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 2024-08-15.

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% 13% 4 10% 6% 5% 4 4 5% 6% 26%	95314
	Night	17% 14% 5% 10% 6% 5% 4 3 4 5% 27%	93406
Transparency	Day	58% 6% 10% 17% 8% 1	95033
	Night	59% 6% 11% 16% 8% 1	93242
Seeing	Day	28% 18% 29% 17% 7% 2	14792
	Night	26% 15% 28% 22% 8% 1	23400

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	13% 18% 10% 17% 11% 6% 5% 3 4 3 11%	2517
	11th to 20th	Day	10% 17% 8% 22% 12% 6% 3 2 2 2 19%	2520
	21st to end	Day	9% 13% 9% 16% 8% 8% 5% 3 4 6% 18%	2772
February	1st to 10th	Day	12% 19% 7% 14% 9% 7% 5% 3 3 3 18%	1544
	11th to 20th	Day	13% 20% 8% 14% 7% 5% 5% 3 4 5% 16%	1848
	21st to end	Day	13% 19% 5% 12% 7% 5% 4 3 4 5% 20%	1570
March	1st to 10th	Day	17% 16% 6% 10% 7% 4 4 2 4 5% 24%	3116
	11th to 20th	Day	14% 23% 6% 14% 5% 4 4 2 3 3 21%	3318
	21st to end	Day	16% 16% 5% 11% 5% 3 3 2 3 4 31%	4056
April	1st to 10th	Day	21% 17% 4 10% 6% 4 3 3 4 5% 24%	2280
	11th to 20th	Day	19% 13% 4 7% 4 4 4 3 4 5% 33%	2333
	21st to end	Day	22% 14% 4 8% 5% 4 3 3 4 6% 27%	2470
May	1st to 10th	Day	21% 10% 4 8% 5% 5% 5% 3 5% 6% 27%	4159
	11th to 20th	Day	19% 9% 3 9% 5% 5% 5% 5% 6% 8% 26%	4398
	21st to end	Day	17% 8% 3 7% 6% 6% 6% 5% 6% 7% 28%	4837
June	1st to 10th	Day	24% 9% 2 6% 5% 5% 5% 4 5% 8% 26%	2779
	11th to 20th	Day	19% 6% 2 7% 5% 4 6% 5% 6% 9% 31%	2850
	21st to end	Day	25% 9% 3 8% 6% 5% 4 4 5% 6% 24%	2780
July	1st to 10th	Day	16% 8% 3 9% 6% 6% 6% 5% 6% 8% 28%	4440
	11th to 20th	Day	17% 8% 3 8% 6% 5% 5% 5% 6% 8% 29%	4440
	21st to end	Day	18% 7% 2 5% 4 4 5% 4 5% 7% 39%	4814
August	1st to 10th	Day	20% 7% 2 9% 6% 5% 5% 5% 6% 9% 25%	2614
	11th to 20th	Day	18% 8% 3 7% 6% 5% 4 4 6% 8% 31%	2359
	21st to end	Day	19% 7% 2 6% 5% 5% 5% 4 6% 7% 33%	2448
September	1st to 10th	Day	18% 9% 3 7% 4 5% 4 5% 5% 7% 34%	2160
	11th to 20th	Day	21% 8% 2 5% 3 3 4 3 6% 6% 39%	1998
	21st to end	Day	20% 7% 2 6% 4 4 5% 4 6% 9% 34%	1980
October	1st to 10th	Day	22% 11% 3 6% 4 3 4 4 4 7% 30%	1980
	11th to 20th	Day	23% 16% 3 8% 5% 5% 5% 3 5% 4 23%	1661
	21st to end	Day	26% 19% 5% 9% 4 3 4 2 4 4 19%	1782
November	1st to 10th	Day	19% 17% 4 9% 5% 4 3 3 3 4 28%	1671
	11th to 20th	Day	18% 18% 7% 12% 6% 3 3 3 4 5% 21%	1710
	21st to end	Day	19% 20% 6% 12% 6% 5% 4 3 4 5% 18%	1464
December	1st to 10th	Day	20% 24% 6% 14% 6% 3 3 2 4 3 15%	1330
	11th to 20th	Day	20% 18% 7% 11% 6% 5% 3 3 3 3 21%	1668
	21st to end	Day	22% 20% 7% 15% 6% 5% 3 2 2 3 15%	2648
January	1st to 10th	Night	13% 19% 9% 17% 8% 5% 4 2 4 3 15%	4429
	11th to 20th	Night	11% 18% 7% 18% 12% 6% 4 3 3 4 15%	4440
	21st to end	Night	9% 17% 8% 15% 8% 7% 6% 4 5% 4 18%	4884
February	1st to 10th	Night	11% 17% 6% 12% 9% 6% 5% 3 4 4 21%	2632
	11th to 20th	Night	11% 19% 7% 15% 7% 6% 6% 3 4 3 20%	2218
	21st to end	Night	13% 16% 6% 11% 7% 5% 4 3 4 4 27%	1884
March	1st to 10th	Night	21% 16% 4 8% 5% 4 6% 3 3 4 28%	3724
	11th to 20th	Night	13% 20% 7% 15% 6% 4 4 3 3 3 23%	3640
