Wren Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Wren Park clear sky chart from 2005-11-06 to 2024-11-02.

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	28% 9% 3 6% 4 3 3 3 4 5% 33%	101685
	Night	32% 10% 2 5% 3 3 3 3 4 5% 30%	97368
Transparency	Day	53% 6% 13% 17% 8% 2	101436
	Night	57% 6% 12% 16% 8% 2	97263
Seeing	Day	31% 11% 22% 22% 10% 3	15262
	Night	36% 7% 17% 23% 15% 1	23471

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	48% 13% 3 7% 4 4 3 2 3 2 11%	2219
	11th to 20th	Day	32% 13% 4 7% 4 3 3 2 2 4 26%	2259
	21st to end	Day	57% 11% 3 4 2 2 2 2 2 3 12%	2794
February	1st to 10th	Day	39% 11% 3 7% 5% 4 3 2 4 4 17%	1705
	11th to 20th	Day	36% 12% 3 8% 4 3 3 2 4 4 22%	1665
	21st to end	Day	30% 18% 3 7% 6% 3 4 3 4 4 20%	1452
March	1st to 10th	Day	31% 19% 3 7% 4 4 3 3 4 5% 18%	3195
	11th to 20th	Day	27% 12% 3 6% 4 3 3 2 3 4 33%	3490
	21st to end	Day	32% 13% 3 7% 5% 3 4 3 4 4 20%	3965
April	1st to 10th	Day	33% 12% 4 7% 6% 3 5% 3 4 5% 17%	2280
	11th to 20th	Day	28% 11% 3 8% 5% 5% 5% 3 4 5% 22%	2314
	21st to end	Day	30% 11% 4 7% 5% 5% 4 4 5% 5% 21%	2551
May	1st to 10th	Day	22% 10% 2 6% 4 4 4 3 4 4 37%	4420
	11th to 20th	Day	20% 7% 2 5% 4 4 4 5% 6% 7% 34%	4377
	21st to end	Day	36% 10% 3 7% 4 4 3 3 4 5% 20%	4831
June	1st to 10th	Day	31% 7% 3 6% 5% 4 4 3 5% 6% 26%	2850
	11th to 20th	Day	32% 9% 3 8% 5% 5% 5% 3 5% 5% 21%	2850
	21st to end	Day	21% 8% 3 6% 4 4 5% 4 5% 6% 34%	2850
July	1st to 10th	Day	12% 4 1 4 3 3 2 3 4 4 61%	4740
	11th to 20th	Day	9% 4 1 2 2 2 2 2 3 5% 68%	4740
	21st to end	Day	18% 4 2 4 3 3 2 2 4 7% 51%	4800
August	1st to 10th	Day	9% 3 1 3 2 2 3 2 4 6% 64%	4401
	11th to 20th	Day	20% 6% 2 4 4 3 4 3 6% 6% 41%	4035
	21st to end	Day	22% 6% 2 5% 4 4 4 3 4 7% 39%	4377
September	1st to 10th	Day	18% 6% 2 6% 3 3 3 2 3 6% 46%	2280
	11th to 20th	Day	23% 7% 3 6% 4 3 4 3 4 4 38%	2280
	21st to end	Day	29% 8% 2 6% 3 2 3 3 4 5% 35%	2007
October	1st to 10th	Day	28% 9% 2 5% 4 3 3 3 3 6% 34%	1900
	11th to 20th	Day	37% 8% 2 6% 4 3 3 2 4 6% 24%	1900
	21st to end	Day	40% 9% 3 5% 3 3 2 3 4 6% 23%	1941
November	1st to 10th	Day	46% 9% 3 6% 4 3 2 2 3 4 17%	1496
	11th to 20th	Day	43% 12% 2 6% 3 3 3 1 3 3 22%	1520
	21st to end	Day	43% 10% 3 5% 3 3 3 3 4 3 19%	1520
December	1st to 10th	Day	38% 14% 2 3 3 2 3 3 3 3 26%	1520
	11th to 20th	Day	41% 14% 3 7% 3 3 3 3 3 3 17%	1719
	21st to end	Day	44% 15% 4 8% 4 4 3 2 3 4 11%	2442
January	1st to 10th	Night	47% 15% 3 7% 3 2 3 2 3 3 13%	4726
	11th to 20th	Night	35% 9% 3 4 3 3 3 2 4 6% 28%	4636
	21st to end	Night	54% 11% 3 6% 3 2 2 1 2 3 13%	4862
February	1st to 10th	Night	40% 11% 3 6% 4 3 3 2 4 4 20%	2470
	11th to 20th	Night	34% 16% 3 6% 4 3 3 2 4 4 22%	2402
	21st to end	Night	33% 14% 3 6% 3 3 3 2 4 4 25%	2001
