Thetford Mines
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Thetford Mines clear sky chart from 2005-11-06 to 2024-01-22.

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% 12% 5% 8% 7% 3 5% 4 5% 6% 26%	74619
	Night	18% 13% 5% 9% 7% 3 5% 4 4 5% 28%	75300
Transparency	Day	59% 5% 10% 17% 8% 1	74324
	Night	59% 6% 10% 17% 8% 1	75130
Seeing	Day	28% 17% 29% 17% 7% 2	13983
	Night	26% 15% 28% 22% 8% 1	22790

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	15% 18% 10% 15% 9% 4 6% 4 3 4 12%	1517
	11th to 20th	Day	15% 19% 8% 12% 9% 4 4 3 3 3 20%	1520
	21st to end	Day	10% 13% 8% 11% 11% 4 7% 5% 4 5% 23%	1592
February	1st to 10th	Day	12% 19% 8% 13% 10% 5% 6% 4 3 4 16%	1463
	11th to 20th	Day	14% 19% 9% 12% 8% 4 5% 5% 4 5% 16%	1748
	21st to end	Day	13% 18% 7% 11% 8% 3 5% 5% 4 5% 20%	1480
March	1st to 10th	Day	14% 15% 6% 10% 9% 4 4 3 5% 5% 25%	1797
	11th to 20th	Day	17% 15% 7% 8% 6% 3 4 4 4 4 27%	1888
	21st to end	Day	17% 14% 6% 9% 9% 2 4 4 4 4 27%	2308
April	1st to 10th	Day	22% 15% 5% 8% 8% 3 4 3 3 5% 24%	2160
	11th to 20th	Day	20% 12% 4 6% 5% 3 4 4 4 5% 34%	2208
	21st to end	Day	22% 14% 4 7% 6% 3 4 4 4 6% 26%	2340
May	1st to 10th	Day	22% 10% 5% 6% 6% 3 5% 3 5% 5% 30%	2365
	11th to 20th	Day	21% 9% 3 7% 5% 3 5% 4 5% 7% 31%	2478
	21st to end	Day	21% 8% 3 7% 6% 4 6% 6% 6% 7% 27%	2725
June	1st to 10th	Day	25% 8% 3 6% 6% 4 5% 5% 5% 8% 26%	2632
	11th to 20th	Day	20% 6% 2 5% 6% 3 5% 6% 6% 9% 31%	2700
	21st to end	Day	25% 8% 4 8% 6% 4 4 5% 5% 6% 25%	2634
July	1st to 10th	Day	17% 8% 3 7% 6% 4 5% 6% 6% 8% 31%	2520
	11th to 20th	Day	18% 7% 4 6% 6% 4 5% 5% 7% 8% 30%	2520
	21st to end	Day	21% 8% 3 5% 5% 3 6% 6% 6% 9% 29%	2744
August	1st to 10th	Day	21% 7% 2 8% 7% 4 5% 5% 6% 9% 25%	2476
	11th to 20th	Day	18% 8% 3 6% 6% 3 5% 5% 6% 7% 31%	2304
	21st to end	Day	19% 7% 3 5% 6% 4 5% 5% 6% 7% 33%	2448
September	1st to 10th	Day	18% 8% 3 6% 5% 4 5% 5% 5% 7% 34%	2160
	11th to 20th	Day	21% 7% 2 5% 4 2 4 4 6% 6% 39%	1998
	21st to end	Day	20% 7% 3 5% 5% 3 4 5% 6% 9% 34%	1980
October	1st to 10th	Day	23% 11% 3 5% 5% 2 4 4 5% 7% 30%	1980
	11th to 20th	Day	23% 15% 4 8% 6% 4 5% 4 5% 5% 23%	1661
	21st to end	Day	26% 18% 5% 8% 6% 2 4 3 4 4 19%	1782
November	1st to 10th	Day	19% 16% 4 8% 6% 3 4 4 3 5% 28%	1671
	11th to 20th	Day	19% 16% 7% 11% 7% 3 3 4 4 5% 21%	1710
	21st to end	Day	19% 19% 6% 10% 7% 3 5% 4 4 5% 18%	1464
December	1st to 10th	Day	20% 22% 8% 12% 8% 3 3 2 4 3 15%	1330
	11th to 20th	Day	20% 17% 8% 10% 6% 4 4 3 3 3 21%	1668
	21st to end	Day	22% 19% 7% 12% 9% 3 4 3 2 3 15%	2648
January	1st to 10th	Night	14% 19% 8% 15% 10% 4 6% 3 3 3 14%	2649
	11th to 20th	Night	15% 17% 8% 13% 10% 4 5% 4 3 4 18%	2660
	21st to end	Night	9% 13% 6% 12% 10% 5% 7% 5% 6% 5% 21%	2798
February	1st to 10th	Night	12% 16% 7% 11% 11% 4 7% 4 4 4 20%	2493
	11th to 20th	Night	12% 18% 7% 13% 7% 4 6% 4 4 4 21%	2098
