Wyrd Works
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Wyrd Works clear sky chart from 2005-11-06 to 2025-07-06.

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	8% 9% 3 8% 5% 5% 5% 4 6% 8% 37%	123859
	Night	7% 9% 4 10% 6% 6% 6% 5% 7% 8% 33%	123649
Transparency	Day	42% 8% 16% 24% 9% 1	123600
	Night	45% 8% 15% 22% 9% 1	123551
Seeing	Day	12% 7% 25% 32% 19% 6%	16276
	Night	12% 6% 28% 37% 16% 2	25352

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	4 10% 6% 16% 8% 7% 5% 3 5% 6% 29%	3179
	11th to 20th	Day	3 10% 4 11% 7% 7% 6% 7% 9% 9% 27%	3159
	21st to end	Day	4 9% 4 10% 6% 5% 5% 4 6% 9% 38%	3911
February	1st to 10th	Day	7% 14% 4 11% 7% 7% 6% 4 6% 7% 27%	1600
	11th to 20th	Day	6% 13% 5% 12% 7% 7% 6% 6% 7% 8% 25%	1755
	21st to end	Day	4 13% 4 13% 9% 7% 7% 4 6% 8% 26%	1557
March	1st to 10th	Day	3 10% 5% 11% 8% 6% 6% 4 7% 8% 31%	4518
	11th to 20th	Day	5% 12% 4 10% 6% 5% 4 4 6% 8% 35%	4994
	21st to end	Day	10% 19% 7% 14% 5% 5% 5% 4 5% 6% 21%	5502
April	1st to 10th	Day	7% 12% 3 10% 6% 5% 6% 5% 6% 9% 32%	2490
	11th to 20th	Day	11% 12% 4 9% 5% 4 6% 5% 7% 9% 29%	2570
	21st to end	Day	12% 10% 3 10% 6% 5% 5% 4 6% 8% 32%	2600
May	1st to 10th	Day	14% 9% 3 6% 4 4 5% 4 6% 7% 38%	6351
	11th to 20th	Day	13% 11% 3 9% 6% 6% 6% 5% 7% 8% 28%	6734
	21st to end	Day	11% 6% 3 7% 5% 5% 5% 4 6% 7% 39%	7405
June	1st to 10th	Day	15% 6% 2 6% 5% 5% 6% 5% 7% 8% 34%	3000
	11th to 20th	Day	18% 8% 3 8% 7% 5% 5% 4 6% 8% 28%	3000
	21st to end	Day	8% 4 2 7% 5% 5% 6% 5% 8% 10% 40%	3000
July	1st to 10th	Day	7% 5% 2 5% 4 4 4 4 6% 9% 52%	4816
	11th to 20th	Day	7% 4 2 4 4 4 5% 4 7% 10% 49%	4740
	21st to end	Day	5% 4 1 5% 4 4 4 4 6% 9% 55%	5138
August	1st to 10th	Day	8% 6% 3 7% 5% 5% 6% 4 6% 9% 42%	4410
	11th to 20th	Day	6% 4 2 6% 5% 5% 5% 5% 8% 12% 42%	4060
	21st to end	Day	10% 4 2 5% 3 4 4 4 6% 8% 49%	4521
September	1st to 10th	Day	10% 6% 2 5% 4 4 4 4 6% 8% 47%	2385
	11th to 20th	Day	15% 8% 3 6% 3 3 3 3 5% 8% 42%	2090
	21st to end	Day	8% 9% 2 6% 3 4 4 4 6% 9% 45%	2090
October	1st to 10th	Day	7% 7% 2 7% 5% 4 6% 4 7% 8% 43%	3301
	11th to 20th	Day	6% 7% 3 8% 5% 5% 4 4 6% 11% 40%	2945
	21st to end	Day	8% 9% 3 7% 6% 5% 5% 4 6% 7% 41%	3101
November	1st to 10th	Day	10% 15% 6% 10% 6% 4 4 4 6% 9% 24%	1582
	11th to 20th	Day	6% 15% 4 11% 6% 5% 5% 3 6% 7% 33%	1525
