Rock Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rock Lake clear sky chart from 2005-11-06 to 2024-11-12.

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	11% 9% 3 8% 5% 5% 5% 4 6% 7% 37%	105576
	Night	9% 9% 4 9% 6% 5% 5% 4 6% 7% 37%	102210
Transparency	Day	45% 6% 15% 25% 8%	105331
	Night	45% 6% 14% 24% 10% 1	102103
Seeing	Day	14% 9% 31% 29% 14% 4	16236
	Night	14% 8% 33% 32% 12% 1	26168

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% 17% 6% 13% 7% 8% 6% 3 7% 6% 22%	2219
	11th to 20th	Day	3 9% 4 15% 12% 10% 14% 9% 7% 6% 12%	2422
	21st to end	Day	7% 12% 4 14% 8% 6% 5% 4 6% 6% 27%	2794
February	1st to 10th	Day	9% 14% 5% 12% 7% 7% 6% 4 7% 7% 21%	1548
	11th to 20th	Day	6% 10% 4 11% 10% 6% 8% 7% 7% 8% 23%	1689
	21st to end	Day	6% 13% 4 11% 8% 5% 9% 4 6% 7% 26%	1570
March	1st to 10th	Day	12% 12% 4 9% 7% 6% 4 4 6% 7% 29%	3130
	11th to 20th	Day	7% 13% 5% 13% 9% 6% 5% 4 6% 8% 24%	3437
	21st to end	Day	9% 11% 6% 13% 8% 5% 5% 3 5% 7% 26%	3869
April	1st to 10th	Day	9% 12% 4 8% 6% 4 4 4 6% 8% 35%	2299
	11th to 20th	Day	13% 12% 4 10% 6% 4 5% 4 6% 7% 30%	2442
	21st to end	Day	15% 10% 4 8% 5% 4 4 4 6% 6% 34%	2470
May	1st to 10th	Day	20% 11% 3 7% 4 3 3 3 5% 8% 34%	4170
	11th to 20th	Day	19% 9% 3 7% 5% 5% 4 4 6% 7% 32%	4609
	21st to end	Day	17% 8% 3 7% 5% 4 4 4 5% 7% 35%	5173
June	1st to 10th	Day	13% 7% 2 6% 5% 4 5% 5% 7% 8% 38%	2850
	11th to 20th	Day	15% 6% 2 7% 5% 5% 5% 4 6% 8% 37%	2850
	21st to end	Day	12% 6% 2 6% 5% 5% 5% 6% 6% 9% 38%	2850
July	1st to 10th	Day	8% 4 2 5% 5% 5% 5% 5% 8% 10% 43%	4750
	11th to 20th	Day	7% 3 2 5% 4 4 4 4 7% 8% 51%	4750
	21st to end	Day	5% 4 1 5% 4 4 4 4 8% 10% 51%	4834
August	1st to 10th	Day	10% 5% 2 6% 4 4 4 4 6% 9% 46%	4387
	11th to 20th	Day	11% 5% 2 5% 3 3 4 3 6% 9% 50%	4041
	21st to end	Day	10% 6% 2 5% 3 4 4 3 5% 8% 49%	4532
September	1st to 10th	Day	11% 5% 2 4 4 4 3 3 5% 7% 52%	2309
	11th to 20th	Day	15% 7% 2 6% 3 4 3 4 5% 6% 45%	2090
	21st to end	Day	13% 7% 2 6% 4 4 4 3 6% 8% 43%	2090
October	1st to 10th	Day	11% 9% 2 5% 4 4 4 3 5% 5% 49%	3353
	11th to 20th	Day	9% 9% 3 7% 4 4 4 3 5% 9% 45%	2932
	21st to end	Day	12% 12% 4 8% 4 4 4 3 6% 7% 35%	3091
November	1st to 10th	Day	16% 15% 5% 10% 3 4 5% 4 4 4 30%	1719
	11th to 20th	Day	7% 15% 5% 16% 7% 5% 4 4 5% 5% 26%	1526
	21st to end	Day	9% 15% 4 12% 6% 5% 6% 4 5% 5% 29%	1330
December	1st to 10th	Day	6% 14% 5% 15% 10% 6% 6% 6% 5% 5% 21%	1330
	11th to 20th	Day	9% 14% 7% 16% 8% 7% 6% 4 6% 6% 19%	1679
	21st to end	Day	8% 9% 4 12% 6% 5% 5% 5% 6% 6% 35%	2442
January	1st to 10th	Night	5% 14% 7% 15% 7% 7% 6% 4 5% 7% 23%	4737
	11th to 20th	Night	5% 9% 5% 15% 9% 8% 10% 7% 8% 7% 16%	4484
	21st to end	Night	8% 13% 5% 15% 8% 5% 5% 4 5% 6% 25%	4873
February	1st to 10th	Night	8% 11% 5% 11% 8% 6% 6% 6% 7% 6% 24%	2631
	11th to 20th	Night	6% 9% 3 11% 7% 6% 7% 6% 7% 7% 31%	2394
