Rattlesnake Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rattlesnake Lake clear sky chart from 2005-11-06 to 2024-10-25.

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	26% 14% 3 6% 4 3 3 3 4 5% 30%	102087
	Night	29% 15% 3 6% 3 3 3 3 4 4 28%	96782
Transparency	Day	57% 6% 9% 15% 10% 2	101848
	Night	61% 6% 9% 14% 9% 2	96667
Seeing	Day	32% 13% 23% 22% 8% 2	14893
	Night	37% 8% 18% 23% 12% 1	23281

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	39% 24% 4 7% 4 2 3 2 3 3 11%	2539
	11th to 20th	Day	28% 15% 5% 8% 4 3 3 3 4 5% 22%	2516
	21st to end	Day	46% 16% 3 7% 3 2 2 2 3 4 12%	2835
February	1st to 10th	Day	34% 19% 4 7% 4 4 3 2 4 4 15%	1710
	11th to 20th	Day	34% 22% 3 5% 3 3 2 2 3 4 18%	1665
	21st to end	Day	31% 27% 3 5% 3 2 4 2 2 3 17%	1501
March	1st to 10th	Day	20% 23% 5% 9% 5% 5% 4 3 4 4 18%	3169
	11th to 20th	Day	22% 21% 3 5% 3 3 2 2 2 3 35%	3490
	21st to end	Day	30% 23% 3 8% 4 4 4 3 4 4 14%	3979
April	1st to 10th	Day	31% 23% 3 6% 5% 3 4 3 4 4 13%	2280
	11th to 20th	Day	28% 19% 4 7% 4 3 3 2 4 4 20%	2252
	21st to end	Day	34% 19% 3 8% 5% 4 3 2 3 3 16%	2522
May	1st to 10th	Day	24% 16% 2 7% 4 3 3 3 4 4 28%	4420
	11th to 20th	Day	26% 13% 2 6% 4 4 4 3 4 7% 28%	4377
	21st to end	Day	38% 17% 3 7% 3 4 4 2 3 4 14%	4813
June	1st to 10th	Day	35% 10% 2 6% 4 4 4 3 5% 5% 21%	2660
	11th to 20th	Day	36% 13% 4 7% 4 5% 4 3 5% 4 15%	2802
	21st to end	Day	22% 9% 3 5% 4 4 4 4 5% 7% 34%	2850
July	1st to 10th	Day	12% 6% 2 4 3 2 3 2 4 4 58%	4711
	11th to 20th	Day	10% 4 1 3 3 3 3 2 3 4 64%	4420
	21st to end	Day	15% 6% 2 4 2 3 3 3 5% 5% 53%	4790
August	1st to 10th	Day	10% 4 1 3 3 3 3 3 4 6% 60%	4358
	11th to 20th	Day	15% 12% 4 8% 4 4 4 3 4 7% 35%	4026
	21st to end	Day	24% 8% 2 6% 3 3 3 2 4 5% 40%	4287
September	1st to 10th	Day	16% 6% 1 5% 3 3 3 3 5% 6% 48%	2280
	11th to 20th	Day	23% 7% 2 6% 5% 4 4 3 4 6% 35%	2280
	21st to end	Day	25% 8% 2 6% 3 3 3 2 4 5% 37%	2020
October	1st to 10th	Day	25% 11% 2 5% 4 4 4 4 4 6% 31%	1900
	11th to 20th	Day	31% 11% 2 5% 3 3 3 2 5% 5% 29%	1900
	21st to end	Day	38% 11% 2 5% 3 3 3 2 3 5% 26%	1896
November	1st to 10th	Day	42% 12% 3 7% 3 3 3 3 3 4 16%	1560
	11th to 20th	Day	41% 16% 2 6% 3 2 3 2 2 3 19%	1520
	21st to end	Day	37% 17% 4 5% 3 3 3 2 3 4 20%	1520
December	1st to 10th	Day	33% 16% 3 5% 3 3 3 3 4 4 23%	1520
	11th to 20th	Day	36% 16% 3 6% 4 3 3 3 4 4 18%	1925
	21st to end	Day	28% 19% 4 8% 5% 4 4 3 4 4 15%	2794
January	1st to 10th	Night	40% 24% 3 6% 3 3 2 2 3 2 10%	4406
	11th to 20th	Night	30% 16% 5% 6% 4 3 3 3 4 6% 21%	4382
	21st to end	Night	41% 15% 3 7% 4 3 4 2 3 4 14%	4817
February	1st to 10th	Night	34% 19% 3 7% 4 4 3 3 4 4 15%	2470
	11th to 20th	Night	30% 21% 3 5% 4 3 3 2 4 4 21%	2402
	21st to end	Night	30% 26% 3 5% 3 3 3 3 3 3 17%	1952
