Crystal Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Crystal Lake clear sky chart from 2005-11-06 to 2024-11-03.

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	13% 9% 3 8% 5% 4 4 4 6% 7% 37%	101321
	Night	14% 10% 4 7% 4 4 4 3 5% 6% 38%	97747
Transparency	Day	45% 7% 12% 22% 13% 1	101109
	Night	45% 6% 11% 22% 14% 2	97631
Seeing	Day	16% 13% 31% 25% 12% 4	15835
	Night	17% 11% 32% 28% 11% 1	25668

By Month

Percentage Cloud Cover SE (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% 14% 9% 11% 6% 5% 3 3 4 4 27%	2527
	11th to 20th	Day	11% 14% 6% 14% 5% 3 6% 8% 7% 5% 20%	2530
	21st to end	Day	17% 21% 9% 10% 4 3 2 3 4 6% 20%	2856
February	1st to 10th	Day	13% 15% 5% 8% 6% 6% 5% 3 5% 6% 28%	1725
	11th to 20th	Day	13% 12% 4 8% 5% 5% 4 3 5% 5% 37%	1848
	21st to end	Day	14% 13% 5% 11% 5% 4 4 4 5% 8% 30%	1570
March	1st to 10th	Day	14% 13% 3 8% 5% 4 3 3 5% 5% 37%	3120
	11th to 20th	Day	11% 6% 4 7% 5% 5% 4 4 6% 8% 41%	3273
	21st to end	Day	19% 14% 5% 13% 5% 5% 5% 3 4 5% 22%	4165
April	1st to 10th	Day	17% 14% 3 8% 5% 4 4 3 5% 5% 31%	2280
	11th to 20th	Day	16% 11% 3 7% 6% 5% 4 4 5% 6% 35%	2254
	21st to end	Day	19% 9% 3 7% 5% 5% 4 4 5% 6% 33%	2380
May	1st to 10th	Day	16% 7% 3 7% 5% 4 4 4 6% 7% 36%	4082
	11th to 20th	Day	15% 6% 2 5% 4 4 4 4 6% 7% 43%	4357
	21st to end	Day	11% 7% 2 6% 4 5% 5% 4 6% 9% 40%	4824
June	1st to 10th	Day	9% 6% 2 6% 5% 5% 4 4 6% 7% 45%	2660
	11th to 20th	Day	9% 6% 2 6% 5% 4 5% 4 7% 9% 44%	2660
	21st to end	Day	10% 7% 3 7% 5% 4 5% 4 6% 8% 40%	2660
July	1st to 10th	Day	11% 8% 3 7% 5% 6% 6% 5% 8% 9% 32%	4440
	11th to 20th	Day	6% 4 2 5% 5% 5% 5% 4 7% 9% 48%	4440
	21st to end	Day	8% 6% 3 7% 6% 5% 5% 4 6% 8% 42%	4813
August	1st to 10th	Day	11% 5% 2 6% 4 4 6% 4 7% 9% 42%	4370
	11th to 20th	Day	10% 5% 2 7% 4 5% 5% 4 6% 9% 42%	3738
	21st to end	Day	7% 5% 3 7% 4 4 5% 4 6% 8% 48%	4180
September	1st to 10th	Day	12% 5% 2 6% 4 4 4 4 5% 8% 47%	2280
	11th to 20th	Day	12% 4 1 4 3 3 4 4 5% 8% 53%	2170
	21st to end	Day	11% 7% 3 6% 4 5% 4 4 6% 8% 43%	2090
October	1st to 10th	Day	13% 6% 3 6% 4 4 4 3 5% 5% 47%	2020
	11th to 20th	Day	18% 8% 4 7% 5% 4 4 3 4 6% 36%	1892
	21st to end	Day	19% 9% 3 7% 4 4 5% 3 4 4 37%	1881
November	1st to 10th	Day	12% 9% 3 6% 4 4 5% 3 6% 5% 45%	1690
	11th to 20th	Day	15% 12% 4 10% 5% 3 4 4 6% 6% 33%	1710
	21st to end	Day	18% 11% 3 9% 4 4 3 2 5% 5% 36%	1615
December	1st to 10th	Day	14% 13% 5% 11% 5% 5% 4 3 5% 6% 30%	1520
	11th to 20th	Day	11% 15% 4 10% 6% 4 5% 4 6% 7% 28%	1918
	21st to end	Day	19% 24% 9% 11% 5% 3 4 3 3 3 15%	2783
January	1st to 10th	Night	14% 14% 7% 12% 5% 4 3 3 3 4 31%	4428
	11th to 20th	Night	15% 16% 7% 14% 5% 4 3 6% 6% 4 19%	4440
	21st to end	Night	21% 18% 7% 10% 4 3 4 3 4 5% 21%	4808
February	1st to 10th	Night	13% 15% 4 8% 6% 5% 3 3 4 6% 32%	2453
	11th to 20th	Night	13% 11% 3 7% 4 5% 4 3 5% 5% 38%	2218
