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 2024-04-03.

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	23% 9% 3 6% 6% 3 4 4 5% 6% 31%	79055
	Night	25% 9% 3 6% 5% 3 4 4 4 5% 32%	81025
Transparency	Day	55% 8% 11% 15% 9% 2	78782
	Night	55% 8% 11% 15% 9% 2	80878
Seeing	Day	27% 11% 26% 25% 10% 2	14040
	Night	31% 6% 18% 31% 14% 1	22856

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% 17% 4 7% 6% 3 4 4 4 3 7%	2539
	11th to 20th	Day	38% 12% 4 6% 6% 3 3 3 3 3 19%	2516
	21st to end	Day	41% 13% 4 7% 5% 3 4 3 2 3 13%	3022
February	1st to 10th	Day	33% 14% 4 7% 5% 3 5% 4 4 6% 16%	1710
	11th to 20th	Day	32% 13% 5% 7% 6% 3 4 3 4 4 17%	1665
	21st to end	Day	34% 15% 4 6% 7% 4 3 3 3 4 17%	1481
March	1st to 10th	Day	31% 13% 4 8% 6% 3 5% 4 3 5% 16%	1985
	11th to 20th	Day	32% 12% 4 7% 6% 3 4 3 4 5% 20%	2090
	21st to end	Day	32% 12% 5% 10% 7% 4 5% 5% 4 4 12%	2350
April	1st to 10th	Day	30% 12% 5% 8% 8% 3 4 4 4 5% 17%	2185
	11th to 20th	Day	26% 14% 3 8% 6% 3 4 5% 5% 4 22%	2136
	21st to end	Day	23% 11% 3 8% 7% 4 6% 5% 5% 7% 22%	2340
May	1st to 10th	Day	17% 9% 3 8% 6% 3 5% 4 5% 6% 34%	2492
	11th to 20th	Day	20% 9% 3 7% 7% 3 5% 5% 7% 7% 28%	2477
	21st to end	Day	24% 7% 3 6% 6% 4 6% 6% 7% 7% 25%	2723
June	1st to 10th	Day	22% 8% 3 7% 7% 4 3 4 5% 7% 30%	2520
	11th to 20th	Day	19% 8% 3 7% 7% 4 5% 7% 6% 8% 25%	2556
	21st to end	Day	10% 5% 3 5% 5% 3 5% 4 6% 7% 47%	2700
July	1st to 10th	Day	8% 5% 2 4 5% 2 4 4 6% 7% 53%	2601
	11th to 20th	Day	9% 3 2 4 3 3 4 4 5% 6% 56%	2520
	21st to end	Day	5% 2 1 3 2 2 3 3 4 7% 68%	2741
August	1st to 10th	Day	6% 4 2 5% 4 2 4 4 6% 8% 56%	2374
	11th to 20th	Day	6% 4 2 3 3 1 3 3 4 8% 62%	2298
	21st to end	Day	8% 6% 2 5% 4 3 4 4 6% 8% 50%	2458
September	1st to 10th	Day	9% 3 2 4 4 3 4 4 5% 7% 56%	2160
	11th to 20th	Day	13% 7% 4 6% 6% 2 5% 5% 5% 7% 42%	2160
	21st to end	Day	18% 6% 2 5% 5% 3 3 4 4 6% 42%	1895
October	1st to 10th	Day	23% 8% 3 6% 5% 3 4 4 5% 6% 34%	1800
	11th to 20th	Day	25% 6% 3 6% 7% 4 4 4 5% 6% 32%	1800
	21st to end	Day	33% 9% 2 6% 5% 3 3 3 4 5% 28%	1926
November	1st to 10th	Day	33% 12% 4 6% 6% 3 6% 5% 6% 5% 14%	1556
	11th to 20th	Day	38% 9% 3 6% 5% 3 3 4 5% 4 19%	1520
	21st to end	Day	34% 11% 4 8% 5% 2 3 4 5% 4 21%	1520
December	1st to 10th	Day	30% 12% 5% 6% 6% 3 4 5% 3 4 22%	1520
	11th to 20th	Day	35% 11% 5% 7% 6% 3 4 4 5% 5% 15%	1925
	21st to end	Day	33% 14% 5% 10% 7% 4 4 5% 4 4 12%	2794
January	1st to 10th	Night	38% 14% 5% 8% 6% 3 4 4 3 3 11%	4406
	11th to 20th	Night	34% 14% 4 7% 5% 2 4 3 3 5% 18%	4382
	21st to end	Night	41% 13% 4 7% 5% 3 4 3 3 4 14%	4640
February	1st to 10th	Night	30% 13% 5% 8% 6% 3 5% 4 4 4 18%	2470
	11th to 20th	Night	29% 13% 3 6% 5% 3 4 4 4 5% 24%	2402
	21st to end	Night	31% 12% 4 7% 6% 3 3 4 4 6% 19%	1972
March	1st to 10th	Night	28% 12% 5% 7% 6% 3 5% 3 4 5% 21%	2194
	11th to 20th	Night	29% 10% 3 7% 6% 3 5% 5% 6% 5% 23%	2089
	21st to end	Night	29% 13% 4 8% 7% 3 4 5% 5% 5% 17%	2247
April	1st to 10th	Night	26% 12% 4 8% 6% 4 3 3 4 5% 23%	1820
