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 2025-07-06.

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% 10% 3 6% 4 4 3 3 4 5% 34%	124200
	Night	26% 10% 3 6% 3 3 3 2 4 5% 34%	123328
Transparency	Day	51% 7% 10% 16% 12% 4	123944
	Night	53% 7% 10% 16% 11% 3	123171
Seeing	Day	27% 12% 23% 24% 12% 2	15380
	Night	31% 8% 17% 29% 14% 1	24345

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	46% 18% 3 6% 3 2 2 2 3 4 10%	3639
	11th to 20th	Day	30% 12% 3 6% 4 3 3 2 4 6% 26%	3640
	21st to end	Day	35% 9% 2 6% 3 3 3 2 3 4 31%	4325
February	1st to 10th	Day	37% 12% 3 7% 4 4 3 3 5% 5% 17%	1800
	11th to 20th	Day	37% 15% 4 7% 5% 4 3 2 2 3 18%	1755
	21st to end	Day	36% 17% 3 7% 3 3 2 3 3 5% 18%	1570
March	1st to 10th	Day	23% 16% 4 9% 5% 4 5% 3 6% 6% 19%	4693
	11th to 20th	Day	31% 16% 4 8% 3 3 3 2 2 3 26%	5000
	21st to end	Day	33% 15% 4 9% 5% 5% 4 3 5% 5% 11%	5630
April	1st to 10th	Day	33% 13% 3 8% 5% 4 3 3 4 6% 16%	2400
	11th to 20th	Day	27% 13% 4 7% 4 4 3 3 4 5% 26%	2369
	21st to end	Day	26% 11% 4 8% 5% 4 5% 3 5% 6% 23%	2590
May	1st to 10th	Day	17% 10% 3 7% 4 4 3 3 4 6% 40%	6274
	11th to 20th	Day	20% 10% 4 9% 5% 4 5% 4 6% 6% 27%	6277
	21st to end	Day	22% 9% 3 7% 4 5% 4 4 6% 7% 30%	6902
June	1st to 10th	Day	25% 8% 3 6% 5% 3 3 4 5% 5% 32%	2800
	11th to 20th	Day	22% 9% 3 8% 6% 5% 5% 4 6% 6% 27%	2800
	21st to end	Day	12% 7% 2 6% 5% 4 4 4 5% 6% 46%	2800
July	1st to 10th	Day	6% 4 1 4 2 2 2 2 4 5% 67%	4491
	11th to 20th	Day	5% 3 1 2 2 2 2 2 3 5% 72%	4420
	21st to end	Day	7% 4 1 4 3 3 3 2 4 5% 64%	4790
August	1st to 10th	Day	5% 4 2 4 3 3 2 3 4 6% 65%	4170
	11th to 20th	Day	7% 6% 2 6% 4 4 4 4 6% 7% 50%	4026
	21st to end	Day	13% 6% 2 5% 3 3 3 3 4 6% 52%	4289
September	1st to 10th	Day	10% 4 1 4 3 3 3 2 4 7% 58%	2280
	11th to 20th	Day	15% 8% 3 6% 5% 4 4 3 4 7% 42%	2280
	21st to end	Day	19% 7% 3 5% 3 4 4 2 4 5% 44%	2005
October	1st to 10th	Day	19% 7% 2 4 2 2 3 3 4 7% 47%	3180
	11th to 20th	Day	25% 7% 2 8% 4 4 4 4 5% 7% 30%	3161
	21st to end	Day	35% 9% 3 7% 4 3 3 2 5% 6% 24%	3336
November	1st to 10th	Day	38% 12% 4 8% 3 3 3 3 5% 5% 16%	1656
	11th to 20th	Day	43% 9% 2 6% 3 4 3 3 4 5% 19%	1600
	21st to end	Day	37% 12% 2 7% 3 4 3 3 3 4 22%	1600
December	1st to 10th	Day	26% 10% 2 5% 3 3 4 3 4 6% 34%	2620
	11th to 20th	Day	41% 14% 4 8% 4 3 3 2 3 4 13%	3028
	21st to end	Day	41% 16% 4 8% 4 3 3 2 3 4 11%	4004
January	1st to 10th	Night	44% 15% 3 7% 4 3 3 2 3 3 13%	6306
	11th to 20th	Night	29% 15% 3 6% 3 2 2 2 3 5% 29%	6320
	21st to end	Night	33% 10% 2 5% 3 3 2 2 3 4 33%	6644
February	1st to 10th	Night	34% 13% 3 7% 5% 4 4 2 4 5% 18%	2600
	11th to 20th	Night	35% 13% 3 5% 4 4 3 2 3 4 25%	2532
	21st to end	Night	35% 14% 3 6% 3 4 3 2 4 5% 21%	2060
March	1st to 10th	Night	25% 16% 3 8% 5% 4 4 3 4 6% 21%	5200
