Waterton
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Waterton clear sky chart from 2005-11-06 to 2024-11-02.

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	5% 9% 3 9% 7% 7% 6% 5% 6% 8% 33%	101692
	Night	4 8% 3 9% 7% 8% 7% 5% 7% 8% 32%	97355
Transparency	Day	37% 9% 20% 20% 11% 3	101446
	Night	36% 11% 22% 18% 10% 3	97247
Seeing	Day	17% 21% 29% 21% 10% 3	15294
	Night	13% 21% 32% 24% 10% 1	24419

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	1 6% 5% 14% 11% 11% 10% 8% 9% 10% 15%	2219
	11th to 20th	Day	1 7% 4 16% 11% 8% 7% 9% 8% 7% 23%	2402
	21st to end	Day	1 8% 5% 11% 11% 14% 8% 6% 7% 8% 20%	2794
February	1st to 10th	Day	2 12% 5% 14% 10% 8% 8% 7% 8% 9% 17%	1572
	11th to 20th	Day	2 13% 5% 14% 9% 9% 10% 5% 6% 7% 19%	1665
	21st to end	Day	2 10% 5% 13% 13% 11% 9% 5% 7% 7% 18%	1565
March	1st to 10th	Day	5% 4 14% 10% 11% 10% 6% 7% 7% 24%	3138
	11th to 20th	Day	1 10% 4 11% 9% 9% 6% 4 5% 7% 33%	3475
	21st to end	Day	4 19% 8% 16% 10% 9% 6% 4 5% 5% 14%	3848
April	1st to 10th	Day	4 14% 6% 15% 10% 9% 7% 6% 6% 7% 18%	2310
	11th to 20th	Day	5% 16% 7% 13% 8% 7% 6% 5% 6% 7% 22%	2440
	21st to end	Day	7% 16% 5% 10% 7% 7% 6% 4 6% 7% 24%	2470
May	1st to 10th	Day	10% 24% 5% 9% 6% 5% 4 4 5% 5% 24%	4110
	11th to 20th	Day	8% 12% 3 10% 7% 7% 7% 5% 7% 7% 27%	4624
	21st to end	Day	13% 12% 4 10% 9% 10% 7% 5% 7% 7% 15%	5161
June	1st to 10th	Day	13% 10% 4 9% 8% 8% 7% 5% 5% 7% 25%	2850
	11th to 20th	Day	15% 11% 3 9% 7% 9% 7% 6% 6% 7% 21%	2850
	21st to end	Day	7% 5% 2 7% 6% 6% 7% 5% 8% 7% 41%	2850
July	1st to 10th	Day	4 4 2 5% 6% 5% 6% 5% 7% 7% 50%	4740
	11th to 20th	Day	2 3 1 3 4 4 4 4 6% 8% 61%	4740
	21st to end	Day	2 2 1 3 2 3 4 4 6% 7% 66%	4833
August	1st to 10th	Day	7% 7% 2 7% 5% 5% 5% 5% 7% 8% 44%	4341
	11th to 20th	Day	5% 4 2 5% 5% 5% 5% 3 6% 8% 53%	4028
	21st to end	Day	7% 3 1 4 3 4 4 4 6% 8% 56%	4521
September	1st to 10th	Day	9% 8% 2 5% 4 4 5% 4 5% 8% 47%	2310
	11th to 20th	Day	9% 6% 2 7% 5% 5% 6% 4 7% 9% 41%	2090
	21st to end	Day	9% 8% 2 5% 4 6% 5% 3 6% 10% 42%	2090
October	1st to 10th	Day	10% 11% 3 9% 5% 6% 5% 4 6% 6% 36%	2024
	11th to 20th	Day	3 8% 4 11% 8% 8% 6% 5% 6% 8% 32%	1793
	21st to end	Day	4 10% 4 11% 6% 8% 7% 5% 7% 9% 29%	1881
November	1st to 10th	Day	4 11% 4 10% 9% 10% 8% 5% 7% 10% 21%	1631
	11th to 20th	Day	1 9% 4 8% 7% 9% 8% 7% 7% 12% 28%	1520
	21st to end	Day	2 10% 3 13% 8% 9% 7% 6% 5% 10% 26%	1353
December	1st to 10th	Day	1 8% 5% 9% 8% 8% 8% 7% 10% 11% 24%	1330
	11th to 20th	Day	2 7% 4 12% 11% 11% 9% 6% 10% 11% 18%	1682
	21st to end	Day	1 8% 4 11% 8% 10% 9% 7% 9% 9% 25%	2442
January	1st to 10th	Night	1 7% 5% 14% 10% 12% 13% 8% 9% 8% 14%	4726
	11th to 20th	Night	1 8% 4 13% 10% 8% 9% 7% 7% 9% 25%	4514
	21st to end	Night	2 9% 4 10% 9% 17% 9% 6% 7% 8% 18%	4862
February	1st to 10th	Night	3 12% 6% 13% 9% 7% 9% 7% 7% 8% 19%	2608
	11th to 20th	Night	1 11% 5% 12% 9% 9% 9% 7% 8% 7% 20%	2402
