Wesley Creek
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Wesley Creek clear sky chart from 2005-11-06 to 2026-05-02.

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	9% 9% 3 9% 6% 6% 6% 5% 7% 8% 34%	135373
	Night	7% 11% 4 10% 6% 6% 6% 5% 7% 8% 31%	135831
Transparency	Day	47% 5% 17% 23% 7%	135045
	Night	49% 5% 16% 22% 8% 1	135738
Seeing	Day	14% 7% 24% 29% 20% 6%	18530
	Night	14% 5% 24% 37% 18% 2	26768

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	7% 16% 6% 13% 8% 8% 6% 4 9% 7% 17%	3527
	11th to 20th	Day	4 10% 4 9% 7% 6% 4 5% 7% 8% 35%	3522
	21st to end	Day	4 12% 6% 13% 8% 7% 6% 5% 6% 7% 27%	4602
February	1st to 10th	Day	7% 13% 4 11% 8% 5% 9% 7% 8% 10% 19%	1680
	11th to 20th	Day	5% 10% 5% 12% 8% 7% 6% 5% 9% 7% 26%	1640
	21st to end	Day	5% 11% 5% 13% 8% 8% 7% 6% 7% 10% 21%	1655
March	1st to 10th	Day	3 10% 5% 12% 7% 7% 7% 5% 7% 8% 30%	4618
	11th to 20th	Day	3 12% 6% 13% 7% 6% 5% 5% 6% 8% 28%	4788
	21st to end	Day	4 10% 4 11% 6% 6% 6% 4 6% 8% 35%	6051
April	1st to 10th	Day	5% 11% 3 8% 7% 7% 6% 4 7% 8% 35%	2539
	11th to 20th	Day	7% 11% 3 8% 6% 6% 5% 5% 7% 9% 33%	2711
	21st to end	Day	10% 11% 4 9% 6% 5% 6% 4 6% 7% 32%	2940
May	1st to 10th	Day	9% 8% 2 7% 5% 5% 6% 5% 7% 9% 38%	6610
	11th to 20th	Day	9% 9% 4 8% 6% 6% 6% 5% 8% 8% 30%	6734
	21st to end	Day	11% 7% 3 7% 5% 6% 6% 5% 7% 9% 34%	7906
June	1st to 10th	Day	13% 7% 3 8% 6% 5% 5% 4 7% 7% 34%	3200
	11th to 20th	Day	21% 9% 3 9% 6% 6% 6% 4 6% 6% 25%	3200
	21st to end	Day	10% 7% 3 7% 6% 5% 6% 4 8% 8% 37%	3200
July	1st to 10th	Day	10% 6% 3 6% 5% 5% 5% 5% 7% 9% 39%	7240
	11th to 20th	Day	6% 5% 2 7% 5% 5% 6% 5% 8% 9% 43%	7240
	21st to end	Day	12% 6% 2 5% 4 4 4 4 6% 8% 44%	7746
August	1st to 10th	Day	10% 5% 2 6% 5% 5% 5% 4 6% 8% 43%	4611
	11th to 20th	Day	11% 7% 3 8% 5% 5% 5% 4 6% 8% 39%	4470
	21st to end	Day	12% 6% 3 8% 5% 5% 4 4 6% 7% 39%	4792
September	1st to 10th	Day	13% 6% 2 7% 4 4 4 4 6% 9% 41%	2439
	11th to 20th	Day	9% 7% 2 7% 5% 5% 6% 5% 6% 9% 39%	2320
	21st to end	Day	10% 8% 3 7% 4 4 6% 5% 7% 9% 38%	2200
October	1st to 10th	Day	12% 9% 3 8% 5% 5% 5% 5% 6% 7% 33%	3295
	11th to 20th	Day	12% 10% 3 9% 5% 4 5% 4 6% 7% 34%	2932
	21st to end	Day	9% 14% 5% 10% 5% 4 5% 3 6% 8% 31%	3183
November	1st to 10th	Day	9% 13% 6% 11% 6% 5% 7% 5% 6% 7% 25%	1468
