Rawson Quarry
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rawson Quarry clear sky chart from 2005-11-06 to 2026-05-17.

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	24% 12% 3 6% 3 3 3 3 4 5% 35%	141182
	Night	27% 13% 3 5% 3 3 3 2 4 5% 34%	138984
Transparency	Day	51% 5% 10% 17% 12% 4	135941
	Night	53% 5% 10% 16% 12% 4	135224
Seeing	Day	33% 9% 24% 23% 9% 2	16436
	Night	36% 6% 16% 25% 15% 2	25490

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	43% 25% 3 6% 3 3 2 1 3 3 8%	4722
	11th to 20th	Day	23% 13% 2 5% 2 3 2 2 4 5% 39%	4740
	21st to end	Day	35% 9% 3 6% 3 3 3 2 3 3 29%	5580
February	1st to 10th	Day	37% 17% 4 6% 4 4 2 2 4 5% 15%	1890
	11th to 20th	Day	36% 21% 4 6% 3 3 2 2 2 3 17%	1845
	21st to end	Day	35% 23% 3 5% 3 3 2 2 3 3 18%	1657
March	1st to 10th	Day	23% 21% 5% 9% 4 3 4 3 4 5% 17%	4783
	11th to 20th	Day	34% 20% 3 6% 3 2 2 2 2 2 25%	5110
	21st to end	Day	35% 21% 3 8% 4 4 3 2 4 4 11%	5775
April	1st to 10th	Day	33% 18% 4 7% 4 3 3 3 4 4 16%	2520
	11th to 20th	Day	30% 17% 4 6% 4 3 3 3 4 4 23%	2489
	21st to end	Day	28% 17% 3 7% 4 4 3 4 3 5% 22%	2703
May	1st to 10th	Day	19% 14% 3 6% 3 3 3 2 4 6% 37%	6447
	11th to 20th	Day	23% 17% 4 8% 4 3 4 3 4 5% 24%	6362
	21st to end	Day	26% 11% 3 6% 4 4 4 3 5% 6% 28%	6902
June	1st to 10th	Day	29% 9% 2 6% 5% 3 4 4 4 5% 29%	2800
	11th to 20th	Day	28% 12% 3 7% 5% 4 4 4 5% 7% 23%	2800
	21st to end	Day	15% 8% 3 5% 4 4 4 3 5% 6% 44%	2800
July	1st to 10th	Day	6% 5% 2 3 2 2 2 2 3 5% 66%	6319
	11th to 20th	Day	5% 3 1 2 2 2 2 2 2 3 77%	6320
	21st to end	Day	7% 5% 1 3 2 2 2 2 4 6% 67%	6880
August	1st to 10th	Day	7% 5% 2 5% 2 3 3 3 4 6% 58%	5918
	11th to 20th	Day	10% 7% 2 6% 4 4 4 3 5% 6% 49%	5796
	21st to end	Day	13% 7% 2 5% 3 4 4 3 5% 6% 48%	6122
September	1st to 10th	Day	12% 5% 1 4 3 3 4 2 4 6% 56%	2400
	11th to 20th	Day	18% 8% 3 6% 4 4 4 2 4 7% 42%	2400
	21st to end	Day	21% 8% 3 5% 3 3 3 2 4 5% 43%	2113
October	1st to 10th	Day	21% 7% 1 5% 2 2 3 3 4 5% 46%	3280
	11th to 20th	Day	27% 9% 3 7% 3 3 4 3 6% 6% 30%	3261
	21st to end	Day	39% 11% 2 6% 3 2 3 3 4 4 23%	3433
November	1st to 10th	Day	41% 14% 3 6% 3 4 3 3 4 5% 15%	1755
	11th to 20th	Day	45% 11% 2 5% 3 3 3 3 4 4 18%	1680
	21st to end	Day	37% 16% 2 6% 3 2 3 3 3 4 22%	1680
December	1st to 10th	Day	28% 12% 3 5% 3 2 3 3 3 4 35%	2700
	11th to 20th	Day	44% 18% 3 7% 4 2 2 2 3 3 12%	3108
	21st to end	Day	42% 19% 3 7% 4 3 3 2 3 3 11%	4092
January	1st to 10th	Night	44% 21% 3 6% 3 3 3 2 3 3 11%	8172
	11th to 20th	Night	22% 16% 3 5% 2 2 2 2 3 5% 39%	8220
	21st to end	Night	33% 10% 3 5% 3 2 2 2 4 5% 30%	8620
February	1st to 10th	Night	34% 18% 3 7% 4 3 3 3 4 4 18%	2730
	11th to 20th	Night	35% 18% 3 5% 3 3 3 2 3 3 22%	2662
	21st to end	Night	33% 21% 3 5% 3 3 3 2 4 5% 19%	2149