	21st to end	Day	6% 14% 4 11% 8% 6% 6% 4 6% 8% 29%	1400
December	1st to 10th	Day	9% 12% 5% 10% 6% 7% 6% 4 6% 8% 27%	2290
	11th to 20th	Day	7% 11% 5% 13% 10% 7% 5% 5% 6% 7% 25%	2642
	21st to end	Day	3 7% 3 11% 6% 5% 5% 4 6% 8% 42%	3498
January	1st to 10th	Night	3 13% 6% 15% 8% 7% 7% 4 7% 8% 23%	6766
	11th to 20th	Night	3 9% 5% 12% 7% 6% 6% 5% 7% 8% 32%	6739
	21st to end	Night	3 10% 4 10% 6% 5% 6% 5% 6% 8% 37%	7090
February	1st to 10th	Night	6% 11% 5% 12% 7% 6% 6% 5% 6% 8% 27%	2799
	11th to 20th	Night	5% 13% 4 12% 7% 7% 6% 5% 8% 7% 26%	2532
	21st to end	Night	4 10% 3 11% 8% 6% 7% 4 8% 10% 30%	2070
March	1st to 10th	Night	3 8% 4 12% 9% 7% 6% 5% 6% 10% 30%	5376
	11th to 20th	Night	5% 8% 4 11% 6% 6% 6% 6% 9% 9% 30%	5004
	21st to end	Night	8% 18% 6% 17% 6% 6% 5% 4 6% 6% 18%	5459
April	1st to 10th	Night	9% 10% 3 8% 9% 6% 5% 5% 6% 8% 31%	1910
	11th to 20th	Night	9% 11% 5% 12% 6% 5% 7% 4 6% 7% 28%	1781
	21st to end	Night	9% 11% 4 9% 5% 6% 5% 5% 7% 7% 32%	1800
May	1st to 10th	Night	15% 10% 3 8% 5% 4 4 4 5% 6% 34%	3615
	11th to 20th	Night	12% 10% 3 9% 7% 6% 6% 5% 6% 9% 27%	3159
	21st to end	Night	12% 8% 3 9% 7% 6% 5% 5% 5% 8% 32%	3470
June	1st to 10th	Night	14% 9% 3 8% 7% 5% 5% 5% 8% 9% 28%	1400
	11th to 20th	Night	16% 9% 3 7% 8% 6% 6% 6% 7% 6% 24%	1400
	21st to end	Night	11% 5% 1 7% 6% 5% 5% 6% 7% 8% 39%	1400
July	1st to 10th	Night	7% 5% 2 7% 5% 5% 6% 4 8% 9% 42%	2255
	11th to 20th	Night	6% 4 1 4 4 5% 5% 5% 9% 11% 46%	2220
	21st to end	Night	4 5% 2 5% 4 4 4 5% 7% 10% 50%	2414
August	1st to 10th	Night	10% 6% 2 6% 5% 3 5% 4 5% 8% 45%	2519
	11th to 20th	Night	5% 5% 3 7% 5% 5% 5% 5% 8% 10% 41%	2777
	21st to end	Night	8% 5% 2 6% 4 4 5% 3 7% 11% 46%	3146
September	1st to 10th	Night	10% 5% 2 6% 3 5% 4 4 6% 8% 47%	1792
	11th to 20th	Night	14% 7% 2 6% 5% 4 5% 3 5% 7% 43%	2090
	21st to end	Night	8% 6% 3 6% 4 3 5% 4 7% 8% 47%	2090
October	1st to 10th	Night	7% 7% 2 6% 4 4 5% 5% 6% 9% 45%	3673
	11th to 20th	Night	7% 8% 3 7% 4 5% 5% 4 7% 9% 42%	3979
	21st to end	Night	7% 8% 3 8% 5% 6% 5% 5% 7% 7% 39%	4457
November	1st to 10th	Night	10% 14% 4 8% 4 6% 5% 3 6% 8% 30%	2697
	11th to 20th	Night	5% 10% 5% 11% 7% 6% 7% 5% 7% 8% 30%	2872
	21st to end	Night	5% 11% 4 12% 8% 6% 5% 4 7% 9% 30%	3000
December	1st to 10th	Night	7% 13% 5% 12% 7% 7% 6% 4 6% 8% 25%	4890
