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 2024-11-25.

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	16% 12% 4 9% 5% 4 4 3 5% 6% 30%	102249
	Night	15% 14% 5% 10% 6% 4 4 3 5% 6% 29%	97216
Transparency	Day	54% 6% 10% 20% 9% 1	105818
	Night	56% 6% 11% 18% 9% 1	101736
Seeing	Day	24% 18% 31% 18% 7% 2	14800
	Night	23% 16% 31% 21% 8% 1	23645

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	14% 20% 7% 18% 7% 4 4 3 4 4 16%	2517
	11th to 20th	Day	10% 15% 8% 20% 12% 6% 4 3 5% 5% 13%	2520
	21st to end	Day	16% 21% 12% 14% 4 4 3 3 3 3 17%	3120
February	1st to 10th	Day	9% 18% 8% 15% 10% 6% 4 3 4 5% 18%	1710
	11th to 20th	Day	11% 16% 7% 15% 7% 5% 5% 3 4 7% 22%	1663
	21st to end	Day	15% 18% 6% 10% 8% 5% 5% 5% 4 5% 20%	1456
March	1st to 10th	Day	15% 19% 5% 10% 5% 4 3 3 5% 5% 25%	3361
	11th to 20th	Day	9% 19% 7% 13% 6% 5% 4 3 4 5% 25%	3480
	21st to end	Day	11% 12% 5% 10% 5% 5% 3 2 4 5% 38%	3846
April	1st to 10th	Day	20% 16% 4 8% 4 4 4 3 4 6% 26%	2280
	11th to 20th	Day	21% 12% 4 6% 4 4 4 3 4 4 34%	2303
	21st to end	Day	21% 14% 4 8% 4 3 3 3 4 4 33%	2470
May	1st to 10th	Day	19% 10% 4 7% 5% 4 4 3 5% 6% 32%	4299
	11th to 20th	Day	15% 10% 3 8% 4 4 4 3 5% 7% 36%	4398
	21st to end	Day	17% 7% 2 6% 4 4 4 3 5% 7% 39%	4837
June	1st to 10th	Day	21% 10% 2 6% 5% 4 4 4 6% 6% 30%	2660
	11th to 20th	Day	15% 8% 2 6% 5% 4 5% 4 6% 8% 36%	2747
	21st to end	Day	19% 8% 3 7% 6% 5% 5% 4 5% 7% 32%	2850
July	1st to 10th	Day	15% 7% 2 7% 5% 6% 6% 4 6% 9% 33%	4671
	11th to 20th	Day	15% 6% 2 6% 5% 5% 5% 4 6% 7% 38%	4440
	21st to end	Day	11% 7% 2 6% 4 4 4 4 6% 8% 44%	4791
August	1st to 10th	Day	16% 7% 3 8% 5% 5% 5% 4 6% 8% 32%	4104
	11th to 20th	Day	19% 8% 2 7% 5% 5% 5% 4 6% 7% 34%	4044
	21st to end	Day	11% 6% 2 6% 5% 5% 5% 4 6% 10% 40%	4322
September	1st to 10th	Day	17% 7% 3 7% 3 3 5% 3 5% 8% 39%	2280
	11th to 20th	Day	16% 7% 2 6% 4 4 3 3 5% 6% 43%	2247
	21st to end	Day	20% 9% 2 7% 5% 5% 4 4 5% 6% 33%	2005
October	1st to 10th	Day	20% 11% 2 8% 4 3 4 4 5% 6% 32%	1900
	11th to 20th	Day	24% 17% 4 8% 5% 5% 4 3 4 4 22%	1900
	21st to end	Day	27% 17% 5% 9% 5% 4 3 3 3 5% 19%	2060
November	1st to 10th	Day	16% 17% 5% 8% 6% 4 4 3 5% 7% 26%	1618
	11th to 20th	Day	16% 18% 7% 13% 6% 5% 3 3 4 6% 20%	1600
	21st to end	Day	20% 21% 8% 13% 6% 4 4 3 3 3 14%	1552
December	1st to 10th	Day	17% 25% 8% 12% 6% 4 3 3 4 5% 13%	1520
	11th to 20th	Day	15% 22% 9% 12% 6% 5% 4 2 4 3 16%	1906
	21st to end	Day	21% 22% 9% 15% 7% 3 2 1 3 4 15%	2772
January	1st to 10th	Night	14% 21% 9% 17% 7% 5% 4 3 4 4 11%	4429
	11th to 20th	Night	10% 16% 6% 20% 13% 8% 4 3 4 4 12%	4440
	21st to end	Night	14% 18% 10% 17% 5% 6% 5% 3 3 4 14%	4532