	21st to end	Night	17% 12% 4 8% 5% 3 3 2 4 5% 36%	1884
March	1st to 10th	Night	18% 10% 3 6% 4 4 4 3 4 5% 41%	3733
	11th to 20th	Night	9% 7% 2 6% 5% 5% 5% 3 5% 7% 46%	3715
	21st to end	Night	22% 12% 5% 10% 5% 4 4 3 4 4 28%	3466
April	1st to 10th	Night	16% 9% 3 6% 5% 4 4 4 4 6% 38%	1900
	11th to 20th	Night	19% 8% 3 7% 4 4 4 4 4 5% 38%	1875
	21st to end	Night	18% 8% 3 6% 5% 4 4 3 5% 6% 39%	1800
May	1st to 10th	Night	15% 7% 3 7% 5% 5% 4 5% 7% 7% 36%	2813
	11th to 20th	Night	15% 6% 2 6% 3 4 4 4 7% 8% 40%	2544
	21st to end	Night	12% 9% 3 6% 4 4 3 3 5% 7% 44%	2743
June	1st to 10th	Night	9% 5% 2 6% 5% 4 4 5% 7% 8% 47%	1520
	11th to 20th	Night	10% 5% 2 5% 5% 4 4 4 6% 8% 48%	1520
	21st to end	Night	9% 6% 2 6% 5% 5% 4 4 7% 9% 42%	1520
July	1st to 10th	Night	12% 6% 2 7% 4 5% 5% 5% 6% 7% 39%	2530
	11th to 20th	Night	5% 4 2 5% 4 4 4 4 6% 9% 53%	2530
	21st to end	Night	5% 4 3 6% 4 6% 6% 4 8% 9% 45%	2750
August	1st to 10th	Night	7% 4 2 6% 4 4 4 4 6% 9% 49%	2564
	11th to 20th	Night	8% 6% 2 6% 4 4 4 3 5% 8% 50%	3087
	21st to end	Night	8% 4 1 5% 3 4 4 4 6% 9% 52%	3476
September	1st to 10th	Night	10% 5% 2 6% 3 4 4 3 3 6% 54%	1900
	11th to 20th	Night	10% 4 2 5% 3 3 4 3 5% 7% 54%	1990
	21st to end	Night	11% 6% 2 6% 4 4 3 3 5% 7% 49%	2090
October	1st to 10th	Night	12% 5% 2 5% 4 4 3 3 5% 7% 51%	2156
	11th to 20th	Night	17% 8% 2 6% 3 3 4 2 4 6% 45%	2287
	21st to end	Night	20% 8% 3 6% 4 4 4 3 5% 6% 38%	2717
November	1st to 10th	Night	11% 8% 3 6% 4 3 3 3 5% 5% 49%	2433
	11th to 20th	Night	14% 11% 4 8% 4 4 4 3 5% 6% 37%	2470
	21st to end	Night	15% 11% 4 7% 5% 4 4 3 4 6% 37%	2564
December	1st to 10th	Night	15% 11% 4 9% 5% 4 4 4 5% 6% 32%	2660
	11th to 20th	Night	15% 13% 4 9% 5% 4 4 4 5% 6% 31%	3279
	21st to end	Night	22% 18% 6% 10% 5% 4 4 4 5% 6% 17%	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	59% 6% 11% 16% 7%	2528
	11th to 20th	Day	60% 7% 12% 14% 7%	2530
	21st to end	Day	67% 4 7% 16% 5%	2856
February	1st to 10th	Day	56% 6% 12% 15% 10% 1	1725
	11th to 20th	Day	49% 6% 10% 23% 10% 2	1858
	21st to end	Day	53% 8% 10% 18% 10% 2	1570
March	1st to 10th	Day	47% 8% 11% 21% 11% 2	3120
	11th to 20th	Day	40% 7% 12% 30% 10% 1	3273
	21st to end	Day	63% 8% 12% 12% 4	4165
April	1st to 10th	Day	55% 6% 10% 20% 10%	2280
	11th to 20th	Day	48% 6% 10% 21% 12% 3	2254
	21st to end	Day	50% 8% 12% 16% 13% 1	2380
May	1st to 10th	Day	44% 9% 11% 23% 13%	4120
	11th to 20th	Day	39% 8% 11% 27% 15%	4361
	21st to end	Day	37% 8% 13% 20% 17% 4	4837
June	1st to 10th	Day	35% 7% 13% 26% 17% 2	2660
	11th to 20th	Day	35% 8% 12% 22% 20% 3	2660
	21st to end	Day	41% 8% 13% 22% 14% 2	2660
July	1st to 10th	Day	45% 8% 12% 22% 11% 2	4371
	11th to 20th	Day	30% 7% 16% 28% 16% 1	4365
	21st to end	Day	39% 8% 15% 17% 20% 3	4662
August	1st to 10th	Day	36% 8% 16% 27% 12% 1	4355
	11th to 20th	Day	36% 6% 13% 29% 14% 1	3774
