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 2024-03-28.

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	10% 4 1 3 3 2 3 3 4 5% 62%	78890
	Night	13% 4 2 3 3 2 3 3 4 6% 58%	81143
Transparency	Day	25% 5% 9% 18% 23% 20%	78604
	Night	29% 5% 10% 18% 21% 17%	80949
Seeing	Day	10% 6% 18% 30% 29% 8%	14314
	Night	12% 3 12% 38% 30% 5%	23771

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 3 4 4 5% 5% 36%	2539
	11th to 20th	Day	25% 9% 3 7% 6% 3 3 4 3 4 33%	2795
	21st to end	Day	24% 8% 3 7% 5% 3 4 4 5% 7% 29%	3146
February	1st to 10th	Day	20% 5% 2 5% 3 3 3 4 4 5% 46%	1710
	11th to 20th	Day	17% 5% 2 4 4 3 4 3 4 6% 48%	1787
	21st to end	Day	18% 5% 2 4 3 3 2 4 4 5% 49%	1570
March	1st to 10th	Day	18% 7% 3 5% 5% 3 5% 5% 5% 6% 37%	1960
	11th to 20th	Day	19% 5% 2 5% 4 3 4 4 5% 7% 43%	2090
	21st to end	Day	15% 5% 3 4 4 3 4 4 4 7% 46%	2340
April	1st to 10th	Day	14% 6% 2 3 4 2 5% 4 5% 7% 48%	2160
	11th to 20th	Day	12% 3 2 3 4 2 3 4 4 7% 56%	2129
	21st to end	Day	8% 3 1 2 3 2 2 4 4 7% 64%	2160
May	1st to 10th	Day	6% 3 1 3 3 2 3 3 4 6% 66%	2195
	11th to 20th	Day	5% 2 1 3 3 2 3 3 4 6% 68%	2477
	21st to end	Day	5% 3 1 3 3 2 3 4 4 6% 66%	2723
June	1st to 10th	Day	5% 2 2 2 3 2 2 3 4 6% 68%	2520
	11th to 20th	Day	1 1 1 2 1 2 2 3 5% 81%	2520
	21st to end	Day	2 1 1 1 1 1 1 1 2 4 84%	2520
July	1st to 10th	Day	1 1 1 1 1 1 2 3 88%	2520
	11th to 20th	Day	1 1 1 1 1 1 2 2 3 87%	2520
	21st to end	Day	1 1 1 1 2 1 2 2 3 4 84%	2554
August	1st to 10th	Day	2 1 1 1 1 1 2 3 3 84%	2328
	11th to 20th	Day	1 1 1 1 1 2 2 4 86%	2156
	21st to end	Day	1 1 1 1 1 1 1 2 2 91%	2376
September	1st to 10th	Day	2 1 1 1 2 2 3 89%	2160
	11th to 20th	Day	3 2 2 2 2 2 3 4 4 77%	2160
	21st to end	Day	4 2 1 2 2 1 2 2 2 4 79%	1945
October	1st to 10th	Day	4 2 1 2 3 2 3 3 3 5% 72%	1800
	11th to 20th	Day	6% 2 1 2 2 2 3 4 3 5% 70%	1800
	21st to end	Day	8% 3 2 3 3 2 2 4 3 5% 65%	1980
November	1st to 10th	Day	12% 3 1 3 3 2 3 4 4 8% 56%	1715
	11th to 20th	Day	13% 3 1 4 4 2 4 4 5% 6% 53%	1710
	21st to end	Day	12% 3 1 4 3 1 4 4 5% 7% 55%	1583
December	1st to 10th	Day	16% 5% 2 4 4 2 4 4 4 7% 47%	1520
	11th to 20th	Day	30% 7% 3 5% 4 2 3 3 4 6% 32%	1928
	21st to end	Day	16% 7% 3 5% 5% 3 5% 6% 7% 8% 35%	2794
January	1st to 10th	Night	17% 8% 3 5% 4 3 3 4 4 7% 41%	4406
	11th to 20th	Night	24% 6% 2 5% 5% 3 4 4 5% 6% 35%	4172
	21st to end	Night	25% 7% 3 6% 5% 3 4 4 5% 6% 32%	4521
February	1st to 10th	Night	19% 5% 2 3 4 2 3 3 3 5% 51%	2470
	11th to 20th	Night	15% 4 2 4 4 3 4 4 5% 8% 48%	2279
	21st to end	Night	17% 4 2 4 4 2 3 4 4 5% 52%	1884
March	1st to 10th	Night	20% 7% 3 5% 5% 2 4 4 4 5% 40%	2218
	11th to 20th	Night	20% 5% 1 3 3 2 3 4 4 6% 47%	2090
	21st to end	Night	18% 5% 2 4 3 2 4 4 4 6% 48%	2169
April	1st to 10th	Night	14% 5% 2 5% 4 3 4 5% 4 6% 49%	1800
	11th to 20th	Night	11% 3 2 5% 3 2 3 4 5% 7% 57%	1779
	21st to end	Night	7% 3 1 3 2 1 2 4 5% 7% 66%	1800
May	1st to 10th	Night	6% 3 1 3 3 1 3 3 4 5% 67%	1757
