Thurso
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Thurso clear sky chart from 2005-11-06 to 2024-03-28.

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	18% 9% 4 7% 6% 3 5% 5% 5% 6% 32%	78570
	Night	18% 11% 4 7% 6% 3 4 4 5% 6% 32%	81407
Transparency	Day	51% 7% 11% 19% 10% 1	78275
	Night	53% 6% 12% 19% 9% 1	81236
Seeing	Day	22% 14% 30% 21% 10% 3	13615
	Night	22% 10% 29% 28% 10% 1	22847

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	17% 16% 7% 11% 8% 4 4 4 4 4 20%	2517
	11th to 20th	Day	15% 12% 7% 12% 7% 4 4 5% 6% 6% 22%	2520
	21st to end	Day	14% 18% 7% 10% 8% 4 6% 5% 5% 5% 18%	2818
February	1st to 10th	Day	12% 16% 5% 11% 8% 4 4 5% 5% 5% 25%	1710
	11th to 20th	Day	13% 15% 6% 11% 7% 3 4 4 3 5% 28%	1689
	21st to end	Day	19% 12% 6% 8% 7% 3 5% 5% 6% 4 26%	1570
March	1st to 10th	Day	17% 11% 5% 9% 7% 4 5% 5% 4 5% 29%	1897
	11th to 20th	Day	17% 11% 3 7% 7% 4 6% 5% 4 5% 30%	2055
	21st to end	Day	20% 8% 3 6% 6% 3 5% 3 4 6% 36%	2397
April	1st to 10th	Day	22% 11% 4 7% 5% 3 4 3 4 5% 32%	2160
	11th to 20th	Day	21% 8% 3 6% 5% 3 4 4 4 6% 36%	2134
	21st to end	Day	22% 10% 4 7% 6% 4 3 5% 4 5% 31%	2291
May	1st to 10th	Day	20% 8% 3 7% 5% 4 5% 4 4 6% 34%	2520
	11th to 20th	Day	18% 6% 3 6% 5% 3 4 4 5% 7% 38%	2478
	21st to end	Day	18% 6% 3 5% 6% 3 5% 5% 6% 8% 36%	2725
June	1st to 10th	Day	21% 8% 3 6% 6% 3 5% 5% 5% 6% 30%	2520
	11th to 20th	Day	15% 6% 3 5% 5% 4 6% 6% 6% 8% 38%	2520
	21st to end	Day	20% 6% 3 6% 5% 4 6% 6% 6% 8% 30%	2520
July	1st to 10th	Day	12% 6% 2 5% 6% 4 5% 6% 7% 8% 39%	2520
	11th to 20th	Day	12% 6% 3 6% 5% 4 5% 6% 7% 8% 37%	2520
	21st to end	Day	12% 6% 2 5% 5% 4 5% 6% 7% 8% 38%	2744
August	1st to 10th	Day	12% 5% 3 6% 6% 4 5% 6% 6% 8% 38%	2506
	11th to 20th	Day	11% 6% 3 6% 5% 3 5% 6% 6% 9% 39%	2265
	21st to end	Day	13% 5% 2 5% 5% 3 4 5% 5% 9% 42%	2376
September	1st to 10th	Day	15% 5% 3 5% 5% 4 5% 5% 6% 8% 41%	2160
	11th to 20th	Day	14% 5% 2 4 5% 4 4 4 5% 8% 47%	2141
	21st to end	Day	19% 5% 2 5% 6% 3 3 4 5% 8% 40%	1953
October	1st to 10th	Day	22% 8% 3 5% 6% 2 4 4 5% 7% 36%	1800
	11th to 20th	Day	25% 10% 4 6% 6% 4 4 5% 4 6% 27%	1800
	21st to end	Day	26% 9% 4 7% 6% 3 5% 4 5% 5% 27%	1806
November	1st to 10th	Day	17% 9% 3 5% 5% 3 5% 5% 6% 8% 34%	1671
	11th to 20th	Day	20% 11% 5% 7% 6% 4 5% 5% 3 6% 27%	1549
	21st to end	Day	23% 13% 4 9% 7% 4 5% 3 5% 6% 22%	1520
December	1st to 10th	Day	23% 15% 6% 9% 6% 4 5% 4 4 5% 18%	1520
	11th to 20th	Day	21% 14% 5% 9% 7% 4 4 3 4 5% 24%	1906
	21st to end	Day	27% 20% 5% 8% 5% 3 3 3 3 4 19%	2772
January	1st to 10th	Night	18% 17% 6% 10% 6% 3 4 4 4 5% 22%	4429
	11th to 20th	Night	13% 14% 6% 10% 9% 5% 5% 5% 5% 5% 23%	4440
	21st to end	Night	16% 19% 7% 10% 6% 3 5% 4 4 4 21%	4820
February	1st to 10th	Night	14% 13% 6% 10% 8% 4 6% 5% 5% 5% 25%	2470
	11th to 20th	Night	13% 12% 6% 10% 8% 5% 5% 4 4 6% 29%	2376
