SWAOG Light Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the SWAOG Light Site clear sky chart from 2005-11-06 to 2024-01-13.

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	14% 9% 4 6% 5% 3 5% 5% 5% 7% 36%	74804
	Night	15% 9% 4 6% 5% 3 4 4 5% 6% 39%	74938
Transparency	Day	47% 7% 12% 21% 12% 2	74505
	Night	45% 6% 12% 22% 14% 2	74758
Seeing	Day	18% 14% 30% 23% 11% 4	14633
	Night	18% 11% 31% 27% 11% 1	24608

By Month

Percentage Cloud Cover SE (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	15% 13% 4 9% 6% 4 5% 3 4 7% 29%	1517
	11th to 20th	Day	15% 16% 7% 12% 7% 3 4 3 4 6% 23%	1456
	21st to end	Day	15% 17% 7% 11% 6% 3 4 4 4 7% 22%	1630
February	1st to 10th	Day	16% 14% 7% 8% 7% 4 5% 5% 4 6% 24%	1656
	11th to 20th	Day	16% 10% 5% 8% 7% 4 5% 3 4 6% 33%	1748
	21st to end	Day	16% 13% 6% 9% 6% 3 4 3 4 6% 30%	1480
March	1st to 10th	Day	16% 12% 6% 9% 6% 3 4 4 5% 5% 30%	1800
	11th to 20th	Day	14% 10% 4 6% 6% 4 5% 4 5% 8% 35%	1854
	21st to end	Day	21% 12% 5% 9% 6% 4 5% 5% 4 6% 25%	2376
April	1st to 10th	Day	18% 11% 4 7% 6% 3 4 4 5% 7% 30%	2160
	11th to 20th	Day	18% 9% 3 5% 6% 3 5% 5% 5% 6% 35%	2134
	21st to end	Day	22% 8% 3 6% 6% 3 5% 5% 5% 6% 32%	2255
May	1st to 10th	Day	18% 9% 3 6% 6% 3 5% 5% 6% 8% 30%	2340
	11th to 20th	Day	19% 8% 3 6% 5% 3 5% 4 5% 7% 34%	2420
	21st to end	Day	14% 6% 3 6% 5% 4 5% 6% 7% 8% 35%	2725
June	1st to 10th	Day	10% 6% 2 5% 5% 3 5% 5% 6% 8% 45%	2520
	11th to 20th	Day	11% 5% 2 5% 5% 3 5% 5% 6% 8% 44%	2520
	21st to end	Day	12% 5% 3 6% 5% 4 6% 6% 8% 8% 37%	2520
July	1st to 10th	Day	8% 4 2 5% 5% 3 6% 6% 6% 10% 46%	2520
	11th to 20th	Day	11% 5% 2 4 5% 3 4 6% 6% 8% 45%	2520
	21st to end	Day	7% 4 2 5% 6% 4 6% 5% 7% 10% 42%	2743
August	1st to 10th	Day	8% 5% 2 6% 6% 4 5% 5% 7% 10% 41%	2460
	11th to 20th	Day	10% 5% 2 5% 5% 4 5% 6% 7% 10% 41%	2135
	21st to end	Day	9% 4 1 4 5% 3 5% 6% 7% 10% 46%	2376
September	1st to 10th	Day	13% 6% 2 4 4 3 5% 5% 5% 7% 45%	2160
	11th to 20th	Day	13% 4 2 4 5% 2 4 4 5% 8% 51%	2047
	21st to end	Day	10% 6% 3 5% 4 4 4 5% 6% 7% 44%	1980
October	1st to 10th	Day	13% 7% 3 6% 4 2 4 4 5% 6% 46%	1931
	11th to 20th	Day	20% 9% 3 6% 6% 3 3 4 4 8% 34%	1791
	21st to end	Day	21% 9% 3 6% 5% 2 4 3 5% 6% 35%	1782
November	1st to 10th	Day	13% 8% 4 4 4 2 4 4 6% 6% 45%	1672
	11th to 20th	Day	16% 11% 5% 7% 6% 3 4 4 5% 7% 33%	1710
