Garden Bay Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Garden Bay Observatory clear sky chart from 2005-11-06 to 2024-12-02.

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% 9% 3 7% 4 4 4 3 5% 6% 34%	105776
	Night	26% 10% 3 7% 5% 4 4 3 4 5% 29%	102459
Transparency	Day	51% 8% 14% 18% 8% 1	105520
	Night	57% 7% 13% 16% 6% 1	102361
Seeing	Day	23% 5% 18% 26% 21% 6%	15631
	Night	31% 4 13% 24% 22% 6%	23700

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	39% 14% 3 7% 4 3 3 3 4 5% 14%	2219
	11th to 20th	Day	27% 15% 5% 10% 4 5% 3 3 6% 5% 16%	2199
	21st to end	Day	49% 13% 4 8% 4 4 3 2 3 2 8%	2699
February	1st to 10th	Day	31% 15% 4 7% 6% 4 4 4 4 7% 14%	1710
	11th to 20th	Day	27% 11% 4 9% 5% 5% 4 3 5% 5% 22%	1665
	21st to end	Day	22% 13% 4 8% 6% 7% 5% 3 5% 6% 21%	1413
March	1st to 10th	Day	24% 14% 4 9% 5% 5% 6% 4 6% 6% 18%	3276
	11th to 20th	Day	20% 11% 3 8% 5% 5% 4 3 4 6% 31%	3490
	21st to end	Day	21% 13% 4 9% 5% 5% 4 4 5% 7% 23%	3872
April	1st to 10th	Day	24% 13% 3 9% 5% 4 5% 4 6% 6% 21%	2280
	11th to 20th	Day	21% 10% 3 7% 6% 5% 4 3 5% 6% 28%	2406
	21st to end	Day	23% 10% 4 7% 5% 5% 4 3 5% 6% 29%	2494
May	1st to 10th	Day	15% 8% 3 6% 5% 4 4 3 4 6% 43%	4420
	11th to 20th	Day	12% 7% 2 6% 4 5% 4 4 7% 12% 36%	4377
	21st to end	Day	26% 9% 3 6% 5% 4 4 4 5% 7% 28%	5064
June	1st to 10th	Day	21% 9% 2 7% 5% 4 4 4 6% 7% 29%	2850
	11th to 20th	Day	17% 9% 3 8% 6% 5% 5% 4 6% 8% 29%	2850
	21st to end	Day	15% 7% 2 7% 6% 4 4 3 5% 7% 38%	2850
July	1st to 10th	Day	7% 4 2 4 3 3 3 2 4 5% 64%	4740
	11th to 20th	Day	6% 2 1 3 2 2 2 2 4 5% 70%	4740
	21st to end	Day	10% 5% 2 5% 4 4 4 3 5% 7% 53%	5019
August	1st to 10th	Day	7% 3 1 3 2 3 2 2 4 6% 69%	4293
	11th to 20th	Day	11% 8% 3 7% 4 4 4 4 6% 8% 42%	4026
	21st to end	Day	15% 6% 2 7% 4 4 5% 4 5% 7% 41%	4494
September	1st to 10th	Day	11% 5% 2 6% 4 3 4 4 5% 7% 48%	2280
	11th to 20th	Day	17% 8% 3 7% 5% 4 5% 3 5% 7% 37%	2226
	21st to end	Day	22% 7% 2 8% 5% 5% 5% 3 5% 7% 32%	2033
October	1st to 10th	Day	23% 8% 3 8% 5% 5% 5% 4 5% 7% 26%	3180
	11th to 20th	Day	32% 9% 3 8% 5% 5% 5% 3 5% 5% 21%	3161
	21st to end	Day	26% 12% 4 10% 6% 5% 5% 4 5% 7% 17%	3145
November	1st to 10th	Day	35% 10% 3 9% 6% 5% 4 3 5% 4 17%	1568
	11th to 20th	Day	33% 13% 4 9% 5% 4 4 3 5% 5% 17%	1600
	21st to end	Day	35% 13% 4 9% 5% 4 3 3 5% 4 16%	1600
December	1st to 10th	Day	28% 16% 4 9% 4 4 4 3 4 5% 19%	1410
	11th to 20th	Day	41% 16% 4 9% 4 3 4 2 4 3 11%	1685
	21st to end	Day	38% 15% 4 10% 5% 4 3 3 3 4 12%	2442
January	1st to 10th	Night	38% 13% 4 9% 5% 4 4 3 3 4 14%	4726
	11th to 20th	Night	31% 10% 3 8% 5% 4 4 3 6% 7% 19%	4699
	21st to end	Night	47% 13% 3 7% 5% 4 3 3 3 3 9%	4957
February	1st to 10th	Night	31% 15% 4 7% 5% 4 3 3 4 5% 19%	2470
	11th to 20th	Night	24% 14% 4 8% 5% 4 4 3 4 5% 25%	2402
	21st to end	Night	27% 14% 3 7% 5% 4 4 3 4 5% 23%	2041