March	1st to 10th	Night	19% 22% 5% 8% 5% 5% 5% 4 5% 5% 18%	3692
	11th to 20th	Night	24% 18% 2 4 2 2 2 2 3 4 37%	3489
	21st to end	Night	34% 23% 3 6% 4 4 3 3 4 3 14%	3674
April	1st to 10th	Night	30% 23% 3 6% 4 3 3 3 5% 5% 14%	1900
	11th to 20th	Night	30% 18% 2 6% 4 3 3 3 4 4 24%	1879
	21st to end	Night	36% 16% 2 6% 4 3 4 2 4 4 18%	1656
May	1st to 10th	Night	29% 14% 2 4 3 2 2 2 3 3 36%	2540
	11th to 20th	Night	22% 17% 3 5% 3 3 3 3 4 5% 33%	2516
	21st to end	Night	40% 19% 3 5% 4 3 3 2 3 3 16%	2762
June	1st to 10th	Night	32% 12% 3 6% 5% 4 3 2 3 5% 25%	1520
	11th to 20th	Night	35% 13% 2 7% 5% 4 3 4 3 4 20%	1371
	21st to end	Night	23% 7% 2 6% 4 3 3 3 4 6% 39%	1330
July	1st to 10th	Night	16% 6% 2 4 2 2 2 2 3 3 58%	2245
	11th to 20th	Night	9% 4 1 2 2 2 2 2 3 3 70%	2540
	21st to end	Night	17% 6% 2 4 2 2 2 2 4 5% 54%	2762
August	1st to 10th	Night	8% 3 1 3 2 2 2 3 4 7% 65%	2558
	11th to 20th	Night	21% 9% 2 5% 3 3 3 2 4 5% 42%	2812
	21st to end	Night	26% 8% 2 4 2 2 2 2 2 5% 46%	3388
September	1st to 10th	Night	17% 6% 2 4 2 3 3 2 4 5% 51%	1900
	11th to 20th	Night	25% 9% 2 7% 3 3 3 3 4 4 37%	1900
	21st to end	Night	24% 8% 2 7% 3 3 4 4 4 5% 37%	2156
October	1st to 10th	Night	25% 9% 2 5% 4 3 3 3 4 6% 36%	2280
	11th to 20th	Night	31% 11% 2 5% 3 4 4 3 4 4 30%	2280
	21st to end	Night	34% 11% 3 6% 3 3 3 2 4 5% 27%	2563
November	1st to 10th	Night	41% 13% 3 6% 3 3 3 3 4 4 17%	2518
	11th to 20th	Night	40% 13% 3 6% 4 3 3 2 3 3 20%	2660
	21st to end	Night	37% 16% 3 6% 3 3 3 2 3 4 19%	2660
December	1st to 10th	Night	32% 15% 4 6% 5% 4 3 3 3 4 22%	2660
	11th to 20th	Night	35% 17% 3 7% 4 3 3 3 3 4 17%	3280
	21st to end	Night	30% 21% 4 7% 5% 5% 4 3 3 3 13%	4862

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	80% 5% 5% 7% 2 1	2539
	11th to 20th	Day	65% 6% 10% 12% 6% 2	2540
	21st to end	Day	79% 5% 5% 7% 5% 1	2835
February	1st to 10th	Day	75% 6% 7% 8% 4 1	1710
	11th to 20th	Day	73% 5% 5% 9% 6% 1	1674
	21st to end	Day	74% 4 7% 11% 5%	1501
March	1st to 10th	Day	67% 6% 9% 11% 7%	3169
	11th to 20th	Day	57% 5% 7% 29% 2	3490
	21st to end	Day	75% 8% 8% 7% 3	3979
April	1st to 10th	Day	75% 6% 11% 7% 1	2280
	11th to 20th	Day	69% 6% 8% 11% 6% 1	2252
	21st to end	Day	75% 4 7% 8% 5% 1	2522
May	1st to 10th	Day	58% 6% 11% 15% 10% 1	4420
	11th to 20th	Day	54% 11% 16% 16% 3	4380
	21st to end	Day	73% 10% 9% 7% 1	4814
June	1st to 10th	Day	65% 7% 13% 10% 6%	2660
	11th to 20th	Day	71% 7% 10% 9% 3	2802
	21st to end	Day	49% 7% 15% 18% 9% 1	2850
July	1st to 10th	Day	30% 5% 8% 17% 21% 19%	4637
	11th to 20th	Day	24% 4 6% 22% 36% 7%	4345
	21st to end	Day	31% 5% 12% 32% 18% 3	4639
August	1st to 10th	Day	25% 4 8% 31% 28% 4	4341
	11th to 20th	Day	48% 7% 12% 22% 10% 2	4065
	21st to end	Day	47% 5% 10% 21% 16% 2	4286
September	1st to 10th	Day	36% 6% 13% 23% 16% 6%	2280
