St. Andrews
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the St. Andrews clear sky chart from 2005-11-06 to 2024-02-10.

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	19% 7% 3 5% 5% 3 4 4 5% 7% 37%	77972
	Night	20% 8% 3 6% 5% 3 4 4 5% 7% 34%	81004
Transparency	Day	46% 6% 13% 21% 12% 2	77674
	Night	49% 6% 12% 20% 11% 1	80837
Seeing	Day	24% 15% 31% 22% 7% 1	15159
	Night	25% 13% 30% 23% 7% 1	23349

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	18% 9% 3 6% 6% 3 5% 4 5% 7% 35%	2278
	11th to 20th	Day	18% 10% 4 6% 4 2 3 3 3 5% 43%	2520
	21st to end	Day	14% 9% 3 8% 6% 3 5% 5% 6% 8% 33%	3000
February	1st to 10th	Day	18% 10% 3 7% 5% 4 5% 4 5% 9% 29%	1701
	11th to 20th	Day	16% 9% 4 7% 5% 4 5% 5% 5% 8% 32%	1573
	21st to end	Day	13% 9% 4 5% 5% 3 5% 5% 6% 7% 37%	1480
March	1st to 10th	Day	17% 10% 3 7% 4 3 6% 5% 5% 7% 34%	1873
	11th to 20th	Day	18% 7% 3 4 5% 4 5% 5% 5% 7% 38%	1980
	21st to end	Day	19% 9% 3 6% 4 3 4 4 4 7% 36%	2178
April	1st to 10th	Day	21% 8% 3 6% 7% 3 5% 5% 5% 6% 31%	2097
	11th to 20th	Day	20% 7% 2 5% 5% 3 4 4 5% 7% 38%	2312
	21st to end	Day	23% 7% 2 5% 5% 3 4 5% 5% 6% 35%	2340
May	1st to 10th	Day	23% 8% 3 6% 5% 3 6% 5% 5% 6% 31%	2340
	11th to 20th	Day	23% 6% 2 4 5% 2 4 4 4 6% 40%	2355
	21st to end	Day	19% 7% 3 5% 6% 3 5% 5% 6% 8% 34%	2795
June	1st to 10th	Day	23% 7% 3 6% 6% 4 5% 4 5% 8% 30%	2700
	11th to 20th	Day	21% 7% 3 5% 4 3 4 4 5% 7% 37%	2700
	21st to end	Day	26% 6% 3 5% 6% 3 5% 5% 5% 7% 29%	2700
July	1st to 10th	Day	18% 5% 2 5% 5% 3 4 5% 6% 9% 37%	2700
	11th to 20th	Day	17% 7% 2 5% 5% 3 5% 5% 6% 8% 38%	2612
	21st to end	Day	17% 7% 3 5% 5% 4 5% 6% 7% 8% 34%	2614
August	1st to 10th	Day	16% 6% 3 5% 5% 3 5% 5% 6% 10% 37%	2327
	11th to 20th	Day	17% 7% 2 6% 6% 3 5% 5% 6% 10% 35%	2304
	21st to end	Day	14% 5% 2 4 4 3 4 5% 5% 8% 47%	2574
September	1st to 10th	Day	12% 5% 2 4 5% 3 3 4 5% 8% 50%	2116
	11th to 20th	Day	17% 4 2 4 4 2 3 5% 4 7% 49%	1980
	21st to end	Day	19% 6% 2 4 4 2 3 3 4 7% 46%	1980
October	1st to 10th	Day	16% 6% 3 5% 4 2 4 4 6% 7% 43%	1859
	11th to 20th	Day	20% 5% 2 4 5% 2 5% 5% 5% 8% 40%	1800
	21st to end	Day	21% 7% 2 6% 5% 3 5% 5% 4 6% 36%	1854
November	1st to 10th	Day	22% 7% 2 5% 5% 3 4 4 5% 6% 39%	1671
	11th to 20th	Day	21% 5% 2 4 4 3 4 4 6% 8% 40%	1520
	21st to end	Day	22% 8% 3 5% 5% 3 5% 3 5% 6% 35%	1520
December	1st to 10th	Day	25% 8% 3 6% 5% 2 4 5% 5% 7% 29%	1520
	11th to 20th	Day	27% 10% 3 6% 5% 3 4 4 5% 6% 27%	1668
	21st to end	Day	25% 8% 3 5% 4 3 4 5% 5% 7% 32%	2431
January	1st to 10th	Night	14% 10% 3 7% 6% 3 4 4 5% 7% 35%	4672
	11th to 20th	Night	15% 9% 4 7% 6% 3 5% 4 5% 7% 34%	4440
	21st to end	Night	16% 10% 4 7% 6% 3 5% 5% 6% 6% 31%	4654
February	1st to 10th	Night	19% 11% 3 4 5% 4 6% 5% 6% 8% 30%	2464
	11th to 20th	Night	17% 10% 3 7% 7% 4 5% 5% 5% 6% 31%	2271
	21st to end	Night	17% 10% 3 6% 5% 3 4 4 4 6% 37%	1776
