Sundre
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sundre clear sky chart from 2005-11-06 to 2025-02-25.

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	9% 9% 3 8% 5% 5% 5% 5% 7% 8% 35%	112190
	Night	7% 10% 4 9% 6% 5% 5% 4 6% 8% 36%	115122
Transparency	Day	43% 8% 15% 22% 10% 2	111938
	Night	43% 7% 15% 22% 11% 2	115020
Seeing	Day	14% 9% 28% 30% 16% 4	15599
	Night	11% 6% 31% 35% 14% 2	24853

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	2 9% 6% 14% 6% 6% 5% 3 6% 9% 33%	3179
	11th to 20th	Day	2 9% 3 11% 6% 7% 7% 4 7% 8% 36%	3223
	21st to end	Day	3 8% 3 7% 5% 4 5% 5% 7% 11% 44%	4004
February	1st to 10th	Day	5% 12% 4 12% 8% 6% 5% 4 6% 9% 29%	1600
	11th to 20th	Day	4 12% 3 13% 7% 7% 6% 5% 7% 7% 29%	1697
	21st to end	Day	2 11% 6% 10% 8% 6% 7% 5% 7% 7% 30%	1581
March	1st to 10th	Day	3 9% 5% 13% 8% 5% 7% 4 7% 9% 31%	3138
	11th to 20th	Day	5% 10% 3 7% 4 3 4 4 7% 10% 43%	3413
	21st to end	Day	7% 21% 7% 13% 5% 4 4 4 5% 6% 25%	3939
April	1st to 10th	Day	7% 14% 5% 11% 8% 6% 7% 5% 6% 7% 24%	2318
	11th to 20th	Day	10% 17% 5% 9% 5% 4 5% 4 6% 7% 27%	2440
	21st to end	Day	11% 12% 4 8% 6% 5% 5% 5% 6% 8% 28%	2470
May	1st to 10th	Day	18% 14% 3 8% 5% 5% 5% 4 6% 6% 26%	4417
	11th to 20th	Day	10% 10% 4 10% 7% 5% 6% 5% 7% 8% 28%	4694
	21st to end	Day	18% 11% 5% 9% 7% 6% 6% 5% 6% 7% 21%	5161
June	1st to 10th	Day	19% 8% 3 8% 6% 6% 5% 5% 7% 7% 26%	2850
	11th to 20th	Day	20% 10% 4 8% 7% 5% 6% 5% 6% 6% 23%	2850
	21st to end	Day	12% 6% 2 7% 5% 5% 7% 6% 8% 9% 33%	2850
July	1st to 10th	Day	9% 4 2 6% 5% 5% 6% 5% 7% 9% 43%	4740
	11th to 20th	Day	9% 3 1 5% 3 4 6% 6% 8% 9% 45%	4740
	21st to end	Day	7% 5% 2 5% 4 4 5% 5% 7% 10% 47%	5023
August	1st to 10th	Day	11% 5% 2 6% 4 5% 5% 5% 7% 9% 41%	4401
	11th to 20th	Day	9% 5% 2 6% 4 5% 6% 5% 8% 11% 40%	4145
	21st to end	Day	11% 4 2 5% 4 4 5% 4 6% 8% 47%	4521
September	1st to 10th	Day	13% 6% 1 6% 4 4 4 4 6% 7% 45%	2350
	11th to 20th	Day	14% 9% 3 6% 4 4 4 3 4 5% 44%	2103
	21st to end	Day	9% 8% 3 6% 6% 4 5% 3 6% 8% 42%	2090
October	1st to 10th	Day	8% 7% 3 7% 4 4 5% 4 7% 10% 43%	3374
	11th to 20th	Day	8% 7% 3 7% 5% 5% 6% 5% 9% 9% 36%	2847
	21st to end	Day	6% 7% 4 7% 6% 5% 5% 4 6% 8% 42%	3101
November	1st to 10th	Day	7% 15% 4 10% 6% 6% 5% 4 5% 6% 32%	1641
	11th to 20th	Day	5% 12% 4 9% 6% 4 4 5% 6% 8% 37%	1460
