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 2026-10-14.

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	25% 9% 3 6% 4 4 4 3 4 6% 33%	153821
	Night	29% 10% 2 6% 3 3 3 3 4 5% 30%	146665
Transparency	Day	52% 5% 15% 19% 8% 1	153531
	Night	55% 5% 14% 16% 7% 1	146537
Seeing	Day	31% 10% 22% 23% 10% 3	17782
	Night	36% 7% 17% 23% 15% 1	25908

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	46% 15% 3 8% 4 4 3 2 3 2 9%	4125
	11th to 20th	Day	23% 10% 3 5% 3 3 3 3 4 5% 38%	4235
	21st to end	Day	41% 9% 3 5% 3 2 2 2 3 3 26%	5186
February	1st to 10th	Day	37% 12% 3 6% 5% 4 3 2 4 5% 18%	1885
	11th to 20th	Day	34% 12% 3 8% 4 3 3 3 4 5% 22%	1845
	21st to end	Day	31% 18% 3 7% 5% 3 3 3 4 3 20%	1600
March	1st to 10th	Day	31% 16% 4 8% 4 4 3 3 4 5% 18%	4703
	11th to 20th	Day	28% 16% 4 8% 5% 4 3 3 3 3 24%	5110
	21st to end	Day	32% 13% 3 8% 5% 4 4 3 5% 5% 16%	5803
April	1st to 10th	Day	32% 12% 4 7% 6% 3 5% 3 4 5% 18%	2520
	11th to 20th	Day	27% 11% 3 8% 5% 5% 5% 4 4 5% 22%	2561
	21st to end	Day	29% 11% 4 7% 4 4 3 4 5% 5% 24%	2819
May	1st to 10th	Day	16% 8% 2 7% 4 4 5% 4 5% 6% 39%	8195
	11th to 20th	Day	23% 11% 4 7% 4 5% 4 4 6% 7% 26%	8160
	21st to end	Day	26% 7% 2 6% 4 4 4 4 6% 8% 28%	9025
June	1st to 10th	Day	29% 7% 3 6% 5% 4 4 3 5% 6% 28%	3150
	11th to 20th	Day	30% 9% 3 8% 5% 5% 5% 3 5% 5% 23%	3150
	21st to end	Day	22% 8% 3 6% 5% 4 5% 4 5% 6% 33%	3150
July	1st to 10th	Day	13% 4 2 5% 3 3 4 3 5% 6% 51%	8820
	11th to 20th	Day	8% 4 1 3 2 3 3 2 4 6% 64%	8820
	21st to end	Day	15% 4 2 4 3 3 3 3 5% 8% 50%	8940
August	1st to 10th	Day	9% 3 2 4 2 2 3 2 3 5% 65%	6441
	11th to 20th	Day	14% 5% 2 4 4 3 4 3 6% 7% 48%	5945
	21st to end	Day	21% 7% 3 6% 4 4 4 3 5% 7% 37%	6368
September	1st to 10th	Day	18% 6% 2 6% 3 3 3 2 4 7% 46%	2520
	11th to 20th	Day	22% 7% 3 6% 4 3 4 3 5% 5% 39%	2520
	21st to end	Day	29% 8% 2 6% 3 3 3 3 4 6% 34%	2218
October	1st to 10th	Day	26% 7% 3 7% 5% 4 4 4 5% 7% 28%	3380
	11th to 20th	Day	40% 7% 2 6% 3 4 3 2 4 5% 23%	3292
	21st to end	Day	37% 13% 4 7% 4 4 3 3 5% 6% 15%	3287
November	1st to 10th	Day	45% 9% 3 6% 4 3 3 3 4 4 17%	1648
	11th to 20th	Day	43% 12% 3 6% 3 3 2 2 3 3 21%	1680
	21st to end	Day	44% 11% 3 5% 3 3 3 3 4 3 18%	1680
December	1st to 10th	Day	29% 11% 3 6% 4 3 4 4 5% 7% 24%	2700
	11th to 20th	Day	45% 15% 4 7% 3 3 3 2 3 3 12%	2765
	21st to end	Day	44% 15% 4 8% 4 4 3 2 3 4 9%	3575
January	1st to 10th	Night	45% 15% 3 8% 3 3 3 2 3 3 12%	8770
	11th to 20th	Night	26% 7% 2 4 3 2 3 3 5% 9% 35%	8660
	21st to end	Night	38% 8% 2 6% 3 2 3 2 3 4 28%	8994
February	1st to 10th	Night	38% 11% 3 7% 4 3 3 2 4 4 20%	2730
	11th to 20th	Night	34% 15% 3 6% 4 3 3 2 3 4 23%	2662
	21st to end	Night	34% 14% 3 6% 3 3 3 2 4 4 24%	2205
March	1st to 10th	Night	28% 18% 3 6% 3 4 3 3 4 5% 22%	5408
