Logan
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Logan 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	8% 10% 3 6% 4 3 4 4 5% 7% 47%	79294
	Night	9% 11% 4 6% 5% 3 4 4 5% 6% 45%	80639
Transparency	Day	39% 3 10% 20% 19% 9%	79015
	Night	40% 4 11% 21% 16% 8%	80439
Seeing	Day	13% 12% 30% 30% 13% 2	14405
	Night	13% 5% 20% 38% 20% 3	24383

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	10% 20% 6% 10% 5% 2 4 4 4 5% 30%	2858
	11th to 20th	Day	10% 22% 7% 11% 4 3 4 3 3 4 28%	2860
	21st to end	Day	10% 21% 6% 9% 6% 3 4 3 3 5% 31%	3146
February	1st to 10th	Day	14% 17% 7% 8% 5% 2 3 4 4 6% 29%	1710
	11th to 20th	Day	11% 20% 6% 9% 5% 2 4 4 4 5% 32%	1707
	21st to end	Day	8% 17% 7% 12% 6% 3 3 4 4 4 29%	1570
March	1st to 10th	Day	9% 15% 6% 8% 6% 3 4 4 6% 7% 33%	2021
	11th to 20th	Day	7% 14% 4 6% 5% 3 4 5% 6% 8% 37%	2090
	21st to end	Day	13% 16% 6% 7% 6% 4 4 4 6% 6% 28%	2201
April	1st to 10th	Day	14% 12% 4 6% 6% 3 4 4 5% 6% 36%	2008
	11th to 20th	Day	11% 12% 4 8% 6% 3 5% 4 5% 6% 37%	2289
	21st to end	Day	9% 12% 3 5% 5% 3 4 5% 5% 8% 42%	2340
May	1st to 10th	Day	9% 7% 3 7% 6% 4 6% 5% 6% 8% 39%	2340
	11th to 20th	Day	8% 6% 3 5% 5% 3 5% 6% 6% 9% 43%	2301
	21st to end	Day	10% 8% 3 6% 6% 4 5% 6% 8% 7% 38%	2569
June	1st to 10th	Day	5% 5% 2 4 4 3 5% 5% 6% 8% 54%	2520
	11th to 20th	Day	7% 4 2 4 4 2 4 4 5% 7% 57%	2598
	21st to end	Day	2 3 1 2 3 2 3 4 5% 6% 71%	2700
July	1st to 10th	Day	2 2 1 2 3 3 4 4 5% 8% 66%	2498
	11th to 20th	Day	3 3 2 2 3 2 3 4 4 6% 68%	2340
	21st to end	Day	4 2 2 3 3 2 4 5% 5% 8% 62%	2545
August	1st to 10th	Day	5% 2 1 4 3 3 4 5% 5% 7% 62%	2328
	11th to 20th	Day	3 2 1 2 3 2 3 5% 4 7% 68%	2299
	21st to end	Day	4 3 1 3 3 1 3 4 5% 6% 66%	2570
September	1st to 10th	Day	3 3 1 3 2 2 3 4 5% 5% 69%	2050
	11th to 20th	Day	5% 3 1 3 3 2 4 4 4 7% 64%	1980
	21st to end	Day	7% 4 1 3 3 1 3 3 4 5% 66%	1980
October	1st to 10th	Day	10% 7% 2 4 4 3 4 5% 3 5% 52%	1886
	11th to 20th	Day	9% 5% 2 4 3 2 4 4 5% 7% 54%	1800
	21st to end	Day	7% 8% 3 5% 4 2 3 4 5% 7% 52%	1944
November	1st to 10th	Day	10% 11% 5% 7% 5% 3 4 4 3 5% 43%	1674
	11th to 20th	Day	15% 9% 2 4 4 2 4 3 6% 7% 43%	1681
	21st to end	Day	8% 14% 5% 6% 4 3 4 4 5% 7% 41%	1520
December	1st to 10th	Day	12% 14% 6% 8% 5% 3 4 3 4 6% 36%	1520
	11th to 20th	Day	13% 15% 6% 8% 5% 2 4 4 5% 8% 29%	1926
	21st to end	Day	8% 14% 6% 8% 5% 4 5% 5% 6% 7% 33%	2925
January	1st to 10th	Night	8% 19% 7% 10% 6% 2 3 3 3 6% 32%	4097
	11th to 20th	Night	13% 21% 6% 12% 5% 2 3 3 3 5% 27%	4110
	21st to end	Night	12% 23% 5% 7% 4 2 3 3 4 6% 31%	4521
February	1st to 10th	Night	12% 19% 6% 7% 5% 3 4 4 4 5% 30%	2470
	11th to 20th	Night	10% 15% 5% 7% 5% 3 4 4 4 6% 39%	2357
	21st to end	Night	6% 17% 7% 9% 6% 3 4 3 4 7% 34%	1884
March	1st to 10th	Night	11% 14% 5% 6% 5% 4 5% 5% 5% 6% 34%	2157
