Suffield
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Suffield clear sky chart from 2005-11-06 to 2026-07-16.

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	8% 7% 3 7% 5% 4 5% 4 6% 8% 43%	142171
	Night	7% 8% 3 8% 5% 5% 5% 4 6% 8% 40%	139245
Transparency	Day	38% 5% 15% 27% 13% 2	141868
	Night	40% 5% 16% 25% 12% 2	139131
Seeing	Day	11% 8% 27% 31% 18% 5%	17768
	Night	11% 9% 31% 34% 13% 1	26926

By Month

Percentage Cloud Cover NW (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	4 13% 6% 14% 7% 6% 5% 4 5% 7% 27%	4125
	11th to 20th	Day	4 9% 5% 11% 6% 5% 7% 6% 6% 8% 33%	4119
	21st to end	Day	3 8% 4 9% 6% 5% 5% 3 6% 7% 45%	4988
February	1st to 10th	Day	8% 13% 4 11% 8% 6% 5% 4 6% 7% 27%	1840
	11th to 20th	Day	7% 11% 5% 9% 7% 7% 5% 6% 8% 7% 26%	1845
	21st to end	Day	4 13% 4 13% 7% 6% 6% 4 6% 7% 31%	1564
March	1st to 10th	Day	5% 8% 3 10% 7% 5% 5% 4 6% 8% 40%	4812
	11th to 20th	Day	6% 8% 3 9% 5% 5% 5% 4 6% 9% 39%	5109
	21st to end	Day	8% 15% 4 10% 5% 5% 6% 4 7% 8% 28%	5607
April	1st to 10th	Day	8% 10% 4 9% 6% 5% 6% 4 6% 8% 34%	2556
	11th to 20th	Day	9% 13% 4 8% 6% 4 5% 3 5% 7% 35%	2700
	21st to end	Day	10% 8% 4 9% 5% 5% 5% 3 6% 8% 36%	2730
May	1st to 10th	Day	11% 8% 2 6% 4 4 5% 4 7% 8% 42%	8061
	11th to 20th	Day	11% 7% 3 8% 5% 6% 6% 5% 8% 9% 34%	8486
	21st to end	Day	10% 6% 2 6% 4 4 5% 5% 6% 8% 43%	9649
June	1st to 10th	Day	14% 6% 2 6% 5% 4 5% 4 6% 9% 39%	3150
	11th to 20th	Day	15% 8% 2 7% 5% 5% 6% 5% 7% 8% 33%	3150
	21st to end	Day	8% 4 1 5% 5% 4 5% 5% 7% 9% 48%	3150
July	1st to 10th	Day	6% 3 2 4 3 3 4 4 6% 8% 56%	6930
	11th to 20th	Day	7% 4 2 5% 4 4 4 4 6% 7% 53%	6856
	21st to end	Day	6% 3 1 4 3 2 3 3 4 7% 65%	7376
August	1st to 10th	Day	5% 4 2 5% 4 4 4 3 6% 9% 54%	4396
	11th to 20th	Day	4 3 1 4 3 4 5% 4 7% 10% 54%	4158
	21st to end	Day	6% 3 1 3 2 3 3 3 5% 8% 62%	4664
September	1st to 10th	Day	9% 4 2 5% 4 3 3 3 4 6% 57%	2474
	11th to 20th	Day	13% 5% 2 4 4 3 4 3 5% 7% 49%	2231
	21st to end	Day	8% 6% 2 5% 3 3 4 3 6% 8% 53%	2200
October	1st to 10th	Day	7% 6% 2 6% 4 4 5% 4 7% 8% 46%	3289
	11th to 20th	Day	5% 5% 2 6% 4 4 5% 4 6% 8% 51%	3250
	21st to end	Day	8% 7% 3 7% 3 4 4 3 5% 7% 50%	3146
November	1st to 10th	Day	11% 13% 3 10% 6% 5% 5% 4 6% 6% 31%	1648
	11th to 20th	Day	6% 10% 4 8% 6% 6% 5% 3 6% 8% 38%	1680
	21st to end	Day	7% 12% 3 9% 7% 5% 5% 5% 7% 7% 34%	1585