	11th to 20th	Night	6% 12% 5% 14% 9% 6% 7% 5% 7% 8% 21%	5550
	21st to end	Night	3 7% 3 9% 6% 5% 6% 4 6% 9% 41%	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	55% 5% 11% 18% 9% 1	3179
	11th to 20th	Day	47% 7% 13% 15% 16% 3	3180
	21st to end	Day	40% 7% 17% 27% 9%	3911
February	1st to 10th	Day	54% 6% 14% 15% 10% 1	1600
	11th to 20th	Day	54% 8% 12% 16% 9% 1	1764
	21st to end	Day	54% 8% 10% 19% 9%	1557
March	1st to 10th	Day	47% 6% 17% 20% 10%	4518
	11th to 20th	Day	44% 8% 13% 22% 12%	4995
	21st to end	Day	62% 7% 10% 15% 6%	5502
April	1st to 10th	Day	46% 9% 16% 19% 9% 1	2490
	11th to 20th	Day	48% 7% 14% 21% 8% 1	2570
	21st to end	Day	48% 8% 14% 23% 6% 2	2600
May	1st to 10th	Day	43% 7% 10% 24% 14% 2	6351
	11th to 20th	Day	49% 10% 14% 21% 6%	6738
	21st to end	Day	40% 9% 18% 24% 9% 1	7406
June	1st to 10th	Day	43% 10% 16% 22% 9% 1	3000
	11th to 20th	Day	51% 10% 13% 20% 5% 1	3000
	21st to end	Day	35% 11% 20% 26% 6% 1	3000
July	1st to 10th	Day	28% 8% 18% 30% 14% 2	4742
	11th to 20th	Day	29% 8% 18% 36% 10%	4659
	21st to end	Day	25% 8% 17% 29% 18% 4	4976
August	1st to 10th	Day	36% 10% 16% 30% 7%	4392
	11th to 20th	Day	31% 10% 26% 26% 6% 1	4099
	21st to end	Day	31% 7% 24% 28% 9% 1	4520
September	1st to 10th	Day	34% 9% 17% 25% 11% 4	2385
	11th to 20th	Day	40% 6% 14% 29% 9% 1	2090
	21st to end	Day	35% 8% 18% 25% 11% 3	2090
October	1st to 10th	Day	38% 6% 21% 28% 6% 1	3301
	11th to 20th	Day	37% 6% 19% 26% 10% 1	2945
	21st to end	Day	41% 6% 10% 34% 8%	3101
November	1st to 10th	Day	55% 7% 14% 17% 6% 1	1582
	11th to 20th	Day	50% 8% 13% 20% 8% 1	1525
	21st to end	Day	51% 8% 15% 17% 7% 1	1400
December	1st to 10th	Day	55% 6% 18% 16% 5% 1	2290
	11th to 20th	Day	57% 8% 15% 17% 3 1	2644
	21st to end	Day	38% 5% 13% 26% 16% 3	3498
January	1st to 10th	Night	56% 7% 11% 18% 6% 1	6766
	11th to 20th	Night	48% 6% 13% 16% 15% 2	6780
	21st to end	Night	42% 7% 17% 25% 8% 1	7090
February	1st to 10th	Night	52% 7% 11% 18% 11%	2799
	11th to 20th	Night	52% 8% 12% 16% 10% 2	2533
	21st to end	Night	46% 8% 14% 20% 12% 1	2070
March	1st to 10th	Night	46% 8% 18% 19% 8%	5376
	11th to 20th	Night	44% 8% 18% 23% 7% 1	5004
	21st to end	Night	62% 9% 10% 13% 6% 1	5459
April	1st to 10th	Night	47% 10% 13% 18% 12%	1910
	11th to 20th	Night	50% 7% 13% 22% 7% 1	1781
