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 2024-11-06.

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	7% 9% 2 6% 3 3 3 3 5% 6% 52%	104906
	Night	8% 10% 3 5% 3 3 4 3 5% 6% 49%	102886
Transparency	Day	33% 6% 9% 18% 20% 14%	104671
	Night	35% 6% 10% 19% 19% 12%	102710
Seeing	Day	12% 15% 32% 29% 10% 2	15004
	Night	13% 7% 23% 35% 19% 3	25414

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	12% 20% 5% 12% 4 3 3 3 4 5% 28%	2858
	11th to 20th	Day	11% 25% 6% 13% 5% 3 3 3 4 5% 24%	2860
	21st to end	Day	11% 16% 5% 10% 4 4 3 3 5% 8% 31%	3146
February	1st to 10th	Day	12% 17% 5% 8% 4 4 4 4 4 6% 33%	1710
	11th to 20th	Day	12% 16% 3 8% 5% 4 4 3 5% 7% 33%	1733
	21st to end	Day	7% 17% 6% 11% 5% 4 4 5% 5% 6% 30%	1570
March	1st to 10th	Day	6% 18% 5% 13% 4 4 4 3 5% 6% 32%	3350
	11th to 20th	Day	7% 12% 3 5% 4 4 4 4 5% 7% 48%	3490
	21st to end	Day	12% 21% 4 9% 5% 5% 4 4 5% 6% 24%	3825
April	1st to 10th	Day	11% 11% 4 6% 4 4 4 5% 6% 7% 40%	2106
	11th to 20th	Day	10% 14% 2 5% 5% 4 4 4 4 6% 42%	2405
	21st to end	Day	10% 9% 3 5% 4 4 4 4 5% 8% 45%	2470
May	1st to 10th	Day	8% 12% 3 6% 4 4 4 4 6% 9% 40%	4110
	11th to 20th	Day	7% 4 1 4 3 3 3 3 6% 8% 59%	4071
	21st to end	Day	8% 6% 2 5% 4 4 4 3 6% 7% 51%	4477
June	1st to 10th	Day	4 4 1 5% 3 3 4 4 7% 8% 56%	2536
	11th to 20th	Day	6% 4 1 4 3 3 3 3 4 6% 64%	2660
	21st to end	Day	3 2 1 2 3 3 3 3 4 4 73%	2477
July	1st to 10th	Day	1 1 1 2 2 2 2 3 4 4 78%	4110
	11th to 20th	Day	2 2 1 3 3 3 4 4 6% 7% 65%	4110
	21st to end	Day	3 2 1 3 3 3 3 3 6% 6% 68%	4454
August	1st to 10th	Day	3 2 1 4 3 3 4 3 5% 6% 66%	4092
	11th to 20th	Day	2 2 1 4 4 3 4 3 5% 6% 66%	4028
	21st to end	Day	2 2 1 3 2 2 3 2 5% 5% 73%	4495
September	1st to 10th	Day	3 3 1 2 2 3 3 2 5% 5% 72%	2142
	11th to 20th	Day	5% 3 1 3 3 3 3 3 5% 6% 65%	2090
	21st to end	Day	7% 3 1 3 2 2 3 2 3 5% 69%	2090
October	1st to 10th	Day	6% 4 1 3 2 3 3 2 3 4 69%	3335
	11th to 20th	Day	9% 6% 1 3 2 3 3 3 4 7% 60%	3150
	21st to end	Day	8% 7% 2 5% 3 4 3 3 4 5% 56%	3413
November	1st to 10th	Day	9% 11% 2 7% 5% 4 3 4 5% 5% 45%	1719
	11th to 20th	Day	14% 10% 3 5% 3 3 3 2 5% 6% 45%	1710
	21st to end	Day	9% 12% 3 7% 5% 5% 4 2 4 5% 44%	1577
December	1st to 10th	Day	11% 14% 3 7% 4 4 4 4 4 6% 40%	1520
	11th to 20th	Day	12% 14% 5% 9% 4 6% 4 4 5% 9% 29%	1926
	21st to end	Day	10% 15% 5% 9% 5% 4 4 3 5% 7% 33%	3091
January	1st to 10th	Night	10% 20% 8% 8% 4 3 3 3 4 6% 32%	4097
	11th to 20th	Night	15% 21% 5% 11% 4 3 3 3 4 5% 26%	4110
	21st to end	Night	10% 17% 3 7% 4 4 4 4 5% 7% 35%	4521
February	1st to 10th	Night	11% 15% 3 7% 4 4 5% 3 6% 7% 34%	2470
