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 2026-10-29.

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	4 7% 2 6% 4 4 4 3 5% 7% 54%	157685
	Night	5% 8% 3 6% 4 3 4 3 5% 7% 52%	152035
Transparency	Day	29% 5% 9% 20% 22% 15%	152433
	Night	31% 5% 10% 21% 21% 12%	148294
Seeing	Day	9% 11% 26% 32% 18% 4	17362
	Night	10% 5% 20% 40% 22% 3	27960

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	8% 19% 5% 11% 5% 4 4 3 5% 6% 31%	5318
	11th to 20th	Day	6% 12% 4 11% 6% 3 3 2 3 4 48%	5340
	21st to end	Day	5% 11% 4 9% 4 3 3 3 5% 6% 49%	5844
February	1st to 10th	Day	10% 13% 4 9% 6% 4 3 2 5% 6% 38%	1890
	11th to 20th	Day	10% 14% 5% 9% 4 4 4 4 5% 7% 35%	1922
	21st to end	Day	7% 14% 5% 9% 4 5% 4 3 5% 6% 38%	1730
March	1st to 10th	Day	5% 15% 5% 9% 4 4 3 3 5% 7% 40%	4971
	11th to 20th	Day	4 11% 5% 8% 5% 5% 5% 4 6% 7% 40%	5110
	21st to end	Day	6% 15% 5% 11% 6% 6% 5% 4 5% 6% 31%	5607
April	1st to 10th	Day	8% 10% 3 6% 5% 4 4 4 5% 6% 44%	2331
	11th to 20th	Day	6% 10% 3 8% 5% 4 4 4 5% 6% 44%	2625
	21st to end	Day	7% 9% 2 6% 4 4 4 3 6% 6% 49%	2730
May	1st to 10th	Day	7% 7% 2 5% 4 4 5% 4 6% 7% 50%	7626
	11th to 20th	Day	5% 6% 2 6% 4 4 4 4 6% 8% 52%	7596
	21st to end	Day	4 4 2 5% 3 4 5% 4 6% 7% 56%	8370
June	1st to 10th	Day	3 3 1 3 3 4 4 4 7% 8% 59%	2730
	11th to 20th	Day	4 3 1 3 3 2 3 3 5% 7% 66%	2730
	21st to end	Day	2 2 1 2 3 3 3 3 4 5% 71%	2730
July	1st to 10th	Day	1 1 1 3 3 3 3 3 4 6% 73%	7649
	11th to 20th	Day	1 2 1 4 4 5% 6% 5% 7% 10% 57%	7650
	21st to end	Day	2 2 1 3 3 3 4 3 5% 7% 67%	8304
August	1st to 10th	Day	1 2 1 3 2 2 4 3 5% 7% 70%	7549
	11th to 20th	Day	1 1 1 3 3 4 5% 4 6% 8% 64%	7565
	21st to end	Day	2 2 1 4 4 4 5% 5% 8% 9% 56%	8262
September	1st to 10th	Day	2 3 1 2 2 3 3 3 5% 7% 68%	2375
	11th to 20th	Day	3 2 1 4 3 3 3 3 5% 7% 65%	2310
	21st to end	Day	5% 3 1 3 3 3 3 2 3 6% 68%	2310
October	1st to 10th	Day	4 3 1 4 3 2 3 2 4 4 70%	3524
	11th to 20th	Day	7% 7% 3 4 3 3 3 3 5% 7% 56%	3350
	21st to end	Day	6% 7% 2 5% 3 3 4 3 5% 5% 59%	3628
November	1st to 10th	Day	8% 9% 2 5% 3 4 4 3 4 6% 53%	1877
	11th to 20th	Day	12% 7% 2 6% 4 3 4 3 5% 7% 48%	1890
	21st to end	Day	6% 11% 4 7% 3 3 3 3 5% 8% 47%	1780
December	1st to 10th	Day	5% 8% 3 7% 3 3 2 3 4 8% 56%	2700
	11th to 20th	Day	6% 11% 4 8% 4 3 5% 4 6% 9% 40%	3153
	21st to end	Day	9% 15% 5% 10% 5% 4 4 4 6% 7% 32%	4609
January	1st to 10th	Night	8% 18% 6% 11% 4 4 3 3 4 6% 33%	7605
	11th to 20th	Night	8% 12% 4 9% 4 3 3 2 3 5% 47%	7650
	21st to end	Night	5% 12% 3 7% 3 3 3 3 4 6% 52%	8370
February	1st to 10th	Night	8% 13% 4 9% 4 4 4 4 5% 6% 40%	2730
	11th to 20th	Night	9% 12% 4 9% 5% 3 3 3 5% 7% 41%	2584
	21st to end	Night	7% 12% 5% 9% 3 3 4 4 5% 6% 43%	2076
March	1st to 10th	Night	6% 17% 6% 8% 4 4 4 3 4 6% 39%	5142
	11th to 20th	Night	5% 12% 4 7% 5% 4 5% 4 6% 8% 40%	5110