	11th to 20th	Day	50% 6% 9% 17% 15% 3	2280
	21st to end	Day	50% 6% 13% 16% 12% 3	2020
October	1st to 10th	Day	54% 5% 8% 22% 9% 1	1900
	11th to 20th	Day	57% 5% 11% 16% 10% 1	1900
	21st to end	Day	64% 4 7% 13% 11% 1	1896
November	1st to 10th	Day	72% 6% 8% 10% 4	1560
	11th to 20th	Day	73% 4 6% 9% 7% 1	1520
	21st to end	Day	71% 4 4 9% 8% 3	1520
December	1st to 10th	Day	68% 5% 6% 12% 8% 1	1520
	11th to 20th	Day	71% 6% 8% 13% 2 1	1928
	21st to end	Day	72% 7% 8% 9% 5%	2794
January	1st to 10th	Night	82% 5% 4 6% 3 1	4406
	11th to 20th	Night	65% 4 8% 14% 6% 2	4420
	21st to end	Night	75% 6% 6% 6% 5% 1	4817
February	1st to 10th	Night	74% 6% 7% 10% 3 1	2470
	11th to 20th	Night	68% 7% 8% 9% 7% 1	2404
	21st to end	Night	74% 3 7% 10% 5%	1952
March	1st to 10th	Night	65% 8% 10% 11% 6% 1	3692
	11th to 20th	Night	53% 4 12% 27% 3 1	3490
	21st to end	Night	74% 9% 8% 7% 1	3674
April	1st to 10th	Night	74% 6% 10% 9% 1	1900
	11th to 20th	Night	65% 7% 8% 11% 8% 1	1879
	21st to end	Night	72% 6% 7% 9% 6% 1	1656
May	1st to 10th	Night	56% 7% 10% 17% 10%	2540
	11th to 20th	Night	52% 9% 17% 17% 4 1	2516
	21st to end	Night	74% 9% 9% 7% 1	2762
June	1st to 10th	Night	64% 8% 12% 11% 6%	1520
	11th to 20th	Night	68% 8% 11% 10% 3	1371
	21st to end	Night	49% 9% 14% 19% 7% 2	1330
July	1st to 10th	Night	34% 6% 7% 16% 15% 22%	2210
	11th to 20th	Night	22% 3 7% 21% 39% 8%	2492
	21st to end	Night	34% 6% 10% 23% 22% 5%	2674
August	1st to 10th	Night	22% 4 10% 31% 30% 4	2550
	11th to 20th	Night	48% 6% 14% 19% 10% 3	2839
	21st to end	Night	45% 4 11% 20% 17% 2	3388
September	1st to 10th	Night	35% 8% 12% 21% 19% 6%	1900
	11th to 20th	Night	55% 5% 6% 16% 13% 6%	1900
	21st to end	Night	51% 8% 10% 15% 12% 4	2156
October	1st to 10th	Night	51% 5% 10% 23% 10% 1	2280
	11th to 20th	Night	59% 5% 7% 18% 10% 1	2280
	21st to end	Night	60% 6% 8% 14% 12% 1	2563
November	1st to 10th	Night	72% 6% 7% 10% 4	2518
	11th to 20th	Night	71% 5% 7% 10% 6% 2	2660
	21st to end	Night	70% 5% 4 9% 9% 2	2660
December	1st to 10th	Night	68% 6% 7% 10% 8% 1	2660
	11th to 20th	Night	71% 6% 8% 10% 5%	3276
	21st to end	Night	75% 7% 8% 8% 3	4862

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	44% 18% 19% 12% 6% 1	180
	11th to 20th	Day	43% 14% 21% 16% 6% 1	180
	21st to end	Day	50% 11% 18% 15% 5%	226
February	1st to 10th	Day	47% 15% 21% 13% 5%	370
	11th to 20th	Day	49% 14% 22% 12% 4	365
	21st to end	Day	38% 19% 22% 19% 2	350
March	1st to 10th	Day	38% 19% 19% 19% 4	460
	11th to 20th	Day	35% 17% 23% 16% 8% 1	460
	21st to end	Day	43% 18% 22% 13% 4	506
April	1st to 10th	Day	43% 17% 18% 15% 6% 1	460
	11th to 20th	Day	39% 19% 23% 13% 6% 1	452
	21st to end	Day	41% 17% 22% 16% 5%	460
May	1st to 10th	Day	29% 14% 30% 21% 5% 1	463
	11th to 20th	Day	37% 12% 24% 17% 9% 1	488
