Churchill
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Churchill clear sky chart from 2005-11-06 to 2024-01-12.

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	14% 9% 4 8% 7% 4 5% 5% 6% 7% 31%	75057
	Night	15% 10% 4 8% 7% 4 5% 5% 5% 7% 31%	74650
Transparency	Day	51% 5% 12% 20% 10% 1	74769
	Night	52% 6% 12% 19% 10% 1	74473
Seeing	Day	19% 8% 28% 25% 15% 6%	13657
	Night	19% 8% 29% 30% 12% 1	22773

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% 14% 6% 10% 10% 6% 7% 6% 6% 5% 18%	1517
	11th to 20th	Day	16% 16% 8% 10% 10% 4 5% 6% 5% 7% 15%	1572
	21st to end	Day	11% 14% 8% 12% 11% 6% 5% 5% 6% 6% 17%	1782
February	1st to 10th	Day	13% 15% 6% 13% 10% 5% 7% 5% 5% 4 16%	1620
	11th to 20th	Day	13% 12% 6% 11% 9% 4 6% 6% 5% 6% 23%	1573
	21st to end	Day	15% 15% 6% 11% 8% 4 5% 5% 4 5% 22%	1372
March	1st to 10th	Day	13% 10% 5% 10% 9% 4 6% 5% 4 6% 29%	1977
	11th to 20th	Day	12% 12% 6% 9% 7% 3 5% 5% 5% 5% 31%	1980
	21st to end	Day	18% 8% 4 8% 6% 3 4 4 5% 5% 35%	2178
April	1st to 10th	Day	17% 12% 4 9% 7% 4 5% 5% 5% 5% 29%	2124
	11th to 20th	Day	19% 9% 4 5% 5% 3 4 5% 5% 7% 35%	2222
	21st to end	Day	19% 8% 4 8% 6% 3 4 4 4 7% 34%	2340
May	1st to 10th	Day	16% 8% 4 7% 6% 4 4 5% 5% 6% 36%	2340
	11th to 20th	Day	14% 6% 3 6% 5% 3 5% 5% 6% 7% 40%	2473
	21st to end	Day	12% 5% 3 5% 6% 3 5% 5% 6% 8% 44%	2725
June	1st to 10th	Day	16% 7% 3 5% 5% 3 5% 6% 6% 7% 39%	2520
	11th to 20th	Day	12% 5% 2 5% 5% 3 5% 5% 7% 8% 42%	2600
	21st to end	Day	13% 6% 2 6% 6% 4 6% 4 5% 9% 40%	2700
July	1st to 10th	Day	9% 5% 2 5% 6% 3 6% 5% 6% 9% 45%	2660
	11th to 20th	Day	10% 6% 3 5% 6% 3 6% 5% 7% 8% 41%	2520
	21st to end	Day	9% 6% 3 6% 6% 4 6% 6% 7% 9% 37%	2590
August	1st to 10th	Day	9% 6% 2 5% 7% 4 5% 6% 7% 9% 40%	2327
	11th to 20th	Day	7% 5% 3 6% 6% 4 6% 6% 8% 10% 39%	2303
	21st to end	Day	12% 6% 2 6% 6% 4 5% 5% 7% 9% 39%	2492
September	1st to 10th	Day	13% 7% 3 6% 5% 4 5% 5% 5% 8% 40%	2160
	11th to 20th	Day	12% 6% 2 6% 6% 4 5% 4 6% 9% 41%	2048
	21st to end	Day	13% 6% 3 7% 6% 4 6% 5% 6% 8% 35%	1947
October	1st to 10th	Day	18% 9% 3 7% 6% 3 5% 5% 6% 7% 32%	1800
	11th to 20th	Day	19% 10% 4 8% 7% 4 5% 6% 5% 6% 25%	1800
	21st to end	Day	25% 13% 4 10% 6% 3 5% 4 5% 6% 19%	1980
November	1st to 10th	Day	15% 12% 4 7% 6% 4 5% 6% 7% 7% 27%	1577
	11th to 20th	Day	13% 16% 3 10% 9% 5% 5% 6% 6% 6% 21%	1520
	21st to end	Day	19% 15% 6% 10% 8% 4 5% 4 5% 6% 17%	1520
December	1st to 10th	Day	15% 18% 8% 14% 8% 5% 5% 5% 5% 7% 11%	1520
	11th to 20th	Day	17% 13% 6% 11% 8% 5% 6% 6% 5% 6% 18%	1906
	21st to end	Day	26% 17% 6% 13% 8% 3 4 4 3 4 11%	2772
January	1st to 10th	Night	15% 15% 7% 10% 10% 5% 6% 5% 6% 6% 17%	2649
	11th to 20th	Night	17% 14% 7% 11% 11% 5% 7% 5% 5% 5% 15%	2424
	21st to end	Night	11% 13% 7% 11% 10% 6% 6% 6% 6% 6% 19%	2574
February	1st to 10th	Night	12% 16% 6% 11% 9% 4 7% 6% 5% 6% 18%	2340
