Thompson observing site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Thompson observing site clear sky chart from 2005-11-06 to 2024-10-24.

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	6% 5% 2 5% 4 4 4 4 6% 8% 52%	101376
	Night	6% 5% 2 5% 4 4 4 4 6% 8% 53%	97601
Transparency	Day	28% 8% 15% 27% 17% 4	101120
	Night	29% 8% 15% 27% 18% 4	97447
Seeing	Day	11% 16% 34% 27% 11% 2	15893
	Night	9% 16% 34% 31% 9% 1	25821

By Month

Percentage Cloud Cover SW (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	1 5% 2 6% 4 4 4 4 6% 9% 55%	2538
	11th to 20th	Day	1 5% 2 7% 5% 5% 4 4 6% 7% 53%	2540
	21st to end	Day	1 4 2 6% 4 4 3 4 5% 7% 58%	2794
February	1st to 10th	Day	3 9% 3 7% 5% 5% 5% 5% 6% 7% 43%	1691
	11th to 20th	Day	4 7% 4 8% 4 4 5% 5% 6% 8% 46%	1812
	21st to end	Day	3 7% 4 6% 6% 5% 5% 4 6% 7% 48%	1570
March	1st to 10th	Day	2 6% 2 5% 4 5% 4 4 5% 7% 54%	3130
	11th to 20th	Day	5% 6% 2 5% 3 2 3 3 5% 9% 56%	3251
	21st to end	Day	12% 12% 3 8% 4 4 4 3 5% 7% 37%	4165
April	1st to 10th	Day	11% 8% 2 4 4 3 4 4 6% 8% 45%	2280
	11th to 20th	Day	10% 8% 3 6% 5% 5% 6% 4 6% 7% 40%	2251
	21st to end	Day	12% 7% 2 6% 4 4 5% 3 6% 8% 42%	2426
May	1st to 10th	Day	14% 8% 3 8% 4 4 5% 4 6% 7% 37%	4213
	11th to 20th	Day	9% 5% 2 5% 3 4 5% 4 7% 9% 47%	4388
	21st to end	Day	14% 6% 2 5% 4 4 4 4 7% 9% 41%	4825
June	1st to 10th	Day	9% 4 1 4 4 4 5% 5% 7% 10% 47%	2660
	11th to 20th	Day	9% 3 2 4 4 4 5% 5% 7% 10% 48%	2660
	21st to end	Day	5% 3 2 4 3 3 4 4 6% 7% 61%	2660
July	1st to 10th	Day	4 3 1 4 4 4 6% 4 7% 10% 53%	4430
	11th to 20th	Day	3 2 1 4 3 4 4 4 7% 9% 60%	4430
	21st to end	Day	3 2 1 3 2 4 4 4 7% 9% 62%	4802
August	1st to 10th	Day	6% 3 1 5% 4 4 5% 5% 8% 9% 51%	4411
	11th to 20th	Day	6% 3 1 4 3 5% 5% 4 8% 10% 52%	3895
	21st to end	Day	5% 2 1 3 2 3 3 3 5% 7% 66%	4180
September	1st to 10th	Day	6% 3 1 4 2 3 3 2 5% 6% 63%	2280
	11th to 20th	Day	7% 3 1 3 3 3 3 3 5% 6% 63%	2195
	21st to end	Day	8% 4 1 3 3 3 2 3 4 6% 62%	2090
October	1st to 10th	Day	10% 5% 2 3 3 3 4 3 4 6% 56%	1999
	11th to 20th	Day	9% 6% 2 2 2 3 3 3 4 7% 58%	1857
	21st to end	Day	5% 5% 2 5% 3 4 4 3 5% 7% 57%	1809
November	1st to 10th	Day	4 4 2 4 3 3 4 3 7% 9% 57%	1673
	11th to 20th	Day	3 5% 2 5% 4 4 3 5% 5% 7% 56%	1710
