Spokane
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Spokane clear sky chart from 2005-11-06 to 2025-08-05.

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	10% 8% 3 7% 4 4 4 4 5% 7% 45%	129247
	Night	11% 9% 3 7% 5% 4 5% 4 5% 6% 39%	127516
Transparency	Day	38% 7% 12% 22% 15% 5%	128973
	Night	43% 8% 11% 19% 14% 5%	127367
Seeing	Day	14% 10% 22% 26% 20% 8%	15710
	Night	17% 7% 18% 34% 21% 3	24827

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	19% 22% 8% 16% 7% 5% 4 3 4 3 8%	3639
	11th to 20th	Day	14% 10% 4 10% 6% 6% 6% 4 5% 7% 27%	3616
	21st to end	Day	18% 15% 5% 8% 5% 4 4 3 6% 6% 25%	4004
February	1st to 10th	Day	19% 15% 4 9% 5% 5% 6% 4 5% 7% 22%	1605
	11th to 20th	Day	14% 15% 4 11% 5% 5% 4 4 6% 7% 26%	1874
	21st to end	Day	14% 15% 4 8% 6% 5% 5% 4 6% 5% 28%	1650
March	1st to 10th	Day	8% 10% 2 7% 6% 6% 7% 6% 7% 9% 32%	4518
	11th to 20th	Day	9% 9% 2 7% 5% 5% 5% 4 7% 7% 40%	4684
	21st to end	Day	12% 12% 4 11% 7% 6% 6% 5% 6% 7% 24%	5922
April	1st to 10th	Day	13% 10% 4 8% 5% 5% 6% 5% 6% 7% 30%	2400
	11th to 20th	Day	10% 8% 3 8% 6% 5% 5% 4 7% 6% 39%	2436
	21st to end	Day	9% 7% 3 8% 5% 5% 5% 4 6% 8% 39%	2600
May	1st to 10th	Day	7% 5% 2 6% 4 4 4 4 7% 9% 48%	6205
	11th to 20th	Day	9% 7% 3 8% 5% 5% 5% 4 6% 8% 39%	6277
	21st to end	Day	7% 6% 2 6% 5% 5% 5% 4 7% 8% 46%	6903
June	1st to 10th	Day	14% 8% 2 6% 4 3 4 3 5% 8% 43%	2990
	11th to 20th	Day	12% 6% 2 5% 5% 5% 5% 4 6% 7% 44%	3000
	21st to end	Day	6% 3 2 4 4 4 4 3 5% 6% 58%	3000
July	1st to 10th	Day	4 2 1 3 2 3 3 2 3 4 73%	6323
	11th to 20th	Day	2 1 1 2 2 2 2 2 3 4 80%	6320
	21st to end	Day	3 2 1 3 2 2 2 2 3 5% 74%	6874
August	1st to 10th	Day	3 2 1 3 2 2 2 3 4 7% 70%	4458
	11th to 20th	Day	3 2 1 3 3 3 3 3 5% 7% 68%	4150
	21st to end	Day	3 2 1 4 3 3 4 3 5% 7% 65%	4252
September	1st to 10th	Day	6% 2 1 3 2 3 3 2 4 6% 68%	2280
	11th to 20th	Day	6% 4 2 5% 4 3 5% 4 5% 7% 54%	2176
	21st to end	Day	7% 4 2 6% 4 4 5% 4 7% 7% 50%	2090
October	1st to 10th	Day	8% 4 2 5% 3 4 3 3 5% 8% 56%	3351
	11th to 20th	Day	9% 5% 2 6% 4 5% 6% 4 6% 8% 44%	2975
	21st to end	Day	15% 9% 3 7% 5% 5% 5% 4 5% 6% 36%	3101
November	1st to 10th	Day	21% 10% 4 8% 4 5% 5% 3 5% 6% 29%	1764
	11th to 20th	Day	19% 13% 4 9% 6% 5% 5% 3 4 5% 27%	1700
	21st to end	Day	15% 18% 5% 12% 6% 5% 5% 3 5% 5% 20%	1474
December	1st to 10th	Day	14% 11% 6% 12% 9% 7% 6% 5% 5% 6% 18%	2290
	11th to 20th	Day	20% 21% 6% 14% 7% 6% 5% 3 4 5% 10%	2642
	21st to end	Day	19% 21% 6% 13% 6% 6% 5% 4 6% 4 11%	3704
January	1st to 10th	Night	23% 19% 5% 13% 7% 6% 4 2 4 4 12%	6306
	11th to 20th	Night	13% 10% 4 10% 6% 6% 8% 5% 6% 8% 26%	6282
	21st to end	Night	16% 15% 5% 7% 4 4 4 5% 10% 7% 22%	6952
February	1st to 10th	Night	17% 16% 4 8% 5% 4 4 3 6% 6% 27%	2795
	11th to 20th	Night	14% 13% 4 8% 6% 4 5% 3 6% 7% 30%	2412
	21st to end	Night	11% 14% 3 7% 6% 3 6% 4 5% 7% 33%	1980
