Stirling-Rawdon
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Stirling-Rawdon clear sky chart from 2005-11-06 to 2026-07-01.

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	16% 10% 3 8% 5% 5% 4 4 5% 7% 34%	138337
	Night	16% 10% 4 8% 5% 4 4 4 5% 6% 33%	133996
Transparency	Day	50% 3 11% 23% 12% 1	141880
	Night	51% 3 11% 22% 12% 1	138540
Seeing	Day	24% 15% 31% 19% 8% 3	16509
	Night	23% 13% 29% 24% 9% 1	25767

By Month

Percentage Cloud Cover NE (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	16% 13% 4 9% 4 5% 4 4 6% 7% 29%	4661
	11th to 20th	Day	11% 22% 8% 15% 8% 5% 4 3 4 3 18%	4650
	21st to end	Day	12% 15% 7% 15% 7% 7% 5% 3 4 5% 20%	5780
February	1st to 10th	Day	14% 14% 5% 12% 7% 5% 4 4 6% 5% 25%	1890
	11th to 20th	Day	13% 15% 5% 12% 7% 6% 4 3 5% 4 27%	1843
	21st to end	Day	19% 15% 5% 9% 5% 6% 4 4 4 5% 24%	1662
March	1st to 10th	Day	20% 12% 4 9% 4 4 3 3 4 6% 31%	4853
	11th to 20th	Day	12% 13% 4 9% 5% 5% 5% 4 5% 7% 31%	5090
	21st to end	Day	20% 10% 3 7% 4 3 3 3 4 4 39%	5715
April	1st to 10th	Day	21% 13% 4 7% 5% 3 3 3 4 6% 32%	2520
	11th to 20th	Day	23% 9% 2 5% 3 4 4 2 4 6% 37%	2494
	21st to end	Day	21% 10% 3 8% 5% 4 4 3 5% 5% 33%	2698
May	1st to 10th	Day	21% 8% 3 8% 5% 4 5% 4 5% 6% 31%	8017
	11th to 20th	Day	16% 8% 3 8% 5% 4 4 4 5% 7% 36%	8221
	21st to end	Day	20% 6% 2 6% 4 4 4 4 5% 7% 38%	9060
June	1st to 10th	Day	17% 7% 3 7% 5% 5% 5% 4 6% 7% 33%	2940
	11th to 20th	Day	13% 6% 2 6% 5% 5% 5% 4 7% 9% 37%	2940
	21st to end	Day	17% 7% 3 6% 4 5% 5% 4 6% 8% 36%	2940
July	1st to 10th	Day	11% 6% 2 7% 5% 5% 5% 4 6% 9% 40%	6360
	11th to 20th	Day	10% 5% 2 5% 4 4 5% 5% 7% 8% 45%	6360
	21st to end	Day	7% 4 2 6% 4 5% 5% 4 7% 9% 46%	6888
August	1st to 10th	Day	16% 7% 3 7% 4 4 5% 3 6% 8% 38%	4234
	11th to 20th	Day	16% 7% 3 6% 5% 4 5% 4 6% 8% 37%	4174
	21st to end	Day	11% 5% 2 6% 4 4 5% 5% 7% 9% 40%	4360
September	1st to 10th	Day	13% 5% 2 6% 5% 5% 4 4 5% 7% 44%	2400
	11th to 20th	Day	10% 5% 2 5% 4 4 3 4 6% 7% 50%	2400
	21st to end	Day	16% 6% 2 7% 4 4 4 3 5% 7% 40%	2090
October	1st to 10th	Day	18% 8% 3 7% 4 4 5% 4 4 7% 36%	2000
	11th to 20th	Day	21% 8% 3 8% 5% 5% 4 3 6% 6% 31%	2000
	21st to end	Day	24% 10% 3 8% 5% 4 5% 3 5% 6% 27%	2155
November	1st to 10th	Day	16% 9% 3 7% 5% 5% 4 3 6% 7% 34%	1788
	11th to 20th	Day	16% 13% 3 9% 6% 4 4 4 6% 6% 31%	1680
	21st to end	Day	21% 14% 4 9% 6% 4 4 3 6% 5% 25%	1680
December	1st to 10th	Day	19% 18% 4 11% 5% 5% 4 4 4 6% 20%	2680
	11th to 20th	Day	17% 18% 6% 10% 4 4 4 2 3 4 26%	3066
	21st to end	Day	25% 14% 4 9% 4 4 4 3 3 5% 24%	4048
January	1st to 10th	Night	15% 15% 6% 12% 6% 5% 5% 3 5% 6% 23%	8234
	11th to 20th	Night	13% 17% 7% 14% 8% 6% 5% 3 5% 5% 17%	8217
	21st to end	Night	12% 14% 6% 11% 6% 5% 5% 4 5% 5% 27%	8401
February	1st to 10th	Night	13% 14% 5% 11% 7% 5% 4 4 5% 5% 27%	2730
