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 2024-03-23.

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	12% 8% 3 6% 5% 3 5% 5% 5% 6% 41%	78349
	Night	14% 10% 4 7% 6% 3 5% 5% 5% 7% 37%	81485
Transparency	Day	43% 8% 13% 19% 13% 4	78075
	Night	46% 8% 13% 17% 12% 4	81339
Seeing	Day	14% 10% 22% 26% 20% 8%	13858
	Night	17% 7% 18% 34% 21% 3	23230

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% 20% 6% 11% 8% 4 6% 5% 5% 5% 11%	2539
	11th to 20th	Day	20% 13% 6% 9% 8% 5% 5% 4 4 5% 21%	2516
	21st to end	Day	23% 20% 7% 10% 8% 3 3 4 4 5% 13%	2794
February	1st to 10th	Day	20% 14% 4 8% 6% 4 6% 5% 5% 7% 21%	1524
	11th to 20th	Day	14% 14% 4 9% 6% 4 5% 5% 6% 7% 27%	1777
	21st to end	Day	14% 14% 5% 8% 6% 4 5% 5% 7% 5% 28%	1570
March	1st to 10th	Day	15% 12% 4 6% 8% 4 5% 6% 6% 8% 26%	1900
	11th to 20th	Day	14% 10% 4 7% 7% 3 5% 6% 6% 7% 31%	1949
	21st to end	Day	16% 13% 4 9% 7% 4 5% 5% 5% 7% 25%	2379
April	1st to 10th	Day	14% 9% 5% 7% 7% 4 7% 6% 7% 7% 29%	2160
	11th to 20th	Day	11% 8% 3 7% 6% 4 6% 5% 7% 6% 37%	2188
	21st to end	Day	10% 7% 3 6% 6% 4 5% 5% 6% 8% 39%	2340
May	1st to 10th	Day	7% 5% 3 5% 6% 3 5% 5% 6% 8% 47%	2470
	11th to 20th	Day	11% 6% 3 5% 5% 4 6% 6% 6% 7% 41%	2477
	21st to end	Day	11% 7% 2 5% 6% 4 6% 5% 6% 7% 40%	2723
June	1st to 10th	Day	15% 7% 2 5% 5% 3 4 4 5% 8% 42%	2690
	11th to 20th	Day	13% 5% 3 5% 5% 3 6% 4 5% 7% 43%	2700
	21st to end	Day	6% 3 2 3 4 2 4 4 5% 7% 59%	2700
July	1st to 10th	Day	4 2 1 3 4 3 2 4 4 5% 68%	2523
	11th to 20th	Day	3 2 1 2 2 2 3 3 4 6% 72%	2520
	21st to end	Day	1 1 1 1 2 1 2 2 3 4 82%	2741
August	1st to 10th	Day	3 2 1 2 3 2 3 3 4 6% 71%	2507
	11th to 20th	Day	4 2 1 2 3 2 2 3 4 7% 71%	2373
	21st to end	Day	4 3 1 4 5% 3 4 4 5% 7% 61%	2422
September	1st to 10th	Day	6% 2 1 3 2 2 3 3 4 6% 68%	2160
	11th to 20th	Day	6% 4 2 4 4 2 5% 5% 5% 8% 55%	2062
	21st to end	Day	7% 4 2 5% 5% 3 5% 5% 6% 7% 50%	1980
October	1st to 10th	Day	12% 5% 3 6% 5% 3 5% 4 4 7% 46%	1906
	11th to 20th	Day	13% 5% 3 5% 4 3 5% 5% 5% 7% 45%	1697
	21st to end	Day	17% 9% 3 6% 5% 3 5% 6% 4 6% 36%	1782
November	1st to 10th	Day	21% 9% 4 7% 5% 4 5% 4 5% 7% 29%	1674
	11th to 20th	Day	18% 12% 5% 8% 7% 4 5% 4 4 5% 27%	1615
	21st to end	Day	16% 16% 6% 10% 7% 4 6% 4 5% 5% 21%	1401
December	1st to 10th	Day	17% 14% 7% 10% 8% 4 5% 5% 5% 7% 19%	1330
	11th to 20th	Day	22% 19% 6% 13% 10% 4 5% 4 3 4 9%	1682
	21st to end	Day	16% 19% 5% 11% 7% 5% 6% 5% 6% 5% 15%	2578
January	1st to 10th	Night	22% 19% 5% 10% 8% 4 5% 3 4 5% 15%	4406
	11th to 20th	Night	19% 13% 5% 10% 7% 3 4 5% 5% 7% 23%	4382
	21st to end	Night	23% 17% 7% 9% 6% 3 4 5% 5% 5% 17%	4862
February	1st to 10th	Night	17% 15% 4 7% 6% 3 4 4 5% 6% 27%	2656
	11th to 20th	Night	14% 12% 5% 7% 7% 3 5% 5% 5% 6% 31%	2289
	21st to end	Night	12% 13% 3 6% 7% 3 5% 6% 5% 7% 33%	1884
March	1st to 10th	Night	15% 10% 4 6% 6% 5% 6% 6% 5% 6% 33%	2280
