Salt Lake City
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Salt Lake City clear sky chart from 2005-11-06 to 2024-01-16.

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% 8% 3 5% 4 3 4 4 5% 7% 49%	74588
	Night	9% 9% 3 5% 4 3 4 4 5% 7% 48%	75202
Transparency	Day	35% 7% 11% 19% 19% 10%	74313
	Night	36% 6% 11% 20% 18% 9%	74998
Seeing	Day	12% 15% 31% 30% 10% 2	13874
	Night	13% 7% 22% 35% 20% 3	24376

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	16% 14% 4 6% 5% 2 4 5% 5% 6% 31%	1708
	11th to 20th	Day	10% 16% 6% 8% 6% 2 4 4 5% 7% 31%	1665
	21st to end	Day	11% 19% 6% 8% 5% 3 4 4 4 7% 29%	1782
February	1st to 10th	Day	11% 15% 5% 7% 6% 3 4 4 4 6% 34%	1620
	11th to 20th	Day	12% 14% 4 8% 6% 3 4 4 5% 7% 34%	1640
	21st to end	Day	8% 15% 7% 10% 6% 3 5% 5% 6% 6% 29%	1480
March	1st to 10th	Day	9% 13% 4 8% 4 3 5% 4 6% 7% 37%	1921
	11th to 20th	Day	8% 10% 3 6% 5% 3 6% 6% 7% 9% 38%	1980
	21st to end	Day	12% 14% 4 7% 6% 3 5% 6% 5% 7% 32%	2178
April	1st to 10th	Day	12% 10% 4 5% 4 3 3 5% 6% 7% 40%	1995
	11th to 20th	Day	11% 13% 3 5% 5% 3 4 5% 4 6% 41%	2276
	21st to end	Day	10% 9% 2 5% 5% 3 3 5% 5% 8% 46%	2340
May	1st to 10th	Day	8% 6% 2 6% 6% 3 5% 5% 7% 10% 43%	2340
	11th to 20th	Day	8% 5% 2 5% 4 3 5% 6% 7% 9% 47%	2301
	21st to end	Day	9% 5% 2 5% 6% 3 6% 6% 7% 9% 44%	2530
June	1st to 10th	Day	4 4 2 4 4 2 4 5% 6% 8% 57%	2402
	11th to 20th	Day	6% 3 2 3 3 2 4 3 4 6% 64%	2520
	21st to end	Day	3 2 1 2 3 2 3 3 4 4 73%	2347
July	1st to 10th	Day	2 1 1 2 3 2 4 5% 5% 7% 67%	2340
	11th to 20th	Day	4 2 2 3 3 2 3 5% 6% 6% 63%	2340
	21st to end	Day	4 2 2 3 4 3 5% 6% 7% 8% 57%	2545
August	1st to 10th	Day	4 2 1 4 4 3 5% 5% 6% 7% 60%	2328
	11th to 20th	Day	3 2 1 3 4 2 4 4 4 7% 66%	2299
	21st to end	Day	4 3 1 3 3 3 3 4 6% 6% 64%	2561
September	1st to 10th	Day	3 2 1 2 2 2 3 3 5% 5% 72%	2030
	11th to 20th	Day	5% 2 1 3 4 2 3 4 5% 6% 65%	1980
	21st to end	Day	8% 3 1 2 2 1 3 3 3 5% 68%	1980
October	1st to 10th	Day	10% 5% 2 3 4 3 4 4 5% 5% 55%	1895
	11th to 20th	Day	8% 6% 2 3 2 3 3 3 4 6% 60%	1800
	21st to end	Day	7% 8% 2 4 3 3 5% 4 4 6% 54%	1967
November	1st to 10th	Day	10% 10% 2 5% 6% 3 3 4 5% 5% 46%	1674
	11th to 20th	Day	14% 9% 4 4 4 2 3 3 5% 7% 46%	1710
	21st to end	Day	9% 11% 4 6% 6% 3 4 3 4 6% 44%	1577
December	1st to 10th	Day	11% 13% 3 7% 5% 3 4 4 4 6% 40%	1520
	11th to 20th	Day	12% 13% 6% 8% 5% 4 5% 5% 5% 9% 29%	1926
	21st to end	Day	10% 14% 6% 8% 6% 3 4 4 5% 7% 33%	3091
January	1st to 10th	Night	15% 13% 4 5% 5% 2 3 5% 5% 8% 34%	2457
	11th to 20th	Night	11% 14% 4 7% 5% 3 3 5% 6% 7% 35%	2405
	21st to end	Night	10% 17% 4 6% 5% 2 4 6% 6% 6% 33%	2574
February	1st to 10th	Night	11% 13% 4 6% 4 3 5% 4 5% 7% 36%	2340
	11th to 20th	Night	10% 13% 4 6% 4 2 4 4 4 5% 42%	2205
	21st to end	Night	7% 15% 6% 8% 5% 3 3 5% 5% 6% 37%	1776
March	1st to 10th	Night	10% 14% 5% 7% 6% 2 4 4 4 7% 37%	2039
