Molalla
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Molalla clear sky chart from 2005-11-06 to 2025-05-11.

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	19% 9% 3 7% 4 4 4 3 5% 6% 37%	118007
	Night	21% 10% 3 7% 4 4 4 3 4 5% 34%	119760
Transparency	Day	48% 6% 12% 17% 13% 5%	117750
	Night	51% 6% 12% 16% 11% 4	119606
Seeing	Day	24% 8% 21% 27% 15% 4	15215
	Night	28% 6% 14% 29% 21% 3	24312

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% 17% 3 9% 5% 4 4 2 4 4 11%	3639
	11th to 20th	Day	27% 11% 3 6% 5% 3 4 4 5% 5% 27%	3640
	21st to end	Day	24% 9% 2 7% 5% 4 4 4 5% 5% 31%	4393
February	1st to 10th	Day	29% 13% 3 8% 5% 4 5% 4 5% 7% 17%	1800
	11th to 20th	Day	26% 15% 4 8% 7% 5% 4 3 4 5% 20%	1755
	21st to end	Day	28% 17% 4 7% 5% 4 4 3 4 5% 20%	1576
March	1st to 10th	Day	16% 12% 4 8% 6% 6% 6% 5% 6% 7% 22%	4727
	11th to 20th	Day	24% 15% 3 8% 5% 4 4 3 4 4 27%	5000
	21st to end	Day	23% 13% 4 10% 7% 6% 6% 5% 7% 7% 13%	5612
April	1st to 10th	Day	27% 15% 4 9% 5% 5% 4 3 5% 6% 17%	2400
	11th to 20th	Day	22% 14% 4 7% 5% 5% 4 4 5% 5% 26%	2369
	21st to end	Day	23% 11% 3 9% 5% 5% 4 3 6% 6% 25%	2575
May	1st to 10th	Day	22% 11% 2 7% 4 4 4 3 4 6% 32%	4491
	11th to 20th	Day	13% 7% 2 6% 4 4 4 3 5% 6% 45%	4380
	21st to end	Day	23% 9% 3 8% 6% 5% 5% 4 6% 6% 25%	4813
June	1st to 10th	Day	23% 10% 3 6% 5% 4 3 4 5% 6% 32%	2660
	11th to 20th	Day	22% 9% 3 7% 6% 5% 5% 4 6% 7% 27%	2660
	21st to end	Day	10% 5% 2 5% 4 4 3 3 4 6% 54%	2660
July	1st to 10th	Day	4 3 1 2 2 3 3 2 4 5% 73%	4420
	11th to 20th	Day	4 2 1 2 2 2 2 2 3 4 75%	4420
	21st to end	Day	5% 3 1 2 2 2 2 2 3 4 73%	4790
August	1st to 10th	Day	3 3 1 4 3 3 3 3 4 6% 67%	4127
	11th to 20th	Day	5% 4 1 5% 3 3 4 4 6% 7% 58%	4026
	21st to end	Day	8% 6% 2 4 3 3 4 3 5% 7% 56%	4280
September	1st to 10th	Day	8% 3 1 4 2 2 2 3 5% 8% 62%	2280
	11th to 20th	Day	11% 6% 3 7% 5% 3 5% 4 6% 6% 44%	2280
	21st to end	Day	16% 6% 2 6% 4 4 3 3 4 7% 46%	2002
October	1st to 10th	Day	17% 5% 2 4 3 3 3 3 4 6% 50%	3180
	11th to 20th	Day	18% 7% 2 8% 5% 5% 5% 4 5% 7% 34%	3161
	21st to end	Day	23% 9% 4 8% 5% 5% 5% 4 6% 8% 23%	3365
November	1st to 10th	Day	30% 9% 4 10% 4 4 4 3 5% 6% 21%	1674
	11th to 20th	Day	30% 10% 4 8% 6% 5% 4 3 5% 5% 20%	1600
	21st to end	Day	25% 12% 4 8% 5% 5% 5% 3 5% 5% 24%	1600
December	1st to 10th	Day	21% 9% 2 6% 4 4 4 4 6% 7% 33%	2620
	11th to 20th	Day	29% 12% 5% 11% 6% 5% 5% 4 5% 6% 12%	3028
	21st to end	Day	34% 16% 4 9% 5% 5% 4 3 4 4 11%	4004
January	1st to 10th	Night	33% 16% 4 9% 5% 5% 4 3 3 4 13%	6306
	11th to 20th	Night	27% 13% 3 6% 4 3 3 3 4 5% 29%	6320
	21st to end	Night	25% 10% 3 7% 4 3 3 2 4 4 34%	6578
February	1st to 10th	Night	27% 14% 4 7% 6% 5% 5% 3 5% 6% 18%	2600
	11th to 20th	Night	30% 14% 3 8% 4 4 4 2 5% 5% 24%	2532
	21st to end	Night	28% 16% 3 7% 4 3 4 3 4 6% 21%	2053