	21st to end	Day	3 6% 2 6% 5% 3 4 4 5% 9% 54%	1521
December	1st to 10th	Day	1 5% 3 6% 5% 5% 4 5% 6% 8% 51%	1520
	11th to 20th	Day	2 4 1 4 3 4 5% 4 6% 9% 56%	1926
	21st to end	Day	6% 9% 3 6% 4 4 4 3 5% 6% 51%	2794
January	1st to 10th	Night	2 6% 3 6% 4 4 6% 5% 6% 7% 51%	4417
	11th to 20th	Night	1 4 2 8% 6% 7% 6% 4 6% 8% 49%	4430
	21st to end	Night	1 4 2 5% 5% 5% 5% 4 6% 8% 55%	4873
February	1st to 10th	Night	4 9% 4 8% 4 5% 4 4 7% 7% 45%	2506
	11th to 20th	Night	2 7% 3 6% 6% 5% 5% 4 6% 8% 47%	2253
	21st to end	Night	4 7% 3 6% 5% 4 5% 4 7% 8% 48%	1884
March	1st to 10th	Night	4 7% 2 7% 4 4 4 4 6% 8% 50%	3734
	11th to 20th	Night	5% 6% 2 5% 4 3 3 3 6% 10% 53%	3718
	21st to end	Night	10% 12% 3 8% 5% 4 4 3 6% 8% 38%	3477
April	1st to 10th	Night	11% 7% 2 5% 4 4 5% 4 5% 8% 46%	1900
	11th to 20th	Night	11% 7% 3 5% 4 4 4 3 5% 8% 48%	1877
	21st to end	Night	11% 6% 2 5% 3 4 5% 3 6% 8% 47%	1753
May	1st to 10th	Night	12% 7% 3 7% 4 4 4 4 5% 6% 45%	2742
	11th to 20th	Night	8% 4 1 4 3 3 4 4 6% 9% 53%	2517
	21st to end	Night	14% 6% 1 5% 3 4 5% 3 6% 8% 43%	2762
June	1st to 10th	Night	9% 4 1 4 3 4 4 3 6% 9% 52%	1520
	11th to 20th	Night	9% 4 1 4 4 3 5% 4 8% 9% 49%	1520
	21st to end	Night	6% 3 1 3 3 3 4 4 7% 8% 57%	1520
July	1st to 10th	Night	5% 3 1 3 4 3 3 4 6% 10% 59%	2540
	11th to 20th	Night	3 2 1 3 3 3 4 4 7% 11% 60%	2540
	21st to end	Night	3 2 1 3 3 4 4 4 6% 8% 61%	2761
August	1st to 10th	Night	7% 4 1 5% 4 4 6% 4 7% 8% 49%	2528
	11th to 20th	Night	5% 4 2 4 3 3 4 4 6% 10% 55%	2939
	21st to end	Night	3 2 1 5% 3 3 4 3 5% 6% 64%	3487
September	1st to 10th	Night	6% 3 1 3 3 2 4 2 4 7% 65%	1900
	11th to 20th	Night	6% 4 1 3 2 2 3 3 6% 7% 62%	1984
	21st to end	Night	11% 4 1 2 2 2 3 2 5% 5% 63%	2090
October	1st to 10th	Night	11% 6% 2 4 3 2 3 3 4 7% 55%	2179
	11th to 20th	Night	8% 5% 2 5% 2 3 3 3 6% 7% 57%	2302
	21st to end	Night	7% 6% 2 4 3 3 3 3 6% 8% 55%	2614
November	1st to 10th	Night	6% 5% 2 5% 3 4 5% 4 7% 8% 52%	2405
	11th to 20th	Night	4 6% 2 4 4 4 4 4 5% 6% 57%	2470
	21st to end	Night	4 5% 2 4 3 4 4 3 6% 8% 56%	2655
December	1st to 10th	Night	3 6% 2 5% 4 4 5% 3 5% 8% 54%	2660
	11th to 20th	Night	2 4 1 5% 4 4 4 4 6% 9% 56%	3271
	21st to end	Night	6% 9% 3 6% 4 4 4 3 5% 6% 49%	4873