	11th to 20th	Night	8% 9% 3 5% 4 3 5% 5% 6% 8% 44%	1980
	21st to end	Night	9% 14% 4 5% 4 2 5% 5% 6% 7% 39%	2178
April	1st to 10th	Night	14% 11% 3 4 4 2 3 3 5% 6% 46%	1963
	11th to 20th	Night	8% 10% 3 5% 4 3 5% 5% 6% 8% 45%	1629
	21st to end	Night	11% 7% 2 5% 5% 3 4 4 4 7% 48%	1620
May	1st to 10th	Night	8% 6% 3 4 6% 4 5% 5% 7% 7% 45%	1620
	11th to 20th	Night	8% 5% 2 3 4 2 4 5% 7% 8% 51%	1594
	21st to end	Night	9% 4 2 5% 6% 3 4 5% 5% 9% 47%	1746
June	1st to 10th	Night	6% 4 2 3 3 2 4 4 5% 8% 58%	1548
	11th to 20th	Night	5% 3 1 3 3 2 3 4 4 8% 65%	1440
	21st to end	Night	4 1 3 3 2 2 3 5% 7% 69%	1601
July	1st to 10th	Night	3 2 2 3 4 3 4 5% 7% 6% 59%	1620
	11th to 20th	Night	3 4 2 4 4 3 5% 5% 7% 7% 56%	1620
	21st to end	Night	3 3 2 4 5% 3 4 5% 6% 9% 55%	1773
August	1st to 10th	Night	4 2 1 3 5% 3 4 5% 5% 8% 60%	1611
	11th to 20th	Night	2 2 1 3 4 4 5% 5% 5% 7% 61%	1602
	21st to end	Night	4 2 1 3 4 3 3 5% 6% 7% 61%	1795
September	1st to 10th	Night	3 3 1 4 4 2 3 3 4 5% 69%	1926
	11th to 20th	Night	6% 2 1 2 3 2 3 3 4 6% 67%	1980
	21st to end	Night	7% 3 1 3 2 2 2 2 3 5% 70%	1980
October	1st to 10th	Night	8% 4 2 4 3 3 4 3 4 6% 59%	2065
	11th to 20th	Night	8% 6% 2 4 3 2 2 3 4 5% 61%	2160
	21st to end	Night	8% 7% 2 3 3 2 3 3 4 6% 59%	2384
November	1st to 10th	Night	10% 9% 2 3 3 2 3 4 6% 7% 50%	2405
	11th to 20th	Night	13% 9% 2 3 4 2 3 3 6% 7% 48%	2470
	21st to end	Night	10% 10% 4 4 4 2 4 5% 4 6% 47%	2580
December	1st to 10th	Night	11% 12% 4 5% 5% 2 4 4 6% 7% 42%	2660
	11th to 20th	Night	14% 12% 4 6% 5% 3 4 4 5% 8% 35%	3271
	21st to end	Night	11% 13% 5% 9% 6% 3 4 4 4 6% 34%	4585

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% 8% 15% 19% 4 1	1709
	11th to 20th	Day	54% 6% 14% 17% 8% 1	1665
	21st to end	Day	55% 8% 16% 13% 6% 2	1782
February	1st to 10th	Day	53% 8% 14% 16% 8% 1	1620
	11th to 20th	Day	51% 8% 12% 17% 10% 1	1649
	21st to end	Day	55% 8% 12% 16% 8% 1	1480
March	1st to 10th	Day	47% 10% 12% 22% 8% 1	1921
	11th to 20th	Day	42% 9% 13% 22% 11% 2	1980
	21st to end	Day	53% 9% 14% 15% 7% 2	2178
April	1st to 10th	Day	44% 8% 13% 17% 13% 5%	1995
	11th to 20th	Day	45% 6% 12% 20% 16% 1	2279
	21st to end	Day	38% 7% 10% 24% 19% 1	2340
May	1st to 10th	Day	36% 9% 11% 23% 18% 3	2340
	11th to 20th	Day	32% 7% 10% 25% 21% 4	2304
	21st to end	Day	36% 10% 12% 23% 17% 3	2530
June	1st to 10th	Day	24% 7% 10% 22% 29% 8%	2402
	11th to 20th	Day	23% 5% 8% 19% 28% 18%	2520
	21st to end	Day	15% 4 5% 11% 31% 33%	2347
July	1st to 10th	Day	17% 4 8% 12% 25% 34%	2276
	11th to 20th	Day	20% 5% 8% 12% 25% 31%	2271
	21st to end	Day	22% 7% 10% 13% 22% 26%	2404
August	1st to 10th	Day	22% 6% 8% 16% 22% 26%	2313
	11th to 20th	Day	18% 5% 8% 11% 31% 27%	2299
	21st to end	Day	19% 5% 7% 16% 32% 20%	2561
September	1st to 10th	Day	16% 5% 6% 16% 28% 29%	2030
