Tualatin River National Wildlife Refuge
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Tualatin River National Wildlife Refuge clear sky chart from 2005-11-06 to 2024-11-12.

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% 9% 3 8% 5% 4 4 3 5% 6% 36%	105497
	Night	19% 9% 3 7% 5% 4 4 3 4 5% 36%	102360
Transparency	Day	46% 9% 12% 16% 12% 4	105240
	Night	48% 9% 13% 16% 10% 3	102206
Seeing	Day	21% 10% 20% 26% 18% 5%	14665
	Night	24% 7% 18% 31% 19% 2	23594

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	36% 15% 4 12% 7% 4 5% 3 4 3 7%	2539
	11th to 20th	Day	37% 14% 4 8% 6% 4 3 2 2 3 16%	2540
	21st to end	Day	33% 14% 5% 10% 6% 5% 4 3 4 4 13%	3063
February	1st to 10th	Day	29% 12% 4 10% 5% 5% 4 5% 5% 5% 15%	1710
	11th to 20th	Day	28% 15% 4 10% 7% 5% 4 2 4 4 17%	1665
	21st to end	Day	28% 15% 4 8% 6% 5% 4 2 4 5% 19%	1484
March	1st to 10th	Day	18% 15% 5% 12% 7% 5% 5% 4 6% 6% 16%	3293
	11th to 20th	Day	19% 9% 4 8% 5% 4 4 3 5% 5% 35%	3490
	21st to end	Day	21% 14% 6% 11% 7% 5% 6% 4 5% 6% 16%	3903
April	1st to 10th	Day	26% 12% 4 10% 7% 4 5% 3 5% 6% 18%	2280
	11th to 20th	Day	22% 12% 4 9% 6% 5% 4 4 4 6% 24%	2249
	21st to end	Day	19% 11% 3 9% 6% 5% 5% 5% 6% 7% 24%	2468
May	1st to 10th	Day	19% 8% 3 8% 6% 4 5% 4 4 5% 34%	4345
	11th to 20th	Day	11% 6% 2 6% 5% 5% 5% 4 5% 7% 46%	4377
	21st to end	Day	20% 8% 3 8% 7% 6% 6% 4 6% 6% 25%	4813
June	1st to 10th	Day	19% 9% 3 8% 5% 4 4 4 6% 6% 32%	2660
	11th to 20th	Day	17% 11% 3 7% 6% 6% 6% 5% 6% 7% 27%	2660
	21st to end	Day	8% 6% 2 6% 5% 4 4 4 5% 7% 50%	2660
July	1st to 10th	Day	4 3 1 3 3 3 3 2 4 4 71%	4420
	11th to 20th	Day	4 2 1 3 2 2 2 2 3 4 74%	4420
	21st to end	Day	5% 3 1 3 3 2 2 2 3 6% 70%	4790
August	1st to 10th	Day	3 3 1 3 3 3 3 3 4 6% 66%	4107
	11th to 20th	Day	5% 4 2 5% 4 4 4 4 6% 8% 53%	4026
	21st to end	Day	8% 6% 2 5% 4 3 3 3 5% 6% 54%	4309
September	1st to 10th	Day	6% 3 1 4 3 4 4 3 5% 7% 60%	2280
	11th to 20th	Day	11% 8% 3 7% 5% 4 6% 4 5% 7% 42%	2278
	21st to end	Day	14% 5% 3 7% 4 4 5% 3 5% 6% 44%	1999
October	1st to 10th	Day	15% 6% 2 6% 4 4 4 3 5% 6% 45%	3180
	11th to 20th	Day	16% 8% 4 9% 6% 6% 5% 4 6% 8% 28%	3161
	21st to end	Day	23% 10% 4 9% 5% 5% 5% 4 6% 8% 21%	3386
November	1st to 10th	Day	29% 14% 4 10% 5% 5% 5% 3 5% 6% 15%	1652
	11th to 20th	Day	28% 12% 5% 10% 6% 4 3 3 4 5% 19%	1528
	21st to end	Day	27% 12% 4 11% 6% 4 4 4 4 4 21%	1520
December	1st to 10th	Day	26% 14% 4 10% 5% 4 3 2 5% 5% 22%	1520
	11th to 20th	Day	29% 14% 4 10% 4 4 3 4 6% 6% 14%	1928
	21st to end	Day	31% 16% 5% 13% 9% 6% 4 3 3 3 7%	2794
January	1st to 10th	Night	33% 15% 4 11% 6% 5% 4 3 4 4 11%	4406
	11th to 20th	Night	36% 15% 4 8% 4 4 3 2 3 4 17%	4420
	21st to end	Night	36% 14% 4 9% 5% 4 3 2 4 4 15%	4600
February	1st to 10th	Night	25% 14% 4 9% 6% 4 4 4 5% 5% 19%	2470
	11th to 20th	Night	28% 11% 4 9% 5% 4 4 3 4 4 24%	2402
