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 2025-03-12.

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	8% 8% 3 7% 5% 4 5% 4 6% 8% 43%	112213
	Night	7% 8% 3 9% 5% 5% 5% 4 6% 8% 40%	115430
Transparency	Day	38% 6% 15% 27% 12% 2	111954
	Night	41% 6% 16% 25% 12% 2	115335
Seeing	Day	11% 8% 26% 31% 19% 5%	15859
	Night	11% 9% 31% 34% 14% 1	25285

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	5% 16% 7% 14% 7% 5% 5% 4 5% 7% 27%	3179
	11th to 20th	Day	5% 10% 5% 11% 6% 5% 7% 6% 6% 8% 31%	3159
	21st to end	Day	3 9% 5% 8% 5% 5% 4 3 6% 7% 45%	3848
February	1st to 10th	Day	9% 13% 5% 11% 9% 6% 5% 4 6% 7% 26%	1752
	11th to 20th	Day	7% 12% 5% 9% 7% 7% 6% 6% 8% 7% 25%	1755
	21st to end	Day	4 12% 4 13% 7% 6% 6% 4 6% 7% 30%	1492
March	1st to 10th	Day	5% 9% 4 12% 8% 5% 5% 4 5% 8% 36%	3380
	11th to 20th	Day	8% 9% 3 7% 4 4 4 4 5% 9% 43%	3501
	21st to end	Day	10% 17% 4 10% 5% 4 5% 4 6% 7% 27%	3825
April	1st to 10th	Day	8% 10% 4 10% 6% 5% 6% 4 7% 8% 32%	2313
	11th to 20th	Day	9% 13% 4 8% 6% 5% 5% 4 5% 7% 34%	2440
	21st to end	Day	10% 8% 4 9% 5% 5% 5% 4 6% 8% 35%	2470
May	1st to 10th	Day	17% 12% 4 8% 4 4 5% 4 5% 6% 32%	4351
	11th to 20th	Day	9% 6% 2 7% 5% 5% 5% 5% 8% 10% 37%	4553
	21st to end	Day	13% 8% 3 8% 5% 5% 5% 5% 6% 8% 32%	5161
June	1st to 10th	Day	14% 6% 2 6% 5% 4 5% 4 6% 9% 39%	2850
	11th to 20th	Day	16% 8% 2 6% 5% 5% 6% 5% 8% 8% 32%	2850
	21st to end	Day	7% 4 1 5% 5% 4 5% 5% 7% 9% 49%	2850
July	1st to 10th	Day	4 4 2 5% 4 4 4 4 7% 8% 54%	4740
	11th to 20th	Day	5% 3 1 4 3 3 4 3 5% 7% 60%	4740
	21st to end	Day	2 2 1 3 2 2 2 3 4 7% 72%	5138
August	1st to 10th	Day	5% 4 2 5% 4 4 4 3 6% 9% 55%	4261
	11th to 20th	Day	4 3 1 4 3 4 5% 4 7% 10% 54%	4028
	21st to end	Day	6% 3 1 3 2 3 3 3 5% 8% 62%	4521
September	1st to 10th	Day	10% 5% 2 5% 4 3 3 3 4 6% 57%	2351
	11th to 20th	Day	14% 5% 2 4 4 3 4 3 6% 8% 47%	2120
	21st to end	Day	9% 6% 3 5% 3 3 4 3 5% 8% 52%	2090
October	1st to 10th	Day	7% 6% 2 6% 4 5% 5% 4 7% 8% 45%	3188
	11th to 20th	Day	4 5% 2 5% 4 4 5% 4 6% 9% 52%	3150
	21st to end	Day	8% 7% 3 7% 3 4 4 3 5% 7% 50%	3049
November	1st to 10th	Day	11% 14% 3 10% 6% 5% 5% 4 6% 6% 31%	1568
	11th to 20th	Day	6% 10% 4 8% 6% 5% 5% 3 6% 8% 38%	1600
	21st to end	Day	7% 12% 3 9% 7% 5% 5% 4 7% 7% 34%	1510
December	1st to 10th	Day	8% 15% 4 9% 6% 5% 5% 5% 6% 8% 31%	2290
	11th to 20th	Day	7% 12% 5% 13% 7% 6% 6% 3 5% 6% 31%	2642
	21st to end	Day	3 8% 4 10% 6% 5% 5% 4 6% 6% 43%	3498
January	1st to 10th	Night	4 11% 5% 14% 7% 5% 5% 4 6% 8% 30%	6766
	11th to 20th	Night	5% 11% 4 12% 6% 5% 6% 4 7% 8% 33%	6739
	21st to end	Night	3 9% 4 12% 6% 5% 5% 4 6% 8% 40%	7139
February	1st to 10th	Night	7% 11% 4 10% 7% 6% 5% 5% 6% 8% 30%	2647
	11th to 20th	Night	6% 11% 5% 9% 6% 6% 7% 5% 8% 8% 29%	2532
	21st to end	Night	5% 10% 4 8% 7% 6% 6% 5% 7% 9% 33%	2135
