Somerton Creek
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Somerton Creek clear sky chart from 2005-11-06 to 2026-07-16.

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	13% 6% 2 6% 4 4 5% 4 6% 8% 42%	137555
	Night	14% 6% 2 6% 4 4 4 3 5% 7% 44%	135097
Transparency	Day	26% 37% 8% 14% 12% 3	141152
	Night	26% 36% 7% 14% 12% 4	139571
Seeing	Day	17% 12% 27% 25% 15% 5%	17495
	Night	16% 9% 29% 32% 13% 1	27147

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	13% 5% 2 5% 3 3 3 3 4 5% 54%	5138
	11th to 20th	Day	14% 7% 1 4 2 3 3 3 3 4 56%	5280
	21st to end	Day	13% 8% 3 7% 4 4 4 3 4 5% 44%	5780
February	1st to 10th	Day	13% 8% 2 7% 4 4 5% 3 5% 7% 43%	1890
	11th to 20th	Day	22% 6% 2 4 4 4 4 3 4 5% 43%	1988
	21st to end	Day	18% 6% 2 6% 4 4 4 4 5% 8% 39%	1730
March	1st to 10th	Day	19% 8% 2 6% 4 4 4 3 4 6% 39%	4954
	11th to 20th	Day	11% 7% 2 5% 3 3 3 3 4 6% 53%	5090
	21st to end	Day	14% 6% 2 5% 4 4 4 3 5% 6% 48%	5711
April	1st to 10th	Day	13% 5% 1 4 4 3 3 3 5% 8% 50%	2520
	11th to 20th	Day	10% 4 2 5% 5% 4 4 4 5% 7% 50%	2494
	21st to end	Day	12% 6% 2 6% 5% 4 4 4 5% 7% 45%	2520
May	1st to 10th	Day	13% 6% 3 7% 5% 5% 6% 4 6% 9% 38%	7054
	11th to 20th	Day	15% 6% 2 6% 4 4 5% 3 6% 8% 41%	7703
	21st to end	Day	15% 7% 3 7% 4 4 5% 4 5% 7% 38%	9045
June	1st to 10th	Day	10% 6% 2 5% 5% 5% 6% 5% 7% 9% 41%	2940
	11th to 20th	Day	9% 5% 2 6% 5% 5% 6% 5% 8% 11% 40%	2940
	21st to end	Day	8% 5% 2 6% 6% 5% 5% 5% 8% 12% 38%	2940
July	1st to 10th	Day	8% 6% 2 6% 5% 5% 6% 6% 8% 13% 35%	6420
	11th to 20th	Day	9% 7% 3 9% 7% 6% 7% 5% 8% 11% 27%	5965
	21st to end	Day	8% 6% 3 8% 6% 6% 6% 6% 8% 11% 32%	6424
August	1st to 10th	Day	18% 9% 4 9% 6% 6% 6% 5% 7% 9% 21%	4234
	11th to 20th	Day	9% 7% 3 8% 5% 6% 6% 5% 8% 12% 32%	3850
	21st to end	Day	7% 4 2 6% 5% 6% 6% 5% 7% 11% 41%	4312
September	1st to 10th	Day	14% 6% 2 7% 5% 4 5% 4 7% 8% 39%	2400
	11th to 20th	Day	15% 7% 3 7% 5% 5% 5% 3 6% 7% 38%	2400
	21st to end	Day	20% 8% 3 7% 5% 4 4 4 4 7% 34%	2122
October	1st to 10th	Day	16% 7% 3 5% 3 4 4 3 4 7% 45%	2000
	11th to 20th	Day	15% 6% 3 5% 3 3 4 2 4 5% 51%	2000
	21st to end	Day	13% 5% 2 5% 3 4 4 3 4 5% 52%	2200
November	1st to 10th	Day	15% 5% 2 5% 3 4 4 2 5% 5% 50%	2012
	11th to 20th	Day	15% 6% 2 5% 3 3 2 3 4 6% 52%	1890
	21st to end	Day	14% 5% 1 4 3 4 3 3 5% 6% 52%	1811
December	1st to 10th	Day	12% 5% 2 5% 4 4 3 3 5% 5% 52%	2680
	11th to 20th	Day	14% 8% 3 7% 4 3 4 3 4 5% 45%	3070
	21st to end	Day	14% 5% 2 6% 4 3 3 3 5% 7% 48%	4048
January	1st to 10th	Night	11% 7% 2 5% 3 3 3 3 5% 6% 51%	7738
	11th to 20th	Night	12% 6% 2 5% 3 3 3 3 3 4 54%	7680
	21st to end	Night	17% 7% 3 6% 4 3 3 2 4 5% 46%	8401
February	1st to 10th	Night	17% 7% 2 5% 4 4 4 3 5% 7% 43%	2730
	11th to 20th	Night	21% 8% 2 5% 4 3 4 4 4 5% 40%	2516
	21st to end	Night	16% 7% 3 5% 4 4 4 3 4 6% 46%	2076