March	1st to 10th	Night	24% 21% 4 7% 4 4 4 3 4 4 19%	5327
	11th to 20th	Night	32% 20% 3 5% 2 2 2 2 2 3 27%	5110
	21st to end	Night	40% 20% 3 6% 4 3 3 2 4 4 12%	5441
April	1st to 10th	Night	31% 19% 3 6% 5% 3 3 2 3 4 21%	2100
	11th to 20th	Night	26% 15% 3 6% 3 3 4 2 4 6% 27%	2079
	21st to end	Night	29% 14% 2 6% 4 4 4 3 3 6% 26%	1914
May	1st to 10th	Night	22% 12% 2 5% 2 3 2 2 3 5% 42%	3731
	11th to 20th	Night	19% 14% 4 8% 4 4 3 3 3 4 34%	3664
	21st to end	Night	21% 10% 2 6% 3 3 4 4 6% 8% 33%	3972
June	1st to 10th	Night	26% 8% 3 5% 3 3 3 3 4 6% 36%	1600
	11th to 20th	Night	22% 11% 3 6% 4 3 3 3 4 5% 37%	1600
	21st to end	Night	13% 7% 2 4 3 3 3 2 4 4 56%	1600
July	1st to 10th	Night	3 2 1 3 2 3 3 2 3 4 74%	3640
	11th to 20th	Night	4 3 1 2 1 1 1 2 2 3 80%	3640
	21st to end	Night	5% 2 1 2 1 2 2 2 3 5% 75%	3970
August	1st to 10th	Night	6% 4 2 4 3 3 2 2 4 6% 63%	3885
	11th to 20th	Night	13% 5% 2 4 3 4 4 3 4 6% 52%	4052
	21st to end	Night	12% 5% 2 4 2 3 3 2 5% 5% 56%	4870
September	1st to 10th	Night	10% 4 1 3 3 3 3 3 3 6% 61%	2000
	11th to 20th	Night	18% 7% 2 5% 4 3 3 3 3 5% 48%	2000
	21st to end	Night	18% 8% 2 4 3 4 3 2 4 5% 48%	2284
October	1st to 10th	Night	18% 5% 2 4 3 3 3 2 4 7% 50%	3920
	11th to 20th	Night	25% 8% 3 5% 3 4 4 3 6% 6% 33%	3897
	21st to end	Night	38% 12% 2 5% 3 3 3 2 4 4 24%	4373
November	1st to 10th	Night	42% 13% 3 5% 3 3 2 3 3 4 19%	2760
	11th to 20th	Night	46% 12% 2 5% 3 2 3 2 3 5% 18%	2940
	21st to end	Night	35% 13% 3 5% 3 3 2 3 3 5% 25%	2940
December	1st to 10th	Night	27% 11% 3 4 3 3 3 2 4 6% 35%	4700
	11th to 20th	Night	44% 18% 4 7% 3 3 2 2 3 4 12%	5316
	21st to end	Night	43% 20% 4 7% 3 3 3 2 2 2 12%	7106

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	82% 3 5% 6% 4	4723
	11th to 20th	Day	48% 3 7% 15% 15% 11%	4740
	21st to end	Day	59% 3 4 13% 17% 4	5580
February	1st to 10th	Day	71% 5% 9% 9% 6%	1890
	11th to 20th	Day	73% 4 6% 11% 4 2	1854
	21st to end	Day	71% 4 8% 8% 8% 2	1657
March	1st to 10th	Day	64% 6% 12% 11% 6%	4783
	11th to 20th	Day	66% 4 6% 18% 6%	5110
	21st to end	Day	75% 7% 9% 6% 3	5775
April	1st to 10th	Day	70% 5% 12% 11% 3	2520
	11th to 20th	Day	65% 5% 9% 12% 8% 2	2492
	21st to end	Day	63% 7% 9% 12% 7% 2	2703
May	1st to 10th	Day	47% 5% 11% 21% 16%	6447
	11th to 20th	Day	57% 8% 15% 14% 5% 1	6365
	21st to end	Day	53% 10% 18% 16% 3	6904
June	1st to 10th	Day	55% 8% 13% 17% 7%	2800
	11th to 20th	Day	59% 8% 15% 13% 6%	2800
	21st to end	Day	38% 8% 15% 25% 10% 5%	2800
July	1st to 10th	Day	19% 5% 11% 26% 19% 20%	6251
	11th to 20th	Day	14% 3 7% 21% 38% 18%	6245
	21st to end	Day	18% 5% 16% 33% 24% 4	6681
August	1st to 10th	Day	23% 5% 10% 26% 26% 12%	4311
	11th to 20th	Day	32% 7% 16% 29% 11% 6%	4195
	21st to end	Day	35% 6% 10% 22% 15% 12%	4413
September	1st to 10th	Day	29% 5% 12% 23% 19% 13%	2400