March	1st to 10th	Night	4 9% 3 12% 8% 5% 6% 5% 6% 8% 34%	3714
	11th to 20th	Night	10% 7% 2 6% 4 5% 5% 4 7% 8% 42%	3506
	21st to end	Night	9% 15% 5% 13% 7% 6% 5% 4 7% 8% 21%	3828
April	1st to 10th	Night	9% 12% 4 9% 7% 4 6% 4 7% 8% 32%	1865
	11th to 20th	Night	9% 10% 3 8% 7% 5% 6% 5% 6% 6% 34%	1691
	21st to end	Night	10% 9% 4 7% 6% 5% 5% 4 6% 9% 36%	1710
May	1st to 10th	Night	20% 10% 3 7% 4 5% 4 3 4 6% 33%	2618
	11th to 20th	Night	7% 5% 2 6% 5% 5% 7% 7% 9% 12% 36%	2341
	21st to end	Night	13% 7% 3 9% 7% 6% 7% 4 7% 9% 30%	2414
June	1st to 10th	Night	16% 8% 3 5% 5% 4 5% 4 7% 9% 36%	1330
	11th to 20th	Night	12% 4 2 7% 6% 5% 5% 5% 8% 9% 37%	1330
	21st to end	Night	5% 4 1 5% 5% 5% 6% 4 6% 8% 51%	1330
July	1st to 10th	Night	6% 3 2 5% 3 4 4 4 6% 8% 55%	2220
	11th to 20th	Night	4 3 1 4 3 3 5% 4 7% 13% 52%	2220
	21st to end	Night	3 2 1 4 3 3 3 3 6% 8% 65%	2414
August	1st to 10th	Night	7% 4 1 6% 4 4 4 4 6% 9% 51%	2671
	11th to 20th	Night	4 3 2 5% 4 4 5% 4 7% 11% 49%	2811
	21st to end	Night	9% 3 1 3 3 3 3 3 5% 7% 61%	3146
September	1st to 10th	Night	8% 5% 2 5% 4 4 5% 4 6% 6% 52%	1829
	11th to 20th	Night	12% 5% 2 6% 4 4 4 3 5% 7% 50%	2057
	21st to end	Night	7% 5% 2 5% 4 4 4 4 6% 8% 51%	2090
October	1st to 10th	Night	8% 5% 2 5% 4 4 5% 4 6% 8% 49%	3769
	11th to 20th	Night	5% 6% 2 7% 4 4 5% 3 6% 9% 50%	3778
	21st to end	Night	6% 9% 3 7% 4 4 5% 4 6% 8% 45%	4474
November	1st to 10th	Night	11% 11% 3 8% 6% 5% 4 4 5% 7% 35%	2730
	11th to 20th	Night	5% 9% 4 9% 6% 6% 5% 5% 7% 7% 38%	2800
	21st to end	Night	5% 13% 4 10% 6% 4 4 4 6% 8% 36%	2888
December	1st to 10th	Night	5% 12% 5% 11% 6% 6% 6% 4 6% 8% 30%	4890
	11th to 20th	Night	7% 11% 5% 12% 6% 5% 6% 4 7% 8% 29%	5550
	21st to end	Night	4 8% 3 9% 5% 5% 5% 4 6% 7% 44%	7458

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% 20% 4	3179
	11th to 20th	Day	49% 6% 13% 16% 15% 1	3180
	21st to end	Day	39% 4 22% 28% 7%	3848
February	1st to 10th	Day	57% 5% 13% 17% 8% 1	1752
	11th to 20th	Day	53% 7% 15% 18% 8%	1764
	21st to end	Day	52% 6% 12% 21% 9% 1	1492
March	1st to 10th	Day	45% 6% 14% 25% 10%	3380
	11th to 20th	Day	37% 5% 21% 25% 11%	3502
	21st to end	Day	54% 8% 18% 15% 5%	3825
April	1st to 10th	Day	47% 7% 14% 22% 10%	2313
	11th to 20th	Day	48% 5% 11% 25% 9% 1	2440
	21st to end	Day	46% 6% 13% 24% 10% 1	2470
May	1st to 10th	Day	52% 5% 11% 25% 6%	4351
	11th to 20th	Day	37% 7% 15% 30% 11%	4557
	21st to end	Day	46% 7% 14% 25% 8% 1	5162
June	1st to 10th	Day	41% 7% 16% 23% 11% 2	2850
	11th to 20th	Day	46% 7% 14% 22% 10% 1	2850
	21st to end	Day	29% 7% 18% 31% 12% 3	2850
July	1st to 10th	Day	26% 7% 16% 26% 20% 4	4666
	11th to 20th	Day	22% 5% 16% 34% 19% 4	4659
	21st to end	Day	13% 3 10% 31% 28% 15%	4976
August	1st to 10th	Day	26% 6% 12% 34% 19% 3	4243
	11th to 20th	Day	24% 7% 16% 39% 12% 2	4067
	21st to end	Day	21% 3 14% 41% 18% 2	4520