	21st to end	Day	19% 10% 4 8% 5% 3 3 4 4 5% 36%	1645
December	1st to 10th	Day	16% 13% 5% 8% 5% 3 5% 4 4 5% 31%	1520
	11th to 20th	Day	13% 13% 6% 9% 7% 3 5% 4 5% 6% 29%	1918
	21st to end	Day	20% 24% 9% 11% 6% 3 4 3 2 3 14%	2783
January	1st to 10th	Night	15% 12% 6% 8% 6% 3 4 4 4 5% 34%	2648
	11th to 20th	Night	16% 16% 5% 8% 6% 3 4 3 4 5% 29%	2549
	21st to end	Night	16% 13% 7% 10% 7% 3 5% 4 4 6% 27%	2722
February	1st to 10th	Night	16% 14% 5% 8% 7% 3 4 4 4 6% 29%	2303
	11th to 20th	Night	15% 11% 4 7% 6% 2 4 4 5% 6% 36%	2098
	21st to end	Night	18% 12% 4 7% 5% 2 3 3 5% 6% 35%	1776
March	1st to 10th	Night	16% 11% 5% 8% 6% 3 5% 4 4 5% 34%	2160
	11th to 20th	Night	14% 8% 3 5% 4 3 4 4 6% 7% 42%	2120
	21st to end	Night	21% 9% 4 6% 5% 4 5% 4 5% 6% 31%	1980
April	1st to 10th	Night	16% 7% 4 6% 5% 3 5% 5% 5% 7% 38%	1800
	11th to 20th	Night	19% 9% 3 6% 4 3 5% 3 5% 6% 38%	1775
	21st to end	Night	18% 8% 3 6% 5% 3 4 5% 5% 6% 37%	1703
May	1st to 10th	Night	15% 8% 2 6% 5% 4 7% 5% 5% 8% 36%	1620
	11th to 20th	Night	17% 6% 2 5% 5% 3 4 5% 5% 8% 40%	1470
	21st to end	Night	13% 5% 3 5% 6% 3 4 4 6% 9% 42%	1551
June	1st to 10th	Night	10% 4 2 3 6% 3 4 6% 5% 7% 49%	1440
	11th to 20th	Night	9% 5% 2 4 5% 3 5% 5% 6% 8% 48%	1440
	21st to end	Night	11% 5% 2 5% 4 3 6% 5% 7% 8% 42%	1440
July	1st to 10th	Night	6% 4 2 5% 4 3 5% 5% 7% 9% 50%	1440
	11th to 20th	Night	7% 3 2 5% 4 4 4 4 7% 9% 53%	1440
	21st to end	Night	6% 3 2 4 4 3 5% 5% 7% 10% 52%	1575
August	1st to 10th	Night	5% 4 2 5% 6% 3 5% 6% 7% 9% 50%	1475
	11th to 20th	Night	7% 3 2 4 3 3 4 4 6% 10% 53%	1763
	21st to end	Night	8% 4 1 4 4 3 4 4 4 8% 56%	1980
September	1st to 10th	Night	10% 7% 3 4 4 3 4 3 4 6% 53%	1800
	11th to 20th	Night	10% 4 2 4 4 3 3 4 4 7% 56%	1894
	21st to end	Night	11% 5% 2 6% 5% 3 4 4 6% 7% 47%	1980
October	1st to 10th	Night	12% 5% 3 5% 4 3 4 4 4 7% 50%	2024
	11th to 20th	Night	18% 8% 2 5% 4 2 3 3 5% 5% 44%	2168
	21st to end	Night	21% 10% 2 6% 5% 2 3 3 4 7% 36%	2574
November	1st to 10th	Night	13% 8% 2 5% 4 2 4 3 5% 5% 49%	2406
	11th to 20th	Night	15% 10% 4 7% 5% 3 4 4 5% 6% 37%	2470
	21st to end	Night	17% 9% 5% 6% 6% 3 4 3 5% 5% 37%	2531
December	1st to 10th	Night	17% 12% 4 8% 6% 3 4 4 5% 6% 32%	2660
	11th to 20th	Night	16% 13% 5% 9% 6% 3 4 4 4 6% 32%	3279
	21st to end	Night	24% 18% 6% 9% 6% 3 4 4 5% 4 16%	4884

