Spanish Fork
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Spanish Fork clear sky chart from 2005-11-06 to 2025-07-06.

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	5% 8% 3 6% 4 4 4 3 5% 7% 52%	123632
	Night	6% 9% 3 6% 4 3 4 3 5% 7% 51%	124130
Transparency	Day	31% 5% 9% 20% 22% 13%	123398
	Night	32% 6% 10% 21% 21% 10%	123951
Seeing	Day	9% 11% 25% 32% 19% 4	15600
	Night	11% 5% 19% 40% 23% 3	26224

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	7% 17% 5% 10% 4 3 4 3 6% 7% 33%	4098
	11th to 20th	Day	7% 15% 5% 14% 7% 4 3 3 3 4 34%	4100
	21st to end	Day	6% 13% 5% 8% 4 3 2 2 4 5% 47%	4510
February	1st to 10th	Day	10% 13% 4 9% 6% 4 3 3 5% 6% 36%	1800
	11th to 20th	Day	10% 14% 5% 8% 4 4 4 4 5% 6% 36%	1828
	21st to end	Day	7% 14% 5% 9% 4 5% 4 3 5% 6% 38%	1650
March	1st to 10th	Day	5% 15% 5% 9% 4 4 4 3 5% 7% 40%	4863
	11th to 20th	Day	4 11% 5% 8% 5% 5% 5% 4 6% 7% 39%	5000
	21st to end	Day	7% 15% 5% 11% 6% 6% 5% 4 5% 6% 30%	5486
April	1st to 10th	Day	8% 10% 3 6% 5% 4 5% 4 5% 6% 43%	2220
	11th to 20th	Day	7% 11% 3 8% 5% 4 4 3 5% 6% 44%	2498
	21st to end	Day	8% 9% 2 6% 4 4 4 3 6% 6% 49%	2600
May	1st to 10th	Day	8% 9% 2 6% 4 4 5% 4 6% 7% 47%	5880
	11th to 20th	Day	6% 6% 2 6% 4 4 4 4 6% 9% 49%	5841
	21st to end	Day	4 4 2 5% 3 4 5% 4 6% 7% 56%	6423
June	1st to 10th	Day	3 3 1 3 3 4 4 4 7% 8% 59%	2600
	11th to 20th	Day	4 3 1 4 3 2 3 3 5% 7% 65%	2600
	21st to end	Day	2 2 1 2 3 3 3 3 4 5% 71%	2600
July	1st to 10th	Day	1 1 1 2 2 2 2 2 4 5% 78%	4176
	11th to 20th	Day	2 2 1 3 4 5% 5% 5% 7% 10% 57%	4110
	21st to end	Day	2 2 1 3 3 4 4 3 6% 7% 66%	4454
August	1st to 10th	Day	2 2 1 4 3 3 4 4 6% 8% 63%	4092
	11th to 20th	Day	2 2 1 3 3 4 4 4 5% 7% 66%	4028
	21st to end	Day	2 2 1 3 2 2 3 4 5% 7% 69%	4461
September	1st to 10th	Day	3 3 1 2 2 3 3 4 5% 7% 68%	2149
	11th to 20th	Day	3 2 1 3 3 3 3 3 5% 7% 66%	2090
	21st to end	Day	5% 3 1 3 3 2 3 2 2 6% 70%	2090
October	1st to 10th	Day	4 3 1 4 3 2 3 2 4 4 70%	3314
	11th to 20th	Day	7% 7% 3 4 3 3 3 3 5% 7% 56%	3150
	21st to end	Day	6% 7% 2 5% 2 3 3 3 4 5% 60%	3438
November	1st to 10th	Day	8% 9% 2 5% 3 4 4 3 4 6% 52%	1786
	11th to 20th	Day	12% 7% 2 6% 4 3 4 3 4 6% 49%	1800
	21st to end	Day	6% 11% 4 7% 4 3 3 3 5% 8% 46%	1695
December	1st to 10th	Day	5% 8% 3 7% 3 3 2 2 4 8% 56%	2620
	11th to 20th	Day	6% 11% 4 8% 4 3 5% 4 6% 9% 40%	3072
	21st to end	Day	9% 15% 5% 9% 5% 4 4 4 6% 7% 32%	4510
January	1st to 10th	Night	7% 18% 6% 11% 4 3 3 3 4 6% 35%	5867
	11th to 20th	Night	10% 15% 5% 12% 5% 4 3 3 4 6% 32%	5880
	21st to end	Night	6% 15% 3 7% 3 3 3 2 3 6% 49%	6468
February	1st to 10th	Night	9% 13% 4 9% 4 4 4 4 5% 6% 38%	2600
	11th to 20th	Night	9% 12% 4 9% 5% 3 3 3 5% 6% 42%	2458
	21st to end	Night	7% 12% 5% 10% 3 3 4 4 6% 6% 41%	1980
March	1st to 10th	Night	6% 17% 7% 8% 4 4 4 3 4 6% 39%	5030