	11th to 20th	Night	14% 14% 5% 10% 6% 5% 4 4 4 5% 28%	2663
	21st to end	Night	16% 12% 3 10% 5% 4 4 4 6% 6% 30%	2143
March	1st to 10th	Night	19% 11% 3 9% 6% 5% 4 3 5% 5% 30%	5202
	11th to 20th	Night	12% 11% 4 8% 5% 5% 5% 4 6% 7% 33%	5089
	21st to end	Night	20% 8% 3 7% 4 4 4 3 4 6% 37%	5459
April	1st to 10th	Night	19% 10% 3 8% 4 4 3 3 5% 5% 34%	2100
	11th to 20th	Night	19% 8% 3 7% 4 4 4 4 4 6% 37%	2075
	21st to end	Night	18% 8% 3 8% 4 4 5% 4 5% 7% 35%	1939
May	1st to 10th	Night	23% 8% 3 6% 4 4 4 4 5% 7% 31%	4882
	11th to 20th	Night	16% 8% 2 6% 4 3 4 3 5% 8% 40%	4639
	21st to end	Night	18% 6% 2 6% 4 4 4 4 5% 7% 40%	5114
June	1st to 10th	Night	14% 6% 2 6% 5% 4 5% 4 5% 9% 39%	1680
	11th to 20th	Night	11% 6% 3 5% 6% 4 4 4 6% 8% 43%	1680
	21st to end	Night	14% 7% 2 6% 5% 4 4 4 6% 7% 41%	1680
July	1st to 10th	Night	9% 6% 3 6% 5% 5% 5% 5% 6% 9% 41%	3600
	11th to 20th	Night	11% 6% 2 5% 4 3 4 4 5% 7% 49%	3600
	21st to end	Night	10% 4 2 5% 4 4 4 3 6% 9% 51%	3961
August	1st to 10th	Night	11% 5% 2 6% 4 4 4 4 5% 8% 47%	2915
	11th to 20th	Night	14% 6% 2 5% 4 4 4 3 5% 8% 46%	2875
	21st to end	Night	9% 4 2 5% 4 4 5% 4 7% 9% 47%	3505
September	1st to 10th	Night	10% 6% 2 6% 3 5% 4 3 5% 8% 47%	2000
	11th to 20th	Night	11% 4 1 4 3 4 4 3 5% 7% 53%	2000
	21st to end	Night	18% 5% 3 7% 3 4 5% 3 4 6% 42%	2304
October	1st to 10th	Night	16% 6% 2 6% 4 5% 5% 4 5% 6% 41%	2400
	11th to 20th	Night	21% 8% 3 8% 5% 5% 4 3 4 6% 33%	2400
	21st to end	Night	22% 10% 3 7% 5% 4 4 4 5% 6% 30%	2685
November	1st to 10th	Night	19% 8% 3 5% 5% 4 4 3 5% 7% 37%	2726
	11th to 20th	Night	17% 11% 3 7% 5% 5% 4 3 6% 7% 31%	2940
	21st to end	Night	20% 12% 3 7% 5% 5% 5% 4 5% 6% 26%	2940
December	1st to 10th	Night	19% 15% 4 8% 5% 5% 5% 5% 7% 8% 20%	4720
	11th to 20th	Night	19% 15% 5% 10% 5% 4 4 3 4 6% 25%	5348
	21st to end	Night	26% 16% 3 10% 4 4 4 3 4 4 21%	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	56% 2 12% 20% 8% 1	4662
	11th to 20th	Day	72% 2 8% 10% 7% 1	4680
	21st to end	Day	68% 2 9% 12% 9% 1	5780
February	1st to 10th	Day	61% 3 9% 19% 7% 1	1890
	11th to 20th	Day	62% 2 7% 17% 11% 1	1852
	21st to end	Day	64% 2 8% 15% 10% 1	1662
March	1st to 10th	Day	57% 2 11% 14% 15% 1	4856
	11th to 20th	Day	54% 2 16% 15% 11% 2	5090
	21st to end	Day	50% 2 6% 23% 17% 3	5715
April	1st to 10th	Day	56% 2 7% 20% 13% 2	2520
	11th to 20th	Day	51% 2 7% 22% 17% 1	2494
	21st to end	Day	55% 2 7% 20% 14% 2	2698
May	1st to 10th	Day	53% 3 9% 19% 13% 2	8027
	11th to 20th	Day	48% 3 11% 21% 15% 1	8225
	21st to end	Day	47% 2 10% 26% 13% 2	9061
June	1st to 10th	Day	49% 4 10% 20% 16% 1	2940
	11th to 20th	Day	43% 4 12% 26% 14% 2	2940
	21st to end	Day	46% 4 13% 23% 13% 1	2940
July	1st to 10th	Day	40% 4 13% 28% 14% 1	6290
	11th to 20th	Day	34% 5% 13% 31% 16% 1	6285
	21st to end	Day	33% 5% 13% 36% 12%	6690
August	1st to 10th	Day	44% 4 15% 25% 12% 1	4221
