Lake Monticello
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lake Monticello clear sky chart from 2005-11-06 to 2024-11-01.

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	14% 6% 2 6% 4 4 5% 4 6% 8% 42%	100962
	Night	15% 6% 2 6% 4 4 4 4 5% 7% 43%	97927
Transparency	Day	39% 6% 12% 23% 16% 4	100774
	Night	40% 6% 11% 22% 17% 4	97785
Seeing	Day	18% 10% 26% 25% 15% 6%	15041
	Night	17% 8% 28% 32% 14% 1	24767

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	18% 5% 2 4 4 3 4 3 5% 5% 48%	2836
	11th to 20th	Day	14% 9% 2 6% 4 5% 4 3 4 5% 43%	2840
	21st to end	Day	19% 8% 3 6% 4 4 5% 3 4 5% 40%	3124
February	1st to 10th	Day	12% 8% 3 6% 4 5% 5% 4 6% 6% 41%	1710
	11th to 20th	Day	19% 6% 2 5% 4 3 3 3 6% 5% 43%	1668
	21st to end	Day	18% 8% 2 6% 5% 4 5% 3 5% 7% 37%	1632
March	1st to 10th	Day	19% 7% 2 7% 4 4 3 3 5% 7% 38%	3435
	11th to 20th	Day	10% 5% 2 5% 4 4 4 3 5% 7% 52%	3480
	21st to end	Day	20% 7% 2 6% 5% 4 4 3 6% 6% 37%	3815
April	1st to 10th	Day	11% 5% 2 5% 5% 4 4 3 5% 7% 49%	2251
	11th to 20th	Day	13% 5% 2 5% 4 3 4 4 5% 7% 48%	2254
	21st to end	Day	16% 6% 2 6% 5% 4 4 4 4 5% 43%	2286
May	1st to 10th	Day	17% 7% 3 7% 4 5% 5% 4 6% 8% 32%	4082
	11th to 20th	Day	21% 7% 2 6% 4 4 5% 4 6% 8% 32%	4081
	21st to end	Day	10% 4 2 5% 4 4 5% 4 7% 10% 45%	4724
June	1st to 10th	Day	11% 4 2 4 5% 4 5% 5% 7% 9% 44%	2660
	11th to 20th	Day	11% 4 2 6% 5% 5% 4 4 8% 10% 40%	2660
	21st to end	Day	8% 4 2 5% 4 5% 6% 5% 8% 10% 43%	2660
July	1st to 10th	Day	6% 4 1 5% 4 5% 6% 5% 10% 12% 42%	4253
	11th to 20th	Day	10% 6% 2 5% 5% 6% 5% 5% 8% 12% 36%	4120
	21st to end	Day	11% 6% 3 7% 7% 6% 6% 5% 7% 9% 32%	4466
August	1st to 10th	Day	15% 6% 2 7% 5% 5% 6% 5% 7% 11% 32%	4104
	11th to 20th	Day	8% 5% 2 6% 5% 6% 6% 4 8% 10% 40%	3932
	21st to end	Day	9% 4 2 5% 3 4 4 4 6% 10% 49%	4180
September	1st to 10th	Day	12% 6% 2 6% 4 5% 4 3 6% 6% 47%	2280
	11th to 20th	Day	13% 6% 2 6% 3 3 4 4 6% 9% 44%	2218
	21st to end	Day	22% 6% 2 6% 4 4 5% 3 5% 6% 37%	2014
October	1st to 10th	Day	16% 5% 2 6% 3 3 3 3 5% 6% 49%	1900
	11th to 20th	Day	16% 4 1 5% 3 3 3 3 5% 5% 52%	1900
	21st to end	Day	14% 5% 2 5% 3 3 3 2 3 6% 54%	2090
November	1st to 10th	Day	13% 4 1 4 4 3 3 3 4 6% 54%	1857
	11th to 20th	Day	14% 5% 2 4 4 3 3 3 5% 6% 51%	1696
	21st to end	Day	15% 5% 2 4 4 3 3 4 5% 7% 50%	1520
December	1st to 10th	Day	17% 7% 2 5% 3 4 4 4 6% 7% 41%	1520
	11th to 20th	Day	17% 6% 2 4 3 4 3 3 4 6% 50%	1910
	21st to end	Day	19% 6% 3 6% 4 4 4 3 6% 6% 38%	2804
January	1st to 10th	Night	13% 7% 2 5% 4 4 4 3 4 6% 48%	4109
	11th to 20th	Night	17% 7% 3 5% 3 3 3 3 4 5% 48%	4120
