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 2024-11-08.

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% 10% 4 9% 6% 5% 5% 4 6% 7% 32%	102015
	Night	14% 11% 4 9% 6% 5% 5% 4 5% 6% 31%	97075
Transparency	Day	50% 5% 13% 21% 10% 1	105616
	Night	50% 6% 13% 20% 10% 1	101563
Seeing	Day	19% 8% 28% 25% 15% 6%	14820
	Night	19% 8% 29% 30% 12% 1	23769

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% 14% 5% 11% 7% 6% 5% 4 5% 4 24%	2517
	11th to 20th	Day	10% 16% 7% 18% 10% 7% 5% 5% 5% 5% 14%	2722
	21st to end	Day	17% 19% 7% 14% 7% 5% 4 3 4 4 14%	3124
February	1st to 10th	Day	12% 15% 6% 14% 9% 7% 6% 4 5% 5% 17%	1710
	11th to 20th	Day	12% 13% 6% 13% 8% 5% 6% 4 5% 6% 22%	1663
	21st to end	Day	14% 15% 5% 12% 7% 6% 5% 4 5% 5% 22%	1456
March	1st to 10th	Day	17% 12% 5% 10% 6% 5% 4 3 4 5% 30%	3432
	11th to 20th	Day	10% 14% 6% 12% 6% 5% 6% 4 5% 5% 27%	3480
	21st to end	Day	15% 8% 3 11% 6% 4 5% 4 4 5% 35%	3815
April	1st to 10th	Day	17% 14% 3 10% 6% 4 4 4 5% 5% 29%	2242
	11th to 20th	Day	19% 10% 3 6% 4 4 4 4 5% 7% 35%	2347
	21st to end	Day	19% 9% 3 9% 5% 4 3 3 4 7% 34%	2470
May	1st to 10th	Day	15% 8% 3 8% 5% 4 4 4 6% 7% 35%	4108
	11th to 20th	Day	15% 9% 4 8% 5% 4 4 4 6% 8% 34%	4393
	21st to end	Day	12% 5% 2 6% 4 4 4 4 5% 7% 46%	4837
June	1st to 10th	Day	15% 8% 3 6% 4 4 5% 5% 7% 7% 37%	2660
	11th to 20th	Day	12% 5% 2 6% 4 4 5% 5% 7% 8% 41%	2745
	21st to end	Day	13% 7% 2 6% 5% 6% 5% 3 6% 8% 38%	2850
July	1st to 10th	Day	11% 5% 2 7% 6% 6% 6% 5% 7% 10% 35%	4678
	11th to 20th	Day	9% 6% 2 5% 5% 5% 5% 4 7% 9% 42%	4440
	21st to end	Day	7% 6% 2 7% 5% 5% 5% 4 6% 8% 43%	4537
August	1st to 10th	Day	13% 8% 3 7% 5% 5% 5% 4 6% 8% 37%	4104
	11th to 20th	Day	12% 7% 3 7% 5% 5% 5% 4 7% 10% 35%	4044
	21st to end	Day	10% 6% 2 6% 5% 4 5% 4 7% 9% 43%	4380
September	1st to 10th	Day	13% 7% 3 7% 4 5% 4 4 6% 8% 41%	2280
	11th to 20th	Day	11% 6% 2 6% 5% 5% 5% 3 6% 9% 42%	2161
	21st to end	Day	14% 6% 3 8% 4 5% 5% 5% 7% 7% 35%	2055
October	1st to 10th	Day	17% 9% 3 8% 5% 4 5% 4 6% 7% 33%	1900
	11th to 20th	Day	18% 11% 4 9% 5% 5% 5% 5% 5% 6% 26%	1900
	21st to end	Day	24% 13% 4 11% 6% 4 5% 3 5% 6% 19%	2090
November	1st to 10th	Day	14% 12% 4 9% 5% 6% 5% 4 7% 7% 27%	1637
	11th to 20th	Day	12% 17% 4 12% 7% 5% 6% 5% 6% 6% 21%	1520
	21st to end	Day	19% 16% 6% 11% 6% 5% 5% 3 6% 5% 17%	1520
December	1st to 10th	Day	15% 20% 7% 14% 7% 6% 5% 4 6% 6% 10%	1520
	11th to 20th	Day	17% 15% 5% 11% 8% 6% 5% 5% 5% 6% 18%	1906
	21st to end	Day	26% 18% 6% 14% 7% 5% 4 3 4 3 11%	2772
January	1st to 10th	Night	15% 17% 7% 13% 7% 6% 5% 4 5% 5% 16%	4429
	11th to 20th	Night	12% 12% 6% 15% 11% 9% 7% 4 5% 5% 14%	4234