	11th to 20th	Night	30% 14% 3 7% 4 3 2 2 3 4 28%	5000
	21st to end	Night	39% 14% 3 8% 4 3 4 3 4 5% 13%	5344
April	1st to 10th	Night	29% 17% 4 8% 5% 4 3 2 3 5% 22%	2000
	11th to 20th	Night	24% 13% 3 6% 4 4 3 4 4 5% 31%	1979
	21st to end	Night	27% 11% 2 6% 4 4 3 3 5% 6% 28%	1808
May	1st to 10th	Night	21% 8% 2 5% 3 2 3 2 4 5% 45%	3686
	11th to 20th	Night	17% 10% 3 6% 4 3 3 3 4 5% 40%	3616
	21st to end	Night	16% 8% 3 7% 3 4 5% 4 6% 8% 36%	3972
June	1st to 10th	Night	22% 8% 3 6% 4 4 4 2 3 5% 40%	1600
	11th to 20th	Night	18% 8% 2 6% 4 3 4 3 4 6% 41%	1600
	21st to end	Night	11% 5% 2 5% 3 3 3 2 4 4 59%	1526
July	1st to 10th	Night	4 1 1 2 2 2 2 1 3 4 79%	2580
	11th to 20th	Night	4 3 1 3 2 2 2 2 2 4 77%	2540
	21st to end	Night	5% 1 1 1 2 1 2 1 3 5% 78%	2761
August	1st to 10th	Night	2 2 1 3 1 2 2 2 4 5% 76%	2751
	11th to 20th	Night	8% 4 1 5% 3 3 4 3 5% 7% 57%	2812
	21st to end	Night	13% 4 1 4 3 2 2 2 3 4 60%	3385
September	1st to 10th	Night	9% 3 1 4 3 2 3 2 4 4 66%	1900
	11th to 20th	Night	15% 6% 2 5% 4 4 3 3 4 5% 48%	1900
	21st to end	Night	14% 6% 2 6% 3 3 4 3 4 6% 49%	2173
October	1st to 10th	Night	16% 5% 2 4 2 3 3 2 4 7% 53%	3800
	11th to 20th	Night	23% 7% 3 5% 4 3 4 4 5% 7% 35%	3777
	21st to end	Night	35% 10% 3 6% 3 3 3 3 3 5% 26%	4228
November	1st to 10th	Night	38% 11% 3 5% 4 4 3 3 3 5% 21%	2640
	11th to 20th	Night	43% 10% 3 6% 3 3 3 3 3 4 21%	2800
	21st to end	Night	33% 10% 2 7% 4 4 3 2 4 5% 27%	2800
December	1st to 10th	Night	26% 9% 2 5% 3 3 3 2 4 7% 36%	4560
	11th to 20th	Night	42% 14% 3 8% 4 3 3 2 3 4 13%	5176
	21st to end	Night	40% 17% 4 9% 4 4 3 2 2 3 12%	6952

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% 5% 5% 6% 5%	3639
	11th to 20th	Day	60% 5% 8% 16% 9% 1	3640
	21st to end	Day	59% 5% 5% 13% 15% 4	4325
February	1st to 10th	Day	70% 8% 9% 9% 5%	1800
	11th to 20th	Day	73% 6% 6% 9% 4 2	1764
	21st to end	Day	71% 6% 8% 8% 7% 1	1570
March	1st to 10th	Day	61% 10% 13% 11% 5%	4693
	11th to 20th	Day	65% 6% 6% 18% 6%	5000
	21st to end	Day	73% 9% 9% 6% 2	5630
April	1st to 10th	Day	70% 8% 11% 10% 2	2400
	11th to 20th	Day	62% 7% 9% 12% 8% 2	2372
	21st to end	Day	62% 9% 9% 12% 7% 1	2590
May	1st to 10th	Day	44% 8% 10% 21% 16% 1	6274
	11th to 20th	Day	51% 15% 15% 14% 5% 1	6280
	21st to end	Day	51% 11% 19% 15% 4	6904
June	1st to 10th	Day	53% 9% 14% 16% 7%	2800
	11th to 20th	Day	57% 10% 14% 14% 5%	2800
	21st to end	Day	37% 8% 16% 25% 10% 4	2800
July	1st to 10th	Day	20% 5% 9% 17% 20% 28%	4422
	11th to 20th	Day	16% 5% 7% 19% 37% 17%	4345
	21st to end	Day	20% 6% 11% 26% 32% 4	4639
August	1st to 10th	Day	21% 5% 9% 26% 28% 12%	4154
	11th to 20th	Day	31% 10% 15% 28% 11% 5%	4065
	21st to end	Day	34% 6% 11% 22% 16% 10%	4288
September	1st to 10th	Day	27% 6% 12% 23% 19% 12%	2280
	11th to 20th	Day	43% 7% 13% 16% 14% 8%	2280