	21st to end	Night	6% 15% 3 7% 4 4 4 3 5% 6% 40%	5610
April	1st to 10th	Night	10% 10% 2 5% 3 3 3 2 4 6% 51%	2287
	11th to 20th	Night	7% 7% 2 6% 4 5% 4 3 6% 7% 49%	1938
	21st to end	Night	9% 7% 2 6% 3 4 4 4 5% 7% 49%	1890
May	1st to 10th	Night	6% 7% 2 5% 4 3 4 4 6% 7% 52%	5321
	11th to 20th	Night	5% 4 1 4 3 4 4 3 5% 8% 58%	5296
	21st to end	Night	5% 4 1 4 3 3 4 4 6% 7% 59%	5837
June	1st to 10th	Night	4 3 2 3 3 3 5% 4 6% 7% 60%	1890
	11th to 20th	Night	3 3 1 3 2 3 3 3 4 6% 68%	1890
	21st to end	Night	2 2 1 3 3 3 2 3 5% 7% 68%	1890
July	1st to 10th	Night	1 2 1 4 3 3 4 3 5% 5% 68%	5340
	11th to 20th	Night	1 3 1 5% 5% 5% 7% 6% 9% 9% 49%	5340
	21st to end	Night	1 2 1 4 3 4 5% 4 6% 8% 62%	5805
August	1st to 10th	Night	1 2 1 4 3 3 3 3 5% 7% 68%	5273
	11th to 20th	Night	2 3 1 6% 4 4 4 4 6% 8% 58%	5291
	21st to end	Night	2 3 2 5% 5% 5% 6% 5% 7% 7% 53%	5953
September	1st to 10th	Night	2 2 1 3 3 3 3 3 5% 5% 70%	2241
	11th to 20th	Night	3 3 1 4 3 2 3 3 5% 7% 65%	2310
	21st to end	Night	6% 3 1 3 2 2 3 2 3 5% 69%	2310
October	1st to 10th	Night	3 3 1 3 2 2 3 2 4 5% 72%	3888
	11th to 20th	Night	8% 6% 2 4 3 3 3 3 5% 8% 57%	4018
	21st to end	Night	4 8% 2 4 2 2 4 3 5% 7% 60%	4348
November	1st to 10th	Night	7% 7% 2 5% 3 3 3 3 5% 7% 55%	2639
	11th to 20th	Night	9% 7% 2 4 3 3 3 4 5% 7% 52%	2730
	21st to end	Night	7% 12% 4 6% 3 4 3 3 4 6% 49%	2814
December	1st to 10th	Night	6% 8% 3 5% 2 3 3 2 4 7% 57%	4710
	11th to 20th	Night	8% 13% 3 5% 4 3 3 3 5% 7% 46%	5298
	21st to end	Night	8% 14% 5% 10% 5% 4 4 4 6% 7% 33%	6611

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	52% 7% 17% 14% 10%	5321
	11th to 20th	Day	40% 5% 11% 25% 16% 2	5340
	21st to end	Day	35% 7% 15% 21% 20% 2	5844
February	1st to 10th	Day	48% 6% 13% 19% 12% 2	1890
	11th to 20th	Day	50% 5% 12% 20% 13% 1	1931
	21st to end	Day	45% 5% 11% 24% 13% 2	1730
March	1st to 10th	Day	41% 8% 9% 23% 14% 5%	4971
	11th to 20th	Day	38% 9% 10% 27% 14% 2	5110
	21st to end	Day	50% 8% 15% 17% 9% 1	5607
April	1st to 10th	Day	38% 6% 11% 22% 18% 5%	2331
	11th to 20th	Day	39% 6% 11% 20% 21% 4	2628
	21st to end	Day	35% 6% 10% 25% 22% 3	2730
May	1st to 10th	Day	30% 6% 9% 24% 26% 6%	7626
	11th to 20th	Day	27% 6% 6% 22% 32% 7%	7599
	21st to end	Day	24% 6% 7% 23% 35% 6%	8371
June	1st to 10th	Day	20% 5% 8% 18% 35% 14%	2730
	11th to 20th	Day	17% 4 6% 13% 32% 28%	2730
	21st to end	Day	15% 3 5% 9% 30% 39%	2730
July	1st to 10th	Day	13% 3 3 6% 16% 59%	7586
	11th to 20th	Day	21% 5% 9% 13% 22% 30%	7581
	21st to end	Day	16% 4 5% 16% 22% 37%	8120
August	1st to 10th	Day	16% 4 6% 16% 22% 36%	5978
	11th to 20th	Day	19% 6% 8% 26% 22% 19%	5964
	21st to end	Day	19% 4 10% 21% 25% 22%	6481
September	1st to 10th	Day	16% 4 8% 13% 29% 30%	2375
	11th to 20th	Day	19% 4 7% 19% 27% 23%	2310
