Scappoose
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Scappoose clear sky chart from 2005-11-06 to 2026-03-18.

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	17% 8% 3 7% 5% 4 4 3 5% 6% 38%	140833
	Night	18% 9% 3 7% 5% 4 4 3 4 5% 38%	137966
Transparency	Day	49% 3 12% 19% 12% 3	135603
	Night	50% 4 13% 20% 11% 3	134207
Seeing	Day	21% 8% 22% 28% 17% 5%	16532
	Night	24% 6% 20% 34% 15% 1	25295

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	34% 15% 4 10% 7% 6% 6% 3 4 4 8%	4722
	11th to 20th	Day	21% 9% 3 8% 5% 4 3 3 4 7% 34%	4740
	21st to end	Day	24% 9% 3 8% 5% 4 5% 3 4 5% 30%	5663
February	1st to 10th	Day	30% 13% 4 8% 5% 5% 5% 4 4 6% 16%	1890
	11th to 20th	Day	30% 14% 4 10% 6% 5% 4 3 4 4 17%	1845
	21st to end	Day	30% 14% 4 8% 5% 4 4 3 4 4 18%	1629
March	1st to 10th	Day	18% 15% 4 10% 6% 5% 6% 5% 7% 7% 18%	4843
	11th to 20th	Day	23% 14% 4 10% 6% 4 4 3 4 4 25%	5078
	21st to end	Day	21% 13% 5% 11% 7% 6% 7% 5% 6% 7% 12%	5604
April	1st to 10th	Day	26% 14% 4 9% 7% 5% 4 4 4 6% 16%	2400
	11th to 20th	Day	22% 12% 4 8% 6% 5% 4 4 4 6% 26%	2379
	21st to end	Day	20% 11% 3 8% 6% 5% 6% 4 5% 6% 25%	2600
May	1st to 10th	Day	14% 7% 2 7% 4 5% 4 3 4 6% 43%	6230
	11th to 20th	Day	13% 8% 3 9% 6% 5% 5% 4 6% 8% 34%	6277
	21st to end	Day	16% 7% 3 8% 5% 5% 5% 4 6% 8% 32%	6902
June	1st to 10th	Day	20% 10% 3 7% 6% 3 4 3 5% 6% 34%	2800
	11th to 20th	Day	17% 8% 3 8% 6% 5% 6% 4 7% 7% 28%	2831
	21st to end	Day	8% 6% 2 7% 5% 4 4 3 5% 7% 48%	3000
July	1st to 10th	Day	4 3 1 4 2 2 2 2 3 5% 71%	6503
	11th to 20th	Day	3 2 1 2 2 2 2 2 2 4 79%	6320
	21st to end	Day	5% 2 1 3 2 2 3 2 4 5% 71%	6880
August	1st to 10th	Day	4 3 1 4 3 3 3 3 4 6% 65%	5833
	11th to 20th	Day	8% 4 2 5% 5% 5% 5% 4 6% 8% 50%	5796
	21st to end	Day	9% 5% 2 6% 3 4 4 4 5% 7% 52%	6172
September	1st to 10th	Day	7% 4 2 5% 3 4 3 3 5% 8% 57%	2400
	11th to 20th	Day	11% 7% 3 7% 4 4 4 5% 5% 8% 43%	2396
	21st to end	Day	15% 7% 2 6% 4 4 4 3 4 6% 44%	2105
October	1st to 10th	Day	15% 6% 2 5% 4 3 4 3 5% 8% 47%	3280
	11th to 20th	Day	17% 7% 3 9% 6% 5% 5% 4 7% 6% 30%	3261
	21st to end	Day	23% 9% 3 8% 6% 5% 5% 4 6% 7% 24%	3472
November	1st to 10th	Day	29% 12% 4 9% 5% 5% 5% 5% 5% 5% 15%	1722
	11th to 20th	Day	32% 11% 4 9% 6% 4 4 3 5% 4 19%	1680
	21st to end	Day	30% 11% 4 10% 6% 4 3 3 5% 5% 20%	1680
December	1st to 10th	Day	21% 10% 2 8% 5% 4 4 3 4 6% 32%	2700
	11th to 20th	Day	33% 12% 4 10% 6% 6% 5% 3 4 5% 13%	3108
	21st to end	Day	30% 14% 4 13% 7% 6% 5% 3 4 4 10%	4092
January	1st to 10th	Night	31% 13% 4 11% 7% 6% 5% 4 4 4 13%	8172
	11th to 20th	Night	19% 9% 2 6% 5% 4 4 3 4 5% 39%	8220
	21st to end	Night	25% 10% 3 8% 5% 4 3 2 4 4 32%	8528
February	1st to 10th	Night	25% 14% 3 9% 6% 5% 5% 3 5% 5% 19%	2730
	11th to 20th	Night	26% 13% 4 8% 5% 5% 4 3 5% 4 24%	2662
	21st to end	Night	27% 12% 3 9% 5% 5% 5% 3 4 4 23%	2176