	21st to end	Night	16% 16% 4 11% 6% 5% 3 3 4 4 29%	3572
April	1st to 10th	Night	21% 15% 3 9% 4 3 4 3 4 5% 28%	1900
	11th to 20th	Night	19% 10% 3 7% 5% 4 3 4 5% 6% 32%	1796
	21st to end	Night	22% 12% 3 7% 4 3 5% 3 5% 5% 30%	1710
May	1st to 10th	Night	23% 8% 4 8% 6% 4 5% 3 5% 6% 28%	2811
	11th to 20th	Night	19% 10% 3 7% 5% 4 4 4 4 7% 33%	2495
	21st to end	Night	18% 7% 2 6% 4 4 5% 4 7% 9% 35%	2738
June	1st to 10th	Night	23% 10% 3 7% 5% 4 5% 4 4 7% 29%	1397
	11th to 20th	Night	18% 6% 3 5% 5% 4 5% 3 6% 8% 36%	1330
	21st to end	Night	22% 8% 2 7% 5% 5% 5% 4 5% 7% 29%	1393
July	1st to 10th	Night	13% 8% 4 8% 7% 5% 6% 5% 6% 7% 31%	2520
	11th to 20th	Night	20% 8% 3 7% 5% 4 4 4 5% 6% 34%	2520
	21st to end	Night	15% 7% 2 6% 4 4 4 4 6% 7% 41%	2739
August	1st to 10th	Night	18% 6% 2 5% 4 4 4 3 6% 10% 37%	1524
	11th to 20th	Night	16% 9% 3 7% 5% 4 5% 4 6% 7% 35%	1641
	21st to end	Night	17% 6% 3 6% 4 4 4 3 6% 7% 42%	1904
September	1st to 10th	Night	19% 7% 2 7% 4 3 4 3 5% 7% 39%	1800
	11th to 20th	Night	17% 7% 2 5% 3 3 4 4 4 5% 45%	1962
	21st to end	Night	18% 8% 2 6% 4 4 4 3 4 7% 41%	1980
October	1st to 10th	Night	19% 9% 2 6% 4 4 5% 3 5% 6% 36%	1980
	11th to 20th	Night	21% 11% 3 7% 5% 5% 5% 3 5% 6% 28%	2295
	21st to end	Night	24% 15% 4 7% 5% 4 4 3 5% 4 24%	2574
November	1st to 10th	Night	19% 16% 4 7% 5% 5% 4 3 5% 5% 27%	2407
	11th to 20th	Night	18% 14% 5% 11% 6% 5% 4 3 4 4 26%	2470
	21st to end	Night	17% 18% 7% 12% 7% 4 3 3 4 4 22%	2708
December	1st to 10th	Night	20% 20% 7% 13% 7% 4 4 2 4 4 14%	2850
	11th to 20th	Night	18% 18% 7% 16% 6% 5% 4 2 4 3 16%	3531
	21st to end	Night	21% 22% 5% 11% 5% 3 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	78% 5% 6% 9% 2	2518
	11th to 20th	Day	74% 3 4 14% 4 1	2520
	21st to end	Day	67% 6% 7% 11% 8% 1	2772
February	1st to 10th	Day	72% 4 6% 11% 7% 1	1544
	11th to 20th	Day	72% 3 8% 9% 7% 1	1857
	21st to end	Day	65% 5% 8% 14% 6% 2	1570
March	1st to 10th	Day	62% 6% 7% 13% 10% 2	3119
	11th to 20th	Day	69% 4 8% 11% 7% 1	3318
	21st to end	Day	58% 3 6% 16% 13% 3	4056
April	1st to 10th	Day	64% 4 8% 14% 8% 2	2280
	11th to 20th	Day	54% 4 9% 20% 12% 2	2333
	21st to end	Day	60% 4 8% 15% 11% 2	2470
May	1st to 10th	Day	55% 6% 10% 17% 10% 1	4173
	11th to 20th	Day	53% 9% 16% 15% 7% 1	4402
	21st to end	Day	51% 8% 10% 18% 12%	4837
June	1st to 10th	Day	55% 7% 10% 20% 6% 1	2779
	11th to 20th	Day	48% 6% 14% 20% 10% 1	2850
	21st to end	Day	60% 7% 9% 16% 8%	2780
July	1st to 10th	Day	52% 8% 13% 22% 6%	4370
	11th to 20th	Day	50% 8% 16% 22% 4	4365
	21st to end	Day	44% 7% 14% 28% 7%	4661
August	1st to 10th	Day	54% 8% 15% 20% 3	2600
	11th to 20th	Day	49% 8% 15% 19% 9%	2359
	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	73% 6% 8% 9% 3	4429
	11th to 20th	Night	74% 5% 6% 10% 3 1	4440
	21st to end	Night	68% 6% 8% 10% 7% 1	4884
February	1st to 10th	Night	66% 4 9% 12% 8% 1	2632
	11th to 20th	Night	70% 4 7% 11% 7% 1	2220
	21st to end	Night	61% 4 8% 14% 11% 2	1884
