Battle Ground
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Battle Ground clear sky chart from 2005-11-06 to 2024-03-18.

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	27% 9% 3 6% 5% 3 4 4 4 5% 32%	78611
	Night	29% 10% 3 5% 4 2 3 3 4 5% 32%	81141
Transparency	Day	55% 7% 10% 15% 10% 3	78314
	Night	56% 7% 10% 15% 9% 3	80959
Seeing	Day	28% 12% 22% 24% 11% 2	13681
	Night	32% 8% 17% 29% 14% 1	22809

By Month

Percentage Cloud Cover SW (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	45% 19% 4 6% 4 2 3 3 3 4 8%	2539
	11th to 20th	Day	43% 12% 3 5% 5% 2 3 2 3 3 19%	2540
	21st to end	Day	46% 12% 3 6% 4 3 3 3 3 3 13%	3017
February	1st to 10th	Day	39% 10% 3 6% 4 3 4 3 4 5% 18%	1710
	11th to 20th	Day	36% 15% 4 6% 6% 3 4 3 2 3 18%	1665
	21st to end	Day	37% 16% 3 5% 4 3 2 3 3 4 18%	1494
March	1st to 10th	Day	34% 14% 4 7% 6% 2 4 3 4 5% 17%	1975
	11th to 20th	Day	38% 11% 3 7% 5% 3 3 3 3 5% 20%	2059
	21st to end	Day	36% 14% 4 8% 6% 4 5% 4 4 4 12%	2232
April	1st to 10th	Day	35% 13% 4 7% 6% 3 3 4 4 5% 16%	2160
	11th to 20th	Day	30% 13% 4 6% 4 2 4 4 4 4 22%	2129
	21st to end	Day	27% 10% 4 7% 6% 3 6% 4 5% 6% 22%	2330
May	1st to 10th	Day	20% 9% 4 7% 6% 3 4 5% 4 6% 33%	2500
	11th to 20th	Day	24% 9% 4 6% 5% 3 4 5% 5% 7% 28%	2477
	21st to end	Day	30% 8% 3 6% 5% 3 5% 5% 5% 5% 25%	2723
June	1st to 10th	Day	27% 8% 3 6% 6% 3 3 4 5% 5% 30%	2520
	11th to 20th	Day	24% 8% 3 6% 7% 3 5% 5% 6% 6% 25%	2520
	21st to end	Day	12% 6% 3 5% 5% 3 4 4 5% 6% 48%	2520
July	1st to 10th	Day	9% 6% 2 4 4 2 4 4 4 6% 54%	2520
	11th to 20th	Day	10% 4 2 4 3 2 4 3 4 7% 58%	2520
	21st to end	Day	6% 4 1 3 3 1 3 2 3 5% 69%	2741
August	1st to 10th	Day	7% 6% 2 3 3 3 2 3 4 7% 59%	2381
	11th to 20th	Day	7% 4 1 3 3 1 3 3 4 6% 65%	2298
	21st to end	Day	10% 5% 2 5% 4 3 4 4 5% 6% 52%	2446
September	1st to 10th	Day	10% 4 1 3 3 2 3 3 4 7% 59%	2160
	11th to 20th	Day	15% 7% 3 5% 5% 3 4 4 3 7% 43%	2160
	21st to end	Day	20% 7% 3 5% 4 2 4 3 3 5% 43%	1900
October	1st to 10th	Day	25% 8% 3 4 4 3 3 4 5% 5% 36%	1800
	11th to 20th	Day	28% 6% 2 6% 5% 2 3 4 5% 7% 34%	1800
	21st to end	Day	35% 8% 2 5% 3 2 3 3 2 4 31%	1921
November	1st to 10th	Day	39% 11% 4 7% 4 2 3 3 5% 5% 16%	1572
	11th to 20th	Day	43% 9% 2 5% 4 2 4 3 4 5% 20%	1520
	21st to end	Day	39% 10% 3 6% 4 2 3 3 3 4 23%	1520
December	1st to 10th	Day	33% 12% 4 6% 5% 2 4 3 3 4 25%	1520
	11th to 20th	Day	39% 12% 3 6% 3 2 4 3 4 5% 18%	1928
	21st to end	Day	37% 14% 5% 7% 5% 3 3 3 4 5% 13%	2794
January	1st to 10th	Night	43% 17% 3 6% 5% 2 3 3 3 3 11%	4406
	11th to 20th	Night	40% 15% 3 6% 4 2 2 3 3 4 18%	4420
	21st to end	Night	44% 13% 3 6% 4 2 3 2 3 4 15%	4645
February	1st to 10th	Night	36% 12% 3 6% 6% 3 4 3 4 5% 19%	2470
	11th to 20th	Night	35% 12% 3 5% 4 3 3 3 3 4 25%	2402
	21st to end	Night	35% 13% 4 6% 4 3 3 3 5% 4 20%	1960