	11th to 20th	Night	13% 14% 6% 10% 7% 5% 6% 6% 5% 6% 22%	2273
	21st to end	Night	14% 12% 5% 11% 8% 4 5% 4 5% 6% 25%	1882
March	1st to 10th	Night	13% 10% 5% 8% 8% 4 5% 4 4 6% 33%	1970
	11th to 20th	Night	14% 11% 5% 8% 7% 3 4 4 4 5% 35%	1979
	21st to end	Night	16% 9% 4 7% 6% 3 5% 5% 4 5% 37%	2178
April	1st to 10th	Night	18% 10% 4 7% 6% 3 5% 4 5% 6% 31%	1836
	11th to 20th	Night	17% 7% 3 6% 5% 3 5% 5% 5% 8% 36%	1703
	21st to end	Night	17% 9% 4 7% 6% 3 4 5% 4 6% 35%	1620
May	1st to 10th	Night	17% 6% 2 5% 5% 3 5% 4 6% 8% 39%	1620
	11th to 20th	Night	13% 6% 3 5% 4 3 4 4 5% 7% 45%	1420
	21st to end	Night	9% 4 2 5% 4 2 5% 5% 5% 8% 51%	1550
June	1st to 10th	Night	13% 4 3 6% 5% 4 5% 5% 5% 8% 41%	1440
	11th to 20th	Night	10% 3 2 6% 7% 3 5% 7% 5% 8% 44%	1353
	21st to end	Night	10% 5% 3 6% 6% 4 5% 5% 5% 8% 44%	1260
July	1st to 10th	Night	5% 4 3 6% 5% 3 4 5% 5% 7% 55%	1296
	11th to 20th	Night	9% 6% 2 5% 4 3 5% 5% 6% 9% 48%	1440
	21st to end	Night	8% 4 3 4 5% 3 6% 5% 6% 8% 48%	1726
August	1st to 10th	Night	8% 4 2 5% 5% 4 4 4 7% 9% 48%	1611
	11th to 20th	Night	7% 4 2 4 5% 3 4 5% 7% 10% 50%	1598
	21st to end	Night	11% 5% 3 4 6% 3 6% 5% 6% 8% 44%	1844
September	1st to 10th	Night	11% 6% 3 5% 6% 3 5% 5% 7% 8% 45%	1800
	11th to 20th	Night	12% 5% 2 5% 4 2 3 4 7% 8% 48%	1908
	21st to end	Night	14% 7% 3 6% 6% 3 4 5% 4 6% 42%	2011
October	1st to 10th	Night	18% 7% 3 6% 6% 3 4 5% 6% 7% 35%	2160
	11th to 20th	Night	18% 11% 4 6% 6% 4 5% 5% 5% 6% 29%	2160
	21st to end	Night	22% 12% 4 7% 7% 4 4 5% 5% 6% 23%	2376
November	1st to 10th	Night	18% 8% 3 7% 6% 3 5% 5% 5% 7% 32%	2497
	11th to 20th	Night	15% 14% 6% 9% 6% 4 5% 6% 5% 7% 24%	2660
	21st to end	Night	18% 14% 6% 9% 6% 5% 5% 5% 5% 7% 20%	2660
December	1st to 10th	Night	18% 16% 8% 12% 8% 4 6% 4 5% 6% 16%	2660
	11th to 20th	Night	15% 15% 6% 12% 8% 5% 6% 4 6% 6% 17%	3288
	21st to end	Night	27% 17% 7% 14% 7% 3 4 4 4 5% 9%	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	65% 6% 12% 13% 4	1518
	11th to 20th	Day	69% 6% 10% 9% 6% 1	1572
	21st to end	Day	66% 5% 9% 13% 6% 1	1782
February	1st to 10th	Day	70% 5% 8% 14% 3	1620
	11th to 20th	Day	63% 4 10% 16% 6% 1	1582
	21st to end	Day	64% 3 9% 16% 7% 1	1372
March	1st to 10th	Day	55% 5% 13% 16% 10% 1	1980
	11th to 20th	Day	55% 4 11% 17% 12% 2	1980
	21st to end	Day	51% 4 10% 18% 15% 2	2178
April	1st to 10th	Day	57% 4 9% 19% 10% 1	2124
	11th to 20th	Day	48% 5% 9% 23% 15% 1	2222
	21st to end	Day	51% 4 12% 19% 12% 3	2340
May	1st to 10th	Day	48% 4 10% 21% 15% 2	2340
	11th to 20th	Day	42% 6% 10% 26% 15% 1	2477
	21st to end	Day	38% 5% 16% 24% 14% 3	2725
June	1st to 10th	Day	42% 6% 13% 23% 15% 1	2520
	11th to 20th	Day	38% 6% 13% 25% 17% 1	2600
	21st to end	Day	42% 6% 13% 25% 14% 1	2700
July	1st to 10th	Day	35% 6% 14% 26% 18% 2	2588
	11th to 20th	Day	38% 6% 14% 29% 11% 1	2445
	21st to end	Day	40% 8% 14% 24% 12% 1	2445