	11th to 20th	Night	6% 2 1 2 2 2 3 3 4 8% 68%	1416
	21st to end	Night	6% 2 1 2 3 2 3 4 4 7% 68%	1552
June	1st to 10th	Night	5% 4 1 3 3 1 2 3 4 7% 68%	1440
	11th to 20th	Night	1 1 1 2 2 1 2 2 3 4 83%	1440
	21st to end	Night	2 1 1 1 1 2 2 2 3 83%	1440
July	1st to 10th	Night	1 1 2 1 2 2 2 89%	1440
	11th to 20th	Night	1 1 1 1 1 1 1 1 3 87%	1440
	21st to end	Night	1 1 1 1 2 1 3 2 3 4 81%	1761
August	1st to 10th	Night	2 2 1 2 2 1 2 2 4 3 80%	1611
	11th to 20th	Night	1 1 1 1 1 2 3 3 4 82%	1746
	21st to end	Night	1 1 1 1 1 1 1 1 1 2 88%	1980
September	1st to 10th	Night	1 1 1 1 1 1 2 3 89%	1800
	11th to 20th	Night	3 2 1 2 2 1 2 2 3 4 79%	1800
	21st to end	Night	2 1 1 2 1 3 2 3 4 80%	2011
October	1st to 10th	Night	6% 3 1 2 2 1 3 3 3 3 73%	2160
	11th to 20th	Night	6% 2 1 2 2 1 2 3 4 6% 71%	2160
	21st to end	Night	6% 2 1 2 3 2 2 2 3 6% 70%	2376
November	1st to 10th	Night	13% 4 1 3 2 2 3 3 5% 8% 56%	2364
	11th to 20th	Night	11% 3 2 3 3 2 3 4 5% 7% 57%	2470
	21st to end	Night	13% 3 2 3 3 2 3 3 3 6% 58%	2593
December	1st to 10th	Night	18% 4 2 3 3 3 3 3 4 6% 50%	2660
	11th to 20th	Night	29% 7% 3 4 4 2 3 3 5% 7% 35%	3276
	21st to end	Night	20% 6% 3 6% 6% 3 5% 5% 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	46% 8% 11% 17% 15% 3	1960
	11th to 20th	Day	41% 5% 9% 24% 16% 5%	2090
	21st to end	Day	38% 8% 13% 22% 16% 3	2340
April	1st to 10th	Day	35% 7% 12% 24% 16% 6%	2160
	11th to 20th	Day	29% 6% 12% 25% 22% 7%	2132
	21st to end	Day	21% 6% 14% 28% 26% 5%	2160
May	1st to 10th	Day	20% 4 12% 25% 29% 10%	2195
	11th to 20th	Day	19% 5% 9% 28% 28% 10%	2480
	21st to end	Day	19% 6% 15% 29% 24% 7%	2724
June	1st to 10th	Day	18% 5% 11% 25% 29% 13%	2520
	11th to 20th	Day	8% 3 9% 21% 34% 26%	2520
	21st to end	Day	8% 2 3 14% 37% 37%	2520
July	1st to 10th	Day	5% 1 3 10% 26% 55%	2451
	11th to 20th	Day	6% 1 4 12% 26% 51%	2445
	21st to end	Day	7% 2 4 8% 24% 55%	2412
August	1st to 10th	Day	8% 2 4 11% 29% 46%	2312
	11th to 20th	Day	5% 1 4 10% 33% 47%	2156
	21st to end	Day	5% 1 2 12% 35% 46%	2376
September	1st to 10th	Day	4 1 3 8% 30% 54%	2160
	11th to 20th	Day	12% 4 6% 20% 36% 22%	2160
	21st to end	Day	12% 2 4 19% 34% 29%	1945
October	1st to 10th	Day	15% 4 8% 17% 28% 28%	1800
	11th to 20th	Day	17% 5% 8% 20% 23% 27%	1800
	21st to end	Day	21% 5% 8% 18% 27% 21%	1980
November	1st to 10th	Day	27% 6% 11% 22% 22% 12%	1715
	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	46% 7% 10% 17% 16% 5%	2218
	11th to 20th	Night	37% 6% 9% 22% 19% 7%	2090
	21st to end	Night	38% 8% 11% 20% 17% 7%	2169
April	1st to 10th	Night	36% 6% 12% 19% 20% 6%	1800
	11th to 20th	Night	28% 5% 14% 25% 17% 11%	1779
	21st to end	Night	19% 6% 13% 31% 25% 6%	1800
May	1st to 10th	Night	19% 6% 12% 22% 29% 12%	1757
	11th to 20th	Night	17% 4 13% 32% 22% 13%	1416
	21st to end	Night	16% 5% 17% 31% 24% 7%	1552
June	1st to 10th	Night	17% 5% 12% 27% 27% 12%	1440
