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 2024-11-04.

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 6% 4 4 4 4 5% 6% 45%	105106
	Night	12% 9% 3 7% 5% 4 4 4 5% 6% 41%	102489
Transparency	Day	37% 8% 13% 21% 15% 6%	104874
	Night	41% 8% 12% 19% 13% 6%	102367
Seeing	Day	14% 10% 22% 26% 20% 8%	14771
	Night	17% 7% 18% 34% 21% 3	23904

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% 21% 5% 12% 6% 6% 5% 4 5% 4 11%	2539
	11th to 20th	Day	20% 14% 5% 10% 7% 6% 5% 3 4 5% 21%	2516
	21st to end	Day	23% 20% 6% 11% 6% 4 4 3 4 4 13%	2794
February	1st to 10th	Day	19% 15% 4 9% 5% 5% 6% 4 5% 7% 21%	1524
	11th to 20th	Day	14% 14% 4 10% 5% 5% 4 4 6% 7% 26%	1777
	21st to end	Day	14% 15% 4 8% 6% 5% 5% 4 6% 5% 28%	1570
March	1st to 10th	Day	11% 12% 3 7% 6% 5% 6% 5% 7% 9% 30%	3138
	11th to 20th	Day	8% 7% 2 6% 5% 4 5% 4 6% 7% 46%	3265
	21st to end	Day	13% 13% 4 10% 7% 7% 6% 5% 6% 6% 25%	4131
April	1st to 10th	Day	13% 10% 4 8% 5% 5% 6% 5% 6% 7% 29%	2280
	11th to 20th	Day	10% 8% 3 8% 6% 5% 5% 4 7% 6% 38%	2312
	21st to end	Day	10% 8% 3 8% 5% 5% 5% 4 6% 8% 38%	2470
May	1st to 10th	Day	9% 6% 2 7% 5% 5% 5% 5% 6% 8% 43%	4344
	11th to 20th	Day	7% 5% 2 6% 4 5% 5% 4 6% 9% 49%	4377
	21st to end	Day	9% 7% 3 7% 6% 6% 6% 5% 7% 8% 37%	4813
June	1st to 10th	Day	15% 8% 2 6% 4 3 4 3 5% 7% 42%	2840
	11th to 20th	Day	12% 6% 2 5% 5% 5% 5% 4 6% 7% 43%	2850
	21st to end	Day	6% 3 2 4 4 4 4 3 5% 6% 58%	2850
July	1st to 10th	Day	2 1 1 2 2 2 2 2 3 4 77%	4423
	11th to 20th	Day	2 1 1 2 2 1 2 2 3 4 80%	4420
	21st to end	Day	2 1 1 2 2 2 3 2 3 5% 77%	4790
August	1st to 10th	Day	3 2 1 3 2 2 2 3 4 6% 71%	4401
	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	20% 10% 4 8% 4 5% 5% 3 5% 6% 29%	1701
	11th to 20th	Day	18% 13% 4 9% 6% 5% 5% 3 4 5% 27%	1615
	21st to end	Day	15% 18% 4 11% 6% 5% 5% 4 5% 5% 21%	1401
December	1st to 10th	Day	17% 15% 6% 11% 8% 5% 4 4 5% 7% 18%	1330
	11th to 20th	Day	21% 20% 6% 15% 8% 6% 5% 3 3 4 9%	1682
	21st to end	Day	16% 19% 5% 12% 6% 7% 5% 4 6% 5% 15%	2578
January	1st to 10th	Night	22% 20% 5% 11% 7% 5% 4 2 4 5% 15%	4406
	11th to 20th	Night	18% 14% 4 11% 6% 4 4 3 5% 7% 23%	4382
	21st to end	Night	22% 18% 6% 9% 5% 4 4 4 5% 5% 17%	4862
February	1st to 10th	Night	17% 16% 4 8% 6% 4 4 3 5% 6% 27%	2656
	11th to 20th	Night	14% 12% 4 8% 6% 4 5% 4 6% 6% 30%	2289
	21st to end	Night	11% 14% 3 8% 6% 4 6% 4 5% 7% 33%	1884
March	1st to 10th	Night	9% 9% 3 6% 5% 6% 6% 4 5% 8% 39%	3736
	11th to 20th	Night	9% 8% 2 5% 3 4 3 3 4 6% 52%	3713
	21st to end	Night	11% 9% 3 8% 6% 7% 7% 6% 7% 9% 27%	3519
April	1st to 10th	Night	10% 9% 3 7% 5% 5% 5% 5% 7% 7% 36%	1900
	11th to 20th	Night	10% 9% 3 7% 5% 4 5% 4 5% 6% 42%	1818
	21st to end	Night	10% 7% 2 7% 5% 5% 5% 5% 7% 7% 40%	1710
May	1st to 10th	Night	9% 5% 2 8% 5% 5% 7% 5% 8% 8% 38%	2615
	11th to 20th	Night	7% 4 2 5% 4 3 4 3 7% 9% 52%	2516
	21st to end	Night	10% 5% 2 7% 6% 5% 6% 4 7% 8% 39%	2762
June	1st to 10th	Night	11% 6% 2 5% 5% 4 4 4 6% 7% 45%	1335
	11th to 20th	Night	10% 5% 2 6% 4 6% 7% 5% 7% 7% 42%	1330
	21st to end	Night	6% 5% 2 4 3 4 4 4 6% 7% 56%	1330
July	1st to 10th	Night	2 2 1 2 2 3 2 2 3 6% 74%	2531
	11th to 20th	Night	2 1 1 2 1 2 2 2 2 4 82%	2540
	21st to end	Night	1 2 1 2 2 2 2 2 3 4 80%	2762
August	1st to 10th	Night	3 3 1 3 2 2 2 2 4 6% 72%	2529
	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	20% 11% 3 7% 5% 4 4 4 6% 8% 29%	2450
	11th to 20th	Night	17% 12% 4 8% 6% 5% 6% 4 5% 5% 28%	2563
	21st to end	Night	18% 13% 3 7% 6% 5% 4 4 5% 6% 27%	2759
