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 2026-10-29.

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 6% 4 3 3 3 4 6% 39%	159047
	Night	24% 9% 2 6% 3 3 3 2 4 5% 38%	150328
Transparency	Day	46% 7% 11% 18% 12% 4	153794
	Night	49% 6% 11% 17% 12% 4	146583
Seeing	Day	26% 12% 23% 25% 12% 2	17098
	Night	31% 8% 17% 29% 14% 1	25966

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% 18% 4 7% 4 3 3 2 3 3 8%	4722
	11th to 20th	Day	24% 10% 3 5% 3 3 3 2 4 6% 37%	4740
	21st to end	Day	33% 8% 2 6% 3 3 3 3 3 4 30%	5602
February	1st to 10th	Day	37% 12% 3 7% 4 4 3 3 5% 5% 17%	1890
	11th to 20th	Day	36% 16% 4 7% 4 4 4 2 2 3 18%	1845
	21st to end	Day	36% 17% 3 7% 3 3 2 2 3 4 19%	1646
March	1st to 10th	Day	23% 16% 4 9% 5% 4 5% 3 5% 6% 19%	4797
	11th to 20th	Day	32% 16% 4 8% 3 3 3 2 2 3 25%	5110
	21st to end	Day	33% 15% 4 9% 5% 5% 4 3 5% 5% 12%	5754
April	1st to 10th	Day	32% 13% 3 8% 5% 4 3 3 4 6% 17%	2520
	11th to 20th	Day	27% 13% 4 7% 4 4 3 4 4 5% 25%	2489
	21st to end	Day	26% 11% 4 8% 5% 4 5% 4 4 5% 24%	2719
May	1st to 10th	Day	14% 8% 2 6% 4 3 3 3 5% 6% 44%	8136
	11th to 20th	Day	18% 10% 4 9% 5% 4 5% 4 6% 8% 28%	8160
	21st to end	Day	19% 8% 2 7% 4 4 4 4 6% 7% 34%	8992
June	1st to 10th	Day	25% 8% 3 7% 5% 3 3 4 5% 5% 32%	2940
	11th to 20th	Day	21% 9% 3 8% 5% 5% 5% 3 6% 6% 29%	2940
	21st to end	Day	12% 7% 2 6% 5% 4 4 4 5% 6% 45%	2940
July	1st to 10th	Day	5% 4 1 4 3 3 3 2 4 6% 66%	8219
	11th to 20th	Day	5% 3 1 2 2 2 2 2 3 4 75%	8220
	21st to end	Day	5% 3 1 3 3 3 3 2 4 5% 68%	8922
August	1st to 10th	Day	5% 4 2 4 3 2 3 3 4 6% 66%	7703
	11th to 20th	Day	8% 5% 2 5% 4 4 4 3 5% 7% 53%	7563
	21st to end	Day	10% 6% 2 5% 3 3 4 3 5% 7% 52%	7959
September	1st to 10th	Day	10% 5% 1 5% 3 4 3 3 4 7% 55%	2520
	11th to 20th	Day	15% 8% 3 6% 4 4 3 3 4 7% 43%	2520
	21st to end	Day	19% 7% 3 6% 3 4 4 2 4 6% 44%	2216
October	1st to 10th	Day	19% 7% 2 4 2 2 2 3 4 7% 47%	3380
	11th to 20th	Day	25% 7% 2 8% 4 4 4 4 5% 7% 31%	3361
	21st to end	Day	35% 9% 3 7% 4 3 4 3 4 6% 24%	3522
November	1st to 10th	Day	39% 11% 4 7% 3 3 3 3 5% 5% 16%	1740
	11th to 20th	Day	42% 9% 3 6% 3 4 3 3 4 5% 19%	1680
	21st to end	Day	37% 12% 2 7% 3 4 3 3 3 4 22%	1680
December	1st to 10th	Day	27% 9% 3 5% 3 3 4 3 4 6% 33%	2700
	11th to 20th	Day	42% 14% 4 8% 4 3 3 2 3 4 13%	3108
	21st to end	Day	40% 16% 5% 8% 4 3 3 2 3 4 11%	4092
January	1st to 10th	Night	43% 17% 3 7% 4 3 3 2 3 3 11%	8172
	11th to 20th	Night	23% 12% 2 6% 3 3 2 2 5% 6% 37%	8220
	21st to end	Night	31% 10% 3 6% 3 3 2 2 3 5% 32%	8599
February	1st to 10th	Night	34% 13% 3 7% 5% 4 4 2 4 5% 19%	2730
	11th to 20th	Night	35% 13% 3 6% 4 4 3 2 3 4 24%	2662
	21st to end	Night	34% 14% 3 6% 3 4 3 2 4 5% 21%	2160
March	1st to 10th	Night	26% 16% 3 8% 5% 4 4 3 4 6% 21%	5316