	21st to end	Day	19% 3 6% 19% 34% 19%	2310
October	1st to 10th	Day	19% 4 4 12% 42% 19%	3524
	11th to 20th	Day	29% 3 6% 23% 30% 8%	3350
	21st to end	Day	26% 4 9% 28% 27% 6%	3628
November	1st to 10th	Day	32% 4 10% 26% 22% 5%	1877
	11th to 20th	Day	36% 6% 12% 27% 18% 2	1890
	21st to end	Day	36% 5% 13% 27% 16% 3	1780
December	1st to 10th	Day	28% 4 11% 43% 12% 2	2700
	11th to 20th	Day	38% 6% 15% 26% 13% 1	3151
	21st to end	Day	49% 7% 12% 17% 15% 1	4609
January	1st to 10th	Night	52% 6% 15% 16% 10%	7605
	11th to 20th	Night	39% 6% 11% 28% 15% 1	7650
	21st to end	Night	32% 7% 15% 22% 23% 1	8370
February	1st to 10th	Night	43% 7% 16% 23% 10% 2	2730
	11th to 20th	Night	43% 6% 11% 22% 16% 1	2585
	21st to end	Night	41% 5% 11% 26% 14% 4	2076
March	1st to 10th	Night	43% 7% 9% 22% 14% 5%	5142
	11th to 20th	Night	37% 8% 10% 27% 15% 2	5110
	21st to end	Night	39% 7% 15% 21% 16% 1	5610
April	1st to 10th	Night	34% 4 11% 24% 20% 6%	2287
	11th to 20th	Night	33% 5% 11% 24% 23% 5%	1938
	21st to end	Night	32% 7% 10% 27% 21% 3	1890
May	1st to 10th	Night	29% 6% 8% 22% 30% 6%	5319
	11th to 20th	Night	22% 6% 6% 24% 34% 9%	5297
	21st to end	Night	21% 5% 7% 25% 38% 4	5838
June	1st to 10th	Night	19% 6% 9% 20% 33% 12%	1890
	11th to 20th	Night	18% 3 6% 15% 28% 29%	1890
	21st to end	Night	16% 3 5% 9% 28% 39%	1890
July	1st to 10th	Night	17% 4 3 5% 15% 56%	5295
	11th to 20th	Night	26% 6% 9% 10% 18% 31%	5286
	21st to end	Night	20% 4 7% 12% 21% 36%	5677
August	1st to 10th	Night	20% 5% 5% 15% 18% 38%	4168
	11th to 20th	Night	26% 5% 9% 20% 20% 19%	4168
	21st to end	Night	21% 5% 9% 17% 24% 24%	4665
September	1st to 10th	Night	17% 3 7% 15% 27% 32%	2241
	11th to 20th	Night	19% 4 7% 19% 27% 23%	2310
	21st to end	Night	19% 3 5% 17% 32% 24%	2310
October	1st to 10th	Night	15% 3 5% 14% 36% 26%	3888
	11th to 20th	Night	27% 3 7% 22% 30% 10%	4018
	21st to end	Night	24% 5% 6% 31% 29% 5%	4348
November	1st to 10th	Night	28% 5% 10% 27% 24% 7%	2639
	11th to 20th	Night	31% 5% 13% 30% 19% 3	2730
	21st to end	Night	37% 4 10% 26% 20% 4	2814
December	1st to 10th	Night	27% 4 12% 39% 16% 2	4710
	11th to 20th	Night	37% 6% 18% 27% 12%	5299
	21st to end	Night	48% 7% 14% 18% 12% 1	6611

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% 11% 25% 26% 12% 3	330
	11th to 20th	Day	12% 11% 25% 33% 16% 2	330
	21st to end	Day	14% 6% 31% 31% 15% 3	363
February	1st to 10th	Day	18% 13% 27% 31% 9% 1	330
	11th to 20th	Day	15% 15% 31% 28% 10% 1	407
	21st to end	Day	11% 14% 35% 30% 9% 1	446
March	1st to 10th	Day	14% 18% 27% 28% 11% 1	540
	11th to 20th	Day	11% 13% 36% 28% 11% 1	540
	21st to end	Day	15% 18% 33% 26% 8% 1	594
April	1st to 10th	Day	13% 16% 26% 28% 15% 3	540
	11th to 20th	Day	14% 22% 28% 25% 10% 2	532
	21st to end	Day	13% 18% 29% 26% 12% 2	540
May	1st to 10th	Day	10% 15% 33% 27% 13% 2	543