	21st to end	Night	2 8% 4 14% 11% 10% 11% 6% 8% 7% 19%	1886
March	1st to 10th	Night	5% 3 15% 12% 12% 10% 7% 7% 8% 21%	3736
	11th to 20th	Night	2 7% 3 9% 9% 9% 8% 4 5% 7% 37%	3504
	21st to end	Night	4 17% 7% 12% 8% 12% 7% 5% 6% 6% 15%	3803
April	1st to 10th	Night	4 12% 4 8% 7% 7% 7% 5% 9% 10% 26%	1869
	11th to 20th	Night	4 13% 4 8% 6% 7% 7% 6% 7% 9% 29%	1691
	21st to end	Night	6% 12% 3 9% 8% 7% 7% 3 5% 7% 32%	1710
May	1st to 10th	Night	9% 19% 5% 9% 6% 6% 4 4 5% 5% 27%	2843
	11th to 20th	Night	6% 7% 3 9% 6% 7% 6% 5% 6% 8% 36%	2268
	21st to end	Night	12% 13% 3 10% 11% 10% 7% 5% 7% 6% 18%	2414
June	1st to 10th	Night	11% 8% 3 8% 8% 8% 5% 4 6% 6% 32%	1330
	11th to 20th	Night	15% 7% 3 6% 6% 7% 7% 4 7% 8% 31%	1330
	21st to end	Night	5% 4 2 6% 4 4 5% 6% 6% 7% 52%	1330
July	1st to 10th	Night	3 3 1 4 4 4 4 4 6% 7% 60%	2220
	11th to 20th	Night	2 2 1 4 3 3 3 3 4 6% 69%	2220
	21st to end	Night	3 2 2 2 3 4 3 4 5% 71%	2717
August	1st to 10th	Night	9% 7% 2 5% 2 3 4 3 4 8% 53%	2589
	11th to 20th	Night	4 3 1 4 4 4 6% 5% 8% 9% 52%	2811
	21st to end	Night	3 4 1 3 3 3 4 4 6% 9% 61%	3146
September	1st to 10th	Night	9% 5% 2 6% 4 3 4 4 5% 7% 52%	1866
	11th to 20th	Night	6% 7% 2 7% 5% 5% 5% 4 7% 9% 45%	2090
	21st to end	Night	7% 8% 2 5% 3 5% 4 4 7% 9% 46%	2090
October	1st to 10th	Night	8% 10% 3 7% 4 4 5% 4 6% 8% 42%	2156
	11th to 20th	Night	3 7% 3 7% 6% 8% 6% 5% 7% 9% 39%	2384
	21st to end	Night	3 9% 4 9% 6% 9% 8% 5% 7% 10% 28%	2717
November	1st to 10th	Night	4 11% 4 10% 8% 10% 7% 6% 7% 9% 23%	2463
	11th to 20th	Night	1 7% 3 10% 8% 10% 9% 9% 7% 10% 26%	2660
	21st to end	Night	2 10% 3 10% 7% 9% 7% 6% 10% 11% 26%	2826
December	1st to 10th	Night	1 9% 5% 11% 7% 8% 8% 8% 9% 12% 21%	2850
	11th to 20th	Night	1 8% 4 13% 10% 11% 9% 7% 9% 8% 19%	3510
	21st to end	Night	1 8% 5% 11% 9% 9% 9% 6% 8% 9% 26%	5214

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	40% 12% 35% 9% 3 1	2219
	11th to 20th	Day	46% 14% 17% 9% 9% 6%	2426
	21st to end	Day	35% 18% 31% 13% 3	2794
February	1st to 10th	Day	48% 16% 20% 11% 4 1	1572
	11th to 20th	Day	46% 11% 25% 12% 5% 1	1674
	21st to end	Day	45% 14% 21% 13% 6% 1	1565
March	1st to 10th	Day	31% 11% 32% 16% 9% 1	3138
	11th to 20th	Day	31% 11% 34% 19% 3 1	3476
	21st to end	Day	54% 10% 22% 10% 4	3848
April	1st to 10th	Day	47% 9% 26% 15% 2	2310
	11th to 20th	Day	49% 9% 20% 17% 4 1	2440
	21st to end	Day	48% 9% 21% 16% 5% 1	2470
May	1st to 10th	Day	55% 7% 15% 19% 4	4110
	11th to 20th	Day	42% 9% 21% 22% 6%	4628
	21st to end	Day	45% 10% 29% 12% 3	5162
June	1st to 10th	Day	47% 10% 19% 18% 7%	2850
	11th to 20th	Day	49% 9% 17% 17% 7% 1	2850
	21st to end	Day	31% 8% 22% 25% 12% 2	2850
July	1st to 10th	Day	26% 6% 11% 31% 18% 8%	4666
	11th to 20th	Day	18% 6% 10% 23% 28% 15%	4659
	21st to end	Day	13% 3 8% 27% 27% 20%	4680
August	1st to 10th	Day	35% 5% 14% 21% 19% 6%	4324
	11th to 20th	Day	26% 4 17% 32% 19% 2	4067