December	1st to 10th	Day	8% 15% 4 9% 6% 5% 5% 5% 6% 8% 30%	2360
	11th to 20th	Day	7% 12% 5% 13% 7% 6% 6% 3 5% 6% 31%	2712
	21st to end	Day	3 8% 4 10% 6% 5% 5% 4 6% 6% 43%	3575
January	1st to 10th	Night	4 10% 5% 12% 7% 5% 5% 5% 7% 9% 31%	8768
	11th to 20th	Night	4 9% 4 10% 5% 5% 6% 4 7% 9% 38%	8779
	21st to end	Night	3 8% 3 11% 6% 6% 6% 4 6% 9% 39%	9237
February	1st to 10th	Night	7% 11% 4 10% 7% 6% 5% 5% 7% 8% 31%	2779
	11th to 20th	Night	6% 11% 5% 9% 6% 6% 7% 5% 7% 8% 30%	2662
	21st to end	Night	6% 10% 4 8% 7% 6% 6% 5% 7% 9% 34%	2239
March	1st to 10th	Night	3 7% 3 10% 7% 5% 6% 5% 7% 10% 36%	5302
	11th to 20th	Night	8% 7% 3 7% 5% 5% 6% 5% 8% 9% 38%	5110
	21st to end	Night	9% 15% 5% 11% 7% 6% 5% 4 7% 8% 23%	5610
April	1st to 10th	Night	9% 11% 4 9% 7% 4 5% 4 7% 8% 33%	2061
	11th to 20th	Night	9% 10% 3 8% 7% 5% 6% 5% 6% 6% 35%	1871
	21st to end	Night	10% 9% 4 7% 6% 5% 5% 4 6% 8% 36%	1890
May	1st to 10th	Night	14% 8% 3 7% 4 4 4 3 5% 7% 41%	4886
	11th to 20th	Night	11% 6% 3 8% 6% 6% 6% 6% 7% 10% 30%	4385
	21st to end	Night	11% 5% 2 7% 5% 6% 6% 5% 7% 8% 38%	4522
June	1st to 10th	Night	16% 7% 2 5% 5% 4 4 4 7% 9% 37%	1470
	11th to 20th	Night	11% 4 2 7% 6% 5% 5% 6% 7% 9% 38%	1470
	21st to end	Night	7% 4 1 5% 5% 4 5% 4 6% 8% 51%	1470
July	1st to 10th	Night	7% 3 2 5% 3 4 4 3 6% 7% 57%	3250
	11th to 20th	Night	7% 3 1 5% 3 4 5% 5% 7% 11% 48%	3215
	21st to end	Night	6% 3 1 4 3 3 3 3 5% 7% 60%	3467
August	1st to 10th	Night	7% 4 1 6% 4 4 4 4 6% 9% 50%	2756
	11th to 20th	Night	5% 3 2 5% 4 4 5% 4 7% 11% 48%	2901
	21st to end	Night	8% 3 1 3 3 3 3 3 5% 7% 61%	3245
September	1st to 10th	Night	8% 4 2 5% 4 4 5% 4 6% 7% 52%	1925
	11th to 20th	Night	11% 5% 2 5% 4 4 4 3 5% 6% 51%	2165
	21st to end	Night	7% 5% 2 5% 4 4 4 4 6% 8% 52%	2200
October	1st to 10th	Night	8% 5% 2 5% 4 4 5% 4 6% 8% 50%	3888
	11th to 20th	Night	5% 6% 2 7% 4 4 5% 3 6% 9% 49%	3898
	21st to end	Night	6% 9% 2 7% 4 4 5% 4 6% 8% 45%	4618
November	1st to 10th	Night	11% 11% 3 8% 6% 4 4 4 6% 7% 36%	2870
	11th to 20th	Night	5% 9% 3 9% 5% 6% 5% 4 7% 7% 38%	2940
	21st to end	Night	5% 12% 4 10% 6% 4 4 4 6% 8% 36%	3033
December	1st to 10th	Night	5% 12% 5% 11% 7% 6% 6% 4 6% 8% 30%	5040
	11th to 20th	Night	7% 11% 5% 12% 6% 5% 6% 4 7% 8% 29%	5700
	21st to end	Night	4 8% 3 9% 5% 5% 5% 4 6% 7% 44%	7623

