Woodland
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Woodland 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	20% 9% 3 7% 4 4 4 3 5% 6% 35%	105789
	Night	22% 10% 3 7% 4 4 4 3 4 5% 35%	101844
Transparency	Day	50% 8% 11% 16% 12% 4	105555
	Night	51% 8% 12% 16% 10% 3	101724
Seeing	Day	26% 12% 26% 25% 10% 2	14909
	Night	30% 6% 19% 31% 13% 1	23498

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	41% 18% 4 7% 5% 4 4 3 4 3 7%	2539
	11th to 20th	Day	38% 12% 4 7% 5% 3 3 2 3 4 19%	2516
	21st to end	Day	41% 14% 4 9% 4 4 4 3 3 3 12%	3022
February	1st to 10th	Day	33% 15% 3 8% 4 4 4 3 5% 5% 16%	1710
	11th to 20th	Day	32% 14% 5% 9% 5% 4 4 3 5% 4 17%	1665
	21st to end	Day	33% 17% 3 7% 6% 5% 3 2 3 5% 17%	1481
March	1st to 10th	Day	23% 18% 4 11% 6% 5% 5% 3 4 5% 16%	3283
	11th to 20th	Day	23% 12% 3 8% 4 3 3 2 4 4 35%	3490
	21st to end	Day	27% 14% 4 11% 6% 5% 4 4 4 5% 15%	3911
April	1st to 10th	Day	30% 13% 4 10% 6% 4 4 3 4 5% 16%	2280
	11th to 20th	Day	25% 14% 3 9% 5% 4 4 4 5% 4 23%	2257
	21st to end	Day	23% 12% 3 9% 6% 5% 5% 4 5% 6% 22%	2470
May	1st to 10th	Day	21% 9% 3 8% 5% 4 4 3 4 5% 34%	4379
	11th to 20th	Day	11% 6% 2 6% 5% 4 5% 5% 7% 9% 39%	4377
	21st to end	Day	23% 8% 3 9% 7% 7% 6% 4 6% 6% 22%	4813
June	1st to 10th	Day	22% 9% 2 8% 6% 4 3 3 5% 7% 30%	2660
	11th to 20th	Day	19% 9% 3 8% 6% 5% 6% 5% 7% 7% 25%	2698
	21st to end	Day	10% 5% 2 5% 5% 5% 4 3 6% 7% 47%	2850
July	1st to 10th	Day	4 3 1 3 3 2 3 2 4 6% 67%	4557
	11th to 20th	Day	5% 2 1 3 2 3 2 2 4 5% 72%	4420
	21st to end	Day	7% 3 1 3 2 2 3 3 4 7% 65%	4790
August	1st to 10th	Day	4 3 1 4 3 3 3 3 5% 7% 65%	4164
	11th to 20th	Day	6% 5% 2 6% 5% 5% 5% 4 6% 9% 48%	4026
	21st to end	Day	11% 7% 2 5% 3 4 4 3 5% 7% 49%	4314
September	1st to 10th	Day	9% 3 2 5% 3 4 4 3 6% 7% 55%	2280
	11th to 20th	Day	13% 7% 3 7% 5% 3 5% 4 5% 7% 41%	2280
	21st to end	Day	17% 6% 2 6% 4 4 3 3 5% 6% 43%	1999
October	1st to 10th	Day	17% 6% 2 5% 3 3 3 3 6% 8% 44%	3180
	11th to 20th	Day	21% 8% 3 8% 5% 5% 5% 4 6% 7% 28%	3161
	21st to end	Day	31% 9% 3 8% 4 4 4 3 5% 6% 23%	3355
November	1st to 10th	Day	33% 12% 4 8% 5% 5% 5% 5% 5% 5% 14%	1583
	11th to 20th	Day	38% 9% 3 7% 4 4 3 3 5% 4 19%	1520
	21st to end	Day	33% 12% 3 8% 4 3 4 3 5% 4 21%	1520
December	1st to 10th	Day	29% 14% 4 7% 5% 4 4 4 3 5% 22%	1520
	11th to 20th	Day	35% 11% 5% 8% 5% 4 4 3 5% 5% 15%	1925
	21st to end	Day	33% 14% 5% 11% 6% 5% 4 4 4 4 12%	2794
January	1st to 10th	Night	38% 14% 4 9% 5% 4 4 3 3 3 11%	4406
	11th to 20th	Night	34% 14% 4 8% 4 3 4 2 3 5% 18%	4382
	21st to end	Night	41% 14% 3 7% 4 4 3 2 4 4 14%	4640
February	1st to 10th	Night	30% 14% 4 8% 5% 4 5% 3 5% 4 18%	2470
	11th to 20th	Night	28% 14% 3 7% 4 4 4 3 4 5% 23%	2402
	21st to end	Night	31% 13% 3 8% 5% 4 3 3 5% 5% 19%	1972