	11th to 20th	Night	22% 12% 5% 6% 7% 3 4 4 6% 6% 27%	1771
	21st to end	Night	24% 9% 3 6% 4 3 5% 4 4 7% 30%	1620
May	1st to 10th	Night	15% 8% 3 7% 5% 3 4 5% 6% 5% 40%	1466
	11th to 20th	Night	17% 6% 3 5% 5% 3 5% 6% 6% 8% 36%	1416
	21st to end	Night	14% 6% 3 7% 6% 4 5% 6% 6% 7% 37%	1552
June	1st to 10th	Night	17% 8% 4 6% 6% 4 3 4 4 6% 38%	1440
	11th to 20th	Night	15% 7% 3 6% 5% 3 3 4 4 8% 41%	1396
	21st to end	Night	9% 4 1 5% 3 2 2 3 4 6% 61%	1260
July	1st to 10th	Night	4 2 2 2 4 2 3 3 5% 7% 66%	1354
	11th to 20th	Night	5% 3 1 3 3 1 3 3 4 6% 68%	1440
	21st to end	Night	3 2 1 1 1 1 2 2 3 5% 80%	1576
August	1st to 10th	Night	3 3 1 2 1 2 3 3 5% 8% 71%	1562
	11th to 20th	Night	3 2 1 3 2 1 2 3 3 6% 72%	1602
	21st to end	Night	8% 3 1 3 4 3 3 4 5% 6% 62%	1898
September	1st to 10th	Night	7% 3 2 2 4 2 3 4 4 4 66%	1800
	11th to 20th	Night	11% 5% 3 5% 6% 3 5% 4 5% 6% 48%	1800
	21st to end	Night	13% 4 2 5% 4 3 3 4 5% 7% 49%	2060
October	1st to 10th	Night	18% 6% 3 5% 4 2 4 3 4 7% 45%	2160
	11th to 20th	Night	20% 7% 3 5% 6% 3 4 4 5% 6% 38%	2160
	21st to end	Night	28% 7% 3 5% 4 2 3 3 4 5% 36%	2430
November	1st to 10th	Night	33% 9% 3 7% 5% 3 5% 4 3 5% 22%	2518
	11th to 20th	Night	37% 9% 3 6% 5% 3 4 3 4 4 22%	2660
	21st to end	Night	30% 9% 4 6% 6% 3 4 4 5% 4 25%	2660
December	1st to 10th	Night	29% 10% 4 6% 5% 3 4 5% 5% 5% 23%	2660
	11th to 20th	Night	31% 13% 4 8% 6% 3 4 4 4 5% 17%	3280
	21st to end	Night	33% 15% 4 9% 5% 4 5% 4 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	70% 7% 10% 8% 5%	1985
	11th to 20th	Day	68% 6% 8% 14% 4 1	2090
	21st to end	Day	75% 8% 9% 7% 1	2350
April	1st to 10th	Day	70% 7% 11% 10% 2	2185
	11th to 20th	Day	65% 6% 11% 10% 6% 1	2136
	21st to end	Day	63% 9% 10% 10% 7% 1	2340
May	1st to 10th	Day	52% 8% 15% 17% 8%	2492
	11th to 20th	Day	54% 11% 14% 15% 5% 1	2480
	21st to end	Day	59% 11% 14% 14% 2	2724
June	1st to 10th	Day	55% 9% 17% 13% 6%	2520
	11th to 20th	Day	56% 12% 17% 11% 4	2556
	21st to end	Day	36% 8% 18% 24% 10% 4	2700
July	1st to 10th	Day	31% 8% 15% 24% 17% 5%	2532
	11th to 20th	Day	27% 7% 11% 28% 22% 4	2445
	21st to end	Day	17% 5% 12% 32% 29% 5%	2589
August	1st to 10th	Day	26% 7% 17% 27% 19% 4	2357
	11th to 20th	Day	22% 7% 15% 31% 18% 7%	2298
	21st to end	Day	31% 8% 12% 28% 17% 3	2458
September	1st to 10th	Day	27% 7% 14% 23% 19% 10%	2160
	11th to 20th	Day	42% 8% 13% 15% 15% 7%	2160
	21st to end	Day	43% 8% 12% 18% 14% 5%	1895
October	1st to 10th	Day	50% 7% 9% 18% 13% 3	1800
	11th to 20th	Day	52% 9% 12% 15% 12% 2	1800
	21st to end	Day	60% 5% 8% 13% 13% 1	1926
November	1st to 10th	Day	70% 10% 6% 10% 4	1556
	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% 7% 11% 13% 4	2194
	11th to 20th	Night	62% 9% 10% 13% 5% 1	2090
	21st to end	Night	70% 10% 11% 9% 1	2247
April	1st to 10th	Night	66% 7% 12% 12% 4	1820
	11th to 20th	Night	58% 9% 12% 12% 7% 2	1771
	21st to end	Night	55% 11% 13% 14% 5% 2	1620
May	1st to 10th	Night	45% 9% 15% 20% 9% 1	1466
	11th to 20th	Night	46% 10% 17% 18% 5% 3	1416
	21st to end	Night	46% 14% 17% 17% 6%	1552