March	1st to 10th	Night	17% 12% 3 9% 6% 6% 6% 5% 6% 6% 23%	5166
	11th to 20th	Night	22% 13% 3 7% 4 4 4 3 4 5% 29%	5000
	21st to end	Night	25% 15% 3 9% 5% 6% 5% 4 6% 7% 14%	5361
April	1st to 10th	Night	25% 16% 4 8% 5% 4 4 4 5% 5% 20%	2000
	11th to 20th	Night	21% 13% 4 7% 3 4 4 3 6% 6% 30%	1979
	21st to end	Night	26% 11% 3 7% 5% 4 4 4 5% 6% 27%	1823
May	1st to 10th	Night	26% 12% 3 6% 3 3 3 3 4 4 34%	2691
	11th to 20th	Night	16% 6% 3 6% 3 3 3 3 4 6% 46%	2519
	21st to end	Night	23% 9% 3 8% 5% 4 4 4 6% 6% 29%	2762
June	1st to 10th	Night	21% 9% 2 6% 4 4 5% 4 4 5% 36%	1520
	11th to 20th	Night	20% 11% 3 7% 5% 3 4 3 4 5% 34%	1520
	21st to end	Night	10% 6% 2 5% 3 2 4 3 3 5% 56%	1520
July	1st to 10th	Night	5% 3 1 4 2 2 2 1 3 3 76%	2540
	11th to 20th	Night	3 2 1 3 2 2 1 2 3 3 76%	2540
	21st to end	Night	4 2 1 3 2 2 2 2 3 4 76%	2761
August	1st to 10th	Night	2 2 1 2 2 2 2 2 4 6% 73%	2807
	11th to 20th	Night	6% 6% 2 6% 3 4 3 3 5% 7% 55%	2812
	21st to end	Night	11% 4 2 5% 2 2 2 2 3 5% 60%	3393
September	1st to 10th	Night	7% 4 1 4 2 2 3 2 4 4 66%	1900
	11th to 20th	Night	12% 6% 2 5% 5% 4 5% 3 4 5% 50%	1900
	21st to end	Night	13% 5% 1 5% 3 3 4 3 6% 7% 49%	2173
October	1st to 10th	Night	15% 5% 2 5% 3 3 3 2 4 6% 52%	3800
	11th to 20th	Night	16% 6% 3 7% 4 4 4 4 6% 8% 37%	3777
	21st to end	Night	24% 10% 4 7% 5% 4 4 4 5% 6% 26%	4199
November	1st to 10th	Night	30% 9% 3 8% 5% 5% 4 3 5% 7% 22%	2620
	11th to 20th	Night	33% 8% 3 9% 5% 4 4 3 5% 4 22%	2800
	21st to end	Night	25% 12% 2 6% 5% 4 5% 4 5% 5% 28%	2800
December	1st to 10th	Night	18% 8% 3 6% 4 4 4 3 5% 7% 39%	4560
	11th to 20th	Night	31% 14% 4 9% 5% 4 4 3 4 5% 14%	5176
	21st to end	Night	31% 13% 4 9% 5% 5% 5% 3 4 5% 16%	6952

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	77% 6% 5% 7% 4 1	3639
	11th to 20th	Day	57% 5% 9% 17% 10% 2	3640
	21st to end	Day	54% 6% 7% 14% 15% 5%	4393
February	1st to 10th	Day	66% 6% 11% 11% 6%	1800
	11th to 20th	Day	69% 6% 8% 10% 5% 2	1764
	21st to end	Day	68% 4 10% 9% 8% 2	1576
March	1st to 10th	Day	59% 5% 16% 15% 5%	4727
	11th to 20th	Day	62% 5% 7% 17% 9% 1	5000
	21st to end	Day	68% 9% 12% 8% 3	5612
April	1st to 10th	Day	68% 5% 12% 11% 3	2400
	11th to 20th	Day	60% 5% 10% 13% 8% 3	2372
	21st to end	Day	60% 6% 12% 14% 7% 1	2575
May	1st to 10th	Day	53% 4 14% 17% 12%	4491
	11th to 20th	Day	35% 9% 17% 26% 12% 1	4383
	21st to end	Day	57% 10% 17% 14% 2	4814
June	1st to 10th	Day	54% 5% 16% 18% 6% 1	2660
	11th to 20th	Day	56% 6% 17% 15% 6%	2660
	21st to end	Day	33% 4 17% 30% 11% 4	2660
July	1st to 10th	Day	15% 4 9% 19% 22% 31%	4351
	11th to 20th	Day	14% 3 7% 18% 37% 22%	4345
	21st to end	Day	15% 3 10% 27% 36% 8%	4639
August	1st to 10th	Day	18% 4 10% 29% 28% 11%	4111
	11th to 20th	Day	23% 7% 18% 34% 14% 4	4065
	21st to end	Day	28% 5% 13% 24% 22% 8%	4279
September	1st to 10th	Day	22% 4 11% 30% 21% 12%	2280