February	1st to 10th	Night	11% 18% 6% 13% 9% 7% 4 4 5% 6% 18%	2470
	11th to 20th	Night	10% 16% 7% 13% 7% 5% 5% 3 5% 5% 24%	2403
	21st to end	Night	11% 18% 5% 13% 7% 6% 5% 4 5% 6% 22%	1998
March	1st to 10th	Night	15% 14% 5% 11% 6% 4 4 3 4 6% 28%	3477
	11th to 20th	Night	12% 19% 8% 11% 6% 4 4 3 4 5% 25%	3479
	21st to end	Night	10% 11% 6% 10% 7% 4 5% 3 5% 6% 32%	3772
April	1st to 10th	Night	19% 17% 5% 7% 4 3 3 3 5% 5% 30%	1900
	11th to 20th	Night	18% 12% 4 7% 4 3 3 3 4 5% 37%	1843
	21st to end	Night	20% 11% 4 8% 5% 5% 4 3 4 6% 31%	1710
May	1st to 10th	Night	18% 10% 2 6% 4 4 4 4 6% 7% 35%	2641
	11th to 20th	Night	17% 9% 3 5% 5% 5% 3 3 6% 7% 37%	2495
	21st to end	Night	12% 8% 3 7% 5% 4 4 4 4 7% 41%	2738
June	1st to 10th	Night	17% 9% 4 7% 5% 5% 5% 4 6% 6% 35%	1520
	11th to 20th	Night	14% 6% 2 6% 4 4 4 4 5% 6% 45%	1425
	21st to end	Night	17% 8% 3 7% 5% 3 5% 3 5% 7% 36%	1330
July	1st to 10th	Night	12% 8% 3 7% 5% 4 5% 5% 5% 7% 40%	2289
	11th to 20th	Night	15% 8% 2 6% 4 3 4 3 5% 7% 43%	2520
	21st to end	Night	11% 7% 2 5% 4 3 4 4 5% 7% 48%	2760
August	1st to 10th	Night	12% 5% 2 6% 4 4 4 5% 6% 8% 46%	2825
	11th to 20th	Night	17% 7% 2 6% 4 4 4 3 5% 6% 42%	2785
	21st to end	Night	14% 5% 2 4 3 4 4 3 6% 9% 46%	3302
September	1st to 10th	Night	12% 6% 2 5% 4 3 4 4 6% 7% 46%	1900
	11th to 20th	Night	15% 8% 2 5% 3 3 2 3 4 7% 48%	1930
	21st to end	Night	18% 9% 3 6% 3 3 4 4 4 6% 39%	2175
October	1st to 10th	Night	19% 12% 2 6% 3 4 4 3 4 6% 37%	2280
	11th to 20th	Night	21% 15% 3 7% 5% 4 4 3 4 6% 27%	2280
	21st to end	Night	24% 18% 5% 7% 5% 4 3 3 5% 4 22%	2536
November	1st to 10th	Night	16% 17% 4 8% 5% 4 5% 3 4 5% 28%	2677
	11th to 20th	Night	16% 16% 6% 10% 6% 5% 4 3 5% 6% 24%	2800
	21st to end	Night	18% 22% 6% 12% 6% 5% 5% 3 4 5% 15%	2723
December	1st to 10th	Night	17% 25% 8% 13% 8% 4 4 3 4 3 12%	2660
	11th to 20th	Night	14% 23% 8% 13% 5% 4 4 3 3 4 18%	3288
	21st to end	Night	21% 22% 8% 16% 7% 3 3 2 3 3 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	72% 5% 9% 8% 6%	2518
	11th to 20th	Day	73% 5% 6% 10% 5% 1	2520
	21st to end	Day	74% 4 5% 10% 6% 1	3120
February	1st to 10th	Day	69% 5% 5% 13% 6% 1	1710
	11th to 20th	Day	63% 5% 10% 12% 9% 1	1672
	21st to end	Day	66% 5% 7% 13% 9% 1	1456
March	1st to 10th	Day	61% 5% 12% 10% 11% 1	3364
	11th to 20th	Day	63% 4 9% 14% 8% 1	3480
	21st to end	Day	48% 5% 8% 21% 15% 4	3846
April	1st to 10th	Day	59% 4 8% 17% 9% 2	2280
	11th to 20th	Day	54% 4 7% 21% 11% 2	2303
	21st to end	Day	56% 4 7% 17% 13% 3	2470
May	1st to 10th	Day	52% 6% 9% 21% 11% 2	4311
	11th to 20th	Day	47% 6% 10% 27% 9% 1	4402
	21st to end	Day	45% 6% 12% 19% 15% 4	4837
June	1st to 10th	Day	53% 7% 10% 20% 10% 1	2660
	11th to 20th	Day	45% 6% 11% 23% 13% 2	2747