	21st to end	Night	7% 10% 4 10% 7% 6% 6% 4 7% 7% 32%	1884
March	1st to 10th	Night	9% 11% 4 9% 7% 8% 5% 4 5% 6% 31%	3734
	11th to 20th	Night	7% 11% 4 9% 6% 4 4 4 6% 8% 37%	3522
	21st to end	Night	7% 10% 5% 13% 7% 6% 5% 4 5% 6% 32%	3761
April	1st to 10th	Night	7% 7% 3 7% 5% 5% 6% 4 6% 8% 40%	1881
	11th to 20th	Night	13% 12% 4 7% 5% 4 5% 4 5% 7% 34%	1689
	21st to end	Night	14% 8% 3 8% 4 4 6% 5% 6% 7% 36%	1710
May	1st to 10th	Night	19% 8% 3 6% 5% 4 5% 3 5% 6% 35%	2798
	11th to 20th	Night	15% 8% 2 6% 5% 4 4 4 6% 7% 40%	2281
	21st to end	Night	17% 7% 2 6% 4 2 4 3 5% 7% 43%	2414
June	1st to 10th	Night	11% 5% 2 5% 5% 3 4 4 6% 9% 45%	1330
	11th to 20th	Night	12% 6% 2 6% 5% 4 6% 5% 6% 7% 42%	1330
	21st to end	Night	9% 4 2 5% 3 3 4 6% 7% 11% 46%	1330
July	1st to 10th	Night	8% 3 2 4 4 3 4 4 6% 10% 52%	2220
	11th to 20th	Night	7% 3 1 4 3 3 4 3 7% 7% 58%	2220
	21st to end	Night	3 4 1 5% 4 4 5% 4 8% 10% 53%	2726
August	1st to 10th	Night	6% 5% 2 5% 4 4 5% 3 5% 7% 54%	2553
	11th to 20th	Night	6% 4 1 5% 4 4 5% 4 7% 10% 51%	2798
	21st to end	Night	9% 6% 2 5% 3 4 3 3 5% 7% 54%	3135
September	1st to 10th	Night	9% 5% 1 4 4 4 4 3 4 7% 55%	1868
	11th to 20th	Night	11% 5% 2 5% 4 3 4 3 6% 7% 49%	2090
	21st to end	Night	14% 8% 2 6% 4 3 4 3 5% 7% 45%	2090
October	1st to 10th	Night	11% 8% 2 6% 4 3 5% 3 5% 7% 47%	3574
	11th to 20th	Night	10% 8% 3 6% 4 5% 4 4 6% 8% 42%	3991
	21st to end	Night	7% 9% 3 8% 5% 5% 5% 4 6% 6% 43%	4467
November	1st to 10th	Night	11% 12% 4 8% 5% 5% 4 5% 6% 7% 33%	2577
	11th to 20th	Night	8% 13% 6% 14% 7% 5% 4 4 5% 6% 28%	2675
	21st to end	Night	9% 14% 4 11% 7% 4 4 4 5% 6% 30%	2850
December	1st to 10th	Night	6% 12% 5% 14% 8% 8% 5% 5% 6% 6% 26%	2850
	11th to 20th	Night	9% 16% 6% 14% 8% 6% 4 4 5% 7% 22%	3518
	21st to end	Night	8% 11% 4 12% 6% 6% 5% 4 6% 5% 34%	5225

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	60% 7% 14% 15% 3	2219
	11th to 20th	Day	68% 7% 11% 11% 4	2446
	21st to end	Day	56% 6% 10% 21% 6%	2794
February	1st to 10th	Day	60% 5% 11% 18% 6%	1548
	11th to 20th	Day	54% 6% 11% 19% 9% 1	1698
	21st to end	Day	54% 8% 12% 18% 8%	1570
March	1st to 10th	Day	52% 7% 14% 19% 8%	3130
	11th to 20th	Day	55% 8% 14% 17% 6%	3439
	21st to end	Day	56% 7% 12% 20% 6%	3869
April	1st to 10th	Day	46% 5% 16% 24% 8% 1	2299
	11th to 20th	Day	52% 5% 13% 19% 11% 1	2442
	21st to end	Day	50% 5% 16% 20% 8% 1	2470
May	1st to 10th	Day	48% 6% 14% 21% 10% 1	4170
	11th to 20th	Day	49% 7% 12% 22% 9% 1	4613
	21st to end	Day	46% 8% 12% 25% 9%	5173
June	1st to 10th	Day	41% 8% 18% 21% 11% 1	2850
	11th to 20th	Day	44% 8% 15% 22% 10% 1	2850
	21st to end	Day	40% 9% 20% 25% 6% 1	2850
July	1st to 10th	Day	33% 8% 26% 26% 5%	4676
	11th to 20th	Day	28% 7% 20% 37% 7%	4669
	21st to end	Day	26% 6% 25% 33% 9%	4682
August	1st to 10th	Day	34% 6% 19% 28% 13% 1	4371
	11th to 20th	Day	31% 5% 20% 35% 8%	4080