	11th to 20th	Day	38% 7% 13% 20% 14% 7%	2280
	21st to end	Day	39% 5% 14% 20% 15% 7%	2002
October	1st to 10th	Day	36% 4 7% 25% 22% 5%	3180
	11th to 20th	Day	48% 6% 16% 17% 11% 2	3161
	21st to end	Day	55% 7% 9% 18% 10% 1	3365
November	1st to 10th	Day	65% 5% 10% 14% 5% 1	1674
	11th to 20th	Day	65% 7% 9% 10% 6% 2	1600
	21st to end	Day	62% 5% 10% 7% 15% 1	1600
December	1st to 10th	Day	48% 5% 11% 10% 22% 3	2620
	11th to 20th	Day	71% 7% 11% 8% 3	3028
	21st to end	Day	75% 7% 8% 7% 2	4004
January	1st to 10th	Night	75% 5% 6% 8% 5% 1	6306
	11th to 20th	Night	57% 5% 9% 19% 7% 3	6320
	21st to end	Night	55% 3 5% 13% 15% 7%	6578
February	1st to 10th	Night	68% 6% 9% 10% 6% 2	2600
	11th to 20th	Night	63% 6% 12% 10% 7% 3	2534
	21st to end	Night	65% 4 10% 12% 6% 2	2053
March	1st to 10th	Night	59% 6% 15% 14% 6% 1	5166
	11th to 20th	Night	57% 6% 11% 14% 11% 1	5000
	21st to end	Night	68% 7% 14% 11% 1	5361
April	1st to 10th	Night	66% 6% 12% 11% 4	2000
	11th to 20th	Night	56% 6% 15% 13% 7% 3	1979
	21st to end	Night	58% 5% 14% 14% 6% 3	1823
May	1st to 10th	Night	53% 5% 13% 19% 9% 1	2691
	11th to 20th	Night	36% 7% 17% 29% 7% 2	2519
	21st to end	Night	52% 12% 23% 11% 3	2762
June	1st to 10th	Night	51% 5% 17% 21% 5%	1520
	11th to 20th	Night	53% 5% 17% 19% 5% 1	1520
	21st to end	Night	32% 4 19% 28% 11% 5%	1520
July	1st to 10th	Night	16% 4 7% 20% 27% 26%	2500
	11th to 20th	Night	15% 3 7% 19% 35% 22%	2492
	21st to end	Night	12% 4 13% 28% 36% 7%	2674
August	1st to 10th	Night	13% 3 11% 37% 27% 9%	2799
	11th to 20th	Night	28% 6% 21% 28% 12% 4	2839
	21st to end	Night	28% 4 12% 29% 17% 10%	3393
September	1st to 10th	Night	21% 4 13% 29% 20% 11%	1900
	11th to 20th	Night	34% 8% 11% 24% 13% 10%	1900
	21st to end	Night	34% 5% 16% 22% 15% 9%	2173
October	1st to 10th	Night	34% 5% 7% 27% 23% 3	3800
	11th to 20th	Night	43% 7% 16% 19% 12% 2	3777
	21st to end	Night	57% 8% 9% 15% 10% 3	4199
November	1st to 10th	Night	63% 5% 12% 11% 9% 1	2620
	11th to 20th	Night	65% 6% 10% 9% 8% 3	2800
	21st to end	Night	57% 7% 9% 11% 13% 4	2800
December	1st to 10th	Night	44% 5% 10% 18% 21% 3	4560
	11th to 20th	Night	71% 6% 10% 8% 4	5176
	21st to end	Night	68% 8% 13% 8% 2 1	6952

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	40% 14% 18% 14% 14% 2	200
	11th to 20th	Day	39% 6% 18% 19% 14% 5%	200
	21st to end	Day	33% 9% 18% 20% 16% 4	388
February	1st to 10th	Day	38% 9% 20% 21% 9% 3	400
	11th to 20th	Day	38% 12% 21% 21% 6% 2	395
	21st to end	Day	41% 11% 20% 18% 10% 1	378
March	1st to 10th	Day	34% 12% 27% 20% 7% 1	500
	11th to 20th	Day	34% 9% 25% 19% 10% 3	500
	21st to end	Day	36% 12% 25% 20% 6% 1	550
April	1st to 10th	Day	37% 10% 21% 20% 10% 2	500
	11th to 20th	Day	31% 13% 24% 18% 10% 4	492
	21st to end	Day	29% 10% 26% 22% 10% 2	500
May	1st to 10th	Day	24% 10% 25% 25% 13% 3	503