March	1st to 10th	Night	22% 18% 5% 9% 6% 5% 4 3 4 5% 19%	3590
	11th to 20th	Night	21% 10% 2 6% 4 3 3 3 5% 5% 37%	3489
	21st to end	Night	29% 16% 4 9% 6% 5% 4 3 4 4 16%	3741
April	1st to 10th	Night	26% 14% 4 9% 6% 5% 3 3 4 5% 23%	1900
	11th to 20th	Night	20% 13% 3 7% 6% 4 4 3 6% 6% 28%	1870
	21st to end	Night	23% 11% 3 7% 4 5% 4 4 4 7% 30%	1710
May	1st to 10th	Night	22% 9% 2 7% 3 3 4 3 5% 4 39%	2580
	11th to 20th	Night	10% 4 2 4 3 2 4 4 5% 8% 53%	2516
	21st to end	Night	12% 8% 3 8% 6% 5% 6% 5% 6% 7% 35%	2762
June	1st to 10th	Night	17% 9% 3 7% 6% 4 4 3 4 6% 38%	1520
	11th to 20th	Night	14% 8% 2 7% 5% 3 3 3 5% 7% 42%	1473
	21st to end	Night	8% 4 1 5% 2 2 3 3 4 6% 60%	1330
July	1st to 10th	Night	2 1 1 2 2 1 2 2 3 5% 79%	2398
	11th to 20th	Night	3 2 1 3 2 1 2 2 2 4 76%	2540
	21st to end	Night	4 2 1 1 1 1 1 2 3 5% 79%	2762
August	1st to 10th	Night	2 2 1 2 1 2 2 1 4 6% 77%	2771
	11th to 20th	Night	6% 4 1 5% 2 3 3 3 4 7% 62%	2812
	21st to end	Night	11% 4 1 4 3 3 3 3 4 5% 59%	3360
September	1st to 10th	Night	7% 3 2 3 3 3 3 3 4 5% 66%	1900
	11th to 20th	Night	11% 5% 3 6% 5% 4 4 3 5% 6% 48%	1900
	21st to end	Night	12% 4 2 5% 4 4 4 3 5% 7% 49%	2175
October	1st to 10th	Night	13% 4 2 4 3 3 4 3 5% 8% 51%	3800
	11th to 20th	Night	20% 7% 3 6% 4 4 4 4 7% 7% 35%	3777
	21st to end	Night	27% 9% 4 7% 4 4 4 3 5% 6% 27%	4211
November	1st to 10th	Night	34% 10% 3 7% 4 4 5% 3 4 5% 22%	2563
	11th to 20th	Night	37% 10% 3 7% 4 4 4 2 4 4 22%	2660
	21st to end	Night	29% 10% 3 7% 5% 4 5% 3 5% 4 25%	2660
December	1st to 10th	Night	29% 11% 4 6% 5% 4 4 4 5% 5% 23%	2660
	11th to 20th	Night	31% 14% 4 9% 5% 4 4 3 4 5% 17%	3280
	21st to end	Night	32% 16% 4 10% 4 5% 4 3 4 4 13%	4862

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	80% 8% 5% 4 2 1	2539
	11th to 20th	Day	71% 6% 6% 10% 5% 2	2540
	21st to end	Day	75% 8% 5% 6% 5%	3022
February	1st to 10th	Day	70% 8% 9% 9% 4	1710
	11th to 20th	Day	72% 8% 6% 10% 4 1	1674
	21st to end	Day	72% 5% 8% 7% 6% 1	1481
March	1st to 10th	Day	66% 10% 13% 7% 4	3283
	11th to 20th	Day	53% 7% 8% 26% 6%	3490
	21st to end	Day	70% 10% 10% 7% 3	3911
April	1st to 10th	Day	70% 8% 11% 10% 2	2280
	11th to 20th	Day	64% 6% 11% 10% 7% 2	2257
	21st to end	Day	63% 9% 10% 11% 6% 1	2470
May	1st to 10th	Day	49% 10% 13% 16% 11%	4379
	11th to 20th	Day	36% 16% 22% 18% 7% 1	4380
	21st to end	Day	60% 14% 15% 10% 1	4814
June	1st to 10th	Day	54% 9% 17% 13% 7%	2660
	11th to 20th	Day	55% 12% 16% 12% 5%	2698
	21st to end	Day	36% 8% 18% 25% 10% 3	2850
July	1st to 10th	Day	19% 5% 9% 18% 21% 28%	4488
	11th to 20th	Day	16% 5% 7% 20% 38% 14%	4345
	21st to end	Day	20% 4 13% 27% 31% 4	4639
August	1st to 10th	Day	20% 5% 11% 25% 29% 10%	4147
	11th to 20th	Day	31% 9% 18% 27% 12% 4	4065
	21st to end	Day	35% 6% 11% 23% 17% 8%	4313
September	1st to 10th	Day	27% 7% 15% 23% 18% 10%	2280