March	1st to 10th	Night	16% 14% 3 9% 6% 6% 6% 4 6% 6% 23%	5258
	11th to 20th	Night	19% 12% 3 9% 6% 5% 5% 4 4 4 29%	5077
	21st to end	Night	24% 14% 4 10% 7% 6% 5% 4 5% 7% 16%	5370
April	1st to 10th	Night	23% 13% 3 8% 6% 5% 5% 3 4 5% 24%	2000
	11th to 20th	Night	18% 10% 4 8% 5% 4 4 3 6% 7% 30%	1966
	21st to end	Night	20% 11% 4 5% 6% 4 4 3 5% 8% 31%	1800
May	1st to 10th	Night	16% 6% 2 5% 3 3 3 2 5% 6% 50%	3732
	11th to 20th	Night	11% 7% 2 6% 4 4 5% 3 5% 7% 46%	3616
	21st to end	Night	9% 7% 3 6% 5% 5% 5% 4 6% 9% 42%	3972
June	1st to 10th	Night	14% 8% 3 8% 6% 5% 3 3 3 6% 42%	1600
	11th to 20th	Night	12% 8% 2 6% 4 5% 3 3 5% 6% 45%	1558
	21st to end	Night	6% 4 2 6% 4 2 3 3 4 6% 62%	1400
July	1st to 10th	Night	2 1 1 1 1 2 2 2 4 5% 80%	3446
	11th to 20th	Night	2 2 1 2 2 1 2 1 2 3 82%	3640
	21st to end	Night	3 2 1 2 1 2 2 2 3 5% 77%	3970
August	1st to 10th	Night	3 3 1 3 2 3 3 3 5% 6% 69%	3960
	11th to 20th	Night	10% 3 1 4 2 3 3 3 5% 6% 60%	4052
	21st to end	Night	9% 4 2 5% 3 3 3 3 4 6% 58%	4818
September	1st to 10th	Night	7% 3 1 3 3 3 2 3 4 5% 65%	2000
	11th to 20th	Night	10% 6% 2 6% 4 4 4 3 5% 5% 51%	2000
	21st to end	Night	11% 4 2 5% 4 4 3 3 4 7% 53%	2295
October	1st to 10th	Night	12% 4 2 5% 3 3 3 2 4 6% 56%	3920
	11th to 20th	Night	16% 6% 3 7% 5% 4 4 4 5% 9% 37%	3897
	21st to end	Night	20% 8% 3 8% 6% 5% 5% 4 5% 7% 32%	4334
November	1st to 10th	Night	29% 10% 3 8% 5% 5% 5% 3 4 6% 23%	2795
	11th to 20th	Night	32% 11% 4 8% 5% 4 4 3 4 5% 21%	2940
	21st to end	Night	25% 10% 3 8% 6% 5% 4 4 4 4 26%	2940
December	1st to 10th	Night	19% 9% 2 6% 4 5% 4 3 5% 6% 36%	4700
	11th to 20th	Night	34% 14% 4 11% 6% 4 4 3 4 5% 13%	5316
	21st to end	Night	33% 13% 4 10% 6% 5% 5% 3 4 4 13%	7106

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% 3 6% 7% 3	4723
	11th to 20th	Day	54% 2 8% 17% 15% 5%	4740
	21st to end	Day	58% 2 7% 15% 15% 2	5663
February	1st to 10th	Day	69% 5% 11% 12% 4	1890
	11th to 20th	Day	72% 5% 7% 11% 5% 1	1854
	21st to end	Day	70% 3 10% 10% 6% 1	1629
March	1st to 10th	Day	64% 3 16% 12% 5%	4843
	11th to 20th	Day	64% 3 6% 21% 6%	5078
	21st to end	Day	71% 4 15% 8% 2	5604
April	1st to 10th	Day	68% 5% 12% 13% 2	2400
	11th to 20th	Day	59% 4 11% 15% 9% 2	2382
	21st to end	Day	59% 6% 13% 14% 8% 1	2600
May	1st to 10th	Day	42% 3 12% 25% 16%	6230
	11th to 20th	Day	47% 5% 18% 24% 6% 1	6280
	21st to end	Day	50% 5% 23% 17% 4	6904
June	1st to 10th	Day	51% 5% 18% 18% 8%	2800
	11th to 20th	Day	53% 6% 18% 17% 6%	2831
	21st to end	Day	35% 4 19% 27% 11% 4	3000
July	1st to 10th	Day	19% 2 11% 27% 21% 20%	6435
	11th to 20th	Day	13% 2 8% 23% 42% 12%	6245
	21st to end	Day	18% 2 18% 35% 24% 3	6681
August	1st to 10th	Day	19% 3 9% 29% 28% 11%	4249
	11th to 20th	Day	34% 2 19% 27% 12% 5%	4195
	21st to end	Day	34% 3 13% 25% 18% 8%	4451