	11th to 20th	Day	27% 8% 20% 26% 15% 4	489
	21st to end	Day	24% 4 22% 30% 16% 5%	529
June	1st to 10th	Day	24% 8% 18% 30% 16% 4	490
	11th to 20th	Day	24% 9% 29% 23% 14% 2	490
	21st to end	Day	10% 5% 25% 38% 17% 6%	490
July	1st to 10th	Day	7% 3 23% 38% 24% 4	486
	11th to 20th	Day	4 5% 21% 43% 22% 5%	484
	21st to end	Day	6% 2 17% 44% 24% 7%	531
August	1st to 10th	Day	5% 3 16% 45% 24% 7%	487
	11th to 20th	Day	5% 2 17% 38% 30% 8%	477
	21st to end	Day	8% 6% 22% 36% 22% 6%	539
September	1st to 10th	Day	9% 5% 23% 35% 22% 6%	490
	11th to 20th	Day	14% 7% 21% 33% 21% 5%	490
	21st to end	Day	20% 7% 21% 31% 17% 4	490
October	1st to 10th	Day	21% 8% 21% 24% 19% 7%	490
	11th to 20th	Day	24% 7% 18% 29% 17% 6%	490
	21st to end	Day	29% 10% 25% 20% 11% 5%	492
November	1st to 10th	Day	36% 11% 16% 22% 11% 3	255
	11th to 20th	Day	32% 13% 20% 15% 14% 7%	200
	21st to end	Day	34% 7% 19% 20% 15% 7%	200
December	1st to 10th	Day	35% 9% 14% 18% 16% 9%	200
	11th to 20th	Day	45% 10% 19% 15% 9% 2	200
	21st to end	Day	48% 8% 18% 12% 12% 3	220
January	1st to 10th	Night	40% 11% 14% 19% 15% 2	800
	11th to 20th	Night	38% 7% 13% 23% 17% 3	800
	21st to end	Night	33% 6% 14% 28% 16% 3	880
February	1st to 10th	Night	35% 8% 17% 26% 13% 2	800
	11th to 20th	Night	38% 9% 15% 23% 15% 1	784
	21st to end	Night	40% 7% 16% 27% 10%	660
March	1st to 10th	Night	32% 9% 17% 28% 13% 1	800
	11th to 20th	Night	31% 8% 17% 29% 14% 1	800
	21st to end	Night	36% 9% 18% 25% 11% 2	880
April	1st to 10th	Night	35% 8% 16% 26% 15% 1	800
	11th to 20th	Night	30% 6% 16% 30% 14% 3	791
	21st to end	Night	33% 5% 15% 30% 15% 2	623
May	1st to 10th	Night	27% 4 17% 31% 19% 2	445
	11th to 20th	Night	23% 5% 15% 29% 27% 1	375
	21st to end	Night	25% 3 13% 32% 23% 3	411
June	1st to 10th	Night	25% 4 13% 33% 23% 2	380
	11th to 20th	Night	27% 4 15% 34% 18% 1	380
	21st to end	Night	13% 3 14% 39% 30% 1	380
July	1st to 10th	Night	9% 2 8% 41% 38% 2	370
	11th to 20th	Night	7% 1 11% 45% 33% 2	368
	21st to end	Night	3 2 6% 44% 41% 5%	416
August	1st to 10th	Night	4 1 5% 32% 49% 8%	539
	11th to 20th	Night	6% 2 6% 30% 47% 9%	564
	21st to end	Night	8% 3 11% 39% 35% 5%	770
September	1st to 10th	Night	9% 2 11% 38% 35% 4	760
	11th to 20th	Night	15% 3 8% 32% 36% 7%	760
	21st to end	Night	17% 3 12% 34% 30% 5%	760
October	1st to 10th	Night	21% 4 14% 30% 26% 4	760
	11th to 20th	Night	22% 6% 11% 30% 26% 5%	760
	21st to end	Night	30% 6% 18% 26% 15% 5%	836
November	1st to 10th	Night	34% 7% 15% 30% 13% 1	780
	11th to 20th	Night	39% 12% 12% 23% 12% 2	800
	21st to end	Night	31% 7% 13% 31% 16% 2	800
December	1st to 10th	Night	33% 5% 13% 30% 16% 3	800
	11th to 20th	Night	41% 7% 15% 24% 13% 1	800
	21st to end	Night	42% 10% 16% 21% 10% 1	880

Page generated at 2025-05-08 06:33:58. Version ac07

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