	11th to 20th	Day	43% 6% 11% 17% 15% 9%	2400
	21st to end	Day	42% 6% 12% 19% 15% 6%	2113
October	1st to 10th	Day	40% 4 6% 22% 25% 3	3280
	11th to 20th	Day	51% 6% 13% 15% 12% 2	3261
	21st to end	Day	62% 4 8% 16% 9% 1	3433
November	1st to 10th	Day	71% 5% 7% 12% 4 1	1755
	11th to 20th	Day	69% 6% 9% 9% 5% 2	1680
	21st to end	Day	67% 5% 7% 8% 12% 2	1680
December	1st to 10th	Day	53% 4 7% 13% 20% 3	2700
	11th to 20th	Day	77% 4 9% 7% 3	3108
	21st to end	Day	78% 4 7% 8% 2	4092
January	1st to 10th	Night	80% 3 6% 7% 4 1	8172
	11th to 20th	Night	49% 4 6% 17% 18% 6%	8220
	21st to end	Night	57% 3 4 12% 19% 5%	8620
February	1st to 10th	Night	69% 7% 8% 10% 6% 1	2730
	11th to 20th	Night	67% 6% 8% 11% 6% 3	2664
	21st to end	Night	68% 4 9% 11% 7% 1	2149
March	1st to 10th	Night	65% 7% 10% 12% 5% 1	5327
	11th to 20th	Night	64% 4 8% 15% 9% 1	5110
	21st to end	Night	75% 5% 10% 8% 2	5441
April	1st to 10th	Night	68% 6% 11% 12% 4	2100
	11th to 20th	Night	58% 8% 10% 13% 8% 3	2079
	21st to end	Night	59% 6% 12% 14% 6% 3	1914
May	1st to 10th	Night	44% 5% 8% 26% 16% 1	3728
	11th to 20th	Night	48% 9% 19% 18% 5% 1	3664
	21st to end	Night	47% 12% 21% 15% 4	3972
June	1st to 10th	Night	49% 7% 14% 21% 8%	1600
	11th to 20th	Night	50% 7% 17% 21% 5%	1600
	21st to end	Night	33% 6% 18% 29% 10% 5%	1600
July	1st to 10th	Night	14% 5% 11% 29% 21% 19%	3600
	11th to 20th	Night	12% 2 8% 21% 41% 15%	3592
	21st to end	Night	12% 4 21% 32% 27% 4	3857
August	1st to 10th	Night	16% 4 10% 33% 29% 8%	2818
	11th to 20th	Night	28% 9% 21% 26% 10% 6%	2929
	21st to end	Night	28% 6% 14% 26% 14% 13%	3502
September	1st to 10th	Night	24% 6% 14% 27% 18% 11%	2000
	11th to 20th	Night	39% 6% 12% 20% 13% 11%	2000
	21st to end	Night	38% 7% 13% 19% 15% 8%	2284
October	1st to 10th	Night	35% 5% 9% 25% 24% 3	3920
	11th to 20th	Night	49% 6% 13% 16% 14% 2	3897
	21st to end	Night	63% 4 7% 14% 9% 2	4373
November	1st to 10th	Night	69% 5% 6% 12% 6% 1	2760
	11th to 20th	Night	70% 5% 7% 8% 8% 2	2940
	21st to end	Night	63% 5% 8% 11% 12% 2	2940
December	1st to 10th	Night	50% 4 8% 14% 22% 1	4700
	11th to 20th	Night	77% 4 7% 7% 4	5316
	21st to end	Night	79% 4 8% 6% 2	7106

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	56% 13% 18% 10% 3	220
	11th to 20th	Day	45% 12% 25% 11% 6%	220
	21st to end	Day	50% 8% 17% 17% 7% 1	379
February	1st to 10th	Day	49% 10% 21% 16% 3 1	430
	11th to 20th	Day	51% 12% 22% 12% 3	425
	21st to end	Day	49% 10% 26% 13% 2	408
March	1st to 10th	Day	46% 10% 25% 13% 5%	540
	11th to 20th	Day	44% 12% 24% 13% 5% 2	540
	21st to end	Day	47% 12% 18% 18% 4 1	594
April	1st to 10th	Day	45% 8% 24% 16% 6% 2	540
	11th to 20th	Day	38% 13% 25% 17% 5% 2	532
	21st to end	Day	38% 10% 25% 21% 5% 1	540
May	1st to 10th	Day	26% 13% 29% 24% 7% 2	543