	11th to 20th	Night	10% 15% 4 7% 4 4 3 3 4 5% 42%	2332
	21st to end	Night	7% 17% 5% 8% 4 3 4 4 5% 6% 38%	1884
March	1st to 10th	Night	8% 15% 4 10% 5% 5% 4 4 5% 7% 34%	3524
	11th to 20th	Night	5% 10% 2 5% 3 3 4 3 6% 7% 49%	3490
	21st to end	Night	11% 22% 3 6% 4 4 4 3 5% 5% 33%	3828
April	1st to 10th	Night	13% 12% 2 5% 4 3 3 3 4 6% 46%	2072
	11th to 20th	Night	8% 11% 3 5% 4 3 4 4 5% 7% 45%	1720
	21st to end	Night	11% 8% 2 6% 4 4 4 4 5% 6% 46%	1710
May	1st to 10th	Night	11% 14% 3 5% 4 4 4 4 6% 6% 40%	2860
	11th to 20th	Night	7% 4 1 4 3 3 3 3 6% 7% 60%	2834
	21st to end	Night	10% 5% 2 5% 4 4 3 3 5% 7% 52%	3110
June	1st to 10th	Night	6% 5% 2 3 3 3 4 3 5% 8% 56%	1634
	11th to 20th	Night	5% 3 1 3 3 3 3 3 5% 8% 64%	1520
	21st to end	Night	4 1 1 4 2 3 2 3 5% 8% 68%	1691
July	1st to 10th	Night	2 2 1 3 3 2 3 3 4 4 74%	2860
	11th to 20th	Night	2 3 1 4 3 4 5% 5% 8% 9% 54%	2860
	21st to end	Night	3 4 1 4 3 4 5% 3 5% 6% 60%	3109
August	1st to 10th	Night	3 2 1 4 4 4 4 5% 6% 7% 62%	2847
	11th to 20th	Night	3 2 1 4 4 5% 5% 4 5% 6% 61%	2811
	21st to end	Night	4 2 1 3 2 3 3 3 4 5% 71%	3172
September	1st to 10th	Night	3 3 1 4 3 2 3 2 4 5% 68%	2034
	11th to 20th	Night	6% 3 1 3 2 3 3 3 4 6% 67%	2090
	21st to end	Night	6% 3 1 3 2 2 2 2 3 5% 71%	2090
October	1st to 10th	Night	5% 3 1 3 2 3 3 2 3 4 71%	3640
	11th to 20th	Night	9% 5% 1 4 2 3 3 2 4 6% 61%	3778
	21st to end	Night	9% 6% 2 4 3 3 4 3 5% 7% 55%	4140
November	1st to 10th	Night	10% 9% 2 4 3 3 4 3 7% 7% 49%	2482
	11th to 20th	Night	13% 9% 2 4 3 3 3 3 6% 7% 48%	2470
	21st to end	Night	10% 11% 3 4 4 3 4 4 4 6% 47%	2580
December	1st to 10th	Night	11% 12% 3 7% 3 3 4 2 6% 7% 41%	2660
	11th to 20th	Night	14% 13% 3 7% 4 4 4 3 5% 8% 35%	3271
	21st to end	Night	11% 14% 5% 10% 5% 4 4 4 5% 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	60% 7% 10% 16% 6% 1	2859
	11th to 20th	Day	63% 6% 14% 12% 5% 1	2860
	21st to end	Day	52% 8% 19% 14% 7% 1	3146
February	1st to 10th	Day	54% 7% 13% 15% 9% 1	1710
	11th to 20th	Day	51% 8% 13% 17% 10% 1	1742
	21st to end	Day	54% 8% 12% 17% 9% 1	1570
March	1st to 10th	Day	51% 10% 10% 18% 10% 1	3350
	11th to 20th	Day	36% 8% 11% 33% 10% 1	3490
	21st to end	Day	61% 8% 13% 12% 5% 1	3825
April	1st to 10th	Day	44% 8% 13% 18% 13% 4	2106
	11th to 20th	Day	44% 6% 12% 20% 16% 1	2408
	21st to end	Day	38% 7% 10% 25% 19% 1	2470
May	1st to 10th	Day	39% 9% 11% 21% 16% 4	4110
	11th to 20th	Day	23% 6% 9% 30% 28% 3	4074
	21st to end	Day	29% 8% 10% 26% 24% 2	4477
June	1st to 10th	Day	24% 7% 10% 23% 28% 8%	2536