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	24% 11% 21% 29% 14% 1	2539
	11th to 20th	Day	28% 9% 18% 28% 12% 5%	2540
	21st to end	Day	23% 10% 19% 32% 14% 1	2794
February	1st to 10th	Day	39% 10% 14% 21% 14% 2	1691
	11th to 20th	Day	36% 8% 16% 22% 14% 4	1822
	21st to end	Day	34% 6% 17% 25% 15% 3	1570
March	1st to 10th	Day	26% 7% 14% 23% 25% 5%	3130
	11th to 20th	Day	24% 7% 20% 34% 15% 1	3251
	21st to end	Day	45% 10% 17% 21% 6%	4165
April	1st to 10th	Day	36% 7% 19% 24% 11% 3	2280
	11th to 20th	Day	40% 8% 15% 22% 12% 2	2254
	21st to end	Day	39% 9% 17% 26% 9% 1	2426
May	1st to 10th	Day	42% 8% 16% 23% 9% 2	4213
	11th to 20th	Day	31% 8% 17% 29% 13% 3	4392
	21st to end	Day	36% 10% 16% 26% 11% 1	4825
June	1st to 10th	Day	29% 11% 20% 25% 12% 2	2660
	11th to 20th	Day	28% 9% 19% 26% 15% 3	2660
	21st to end	Day	20% 8% 15% 30% 22% 5%	2660
July	1st to 10th	Day	23% 8% 13% 31% 22% 3	4361
	11th to 20th	Day	18% 7% 12% 30% 25% 8%	4355
	21st to end	Day	16% 8% 12% 27% 28% 10%	4651
August	1st to 10th	Day	25% 10% 17% 20% 18% 9%	4396
	11th to 20th	Day	25% 9% 16% 28% 18% 4	3934
	21st to end	Day	19% 5% 11% 25% 28% 12%	4179
September	1st to 10th	Day	22% 5% 10% 26% 27% 10%	2280
	11th to 20th	Day	22% 6% 11% 29% 25% 8%	2195
	21st to end	Day	24% 5% 9% 33% 26% 4	2090
October	1st to 10th	Day	29% 7% 13% 23% 22% 5%	1999
	11th to 20th	Day	26% 5% 12% 30% 21% 5%	1857
	21st to end	Day	27% 7% 17% 28% 16% 5%	1809
November	1st to 10th	Day	23% 7% 16% 25% 22% 6%	1673
	11th to 20th	Day	26% 6% 13% 28% 21% 5%	1710
	21st to end	Day	27% 6% 15% 31% 17% 4	1521
December	1st to 10th	Day	30% 7% 17% 26% 18% 2	1520
	11th to 20th	Day	23% 9% 19% 35% 13% 2	1924
	21st to end	Day	35% 6% 10% 30% 18% 2	2794
January	1st to 10th	Night	30% 10% 14% 30% 14% 2	4417
	11th to 20th	Night	33% 8% 16% 27% 14% 2	4430
	21st to end	Night	23% 12% 17% 30% 15% 2	4873
February	1st to 10th	Night	36% 8% 17% 22% 14% 2	2506
	11th to 20th	Night	34% 8% 15% 25% 15% 4	2253
	21st to end	Night	33% 7% 14% 25% 14% 6%	1884
March	1st to 10th	Night	30% 7% 12% 26% 22% 2	3734
	11th to 20th	Night	27% 7% 19% 28% 18% 1	3718
	21st to end	Night	42% 10% 20% 20% 7% 1	3477
April	1st to 10th	Night	37% 9% 14% 24% 14% 3	1900
	11th to 20th	Night	36% 7% 13% 26% 16% 2	1877
	21st to end	Night	34% 8% 16% 27% 13% 1	1753
May	1st to 10th	Night	38% 8% 13% 23% 16% 2	2742
	11th to 20th	Night	25% 10% 16% 37% 11%	2518
	21st to end	Night	36% 9% 14% 28% 12% 1	2762
June	1st to 10th	Night	28% 10% 19% 29% 13% 2	1520
	11th to 20th	Night	30% 9% 21% 22% 14% 3	1520
	21st to end	Night	23% 9% 16% 26% 21% 5%	1520
July	1st to 10th	Night	20% 7% 16% 30% 24% 3	2500
	11th to 20th	Night	17% 7% 16% 32% 22% 6%	2492
	21st to end	Night	18% 7% 14% 30% 24% 7%	2674
August	1st to 10th	Night	29% 9% 15% 19% 19% 9%	2520
	11th to 20th	Night	24% 8% 19% 25% 19% 4	2966
	21st to end	Night	21% 6% 12% 24% 29% 8%	3487
September	1st to 10th	Night	20% 4 8% 29% 28% 10%	1900
	11th to 20th	Night	22% 6% 11% 27% 26% 8%	1984
	21st to end	Night	25% 4 9% 29% 25% 8%	2090
October	1st to 10th	Night	31% 6% 11% 24% 21% 6%	2179
	11th to 20th	Night	27% 6% 10% 27% 22% 7%	2302
	21st to end	Night	28% 6% 16% 25% 19% 6%	2614
November	1st to 10th	Night	30% 6% 16% 22% 20% 6%	2405
	11th to 20th	Night	27% 6% 13% 27% 22% 5%	2470
	21st to end	Night	26% 8% 14% 28% 19% 5%	2655
December	1st to 10th	Night	29% 7% 15% 29% 17% 3	2660
	11th to 20th	Night	23% 7% 16% 37% 15% 1	3272
	21st to end	Night	35% 7% 11% 31% 14% 2	4873