	21st to end	Night	18% 15% 7% 12% 8% 7% 5% 4 5% 5% 14%	4532
February	1st to 10th	Night	11% 18% 5% 12% 8% 6% 6% 5% 5% 5% 19%	2470
	11th to 20th	Night	12% 15% 6% 11% 7% 6% 6% 4 5% 6% 22%	2403
	21st to end	Night	14% 12% 5% 12% 7% 5% 5% 4 6% 6% 26%	1995
March	1st to 10th	Night	16% 10% 4 9% 6% 5% 4 3 5% 6% 31%	3408
	11th to 20th	Night	12% 12% 4 10% 5% 4 5% 4 6% 6% 33%	3479
	21st to end	Night	14% 8% 4 11% 5% 5% 5% 4 6% 6% 33%	3817
April	1st to 10th	Night	18% 12% 3 8% 5% 4 5% 3 5% 6% 30%	1938
	11th to 20th	Night	18% 8% 3 7% 4 5% 4 5% 5% 7% 36%	1798
	21st to end	Night	16% 10% 4 8% 5% 4 4 4 4 6% 35%	1710
May	1st to 10th	Night	16% 7% 2 7% 5% 4 5% 3 5% 7% 39%	2833
	11th to 20th	Night	14% 7% 3 6% 4 4 5% 4 6% 8% 38%	2500
	21st to end	Night	9% 5% 2 6% 4 4 4 3 5% 8% 49%	2738
June	1st to 10th	Night	13% 5% 3 7% 4 6% 5% 4 5% 8% 40%	1520
	11th to 20th	Night	9% 3 2 7% 6% 5% 6% 5% 6% 8% 43%	1428
	21st to end	Night	10% 6% 3 6% 5% 5% 5% 4 5% 8% 43%	1330
July	1st to 10th	Night	5% 5% 2 7% 5% 5% 5% 4 6% 8% 49%	2272
	11th to 20th	Night	11% 5% 2 5% 3 4 3 4 5% 8% 50%	2520
	21st to end	Night	7% 6% 2 5% 4 4 5% 4 7% 9% 48%	3014
August	1st to 10th	Night	10% 6% 2 6% 4 5% 3 4 6% 8% 46%	2825
	11th to 20th	Night	13% 5% 2 5% 3 3 3 4 6% 8% 46%	2785
	21st to end	Night	10% 6% 3 6% 4 4 5% 4 6% 8% 45%	3242
September	1st to 10th	Night	11% 6% 2 6% 5% 4 4 4 6% 8% 46%	1900
	11th to 20th	Night	11% 5% 2 5% 4 3 3 4 6% 7% 50%	2014
	21st to end	Night	15% 7% 3 7% 5% 4 3 4 5% 6% 41%	2123
October	1st to 10th	Night	17% 7% 3 6% 6% 4 4 4 5% 7% 37%	2280
	11th to 20th	Night	17% 11% 3 7% 5% 5% 6% 4 5% 6% 31%	2280
	21st to end	Night	21% 12% 3 8% 6% 5% 4 4 6% 6% 24%	2508
November	1st to 10th	Night	17% 10% 3 8% 5% 4 5% 4 6% 6% 32%	2598
	11th to 20th	Night	15% 15% 5% 10% 6% 5% 5% 5% 6% 6% 24%	2660
	21st to end	Night	18% 15% 5% 10% 6% 6% 5% 4 6% 6% 20%	2660
December	1st to 10th	Night	17% 18% 6% 13% 7% 5% 5% 3 5% 5% 16%	2660
	11th to 20th	Night	15% 17% 5% 13% 7% 6% 6% 3 6% 6% 17%	3288
	21st to end	Night	26% 18% 6% 15% 6% 4 4 3 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	61% 6% 16% 13% 4	2518
	11th to 20th	Day	71% 5% 11% 9% 3	2722
	21st to end	Day	72% 5% 9% 10% 4 1	3124
February	1st to 10th	Day	68% 5% 8% 14% 4	1710
	11th to 20th	Day	62% 4 10% 16% 6% 1	1672
	21st to end	Day	63% 3 10% 16% 7% 1	1456
March	1st to 10th	Day	56% 4 14% 16% 10%	3435
	11th to 20th	Day	58% 5% 11% 18% 7% 1	3480
	21st to end	Day	48% 7% 10% 19% 14% 2	3815
April	1st to 10th	Day	57% 4 9% 19% 10% 1	2242
	11th to 20th	Day	49% 5% 9% 22% 15% 1	2347
	21st to end	Day	51% 4 11% 19% 12% 3	2470
May	1st to 10th	Day	46% 5% 12% 22% 14% 2	4120