March	1st to 10th	Night	34% 12% 3 6% 4 3 4 3 3 5% 23%	2204
	11th to 20th	Night	32% 12% 3 5% 5% 3 4 4 4 6% 23%	2067
	21st to end	Night	36% 14% 4 7% 4 3 4 4 3 5% 17%	2123
April	1st to 10th	Night	30% 16% 5% 6% 6% 2 3 3 3 5% 22%	1800
	11th to 20th	Night	27% 12% 3 5% 4 3 4 4 4 6% 27%	1779
	21st to end	Night	29% 9% 3 6% 5% 3 4 4 5% 6% 27%	1628
May	1st to 10th	Night	19% 9% 3 5% 6% 2 4 4 4 5% 39%	1458
	11th to 20th	Night	20% 8% 3 5% 5% 3 4 5% 5% 7% 35%	1416
	21st to end	Night	19% 7% 4 6% 4 3 5% 5% 5% 7% 34%	1552
June	1st to 10th	Night	22% 7% 4 5% 5% 3 3 4 3 6% 38%	1440
	11th to 20th	Night	20% 8% 3 6% 5% 2 4 3 4 6% 39%	1440
	21st to end	Night	11% 5% 2 5% 3 2 3 2 3 4 60%	1374
July	1st to 10th	Night	6% 3 2 3 3 2 3 3 4 5% 66%	1440
	11th to 20th	Night	6% 3 2 3 3 2 3 3 2 6% 69%	1440
	21st to end	Night	3 1 1 1 2 1 1 2 2 5% 81%	1576
August	1st to 10th	Night	4 3 1 3 2 2 2 2 4 6% 71%	1556
	11th to 20th	Night	5% 2 1 2 3 2 2 3 3 5% 72%	1602
	21st to end	Night	8% 3 1 3 3 2 3 3 5% 6% 63%	1909
September	1st to 10th	Night	9% 3 1 3 3 2 3 2 4 3 67%	1800
	11th to 20th	Night	14% 6% 3 4 5% 3 4 4 4 5% 49%	1800
	21st to end	Night	15% 6% 2 5% 4 2 3 4 4 6% 49%	2058
October	1st to 10th	Night	21% 6% 2 4 4 2 3 3 3 5% 46%	2160
	11th to 20th	Night	24% 8% 3 5% 4 2 4 3 5% 6% 38%	2160
	21st to end	Night	32% 7% 2 4 3 2 3 3 3 5% 36%	2434
November	1st to 10th	Night	38% 10% 3 4 5% 3 3 3 4 5% 22%	2504
	11th to 20th	Night	42% 9% 3 5% 3 2 3 3 3 4 22%	2660
	21st to end	Night	34% 9% 3 6% 5% 3 3 3 4 4 28%	2660
December	1st to 10th	Night	35% 10% 3 4 4 3 3 3 4 6% 25%	2660
	11th to 20th	Night	37% 13% 3 6% 5% 2 3 3 4 5% 20%	3276
	21st to end	Night	36% 15% 3 8% 5% 3 4 3 3 4 16%	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	81% 6% 6% 4 2 1	2539
	11th to 20th	Day	72% 4 7% 10% 4 2	2540
	21st to end	Day	76% 6% 6% 7% 5%	3017
February	1st to 10th	Day	70% 7% 9% 9% 5%	1710
	11th to 20th	Day	72% 6% 6% 10% 3 2	1674
	21st to end	Day	71% 6% 8% 8% 6% 1	1494
March	1st to 10th	Day	69% 8% 9% 9% 6%	1975
	11th to 20th	Day	69% 5% 7% 13% 5% 1	2059
	21st to end	Day	77% 7% 8% 8% 1	2232
April	1st to 10th	Day	71% 7% 10% 9% 3	2160
	11th to 20th	Day	66% 7% 8% 10% 7% 2	2132
	21st to end	Day	63% 9% 9% 11% 7% 1	2330
May	1st to 10th	Day	54% 6% 14% 17% 8%	2500
	11th to 20th	Day	55% 10% 12% 16% 5% 1	2480
	21st to end	Day	60% 10% 13% 15% 3	2724
June	1st to 10th	Day	56% 9% 14% 15% 6%	2520
	11th to 20th	Day	59% 10% 15% 12% 4	2520
	21st to end	Day	37% 8% 16% 25% 10% 4	2520
July	1st to 10th	Day	31% 8% 14% 24% 18% 5%	2451
	11th to 20th	Day	26% 7% 11% 25% 25% 5%	2445
	21st to end	Day	18% 5% 10% 30% 31% 6%	2589
August	1st to 10th	Day	27% 6% 13% 30% 19% 5%	2364
	11th to 20th	Day	21% 7% 14% 31% 19% 8%	2298
	21st to end	Day	31% 8% 12% 27% 18% 4	2446
September	1st to 10th	Day	27% 6% 12% 24% 19% 12%	2160