	11th to 20th	Night	30% 14% 3 7% 4 3 2 2 3 4 27%	5110
	21st to end	Night	38% 14% 3 8% 4 4 4 3 4 5% 14%	5462
April	1st to 10th	Night	28% 16% 3 7% 6% 4 3 2 3 5% 23%	2100
	11th to 20th	Night	24% 13% 3 6% 4 4 3 4 4 6% 29%	2079
	21st to end	Night	27% 11% 2 6% 4 4 3 3 5% 6% 30%	1898
May	1st to 10th	Night	17% 7% 2 4 3 3 3 2 4 6% 48%	4783
	11th to 20th	Night	17% 10% 4 7% 4 4 4 3 5% 6% 38%	4700
	21st to end	Night	14% 7% 2 6% 3 3 4 4 6% 8% 40%	5181
June	1st to 10th	Night	21% 8% 3 6% 4 4 4 2 3 5% 39%	1680
	11th to 20th	Night	17% 8% 2 6% 4 3 4 3 4 6% 43%	1680
	21st to end	Night	12% 5% 2 5% 3 3 3 2 4 4 58%	1602
July	1st to 10th	Night	3 1 1 2 2 2 2 2 4 5% 77%	4740
	11th to 20th	Night	3 2 1 3 2 2 2 2 2 4 76%	4740
	21st to end	Night	5% 2 1 2 2 1 3 2 4 5% 73%	5153
August	1st to 10th	Night	3 3 1 3 2 2 3 2 4 6% 72%	5095
	11th to 20th	Night	10% 3 1 5% 3 3 3 3 5% 6% 57%	5292
	21st to end	Night	10% 4 1 5% 3 3 3 3 4 5% 59%	6278
September	1st to 10th	Night	9% 3 2 4 3 3 3 2 4 4 63%	2100
	11th to 20th	Night	14% 6% 2 5% 4 4 3 3 4 5% 49%	2100
	21st to end	Night	14% 6% 2 6% 3 3 4 3 5% 6% 49%	2402
October	1st to 10th	Night	15% 5% 2 4 3 3 3 2 4 6% 53%	4040
	11th to 20th	Night	22% 7% 2 5% 4 3 4 4 6% 7% 35%	4017
	21st to end	Night	34% 10% 3 6% 3 3 3 3 3 5% 26%	4460
November	1st to 10th	Night	38% 11% 3 6% 4 4 3 3 4 5% 20%	2775
	11th to 20th	Night	43% 10% 3 6% 3 3 3 2 3 4 21%	2940
	21st to end	Night	34% 10% 2 7% 4 4 3 2 4 5% 26%	2940
December	1st to 10th	Night	26% 9% 2 5% 3 3 3 2 4 7% 35%	4700
	11th to 20th	Night	43% 14% 3 8% 4 3 3 2 3 4 13%	5316
	21st to end	Night	40% 17% 4 9% 4 4 3 2 2 3 13%	7106

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	82% 5% 4 5% 4	4723
	11th to 20th	Day	49% 4 9% 14% 14% 10%	4740
	21st to end	Day	59% 4 4 12% 17% 3	5602
February	1st to 10th	Day	69% 7% 9% 9% 5%	1890
	11th to 20th	Day	72% 6% 6% 9% 4 2	1854
	21st to end	Day	70% 6% 7% 8% 7% 1	1646
March	1st to 10th	Day	61% 10% 13% 10% 5%	4797
	11th to 20th	Day	65% 6% 6% 17% 6%	5110
	21st to end	Day	73% 9% 9% 6% 3	5754
April	1st to 10th	Day	68% 8% 11% 11% 2	2520
	11th to 20th	Day	62% 8% 9% 12% 8% 2	2492
	21st to end	Day	61% 9% 9% 12% 7% 1	2719
May	1st to 10th	Day	39% 8% 12% 25% 15% 1	8136
	11th to 20th	Day	49% 14% 16% 15% 6%	8163
	21st to end	Day	46% 10% 20% 19% 5%	8994
June	1st to 10th	Day	53% 9% 14% 16% 8% 1	2940
	11th to 20th	Day	54% 9% 14% 15% 7% 1	2940
	21st to end	Day	38% 8% 16% 24% 10% 4	2940
July	1st to 10th	Day	20% 6% 12% 30% 16% 16%	8151
	11th to 20th	Day	15% 4 7% 20% 37% 18%	8145
	21st to end	Day	17% 6% 16% 34% 25% 3	8723
August	1st to 10th	Day	18% 4 8% 26% 25% 19%	6096
	11th to 20th	Day	26% 9% 16% 35% 10% 4	5962
	21st to end	Day	30% 6% 13% 28% 15% 7%	6238
September	1st to 10th	Day	30% 6% 12% 23% 18% 11%	2520
	11th to 20th	Day	42% 7% 12% 17% 14% 7%	2520
