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 2024-01-14.

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	17% 12% 5% 8% 7% 3 5% 4 5% 6% 29%	75097
	Night	16% 13% 5% 8% 7% 3 4 4 4 6% 29%	74642
Transparency	Day	56% 6% 9% 18% 9% 1	74801
	Night	57% 6% 10% 17% 10% 1	74473
Seeing	Day	24% 18% 31% 18% 7% 2	13613
	Night	23% 16% 31% 21% 8% 1	22597

By Month

Percentage Cloud Cover NE (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	13% 19% 9% 14% 10% 3 5% 3 4 5% 15%	1517
	11th to 20th	Day	15% 18% 8% 13% 7% 4 4 4 4 5% 19%	1464
	21st to end	Day	12% 14% 7% 14% 8% 5% 6% 5% 5% 4 21%	1778
February	1st to 10th	Day	10% 17% 9% 13% 12% 4 5% 4 4 4 17%	1620
	11th to 20th	Day	12% 14% 7% 12% 9% 3 6% 4 4 7% 22%	1573
	21st to end	Day	15% 17% 7% 9% 9% 3 6% 6% 3 5% 19%	1372
March	1st to 10th	Day	13% 14% 6% 11% 8% 5% 5% 4 4 5% 26%	1931
	11th to 20th	Day	12% 15% 7% 11% 8% 5% 4 4 4 5% 26%	1980
	21st to end	Day	16% 12% 5% 9% 5% 3 3 4 4 6% 34%	2196
April	1st to 10th	Day	20% 14% 5% 8% 5% 3 4 4 4 7% 26%	2160
	11th to 20th	Day	21% 11% 4 6% 5% 3 5% 4 4 4 35%	2180
	21st to end	Day	21% 13% 4 7% 5% 3 3 3 3 5% 33%	2340
May	1st to 10th	Day	19% 10% 4 6% 5% 3 4 4 5% 7% 34%	2447
	11th to 20th	Day	19% 10% 4 6% 6% 3 4 4 4 6% 36%	2478
	21st to end	Day	15% 7% 3 6% 6% 4 5% 4 5% 7% 39%	2725
June	1st to 10th	Day	21% 9% 3 6% 6% 3 4 5% 5% 7% 31%	2520
	11th to 20th	Day	16% 7% 3 6% 5% 3 5% 5% 5% 8% 37%	2602
	21st to end	Day	18% 7% 3 6% 6% 4 5% 6% 5% 7% 33%	2700
July	1st to 10th	Day	14% 5% 2 5% 6% 4 6% 5% 6% 8% 38%	2653
	11th to 20th	Day	14% 6% 3 6% 7% 4 5% 5% 5% 8% 37%	2520
	21st to end	Day	13% 7% 2 7% 6% 4 5% 6% 7% 8% 34%	2734
August	1st to 10th	Day	15% 6% 3 7% 7% 4 6% 5% 6% 8% 34%	2327
	11th to 20th	Day	16% 7% 2 6% 6% 4 5% 6% 6% 7% 34%	2303
	21st to end	Day	16% 7% 3 6% 6% 3 6% 5% 6% 9% 32%	2462
September	1st to 10th	Day	17% 7% 3 6% 4 3 4 5% 5% 8% 38%	2160
	11th to 20th	Day	17% 7% 2 6% 5% 3 4 4 5% 6% 41%	2129
	21st to end	Day	20% 8% 3 7% 6% 4 4 5% 5% 6% 33%	1900
October	1st to 10th	Day	21% 11% 3 6% 6% 3 4 5% 5% 6% 31%	1800
	11th to 20th	Day	26% 15% 4 7% 6% 4 4 4 4 5% 20%	1800
	21st to end	Day	28% 17% 5% 7% 7% 3 3 4 3 5% 18%	1952
November	1st to 10th	Day	16% 15% 6% 7% 7% 3 4 4 4 7% 27%	1536
	11th to 20th	Day	18% 16% 8% 11% 7% 3 4 4 4 6% 20%	1520
	21st to end	Day	20% 19% 9% 12% 7% 3 4 4 3 4 14%	1520