August	1st to 10th	Day	38% 6% 18% 25% 12% 2	2314
	11th to 20th	Day	37% 7% 19% 27% 10%	2303
	21st to end	Day	40% 6% 16% 26% 11% 1	2492
September	1st to 10th	Day	42% 6% 14% 27% 10% 2	2160
	11th to 20th	Day	40% 5% 14% 28% 12% 1	2048
	21st to end	Day	46% 6% 14% 26% 7% 1	1947
October	1st to 10th	Day	51% 4 13% 19% 11% 1	1800
	11th to 20th	Day	58% 5% 13% 17% 6% 1	1800
	21st to end	Day	65% 5% 13% 11% 5%	1980
November	1st to 10th	Day	53% 7% 14% 18% 7% 1	1577
	11th to 20th	Day	60% 7% 13% 13% 7% 1	1520
	21st to end	Day	68% 6% 12% 12% 2	1520
December	1st to 10th	Day	73% 5% 12% 9% 1	1520
	11th to 20th	Day	66% 8% 11% 12% 3	1906
	21st to end	Day	78% 4 8% 8% 1	2772
January	1st to 10th	Night	65% 7% 11% 12% 4	2649
	11th to 20th	Night	70% 6% 10% 8% 4 1	2424
	21st to end	Night	63% 5% 10% 14% 5% 1	2574
February	1st to 10th	Night	65% 5% 10% 16% 4	2340
	11th to 20th	Night	61% 5% 11% 17% 6%	2275
	21st to end	Night	58% 6% 12% 16% 8%	1882
March	1st to 10th	Night	53% 5% 12% 19% 9% 1	1980
	11th to 20th	Night	52% 4 10% 22% 11% 2	1980
	21st to end	Night	48% 4 10% 21% 14% 2	2178
April	1st to 10th	Night	54% 4 10% 19% 12% 1	1836
	11th to 20th	Night	47% 4 10% 21% 16% 2	1703
	21st to end	Night	50% 5% 10% 18% 15% 2	1620
May	1st to 10th	Night	43% 5% 11% 21% 17% 3	1620
	11th to 20th	Night	39% 4 11% 25% 18% 3	1421
	21st to end	Night	31% 5% 17% 26% 17% 4	1551
June	1st to 10th	Night	41% 5% 11% 25% 16% 2	1440
	11th to 20th	Night	36% 7% 12% 24% 20% 2	1353
	21st to end	Night	38% 7% 13% 27% 15% 1	1260
July	1st to 10th	Night	29% 5% 11% 30% 22% 3	1259
	11th to 20th	Night	33% 5% 12% 33% 16% 1	1392
	21st to end	Night	32% 7% 14% 30% 15% 2	1630
August	1st to 10th	Night	31% 6% 18% 31% 14% 1	1600
	11th to 20th	Night	28% 6% 18% 31% 16% 1	1598
	21st to end	Night	36% 7% 14% 27% 14% 1	1844
September	1st to 10th	Night	35% 7% 16% 28% 13% 2	1800
	11th to 20th	Night	32% 6% 13% 32% 15% 1	1908
	21st to end	Night	44% 4 13% 27% 11%	2011
October	1st to 10th	Night	47% 7% 12% 20% 13% 1	2160
	11th to 20th	Night	53% 7% 13% 20% 7%	2160
	21st to end	Night	61% 6% 10% 15% 8%	2376
November	1st to 10th	Night	50% 6% 12% 22% 8% 1	2497
	11th to 20th	Night	58% 6% 13% 15% 7% 1	2660
	21st to end	Night	63% 7% 15% 14% 2	2660
December	1st to 10th	Night	68% 6% 12% 11% 3	2660
	11th to 20th	Night	66% 7% 12% 12% 3	3288
	21st to end	Night	79% 4 9% 7% 2	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	17% 13% 36% 24% 9% 2	180
	11th to 20th	Day	23% 10% 37% 21% 7% 2	217
	21st to end	Day	20% 11% 39% 22% 6% 1	264
February	1st to 10th	Day	19% 13% 48% 15% 4	240
	11th to 20th	Day	20% 18% 39% 22% 1	240
	21st to end	Day	26% 21% 34% 17% 1	202
March	1st to 10th	Day	20% 9% 40% 24% 8%	420
	11th to 20th	Day	20% 11% 36% 25% 8% 1	420
	21st to end	Day	27% 7% 33% 23% 9% 1	462
April	1st to 10th	Day	22% 12% 35% 20% 9% 2	420
	11th to 20th	Day	29% 9% 26% 18% 13% 5%	412