	21st to end	Day	42% 6% 13% 19% 15% 5%	2216
October	1st to 10th	Day	38% 5% 7% 24% 23% 2	3380
	11th to 20th	Day	51% 7% 13% 15% 12% 2	3361
	21st to end	Day	61% 7% 8% 16% 8% 1	3522
November	1st to 10th	Day	71% 7% 9% 10% 4	1740
	11th to 20th	Day	68% 6% 10% 9% 5% 2	1680
	21st to end	Day	66% 7% 5% 9% 11% 1	1680
December	1st to 10th	Day	53% 5% 8% 14% 18% 2	2700
	11th to 20th	Day	76% 6% 9% 7% 2	3108
	21st to end	Day	78% 7% 7% 6% 2	4092
January	1st to 10th	Night	79% 5% 6% 6% 4 1	8172
	11th to 20th	Night	48% 5% 7% 17% 15% 7%	8220
	21st to end	Night	57% 3 4 11% 19% 5%	8599
February	1st to 10th	Night	68% 8% 8% 10% 5% 1	2730
	11th to 20th	Night	66% 7% 8% 11% 6% 2	2664
	21st to end	Night	66% 7% 9% 10% 7% 1	2160
March	1st to 10th	Night	63% 8% 11% 13% 5% 1	5316
	11th to 20th	Night	61% 7% 9% 14% 8% 1	5110
	21st to end	Night	73% 8% 10% 8% 1	5462
April	1st to 10th	Night	65% 7% 11% 12% 4	2100
	11th to 20th	Night	56% 8% 12% 13% 9% 2	2079
	21st to end	Night	56% 9% 12% 14% 6% 2	1898
May	1st to 10th	Night	36% 8% 9% 29% 17% 1	4781
	11th to 20th	Night	45% 11% 20% 18% 6% 1	4700
	21st to end	Night	39% 12% 23% 22% 4	5182
June	1st to 10th	Night	49% 7% 14% 22% 7% 1	1680
	11th to 20th	Night	44% 8% 18% 23% 7%	1680
	21st to end	Night	32% 6% 17% 30% 11% 4	1602
July	1st to 10th	Night	11% 6% 14% 35% 18% 16%	4700
	11th to 20th	Night	15% 3 8% 20% 40% 14%	4692
	21st to end	Night	14% 5% 19% 34% 25% 4	5040
August	1st to 10th	Night	10% 3 8% 33% 30% 17%	4028
	11th to 20th	Night	23% 8% 22% 33% 10% 4	4169
	21st to end	Night	25% 6% 18% 30% 13% 8%	4923
September	1st to 10th	Night	24% 7% 13% 27% 19% 10%	2100
	11th to 20th	Night	37% 7% 12% 21% 13% 10%	2100
	21st to end	Night	36% 8% 15% 18% 15% 7%	2402
October	1st to 10th	Night	33% 5% 9% 28% 23% 2	4040
	11th to 20th	Night	47% 7% 13% 17% 14% 2	4017
	21st to end	Night	60% 6% 8% 15% 9% 2	4460
November	1st to 10th	Night	67% 7% 6% 13% 6% 1	2775
	11th to 20th	Night	69% 6% 8% 9% 7% 2	2940
	21st to end	Night	63% 5% 9% 9% 12% 2	2940
December	1st to 10th	Night	50% 6% 10% 14% 19% 1	4700
	11th to 20th	Night	77% 5% 7% 7% 4	5316
	21st to end	Night	77% 8% 7% 6% 2	7106

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% 14% 17% 12% 6%	220
	11th to 20th	Day	41% 11% 21% 15% 9% 2	220
	21st to end	Day	40% 13% 17% 17% 11% 2	388
February	1st to 10th	Day	44% 13% 18% 16% 7% 1	430
	11th to 20th	Day	44% 14% 24% 13% 4 1	425
	21st to end	Day	44% 13% 23% 18% 3	402
March	1st to 10th	Day	41% 14% 23% 17% 5%	540
	11th to 20th	Day	38% 17% 22% 16% 5% 2	540
	21st to end	Day	38% 19% 19% 18% 6% 1	594
April	1st to 10th	Day	36% 15% 22% 17% 7% 3	540
	11th to 20th	Day	31% 19% 23% 17% 7% 2	532
	21st to end	Day	28% 15% 26% 21% 9% 1	540
May	1st to 10th	Day	20% 16% 27% 24% 10% 2	543
