Fort Severn
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fort Severn clear sky chart from 2005-11-06 to 2024-02-05.

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	15% 12% 5% 10% 8% 5% 7% 6% 6% 7% 20%	77233
	Night	12% 12% 6% 11% 9% 5% 7% 7% 7% 7% 17%	81659
Transparency	Day	61% 8% 11% 15% 5%	76894
	Night	63% 7% 11% 14% 4	81531
Seeing	Day	20% 8% 27% 28% 13% 4	14623
	Night	18% 6% 25% 32% 15% 3	23940

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	8% 8% 4 13% 12% 9% 13% 9% 7% 9% 6%	1899
	11th to 20th	Day	4 13% 8% 17% 10% 5% 9% 9% 10% 8% 7%	1900
	21st to end	Day	8% 18% 7% 14% 9% 5% 7% 8% 11% 8% 4	2500
February	1st to 10th	Day	4 10% 5% 9% 12% 8% 11% 11% 10% 9% 10%	1472
	11th to 20th	Day	3 7% 6% 9% 10% 5% 12% 10% 12% 10% 16%	1413
	21st to end	Day	3 7% 6% 9% 8% 4 10% 14% 11% 9% 19%	1426
March	1st to 10th	Day	5% 7% 5% 12% 10% 6% 9% 10% 9% 9% 17%	1798
	11th to 20th	Day	8% 8% 4 10% 9% 8% 11% 10% 10% 8% 15%	1843
	21st to end	Day	7% 10% 4 7% 8% 7% 12% 11% 9% 8% 17%	2376
April	1st to 10th	Day	7% 9% 5% 13% 11% 7% 10% 8% 5% 6% 18%	2160
	11th to 20th	Day	7% 9% 5% 10% 10% 8% 8% 5% 5% 6% 27%	2326
	21st to end	Day	10% 10% 6% 12% 12% 5% 6% 4 5% 7% 23%	2520
May	1st to 10th	Day	16% 14% 5% 14% 10% 3 4 3 4 6% 20%	2599
	11th to 20th	Day	15% 13% 8% 14% 7% 3 5% 5% 4 6% 21%	2657
	21st to end	Day	18% 13% 8% 10% 6% 3 5% 4 5% 6% 22%	3112
June	1st to 10th	Day	14% 11% 5% 9% 8% 4 4 4 6% 8% 27%	2880
	11th to 20th	Day	17% 9% 3 6% 5% 3 5% 4 6% 8% 34%	2880
	21st to end	Day	18% 9% 4 6% 5% 3 5% 4 5% 7% 33%	2880
July	1st to 10th	Day	19% 10% 4 6% 5% 4 6% 5% 6% 8% 27%	2880
	11th to 20th	Day	19% 8% 4 7% 6% 3 6% 6% 6% 8% 28%	2880
	21st to end	Day	21% 10% 4 7% 7% 4 5% 5% 5% 6% 25%	3092
August	1st to 10th	Day	25% 10% 3 7% 6% 3 4 4 5% 6% 27%	2517
	11th to 20th	Day	24% 10% 3 6% 6% 3 5% 5% 5% 7% 25%	2479
	21st to end	Day	24% 11% 4 7% 6% 3 5% 4 4 6% 26%	2659
September	1st to 10th	Day	26% 14% 4 8% 7% 3 6% 4 5% 6% 18%	2174
	11th to 20th	Day	26% 14% 4 9% 5% 3 4 3 5% 6% 20%	2084
	21st to end	Day	24% 15% 4 7% 6% 3 4 3 4 5% 24%	1980
October	1st to 10th	Day	25% 21% 5% 9% 6% 3 4 5% 4 4 13%	1803
	11th to 20th	Day	23% 23% 5% 9% 7% 4 4 3 4 5% 13%	1620
	21st to end	Day	17% 23% 7% 10% 8% 3 4 4 4 4 16%	1771
November	1st to 10th	Day	16% 19% 6% 11% 8% 4 7% 5% 4 5% 15%	1351
	11th to 20th	Day	11% 17% 10% 12% 7% 5% 7% 4 6% 6% 14%	1330
	21st to end	Day	11% 16% 7% 13% 9% 5% 8% 6% 5% 7% 12%	1306
December	1st to 10th	Day	9% 11% 6% 16% 13% 6% 6% 8% 8% 6% 12%	1140
	11th to 20th	Day	5% 13% 6% 12% 11% 7% 8% 7% 8% 9% 15%	1436
	21st to end	Day	7% 13% 7% 11% 10% 7% 11% 5% 9% 7% 13%	2090
January	1st to 10th	Night	6% 9% 5% 16% 16% 9% 11% 9% 8% 7% 5%	5057
	11th to 20th	Night	3 10% 7% 17% 15% 7% 10% 9% 8% 6% 8%	5070
	21st to end	Night	7% 15% 6% 15% 10% 6% 7% 9% 9% 8% 7%	5163
February	1st to 10th	Night	4 8% 5% 10% 11% 8% 14% 12% 11% 7% 10%	2583