	11th to 20th	Night	32% 15% 3 7% 4 3 3 2 3 4 25%	5109
	21st to end	Night	42% 12% 3 7% 4 3 3 2 4 3 17%	5414
April	1st to 10th	Night	31% 12% 3 8% 5% 4 4 3 5% 5% 21%	2100
	11th to 20th	Night	25% 11% 3 7% 5% 5% 4 4 5% 5% 26%	2007
	21st to end	Night	32% 9% 3 6% 5% 4 3 4 4 5% 25%	1801
May	1st to 10th	Night	15% 8% 3 6% 3 3 4 3 4 5% 46%	4724
	11th to 20th	Night	25% 9% 3 6% 4 4 4 4 5% 6% 30%	4700
	21st to end	Night	22% 8% 2 8% 4 4 4 4 6% 7% 31%	5142
June	1st to 10th	Night	25% 9% 2 8% 4 4 5% 4 4 5% 30%	1470
	11th to 20th	Night	23% 10% 3 8% 5% 4 4 4 6% 6% 27%	1470
	21st to end	Night	20% 8% 2 6% 4 3 4 3 5% 7% 40%	1470
July	1st to 10th	Night	11% 4 1 4 2 2 3 3 5% 7% 56%	4140
	11th to 20th	Night	7% 3 1 3 2 2 2 2 3 4 71%	4140
	21st to end	Night	9% 5% 2 4 3 3 3 3 5% 7% 56%	5125
August	1st to 10th	Night	6% 2 1 2 2 1 2 2 4 7% 70%	3709
	11th to 20th	Night	11% 4 1 4 3 3 4 3 6% 7% 53%	4115
	21st to end	Night	20% 6% 2 6% 3 3 3 3 5% 8% 40%	4788
September	1st to 10th	Night	13% 5% 1 4 3 3 4 3 5% 7% 51%	2100
	11th to 20th	Night	23% 6% 1 5% 4 3 3 2 4 6% 42%	2100
	21st to end	Night	26% 8% 2 6% 3 3 3 3 4 6% 36%	2398
October	1st to 10th	Night	26% 10% 3 7% 5% 4 4 3 4 5% 27%	4040
	11th to 20th	Night	38% 7% 2 5% 2 3 3 2 4 6% 28%	3933
	21st to end	Night	36% 12% 3 8% 4 3 3 2 4 4 20%	4512
November	1st to 10th	Night	45% 10% 2 5% 4 3 3 3 3 4 17%	2870
	11th to 20th	Night	44% 10% 3 6% 4 3 2 2 3 3 20%	2940
	21st to end	Night	42% 12% 2 6% 3 4 3 2 3 3 19%	2940
December	1st to 10th	Night	30% 11% 2 6% 4 4 4 3 6% 8% 22%	4700
	11th to 20th	Night	46% 13% 3 7% 4 3 3 2 3 3 12%	5656
	21st to end	Night	45% 15% 4 8% 3 3 3 2 3 3 11%	7623

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	81% 5% 6% 6% 2	4125
	11th to 20th	Day	49% 4 8% 23% 12% 3	4256
	21st to end	Day	64% 3 7% 18% 6% 2	5187
February	1st to 10th	Day	70% 5% 9% 7% 7% 2	1885
	11th to 20th	Day	66% 5% 8% 12% 8% 2	1854
	21st to end	Day	70% 3 9% 11% 5% 2	1600
March	1st to 10th	Day	65% 6% 9% 15% 4	4703
	11th to 20th	Day	65% 6% 8% 19% 2	5110
	21st to end	Day	68% 7% 12% 10% 3	5803
April	1st to 10th	Day	67% 7% 13% 11% 2	2520
	11th to 20th	Day	63% 6% 9% 12% 7% 3	2561
	21st to end	Day	61% 6% 12% 12% 7% 1	2819
May	1st to 10th	Day	44% 4 15% 27% 9% 1	8195
	11th to 20th	Day	54% 8% 20% 14% 3	8163
	21st to end	Day	52% 7% 21% 18% 3	9026
June	1st to 10th	Day	57% 6% 15% 15% 5% 2	3150
	11th to 20th	Day	62% 5% 14% 13% 5%	3150
	21st to end	Day	51% 7% 16% 18% 8% 1	3150
July	1st to 10th	Day	33% 5% 18% 23% 16% 5%	8746
	11th to 20th	Day	23% 3 16% 35% 20% 3	8739
	21st to end	Day	32% 4 25% 28% 10% 1	8746
August	1st to 10th	Day	22% 4 16% 33% 22% 3	6424
	11th to 20th	Day	35% 5% 28% 24% 6% 1	5984
	21st to end	Day	46% 6% 19% 21% 8% 1	6367
September	1st to 10th	Day	40% 6% 15% 23% 12% 4	2520