	21st to end	Night	26% 14% 3 9% 5% 4 5% 4 4 5% 21%	1970
March	1st to 10th	Night	16% 16% 4 11% 6% 6% 5% 4 5% 6% 22%	3564
	11th to 20th	Night	16% 10% 2 6% 5% 4 4 3 5% 6% 40%	3490
	21st to end	Night	21% 13% 4 12% 8% 6% 6% 4 5% 5% 17%	3750
April	1st to 10th	Night	24% 14% 4 9% 5% 5% 4 3 5% 5% 23%	1900
	11th to 20th	Night	18% 11% 3 7% 5% 4 4 3 5% 7% 32%	1878
	21st to end	Night	22% 10% 3 7% 5% 3 4 3 5% 7% 29%	1710
May	1st to 10th	Night	19% 9% 3 6% 4 4 3 3 4 5% 40%	2614
	11th to 20th	Night	10% 5% 2 5% 3 3 3 3 4 7% 56%	2516
	21st to end	Night	12% 8% 3 8% 5% 5% 6% 5% 7% 7% 35%	2762
June	1st to 10th	Night	16% 8% 3 9% 5% 5% 5% 3 4 8% 37%	1520
	11th to 20th	Night	13% 9% 4 8% 6% 4 4 3 5% 6% 38%	1520
	21st to end	Night	7% 5% 2 4 3 4 3 3 5% 6% 60%	1520
July	1st to 10th	Night	3 3 1 2 2 2 1 2 2 3 79%	2540
	11th to 20th	Night	4 3 1 3 2 2 2 1 2 3 77%	2540
	21st to end	Night	3 2 1 2 2 2 2 2 4 4 78%	2761
August	1st to 10th	Night	2 2 1 2 2 1 2 2 4 5% 76%	2816
	11th to 20th	Night	7% 4 2 5% 4 4 4 3 5% 6% 57%	2812
	21st to end	Night	9% 5% 2 5% 3 3 3 2 3 5% 61%	3365
September	1st to 10th	Night	6% 3 2 4 2 2 3 2 4 5% 66%	1900
	11th to 20th	Night	10% 6% 3 6% 5% 5% 4 4 5% 5% 49%	1900
	21st to end	Night	11% 4 2 5% 4 4 4 3 5% 7% 52%	2180
October	1st to 10th	Night	11% 5% 2 6% 3 4 4 4 5% 7% 50%	3800
	11th to 20th	Night	16% 6% 3 7% 4 4 5% 4 6% 9% 36%	3777
	21st to end	Night	21% 10% 4 8% 5% 5% 5% 3 5% 6% 28%	4181
November	1st to 10th	Night	27% 11% 3 9% 6% 5% 4 3 5% 5% 23%	2644
	11th to 20th	Night	32% 10% 4 8% 5% 4 3 3 4 5% 21%	2674
	21st to end	Night	25% 10% 3 9% 6% 4 4 3 5% 5% 27%	2660
December	1st to 10th	Night	28% 11% 4 7% 5% 4 3 3 5% 6% 23%	2660
	11th to 20th	Night	29% 12% 4 10% 5% 4 4 3 4 6% 19%	3276
	21st to end	Night	28% 13% 5% 11% 7% 5% 5% 3 4 4 14%	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	78% 12% 5% 3 2 1	2539
	11th to 20th	Day	75% 5% 6% 9% 3 1	2540
	21st to end	Day	72% 10% 7% 7% 5%	3063
February	1st to 10th	Day	67% 11% 10% 8% 4	1710
	11th to 20th	Day	68% 11% 7% 8% 4 2	1674
	21st to end	Day	68% 7% 10% 8% 5% 1	1484
March	1st to 10th	Day	58% 15% 14% 9% 3	3293
	11th to 20th	Day	49% 10% 9% 23% 10%	3490
	21st to end	Day	63% 15% 11% 7% 4	3903
April	1st to 10th	Day	64% 10% 12% 11% 3	2280
	11th to 20th	Day	60% 9% 10% 12% 8% 2	2252
	21st to end	Day	57% 11% 12% 11% 8% 1	2468
May	1st to 10th	Day	46% 12% 15% 15% 12%	4345
	11th to 20th	Day	30% 14% 21% 23% 11% 1	4380
	21st to end	Day	51% 18% 17% 12% 2	4814
June	1st to 10th	Day	50% 9% 16% 17% 6%	2660
	11th to 20th	Day	51% 12% 17% 13% 6%	2660
	21st to end	Day	32% 7% 18% 27% 10% 4	2660
July	1st to 10th	Day	17% 6% 8% 17% 21% 31%	4351
	11th to 20th	Day	14% 4 6% 19% 37% 19%	4345
	21st to end	Day	16% 5% 11% 27% 35% 6%	4639
August	1st to 10th	Day	18% 5% 11% 26% 26% 13%	4091
	11th to 20th	Day	26% 9% 18% 29% 13% 4	4065
	21st to end	Day	29% 7% 12% 25% 21% 7%	4308