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	56% 5% 12% 16% 11%	1518
	11th to 20th	Day	63% 5% 13% 14% 5% 1	1456
	21st to end	Day	63% 6% 9% 13% 9%	1630
February	1st to 10th	Day	61% 6% 10% 13% 8% 1	1656
	11th to 20th	Day	54% 4 10% 21% 9% 2	1758
	21st to end	Day	57% 6% 10% 18% 8% 2	1480
March	1st to 10th	Day	56% 7% 10% 20% 7% 1	1800
	11th to 20th	Day	48% 5% 12% 22% 10% 2	1854
	21st to end	Day	61% 6% 10% 16% 5% 1	2376
April	1st to 10th	Day	54% 5% 11% 19% 11%	2160
	11th to 20th	Day	49% 7% 10% 20% 11% 4	2134
	21st to end	Day	51% 7% 12% 16% 12% 2	2255
May	1st to 10th	Day	50% 9% 12% 21% 8%	2340
	11th to 20th	Day	50% 7% 11% 21% 11% 1	2424
	21st to end	Day	44% 8% 13% 18% 15% 2	2725
June	1st to 10th	Day	36% 7% 12% 26% 17% 2	2520
	11th to 20th	Day	37% 8% 11% 22% 20% 3	2520
	21st to end	Day	42% 9% 13% 21% 13% 2	2520
July	1st to 10th	Day	32% 9% 14% 26% 14% 4	2451
	11th to 20th	Day	34% 8% 15% 25% 16% 2	2445
	21st to end	Day	34% 10% 16% 24% 14% 3	2591
August	1st to 10th	Day	36% 8% 16% 26% 11% 2	2445
	11th to 20th	Day	36% 9% 15% 25% 14% 1	2135
	21st to end	Day	30% 9% 13% 25% 19% 3	2376
September	1st to 10th	Day	37% 7% 12% 23% 17% 4	2160
	11th to 20th	Day	31% 7% 11% 30% 18% 3	2047
	21st to end	Day	38% 6% 11% 25% 19% 1	1980
October	1st to 10th	Day	40% 6% 12% 24% 16% 2	1931
	11th to 20th	Day	50% 5% 11% 20% 13% 1	1791
	21st to end	Day	50% 5% 11% 22% 9% 2	1782
November	1st to 10th	Day	39% 5% 14% 23% 16% 2	1672
	11th to 20th	Day	51% 5% 11% 22% 10% 1	1710
	21st to end	Day	52% 5% 11% 23% 9%	1645
December	1st to 10th	Day	56% 5% 13% 18% 8% 1	1520
	11th to 20th	Day	55% 5% 14% 18% 7% 1	1915
	21st to end	Day	77% 4 6% 9% 3	2783
January	1st to 10th	Night	52% 5% 11% 19% 11% 1	2648
	11th to 20th	Night	58% 6% 12% 14% 9%	2549
	21st to end	Night	59% 5% 10% 15% 9% 1	2722
February	1st to 10th	Night	57% 4 11% 16% 10% 1	2303
	11th to 20th	Night	49% 5% 12% 20% 12% 1	2099
	21st to end	Night	52% 5% 11% 18% 11% 3	1776
March	1st to 10th	Night	53% 5% 12% 20% 9% 1	2160
	11th to 20th	Night	42% 6% 13% 21% 16% 3	2120
	21st to end	Night	54% 6% 10% 18% 10% 1	1980
April	1st to 10th	Night	45% 5% 13% 23% 12% 2	1800
	11th to 20th	Night	47% 6% 8% 20% 15% 5%	1775
	21st to end	Night	46% 7% 11% 22% 12% 3	1703
May	1st to 10th	Night	47% 6% 12% 24% 11%	1620
	11th to 20th	Night	41% 8% 12% 23% 15% 1	1471
	21st to end	Night	39% 8% 13% 20% 17% 3	1552
June	1st to 10th	Night	32% 7% 13% 25% 20% 4	1440
	11th to 20th	Night	33% 7% 12% 24% 22% 2	1440
	21st to end	Night	37% 9% 15% 20% 16% 2	1440
July	1st to 10th	Night	28% 8% 17% 27% 16% 5%	1400
	11th to 20th	Night	27% 8% 15% 26% 20% 4	1392
	21st to end	Night	26% 8% 17% 25% 19% 5%	1487
August	1st to 10th	Night	28% 8% 17% 31% 15% 2	1466
	11th to 20th	Night	27% 7% 17% 28% 19% 2	1763
	21st to end	Night	27% 6% 13% 29% 19% 5%	1980
September	1st to 10th	Night	32% 5% 13% 25% 22% 3	1800
	11th to 20th	Night	29% 5% 8% 32% 24% 2	1894
	21st to end	Night	35% 7% 11% 30% 16% 2	1980
October	1st to 10th	Night	34% 6% 10% 27% 21% 2	2024
	11th to 20th	Night	42% 4 10% 24% 19% 2	2168
	21st to end	Night	48% 5% 10% 23% 12% 1	2574
November	1st to 10th	Night	38% 6% 9% 26% 19% 3	2406
	11th to 20th	Night	48% 5% 12% 22% 12% 2	2470
	21st to end	Night	49% 5% 11% 23% 11%	2531
December	1st to 10th	Night	53% 6% 11% 21% 9% 1	2660
	11th to 20th	Night	54% 5% 12% 18% 9% 1	3281
	21st to end	Night	69% 6% 9% 12% 4	4884