	11th to 20th	Day	49% 5% 11% 19% 14% 2	2520
	21st to end	Day	52% 6% 15% 16% 9% 1	2218
October	1st to 10th	Day	54% 5% 16% 18% 6%	3380
	11th to 20th	Day	63% 5% 11% 12% 7% 1	3292
	21st to end	Day	69% 5% 9% 12% 5%	3287
November	1st to 10th	Day	71% 5% 10% 10% 3 1	1648
	11th to 20th	Day	72% 3 8% 9% 5% 2	1680
	21st to end	Day	70% 5% 7% 10% 7% 1	1680
December	1st to 10th	Day	59% 5% 13% 14% 8%	2700
	11th to 20th	Day	75% 6% 7% 9% 2 1	2768
	21st to end	Day	76% 8% 8% 6% 2	3575
January	1st to 10th	Night	78% 5% 7% 8% 2	8770
	11th to 20th	Night	47% 5% 13% 17% 15% 3	8701
	21st to end	Night	61% 4 9% 17% 9% 1	8994
February	1st to 10th	Night	69% 5% 8% 10% 6% 3	2730
	11th to 20th	Night	66% 5% 8% 11% 8% 2	2664
	21st to end	Night	67% 3 8% 14% 6% 2	2205
March	1st to 10th	Night	61% 8% 11% 13% 7%	5408
	11th to 20th	Night	61% 7% 11% 18% 2	5110
	21st to end	Night	70% 7% 14% 7% 1	5414
April	1st to 10th	Night	65% 7% 14% 13% 2	2100
	11th to 20th	Night	59% 6% 12% 13% 7% 3	2007
	21st to end	Night	60% 5% 14% 14% 6% 1	1801
May	1st to 10th	Night	41% 5% 14% 30% 9%	4721
	11th to 20th	Night	54% 8% 20% 15% 3	4700
	21st to end	Night	51% 6% 22% 17% 3	5146
June	1st to 10th	Night	55% 6% 18% 14% 6% 2	1470
	11th to 20th	Night	56% 7% 16% 17% 4	1470
	21st to end	Night	43% 6% 21% 20% 7% 3	1470
July	1st to 10th	Night	29% 4 19% 29% 13% 6%	4105
	11th to 20th	Night	19% 3 16% 37% 24% 1	4098
	21st to end	Night	28% 3 24% 29% 14% 2	5014
August	1st to 10th	Night	16% 3 19% 36% 21% 4	3701
	11th to 20th	Night	29% 5% 36% 23% 6% 2	4142
	21st to end	Night	42% 8% 23% 20% 8%	4788
September	1st to 10th	Night	32% 7% 19% 24% 13% 4	2100
	11th to 20th	Night	44% 6% 14% 18% 14% 3	2100
	21st to end	Night	49% 6% 15% 19% 8% 2	2398
October	1st to 10th	Night	58% 5% 17% 15% 5% 1	4040
	11th to 20th	Night	59% 4 12% 17% 8% 1	3933
	21st to end	Night	66% 5% 10% 13% 5%	4512
November	1st to 10th	Night	70% 5% 10% 10% 3 1	2870
	11th to 20th	Night	71% 5% 9% 8% 5% 2	2940
	21st to end	Night	71% 5% 8% 8% 7% 1	2940
December	1st to 10th	Night	59% 6% 17% 13% 5% 1	4700
	11th to 20th	Night	76% 5% 7% 8% 2 1	5652
	21st to end	Night	76% 6% 8% 7% 3	7623

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	50% 12% 15% 13% 8% 2	220
	11th to 20th	Day	44% 10% 19% 17% 9% 2	220
	21st to end	Day	42% 12% 19% 16% 9% 2	242
February	1st to 10th	Day	46% 12% 19% 15% 6% 2	425
	11th to 20th	Day	41% 12% 22% 17% 6% 1	425
	21st to end	Day	44% 14% 24% 12% 6% 1	378
March	1st to 10th	Day	44% 14% 18% 18% 7%	540
	11th to 20th	Day	43% 12% 18% 17% 9% 1	540
	21st to end	Day	42% 15% 21% 16% 6% 1	594
April	1st to 10th	Day	36% 15% 22% 17% 8% 1	540
	11th to 20th	Day	30% 14% 25% 20% 8% 2	532
	21st to end	Day	32% 17% 24% 16% 9% 2	540
May	1st to 10th	Day	25% 12% 30% 24% 7% 2	543
	11th to 20th	Day	31% 10% 23% 25% 9% 3	568