September	1st to 10th	Day	28% 4 15% 26% 18% 10%	2400
	11th to 20th	Day	41% 5% 14% 18% 16% 6%	2396
	21st to end	Day	42% 4 14% 19% 16% 4	2105
October	1st to 10th	Day	38% 3 8% 31% 18% 2	3280
	11th to 20th	Day	54% 4 13% 16% 12% 1	3261
	21st to end	Day	60% 2 7% 21% 10%	3472
November	1st to 10th	Day	70% 6% 9% 12% 4	1722
	11th to 20th	Day	68% 4 11% 10% 5% 2	1680
	21st to end	Day	67% 4 8% 10% 10%	1680
December	1st to 10th	Day	55% 2 8% 19% 15%	2700
	11th to 20th	Day	75% 3 10% 10% 1	3108
	21st to end	Day	79% 3 9% 7% 2	4092
January	1st to 10th	Night	75% 3 9% 9% 3	8172
	11th to 20th	Night	50% 2 8% 20% 17% 3	8220
	21st to end	Night	57% 2 6% 15% 17% 3	8528
February	1st to 10th	Night	67% 5% 10% 13% 5%	2730
	11th to 20th	Night	64% 5% 11% 12% 6% 2	2664
	21st to end	Night	65% 5% 11% 12% 7% 1	2176
March	1st to 10th	Night	61% 3 14% 15% 6%	5258
	11th to 20th	Night	59% 4 11% 21% 6%	5077
	21st to end	Night	69% 5% 14% 11% 1	5370
April	1st to 10th	Night	63% 5% 14% 15% 3	2000
	11th to 20th	Night	52% 6% 14% 16% 9% 2	1966
	21st to end	Night	53% 6% 15% 18% 6% 2	1800
May	1st to 10th	Night	36% 5% 11% 34% 14% 1	3729
	11th to 20th	Night	38% 4 21% 28% 7% 1	3616
	21st to end	Night	40% 6% 30% 20% 4	3972
June	1st to 10th	Night	47% 4 16% 25% 7% 1	1600
	11th to 20th	Night	40% 5% 20% 28% 7%	1558
	21st to end	Night	26% 4 22% 35% 11% 4	1400
July	1st to 10th	Night	10% 2 15% 32% 21% 21%	3406
	11th to 20th	Night	11% 2 8% 24% 40% 15%	3592
	21st to end	Night	12% 2 19% 37% 25% 4	3857
August	1st to 10th	Night	12% 2 12% 35% 32% 8%	2881
	11th to 20th	Night	23% 3 29% 30% 10% 6%	2929
	21st to end	Night	28% 2 17% 27% 21% 5%	3463
September	1st to 10th	Night	22% 4 15% 30% 19% 10%	2000
	11th to 20th	Night	35% 6% 15% 22% 14% 8%	2000
	21st to end	Night	32% 5% 17% 22% 18% 6%	2295
October	1st to 10th	Night	32% 3 11% 34% 19% 2	3920
	11th to 20th	Night	46% 4 17% 21% 11% 1	3897
	21st to end	Night	54% 3 10% 22% 10% 1	4334
November	1st to 10th	Night	65% 5% 9% 14% 6%	2795
	11th to 20th	Night	68% 5% 10% 10% 6% 1	2940
	21st to end	Night	62% 5% 9% 12% 11% 1	2940
December	1st to 10th	Night	50% 3 9% 22% 15%	4700
	11th to 20th	Night	77% 3 9% 9% 3	5316
	21st to end	Night	75% 4 10% 9% 2	7106

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	45% 7% 13% 20% 10% 4	220
	11th to 20th	Day	33% 8% 16% 22% 14% 8%	220
	21st to end	Day	34% 7% 15% 22% 16% 6%	410
February	1st to 10th	Day	38% 8% 19% 21% 11% 3	430
	11th to 20th	Day	38% 8% 25% 18% 9% 1	425
	21st to end	Day	36% 14% 19% 21% 8% 2	394
March	1st to 10th	Day	31% 12% 23% 23% 10% 1	540
	11th to 20th	Day	31% 9% 24% 21% 11% 5%	529
	21st to end	Day	31% 13% 21% 21% 11% 2	550
April	1st to 10th	Day	29% 12% 20% 22% 11% 5%	500
	11th to 20th	Day	23% 16% 24% 23% 9% 4	492
	21st to end	Day	23% 9% 28% 24% 13% 4	500
May	1st to 10th	Day	15% 15% 24% 28% 15% 4	503