	11th to 20th	Night	4 8% 5% 10% 9% 7% 12% 11% 13% 9% 13%	2431
	21st to end	Night	3 9% 5% 9% 8% 6% 9% 12% 12% 10% 19%	1830
March	1st to 10th	Night	4 8% 4 11% 9% 6% 10% 10% 11% 10% 17%	2149
	11th to 20th	Night	8% 9% 5% 9% 7% 6% 10% 10% 10% 9% 18%	2126
	21st to end	Night	7% 8% 4 8% 7% 7% 9% 11% 7% 7% 24%	1985
April	1st to 10th	Night	9% 12% 5% 12% 9% 6% 8% 7% 4 6% 23%	1800
	11th to 20th	Night	8% 11% 5% 8% 9% 7% 7% 5% 5% 6% 29%	1579
	21st to end	Night	9% 9% 5% 12% 9% 5% 6% 5% 6% 6% 28%	1440
May	1st to 10th	Night	14% 13% 7% 13% 9% 2 3 4 5% 4 26%	1360
	11th to 20th	Night	17% 13% 7% 11% 8% 2 4 3 4 5% 24%	1235
	21st to end	Night	19% 11% 7% 12% 6% 3 4 5% 5% 7% 21%	1164
June	1st to 10th	Night	18% 9% 7% 7% 6% 4 5% 6% 6% 7% 27%	1080
	11th to 20th	Night	20% 8% 4 7% 4 3 3 5% 7% 7% 32%	1080
	21st to end	Night	17% 9% 4 5% 7% 4 5% 5% 6% 6% 32%	1080
July	1st to 10th	Night	17% 11% 4 10% 9% 3 5% 5% 6% 6% 25%	1080
	11th to 20th	Night	17% 8% 5% 8% 5% 3 7% 6% 6% 7% 27%	1080
	21st to end	Night	19% 13% 3 7% 7% 4 5% 4 6% 9% 23%	1224
August	1st to 10th	Night	21% 11% 5% 7% 6% 4 4 5% 5% 6% 26%	1419
	11th to 20th	Night	24% 11% 5% 8% 7% 4 4 5% 4 6% 24%	1422
	21st to end	Night	24% 10% 3 7% 6% 2 4 4 5% 6% 28%	1697
September	1st to 10th	Night	22% 11% 4 8% 6% 4 5% 5% 5% 6% 25%	1783
	11th to 20th	Night	24% 15% 5% 7% 5% 3 4 4 5% 7% 22%	1858
	21st to end	Night	23% 14% 5% 7% 5% 2 4 3 5% 6% 26%	1980
October	1st to 10th	Night	26% 18% 5% 7% 6% 3 4 3 4 6% 18%	2154
	11th to 20th	Night	24% 20% 5% 8% 7% 3 4 3 3 5% 17%	2340
	21st to end	Night	20% 19% 6% 10% 7% 3 5% 4 4 5% 16%	2582
November	1st to 10th	Night	19% 17% 7% 11% 7% 5% 5% 5% 5% 5% 15%	2727
	11th to 20th	Night	10% 16% 8% 12% 9% 4 6% 6% 6% 5% 18%	2850
	21st to end	Night	12% 16% 8% 14% 8% 4 6% 5% 5% 8% 14%	2873
December	1st to 10th	Night	8% 15% 7% 15% 10% 5% 7% 7% 7% 7% 11%	3040
	11th to 20th	Night	5% 12% 6% 14% 12% 7% 8% 6% 7% 7% 14%	3761
	21st to end	Night	7% 13% 6% 13% 11% 7% 9% 8% 6% 5% 14%	5577

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	69% 9% 10% 9% 3	1900
	11th to 20th	Day	70% 6% 15% 7% 2	1900
	21st to end	Day	70% 6% 7% 10% 7%	2500
February	1st to 10th	Day	62% 8% 10% 14% 6%	1472
	11th to 20th	Day	55% 7% 15% 18% 5%	1421
	21st to end	Day	49% 8% 11% 21% 11%	1426
March	1st to 10th	Day	58% 6% 12% 18% 6%	1800
	11th to 20th	Day	58% 7% 13% 15% 6%	1843
	21st to end	Day	58% 7% 10% 17% 7% 1	2376
April	1st to 10th	Day	64% 5% 8% 16% 7%	2160
	11th to 20th	Day	57% 5% 10% 17% 10%	2326
	21st to end	Day	59% 6% 9% 16% 8% 1	2520
May	1st to 10th	Day	66% 6% 8% 15% 6%	2599
	11th to 20th	Day	64% 7% 8% 16% 4	2661
	21st to end	Day	62% 6% 12% 17% 4	3112
June	1st to 10th	Day	55% 8% 10% 17% 9%	2880
	11th to 20th	Day	47% 8% 14% 24% 7%	2880
	21st to end	Day	49% 9% 12% 22% 8%	2880
July	1st to 10th	Day	53% 11% 14% 19% 3	2801
	11th to 20th	Day	51% 11% 16% 18% 4	2793