June	1st to 10th	Night	50% 6% 16% 21% 6% 1	1440
	11th to 20th	Night	45% 10% 22% 19% 5%	1396
	21st to end	Night	29% 5% 21% 30% 11% 4	1260
July	1st to 10th	Night	20% 8% 18% 28% 19% 6%	1314
	11th to 20th	Night	20% 5% 13% 29% 26% 6%	1392
	21st to end	Night	9% 4 12% 37% 29% 9%	1488
August	1st to 10th	Night	14% 7% 20% 34% 20% 5%	1554
	11th to 20th	Night	14% 7% 19% 34% 17% 9%	1602
	21st to end	Night	22% 7% 14% 33% 18% 5%	1898
September	1st to 10th	Night	22% 6% 14% 28% 19% 10%	1800
	11th to 20th	Night	37% 8% 13% 20% 12% 10%	1800
	21st to end	Night	35% 8% 16% 17% 17% 6%	2060
October	1st to 10th	Night	42% 6% 11% 22% 17% 3	2160
	11th to 20th	Night	47% 8% 11% 17% 15% 2	2160
	21st to end	Night	52% 7% 10% 15% 14% 3	2430
November	1st to 10th	Night	67% 6% 9% 12% 6%	2518
	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	39% 12% 22% 16% 8% 2	429
	11th to 20th	Day	34% 19% 22% 16% 6% 2	412
	21st to end	Day	28% 18% 29% 16% 8%	420
May	1st to 10th	Day	20% 19% 26% 24% 9% 2	423
	11th to 20th	Day	29% 13% 23% 23% 10% 2	448
	21st to end	Day	26% 10% 26% 26% 9% 2	485
June	1st to 10th	Day	26% 10% 27% 25% 12% 1	450
	11th to 20th	Day	21% 17% 32% 22% 6% 1	486
	21st to end	Day	11% 10% 34% 33% 11% 1	630
July	1st to 10th	Day	10% 7% 34% 38% 10% 1	527
	11th to 20th	Day	7% 9% 31% 36% 14% 2	444
	21st to end	Day	3 5% 31% 42% 16% 2	487
August	1st to 10th	Day	8% 5% 26% 43% 15% 4	447
	11th to 20th	Day	4 5% 25% 42% 21% 4	437
	21st to end	Day	10% 10% 31% 33% 14% 2	495
September	1st to 10th	Day	9% 7% 34% 37% 12% 2	450
	11th to 20th	Day	17% 9% 22% 36% 15% 2	450
	21st to end	Day	22% 12% 25% 30% 10% 2	450
October	1st to 10th	Day	26% 9% 25% 24% 14% 2	450
	11th to 20th	Day	29% 8% 22% 22% 17% 1	450
	21st to end	Day	35% 12% 22% 18% 10% 3	441
November	1st to 10th	Day	41% 14% 22% 17% 6%	214
	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% 11% 17% 22% 11%	836
April	1st to 10th	Night	36% 9% 20% 23% 12% 1	728
	11th to 20th	Night	29% 9% 22% 27% 11% 1	703
	21st to end	Night	30% 5% 21% 30% 13% 1	540
May	1st to 10th	Night	19% 8% 27% 33% 13% 1	386
	11th to 20th	Night	21% 4 20% 37% 17% 1	354
	21st to end	Night	18% 6% 23% 35% 17% 1	389
June	1st to 10th	Night	23% 4 21% 41% 11%	360
	11th to 20th	Night	22% 5% 24% 37% 11%	360
	21st to end	Night	11% 3 26% 48% 12%	360
July	1st to 10th	Night	7% 2 23% 52% 16% 1	350
	11th to 20th	Night	7% 3 27% 48% 16%	348
	21st to end	Night	4 2 24% 55% 14% 1	394
August	1st to 10th	Night	4 2 15% 49% 28% 2	488
	11th to 20th	Night	5% 2 12% 46% 33% 2	534
	21st to end	Night	10% 4 21% 43% 21% 1	710
September	1st to 10th	Night	10% 4 21% 46% 19% 1	720
	11th to 20th	Night	15% 4 15% 35% 28% 3	720
	21st to end	Night	16% 4 20% 41% 18% 1	720
October	1st to 10th	Night	23% 4 17% 35% 19% 2	720
	11th to 20th	Night	27% 4 15% 32% 19% 3	720
	21st to end	Night	36% 5% 17% 27% 14% 1	792
November	1st to 10th	Night	41% 7% 17% 26% 7%	740
	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 2024-03-31 03:08:54. Version ac07

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