March	1st to 10th	Night	30% 18% 3 6% 4 4 3 3 4 5% 21%	3676
	11th to 20th	Night	30% 10% 2 5% 3 3 3 2 3 4 35%	3489
	21st to end	Night	38% 12% 3 7% 4 4 3 3 4 2 20%	3688
April	1st to 10th	Night	32% 12% 3 8% 5% 4 4 3 5% 4 21%	1900
	11th to 20th	Night	26% 11% 3 7% 6% 5% 4 3 4 5% 26%	1815
	21st to end	Night	34% 9% 3 6% 5% 4 4 4 4 5% 21%	1629
May	1st to 10th	Night	21% 10% 3 5% 3 2 3 2 3 4 43%	2540
	11th to 20th	Night	18% 5% 2 5% 4 4 4 4 5% 7% 42%	2516
	21st to end	Night	34% 9% 2 7% 4 3 3 3 4 5% 25%	2740
June	1st to 10th	Night	26% 9% 2 8% 4 4 5% 4 4 5% 29%	1330
	11th to 20th	Night	25% 11% 3 8% 5% 4 4 4 6% 6% 24%	1330
	21st to end	Night	19% 8% 2 6% 4 3 4 3 5% 6% 41%	1330
July	1st to 10th	Night	7% 4 1 4 2 2 3 2 3 5% 67%	2220
	11th to 20th	Night	6% 3 1 2 2 2 1 2 3 4 74%	2220
	21st to end	Night	11% 4 2 3 3 3 3 3 4 5% 59%	2749
August	1st to 10th	Night	7% 3 1 2 2 2 2 2 5% 8% 67%	2529
	11th to 20th	Night	14% 5% 2 5% 3 4 3 3 6% 7% 49%	2799
	21st to end	Night	21% 6% 2 5% 3 4 3 3 6% 9% 38%	3294
September	1st to 10th	Night	13% 5% 1 4 4 3 4 2 5% 6% 51%	1900
	11th to 20th	Night	24% 6% 1 5% 4 3 3 2 4 6% 42%	1900
	21st to end	Night	26% 7% 2 6% 3 3 3 3 4 5% 37%	2170
October	1st to 10th	Night	26% 8% 2 5% 5% 4 4 3 3 5% 35%	2280
	11th to 20th	Night	36% 7% 2 6% 2 3 3 2 4 6% 28%	2280
	21st to end	Night	38% 8% 2 6% 3 3 3 3 4 4 26%	2655
November	1st to 10th	Night	46% 10% 2 5% 4 3 3 3 3 4 17%	2616
	11th to 20th	Night	44% 9% 3 5% 4 3 2 3 3 3 22%	2660
	21st to end	Night	43% 11% 2 5% 3 3 3 3 3 3 20%	2660
December	1st to 10th	Night	35% 11% 2 5% 4 3 3 3 4 5% 25%	2660
	11th to 20th	Night	48% 13% 2 6% 4 3 3 2 3 3 14%	3482
	21st to end	Night	46% 13% 3 7% 3 3 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	76% 8% 6% 6% 3 1	2219
	11th to 20th	Day	63% 5% 6% 14% 7% 4	2280
	21st to end	Day	79% 5% 6% 8% 3 1	2794
February	1st to 10th	Day	71% 5% 9% 7% 6% 2	1705
	11th to 20th	Day	66% 6% 8% 11% 8% 2	1674
	21st to end	Day	69% 4 9% 11% 5% 2	1452
March	1st to 10th	Day	63% 8% 11% 13% 4 1	3195
	11th to 20th	Day	55% 6% 11% 25% 3 1	3490
	21st to end	Day	66% 7% 13% 10% 4 1	3965
April	1st to 10th	Day	69% 7% 12% 10% 2	2280
	11th to 20th	Day	64% 5% 9% 11% 8% 3	2314
	21st to end	Day	64% 6% 12% 11% 7% 1	2551
May	1st to 10th	Day	49% 5% 15% 22% 9% 1	4420
	11th to 20th	Day	43% 10% 25% 18% 4	4380
	21st to end	Day	65% 8% 15% 10% 1	4832
June	1st to 10th	Day	60% 6% 15% 13% 5% 2	2850
	11th to 20th	Day	65% 5% 15% 11% 4	2850
	21st to end	Day	50% 7% 16% 18% 8% 1	2850
July	1st to 10th	Day	27% 5% 10% 24% 24% 10%	4666
	11th to 20th	Day	21% 3 12% 38% 24% 2	4659
	21st to end	Day	32% 5% 21% 28% 12% 2	4648
August	1st to 10th	Day	22% 4 16% 38% 18% 1	4384
	11th to 20th	Day	43% 6% 22% 20% 8% 1	4074
	21st to end	Day	46% 5% 17% 21% 10% 1	4376