September	1st to 10th	Day	23% 7% 14% 26% 19% 12%	2280
	11th to 20th	Day	39% 9% 15% 17% 13% 6%	2278
	21st to end	Day	38% 9% 15% 19% 14% 5%	1999
October	1st to 10th	Day	39% 6% 7% 25% 21% 2	3180
	11th to 20th	Day	52% 9% 14% 13% 11% 1	3161
	21st to end	Day	60% 6% 8% 16% 9% 1	3386
November	1st to 10th	Day	69% 8% 9% 10% 3	1652
	11th to 20th	Day	67% 7% 11% 8% 6% 1	1528
	21st to end	Day	65% 8% 6% 9% 11% 1	1520
December	1st to 10th	Day	65% 6% 9% 10% 8% 1	1520
	11th to 20th	Day	66% 12% 11% 9% 2	1928
	21st to end	Day	77% 11% 6% 3 2	2794
January	1st to 10th	Night	73% 12% 7% 5% 3 1	4406
	11th to 20th	Night	72% 7% 6% 10% 4 1	4420
	21st to end	Night	71% 8% 8% 7% 5% 1	4600
February	1st to 10th	Night	64% 11% 10% 10% 4 1	2470
	11th to 20th	Night	61% 9% 12% 10% 6% 2	2404
	21st to end	Night	62% 9% 12% 10% 5% 2	1970
March	1st to 10th	Night	57% 13% 14% 12% 3	3564
	11th to 20th	Night	40% 12% 14% 22% 11% 1	3490
	21st to end	Night	63% 15% 12% 10% 1	3750
April	1st to 10th	Night	62% 9% 13% 11% 5%	1900
	11th to 20th	Night	49% 11% 16% 13% 7% 3	1878
	21st to end	Night	52% 10% 14% 15% 7% 2	1710
May	1st to 10th	Night	42% 12% 16% 20% 9% 1	2614
	11th to 20th	Night	27% 8% 23% 32% 8% 2	2516
	21st to end	Night	40% 20% 27% 10% 3	2762
June	1st to 10th	Night	46% 8% 18% 22% 5% 1	1520
	11th to 20th	Night	45% 9% 19% 21% 6%	1520
	21st to end	Night	26% 7% 19% 31% 12% 4	1520
July	1st to 10th	Night	13% 4 9% 20% 25% 29%	2500
	11th to 20th	Night	14% 4 7% 19% 35% 22%	2492
	21st to end	Night	11% 4 13% 28% 37% 7%	2674
August	1st to 10th	Night	12% 3 11% 34% 30% 10%	2808
	11th to 20th	Night	27% 7% 21% 30% 11% 4	2839
	21st to end	Night	27% 5% 14% 27% 20% 6%	3365
September	1st to 10th	Night	19% 7% 14% 28% 20% 12%	1900
	11th to 20th	Night	34% 9% 14% 23% 12% 9%	1900
	21st to end	Night	31% 7% 18% 20% 17% 7%	2180
October	1st to 10th	Night	32% 6% 10% 31% 19% 2	3800
	11th to 20th	Night	43% 8% 18% 19% 11% 2	3777
	21st to end	Night	55% 7% 11% 15% 10% 1	4181
November	1st to 10th	Night	60% 10% 9% 14% 6%	2644
	11th to 20th	Night	64% 8% 10% 8% 7% 2	2674
	21st to end	Night	57% 10% 9% 10% 12% 2	2660
December	1st to 10th	Night	60% 9% 9% 11% 10% 1	2660
	11th to 20th	Night	66% 11% 9% 11% 4	3276
	21st to end	Night	67% 14% 11% 6% 2	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	46% 11% 16% 14% 11% 1	180
	11th to 20th	Day	41% 9% 21% 19% 8% 2	180
	21st to end	Day	34% 11% 19% 20% 13% 3	363
February	1st to 10th	Day	34% 12% 19% 19% 13% 3	370
	11th to 20th	Day	33% 14% 24% 17% 9% 2	365
	21st to end	Day	35% 16% 22% 18% 9% 1	341
March	1st to 10th	Day	31% 15% 23% 22% 8% 2	460
	11th to 20th	Day	27% 13% 22% 22% 12% 4	460
	21st to end	Day	30% 17% 23% 18% 11% 1	506
April	1st to 10th	Day	30% 15% 22% 21% 8% 4	460
	11th to 20th	Day	29% 14% 26% 19% 8% 3	452
	21st to end	Day	23% 14% 27% 22% 13% 1	460
