Folsom Lake State Recration Area
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Folsom Lake State Recration Area clear sky chart from 2005-11-06 to 2024-11-04.

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	8% 3 1 3 2 2 2 2 4 5% 66%	105132
	Night	11% 4 1 4 3 2 3 2 4 5% 62%	102618
Transparency	Day	22% 4 8% 18% 23% 25%	104883
	Night	26% 5% 8% 18% 22% 21%	102454
Seeing	Day	9% 6% 18% 31% 29% 8%	15196
	Night	12% 3 12% 38% 30% 5%	24489

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	27% 8% 2 3 3 4 3 3 5% 5% 36%	2539
	11th to 20th	Day	25% 9% 3 8% 5% 4 4 3 3 4 33%	2795
	21st to end	Day	24% 9% 3 8% 4 4 4 4 5% 7% 29%	3146
February	1st to 10th	Day	20% 5% 2 5% 3 4 3 4 4 5% 46%	1710
	11th to 20th	Day	17% 5% 2 5% 3 4 3 3 4 6% 48%	1787
	21st to end	Day	18% 6% 2 5% 3 3 2 3 4 5% 49%	1570
March	1st to 10th	Day	18% 10% 4 8% 5% 4 6% 4 5% 5% 31%	3246
	11th to 20th	Day	14% 4 1 4 2 2 3 2 4 6% 57%	3490
	21st to end	Day	15% 7% 3 7% 4 4 5% 4 5% 9% 37%	3972
April	1st to 10th	Day	14% 6% 2 4 3 3 4 4 5% 7% 49%	2280
	11th to 20th	Day	11% 4 1 4 3 3 3 3 5% 7% 56%	2249
	21st to end	Day	8% 3 1 3 2 2 2 3 4 8% 63%	2280
May	1st to 10th	Day	7% 2 1 2 1 2 2 2 2 5% 74%	3874
	11th to 20th	Day	3 1 1 2 1 1 2 2 3 4 81%	4377
	21st to end	Day	3 2 1 2 2 2 2 2 3 5% 76%	4813
June	1st to 10th	Day	5% 3 1 3 3 2 2 3 5% 6% 68%	2660
	11th to 20th	Day	1 1 2 2 1 2 2 3 5% 81%	2660
	21st to end	Day	2 1 1 1 1 1 1 1 3 4 84%	2660
July	1st to 10th	Day	1 1 1 1 1 2 93%	4420
	11th to 20th	Day	1 1 1 1 1 2 2 3 3 85%	4420
	21st to end	Day	1 1 1 1 1 2 3 89%	4463
August	1st to 10th	Day	2 2 1 2 1 2 1 2 4 5% 80%	4091
	11th to 20th	Day	1 1 1 1 1 1 2 3 89%	3770
	21st to end	Day	2 1 1 1 1 1 1 2 2 89%	4180
September	1st to 10th	Day	2 1 1 2 2 3 89%	2280
	11th to 20th	Day	3 2 2 1 2 3 2 4 4 76%	2280
	21st to end	Day	3 2 1 2 1 2 2 1 2 4 80%	2052
October	1st to 10th	Day	2 2 1 3 2 2 2 2 4 6% 75%	3180
	11th to 20th	Day	4 2 1 2 2 2 3 2 3 5% 74%	3161
	21st to end	Day	5% 3 2 4 3 3 3 3 4 7% 65%	3448
November	1st to 10th	Day	12% 4 1 4 3 3 3 3 4 8% 56%	1744
	11th to 20th	Day	13% 4 1 4 4 4 4 3 5% 7% 53%	1710
	21st to end	Day	12% 4 1 4 3 2 4 4 5% 7% 55%	1583
December	1st to 10th	Day	16% 5% 2 5% 3 4 4 3 4 7% 47%	1520
	11th to 20th	Day	30% 8% 2 6% 4 3 3 2 4 6% 32%	1928
	21st to end	Day	15% 8% 2 6% 4 4 5% 5% 7% 8% 34%	2794
January	1st to 10th	Night	17% 8% 3 6% 4 4 3 3 4 7% 41%	4406
	11th to 20th	Night	23% 7% 2 6% 4 4 5% 3 5% 5% 35%	4172
	21st to end	Night	25% 7% 3 7% 5% 4 4 3 5% 6% 32%	4521
February	1st to 10th	Night	19% 6% 2 4 3 3 2 3 4 5% 51%	2470
	11th to 20th	Night	15% 4 2 4 3 4 4 3 5% 8% 48%	2279
	21st to end	Night	17% 5% 1 4 4 2 3 2 4 5% 52%	1884
March	1st to 10th	Night	23% 10% 3 6% 5% 3 4 3 4 5% 34%	3626
	11th to 20th	Night	18% 4 1 3 2 2 2 2 3 4 58%	3490