	11th to 20th	Night	5% 12% 4 7% 5% 4 5% 5% 6% 8% 40%	5000
	21st to end	Night	6% 15% 3 7% 4 4 4 3 5% 6% 40%	5489
April	1st to 10th	Night	10% 10% 2 6% 3 3 3 3 4 6% 51%	2178
	11th to 20th	Night	7% 7% 2 6% 4 5% 4 3 6% 7% 49%	1845
	21st to end	Night	9% 7% 2 7% 4 4 4 3 5% 7% 49%	1800
May	1st to 10th	Night	8% 8% 2 6% 4 3 4 4 6% 7% 48%	4100
	11th to 20th	Night	4 4 2 5% 4 4 4 4 5% 8% 57%	4074
	21st to end	Night	5% 4 1 4 3 3 3 4 6% 7% 60%	4474
June	1st to 10th	Night	4 3 2 3 3 3 5% 4 6% 7% 59%	1800
	11th to 20th	Night	3 3 1 3 2 4 3 3 4 6% 67%	1800
	21st to end	Night	2 2 1 3 3 3 2 3 5% 7% 69%	1800
July	1st to 10th	Night	1 2 1 3 2 3 4 3 4 4 72%	2905
	11th to 20th	Night	2 3 1 5% 5% 5% 7% 6% 8% 10% 47%	2860
	21st to end	Night	1 4 1 6% 4 5% 6% 4 5% 7% 58%	3109
August	1st to 10th	Night	3 2 1 4 4 4 5% 4 6% 9% 58%	2847
	11th to 20th	Night	2 3 1 5% 4 4 4 4 5% 6% 60%	2811
	21st to end	Night	1 1 1 3 3 2 3 3 4 6% 73%	3205
September	1st to 10th	Night	2 2 1 3 3 3 3 3 4 6% 71%	2027
	11th to 20th	Night	4 3 1 4 2 2 3 3 5% 7% 66%	2090
	21st to end	Night	6% 3 1 3 2 2 3 2 3 5% 71%	2090
October	1st to 10th	Night	4 3 1 3 2 2 3 2 4 5% 72%	3658
	11th to 20th	Night	7% 5% 2 4 3 3 3 3 4 8% 58%	3778
	21st to end	Night	4 8% 2 4 2 2 4 3 5% 7% 59%	4120
November	1st to 10th	Night	7% 8% 2 5% 3 3 3 3 5% 7% 54%	2510
	11th to 20th	Night	9% 8% 2 4 3 3 3 4 5% 7% 52%	2600
	21st to end	Night	8% 12% 4 6% 3 4 3 2 4 6% 48%	2680
December	1st to 10th	Night	6% 8% 2 5% 2 3 3 2 4 7% 58%	4570
	11th to 20th	Night	8% 13% 3 5% 4 3 3 3 5% 7% 45%	5159
	21st to end	Night	8% 14% 5% 10% 5% 4 4 4 6% 7% 33%	6468

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% 16% 16% 13%	4099
	11th to 20th	Day	51% 6% 11% 18% 12% 1	4100
	21st to end	Day	39% 7% 13% 19% 21% 2	4510
February	1st to 10th	Day	49% 6% 14% 18% 12% 2	1800
	11th to 20th	Day	49% 5% 12% 20% 13% 1	1837
	21st to end	Day	45% 5% 11% 23% 14% 2	1650
March	1st to 10th	Day	41% 8% 9% 23% 14% 5%	4863
	11th to 20th	Day	38% 10% 10% 27% 14% 1	5000
	21st to end	Day	51% 8% 15% 17% 8% 1	5486
April	1st to 10th	Day	39% 6% 11% 21% 17% 5%	2220
	11th to 20th	Day	40% 5% 12% 19% 20% 4	2501
	21st to end	Day	35% 6% 10% 25% 22% 3	2600
May	1st to 10th	Day	34% 6% 11% 22% 22% 5%	5880
	11th to 20th	Day	28% 7% 8% 24% 29% 4	5844
	21st to end	Day	24% 6% 7% 24% 33% 5%	6424
June	1st to 10th	Day	20% 5% 8% 19% 34% 13%	2600
	11th to 20th	Day	18% 4 6% 14% 31% 27%	2600
	21st to end	Day	15% 3 5% 9% 30% 39%	2600
July	1st to 10th	Day	10% 3 4 7% 13% 62%	4112
	11th to 20th	Day	20% 5% 5% 11% 28% 31%	4041
	21st to end	Day	17% 5% 7% 12% 21% 39%	4314
August	1st to 10th	Day	18% 4 7% 20% 26% 24%	4078
	11th to 20th	Day	18% 4 7% 15% 29% 27%	4067
	21st to end	Day	15% 3 6% 13% 31% 32%	4460
September	1st to 10th	Day	16% 4 8% 13% 29% 31%	2149
	11th to 20th	Day	19% 4 7% 19% 26% 25%	2090