March	1st to 10th	Night	24% 15% 3 8% 5% 5% 4 3 5% 6% 23%	3594
	11th to 20th	Night	22% 10% 4 7% 4 4 4 3 4 5% 32%	3489
	21st to end	Night	25% 14% 4 10% 6% 4 4 3 4 4 22%	3781
April	1st to 10th	Night	24% 12% 3 8% 7% 6% 5% 3 5% 6% 22%	1900
	11th to 20th	Night	19% 11% 4 9% 7% 4 5% 4 5% 7% 26%	1723
	21st to end	Night	25% 11% 3 6% 5% 3 4 5% 5% 6% 27%	1686
May	1st to 10th	Night	17% 9% 3 6% 3 3 3 2 4 6% 45%	2540
	11th to 20th	Night	15% 6% 2 6% 4 4 4 3 6% 11% 38%	2516
	21st to end	Night	23% 12% 4 10% 6% 5% 4 3 4 5% 25%	2508
June	1st to 10th	Night	20% 10% 3 6% 6% 5% 5% 4 5% 5% 32%	1330
	11th to 20th	Night	19% 9% 3 8% 6% 4 4 4 6% 6% 30%	1330
	21st to end	Night	15% 8% 3 6% 4 4 4 3 6% 7% 40%	1330
July	1st to 10th	Night	6% 4 3 5% 4 3 3 2 3 5% 62%	2220
	11th to 20th	Night	5% 3 1 3 2 2 3 2 4 5% 71%	2220
	21st to end	Night	9% 6% 3 6% 4 4 4 3 5% 6% 51%	2531
August	1st to 10th	Night	4 2 1 2 2 2 3 2 4 5% 73%	2624
	11th to 20th	Night	14% 5% 2 5% 4 4 5% 4 5% 8% 44%	2812
	21st to end	Night	16% 6% 3 7% 4 4 3 3 4 6% 45%	3173
September	1st to 10th	Night	8% 4 2 6% 4 4 3 3 4 6% 56%	1900
	11th to 20th	Night	18% 8% 2 6% 4 4 3 3 5% 6% 41%	1952
	21st to end	Night	22% 7% 3 6% 3 3 3 3 4 5% 39%	2146
October	1st to 10th	Night	25% 9% 3 7% 5% 5% 4 3 4 6% 28%	3800
	11th to 20th	Night	31% 11% 3 7% 4 3 3 3 4 6% 26%	3777
	21st to end	Night	28% 10% 3 8% 5% 5% 4 3 4 6% 25%	4414
November	1st to 10th	Night	36% 10% 3 8% 5% 4 4 3 4 5% 17%	2730
	11th to 20th	Night	34% 12% 3 8% 5% 4 4 3 4 3 20%	2800
	21st to end	Night	33% 11% 4 8% 5% 4 4 3 4 4 19%	2800
December	1st to 10th	Night	29% 13% 3 7% 6% 4 4 3 4 4 23%	2804
	11th to 20th	Night	42% 15% 4 9% 4 3 3 2 3 3 11%	3520
	21st to end	Night	38% 15% 4 9% 5% 4 3 2 3 3 14%	5214

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	71% 7% 10% 9% 2 1	2219
	11th to 20th	Day	68% 10% 9% 7% 5% 1	2220
	21st to end	Day	83% 7% 4 5% 1	2699
February	1st to 10th	Day	72% 7% 8% 7% 4 2	1710
	11th to 20th	Day	65% 8% 10% 12% 5% 1	1674
	21st to end	Day	63% 8% 12% 10% 4 2	1413
March	1st to 10th	Day	64% 10% 11% 9% 5%	3276
	11th to 20th	Day	54% 8% 11% 22% 3 1	3490
	21st to end	Day	59% 12% 16% 11% 2	3872
April	1st to 10th	Day	62% 8% 14% 11% 4	2280
	11th to 20th	Day	57% 7% 11% 15% 10% 1	2406
	21st to end	Day	57% 7% 12% 16% 8% 1	2494
May	1st to 10th	Day	42% 6% 16% 23% 11% 1	4420
	11th to 20th	Day	38% 11% 23% 23% 5%	4380
	21st to end	Day	55% 8% 17% 15% 5%	5065
June	1st to 10th	Day	53% 8% 17% 15% 5% 2	2850
	11th to 20th	Day	52% 9% 18% 15% 5% 1	2850
	21st to end	Day	45% 8% 19% 18% 9% 1	2850
July	1st to 10th	Day	24% 5% 13% 25% 24% 9%	4666
	11th to 20th	Day	18% 5% 17% 38% 20% 2	4659
	21st to end	Day	30% 8% 21% 26% 11% 3	4860
August	1st to 10th	Day	18% 6% 15% 48% 12% 1	4276
	11th to 20th	Day	41% 11% 21% 17% 8% 1	4065
	21st to end	Day	40% 12% 19% 21% 7% 1	4493