	21st to end	Night	21% 6% 2 5% 3 4 4 4 5% 7% 38%	3679
April	1st to 10th	Night	13% 5% 2 5% 3 4 4 4 4 6% 51%	1900
	11th to 20th	Night	11% 4 1 5% 3 3 3 3 5% 6% 57%	1879
	21st to end	Night	7% 3 1 3 2 2 3 3 5% 7% 66%	1900
May	1st to 10th	Night	5% 3 1 3 2 2 2 2 3 5% 71%	3095
	11th to 20th	Night	3 1 1 1 1 1 2 2 2 5% 81%	2516
	21st to end	Night	3 1 1 1 1 2 2 3 5% 80%	2762
June	1st to 10th	Night	4 4 1 3 3 2 2 3 5% 6% 68%	1520
	11th to 20th	Night	1 1 1 2 2 1 1 2 3 4 83%	1520
	21st to end	Night	2 1 2 1 1 2 2 2 3 84%	1520
July	1st to 10th	Night	1 1 1 1 1 1 94%	2540
	11th to 20th	Night	2 2 2 1 1 2 1 2 4 83%	2540
	21st to end	Night	1 1 1 1 2 1 2 4 86%	3097
August	1st to 10th	Night	3 2 1 2 2 1 2 2 4 5% 77%	2848
	11th to 20th	Night	1 1 1 1 2 1 2 3 88%	3066
	21st to end	Night	3 1 1 1 1 1 1 1 2 88%	3498
September	1st to 10th	Night	1 1 1 1 1 1 2 3 89%	1900
	11th to 20th	Night	3 2 1 2 2 1 2 1 3 4 78%	1900
	21st to end	Night	2 1 1 2 2 2 2 3 4 81%	2124
October	1st to 10th	Night	3 2 1 3 2 2 2 2 3 3 78%	3800
	11th to 20th	Night	4 1 1 2 2 1 1 2 3 5% 79%	3777
	21st to end	Night	7% 2 1 3 3 3 3 2 4 5% 67%	4121
November	1st to 10th	Night	13% 4 1 3 2 2 3 3 5% 7% 56%	2407
	11th to 20th	Night	11% 4 2 4 2 3 3 3 5% 7% 57%	2470
	21st to end	Night	13% 4 2 4 3 2 3 3 3 6% 58%	2593
December	1st to 10th	Night	18% 4 2 4 3 4 3 2 4 6% 50%	2660
	11th to 20th	Night	29% 7% 2 5% 3 3 3 3 5% 6% 34%	3276
	21st to end	Night	20% 6% 2 7% 5% 5% 4 4 5% 6% 35%	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	48% 7% 15% 19% 9% 2	2539
	11th to 20th	Day	55% 7% 8% 12% 11% 6%	2795
	21st to end	Day	52% 9% 11% 14% 10% 4	3146
February	1st to 10th	Day	41% 6% 10% 18% 17% 8%	1710
	11th to 20th	Day	37% 6% 11% 19% 20% 7%	1796
	21st to end	Day	37% 6% 11% 21% 18% 6%	1570
March	1st to 10th	Day	50% 11% 10% 14% 12% 2	3246
	11th to 20th	Day	29% 5% 10% 32% 14% 11%	3490
	21st to end	Day	40% 12% 16% 20% 10% 2	3972
April	1st to 10th	Day	34% 7% 12% 25% 16% 6%	2280
	11th to 20th	Day	29% 6% 13% 25% 21% 6%	2252
	21st to end	Day	20% 6% 14% 29% 26% 5%	2280
May	1st to 10th	Day	15% 3 10% 29% 25% 18%	3874
	11th to 20th	Day	11% 3 6% 26% 42% 12%	4380
	21st to end	Day	12% 4 12% 36% 30% 7%	4814
June	1st to 10th	Day	17% 5% 11% 26% 29% 12%	2660
	11th to 20th	Day	8% 3 8% 20% 36% 25%	2660
	21st to end	Day	8% 2 3 13% 36% 39%	2660
July	1st to 10th	Day	3 1 1 6% 14% 75%	4351
	11th to 20th	Day	7% 1 2 7% 16% 66%	4345
	21st to end	Day	5% 1 2 5% 24% 63%	4322
August	1st to 10th	Day	10% 2 2 7% 21% 58%	4076
	11th to 20th	Day	4 1 2 6% 36% 51%	3806
	21st to end	Day	6% 1 2 9% 37% 44%	4179
September	1st to 10th	Day	4 1 3 8% 30% 55%	2280
	11th to 20th	Day	12% 3 6% 20% 37% 21%	2280
	21st to end	Day	11% 2 4 18% 35% 30%	2052