	11th to 20th	Day	30% 16% 21% 19% 10% 3	568
	21st to end	Day	24% 12% 24% 23% 15% 3	617
June	1st to 10th	Day	25% 12% 22% 24% 13% 3	570
	11th to 20th	Day	20% 13% 30% 26% 8% 2	570
	21st to end	Day	11% 11% 29% 28% 18% 3	570
July	1st to 10th	Day	11% 9% 26% 38% 14% 2	566
	11th to 20th	Day	7% 7% 29% 36% 17% 4	564
	21st to end	Day	6% 6% 23% 39% 21% 5%	619
August	1st to 10th	Day	9% 6% 20% 40% 20% 6%	567
	11th to 20th	Day	7% 5% 22% 39% 22% 6%	557
	21st to end	Day	11% 11% 24% 34% 15% 5%	627
September	1st to 10th	Day	12% 7% 26% 34% 17% 4	570
	11th to 20th	Day	18% 10% 20% 31% 19% 2	570
	21st to end	Day	18% 11% 28% 29% 12% 2	570
October	1st to 10th	Day	22% 9% 23% 29% 14% 2	570
	11th to 20th	Day	27% 9% 22% 25% 15% 2	570
	21st to end	Day	35% 16% 21% 18% 8% 2	548
November	1st to 10th	Day	44% 14% 17% 17% 7% 1	269
	11th to 20th	Day	42% 15% 19% 15% 7% 1	220
	21st to end	Day	44% 12% 15% 21% 8%	220
December	1st to 10th	Day	43% 11% 18% 15% 8% 5%	220
	11th to 20th	Day	56% 10% 19% 11% 3	220
	21st to end	Day	45% 14% 20% 16% 4	242
January	1st to 10th	Night	47% 12% 16% 18% 5%	840
	11th to 20th	Night	42% 6% 19% 25% 8%	840
	21st to end	Night	38% 9% 19% 23% 9% 1	924
February	1st to 10th	Night	38% 10% 20% 24% 7% 1	840
	11th to 20th	Night	42% 9% 18% 22% 8%	824
	21st to end	Night	44% 10% 14% 24% 7%	692
March	1st to 10th	Night	38% 11% 15% 25% 10% 1	840
	11th to 20th	Night	38% 12% 19% 22% 9%	840
	21st to end	Night	41% 11% 15% 24% 9% 1	924
April	1st to 10th	Night	35% 10% 16% 25% 12% 1	840
	11th to 20th	Night	30% 9% 22% 26% 12% 1	831
	21st to end	Night	32% 8% 17% 30% 13%	638
May	1st to 10th	Night	18% 11% 21% 34% 15% 1	441
	11th to 20th	Night	20% 6% 17% 35% 20% 1	414
	21st to end	Night	20% 7% 19% 32% 22% 1	455
June	1st to 10th	Night	24% 7% 17% 35% 17%	420
	11th to 20th	Night	20% 5% 21% 38% 15%	420
	21st to end	Night	13% 5% 18% 42% 22%	420
July	1st to 10th	Night	6% 2 13% 51% 27%	410
	11th to 20th	Night	5% 3 14% 54% 23%	408
	21st to end	Night	3 3 11% 53% 30% 1	460
August	1st to 10th	Night	6% 2 10% 41% 39% 3	563
	11th to 20th	Night	6% 2 7% 42% 38% 4	624
	21st to end	Night	9% 5% 13% 44% 26% 2	842
September	1st to 10th	Night	11% 3 16% 42% 26% 2	840
	11th to 20th	Night	16% 4 14% 35% 29% 3	840
	21st to end	Night	17% 5% 17% 38% 20% 2	840
October	1st to 10th	Night	21% 5% 17% 34% 21% 2	840
	11th to 20th	Night	27% 7% 14% 32% 18% 2	840
	21st to end	Night	34% 10% 19% 27% 9% 2	912
November	1st to 10th	Night	42% 8% 18% 24% 7%	820
	11th to 20th	Night	48% 9% 16% 21% 5% 1	840
	21st to end	Night	39% 8% 19% 27% 7%	840
December	1st to 10th	Night	39% 7% 23% 21% 9% 1	840
	11th to 20th	Night	51% 8% 18% 20% 3	840
	21st to end	Night	51% 12% 18% 13% 6%	924

Page generated at 2026-10-26 01:37:50. Version ac07

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