	21st to end	Night	47% 9% 13% 22% 8% 2	1800
May	1st to 10th	Night	47% 6% 9% 23% 13% 2	3612
	11th to 20th	Night	48% 10% 14% 21% 7%	3159
	21st to end	Night	47% 10% 15% 21% 6% 1	3470
June	1st to 10th	Night	49% 10% 14% 18% 9% 1	1400
	11th to 20th	Night	55% 9% 13% 16% 6% 1	1400
	21st to end	Night	38% 10% 19% 25% 7% 1	1400
July	1st to 10th	Night	33% 12% 18% 23% 13% 1	2220
	11th to 20th	Night	26% 11% 18% 35% 7% 3	2178
	21st to end	Night	27% 8% 17% 29% 16% 3	2337
August	1st to 10th	Night	36% 9% 16% 30% 9%	2512
	11th to 20th	Night	33% 10% 22% 29% 6% 1	2804
	21st to end	Night	31% 8% 23% 29% 7% 1	3146
September	1st to 10th	Night	33% 8% 16% 24% 13% 5%	1792
	11th to 20th	Night	39% 8% 14% 26% 10% 3	2090
	21st to end	Night	33% 7% 17% 27% 15% 2	2090
October	1st to 10th	Night	34% 6% 20% 28% 11% 1	3673
	11th to 20th	Night	37% 6% 17% 30% 8% 1	3979
	21st to end	Night	40% 8% 15% 29% 7%	4457
November	1st to 10th	Night	50% 7% 12% 22% 8% 1	2697
	11th to 20th	Night	49% 9% 13% 18% 10% 1	2872
	21st to end	Night	48% 9% 17% 18% 6% 2	3000
December	1st to 10th	Night	55% 7% 15% 16% 5% 1	4890
	11th to 20th	Night	57% 9% 15% 14% 5%	5547
	21st to end	Night	38% 6% 12% 24% 17% 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	7% 5% 27% 34% 20% 9%	200
	11th to 20th	Day	8% 6% 35% 31% 19% 3	200
	21st to end	Day	6% 9% 29% 30% 20% 6%	220
February	1st to 10th	Day	10% 10% 25% 36% 13% 7%	200
	11th to 20th	Day	11% 5% 26% 37% 17% 4	300
	21st to end	Day	7% 6% 25% 36% 20% 6%	321
March	1st to 10th	Day	8% 5% 29% 34% 19% 5%	500
	11th to 20th	Day	8% 4 25% 37% 20% 6%	500
	21st to end	Day	13% 5% 27% 31% 18% 6%	550
April	1st to 10th	Day	9% 12% 29% 30% 13% 7%	500
	11th to 20th	Day	14% 10% 31% 28% 13% 4	492
	21st to end	Day	17% 9% 26% 31% 13% 4	500
May	1st to 10th	Day	16% 10% 24% 27% 17% 6%	611
	11th to 20th	Day	13% 8% 22% 34% 21% 4	725
	21st to end	Day	17% 5% 21% 28% 22% 7%	789
June	1st to 10th	Day	15% 8% 26% 34% 14% 4	730
	11th to 20th	Day	19% 8% 24% 30% 15% 5%	730
	21st to end	Day	9% 4 23% 31% 25% 8%	730
July	1st to 10th	Day	10% 4 18% 36% 24% 8%	697
	11th to 20th	Day	11% 4 18% 35% 25% 7%	668
	21st to end	Day	7% 3 19% 34% 27% 10%	739
August	1st to 10th	Day	9% 5% 25% 30% 21% 10%	496
	11th to 20th	Day	7% 6% 20% 32% 29% 6%	477
	21st to end	Day	10% 8% 23% 29% 22% 8%	539
