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 2024-11-04.

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 8% 5% 5% 5% 4 6% 8% 37%	105668
	Night	7% 9% 4 9% 6% 5% 6% 4 7% 8% 34%	101939
Transparency	Day	42% 8% 16% 24% 9% 1	105409
	Night	44% 8% 15% 22% 9% 1	101844
Seeing	Day	12% 7% 25% 31% 19% 6%	15436
	Night	12% 6% 28% 37% 16% 2	24450

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 12% 5% 13% 6% 6% 6% 4 6% 8% 30%	2219
	11th to 20th	Day	4 10% 4 10% 5% 6% 7% 8% 10% 8% 27%	2199
	21st to end	Day	5% 9% 4 11% 7% 5% 6% 4 7% 10% 33%	2729
February	1st to 10th	Day	7% 15% 4 10% 6% 7% 5% 4 6% 7% 28%	1520
	11th to 20th	Day	6% 14% 5% 11% 7% 6% 6% 5% 6% 8% 26%	1665
	21st to end	Day	4 13% 4 13% 9% 7% 7% 4 5% 8% 25%	1481
March	1st to 10th	Day	4 13% 6% 13% 9% 7% 7% 4 5% 7% 25%	3138
	11th to 20th	Day	6% 9% 3 7% 5% 5% 4 4 7% 10% 40%	3484
	21st to end	Day	8% 21% 7% 14% 5% 4 4 3 5% 6% 23%	3841
April	1st to 10th	Day	8% 12% 4 10% 6% 5% 5% 5% 6% 9% 31%	2365
	11th to 20th	Day	11% 12% 4 9% 5% 4 6% 5% 7% 8% 28%	2440
	21st to end	Day	12% 10% 3 10% 6% 5% 5% 4 6% 9% 31%	2470
May	1st to 10th	Day	19% 12% 4 8% 5% 5% 5% 3 6% 6% 28%	4432
	11th to 20th	Day	10% 10% 3 8% 6% 6% 6% 5% 7% 8% 32%	4694
	21st to end	Day	15% 8% 3 9% 6% 6% 5% 5% 7% 8% 27%	5161
June	1st to 10th	Day	16% 6% 2 6% 5% 5% 6% 5% 8% 8% 33%	2850
	11th to 20th	Day	18% 8% 3 8% 7% 5% 5% 5% 6% 8% 27%	2850
	21st to end	Day	8% 4 2 6% 5% 5% 6% 5% 8% 10% 40%	2850
July	1st to 10th	Day	7% 5% 2 5% 4 4 4 4 6% 9% 51%	4740
	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%	1526
	11th to 20th	Day	6% 15% 4 11% 6% 5% 5% 3 6% 7% 34%	1449
	21st to end	Day	6% 13% 4 11% 7% 6% 5% 4 6% 8% 31%	1330
December	1st to 10th	Day	6% 12% 5% 12% 8% 8% 6% 4 5% 6% 27%	1330
	11th to 20th	Day	4 11% 6% 14% 8% 6% 5% 5% 7% 8% 26%	1682
	21st to end	Day	4 8% 3 10% 6% 4 4 4 6% 9% 41%	2442
January	1st to 10th	Night	4 13% 5% 12% 7% 6% 6% 5% 8% 9% 24%	4726
	11th to 20th	Night	4 9% 5% 13% 7% 6% 6% 6% 7% 8% 30%	4699
	21st to end	Night	4 12% 4 11% 6% 5% 6% 5% 7% 8% 32%	4958
February	1st to 10th	Night	7% 11% 5% 12% 7% 6% 6% 5% 6% 8% 28%	2660
	11th to 20th	Night	5% 14% 4 12% 7% 7% 6% 4 7% 7% 26%	2402
	21st to end	Night	4 11% 4 11% 8% 6% 6% 4 8% 9% 30%	1970
March	1st to 10th	Night	3 9% 5% 15% 11% 8% 7% 5% 6% 7% 26%	3736
	11th to 20th	Night	7% 8% 3 8% 5% 5% 6% 6% 8% 8% 36%	3494
	21st to end	Night	6% 19% 7% 18% 6% 5% 5% 5% 6% 7% 16%	3811
April	1st to 10th	Night	9% 10% 4 8% 9% 6% 5% 5% 7% 8% 30%	1815
	11th to 20th	Night	9% 11% 5% 12% 6% 5% 7% 4 6% 8% 28%	1691
	21st to end	Night	10% 11% 4 9% 5% 5% 5% 5% 6% 7% 32%	1710
May	1st to 10th	Night	21% 12% 3 9% 5% 4 4 4 5% 6% 27%	2529
	11th to 20th	Night	9% 8% 2 8% 7% 6% 6% 5% 7% 10% 32%	2199