December	1st to 10th	Night	16% 14% 6% 9% 5% 4 5% 4 6% 7% 24%	2850
	11th to 20th	Night	20% 18% 5% 13% 7% 6% 4 4 5% 5% 14%	3510
	21st to end	Night	18% 15% 5% 12% 7% 7% 6% 4 5% 6% 14%	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	45% 11% 14% 18% 11% 1	3138
	11th to 20th	Day	34% 9% 18% 34% 5%	3265
	21st to end	Day	55% 13% 15% 12% 5%	4131
April	1st to 10th	Day	52% 9% 18% 16% 5%	2280
	11th to 20th	Day	44% 8% 17% 18% 11% 2	2312
	21st to end	Day	43% 10% 17% 20% 9% 2	2470
May	1st to 10th	Day	34% 10% 15% 30% 10% 1	4344
	11th to 20th	Day	27% 10% 16% 33% 13% 1	4380
	21st to end	Day	39% 12% 20% 23% 6% 1	4814
June	1st to 10th	Day	42% 7% 12% 22% 14% 2	2840
	11th to 20th	Day	37% 9% 14% 24% 12% 3	2850
	21st to end	Day	25% 6% 13% 30% 21% 5%	2850
July	1st to 10th	Day	13% 3 6% 18% 31% 29%	4354
	11th to 20th	Day	11% 2 5% 12% 27% 42%	4345
	21st to end	Day	11% 3 6% 18% 37% 25%	4639
August	1st to 10th	Day	16% 3 6% 22% 38% 16%	4384
	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	55% 10% 15% 16% 4 1	1701
	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	40% 10% 13% 25% 11% 1	3736
	11th to 20th	Night	33% 6% 15% 34% 11%	3714
	21st to end	Night	48% 13% 16% 19% 4	3519
April	1st to 10th	Night	43% 8% 15% 23% 10% 1	1900
	11th to 20th	Night	41% 8% 12% 22% 15% 2	1818
	21st to end	Night	41% 9% 12% 22% 15% 2	1710
May	1st to 10th	Night	35% 10% 14% 25% 15% 1	2615
	11th to 20th	Night	25% 10% 12% 31% 21% 1	2516
	21st to end	Night	36% 13% 16% 24% 11%	2762
June	1st to 10th	Night	36% 8% 11% 22% 19% 4	1335
	11th to 20th	Night	36% 9% 12% 22% 15% 6%	1330
	21st to end	Night	26% 6% 10% 25% 25% 8%	1330
July	1st to 10th	Night	12% 3 5% 15% 29% 35%	2491
	11th to 20th	Night	9% 2 4 11% 20% 54%	2492
	21st to end	Night	10% 2 3 16% 31% 38%	2674
August	1st to 10th	Night	14% 3 4 16% 39% 24%	2521
	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% 8% 16% 16% 6% 1	2450
	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% 22% 23% 6%	460
	21st to end	Day	19% 16% 24% 26% 12% 2	506
April	1st to 10th	Day	18% 16% 25% 25% 10% 6%	460
	11th to 20th	Day	14% 17% 28% 20% 14% 7%	452
	21st to end	Day	10% 14% 25% 30% 17% 5%	460
May	1st to 10th	Day	9% 11% 26% 29% 21% 5%	463
	11th to 20th	Day	15% 8% 20% 24% 22% 10%	488
	21st to end	Day	11% 8% 20% 27% 24% 10%	529
June	1st to 10th	Day	16% 7% 20% 27% 22% 7%	670
	11th to 20th	Day	12% 11% 31% 26% 15% 5%	680
	21st to end	Day	5% 6% 21% 28% 29% 11%	680
July	1st to 10th	Day	4 3 22% 31% 33% 6%	489
	11th to 20th	Day	3 6% 20% 37% 23% 12%	484
	21st to end	Day	2 4 18% 31% 32% 12%	531
August	1st to 10th	Day	5% 6% 17% 30% 28% 15%	487
	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% 28% 15% 1	279
	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% 13% 2	836
April	1st to 10th	Night	15% 7% 22% 35% 18% 2	760
	11th to 20th	Night	14% 8% 25% 36% 15% 2	690
	21st to end	Night	11% 8% 24% 36% 19% 2	570
May	1st to 10th	Night	7% 8% 21% 38% 22% 4	429
	11th to 20th	Night	13% 5% 13% 33% 28% 7%	374
	21st to end	Night	9% 6% 19% 33% 28% 4	411
June	1st to 10th	Night	13% 4 17% 40% 21% 5%	380
	11th to 20th	Night	11% 5% 26% 34% 21% 3	380
	21st to end	Night	8% 3 14% 40% 31% 4	380
July	1st to 10th	Night	4 2 11% 42% 38% 3	370
	11th to 20th	Night	3 1 15% 46% 33% 2	368
	21st to end	Night	1 2 9% 43% 41% 5%	416
August	1st to 10th	Night	3 1 11% 38% 41% 6%	378
	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	26% 8% 17% 35% 14%	754
	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 2024-11-01 19:47:41. Version ac07

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