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 2024-11-03.

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% 10% 3 6% 4 3 3 3 4 5% 35%	101571
	Night	26% 10% 2 6% 3 3 3 2 4 5% 35%	97504
Transparency	Day	51% 8% 10% 15% 12% 4	101314
	Night	52% 7% 11% 16% 10% 4	97350
Seeing	Day	27% 12% 23% 24% 12% 2	14594
	Night	31% 8% 17% 29% 14% 1	23506

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% 20% 4 7% 3 2 3 2 3 4 8%	2539
	11th to 20th	Day	42% 12% 3 6% 4 3 2 2 3 3 19%	2540
	21st to end	Day	46% 13% 3 7% 3 3 3 2 3 3 13%	3017
February	1st to 10th	Day	39% 11% 3 6% 4 4 3 3 4 5% 18%	1710
	11th to 20th	Day	36% 15% 4 7% 5% 4 4 2 3 3 18%	1665
	21st to end	Day	36% 17% 3 7% 3 3 2 3 3 4 18%	1494
March	1st to 10th	Day	27% 19% 4 9% 5% 4 4 2 4 5% 17%	3261
	11th to 20th	Day	26% 12% 3 7% 3 3 2 2 2 4 36%	3490
	21st to end	Day	31% 17% 4 9% 5% 4 4 3 4 4 15%	3930
April	1st to 10th	Day	34% 14% 4 8% 5% 3 3 3 4 5% 16%	2280
	11th to 20th	Day	28% 14% 4 7% 4 4 3 3 4 4 24%	2249
	21st to end	Day	27% 11% 4 8% 5% 5% 5% 3 5% 6% 22%	2460
May	1st to 10th	Day	23% 11% 3 8% 4 3 3 3 4 5% 33%	4387
	11th to 20th	Day	14% 9% 3 6% 4 4 5% 4 6% 7% 38%	4377
	21st to end	Day	28% 10% 3 8% 5% 5% 5% 4 5% 5% 22%	4813
June	1st to 10th	Day	27% 9% 3 7% 5% 3 3 4 5% 5% 30%	2660
	11th to 20th	Day	23% 10% 3 8% 6% 5% 5% 4 6% 6% 26%	2660
	21st to end	Day	12% 7% 2 6% 5% 4 4 4 5% 6% 47%	2660
July	1st to 10th	Day	6% 4 1 4 2 2 2 2 4 5% 67%	4420
	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	24% 8% 2 5% 3 3 3 4 5% 5% 38%	1900
	11th to 20th	Day	27% 6% 2 6% 4 3 3 3 5% 7% 33%	1900
	21st to end	Day	35% 8% 2 6% 3 3 3 2 3 4 30%	2027
November	1st to 10th	Day	39% 11% 4 8% 4 3 3 3 5% 5% 16%	1590
	11th to 20th	Day	42% 9% 2 5% 3 4 3 3 4 5% 20%	1520
	21st to end	Day	38% 12% 2 7% 3 3 3 3 3 4 23%	1520
December	1st to 10th	Day	33% 13% 4 7% 4 3 3 2 3 4 24%	1520
	11th to 20th	Day	39% 12% 3 7% 3 3 3 3 4 5% 18%	1928
	21st to end	Day	37% 15% 4 8% 5% 3 4 3 3 5% 13%	2794
January	1st to 10th	Night	43% 17% 3 7% 4 3 3 2 3 3 11%	4406
	11th to 20th	Night	39% 16% 3 7% 3 3 2 2 3 4 18%	4420
	21st to end	Night	44% 14% 3 6% 3 3 3 2 4 3 15%	4645
February	1st to 10th	Night	35% 13% 3 6% 5% 3 3 2 4 5% 19%	2470
	11th to 20th	Night	35% 13% 3 5% 4 4 3 2 3 4 25%	2402
	21st to end	Night	34% 15% 4 7% 3 4 3 2 5% 4 20%	1960
March	1st to 10th	Night	27% 18% 3 8% 4 4 3 3 4 5% 20%	3612
	11th to 20th	Night	24% 11% 2 5% 3 3 2 2 3 5% 39%	3490
	21st to end	Night	35% 17% 3 8% 4 4 4 2 3 4 15%	3722
April	1st to 10th	Night	29% 17% 4 7% 5% 3 3 2 3 5% 22%	1900
	11th to 20th	Night	25% 13% 3 6% 4 4 3 4 4 6% 29%	1879
	21st to end	Night	29% 11% 2 6% 4 4 3 3 5% 6% 27%	1718
May	1st to 10th	Night	27% 11% 3 6% 3 3 2 2 3 3 38%	2572
	11th to 20th	Night	12% 6% 2 4 3 3 3 3 5% 5% 53%	2516
	21st to end	Night	18% 9% 3 8% 4 4 5% 4 6% 6% 33%	2762
June	1st to 10th	Night	22% 8% 3 6% 4 4 4 2 3 5% 38%	1520
	11th to 20th	Night	19% 9% 2 6% 4 3 4 3 4 6% 40%	1520
	21st to end	Night	10% 5% 2 5% 3 3 3 2 4 4 59%	1450
July	1st to 10th	Night	4 1 1 2 2 2 2 1 3 3 80%	2540
	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	21% 6% 2 5% 3 3 3 2 3 5% 47%	2280
	11th to 20th	Night	24% 8% 3 5% 3 3 4 2 4 6% 37%	2280
	21st to end	Night	32% 8% 2 5% 3 3 3 2 3 5% 35%	2570
November	1st to 10th	Night	38% 11% 2 5% 4 4 3 3 4 5% 21%	2530