	11th to 20th	Day	10% 12% 30% 28% 17% 3	568
	21st to end	Day	8% 11% 26% 29% 22% 4	617
June	1st to 10th	Day	4 13% 24% 36% 18% 4	570
	11th to 20th	Day	5% 15% 32% 32% 13% 2	570
	21st to end	Day	3 10% 32% 37% 15% 4	570
July	1st to 10th	Day	2 5% 27% 39% 23% 5%	566
	11th to 20th	Day	3 3 24% 41% 25% 5%	564
	21st to end	Day	3 2 17% 42% 30% 6%	619
August	1st to 10th	Day	5% 5% 21% 39% 26% 5%	567
	11th to 20th	Day	3 3 24% 39% 26% 6%	557
	21st to end	Day	3 4 22% 37% 27% 6%	627
September	1st to 10th	Day	4 4 22% 34% 27% 9%	570
	11th to 20th	Day	4 10% 27% 31% 22% 6%	570
	21st to end	Day	5% 9% 21% 30% 29% 6%	570
October	1st to 10th	Day	5% 9% 23% 29% 26% 8%	462
	11th to 20th	Day	8% 12% 25% 25% 23% 8%	360
	21st to end	Day	9% 8% 27% 32% 22% 2	387
November	1st to 10th	Day	14% 14% 19% 28% 19% 6%	330
	11th to 20th	Day	11% 8% 22% 35% 18% 6%	330
	21st to end	Day	12% 6% 25% 31% 22% 5%	330
December	1st to 10th	Day	12% 11% 22% 35% 15% 7%	330
	11th to 20th	Day	12% 10% 24% 36% 16% 2	330
	21st to end	Day	20% 12% 23% 31% 12% 2	363
January	1st to 10th	Night	18% 5% 18% 37% 17% 4	840
	11th to 20th	Night	15% 5% 20% 37% 22% 2	840
	21st to end	Night	15% 4 21% 39% 18% 2	924
February	1st to 10th	Night	13% 6% 26% 41% 11% 3	840
	11th to 20th	Night	14% 6% 25% 39% 15% 1	824
	21st to end	Night	12% 5% 28% 40% 13% 1	692
March	1st to 10th	Night	16% 8% 22% 39% 13% 2	840
	11th to 20th	Night	9% 6% 24% 41% 19% 1	840
	21st to end	Night	13% 9% 25% 40% 12% 1	924
April	1st to 10th	Night	14% 8% 21% 41% 14% 1	817
	11th to 20th	Night	11% 9% 27% 40% 13%	623
	21st to end	Night	11% 8% 23% 40% 17% 1	630
May	1st to 10th	Night	9% 6% 27% 39% 17% 2	630
	11th to 20th	Night	8% 4 20% 40% 25% 2	621
	21st to end	Night	8% 7% 18% 40% 23% 2	683
June	1st to 10th	Night	5% 5% 20% 41% 28% 2	630
	11th to 20th	Night	6% 5% 26% 42% 20% 1	630
	21st to end	Night	3 4 21% 40% 29% 2	630
July	1st to 10th	Night	3 1 18% 38% 38% 3	615
	11th to 20th	Night	4 2 10% 46% 35% 3	612
	21st to end	Night	3 3 10% 38% 44% 3	690
August	1st to 10th	Night	4 1 14% 46% 33% 2	627
	11th to 20th	Night	3 3 14% 46% 33% 2	624
	21st to end	Night	3 2 14% 43% 36% 2	693
September	1st to 10th	Night	3 2 16% 40% 34% 5%	771
	11th to 20th	Night	5% 4 18% 36% 31% 5%	840
	21st to end	Night	7% 4 18% 35% 30% 7%	840
October	1st to 10th	Night	7% 5% 20% 43% 23% 3	840
	11th to 20th	Night	10% 5% 21% 38% 23% 4	840
	21st to end	Night	8% 5% 21% 39% 24% 3	912
November	1st to 10th	Night	10% 6% 21% 36% 24% 3	820
	11th to 20th	Night	13% 6% 20% 39% 19% 3	840
	21st to end	Night	12% 6% 21% 36% 20% 4	924
December	1st to 10th	Night	16% 4 20% 41% 17% 2	1050
	11th to 20th	Night	19% 6% 21% 40% 13% 1	1040
	21st to end	Night	21% 7% 18% 40% 12% 2	924

Page generated at 2026-10-26 02:37:51. Version ac07

Copyright © 2026 Attilla Danko.