	11th to 20th	Night	13% 10% 3 6% 5% 3 4 5% 5% 7% 36%	2229
	21st to end	Night	14% 9% 4 7% 7% 4 6% 7% 6% 8% 28%	2019
April	1st to 10th	Night	10% 8% 3 7% 6% 3 6% 6% 7% 8% 36%	1800
	11th to 20th	Night	10% 8% 4 7% 6% 3 5% 5% 5% 6% 41%	1722
	21st to end	Night	9% 7% 3 6% 6% 3 6% 6% 7% 7% 40%	1620
May	1st to 10th	Night	7% 4 2 5% 6% 3 6% 5% 7% 9% 46%	1487
	11th to 20th	Night	10% 5% 2 6% 5% 3 5% 4 7% 10% 44%	1416
	21st to end	Night	9% 5% 3 5% 7% 3 6% 5% 7% 8% 42%	1552
June	1st to 10th	Night	11% 6% 2 5% 6% 3 5% 5% 5% 7% 45%	1265
	11th to 20th	Night	10% 5% 2 5% 4 4 7% 6% 7% 8% 42%	1260
	21st to end	Night	6% 4 2 3 4 3 4 5% 6% 7% 56%	1260
July	1st to 10th	Night	2 2 1 2 3 3 3 4 4 8% 69%	1431
	11th to 20th	Night	3 1 1 2 2 2 3 3 3 6% 73%	1440
	21st to end	Night	1 1 2 2 2 2 2 3 4 80%	1576
August	1st to 10th	Night	3 2 1 2 2 1 2 2 4 7% 73%	1432
	11th to 20th	Night	3 2 1 2 2 2 3 3 5% 6% 71%	1526
	21st to end	Night	3 2 1 3 3 2 3 4 5% 7% 66%	1931
September	1st to 10th	Night	4 2 1 3 3 2 3 4 4 6% 68%	1800
	11th to 20th	Night	6% 4 1 5% 5% 2 5% 4 5% 7% 56%	1898
	21st to end	Night	10% 5% 2 3 4 3 3 4 5% 8% 54%	1980
October	1st to 10th	Night	12% 5% 2 6% 5% 3 4 4 4 6% 50%	2052
	11th to 20th	Night	11% 5% 2 5% 5% 3 4 5% 5% 7% 48%	2263
	21st to end	Night	15% 6% 3 6% 5% 3 5% 4 5% 7% 43%	2574
November	1st to 10th	Night	20% 10% 4 7% 5% 3 4 5% 5% 8% 29%	2405
	11th to 20th	Night	18% 11% 5% 7% 6% 4 6% 6% 5% 6% 28%	2563
	21st to end	Night	18% 12% 4 6% 7% 4 5% 5% 5% 6% 27%	2759
December	1st to 10th	Night	16% 13% 6% 8% 5% 3 5% 5% 6% 8% 24%	2850
	11th to 20th	Night	20% 17% 5% 12% 8% 4 5% 5% 5% 5% 14%	3510
	21st to end	Night	18% 14% 6% 10% 9% 5% 7% 6% 5% 6% 15%	5106

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	71% 11% 11% 6% 1	2539
	11th to 20th	Day	63% 8% 12% 13% 2 2	2540
	21st to end	Day	73% 8% 11% 7% 1 1	2794
February	1st to 10th	Day	61% 11% 13% 9% 5% 1	1524
	11th to 20th	Day	56% 11% 13% 13% 7%	1786
	21st to end	Day	56% 10% 11% 16% 6%	1570
March	1st to 10th	Day	54% 10% 16% 14% 6% 1	1900
	11th to 20th	Day	50% 9% 15% 19% 6%	1949
	21st to end	Day	59% 10% 17% 11% 3	2379
April	1st to 10th	Day	52% 9% 17% 16% 5%	2160
	11th to 20th	Day	45% 9% 17% 18% 10% 1	2188
	21st to end	Day	43% 9% 17% 20% 9% 2	2340
May	1st to 10th	Day	33% 8% 19% 27% 12% 1	2470
	11th to 20th	Day	40% 10% 16% 24% 11%	2480
	21st to end	Day	41% 9% 17% 23% 8% 1	2724
June	1st to 10th	Day	42% 7% 13% 23% 13% 2	2690
	11th to 20th	Day	38% 9% 15% 24% 11% 3	2700
	21st to end	Day	25% 6% 14% 30% 21% 5%	2700
July	1st to 10th	Day	20% 5% 10% 26% 26% 14%	2454
	11th to 20th	Day	16% 4 9% 21% 35% 16%	2445
	21st to end	Day	9% 3 5% 20% 45% 17%	2589
August	1st to 10th	Day	16% 4 8% 24% 33% 15%	2490
	11th to 20th	Day	14% 5% 11% 27% 34% 9%	2373
	21st to end	Day	22% 5% 10% 28% 29% 5%	2422
September	1st to 10th	Day	19% 5% 12% 28% 26% 10%	2160