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	5% 16% 36% 26% 14% 3	270
	11th to 20th	Day	11% 19% 36% 22% 10% 2	270
	21st to end	Day	9% 30% 36% 19% 6% 1	297
February	1st to 10th	Day	12% 24% 43% 15% 6%	270
	11th to 20th	Day	11% 21% 45% 17% 5%	270
	21st to end	Day	8% 24% 47% 16% 3 1	225
March	1st to 10th	Day	6% 26% 43% 16% 7% 1	270
	11th to 20th	Day	10% 19% 39% 21% 9% 1	298
	21st to end	Day	20% 21% 33% 17% 7% 1	506
April	1st to 10th	Day	18% 22% 38% 18% 4	460
	11th to 20th	Day	21% 29% 35% 12% 2	452
	21st to end	Day	17% 19% 32% 24% 8% 1	606
May	1st to 10th	Day	18% 20% 30% 21% 9% 2	653
	11th to 20th	Day	20% 13% 29% 24% 11% 3	675
	21st to end	Day	17% 14% 35% 21% 10% 2	734
June	1st to 10th	Day	9% 11% 32% 32% 14% 3	680
	11th to 20th	Day	13% 15% 37% 26% 8% 1	680
	21st to end	Day	8% 11% 35% 31% 14% 2	680
July	1st to 10th	Day	4 6% 31% 41% 16% 2	671
	11th to 20th	Day	3 8% 35% 37% 16% 1	668
	21st to end	Day	5% 8% 28% 40% 17% 3	739
August	1st to 10th	Day	5% 7% 34% 38% 15% 2	676
	11th to 20th	Day	6% 6% 33% 39% 12% 3	556
	21st to end	Day	4 11% 32% 35% 15% 4	539
September	1st to 10th	Day	7% 9% 34% 33% 12% 5%	490
	11th to 20th	Day	8% 10% 29% 36% 14% 3	405
	21st to end	Day	13% 18% 32% 21% 12% 3	300
October	1st to 10th	Day	17% 12% 32% 22% 13% 4	300
	11th to 20th	Day	19% 21% 28% 18% 10% 4	300
	21st to end	Day	11% 24% 38% 20% 7% 1	306
November	1st to 10th	Day	11% 24% 33% 23% 7% 3	270
	11th to 20th	Day	11% 20% 41% 17% 10% 1	270
	21st to end	Day	10% 21% 33% 25% 10% 1	270
December	1st to 10th	Day	9% 23% 39% 20% 7% 1	270
	11th to 20th	Day	10% 21% 41% 22% 5%	270
	21st to end	Day	10% 23% 37% 25% 5% 1	297
January	1st to 10th	Night	7% 20% 38% 24% 10% 1	950
	11th to 20th	Night	7% 27% 36% 22% 7% 1	950
	21st to end	Night	6% 25% 38% 25% 5%	1045
February	1st to 10th	Night	8% 23% 40% 22% 7%	796
	11th to 20th	Night	8% 21% 38% 26% 8% 1	744
	21st to end	Night	8% 19% 39% 27% 7% 1	628
March	1st to 10th	Night	8% 19% 38% 29% 5% 1	760
	11th to 20th	Night	9% 13% 39% 32% 6% 1	744
	21st to end	Night	15% 15% 30% 31% 7% 1	627
April	1st to 10th	Night	15% 13% 37% 30% 5%	570
	11th to 20th	Night	18% 17% 37% 23% 5%	563
	21st to end	Night	14% 16% 29% 31% 9% 1	570
May	1st to 10th	Night	13% 12% 32% 30% 13% 1	570
	11th to 20th	Night	16% 10% 29% 32% 11% 1	561
	21st to end	Night	18% 10% 37% 25% 9%	617
June	1st to 10th	Night	10% 11% 33% 33% 13% 1	570
	11th to 20th	Night	11% 10% 38% 34% 6%	570
	21st to end	Night	7% 8% 33% 41% 11%	570
July	1st to 10th	Night	6% 5% 29% 43% 17% 1	555
	11th to 20th	Night	4 4 29% 51% 12% 1	552
	21st to end	Night	3 3 28% 51% 16%	624
August	1st to 10th	Night	6% 3 26% 49% 14% 1	567
	11th to 20th	Night	4 4 29% 46% 17% 1	564
	21st to end	Night	4 6% 25% 46% 18% 1	627
September	1st to 10th	Night	7% 6% 26% 43% 16% 2	570
	11th to 20th	Night	7% 9% 28% 41% 14% 1	570
	21st to end	Night	14% 10% 30% 33% 11% 1	570
October	1st to 10th	Night	14% 12% 28% 34% 11% 1	659
	11th to 20th	Night	11% 15% 33% 30% 10% 1	782
	21st to end	Night	12% 19% 33% 27% 8% 1	1006
November	1st to 10th	Night	8% 18% 37% 29% 6% 2	925
	11th to 20th	Night	10% 20% 35% 27% 6% 1	950
	21st to end	Night	7% 23% 37% 27% 5%	950
December	1st to 10th	Night	8% 25% 37% 25% 5%	950
	11th to 20th	Night	7% 20% 38% 27% 7% 1	950
	21st to end	Night	11% 23% 35% 24% 6%	1045

Page generated at 2024-10-21 00:20:00. Version ac07

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