Marysville Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Marysville Observatory clear sky chart from 2005-11-06 to 2024-11-05.

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	22% 9% 3 7% 4 4 4 3 5% 6% 33%	105622
	Night	26% 10% 3 7% 4 4 4 3 4 5% 30%	102007
Transparency	Day	53% 6% 13% 18% 8% 1	105377
	Night	58% 6% 13% 16% 7% 1	101898
Seeing	Day	26% 9% 19% 25% 16% 6%	15125
	Night	33% 7% 12% 24% 20% 5%	23458

By Month

Percentage Cloud Cover NW (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	40% 18% 4 7% 5% 3 3 2 3 3 11%	2219
	11th to 20th	Day	27% 12% 3 7% 5% 4 4 3 5% 6% 23%	2463
	21st to end	Day	39% 15% 4 10% 4 3 4 2 4 5% 10%	2830
February	1st to 10th	Day	34% 13% 4 7% 5% 4 4 4 4 5% 17%	1710
	11th to 20th	Day	29% 13% 4 9% 5% 3 3 4 4 5% 20%	1665
	21st to end	Day	30% 15% 4 8% 5% 4 4 2 4 4 19%	1475
March	1st to 10th	Day	21% 15% 4 8% 5% 5% 6% 4 5% 6% 21%	3195
	11th to 20th	Day	22% 10% 3 6% 4 4 4 3 4 6% 34%	3490
	21st to end	Day	28% 12% 4 10% 5% 5% 5% 4 5% 5% 17%	3967
April	1st to 10th	Day	27% 14% 3 7% 5% 6% 6% 4 6% 6% 17%	2280
	11th to 20th	Day	24% 10% 4 8% 6% 5% 5% 4 5% 5% 24%	2279
	21st to end	Day	23% 12% 3 9% 5% 6% 5% 4 5% 6% 22%	2532
May	1st to 10th	Day	20% 8% 2 6% 4 4 4 3 5% 5% 39%	4420
	11th to 20th	Day	17% 7% 2 5% 4 4 5% 4 6% 9% 37%	4377
	21st to end	Day	30% 11% 3 8% 5% 4 3 3 4 5% 22%	4813
June	1st to 10th	Day	23% 9% 3 8% 4 4 5% 4 5% 7% 29%	2741
	11th to 20th	Day	24% 9% 3 9% 5% 4 4 4 6% 7% 24%	2850
	21st to end	Day	15% 7% 2 7% 4 4 5% 4 6% 8% 38%	2850
July	1st to 10th	Day	8% 4 2 4 3 2 3 2 4 5% 64%	4740
	11th to 20th	Day	7% 3 1 2 2 2 3 2 3 4 69%	4585
	21st to end	Day	12% 4 2 4 3 3 3 3 4 6% 56%	4790
August	1st to 10th	Day	6% 3 1 3 2 3 3 3 5% 7% 63%	4373
	11th to 20th	Day	10% 7% 3 8% 5% 4 4 4 5% 8% 44%	4026
	21st to end	Day	16% 7% 3 7% 3 4 4 3 4 7% 41%	4340
September	1st to 10th	Day	12% 6% 2 6% 4 3 3 3 4 7% 49%	2280
	11th to 20th	Day	15% 7% 3 8% 5% 4 3 4 5% 7% 39%	2280
	21st to end	Day	21% 6% 2 6% 4 4 3 3 4 7% 38%	2013
October	1st to 10th	Day	19% 6% 2 7% 5% 4 5% 5% 7% 10% 31%	3180
	11th to 20th	Day	36% 9% 3 7% 4 3 3 3 4 6% 24%	3161
	21st to end	Day	30% 10% 3 9% 6% 5% 4 3 5% 6% 19%	3228
November	1st to 10th	Day	37% 10% 2 7% 5% 3 4 4 5% 5% 17%	1553
	11th to 20th	Day	36% 10% 3 6% 5% 4 3 2 4 4 21%	1520