March	1st to 10th	Night	8% 9% 2 7% 5% 5% 7% 5% 6% 8% 39%	5376
	11th to 20th	Night	10% 12% 3 7% 4 4 3 3 4 5% 44%	5314
	21st to end	Night	11% 9% 3 9% 7% 7% 7% 6% 8% 9% 25%	5050
April	1st to 10th	Night	10% 9% 3 8% 5% 5% 6% 5% 7% 7% 35%	2000
	11th to 20th	Night	9% 9% 3 7% 5% 4 5% 4 5% 6% 43%	1914
	21st to end	Night	9% 7% 2 7% 5% 5% 5% 5% 7% 7% 41%	1800
May	1st to 10th	Night	7% 4 2 6% 4 4 5% 4 7% 8% 48%	3743
	11th to 20th	Night	10% 7% 3 8% 5% 4 5% 4 7% 8% 40%	3616
	21st to end	Night	8% 4 2 6% 4 4 5% 4 6% 8% 49%	3972
June	1st to 10th	Night	11% 6% 2 5% 5% 4 4 4 6% 7% 46%	1405
	11th to 20th	Night	9% 5% 2 6% 4 6% 7% 5% 7% 8% 43%	1400
	21st to end	Night	6% 5% 2 4 3 4 4 3 6% 7% 56%	1400
July	1st to 10th	Night	3 2 2 2 2 2 2 4 6% 74%	3631
	11th to 20th	Night	2 2 1 2 2 2 2 2 2 4 81%	3640
	21st to end	Night	2 2 1 3 1 2 2 2 3 5% 76%	3969
August	1st to 10th	Night	3 3 1 3 2 2 2 2 4 6% 72%	2561
	11th to 20th	Night	2 3 1 4 4 4 4 3 6% 6% 63%	2683
	21st to end	Night	3 2 1 4 3 3 4 3 5% 6% 65%	3421
September	1st to 10th	Night	4 2 1 3 2 2 3 3 5% 7% 68%	1900
	11th to 20th	Night	5% 4 2 6% 5% 3 5% 3 5% 7% 54%	2004
	21st to end	Night	9% 5% 2 3 3 4 3 3 5% 8% 55%	2090
October	1st to 10th	Night	7% 3 1 4 3 3 4 3 5% 7% 60%	3614
	11th to 20th	Night	10% 4 2 5% 4 4 4 4 5% 7% 51%	3957
	21st to end	Night	13% 5% 3 7% 4 4 5% 4 6% 6% 43%	4457
November	1st to 10th	Night	19% 11% 3 7% 5% 4 4 4 6% 8% 29%	2535
	11th to 20th	Night	17% 12% 4 8% 6% 5% 6% 4 5% 5% 28%	2698
	21st to end	Night	18% 14% 3 8% 6% 5% 4 4 5% 6% 26%	2905
December	1st to 10th	Night	10% 10% 5% 9% 8% 6% 9% 5% 6% 7% 24%	4890
	11th to 20th	Night	21% 19% 6% 13% 7% 5% 5% 4 5% 4 11%	5550
	21st to end	Night	21% 17% 6% 13% 6% 6% 6% 4 4 5% 13%	7294

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	78% 9% 8% 4 1	3639
	11th to 20th	Day	53% 10% 15% 17% 4 1	3640
	21st to end	Day	58% 7% 13% 17% 5%	4004
February	1st to 10th	Day	61% 11% 13% 9% 6% 1	1605
	11th to 20th	Day	57% 11% 13% 13% 7%	1883
	21st to end	Day	56% 10% 12% 16% 6%	1650
March	1st to 10th	Day	42% 10% 14% 19% 15%	4518
	11th to 20th	Day	40% 8% 16% 29% 7%	4684
	21st to end	Day	55% 12% 16% 13% 4	5922
April	1st to 10th	Day	51% 9% 18% 17% 5%	2400
	11th to 20th	Day	42% 8% 17% 20% 11% 2	2436
	21st to end	Day	42% 10% 17% 21% 10% 2	2600
May	1st to 10th	Day	29% 8% 13% 29% 21% 1	6205
	11th to 20th	Day	37% 9% 14% 28% 11% 1	6280
	21st to end	Day	32% 10% 18% 29% 10% 1	6904
June	1st to 10th	Day	40% 7% 12% 22% 16% 2	2990
	11th to 20th	Day	37% 8% 14% 24% 14% 3	3000
	21st to end	Day	25% 6% 13% 30% 21% 5%	3000
July	1st to 10th	Day	16% 4 6% 21% 29% 24%	6254
	11th to 20th	Day	11% 3 4 21% 31% 30%	6245
	21st to end	Day	14% 3 5% 27% 32% 18%	6681
August	1st to 10th	Day	16% 3 6% 22% 38% 15%	4441
	11th to 20th	Day	16% 4 9% 39% 26% 5%	4192
	21st to end	Day	19% 5% 11% 33% 28% 4	4251
September	1st to 10th	Day	19% 5% 11% 28% 26% 11%	2280