	11th to 20th	Day	43% 4 14% 29% 9% 1	4213
	21st to end	Day	38% 4 13% 34% 10% 1	4360
September	1st to 10th	Day	39% 4 13% 31% 12% 1	2400
	11th to 20th	Day	33% 3 13% 35% 16% 1	2400
	21st to end	Day	44% 4 13% 28% 10%	2090
October	1st to 10th	Day	41% 4 12% 31% 12% 1	3260
	11th to 20th	Day	45% 4 15% 25% 11% 1	3240
	21st to end	Day	52% 4 13% 22% 9%	3457
November	1st to 10th	Day	50% 3 14% 23% 10% 1	1788
	11th to 20th	Day	54% 3 13% 18% 12% 1	1680
	21st to end	Day	62% 3 12% 15% 8%	1680
December	1st to 10th	Day	66% 3 15% 11% 4	2680
	11th to 20th	Day	64% 3 9% 15% 9%	3066
	21st to end	Day	64% 3 8% 16% 9%	4048
January	1st to 10th	Night	64% 2 11% 16% 8%	8234
	11th to 20th	Night	70% 2 10% 11% 6% 1	8262
	21st to end	Night	59% 3 10% 14% 14% 1	8401
February	1st to 10th	Night	59% 3 10% 20% 7% 1	2730
	11th to 20th	Night	59% 3 8% 21% 9% 1	2665
	21st to end	Night	54% 3 10% 22% 10% 1	2143
March	1st to 10th	Night	57% 2 6% 19% 12% 4	5212
	11th to 20th	Night	51% 2 16% 20% 9% 2	5090
	21st to end	Night	50% 2 7% 21% 18% 2	5459
April	1st to 10th	Night	53% 3 7% 22% 14% 2	2100
	11th to 20th	Night	49% 3 9% 21% 17% 1	2075
	21st to end	Night	49% 4 9% 20% 15% 3	1939
May	1st to 10th	Night	54% 2 8% 20% 13% 3	4888
	11th to 20th	Night	44% 3 13% 24% 15% 1	4640
	21st to end	Night	45% 2 12% 22% 17% 2	5115
June	1st to 10th	Night	43% 3 11% 25% 17% 1	1680
	11th to 20th	Night	39% 2 12% 24% 19% 2	1680
	21st to end	Night	42% 3 14% 25% 13% 2	1680
July	1st to 10th	Night	39% 5% 15% 22% 18% 1	3560
	11th to 20th	Night	34% 5% 13% 33% 15% 1	3552
	21st to end	Night	31% 5% 13% 35% 15% 1	3844
August	1st to 10th	Night	37% 3 13% 30% 15% 1	2904
	11th to 20th	Night	37% 4 18% 28% 13% 1	2902
	21st to end	Night	32% 5% 13% 38% 12% 1	3505
September	1st to 10th	Night	36% 3 15% 31% 14% 1	2000
	11th to 20th	Night	31% 3 14% 34% 17% 1	2000
	21st to end	Night	44% 3 10% 28% 13% 1	2304
October	1st to 10th	Night	36% 3 10% 30% 20%	3920
	11th to 20th	Night	44% 3 13% 30% 9%	3899
	21st to end	Night	47% 4 13% 27% 10%	4333
November	1st to 10th	Night	47% 3 12% 25% 12% 1	2726
	11th to 20th	Night	52% 3 13% 21% 10% 2	2940
	21st to end	Night	57% 4 14% 18% 6%	2940
December	1st to 10th	Night	61% 4 14% 17% 4	4720
	11th to 20th	Night	61% 4 12% 14% 8% 1	5348
	21st to end	Night	68% 2 9% 12% 9%	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	26% 21% 35% 14% 4 1	220
	11th to 20th	Day	35% 18% 27% 15% 4 1	220
	21st to end	Day	30% 22% 31% 12% 4 1	363
February	1st to 10th	Day	32% 22% 31% 12% 3 1	330
	11th to 20th	Day	31% 25% 35% 8% 1	330
	21st to end	Day	36% 19% 35% 8% 2	378
March	1st to 10th	Day	28% 20% 33% 15% 4	540
	11th to 20th	Day	33% 19% 31% 14% 3	540
	21st to end	Day	37% 17% 29% 11% 5% 1	594
April	1st to 10th	Day	35% 18% 32% 10% 5%	540
	11th to 20th	Day	37% 18% 22% 14% 6% 3	532
	21st to end	Day	31% 19% 32% 13% 4 2	540
