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 2024-03-23.

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	6% 8% 3 6% 5% 3 4 4 5% 7% 49%	78684
	Night	7% 9% 3 6% 4 3 4 4 5% 7% 48%	81265
Transparency	Day	34% 5% 11% 19% 20% 11%	78409
	Night	35% 6% 11% 21% 18% 9%	81061
Seeing	Day	9% 10% 25% 33% 19% 5%	13855
	Night	11% 4 17% 41% 24% 3	24556

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	9% 17% 6% 11% 6% 3 4 4 5% 5% 30%	2858
	11th to 20th	Day	11% 20% 6% 12% 5% 2 3 3 3 5% 30%	2860
	21st to end	Day	9% 15% 6% 9% 5% 3 3 3 4 6% 38%	3146
February	1st to 10th	Day	10% 13% 5% 8% 6% 3 4 3 5% 6% 36%	1710
	11th to 20th	Day	10% 13% 4 7% 5% 3 4 4 5% 7% 37%	1734
	21st to end	Day	8% 13% 6% 8% 5% 4 5% 4 5% 6% 36%	1570
March	1st to 10th	Day	7% 12% 6% 6% 6% 3 4 4 5% 7% 40%	2046
	11th to 20th	Day	7% 10% 3 6% 5% 3 4 6% 6% 8% 43%	2090
	21st to end	Day	8% 14% 4 8% 7% 4 5% 4 6% 7% 33%	2201
April	1st to 10th	Day	9% 10% 3 6% 6% 3 5% 5% 5% 7% 42%	1998
	11th to 20th	Day	7% 10% 4 7% 5% 3 5% 4 5% 6% 43%	2244
	21st to end	Day	8% 9% 2 6% 4 3 4 4 5% 6% 49%	2340
May	1st to 10th	Day	7% 6% 2 5% 5% 3 5% 6% 7% 8% 46%	2340
	11th to 20th	Day	6% 6% 2 5% 4 3 5% 5% 7% 9% 49%	2301
	21st to end	Day	6% 5% 2 5% 5% 4 5% 6% 8% 9% 45%	2530
June	1st to 10th	Day	3 3 1 2 4 4 4 5% 7% 8% 59%	2340
	11th to 20th	Day	4 3 1 3 4 1 4 4 5% 7% 64%	2340
	21st to end	Day	2 2 1 2 3 2 4 4 5% 5% 70%	2340
July	1st to 10th	Day	2 2 1 3 4 3 4 4 6% 8% 64%	2340
	11th to 20th	Day	3 3 1 3 5% 3 5% 5% 6% 9% 57%	2340
	21st to end	Day	3 3 1 4 4 3 5% 6% 7% 10% 54%	2545
August	1st to 10th	Day	3 3 1 4 4 3 4 7% 6% 9% 55%	2328
	11th to 20th	Day	3 3 1 3 4 3 4 5% 5% 7% 63%	2299
	21st to end	Day	3 2 1 3 4 2 4 6% 6% 8% 62%	2540
September	1st to 10th	Day	3 3 1 2 3 2 3 4 4 7% 68%	2036
	11th to 20th	Day	3 2 1 3 3 3 3 4 5% 7% 66%	1980
	21st to end	Day	5% 3 1 3 3 2 3 3 2 6% 69%	1980
October	1st to 10th	Day	7% 5% 2 4 5% 2 3 4 5% 6% 56%	1888
	11th to 20th	Day	7% 5% 3 3 3 1 3 3 4 7% 62%	1800
	21st to end	Day	6% 7% 2 3 3 2 4 4 5% 6% 58%	1980
November	1st to 10th	Day	8% 9% 2 5% 3 3 4 4 4 6% 52%	1695
	11th to 20th	Day	13% 6% 2 5% 4 2 4 4 4 7% 49%	1710
	21st to end	Day	6% 10% 5% 6% 4 2 3 4 5% 8% 47%	1611
December	1st to 10th	Day	9% 12% 6% 7% 4 2 3 3 4 6% 44%	1520
	11th to 20th	Day	9% 11% 5% 9% 6% 3 5% 5% 6% 7% 34%	1958
	21st to end	Day	8% 13% 5% 8% 6% 3 4 5% 6% 8% 35%	3146
January	1st to 10th	Night	7% 18% 7% 10% 5% 3 3 4 4 6% 33%	4097
	11th to 20th	Night	13% 18% 7% 11% 5% 3 4 3 3 5% 29%	4110
	21st to end	Night	9% 17% 5% 6% 4 2 4 4 4 7% 37%	4521
February	1st to 10th	Night	9% 13% 5% 8% 5% 3 4 4 5% 6% 39%	2470
	11th to 20th	Night	9% 11% 4 7% 6% 2 3 4 4 6% 42%	2332
	21st to end	Night	7% 12% 5% 10% 3 2 4 5% 6% 6% 40%	1884
March	1st to 10th	Night	9% 12% 6% 6% 4 3 4 4 5% 7% 38%	2133