	11th to 20th	Day	28% 8% 13% 24% 22% 5%	2176
	21st to end	Day	31% 9% 18% 26% 12% 4	2090
October	1st to 10th	Day	28% 4 14% 36% 18% 1	3351
	11th to 20th	Day	39% 6% 18% 24% 13% 1	2975
	21st to end	Day	47% 9% 16% 19% 9% 1	3101
November	1st to 10th	Day	54% 10% 16% 16% 4 1	1764
	11th to 20th	Day	60% 10% 14% 11% 4 1	1700
	21st to end	Day	65% 10% 12% 9% 3 1	1474
December	1st to 10th	Day	64% 10% 13% 10% 2	2290
	11th to 20th	Day	75% 8% 9% 7% 2	2644
	21st to end	Day	70% 12% 10% 6% 2	3704
January	1st to 10th	Night	75% 7% 9% 8% 1	6306
	11th to 20th	Night	53% 10% 14% 15% 7% 1	6320
	21st to end	Night	54% 10% 14% 17% 5%	6952
February	1st to 10th	Night	58% 9% 14% 12% 6% 1	2795
	11th to 20th	Night	53% 8% 18% 12% 8% 1	2414
	21st to end	Night	50% 8% 15% 18% 8% 1	1980
March	1st to 10th	Night	38% 10% 13% 24% 15% 1	5376
	11th to 20th	Night	42% 5% 11% 28% 13%	5315
	21st to end	Night	50% 12% 15% 19% 4	5050
April	1st to 10th	Night	43% 9% 15% 23% 10% 1	2000
	11th to 20th	Night	39% 8% 11% 24% 16% 2	1914
	21st to end	Night	40% 8% 11% 23% 16% 2	1800
May	1st to 10th	Night	29% 8% 10% 24% 27% 2	3740
	11th to 20th	Night	37% 9% 12% 24% 16% 1	3616
	21st to end	Night	28% 10% 15% 32% 14% 1	3972
June	1st to 10th	Night	35% 8% 11% 22% 20% 5%	1405
	11th to 20th	Night	35% 9% 11% 21% 18% 6%	1400
	21st to end	Night	27% 6% 10% 25% 25% 8%	1400
July	1st to 10th	Night	12% 3 4 19% 32% 30%	3591
	11th to 20th	Night	10% 2 3 15% 29% 40%	3592
	21st to end	Night	12% 2 4 21% 34% 27%	3857
August	1st to 10th	Night	15% 3 4 16% 39% 24%	2553
	11th to 20th	Night	20% 5% 6% 28% 32% 9%	2707
	21st to end	Night	19% 5% 10% 26% 30% 10%	3421
September	1st to 10th	Night	17% 4 9% 26% 29% 15%	1900
	11th to 20th	Night	28% 7% 10% 23% 23% 9%	2004
	21st to end	Night	28% 7% 14% 29% 15% 7%	2090
October	1st to 10th	Night	24% 4 9% 40% 23% 1	3614
	11th to 20th	Night	32% 7% 15% 24% 21% 1	3957
	21st to end	Night	39% 8% 12% 29% 10% 2	4457
November	1st to 10th	Night	53% 9% 17% 16% 6% 1	2535
	11th to 20th	Night	56% 9% 14% 13% 6% 2	2698
	21st to end	Night	57% 9% 16% 12% 5%	2905
December	1st to 10th	Night	56% 12% 15% 15% 2	4890
	11th to 20th	Night	74% 8% 10% 7% 1	5547
	21st to end	Night	69% 11% 10% 7% 2	7294

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	29% 14% 19% 18% 18% 4	200
	11th to 20th	Day	27% 9% 22% 18% 18% 8%	200
	21st to end	Day	27% 9% 23% 26% 12% 3	220
February	1st to 10th	Day	27% 12% 26% 24% 9% 1	205
	11th to 20th	Day	24% 16% 20% 26% 13% 1	456
	21st to end	Day	22% 13% 25% 24% 13% 3	414
March	1st to 10th	Day	17% 18% 28% 22% 12% 4	500
	11th to 20th	Day	17% 13% 22% 21% 22% 5%	500
	21st to end	Day	20% 16% 25% 25% 12% 2	550
April	1st to 10th	Day	17% 16% 25% 25% 11% 6%	500
	11th to 20th	Day	14% 17% 28% 20% 14% 7%	492
	21st to end	Day	9% 14% 24% 29% 18% 6%	500
May	1st to 10th	Day	8% 10% 26% 29% 21% 5%	503