	21st to end	Night	17% 9% 4 9% 7% 7% 5% 5% 6% 8% 22%	2414
June	1st to 10th	Night	15% 8% 3 8% 7% 5% 5% 5% 8% 9% 28%	1330
	11th to 20th	Night	16% 9% 3 7% 8% 6% 6% 6% 6% 7% 25%	1330
	21st to end	Night	10% 6% 1 7% 6% 5% 5% 6% 7% 8% 40%	1330
July	1st to 10th	Night	7% 5% 2 7% 5% 5% 6% 4 8% 9% 42%	2220
	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% 9% 30%	2606
	11th to 20th	Night	5% 10% 4 11% 7% 6% 7% 4 7% 8% 31%	2728
	21st to end	Night	4 11% 4 11% 7% 6% 5% 4 7% 9% 32%	2850
December	1st to 10th	Night	6% 13% 4 12% 7% 7% 4 4 5% 9% 29%	2850
	11th to 20th	Night	3 10% 4 14% 8% 6% 7% 5% 6% 8% 28%	3510
	21st to end	Night	3 8% 3 8% 5% 5% 5% 4 6% 8% 43%	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	50% 7% 14% 20% 9% 1	2219
	11th to 20th	Day	46% 8% 14% 15% 15% 2	2220
	21st to end	Day	42% 9% 17% 26% 7%	2729
February	1st to 10th	Day	53% 6% 15% 16% 10% 1	1520
	11th to 20th	Day	54% 9% 13% 15% 8% 1	1674
	21st to end	Day	56% 7% 10% 18% 9%	1481
March	1st to 10th	Day	56% 8% 14% 13% 9%	3138
	11th to 20th	Day	37% 10% 18% 23% 12%	3485
	21st to end	Day	61% 7% 11% 15% 5%	3841
April	1st to 10th	Day	47% 10% 17% 18% 8% 1	2365
	11th to 20th	Day	49% 8% 14% 21% 8% 1	2440
	21st to end	Day	49% 8% 14% 22% 6% 2	2470
May	1st to 10th	Day	54% 8% 12% 22% 5%	4432
	11th to 20th	Day	43% 11% 14% 24% 8%	4698
	21st to end	Day	49% 11% 16% 17% 6% 1	5162
June	1st to 10th	Day	44% 10% 17% 21% 8% 1	2850
	11th to 20th	Day	52% 10% 13% 19% 5% 1	2850
	21st to end	Day	35% 11% 20% 26% 7% 1	2850
July	1st to 10th	Day	28% 8% 18% 30% 15% 2	4666
	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	54% 8% 14% 16% 6% 1	1526
	11th to 20th	Day	49% 8% 13% 21% 8% 1	1449
	21st to end	Day	49% 8% 16% 18% 8% 1	1330
December	1st to 10th	Day	56% 7% 13% 14% 8% 2	1330
	11th to 20th	Day	52% 10% 14% 19% 4 1	1684
	21st to end	Day	38% 6% 13% 24% 16% 4	2442
January	1st to 10th	Night	52% 9% 12% 19% 6% 2	4726
	11th to 20th	Night	50% 7% 12% 16% 13% 3	4740
	21st to end	Night	45% 9% 15% 22% 8% 1	4958
February	1st to 10th	Night	52% 7% 12% 19% 10%	2660
	11th to 20th	Night	52% 8% 13% 15% 10% 2	2403
	21st to end	Night	46% 9% 13% 20% 11% 1	1970
March	1st to 10th	Night	53% 9% 13% 19% 6%	3736
	11th to 20th	Night	39% 10% 22% 21% 8% 1	3494
	21st to end	Night	63% 10% 11% 11% 4	3811
April	1st to 10th	Night	48% 10% 13% 17% 11%	1815
	11th to 20th	Night	51% 7% 13% 22% 7% 1	1691
	21st to end	Night	47% 9% 13% 21% 7% 2	1710
May	1st to 10th	Night	55% 7% 10% 21% 6%	2529
	11th to 20th	Night	41% 11% 16% 22% 10%	2199
	21st to end	Night	55% 12% 13% 15% 4 1	2414
June	1st to 10th	Night	49% 10% 14% 18% 9%	1330
	11th to 20th	Night	55% 9% 13% 16% 6% 1	1330
	21st to end	Night	38% 10% 18% 25% 8% 1	1330
July	1st to 10th	Night	34% 12% 18% 23% 13% 1	2185