	21st to end	Day	22% 4 12% 41% 19% 2	4520
September	1st to 10th	Day	31% 4 15% 25% 16% 8%	2310
	11th to 20th	Day	31% 7% 18% 26% 14% 3	2090
	21st to end	Day	30% 8% 22% 26% 11% 3	2090
October	1st to 10th	Day	39% 8% 19% 23% 9% 2	2024
	11th to 20th	Day	36% 10% 24% 19% 9% 2	1793
	21st to end	Day	38% 11% 22% 21% 7% 1	1881
November	1st to 10th	Day	40% 15% 26% 13% 5% 1	1631
	11th to 20th	Day	33% 18% 29% 13% 6% 1	1520
	21st to end	Day	40% 15% 25% 11% 8% 2	1353
December	1st to 10th	Day	38% 20% 22% 13% 5% 3	1330
	11th to 20th	Day	38% 21% 27% 11% 3 1	1684
	21st to end	Day	34% 14% 22% 14% 12% 3	2442
January	1st to 10th	Night	41% 15% 31% 9% 4 1	4726
	11th to 20th	Night	45% 12% 19% 12% 6% 6%	4552
	21st to end	Night	35% 21% 26% 14% 4	4862
February	1st to 10th	Night	47% 13% 18% 12% 7% 2	2608
	11th to 20th	Night	42% 15% 25% 12% 6% 1	2403
	21st to end	Night	45% 12% 22% 15% 5% 1	1886
March	1st to 10th	Night	36% 13% 29% 14% 7%	3736
	11th to 20th	Night	28% 13% 34% 20% 5%	3504
	21st to end	Night	52% 11% 23% 10% 3	3803
April	1st to 10th	Night	39% 10% 27% 19% 5%	1869
	11th to 20th	Night	42% 10% 21% 21% 6%	1691
	21st to end	Night	43% 9% 19% 22% 7% 1	1710
May	1st to 10th	Night	52% 8% 14% 19% 6%	2843
	11th to 20th	Night	32% 8% 23% 26% 11%	2268
	21st to end	Night	49% 9% 27% 12% 3	2414
June	1st to 10th	Night	40% 8% 22% 21% 8%	1330
	11th to 20th	Night	42% 7% 19% 19% 11% 1	1330
	21st to end	Night	24% 8% 24% 27% 15% 3	1330
July	1st to 10th	Night	19% 4 15% 30% 22% 10%	2185
	11th to 20th	Night	15% 4 10% 26% 27% 17%	2178
	21st to end	Night	14% 3 8% 26% 29% 19%	2631
August	1st to 10th	Night	29% 3 16% 23% 20% 9%	2581
	11th to 20th	Night	25% 4 19% 34% 15% 2	2838
	21st to end	Night	19% 4 11% 40% 23% 4	3146
September	1st to 10th	Night	28% 6% 17% 26% 17% 7%	1866
	11th to 20th	Night	30% 6% 18% 27% 14% 4	2090
	21st to end	Night	28% 7% 24% 24% 15% 3	2090
October	1st to 10th	Night	33% 10% 18% 24% 13% 2	2156
	11th to 20th	Night	29% 9% 26% 22% 11% 2	2384
	21st to end	Night	37% 13% 22% 20% 8%	2717
November	1st to 10th	Night	42% 14% 24% 13% 6% 2	2463
	11th to 20th	Night	33% 17% 29% 15% 6%	2660
	21st to end	Night	37% 16% 26% 12% 8% 2	2826
December	1st to 10th	Night	37% 18% 24% 13% 6% 2	2850
	11th to 20th	Night	42% 18% 25% 12% 3 1	3507
	21st to end	Night	35% 12% 25% 15% 9% 4	5214

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	13% 31% 29% 15% 7% 4	180
	11th to 20th	Day	12% 28% 29% 24% 3 2	180
	21st to end	Day	20% 30% 32% 12% 5% 3	198
February	1st to 10th	Day	20% 22% 36% 16% 5%	204
	11th to 20th	Day	13% 29% 36% 16% 7%	270
	21st to end	Day	18% 29% 33% 15% 5%	377
March	1st to 10th	Day	16% 30% 32% 16% 5% 2	460
	11th to 20th	Day	16% 23% 31% 18% 10% 2	460
	21st to end	Day	18% 27% 32% 16% 6% 2	506
April	1st to 10th	Day	20% 26% 36% 13% 5%	460
	11th to 20th	Day	17% 31% 27% 17% 7% 1	452
	21st to end	Day	22% 23% 29% 18% 7% 3	460