March	1st to 10th	Night	17% 11% 3 6% 6% 3 5% 5% 5% 6% 33%	2073
	11th to 20th	Night	18% 9% 3 6% 6% 4 5% 5% 6% 6% 32%	1979
	21st to end	Night	18% 10% 3 6% 5% 2 4 4 4 7% 37%	2178
April	1st to 10th	Night	25% 9% 3 6% 6% 3 4 4 3 5% 32%	1859
	11th to 20th	Night	22% 8% 3 5% 4 3 4 5% 5% 6% 34%	1598
	21st to end	Night	28% 8% 2 6% 4 3 4 4 4 7% 30%	1620
May	1st to 10th	Night	24% 7% 3 6% 5% 3 4 4 4 6% 34%	1620
	11th to 20th	Night	26% 6% 3 6% 5% 3 5% 5% 5% 5% 32%	1536
	21st to end	Night	21% 8% 3 6% 5% 3 4 4 6% 7% 33%	1494
June	1st to 10th	Night	26% 7% 3 7% 5% 3 4 5% 5% 7% 28%	1260
	11th to 20th	Night	22% 7% 4 6% 4 3 4 4 5% 7% 34%	1260
	21st to end	Night	29% 7% 3 6% 5% 3 4 4 5% 6% 29%	1260
July	1st to 10th	Night	19% 8% 4 5% 5% 3 5% 5% 6% 9% 31%	1260
	11th to 20th	Night	21% 8% 3 4 5% 3 5% 5% 6% 8% 33%	1344
	21st to end	Night	22% 8% 2 6% 6% 3 6% 4 6% 7% 30%	1684
August	1st to 10th	Night	16% 8% 2 5% 5% 3 5% 5% 6% 8% 36%	1612
	11th to 20th	Night	19% 9% 2 5% 6% 3 4 5% 5% 9% 33%	1596
	21st to end	Night	16% 5% 2 5% 6% 3 3 4 5% 8% 43%	1782
September	1st to 10th	Night	16% 6% 2 3 4 3 3 4 5% 7% 45%	1841
	11th to 20th	Night	17% 6% 2 4 4 2 3 3 4 6% 48%	1980
	21st to end	Night	19% 6% 2 3 3 2 3 4 5% 6% 46%	1980
October	1st to 10th	Night	19% 7% 2 4 4 3 4 4 6% 7% 40%	2101
	11th to 20th	Night	20% 6% 2 5% 4 3 4 4 4 6% 40%	2160
	21st to end	Night	25% 7% 2 5% 5% 3 4 4 4 6% 35%	2499
November	1st to 10th	Night	21% 6% 2 4 5% 3 4 5% 5% 7% 38%	2407
	11th to 20th	Night	20% 6% 2 5% 5% 3 5% 4 4 7% 38%	2658
	21st to end	Night	22% 6% 3 5% 5% 3 4 4 5% 9% 34%	2660
December	1st to 10th	Night	27% 9% 3 6% 5% 3 4 4 4 7% 28%	2660
	11th to 20th	Night	25% 10% 2 6% 5% 3 5% 4 5% 6% 29%	3530
	21st to end	Night	24% 9% 3 5% 5% 3 4 5% 5% 7% 31%	5236

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	49% 6% 18% 20% 7% 1	2279
	11th to 20th	Day	46% 5% 9% 26% 12% 3	2520
	21st to end	Day	50% 7% 14% 16% 13% 1	3000
February	1st to 10th	Day	54% 6% 10% 17% 12% 2	1701
	11th to 20th	Day	51% 6% 12% 18% 11% 1	1581
	21st to end	Day	45% 5% 12% 23% 11% 4	1480
March	1st to 10th	Day	50% 5% 11% 20% 11% 2	1877
	11th to 20th	Day	44% 7% 12% 19% 16% 3	1980
	21st to end	Day	48% 4 11% 20% 13% 4	2178
April	1st to 10th	Day	53% 5% 11% 14% 13% 3	2097
	11th to 20th	Day	45% 5% 12% 22% 13% 2	2312
	21st to end	Day	49% 6% 10% 18% 13% 4	2340
May	1st to 10th	Day	53% 7% 9% 18% 11% 2	2340
	11th to 20th	Day	46% 6% 11% 23% 12% 2	2359
	21st to end	Day	48% 8% 13% 21% 9% 1	2795
June	1st to 10th	Day	52% 7% 13% 18% 9% 1	2700
	11th to 20th	Day	47% 6% 11% 20% 14% 1	2700
	21st to end	Day	54% 8% 12% 15% 10% 2	2700
July	1st to 10th	Day	42% 9% 16% 20% 11% 2	2625
	11th to 20th	Day	42% 9% 15% 23% 10% 1	2531
	21st to end	Day	44% 8% 17% 21% 9% 1	2468
August	1st to 10th	Day	40% 10% 17% 23% 9% 1	2314
	11th to 20th	Day	44% 9% 15% 21% 11%	2304