	11th to 20th	Day	22% 5% 7% 19% 28% 18%	2660
	21st to end	Day	15% 4 5% 11% 31% 34%	2477
July	1st to 10th	Day	11% 3 4 7% 15% 60%	4046
	11th to 20th	Day	17% 5% 5% 10% 24% 40%	4041
	21st to end	Day	16% 4 6% 10% 25% 38%	4314
August	1st to 10th	Day	18% 5% 5% 16% 29% 27%	4078
	11th to 20th	Day	18% 5% 6% 13% 33% 25%	4067
	21st to end	Day	14% 3 5% 15% 32% 31%	4494
September	1st to 10th	Day	16% 5% 6% 16% 29% 29%	2142
	11th to 20th	Day	20% 6% 7% 19% 28% 20%	2090
	21st to end	Day	19% 4 6% 21% 34% 16%	2090
October	1st to 10th	Day	21% 4 4 12% 37% 21%	3335
	11th to 20th	Day	26% 4 6% 29% 28% 7%	3150
	21st to end	Day	30% 5% 10% 31% 20% 4	3413
November	1st to 10th	Day	40% 7% 12% 21% 17% 3	1719
	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	54% 6% 12% 19% 9% 1	4097
	11th to 20th	Night	61% 6% 12% 14% 6% 1	4110
	21st to end	Night	48% 8% 19% 16% 7% 2	4521
February	1st to 10th	Night	49% 8% 14% 20% 9% 1	2470
	11th to 20th	Night	46% 6% 11% 20% 16% 2	2333
	21st to end	Night	47% 7% 11% 21% 12% 3	1884
March	1st to 10th	Night	49% 8% 10% 18% 15%	3524
	11th to 20th	Night	32% 8% 12% 31% 16% 1	3490
	21st to end	Night	53% 7% 9% 19% 10% 2	3828
April	1st to 10th	Night	40% 5% 13% 20% 15% 6%	2072
	11th to 20th	Night	37% 7% 11% 22% 21% 3	1720
	21st to end	Night	38% 6% 13% 22% 20% 2	1710
May	1st to 10th	Night	41% 7% 11% 19% 20% 2	2860
	11th to 20th	Night	22% 6% 10% 28% 28% 6%	2835
	21st to end	Night	29% 7% 11% 24% 27% 2	3110
June	1st to 10th	Night	26% 6% 9% 22% 28% 9%	1634
	11th to 20th	Night	20% 5% 8% 19% 29% 19%	1520
	21st to end	Night	16% 3 5% 10% 28% 38%	1691
July	1st to 10th	Night	14% 4 4 8% 12% 58%	2815
	11th to 20th	Night	23% 6% 4 9% 24% 34%	2806
	21st to end	Night	24% 5% 5% 10% 23% 34%	3011
August	1st to 10th	Night	19% 6% 6% 11% 29% 29%	2838
	11th to 20th	Night	24% 5% 6% 11% 28% 27%	2838
	21st to end	Night	16% 4 5% 10% 29% 35%	3172
September	1st to 10th	Night	20% 4 6% 14% 24% 32%	2034
	11th to 20th	Night	20% 5% 7% 17% 28% 23%	2090
	21st to end	Night	19% 4 4 17% 34% 22%	2090
October	1st to 10th	Night	19% 4 5% 13% 34% 25%	3640
	11th to 20th	Night	26% 4 4 27% 28% 11%	3778
	21st to end	Night	29% 6% 6% 29% 26% 4	4140
November	1st to 10th	Night	35% 5% 11% 23% 20% 6%	2482
	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	20% 13% 29% 24% 11% 1	270
	21st to end	Day	19% 10% 29% 32% 8% 2	297
February	1st to 10th	Day	21% 20% 30% 21% 7%	270
	11th to 20th	Day	19% 18% 33% 23% 7% 1	338
	21st to end	Day	14% 21% 40% 20% 4 1	382
March	1st to 10th	Day	18% 23% 32% 19% 7% 1	460
	11th to 20th	Day	14% 18% 35% 25% 8%	460
	21st to end	Day	21% 24% 33% 21% 2	506