	11th to 20th	Day	16% 8% 22% 24% 21% 9%	528
	21st to end	Day	10% 8% 20% 26% 24% 12%	573
June	1st to 10th	Day	15% 7% 21% 27% 23% 7%	720
	11th to 20th	Day	12% 12% 31% 25% 15% 5%	730
	21st to end	Day	6% 6% 22% 27% 29% 11%	730
July	1st to 10th	Day	5% 4 22% 32% 31% 7%	529
	11th to 20th	Day	3 6% 21% 36% 22% 12%	524
	21st to end	Day	3 4 18% 31% 32% 13%	575
August	1st to 10th	Day	5% 6% 17% 31% 27% 14%	504
	11th to 20th	Day	3 3 16% 29% 32% 18%	477
	21st to end	Day	6% 7% 21% 25% 25% 15%	539
September	1st to 10th	Day	7% 8% 18% 26% 27% 15%	490
	11th to 20th	Day	7% 8% 21% 28% 24% 11%	490
	21st to end	Day	11% 9% 23% 28% 21% 7%	490
October	1st to 10th	Day	13% 7% 23% 28% 21% 7%	490
	11th to 20th	Day	16% 11% 19% 22% 22% 10%	381
	21st to end	Day	25% 11% 21% 28% 11% 5%	330
November	1st to 10th	Day	25% 11% 19% 27% 16% 1	300
	11th to 20th	Day	29% 15% 17% 18% 16% 5%	250
	21st to end	Day	24% 10% 21% 24% 18% 4	200
December	1st to 10th	Day	25% 10% 18% 23% 19% 7%	200
	11th to 20th	Day	33% 10% 22% 23% 12% 2	200
	21st to end	Day	30% 9% 25% 23% 10% 3	220
January	1st to 10th	Night	32% 11% 20% 24% 11% 2	800
	11th to 20th	Night	24% 9% 20% 30% 15% 3	800
	21st to end	Night	22% 6% 18% 34% 18% 2	880
February	1st to 10th	Night	24% 9% 22% 34% 10% 2	800
	11th to 20th	Night	21% 9% 20% 32% 17% 1	784
	21st to end	Night	20% 8% 22% 32% 16% 2	660
March	1st to 10th	Night	18% 9% 20% 33% 18% 2	800
	11th to 20th	Night	19% 11% 19% 30% 20% 2	800
	21st to end	Night	18% 7% 24% 36% 13% 2	880
April	1st to 10th	Night	14% 8% 23% 35% 18% 2	800
	11th to 20th	Night	14% 8% 25% 36% 15% 2	726
	21st to end	Night	11% 8% 23% 36% 20% 2	600
May	1st to 10th	Night	7% 8% 20% 39% 22% 4	451
	11th to 20th	Night	13% 6% 13% 33% 27% 7%	394
	21st to end	Night	9% 5% 19% 33% 28% 5%	433
June	1st to 10th	Night	13% 4 17% 40% 22% 5%	400
	11th to 20th	Night	11% 6% 26% 35% 21% 3	400
	21st to end	Night	8% 3 15% 41% 30% 4	400
July	1st to 10th	Night	4 2 11% 42% 37% 4	390
	11th to 20th	Night	3 2 14% 47% 32% 2	388
	21st to end	Night	1 2 8% 43% 41% 4	438
August	1st to 10th	Night	3 1 11% 37% 41% 6%	386
	11th to 20th	Night	3 1 10% 36% 40% 10%	484
	21st to end	Night	3 3 14% 38% 38% 4	785
September	1st to 10th	Night	5% 2 13% 41% 33% 7%	760
	11th to 20th	Night	7% 4 15% 32% 34% 8%	760
	21st to end	Night	10% 6% 18% 34% 28% 5%	760
October	1st to 10th	Night	13% 4 15% 39% 27% 3	760
	11th to 20th	Night	14% 6% 17% 31% 28% 4	760
	21st to end	Night	19% 4 24% 33% 16% 4	836
November	1st to 10th	Night	25% 8% 17% 35% 15% 1	780
	11th to 20th	Night	25% 10% 23% 28% 13% 2	800
	21st to end	Night	26% 9% 15% 29% 19% 2	905
December	1st to 10th	Night	20% 8% 17% 34% 18% 2	1000
	11th to 20th	Night	29% 9% 17% 32% 13%	1000
	21st to end	Night	34% 10% 17% 29% 10% 1	1027

Page generated at 2025-08-01 22:32:22. Version ac07

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