	21st to end	Day	33% 6% 13% 25% 20% 2	4179
September	1st to 10th	Day	35% 7% 13% 25% 17% 4	2280
	11th to 20th	Day	29% 6% 12% 31% 20% 2	2170
	21st to end	Day	38% 6% 11% 27% 18% 1	2090
October	1st to 10th	Day	38% 7% 11% 26% 17% 1	2020
	11th to 20th	Day	49% 5% 11% 21% 13% 1	1892
	21st to end	Day	48% 6% 10% 23% 10% 2	1881
November	1st to 10th	Day	39% 7% 13% 23% 16% 2	1690
	11th to 20th	Day	51% 6% 12% 21% 9% 1	1710
	21st to end	Day	51% 5% 11% 23% 8%	1615
December	1st to 10th	Day	54% 6% 13% 19% 8% 1	1520
	11th to 20th	Day	54% 7% 13% 17% 7% 2	1915
	21st to end	Day	75% 4 7% 9% 4	2783
January	1st to 10th	Night	58% 5% 10% 18% 9% 1	4428
	11th to 20th	Night	64% 5% 10% 13% 8%	4440
	21st to end	Night	66% 5% 9% 13% 6% 1	4808
February	1st to 10th	Night	54% 5% 10% 17% 12% 2	2453
	11th to 20th	Night	47% 5% 12% 20% 14% 1	2219
	21st to end	Night	51% 5% 10% 21% 10% 4	1884
March	1st to 10th	Night	45% 7% 11% 23% 9% 4	3733
	11th to 20th	Night	35% 7% 10% 28% 17% 2	3715
	21st to end	Night	59% 7% 8% 18% 7% 1	3466
April	1st to 10th	Night	45% 7% 11% 22% 13% 1	1900
	11th to 20th	Night	47% 5% 7% 20% 16% 4	1875
	21st to end	Night	45% 7% 10% 22% 13% 3	1800
May	1st to 10th	Night	44% 8% 12% 19% 14% 3	2840
	11th to 20th	Night	37% 10% 14% 27% 11% 1	2545
	21st to end	Night	38% 8% 10% 19% 20% 6%	2751
June	1st to 10th	Night	32% 9% 13% 25% 19% 3	1520
	11th to 20th	Night	34% 7% 10% 26% 22% 2	1520
	21st to end	Night	37% 8% 15% 21% 17% 2	1520
July	1st to 10th	Night	42% 8% 14% 20% 12% 4	2490
	11th to 20th	Night	26% 7% 15% 33% 17% 1	2482
	21st to end	Night	32% 9% 14% 19% 23% 3	2662
August	1st to 10th	Night	30% 8% 15% 28% 18% 1	2555
	11th to 20th	Night	31% 7% 13% 30% 18% 1	3117
	21st to end	Night	28% 6% 13% 33% 17% 3	3476
September	1st to 10th	Night	31% 6% 10% 26% 24% 3	1900
	11th to 20th	Night	28% 7% 7% 32% 23% 2	1990
	21st to end	Night	35% 6% 11% 30% 16% 2	2090
October	1st to 10th	Night	34% 6% 10% 29% 20% 2	2156
	11th to 20th	Night	41% 5% 10% 23% 19% 2	2287
	21st to end	Night	47% 6% 11% 23% 13% 1	2717
November	1st to 10th	Night	38% 6% 8% 27% 18% 3	2433
	11th to 20th	Night	48% 5% 11% 22% 12% 1	2470
	21st to end	Night	49% 5% 12% 23% 11%	2564
December	1st to 10th	Night	52% 7% 11% 21% 9% 1	2660
	11th to 20th	Night	52% 6% 13% 19% 9% 1	3281
	21st to end	Night	67% 6% 10% 12% 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	20% 17% 39% 20% 4	270
	11th to 20th	Day	21% 21% 37% 19% 2 1	270
	21st to end	Day	24% 18% 35% 18% 4 1	297
February	1st to 10th	Day	19% 21% 41% 16% 3	270
	11th to 20th	Day	24% 22% 34% 17% 2	270
	21st to end	Day	23% 22% 38% 12% 4	225
March	1st to 10th	Day	20% 29% 35% 14% 2	270
	11th to 20th	Day	27% 18% 34% 16% 5%	284
	21st to end	Day	26% 15% 32% 18% 7% 2	506
April	1st to 10th	Day	25% 17% 31% 22% 5%	460
	11th to 20th	Day	23% 21% 26% 20% 8% 2	452
	21st to end	Day	23% 15% 31% 21% 8% 1	460