	21st to end	Day	37% 11% 3 6% 4 4 4 3 4 5% 20%	1520
December	1st to 10th	Day	31% 15% 3 7% 4 3 3 3 4 3 25%	1520
	11th to 20th	Day	34% 14% 3 8% 4 4 4 3 3 6% 17%	1915
	21st to end	Day	29% 15% 5% 11% 5% 4 4 3 5% 5% 14%	2442
January	1st to 10th	Night	39% 15% 4 9% 5% 4 3 2 3 4 11%	4726
	11th to 20th	Night	30% 12% 3 6% 4 3 3 3 4 7% 25%	4418
	21st to end	Night	39% 13% 4 9% 5% 4 3 3 3 4 12%	4824
February	1st to 10th	Night	34% 12% 3 7% 5% 5% 4 2 3 5% 20%	2470
	11th to 20th	Night	30% 13% 4 8% 5% 3 4 3 4 4 23%	2402
	21st to end	Night	31% 14% 3 7% 5% 4 4 3 4 5% 21%	1979
March	1st to 10th	Night	22% 16% 4 10% 6% 6% 5% 4 5% 5% 17%	3678
	11th to 20th	Night	24% 11% 3 6% 3 3 3 2 4 6% 37%	3489
	21st to end	Night	32% 15% 4 9% 5% 4 4 3 5% 4 16%	3685
April	1st to 10th	Night	27% 12% 3 7% 7% 5% 5% 4 5% 6% 19%	1900
	11th to 20th	Night	26% 10% 4 6% 5% 4 5% 4 5% 5% 27%	1850
	21st to end	Night	26% 10% 4 9% 5% 5% 5% 4 5% 5% 21%	1648
May	1st to 10th	Night	18% 10% 3 7% 4 3 3 3 3 4 43%	2540
	11th to 20th	Night	18% 7% 2 7% 4 4 3 2 5% 6% 41%	2516
	21st to end	Night	30% 9% 3 8% 5% 4 4 3 4 5% 25%	2762
June	1st to 10th	Night	23% 9% 2 7% 5% 3 4 4 4 6% 31%	1435
	11th to 20th	Night	27% 10% 3 8% 5% 4 4 2 4 6% 26%	1330
	21st to end	Night	16% 6% 2 5% 4 4 5% 4 7% 8% 40%	1330
July	1st to 10th	Night	9% 4 1 4 2 2 3 2 2 5% 66%	2220
	11th to 20th	Night	5% 3 1 2 2 2 2 2 4 4 73%	2371
	21st to end	Night	13% 4 2 5% 3 3 3 2 4 4 56%	2762
August	1st to 10th	Night	5% 2 1 3 3 2 3 3 4 6% 70%	2555
	11th to 20th	Night	14% 7% 2 5% 3 3 3 3 4 6% 50%	2812
	21st to end	Night	18% 6% 2 6% 3 3 3 3 4 5% 47%	3333
September	1st to 10th	Night	11% 4 2 5% 3 3 4 3 5% 5% 55%	1900
	11th to 20th	Night	19% 7% 4 6% 5% 3 3 3 4 5% 41%	1900
	21st to end	Night	20% 7% 3 7% 4 3 3 3 4 5% 40%	2165
October	1st to 10th	Night	18% 8% 3 7% 5% 5% 5% 3 5% 8% 34%	3800
	11th to 20th	Night	31% 8% 3 5% 3 3 3 3 5% 7% 29%	3777
	21st to end	Night	35% 12% 3 7% 4 4 3 3 4 5% 21%	4332
November	1st to 10th	Night	38% 10% 3 7% 4 3 4 2 4 5% 19%	2620
	11th to 20th	Night	36% 10% 3 6% 4 4 3 3 4 4 22%	2660
	21st to end	Night	36% 11% 3 6% 4 3 4 4 4 5% 20%	2660
December	1st to 10th	Night	31% 12% 3 7% 4 3 3 3 5% 4 25%	2660
	11th to 20th	Night	33% 14% 3 9% 4 4 4 3 4 5% 15%	3284
	21st to end	Night	31% 16% 5% 10% 5% 5% 5% 3 5% 4 12%	5214