September	1st to 10th	Day	40% 6% 14% 23% 12% 5%	2280
	11th to 20th	Day	50% 5% 10% 17% 15% 3	2280
	21st to end	Day	52% 6% 15% 16% 10% 1	2007
October	1st to 10th	Day	53% 5% 15% 17% 11%	1900
	11th to 20th	Day	61% 5% 12% 16% 5% 1	1900
	21st to end	Day	64% 5% 10% 12% 8% 1	1941
November	1st to 10th	Day	72% 4 9% 10% 3 1	1496
	11th to 20th	Day	71% 3 8% 9% 6% 2	1520
	21st to end	Day	69% 5% 6% 11% 8% 2	1520
December	1st to 10th	Day	66% 5% 8% 11% 10% 1	1520
	11th to 20th	Day	70% 6% 8% 11% 3 1	1722
	21st to end	Day	74% 10% 7% 7% 2 1	2442
January	1st to 10th	Night	76% 7% 5% 9% 2	4726
	11th to 20th	Night	57% 5% 9% 16% 9% 5%	4677
	21st to end	Night	77% 5% 6% 8% 3 1	4862
February	1st to 10th	Night	71% 4 9% 9% 4 2	2470
	11th to 20th	Night	68% 5% 8% 11% 7% 2	2404
	21st to end	Night	65% 4 9% 14% 6% 2	2001
March	1st to 10th	Night	61% 9% 11% 12% 7%	3676
	11th to 20th	Night	51% 7% 15% 24% 3	3490
	21st to end	Night	67% 8% 14% 9% 2	3688
April	1st to 10th	Night	65% 7% 13% 12% 2	1900
	11th to 20th	Night	60% 6% 10% 14% 7% 3	1815
	21st to end	Night	64% 5% 12% 12% 6% 1	1629
May	1st to 10th	Night	45% 5% 14% 25% 10% 1	2540
	11th to 20th	Night	41% 8% 26% 20% 5%	2516
	21st to end	Night	62% 8% 16% 12% 3	2740
June	1st to 10th	Night	56% 6% 17% 13% 5% 2	1330
	11th to 20th	Night	59% 7% 18% 13% 3	1330
	21st to end	Night	42% 6% 22% 20% 7% 3	1330
July	1st to 10th	Night	22% 5% 10% 33% 21% 10%	2185
	11th to 20th	Night	17% 4 10% 40% 27% 2	2178
	21st to end	Night	28% 4 15% 28% 22% 3	2662
August	1st to 10th	Night	18% 4 18% 39% 20% 2	2521
	11th to 20th	Night	34% 6% 28% 21% 8% 3	2826
	21st to end	Night	43% 6% 20% 20% 10%	3294
September	1st to 10th	Night	33% 7% 18% 24% 14% 4	1900
	11th to 20th	Night	45% 6% 14% 17% 15% 4	1900
	21st to end	Night	48% 7% 16% 19% 9% 2	2170
October	1st to 10th	Night	52% 6% 15% 19% 8% 1	2280
	11th to 20th	Night	59% 5% 14% 16% 6% 1	2280
	21st to end	Night	61% 6% 11% 14% 8%	2655
November	1st to 10th	Night	71% 5% 10% 11% 3 1	2616
	11th to 20th	Night	69% 5% 10% 8% 6% 2	2660
	21st to end	Night	70% 5% 8% 8% 8% 2	2660
December	1st to 10th	Night	61% 7% 11% 12% 8% 1	2660
	11th to 20th	Night	76% 6% 7% 6% 3 1	3478
	21st to end	Night	74% 6% 8% 7% 4	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	49% 14% 14% 10% 9% 3	180
	11th to 20th	Day	49% 11% 18% 14% 6% 1	180
	21st to end	Day	45% 14% 20% 14% 7% 1	198
February	1st to 10th	Day	47% 13% 19% 14% 4 2	365
	11th to 20th	Day	42% 14% 23% 16% 5% 1	365
	21st to end	Day	41% 16% 25% 12% 5% 1	326
March	1st to 10th	Day	42% 15% 19% 17% 7%	460
	11th to 20th	Day	39% 13% 19% 19% 10% 1	460
	21st to end	Day	42% 16% 19% 15% 7% 1	506
April	1st to 10th	Day	38% 17% 21% 16% 7% 1	460
	11th to 20th	Day	31% 15% 26% 17% 9% 1	452
	21st to end	Day	33% 16% 25% 15% 9% 1	460
May	1st to 10th	Day	25% 13% 30% 24% 7% 1	463