	21st to end	Day	5% 13% 4 10% 6% 4 5% 5% 6% 9% 34%	1400
December	1st to 10th	Day	5% 10% 4 10% 7% 8% 8% 6% 7% 8% 29%	2290
	11th to 20th	Day	3 11% 4 10% 5% 6% 6% 5% 6% 10% 34%	2642
	21st to end	Day	3 11% 4 9% 6% 4 5% 4 7% 8% 39%	3498
January	1st to 10th	Night	2 13% 6% 14% 7% 6% 6% 5% 6% 7% 27%	6766
	11th to 20th	Night	2 8% 4 13% 8% 6% 6% 6% 6% 7% 35%	6719
	21st to end	Night	2 9% 4 9% 5% 5% 5% 4 7% 9% 40%	6952
February	1st to 10th	Night	5% 10% 5% 13% 8% 8% 6% 4 7% 7% 28%	2800
	11th to 20th	Night	4 11% 4 12% 7% 7% 7% 4 6% 8% 30%	2589
	21st to end	Night	2 10% 4 11% 7% 6% 5% 4 6% 7% 37%	1964
March	1st to 10th	Night	2 9% 4 13% 7% 7% 8% 6% 8% 8% 27%	3736
	11th to 20th	Night	6% 8% 2 7% 4 4 4 4 8% 9% 42%	3565
	21st to end	Night	7% 17% 6% 12% 6% 5% 6% 4 6% 7% 24%	3710
April	1st to 10th	Night	7% 13% 5% 9% 7% 6% 5% 4 6% 8% 30%	1862
	11th to 20th	Night	9% 14% 6% 11% 7% 5% 5% 4 4 7% 29%	1691
	21st to end	Night	10% 11% 4 9% 6% 6% 6% 4 7% 8% 30%	1710
May	1st to 10th	Night	20% 14% 3 8% 5% 4 4 4 4 5% 30%	2526
	11th to 20th	Night	10% 8% 3 8% 5% 5% 6% 4 8% 9% 33%	2199
	21st to end	Night	16% 11% 3 8% 6% 6% 6% 5% 6% 7% 25%	2414
June	1st to 10th	Night	18% 9% 2 7% 6% 4 5% 4 6% 7% 32%	1330
	11th to 20th	Night	17% 8% 3 9% 6% 7% 5% 5% 6% 7% 27%	1330
	21st to end	Night	9% 7% 2 5% 5% 6% 5% 5% 8% 9% 40%	1330
July	1st to 10th	Night	10% 5% 2 7% 5% 5% 5% 4 7% 8% 42%	2220
	11th to 20th	Night	7% 3 1 4 4 3 4 5% 8% 10% 52%	2220
	21st to end	Night	6% 5% 2 5% 4 3 5% 3 6% 10% 52%	2526
August	1st to 10th	Night	12% 6% 2 6% 5% 5% 4 4 5% 8% 45%	2529
	11th to 20th	Night	9% 5% 2 6% 4 4 5% 5% 7% 10% 42%	2688
	21st to end	Night	11% 5% 2 5% 4 4 4 3 6% 8% 49%	3146
September	1st to 10th	Night	12% 5% 1 7% 4 4 4 3 5% 7% 48%	1829
	11th to 20th	Night	14% 8% 2 6% 3 3 4 3 7% 7% 42%	2076
	21st to end	Night	11% 7% 2 6% 4 4 5% 4 6% 7% 45%	2090
October	1st to 10th	Night	8% 7% 3 7% 4 4 4 4 5% 8% 46%	3601
	11th to 20th	Night	6% 7% 3 6% 5% 5% 5% 4 5% 9% 45%	4077
	21st to end	Night	6% 8% 3 8% 4 5% 5% 4 7% 7% 43%	4457
November	1st to 10th	Night	7% 14% 5% 9% 5% 4 5% 4 6% 7% 33%	2637
	11th to 20th	Night	4 11% 4 10% 6% 6% 5% 5% 7% 8% 35%	2935
	21st to end	Night	3 11% 4 10% 6% 6% 5% 5% 6% 9% 34%	3000
December	1st to 10th	Night	5% 12% 4 10% 6% 7% 5% 5% 7% 8% 31%	4890
