Cascadia State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cascadia State Park clear sky chart from 2005-11-06 to 2024-03-01.

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% 11% 3 5% 4 2 3 3 4 5% 37%	78452
	Night	26% 13% 3 5% 4 2 3 3 4 5% 33%	80967
Transparency	Day	52% 4 9% 17% 13% 4	78156
	Night	56% 4 9% 15% 12% 5%	80784
Seeing	Day	27% 12% 25% 22% 10% 3	13729
	Night	31% 6% 14% 28% 18% 2	22898

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% 27% 4 5% 5% 3 3 2 3 2 12%	2539
	11th to 20th	Day	39% 16% 3 5% 4 3 3 2 3 3 20%	2540
	21st to end	Day	38% 15% 3 5% 5% 2 2 4 4 4 19%	3096
February	1st to 10th	Day	31% 14% 5% 7% 5% 2 4 4 3 5% 20%	1710
	11th to 20th	Day	28% 19% 3 5% 5% 2 4 4 4 4 21%	1665
	21st to end	Day	30% 22% 4 5% 4 3 3 3 3 3 19%	1516
March	1st to 10th	Day	30% 18% 3 6% 5% 3 4 4 5% 5% 17%	1881
	11th to 20th	Day	29% 17% 3 5% 4 2 4 4 4 6% 21%	1980
	21st to end	Day	34% 19% 4 6% 5% 2 4 3 4 4 15%	2228
April	1st to 10th	Day	31% 21% 4 7% 6% 3 3 3 3 4 16%	2160
	11th to 20th	Day	27% 17% 5% 6% 5% 3 4 3 2 5% 24%	2129
	21st to end	Day	29% 13% 3 5% 5% 2 4 4 4 6% 26%	2290
May	1st to 10th	Day	23% 11% 3 6% 4 2 4 3 4 5% 34%	2461
	11th to 20th	Day	26% 9% 3 6% 5% 3 4 4 5% 7% 28%	2477
	21st to end	Day	32% 9% 3 5% 4 3 3 4 5% 6% 28%	2723
June	1st to 10th	Day	28% 8% 4 5% 5% 2 4 3 3 5% 32%	2520
	11th to 20th	Day	25% 9% 3 5% 5% 3 4 4 5% 6% 32%	2520
	21st to end	Day	11% 4 2 4 3 2 3 3 4 6% 57%	2520
July	1st to 10th	Day	6% 3 1 3 3 1 3 3 3 6% 69%	2520
	11th to 20th	Day	7% 3 1 3 2 2 2 3 3 5% 70%	2520
	21st to end	Day	3 2 1 2 2 1 2 2 2 4 78%	2737
August	1st to 10th	Day	4 2 1 2 2 2 2 3 4 7% 71%	2328
	11th to 20th	Day	5% 3 1 2 3 2 2 3 4 5% 70%	2298
	21st to end	Day	5% 4 1 3 3 2 3 3 4 6% 66%	2421
September	1st to 10th	Day	8% 3 2 2 3 1 1 2 2 5% 69%	2160
	11th to 20th	Day	13% 7% 3 4 4 2 3 3 5% 6% 50%	2160
	21st to end	Day	18% 5% 2 5% 5% 3 3 4 4 5% 47%	1901
October	1st to 10th	Day	21% 8% 2 3 4 2 3 4 4 5% 45%	1800
	11th to 20th	Day	25% 7% 2 5% 5% 2 3 3 4 6% 38%	1800
	21st to end	Day	27% 9% 3 6% 4 2 4 3 3 5% 34%	1949
November	1st to 10th	Day	38% 11% 4 6% 4 3 4 3 3 5% 21%	1621
	11th to 20th	Day	36% 9% 3 7% 5% 3 3 3 6% 4 22%	1520
	21st to end	Day	29% 12% 3 6% 5% 3 3 3 4 4 27%	1520
December	1st to 10th	Day	27% 13% 3 6% 4 2 4 3 3 5% 30%	1520
	11th to 20th	Day	32% 16% 3 6% 5% 2 4 4 4 6% 19%	1928
	21st to end	Day	32% 18% 4 7% 5% 2 3 3 3 4 18%	2794
January	1st to 10th	Night	37% 23% 4 5% 4 2 3 3 3 4 12%	4406
	11th to 20th	Night	39% 16% 3 5% 3 2 3 3 3 3 20%	4420
	21st to end	Night	37% 17% 3 6% 4 3 3 2 3 4 18%	4553
February	1st to 10th	Night	27% 19% 5% 6% 5% 3 4 3 4 4 20%	2470
	11th to 20th	Night	28% 19% 3 5% 4 3 3 3 3 4 24%	2402
	21st to end	Night	30% 22% 3 4 4 3 2 4 3 5% 20%	1937