September	1st to 10th	Day	14% 6% 28% 29% 19% 5%	490
	11th to 20th	Day	19% 7% 22% 28% 21% 4	490
	21st to end	Day	12% 13% 29% 28% 14% 5%	490
October	1st to 10th	Day	19% 6% 24% 28% 17% 6%	379
	11th to 20th	Day	11% 9% 35% 26% 15% 4	300
	21st to end	Day	15% 12% 31% 28% 13% 1	330
November	1st to 10th	Day	20% 6% 25% 34% 12% 3	300
	11th to 20th	Day	14% 7% 32% 30% 14% 2	263
	21st to end	Day	9% 7% 29% 33% 16% 7%	200
December	1st to 10th	Day	12% 3 28% 34% 20% 4	200
	11th to 20th	Day	7% 7% 32% 38% 15% 4	200
	21st to end	Day	9% 3 20% 37% 23% 8%	220
January	1st to 10th	Night	11% 6% 31% 35% 15% 2	1000
	11th to 20th	Night	11% 7% 32% 36% 14% 1	1000
	21st to end	Night	11% 8% 30% 37% 12% 2	940
February	1st to 10th	Night	12% 6% 27% 36% 18% 3	800
	11th to 20th	Night	10% 5% 32% 37% 16% 1	784
	21st to end	Night	7% 4 24% 41% 19% 5%	660
March	1st to 10th	Night	8% 5% 27% 40% 17% 4	800
	11th to 20th	Night	9% 5% 29% 38% 16% 3	800
	21st to end	Night	13% 5% 26% 36% 18% 2	880
April	1st to 10th	Night	12% 7% 29% 33% 17% 2	710
	11th to 20th	Night	13% 7% 33% 35% 10% 1	593
	21st to end	Night	14% 9% 27% 35% 15% 1	600
May	1st to 10th	Night	16% 8% 26% 36% 12% 1	510
	11th to 20th	Night	12% 6% 28% 37% 16% 2	394
	21st to end	Night	18% 7% 23% 33% 18% 1	433
June	1st to 10th	Night	17% 7% 27% 34% 13% 3	400
	11th to 20th	Night	19% 4 29% 31% 17% 1	400
	21st to end	Night	13% 3 22% 40% 21% 2	400
July	1st to 10th	Night	10% 3 17% 46% 22% 1	380
	11th to 20th	Night	13% 3 18% 42% 21% 2	368
	21st to end	Night	6% 3 19% 40% 28% 3	416
August	1st to 10th	Night	13% 2 18% 38% 26% 3	378
	11th to 20th	Night	8% 5% 17% 44% 25% 1	542
	21st to end	Night	8% 6% 20% 44% 22%	627
September	1st to 10th	Night	12% 3 23% 41% 19% 2	619
	11th to 20th	Night	14% 5% 21% 39% 20% 1	760
	21st to end	Night	11% 4 28% 38% 16% 2	760
October	1st to 10th	Night	15% 5% 26% 36% 18% 1	760
	11th to 20th	Night	11% 5% 31% 36% 15% 2	760
	21st to end	Night	13% 7% 30% 36% 13% 1	836
November	1st to 10th	Night	15% 8% 30% 35% 10% 1	942
	11th to 20th	Night	8% 8% 38% 34% 11% 3	1000
	21st to end	Night	9% 5% 35% 38% 13% 2	1000
December	1st to 10th	Night	12% 6% 30% 34% 15% 2	1000
	11th to 20th	Night	9% 6% 34% 37% 12% 2	1000
	21st to end	Night	11% 4 30% 37% 16% 2	1100

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