	11th to 20th	Night	6% 10% 3 4 6% 4 6% 5% 6% 8% 42%	2090
	21st to end	Night	10% 14% 4 6% 6% 3 5% 4 5% 6% 38%	2200
April	1st to 10th	Night	12% 11% 3 5% 5% 2 5% 4 4 6% 41%	1951
	11th to 20th	Night	8% 12% 4 6% 4 3 4 4 5% 8% 42%	1615
	21st to end	Night	9% 8% 3 5% 4 3 4 3 5% 7% 48%	1620
May	1st to 10th	Night	9% 9% 4 5% 5% 3 4 4 6% 7% 45%	1620
	11th to 20th	Night	8% 5% 2 5% 5% 3 4 5% 7% 8% 48%	1594
	21st to end	Night	10% 6% 2 6% 7% 3 5% 5% 6% 8% 42%	1704
June	1st to 10th	Night	5% 3 2 4 4 2 4 6% 5% 10% 55%	1440
	11th to 20th	Night	6% 4 2 2 3 2 3 4 5% 7% 62%	1354
	21st to end	Night	3 3 1 3 2 2 3 3 5% 7% 69%	1260
July	1st to 10th	Night	3 3 2 3 4 2 4 4 6% 8% 62%	1451
	11th to 20th	Night	3 3 2 3 4 2 5% 4 5% 6% 63%	1620
	21st to end	Night	3 3 2 4 4 2 4 6% 6% 8% 60%	1773
August	1st to 10th	Night	4 2 2 4 5% 3 4 5% 6% 8% 57%	1611
	11th to 20th	Night	3 3 2 4 3 2 3 4 5% 8% 62%	1602
	21st to end	Night	3 3 1 2 4 2 3 5% 5% 7% 64%	1786
September	1st to 10th	Night	3 3 1 3 4 2 3 3 5% 6% 68%	1907
	11th to 20th	Night	6% 2 1 3 4 2 3 4 4 6% 65%	1980
	21st to end	Night	6% 4 1 3 3 2 3 3 3 5% 67%	1980
October	1st to 10th	Night	9% 4 2 4 3 2 4 5% 4 6% 57%	2074
	11th to 20th	Night	10% 6% 2 4 3 2 3 3 4 6% 58%	2160
	21st to end	Night	7% 7% 2 4 3 2 4 4 5% 7% 55%	2408
November	1st to 10th	Night	11% 9% 3 5% 4 3 3 3 5% 7% 47%	2405
	11th to 20th	Night	11% 9% 3 5% 4 2 4 4 5% 7% 46%	2477
	21st to end	Night	9% 11% 3 5% 5% 2 4 5% 5% 6% 44%	2660
December	1st to 10th	Night	12% 14% 4 8% 6% 2 4 4 4 5% 38%	2660
	11th to 20th	Night	13% 13% 5% 8% 6% 3 4 5% 5% 6% 31%	3271
	21st to end	Night	10% 13% 6% 8% 6% 3 4 5% 5% 6% 33%	4770

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	59% 3 14% 18% 5% 1	2859
	11th to 20th	Day	63% 3 14% 13% 5% 1	2860
	21st to end	Day	59% 4 15% 15% 7% 1	3146
February	1st to 10th	Day	58% 5% 13% 17% 6% 1	1710
	11th to 20th	Day	58% 3 12% 18% 8% 2	1716
	21st to end	Day	59% 3 12% 17% 8% 1	1570
March	1st to 10th	Day	52% 5% 12% 22% 8% 2	2021
	11th to 20th	Day	45% 4 15% 23% 12%	2090
	21st to end	Day	57% 4 12% 18% 8% 1	2201
April	1st to 10th	Day	50% 3 12% 20% 12% 3	2008
	11th to 20th	Day	48% 4 8% 24% 16% 1	2292
	21st to end	Day	43% 3 10% 26% 18% 1	2340
May	1st to 10th	Day	43% 5% 8% 24% 18% 2	2340
	11th to 20th	Day	37% 4 9% 29% 16% 4	2304
	21st to end	Day	43% 5% 9% 28% 14% 2	2569
June	1st to 10th	Day	28% 3 11% 27% 26% 5%	2520
	11th to 20th	Day	27% 4 6% 19% 27% 16%	2598
	21st to end	Day	16% 2 3 16% 34% 29%	2700
July	1st to 10th	Day	18% 3 3 17% 28% 31%	2430
	11th to 20th	Day	17% 3 4 14% 28% 34%	2271
	21st to end	Day	21% 3 5% 13% 30% 28%	2404
August	1st to 10th	Day	22% 3 4 19% 26% 27%	2313
	11th to 20th	Day	17% 3 3 17% 37% 24%	2299
	21st to end	Day	19% 3 5% 16% 34% 24%	2570
September	1st to 10th	Day	17% 2 5% 17% 30% 28%	2050