	21st to end	Day	29% 12% 26% 21% 9% 3	623
June	1st to 10th	Day	28% 13% 27% 23% 7% 2	780
	11th to 20th	Day	28% 15% 28% 21% 7% 2	780
	21st to end	Day	26% 9% 24% 27% 12% 3	780
July	1st to 10th	Day	18% 9% 29% 32% 10% 2	771
	11th to 20th	Day	14% 9% 28% 35% 11% 3	768
	21st to end	Day	13% 5% 25% 37% 13% 6%	630
August	1st to 10th	Day	15% 6% 23% 32% 16% 8%	567
	11th to 20th	Day	13% 5% 22% 34% 19% 6%	557
	21st to end	Day	20% 9% 22% 29% 14% 6%	627
September	1st to 10th	Day	22% 8% 23% 28% 14% 5%	570
	11th to 20th	Day	25% 8% 20% 28% 15% 4	570
	21st to end	Day	31% 9% 20% 25% 12% 3	570
October	1st to 10th	Day	31% 8% 22% 21% 16% 2	570
	11th to 20th	Day	41% 8% 16% 19% 14% 2	543
	21st to end	Day	46% 9% 18% 18% 8% 2	427
November	1st to 10th	Day	45% 13% 18% 16% 7%	220
	11th to 20th	Day	54% 7% 12% 11% 12% 3	220
	21st to end	Day	52% 6% 19% 9% 10% 4	220
December	1st to 10th	Day	50% 10% 11% 10% 14% 5%	220
	11th to 20th	Day	58% 7% 15% 14% 5% 1	220
	21st to end	Day	52% 10% 19% 14% 5%	242
January	1st to 10th	Night	54% 10% 15% 15% 6% 1	950
	11th to 20th	Night	46% 7% 18% 22% 7%	928
	21st to end	Night	44% 9% 19% 20% 8%	924
February	1st to 10th	Night	45% 11% 22% 18% 5%	840
	11th to 20th	Night	43% 9% 21% 22% 5%	824
	21st to end	Night	41% 10% 23% 19% 7%	692
March	1st to 10th	Night	37% 11% 19% 21% 11%	840
	11th to 20th	Night	45% 8% 18% 20% 8%	840
	21st to end	Night	42% 9% 20% 21% 8%	924
April	1st to 10th	Night	38% 8% 18% 26% 10% 1	840
	11th to 20th	Night	29% 10% 25% 25% 10% 1	759
	21st to end	Night	36% 7% 18% 27% 11% 1	541
May	1st to 10th	Night	25% 6% 16% 30% 21% 1	420
	11th to 20th	Night	25% 3 11% 34% 25% 2	414
	21st to end	Night	25% 4 13% 34% 24%	455
June	1st to 10th	Night	28% 6% 16% 30% 18% 1	420
	11th to 20th	Night	26% 6% 15% 31% 18% 3	420
	21st to end	Night	23% 4 11% 33% 27% 2	420
July	1st to 10th	Night	14% 4 10% 32% 37% 2	410
	11th to 20th	Night	12% 4 10% 35% 33% 6%	408
	21st to end	Night	10% 1 6% 33% 45% 5%	460
August	1st to 10th	Night	13% 1 6% 27% 47% 7%	418
	11th to 20th	Night	11% 2 7% 28% 44% 8%	610
	21st to end	Night	16% 3 11% 31% 37% 2	785
September	1st to 10th	Night	16% 2 14% 36% 29% 3	840
	11th to 20th	Night	25% 4 13% 24% 30% 5%	840
	21st to end	Night	31% 5% 14% 31% 19% 1	840
October	1st to 10th	Night	31% 5% 18% 25% 20% 1	840
	11th to 20th	Night	40% 5% 18% 21% 15% 1	812
	21st to end	Night	43% 9% 20% 20% 7% 1	880
November	1st to 10th	Night	50% 9% 20% 19% 2	820
	11th to 20th	Night	52% 8% 18% 14% 7% 1	840
	21st to end	Night	48% 10% 18% 15% 8% 1	840
December	1st to 10th	Night	40% 9% 20% 22% 9%	840
	11th to 20th	Night	55% 9% 20% 13% 2	929
	21st to end	Night	52% 10% 24% 12% 2	1045

Page generated at 2026-10-11 02:06:32. Version ac07

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