	21st to end	Day	34% 5% 19% 33% 9%	4531
September	1st to 10th	Day	32% 6% 17% 31% 13% 1	2309
	11th to 20th	Day	40% 6% 17% 25% 10% 1	2090
	21st to end	Day	38% 6% 16% 30% 10%	2090
October	1st to 10th	Day	38% 4 10% 38% 10% 1	3353
	11th to 20th	Day	38% 4 10% 36% 12%	2932
	21st to end	Day	48% 4 11% 27% 10%	3091
November	1st to 10th	Day	57% 4 11% 18% 8% 1	1719
	11th to 20th	Day	59% 5% 15% 14% 6%	1526
	21st to end	Day	57% 7% 11% 18% 7%	1330
December	1st to 10th	Day	62% 8% 11% 15% 4	1330
	11th to 20th	Day	64% 7% 10% 14% 5%	1680
	21st to end	Day	47% 6% 12% 20% 14% 1	2442
January	1st to 10th	Night	59% 8% 11% 17% 5%	4737
	11th to 20th	Night	62% 9% 12% 12% 5%	4522
	21st to end	Night	58% 7% 9% 20% 6%	4873
February	1st to 10th	Night	56% 6% 12% 16% 9% 1	2631
	11th to 20th	Night	48% 6% 14% 19% 12% 1	2395
	21st to end	Night	49% 6% 13% 22% 11% 1	1884
March	1st to 10th	Night	52% 6% 14% 21% 7%	3734
	11th to 20th	Night	43% 5% 17% 23% 10% 1	3522
	21st to end	Night	51% 7% 11% 22% 8%	3761
April	1st to 10th	Night	39% 5% 12% 25% 16% 2	1881
	11th to 20th	Night	50% 6% 11% 20% 13% 1	1689
	21st to end	Night	44% 7% 15% 22% 11% 1	1710
May	1st to 10th	Night	47% 6% 11% 25% 11% 1	2798
	11th to 20th	Night	41% 8% 12% 25% 10% 4	2281
	21st to end	Night	40% 7% 13% 30% 10%	2414
June	1st to 10th	Night	34% 8% 18% 27% 10% 2	1330
	11th to 20th	Night	40% 8% 15% 24% 12% 2	1330
	21st to end	Night	31% 8% 21% 33% 6% 1	1330
July	1st to 10th	Night	27% 8% 27% 28% 8% 1	2185
	11th to 20th	Night	24% 6% 18% 40% 11%	2178
	21st to end	Night	25% 5% 24% 34% 11% 1	2640
August	1st to 10th	Night	29% 6% 16% 34% 15% 1	2545
	11th to 20th	Night	28% 5% 21% 34% 11% 1	2825
	21st to end	Night	31% 4 18% 35% 11% 1	3135
September	1st to 10th	Night	30% 5% 13% 35% 15% 2	1868
	11th to 20th	Night	33% 6% 18% 30% 12% 1	2090
	21st to end	Night	40% 5% 11% 31% 12% 1	2090
October	1st to 10th	Night	37% 5% 12% 30% 15% 2	3574
	11th to 20th	Night	39% 4 12% 29% 15%	3991
	21st to end	Night	41% 5% 12% 33% 8%	4467
November	1st to 10th	Night	49% 7% 14% 20% 9% 2	2577
	11th to 20th	Night	57% 6% 13% 16% 7% 1	2675
	21st to end	Night	55% 7% 15% 17% 6%	2850
December	1st to 10th	Night	57% 7% 14% 16% 6%	2850
	11th to 20th	Night	62% 6% 14% 13% 5% 1	3516
	21st to end	Night	50% 5% 11% 20% 13% 1	5225

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	9% 10% 35% 29% 13% 4	270
	11th to 20th	Day	10% 8% 36% 33% 11% 1	270
	21st to end	Day	16% 8% 37% 26% 11% 3	297
February	1st to 10th	Day	14% 9% 41% 28% 6% 3	270
	11th to 20th	Day	10% 10% 36% 32% 11% 1	270
	21st to end	Day	6% 8% 40% 32% 12% 2	225
March	1st to 10th	Day	14% 13% 33% 28% 10% 2	270
	11th to 20th	Day	11% 12% 34% 27% 14% 2	270
	21st to end	Day	15% 8% 31% 27% 14% 4	327
April	1st to 10th	Day	13% 12% 33% 30% 9% 2	479
	11th to 20th	Day	20% 10% 32% 24% 13% 2	640
	21st to end	Day	19% 10% 31% 25% 13% 2	650