	11th to 20th	Night	4 12% 5% 11% 9% 6% 6% 5% 7% 8% 27%	5550
	21st to end	Night	3 11% 4 10% 5% 4 5% 4 6% 7% 41%	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	47% 5% 12% 21% 12% 3	3179
	11th to 20th	Day	44% 7% 11% 16% 19% 4	3244
	21st to end	Day	32% 7% 15% 33% 12% 1	4004
February	1st to 10th	Day	50% 7% 14% 17% 9% 3	1600
	11th to 20th	Day	49% 8% 14% 18% 10% 2	1706
	21st to end	Day	49% 8% 12% 18% 12% 2	1581
March	1st to 10th	Day	46% 9% 15% 16% 12% 1	3138
	11th to 20th	Day	33% 7% 21% 24% 14% 1	3414
	21st to end	Day	58% 10% 11% 14% 7%	3939
April	1st to 10th	Day	54% 9% 16% 14% 7%	2318
	11th to 20th	Day	54% 8% 12% 18% 8% 1	2440
	21st to end	Day	51% 10% 15% 17% 6% 1	2470
May	1st to 10th	Day	55% 9% 12% 19% 5%	4417
	11th to 20th	Day	45% 12% 15% 19% 8%	4698
	21st to end	Day	58% 11% 14% 12% 5%	5162
June	1st to 10th	Day	53% 9% 16% 15% 6% 2	2850
	11th to 20th	Day	58% 9% 14% 12% 6% 1	2850
	21st to end	Day	42% 11% 19% 19% 7% 1	2850
July	1st to 10th	Day	36% 7% 14% 22% 16% 5%	4666
	11th to 20th	Day	32% 7% 19% 31% 10% 1	4659
	21st to end	Day	31% 7% 14% 26% 18% 4	4864
August	1st to 10th	Day	38% 6% 18% 30% 8% 1	4384
	11th to 20th	Day	36% 6% 23% 26% 7% 1	4187
	21st to end	Day	33% 7% 19% 31% 8% 2	4520
September	1st to 10th	Day	36% 8% 19% 22% 11% 4	2350
	11th to 20th	Day	42% 7% 15% 25% 10% 2	2103
	21st to end	Day	39% 7% 17% 23% 12% 3	2090
October	1st to 10th	Day	36% 5% 20% 31% 6% 1	3374
	11th to 20th	Day	41% 6% 19% 21% 11% 2	2847
	21st to end	Day	40% 5% 11% 32% 11% 1	3101
November	1st to 10th	Day	52% 7% 12% 17% 10% 1	1641
	11th to 20th	Day	43% 8% 13% 22% 11% 2	1460
	21st to end	Day	44% 9% 16% 20% 8% 4	1400
December	1st to 10th	Day	51% 6% 13% 20% 8% 1	2290
	11th to 20th	Day	45% 7% 21% 19% 7% 1	2644
	21st to end	Day	41% 6% 9% 21% 19% 4	3498
January	1st to 10th	Night	53% 7% 12% 19% 7% 2	6766
	11th to 20th	Night	47% 6% 11% 18% 14% 5%	6760
	21st to end	Night	37% 8% 16% 25% 14% 1	6952
February	1st to 10th	Night	51% 9% 9% 17% 11% 3	2800
	11th to 20th	Night	49% 8% 12% 17% 13% 2	2590
	21st to end	Night	45% 5% 11% 22% 14% 2	1964
March	1st to 10th	Night	46% 11% 13% 20% 9% 1	3736
	11th to 20th	Night	32% 11% 19% 22% 15% 1	3565
	21st to end	Night	55% 10% 13% 15% 6% 1	3710
April	1st to 10th	Night	49% 8% 13% 19% 10% 1	1862
	11th to 20th	Night	52% 7% 13% 18% 8% 1	1691