	11th to 20th	Day	48% 5% 15% 22% 10% 1	4397
	21st to end	Day	37% 5% 14% 24% 17% 3	4837
June	1st to 10th	Day	43% 7% 12% 23% 15% 1	2660
	11th to 20th	Day	38% 6% 13% 25% 17% 1	2745
	21st to end	Day	43% 6% 13% 24% 14% 1	2850
July	1st to 10th	Day	41% 6% 15% 22% 14% 1	4606
	11th to 20th	Day	35% 6% 14% 34% 10% 1	4365
	21st to end	Day	37% 6% 12% 27% 16% 1	4392
August	1st to 10th	Day	43% 5% 15% 25% 12% 1	4091
	11th to 20th	Day	41% 6% 18% 25% 9%	4083
	21st to end	Day	36% 6% 14% 33% 11% 1	4380
September	1st to 10th	Day	41% 6% 14% 27% 10% 2	2280
	11th to 20th	Day	38% 5% 14% 28% 14% 1	2161
	21st to end	Day	46% 6% 14% 25% 9%	2055
October	1st to 10th	Day	43% 5% 13% 25% 12% 1	3160
	11th to 20th	Day	44% 5% 17% 22% 12%	3140
	21st to end	Day	59% 6% 15% 16% 4	3428
November	1st to 10th	Day	53% 7% 14% 18% 7% 1	1637
	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% 9% 12% 10% 3	4429
	11th to 20th	Night	70% 7% 12% 8% 3	4234
	21st to end	Night	71% 4 12% 9% 3 1	4532
February	1st to 10th	Night	64% 5% 10% 17% 4	2470
	11th to 20th	Night	60% 6% 11% 17% 6%	2405
	21st to end	Night	57% 6% 12% 16% 8%	1995
March	1st to 10th	Night	54% 4 11% 22% 8% 1	3418
	11th to 20th	Night	47% 7% 14% 21% 8% 2	3480
	21st to end	Night	45% 10% 9% 22% 13% 1	3817
April	1st to 10th	Night	55% 4 9% 20% 11% 1	1938
	11th to 20th	Night	47% 4 10% 21% 16% 2	1798
	21st to end	Night	50% 5% 10% 18% 15% 2	1710
May	1st to 10th	Night	44% 5% 13% 19% 17% 3	2840
	11th to 20th	Night	43% 5% 15% 24% 12% 2	2501
	21st to end	Night	32% 5% 14% 27% 19% 2	2739
June	1st to 10th	Night	41% 5% 11% 25% 16% 2	1520
	11th to 20th	Night	36% 7% 12% 24% 20% 1	1428
	21st to end	Night	38% 6% 13% 26% 15% 1	1330
July	1st to 10th	Night	33% 5% 15% 27% 18% 3	2235
	11th to 20th	Night	33% 4 12% 35% 15% 1	2472
	21st to end	Night	31% 7% 13% 31% 16% 1	2918
August	1st to 10th	Night	35% 5% 14% 29% 15% 1	2814
	11th to 20th	Night	34% 5% 20% 28% 13% 1	2812
	21st to end	Night	34% 6% 14% 32% 13% 1	3242
September	1st to 10th	Night	34% 7% 16% 29% 13% 1	1900
	11th to 20th	Night	31% 6% 13% 32% 17% 1	2014
	21st to end	Night	45% 5% 13% 27% 11%	2123
October	1st to 10th	Night	35% 5% 10% 28% 21% 1	3800
	11th to 20th	Night	43% 6% 16% 22% 13%	3779
	21st to end	Night	46% 7% 16% 24% 7%	4120
November	1st to 10th	Night	50% 6% 12% 22% 8% 1	2598
	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% 35% 24% 9% 2	180
	11th to 20th	Day	23% 10% 38% 20% 6% 2	239
	21st to end	Day	22% 10% 37% 24% 6% 1	297
February	1st to 10th	Day	17% 12% 48% 16% 5% 1	270
	11th to 20th	Day	19% 18% 39% 22% 1	270
	21st to end	Day	25% 20% 34% 18% 2	230
March	1st to 10th	Day	21% 8% 39% 23% 8%	460
