% 15% 29% 19% 2	3631
	11th to 20th	Night	32% 6% 19% 24% 17% 2	4008
	21st to end	Night	37% 5% 11% 32% 14%	4457
November	1st to 10th	Night	48% 6% 12% 21% 12% 2	2637
	11th to 20th	Night	42% 7% 15% 21% 14% 1	2860
	21st to end	Night	41% 6% 17% 22% 10% 3	3000
December	1st to 10th	Night	46% 7% 18% 20% 7% 2	4890
	11th to 20th	Night	49% 7% 19% 18% 6%	5547
	21st to end	Night	41% 4 10% 26% 16% 3	7458

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	4 10% 21% 38% 17% 11%	200
	11th to 20th	Day	9% 5% 27% 38% 16% 6%	200
	21st to end	Day	7% 10% 19% 44% 18% 3	220
February	1st to 10th	Day	9% 10% 29% 36% 14% 3	200
	11th to 20th	Day	7% 6% 33% 34% 18% 2	300
	21st to end	Day	7% 9% 29% 36% 17% 3	372
March	1st to 10th	Day	7% 11% 33% 30% 13% 5%	500
	11th to 20th	Day	8% 10% 29% 34% 15% 4	500
	21st to end	Day	12% 16% 29% 27% 11% 5%	550
April	1st to 10th	Day	12% 14% 35% 25% 12% 2	500
	11th to 20th	Day	14% 13% 26% 30% 13% 4	453
	21st to end	Day	15% 17% 28% 25% 12% 3	460
May	1st to 10th	Day	19% 9% 25% 24% 17% 6%	496
	11th to 20th	Day	17% 5% 22% 29% 20% 6%	675
	21st to end	Day	18% 7% 19% 28% 21% 7%	734
June	1st to 10th	Day	16% 9% 25% 31% 15% 4	680
	11th to 20th	Day	21% 9% 25% 28% 14% 2	680
	21st to end	Day	11% 5% 24% 33% 20% 6%	680
July	1st to 10th	Day	9% 5% 21% 33% 26% 7%	671
	11th to 20th	Day	11% 5% 22% 34% 24% 5%	668
	21st to end	Day	5% 7% 25% 33% 23% 7%	661
August	1st to 10th	Day	11% 5% 25% 32% 20% 7%	487
	11th to 20th	Day	9% 4 22% 35% 24% 8%	477
	21st to end	Day	12% 7% 23% 29% 19% 10%	539
September	1st to 10th	Day	12% 7% 26% 30% 19% 6%	490
	11th to 20th	Day	18% 6% 24% 29% 17% 6%	490
	21st to end	Day	12% 14% 27% 31% 12% 4	490
October	1st to 10th	Day	13% 7% 26% 29% 22% 4	409
	11th to 20th	Day	13% 9% 29% 29% 16% 4	300
	21st to end	Day	13% 10% 35% 25% 13% 3	330
November	1st to 10th	Day	17% 7% 28% 33% 11% 3	300
	11th to 20th	Day	12% 9% 36% 31% 9% 3	267
	21st to end	Day	7% 10% 29% 31% 15% 10%	200
December	1st to 10th	Day	7% 6% 27% 41% 15% 5%	200
	11th to 20th	Day	7% 9% 30% 39% 13% 4	200
	21st to end	Day	9% 5% 20% 38% 22% 5%	220
January	1st to 10th	Night	9% 9% 31% 38% 12% 2	1000
	11th to 20th	Night	8% 6% 35% 37% 12% 1	980
	21st to end	Night	9% 10% 32% 37% 10% 2	880
February	1st to 10th	Night	9% 7% 31% 34% 16% 4	800
	11th to 20th	Night	10% 5% 31% 40% 12% 1	784
	21st to end	Night	7% 5% 29% 37% 19% 3	660
March	1st to 10th	Night	8% 6% 32% 36% 15% 4	800
	11th to 20th	Night	9% 8% 32% 37% 12% 2	800
	21st to end	Night	14% 5% 30% 35% 13% 3	880
April	1st to 10th	Night	13% 8% 31% 33% 14% 2	745
	11th to 20th	Night	17% 7% 30% 33% 12%	565
	21st to end	Night	18% 8% 29% 32% 13%	570
May	1st to 10th	Night	17% 8% 24% 34% 16% 1	489
	11th to 20th	Night	13% 7% 24% 35% 21%	374
	21st to end	Night	22% 4 22% 33% 19%	411
June	1st to 10th	Night	16% 7% 26% 36% 14% 1	380
	11th to 20th	Night	22% 2 24% 36% 16%	380
	21st to end	Night	10% 4 18% 41% 26% 2	380
July	1st to 10th	Night	10% 4 16% 42% 26% 1	370
	11th to 20th	Night	9% 2 19% 45% 22% 3	368
	21st to end	Night	6% 3 20% 45% 24% 2	416
August	1st to 10th	Night	11% 4 12% 39% 32% 2	378
	11th to 20th	Night	9% 3 16% 46% 23% 2	543
	21st to end	Night	9% 3 22% 42% 23% 1	627
September	1st to 10th	Night	12% 4 22% 38% 21% 3	668
	11th to 20th	Night	16% 4 19% 38% 20% 2	760
	21st to end	Night	13% 4 30% 36% 15% 2	760
October	1st to 10th	Night	15% 4 25% 39% 16% 2	760
	11th to 20th	Night	12% 4 30% 36% 15% 3	760
	21st to end	Night	11% 6% 33% 36% 13% 1	836
November	1st to 10th	Night	15% 8% 35% 32% 10% 1	882
	11th to 20th	Night	10% 10% 38% 32% 9% 2	1000
	21st to end	Night	9% 6% 35% 37% 11% 2	1000
December	1st to 10th	Night	9% 5% 34% 36% 13% 2	1000
	11th to 20th	Night	6% 5% 37% 41% 10% 1	1000
	21st to end	Night	9% 6% 31% 39% 12% 3	1100

Page generated at 2025-04-08 06:17:24. Version ac07

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