December	1st to 10th	Day	18% 23% 9% 11% 8% 3 3 3 4 5% 13%	1520
	11th to 20th	Day	15% 20% 10% 11% 8% 4 5% 3 4 3 17%	1906
	21st to end	Day	21% 21% 9% 12% 9% 2 2 2 3 4 15%	2772
January	1st to 10th	Night	14% 19% 9% 14% 8% 4 5% 5% 5% 4 13%	2649
	11th to 20th	Night	14% 18% 8% 13% 10% 5% 5% 3 4 5% 16%	2569
	21st to end	Night	11% 14% 6% 12% 8% 4 7% 5% 5% 5% 23%	2574
February	1st to 10th	Night	11% 17% 8% 12% 10% 6% 5% 5% 5% 6% 17%	2340
	11th to 20th	Night	11% 14% 8% 12% 8% 4 5% 4 5% 5% 25%	2273
	21st to end	Night	11% 17% 7% 11% 8% 4 5% 4 5% 5% 22%	1884
March	1st to 10th	Night	13% 12% 6% 11% 8% 3 5% 4 4 5% 30%	2014
	11th to 20th	Night	13% 13% 7% 9% 7% 4 4 4 4 5% 30%	1979
	21st to end	Night	11% 13% 5% 8% 6% 3 4 4 4 7% 37%	2160
April	1st to 10th	Night	19% 15% 6% 6% 5% 3 4 3 5% 5% 30%	1800
	11th to 20th	Night	18% 11% 4 6% 5% 2 4 4 4 5% 37%	1745
	21st to end	Night	20% 10% 4 7% 6% 4 4 4 4 6% 31%	1620
May	1st to 10th	Night	19% 8% 3 5% 5% 3 4 5% 6% 9% 35%	1512
	11th to 20th	Night	17% 8% 3 4 5% 3 3 4 6% 7% 40%	1415
	21st to end	Night	12% 6% 3 5% 4 3 5% 5% 4 9% 44%	1550
June	1st to 10th	Night	18% 7% 4 6% 5% 4 5% 5% 6% 6% 35%	1440
	11th to 20th	Night	14% 5% 2 6% 5% 3 4 5% 5% 7% 45%	1350
	21st to end	Night	16% 8% 3 6% 5% 3 5% 5% 5% 7% 37%	1260
July	1st to 10th	Night	11% 6% 2 4 5% 2 4 5% 5% 8% 49%	1300
	11th to 20th	Night	13% 7% 3 5% 5% 3 4 4 5% 8% 44%	1440
	21st to end	Night	10% 5% 2 5% 5% 3 5% 6% 6% 9% 44%	1582
August	1st to 10th	Night	12% 5% 2 4 5% 2 4 6% 5% 8% 46%	1611
	11th to 20th	Night	10% 6% 2 5% 5% 4 4 5% 6% 8% 44%	1598
	21st to end	Night	14% 7% 3 4 5% 3 4 4 6% 9% 40%	1876
September	1st to 10th	Night	12% 6% 2 4 5% 2 4 5% 6% 7% 46%	1800
	11th to 20th	Night	16% 9% 2 5% 4 2 3 4 4 7% 46%	1828
	21st to end	Night	18% 8% 3 5% 4 3 4 5% 4 7% 39%	2060
October	1st to 10th	Night	19% 11% 2 6% 4 3 4 4 4 6% 36%	2160
	11th to 20th	Night	23% 14% 4 6% 5% 4 4 4 4 6% 25%	2160
	21st to end	Night	25% 17% 5% 6% 6% 3 3 3 5% 4 22%	2402
November	1st to 10th	Night	16% 16% 5% 6% 6% 3 5% 4 4 5% 29%	2539
	11th to 20th	Night	17% 14% 7% 9% 7% 4 5% 4 4 5% 24%	2660
	21st to end	Night	17% 21% 7% 10% 8% 4 5% 4 4 5% 16%	2660
December	1st to 10th	Night	18% 23% 9% 12% 9% 3 4 4 4 3 12%	2660
	11th to 20th	Night	14% 22% 9% 12% 7% 3 4 4 3 4 18%	3288
	21st to end	Night	21% 21% 8% 13% 10% 2 3 3 3 4 11%	4884