September	1st to 10th	Day	36% 10% 17% 23% 12% 2	2280
	11th to 20th	Day	46% 10% 15% 16% 12% 1	2226
	21st to end	Day	52% 9% 15% 15% 8% 1	2033
October	1st to 10th	Day	56% 9% 16% 14% 5%	3180
	11th to 20th	Day	66% 6% 12% 11% 4	3161
	21st to end	Day	66% 10% 12% 9% 3	3145
November	1st to 10th	Day	71% 6% 8% 8% 5% 1	1568
	11th to 20th	Day	71% 6% 9% 9% 4 2	1600
	21st to end	Day	71% 6% 8% 9% 5%	1600
December	1st to 10th	Day	68% 8% 7% 11% 5% 1	1410
	11th to 20th	Day	78% 7% 7% 5% 3 1	1688
	21st to end	Day	77% 6% 8% 5% 2 1	2442
January	1st to 10th	Night	74% 7% 7% 9% 3	4726
	11th to 20th	Night	61% 11% 14% 9% 4 1	4740
	21st to end	Night	81% 6% 5% 6% 2	4957
February	1st to 10th	Night	69% 6% 10% 9% 5% 2	2470
	11th to 20th	Night	62% 7% 12% 11% 6% 1	2404
	21st to end	Night	64% 5% 10% 14% 5% 2	2041
March	1st to 10th	Night	62% 7% 12% 14% 6%	3594
	11th to 20th	Night	53% 6% 14% 23% 3	3490
	21st to end	Night	65% 9% 12% 13% 2	3781
April	1st to 10th	Night	63% 6% 13% 15% 3	1900
	11th to 20th	Night	57% 7% 9% 16% 9% 2	1723
	21st to end	Night	57% 8% 11% 16% 8%	1686
May	1st to 10th	Night	42% 6% 14% 27% 11%	2540
	11th to 20th	Night	36% 10% 22% 26% 5%	2516
	21st to end	Night	61% 6% 14% 15% 4	2508
June	1st to 10th	Night	55% 6% 14% 17% 6% 2	1330
	11th to 20th	Night	54% 6% 18% 17% 5%	1330
	21st to end	Night	42% 8% 21% 19% 8% 2	1330
July	1st to 10th	Night	25% 6% 11% 27% 24% 7%	2185
	11th to 20th	Night	16% 6% 15% 42% 20% 1	2178
	21st to end	Night	30% 8% 16% 27% 16% 3	2451
August	1st to 10th	Night	16% 4 13% 46% 20% 2	2616
	11th to 20th	Night	39% 9% 26% 15% 8% 2	2839
	21st to end	Night	41% 7% 22% 23% 8%	3173
September	1st to 10th	Night	29% 6% 18% 30% 14% 3	1900
	11th to 20th	Night	45% 7% 12% 16% 16% 3	1952
	21st to end	Night	49% 7% 15% 19% 8% 2	2146
October	1st to 10th	Night	57% 7% 16% 13% 7%	3800
	11th to 20th	Night	61% 4 12% 19% 3	3777
	21st to end	Night	61% 8% 14% 13% 4	4414
November	1st to 10th	Night	70% 7% 10% 8% 4 1	2730
	11th to 20th	Night	70% 6% 11% 8% 3 1	2800
	21st to end	Night	69% 7% 8% 10% 6% 1	2800
December	1st to 10th	Night	66% 8% 10% 11% 5% 1	2804
	11th to 20th	Night	79% 6% 6% 5% 4	3516
	21st to end	Night	77% 5% 8% 7% 2 1	5214

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	40% 6% 17% 22% 8% 7%	180
	11th to 20th	Day	37% 12% 13% 24% 14%	180
	21st to end	Day	43% 4 16% 21% 12% 3	252
February	1st to 10th	Day	41% 6% 19% 20% 13% 1	370
	11th to 20th	Day	35% 4 21% 25% 14% 1	365
	21st to end	Day	28% 10% 23% 22% 12% 5%	307
March	1st to 10th	Day	32% 5% 21% 22% 17% 3	447
	11th to 20th	Day	30% 7% 17% 23% 18% 4	460
	21st to end	Day	30% 5% 25% 25% 12% 3	506
April	1st to 10th	Day	31% 7% 23% 23% 13% 3	460
	11th to 20th	Day	26% 4 27% 23% 16% 3	452
	21st to end	Day	23% 7% 23% 28% 15% 3	460
May	1st to 10th	Day	17% 4 21% 29% 26% 4	463