	11th to 20th	Night	7% 8% 3 5% 5% 2 5% 4 6% 8% 47%	2090
	21st to end	Night	8% 12% 3 6% 5% 4 5% 5% 5% 8% 41%	2200
April	1st to 10th	Night	11% 9% 3 5% 4 2 4 3 3 6% 49%	1961
	11th to 20th	Night	8% 7% 2 4 5% 4 4 5% 6% 7% 48%	1659
	21st to end	Night	9% 6% 3 6% 4 2 4 4 5% 7% 51%	1620
May	1st to 10th	Night	9% 4 2 5% 6% 3 5% 5% 7% 8% 46%	1620
	11th to 20th	Night	7% 4 2 3 4 3 4 5% 6% 8% 53%	1594
	21st to end	Night	7% 4 2 5% 4 4 5% 6% 7% 7% 50%	1746
June	1st to 10th	Night	4 2 2 3 4 3 4 5% 6% 7% 60%	1620
	11th to 20th	Night	4 3 2 3 2 3 3 3 4 6% 67%	1620
	21st to end	Night	2 2 1 3 3 2 2 4 5% 6% 69%	1620
July	1st to 10th	Night	2 2 1 4 4 3 5% 7% 6% 8% 59%	1620
	11th to 20th	Night	3 4 2 5% 5% 3 6% 6% 6% 9% 51%	1620
	21st to end	Night	2 4 1 5% 5% 4 6% 7% 7% 8% 51%	1773
August	1st to 10th	Night	4 3 1 3 4 3 4 5% 6% 9% 57%	1611
	11th to 20th	Night	3 3 1 4 5% 3 3 4 6% 7% 59%	1602
	21st to end	Night	2 2 1 3 4 3 4 5% 6% 8% 63%	1815
September	1st to 10th	Night	2 2 1 3 3 2 3 4 4 6% 71%	1920
	11th to 20th	Night	4 3 1 3 3 2 3 4 5% 7% 66%	1980
	21st to end	Night	6% 2 1 3 3 1 2 3 3 5% 71%	1980
October	1st to 10th	Night	6% 5% 2 4 3 2 3 3 5% 6% 61%	2070
	11th to 20th	Night	7% 5% 2 3 3 2 3 3 4 6% 62%	2160
	21st to end	Night	6% 7% 2 4 3 1 3 4 4 7% 61%	2376
November	1st to 10th	Night	7% 7% 2 5% 3 2 3 3 5% 7% 55%	2381
	11th to 20th	Night	10% 7% 2 4 3 2 3 4 4 7% 53%	2470
	21st to end	Night	8% 11% 5% 6% 4 3 4 3 4 6% 48%	2546
December	1st to 10th	Night	11% 11% 4 5% 4 2 3 3 4 6% 47%	2660
	11th to 20th	Night	11% 13% 4 6% 5% 3 4 5% 5% 8% 36%	3263
	21st to end	Night	8% 14% 6% 10% 6% 3 4 5% 6% 6% 33%	4521

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	54% 7% 12% 16% 9%	2859
	11th to 20th	Day	58% 6% 15% 13% 7% 1	2860
	21st to end	Day	47% 8% 17% 17% 9% 2	3146
February	1st to 10th	Day	49% 6% 14% 18% 10% 2	1710
	11th to 20th	Day	48% 5% 12% 21% 13% 1	1743
	21st to end	Day	47% 5% 12% 23% 13% 1	1570
March	1st to 10th	Day	42% 6% 13% 23% 14% 2	2046
	11th to 20th	Day	39% 6% 13% 25% 14% 3	2090
	21st to end	Day	50% 5% 13% 19% 10% 2	2201
April	1st to 10th	Day	41% 5% 11% 19% 17% 6%	1998
	11th to 20th	Day	41% 5% 12% 18% 20% 4	2247
	21st to end	Day	35% 5% 10% 24% 22% 3	2340
May	1st to 10th	Day	33% 5% 11% 22% 24% 5%	2340
	11th to 20th	Day	30% 5% 10% 23% 25% 6%	2304
	21st to end	Day	33% 8% 12% 21% 22% 5%	2530
June	1st to 10th	Day	21% 5% 8% 18% 34% 14%	2340
	11th to 20th	Day	19% 4 7% 14% 31% 25%	2340
	21st to end	Day	15% 2 5% 8% 29% 40%	2340
July	1st to 10th	Day	18% 4 7% 13% 21% 37%	2276
	11th to 20th	Day	23% 5% 9% 12% 23% 28%	2271
	21st to end	Day	24% 6% 12% 15% 20% 24%	2404
August	1st to 10th	Day	23% 5% 10% 16% 20% 25%	2313
	11th to 20th	Day	21% 4 6% 12% 27% 31%	2299
	21st to end	Day	20% 4 8% 16% 30% 22%	2540
September	1st to 10th	Day	16% 4 8% 12% 27% 32%	2036
	11th to 20th	Day	19% 4 8% 19% 25% 25%	1980