	21st to end	Night	13% 15% 7% 10% 8% 4 5% 4 4 4 27%	1776
March	1st to 10th	Night	14% 14% 6% 9% 8% 4 6% 4 5% 4 25%	2150
	11th to 20th	Night	15% 14% 5% 9% 7% 3 5% 5% 4 4 28%	2070
	21st to end	Night	17% 11% 4 9% 6% 4 5% 4 4 4 32%	2044
April	1st to 10th	Night	22% 13% 4 8% 5% 2 5% 5% 4 5% 27%	1800
	11th to 20th	Night	19% 9% 3 6% 6% 3 4 4 5% 6% 34%	1701
	21st to end	Night	23% 11% 4 6% 5% 3 5% 4 5% 5% 30%	1620
May	1st to 10th	Night	23% 9% 3 7% 5% 3 4 4 5% 6% 31%	1611
	11th to 20th	Night	18% 9% 3 6% 6% 2 5% 5% 4 7% 35%	1415
	21st to end	Night	21% 7% 3 6% 5% 3 4 4 6% 7% 35%	1550
June	1st to 10th	Night	23% 9% 3 6% 5% 3 5% 6% 4 7% 29%	1324
	11th to 20th	Night	19% 6% 3 5% 5% 3 5% 5% 6% 7% 36%	1260
	21st to end	Night	21% 7% 3 7% 6% 3 5% 6% 5% 8% 30%	1319
July	1st to 10th	Night	15% 6% 3 6% 6% 3 7% 5% 6% 8% 36%	1440
	11th to 20th	Night	14% 7% 4 5% 6% 3 6% 6% 7% 7% 36%	1440
	21st to end	Night	16% 7% 3 6% 6% 3 5% 6% 6% 8% 36%	1574
August	1st to 10th	Night	17% 5% 2 4 5% 3 5% 4 7% 10% 38%	1443
	11th to 20th	Night	17% 8% 3 6% 6% 3 4 5% 6% 7% 35%	1596
	21st to end	Night	17% 6% 3 6% 5% 3 4 3 6% 7% 42%	1904
September	1st to 10th	Night	19% 6% 3 6% 5% 2 5% 4 5% 7% 39%	1800
	11th to 20th	Night	17% 7% 3 4 4 2 4 5% 4 5% 45%	1962
	21st to end	Night	18% 7% 2 5% 4 3 4 4 4 7% 41%	1980
October	1st to 10th	Night	19% 8% 3 5% 5% 3 4 4 5% 7% 36%	1980
	11th to 20th	Night	22% 11% 3 6% 6% 4 5% 4 5% 6% 28%	2295
	21st to end	Night	25% 14% 5% 7% 6% 3 4 4 5% 4 24%	2574
November	1st to 10th	Night	20% 15% 5% 7% 5% 4 4 4 5% 5% 27%	2407
	11th to 20th	Night	18% 12% 6% 10% 7% 4 4 4 4 4 26%	2470
	21st to end	Night	17% 17% 7% 11% 8% 3 4 4 4 5% 22%	2708
December	1st to 10th	Night	21% 19% 8% 11% 8% 3 4 3 4 4 14%	2850
	11th to 20th	Night	19% 17% 8% 14% 8% 4 4 3 4 4 17%	3531
	21st to end	Night	21% 22% 6% 10% 6% 2 3 3 2 3 21%	5008

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	77% 4 6% 9% 4	1518
	11th to 20th	Day	72% 3 6% 13% 5% 1	1520
	21st to end	Day	64% 4 7% 15% 8% 2	1592
February	1st to 10th	Day	73% 3 6% 10% 6% 1	1463
	11th to 20th	Day	73% 3 8% 9% 7% 1	1757
	21st to end	Day	66% 4 7% 15% 6% 2	1480
March	1st to 10th	Day	63% 4 8% 14% 10% 2	1800
	11th to 20th	Day	61% 3 9% 14% 11% 1	1888
	21st to end	Day	62% 4 7% 15% 10% 2	2308
April	1st to 10th	Day	64% 4 9% 13% 8% 2	2160
	11th to 20th	Day	54% 4 10% 20% 12% 2	2208
	21st to end	Day	61% 4 8% 14% 10% 2	2340
May	1st to 10th	Day	56% 5% 8% 16% 13% 2	2365
	11th to 20th	Day	53% 5% 11% 19% 11% 1	2482
	21st to end	Day	55% 7% 10% 17% 11%	2725
June	1st to 10th	Day	56% 7% 10% 19% 7% 1	2632
	11th to 20th	Day	49% 7% 13% 21% 10% 1	2700
	21st to end	Day	59% 7% 9% 16% 8%	2634
July	1st to 10th	Day	49% 9% 13% 22% 6%	2450
	11th to 20th	Day	50% 8% 15% 21% 7%	2445
	21st to end	Day	52% 8% 13% 20% 6%	2591
August	1st to 10th	Day	55% 8% 15% 19% 3	2462