	11th to 20th	Day	20% 11% 37% 25% 7% 1	460
	21st to end	Day	26% 7% 34% 22% 9% 1	506
April	1st to 10th	Day	23% 12% 35% 20% 9% 2	460
	11th to 20th	Day	30% 10% 27% 17% 12% 5%	452
	21st to end	Day	26% 8% 27% 25% 10% 3	460
May	1st to 10th	Day	20% 6% 25% 29% 15% 5%	463
	11th to 20th	Day	17% 6% 24% 27% 19% 7%	487
	21st to end	Day	15% 4 24% 29% 20% 7%	529
June	1st to 10th	Day	17% 6% 25% 30% 19% 3	490
	11th to 20th	Day	15% 6% 23% 31% 20% 4	575
	21st to end	Day	17% 7% 28% 29% 14% 5%	680
July	1st to 10th	Day	11% 4 21% 34% 23% 7%	630
	11th to 20th	Day	13% 3 22% 29% 24% 10%	484
	21st to end	Day	10% 3 17% 38% 20% 11%	532
August	1st to 10th	Day	11% 2 19% 27% 27% 14%	486
	11th to 20th	Day	9% 4 17% 28% 27% 15%	479
	21st to end	Day	14% 3 22% 28% 22% 11%	539
September	1st to 10th	Day	14% 6% 21% 24% 23% 11%	490
	11th to 20th	Day	11% 3 19% 25% 23% 19%	490
	21st to end	Day	14% 6% 27% 24% 20% 9%	490
October	1st to 10th	Day	22% 6% 28% 22% 14% 9%	490
	11th to 20th	Day	21% 12% 33% 22% 9% 2	490
	21st to end	Day	29% 12% 29% 22% 7%	539
November	1st to 10th	Day	22% 17% 31% 18% 11% 1	255
	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% 25% 7% 1	760
	21st to end	Night	19% 9% 32% 30% 9% 1	836
February	1st to 10th	Night	20% 10% 39% 26% 4	760
	11th to 20th	Night	20% 11% 37% 27% 5%	743
	21st to end	Night	20% 12% 34% 29% 5%	628
March	1st to 10th	Night	19% 11% 36% 28% 6%	760
	11th to 20th	Night	19% 11% 35% 27% 7% 1	760
	21st to end	Night	21% 8% 33% 28% 11%	836
April	1st to 10th	Night	24% 10% 32% 30% 5%	760
	11th to 20th	Night	20% 7% 33% 28% 10% 2	674
	21st to end	Night	22% 6% 28% 32% 12%	570
May	1st to 10th	Night	18% 3 24% 37% 16% 2	570
	11th to 20th	Night	16% 4 27% 38% 13% 1	379
	21st to end	Night	10% 5% 23% 43% 18% 1	411
June	1st to 10th	Night	14% 4 26% 40% 14% 1	380
	11th to 20th	Night	11% 6% 22% 44% 17% 1	380
	21st to end	Night	12% 4 22% 41% 19% 2	380
July	1st to 10th	Night	7% 4 16% 49% 23% 2	370
	11th to 20th	Night	11% 4 20% 40% 23% 2	368
	21st to end	Night	10% 2 19% 41% 27% 1	577
August	1st to 10th	Night	12% 2 14% 42% 29% 2	567
	11th to 20th	Night	7% 3 13% 38% 34% 4	564
	21st to end	Night	13% 3 20% 34% 26% 3	693
September	1st to 10th	Night	12% 5% 21% 34% 22% 6%	760
	11th to 20th	Night	13% 3 19% 32% 25% 7%	760
	21st to end	Night	18% 7% 18% 32% 20% 4	760
October	1st to 10th	Night	19% 5% 29% 28% 17% 3	760
	11th to 20th	Night	23% 10% 29% 27% 10% 1	760
	21st to end	Night	30% 8% 30% 25% 7%	836
November	1st to 10th	Night	22% 10% 29% 27% 11% 1	771
	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 2024-11-05 08:15:53. Version ac07

Copyright © 2024 Attilla Danko.