March	1st to 10th	Night	29% 18% 3 6% 4 2 3 4 4 5% 21%	2081
	11th to 20th	Night	28% 15% 3 5% 4 2 4 4 5% 6% 23%	1980
	21st to end	Night	32% 20% 5% 6% 4 2 4 3 3 4 17%	2127
April	1st to 10th	Night	32% 19% 3 6% 4 2 3 3 4 4 20%	1800
	11th to 20th	Night	28% 18% 3 4 4 2 3 4 3 4 26%	1779
	21st to end	Night	29% 14% 3 4 5% 2 4 3 4 5% 27%	1666
May	1st to 10th	Night	21% 13% 3 5% 4 2 3 4 3 6% 37%	1499
	11th to 20th	Night	22% 10% 4 5% 5% 3 4 4 4 6% 32%	1416
	21st to end	Night	26% 11% 4 5% 6% 3 4 4 4 6% 28%	1552
June	1st to 10th	Night	26% 8% 2 4 4 3 4 4 4 6% 34%	1440
	11th to 20th	Night	21% 9% 3 4 4 3 4 3 5% 6% 38%	1440
	21st to end	Night	12% 5% 2 4 5% 2 3 2 3 4 59%	1440
July	1st to 10th	Night	7% 3 1 3 2 1 2 3 3 4 70%	1440
	11th to 20th	Night	5% 3 1 3 2 1 3 3 3 4 72%	1440
	21st to end	Night	3 1 1 1 1 2 2 3 4 82%	1576
August	1st to 10th	Night	3 3 1 2 2 1 3 3 4 6% 71%	1611
	11th to 20th	Night	5% 2 1 3 3 1 3 2 3 4 73%	1602
	21st to end	Night	5% 3 1 3 3 2 2 2 3 6% 70%	1934
September	1st to 10th	Night	7% 3 1 2 2 1 2 3 3 5% 70%	1800
	11th to 20th	Night	13% 5% 2 3 3 3 3 4 4 5% 55%	1800
	21st to end	Night	16% 7% 1 3 3 2 4 4 4 6% 50%	2055
October	1st to 10th	Night	19% 8% 3 4 4 2 3 3 3 4 47%	2160
	11th to 20th	Night	23% 8% 2 4 3 2 3 3 3 6% 43%	2160
	21st to end	Night	27% 9% 3 4 3 2 3 3 4 4 37%	2406
November	1st to 10th	Night	34% 12% 3 6% 4 2 3 4 4 5% 24%	2457
	11th to 20th	Night	37% 11% 2 5% 4 2 4 4 4 4 22%	2660
	21st to end	Night	28% 12% 3 5% 4 3 3 4 4 4 30%	2660
December	1st to 10th	Night	29% 11% 4 5% 4 2 4 3 4 6% 28%	2660
	11th to 20th	Night	31% 15% 4 5% 4 3 3 4 4 5% 21%	3276
	21st to end	Night	29% 16% 4 7% 6% 3 4 4 3 3 22%	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% 2 5% 8% 3 1	2539
	11th to 20th	Day	73% 2 5% 11% 5% 5%	2540
	21st to end	Day	71% 4 7% 10% 7% 2	3096
February	1st to 10th	Day	68% 5% 8% 10% 7% 1	1710
	11th to 20th	Day	69% 3 8% 10% 7% 3	1674
	21st to end	Day	71% 3 7% 10% 6% 2	1516
March	1st to 10th	Day	69% 5% 8% 12% 5%	1881
	11th to 20th	Day	66% 4 8% 15% 6% 1	1980
	21st to end	Day	75% 5% 8% 9% 3	2228
April	1st to 10th	Day	75% 3 8% 9% 5%	2160
	11th to 20th	Day	66% 4 9% 11% 7% 3	2132
	21st to end	Day	61% 5% 12% 14% 7% 2	2290
May	1st to 10th	Day	53% 5% 14% 19% 8% 1	2461
	11th to 20th	Day	56% 5% 12% 19% 7%	2480
	21st to end	Day	58% 6% 14% 18% 3 1	2724
June	1st to 10th	Day	56% 4 14% 20% 6%	2520
	11th to 20th	Day	54% 5% 16% 20% 5% 1	2520
	21st to end	Day	30% 3 16% 31% 14% 5%	2520
July	1st to 10th	Day	19% 4 13% 26% 28% 9%	2451
	11th to 20th	Day	19% 3 8% 22% 34% 14%	2445
	21st to end	Day	13% 2 4 26% 41% 14%	2585
August	1st to 10th	Day	16% 3 13% 34% 26% 8%	2312
	11th to 20th	Day	18% 3 10% 30% 30% 10%	2298
	21st to end	Day	21% 3 10% 29% 29% 8%	2421
September	1st to 10th	Day	21% 2 5% 30% 25% 16%	2160
	11th to 20th	Day	36% 3 10% 23% 18% 10%	2160