	21st to end	Night	16% 14% 5% 8% 6% 3 4 4 5% 6% 29%	1884
March	1st to 10th	Night	17% 12% 5% 8% 8% 4 5% 4 4 5% 28%	2270
	11th to 20th	Night	17% 13% 4 7% 6% 3 5% 3 4 5% 32%	2122
	21st to end	Night	17% 9% 3 7% 5% 3 3 3 4 5% 40%	2113
April	1st to 10th	Night	23% 8% 3 6% 6% 3 5% 4 4 6% 33%	1800
	11th to 20th	Night	19% 8% 3 6% 5% 3 3 5% 5% 5% 37%	1775
	21st to end	Night	21% 8% 4 7% 5% 3 4 4 5% 6% 34%	1684
May	1st to 10th	Night	21% 7% 3 6% 5% 4 4 5% 4 6% 37%	1440
	11th to 20th	Night	19% 6% 3 6% 4 3 3 4 5% 6% 42%	1415
	21st to end	Night	15% 6% 2 5% 5% 3 6% 5% 5% 6% 42%	1550
June	1st to 10th	Night	18% 6% 3 6% 4 4 5% 5% 6% 9% 33%	1440
	11th to 20th	Night	14% 6% 3 6% 4 3 5% 5% 5% 7% 42%	1440
	21st to end	Night	17% 6% 3 5% 5% 3 6% 5% 6% 9% 35%	1440
July	1st to 10th	Night	11% 4 2 5% 6% 3 5% 5% 6% 7% 46%	1440
	11th to 20th	Night	11% 6% 3 5% 4 3 4 4 7% 9% 43%	1440
	21st to end	Night	9% 6% 3 5% 6% 4 6% 6% 6% 8% 42%	1574
August	1st to 10th	Night	10% 6% 3 5% 5% 3 4 6% 8% 8% 43%	1432
	11th to 20th	Night	11% 5% 2 5% 5% 4 4 5% 6% 8% 45%	1615
	21st to end	Night	12% 5% 3 6% 6% 3 5% 5% 6% 7% 44%	1980
September	1st to 10th	Night	12% 5% 2 5% 6% 3 5% 5% 5% 7% 45%	1800
	11th to 20th	Night	16% 5% 2 4 4 2 4 4 5% 7% 48%	1818
	21st to end	Night	17% 6% 2 5% 5% 3 4 3 4 6% 44%	2006
October	1st to 10th	Night	19% 7% 3 6% 5% 3 4 6% 5% 6% 38%	2160
	11th to 20th	Night	21% 7% 3 6% 6% 4 5% 5% 5% 6% 32%	2160
	21st to end	Night	23% 9% 4 6% 7% 3 5% 4 4 6% 29%	2548
November	1st to 10th	Night	20% 9% 3 6% 6% 3 5% 4 6% 6% 33%	2407
	11th to 20th	Night	19% 10% 5% 7% 6% 4 5% 5% 5% 6% 30%	2627
	21st to end	Night	21% 13% 5% 9% 6% 3 5% 4 5% 6% 24%	2660
December	1st to 10th	Night	22% 15% 7% 9% 7% 3 5% 4 4 5% 19%	2660
	11th to 20th	Night	23% 14% 5% 7% 6% 3 4 3 4 4 27%	3288
	21st to end	Night	30% 18% 4 8% 5% 2 3 3 3 3 20%	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	66% 9% 8% 11% 5% 1	2518
	11th to 20th	Day	61% 7% 12% 13% 6% 1	2520
	21st to end	Day	66% 8% 10% 10% 5%	2818
February	1st to 10th	Day	61% 5% 9% 18% 5% 2	1710
	11th to 20th	Day	59% 6% 11% 15% 9% 1	1698
	21st to end	Day	59% 5% 10% 13% 10% 1	1570
March	1st to 10th	Day	56% 7% 9% 16% 10% 1	1900
	11th to 20th	Day	54% 6% 11% 14% 11% 2	2055
	21st to end	Day	50% 5% 9% 18% 14% 4	2397
April	1st to 10th	Day	55% 4 8% 18% 12% 3	2160
	11th to 20th	Day	50% 5% 7% 21% 15% 2	2134
	21st to end	Day	56% 6% 7% 14% 13% 4	2291
May	1st to 10th	Day	51% 6% 6% 20% 14% 3	2520
	11th to 20th	Day	45% 6% 9% 21% 16% 3	2482
	21st to end	Day	45% 8% 12% 19% 14% 2	2725
June	1st to 10th	Day	52% 7% 11% 18% 11% 1	2520
	11th to 20th	Day	42% 8% 12% 23% 12% 2	2520
	21st to end	Day	49% 10% 13% 18% 10% 1	2520
July	1st to 10th	Day	39% 9% 13% 25% 13% 1	2450
	11th to 20th	Day	41% 9% 14% 26% 11%	2445
	21st to end	Day	40% 10% 15% 25% 10%	2591
August	1st to 10th	Day	42% 9% 16% 24% 9%	2492