	11th to 20th	Day	50% 8% 14% 19% 9%	2304
	21st to end	Day	49% 6% 14% 22% 10%	2448
September	1st to 10th	Day	48% 7% 14% 21% 9% 1	2160
	11th to 20th	Day	45% 5% 12% 26% 12%	1998
	21st to end	Day	46% 8% 13% 23% 10%	1980
October	1st to 10th	Day	54% 5% 11% 22% 8%	1980
	11th to 20th	Day	64% 6% 12% 15% 3	1661
	21st to end	Day	69% 4 8% 14% 5% 1	1782
November	1st to 10th	Day	60% 5% 10% 17% 7%	1671
	11th to 20th	Day	66% 5% 9% 13% 6% 1	1710
	21st to end	Day	70% 6% 10% 11% 3	1464
December	1st to 10th	Day	76% 3 7% 9% 4	1330
	11th to 20th	Day	70% 4 6% 13% 7%	1668
	21st to end	Day	76% 4 4 9% 5% 1	2648
January	1st to 10th	Night	76% 3 6% 10% 4	2649
	11th to 20th	Night	72% 5% 6% 10% 6% 1	2660
	21st to end	Night	65% 5% 9% 12% 7% 2	2798
February	1st to 10th	Night	67% 4 8% 12% 7% 1	2493
	11th to 20th	Night	69% 4 7% 11% 7% 1	2100
	21st to end	Night	62% 4 7% 14% 11% 2	1776
March	1st to 10th	Night	62% 5% 8% 16% 8% 1	2160
	11th to 20th	Night	59% 6% 8% 12% 12% 2	2071
	21st to end	Night	56% 4 9% 18% 10% 3	2044
April	1st to 10th	Night	60% 4 9% 14% 11% 2	1800
	11th to 20th	Night	50% 6% 10% 20% 12% 2	1701
	21st to end	Night	56% 5% 10% 16% 11% 2	1620
May	1st to 10th	Night	55% 5% 9% 16% 14% 2	1611
	11th to 20th	Night	50% 6% 9% 19% 14% 1	1416
	21st to end	Night	48% 6% 12% 21% 12% 1	1551
June	1st to 10th	Night	53% 7% 12% 19% 8%	1324
	11th to 20th	Night	47% 6% 9% 24% 12% 2	1260
	21st to end	Night	53% 7% 12% 19% 8%	1319
July	1st to 10th	Night	44% 9% 16% 22% 8%	1400
	11th to 20th	Night	44% 8% 17% 22% 9%	1392
	21st to end	Night	47% 9% 14% 21% 8%	1486
August	1st to 10th	Night	41% 9% 17% 27% 5%	1433
	11th to 20th	Night	46% 9% 16% 21% 7%	1596
	21st to end	Night	42% 7% 13% 27% 10%	1904
September	1st to 10th	Night	45% 7% 14% 24% 9% 1	1800
	11th to 20th	Night	41% 7% 14% 29% 9% 1	1962
	21st to end	Night	43% 8% 11% 25% 13% 1	1980
October	1st to 10th	Night	49% 7% 9% 22% 13%	1980
	11th to 20th	Night	57% 6% 12% 20% 5%	2295
	21st to end	Night	62% 5% 11% 13% 8%	2574
November	1st to 10th	Night	59% 6% 12% 17% 6% 1	2407
	11th to 20th	Night	62% 4 11% 14% 8% 1	2470
	21st to end	Night	67% 5% 10% 13% 5%	2708
December	1st to 10th	Night	74% 4 9% 9% 3	2850
	11th to 20th	Night	72% 5% 6% 10% 6%	3532
	21st to end	Night	70% 3 7% 14% 6%	5008

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	32% 20% 36% 11% 2	180
	11th to 20th	Day	34% 23% 30% 11% 2	180
	21st to end	Day	24% 28% 30% 16% 2 1	178
February	1st to 10th	Day	40% 24% 26% 7% 2 1	180
	11th to 20th	Day	31% 26% 32% 9% 1	416
	21st to end	Day	33% 23% 26% 15% 3	346
March	1st to 10th	Day	28% 23% 31% 14% 4	420
	11th to 20th	Day	32% 23% 27% 13% 4 1	420
	21st to end	Day	31% 23% 27% 12% 7% 1	462
April	1st to 10th	Day	38% 20% 24% 11% 5% 2	420
	11th to 20th	Day	34% 20% 25% 14% 6% 1	412
	21st to end	Day	34% 22% 26% 12% 4 2	420