	11th to 20th	Day	17% 4 15% 30% 27% 7%	488
	21st to end	Day	17% 5% 19% 31% 23% 6%	676
June	1st to 10th	Day	20% 5% 21% 28% 20% 4	680
	11th to 20th	Day	16% 5% 24% 30% 22% 4	680
	21st to end	Day	17% 2 16% 31% 28% 5%	680
July	1st to 10th	Day	14% 3 15% 30% 32% 7%	671
	11th to 20th	Day	8% 3 14% 34% 33% 9%	668
	21st to end	Day	7% 3 13% 27% 39% 12%	669
August	1st to 10th	Day	12% 2 8% 25% 34% 19%	487
	11th to 20th	Day	10% 3 11% 27% 35% 14%	477
	21st to end	Day	16% 3 16% 28% 29% 8%	539
September	1st to 10th	Day	13% 2 17% 32% 26% 9%	490
	11th to 20th	Day	25% 6% 14% 25% 21% 10%	490
	21st to end	Day	27% 4 19% 26% 17% 7%	490
October	1st to 10th	Day	27% 5% 18% 23% 19% 9%	490
	11th to 20th	Day	37% 5% 14% 20% 16% 8%	490
	21st to end	Day	34% 8% 19% 23% 12% 4	404
November	1st to 10th	Day	38% 6% 24% 21% 10% 2	200
	11th to 20th	Day	38% 9% 14% 19% 13% 9%	200
	21st to end	Day	44% 8% 18% 14% 10% 8%	200
December	1st to 10th	Day	37% 3 24% 14% 14% 9%	182
	11th to 20th	Day	39% 13% 14% 19% 11% 3	180
	21st to end	Day	45% 7% 18% 20% 8% 3	198
January	1st to 10th	Night	47% 6% 15% 17% 12% 3	850
	11th to 20th	Night	41% 5% 14% 19% 18% 2	850
	21st to end	Night	40% 3 16% 21% 15% 4	888
February	1st to 10th	Night	39% 5% 14% 28% 12% 2	760
	11th to 20th	Night	31% 4 18% 27% 18% 1	744
	21st to end	Night	34% 7% 17% 23% 16% 4	628
March	1st to 10th	Night	34% 5% 18% 22% 17% 4	760
	11th to 20th	Night	39% 5% 14% 20% 17% 5%	760
	21st to end	Night	33% 4 16% 24% 18% 5%	836
April	1st to 10th	Night	31% 5% 14% 29% 16% 6%	760
	11th to 20th	Night	26% 5% 18% 30% 19% 3	595
	21st to end	Night	29% 5% 13% 31% 18% 4	546
May	1st to 10th	Night	22% 3 12% 29% 27% 6%	380
	11th to 20th	Night	20% 4 8% 24% 35% 8%	374
	21st to end	Night	19% 2 12% 29% 29% 8%	411
June	1st to 10th	Night	25% 3 11% 30% 28% 4	380
	11th to 20th	Night	22% 4 13% 29% 24% 8%	380
	21st to end	Night	19% 2 9% 29% 32% 8%	380
July	1st to 10th	Night	12% 2 9% 24% 39% 14%	370
	11th to 20th	Night	10% 2 8% 25% 45% 11%	368
	21st to end	Night	8% 2 5% 20% 47% 17%	416
August	1st to 10th	Night	9% 1 5% 21% 42% 23%	434
	11th to 20th	Night	9% 1 4 22% 49% 15%	564
	21st to end	Night	15% 3 10% 21% 39% 12%	641
September	1st to 10th	Night	11% 2 7% 30% 36% 14%	760
	11th to 20th	Night	21% 4 10% 18% 31% 17%	760
	21st to end	Night	25% 3 12% 27% 27% 7%	760
October	1st to 10th	Night	26% 3 9% 26% 27% 9%	760
	11th to 20th	Night	36% 4 10% 23% 21% 6%	760
	21st to end	Night	36% 5% 15% 25% 14% 5%	836
November	1st to 10th	Night	43% 6% 14% 23% 14% 1	780
	11th to 20th	Night	42% 5% 15% 22% 14% 3	800
	21st to end	Night	41% 5% 15% 22% 13% 4	800
December	1st to 10th	Night	35% 5% 15% 24% 17% 4	824
	11th to 20th	Night	48% 5% 15% 21% 10% 1	850
	21st to end	Night	43% 6% 18% 21% 10% 1	935

Page generated at 2024-11-29 07:43:07. Version ac07

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