	11th to 20th	Day	39% 10% 17% 25% 9% 1	2265
	21st to end	Day	38% 8% 15% 27% 12% 1	2376
September	1st to 10th	Day	40% 7% 13% 27% 13%	2160
	11th to 20th	Day	35% 8% 12% 31% 12% 1	2141
	21st to end	Day	43% 7% 14% 28% 8%	1953
October	1st to 10th	Day	49% 6% 12% 22% 11% 1	1800
	11th to 20th	Day	57% 8% 13% 16% 6% 1	1800
	21st to end	Day	59% 5% 12% 16% 7% 1	1806
November	1st to 10th	Day	48% 7% 15% 22% 6% 1	1671
	11th to 20th	Day	58% 6% 12% 15% 9% 1	1549
	21st to end	Day	63% 7% 12% 12% 6% 1	1520
December	1st to 10th	Day	68% 6% 12% 10% 3	1520
	11th to 20th	Day	63% 6% 13% 14% 5%	1906
	21st to end	Day	71% 5% 6% 14% 4	2772
January	1st to 10th	Night	64% 7% 15% 10% 4	4429
	11th to 20th	Night	60% 8% 14% 12% 5%	4440
	21st to end	Night	66% 6% 11% 10% 6% 1	4820
February	1st to 10th	Night	60% 5% 11% 17% 6% 1	2470
	11th to 20th	Night	56% 6% 10% 20% 8%	2378
	21st to end	Night	55% 6% 10% 18% 11% 1	1884
March	1st to 10th	Night	57% 5% 9% 17% 9% 2	2280
	11th to 20th	Night	55% 4 10% 17% 11% 3	2123
	21st to end	Night	48% 5% 7% 20% 15% 4	2113
April	1st to 10th	Night	53% 5% 9% 17% 14% 2	1800
	11th to 20th	Night	48% 5% 9% 21% 16% 1	1775
	21st to end	Night	50% 5% 9% 17% 15% 3	1684
May	1st to 10th	Night	48% 5% 9% 18% 16% 5%	1440
	11th to 20th	Night	44% 5% 8% 20% 18% 4	1416
	21st to end	Night	41% 7% 14% 19% 17% 2	1551
June	1st to 10th	Night	45% 8% 13% 24% 10%	1440
	11th to 20th	Night	41% 8% 11% 22% 16% 2	1440
	21st to end	Night	43% 10% 13% 19% 14% 1	1440
July	1st to 10th	Night	34% 9% 13% 26% 16% 1	1400
	11th to 20th	Night	36% 7% 13% 31% 12% 1	1392
	21st to end	Night	37% 9% 16% 24% 14%	1486
August	1st to 10th	Night	36% 9% 20% 24% 11% 1	1422
	11th to 20th	Night	36% 7% 18% 27% 10%	1615
	21st to end	Night	36% 8% 17% 28% 10%	1980
September	1st to 10th	Night	38% 7% 12% 28% 14% 1	1800
	11th to 20th	Night	35% 7% 13% 34% 10% 1	1818
	21st to end	Night	41% 6% 12% 31% 10%	2006
October	1st to 10th	Night	47% 7% 10% 23% 12% 1	2160
	11th to 20th	Night	52% 8% 11% 20% 8%	2160
	21st to end	Night	57% 5% 13% 16% 8% 1	2548
November	1st to 10th	Night	51% 6% 14% 21% 9%	2407
	11th to 20th	Night	55% 6% 13% 16% 9% 1	2627
	21st to end	Night	60% 8% 12% 16% 5%	2660
December	1st to 10th	Night	67% 6% 10% 13% 4	2660
	11th to 20th	Night	61% 5% 9% 17% 7% 1	3288
	21st to end	Night	71% 4 8% 13% 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	27% 13% 31% 25% 3	180
	11th to 20th	Day	23% 19% 37% 17% 4 1	180
	21st to end	Day	21% 16% 35% 23% 5%	213
February	1st to 10th	Day	26% 26% 34% 12% 2	270
	11th to 20th	Day	25% 25% 36% 13% 1	296
	21st to end	Day	29% 17% 33% 19% 2	382
March	1st to 10th	Day	25% 16% 32% 20% 6%	460
	11th to 20th	Day	24% 19% 35% 18% 4 1	460
	21st to end	Day	29% 16% 31% 14% 8% 2	490
April	1st to 10th	Day	26% 19% 32% 15% 7% 1	420
	11th to 20th	Day	29% 19% 22% 19% 9% 2	412
	21st to end	Day	29% 16% 32% 15% 7% 2	420