	11th to 20th	Day	28% 10% 23% 26% 10% 3	488
	21st to end	Day	30% 13% 24% 21% 8% 3	534
June	1st to 10th	Day	29% 14% 26% 23% 7% 1	680
	11th to 20th	Day	30% 14% 28% 20% 7% 2	680
	21st to end	Day	25% 9% 24% 27% 12% 2	680
July	1st to 10th	Day	18% 8% 29% 32% 10% 3	671
	11th to 20th	Day	14% 9% 26% 37% 12% 3	668
	21st to end	Day	13% 6% 24% 37% 14% 6%	541
August	1st to 10th	Day	15% 6% 22% 33% 16% 8%	487
	11th to 20th	Day	13% 5% 23% 34% 20% 6%	477
	21st to end	Day	20% 10% 23% 28% 14% 5%	539
September	1st to 10th	Day	23% 8% 24% 28% 13% 4	490
	11th to 20th	Day	27% 9% 21% 27% 14% 2	490
	21st to end	Day	31% 9% 20% 25% 12% 3	490
October	1st to 10th	Day	33% 8% 21% 19% 16% 2	490
	11th to 20th	Day	41% 7% 15% 19% 14% 2	490
	21st to end	Day	44% 9% 18% 18% 9% 2	392
November	1st to 10th	Day	45% 16% 18% 14% 7%	182
	11th to 20th	Day	52% 7% 14% 10% 14% 3	180
	21st to end	Day	50% 7% 20% 8% 11% 4	180
December	1st to 10th	Day	49% 13% 13% 9% 13% 3	180
	11th to 20th	Day	54% 8% 17% 16% 5% 1	180
	21st to end	Day	52% 11% 20% 14% 3	198
January	1st to 10th	Night	54% 11% 15% 14% 6% 1	850
	11th to 20th	Night	49% 8% 17% 20% 6%	832
	21st to end	Night	46% 10% 19% 19% 7%	836
February	1st to 10th	Night	46% 11% 21% 17% 5%	760
	11th to 20th	Night	44% 10% 21% 21% 5%	744
	21st to end	Night	39% 11% 23% 20% 7%	628
March	1st to 10th	Night	35% 12% 20% 21% 12%	760
	11th to 20th	Night	42% 9% 19% 20% 9%	760
	21st to end	Night	42% 10% 19% 21% 8%	836
April	1st to 10th	Night	38% 8% 19% 26% 9% 1	760
	11th to 20th	Night	30% 10% 26% 24% 10%	687
	21st to end	Night	37% 7% 18% 27% 10% 1	489
May	1st to 10th	Night	26% 7% 16% 29% 21% 1	380
	11th to 20th	Night	22% 3 11% 35% 26% 2	374
	21st to end	Night	26% 5% 13% 31% 24%	411
June	1st to 10th	Night	28% 6% 17% 29% 18% 2	380
	11th to 20th	Night	28% 6% 16% 29% 18% 3	380
	21st to end	Night	22% 4 11% 34% 27% 2	380
July	1st to 10th	Night	14% 4 11% 31% 38% 2	370
	11th to 20th	Night	12% 4 11% 32% 36% 7%	368
	21st to end	Night	9% 1 6% 32% 46% 5%	416
August	1st to 10th	Night	12% 1 5% 25% 49% 7%	378
	11th to 20th	Night	10% 2 8% 29% 43% 8%	551
	21st to end	Night	16% 3 12% 31% 36% 3	710
September	1st to 10th	Night	16% 2 14% 36% 29% 2	760
	11th to 20th	Night	26% 4 13% 24% 29% 4	760
	21st to end	Night	30% 5% 14% 31% 20% 1	760
October	1st to 10th	Night	31% 5% 18% 25% 20% 1	760
	11th to 20th	Night	40% 4 18% 21% 15% 1	760
	21st to end	Night	42% 10% 20% 21% 7% 1	836
November	1st to 10th	Night	50% 9% 19% 19% 2	748
	11th to 20th	Night	50% 8% 19% 14% 7% 1	760
	21st to end	Night	48% 10% 18% 15% 8% 1	760
December	1st to 10th	Night	39% 9% 22% 22% 8%	760
	11th to 20th	Night	53% 9% 21% 14% 3	832
	21st to end	Night	52% 10% 24% 11% 2	935

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