	11th to 20th	Day	7% 13% 5% 13% 6% 7% 7% 6% 6% 9% 21%	1470
	21st to end	Day	6% 15% 6% 11% 8% 5% 5% 4 7% 7% 26%	1444
December	1st to 10th	Day	11% 16% 5% 16% 9% 8% 7% 4 5% 5% 15%	2020
	11th to 20th	Day	9% 14% 5% 10% 10% 8% 7% 6% 6% 9% 17%	2322
	21st to end	Day	3 9% 4 14% 10% 6% 5% 4 5% 7% 33%	3058
January	1st to 10th	Night	7% 16% 7% 16% 8% 6% 5% 4 6% 7% 19%	9366
	11th to 20th	Night	5% 10% 4 9% 5% 5% 7% 5% 8% 8% 35%	9376
	21st to end	Night	7% 14% 5% 13% 7% 6% 6% 5% 6% 8% 23%	9635
February	1st to 10th	Night	7% 12% 4 12% 6% 6% 6% 5% 7% 8% 27%	2940
	11th to 20th	Night	5% 12% 5% 13% 8% 6% 6% 4 5% 7% 28%	2866
	21st to end	Night	3 10% 4 12% 7% 6% 6% 5% 7% 9% 30%	2150
March	1st to 10th	Night	3 8% 4 10% 7% 7% 8% 6% 9% 9% 32%	5496
	11th to 20th	Night	4 11% 4 11% 7% 6% 6% 5% 8% 10% 28%	5431
	21st to end	Night	5% 10% 4 10% 5% 5% 5% 3 6% 8% 38%	5162
April	1st to 10th	Night	5% 11% 4 9% 6% 5% 5% 4 7% 8% 37%	2081
	11th to 20th	Night	8% 11% 3 10% 5% 5% 5% 6% 7% 9% 32%	1856
	21st to end	Night	10% 11% 4 8% 6% 6% 6% 5% 6% 7% 32%	1680
May	1st to 10th	Night	8% 8% 3 9% 6% 5% 5% 4 5% 7% 41%	3372
	11th to 20th	Night	8% 9% 3 10% 7% 6% 6% 5% 8% 8% 30%	3159
	21st to end	Night	9% 6% 3 7% 5% 5% 5% 5% 8% 9% 37%	2968
June	1st to 10th	Night	11% 7% 3 7% 6% 7% 5% 6% 6% 8% 34%	1200
	11th to 20th	Night	17% 9% 3 8% 5% 6% 5% 4 6% 10% 27%	1200
	21st to end	Night	9% 5% 3 7% 5% 4 5% 5% 8% 10% 39%	1200
July	1st to 10th	Night	14% 7% 3 7% 6% 5% 5% 4 6% 8% 36%	2720
	11th to 20th	Night	6% 6% 3 8% 5% 5% 5% 4 7% 10% 41%	2720
	21st to end	Night	10% 5% 2 5% 4 4 5% 4 7% 9% 45%	3096
August	1st to 10th	Night	9% 6% 2 6% 4 4 5% 4 6% 7% 45%	2537
	11th to 20th	Night	10% 6% 2 7% 5% 4 5% 4 5% 7% 44%	2577
	21st to end	Night	12% 5% 2 6% 4 5% 5% 5% 8% 8% 40%	3112
September	1st to 10th	Night	12% 7% 3 7% 4 5% 5% 4 6% 8% 39%	1959
	11th to 20th	Night	8% 7% 2 8% 5% 5% 5% 4 6% 8% 41%	2080
	21st to end	Night	8% 10% 3 8% 5% 4 5% 4 6% 8% 40%	2200
October	1st to 10th	Night	9% 10% 4 8% 6% 5% 5% 4 6% 7% 35%	3899
	11th to 20th	Night	8% 8% 3 8% 5% 5% 5% 5% 7% 9% 39%	4216
	21st to end	Night	8% 12% 4 9% 6% 6% 6% 4 6% 7% 32%	4615
November	1st to 10th	Night	11% 14% 5% 11% 6% 6% 5% 4 6% 6% 27%	3028
	11th to 20th	Night	9% 14% 5% 12% 7% 7% 6% 4 6% 7% 24%	3150
	21st to end	Night	6% 14% 5% 12% 8% 6% 5% 4 6% 7% 26%	3174