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% 20% 36% 19% 3	270
	11th to 20th	Day	27% 19% 36% 14% 3	246
	21st to end	Day	25% 24% 32% 14% 4 1	264
February	1st to 10th	Day	28% 23% 37% 11% 1	240
	11th to 20th	Day	30% 24% 31% 14% 1	240
	21st to end	Day	26% 27% 38% 7% 2 1	198
March	1st to 10th	Day	24% 32% 33% 10% 1	240
	11th to 20th	Day	29% 22% 31% 14% 3	262
	21st to end	Day	30% 18% 28% 18% 5% 1	462
April	1st to 10th	Day	25% 18% 31% 21% 5%	420
	11th to 20th	Day	25% 22% 22% 19% 9% 2	412
	21st to end	Day	25% 18% 30% 19% 7% 1	420
May	1st to 10th	Day	23% 18% 30% 20% 7% 2	423
	11th to 20th	Day	21% 13% 36% 20% 8% 2	566
	21st to end	Day	16% 12% 33% 21% 13% 4	679
June	1st to 10th	Day	10% 11% 34% 28% 12% 4	630
	11th to 20th	Day	14% 9% 34% 28% 11% 3	630
	21st to end	Day	13% 12% 34% 27% 10% 4	630
July	1st to 10th	Day	7% 5% 28% 29% 19% 11%	621
	11th to 20th	Day	12% 7% 30% 30% 14% 7%	618
	21st to end	Day	6% 8% 33% 33% 15% 5%	684
August	1st to 10th	Day	8% 3 26% 35% 20% 8%	579
	11th to 20th	Day	10% 6% 21% 32% 21% 10%	439
	21st to end	Day	8% 6% 23% 32% 23% 7%	495
September	1st to 10th	Day	14% 9% 24% 31% 18% 4	450
	11th to 20th	Day	12% 5% 22% 31% 22% 7%	450
	21st to end	Day	14% 14% 24% 26% 16% 6%	450
October	1st to 10th	Day	18% 13% 26% 27% 13% 3	401
	11th to 20th	Day	26% 24% 33% 13% 4	270
	21st to end	Day	36% 18% 31% 10% 5%	297
November	1st to 10th	Day	19% 19% 34% 19% 6% 2	270
	11th to 20th	Day	28% 21% 32% 13% 6%	270
	21st to end	Day	27% 18% 34% 17% 3	270
December	1st to 10th	Day	19% 26% 36% 13% 5%	270
	11th to 20th	Day	21% 24% 36% 15% 4	270
	21st to end	Day	28% 25% 34% 11% 2	297
January	1st to 10th	Night	20% 16% 40% 20% 4	950
	11th to 20th	Night	24% 16% 35% 21% 4 1	911
	21st to end	Night	21% 15% 36% 24% 4	990
February	1st to 10th	Night	25% 15% 36% 20% 4	863
	11th to 20th	Night	22% 16% 35% 23% 4	703
	21st to end	Night	24% 17% 37% 19% 4	592
March	1st to 10th	Night	21% 17% 34% 21% 6%	720
	11th to 20th	Night	18% 11% 39% 24% 7%	702
	21st to end	Night	24% 13% 32% 23% 7% 1	594
April	1st to 10th	Night	20% 14% 35% 24% 6% 1	540
	11th to 20th	Night	22% 17% 28% 26% 7%	533
	21st to end	Night	21% 12% 34% 25% 8%	540
May	1st to 10th	Night	19% 9% 36% 28% 8% 1	540
	11th to 20th	Night	19% 8% 29% 31% 13%	531
	21st to end	Night	14% 5% 29% 33% 18% 1	584
June	1st to 10th	Night	11% 5% 29% 39% 16%	540
	11th to 20th	Night	11% 6% 32% 37% 13% 1	540
	21st to end	Night	11% 6% 30% 37% 16% 1	540
July	1st to 10th	Night	7% 2 20% 42% 26% 3	525
	11th to 20th	Night	7% 4 25% 38% 23% 2	522
	21st to end	Night	7% 1 22% 47% 22% 2	591
August	1st to 10th	Night	5% 2 18% 44% 27% 4	537
	11th to 20th	Night	6% 2 17% 40% 30% 4	534
	21st to end	Night	9% 2 19% 38% 30% 2	594
September	1st to 10th	Night	13% 5% 22% 33% 24% 3	540
	11th to 20th	Night	11% 4 23% 33% 25% 4	634
	21st to end	Night	12% 9% 24% 31% 21% 3	720
October	1st to 10th	Night	14% 7% 28% 33% 17% 2	720
	11th to 20th	Night	21% 15% 31% 25% 8%	720
	21st to end	Night	26% 14% 31% 21% 8%	792
November	1st to 10th	Night	16% 13% 39% 21% 9% 1	740
	11th to 20th	Night	21% 17% 33% 23% 5%	760
	21st to end	Night	21% 15% 37% 21% 5%	821
December	1st to 10th	Night	24% 14% 36% 21% 4	950
	11th to 20th	Night	23% 14% 35% 24% 4	950
	21st to end	Night	30% 16% 34% 18% 2	1045

Page generated at 2024-01-10 00:25:01. Version ac07

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