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 2024-11-01.

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	20% 11% 2 5% 3 3 3 3 4 5% 41%	101499
	Night	23% 13% 2 5% 3 3 3 2 4 4 37%	97609
Transparency	Day	47% 4 9% 18% 14% 7%	101243
	Night	52% 4 9% 16% 12% 6%	97454
Seeing	Day	26% 12% 26% 22% 10% 3	14706
	Night	31% 6% 14% 28% 18% 2	23668

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 7% 4 3 3 2 3 2 12%	2539
	11th to 20th	Day	39% 16% 3 6% 3 4 3 2 3 3 20%	2540
	21st to end	Day	38% 15% 3 6% 4 3 2 3 4 4 18%	3096
February	1st to 10th	Day	31% 15% 4 7% 4 3 4 3 4 5% 20%	1710
	11th to 20th	Day	27% 20% 3 6% 4 3 4 4 4 4 21%	1665
	21st to end	Day	29% 24% 3 6% 3 4 3 2 3 3 19%	1516
March	1st to 10th	Day	21% 25% 4 6% 4 4 3 3 5% 5% 21%	3283
	11th to 20th	Day	20% 17% 2 5% 3 3 3 2 3 4 38%	3490
	21st to end	Day	29% 22% 4 8% 5% 4 4 3 4 4 14%	3913
April	1st to 10th	Day	30% 22% 4 7% 5% 3 3 3 4 3 16%	2280
	11th to 20th	Day	25% 19% 4 7% 5% 4 3 3 3 4 24%	2249
	21st to end	Day	29% 14% 3 6% 4 4 3 3 5% 5% 25%	2418
May	1st to 10th	Day	26% 14% 3 6% 3 3 3 2 3 4 33%	4322
	11th to 20th	Day	15% 6% 2 4 3 3 3 3 5% 6% 50%	4377
	21st to end	Day	23% 13% 2 6% 4 4 4 3 5% 6% 29%	4813
June	1st to 10th	Day	27% 9% 3 6% 5% 4 3 3 3 5% 33%	2660
	11th to 20th	Day	24% 9% 2 6% 4 4 4 3 6% 6% 32%	2660
	21st to end	Day	11% 5% 2 4 3 3 2 3 4 6% 57%	2660
July	1st to 10th	Day	4 2 1 2 2 1 1 1 2 3 81%	4420
	11th to 20th	Day	4 2 1 2 2 1 2 2 3 3 78%	4420
	21st to end	Day	3 3 1 2 1 2 2 2 3 4 78%	4774
August	1st to 10th	Day	3 2 1 3 2 2 2 2 3 5% 73%	4091
	11th to 20th	Day	4 3 2 4 3 3 3 3 4 6% 65%	4026
	21st to end	Day	6% 4 1 4 3 3 3 3 4 5% 64%	4251
September	1st to 10th	Day	7% 3 2 3 2 2 1 2 3 5% 69%	2280
	11th to 20th	Day	13% 8% 3 5% 3 3 3 3 5% 5% 49%	2280
	21st to end	Day	17% 5% 2 6% 4 4 3 2 4 5% 49%	2006
October	1st to 10th	Day	20% 8% 2 4 3 3 3 3 4 5% 46%	1900
	11th to 20th	Day	24% 8% 2 6% 4 3 3 3 5% 6% 38%	1900
	21st to end	Day	27% 9% 3 7% 4 4 4 2 3 5% 33%	2057
November	1st to 10th	Day	37% 12% 4 6% 4 4 3 2 3 5% 21%	1621
	11th to 20th	Day	36% 10% 3 8% 4 3 3 3 6% 4 21%	1520
	21st to end	Day	28% 13% 3 7% 4 4 4 2 4 4 27%	1520
December	1st to 10th	Day	26% 14% 3 6% 3 4 3 3 3 4 30%	1520
	11th to 20th	Day	32% 16% 3 7% 4 2 4 3 4 6% 19%	1928
	21st to end	Day	32% 18% 4 8% 4 3 3 2 3 3 18%	2794
January	1st to 10th	Night	36% 23% 3 6% 4 3 3 2 3 4 12%	4406
	11th to 20th	Night	38% 17% 3 5% 3 2 3 2 3 3 20%	4420
	21st to end	Night	37% 17% 3 7% 3 3 3 2 3 4 18%	4553
February	1st to 10th	Night	27% 21% 4 7% 5% 4 4 3 4 4 19%	2470
	11th to 20th	Night	28% 20% 3 6% 4 3 3 2 4 4 24%	2402
	21st to end	Night	29% 24% 3 5% 3 3 2 3 3 5% 20%	1937
March	1st to 10th	Night	21% 26% 4 7% 3 3 3 3 5% 5% 20%	3587
	11th to 20th	Night	21% 17% 2 4 2 2 2 2 3 4 40%	3490
	21st to end	Night	29% 27% 3 7% 4 3 3 3 3 4 15%	3739
April	1st to 10th	Night	30% 21% 3 7% 3 3 3 2 3 4 20%	1900
	11th to 20th	Night	26% 20% 2 5% 4 3 3 3 4 4 26%	1879
	21st to end	Night	29% 15% 3 5% 4 4 3 3 4 5% 27%	1758
May	1st to 10th	Night	25% 18% 3 5% 3 2 2 2 3 4 32%	2641