	21st to end	Day	18% 3 6% 18% 35% 20%	2090
October	1st to 10th	Day	19% 4 5% 11% 42% 20%	3314
	11th to 20th	Day	29% 3 6% 23% 30% 9%	3150
	21st to end	Day	26% 4 9% 28% 27% 6%	3438
November	1st to 10th	Day	33% 4 11% 25% 22% 5%	1786
	11th to 20th	Day	35% 6% 12% 27% 19% 2	1800
	21st to end	Day	37% 5% 12% 26% 17% 3	1695
December	1st to 10th	Day	27% 4 10% 44% 12% 2	2620
	11th to 20th	Day	38% 6% 15% 26% 13% 1	3070
	21st to end	Day	49% 7% 12% 17% 15% 1	4510
January	1st to 10th	Night	49% 6% 12% 18% 13% 1	5867
	11th to 20th	Night	50% 8% 10% 22% 9% 1	5880
	21st to end	Night	36% 7% 14% 21% 20% 1	6468
February	1st to 10th	Night	45% 7% 16% 21% 9% 2	2600
	11th to 20th	Night	43% 6% 11% 22% 16% 2	2459
	21st to end	Night	42% 5% 11% 24% 14% 4	1980
March	1st to 10th	Night	43% 7% 9% 22% 14% 6%	5030
	11th to 20th	Night	37% 8% 10% 27% 15% 2	5000
	21st to end	Night	40% 7% 15% 21% 16% 1	5489
April	1st to 10th	Night	35% 4 12% 23% 19% 7%	2178
	11th to 20th	Night	33% 5% 11% 24% 23% 5%	1845
	21st to end	Night	33% 7% 11% 27% 20% 3	1800
May	1st to 10th	Night	32% 5% 9% 21% 27% 4	4097
	11th to 20th	Night	22% 6% 7% 28% 33% 4	4075
	21st to end	Night	20% 5% 7% 26% 38% 4	4474
June	1st to 10th	Night	20% 6% 9% 20% 31% 13%	1800
	11th to 20th	Night	18% 4 6% 16% 29% 27%	1800
	21st to end	Night	16% 3 5% 9% 28% 40%	1800
July	1st to 10th	Night	15% 4 5% 6% 11% 60%	2860
	11th to 20th	Night	26% 7% 5% 11% 24% 26%	2806
	21st to end	Night	25% 5% 8% 11% 19% 32%	3011
August	1st to 10th	Night	21% 6% 8% 21% 21% 23%	2838
	11th to 20th	Night	22% 5% 8% 14% 24% 27%	2838
	21st to end	Night	13% 3 7% 11% 29% 35%	3205
September	1st to 10th	Night	16% 3 7% 15% 26% 33%	2027
	11th to 20th	Night	18% 4 7% 19% 26% 25%	2090
	21st to end	Night	18% 3 5% 16% 33% 25%	2090
October	1st to 10th	Night	16% 3 5% 14% 35% 27%	3658
	11th to 20th	Night	26% 3 7% 22% 31% 10%	3778
	21st to end	Night	24% 5% 6% 30% 29% 5%	4120
November	1st to 10th	Night	29% 5% 10% 26% 23% 6%	2510
	11th to 20th	Night	30% 5% 13% 30% 20% 3	2600
	21st to end	Night	38% 4 8% 25% 21% 4	2680
December	1st to 10th	Night	26% 4 11% 40% 17% 2	4570
	11th to 20th	Night	37% 6% 18% 27% 12%	5160
	21st to end	Night	48% 7% 14% 19% 12% 1	6468

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	23% 9% 24% 28% 13% 4	300
	11th to 20th	Day	14% 12% 22% 33% 16% 2	300
	21st to end	Day	15% 5% 29% 31% 17% 3	330
February	1st to 10th	Day	19% 14% 26% 31% 9% 1	300
	11th to 20th	Day	14% 15% 29% 30% 11% 1	373
	21st to end	Day	10% 14% 35% 29% 10% 1	414
March	1st to 10th	Day	14% 19% 26% 28% 12% 1	500
	11th to 20th	Day	11% 12% 36% 29% 12% 1	500
	21st to end	Day	16% 19% 33% 24% 8% 1	550
April	1st to 10th	Day	13% 16% 26% 27% 14% 3	500
	11th to 20th	Day	14% 22% 28% 25% 10% 2	492
	21st to end	Day	12% 18% 28% 27% 13% 2	500
May	1st to 10th	Day	10% 15% 32% 28% 13% 2	503