	11th to 20th	Day	38% 13% 19% 19% 8% 4	553
	21st to end	Day	35% 7% 20% 24% 10% 4	573
June	1st to 10th	Day	31% 9% 20% 23% 14% 4	530
	11th to 20th	Day	28% 12% 30% 20% 7% 2	530
	21st to end	Day	13% 10% 31% 27% 16% 3	530
July	1st to 10th	Day	16% 8% 25% 35% 12% 4	526
	11th to 20th	Day	8% 8% 28% 36% 16% 4	524
	21st to end	Day	8% 6% 22% 40% 18% 6%	575
August	1st to 10th	Day	12% 6% 21% 37% 18% 7%	527
	11th to 20th	Day	9% 4 25% 38% 19% 6%	517
	21st to end	Day	14% 9% 25% 34% 13% 4	583
September	1st to 10th	Day	14% 5% 31% 33% 13% 3	530
	11th to 20th	Day	21% 8% 23% 31% 16% 2	530
	21st to end	Day	22% 8% 28% 29% 10% 2	530
October	1st to 10th	Day	28% 8% 26% 27% 10% 2	530
	11th to 20th	Day	34% 8% 23% 23% 10% 2	530
	21st to end	Day	43% 10% 22% 16% 6% 2	507
November	1st to 10th	Day	54% 9% 19% 12% 5% 1	278
	11th to 20th	Day	50% 12% 22% 10% 6%	220
	21st to end	Day	48% 9% 22% 19% 3	220
December	1st to 10th	Day	47% 8% 20% 19% 5%	220
	11th to 20th	Day	63% 9% 17% 9% 2	220
	21st to end	Day	53% 10% 21% 12% 2	242
January	1st to 10th	Night	53% 10% 19% 14% 3	840
	11th to 20th	Night	46% 8% 22% 19% 5%	840
	21st to end	Night	42% 10% 22% 18% 7% 1	924
February	1st to 10th	Night	44% 9% 20% 20% 5% 1	840
	11th to 20th	Night	48% 8% 15% 21% 7%	824
	21st to end	Night	48% 9% 16% 20% 6%	692
March	1st to 10th	Night	43% 8% 15% 23% 10% 1	840
	11th to 20th	Night	44% 8% 18% 20% 10%	840
	21st to end	Night	49% 6% 12% 23% 8% 1	924
April	1st to 10th	Night	42% 7% 13% 24% 13% 1	840
	11th to 20th	Night	35% 7% 20% 22% 13% 2	831
	21st to end	Night	38% 7% 14% 28% 14% 1	654
May	1st to 10th	Night	27% 5% 18% 29% 20% 1	431
	11th to 20th	Night	27% 5% 13% 27% 26% 3	406
	21st to end	Night	25% 5% 11% 30% 25% 3	433
June	1st to 10th	Night	30% 4 12% 28% 25% 3	400
	11th to 20th	Night	26% 6% 16% 33% 19% 1	400
	21st to end	Night	14% 4 15% 35% 30% 1	400
July	1st to 10th	Night	9% 2 10% 37% 40% 3	390
	11th to 20th	Night	8% 1 11% 44% 34% 3	388
	21st to end	Night	4 2 8% 40% 42% 4	438
August	1st to 10th	Night	8% 1 6% 32% 46% 7%	524
	11th to 20th	Night	10% 1 6% 33% 41% 9%	594
	21st to end	Night	12% 3 11% 41% 30% 4	813
September	1st to 10th	Night	13% 3 16% 36% 29% 4	800
	11th to 20th	Night	20% 3 12% 32% 29% 5%	800
	21st to end	Night	21% 4 15% 34% 24% 2	800
October	1st to 10th	Night	25% 5% 17% 31% 19% 3	800
	11th to 20th	Night	32% 6% 14% 29% 17% 3	800
	21st to end	Night	41% 6% 19% 24% 9% 2	880
November	1st to 10th	Night	48% 6% 17% 21% 8%	820
	11th to 20th	Night	53% 7% 18% 18% 4	840
	21st to end	Night	43% 8% 23% 22% 4	840
December	1st to 10th	Night	42% 9% 23% 18% 7% 1	840
	11th to 20th	Night	54% 8% 18% 18% 3	840
	21st to end	Night	56% 9% 16% 14% 3	924

Page generated at 2026-05-13 22:58:54. Version ac07

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