	11th to 20th	Night	41% 9% 3 6% 3 3 3 3 3 4 22%	2660
	21st to end	Night	34% 10% 2 6% 4 4 3 2 4 5% 27%	2660
December	1st to 10th	Night	34% 11% 2 5% 4 4 3 2 4 5% 24%	2660
	11th to 20th	Night	36% 13% 3 7% 3 3 3 2 4 5% 20%	3276
	21st to end	Night	36% 16% 3 9% 4 4 3 2 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	65% 11% 11% 9% 4	3261
	11th to 20th	Day	54% 6% 7% 24% 9%	3490
	21st to end	Day	72% 9% 9% 7% 3	3930
April	1st to 10th	Day	70% 8% 11% 9% 3	2280
	11th to 20th	Day	64% 8% 9% 10% 8% 2	2252
	21st to end	Day	63% 9% 9% 11% 7% 1	2460
May	1st to 10th	Day	52% 9% 12% 15% 12%	4387
	11th to 20th	Day	38% 16% 19% 19% 8% 1	4380
	21st to end	Day	62% 12% 14% 11% 1	4814
June	1st to 10th	Day	55% 9% 14% 15% 7%	2660
	11th to 20th	Day	58% 10% 15% 12% 5%	2660
	21st to end	Day	37% 8% 16% 25% 10% 4	2660
July	1st to 10th	Day	20% 5% 9% 17% 20% 29%	4351
	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	49% 6% 8% 19% 15% 3	1900
	11th to 20th	Day	52% 6% 13% 15% 12% 2	1900
	21st to end	Day	59% 5% 8% 13% 13% 1	2027
November	1st to 10th	Day	71% 7% 8% 9% 4 1	1590
	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	64% 10% 11% 13% 3	3612
	11th to 20th	Night	48% 8% 12% 20% 12% 1	3490
	21st to end	Night	74% 8% 8% 9% 2	3722
April	1st to 10th	Night	67% 7% 10% 11% 5%	1900
	11th to 20th	Night	57% 9% 12% 12% 8% 3	1879
	21st to end	Night	59% 9% 12% 12% 5% 3	1718
May	1st to 10th	Night	50% 10% 10% 20% 9% 1	2572
	11th to 20th	Night	31% 11% 22% 27% 7% 2	2516
	21st to end	Night	48% 16% 22% 10% 3	2762
June	1st to 10th	Night	50% 7% 15% 21% 6% 1	1520
	11th to 20th	Night	47% 8% 19% 20% 5%	1520
	21st to end	Night	30% 6% 18% 31% 10% 5%	1450
July	1st to 10th	Night	13% 5% 8% 24% 23% 28%	2500
	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	41% 6% 9% 22% 18% 3	2280
	11th to 20th	Night	48% 7% 9% 16% 16% 3	2280
	21st to end	Night	54% 5% 9% 14% 14% 3	2570
November	1st to 10th	Night	67% 7% 6% 14% 6% 1	2530
	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	34% 16% 24% 17% 6% 2	460
	21st to end	Day	39% 19% 17% 18% 6% 1	506
April	1st to 10th	Day	38% 16% 22% 15% 6% 2	460
	11th to 20th	Day	32% 21% 22% 15% 7% 2	452
	21st to end	Day	31% 16% 27% 18% 8%	460
May	1st to 10th	Day	22% 17% 26% 23% 9% 2	463
	11th to 20th	Day	30% 16% 21% 20% 10% 3	488
	21st to end	Day	26% 13% 24% 20% 14% 3	529
June	1st to 10th	Day	27% 11% 20% 25% 13% 3	490
	11th to 20th	Day	23% 14% 29% 25% 7% 2	490
	21st to end	Day	11% 10% 30% 28% 19% 3	490
July	1st to 10th	Day	12% 10% 24% 38% 15% 2	486
	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	44% 15% 17% 16% 6% 1	227
	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% 23% 9%	760
	21st to end	Night	42% 12% 14% 23% 9% 1	836
April	1st to 10th	Night	37% 11% 17% 23% 12% 1	760
	11th to 20th	Night	31% 9% 22% 25% 13% 1	751
	21st to end	Night	33% 9% 17% 29% 12%	578
May	1st to 10th	Night	20% 11% 23% 31% 15% 1	399
	11th to 20th	Night	21% 5% 16% 35% 22% 2	374
	21st to end	Night	21% 7% 18% 30% 23% 1	411
June	1st to 10th	Night	25% 7% 16% 35% 17%	380
	11th to 20th	Night	23% 6% 19% 36% 16%	380
	21st to end	Night	12% 4 19% 44% 21%	380
July	1st to 10th	Night	7% 2 12% 51% 27% 1	370
	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% 24% 8%	748
	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

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