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	56% 5% 14% 19% 6%	4125
	11th to 20th	Day	47% 6% 15% 17% 13% 2	4140
	21st to end	Day	39% 4 21% 27% 8%	4989
February	1st to 10th	Day	55% 5% 13% 17% 9% 1	1840
	11th to 20th	Day	52% 6% 14% 19% 9% 1	1854
	21st to end	Day	51% 6% 11% 22% 9% 1	1564
March	1st to 10th	Day	41% 5% 15% 26% 13%	4812
	11th to 20th	Day	42% 5% 17% 24% 12%	5110
	21st to end	Day	52% 8% 19% 16% 6%	5607
April	1st to 10th	Day	45% 7% 15% 23% 10%	2556
	11th to 20th	Day	48% 5% 12% 26% 8% 1	2700
	21st to end	Day	45% 6% 12% 26% 10% 1	2730
May	1st to 10th	Day	38% 4 11% 27% 15% 4	8061
	11th to 20th	Day	42% 7% 12% 27% 11% 1	8490
	21st to end	Day	36% 6% 13% 32% 14%	9650
June	1st to 10th	Day	41% 6% 15% 23% 12% 2	3150
	11th to 20th	Day	45% 7% 14% 23% 10% 1	3150
	21st to end	Day	30% 6% 18% 31% 12% 2	3150
July	1st to 10th	Day	25% 6% 15% 25% 23% 6%	6856
	11th to 20th	Day	29% 5% 17% 31% 15% 3	6775
	21st to end	Day	21% 4 14% 31% 20% 10%	7169
August	1st to 10th	Day	26% 6% 13% 33% 18% 3	4378
	11th to 20th	Day	24% 7% 16% 39% 12% 2	4197
	21st to end	Day	21% 3 14% 41% 19% 2	4663
September	1st to 10th	Day	29% 4 13% 29% 18% 7%	2474
	11th to 20th	Day	34% 6% 12% 31% 14% 3	2231
	21st to end	Day	31% 4 15% 32% 15% 3	2200
October	1st to 10th	Day	33% 5% 15% 32% 13% 2	3289
	11th to 20th	Day	30% 4 17% 34% 14% 1	3250
	21st to end	Day	33% 4 10% 37% 14% 1	3146
November	1st to 10th	Day	53% 6% 14% 19% 7% 2	1648
	11th to 20th	Day	44% 5% 19% 24% 8%	1680
	21st to end	Day	47% 6% 17% 22% 7% 1	1585
December	1st to 10th	Day	51% 5% 20% 19% 3 1	2360
	11th to 20th	Day	54% 5% 18% 19% 3	2714
	21st to end	Day	41% 4 15% 25% 14% 1	3575
January	1st to 10th	Night	49% 5% 18% 20% 8% 1	8769
	11th to 20th	Night	42% 5% 18% 20% 13% 1	8820
	21st to end	Night	41% 5% 20% 25% 8% 1	9237
February	1st to 10th	Night	48% 5% 14% 20% 11% 1	2779
	11th to 20th	Night	48% 7% 14% 19% 11% 1	2663
	21st to end	Night	45% 6% 15% 23% 9% 1	2239
March	1st to 10th	Night	41% 6% 19% 23% 11%	5302
	11th to 20th	Night	38% 6% 17% 30% 10%	5110
	21st to end	Night	56% 7% 17% 14% 5%	5610
April	1st to 10th	Night	48% 6% 12% 23% 10%	2061
	11th to 20th	Night	47% 6% 11% 23% 12% 1	1871
	21st to end	Night	44% 5% 12% 26% 11% 1	1890
May	1st to 10th	Night	43% 4 8% 27% 15% 4	4883
	11th to 20th	Night	44% 7% 15% 21% 13%	4385
	21st to end	Night	39% 7% 13% 29% 11% 1	4526
June	1st to 10th	Night	42% 5% 16% 23% 11% 2	1470
	11th to 20th	Night	39% 7% 14% 26% 13% 2	1470
	21st to end	Night	30% 6% 17% 33% 12% 2	1470
July	1st to 10th	Night	25% 5% 17% 25% 24% 4	3215
	11th to 20th	Night	28% 6% 15% 31% 16% 3	3173
	21st to end	Night	23% 4 13% 31% 20% 8%	3369
August	1st to 10th	Night	29% 6% 14% 30% 18% 2	2749
	11th to 20th	Night	27% 7% 16% 31% 16% 3	2928
	21st to end	Night	23% 4 12% 37% 20% 4	3245
September	1st to 10th	Night	30% 5% 12% 26% 19% 8%	1925
	11th to 20th	Night	34% 5% 13% 29% 15% 5%	2165
	21st to end	Night	28% 6% 14% 32% 18% 3	2200
October	1st to 10th	Night	31% 4 12% 36% 15% 2	3888
	11th to 20th	Night	31% 4 14% 32% 16% 2	3898
	21st to end	Night	36% 5% 12% 35% 12%	4618
November	1st to 10th	Night	47% 6% 14% 22% 9% 1	2870
	11th to 20th	Night	43% 6% 20% 20% 11%	2940
	21st to end	Night	45% 5% 22% 19% 8% 1	3033
December	1st to 10th	Night	52% 6% 20% 17% 5%	5040
	11th to 20th	Night	52% 6% 24% 15% 3	5697
	21st to end	Night	38% 4 13% 26% 16% 3	7623