	21st to end	Day	42% 6% 13% 19% 14% 6%	2005
October	1st to 10th	Day	39% 5% 7% 24% 24% 2	3180
	11th to 20th	Day	53% 7% 13% 15% 11% 1	3161
	21st to end	Day	60% 7% 8% 16% 9% 1	3336
November	1st to 10th	Day	71% 7% 8% 10% 4	1656
	11th to 20th	Day	68% 6% 10% 9% 5% 2	1600
	21st to end	Day	67% 7% 5% 9% 12% 2	1600
December	1st to 10th	Day	52% 5% 8% 14% 19% 2	2620
	11th to 20th	Day	76% 6% 9% 7% 2	3028
	21st to end	Day	78% 7% 7% 6% 2	4004
January	1st to 10th	Night	77% 5% 6% 7% 5% 1	6306
	11th to 20th	Night	58% 6% 7% 18% 9% 2	6320
	21st to end	Night	57% 4 5% 13% 15% 6%	6644
February	1st to 10th	Night	69% 8% 8% 10% 5% 1	2600
	11th to 20th	Night	66% 7% 9% 11% 6% 2	2534
	21st to end	Night	66% 7% 9% 9% 7% 1	2060
March	1st to 10th	Night	62% 8% 11% 13% 5% 1	5200
	11th to 20th	Night	61% 7% 9% 14% 8% 1	5000
	21st to end	Night	73% 7% 10% 8% 1	5344
April	1st to 10th	Night	67% 8% 10% 11% 4	2000
	11th to 20th	Night	55% 8% 12% 13% 9% 2	1979
	21st to end	Night	57% 9% 12% 13% 5% 3	1808
May	1st to 10th	Night	40% 8% 9% 25% 17% 1	3683
	11th to 20th	Night	43% 11% 20% 20% 5% 1	3616
	21st to end	Night	43% 14% 24% 15% 5%	3972
June	1st to 10th	Night	48% 7% 15% 23% 7% 1	1600
	11th to 20th	Night	46% 8% 19% 22% 6%	1600
	21st to end	Night	31% 6% 18% 31% 10% 4	1526
July	1st to 10th	Night	13% 5% 9% 24% 23% 27%	2540
	11th to 20th	Night	15% 3 7% 21% 34% 20%	2492
	21st to end	Night	11% 4 13% 29% 36% 7%	2674
August	1st to 10th	Night	14% 4 11% 32% 30% 9%	2743
	11th to 20th	Night	26% 9% 23% 27% 10% 5%	2839
	21st to end	Night	28% 6% 15% 25% 16% 11%	3385
September	1st to 10th	Night	23% 6% 13% 28% 20% 11%	1900
	11th to 20th	Night	38% 7% 12% 21% 10% 11%	1900
	21st to end	Night	37% 8% 16% 17% 15% 8%	2173
October	1st to 10th	Night	33% 5% 9% 28% 22% 2	3800
	11th to 20th	Night	47% 7% 13% 17% 13% 2	3777
	21st to end	Night	61% 6% 8% 15% 9% 2	4228
November	1st to 10th	Night	67% 7% 6% 14% 6% 1	2640
	11th to 20th	Night	69% 6% 8% 9% 7% 2	2800
	21st to end	Night	62% 5% 9% 9% 13% 2	2800
December	1st to 10th	Night	49% 6% 10% 14% 20% 1	4560
	11th to 20th	Night	77% 5% 7% 7% 4	5176
	21st to end	Night	77% 8% 7% 5% 2	6952

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% 17% 13% 6% 1	200
	11th to 20th	Day	45% 12% 21% 13% 9% 2	200
	21st to end	Day	41% 13% 17% 16% 11% 2	359
February	1st to 10th	Day	45% 13% 18% 17% 7% 1	400
	11th to 20th	Day	46% 13% 23% 13% 5% 1	395
	21st to end	Day	44% 13% 22% 17% 3	374
March	1st to 10th	Day	40% 13% 23% 18% 5%	500
	11th to 20th	Day	35% 17% 24% 16% 6% 2	500
	21st to end	Day	40% 19% 17% 18% 6% 1	550
April	1st to 10th	Day	38% 15% 23% 15% 7% 2	500
	11th to 20th	Day	30% 21% 23% 17% 7% 2	492
	21st to end	Day	29% 15% 26% 21% 9% 1	500
May	1st to 10th	Day	21% 17% 27% 23% 9% 2	503
	11th to 20th	Day	31% 16% 21% 20% 9% 3	528