September	1st to 10th	Day	30% 4 13% 27% 18% 8%	2351
	11th to 20th	Day	35% 6% 12% 31% 13% 3	2120
	21st to end	Day	32% 5% 15% 31% 14% 3	2090
October	1st to 10th	Day	34% 5% 15% 31% 13% 2	3188
	11th to 20th	Day	29% 4 18% 34% 14% 1	3150
	21st to end	Day	34% 4 11% 37% 13% 1	3049
November	1st to 10th	Day	53% 6% 13% 19% 7% 1	1568
	11th to 20th	Day	44% 5% 18% 24% 8%	1600
	21st to end	Day	47% 6% 17% 22% 7% 1	1510
December	1st to 10th	Day	51% 5% 20% 19% 4 1	2290
	11th to 20th	Day	54% 5% 18% 19% 4	2644
	21st to end	Day	41% 4 14% 25% 15% 2	3498
January	1st to 10th	Night	51% 5% 19% 19% 5% 1	6766
	11th to 20th	Night	48% 5% 14% 16% 15% 1	6780
	21st to end	Night	42% 5% 18% 28% 7% 1	7139
February	1st to 10th	Night	49% 5% 14% 19% 11% 1	2647
	11th to 20th	Night	48% 7% 15% 19% 10% 1	2533
	21st to end	Night	45% 6% 15% 23% 9% 2	2135
March	1st to 10th	Night	45% 8% 15% 23% 9%	3714
	11th to 20th	Night	37% 6% 20% 27% 10% 1	3506
	21st to end	Night	58% 7% 16% 14% 4	3828
April	1st to 10th	Night	49% 6% 12% 24% 10%	1865
	11th to 20th	Night	47% 6% 11% 22% 12% 1	1691
	21st to end	Night	44% 5% 13% 26% 11% 1	1710
May	1st to 10th	Night	52% 4 12% 22% 10%	2618
	11th to 20th	Night	34% 9% 17% 27% 13% 1	2341
	21st to end	Night	47% 8% 16% 23% 7% 1	2414
June	1st to 10th	Night	42% 6% 17% 24% 9% 2	1330
	11th to 20th	Night	40% 7% 14% 25% 13% 2	1330
	21st to end	Night	29% 6% 17% 32% 13% 3	1330
July	1st to 10th	Night	25% 5% 20% 26% 22% 3	2185
	11th to 20th	Night	22% 6% 14% 35% 17% 5%	2178
	21st to end	Night	16% 4 8% 31% 28% 12%	2337
August	1st to 10th	Night	28% 6% 14% 31% 19% 2	2664
	11th to 20th	Night	27% 7% 16% 31% 16% 3	2838
	21st to end	Night	24% 4 12% 37% 20% 4	3146
September	1st to 10th	Night	30% 5% 12% 25% 19% 8%	1829
	11th to 20th	Night	35% 5% 13% 28% 14% 5%	2057
	21st to end	Night	29% 6% 14% 31% 17% 3	2090
October	1st to 10th	Night	31% 4 12% 35% 15% 2	3769
	11th to 20th	Night	31% 4 15% 32% 16% 2	3778
	21st to end	Night	37% 5% 12% 35% 12%	4474
November	1st to 10th	Night	48% 6% 15% 21% 9% 1	2730
	11th to 20th	Night	43% 6% 20% 21% 11%	2800
	21st to end	Night	46% 5% 22% 18% 8% 1	2888
December	1st to 10th	Night	51% 6% 20% 17% 5%	4890
	11th to 20th	Night	52% 6% 24% 15% 3	5547
	21st to end	Night	38% 4 13% 26% 16% 3	7458

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% 7% 34% 29% 18% 5%	200
	11th to 20th	Day	12% 9% 31% 35% 12% 3	200
	21st to end	Day	9% 9% 37% 30% 12% 3	220
February	1st to 10th	Day	18% 14% 31% 25% 9% 2	277
	11th to 20th	Day	10% 6% 31% 35% 15% 3	300
	21st to end	Day	7% 9% 29% 36% 16% 4	256
March	1st to 10th	Day	10% 11% 30% 28% 16% 4	500
	11th to 20th	Day	9% 8% 33% 32% 12% 6%	465
	21st to end	Day	13% 10% 32% 26% 15% 4	506
April	1st to 10th	Day	11% 12% 33% 30% 12% 2	460
	11th to 20th	Day	13% 11% 31% 30% 13% 1	452
	21st to end	Day	15% 10% 27% 30% 15% 3	460
May	1st to 10th	Day	15% 8% 21% 31% 17% 8%	600
