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 2024-02-25.

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	29% 13% 3 5% 4 2 4 3 4 5% 26%	78762
	Night	31% 14% 3 5% 4 2 3 3 4 4 25%	80491
Transparency	Day	61% 6% 9% 14% 8% 1	78484
	Night	64% 6% 8% 13% 8% 1	80349
Seeing	Day	33% 12% 23% 22% 8% 2	13894
	Night	37% 8% 18% 23% 12% 1	22537

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% 23% 4 6% 4 2 3 2 3 3 11%	2539
	11th to 20th	Day	29% 15% 5% 7% 5% 2 3 3 4 6% 22%	2516
	21st to end	Day	46% 16% 3 6% 4 2 2 3 3 4 12%	2835
February	1st to 10th	Day	34% 18% 5% 6% 5% 3 4 3 4 4 15%	1710
	11th to 20th	Day	34% 22% 4 5% 3 2 2 3 3 4 18%	1665
	21st to end	Day	31% 25% 4 5% 3 2 3 3 2 4 18%	1452
March	1st to 10th	Day	30% 21% 5% 7% 5% 3 4 3 3 4 17%	1818
	11th to 20th	Day	34% 21% 3 5% 5% 3 3 4 3 4 15%	1980
	21st to end	Day	35% 23% 3 5% 5% 4 4 4 4 4 10%	2268
April	1st to 10th	Day	32% 21% 4 6% 6% 2 4 4 4 4 12%	2160
	11th to 20th	Day	31% 18% 5% 6% 5% 3 4 3 4 4 19%	2132
	21st to end	Day	34% 18% 4 7% 6% 3 3 3 3 3 17%	2388
May	1st to 10th	Day	29% 15% 3 5% 6% 3 4 4 4 5% 24%	2520
	11th to 20th	Day	29% 12% 3 6% 5% 3 5% 4 5% 6% 23%	2477
	21st to end	Day	37% 12% 4 6% 4 3 4 4 4 5% 18%	2723
June	1st to 10th	Day	36% 10% 3 5% 5% 3 3 4 5% 5% 21%	2520
	11th to 20th	Day	37% 12% 4 7% 5% 3 5% 4 4 5% 15%	2654
	21st to end	Day	22% 8% 3 5% 4 3 4 5% 5% 7% 35%	2700
July	1st to 10th	Day	18% 8% 3 5% 4 2 3 3 4 6% 43%	2685
	11th to 20th	Day	17% 7% 2 4 4 2 4 4 5% 6% 45%	2520
	21st to end	Day	12% 5% 2 3 2 2 3 3 4 5% 58%	2741
August	1st to 10th	Day	17% 6% 2 4 4 2 3 3 4 7% 49%	2490
	11th to 20th	Day	13% 6% 2 3 3 2 3 3 5% 7% 53%	2298
	21st to end	Day	20% 8% 2 5% 4 2 4 3 4 6% 41%	2444
September	1st to 10th	Day	17% 6% 2 4 3 2 4 4 4 6% 48%	2160
	11th to 20th	Day	23% 7% 2 5% 5% 3 4 4 4 6% 37%	2160
	21st to end	Day	26% 8% 2 5% 4 2 3 3 4 5% 37%	1915
October	1st to 10th	Day	26% 10% 2 5% 5% 3 4 5% 4 5% 31%	1800
	11th to 20th	Day	31% 10% 2 4 4 3 3 3 5% 5% 30%	1800
	21st to end	Day	38% 10% 2 4 4 2 3 2 3 4 26%	1853
November	1st to 10th	Day	42% 11% 4 6% 4 2 3 4 3 4 16%	1560
	11th to 20th	Day	41% 15% 3 6% 3 1 3 3 2 3 20%	1520
	21st to end	Day	38% 15% 4 5% 3 2 3 2 3 4 20%	1520
December	1st to 10th	Day	34% 15% 4 5% 3 3 3 3 4 4 23%	1520
	11th to 20th	Day	36% 16% 3 5% 5% 2 3 3 4 4 18%	1925
	21st to end	Day	29% 19% 4 8% 6% 3 4 4 4 4 15%	2794
January	1st to 10th	Night	41% 24% 3 5% 4 2 2 2 3 2 10%	4406
	11th to 20th	Night	31% 15% 5% 5% 4 3 3 3 4 6% 21%	4382
	21st to end	Night	42% 14% 3 6% 5% 3 4 3 3 4 14%	4817
February	1st to 10th	Night	34% 18% 4 6% 5% 3 4 3 4 4 15%	2470
	11th to 20th	Night	30% 20% 3 5% 4 2 3 3 3 4 21%	2402
	21st to end	Night	30% 25% 3 4 4 2 4 4 3 3 18%	1897
March	1st to 10th	Night	30% 18% 3 4 4 2 4 4 4 5% 21%	2142
	11th to 20th	Night	32% 17% 4 5% 4 2 4 3 4 4 21%	1979
	21st to end	Night	34% 19% 4 6% 5% 3 3 4 5% 4 14%	2088
April	1st to 10th	Night	30% 21% 4 5% 5% 3 4 3 4 6% 15%	1800
	11th to 20th	Night	32% 16% 3 5% 4 2 3 3 4 4 23%	1779
	21st to end	Night	36% 15% 3 6% 5% 2 4 3 4 4 18%	1570