	21st to end	Day	58% 11% 14% 14% 3	2920
August	1st to 10th	Day	57% 9% 17% 15% 1	2501
	11th to 20th	Day	57% 10% 16% 15% 3	2479
	21st to end	Day	59% 8% 11% 18% 3	2659
September	1st to 10th	Day	66% 9% 12% 11% 2	2174
	11th to 20th	Day	65% 6% 14% 13% 2	2084
	21st to end	Day	64% 6% 11% 16% 3	1980
October	1st to 10th	Day	73% 7% 9% 9% 2	1803
	11th to 20th	Day	76% 7% 10% 6% 1	1620
	21st to end	Day	71% 7% 9% 10% 2	1771
November	1st to 10th	Day	72% 7% 13% 7% 1	1351
	11th to 20th	Day	71% 8% 12% 8% 1	1330
	21st to end	Day	70% 8% 10% 11% 1	1306
December	1st to 10th	Day	68% 8% 9% 12% 3	1140
	11th to 20th	Day	61% 8% 11% 12% 7% 1	1436
	21st to end	Day	67% 6% 9% 15% 3	2090
January	1st to 10th	Night	74% 7% 10% 7% 2	5057
	11th to 20th	Night	70% 6% 13% 8% 3	5070
	21st to end	Night	69% 5% 8% 14% 5%	5163
February	1st to 10th	Night	63% 8% 9% 14% 6%	2583
	11th to 20th	Night	57% 8% 11% 20% 4	2433
	21st to end	Night	51% 6% 15% 18% 10%	1830
March	1st to 10th	Night	55% 8% 10% 20% 6% 1	2160
	11th to 20th	Night	56% 7% 11% 19% 7% 1	2127
	21st to end	Night	53% 7% 10% 18% 12% 1	1985
April	1st to 10th	Night	60% 5% 7% 18% 9% 1	1800
	11th to 20th	Night	55% 5% 8% 19% 12% 1	1579
	21st to end	Night	54% 6% 8% 19% 12%	1440
May	1st to 10th	Night	61% 4 8% 18% 9% 1	1360
	11th to 20th	Night	62% 6% 9% 14% 8%	1236
	21st to end	Night	62% 5% 11% 16% 6%	1164
June	1st to 10th	Night	55% 8% 8% 17% 10% 1	1080
	11th to 20th	Night	49% 6% 12% 22% 10% 1	1080
	21st to end	Night	51% 8% 10% 23% 8%	1080
July	1st to 10th	Night	60% 9% 8% 19% 4	1050
	11th to 20th	Night	52% 12% 12% 22% 2	1044
	21st to end	Night	57% 10% 15% 15% 3	1156
August	1st to 10th	Night	58% 11% 15% 17%	1411
	11th to 20th	Night	60% 9% 13% 15% 3	1422
	21st to end	Night	56% 9% 14% 17% 3 1	1697
September	1st to 10th	Night	58% 9% 17% 13% 3	1783
	11th to 20th	Night	64% 7% 13% 15% 1	1858
	21st to end	Night	60% 6% 12% 18% 4	1980
October	1st to 10th	Night	68% 7% 10% 12% 2	2154
	11th to 20th	Night	71% 7% 13% 8% 1	2340
	21st to end	Night	70% 9% 11% 8% 2	2582
November	1st to 10th	Night	71% 8% 10% 10% 1	2727
	11th to 20th	Night	65% 10% 13% 11% 1	2850
	21st to end	Night	69% 8% 10% 12% 1	2873
December	1st to 10th	Night	68% 8% 10% 12% 2	3040
	11th to 20th	Night	66% 7% 9% 14% 4 1	3760
	21st to end	Night	67% 7% 8% 14% 3	5577

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	11% 4 29% 36% 18% 3	180
	11th to 20th	Day	9% 9% 31% 31% 14% 6%	180
	21st to end	Day	8% 6% 24% 36% 18% 8%	271
February	1st to 10th	Day	6% 4 28% 38% 19% 4	252
	11th to 20th	Day	7% 6% 33% 35% 15% 3	240
	21st to end	Day	6% 4 28% 36% 20% 7%	198
March	1st to 10th	Day	8% 5% 26% 28% 19% 15%	240
	11th to 20th	Day	7% 7% 33% 32% 17% 4	272
	21st to end	Day	11% 9% 27% 29% 15% 9%	462
April	1st to 10th	Day	11% 5% 26% 34% 17% 7%	420
	11th to 20th	Day	12% 8% 26% 31% 17% 6%	429
	21st to end	Day	14% 7% 27% 30% 18% 5%	600