	21st to end	Day	50% 7% 12% 20% 10% 1	2850
July	1st to 10th	Day	46% 7% 14% 24% 9% 1	4599
	11th to 20th	Day	42% 7% 14% 29% 8%	4365
	21st to end	Day	37% 6% 11% 31% 14%	4638
August	1st to 10th	Day	48% 8% 12% 24% 7% 1	4091
	11th to 20th	Day	47% 7% 13% 26% 6% 1	4083
	21st to end	Day	38% 7% 12% 32% 10%	4322
September	1st to 10th	Day	44% 7% 12% 25% 11% 1	2280
	11th to 20th	Day	41% 6% 12% 28% 13%	2247
	21st to end	Day	51% 7% 10% 23% 9%	2005
October	1st to 10th	Day	51% 6% 11% 23% 7% 1	3160
	11th to 20th	Day	57% 5% 9% 19% 9% 1	3140
	21st to end	Day	66% 5% 11% 14% 4	3374
November	1st to 10th	Day	58% 6% 12% 18% 5% 1	1618
	11th to 20th	Day	66% 5% 9% 12% 7% 1	1600
	21st to end	Day	76% 4 8% 7% 4 1	1552
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	75% 5% 9% 7% 3	4429
	11th to 20th	Night	75% 7% 7% 7% 5% 1	4440
	21st to end	Night	75% 4 7% 8% 6% 1	4532
February	1st to 10th	Night	67% 6% 9% 12% 6% 1	2470
	11th to 20th	Night	63% 4 9% 16% 8% 1	2405
	21st to end	Night	62% 5% 8% 16% 8% 1	1998
March	1st to 10th	Night	58% 4 11% 14% 11% 1	3487
	11th to 20th	Night	60% 5% 13% 15% 7% 1	3480
	21st to end	Night	50% 6% 8% 20% 13% 2	3772
April	1st to 10th	Night	57% 4 8% 18% 12% 1	1900
	11th to 20th	Night	51% 4 6% 23% 14% 1	1843
	21st to end	Night	55% 5% 7% 16% 15% 2	1710
May	1st to 10th	Night	47% 6% 12% 23% 10% 2	2648
	11th to 20th	Night	46% 6% 11% 25% 10% 1	2496
	21st to end	Night	43% 6% 11% 24% 15% 1	2739
June	1st to 10th	Night	49% 6% 12% 20% 13% 1	1520
	11th to 20th	Night	38% 6% 13% 26% 16% 1	1425
	21st to end	Night	46% 7% 14% 21% 11%	1330
July	1st to 10th	Night	42% 7% 15% 21% 14% 1	2252
	11th to 20th	Night	41% 6% 12% 32% 9% 1	2472
	21st to end	Night	34% 7% 12% 32% 14% 1	2672
August	1st to 10th	Night	35% 7% 17% 26% 13% 1	2814
	11th to 20th	Night	42% 7% 18% 25% 7% 1	2812
	21st to end	Night	34% 7% 15% 31% 10% 2	3302
September	1st to 10th	Night	34% 9% 15% 28% 12% 1	1900
	11th to 20th	Night	38% 5% 14% 30% 13%	1930
	21st to end	Night	45% 6% 13% 26% 10%	2175
October	1st to 10th	Night	42% 6% 11% 27% 15%	3800
	11th to 20th	Night	52% 5% 13% 18% 12%	3779
	21st to end	Night	58% 5% 18% 13% 6%	4172
November	1st to 10th	Night	57% 6% 12% 18% 7%	2677
	11th to 20th	Night	62% 6% 11% 14% 6% 1	2800
	21st to end	Night	72% 6% 10% 9% 3	2723
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% 18% 34% 13% 3 1	180
	21st to end	Day	26% 20% 35% 15% 4	295
February	1st to 10th	Day	28% 29% 33% 6% 3	270
	11th to 20th	Day	25% 33% 35% 7%	270
	21st to end	Day	36% 26% 30% 7% 1	268
March	1st to 10th	Day	26% 22% 37% 13% 2	460
	11th to 20th	Day	27% 22% 34% 12% 4 1	460
	21st to end	Day	30% 23% 29% 14% 4	506
April	1st to 10th	Day	28% 22% 33% 12% 4 1	460