May	1st to 10th	Day	20% 13% 22% 25% 15% 4	463
	11th to 20th	Day	26% 10% 16% 28% 16% 5%	488
	21st to end	Day	19% 10% 18% 29% 19% 6%	529
June	1st to 10th	Day	21% 9% 20% 27% 19% 4	490
	11th to 20th	Day	17% 12% 26% 27% 14% 3	490
	21st to end	Day	7% 6% 20% 37% 24% 6%	490
July	1st to 10th	Day	7% 5% 19% 35% 28% 7%	486
	11th to 20th	Day	4 4 21% 40% 25% 5%	484
	21st to end	Day	4 3 16% 37% 31% 8%	531
August	1st to 10th	Day	5% 3 11% 39% 32% 10%	487
	11th to 20th	Day	4 2 13% 34% 35% 12%	477
	21st to end	Day	7% 4 21% 33% 26% 8%	539
September	1st to 10th	Day	7% 4 23% 29% 28% 8%	490
	11th to 20th	Day	13% 6% 18% 29% 27% 7%	490
	21st to end	Day	14% 8% 21% 33% 20% 3	490
October	1st to 10th	Day	20% 8% 21% 25% 18% 8%	490
	11th to 20th	Day	21% 9% 18% 28% 18% 7%	490
	21st to end	Day	31% 11% 23% 20% 11% 5%	501
November	1st to 10th	Day	32% 11% 23% 18% 12% 3	243
	11th to 20th	Day	26% 20% 20% 16% 13% 4	182
	21st to end	Day	28% 13% 20% 19% 19% 2	180
December	1st to 10th	Day	36% 11% 18% 21% 11% 4	180
	11th to 20th	Day	39% 12% 24% 17% 6% 1	180
	21st to end	Day	40% 15% 16% 16% 12% 1	198
January	1st to 10th	Night	41% 9% 17% 20% 11% 1	760
	11th to 20th	Night	36% 10% 16% 23% 15% 1	760
	21st to end	Night	33% 7% 16% 30% 12% 2	836
February	1st to 10th	Night	32% 8% 16% 28% 14% 1	760
	11th to 20th	Night	32% 10% 19% 23% 16%	744
	21st to end	Night	32% 12% 19% 30% 8%	628
March	1st to 10th	Night	28% 9% 21% 28% 13% 1	760
	11th to 20th	Night	25% 10% 19% 32% 13% 1	760
	21st to end	Night	28% 9% 23% 27% 12% 1	836
April	1st to 10th	Night	30% 8% 18% 27% 16% 1	760
	11th to 20th	Night	22% 9% 23% 30% 14% 1	750
	21st to end	Night	27% 6% 21% 30% 15% 1	570
May	1st to 10th	Night	17% 7% 25% 33% 17% 1	428
	11th to 20th	Night	18% 5% 18% 36% 22% 2	374
	21st to end	Night	17% 6% 22% 34% 21%	411
June	1st to 10th	Night	18% 4 24% 34% 20% 1	380
	11th to 20th	Night	14% 6% 25% 41% 12% 1	380
	21st to end	Night	9% 2 24% 44% 20%	380
July	1st to 10th	Night	5% 3 15% 51% 26% 1	370
	11th to 20th	Night	7% 1 23% 46% 23% 1	368
	21st to end	Night	2 2 17% 50% 29% 1	416
August	1st to 10th	Night	5% 1 10% 41% 39% 5%	548
	11th to 20th	Night	5% 2 8% 36% 45% 4	564
	21st to end	Night	8% 3 15% 43% 29% 2	755
September	1st to 10th	Night	7% 3 17% 40% 30% 2	760
	11th to 20th	Night	12% 3 14% 33% 35% 4	760
	21st to end	Night	13% 3 16% 40% 26% 3	760
October	1st to 10th	Night	18% 3 20% 32% 25% 3	760
	11th to 20th	Night	19% 6% 15% 31% 26% 3	760
	21st to end	Night	25% 9% 18% 29% 16% 3	836
November	1st to 10th	Night	30% 8% 17% 31% 14%	780
	11th to 20th	Night	35% 9% 18% 25% 12% 1	764
	21st to end	Night	29% 6% 20% 29% 16% 1	760
December	1st to 10th	Night	31% 8% 18% 28% 13% 1	760
	11th to 20th	Night	38% 7% 20% 23% 12% 1	760
	21st to end	Night	38% 9% 20% 22% 9% 1	836

Page generated at 2024-11-08 19:45:36. Version ac07

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