May	1st to 10th	Day	20% 8% 28% 26% 13% 4	603
	11th to 20th	Day	18% 10% 32% 27% 10% 2	625
	21st to end	Day	22% 10% 35% 24% 9% 1	679
June	1st to 10th	Day	20% 9% 30% 27% 11% 4	630
	11th to 20th	Day	19% 8% 30% 28% 13% 3	630
	21st to end	Day	21% 6% 30% 27% 12% 3	630
July	1st to 10th	Day	20% 8% 28% 28% 13% 4	621
	11th to 20th	Day	20% 7% 29% 27% 13% 4	618
	21st to end	Day	27% 5% 21% 27% 17% 4	684
August	1st to 10th	Day	28% 6% 24% 23% 14% 4	626
	11th to 20th	Day	27% 7% 20% 28% 12% 5%	615
	21st to end	Day	31% 5% 21% 27% 12% 4	580
September	1st to 10th	Day	35% 9% 23% 22% 10% 1	450
	11th to 20th	Day	28% 9% 25% 27% 9% 2	450
	21st to end	Day	30% 8% 29% 20% 12% 2	450
October	1st to 10th	Day	29% 13% 28% 22% 8% 1	298
	11th to 20th	Day	29% 11% 25% 17% 13% 4	270
	21st to end	Day	25% 12% 26% 26% 10% 2	297
November	1st to 10th	Day	25% 16% 22% 21% 12% 4	205
	11th to 20th	Day	17% 11% 29% 28% 13% 2	180
	21st to end	Day	22% 7% 31% 22% 12% 6%	180
December	1st to 10th	Day	16% 4 26% 34% 17% 3	180
	11th to 20th	Day	14% 7% 24% 30% 20% 4	180
	21st to end	Day	8% 6% 19% 41% 19% 7%	198
January	1st to 10th	Night	13% 6% 26% 35% 15% 5%	950
	11th to 20th	Night	11% 5% 28% 35% 17% 3	950
	21st to end	Night	10% 5% 26% 33% 20% 6%	1045
February	1st to 10th	Night	7% 6% 25% 40% 21% 2	923
	11th to 20th	Night	7% 4 26% 39% 19% 5%	879
	21st to end	Night	6% 5% 23% 34% 24% 7%	646
March	1st to 10th	Night	8% 4 22% 39% 23% 4	720
	11th to 20th	Night	12% 8% 30% 35% 14% 2	720
	21st to end	Night	11% 10% 21% 34% 19% 6%	599
April	1st to 10th	Night	13% 5% 24% 37% 15% 6%	540
	11th to 20th	Night	14% 4 23% 37% 19% 3	533
	21st to end	Night	13% 5% 25% 36% 17% 3	540
May	1st to 10th	Night	20% 7% 23% 32% 16% 2	460
	11th to 20th	Night	22% 7% 30% 31% 10%	354
	21st to end	Night	24% 6% 29% 30% 9% 1	389
June	1st to 10th	Night	23% 6% 28% 30% 12%	360
	11th to 20th	Night	23% 5% 26% 33% 13% 1	360
	21st to end	Night	18% 6% 25% 37% 13% 1	360
July	1st to 10th	Night	21% 6% 22% 38% 13%	350
	11th to 20th	Night	20% 3 24% 36% 15% 2	348
	21st to end	Night	24% 4 20% 35% 16% 1	394
August	1st to 10th	Night	26% 4 19% 31% 18% 2	524
	11th to 20th	Night	30% 4 17% 31% 16% 1	534
	21st to end	Night	31% 3 20% 33% 12% 1	594
September	1st to 10th	Night	27% 7% 25% 27% 13% 1	540
	11th to 20th	Night	32% 7% 26% 25% 10% 1	598
	21st to end	Night	30% 7% 25% 26% 11% 1	720
October	1st to 10th	Night	37% 8% 26% 23% 4 1	720
	11th to 20th	Night	35% 6% 20% 25% 12% 2	720
	21st to end	Night	27% 9% 27% 22% 12% 3	800
November	1st to 10th	Night	26% 9% 24% 25% 13% 3	925
	11th to 20th	Night	17% 9% 30% 30% 11% 3	950
	21st to end	Night	20% 9% 31% 27% 10% 3	950
December	1st to 10th	Night	14% 8% 34% 32% 9% 2	950
	11th to 20th	Night	12% 7% 24% 34% 19% 4	950
	21st to end	Night	12% 6% 24% 34% 18% 6%	1045

Page generated at 2024-02-02 05:20:31. Version ac07

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