	21st to end	Day	41% 4 9% 20% 18% 9%	1901
October	1st to 10th	Day	44% 4 7% 18% 19% 8%	1800
	11th to 20th	Day	48% 5% 9% 13% 18% 6%	1800
	21st to end	Day	56% 4 6% 12% 17% 4	1949
November	1st to 10th	Day	69% 3 6% 11% 9% 2	1621
	11th to 20th	Day	66% 4 8% 9% 9% 3	1520
	21st to end	Day	62% 4 6% 10% 13% 6%	1520
December	1st to 10th	Day	58% 4 8% 13% 13% 4	1520
	11th to 20th	Day	68% 4 10% 9% 8% 1	1928
	21st to end	Day	73% 2 6% 15% 3 2	2794
January	1st to 10th	Night	79% 3 6% 6% 4 1	4406
	11th to 20th	Night	71% 3 6% 10% 6% 4	4420
	21st to end	Night	74% 2 6% 8% 7% 2	4553
February	1st to 10th	Night	70% 3 8% 9% 7% 2	2470
	11th to 20th	Night	66% 4 8% 11% 7% 4	2404
	21st to end	Night	68% 3 7% 13% 7% 2	1937
March	1st to 10th	Night	66% 6% 9% 13% 6% 1	2081
	11th to 20th	Night	62% 6% 10% 15% 6% 1	1980
	21st to end	Night	73% 5% 9% 10% 3	2127
April	1st to 10th	Night	70% 4 10% 10% 6%	1800
	11th to 20th	Night	63% 5% 11% 11% 7% 3	1779
	21st to end	Night	62% 5% 12% 13% 6% 3	1666
May	1st to 10th	Night	51% 4 14% 20% 11% 1	1499
	11th to 20th	Night	53% 7% 13% 19% 5% 3	1416
	21st to end	Night	57% 7% 13% 18% 5%	1552
June	1st to 10th	Night	52% 7% 15% 22% 5%	1440
	11th to 20th	Night	49% 6% 17% 22% 6% 1	1440
	21st to end	Night	32% 3 15% 31% 14% 5%	1440
July	1st to 10th	Night	20% 4 12% 25% 26% 12%	1400
	11th to 20th	Night	19% 3 8% 21% 31% 18%	1392
	21st to end	Night	8% 3 5% 26% 43% 16%	1488
August	1st to 10th	Night	15% 3 11% 37% 26% 7%	1602
	11th to 20th	Night	19% 2 8% 29% 33% 9%	1602
	21st to end	Night	18% 3 9% 31% 29% 9%	1934
September	1st to 10th	Night	19% 3 9% 28% 26% 15%	1800
	11th to 20th	Night	33% 4 9% 26% 15% 13%	1800
	21st to end	Night	36% 4 11% 20% 17% 12%	2055
October	1st to 10th	Night	42% 5% 9% 17% 19% 8%	2160
	11th to 20th	Night	45% 5% 10% 15% 18% 6%	2160
	21st to end	Night	53% 5% 6% 12% 16% 7%	2406
November	1st to 10th	Night	65% 5% 6% 10% 12% 2	2457
	11th to 20th	Night	66% 5% 8% 9% 9% 4	2660
	21st to end	Night	59% 3 7% 10% 13% 8%	2660
December	1st to 10th	Night	59% 4 8% 13% 13% 3	2660
	11th to 20th	Night	67% 3 11% 9% 9% 1	3276
	21st to end	Night	67% 5% 9% 13% 4 1	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	53% 13% 14% 12% 8% 1	180
	11th to 20th	Day	45% 8% 21% 16% 7% 3	180
	21st to end	Day	39% 11% 18% 19% 11% 2	383
February	1st to 10th	Day	40% 11% 21% 18% 10% 1	370
	11th to 20th	Day	41% 16% 23% 13% 5% 1	365
	21st to end	Day	44% 14% 19% 17% 5%	357
March	1st to 10th	Day	41% 16% 19% 19% 5%	421
	11th to 20th	Day	39% 11% 25% 19% 5% 2	420
	21st to end	Day	45% 16% 19% 16% 4 1	462
April	1st to 10th	Day	42% 14% 21% 15% 7% 1	420
	11th to 20th	Day	42% 16% 23% 12% 7% 1	412
	21st to end	Day	38% 16% 22% 16% 7% 1	420
May	1st to 10th	Day	26% 15% 27% 23% 6% 2	423
	11th to 20th	Day	35% 11% 23% 20% 7% 3	448