May	1st to 10th	Day	23% 14% 35% 20% 6% 3	423
	11th to 20th	Day	19% 17% 32% 20% 9% 2	447
	21st to end	Day	18% 15% 34% 22% 9% 2	485
June	1st to 10th	Day	24% 12% 29% 24% 10% 1	450
	11th to 20th	Day	16% 14% 30% 24% 14% 2	450
	21st to end	Day	21% 11% 28% 24% 13% 2	450
July	1st to 10th	Day	13% 10% 27% 31% 15% 5%	445
	11th to 20th	Day	12% 9% 33% 25% 18% 3	444
	21st to end	Day	14% 7% 29% 31% 15% 3	488
August	1st to 10th	Day	13% 7% 26% 35% 15% 4	446
	11th to 20th	Day	13% 6% 21% 33% 18% 8%	439
	21st to end	Day	13% 11% 28% 25% 15% 8%	495
September	1st to 10th	Day	16% 9% 29% 21% 17% 8%	450
	11th to 20th	Day	13% 10% 23% 22% 20% 12%	450
	21st to end	Day	19% 12% 27% 22% 14% 6%	450
October	1st to 10th	Day	25% 14% 22% 22% 14% 3	450
	11th to 20th	Day	26% 19% 28% 17% 9% 1	450
	21st to end	Day	30% 14% 30% 21% 5%	408
November	1st to 10th	Day	26% 16% 26% 23% 8% 1	365
	11th to 20th	Day	27% 20% 34% 13% 4 1	209
	21st to end	Day	27% 20% 32% 16% 5% 1	180
December	1st to 10th	Day	31% 12% 31% 22% 4	180
	11th to 20th	Day	26% 18% 41% 13% 2 1	180
	21st to end	Day	34% 16% 36% 11% 3 1	198
January	1st to 10th	Night	28% 12% 35% 21% 5%	760
	11th to 20th	Night	28% 13% 30% 23% 6% 1	760
	21st to end	Night	19% 10% 35% 28% 6% 1	836
February	1st to 10th	Night	19% 12% 39% 25% 4	760
	11th to 20th	Night	21% 14% 38% 23% 4 1	743
	21st to end	Night	25% 13% 30% 29% 3	628
March	1st to 10th	Night	24% 13% 32% 26% 5%	760
	11th to 20th	Night	25% 13% 33% 23% 5%	760
	21st to end	Night	22% 11% 33% 24% 8%	821
April	1st to 10th	Night	26% 13% 29% 27% 5%	720
	11th to 20th	Night	23% 13% 33% 24% 7% 1	711
	21st to end	Night	26% 11% 31% 24% 7% 1	604
May	1st to 10th	Night	24% 10% 28% 27% 9% 2	360
	11th to 20th	Night	24% 9% 25% 32% 9% 1	354
	21st to end	Night	15% 6% 36% 29% 13% 1	389
June	1st to 10th	Night	17% 5% 28% 39% 11%	360
	11th to 20th	Night	16% 6% 27% 37% 13% 1	360
	21st to end	Night	17% 6% 26% 34% 15% 2	360
July	1st to 10th	Night	9% 4 29% 40% 19%	350
	11th to 20th	Night	13% 5% 18% 44% 20% 1	348
	21st to end	Night	10% 4 23% 43% 18% 2	394
August	1st to 10th	Night	12% 3 18% 46% 20% 1	358
	11th to 20th	Night	13% 3 19% 36% 26% 3	551
	21st to end	Night	13% 6% 23% 36% 20% 2	792
September	1st to 10th	Night	14% 5% 26% 34% 20% 1	720
	11th to 20th	Night	17% 7% 20% 32% 22% 3	720
	21st to end	Night	18% 8% 25% 28% 19% 2	720
October	1st to 10th	Night	21% 8% 27% 29% 14% 1	720
	11th to 20th	Night	25% 9% 28% 29% 8% 1	720
	21st to end	Night	27% 11% 30% 27% 6%	792
November	1st to 10th	Night	26% 10% 27% 28% 9% 1	740
	11th to 20th	Night	25% 14% 31% 19% 10% 1	760
	21st to end	Night	27% 15% 29% 24% 6%	760
December	1st to 10th	Night	29% 13% 32% 22% 4	760
	11th to 20th	Night	28% 14% 30% 22% 5% 1	760
	21st to end	Night	35% 12% 30% 19% 3	836

Page generated at 2024-03-24 23:37:04. Version ac07

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