May	1st to 10th	Day	25% 17% 31% 17% 5% 4	543
	11th to 20th	Day	21% 14% 35% 20% 7% 3	567
	21st to end	Day	21% 15% 34% 17% 11% 3	617
June	1st to 10th	Day	21% 13% 35% 22% 7% 2	570
	11th to 20th	Day	16% 15% 35% 22% 11% 2	570
	21st to end	Day	23% 14% 29% 23% 10% 2	570
July	1st to 10th	Day	12% 10% 32% 30% 13% 4	525
	11th to 20th	Day	16% 9% 29% 27% 15% 5%	524
	21st to end	Day	11% 9% 38% 26% 12% 4	576
August	1st to 10th	Day	13% 7% 30% 29% 15% 7%	526
	11th to 20th	Day	15% 6% 29% 28% 16% 7%	519
	21st to end	Day	16% 8% 31% 25% 13% 7%	583
September	1st to 10th	Day	14% 11% 31% 25% 11% 8%	530
	11th to 20th	Day	12% 6% 27% 25% 19% 12%	530
	21st to end	Day	19% 12% 27% 25% 11% 5%	530
October	1st to 10th	Day	25% 14% 24% 19% 13% 5%	530
	11th to 20th	Day	27% 16% 34% 14% 7% 2	530
	21st to end	Day	30% 16% 29% 20% 4	558
November	1st to 10th	Day	31% 16% 27% 16% 9% 1	362
	11th to 20th	Day	31% 19% 33% 12% 5%	220
	21st to end	Day	32% 22% 30% 12% 3 1	220
December	1st to 10th	Day	34% 13% 34% 15% 4	220
	11th to 20th	Day	36% 22% 30% 9% 2	220
	21st to end	Day	39% 17% 31% 10% 2 1	242
January	1st to 10th	Night	28% 18% 32% 17% 4 1	840
	11th to 20th	Night	30% 18% 28% 19% 5%	840
	21st to end	Night	23% 17% 34% 22% 4 1	924
February	1st to 10th	Night	24% 20% 34% 20% 2	840
	11th to 20th	Night	25% 21% 33% 17% 4	823
	21st to end	Night	26% 19% 34% 18% 3	692
March	1st to 10th	Night	25% 17% 35% 20% 3	840
	11th to 20th	Night	27% 18% 32% 19% 3 1	840
	21st to end	Night	24% 17% 30% 21% 6% 1	924
April	1st to 10th	Night	27% 17% 31% 22% 3	840
	11th to 20th	Night	26% 20% 26% 20% 7%	831
	21st to end	Night	23% 13% 30% 24% 8% 1	679
May	1st to 10th	Night	24% 10% 27% 26% 11% 2	499
	11th to 20th	Night	18% 9% 34% 30% 10%	414
	21st to end	Night	15% 8% 34% 30% 13% 1	455
June	1st to 10th	Night	16% 8% 32% 32% 11% 1	420
	11th to 20th	Night	14% 12% 30% 30% 13% 1	420
	21st to end	Night	16% 7% 27% 35% 14% 1	420
July	1st to 10th	Night	7% 5% 29% 44% 14% 1	390
	11th to 20th	Night	11% 2 29% 37% 20% 1	388
	21st to end	Night	11% 2 31% 39% 15% 1	448
August	1st to 10th	Night	10% 3 24% 34% 25% 3	597
	11th to 20th	Night	11% 5% 20% 38% 23% 3	594
	21st to end	Night	12% 5% 28% 34% 19% 2	825
September	1st to 10th	Night	13% 6% 28% 32% 18% 3	800
	11th to 20th	Night	13% 5% 23% 26% 29% 5%	800
	21st to end	Night	20% 8% 23% 28% 18% 3	800
October	1st to 10th	Night	20% 11% 26% 24% 17% 2	800
	11th to 20th	Night	26% 12% 31% 22% 8%	800
	21st to end	Night	28% 14% 30% 23% 5%	880
November	1st to 10th	Night	26% 13% 25% 26% 9%	820
	11th to 20th	Night	25% 18% 31% 19% 6% 1	840
	21st to end	Night	30% 16% 28% 20% 5%	840
December	1st to 10th	Night	30% 18% 28% 20% 4	840
	11th to 20th	Night	28% 18% 33% 17% 3	840
	21st to end	Night	36% 15% 30% 16% 2	924

Page generated at 2026-06-28 02:10:49. Version ac07

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