April	1st to 10th	Day	20% 19% 30% 24% 6% 2	460
	11th to 20th	Day	21% 23% 32% 19% 5% 1	452
	21st to end	Day	19% 22% 27% 25% 7% 1	460
May	1st to 10th	Day	13% 25% 35% 21% 7% 1	463
	11th to 20th	Day	11% 19% 32% 26% 10% 2	488
	21st to end	Day	11% 16% 32% 28% 12% 2	529
June	1st to 10th	Day	6% 14% 34% 33% 10% 2	556
	11th to 20th	Day	8% 15% 34% 29% 13% 1	680
	21st to end	Day	3 15% 38% 35% 9% 1	497
July	1st to 10th	Day	2 9% 38% 38% 10% 2	486
	11th to 20th	Day	3 7% 38% 37% 12% 2	484
	21st to end	Day	3 3 34% 44% 12% 3	531
August	1st to 10th	Day	6% 8% 36% 36% 13% 2	487
	11th to 20th	Day	4 6% 35% 39% 13% 4	477
	21st to end	Day	6% 8% 30% 40% 14% 2	539
September	1st to 10th	Day	4 9% 30% 36% 18% 3	490
	11th to 20th	Day	8% 16% 29% 34% 12% 2	490
	21st to end	Day	9% 12% 26% 36% 17% 1	490
October	1st to 10th	Day	12% 14% 27% 29% 18% 1	400
	11th to 20th	Day	12% 17% 23% 28% 18% 2	300
	21st to end	Day	13% 14% 35% 28% 9%	330
November	1st to 10th	Day	23% 18% 21% 28% 8% 2	285
	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	19% 6% 23% 33% 14% 5%	760
	21st to end	Night	17% 7% 22% 34% 17% 3	836
February	1st to 10th	Night	19% 8% 24% 36% 11% 2	760
	11th to 20th	Night	16% 8% 27% 32% 15% 2	744
	21st to end	Night	14% 10% 32% 29% 14% 1	628
March	1st to 10th	Night	16% 12% 28% 31% 11% 3	760
	11th to 20th	Night	12% 8% 25% 34% 17% 3	760
	21st to end	Night	16% 15% 24% 33% 11% 2	836
April	1st to 10th	Night	19% 12% 25% 32% 11% 2	742
	11th to 20th	Night	14% 13% 28% 32% 12% 2	563
	21st to end	Night	13% 10% 22% 34% 19% 2	570
May	1st to 10th	Night	11% 9% 30% 33% 15% 2	570
	11th to 20th	Night	9% 7% 22% 37% 21% 4	561
	21st to end	Night	10% 8% 22% 36% 20% 4	617
June	1st to 10th	Night	8% 8% 19% 39% 23% 2	570
	11th to 20th	Night	6% 10% 24% 41% 18% 1	570
	21st to end	Night	4 4 24% 37% 29% 3	570
July	1st to 10th	Night	3 6% 22% 34% 34% 3	555
	11th to 20th	Night	5% 3 18% 45% 27% 2	552
	21st to end	Night	4 3 13% 40% 38% 2	624
August	1st to 10th	Night	5% 2 18% 46% 26% 2	567
	11th to 20th	Night	3 2 19% 44% 30% 2	564
	21st to end	Night	5% 5% 18% 43% 27% 2	627
September	1st to 10th	Night	5% 6% 15% 46% 23% 4	704
	11th to 20th	Night	6% 6% 21% 37% 24% 6%	760
	21st to end	Night	8% 5% 22% 30% 27% 8%	760
October	1st to 10th	Night	10% 7% 24% 36% 19% 4	760
	11th to 20th	Night	11% 5% 22% 34% 24% 5%	760
	21st to end	Night	12% 7% 24% 33% 21% 4	836
November	1st to 10th	Night	15% 10% 19% 33% 20% 3	764
	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 2024-11-03 11:19:04. Version ac07

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