	21st to end	Night	50% 9% 15% 20% 6% 2	1710
May	1st to 10th	Night	55% 6% 12% 21% 6%	2526
	11th to 20th	Night	39% 11% 16% 22% 11%	2199
	21st to end	Night	51% 12% 15% 16% 5% 1	2414
June	1st to 10th	Night	48% 8% 15% 18% 10% 1	1330
	11th to 20th	Night	53% 8% 14% 15% 7% 2	1330
	21st to end	Night	38% 11% 19% 23% 6% 2	1330
July	1st to 10th	Night	38% 6% 14% 23% 13% 5%	2185
	11th to 20th	Night	26% 7% 24% 30% 8% 5%	2178
	21st to end	Night	28% 6% 13% 34% 17% 1	2446
August	1st to 10th	Night	38% 7% 14% 33% 8%	2521
	11th to 20th	Night	35% 6% 27% 25% 6% 1	2712
	21st to end	Night	34% 5% 21% 30% 9% 1	3146
September	1st to 10th	Night	34% 7% 17% 24% 13% 4	1829
	11th to 20th	Night	38% 8% 16% 22% 11% 4	2076
	21st to end	Night	36% 7% 17% 22% 14% 3	2090
October	1st to 10th	Night	36% 5% 17% 26% 14% 1	3601
	11th to 20th	Night	36% 5% 18% 27% 12% 1	4077
	21st to end	Night	39% 5% 12% 30% 13%	4457
November	1st to 10th	Night	48% 8% 11% 20% 11% 2	2637
	11th to 20th	Night	43% 9% 15% 19% 12% 2	2935
	21st to end	Night	43% 9% 15% 20% 9% 4	3000
December	1st to 10th	Night	50% 5% 17% 19% 7% 2	4890
	11th to 20th	Night	52% 7% 15% 17% 8% 1	5547
	21st to end	Night	40% 5% 10% 23% 17% 4	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	6% 9% 26% 33% 18% 9%	200
	11th to 20th	Day	7% 8% 34% 31% 16% 5%	200
	21st to end	Day	8% 11% 30% 35% 13% 3	220
February	1st to 10th	Day	11% 10% 33% 31% 12% 5%	200
	11th to 20th	Day	9% 7% 36% 31% 15% 1	271
	21st to end	Day	5% 11% 31% 33% 16% 3	369
March	1st to 10th	Day	8% 13% 36% 26% 12% 3	460
	11th to 20th	Day	8% 13% 35% 29% 11% 5%	460
	21st to end	Day	13% 15% 31% 26% 10% 4	506
April	1st to 10th	Day	14% 16% 33% 24% 11% 2	460
	11th to 20th	Day	15% 13% 27% 30% 12% 3	452
	21st to end	Day	17% 13% 27% 28% 12% 3	460
May	1st to 10th	Day	20% 13% 24% 25% 16% 3	501
	11th to 20th	Day	15% 9% 22% 33% 16% 5%	675
	21st to end	Day	20% 6% 20% 29% 21% 4	734
June	1st to 10th	Day	17% 10% 27% 32% 12% 3	680
	11th to 20th	Day	25% 9% 24% 28% 12% 4	680
	21st to end	Day	14% 6% 24% 31% 19% 7%	680
July	1st to 10th	Day	14% 5% 20% 31% 24% 5%	671
	11th to 20th	Day	15% 4 23% 32% 22% 4	668
	21st to end	Day	9% 5% 26% 34% 20% 7%	673
August	1st to 10th	Day	13% 5% 28% 31% 17% 7%	487
	11th to 20th	Day	11% 5% 25% 34% 20% 4	477
	21st to end	Day	12% 6% 29% 29% 18% 6%	539
September	1st to 10th	Day	16% 7% 29% 28% 14% 6%	490