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	79% 6% 5% 7% 2 1	2219
	11th to 20th	Day	61% 6% 13% 14% 5% 1	2487
	21st to end	Day	79% 5% 6% 8% 2	2830
February	1st to 10th	Day	71% 6% 10% 8% 3 2	1710
	11th to 20th	Day	68% 6% 9% 9% 8% 1	1674
	21st to end	Day	70% 5% 9% 11% 5% 1	1475
March	1st to 10th	Day	63% 7% 12% 12% 5%	3195
	11th to 20th	Day	53% 7% 14% 23% 2	3490
	21st to end	Day	69% 8% 12% 10% 1	3967
April	1st to 10th	Day	68% 7% 14% 9% 1	2280
	11th to 20th	Day	63% 6% 11% 12% 6% 1	2279
	21st to end	Day	65% 7% 11% 12% 5%	2532
May	1st to 10th	Day	48% 7% 11% 23% 10%	4420
	11th to 20th	Day	44% 10% 24% 19% 4	4380
	21st to end	Day	67% 6% 17% 9% 1	4814
June	1st to 10th	Day	56% 8% 16% 13% 6% 1	2741
	11th to 20th	Day	62% 6% 16% 12% 4	2850
	21st to end	Day	46% 7% 19% 20% 7% 1	2850
July	1st to 10th	Day	26% 5% 10% 23% 25% 12%	4666
	11th to 20th	Day	21% 4 9% 32% 31% 3	4504
	21st to end	Day	32% 3 18% 32% 14% 2	4639
August	1st to 10th	Day	23% 4 14% 40% 17% 1	4356
	11th to 20th	Day	41% 4 23% 24% 6% 2	4065
	21st to end	Day	45% 5% 12% 27% 11% 1	4339
September	1st to 10th	Day	38% 4 15% 25% 13% 5%	2280
	11th to 20th	Day	46% 6% 13% 18% 15% 2	2280
	21st to end	Day	47% 6% 18% 17% 9% 2	2013
October	1st to 10th	Day	48% 4 18% 25% 5%	3180
	11th to 20th	Day	64% 3 10% 15% 8%	3161
	21st to end	Day	67% 3 12% 11% 8%	3228
November	1st to 10th	Day	69% 7% 12% 8% 4	1553
	11th to 20th	Day	68% 6% 8% 10% 6% 2	1520
	21st to end	Day	68% 5% 5% 11% 9% 1	1520
December	1st to 10th	Day	66% 5% 9% 10% 9% 1	1520
	11th to 20th	Day	70% 4 12% 10% 3 1	1918
	21st to end	Day	73% 7% 10% 8% 2	2442
January	1st to 10th	Night	78% 6% 6% 7% 2 1	4726
	11th to 20th	Night	60% 6% 12% 16% 5% 1	4456
	21st to end	Night	77% 5% 7% 8% 3	4824
February	1st to 10th	Night	70% 4 9% 11% 4 1	2470
	11th to 20th	Night	66% 5% 11% 10% 6% 1	2404
	21st to end	Night	66% 5% 10% 13% 5% 1	1979
March	1st to 10th	Night	66% 8% 11% 10% 5% 1	3678
	11th to 20th	Night	51% 5% 18% 23% 2 1	3490
	21st to end	Night	72% 6% 13% 9%	3685
April	1st to 10th	Night	66% 8% 13% 11% 2	1900
	11th to 20th	Night	60% 6% 13% 12% 7% 2	1850
	21st to end	Night	64% 8% 10% 11% 6% 1	1648
May	1st to 10th	Night	46% 6% 13% 27% 9%	2540
	11th to 20th	Night	44% 8% 24% 19% 5%	2516
	21st to end	Night	63% 10% 16% 10% 1	2762
June	1st to 10th	Night	54% 6% 18% 16% 6% 1	1435
	11th to 20th	Night	60% 7% 16% 14% 3	1330
	21st to end	Night	41% 8% 22% 21% 5% 3	1330
July	1st to 10th	Night	24% 4 10% 25% 22% 15%	2185
	11th to 20th	Night	18% 4 9% 28% 39% 1	2329
	21st to end	Night	33% 4 12% 30% 18% 3	2674
August	1st to 10th	Night	18% 4 15% 43% 19% 2	2547
	11th to 20th	Night	38% 4 24% 25% 9% 2	2839
	21st to end	Night	41% 4 17% 28% 9% 1	3333
September	1st to 10th	Night	32% 6% 15% 29% 14% 4	1900
	11th to 20th	Night	48% 5% 10% 19% 14% 3	1900
	21st to end	Night	48% 5% 14% 21% 10% 2	2165
October	1st to 10th	Night	49% 4 18% 25% 4	3800
	11th to 20th	Night	56% 3 14% 18% 7%	3777
	21st to end	Night	67% 4 11% 11% 6%	4332
November	1st to 10th	Night	70% 5% 11% 11% 3 1	2620
	11th to 20th	Night	68% 5% 9% 11% 5% 2	2660
	21st to end	Night	67% 6% 7% 11% 8% 1	2660
December	1st to 10th	Night	64% 5% 11% 13% 7% 1	2660
	11th to 20th	Night	72% 6% 9% 9% 3 1	3280
	21st to end	Night	74% 7% 8% 7% 3	5214