	21st to end	Day	25% 9% 27% 25% 11% 3	420
May	1st to 10th	Day	21% 6% 25% 29% 14% 5%	423
	11th to 20th	Day	18% 6% 25% 28% 17% 7%	447
	21st to end	Day	15% 4 24% 29% 20% 8%	485
June	1st to 10th	Day	16% 6% 25% 30% 19% 4	450
	11th to 20th	Day	16% 6% 22% 29% 22% 5%	530
	21st to end	Day	17% 5% 27% 31% 15% 6%	630
July	1st to 10th	Day	11% 3 21% 34% 24% 7%	583
	11th to 20th	Day	12% 2 21% 30% 25% 10%	444
	21st to end	Day	10% 3 17% 40% 20% 9%	488
August	1st to 10th	Day	11% 2 17% 28% 28% 15%	446
	11th to 20th	Day	8% 3 17% 29% 28% 15%	439
	21st to end	Day	14% 4 23% 28% 21% 11%	495
September	1st to 10th	Day	14% 6% 21% 25% 23% 12%	450
	11th to 20th	Day	12% 3 21% 26% 22% 16%	450
	21st to end	Day	14% 7% 27% 24% 20% 9%	450
October	1st to 10th	Day	23% 5% 26% 22% 14% 10%	450
	11th to 20th	Day	23% 12% 34% 22% 8% 1	450
	21st to end	Day	31% 12% 29% 21% 7%	495
November	1st to 10th	Day	23% 16% 30% 19% 11% 1	237
	11th to 20th	Day	24% 16% 33% 20% 6% 2	180
	21st to end	Day	29% 10% 40% 17% 4	180
December	1st to 10th	Day	23% 14% 37% 21% 4 1	180
	11th to 20th	Day	21% 19% 36% 17% 4 2	180
	21st to end	Day	27% 11% 42% 18% 3	198
January	1st to 10th	Night	22% 12% 38% 21% 7% 1	760
	11th to 20th	Night	23% 11% 33% 26% 7% 1	728
	21st to end	Night	18% 9% 32% 30% 9% 1	792
February	1st to 10th	Night	21% 11% 40% 25% 3	720
	11th to 20th	Night	20% 11% 37% 26% 5%	703
	21st to end	Night	21% 11% 35% 29% 4	592
March	1st to 10th	Night	19% 11% 36% 28% 7%	720
	11th to 20th	Night	19% 11% 35% 27% 7% 1	720
	21st to end	Night	21% 8% 31% 29% 11%	792
April	1st to 10th	Night	23% 10% 32% 30% 5%	720
	11th to 20th	Night	19% 8% 33% 28% 10% 2	639
	21st to end	Night	22% 6% 27% 32% 12%	540
May	1st to 10th	Night	19% 3 24% 36% 15% 2	540
	11th to 20th	Night	16% 4 28% 37% 13% 1	359
	21st to end	Night	10% 5% 23% 43% 18% 1	389
June	1st to 10th	Night	14% 4 27% 39% 14% 1	360
	11th to 20th	Night	11% 6% 22% 43% 18% 1	360
	21st to end	Night	12% 3 21% 42% 20% 2	360
July	1st to 10th	Night	7% 4 15% 48% 25% 2	350
	11th to 20th	Night	11% 3 21% 40% 23% 2	348
	21st to end	Night	10% 2 19% 42% 25% 1	546
August	1st to 10th	Night	12% 2 14% 42% 29% 2	537
	11th to 20th	Night	7% 2 13% 40% 34% 4	534
	21st to end	Night	14% 3 20% 34% 26% 3	656
September	1st to 10th	Night	12% 4 21% 34% 23% 6%	720
	11th to 20th	Night	14% 3 20% 32% 23% 7%	720
	21st to end	Night	17% 7% 19% 33% 19% 4	720
October	1st to 10th	Night	20% 5% 28% 27% 17% 3	720
	11th to 20th	Night	23% 9% 30% 27% 9% 1	720
	21st to end	Night	31% 8% 30% 24% 7%	792
November	1st to 10th	Night	23% 9% 29% 27% 11% 1	740
	11th to 20th	Night	21% 15% 33% 22% 8% 1	760
	21st to end	Night	27% 12% 31% 24% 5%	760
December	1st to 10th	Night	26% 13% 36% 19% 5% 1	760
	11th to 20th	Night	22% 14% 37% 22% 5%	760
	21st to end	Night	29% 10% 34% 22% 4	836

Page generated at 2024-01-09 16:24:27. Version ac07

Copyright 2024 Attilla Danko