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	71% 4 7% 12% 5%	1518
	11th to 20th	Day	69% 4 6% 10% 9% 2	1464
	21st to end	Day	65% 6% 6% 10% 10% 2	1778
February	1st to 10th	Day	70% 5% 4 13% 7% 1	1620
	11th to 20th	Day	63% 5% 10% 12% 9% 1	1582
	21st to end	Day	67% 5% 7% 12% 9%	1372
March	1st to 10th	Day	61% 4 10% 13% 9% 2	1934
	11th to 20th	Day	62% 4 8% 15% 9% 2	1980
	21st to end	Day	53% 4 7% 18% 13% 5%	2196
April	1st to 10th	Day	60% 4 8% 16% 9% 2	2160
	11th to 20th	Day	53% 4 8% 22% 12% 2	2180
	21st to end	Day	56% 4 7% 17% 13% 3	2340
May	1st to 10th	Day	51% 5% 9% 19% 13% 3	2447
	11th to 20th	Day	50% 5% 8% 22% 13% 2	2482
	21st to end	Day	45% 7% 12% 20% 13% 3	2725
June	1st to 10th	Day	52% 6% 10% 20% 11% 1	2520
	11th to 20th	Day	45% 6% 11% 23% 14% 2	2602
	21st to end	Day	49% 8% 12% 20% 10% 1	2700
July	1st to 10th	Day	41% 6% 12% 27% 12% 1	2581
	11th to 20th	Day	44% 7% 12% 26% 10% 1	2445
	21st to end	Day	46% 7% 12% 25% 9%	2581
August	1st to 10th	Day	47% 9% 13% 21% 8% 1	2314
	11th to 20th	Day	47% 8% 14% 23% 7% 1	2303
	21st to end	Day	48% 7% 13% 22% 10% 1	2462
September	1st to 10th	Day	44% 7% 12% 25% 11% 1	2160
	11th to 20th	Day	43% 6% 12% 28% 11%	2129
	21st to end	Day	52% 7% 10% 24% 7%	1900
October	1st to 10th	Day	53% 6% 12% 18% 10% 1	1800
	11th to 20th	Day	67% 5% 9% 12% 5% 1	1800
	21st to end	Day	70% 4 8% 11% 5% 1	1952
November	1st to 10th	Day	57% 6% 13% 18% 6% 1	1536
	11th to 20th	Day	66% 5% 10% 12% 6% 1	1520
	21st to end	Day	76% 4 8% 8% 4 1	1520
December	1st to 10th	Day	75% 4 7% 9% 4 1	1520
	11th to 20th	Day	73% 4 5% 9% 7% 1	1906
	21st to end	Day	76% 3 4 12% 4	2772
January	1st to 10th	Night	74% 5% 8% 8% 5%	2649
	11th to 20th	Night	72% 4 6% 9% 7% 1	2569
	21st to end	Night	62% 5% 7% 13% 11% 1	2574
February	1st to 10th	Night	69% 5% 8% 11% 6% 1	2340
	11th to 20th	Night	62% 4 9% 16% 9% 1	2275
	21st to end	Night	62% 5% 7% 16% 8% 1	1884
March	1st to 10th	Night	58% 3 9% 15% 12% 2	2024
	11th to 20th	Night	55% 5% 11% 16% 11% 2	1980
	21st to end	Night	48% 5% 9% 20% 15% 3	2160
April	1st to 10th	Night	57% 4 7% 18% 12% 2	1800
	11th to 20th	Night	50% 4 7% 23% 14% 1	1745
	21st to end	Night	56% 5% 7% 16% 15% 2	1620
May	1st to 10th	Night	45% 6% 11% 19% 16% 3	1512
	11th to 20th	Night	43% 6% 9% 24% 16% 2	1416
	21st to end	Night	38% 7% 15% 20% 16% 3	1551
June	1st to 10th	Night	48% 6% 12% 21% 13% 1	1440
	11th to 20th	Night	38% 6% 13% 26% 16% 1	1350
	21st to end	Night	45% 7% 15% 21% 11%	1260
July	1st to 10th	Night	32% 8% 14% 26% 19% 1	1263
	11th to 20th	Night	39% 5% 13% 30% 12% 1	1392
	21st to end	Night	35% 7% 17% 29% 11% 1	1494
August	1st to 10th	Night	35% 8% 18% 27% 12% 1	1600
	11th to 20th	Night	35% 9% 19% 26% 9% 1	1598
	21st to end	Night	39% 7% 17% 26% 9% 1	1876
September	1st to 10th	Night	35% 10% 15% 27% 12% 1	1800
	11th to 20th	Night	40% 5% 14% 30% 11%	1828
	21st to end	Night	45% 7% 13% 27% 8%	2060
October	1st to 10th	Night	49% 6% 11% 19% 14%	2160
	11th to 20th	Night	60% 6% 12% 16% 6%	2160
	21st to end	Night	66% 5% 8% 12% 8% 1	2402
November	1st to 10th	Night	57% 6% 12% 18% 7%	2539
	11th to 20th	Night	62% 6% 12% 13% 6% 1	2660
	21st to end	Night	71% 6% 10% 10% 4	2660
December	1st to 10th	Night	77% 5% 6% 8% 3	2660
	11th to 20th	Night	71% 4 6% 12% 7% 1	3288
	21st to end	Night	80% 4 5% 7% 4	4884