	11th to 20th	Day	14% 6% 20% 33% 20% 6%	675
	21st to end	Day	18% 5% 19% 25% 24% 9%	734
June	1st to 10th	Day	13% 11% 23% 31% 19% 4	680
	11th to 20th	Day	16% 11% 29% 27% 15% 3	680
	21st to end	Day	10% 6% 23% 33% 20% 8%	680
July	1st to 10th	Day	5% 5% 21% 37% 26% 7%	671
	11th to 20th	Day	7% 5% 23% 35% 24% 5%	668
	21st to end	Day	4 6% 18% 33% 29% 9%	739
August	1st to 10th	Day	5% 4 18% 38% 25% 9%	527
	11th to 20th	Day	7% 2 21% 32% 29% 10%	477
	21st to end	Day	7% 6% 21% 30% 27% 9%	539
September	1st to 10th	Day	11% 9% 25% 27% 25% 4	490
	11th to 20th	Day	15% 5% 22% 32% 22% 5%	490
	21st to end	Day	15% 8% 30% 30% 14% 4	490
October	1st to 10th	Day	15% 5% 26% 30% 19% 5%	318
	11th to 20th	Day	9% 9% 31% 30% 19% 2	300
	21st to end	Day	18% 12% 32% 24% 13% 2	330
November	1st to 10th	Day	19% 11% 31% 29% 9% 1	300
	11th to 20th	Day	12% 13% 37% 30% 8% 1	300
	21st to end	Day	11% 10% 37% 28% 7% 6%	255
December	1st to 10th	Day	11% 11% 43% 23% 12% 1	200
	11th to 20th	Day	12% 12% 42% 27% 9%	200
	21st to end	Day	14% 9% 21% 39% 15% 2	220
January	1st to 10th	Night	10% 12% 35% 29% 12% 1	1000
	11th to 20th	Night	12% 10% 36% 32% 9% 1	1000
	21st to end	Night	9% 12% 37% 29% 10% 2	963
February	1st to 10th	Night	13% 9% 29% 31% 15% 3	800
	11th to 20th	Night	11% 10% 31% 37% 10% 1	784
	21st to end	Night	9% 8% 28% 35% 18% 2	660
March	1st to 10th	Night	8% 8% 35% 35% 12% 3	800
	11th to 20th	Night	11% 10% 33% 32% 12% 2	766
	21st to end	Night	11% 11% 28% 36% 13% 1	836
April	1st to 10th	Night	13% 11% 34% 27% 12% 2	618
	11th to 20th	Night	14% 8% 32% 34% 11% 1	563
	21st to end	Night	15% 9% 25% 38% 12% 1	570
May	1st to 10th	Night	15% 8% 21% 35% 20% 2	570
	11th to 20th	Night	10% 7% 26% 35% 20% 3	464
	21st to end	Night	19% 4 25% 28% 21% 2	411
June	1st to 10th	Night	19% 9% 27% 27% 17% 2	380
	11th to 20th	Night	16% 7% 33% 33% 12%	380
	21st to end	Night	7% 5% 27% 41% 19% 2	380
July	1st to 10th	Night	6% 4 21% 48% 21% 1	370
	11th to 20th	Night	7% 4 24% 44% 20% 1	368
	21st to end	Night	4 4 21% 47% 22% 2	416
August	1st to 10th	Night	7% 3 23% 37% 28% 2	498
	11th to 20th	Night	6% 4 21% 41% 27% 1	564
	21st to end	Night	8% 4 26% 38% 23% 1	627
September	1st to 10th	Night	11% 4 25% 42% 16% 2	570
	11th to 20th	Night	14% 5% 22% 41% 17% 1	727
	21st to end	Night	9% 7% 33% 35% 13% 3	760
October	1st to 10th	Night	15% 6% 28% 35% 15% 1	760
	11th to 20th	Night	11% 8% 34% 32% 12% 2	760
	21st to end	Night	10% 13% 33% 34% 9%	845
November	1st to 10th	Night	16% 9% 37% 29% 8%	975
	11th to 20th	Night	12% 13% 39% 27% 7% 2	1000
	21st to end	Night	11% 10% 40% 31% 8% 1	1000
December	1st to 10th	Night	13% 9% 36% 28% 13% 2	1000
	11th to 20th	Night	10% 10% 40% 29% 11% 1	1000
	21st to end	Night	12% 9% 34% 33% 10% 2	1100

Page generated at 2025-03-09 06:08:48. Version ac07

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