	11th to 20th	Day	35% 21% 22% 13% 7% 2	452
	21st to end	Day	30% 19% 31% 13% 5% 2	460
May	1st to 10th	Day	26% 17% 31% 18% 6% 2	463
	11th to 20th	Day	22% 18% 32% 18% 9% 2	487
	21st to end	Day	20% 19% 30% 21% 8% 2	529
June	1st to 10th	Day	25% 14% 34% 21% 4 1	490
	11th to 20th	Day	18% 14% 37% 21% 8% 2	577
	21st to end	Day	22% 16% 33% 20% 8% 1	680
July	1st to 10th	Day	14% 13% 34% 29% 9% 1	623
	11th to 20th	Day	15% 14% 33% 24% 11% 3	484
	21st to end	Day	13% 12% 35% 28% 9% 3	532
August	1st to 10th	Day	18% 10% 31% 26% 9% 6%	486
	11th to 20th	Day	16% 10% 28% 28% 12% 6%	479
	21st to end	Day	17% 12% 32% 23% 11% 4	539
September	1st to 10th	Day	18% 13% 33% 20% 11% 5%	490
	11th to 20th	Day	18% 11% 24% 22% 17% 9%	490
	21st to end	Day	23% 18% 24% 20% 12% 4	490
October	1st to 10th	Day	25% 20% 26% 16% 11% 3	490
	11th to 20th	Day	29% 24% 30% 12% 4 1	490
	21st to end	Day	38% 19% 27% 13% 3	522
November	1st to 10th	Day	32% 21% 32% 11% 4	252
	11th to 20th	Day	34% 19% 33% 11% 4 1	200
	21st to end	Day	32% 27% 31% 8% 1 1	188
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	28% 20% 31% 17% 4 1	760
	21st to end	Night	18% 19% 35% 21% 7% 1	836
February	1st to 10th	Night	20% 23% 38% 15% 3	760
	11th to 20th	Night	20% 21% 41% 15% 3	743
	21st to end	Night	23% 23% 33% 18% 3	628
March	1st to 10th	Night	21% 25% 32% 19% 3	760
	11th to 20th	Night	22% 20% 37% 15% 5% 1	760
	21st to end	Night	18% 20% 35% 20% 6% 1	836
April	1st to 10th	Night	28% 17% 33% 18% 4	760
	11th to 20th	Night	26% 18% 29% 18% 9%	719
	21st to end	Night	25% 13% 30% 21% 10%	570
May	1st to 10th	Night	24% 10% 27% 28% 10% 1	456
	11th to 20th	Night	22% 10% 34% 27% 8%	374
	21st to end	Night	16% 10% 35% 28% 10%	411
June	1st to 10th	Night	19% 12% 34% 28% 7%	380
	11th to 20th	Night	18% 8% 32% 31% 11%	380
	21st to end	Night	21% 9% 27% 31% 12% 1	380
July	1st to 10th	Night	13% 6% 31% 35% 14% 1	370
	11th to 20th	Night	16% 6% 29% 34% 14% 1	368
	21st to end	Night	11% 6% 34% 36% 12% 1	425
August	1st to 10th	Night	14% 5% 25% 36% 18% 2	567
	11th to 20th	Night	12% 6% 23% 34% 22% 3	564
	21st to end	Night	16% 8% 30% 28% 16% 2	727
September	1st to 10th	Night	13% 10% 30% 30% 16% 2	760
	11th to 20th	Night	20% 8% 24% 25% 19% 4	760
	21st to end	Night	23% 10% 23% 27% 15% 2	760
October	1st to 10th	Night	25% 16% 26% 21% 11% 2	760
	11th to 20th	Night	29% 17% 29% 16% 8% 1	760
	21st to end	Night	33% 18% 29% 16% 4	836
November	1st to 10th	Night	31% 17% 28% 19% 5% 1	780
	11th to 20th	Night	26% 24% 28% 16% 6%	800
	21st to end	Night	31% 20% 28% 17% 3	779
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 2024-11-22 08:02:23. Version ac07

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