	11th to 20th	Day	23% 2 7% 19% 31% 18%	1980
	21st to end	Day	22% 2 5% 23% 37% 9%	1980
October	1st to 10th	Day	37% 2 8% 25% 22% 6%	1886
	11th to 20th	Day	31% 3 12% 28% 22% 4	1800
	21st to end	Day	34% 3 15% 30% 18% 1	1944
November	1st to 10th	Day	45% 4 11% 23% 14% 2	1674
	11th to 20th	Day	42% 3 16% 26% 13% 1	1681
	21st to end	Day	44% 4 15% 24% 13% 1	1520
December	1st to 10th	Day	51% 6% 16% 16% 8% 3	1520
	11th to 20th	Day	55% 3 17% 20% 5%	1924
	21st to end	Day	50% 4 14% 19% 12% 1	2925
January	1st to 10th	Night	56% 4 11% 20% 8% 1	4097
	11th to 20th	Night	63% 4 13% 14% 5% 1	4110
	21st to end	Night	56% 3 16% 16% 7% 1	4521
February	1st to 10th	Night	56% 5% 13% 19% 7%	2470
	11th to 20th	Night	48% 4 12% 22% 13% 1	2358
	21st to end	Night	51% 4 10% 23% 11% 2	1884
March	1st to 10th	Night	49% 6% 10% 24% 10%	2157
	11th to 20th	Night	40% 4 14% 26% 14% 2	2090
	21st to end	Night	47% 4 13% 26% 9% 1	2200
April	1st to 10th	Night	45% 4 13% 21% 11% 6%	1951
	11th to 20th	Night	41% 4 10% 25% 19% 1	1615
	21st to end	Night	36% 3 11% 29% 19% 2	1620
May	1st to 10th	Night	39% 3 9% 25% 20% 4	1620
	11th to 20th	Night	32% 4 11% 29% 18% 5%	1595
	21st to end	Night	39% 5% 12% 28% 15% 2	1704
June	1st to 10th	Night	25% 4 14% 25% 27% 5%	1440
	11th to 20th	Night	22% 3 8% 23% 28% 16%	1354
	21st to end	Night	17% 2 2 17% 31% 31%	1260
July	1st to 10th	Night	21% 2 5% 15% 27% 30%	1410
	11th to 20th	Night	23% 3 2 13% 27% 33%	1566
	21st to end	Night	21% 3 5% 15% 26% 29%	1674
August	1st to 10th	Night	24% 3 6% 17% 22% 28%	1602
	11th to 20th	Night	21% 2 3 13% 33% 27%	1602
	21st to end	Night	19% 4 5% 13% 33% 26%	1786
September	1st to 10th	Night	18% 3 4 18% 24% 34%	1907
	11th to 20th	Night	21% 3 6% 15% 33% 22%	1980
	21st to end	Night	22% 3 4 23% 34% 14%	1980
October	1st to 10th	Night	28% 3 8% 26% 27% 8%	2074
	11th to 20th	Night	30% 2 7% 32% 23% 6%	2160
	21st to end	Night	30% 3 11% 33% 20% 3	2408
November	1st to 10th	Night	38% 3 11% 25% 17% 4	2405
	11th to 20th	Night	39% 3 14% 27% 15% 1	2477
	21st to end	Night	42% 4 12% 26% 13% 3	2660
December	1st to 10th	Night	49% 4 17% 19% 7% 4	2660
	11th to 20th	Night	53% 4 14% 21% 8%	3272
	21st to end	Night	52% 4 14% 17% 12%	4770

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% 8% 27% 28% 11% 1	270
	11th to 20th	Day	23% 10% 28% 27% 10% 1	270
	21st to end	Day	20% 9% 27% 31% 12% 1	297
February	1st to 10th	Day	26% 16% 31% 20% 7% 1	270
	11th to 20th	Day	21% 14% 37% 19% 8% 2	312
	21st to end	Day	19% 20% 36% 19% 5% 1	382
March	1st to 10th	Day	20% 19% 32% 23% 5% 1	460
	11th to 20th	Day	16% 19% 32% 27% 5%	460
	21st to end	Day	24% 19% 33% 20% 4	471
April	1st to 10th	Day	20% 17% 32% 23% 6% 1	420
	11th to 20th	Day	23% 21% 33% 17% 6% 1	412
	21st to end	Day	17% 19% 29% 24% 9% 2	420
May	1st to 10th	Day	12% 20% 30% 30% 8% 1	423