May	1st to 10th	Day	17% 10% 25% 30% 15% 3	653
	11th to 20th	Day	19% 8% 31% 25% 14% 3	675
	21st to end	Day	20% 9% 22% 30% 16% 3	734
June	1st to 10th	Day	14% 10% 30% 28% 12% 6%	680
	11th to 20th	Day	15% 8% 35% 28% 11% 4	680
	21st to end	Day	13% 9% 28% 30% 16% 4	680
July	1st to 10th	Day	9% 5% 28% 30% 20% 8%	671
	11th to 20th	Day	9% 7% 28% 30% 20% 5%	668
	21st to end	Day	6% 4 26% 36% 18% 8%	739
August	1st to 10th	Day	9% 5% 24% 34% 21% 6%	676
	11th to 20th	Day	13% 6% 23% 30% 21% 8%	665
	21st to end	Day	13% 7% 25% 32% 19% 4	748
September	1st to 10th	Day	13% 8% 35% 28% 13% 3	519
	11th to 20th	Day	17% 10% 27% 34% 11% 2	300
	21st to end	Day	20% 13% 30% 25% 11% 2	300
October	1st to 10th	Day	23% 14% 26% 24% 10% 3	300
	11th to 20th	Day	19% 8% 39% 24% 8% 3	300
	21st to end	Day	24% 8% 37% 23% 6% 2	330
November	1st to 10th	Day	26% 9% 32% 22% 9% 2	300
	11th to 20th	Day	14% 14% 35% 29% 8%	273
	21st to end	Day	16% 15% 39% 24% 5% 1	270
December	1st to 10th	Day	14% 9% 36% 27% 11% 3	270
	11th to 20th	Day	13% 14% 38% 28% 6% 1	270
	21st to end	Day	13% 8% 40% 27% 10% 3	297
January	1st to 10th	Night	11% 10% 37% 29% 10% 1	950
	11th to 20th	Night	14% 9% 39% 29% 8% 1	950
	21st to end	Night	13% 11% 37% 30% 7% 1	1045
February	1st to 10th	Night	13% 9% 37% 31% 10% 1	950
	11th to 20th	Night	10% 9% 36% 31% 11% 2	920
	21st to end	Night	12% 7% 33% 34% 11% 2	628
March	1st to 10th	Night	14% 8% 35% 29% 12% 3	760
	11th to 20th	Night	12% 8% 37% 31% 12% 1	599
	21st to end	Night	14% 6% 31% 33% 13% 2	627
April	1st to 10th	Night	10% 6% 39% 33% 11% 1	570
	11th to 20th	Night	19% 8% 30% 33% 9% 1	563
	21st to end	Night	16% 6% 34% 30% 13% 1	570
May	1st to 10th	Night	18% 7% 30% 31% 13% 1	570
	11th to 20th	Night	19% 8% 26% 34% 13%	561
	21st to end	Night	21% 7% 26% 32% 13%	617
June	1st to 10th	Night	12% 8% 33% 32% 13% 1	570
	11th to 20th	Night	14% 6% 35% 29% 16% 1	570
	21st to end	Night	12% 3 25% 41% 18%	570
July	1st to 10th	Night	6% 3 25% 42% 23% 1	555
	11th to 20th	Night	8% 5% 27% 42% 18% 1	552
	21st to end	Night	6% 2 23% 47% 19% 3	624
August	1st to 10th	Night	8% 3 22% 48% 18% 1	567
	11th to 20th	Night	8% 3 26% 39% 21% 3	564
	21st to end	Night	11% 5% 27% 40% 16% 1	627
September	1st to 10th	Night	11% 5% 31% 34% 17% 3	570
	11th to 20th	Night	15% 6% 31% 37% 11% 1	570
	21st to end	Night	18% 7% 32% 30% 12% 1	570
October	1st to 10th	Night	19% 8% 32% 31% 10%	625
	11th to 20th	Night	20% 10% 30% 31% 9%	883
	21st to end	Night	15% 11% 36% 30% 7% 1	1045
November	1st to 10th	Night	17% 10% 36% 28% 7% 1	975
	11th to 20th	Night	14% 11% 38% 26% 8% 2	956
	21st to end	Night	18% 13% 38% 24% 6% 1	950
December	1st to 10th	Night	11% 10% 37% 31% 10% 2	950
	11th to 20th	Night	17% 10% 33% 28% 9% 2	950
	21st to end	Night	18% 6% 34% 30% 9% 2	1045

Page generated at 2024-11-08 21:45:37. Version ac07

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