	11th to 20th	Day	9% 12% 29% 29% 17% 3	528
	21st to end	Day	8% 10% 26% 29% 23% 4	573
June	1st to 10th	Day	4 12% 23% 38% 19% 5%	530
	11th to 20th	Day	5% 15% 31% 33% 14% 3	530
	21st to end	Day	3 9% 30% 38% 16% 4	530
July	1st to 10th	Day	2 5% 25% 38% 25% 5%	507
	11th to 20th	Day	3 2 24% 41% 24% 5%	484
	21st to end	Day	2 1 15% 44% 31% 7%	531
August	1st to 10th	Day	6% 4 18% 41% 26% 5%	487
	11th to 20th	Day	3 3 23% 38% 27% 7%	477
	21st to end	Day	2 4 23% 35% 28% 7%	539
September	1st to 10th	Day	4 4 20% 33% 29% 10%	490
	11th to 20th	Day	5% 10% 24% 31% 23% 7%	490
	21st to end	Day	6% 9% 19% 29% 31% 7%	490
October	1st to 10th	Day	5% 10% 23% 29% 25% 9%	392
	11th to 20th	Day	7% 11% 22% 25% 26% 9%	300
	21st to end	Day	9% 8% 25% 33% 22% 2	330
November	1st to 10th	Day	15% 14% 18% 28% 19% 6%	300
	11th to 20th	Day	11% 9% 21% 34% 19% 7%	300
	21st to end	Day	13% 6% 23% 31% 23% 5%	300
December	1st to 10th	Day	11% 11% 20% 35% 16% 7%	300
	11th to 20th	Day	11% 10% 23% 37% 16% 2	300
	21st to end	Day	19% 11% 23% 32% 12% 2	330
January	1st to 10th	Night	18% 5% 16% 39% 18% 4	800
	11th to 20th	Night	16% 5% 18% 37% 22% 2	800
	21st to end	Night	16% 4 18% 40% 19% 3	880
February	1st to 10th	Night	14% 6% 25% 41% 12% 3	800
	11th to 20th	Night	14% 5% 24% 40% 15% 1	784
	21st to end	Night	12% 5% 26% 42% 14% 1	660
March	1st to 10th	Night	16% 8% 20% 40% 14% 2	800
	11th to 20th	Night	9% 6% 21% 43% 20% 1	800
	21st to end	Night	13% 9% 24% 40% 12% 1	880
April	1st to 10th	Night	14% 8% 22% 40% 15% 1	778
	11th to 20th	Night	10% 8% 27% 40% 14%	593
	21st to end	Night	11% 8% 23% 39% 18% 1	600
May	1st to 10th	Night	10% 6% 25% 39% 18% 2	600
	11th to 20th	Night	8% 5% 19% 40% 26% 2	591
	21st to end	Night	8% 7% 17% 41% 25% 3	650
June	1st to 10th	Night	5% 6% 18% 41% 29% 2	600
	11th to 20th	Night	6% 5% 25% 42% 21% 1	600
	21st to end	Night	3 4 20% 42% 31% 2	600
July	1st to 10th	Night	3 1 15% 36% 41% 3	570
	11th to 20th	Night	4 1 9% 46% 37% 3	552
	21st to end	Night	3 2 8% 37% 48% 3	624
August	1st to 10th	Night	4 1 11% 46% 36% 2	567
	11th to 20th	Night	3 3 13% 44% 36% 2	564
	21st to end	Night	4 2 13% 41% 39% 2	627
September	1st to 10th	Night	3 1 12% 41% 37% 5%	697
	11th to 20th	Night	5% 3 15% 37% 34% 6%	760
	21st to end	Night	7% 3 15% 34% 33% 8%	760
October	1st to 10th	Night	7% 4 18% 42% 25% 3	760
	11th to 20th	Night	9% 3 19% 40% 25% 4	760
	21st to end	Night	9% 4 18% 39% 26% 4	836
November	1st to 10th	Night	10% 6% 18% 37% 25% 3	780
	11th to 20th	Night	12% 6% 19% 40% 20% 4	800
	21st to end	Night	13% 6% 19% 37% 21% 5%	880
December	1st to 10th	Night	16% 4 18% 43% 18% 2	1000
	11th to 20th	Night	20% 5% 20% 40% 14% 1	991
	21st to end	Night	21% 6% 18% 41% 13% 2	880

Page generated at 2025-07-02 23:30:16. Version ac07

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