March	1st to 10th	Night	20% 7% 2 5% 4 4 4 3 4 4 42%	5102
	11th to 20th	Night	12% 5% 2 5% 4 4 4 3 4 6% 51%	5090
	21st to end	Night	15% 5% 2 5% 3 4 4 3 4 5% 49%	5461
April	1st to 10th	Night	12% 6% 2 5% 4 4 4 4 5% 7% 46%	2100
	11th to 20th	Night	11% 6% 2 5% 4 4 3 3 5% 7% 52%	2075
	21st to end	Night	13% 4 2 6% 4 4 4 3 6% 7% 48%	2100
May	1st to 10th	Night	12% 7% 3 8% 5% 5% 5% 4 6% 9% 35%	5833
	11th to 20th	Night	16% 7% 2 6% 4 4 3 3 5% 7% 43%	5149
	21st to end	Night	18% 8% 3 7% 4 4 5% 4 5% 7% 36%	5108
June	1st to 10th	Night	10% 4 2 5% 5% 5% 4 5% 7% 11% 42%	1680
	11th to 20th	Night	9% 6% 2 7% 5% 5% 5% 4 7% 10% 39%	1680
	21st to end	Night	7% 5% 1 6% 5% 5% 5% 5% 7% 10% 45%	1680
July	1st to 10th	Night	8% 6% 3 7% 5% 5% 5% 6% 9% 13% 34%	3739
	11th to 20th	Night	10% 9% 3 9% 6% 5% 6% 6% 8% 11% 27%	4102
	21st to end	Night	12% 7% 3 7% 5% 5% 5% 5% 7% 9% 34%	4427
August	1st to 10th	Night	20% 8% 3 8% 5% 4 4 4 6% 9% 28%	2915
	11th to 20th	Night	9% 8% 3 9% 5% 5% 5% 4 7% 9% 37%	3166
	21st to end	Night	8% 5% 2 6% 4 4 4 5% 8% 9% 45%	3586
September	1st to 10th	Night	12% 6% 2 6% 3 4 4 3 7% 8% 45%	2000
	11th to 20th	Night	13% 7% 2 7% 5% 4 4 3 5% 6% 43%	2000
	21st to end	Night	19% 8% 3 8% 4 4 4 3 5% 7% 35%	2271
October	1st to 10th	Night	14% 6% 2 6% 3 3 4 3 5% 5% 49%	2400
	11th to 20th	Night	15% 7% 2 5% 3 3 3 2 4 5% 51%	2400
	21st to end	Night	13% 5% 2 5% 4 3 3 3 4 5% 53%	2640
November	1st to 10th	Night	16% 6% 1 5% 3 3 3 3 5% 5% 50%	2503
	11th to 20th	Night	15% 6% 2 4 3 3 3 3 5% 6% 49%	2730
	21st to end	Night	12% 5% 1 6% 4 4 4 3 5% 6% 50%	2804
December	1st to 10th	Night	11% 5% 2 7% 4 4 3 3 4 6% 52%	4720
	11th to 20th	Night	16% 7% 3 8% 5% 5% 5% 3 5% 6% 38%	5345
	21st to end	Night	13% 6% 2 5% 4 4 4 3 5% 7% 49%	7150

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	26% 21% 8% 18% 16% 10%	5139
	11th to 20th	Day	25% 21% 3 10% 32% 9%	5280
	21st to end	Day	34% 23% 5% 20% 13% 4	5780
February	1st to 10th	Day	18% 59% 5% 10% 7% 1	1890
	11th to 20th	Day	21% 58% 4 7% 7% 3	1997
	21st to end	Day	18% 60% 5% 8% 8% 2	1730
March	1st to 10th	Day	37% 30% 5% 11% 11% 7%	4954
	11th to 20th	Day	22% 29% 5% 14% 21% 9%	5090
	21st to end	Day	25% 29% 11% 14% 17% 5%	5711
April	1st to 10th	Day	15% 60% 5% 9% 9% 2	2520
	11th to 20th	Day	14% 60% 5% 12% 7% 2	2494
	21st to end	Day	16% 60% 6% 10% 6% 2	2520
May	1st to 10th	Day	34% 27% 12% 15% 11% 1	7086
	11th to 20th	Day	31% 26% 10% 20% 13%	7707
	21st to end	Day	36% 26% 8% 16% 12% 2	9061
June	1st to 10th	Day	16% 61% 5% 9% 8% 1	2940
	11th to 20th	Day	13% 62% 8% 11% 6% 1	2940
	21st to end	Day	13% 60% 7% 13% 6%	2940
July	1st to 10th	Day	28% 32% 16% 15% 7% 2	6351
	11th to 20th	Day	38% 34% 19% 8% 1	5896
	21st to end	Day	31% 32% 11% 15% 9% 1	6240
August	1st to 10th	Day	41% 40% 10% 8% 1	4221
	11th to 20th	Day	26% 41% 10% 16% 7%	3886