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	39% 8% 16% 13% 14% 10%	180
	11th to 20th	Day	38% 13% 11% 17% 13% 8%	180
	21st to end	Day	45% 10% 12% 14% 13% 6%	221
February	1st to 10th	Day	46% 7% 18% 17% 10% 2	370
	11th to 20th	Day	42% 8% 20% 19% 9% 2	365
	21st to end	Day	38% 13% 18% 23% 7% 1	337
March	1st to 10th	Day	33% 15% 23% 18% 10% 2	460
	11th to 20th	Day	32% 15% 13% 18% 16% 5%	460
	21st to end	Day	37% 12% 23% 17% 10% 2	506
April	1st to 10th	Day	32% 14% 20% 21% 10% 3	460
	11th to 20th	Day	27% 14% 25% 19% 10% 5%	452
	21st to end	Day	26% 15% 23% 22% 11% 3	460
May	1st to 10th	Day	17% 13% 24% 29% 14% 3	463
	11th to 20th	Day	27% 6% 18% 24% 18% 6%	488
	21st to end	Day	27% 10% 17% 25% 14% 6%	529
June	1st to 10th	Day	23% 9% 24% 27% 15% 3	571
	11th to 20th	Day	25% 9% 25% 25% 13% 3	680
	21st to end	Day	16% 6% 22% 33% 19% 5%	680
July	1st to 10th	Day	14% 3 21% 33% 26% 3	671
	11th to 20th	Day	10% 6% 19% 36% 23% 7%	578
	21st to end	Day	8% 3 18% 39% 22% 10%	531
August	1st to 10th	Day	11% 4 11% 38% 25% 11%	487
	11th to 20th	Day	11% 2 14% 36% 23% 13%	477
	21st to end	Day	15% 5% 23% 30% 17% 9%	539
September	1st to 10th	Day	18% 5% 21% 33% 16% 7%	490
	11th to 20th	Day	17% 8% 20% 28% 22% 5%	490
	21st to end	Day	23% 9% 19% 28% 14% 8%	490
October	1st to 10th	Day	26% 7% 20% 23% 18% 7%	490
	11th to 20th	Day	34% 7% 16% 19% 17% 7%	490
	21st to end	Day	36% 9% 16% 20% 13% 6%	407
November	1st to 10th	Day	42% 9% 21% 16% 8% 4	205
	11th to 20th	Day	44% 8% 8% 13% 15% 12%	180
	21st to end	Day	39% 9% 16% 13% 11% 12%	180
December	1st to 10th	Day	48% 9% 9% 8% 13% 13%	180
	11th to 20th	Day	44% 12% 12% 16% 12% 3	180
	21st to end	Day	44% 7% 14% 21% 12% 3	198
January	1st to 10th	Night	49% 8% 10% 16% 14% 3	850
	11th to 20th	Night	42% 9% 11% 17% 19% 3	771
	21st to end	Night	41% 6% 12% 22% 15% 4	836
February	1st to 10th	Night	41% 7% 10% 26% 11% 3	760
	11th to 20th	Night	39% 7% 10% 26% 16% 2	744
	21st to end	Night	39% 7% 13% 24% 14% 3	628
March	1st to 10th	Night	37% 11% 12% 23% 15% 1	760
	11th to 20th	Night	38% 11% 11% 22% 15% 3	760
	21st to end	Night	39% 10% 16% 23% 11% 1	836
April	1st to 10th	Night	33% 9% 16% 25% 15% 3	760
	11th to 20th	Night	30% 10% 17% 25% 15% 4	722
	21st to end	Night	32% 9% 16% 25% 15% 3	508
May	1st to 10th	Night	21% 7% 14% 30% 24% 3	380
	11th to 20th	Night	21% 6% 10% 27% 31% 5%	374
	21st to end	Night	26% 6% 13% 25% 24% 6%	411
June	1st to 10th	Night	28% 4 13% 30% 22% 3	380
	11th to 20th	Night	29% 6% 11% 32% 19% 3	380
	21st to end	Night	19% 4 9% 36% 27% 5%	380
July	1st to 10th	Night	13% 3 9% 35% 36% 5%	370
	11th to 20th	Night	10% 2 11% 34% 36% 6%	368
	21st to end	Night	10% 2 10% 31% 40% 8%	416
August	1st to 10th	Night	10% 3 5% 25% 44% 14%	391
	11th to 20th	Night	10% 2 6% 24% 41% 18%	564
	21st to end	Night	14% 6% 9% 29% 34% 9%	736
September	1st to 10th	Night	14% 4 8% 33% 33% 8%	760
	11th to 20th	Night	23% 4 9% 22% 31% 11%	760
	21st to end	Night	26% 4 12% 26% 26% 6%	760
October	1st to 10th	Night	24% 4 9% 28% 27% 7%	760
	11th to 20th	Night	33% 6% 12% 22% 21% 6%	760
	21st to end	Night	38% 6% 14% 23% 15% 4	836
November	1st to 10th	Night	45% 8% 13% 23% 11% 1	760
	11th to 20th	Night	42% 7% 14% 20% 13% 4	760
	21st to end	Night	44% 5% 12% 19% 15% 5%	760
December	1st to 10th	Night	37% 6% 11% 25% 16% 5%	760
	11th to 20th	Night	46% 8% 12% 20% 12% 1	762
	21st to end	Night	48% 7% 14% 19% 11% 1	935

Page generated at 2024-11-02 23:11:14. Version ac07

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