	11th to 20th	Day	43% 8% 14% 15% 14% 6%	2280
	21st to end	Day	42% 8% 13% 19% 14% 5%	1999
October	1st to 10th	Day	38% 5% 7% 26% 22% 2	3180
	11th to 20th	Day	53% 8% 12% 15% 11% 1	3161
	21st to end	Day	62% 5% 8% 15% 10%	3355
November	1st to 10th	Day	70% 9% 7% 10% 4	1583
	11th to 20th	Day	68% 8% 9% 8% 5% 2	1520
	21st to end	Day	67% 6% 5% 8% 12% 1	1520
December	1st to 10th	Day	67% 7% 7% 10% 8% 2	1520
	11th to 20th	Day	69% 8% 11% 10% 2	1928
	21st to end	Day	73% 10% 8% 5% 3	2794
January	1st to 10th	Night	77% 8% 7% 5% 3 1	4406
	11th to 20th	Night	68% 8% 7% 11% 4 2	4420
	21st to end	Night	74% 6% 7% 7% 5% 1	4640
February	1st to 10th	Night	68% 9% 8% 10% 4	2470
	11th to 20th	Night	65% 8% 9% 10% 6% 2	2404
	21st to end	Night	67% 7% 10% 9% 6% 1	1972
March	1st to 10th	Night	65% 9% 11% 12% 3	3590
	11th to 20th	Night	48% 10% 12% 23% 7% 1	3490
	21st to end	Night	71% 10% 9% 9% 1	3741
April	1st to 10th	Night	66% 7% 12% 12% 3	1900
	11th to 20th	Night	56% 9% 12% 12% 8% 2	1870
	21st to end	Night	55% 11% 13% 14% 4 2	1710
May	1st to 10th	Night	47% 9% 14% 19% 10% 1	2580
	11th to 20th	Night	29% 8% 28% 24% 9% 2	2516
	21st to end	Night	45% 18% 23% 10% 3	2762
June	1st to 10th	Night	50% 6% 17% 21% 6% 1	1520
	11th to 20th	Night	43% 9% 21% 21% 6%	1473
	21st to end	Night	28% 5% 21% 31% 11% 4	1330
July	1st to 10th	Night	11% 5% 10% 24% 20% 29%	2358
	11th to 20th	Night	15% 3 8% 22% 36% 16%	2492
	21st to end	Night	11% 4 13% 32% 34% 6%	2674
August	1st to 10th	Night	11% 5% 12% 33% 32% 7%	2763
	11th to 20th	Night	23% 8% 28% 26% 10% 5%	2839
	21st to end	Night	28% 6% 16% 25% 19% 7%	3360
September	1st to 10th	Night	22% 6% 15% 27% 19% 10%	1900
	11th to 20th	Night	37% 8% 14% 20% 12% 9%	1900
	21st to end	Night	35% 8% 17% 18% 16% 6%	2175
October	1st to 10th	Night	32% 5% 11% 29% 22% 2	3800
	11th to 20th	Night	48% 7% 14% 19% 12% 1	3777
	21st to end	Night	59% 6% 8% 17% 9% 1	4211
November	1st to 10th	Night	67% 6% 9% 12% 6%	2563
	11th to 20th	Night	67% 7% 9% 9% 6% 2	2660
	21st to end	Night	62% 7% 8% 9% 13% 1	2660
December	1st to 10th	Night	63% 8% 9% 10% 9% 1	2660
	11th to 20th	Night	69% 8% 9% 9% 5%	3276
	21st to end	Night	73% 11% 7% 7% 2	4862

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% 13% 17% 12% 7% 1	180
	11th to 20th	Day	52% 10% 21% 8% 7% 2	180
	21st to end	Day	45% 9% 18% 17% 9% 1	335
February	1st to 10th	Day	47% 11% 17% 16% 6% 2	370
	11th to 20th	Day	44% 13% 23% 15% 4 1	365
	21st to end	Day	44% 13% 24% 15% 4	341
March	1st to 10th	Day	39% 16% 25% 14% 6%	460
	11th to 20th	Day	34% 13% 25% 17% 7% 3	460
	21st to end	Day	39% 16% 23% 16% 6% 1	506
April	1st to 10th	Day	38% 13% 23% 16% 8% 2	460
	11th to 20th	Day	32% 20% 25% 16% 5% 2	452
	21st to end	Day	29% 18% 29% 16% 7%	460
May	1st to 10th	Day	20% 19% 27% 24% 8% 2	463