	11th to 20th	Day	20% 7% 21% 30% 17% 5%	490
	21st to end	Day	15% 11% 30% 29% 11% 3	490
October	1st to 10th	Day	15% 10% 27% 26% 17% 6%	426
	11th to 20th	Day	15% 9% 34% 25% 14% 4	300
	21st to end	Day	15% 13% 33% 26% 12% 2	330
November	1st to 10th	Day	16% 9% 29% 31% 12% 3	300
	11th to 20th	Day	15% 12% 30% 31% 11% 1	230
	21st to end	Day	6% 9% 37% 29% 14% 7%	200
December	1st to 10th	Day	7% 8% 34% 33% 15% 5%	200
	11th to 20th	Day	6% 10% 42% 29% 9% 5%	200
	21st to end	Day	5% 6% 28% 34% 20% 8%	220
January	1st to 10th	Night	8% 9% 36% 33% 13% 1	1000
	11th to 20th	Night	8% 8% 38% 35% 10% 1	993
	21st to end	Night	9% 10% 37% 32% 10% 1	880
February	1st to 10th	Night	9% 9% 31% 34% 14% 4	800
	11th to 20th	Night	8% 7% 35% 36% 13% 2	784
	21st to end	Night	6% 4 33% 35% 19% 4	646
March	1st to 10th	Night	8% 4 36% 36% 13% 3	760
	11th to 20th	Night	9% 6% 36% 36% 12% 2	760
	21st to end	Night	11% 7% 33% 31% 15% 3	836
April	1st to 10th	Night	11% 7% 33% 33% 15% 1	722
	11th to 20th	Night	14% 9% 34% 33% 10% 1	563
	21st to end	Night	15% 11% 27% 35% 11%	570
May	1st to 10th	Night	21% 8% 23% 34% 13%	419
	11th to 20th	Night	12% 4 26% 41% 16% 1	374
	21st to end	Night	21% 5% 17% 37% 19%	411
June	1st to 10th	Night	20% 7% 22% 37% 14% 1	380
	11th to 20th	Night	21% 4 23% 36% 15% 1	380
	21st to end	Night	9% 2 23% 39% 25% 2	380
July	1st to 10th	Night	15% 2 14% 44% 24% 1	370
	11th to 20th	Night	14% 2 20% 41% 21% 2	368
	21st to end	Night	9% 2 17% 44% 25% 2	416
August	1st to 10th	Night	13% 3 12% 36% 33% 3	378
	11th to 20th	Night	11% 3 15% 44% 25% 2	489
	21st to end	Night	11% 3 21% 44% 21% 1	627
September	1st to 10th	Night	15% 3 20% 40% 19% 3	689
	11th to 20th	Night	18% 4 18% 36% 21% 3	760
	21st to end	Night	13% 6% 30% 37% 13% 2	760
October	1st to 10th	Night	17% 4 28% 34% 15% 2	760
	11th to 20th	Night	11% 5% 35% 34% 13% 2	760
	21st to end	Night	11% 9% 33% 36% 11% 1	836
November	1st to 10th	Night	14% 9% 36% 30% 10% 1	882
	11th to 20th	Night	8% 10% 45% 28% 8% 1	1000
	21st to end	Night	8% 7% 38% 37% 9% 2	1000
December	1st to 10th	Night	10% 7% 39% 32% 11% 2	1000
	11th to 20th	Night	7% 7% 39% 35% 11% 1	1000
	21st to end	Night	9% 6% 37% 33% 12% 3	1100

Page generated at 2025-02-22 04:51:38. Version ac07

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