May	1st to 10th	Day	18% 17% 32% 24% 7% 2	463
	11th to 20th	Day	19% 14% 31% 24% 9% 2	646
	21st to end	Day	16% 11% 31% 23% 15% 5%	734
June	1st to 10th	Day	10% 9% 34% 28% 14% 4	680
	11th to 20th	Day	11% 8% 35% 30% 12% 4	680
	21st to end	Day	12% 12% 30% 30% 12% 4	680
July	1st to 10th	Day	8% 5% 24% 32% 20% 12%	671
	11th to 20th	Day	10% 5% 29% 32% 16% 7%	668
	21st to end	Day	7% 5% 28% 36% 17% 7%	739
August	1st to 10th	Day	10% 4 23% 33% 20% 10%	649
	11th to 20th	Day	9% 5% 23% 29% 22% 12%	479
	21st to end	Day	9% 3 22% 34% 23% 9%	539
September	1st to 10th	Day	15% 6% 25% 27% 22% 6%	490
	11th to 20th	Day	10% 5% 20% 31% 24% 11%	490
	21st to end	Day	13% 13% 26% 25% 16% 7%	490
October	1st to 10th	Day	14% 12% 28% 26% 15% 5%	420
	11th to 20th	Day	22% 21% 30% 20% 6%	300
	21st to end	Day	30% 17% 33% 14% 5% 1	330
November	1st to 10th	Day	15% 15% 40% 21% 8% 2	276
	11th to 20th	Day	22% 22% 34% 15% 6% 1	270
	21st to end	Day	24% 13% 41% 20% 2	270
December	1st to 10th	Day	17% 21% 41% 16% 5%	270
	11th to 20th	Day	17% 21% 39% 17% 6%	270
	21st to end	Day	24% 24% 38% 12% 1	297
January	1st to 10th	Night	18% 18% 38% 22% 4	950
	11th to 20th	Night	20% 17% 38% 20% 5% 1	950
	21st to end	Night	22% 13% 36% 25% 4	1045
February	1st to 10th	Night	22% 13% 38% 22% 5%	933
	11th to 20th	Night	20% 16% 36% 24% 3	743
	21st to end	Night	24% 16% 37% 19% 3	628
March	1st to 10th	Night	20% 16% 36% 22% 6%	760
	11th to 20th	Night	16% 11% 41% 25% 7%	728
	21st to end	Night	23% 12% 31% 26% 7% 1	627
April	1st to 10th	Night	22% 13% 36% 23% 6%	570
	11th to 20th	Night	23% 15% 31% 24% 7% 1	563
	21st to end	Night	22% 12% 31% 28% 7%	570
May	1st to 10th	Night	17% 10% 36% 29% 7% 1	570
	11th to 20th	Night	17% 9% 30% 31% 12%	561
	21st to end	Night	14% 7% 27% 34% 17% 1	617
June	1st to 10th	Night	9% 5% 29% 40% 16% 1	570
	11th to 20th	Night	12% 4 33% 38% 12% 1	570
	21st to end	Night	10% 7% 30% 36% 17% 1	570
July	1st to 10th	Night	7% 2 20% 40% 28% 3	555
	11th to 20th	Night	7% 4 25% 38% 23% 3	552
	21st to end	Night	5% 2 20% 47% 24% 2	624
August	1st to 10th	Night	5% 2 16% 49% 24% 3	567
	11th to 20th	Night	8% 3 17% 39% 30% 4	564
	21st to end	Night	8% 2 19% 40% 29% 2	627
September	1st to 10th	Night	12% 3 22% 34% 25% 4	570
	11th to 20th	Night	11% 4 20% 32% 29% 4	660
	21st to end	Night	13% 8% 25% 32% 20% 2	760
October	1st to 10th	Night	14% 7% 27% 32% 18% 2	760
	11th to 20th	Night	21% 14% 32% 24% 10%	760
	21st to end	Night	26% 11% 33% 22% 8%	836
November	1st to 10th	Night	16% 12% 38% 24% 10% 1	749
	11th to 20th	Night	21% 17% 33% 23% 5% 1	760
	21st to end	Night	20% 14% 39% 21% 6%	854
December	1st to 10th	Night	20% 16% 38% 21% 4	950
	11th to 20th	Night	23% 13% 36% 23% 4	950
	21st to end	Night	28% 16% 35% 18% 2	1045

Page generated at 2024-10-31 02:39:26. Version ac07

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