October	1st to 10th	Day	12% 3 5% 11% 24% 46%	3180
	11th to 20th	Day	15% 4 5% 22% 35% 19%	3161
	21st to end	Day	21% 4 7% 18% 34% 16%	3448
November	1st to 10th	Day	28% 6% 11% 22% 22% 12%	1744
	11th to 20th	Day	31% 7% 11% 23% 21% 7%	1710
	21st to end	Day	29% 6% 13% 21% 22% 10%	1583
December	1st to 10th	Day	39% 6% 12% 19% 16% 9%	1520
	11th to 20th	Day	54% 6% 11% 13% 12% 5%	1928
	21st to end	Day	41% 12% 20% 16% 9% 3	2794
January	1st to 10th	Night	41% 9% 15% 22% 9% 4	4406
	11th to 20th	Night	48% 8% 13% 12% 10% 8%	4172
	21st to end	Night	52% 7% 11% 13% 12% 6%	4521
February	1st to 10th	Night	38% 4 9% 22% 19% 9%	2470
	11th to 20th	Night	35% 5% 9% 22% 20% 8%	2280
	21st to end	Night	33% 6% 10% 25% 19% 7%	1884
March	1st to 10th	Night	49% 11% 10% 14% 12% 4	3626
	11th to 20th	Night	30% 6% 8% 27% 18% 12%	3490
	21st to end	Night	42% 10% 13% 20% 11% 4	3679
April	1st to 10th	Night	35% 6% 12% 21% 21% 6%	1900
	11th to 20th	Night	29% 5% 14% 27% 16% 10%	1879
	21st to end	Night	19% 6% 13% 31% 25% 6%	1900
May	1st to 10th	Night	14% 7% 15% 22% 24% 19%	3095
	11th to 20th	Night	9% 2 7% 28% 40% 13%	2516
	21st to end	Night	9% 3 13% 39% 28% 7%	2762
June	1st to 10th	Night	17% 6% 12% 27% 27% 12%	1520
	11th to 20th	Night	9% 2 8% 22% 33% 27%	1520
	21st to end	Night	8% 2 3 12% 32% 42%	1520
July	1st to 10th	Night	2 1 2 6% 16% 73%	2500
	11th to 20th	Night	10% 1 2 6% 16% 65%	2492
	21st to end	Night	5% 2 2 6% 27% 59%	3000
August	1st to 10th	Night	12% 2 2 8% 25% 51%	2839
	11th to 20th	Night	4 1 2 8% 38% 46%	3095
	21st to end	Night	8% 1 2 9% 35% 46%	3498
September	1st to 10th	Night	5% 1 2 7% 30% 54%	1900
	11th to 20th	Night	12% 3 5% 19% 39% 23%	1900
	21st to end	Night	9% 3 6% 17% 31% 35%	2124
October	1st to 10th	Night	14% 2 3 10% 19% 52%	3800
	11th to 20th	Night	12% 2 6% 26% 31% 23%	3777
	21st to end	Night	22% 3 4 19% 31% 21%	4121
November	1st to 10th	Night	27% 5% 11% 22% 19% 16%	2407
	11th to 20th	Night	27% 5% 11% 25% 23% 10%	2470
	21st to end	Night	29% 4 8% 22% 24% 13%	2593
December	1st to 10th	Night	35% 6% 12% 18% 18% 11%	2660
	11th to 20th	Night	50% 5% 9% 15% 15% 6%	3276
	21st to end	Night	47% 11% 13% 16% 10% 4	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	38% 7% 14% 22% 16% 3	180
	11th to 20th	Day	21% 8% 15% 28% 22% 6%	331
	21st to end	Day	21% 5% 20% 25% 23% 6%	407
February	1st to 10th	Day	23% 10% 14% 24% 24% 6%	370
	11th to 20th	Day	19% 12% 23% 24% 19% 5%	425
	21st to end	Day	18% 9% 24% 29% 16% 3	382
March	1st to 10th	Day	22% 13% 24% 25% 12% 3	460
	11th to 20th	Day	21% 11% 24% 23% 16% 6%	460
	21st to end	Day	17% 12% 27% 24% 17% 2	506
April	1st to 10th	Day	17% 10% 26% 24% 18% 5%	460
	11th to 20th	Day	14% 8% 29% 24% 19% 6%	452
	21st to end	Day	7% 8% 22% 30% 23% 10%	460
May	1st to 10th	Day	6% 10% 29% 28% 20% 7%	463