	11th to 20th	Day	43% 7% 12% 16% 14% 9%	2160
	21st to end	Day	44% 7% 11% 17% 15% 6%	1900
October	1st to 10th	Day	51% 7% 8% 18% 14% 3	1800
	11th to 20th	Day	52% 6% 12% 15% 13% 2	1800
	21st to end	Day	59% 5% 8% 13% 14% 1	1921
November	1st to 10th	Day	70% 7% 8% 9% 4 1	1572
	11th to 20th	Day	67% 7% 10% 9% 6% 2	1520
	21st to end	Day	67% 6% 4 9% 12% 2	1520
December	1st to 10th	Day	66% 6% 7% 11% 9% 2	1520
	11th to 20th	Day	69% 6% 12% 9% 3	1928
	21st to end	Day	74% 8% 9% 6% 3	2794
January	1st to 10th	Night	78% 6% 7% 5% 3 1	4406
	11th to 20th	Night	71% 7% 6% 11% 4 2	4420
	21st to end	Night	75% 5% 6% 8% 5% 1	4645
February	1st to 10th	Night	69% 8% 8% 10% 5% 1	2470
	11th to 20th	Night	66% 7% 9% 11% 6% 2	2404
	21st to end	Night	67% 7% 9% 9% 7% 1	1960
March	1st to 10th	Night	65% 7% 10% 14% 5%	2204
	11th to 20th	Night	62% 7% 10% 13% 6% 1	2067
	21st to end	Night	71% 9% 9% 9% 1	2123
April	1st to 10th	Night	67% 8% 9% 11% 5%	1800
	11th to 20th	Night	59% 9% 11% 11% 8% 3	1779
	21st to end	Night	59% 9% 12% 12% 5% 3	1628
May	1st to 10th	Night	48% 8% 14% 19% 10% 1	1458
	11th to 20th	Night	49% 10% 16% 17% 4 4	1416
	21st to end	Night	49% 12% 16% 18% 5%	1552
June	1st to 10th	Night	50% 7% 15% 22% 6% 1	1440
	11th to 20th	Night	49% 8% 19% 19% 5%	1440
	21st to end	Night	30% 5% 18% 31% 10% 5%	1374
July	1st to 10th	Night	23% 7% 14% 29% 21% 6%	1400
	11th to 20th	Night	20% 5% 13% 28% 28% 6%	1392
	21st to end	Night	9% 4 11% 36% 30% 10%	1488
August	1st to 10th	Night	17% 5% 17% 35% 20% 6%	1548
	11th to 20th	Night	17% 5% 16% 34% 18% 9%	1602
	21st to end	Night	22% 7% 13% 34% 19% 6%	1909
September	1st to 10th	Night	23% 6% 12% 28% 20% 10%	1800
	11th to 20th	Night	38% 7% 12% 21% 11% 11%	1800
	21st to end	Night	38% 7% 15% 16% 16% 8%	2058
October	1st to 10th	Night	43% 6% 9% 21% 18% 4	2160
	11th to 20th	Night	48% 7% 9% 15% 17% 3	2160
	21st to end	Night	53% 5% 9% 14% 15% 3	2434
November	1st to 10th	Night	66% 7% 7% 14% 6% 1	2504
	11th to 20th	Night	68% 6% 8% 9% 7% 2	2660
	21st to end	Night	62% 5% 8% 9% 13% 2	2660
December	1st to 10th	Night	63% 7% 9% 10% 10% 1	2660
	11th to 20th	Night	68% 6% 9% 10% 6%	3276
	21st to end	Night	73% 8% 9% 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	52% 13% 15% 13% 6% 1	180
	11th to 20th	Day	48% 12% 21% 11% 7% 1	180
	21st to end	Day	44% 13% 17% 16% 10% 1	330
February	1st to 10th	Day	46% 12% 17% 17% 7% 1	370
	11th to 20th	Day	45% 14% 23% 13% 5% 1	365
	21st to end	Day	44% 14% 23% 15% 3	346
March	1st to 10th	Day	42% 14% 23% 17% 5%	460
	11th to 20th	Day	35% 16% 24% 18% 6% 2	449
	21st to end	Day	40% 18% 17% 18% 7% 1	462
April	1st to 10th	Day	40% 15% 22% 15% 6% 2	420
	11th to 20th	Day	35% 20% 20% 15% 7% 3	412
	21st to end	Day	30% 16% 27% 18% 8%	420
May	1st to 10th	Day	23% 17% 26% 23% 9% 2	423