	11th to 20th	Day	27% 8% 13% 24% 23% 5%	2062
	21st to end	Day	32% 10% 18% 25% 12% 4	1980
October	1st to 10th	Day	38% 6% 14% 28% 12% 1	1906
	11th to 20th	Day	40% 7% 16% 28% 9% 1	1697
	21st to end	Day	48% 9% 16% 19% 8%	1782
November	1st to 10th	Day	54% 10% 15% 16% 4 1	1674
	11th to 20th	Day	60% 9% 14% 12% 4 2	1615
	21st to end	Day	63% 11% 12% 10% 3 1	1401
December	1st to 10th	Day	65% 9% 13% 10% 3	1330
	11th to 20th	Day	76% 9% 9% 5% 1	1684
	21st to end	Day	63% 13% 13% 7% 3	2578
January	1st to 10th	Night	71% 8% 10% 9% 1 1	4406
	11th to 20th	Night	59% 8% 14% 13% 5% 2	4420
	21st to end	Night	66% 11% 13% 8% 2 1	4862
February	1st to 10th	Night	58% 9% 14% 12% 5% 1	2656
	11th to 20th	Night	53% 9% 18% 12% 8%	2291
	21st to end	Night	50% 8% 15% 17% 8% 1	1884
March	1st to 10th	Night	50% 9% 14% 18% 8% 1	2280
	11th to 20th	Night	47% 7% 14% 21% 10%	2230
	21st to end	Night	52% 9% 14% 18% 6% 1	2019
April	1st to 10th	Night	43% 8% 15% 23% 10% 1	1800
	11th to 20th	Night	42% 8% 11% 23% 15% 2	1722
	21st to end	Night	41% 8% 12% 22% 14% 2	1620
May	1st to 10th	Night	32% 8% 15% 29% 15% 2	1487
	11th to 20th	Night	36% 8% 13% 25% 16% 2	1416
	21st to end	Night	36% 9% 17% 28% 11%	1552
June	1st to 10th	Night	37% 8% 11% 22% 19% 3	1265
	11th to 20th	Night	37% 9% 12% 23% 15% 5%	1260
	21st to end	Night	26% 7% 10% 25% 25% 8%	1260
July	1st to 10th	Night	16% 3 8% 20% 33% 20%	1391
	11th to 20th	Night	14% 4 6% 19% 31% 26%	1392
	21st to end	Night	9% 2 5% 15% 36% 33%	1488
August	1st to 10th	Night	14% 3 7% 14% 38% 24%	1424
	11th to 20th	Night	15% 4 7% 23% 34% 17%	1526
	21st to end	Night	16% 6% 10% 24% 30% 14%	1931
September	1st to 10th	Night	17% 4 9% 26% 29% 14%	1800
	11th to 20th	Night	27% 6% 10% 23% 24% 10%	1898
	21st to end	Night	29% 7% 14% 28% 15% 7%	1980
October	1st to 10th	Night	36% 5% 9% 30% 18% 1	2052
	11th to 20th	Night	36% 8% 15% 25% 16% 1	2263
	21st to end	Night	41% 8% 13% 24% 12% 2	2574
November	1st to 10th	Night	53% 9% 16% 16% 6% 1	2405
	11th to 20th	Night	56% 10% 15% 12% 6% 2	2563
	21st to end	Night	56% 9% 16% 13% 6%	2759
December	1st to 10th	Night	58% 10% 13% 15% 4	2850
	11th to 20th	Night	70% 10% 10% 7% 2	3507
	21st to end	Night	63% 14% 12% 8% 3	5106

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% 17% 18% 17% 4	180
	11th to 20th	Day	28% 10% 22% 16% 16% 8%	180
	21st to end	Day	29% 10% 24% 24% 12% 2	198
February	1st to 10th	Day	28% 12% 27% 24% 9% 1	184
	11th to 20th	Day	24% 17% 21% 26% 12% 1	419
	21st to end	Day	22% 13% 25% 24% 13% 3	382
March	1st to 10th	Day	18% 19% 26% 21% 12% 4	460
	11th to 20th	Day	15% 12% 22% 21% 23% 6%	460
	21st to end	Day	20% 17% 25% 25% 11% 2	471
April	1st to 10th	Day	19% 15% 24% 26% 10% 6%	420
	11th to 20th	Day	15% 18% 29% 19% 13% 7%	412
	21st to end	Day	10% 14% 23% 30% 17% 5%	420
May	1st to 10th	Day	9% 10% 26% 30% 21% 4	423