	21st to end	Day	35% 7% 16% 26% 14% 1	2574
September	1st to 10th	Day	33% 7% 14% 28% 17% 1	2116
	11th to 20th	Day	35% 6% 12% 25% 18% 3	1980
	21st to end	Day	39% 5% 11% 29% 16% 1	1980
October	1st to 10th	Day	41% 6% 13% 26% 14%	1859
	11th to 20th	Day	43% 6% 16% 26% 9%	1800
	21st to end	Day	49% 6% 12% 20% 12%	1854
November	1st to 10th	Day	47% 5% 12% 22% 13% 1	1671
	11th to 20th	Day	42% 6% 14% 21% 15% 2	1520
	21st to end	Day	50% 5% 15% 20% 8% 1	1520
December	1st to 10th	Day	55% 6% 12% 19% 8%	1520
	11th to 20th	Day	58% 4 11% 17% 9% 1	1668
	21st to end	Day	52% 7% 14% 15% 10% 2	2431
January	1st to 10th	Night	47% 6% 14% 25% 8% 1	4672
	11th to 20th	Night	50% 6% 12% 20% 10% 1	4440
	21st to end	Night	51% 7% 12% 20% 9% 1	4654
February	1st to 10th	Night	51% 7% 12% 16% 12% 2	2464
	11th to 20th	Night	53% 6% 9% 18% 12% 2	2274
	21st to end	Night	50% 5% 10% 19% 14% 3	1776
March	1st to 10th	Night	52% 6% 8% 18% 14% 2	2082
	11th to 20th	Night	51% 6% 12% 14% 13% 3	1980
	21st to end	Night	48% 4 9% 20% 15% 3	2178
April	1st to 10th	Night	54% 5% 10% 15% 13% 4	1859
	11th to 20th	Night	49% 5% 11% 18% 16% 1	1598
	21st to end	Night	55% 5% 9% 15% 13% 2	1620
May	1st to 10th	Night	52% 5% 10% 19% 13% 2	1620
	11th to 20th	Night	53% 6% 9% 19% 11% 2	1537
	21st to end	Night	50% 6% 13% 18% 11% 1	1495
June	1st to 10th	Night	55% 6% 14% 17% 6% 1	1260
	11th to 20th	Night	50% 6% 11% 20% 11% 2	1260
	21st to end	Night	57% 5% 10% 18% 7% 3	1260
July	1st to 10th	Night	48% 9% 15% 17% 11%	1225
	11th to 20th	Night	49% 8% 13% 19% 10% 1	1302
	21st to end	Night	53% 7% 13% 17% 9% 1	1590
August	1st to 10th	Night	45% 9% 14% 22% 10%	1600
	11th to 20th	Night	49% 7% 15% 21% 8%	1596
	21st to end	Night	39% 8% 12% 25% 16% 1	1782
September	1st to 10th	Night	38% 7% 11% 28% 14% 1	1841
	11th to 20th	Night	38% 5% 12% 23% 19% 1	1980
	21st to end	Night	39% 4 11% 28% 17% 2	1980
October	1st to 10th	Night	42% 6% 10% 25% 15% 2	2101
	11th to 20th	Night	44% 5% 13% 25% 11% 1	2160
	21st to end	Night	51% 5% 12% 19% 12% 1	2499
November	1st to 10th	Night	45% 7% 12% 21% 14% 1	2407
	11th to 20th	Night	47% 5% 12% 21% 14% 1	2658
	21st to end	Night	48% 7% 15% 19% 10% 1	2660
December	1st to 10th	Night	58% 5% 10% 18% 9%	2660
	11th to 20th	Night	55% 6% 11% 18% 10% 1	3531
	21st to end	Night	51% 6% 15% 17% 7% 4	5236

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	29% 19% 33% 16% 3 1	180
	11th to 20th	Day	34% 24% 30% 9% 3 1	180
	21st to end	Day	22% 19% 37% 18% 4	335
February	1st to 10th	Day	27% 21% 32% 17% 2	367
	11th to 20th	Day	24% 24% 36% 12% 3	336
	21st to end	Day	23% 25% 34% 16% 2	346
March	1st to 10th	Day	22% 25% 34% 16% 2	420
	11th to 20th	Day	23% 24% 32% 15% 6%	420
	21st to end	Day	25% 22% 31% 15% 5% 2	462
April	1st to 10th	Day	31% 22% 30% 13% 3 1	420
	11th to 20th	Day	25% 19% 33% 18% 4 1	412