March	1st to 10th	Night	58% 7% 10% 14% 8% 2	3734
	11th to 20th	Night	67% 5% 7% 13% 7% 1	3641
	21st to end	Night	61% 3 7% 18% 9% 2	3572
April	1st to 10th	Night	59% 4 9% 15% 12% 2	1900
	11th to 20th	Night	51% 5% 10% 20% 12% 2	1796
	21st to end	Night	55% 5% 10% 16% 11% 2	1710
May	1st to 10th	Night	56% 6% 12% 16% 8% 1	2817
	11th to 20th	Night	49% 9% 11% 19% 10% 1	2496
	21st to end	Night	44% 7% 15% 18% 15% 1	2739
June	1st to 10th	Night	52% 7% 12% 20% 7%	1397
	11th to 20th	Night	46% 6% 11% 24% 12% 2	1330
	21st to end	Night	54% 7% 12% 19% 9%	1393
July	1st to 10th	Night	49% 8% 16% 19% 7%	2480
	11th to 20th	Night	48% 7% 19% 20% 6%	2472
	21st to end	Night	42% 7% 18% 26% 6%	2651
August	1st to 10th	Night	43% 9% 17% 27% 5%	1514
	11th to 20th	Night	46% 9% 16% 22% 7%	1641
	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% 24% 29% 11% 2	180
	21st to end	Day	23% 26% 32% 16% 2 1	198
February	1st to 10th	Day	38% 24% 27% 7% 2 1	201
	11th to 20th	Day	30% 28% 32% 10% 1	456
	21st to end	Day	32% 23% 27% 15% 3	382
March	1st to 10th	Day	29% 22% 30% 15% 4	460
	11th to 20th	Day	32% 24% 27% 12% 4 1	460
	21st to end	Day	31% 24% 27% 11% 7% 1	506
April	1st to 10th	Day	38% 20% 25% 11% 5% 2	460
	11th to 20th	Day	34% 21% 24% 13% 6% 1	452
	21st to end	Day	33% 23% 27% 12% 3 2	460
May	1st to 10th	Day	34% 16% 30% 15% 5% 1	463
	11th to 20th	Day	24% 15% 32% 19% 8% 2	487
	21st to end	Day	23% 21% 36% 14% 6% 1	529
June	1st to 10th	Day	30% 14% 29% 17% 9% 1	609
	11th to 20th	Day	22% 14% 29% 24% 10% 1	680
	21st to end	Day	27% 12% 30% 20% 9% 2	610
July	1st to 10th	Day	21% 13% 31% 27% 7% 1	485
	11th to 20th	Day	19% 13% 41% 19% 8%	484
	21st to end	Day	23% 10% 34% 26% 6% 2	532
August	1st to 10th	Day	23% 14% 29% 22% 10% 2	486
	11th to 20th	Day	21% 10% 29% 28% 11% 2	456
	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% 14% 5%	760
	21st to end	Night	19% 20% 35% 21% 4 1	836
February	1st to 10th	Night	22% 24% 33% 18% 5%	760
	11th to 20th	Night	25% 22% 35% 15% 3	743
	21st to end	Night	25% 17% 34% 19% 5%	628
March	1st to 10th	Night	26% 18% 35% 19% 3	760
	11th to 20th	Night	26% 21% 31% 18% 4 1	760
	21st to end	Night	25% 17% 28% 25% 5% 1	836
April	1st to 10th	Night	32% 16% 27% 20% 5%	760
	11th to 20th	Night	27% 15% 30% 21% 7%	672
	21st to end	Night	30% 16% 27% 20% 6%	570
May	1st to 10th	Night	28% 13% 29% 24% 6% 1	560
	11th to 20th	Night	23% 8% 31% 30% 6% 1	374
	21st to end	Night	23% 8% 34% 27% 7% 1	411
June	1st to 10th	Night	26% 12% 25% 28% 8% 1	380
	11th to 20th	Night	22% 8% 25% 33% 13%	380
	21st to end	Night	23% 8% 29% 29% 11% 1	380
July	1st to 10th	Night	15% 6% 32% 35% 12% 1	370
	11th to 20th	Night	15% 7% 26% 39% 13% 1	368
	21st to end	Night	18% 7% 24% 41% 10%	416
August	1st to 10th	Night	20% 4 20% 38% 18% 1	390
	11th to 20th	Night	19% 7% 23% 33% 18% 1	547
	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 2024-08-12 09:52:50. Version ac07

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