	11th to 20th	Night	16% 9% 2 4 3 3 3 3 4 4 49%	2516
	21st to end	Night	23% 13% 2 4 4 3 3 3 4 6% 33%	2762
June	1st to 10th	Night	26% 9% 2 5% 4 3 4 4 4 6% 34%	1520
	11th to 20th	Night	21% 10% 2 5% 3 4 3 3 5% 6% 39%	1520
	21st to end	Night	11% 5% 2 5% 4 3 2 2 3 4 59%	1520
July	1st to 10th	Night	4 2 1 2 1 1 1 1 2 3 81%	2540
	11th to 20th	Night	3 2 1 3 1 2 2 2 2 3 79%	2540
	21st to end	Night	5% 1 1 1 1 1 2 1 2 3 81%	2774
August	1st to 10th	Night	2 2 1 2 2 2 3 2 4 5% 74%	2848
	11th to 20th	Night	4 3 1 4 4 3 4 3 4 6% 62%	2812
	21st to end	Night	8% 4 2 4 2 2 2 2 3 5% 67%	3424
September	1st to 10th	Night	7% 3 1 3 2 2 3 2 3 5% 69%	1900
	11th to 20th	Night	13% 5% 2 4 3 4 4 3 4 5% 54%	1900
	21st to end	Night	16% 7% 1 3 3 3 3 3 4 6% 51%	2170
October	1st to 10th	Night	18% 8% 3 5% 3 2 3 2 3 4 48%	2280
	11th to 20th	Night	23% 8% 2 4 3 3 3 3 4 6% 42%	2280
	21st to end	Night	27% 10% 3 5% 3 3 3 3 4 4 35%	2540
November	1st to 10th	Night	34% 12% 3 7% 4 3 3 3 4 5% 23%	2463
	11th to 20th	Night	37% 11% 2 6% 3 3 4 3 4 4 22%	2660
	21st to end	Night	27% 13% 2 6% 4 4 3 3 4 4 30%	2660
December	1st to 10th	Night	28% 13% 3 6% 4 2 4 3 4 6% 28%	2660
	11th to 20th	Night	31% 16% 3 6% 4 4 4 3 5% 5% 20%	3276
	21st to end	Night	29% 17% 4 8% 5% 4 3 3 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	64% 4 6% 18% 7%	3283
	11th to 20th	Day	52% 4 6% 24% 14% 1	3490
	21st to end	Day	75% 5% 8% 8% 4	3913
April	1st to 10th	Day	74% 4 8% 9% 5%	2280
	11th to 20th	Day	66% 4 9% 11% 7% 3	2252
	21st to end	Day	61% 5% 12% 14% 6% 2	2418
May	1st to 10th	Day	56% 4 10% 19% 10%	4322
	11th to 20th	Day	34% 5% 14% 32% 14%	4380
	21st to end	Day	56% 6% 21% 15% 2	4814
June	1st to 10th	Day	56% 4 14% 19% 6% 1	2660
	11th to 20th	Day	52% 5% 16% 20% 6% 1	2660
	21st to end	Day	29% 4 16% 32% 14% 5%	2660
July	1st to 10th	Day	11% 3 8% 16% 29% 34%	4351
	11th to 20th	Day	13% 2 5% 15% 28% 37%	4345
	21st to end	Day	12% 2 7% 25% 39% 14%	4623
August	1st to 10th	Day	15% 2 8% 26% 32% 16%	4076
	11th to 20th	Day	20% 5% 13% 38% 20% 5%	4065
	21st to end	Day	23% 5% 12% 24% 22% 15%	4250
September	1st to 10th	Day	20% 2 6% 31% 24% 16%	2280
	11th to 20th	Day	36% 4 11% 23% 17% 9%	2280
	21st to end	Day	39% 4 9% 22% 17% 9%	2006
October	1st to 10th	Day	43% 4 6% 18% 20% 9%	1900
	11th to 20th	Day	48% 6% 9% 14% 18% 5%	1900
	21st to end	Day	56% 4 6% 12% 17% 4	2057
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	65% 5% 10% 15% 4 1	3587
	11th to 20th	Night	51% 3 9% 22% 14%	3490
	21st to end	Night	76% 4 9% 9% 2	3739
April	1st to 10th	Night	70% 4 10% 10% 6%	1900
	11th to 20th	Night	62% 5% 12% 11% 7% 3	1879
	21st to end	Night	62% 5% 11% 14% 6% 3	1758
May	1st to 10th	Night	57% 5% 10% 16% 12% 1	2641
	11th to 20th	Night	37% 7% 9% 35% 10% 1	2516
	21st to end	Night	52% 7% 23% 15% 3	2762
June	1st to 10th	Night	52% 7% 14% 22% 6%	1520
	11th to 20th	Night	48% 6% 16% 23% 6% 1	1520
	21st to end	Night	31% 3 16% 31% 14% 5%	1520
July	1st to 10th	Night	12% 2 7% 18% 26% 35%	2500
	11th to 20th	Night	13% 2 5% 16% 29% 35%	2492