May	1st to 10th	Night	31% 12% 3 4 4 2 3 3 4 5% 29%	1440
	11th to 20th	Night	28% 12% 3 4 4 2 4 4 6% 5% 28%	1416
	21st to end	Night	35% 10% 3 4 5% 3 4 4 4 5% 23%	1552
June	1st to 10th	Night	33% 10% 3 6% 5% 3 4 3 4 5% 25%	1440
	11th to 20th	Night	36% 12% 3 6% 5% 2 3 5% 3 5% 20%	1299
	21st to end	Night	22% 6% 2 5% 5% 2 3 4 4 6% 41%	1260
July	1st to 10th	Night	19% 7% 3 4 4 3 3 3 4 4 46%	1271
	11th to 20th	Night	15% 7% 2 4 3 2 3 3 2 4 53%	1440
	21st to end	Night	13% 5% 2 3 2 2 2 2 4 5% 60%	1576
August	1st to 10th	Night	14% 6% 2 2 3 1 2 3 4 7% 56%	1447
	11th to 20th	Night	11% 6% 2 3 3 2 3 2 4 6% 59%	1602
	21st to end	Night	18% 7% 2 4 3 2 3 3 4 6% 49%	1912
September	1st to 10th	Night	17% 6% 2 3 3 2 3 3 4 5% 51%	1800
	11th to 20th	Night	25% 8% 2 6% 4 2 3 4 4 4 39%	1800
	21st to end	Night	24% 8% 2 6% 5% 2 4 4 3 4 37%	2042
October	1st to 10th	Night	26% 8% 3 5% 4 2 3 4 4 5% 36%	2160
	11th to 20th	Night	31% 11% 3 4 4 3 4 4 4 4 30%	2160
	21st to end	Night	35% 10% 3 5% 4 2 3 3 4 5% 27%	2502
November	1st to 10th	Night	41% 13% 3 5% 4 2 3 4 4 4 17%	2518
	11th to 20th	Night	41% 12% 3 5% 5% 2 3 3 3 3 20%	2660
	21st to end	Night	38% 15% 3 6% 4 2 3 2 3 5% 19%	2660
December	1st to 10th	Night	33% 14% 4 5% 5% 2 4 4 3 4 22%	2660
	11th to 20th	Night	35% 17% 4 6% 5% 2 3 4 3 4 17%	3280
	21st to end	Night	30% 20% 4 7% 5% 3 5% 4 3 4 14%	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	73% 4 7% 11% 5%	1452
March	1st to 10th	Day	73% 6% 7% 11% 3	1818
	11th to 20th	Day	73% 6% 7% 10% 4	1980
	21st to end	Day	79% 6% 7% 7% 1	2268
April	1st to 10th	Day	76% 5% 11% 7% 1	2160
	11th to 20th	Day	71% 6% 7% 11% 5% 1	2132
	21st to end	Day	74% 4 8% 8% 5% 1	2388
May	1st to 10th	Day	63% 6% 13% 14% 4	2520
	11th to 20th	Day	62% 8% 13% 13% 4	2480
	21st to end	Day	69% 9% 9% 12% 1	2724
June	1st to 10th	Day	65% 7% 13% 10% 5%	2520
	11th to 20th	Day	72% 7% 10% 8% 2	2654
	21st to end	Day	49% 8% 14% 18% 9% 1	2700
July	1st to 10th	Day	44% 6% 12% 21% 14% 2	2611
	11th to 20th	Day	39% 6% 10% 26% 18% 1	2445
	21st to end	Day	26% 5% 11% 32% 22% 5%	2589
August	1st to 10th	Day	36% 6% 12% 26% 17% 3	2473
	11th to 20th	Day	31% 6% 15% 28% 17% 3	2298
	21st to end	Day	43% 6% 11% 26% 12% 2	2444
September	1st to 10th	Day	36% 6% 13% 24% 15% 5%	2160
	11th to 20th	Day	49% 6% 9% 17% 16% 3	2160
	21st to end	Day	51% 6% 12% 16% 12% 3	1915
October	1st to 10th	Day	55% 5% 9% 21% 9% 1	1800
	11th to 20th	Day	57% 5% 11% 16% 10% 1	1800
	21st to end	Day	64% 4 7% 14% 11% 1	1853
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	73% 4 7% 11% 5%	1897
March	1st to 10th	Night	67% 7% 8% 14% 5%	2142
	11th to 20th	Night	67% 6% 8% 14% 4 1	1980
	21st to end	Night	75% 7% 9% 8% 1	2088
April	1st to 10th	Night	74% 6% 10% 9% 1	1800
	11th to 20th	Night	66% 7% 8% 12% 7% 1	1779
	21st to end	Night	71% 6% 7% 9% 6% 1	1570
May	1st to 10th	Night	60% 8% 11% 13% 6% 1	1440
	11th to 20th	Night	58% 8% 15% 12% 5% 1	1416
	21st to end	Night	65% 11% 10% 13% 1	1552
June	1st to 10th	Night	64% 7% 12% 11% 6%	1440
	11th to 20th	Night	68% 8% 11% 10% 3	1299
	21st to end	Night	47% 10% 14% 19% 7% 2	1260