	11th to 20th	Day	27% 14% 24% 22% 10% 2	488
	21st to end	Day	26% 11% 26% 26% 10% 2	529
June	1st to 10th	Day	26% 10% 27% 26% 11% 1	490
	11th to 20th	Day	21% 17% 32% 22% 6% 1	528
	21st to end	Day	10% 11% 35% 32% 10% 2	680
July	1st to 10th	Day	10% 8% 35% 36% 10% 1	571
	11th to 20th	Day	7% 8% 31% 38% 14% 3	484
	21st to end	Day	5% 6% 31% 40% 16% 3	531
August	1st to 10th	Day	8% 5% 26% 43% 15% 3	487
	11th to 20th	Day	4 5% 25% 41% 21% 4	477
	21st to end	Day	11% 10% 30% 33% 14% 3	539
September	1st to 10th	Day	9% 7% 32% 37% 13% 2	490
	11th to 20th	Day	17% 9% 23% 35% 14% 2	490
	21st to end	Day	20% 11% 26% 30% 11% 1	490
October	1st to 10th	Day	25% 9% 26% 24% 14% 2	490
	11th to 20th	Day	28% 9% 22% 22% 17% 1	490
	21st to end	Day	35% 12% 23% 17% 9% 2	482
November	1st to 10th	Day	43% 14% 21% 16% 5%	223
	11th to 20th	Day	42% 9% 22% 16% 9% 2	180
	21st to end	Day	42% 12% 17% 18% 11%	180
December	1st to 10th	Day	46% 10% 19% 14% 9% 2	180
	11th to 20th	Day	52% 11% 18% 16% 4	180
	21st to end	Day	45% 13% 20% 16% 6%	198
January	1st to 10th	Night	48% 9% 15% 19% 9%	760
	11th to 20th	Night	45% 6% 15% 22% 11% 1	760
	21st to end	Night	40% 5% 16% 26% 11% 1	836
February	1st to 10th	Night	41% 7% 17% 26% 8% 1	760
	11th to 20th	Night	40% 8% 16% 26% 10%	744
	21st to end	Night	41% 8% 18% 24% 8%	628
March	1st to 10th	Night	38% 9% 18% 23% 11% 1	760
	11th to 20th	Night	36% 9% 18% 28% 11%	760
	21st to end	Night	40% 10% 17% 22% 11%	836
April	1st to 10th	Night	36% 9% 20% 22% 11% 1	760
	11th to 20th	Night	28% 10% 23% 27% 11% 1	742
	21st to end	Night	31% 5% 21% 30% 12% 1	570
May	1st to 10th	Night	19% 7% 27% 33% 12% 1	407
	11th to 20th	Night	20% 5% 21% 36% 17% 1	374
	21st to end	Night	18% 7% 22% 36% 17%	411
June	1st to 10th	Night	23% 4 23% 40% 10%	380
	11th to 20th	Night	21% 6% 26% 37% 11%	380
	21st to end	Night	11% 3 28% 47% 11%	380
July	1st to 10th	Night	6% 2 24% 52% 15% 1	370
	11th to 20th	Night	7% 2 29% 47% 15%	368
	21st to end	Night	4 4 25% 53% 14% 1	416
August	1st to 10th	Night	4 3 17% 48% 27% 2	516
	11th to 20th	Night	5% 2 12% 46% 32% 2	564
	21st to end	Night	10% 4 21% 43% 21% 1	750
September	1st to 10th	Night	9% 4 21% 46% 19% 1	760
	11th to 20th	Night	15% 4 17% 34% 27% 2	760
	21st to end	Night	16% 4 20% 42% 18% 1	760
October	1st to 10th	Night	22% 4 18% 36% 19% 2	760
	11th to 20th	Night	27% 4 15% 33% 18% 3	760
	21st to end	Night	36% 5% 18% 27% 13% 1	836
November	1st to 10th	Night	41% 7% 17% 26% 7%	754
	11th to 20th	Night	46% 8% 15% 23% 8% 1	760
	21st to end	Night	38% 8% 17% 26% 10% 1	760
December	1st to 10th	Night	38% 7% 20% 23% 11% 1	760
	11th to 20th	Night	47% 7% 17% 21% 8% 1	760
	21st to end	Night	51% 9% 18% 15% 6%	836

Page generated at 2024-11-01 19:47:33. Version ac07

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