	11th to 20th	Day	21% 14% 23% 20% 17% 5%	528
	21st to end	Day	19% 9% 22% 25% 20% 5%	573
June	1st to 10th	Day	21% 7% 23% 29% 17% 4	530
	11th to 20th	Day	15% 11% 30% 30% 12% 2	561
	21st to end	Day	7% 6% 30% 34% 18% 4	730
July	1st to 10th	Day	7% 6% 28% 34% 19% 6%	606
	11th to 20th	Day	5% 5% 23% 39% 22% 6%	524
	21st to end	Day	3 4 20% 38% 29% 6%	575
August	1st to 10th	Day	6% 4 17% 39% 28% 7%	527
	11th to 20th	Day	3 3 16% 36% 31% 11%	517
	21st to end	Day	8% 5% 22% 36% 21% 8%	583
September	1st to 10th	Day	7% 6% 20% 37% 22% 7%	530
	11th to 20th	Day	13% 5% 19% 33% 22% 8%	530
	21st to end	Day	16% 5% 24% 30% 21% 4	530
October	1st to 10th	Day	19% 8% 19% 28% 20% 5%	530
	11th to 20th	Day	21% 7% 22% 26% 18% 7%	530
	21st to end	Day	29% 8% 24% 23% 11% 4	533
November	1st to 10th	Day	29% 11% 20% 25% 12% 3	260
	11th to 20th	Day	32% 9% 25% 18% 12% 5%	220
	21st to end	Day	30% 10% 19% 22% 14% 5%	220
December	1st to 10th	Day	38% 6% 15% 21% 14% 6%	220
	11th to 20th	Day	41% 8% 22% 20% 8% 2	220
	21st to end	Day	34% 11% 17% 25% 11% 2	242
January	1st to 10th	Night	40% 6% 15% 25% 12% 2	840
	11th to 20th	Night	35% 7% 11% 28% 18% 1	840
	21st to end	Night	30% 6% 14% 31% 17% 2	924
February	1st to 10th	Night	31% 6% 18% 30% 14% 1	840
	11th to 20th	Night	32% 7% 17% 28% 16% 1	824
	21st to end	Night	31% 9% 17% 30% 12%	692
March	1st to 10th	Night	29% 8% 17% 31% 14% 1	840
	11th to 20th	Night	27% 7% 19% 33% 13% 1	828
	21st to end	Night	31% 8% 18% 30% 13%	880
April	1st to 10th	Night	28% 9% 18% 29% 14% 1	800
	11th to 20th	Night	21% 9% 24% 33% 11% 1	778
	21st to end	Night	25% 7% 21% 32% 14% 1	600
May	1st to 10th	Night	16% 7% 29% 34% 13% 1	440
	11th to 20th	Night	17% 5% 23% 40% 15% 1	394
	21st to end	Night	13% 7% 26% 39% 14%	433
June	1st to 10th	Night	16% 6% 29% 39% 10%	400
	11th to 20th	Night	13% 7% 31% 41% 8% 1	400
	21st to end	Night	6% 3 35% 47% 9%	400
July	1st to 10th	Night	3 3 34% 50% 10% 1	390
	11th to 20th	Night	5% 4 37% 44% 10%	388
	21st to end	Night	3 1 37% 49% 9%	438
August	1st to 10th	Night	5% 1 25% 46% 22% 1	561
	11th to 20th	Night	6% 1 15% 49% 26% 2	594
	21st to end	Night	8% 4 26% 43% 18% 1	787
September	1st to 10th	Night	8% 4 24% 45% 18% 1	800
	11th to 20th	Night	12% 4 17% 36% 28% 3	800
	21st to end	Night	11% 4 21% 43% 20% 2	800
October	1st to 10th	Night	19% 5% 17% 36% 22% 2	800
	11th to 20th	Night	20% 5% 17% 32% 24% 2	800
	21st to end	Night	26% 5% 18% 33% 16% 2	880
November	1st to 10th	Night	32% 6% 16% 33% 12% 1	820
	11th to 20th	Night	36% 7% 16% 27% 13% 2	840
	21st to end	Night	28% 5% 16% 32% 17% 2	840
December	1st to 10th	Night	30% 8% 13% 31% 16% 3	840
	11th to 20th	Night	39% 8% 16% 24% 12% 1	840
	21st to end	Night	40% 7% 18% 23% 10% 1	924

Page generated at 2026-03-14 23:23:50. Version ac07

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