December	1st to 10th	Night	11% 14% 5% 14% 8% 6% 6% 4 6% 7% 19%	5380
	11th to 20th	Night	8% 16% 6% 12% 7% 6% 5% 5% 7% 7% 20%	6090
	21st to end	Night	3 10% 5% 13% 9% 7% 6% 4 6% 8% 30%	8140

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	64% 3 11% 14% 7%	3527
	11th to 20th	Day	46% 3 18% 18% 14% 1	3540
	21st to end	Day	56% 6% 19% 15% 4	4603
February	1st to 10th	Day	54% 7% 14% 15% 10%	1680
	11th to 20th	Day	52% 7% 17% 17% 7%	1648
	21st to end	Day	55% 7% 16% 15% 7%	1655
March	1st to 10th	Day	51% 4 16% 23% 6%	4618
	11th to 20th	Day	51% 7% 17% 20% 5%	4788
	21st to end	Day	45% 5% 11% 25% 13% 1	6051
April	1st to 10th	Day	45% 5% 17% 24% 9%	2539
	11th to 20th	Day	47% 5% 15% 23% 9% 1	2711
	21st to end	Day	49% 6% 12% 24% 8% 1	2940
May	1st to 10th	Day	40% 6% 11% 28% 14% 2	6610
	11th to 20th	Day	49% 5% 14% 24% 8% 1	6738
	21st to end	Day	43% 5% 18% 22% 10% 1	7907
June	1st to 10th	Day	46% 5% 15% 25% 8% 1	3200
	11th to 20th	Day	58% 6% 13% 18% 5%	3200
	21st to end	Day	42% 6% 19% 25% 8%	3200
July	1st to 10th	Day	40% 3 23% 25% 7%	7161
	11th to 20th	Day	37% 3 16% 35% 9%	7153
	21st to end	Day	39% 3 21% 30% 7%	7527
August	1st to 10th	Day	38% 5% 20% 33% 3	4593
	11th to 20th	Day	43% 4 18% 24% 9%	4512
	21st to end	Day	43% 5% 27% 22% 4	4791
September	1st to 10th	Day	41% 5% 25% 24% 4	2439
	11th to 20th	Day	40% 6% 24% 26% 5%	2320
	21st to end	Day	42% 6% 21% 23% 9%	2200
October	1st to 10th	Day	48% 4 21% 23% 5%	3295
	11th to 20th	Day	50% 3 17% 27% 3	2932
	21st to end	Day	51% 4 23% 19% 3	3183
November	1st to 10th	Day	56% 7% 14% 20% 4	1468
	11th to 20th	Day	57% 8% 16% 15% 3	1470
	21st to end	Day	55% 6% 15% 18% 5% 1	1444
December	1st to 10th	Day	71% 4 10% 9% 5%	2020
	11th to 20th	Day	62% 6% 15% 14% 3	2324
	21st to end	Day	50% 5% 14% 24% 6% 1	3058
January	1st to 10th	Night	64% 4 9% 15% 7%	9367
	11th to 20th	Night	45% 5% 16% 18% 15% 1	9420
	21st to end	Night	58% 7% 18% 15% 3	9635
February	1st to 10th	Night	53% 5% 14% 18% 9% 1	2940
	11th to 20th	Night	54% 5% 14% 18% 8% 1	2868
	21st to end	Night	48% 6% 18% 20% 8%	2150
March	1st to 10th	Night	45% 4 16% 25% 10%	5496
	11th to 20th	Night	47% 6% 16% 24% 6%	5432
	21st to end	Night	41% 6% 9% 29% 14% 1	5162
April	1st to 10th	Night	43% 5% 11% 26% 14% 1	2081
	11th to 20th	Night	47% 5% 13% 22% 12% 1	1856