	21st to end	Night	10% 2 8% 26% 41% 12%	2687
August	1st to 10th	Night	13% 3 7% 31% 30% 14%	2839
	11th to 20th	Night	23% 5% 15% 31% 20% 5%	2839
	21st to end	Night	22% 3 13% 25% 24% 13%	3424
September	1st to 10th	Night	19% 3 9% 28% 26% 15%	1900
	11th to 20th	Night	34% 4 10% 26% 14% 12%	1900
	21st to end	Night	35% 4 11% 22% 17% 11%	2170
October	1st to 10th	Night	41% 5% 8% 17% 21% 8%	2280
	11th to 20th	Night	45% 5% 11% 16% 17% 6%	2280
	21st to end	Night	54% 4 6% 12% 16% 7%	2540
November	1st to 10th	Night	65% 5% 6% 10% 12% 2	2463
	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	45% 14% 18% 17% 5%	357
March	1st to 10th	Day	39% 17% 20% 18% 4	460
	11th to 20th	Day	37% 11% 25% 19% 6% 2	460
	21st to end	Day	44% 17% 20% 15% 3 1	506
April	1st to 10th	Day	41% 15% 22% 15% 7% 1	460
	11th to 20th	Day	38% 17% 25% 13% 6% 1	452
	21st to end	Day	40% 15% 21% 16% 7% 1	460
May	1st to 10th	Day	27% 16% 27% 21% 6% 2	463
	11th to 20th	Day	33% 11% 24% 21% 8% 4	488
	21st to end	Day	30% 10% 24% 22% 11% 4	529
June	1st to 10th	Day	29% 13% 21% 24% 10% 3	490
	11th to 20th	Day	26% 15% 29% 18% 10% 1	490
	21st to end	Day	10% 10% 36% 29% 12% 4	490
July	1st to 10th	Day	9% 9% 39% 25% 13% 5%	486
	11th to 20th	Day	4 12% 37% 28% 14% 6%	484
	21st to end	Day	3 9% 37% 28% 17% 7%	531
August	1st to 10th	Day	2 11% 33% 33% 13% 8%	487
	11th to 20th	Day	3 10% 28% 33% 18% 7%	477
	21st to end	Day	8% 11% 33% 31% 12% 5%	539
September	1st to 10th	Day	9% 10% 33% 28% 16% 4	490
	11th to 20th	Day	17% 9% 30% 30% 14% 1	490
	21st to end	Day	17% 13% 27% 28% 12% 2	490
October	1st to 10th	Day	22% 10% 27% 25% 13% 2	490
	11th to 20th	Day	27% 8% 20% 26% 16% 4	490
	21st to end	Day	32% 14% 22% 18% 11% 3	506
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	40% 10% 13% 27% 9% 1	760
	11th to 20th	Night	36% 8% 15% 28% 12% 1	760
	21st to end	Night	43% 10% 14% 22% 10% 1	836
April	1st to 10th	Night	43% 8% 14% 22% 11% 2	760
	11th to 20th	Night	38% 8% 14% 24% 14% 2	751
	21st to end	Night	38% 8% 13% 26% 13% 2	618
May	1st to 10th	Night	28% 9% 15% 25% 20% 2	442
	11th to 20th	Night	28% 5% 8% 29% 27% 2	374
	21st to end	Night	31% 5% 13% 23% 27% 1	411
June	1st to 10th	Night	29% 6% 10% 26% 27% 3	380
	11th to 20th	Night	25% 5% 12% 35% 22% 2	380
	21st to end	Night	14% 2 11% 37% 36% 1	380
July	1st to 10th	Night	8% 3 7% 40% 40% 2	370
	11th to 20th	Night	5% 1 11% 50% 32%	368
	21st to end	Night	3 3 6% 38% 48% 2	417
August	1st to 10th	Night	6% 1 4 33% 47% 9%	567
	11th to 20th	Night	6% 2 7% 31% 45% 9%	564
	21st to end	Night	6% 4 12% 42% 32% 3	788
September	1st to 10th	Night	9% 2 15% 39% 33% 4	760
	11th to 20th	Night	15% 4 8% 35% 32% 5%	760
	21st to end	Night	18% 5% 11% 38% 26% 3	760
October	1st to 10th	Night	22% 5% 14% 32% 23% 4	760
	11th to 20th	Night	25% 6% 11% 33% 21% 4	760
	21st to end	Night	31% 9% 18% 26% 11% 5%	836
November	1st to 10th	Night	42% 6% 15% 28% 8% 1	742
	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 2024-10-29 08:20:51. Version ac07

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