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	25% 26% 31% 13% 3 2	180
	11th to 20th	Day	31% 15% 35% 14% 4 1	166
	21st to end	Day	26% 21% 34% 14% 5%	262
February	1st to 10th	Day	30% 31% 32% 5% 2	240
	11th to 20th	Day	27% 32% 36% 5%	240
	21st to end	Day	37% 25% 30% 8% 1	238
March	1st to 10th	Day	26% 23% 36% 13% 1	420
	11th to 20th	Day	27% 22% 32% 13% 5% 1	420
	21st to end	Day	30% 22% 29% 15% 4	462
April	1st to 10th	Day	27% 22% 33% 13% 5% 1	420
	11th to 20th	Day	32% 20% 22% 15% 8% 3	412
	21st to end	Day	30% 18% 32% 13% 5% 2	420
May	1st to 10th	Day	26% 17% 31% 18% 6% 2	423
	11th to 20th	Day	23% 18% 32% 15% 9% 2	447
	21st to end	Day	20% 19% 30% 20% 8% 3	485
June	1st to 10th	Day	24% 14% 35% 21% 4 1	450
	11th to 20th	Day	19% 14% 36% 20% 9% 2	532
	21st to end	Day	19% 16% 34% 21% 8% 1	630
July	1st to 10th	Day	13% 12% 34% 30% 10% 1	576
	11th to 20th	Day	15% 14% 31% 25% 12% 3	444
	21st to end	Day	13% 12% 36% 28% 8% 2	488
August	1st to 10th	Day	18% 9% 33% 25% 9% 6%	446
	11th to 20th	Day	16% 9% 28% 29% 12% 6%	439
	21st to end	Day	19% 13% 31% 22% 11% 4	495
September	1st to 10th	Day	17% 13% 33% 20% 12% 5%	450
	11th to 20th	Day	20% 12% 26% 22% 14% 6%	450
	21st to end	Day	23% 17% 25% 20% 12% 4	450
October	1st to 10th	Day	26% 19% 24% 16% 12% 3	450
	11th to 20th	Day	31% 24% 29% 12% 3 1	450
	21st to end	Day	39% 18% 27% 13% 3	480
November	1st to 10th	Day	30% 22% 32% 12% 4	230
	11th to 20th	Day	33% 19% 32% 11% 4 1	180
	21st to end	Day	32% 25% 32% 8% 1 1	180
December	1st to 10th	Day	34% 18% 33% 14% 1	180
	11th to 20th	Day	34% 26% 31% 8% 1 1	180
	21st to end	Day	30% 28% 27% 12% 3 1	198
January	1st to 10th	Night	26% 21% 36% 14% 3	760
	11th to 20th	Night	29% 19% 30% 17% 4 1	735
	21st to end	Night	17% 19% 34% 22% 7% 1	792
February	1st to 10th	Night	21% 24% 39% 13% 3	720
	11th to 20th	Night	20% 21% 40% 16% 3	703
	21st to end	Night	24% 22% 33% 18% 3	592
March	1st to 10th	Night	22% 24% 32% 18% 3	720
	11th to 20th	Night	22% 20% 36% 15% 5% 1	720
	21st to end	Night	18% 19% 35% 20% 6% 1	792
April	1st to 10th	Night	28% 17% 33% 18% 4	720
	11th to 20th	Night	25% 18% 28% 19% 9%	681
	21st to end	Night	24% 13% 30% 22% 10%	540
May	1st to 10th	Night	24% 10% 27% 28% 10% 1	432
	11th to 20th	Night	22% 10% 34% 26% 7%	354
	21st to end	Night	16% 10% 36% 27% 10%	389
June	1st to 10th	Night	19% 12% 34% 28% 6%	360
	11th to 20th	Night	18% 8% 32% 31% 11%	360
	21st to end	Night	19% 9% 27% 32% 12% 1	360
July	1st to 10th	Night	13% 6% 31% 35% 15% 1	350
	11th to 20th	Night	16% 6% 28% 34% 14% 1	348
	21st to end	Night	11% 6% 35% 35% 12% 1	402
August	1st to 10th	Night	14% 4 26% 36% 18% 2	537
	11th to 20th	Night	10% 6% 24% 35% 22% 3	534
	21st to end	Night	16% 8% 31% 26% 17% 2	688
September	1st to 10th	Night	12% 10% 31% 29% 16% 2	720
	11th to 20th	Night	21% 9% 25% 25% 16% 3	720
	21st to end	Night	22% 10% 24% 27% 15% 2	720
October	1st to 10th	Night	26% 16% 25% 21% 10% 2	720
	11th to 20th	Night	29% 17% 30% 16% 7% 1	720
	21st to end	Night	34% 18% 29% 16% 4	792
November	1st to 10th	Night	30% 17% 29% 19% 5% 1	740
	11th to 20th	Night	26% 24% 29% 16% 6%	760
	21st to end	Night	31% 20% 29% 17% 3	760
December	1st to 10th	Night	31% 22% 33% 11% 3 1	760
	11th to 20th	Night	25% 23% 34% 14% 3 1	760
	21st to end	Night	34% 19% 30% 14% 3 1	836

Page generated at 2024-01-11 04:22:40. Version ac07

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