	21st to end	Day	19% 40% 9% 21% 11% 1	4312
September	1st to 10th	Day	19% 59% 7% 8% 5% 1	2400
	11th to 20th	Day	21% 58% 6% 7% 6% 2	2400
	21st to end	Day	25% 58% 4 9% 3	2122
October	1st to 10th	Day	19% 38% 7% 15% 19% 2	3260
	11th to 20th	Day	12% 35% 3 11% 29% 9%	3240
	21st to end	Day	9% 36% 4 21% 20% 11%	3538
November	1st to 10th	Day	19% 54% 4 12% 9% 2	2012
	11th to 20th	Day	17% 54% 3 10% 13% 3	1890
	21st to end	Day	16% 55% 4 12% 11% 2	1811
December	1st to 10th	Day	22% 35% 4 19% 15% 4	2680
	11th to 20th	Day	31% 32% 8% 13% 12% 5%	3066
	21st to end	Day	26% 27% 9% 22% 16%	4048
January	1st to 10th	Night	27% 21% 9% 17% 18% 7%	7739
	11th to 20th	Night	26% 21% 3 14% 28% 8%	7680
	21st to end	Night	34% 23% 5% 18% 15% 5%	8401
February	1st to 10th	Night	17% 60% 6% 10% 7% 2	2730
	11th to 20th	Night	22% 58% 3 8% 7% 2	2518
	21st to end	Night	18% 59% 3 10% 7% 4	2076
March	1st to 10th	Night	36% 30% 5% 11% 11% 7%	5102
	11th to 20th	Night	25% 29% 6% 11% 18% 12%	5090
	21st to end	Night	26% 29% 7% 19% 12% 5%	5461
April	1st to 10th	Night	16% 61% 6% 7% 9% 1	2100
	11th to 20th	Night	14% 59% 6% 11% 7% 2	2075
	21st to end	Night	15% 60% 6% 11% 7% 1	2100
May	1st to 10th	Night	35% 27% 13% 17% 7% 1	5863
	11th to 20th	Night	31% 26% 10% 23% 10%	5150
	21st to end	Night	40% 26% 9% 15% 9% 2	5115
June	1st to 10th	Night	15% 62% 7% 8% 7% 2	1680
	11th to 20th	Night	14% 62% 8% 10% 6%	1680
	21st to end	Night	12% 60% 6% 14% 7% 1	1680
July	1st to 10th	Night	29% 34% 15% 15% 6% 1	3700
	11th to 20th	Night	39% 35% 16% 8% 1	4051
	21st to end	Night	34% 30% 9% 14% 12%	4297
August	1st to 10th	Night	40% 38% 11% 10% 1	2904
	11th to 20th	Night	27% 40% 11% 14% 8%	3196
	21st to end	Night	19% 38% 8% 19% 15% 1	3586
September	1st to 10th	Night	17% 60% 9% 9% 5% 1	2000
	11th to 20th	Night	20% 58% 4 8% 8% 2	2000
	21st to end	Night	25% 58% 6% 7% 3	2271
October	1st to 10th	Night	23% 38% 7% 16% 15% 1	3920
	11th to 20th	Night	13% 36% 3 12% 24% 12%	3899
	21st to end	Night	9% 35% 5% 22% 17% 12%	4252
November	1st to 10th	Night	20% 54% 4 11% 10% 2	2503
	11th to 20th	Night	17% 54% 4 9% 10% 6%	2730
	21st to end	Night	15% 55% 3 12% 12% 2	2804
December	1st to 10th	Night	21% 36% 4 17% 17% 6%	4720
	11th to 20th	Night	36% 32% 6% 11% 10% 5%	5348
	21st to end	Night	26% 28% 11% 21% 13% 1	7150

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	24% 25% 35% 12% 4	308
	11th to 20th	Day	22% 30% 34% 13% 1	330
	21st to end	Day	23% 26% 38% 12% 1 1	363
February	1st to 10th	Day	18% 28% 38% 13% 3	330
	11th to 20th	Day	30% 24% 30% 13% 3	476
	21st to end	Day	26% 20% 33% 17% 4	446
March	1st to 10th	Day	21% 21% 35% 17% 5%	540
	11th to 20th	Day	22% 20% 34% 18% 5% 1	540
	21st to end	Day	21% 20% 38% 16% 4 2	594
April	1st to 10th	Day	19% 18% 37% 18% 6% 1	540
	11th to 20th	Day	14% 18% 34% 21% 10% 2	532
	21st to end	Day	16% 14% 31% 27% 10% 1	540