	11th to 20th	Day	32% 15% 20% 21% 10% 3	448
	21st to end	Day	27% 12% 24% 21% 13% 3	485
June	1st to 10th	Day	27% 11% 21% 26% 12% 3	450
	11th to 20th	Day	23% 15% 29% 24% 6% 2	450
	21st to end	Day	10% 10% 30% 28% 19% 2	450
July	1st to 10th	Day	13% 10% 24% 38% 14% 2	446
	11th to 20th	Day	8% 8% 28% 35% 17% 4	444
	21st to end	Day	6% 6% 22% 41% 20% 5%	487
August	1st to 10th	Day	9% 6% 20% 39% 20% 6%	447
	11th to 20th	Day	6% 4 22% 40% 22% 5%	437
	21st to end	Day	11% 11% 25% 34% 15% 4	495
September	1st to 10th	Day	12% 6% 29% 34% 16% 2	450
	11th to 20th	Day	19% 10% 18% 31% 21% 2	450
	21st to end	Day	19% 11% 27% 29% 12% 2	450
October	1st to 10th	Day	26% 9% 22% 27% 14% 2	450
	11th to 20th	Day	30% 9% 20% 24% 14% 2	450
	21st to end	Day	35% 16% 19% 18% 9% 3	436
November	1st to 10th	Day	44% 15% 17% 17% 6% 1	221
	11th to 20th	Day	40% 16% 18% 16% 8% 2	180
	21st to end	Day	46% 12% 17% 19% 7%	180
December	1st to 10th	Day	44% 12% 21% 14% 8% 1	180
	11th to 20th	Day	54% 12% 18% 13% 3	180
	21st to end	Day	44% 14% 22% 17% 3 1	198
January	1st to 10th	Night	47% 13% 17% 17% 6%	760
	11th to 20th	Night	46% 7% 18% 22% 7%	760
	21st to end	Night	40% 10% 18% 22% 8% 1	836
February	1st to 10th	Night	40% 10% 19% 23% 7% 1	760
	11th to 20th	Night	43% 8% 17% 23% 8% 1	744
	21st to end	Night	44% 11% 14% 23% 7%	628
March	1st to 10th	Night	39% 11% 15% 24% 10% 1	760
	11th to 20th	Night	37% 11% 19% 24% 9%	752
	21st to end	Night	42% 11% 13% 23% 10% 1	792
April	1st to 10th	Night	38% 9% 17% 23% 12% 1	720
	11th to 20th	Night	32% 8% 21% 25% 13% 2	711
	21st to end	Night	34% 7% 17% 29% 13%	548
May	1st to 10th	Night	19% 11% 22% 31% 15% 1	378
	11th to 20th	Night	21% 5% 16% 34% 23% 2	354
	21st to end	Night	22% 6% 19% 30% 22% 1	389
June	1st to 10th	Night	24% 6% 16% 35% 18%	360
	11th to 20th	Night	24% 6% 18% 36% 16%	360
	21st to end	Night	13% 3 19% 43% 21%	360
July	1st to 10th	Night	7% 2 11% 51% 28% 1	350
	11th to 20th	Night	6% 4 13% 53% 24% 1	348
	21st to end	Night	3 2 10% 55% 29% 1	394
August	1st to 10th	Night	6% 2 9% 41% 39% 3	482
	11th to 20th	Night	6% 1 8% 40% 41% 4	534
	21st to end	Night	9% 5% 13% 46% 26% 2	721
September	1st to 10th	Night	12% 3 16% 43% 24% 2	720
	11th to 20th	Night	17% 3 13% 34% 31% 3	720
	21st to end	Night	18% 5% 17% 38% 20% 2	720
October	1st to 10th	Night	23% 5% 18% 32% 20% 3	720
	11th to 20th	Night	28% 7% 13% 30% 19% 3	720
	21st to end	Night	34% 10% 18% 26% 10% 2	792
November	1st to 10th	Night	41% 8% 18% 25% 8%	740
	11th to 20th	Night	47% 9% 17% 21% 5% 1	760
	21st to end	Night	38% 8% 20% 27% 6%	760
December	1st to 10th	Night	39% 8% 24% 21% 8% 1	760
	11th to 20th	Night	50% 8% 18% 21% 4	760
	21st to end	Night	51% 12% 18% 13% 6%	836

Page generated at 2024-03-15 11:01:40. Version ac07

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