	21st to end	Night	48% 6% 11% 24% 10% 1	1680
May	1st to 10th	Night	42% 4 12% 23% 17% 2	3369
	11th to 20th	Night	47% 6% 12% 24% 11% 1	3159
	21st to end	Night	40% 5% 19% 27% 7% 1	2968
June	1st to 10th	Night	46% 5% 12% 25% 11% 1	1200
	11th to 20th	Night	52% 5% 15% 23% 5%	1200
	21st to end	Night	37% 7% 20% 25% 10% 1	1200
July	1st to 10th	Night	47% 3 17% 23% 9%	2690
	11th to 20th	Night	39% 3 13% 35% 9% 1	2684
	21st to end	Night	35% 3 20% 32% 9% 1	3010
August	1st to 10th	Night	38% 5% 17% 36% 3	2530
	11th to 20th	Night	38% 5% 19% 24% 14%	2601
	21st to end	Night	41% 3 28% 22% 5%	3112
September	1st to 10th	Night	40% 7% 20% 25% 7% 1	1959
	11th to 20th	Night	39% 5% 21% 27% 8%	2080
	21st to end	Night	41% 6% 17% 26% 9% 1	2200
October	1st to 10th	Night	47% 4 19% 21% 9%	3899
	11th to 20th	Night	42% 4 18% 29% 6%	4216
	21st to end	Night	51% 4 20% 22% 3	4615
November	1st to 10th	Night	56% 6% 14% 21% 4	3028
	11th to 20th	Night	58% 7% 13% 17% 4	3150
	21st to end	Night	55% 7% 17% 16% 5% 1	3174
December	1st to 10th	Night	65% 5% 11% 14% 5%	5380
	11th to 20th	Night	61% 5% 16% 14% 4	6087
	21st to end	Night	51% 4 16% 22% 5%	8140

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	13% 5% 26% 30% 20% 5%	220
	11th to 20th	Day	17% 6% 26% 30% 17% 3	220
	21st to end	Day	12% 4 31% 31% 18% 3	242
February	1st to 10th	Day	10% 5% 30% 32% 16% 7%	220
	11th to 20th	Day	10% 5% 29% 32% 17% 7%	220
	21st to end	Day	11% 5% 32% 29% 17% 5%	395
March	1st to 10th	Day	9% 8% 26% 32% 20% 6%	540
	11th to 20th	Day	10% 5% 30% 30% 21% 4	540
	21st to end	Day	14% 6% 27% 29% 17% 6%	594
April	1st to 10th	Day	10% 7% 27% 33% 17% 6%	540
	11th to 20th	Day	13% 9% 29% 23% 19% 7%	532
	21st to end	Day	15% 9% 26% 27% 16% 6%	540
May	1st to 10th	Day	12% 10% 29% 26% 18% 5%	627
	11th to 20th	Day	12% 8% 18% 34% 20% 8%	725
	21st to end	Day	15% 6% 19% 30% 24% 6%	1005
June	1st to 10th	Day	16% 9% 26% 27% 20% 3	930
	11th to 20th	Day	24% 6% 17% 28% 20% 6%	930
	21st to end	Day	12% 6% 17% 29% 26% 10%	930
July	1st to 10th	Day	15% 5% 18% 30% 26% 7%	916
	11th to 20th	Day	11% 6% 16% 29% 28% 10%	912
	21st to end	Day	14% 4 18% 31% 22% 10%	957
August	1st to 10th	Day	15% 7% 17% 23% 25% 14%	571
	11th to 20th	Day	10% 9% 28% 31% 18% 4	517
	21st to end	Day	16% 7% 25% 26% 17% 9%	583
September	1st to 10th	Day	17% 5% 24% 29% 19% 6%	530
