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 2025-06-10.

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	28% 10% 3 6% 4 4 3 3 4 5% 31%	123295
	Night	31% 10% 3 6% 4 3 3 3 4 5% 28%	123646
Transparency	Day	55% 6% 13% 17% 8% 1	123046
	Night	58% 6% 13% 16% 7% 1	123538
Seeing	Day	31% 11% 22% 22% 10% 3	15946
	Night	36% 7% 17% 23% 15% 1	24288

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	45% 14% 3 7% 4 4 3 2 3 3 11%	3179
	11th to 20th	Day	23% 12% 4 6% 4 3 3 2 3 5% 34%	3247
	21st to end	Day	45% 10% 3 4 2 2 2 2 2 3 26%	4004
February	1st to 10th	Day	37% 12% 3 7% 5% 4 3 2 4 4 18%	1795
	11th to 20th	Day	35% 12% 3 8% 4 3 3 2 4 4 22%	1755
	21st to end	Day	31% 17% 3 7% 6% 4 3 3 4 3 19%	1526
March	1st to 10th	Day	31% 17% 4 8% 4 4 3 3 4 5% 18%	4601
	11th to 20th	Day	27% 16% 4 8% 5% 4 3 3 3 3 24%	5000
	21st to end	Day	33% 13% 3 8% 5% 4 4 3 5% 5% 16%	5678
April	1st to 10th	Day	33% 12% 4 7% 6% 3 5% 3 4 5% 17%	2400
	11th to 20th	Day	27% 11% 3 8% 5% 5% 5% 3 4 5% 23%	2438
	21st to end	Day	30% 11% 4 7% 5% 4 4 4 5% 5% 23%	2685
May	1st to 10th	Day	20% 9% 2 7% 4 4 4 3 4 5% 38%	6320
	11th to 20th	Day	25% 11% 4 7% 4 5% 4 4 5% 6% 25%	6277
	21st to end	Day	29% 8% 3 7% 4 4 4 4 6% 8% 24%	6935
June	1st to 10th	Day	29% 7% 3 6% 5% 4 4 3 5% 6% 28%	2989
	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	26% 7% 3 7% 5% 4 4 4 5% 7% 28%	3180
	11th to 20th	Day	41% 7% 2 6% 3 4 3 2 4 5% 22%	3161
	21st to end	Day	37% 12% 4 7% 4 4 3 3 5% 6% 16%	3186
November	1st to 10th	Day	45% 9% 3 6% 4 4 2 3 4 4 17%	1568
	11th to 20th	Day	42% 13% 3 6% 3 3 2 1 3 3 21%	1600
	21st to end	Day	43% 11% 3 5% 3 3 3 3 4 3 18%	1600
December	1st to 10th	Day	28% 11% 3 6% 4 3 4 4 5% 7% 25%	2620
	11th to 20th	Day	45% 15% 3 7% 3 3 3 2 3 3 12%	2693
	21st to end	Day	44% 15% 4 8% 4 4 3 2 3 4 9%	3498
January	1st to 10th	Night	45% 13% 3 7% 3 3 3 2 3 3 14%	6766
	11th to 20th	Night	25% 9% 2 4 4 3 4 3 5% 9% 32%	6648
	21st to end	Night	41% 9% 2 5% 3 2 2 2 2 4 27%	6952
February	1st to 10th	Night	38% 12% 3 7% 4 3 3 2 4 4 20%	2600
	11th to 20th	Night	34% 15% 3 6% 4 3 3 2 3 4 22%	2532
	21st to end	Night	33% 14% 3 6% 3 3 3 2 4 4 24%	2103
March	1st to 10th	Night	28% 18% 3 6% 4 4 3 3 4 5% 21%	5290
	11th to 20th	Night	31% 15% 3 7% 4 3 3 2 3 4 25%	4999
	21st to end	Night	43% 12% 3 6% 4 3 3 2 4 3 17%	5297
April	1st to 10th	Night	32% 12% 3 8% 5% 4 4 3 4 5% 21%	2000
	11th to 20th	Night	25% 11% 3 7% 5% 5% 4 3 5% 5% 27%	1911
	21st to end	Night	32% 9% 3 7% 5% 4 4 4 4 5% 23%	1715
May	1st to 10th	Night	19% 10% 3 6% 3 3 3 2 3 4 44%	3640
	11th to 20th	Night	24% 9% 3 6% 4 4 4 4 5% 6% 32%	3616