	21st to end	Day	40% 12% 20% 20% 6% 2	529
June	1st to 10th	Day	33% 13% 22% 22% 8% 1	490
	11th to 20th	Day	37% 18% 24% 15% 5% 1	632
	21st to end	Day	23% 8% 28% 29% 9% 2	680
July	1st to 10th	Day	19% 8% 30% 33% 9% 1	655
	11th to 20th	Day	15% 10% 29% 31% 11% 3	484
	21st to end	Day	12% 7% 31% 31% 15% 4	531
August	1st to 10th	Day	15% 7% 23% 35% 13% 6%	487
	11th to 20th	Day	11% 7% 23% 40% 13% 5%	477
	21st to end	Day	20% 12% 23% 30% 10% 4	539
September	1st to 10th	Day	19% 10% 29% 31% 9% 2	490
	11th to 20th	Day	26% 11% 25% 25% 13% 1	490
	21st to end	Day	26% 10% 23% 29% 12%	490
October	1st to 10th	Day	29% 10% 24% 21% 14% 1	490
	11th to 20th	Day	37% 10% 21% 21% 10% 1	490
	21st to end	Day	40% 14% 20% 17% 7% 2	385
November	1st to 10th	Day	46% 14% 14% 21% 4	216
	11th to 20th	Day	44% 14% 15% 18% 6% 3	180
	21st to end	Day	43% 13% 19% 11% 13%	180
December	1st to 10th	Day	52% 8% 16% 11% 12% 1	180
	11th to 20th	Day	49% 12% 23% 14% 2	180
	21st to end	Day	45% 11% 23% 15% 6%	198
January	1st to 10th	Night	53% 11% 19% 15% 2	760
	11th to 20th	Night	43% 13% 21% 18% 6%	760
	21st to end	Night	42% 11% 22% 21% 4	836
February	1st to 10th	Night	42% 12% 27% 16% 3	760
	11th to 20th	Night	42% 9% 21% 22% 5%	744
	21st to end	Night	45% 10% 23% 16% 5% 1	628
March	1st to 10th	Night	37% 12% 22% 20% 9% 1	760
	11th to 20th	Night	41% 9% 21% 21% 8% 1	760
	21st to end	Night	42% 12% 19% 20% 6% 1	836
April	1st to 10th	Night	41% 12% 15% 23% 8% 1	760
	11th to 20th	Night	36% 10% 23% 23% 7% 1	751
	21st to end	Night	43% 8% 17% 24% 8%	516
May	1st to 10th	Night	33% 8% 14% 29% 14% 1	380
	11th to 20th	Night	31% 6% 13% 29% 18% 3	374
	21st to end	Night	37% 7% 14% 20% 20% 2	411
June	1st to 10th	Night	36% 6% 11% 29% 17% 1	380
	11th to 20th	Night	39% 8% 12% 24% 16%	380
	21st to end	Night	24% 4 15% 31% 25% 2	380
July	1st to 10th	Night	18% 7% 13% 30% 31% 1	370
	11th to 20th	Night	18% 5% 10% 33% 31% 4	368
	21st to end	Night	13% 5% 9% 31% 38% 4	416
August	1st to 10th	Night	15% 2 8% 28% 42% 6%	394
	11th to 20th	Night	17% 3 7% 28% 36% 10%	564
	21st to end	Night	21% 5% 11% 32% 29% 3	765
September	1st to 10th	Night	20% 2 13% 39% 23% 3	760
	11th to 20th	Night	27% 5% 14% 23% 26% 4	760
	21st to end	Night	28% 6% 14% 33% 19% 1	760
October	1st to 10th	Night	29% 4 18% 31% 16% 1	760
	11th to 20th	Night	37% 5% 19% 23% 14% 1	760
	21st to end	Night	39% 9% 22% 21% 8% 1	812
November	1st to 10th	Night	48% 8% 24% 18% 2	740
	11th to 20th	Night	48% 11% 20% 18% 2 1	760
	21st to end	Night	44% 10% 23% 21% 2	760
December	1st to 10th	Night	37% 12% 25% 21% 5%	760
	11th to 20th	Night	48% 12% 25% 12% 4	760
	21st to end	Night	54% 11% 20% 13% 2	836

Page generated at 2024-10-22 17:21:06. Version ac07

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