	21st to end	Day	31% 10% 22% 22% 11% 4	485
June	1st to 10th	Day	28% 14% 21% 23% 10% 4	450
	11th to 20th	Day	27% 15% 28% 19% 9% 2	450
	21st to end	Day	10% 9% 34% 30% 12% 4	450
July	1st to 10th	Day	9% 8% 39% 26% 13% 5%	446
	11th to 20th	Day	4 12% 36% 28% 14% 6%	444
	21st to end	Day	3 8% 38% 29% 17% 7%	487
August	1st to 10th	Day	2 11% 32% 34% 13% 8%	447
	11th to 20th	Day	3 10% 28% 34% 18% 8%	437
	21st to end	Day	7% 11% 34% 32% 12% 4	495
September	1st to 10th	Day	10% 10% 34% 27% 15% 4	450
	11th to 20th	Day	17% 7% 30% 31% 14% 2	450
	21st to end	Day	18% 13% 26% 28% 12% 3	450
October	1st to 10th	Day	24% 11% 27% 24% 13% 2	450
	11th to 20th	Day	28% 8% 19% 26% 16% 4	450
	21st to end	Day	32% 14% 21% 19% 11% 3	464
November	1st to 10th	Day	38% 10% 18% 23% 10% 1	245
	11th to 20th	Day	36% 11% 21% 16% 13% 3	180
	21st to end	Day	34% 12% 17% 25% 10% 2	180
December	1st to 10th	Day	39% 12% 20% 15% 10% 4	180
	11th to 20th	Day	48% 8% 21% 18% 3 1	180
	21st to end	Day	42% 15% 15% 19% 7% 2	198
January	1st to 10th	Night	48% 8% 16% 18% 8% 2	760
	11th to 20th	Night	40% 8% 18% 19% 11% 4	760
	21st to end	Night	37% 7% 18% 25% 10% 2	836
February	1st to 10th	Night	38% 8% 18% 26% 9% 1	760
	11th to 20th	Night	40% 9% 17% 26% 8%	744
	21st to end	Night	44% 9% 17% 22% 8%	628
March	1st to 10th	Night	41% 9% 13% 27% 9% 1	722
	11th to 20th	Night	36% 8% 14% 29% 12% 1	720
	21st to end	Night	44% 10% 13% 22% 10% 1	792
April	1st to 10th	Night	44% 8% 13% 22% 11% 2	720
	11th to 20th	Night	39% 8% 13% 24% 15% 2	711
	21st to end	Night	37% 8% 13% 26% 13% 2	586
May	1st to 10th	Night	27% 9% 14% 26% 21% 3	419
	11th to 20th	Night	28% 5% 8% 28% 28% 2	354
	21st to end	Night	31% 5% 13% 22% 26% 2	389
June	1st to 10th	Night	29% 6% 10% 25% 27% 3	360
	11th to 20th	Night	26% 5% 11% 35% 22% 2	360
	21st to end	Night	14% 1 11% 37% 36% 1	360
July	1st to 10th	Night	9% 3 6% 39% 41% 2	350
	11th to 20th	Night	5% 1 11% 49% 33%	348
	21st to end	Night	3 3 5% 39% 49% 2	394
August	1st to 10th	Night	6% 1 4 32% 47% 9%	537
	11th to 20th	Night	6% 2 6% 29% 47% 9%	534
	21st to end	Night	6% 4 12% 42% 32% 4	746
September	1st to 10th	Night	9% 2 15% 38% 33% 4	720
	11th to 20th	Night	15% 4 8% 34% 34% 5%	720
	21st to end	Night	18% 5% 10% 38% 25% 3	720
October	1st to 10th	Night	23% 6% 14% 30% 24% 4	720
	11th to 20th	Night	26% 6% 11% 32% 22% 4	720
	21st to end	Night	32% 8% 17% 26% 12% 5%	792
November	1st to 10th	Night	41% 6% 15% 28% 9% 1	740
	11th to 20th	Night	45% 7% 17% 22% 8% 1	760
	21st to end	Night	35% 7% 17% 31% 9% 1	760
December	1st to 10th	Night	37% 7% 20% 24% 11% 2	760
	11th to 20th	Night	44% 7% 18% 21% 9% 1	760
	21st to end	Night	48% 8% 19% 19% 6% 1	836

Page generated at 2024-02-27 03:30:18. Version ac07

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