May	1st to 10th	Day	16% 16% 36% 22% 8% 2	543
	11th to 20th	Day	19% 8% 29% 27% 14% 3	567
	21st to end	Day	20% 6% 23% 27% 19% 5%	617
June	1st to 10th	Day	12% 7% 25% 31% 20% 5%	570
	11th to 20th	Day	11% 6% 22% 32% 21% 7%	570
	21st to end	Day	9% 4 19% 38% 25% 6%	570
July	1st to 10th	Day	10% 2 13% 35% 31% 8%	565
	11th to 20th	Day	8% 2 13% 36% 31% 10%	544
	21st to end	Day	8% 3 16% 38% 26% 10%	576
August	1st to 10th	Day	14% 4 20% 31% 23% 8%	526
	11th to 20th	Day	13% 4 15% 27% 29% 12%	519
	21st to end	Day	9% 4 16% 31% 26% 13%	583
September	1st to 10th	Day	15% 4 20% 27% 21% 14%	530
	11th to 20th	Day	17% 6% 17% 26% 22% 12%	530
	21st to end	Day	26% 8% 20% 24% 15% 6%	530
October	1st to 10th	Day	18% 7% 19% 25% 21% 10%	530
	11th to 20th	Day	17% 11% 27% 26% 17% 3	530
	21st to end	Day	15% 12% 29% 25% 15% 5%	583
November	1st to 10th	Day	17% 9% 32% 26% 12% 3	510
	11th to 20th	Day	19% 16% 31% 23% 10% 1	430
	21st to end	Day	19% 18% 26% 23% 12% 2	351
December	1st to 10th	Day	23% 15% 42% 14% 5% 1	220
	11th to 20th	Day	20% 17% 36% 21% 6%	220
	21st to end	Day	21% 20% 30% 19% 8% 1	242
January	1st to 10th	Night	18% 17% 37% 25% 3	840
	11th to 20th	Night	20% 15% 36% 24% 5%	840
	21st to end	Night	19% 13% 41% 25% 2	924
February	1st to 10th	Night	21% 13% 40% 23% 4	840
	11th to 20th	Night	26% 15% 40% 17% 2	823
	21st to end	Night	20% 17% 38% 22% 3	692
March	1st to 10th	Night	18% 14% 37% 27% 4	840
	11th to 20th	Night	20% 15% 39% 21% 5%	840
	21st to end	Night	19% 14% 39% 24% 5%	924
April	1st to 10th	Night	16% 14% 43% 22% 4	840
	11th to 20th	Night	14% 12% 40% 25% 8%	831
	21st to end	Night	15% 8% 37% 34% 6%	840
May	1st to 10th	Night	15% 12% 36% 30% 7%	840
	11th to 20th	Night	16% 6% 28% 39% 10% 1	601
	21st to end	Night	14% 3 18% 47% 17% 1	455
June	1st to 10th	Night	10% 3 22% 47% 17% 1	420
	11th to 20th	Night	7% 4 23% 45% 20% 1	420
	21st to end	Night	8% 2 19% 49% 21% 1	420
July	1st to 10th	Night	10% 2 13% 49% 24% 2	431
	11th to 20th	Night	8% 1 11% 43% 33% 4	597
	21st to end	Night	8% 2 16% 44% 28% 2	657
August	1st to 10th	Night	11% 3 12% 44% 27% 4	597
	11th to 20th	Night	13% 2 13% 43% 26% 3	771
	21st to end	Night	12% 3 12% 35% 35% 4	880
September	1st to 10th	Night	14% 3 14% 38% 27% 5%	800
	11th to 20th	Night	16% 4 15% 33% 28% 4	800
	21st to end	Night	23% 6% 18% 33% 19% 1	800
October	1st to 10th	Night	16% 4 18% 33% 26% 4	800
	11th to 20th	Night	20% 6% 27% 31% 16% 1	800
	21st to end	Night	16% 7% 27% 31% 16% 2	880
November	1st to 10th	Night	17% 7% 27% 33% 13% 3	820
	11th to 20th	Night	18% 10% 32% 32% 8%	840
	21st to end	Night	15% 10% 30% 34% 10% 1	840
December	1st to 10th	Night	21% 12% 33% 28% 6%	840
	11th to 20th	Night	18% 10% 35% 31% 7%	840
	21st to end	Night	17% 13% 34% 30% 6%	924

Page generated at 2026-07-13 03:14:53. Version ac07

Copyright © 2026 Attilla Danko.