	11th to 20th	Day	21% 6% 7% 19% 27% 20%	1980
	21st to end	Day	20% 4 7% 20% 34% 15%	1980
October	1st to 10th	Day	32% 6% 7% 21% 27% 8%	1895
	11th to 20th	Day	27% 6% 10% 30% 23% 5%	1800
	21st to end	Day	30% 7% 14% 27% 20% 2	1967
November	1st to 10th	Day	40% 7% 12% 21% 17% 3	1674
	11th to 20th	Day	41% 5% 10% 28% 15% 1	1710
	21st to end	Day	44% 6% 11% 23% 15% 1	1577
December	1st to 10th	Day	45% 9% 16% 18% 9% 3	1520
	11th to 20th	Day	53% 7% 13% 18% 9%	1924
	21st to end	Day	49% 8% 13% 16% 14% 1	3091
January	1st to 10th	Night	49% 7% 14% 21% 6% 1	2457
	11th to 20th	Night	48% 7% 14% 19% 10% 2	2405
	21st to end	Night	49% 7% 16% 17% 7% 3	2574
February	1st to 10th	Night	48% 7% 14% 21% 9% 1	2340
	11th to 20th	Night	45% 6% 11% 20% 16% 2	2206
	21st to end	Night	47% 7% 11% 21% 11% 2	1776
March	1st to 10th	Night	49% 6% 10% 21% 13%	2039
	11th to 20th	Night	37% 8% 12% 24% 16% 2	1980
	21st to end	Night	44% 9% 13% 22% 9% 3	2178
April	1st to 10th	Night	41% 5% 13% 19% 15% 7%	1963
	11th to 20th	Night	37% 7% 11% 22% 20% 3	1629
	21st to end	Night	38% 5% 12% 22% 21% 2	1620
May	1st to 10th	Night	37% 7% 11% 21% 21% 3	1620
	11th to 20th	Night	29% 8% 10% 25% 21% 6%	1595
	21st to end	Night	33% 8% 14% 24% 17% 4	1746
June	1st to 10th	Night	26% 6% 8% 22% 28% 9%	1548
	11th to 20th	Night	19% 5% 9% 19% 28% 20%	1440
	21st to end	Night	16% 3 5% 11% 28% 37%	1601
July	1st to 10th	Night	22% 6% 7% 14% 18% 34%	1575
	11th to 20th	Night	26% 7% 6% 12% 20% 29%	1566
	21st to end	Night	24% 6% 9% 14% 19% 27%	1674
August	1st to 10th	Night	22% 6% 10% 15% 21% 27%	1602
	11th to 20th	Night	23% 5% 7% 10% 27% 28%	1602
	21st to end	Night	21% 6% 7% 13% 29% 24%	1795
September	1st to 10th	Night	19% 4 6% 15% 23% 33%	1926
	11th to 20th	Night	20% 5% 7% 17% 27% 24%	1980
	21st to end	Night	20% 4 5% 17% 34% 21%	1980
October	1st to 10th	Night	28% 5% 8% 21% 28% 9%	2065
	11th to 20th	Night	27% 4 7% 27% 28% 7%	2160
	21st to end	Night	28% 5% 10% 26% 26% 5%	2384
November	1st to 10th	Night	34% 5% 11% 23% 20% 6%	2405
	11th to 20th	Night	36% 6% 13% 26% 17% 3	2470
	21st to end	Night	39% 6% 11% 26% 15% 4	2580
December	1st to 10th	Night	42% 7% 14% 22% 10% 4	2660
	11th to 20th	Night	48% 7% 14% 19% 11%	3272
	21st to end	Night	50% 7% 15% 15% 12% 1	4585

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	26% 14% 25% 22% 11% 2	270
	11th to 20th	Day	21% 14% 27% 25% 11% 2	255
	21st to end	Day	20% 10% 33% 28% 8% 2	264
February	1st to 10th	Day	20% 20% 30% 23% 8%	240
	11th to 20th	Day	17% 17% 34% 23% 8% 1	305
	21st to end	Day	13% 22% 39% 20% 4 1	346
March	1st to 10th	Day	17% 23% 32% 20% 8% 1	420
	11th to 20th	Day	15% 18% 35% 25% 7%	420
	21st to end	Day	20% 24% 34% 21% 2	462
April	1st to 10th	Day	20% 19% 31% 24% 5% 1	420
	11th to 20th	Day	21% 23% 31% 18% 5% 1	412
	21st to end	Day	20% 23% 25% 25% 7% 1	420
May	1st to 10th	Day	11% 24% 35% 22% 7% 1	423