	11th to 20th	Day	13% 16% 27% 30% 12% 2	448
	21st to end	Day	11% 14% 22% 32% 17% 4	524
June	1st to 10th	Day	6% 11% 26% 33% 19% 5%	630
	11th to 20th	Day	10% 12% 27% 34% 15% 2	630
	21st to end	Day	3 9% 30% 34% 20% 4	630
July	1st to 10th	Day	2 7% 38% 38% 12% 3	446
	11th to 20th	Day	4 7% 38% 35% 12% 3	444
	21st to end	Day	5% 3 26% 44% 18% 3	487
August	1st to 10th	Day	7% 6% 34% 35% 15% 3	447
	11th to 20th	Day	3 5% 30% 41% 19% 3	437
	21st to end	Day	4 7% 27% 40% 18% 4	495
September	1st to 10th	Day	3 9% 28% 36% 20% 3	450
	11th to 20th	Day	6% 10% 31% 30% 19% 4	450
	21st to end	Day	8% 12% 29% 30% 19% 3	450
October	1st to 10th	Day	10% 9% 29% 30% 19% 2	356
	11th to 20th	Day	9% 13% 26% 29% 19% 5%	270
	21st to end	Day	12% 14% 32% 27% 14%	297
November	1st to 10th	Day	21% 11% 24% 29% 10% 4	270
	11th to 20th	Day	17% 9% 29% 30% 11% 3	270
	21st to end	Day	17% 7% 28% 30% 13% 4	270
December	1st to 10th	Day	18% 10% 27% 29% 13% 3	270
	11th to 20th	Day	23% 7% 27% 33% 9% 1	270
	21st to end	Day	20% 11% 31% 28% 9% 1	297
January	1st to 10th	Night	20% 4 21% 34% 18% 3	760
	11th to 20th	Night	21% 5% 20% 34% 16% 3	760
	21st to end	Night	22% 4 19% 37% 15% 3	836
February	1st to 10th	Night	21% 7% 24% 36% 10% 2	760
	11th to 20th	Night	17% 5% 26% 35% 15% 2	744
	21st to end	Night	14% 9% 27% 35% 13% 2	628
March	1st to 10th	Night	18% 7% 25% 36% 12% 3	760
	11th to 20th	Night	12% 8% 24% 38% 16% 1	760
	21st to end	Night	16% 8% 23% 38% 13% 1	800
April	1st to 10th	Night	18% 7% 25% 35% 14% 2	691
	11th to 20th	Night	14% 10% 25% 35% 15% 2	533
	21st to end	Night	14% 6% 22% 37% 19% 2	540
May	1st to 10th	Night	13% 7% 23% 37% 19% 2	540
	11th to 20th	Night	10% 6% 18% 35% 29% 3	531
	21st to end	Night	12% 5% 17% 35% 27% 4	584
June	1st to 10th	Night	7% 6% 17% 37% 30% 2	540
	11th to 20th	Night	7% 6% 20% 42% 24% 1	454
	21st to end	Night	4 3 18% 41% 29% 5%	360
July	1st to 10th	Night	5% 3 19% 35% 35% 4	367
	11th to 20th	Night	3 3 16% 45% 32% 1	522
	21st to end	Night	3 2 9% 46% 36% 5%	591
August	1st to 10th	Night	4 2 11% 47% 33% 2	537
	11th to 20th	Night	3 2 14% 47% 30% 4	534
	21st to end	Night	4 3 14% 43% 32% 4	594
September	1st to 10th	Night	4 4 14% 46% 29% 4	647
	11th to 20th	Night	7% 4 14% 42% 27% 7%	720
	21st to end	Night	8% 4 17% 37% 25% 9%	720
October	1st to 10th	Night	10% 4 16% 45% 20% 5%	720
	11th to 20th	Night	13% 3 17% 37% 26% 3	720
	21st to end	Night	10% 4 21% 38% 23% 4	792
November	1st to 10th	Night	15% 7% 19% 38% 19% 3	740
	11th to 20th	Night	15% 5% 22% 38% 16% 4	767
	21st to end	Night	14% 8% 20% 37% 17% 4	950
December	1st to 10th	Night	19% 6% 24% 37% 13% 1	950
	11th to 20th	Night	20% 6% 25% 35% 13% 2	950
	21st to end	Night	24% 6% 24% 34% 11% 1	981

Page generated at 2024-03-19 21:31:06. Version ac07

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