May	1st to 10th	Day	20% 21% 25% 20% 11% 3	463
	11th to 20th	Day	25% 14% 25% 18% 15% 4	631
	21st to end	Day	27% 12% 21% 21% 16% 4	734
June	1st to 10th	Day	18% 22% 24% 23% 12% 2	680
	11th to 20th	Day	24% 21% 24% 18% 11% 2	680
	21st to end	Day	12% 14% 26% 28% 16% 4	680
July	1st to 10th	Day	7% 13% 28% 30% 18% 4	671
	11th to 20th	Day	8% 11% 32% 32% 14% 3	668
	21st to end	Day	6% 12% 33% 30% 14% 4	561
August	1st to 10th	Day	13% 12% 27% 28% 16% 5%	487
	11th to 20th	Day	8% 8% 34% 31% 16% 4	477
	21st to end	Day	14% 15% 31% 27% 11% 3	539
September	1st to 10th	Day	16% 19% 26% 23% 12% 3	490
	11th to 20th	Day	13% 18% 32% 23% 12% 2	490
	21st to end	Day	24% 23% 27% 18% 7% 1	490
October	1st to 10th	Day	18% 22% 30% 17% 12% 1	424
	11th to 20th	Day	20% 22% 29% 18% 9% 3	300
	21st to end	Day	25% 25% 29% 13% 7% 2	330
November	1st to 10th	Day	21% 30% 31% 15% 4	273
	11th to 20th	Day	22% 34% 30% 12% 1	270
	21st to end	Day	19% 38% 18% 13% 8% 4	191
December	1st to 10th	Day	18% 34% 29% 13% 6% 1	180
	11th to 20th	Day	23% 26% 29% 20% 2 1	180
	21st to end	Day	12% 28% 30% 19% 9% 3	198
January	1st to 10th	Night	15% 31% 33% 15% 4 1	950
	11th to 20th	Night	12% 28% 36% 17% 5% 1	840
	21st to end	Night	11% 31% 37% 15% 5% 2	836
February	1st to 10th	Night	13% 21% 36% 21% 8% 1	760
	11th to 20th	Night	11% 25% 36% 21% 6%	744
	21st to end	Night	11% 25% 32% 23% 8%	628
March	1st to 10th	Night	8% 23% 37% 24% 7% 1	760
	11th to 20th	Night	11% 24% 32% 24% 8% 2	760
	21st to end	Night	12% 20% 29% 26% 10% 2	836
April	1st to 10th	Night	12% 22% 32% 24% 9% 1	729
	11th to 20th	Night	12% 20% 36% 23% 8% 1	563
	21st to end	Night	13% 17% 34% 26% 9% 1	570
May	1st to 10th	Night	16% 16% 25% 28% 13% 2	566
	11th to 20th	Night	14% 9% 24% 35% 18% 2	374
	21st to end	Night	26% 9% 20% 25% 18% 2	411
June	1st to 10th	Night	17% 14% 26% 28% 14% 1	380
	11th to 20th	Night	19% 16% 29% 25% 10% 1	380
	21st to end	Night	7% 7% 32% 33% 19% 1	380
July	1st to 10th	Night	7% 9% 20% 40% 22% 1	370
	11th to 20th	Night	8% 5% 30% 41% 15% 1	368
	21st to end	Night	7% 6% 22% 43% 20% 2	416
August	1st to 10th	Night	9% 3 21% 41% 24% 2	412
	11th to 20th	Night	6% 5% 24% 37% 24% 3	564
	21st to end	Night	11% 11% 26% 37% 14% 2	627
September	1st to 10th	Night	14% 9% 26% 29% 17% 5%	693
	11th to 20th	Night	11% 11% 24% 31% 17% 5%	760
	21st to end	Night	15% 16% 31% 23% 12% 3	760
October	1st to 10th	Night	17% 17% 25% 28% 12% 1	760
	11th to 20th	Night	12% 20% 28% 29% 9% 1	760
	21st to end	Night	17% 25% 34% 18% 5% 1	836
November	1st to 10th	Night	16% 28% 33% 17% 4	781
	11th to 20th	Night	16% 33% 35% 13% 2 1	950
	21st to end	Night	15% 30% 33% 17% 5% 1	950
December	1st to 10th	Night	12% 25% 37% 19% 5% 1	950
	11th to 20th	Night	11% 29% 39% 17% 4	950
	21st to end	Night	13% 25% 38% 18% 5%	1045

Page generated at 2024-10-30 11:19:22. Version ac07

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