	11th to 20th	Night	9% 2 8% 22% 32% 27%	1440
	21st to end	Night	9% 2 3 13% 33% 40%	1440
July	1st to 10th	Night	4 2 3 11% 28% 53%	1400
	11th to 20th	Night	7% 1 4 11% 23% 54%	1392
	21st to end	Night	8% 2 4 10% 24% 52%	1663
August	1st to 10th	Night	10% 2 4 13% 27% 43%	1602
	11th to 20th	Night	6% 2 3 10% 31% 46%	1746
	21st to end	Night	6% 1 2 10% 31% 50%	1980
September	1st to 10th	Night	5% 2 2 7% 30% 53%	1800
	11th to 20th	Night	11% 3 6% 18% 39% 24%	1800
	21st to end	Night	9% 3 6% 18% 30% 34%	2011
October	1st to 10th	Night	17% 3 6% 17% 27% 29%	2160
	11th to 20th	Night	16% 3 7% 18% 26% 30%	2160
	21st to end	Night	18% 4 7% 20% 27% 25%	2376
November	1st to 10th	Night	27% 5% 11% 22% 19% 16%	2364
	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% 11% 27% 24% 18% 2	491
April	1st to 10th	Day	18% 11% 26% 24% 18% 4	420
	11th to 20th	Day	14% 9% 30% 25% 17% 5%	412
	21st to end	Day	8% 8% 23% 30% 22% 10%	420
May	1st to 10th	Day	6% 10% 28% 28% 21% 8%	423
	11th to 20th	Day	8% 6% 24% 27% 27% 7%	448
	21st to end	Day	6% 6% 19% 27% 29% 13%	485
June	1st to 10th	Day	5% 6% 19% 29% 30% 11%	450
	11th to 20th	Day	2 5% 21% 36% 31% 5%	450
	21st to end	Day	1 2 15% 35% 39% 8%	450
July	1st to 10th	Day	1 9% 42% 43% 6%	446
	11th to 20th	Day	7% 38% 47% 7%	444
	21st to end	Day	1 8% 39% 42% 10%	487
August	1st to 10th	Day	3 13% 40% 36% 7%	447
	11th to 20th	Day	1 1 12% 37% 40% 10%	437
	21st to end	Day	1 1 9% 34% 47% 7%	495
September	1st to 10th	Day	2 1 9% 42% 36% 10%	450
	11th to 20th	Day	5% 2 16% 36% 32% 9%	450
	21st to end	Day	3 1 19% 35% 31% 10%	450
October	1st to 10th	Day	2 6% 20% 30% 30% 11%	450
	11th to 20th	Day	7% 4 14% 26% 36% 14%	450
	21st to end	Day	10% 6% 15% 28% 29% 12%	495
November	1st to 10th	Day	13% 8% 12% 27% 29% 11%	311
	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% 37% 19% 2	820
April	1st to 10th	Night	15% 3 15% 40% 24% 3	720
	11th to 20th	Night	10% 5% 20% 34% 26% 5%	711
	21st to end	Night	8% 3 16% 40% 29% 4	720
May	1st to 10th	Night	7% 4 20% 38% 28% 4	677
	11th to 20th	Night	6% 2 12% 43% 34% 3	354
	21st to end	Night	6% 2 13% 39% 39% 1	389
June	1st to 10th	Night	6% 3 15% 40% 34% 3	360
	11th to 20th	Night	1 1 13% 50% 34% 2	360
	21st to end	Night	3 1 8% 46% 41% 1	360
July	1st to 10th	Night	1 6% 48% 44% 2	350
	11th to 20th	Night	2 3 53% 40% 1	348
	21st to end	Night	1 3 42% 50% 4	579
August	1st to 10th	Night	3 6% 45% 43% 2	537
	11th to 20th	Night	1 4 47% 44% 4	678
	21st to end	Night	2 4 41% 49% 4	792
September	1st to 10th	Night	2 1 5% 38% 50% 5%	720
	11th to 20th	Night	4 1 8% 37% 43% 7%	720
	21st to end	Night	2 1 12% 37% 38% 10%	720
October	1st to 10th	Night	6% 1 11% 41% 33% 9%	720
	11th to 20th	Night	7% 2 10% 34% 41% 6%	720
	21st to end	Night	7% 2 11% 36% 31% 13%	792
November	1st to 10th	Night	13% 3 10% 35% 31% 8%	740
	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 2024-03-24 20:37:01. Version ac07

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