	21st to end	Night	26% 9% 3 8% 4 4 4 4 5% 6% 27%	3936
June	1st to 10th	Night	25% 9% 2 8% 4 4 5% 4 4 5% 31%	1395
	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	27% 10% 3 7% 5% 4 4 3 4 5% 27%	3800
	11th to 20th	Night	38% 7% 2 5% 2 3 3 2 4 6% 27%	3777
	21st to end	Night	36% 12% 3 8% 4 3 3 2 4 4 20%	4372
November	1st to 10th	Night	46% 10% 2 5% 3 3 3 3 3 4 17%	2730
	11th to 20th	Night	44% 10% 3 5% 4 3 2 2 3 3 21%	2800
	21st to end	Night	42% 12% 2 5% 3 4 3 3 3 3 20%	2800
December	1st to 10th	Night	29% 11% 2 6% 4 4 4 3 6% 9% 23%	4560
	11th to 20th	Night	46% 13% 3 7% 4 3 3 2 3 4 12%	5508
	21st to end	Night	46% 15% 4 8% 3 3 3 2 3 3 11%	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	77% 6% 6% 8% 2	3179
	11th to 20th	Day	53% 5% 9% 20% 9% 3	3268
	21st to end	Day	65% 4 7% 17% 7%	4004
February	1st to 10th	Day	70% 5% 9% 8% 7% 2	1795
	11th to 20th	Day	66% 5% 8% 11% 8% 2	1764
	21st to end	Day	70% 3 9% 11% 5% 2	1526
March	1st to 10th	Day	65% 7% 9% 15% 4	4601
	11th to 20th	Day	64% 6% 8% 19% 2	5000
	21st to end	Day	68% 7% 12% 10% 3	5678
April	1st to 10th	Day	68% 7% 13% 10% 2	2400
	11th to 20th	Day	62% 5% 9% 13% 8% 3	2438
	21st to end	Day	63% 6% 12% 12% 7% 1	2685
May	1st to 10th	Day	47% 5% 14% 25% 9%	6320
	11th to 20th	Day	56% 9% 19% 13% 3	6280
	21st to end	Day	56% 7% 18% 16% 2	6936
June	1st to 10th	Day	57% 6% 16% 14% 5% 2	2989
	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	54% 5% 16% 18% 7%	3180
	11th to 20th	Day	64% 5% 11% 12% 7% 1	3161
	21st to end	Day	69% 5% 9% 12% 5%	3186
November	1st to 10th	Day	71% 5% 10% 10% 3 1	1568
	11th to 20th	Day	71% 3 8% 9% 6% 2	1600
	21st to end	Day	69% 5% 7% 10% 7% 1	1600
December	1st to 10th	Day	58% 5% 13% 15% 9%	2620
	11th to 20th	Day	75% 6% 7% 9% 2 1	2696
	21st to end	Day	76% 8% 8% 6% 2	3498
January	1st to 10th	Night	75% 5% 7% 10% 3	6766
	11th to 20th	Night	49% 7% 15% 17% 9% 4	6689
	21st to end	Night	62% 4 10% 17% 6% 1	6952
February	1st to 10th	Night	70% 5% 9% 9% 5% 3	2600
	11th to 20th	Night	67% 5% 8% 11% 7% 2	2534
	21st to end	Night	66% 4 9% 14% 6% 2	2103
March	1st to 10th	Night	61% 8% 11% 13% 7%	5290
	11th to 20th	Night	61% 7% 11% 18% 2	5000
	21st to end	Night	71% 7% 14% 7% 1	5297
April	1st to 10th	Night	66% 7% 13% 12% 2	2000
	11th to 20th	Night	59% 6% 11% 14% 7% 3	1911
	21st to end	Night	62% 5% 14% 13% 5% 1	1715
May	1st to 10th	Night	45% 5% 13% 28% 10%	3637
	11th to 20th	Night	52% 7% 22% 15% 4	3616
	21st to end	Night	57% 7% 17% 16% 2	3936
June	1st to 10th	Night	54% 6% 18% 13% 6% 2	1395
	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	58% 5% 16% 15% 5% 1	3800