	11th to 20th	Day	14% 8% 22% 32% 18% 7%	530
	21st to end	Day	15% 13% 30% 25% 14% 3	530
October	1st to 10th	Day	17% 10% 26% 29% 14% 3	502
	11th to 20th	Day	20% 6% 28% 28% 15% 3	330
	21st to end	Day	18% 6% 30% 29% 13% 3	360
November	1st to 10th	Day	15% 8% 34% 26% 14% 3	220
	11th to 20th	Day	15% 5% 35% 27% 15% 3	220
	21st to end	Day	10% 8% 33% 30% 18% 1	220
December	1st to 10th	Day	12% 7% 30% 33% 13% 5%	220
	11th to 20th	Day	12% 8% 23% 40% 15% 2	220
	21st to end	Day	9% 5% 23% 38% 21% 4	242
January	1st to 10th	Night	14% 4 27% 38% 15% 3	1160
	11th to 20th	Night	13% 7% 30% 34% 14% 1	1160
	21st to end	Night	18% 9% 28% 33% 11% 1	1094
February	1st to 10th	Night	13% 4 25% 35% 20% 3	840
	11th to 20th	Night	11% 5% 25% 42% 16% 1	824
	21st to end	Night	6% 4 29% 39% 18% 3	692
March	1st to 10th	Night	10% 5% 27% 35% 20% 3	840
	11th to 20th	Night	13% 5% 23% 41% 18% 1	840
	21st to end	Night	13% 5% 21% 37% 23% 2	924
April	1st to 10th	Night	10% 5% 22% 42% 19% 2	821
	11th to 20th	Night	13% 5% 24% 34% 22% 3	608
	21st to end	Night	16% 3 24% 39% 17% 2	420
May	1st to 10th	Night	13% 5% 18% 39% 23% 2	402
	11th to 20th	Night	9% 6% 23% 37% 22% 2	394
	21st to end	Night	17% 3 14% 39% 25% 2	433
June	1st to 10th	Night	14% 5% 15% 41% 25%	400
	11th to 20th	Night	20% 4 13% 34% 26% 4	400
	21st to end	Night	11% 3 15% 39% 28% 4	400
July	1st to 10th	Night	15% 3 14% 37% 29% 3	390
	11th to 20th	Night	12% 3 11% 38% 34% 3	388
	21st to end	Night	13% 2 14% 34% 34% 3	438
August	1st to 10th	Night	10% 3 9% 35% 37% 6%	398
	11th to 20th	Night	10% 2 20% 46% 21% 2	396
	21st to end	Night	16% 2 15% 40% 23% 3	579
September	1st to 10th	Night	17% 2 16% 37% 25% 3	759
	11th to 20th	Night	11% 4 17% 43% 24% 3	800
	21st to end	Night	13% 9% 29% 32% 15% 3	800
October	1st to 10th	Night	17% 7% 25% 35% 15% 2	800
	11th to 20th	Night	14% 6% 27% 36% 15% 2	800
	21st to end	Night	19% 9% 22% 36% 13% 1	880
November	1st to 10th	Night	18% 7% 25% 34% 14% 2	978
	11th to 20th	Night	15% 8% 28% 38% 10% 1	1050
	21st to end	Night	13% 7% 30% 37% 11% 1	1064
December	1st to 10th	Night	16% 6% 30% 34% 12% 2	1160
	11th to 20th	Night	15% 6% 28% 38% 12% 2	1160
	21st to end	Night	11% 4 26% 35% 21% 3	1276

Page generated at 2026-04-29 00:21:42. Version ac07

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