	11th to 20th	Day	7% 6% 23% 27% 29% 8%	488
	21st to end	Day	6% 5% 18% 29% 29% 13%	529
June	1st to 10th	Day	5% 6% 19% 30% 31% 10%	490
	11th to 20th	Day	2 5% 21% 35% 32% 5%	490
	21st to end	Day	1 1 15% 35% 39% 9%	490
July	1st to 10th	Day	1 9% 41% 42% 7%	486
	11th to 20th	Day	1 7% 38% 47% 7%	484
	21st to end	Day	1 8% 40% 42% 10%	531
August	1st to 10th	Day	3 12% 40% 37% 7%	487
	11th to 20th	Day	1 1 13% 38% 37% 9%	477
	21st to end	Day	1 1 10% 33% 46% 9%	539
September	1st to 10th	Day	2 1 10% 41% 35% 10%	490
	11th to 20th	Day	5% 3 17% 36% 31% 9%	490
	21st to end	Day	3 1 18% 34% 32% 11%	490
October	1st to 10th	Day	2 6% 19% 30% 31% 13%	490
	11th to 20th	Day	7% 5% 14% 26% 36% 13%	490
	21st to end	Day	9% 6% 15% 30% 29% 11%	539
November	1st to 10th	Day	13% 8% 13% 28% 28% 10%	322
	11th to 20th	Day	12% 3 16% 30% 29% 10%	270
	21st to end	Day	12% 3 19% 28% 32% 7%	210
December	1st to 10th	Day	19% 9% 16% 25% 22% 9%	180
	11th to 20th	Day	18% 7% 22% 24% 19% 10%	180
	21st to end	Day	19% 8% 23% 27% 19% 5%	198
January	1st to 10th	Night	23% 4 14% 30% 23% 7%	760
	11th to 20th	Night	18% 3 11% 39% 23% 6%	760
	21st to end	Night	21% 3 14% 35% 22% 6%	836
February	1st to 10th	Night	21% 4 14% 36% 22% 4	760
	11th to 20th	Night	17% 5% 16% 36% 21% 5%	744
	21st to end	Night	18% 4 18% 39% 18% 3	628
March	1st to 10th	Night	23% 7% 14% 33% 20% 4	760
	11th to 20th	Night	21% 4 14% 32% 26% 4	760
	21st to end	Night	19% 4 19% 36% 19% 2	836
April	1st to 10th	Night	15% 3 16% 40% 24% 2	760
	11th to 20th	Night	10% 5% 19% 34% 26% 5%	751
	21st to end	Night	7% 3 16% 41% 29% 4	760
May	1st to 10th	Night	7% 4 21% 38% 27% 4	714
	11th to 20th	Night	6% 2 12% 44% 34% 3	374
	21st to end	Night	6% 1 13% 41% 38% 1	411
June	1st to 10th	Night	5% 2 15% 42% 33% 2	380
	11th to 20th	Night	1 1 14% 49% 33% 2	380
	21st to end	Night	3 1 8% 47% 41% 1	380
July	1st to 10th	Night	1 6% 49% 44% 2	370
	11th to 20th	Night	2 4 53% 39% 1	368
	21st to end	Night	1 4 42% 49% 4	612
August	1st to 10th	Night	3 6% 46% 43% 2	567
	11th to 20th	Night	1 5% 48% 42% 3	716
	21st to end	Night	2 5% 40% 49% 3	836
September	1st to 10th	Night	2 1 6% 39% 49% 5%	760
	11th to 20th	Night	4 1 9% 38% 41% 6%	760
	21st to end	Night	2 1 12% 38% 38% 9%	760
October	1st to 10th	Night	6% 1 11% 41% 34% 8%	760
	11th to 20th	Night	6% 2 11% 35% 40% 6%	760
	21st to end	Night	7% 1 12% 38% 30% 12%	836
November	1st to 10th	Night	13% 3 10% 35% 31% 8%	754
	11th to 20th	Night	12% 2 13% 39% 28% 7%	760
	21st to end	Night	15% 1 13% 39% 24% 7%	760
December	1st to 10th	Night	18% 4 14% 35% 22% 7%	760
	11th to 20th	Night	28% 3 10% 33% 22% 4	760
	21st to end	Night	24% 4 18% 32% 18% 4	836

Page generated at 2024-11-01 19:47:52. Version ac07

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