	21st to end	Day	19% 3 6% 18% 35% 20%	1980
October	1st to 10th	Day	29% 5% 8% 18% 31% 9%	1888
	11th to 20th	Day	25% 3 7% 26% 31% 8%	1800
	21st to end	Day	26% 4 12% 30% 24% 4	1980
November	1st to 10th	Day	34% 4 11% 25% 22% 5%	1695
	11th to 20th	Day	35% 6% 12% 26% 19% 2	1710
	21st to end	Day	37% 5% 13% 26% 16% 3	1611
December	1st to 10th	Day	41% 4 17% 24% 10% 3	1520
	11th to 20th	Day	45% 7% 13% 23% 11%	1956
	21st to end	Day	44% 8% 15% 13% 18% 1	3146
January	1st to 10th	Night	51% 7% 12% 18% 10%	4097
	11th to 20th	Night	57% 7% 13% 15% 6% 1	4110
	21st to end	Night	45% 10% 20% 17% 7% 2	4521
February	1st to 10th	Night	44% 7% 17% 22% 8% 2	2470
	11th to 20th	Night	43% 6% 11% 22% 16% 2	2333
	21st to end	Night	43% 5% 11% 24% 14% 3	1884
March	1st to 10th	Night	43% 6% 12% 26% 13% 1	2133
	11th to 20th	Night	33% 6% 13% 27% 18% 3	2090
	21st to end	Night	41% 6% 13% 24% 12% 3	2200
April	1st to 10th	Night	37% 4 12% 21% 19% 7%	1961
	11th to 20th	Night	34% 5% 12% 24% 22% 4	1659
	21st to end	Night	32% 6% 11% 27% 21% 3	1620
May	1st to 10th	Night	34% 6% 10% 22% 22% 5%	1620
	11th to 20th	Night	28% 6% 8% 23% 27% 8%	1595
	21st to end	Night	29% 6% 13% 26% 21% 5%	1746
June	1st to 10th	Night	21% 6% 9% 21% 31% 12%	1620
	11th to 20th	Night	18% 3 7% 17% 29% 26%	1620
	21st to end	Night	16% 2 5% 9% 26% 41%	1620
July	1st to 10th	Night	21% 5% 8% 11% 19% 36%	1575
	11th to 20th	Night	27% 5% 8% 14% 20% 25%	1566
	21st to end	Night	27% 6% 13% 13% 18% 22%	1674
August	1st to 10th	Night	23% 5% 12% 19% 18% 24%	1602
	11th to 20th	Night	22% 5% 8% 14% 21% 29%	1602
	21st to end	Night	19% 4 9% 15% 26% 26%	1815
September	1st to 10th	Night	16% 3 7% 15% 25% 34%	1920
	11th to 20th	Night	18% 4 7% 19% 25% 26%	1980
	21st to end	Night	19% 3 5% 16% 33% 25%	1980
October	1st to 10th	Night	25% 4 8% 22% 29% 12%	2070
	11th to 20th	Night	24% 3 6% 24% 33% 9%	2160
	21st to end	Night	24% 5% 10% 30% 26% 6%	2376
November	1st to 10th	Night	29% 5% 10% 27% 23% 6%	2381
	11th to 20th	Night	30% 5% 13% 30% 19% 3	2470
	21st to end	Night	38% 4 8% 25% 20% 4	2546
December	1st to 10th	Night	39% 5% 16% 27% 11% 3	2660
	11th to 20th	Night	44% 8% 14% 22% 12%	3264
	21st to end	Night	49% 8% 13% 14% 15% 1	4521

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% 7% 21% 30% 14% 4	270
	11th to 20th	Day	15% 11% 22% 34% 16% 3	270
	21st to end	Day	16% 5% 26% 31% 19% 3	297
February	1st to 10th	Day	18% 12% 26% 33% 10% 1	270
	11th to 20th	Day	14% 12% 30% 31% 12% 1	339
	21st to end	Day	10% 14% 36% 30% 9% 1	382
March	1st to 10th	Day	15% 18% 25% 29% 12% 1	460
	11th to 20th	Day	10% 12% 36% 29% 13% 1	460
	21st to end	Day	17% 18% 33% 25% 7%	471
April	1st to 10th	Day	15% 16% 26% 27% 14% 3	420
	11th to 20th	Day	15% 21% 29% 24% 9% 2	412
	21st to end	Day	13% 20% 25% 25% 14% 2	420
May	1st to 10th	Day	10% 14% 34% 27% 13% 2	423