	11th to 20th	Day	17% 7% 20% 24% 22% 11%	448
	21st to end	Day	11% 8% 18% 27% 24% 11%	485
June	1st to 10th	Day	16% 7% 21% 27% 21% 8%	620
	11th to 20th	Day	12% 11% 31% 25% 15% 5%	630
	21st to end	Day	6% 5% 20% 28% 30% 12%	630
July	1st to 10th	Day	5% 4 21% 33% 33% 5%	449
	11th to 20th	Day	4 7% 22% 36% 22% 10%	444
	21st to end	Day	1 4 18% 30% 33% 13%	487
August	1st to 10th	Day	4 5% 16% 31% 28% 16%	447
	11th to 20th	Day	3 3 15% 27% 33% 19%	437
	21st to end	Day	6% 6% 21% 27% 25% 14%	495
September	1st to 10th	Day	7% 7% 19% 27% 27% 13%	450
	11th to 20th	Day	7% 8% 21% 27% 25% 12%	450
	21st to end	Day	11% 9% 23% 28% 22% 7%	450
October	1st to 10th	Day	14% 6% 24% 27% 21% 7%	450
	11th to 20th	Day	16% 11% 19% 22% 23% 10%	347
	21st to end	Day	25% 11% 21% 27% 10% 6%	297
November	1st to 10th	Day	24% 11% 19% 29% 15% 1	270
	11th to 20th	Day	27% 16% 16% 20% 16% 6%	225
	21st to end	Day	23% 9% 19% 24% 19% 4	180
December	1st to 10th	Day	26% 10% 20% 23% 14% 7%	180
	11th to 20th	Day	33% 10% 21% 23% 12% 2	180
	21st to end	Day	28% 9% 24% 24% 11% 4	198
January	1st to 10th	Night	32% 11% 20% 23% 12% 2	760
	11th to 20th	Night	25% 9% 20% 28% 15% 3	760
	21st to end	Night	23% 6% 19% 34% 17% 1	836
February	1st to 10th	Night	24% 9% 21% 34% 11% 2	760
	11th to 20th	Night	20% 9% 21% 31% 18% 1	744
	21st to end	Night	19% 8% 23% 32% 16% 2	628
March	1st to 10th	Night	18% 10% 21% 32% 18% 2	760
	11th to 20th	Night	18% 11% 19% 30% 21% 2	760
	21st to end	Night	18% 7% 24% 37% 12% 2	800
April	1st to 10th	Night	15% 7% 21% 35% 19% 2	720
	11th to 20th	Night	15% 8% 25% 35% 15% 2	654
	21st to end	Night	11% 7% 23% 37% 19% 2	540
May	1st to 10th	Night	7% 8% 20% 38% 23% 4	407
	11th to 20th	Night	14% 5% 13% 32% 28% 8%	354
	21st to end	Night	10% 5% 19% 33% 28% 5%	389
June	1st to 10th	Night	14% 4 17% 40% 21% 5%	360
	11th to 20th	Night	12% 5% 26% 33% 21% 3	360
	21st to end	Night	8% 2 14% 41% 31% 4	360
July	1st to 10th	Night	4 2 10% 42% 39% 3	350
	11th to 20th	Night	3 1 16% 44% 34% 2	348
	21st to end	Night	1 1 9% 43% 42% 5%	394
August	1st to 10th	Night	3 1 11% 36% 42% 6%	358
	11th to 20th	Night	3 1 8% 35% 41% 10%	458
	21st to end	Night	3 2 14% 38% 38% 4	743
September	1st to 10th	Night	5% 2 13% 42% 32% 6%	720
	11th to 20th	Night	7% 3 15% 31% 35% 8%	720
	21st to end	Night	10% 5% 18% 34% 28% 5%	720
October	1st to 10th	Night	14% 3 15% 39% 27% 3	720
	11th to 20th	Night	14% 6% 17% 32% 27% 4	720
	21st to end	Night	19% 4 23% 33% 17% 4	792
November	1st to 10th	Night	25% 8% 17% 35% 14%	740
	11th to 20th	Night	25% 9% 23% 28% 13% 2	760
	21st to end	Night	25% 9% 16% 29% 19% 2	859
December	1st to 10th	Night	21% 9% 18% 34% 17% 1	950
	11th to 20th	Night	29% 8% 16% 33% 13%	950
	21st to end	Night	33% 9% 17% 29% 10% 1	976

Page generated at 2024-03-19 20:31:07. Version ac07

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