July	1st to 10th	Night	44% 8% 11% 21% 13% 3	1236
	11th to 20th	Night	38% 6% 11% 26% 17% 2	1392
	21st to end	Night	28% 7% 8% 29% 21% 7%	1488
August	1st to 10th	Night	30% 7% 12% 26% 21% 4	1439
	11th to 20th	Night	30% 5% 14% 29% 17% 5%	1602
	21st to end	Night	39% 7% 12% 25% 15% 2	1912
September	1st to 10th	Night	35% 8% 12% 21% 18% 5%	1800
	11th to 20th	Night	53% 5% 6% 17% 13% 6%	1800
	21st to end	Night	51% 8% 9% 16% 13% 4	2042
October	1st to 10th	Night	52% 5% 10% 22% 10% 1	2160
	11th to 20th	Night	59% 5% 7% 18% 10% 1	2160
	21st to end	Night	60% 6% 8% 14% 12% 1	2502
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	37% 18% 24% 20% 3	331
March	1st to 10th	Day	40% 17% 20% 18% 4	420
	11th to 20th	Day	38% 15% 24% 16% 6% 1	420
	21st to end	Day	45% 16% 21% 13% 5%	462
April	1st to 10th	Day	44% 15% 19% 15% 6% 1	420
	11th to 20th	Day	42% 16% 22% 14% 6% 1	412
	21st to end	Day	41% 16% 22% 16% 4	420
May	1st to 10th	Day	29% 14% 31% 21% 4 1	423
	11th to 20th	Day	39% 10% 24% 17% 9% 1	448
	21st to end	Day	39% 11% 20% 21% 6% 2	485
June	1st to 10th	Day	33% 14% 21% 22% 8% 1	450
	11th to 20th	Day	36% 17% 25% 15% 5% 1	584
	21st to end	Day	22% 8% 27% 30% 9% 2	630
July	1st to 10th	Day	20% 8% 29% 33% 9% 1	606
	11th to 20th	Day	17% 11% 29% 30% 11% 2	444
	21st to end	Day	11% 6% 31% 32% 16% 4	487
August	1st to 10th	Day	17% 7% 21% 36% 14% 6%	447
	11th to 20th	Day	10% 6% 23% 41% 14% 5%	437
	21st to end	Day	19% 13% 24% 31% 10% 4	495
September	1st to 10th	Day	20% 10% 30% 30% 8% 2	450
	11th to 20th	Day	25% 11% 24% 26% 14% 1	450
	21st to end	Day	26% 10% 21% 30% 12%	450
October	1st to 10th	Day	29% 10% 24% 21% 15% 2	450
	11th to 20th	Day	36% 9% 20% 22% 11% 2	450
	21st to end	Day	40% 14% 20% 17% 7% 2	368
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	44% 10% 23% 17% 5% 1	610
March	1st to 10th	Night	38% 11% 21% 20% 9% 1	720
	11th to 20th	Night	43% 8% 21% 20% 7% 1	720
	21st to end	Night	43% 11% 19% 20% 6% 1	792
April	1st to 10th	Night	41% 11% 15% 23% 8% 2	720
	11th to 20th	Night	37% 10% 21% 24% 7% 1	711
	21st to end	Night	43% 8% 17% 24% 8%	490
May	1st to 10th	Night	33% 8% 14% 29% 15% 1	360
	11th to 20th	Night	32% 5% 13% 29% 18% 3	354
	21st to end	Night	37% 6% 14% 21% 21% 2	389
June	1st to 10th	Night	36% 4 12% 29% 17% 1	360
	11th to 20th	Night	39% 9% 12% 24% 16%	360
	21st to end	Night	22% 4 15% 31% 26% 2	360
July	1st to 10th	Night	18% 7% 12% 29% 33% 1	350
	11th to 20th	Night	19% 5% 10% 31% 31% 4	348
	21st to end	Night	12% 5% 9% 30% 39% 5%	394
August	1st to 10th	Night	16% 2 8% 26% 42% 6%	373
	11th to 20th	Night	15% 3 7% 28% 37% 10%	534
	21st to end	Night	20% 5% 10% 32% 30% 3	724
September	1st to 10th	Night	20% 2 13% 39% 23% 3	720
	11th to 20th	Night	26% 5% 14% 24% 27% 4	720
	21st to end	Night	28% 5% 14% 33% 19% 1	720
October	1st to 10th	Night	30% 4 17% 32% 17% 1	720
	11th to 20th	Night	36% 5% 18% 24% 15% 2	720
	21st to end	Night	40% 8% 22% 21% 8% 1	792
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 2024-02-22 03:05:42. Version ac07

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