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	8% 8% 35% 29% 16% 5%	220
	11th to 20th	Day	12% 10% 33% 32% 10% 3	220
	21st to end	Day	8% 9% 37% 29% 14% 3	242
February	1st to 10th	Day	16% 14% 33% 26% 9% 2	305
	11th to 20th	Day	10% 6% 30% 35% 16% 2	330
	21st to end	Day	8% 10% 28% 34% 15% 4	280
March	1st to 10th	Day	11% 10% 31% 29% 15% 4	540
	11th to 20th	Day	9% 9% 34% 32% 10% 5%	540
	21st to end	Day	13% 11% 32% 26% 13% 4	594
April	1st to 10th	Day	11% 12% 32% 30% 13% 3	540
	11th to 20th	Day	13% 11% 32% 31% 13% 1	532
	21st to end	Day	14% 10% 25% 29% 18% 4	540
May	1st to 10th	Day	14% 9% 22% 32% 17% 6%	694
	11th to 20th	Day	14% 7% 22% 31% 20% 6%	775
	21st to end	Day	17% 5% 20% 26% 23% 9%	844
June	1st to 10th	Day	14% 11% 23% 30% 18% 4	780
	11th to 20th	Day	15% 10% 29% 29% 15% 2	780
	21st to end	Day	11% 6% 23% 33% 20% 7%	780
July	1st to 10th	Day	5% 4 21% 37% 26% 6%	771
	11th to 20th	Day	9% 5% 24% 35% 23% 5%	744
	21st to end	Day	4 6% 18% 32% 30% 10%	794
August	1st to 10th	Day	6% 4 18% 38% 25% 9%	569
	11th to 20th	Day	6% 2 22% 32% 29% 10%	517
	21st to end	Day	7% 6% 20% 30% 28% 9%	583
September	1st to 10th	Day	10% 8% 24% 26% 26% 5%	530
	11th to 20th	Day	14% 5% 20% 32% 24% 5%	530
	21st to end	Day	14% 7% 31% 31% 14% 4	530
October	1st to 10th	Day	14% 5% 27% 29% 19% 6%	349
	11th to 20th	Day	10% 10% 31% 29% 18% 2	330
	21st to end	Day	18% 12% 33% 23% 13% 2	363
November	1st to 10th	Day	18% 12% 32% 28% 8% 1	330
	11th to 20th	Day	12% 12% 37% 29% 8% 1	330
	21st to end	Day	11% 10% 38% 28% 8% 6%	280
December	1st to 10th	Day	11% 11% 42% 24% 10% 1	220
	11th to 20th	Day	12% 14% 41% 26% 8%	220
	21st to end	Day	13% 9% 24% 38% 14% 2	242
January	1st to 10th	Night	10% 12% 36% 30% 11% 1	1050
	11th to 20th	Night	12% 11% 35% 32% 8% 1	1050
	21st to end	Night	9% 12% 37% 30% 10% 2	1011
February	1st to 10th	Night	13% 9% 29% 32% 15% 2	840
	11th to 20th	Night	11% 10% 31% 37% 10% 1	824
	21st to end	Night	10% 8% 27% 35% 18% 2	692
March	1st to 10th	Night	8% 8% 35% 35% 11% 3	840
	11th to 20th	Night	11% 11% 32% 33% 11% 2	840
	21st to end	Night	11% 11% 29% 35% 12% 1	924
April	1st to 10th	Night	13% 11% 34% 28% 13% 2	683
	11th to 20th	Night	14% 9% 32% 33% 11% 1	623
	21st to end	Night	15% 8% 25% 38% 13% 1	630
May	1st to 10th	Night	14% 8% 21% 36% 19% 2	630
	11th to 20th	Night	11% 8% 27% 34% 18% 2	514
	21st to end	Night	18% 4 24% 29% 22% 2	455
June	1st to 10th	Night	19% 10% 27% 27% 16% 2	420
	11th to 20th	Night	14% 6% 34% 34% 11%	420
	21st to end	Night	8% 5% 26% 41% 18% 2	420
July	1st to 10th	Night	6% 3 22% 48% 21%	410
	11th to 20th	Night	7% 5% 24% 43% 20% 1	398
	21st to end	Night	4 4 20% 47% 22% 2	438
August	1st to 10th	Night	7% 3 23% 37% 28% 2	525
	11th to 20th	Night	6% 4 21% 41% 26% 2	594
	21st to end	Night	8% 4 25% 39% 22% 1	660
September	1st to 10th	Night	10% 4 24% 43% 17% 2	600
	11th to 20th	Night	14% 4 21% 41% 19% 1	765
	21st to end	Night	9% 7% 32% 36% 13% 3	800
October	1st to 10th	Night	15% 6% 29% 34% 15% 1	800
	11th to 20th	Night	11% 8% 34% 33% 12% 2	800
	21st to end	Night	10% 13% 34% 33% 9%	890
November	1st to 10th	Night	16% 10% 37% 29% 8%	1025
	11th to 20th	Night	12% 13% 38% 28% 7% 1	1050
	21st to end	Night	10% 10% 40% 31% 8% 1	1050
December	1st to 10th	Night	13% 9% 37% 28% 12% 2	1050
	11th to 20th	Night	10% 11% 40% 28% 10% 1	1050
	21st to end	Night	13% 9% 35% 32% 9% 2	1155

Page generated at 2026-07-13 01:14:48. Version ac07

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