	11th to 20th	Day	11% 19% 33% 26% 9% 2	448
	21st to end	Day	11% 15% 32% 28% 12% 2	485
June	1st to 10th	Day	6% 14% 35% 32% 10% 2	512
	11th to 20th	Day	8% 14% 33% 30% 13% 1	630
	21st to end	Day	3 14% 35% 37% 9% 1	457
July	1st to 10th	Day	2 7% 37% 40% 11% 2	446
	11th to 20th	Day	3 7% 40% 36% 12% 2	444
	21st to end	Day	3 3 33% 44% 13% 3	487
August	1st to 10th	Day	6% 7% 35% 36% 13% 2	447
	11th to 20th	Day	3 5% 32% 41% 14% 4	437
	21st to end	Day	5% 7% 29% 42% 14% 2	495
September	1st to 10th	Day	5% 9% 30% 35% 18% 3	450
	11th to 20th	Day	7% 14% 29% 36% 13% 2	450
	21st to end	Day	10% 13% 24% 36% 17% 1	450
October	1st to 10th	Day	13% 15% 28% 28% 15% 1	365
	11th to 20th	Day	11% 18% 22% 29% 19% 2	270
	21st to end	Day	12% 14% 35% 28% 10%	297
November	1st to 10th	Day	23% 17% 20% 29% 9% 2	270
	11th to 20th	Day	17% 13% 31% 26% 9% 5%	270
	21st to end	Day	15% 13% 24% 29% 16% 3	270
December	1st to 10th	Day	19% 14% 25% 29% 12% 2	270
	11th to 20th	Day	20% 10% 32% 29% 8% 1	270
	21st to end	Day	24% 14% 29% 26% 6% 1	297
January	1st to 10th	Night	19% 6% 24% 30% 18% 3	760
	11th to 20th	Night	18% 6% 23% 33% 15% 5%	740
	21st to end	Night	18% 7% 22% 32% 17% 4	792
February	1st to 10th	Night	18% 7% 24% 37% 12% 3	720
	11th to 20th	Night	16% 7% 26% 34% 15% 2	704
	21st to end	Night	14% 10% 31% 29% 15% 1	592
March	1st to 10th	Night	16% 11% 27% 31% 11% 3	720
	11th to 20th	Night	13% 8% 24% 35% 18% 3	720
	21st to end	Night	15% 14% 24% 34% 11% 2	792
April	1st to 10th	Night	20% 11% 24% 32% 12% 2	703
	11th to 20th	Night	14% 13% 27% 33% 12% 2	533
	21st to end	Night	13% 10% 21% 35% 19% 2	540
May	1st to 10th	Night	11% 8% 29% 34% 16% 2	540
	11th to 20th	Night	10% 6% 20% 37% 22% 4	531
	21st to end	Night	10% 8% 21% 35% 21% 4	584
June	1st to 10th	Night	9% 8% 19% 38% 25% 2	540
	11th to 20th	Night	5% 10% 22% 42% 19% 1	540
	21st to end	Night	4 4 21% 38% 30% 3	540
July	1st to 10th	Night	3 5% 19% 34% 35% 3	525
	11th to 20th	Night	5% 3 19% 43% 28% 2	522
	21st to end	Night	4 3 11% 41% 39% 2	591
August	1st to 10th	Night	5% 2 17% 46% 28% 2	537
	11th to 20th	Night	3 2 16% 46% 32% 2	534
	21st to end	Night	5% 4 17% 44% 28% 2	594
September	1st to 10th	Night	5% 6% 15% 46% 24% 4	666
	11th to 20th	Night	7% 5% 19% 38% 25% 6%	720
	21st to end	Night	8% 5% 20% 30% 28% 9%	720
October	1st to 10th	Night	10% 7% 23% 35% 21% 4	720
	11th to 20th	Night	10% 5% 20% 34% 25% 5%	720
	21st to end	Night	12% 7% 22% 34% 22% 4	792
November	1st to 10th	Night	15% 10% 18% 34% 20% 3	740
	11th to 20th	Night	17% 6% 24% 33% 15% 5%	760
	21st to end	Night	15% 8% 23% 32% 17% 5%	870
December	1st to 10th	Night	17% 7% 26% 33% 15% 1	950
	11th to 20th	Night	22% 7% 25% 33% 12% 2	950
	21st to end	Night	25% 10% 23% 32% 11% 1	874

Page generated at 2024-01-12 23:38:13. Version ac07

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