	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% 13% 21% 8% 1	2606
	11th to 20th	Night	48% 9% 14% 18% 10% 1	2728
	21st to end	Night	46% 9% 18% 18% 7% 2	2850
December	1st to 10th	Night	52% 7% 10% 20% 9% 2	2850
	11th to 20th	Night	50% 10% 16% 18% 6%	3507
	21st to end	Night	37% 7% 13% 24% 16% 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	6% 4 27% 36% 19% 9%	180
	11th to 20th	Day	8% 4 34% 30% 20% 3	180
	21st to end	Day	6% 8% 29% 29% 21% 7%	198
February	1st to 10th	Day	11% 10% 24% 36% 13% 7%	180
	11th to 20th	Day	12% 6% 25% 36% 17% 4	270
	21st to end	Day	8% 6% 25% 36% 19% 6%	293
March	1st to 10th	Day	9% 6% 29% 34% 17% 5%	460
	11th to 20th	Day	7% 4 26% 36% 20% 7%	460
	21st to end	Day	13% 6% 27% 30% 18% 6%	506
April	1st to 10th	Day	10% 13% 30% 30% 12% 6%	460
	11th to 20th	Day	13% 8% 31% 29% 14% 5%	452
	21st to end	Day	17% 10% 26% 31% 13% 3	460
May	1st to 10th	Day	18% 10% 23% 26% 18% 6%	565
	11th to 20th	Day	12% 8% 22% 34% 20% 4	675
	21st to end	Day	17% 5% 21% 27% 22% 7%	734
June	1st to 10th	Day	15% 7% 26% 34% 14% 4	680
	11th to 20th	Day	19% 8% 25% 30% 14% 5%	680
	21st to end	Day	9% 5% 23% 31% 25% 8%	680
July	1st to 10th	Day	11% 4 18% 36% 24% 8%	671
	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% 7% 24% 33% 13% 3	279
	11th to 20th	Day	16% 7% 30% 31% 14% 2	237
	21st to end	Day	8% 6% 30% 33% 16% 7%	180
December	1st to 10th	Day	11% 2 28% 34% 21% 4	180
	11th to 20th	Day	6% 6% 34% 37% 14% 3	180
	21st to end	Day	10% 3 21% 38% 22% 7%	198
January	1st to 10th	Night	12% 6% 31% 35% 15% 2	950
	11th to 20th	Night	11% 6% 31% 36% 14% 1	950
	21st to end	Night	11% 8% 29% 37% 12% 2	893
February	1st to 10th	Night	12% 6% 26% 35% 18% 3	760
	11th to 20th	Night	11% 5% 31% 36% 16% 1	744
	21st to end	Night	7% 4 24% 41% 19% 5%	628
March	1st to 10th	Night	9% 5% 27% 40% 16% 4	760
	11th to 20th	Night	9% 5% 29% 38% 16% 3	760
	21st to end	Night	13% 5% 26% 35% 18% 2	836
April	1st to 10th	Night	12% 7% 29% 33% 17% 2	675
	11th to 20th	Night	14% 7% 33% 35% 11% 1	563
	21st to end	Night	15% 9% 27% 34% 14% 1	570
May	1st to 10th	Night	17% 8% 26% 36% 13% 1	485
	11th to 20th	Night	11% 6% 27% 39% 16% 2	374
	21st to end	Night	19% 7% 23% 32% 18% 1	411
June	1st to 10th	Night	17% 7% 26% 34% 13% 3	380
	11th to 20th	Night	19% 4 29% 31% 17% 1	380
	21st to end	Night	13% 3 22% 39% 21% 2	380
July	1st to 10th	Night	11% 3 16% 46% 22% 1	370
	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% 29% 35% 10% 1	910
	11th to 20th	Night	8% 7% 38% 34% 10% 2	950
	21st to end	Night	9% 5% 35% 38% 13% 2	950
December	1st to 10th	Night	11% 6% 29% 35% 16% 2	950
	11th to 20th	Night	9% 5% 34% 37% 12% 2	950
	21st to end	Night	11% 4 30% 37% 15% 2	1045

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