	21st to end	Day	25% 12% 25% 21% 14% 3	573
June	1st to 10th	Day	26% 12% 21% 25% 14% 3	530
	11th to 20th	Day	22% 14% 31% 25% 7% 2	530
	21st to end	Day	11% 10% 29% 28% 19% 3	530
July	1st to 10th	Day	11% 10% 24% 38% 15% 2	507
	11th to 20th	Day	7% 7% 28% 36% 18% 4	484
	21st to end	Day	6% 6% 22% 40% 20% 5%	531
August	1st to 10th	Day	8% 6% 20% 40% 20% 6%	487
	11th to 20th	Day	7% 5% 22% 39% 23% 5%	477
	21st to end	Day	11% 11% 25% 33% 15% 4	539
September	1st to 10th	Day	12% 6% 27% 34% 18% 3	490
	11th to 20th	Day	19% 10% 19% 31% 20% 2	490
	21st to end	Day	19% 11% 28% 29% 12% 2	490
October	1st to 10th	Day	24% 10% 22% 27% 15% 2	490
	11th to 20th	Day	29% 9% 21% 24% 14% 2	490
	21st to end	Day	35% 16% 21% 17% 8% 2	476
November	1st to 10th	Day	43% 15% 16% 17% 8% 1	245
	11th to 20th	Day	43% 16% 18% 15% 8% 2	200
	21st to end	Day	43% 12% 16% 21% 9% 1	200
December	1st to 10th	Day	41% 12% 19% 15% 9% 6%	200
	11th to 20th	Day	53% 12% 21% 12% 3	200
	21st to end	Day	47% 14% 21% 15% 3	220
January	1st to 10th	Night	47% 12% 17% 18% 6%	800
	11th to 20th	Night	44% 7% 18% 24% 8%	800
	21st to end	Night	39% 9% 19% 23% 9% 1	880
February	1st to 10th	Night	39% 10% 20% 23% 7% 1	800
	11th to 20th	Night	43% 9% 18% 22% 8% 1	784
	21st to end	Night	44% 11% 15% 23% 7%	660
March	1st to 10th	Night	38% 11% 16% 25% 10% 1	800
	11th to 20th	Night	37% 12% 19% 23% 9%	800
	21st to end	Night	42% 11% 14% 23% 9% 1	880
April	1st to 10th	Night	37% 11% 16% 24% 12% 1	800
	11th to 20th	Night	29% 9% 23% 25% 13% 1	791
	21st to end	Night	32% 8% 17% 30% 13%	608
May	1st to 10th	Night	19% 11% 22% 33% 14% 1	420
	11th to 20th	Night	21% 6% 17% 34% 21% 2	394
	21st to end	Night	21% 7% 18% 30% 23% 1	433
June	1st to 10th	Night	24% 7% 17% 35% 18% 1	400
	11th to 20th	Night	22% 6% 21% 36% 16%	400
	21st to end	Night	12% 4 18% 43% 22%	400
July	1st to 10th	Night	7% 2 13% 50% 27% 1	380
	11th to 20th	Night	5% 4 13% 54% 24% 1	368
	21st to end	Night	3 2 11% 54% 29% 1	416
August	1st to 10th	Night	6% 2 9% 41% 39% 4	509
	11th to 20th	Night	6% 2 8% 40% 40% 4	564
	21st to end	Night	9% 5% 13% 45% 25% 2	762
September	1st to 10th	Night	11% 3 15% 43% 25% 2	760
	11th to 20th	Night	17% 4 13% 34% 30% 3	760
	21st to end	Night	17% 5% 18% 38% 20% 2	760
October	1st to 10th	Night	22% 5% 18% 33% 19% 3	760
	11th to 20th	Night	28% 7% 13% 31% 18% 3	760
	21st to end	Night	34% 10% 18% 26% 10% 2	836
November	1st to 10th	Night	41% 8% 18% 25% 8%	780
	11th to 20th	Night	49% 9% 16% 21% 5% 1	800
	21st to end	Night	38% 8% 20% 27% 7%	800
December	1st to 10th	Night	38% 8% 23% 21% 9% 1	800
	11th to 20th	Night	51% 8% 18% 20% 4	800
	21st to end	Night	52% 12% 18% 13% 5%	880

Page generated at 2025-07-02 22:30:15. Version ac07

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