	11th to 20th	Day	8% 11% 29% 31% 17% 4	448
	21st to end	Day	8% 10% 25% 29% 22% 5%	485
June	1st to 10th	Day	4 12% 24% 36% 19% 5%	450
	11th to 20th	Day	5% 13% 30% 34% 15% 3	450
	21st to end	Day	3 7% 29% 40% 17% 4	450
July	1st to 10th	Day	2 3 22% 39% 27% 6%	446
	11th to 20th	Day	3 3 25% 42% 22% 5%	444
	21st to end	Day	2 14% 44% 31% 8%	487
August	1st to 10th	Day	6% 4 19% 40% 26% 5%	447
	11th to 20th	Day	3 3 20% 38% 28% 8%	437
	21st to end	Day	2 3 21% 36% 29% 8%	495
September	1st to 10th	Day	4 4 21% 33% 27% 11%	450
	11th to 20th	Day	5% 8% 23% 31% 25% 8%	450
	21st to end	Day	6% 10% 18% 28% 31% 7%	450
October	1st to 10th	Day	5% 11% 25% 28% 23% 9%	358
	11th to 20th	Day	7% 10% 20% 26% 27% 10%	270
	21st to end	Day	9% 7% 25% 33% 23% 2	297
November	1st to 10th	Day	15% 14% 16% 27% 20% 7%	270
	11th to 20th	Day	11% 8% 19% 34% 21% 7%	270
	21st to end	Day	11% 6% 21% 32% 26% 5%	270
December	1st to 10th	Day	12% 11% 19% 35% 15% 7%	270
	11th to 20th	Day	12% 9% 21% 39% 17% 2	270
	21st to end	Day	18% 9% 21% 35% 13% 3	297
January	1st to 10th	Night	18% 4 15% 41% 18% 5%	760
	11th to 20th	Night	16% 5% 17% 37% 23% 3	760
	21st to end	Night	17% 4 15% 42% 19% 3	836
February	1st to 10th	Night	14% 5% 23% 43% 12% 3	760
	11th to 20th	Night	14% 4 23% 42% 16% 1	744
	21st to end	Night	13% 5% 24% 43% 14% 1	628
March	1st to 10th	Night	16% 8% 19% 41% 14% 2	760
	11th to 20th	Night	9% 5% 19% 44% 21% 1	760
	21st to end	Night	13% 8% 23% 41% 13% 2	800
April	1st to 10th	Night	15% 8% 20% 41% 15% 1	701
	11th to 20th	Night	11% 8% 24% 41% 16%	533
	21st to end	Night	11% 8% 20% 39% 20% 1	540
May	1st to 10th	Night	10% 6% 24% 39% 19% 2	540
	11th to 20th	Night	9% 4 17% 40% 29% 3	531
	21st to end	Night	9% 7% 16% 41% 25% 3	584
June	1st to 10th	Night	5% 5% 18% 40% 29% 2	540
	11th to 20th	Night	6% 6% 23% 41% 24% 1	540
	21st to end	Night	3 3 17% 42% 34% 2	540
July	1st to 10th	Night	3 1 13% 36% 44% 4	525
	11th to 20th	Night	4 2 8% 45% 38% 3	522
	21st to end	Night	3 2 6% 36% 50% 3	591
August	1st to 10th	Night	4 1 10% 45% 38% 2	537
	11th to 20th	Night	2 2 10% 45% 38% 2	534
	21st to end	Night	4 2 11% 41% 41% 2	594
September	1st to 10th	Night	3 2 11% 40% 39% 6%	660
	11th to 20th	Night	5% 2 12% 38% 36% 6%	720
	21st to end	Night	8% 3 13% 33% 35% 9%	720
October	1st to 10th	Night	8% 5% 18% 40% 26% 4	720
	11th to 20th	Night	9% 3 16% 42% 27% 4	720
	21st to end	Night	9% 4 16% 40% 27% 4	792
November	1st to 10th	Night	10% 6% 17% 38% 26% 4	740
	11th to 20th	Night	13% 4 17% 41% 21% 4	760
	21st to end	Night	12% 5% 18% 38% 22% 5%	836
December	1st to 10th	Night	17% 4 17% 43% 18% 2	950
	11th to 20th	Night	20% 5% 18% 42% 15% 1	942
	21st to end	Night	21% 6% 17% 42% 13% 2	836

Page generated at 2024-03-19 21:31:10. Version ac07

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