	21st to end	Day	28% 15% 32% 20% 5% 1	420
May	1st to 10th	Day	26% 18% 32% 18% 5%	423
	11th to 20th	Day	23% 16% 35% 20% 6% 1	501
	21st to end	Day	26% 14% 31% 20% 8% 1	680
June	1st to 10th	Day	25% 12% 33% 22% 7% 1	630
	11th to 20th	Day	23% 11% 29% 25% 10% 1	630
	21st to end	Day	30% 7% 27% 24% 10% 1	630
July	1st to 10th	Day	23% 5% 31% 29% 11% 1	620
	11th to 20th	Day	22% 5% 29% 30% 12% 2	530
	21st to end	Day	17% 7% 35% 32% 10% 1	488
August	1st to 10th	Day	15% 7% 33% 33% 11% 1	446
	11th to 20th	Day	20% 7% 27% 32% 12% 1	439
	21st to end	Day	18% 10% 28% 28% 15% 1	495
September	1st to 10th	Day	12% 6% 34% 37% 10% 1	450
	11th to 20th	Day	22% 12% 27% 25% 12% 3	450
	21st to end	Day	18% 12% 30% 26% 11% 3	450
October	1st to 10th	Day	19% 16% 27% 23% 13% 2	390
	11th to 20th	Day	21% 13% 29% 25% 9% 2	360
	21st to end	Day	26% 16% 32% 20% 5% 1	396
November	1st to 10th	Day	25% 17% 30% 21% 5% 2	365
	11th to 20th	Day	25% 22% 30% 16% 6%	370
	21st to end	Day	28% 22% 29% 17% 3 1	370
December	1st to 10th	Day	28% 18% 36% 14% 3	370
	11th to 20th	Day	38% 26% 24% 11% 2	180
	21st to end	Day	27% 30% 27% 11% 5% 1	198
January	1st to 10th	Night	26% 20% 31% 20% 3	826
	11th to 20th	Night	28% 19% 33% 17% 3	760
	21st to end	Night	18% 23% 38% 18% 3	836
February	1st to 10th	Night	26% 19% 33% 18% 3	759
	11th to 20th	Night	25% 24% 30% 17% 3 1	703
	21st to end	Night	24% 18% 34% 20% 4	592
March	1st to 10th	Night	23% 18% 38% 19% 2	720
	11th to 20th	Night	23% 19% 30% 24% 5%	720
	21st to end	Night	23% 17% 34% 20% 6% 1	792
April	1st to 10th	Night	31% 15% 33% 17% 3	666
	11th to 20th	Night	25% 11% 37% 22% 5%	534
	21st to end	Night	31% 9% 32% 20% 7%	540
May	1st to 10th	Night	26% 8% 32% 26% 8%	540
	11th to 20th	Night	28% 8% 31% 28% 5%	532
	21st to end	Night	24% 8% 34% 26% 7% 1	527
June	1st to 10th	Night	29% 6% 23% 33% 8%	360
	11th to 20th	Night	24% 7% 27% 29% 13% 1	360
	21st to end	Night	34% 3 21% 33% 8% 1	360
July	1st to 10th	Night	25% 4 23% 37% 11%	350
	11th to 20th	Night	24% 5% 20% 38% 13% 1	348
	21st to end	Night	25% 3 21% 38% 13%	504
August	1st to 10th	Night	17% 5% 25% 41% 12%	538
	11th to 20th	Night	24% 4 20% 37% 14%	532
	21st to end	Night	18% 4 24% 37% 16% 1	594
September	1st to 10th	Night	20% 3 30% 31% 14% 1	609
	11th to 20th	Night	21% 7% 26% 28% 17% 2	720
	21st to end	Night	22% 7% 28% 29% 13% 1	720
October	1st to 10th	Night	23% 7% 28% 28% 13% 1	720
	11th to 20th	Night	21% 12% 32% 23% 11% 1	720
	21st to end	Night	28% 17% 29% 21% 6%	792
November	1st to 10th	Night	25% 13% 31% 22% 9% 1	740
	11th to 20th	Night	25% 18% 30% 20% 8% 1	850
	21st to end	Night	27% 20% 30% 18% 5%	850
December	1st to 10th	Night	35% 14% 34% 14% 4	850
	11th to 20th	Night	29% 23% 31% 14% 2 1	850
	21st to end	Night	30% 21% 30% 14% 4	935

Page generated at 2024-02-07 07:11:53. Version ac07

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