	11th to 20th	Night	59% 4 12% 17% 7%	3777
	21st to end	Night	66% 5% 10% 13% 5%	4372
November	1st to 10th	Night	70% 5% 10% 10% 3 1	2730
	11th to 20th	Night	70% 5% 9% 8% 6% 2	2800
	21st to end	Night	71% 5% 8% 8% 7% 1	2800
December	1st to 10th	Night	58% 6% 17% 13% 6% 1	4560
	11th to 20th	Night	76% 5% 7% 8% 2 1	5504
	21st to end	Night	76% 6% 8% 7% 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	49% 14% 15% 12% 9% 3	200
	11th to 20th	Day	46% 11% 19% 17% 8% 2	200
	21st to end	Day	42% 13% 20% 16% 8% 2	220
February	1st to 10th	Day	47% 13% 19% 14% 5% 2	395
	11th to 20th	Day	41% 13% 23% 17% 5% 1	395
	21st to end	Day	42% 14% 25% 12% 5% 1	352
March	1st to 10th	Day	42% 14% 19% 18% 7%	500
	11th to 20th	Day	40% 12% 18% 18% 10% 1	500
	21st to end	Day	42% 16% 20% 15% 6% 1	550
April	1st to 10th	Day	38% 16% 21% 17% 7% 1	500
	11th to 20th	Day	30% 15% 26% 18% 9% 2	492
	21st to end	Day	33% 16% 24% 16% 10% 2	500
May	1st to 10th	Day	25% 13% 30% 23% 8% 1	503
	11th to 20th	Day	30% 10% 22% 25% 9% 3	528
	21st to end	Day	29% 13% 25% 21% 9% 3	579
June	1st to 10th	Day	27% 14% 27% 24% 7% 2	727
	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% 19% 18% 9% 2	392
November	1st to 10th	Day	45% 15% 17% 17% 8%	200
	11th to 20th	Day	52% 8% 14% 11% 13% 3	200
	21st to end	Day	51% 7% 19% 8% 11% 5%	200
December	1st to 10th	Day	46% 12% 13% 10% 16% 5%	200
	11th to 20th	Day	56% 7% 16% 15% 6% 1	200
	21st to end	Day	53% 11% 19% 13% 4	220
January	1st to 10th	Night	53% 10% 16% 15% 6% 1	900
	11th to 20th	Night	46% 7% 18% 22% 6%	880
	21st to end	Night	44% 9% 20% 19% 7%	880
February	1st to 10th	Night	45% 11% 22% 18% 5%	800
	11th to 20th	Night	44% 9% 21% 21% 5%	784
	21st to end	Night	40% 10% 23% 20% 7%	660
March	1st to 10th	Night	36% 12% 20% 21% 11%	800
	11th to 20th	Night	43% 9% 18% 21% 9%	800
	21st to end	Night	43% 9% 19% 20% 8%	880
April	1st to 10th	Night	39% 8% 18% 26% 9% 1	800
	11th to 20th	Night	29% 10% 26% 25% 10%	723
	21st to end	Night	36% 7% 17% 27% 12% 2	515
May	1st to 10th	Night	26% 7% 17% 31% 20% 1	400
	11th to 20th	Night	24% 3 11% 35% 25% 2	394
	21st to end	Night	25% 4 13% 33% 23%	433
June	1st to 10th	Night	27% 6% 17% 29% 20% 2	399
	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% 19% 21% 7% 1	836
November	1st to 10th	Night	50% 9% 19% 19% 2	780
	11th to 20th	Night	52% 8% 19% 14% 7% 1	800
	21st to end	Night	48% 10% 17% 16% 8% 1	800
December	1st to 10th	Night	39% 9% 21% 23% 9%	800
	11th to 20th	Night	53% 9% 21% 14% 3	881
	21st to end	Night	53% 10% 24% 11% 2	990

Page generated at 2025-06-07 07:28:12. Version ac07

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