May	1st to 10th	Day	34% 16% 30% 14% 4 1	423
	11th to 20th	Day	26% 15% 32% 19% 6% 2	447
	21st to end	Day	24% 21% 34% 14% 6% 1	485
June	1st to 10th	Day	31% 15% 30% 16% 7% 1	562
	11th to 20th	Day	22% 15% 28% 24% 11% 1	630
	21st to end	Day	25% 13% 30% 21% 10% 2	564
July	1st to 10th	Day	21% 11% 31% 28% 8% 1	445
	11th to 20th	Day	19% 12% 41% 20% 9%	444
	21st to end	Day	24% 9% 34% 25% 7% 1	488
August	1st to 10th	Day	24% 13% 29% 22% 11% 2	446
	11th to 20th	Day	22% 9% 30% 27% 11% 2	439
	21st to end	Day	25% 13% 25% 19% 11% 6%	495
September	1st to 10th	Day	21% 15% 29% 22% 8% 5%	450
	11th to 20th	Day	25% 12% 23% 23% 12% 4	450
	21st to end	Day	22% 17% 25% 21% 10% 5%	450
October	1st to 10th	Day	26% 17% 27% 18% 10% 3	450
	11th to 20th	Day	32% 16% 28% 16% 8% 1	378
	21st to end	Day	40% 18% 22% 16% 3 1	396
November	1st to 10th	Day	34% 16% 29% 16% 4	365
	11th to 20th	Day	29% 21% 26% 16% 7% 1	370
	21st to end	Day	35% 21% 30% 12% 1	214
December	1st to 10th	Day	37% 17% 27% 13% 4 1	180
	11th to 20th	Day	37% 24% 26% 10% 3	180
	21st to end	Day	36% 23% 28% 11% 2 1	198
January	1st to 10th	Night	28% 22% 32% 15% 2 1	760
	11th to 20th	Night	29% 22% 30% 15% 5%	760
	21st to end	Night	20% 20% 35% 21% 4 1	800
February	1st to 10th	Night	22% 24% 32% 17% 4	720
	11th to 20th	Night	26% 21% 34% 15% 3	703
	21st to end	Night	26% 17% 33% 19% 5%	592
March	1st to 10th	Night	25% 18% 36% 18% 3	720
	11th to 20th	Night	26% 22% 31% 17% 4 1	720
	21st to end	Night	25% 16% 27% 25% 5% 1	792
April	1st to 10th	Night	32% 16% 27% 19% 5%	720
	11th to 20th	Night	27% 15% 30% 22% 7%	637
	21st to end	Night	31% 16% 27% 20% 6%	540
May	1st to 10th	Night	28% 13% 28% 24% 6% 1	531
	11th to 20th	Night	23% 8% 31% 30% 5% 1	354
	21st to end	Night	23% 8% 34% 26% 7% 1	389
June	1st to 10th	Night	26% 12% 26% 28% 8% 1	360
	11th to 20th	Night	22% 8% 25% 33% 12%	360
	21st to end	Night	22% 8% 30% 29% 11% 1	360
July	1st to 10th	Night	15% 6% 32% 34% 12% 1	350
	11th to 20th	Night	15% 6% 27% 39% 13% 1	348
	21st to end	Night	18% 7% 24% 41% 10%	394
August	1st to 10th	Night	19% 4 21% 37% 18% 1	369
	11th to 20th	Night	19% 7% 23% 33% 17% 1	532
	21st to end	Night	21% 7% 23% 29% 16% 3	716
September	1st to 10th	Night	21% 8% 26% 30% 13% 2	720
	11th to 20th	Night	22% 8% 23% 28% 18% 2	720
	21st to end	Night	23% 9% 28% 25% 14% 1	720
October	1st to 10th	Night	24% 12% 27% 25% 10% 1	720
	11th to 20th	Night	28% 15% 25% 21% 9% 2	720
	21st to end	Night	35% 16% 26% 19% 4	792
November	1st to 10th	Night	30% 17% 26% 21% 5%	740
	11th to 20th	Night	28% 18% 27% 17% 10% 1	760
	21st to end	Night	31% 19% 26% 18% 5%	801
December	1st to 10th	Night	34% 19% 26% 15% 5%	850
	11th to 20th	Night	30% 23% 25% 17% 5% 1	850
	21st to end	Night	36% 20% 26% 14% 4	870

Page generated at 2024-01-19 09:28:31. Version ac07

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