	21st to end	Night	20% 8% 2 6% 4 4 3 2 3 5% 43%	4532
February	1st to 10th	Night	14% 7% 2 4 4 4 5% 4 5% 7% 43%	2470
	11th to 20th	Night	20% 7% 1 5% 4 3 3 3 4 6% 43%	2396
	21st to end	Night	16% 7% 2 5% 4 3 5% 3 5% 6% 44%	1820
March	1st to 10th	Night	19% 7% 3 6% 4 4 5% 4 5% 6% 37%	3418
	11th to 20th	Night	12% 5% 2 4 3 3 3 3 6% 8% 51%	3480
	21st to end	Night	15% 6% 2 5% 4 3 3 3 4 6% 48%	3817
April	1st to 10th	Night	14% 6% 2 6% 4 4 3 3 5% 7% 46%	1927
	11th to 20th	Night	12% 5% 2 5% 4 4 4 3 5% 8% 49%	1875
	21st to end	Night	15% 4 2 4 4 4 4 4 5% 8% 45%	1900
May	1st to 10th	Night	19% 9% 3 6% 5% 4 4 3 5% 8% 34%	2823
	11th to 20th	Night	24% 7% 2 6% 4 4 4 4 6% 7% 32%	2812
	21st to end	Night	10% 4 2 6% 5% 4 5% 4 6% 9% 43%	2826
June	1st to 10th	Night	10% 5% 2 6% 5% 4 5% 5% 7% 8% 43%	1520
	11th to 20th	Night	10% 5% 2 6% 4 5% 5% 5% 7% 10% 42%	1520
	21st to end	Night	8% 4 1 6% 5% 6% 5% 4 7% 11% 43%	1520
July	1st to 10th	Night	7% 5% 3 7% 4 5% 6% 6% 8% 10% 39%	2701
	11th to 20th	Night	8% 7% 3 8% 6% 6% 6% 6% 8% 11% 34%	2840
	21st to end	Night	10% 8% 3 9% 7% 7% 6% 5% 7% 8% 30%	3087
August	1st to 10th	Night	16% 6% 3 7% 5% 5% 6% 4 7% 10% 32%	2825
	11th to 20th	Night	10% 7% 3 8% 5% 5% 6% 6% 7% 8% 36%	2863
	21st to end	Night	10% 6% 2 8% 4 4 5% 4 6% 8% 42%	3476
September	1st to 10th	Night	14% 5% 2 6% 3 4 4 4 5% 7% 45%	1900
	11th to 20th	Night	13% 6% 2 6% 4 5% 4 4 5% 7% 45%	1958
	21st to end	Night	23% 7% 2 6% 3 3 4 3 4 6% 38%	2164
October	1st to 10th	Night	17% 6% 2 5% 3 3 4 3 5% 7% 46%	2280
	11th to 20th	Night	15% 5% 2 4 4 3 3 3 4 6% 49%	2280
	21st to end	Night	14% 4 1 4 4 4 3 3 5% 6% 53%	2508
November	1st to 10th	Night	13% 6% 2 6% 4 4 3 2 3 5% 53%	2228
	11th to 20th	Night	14% 5% 2 5% 4 4 3 3 5% 6% 50%	2479
	21st to end	Night	13% 4 1 5% 4 4 4 4 5% 5% 50%	2660
December	1st to 10th	Night	16% 8% 3 6% 4 4 4 3 4 6% 42%	2660
	11th to 20th	Night	17% 7% 2 5% 4 3 4 3 4 6% 47%	3285
	21st to end	Night	17% 6% 2 6% 4 4 5% 4 6% 7% 41%	4848

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	38% 4 6% 30% 17% 6%	2837
	11th to 20th	Day	42% 4 7% 19% 21% 6%	2840
	21st to end	Day	47% 4 8% 22% 15% 3	3124
February	1st to 10th	Day	42% 5% 9% 25% 15% 3	1710
	11th to 20th	Day	42% 3 7% 22% 20% 5%	1677
	21st to end	Day	47% 5% 11% 15% 17% 5%	1632
March	1st to 10th	Day	46% 5% 10% 19% 13% 7%	3435
	11th to 20th	Day	31% 5% 8% 24% 23% 9%	3480
	21st to end	Day	47% 6% 9% 18% 17% 3	3815
April	1st to 10th	Day	33% 5% 12% 22% 19% 9%	2251
	11th to 20th	Day	35% 5% 11% 21% 22% 6%	2254
	21st to end	Day	42% 5% 10% 23% 15% 4	2286
May	1st to 10th	Day	47% 9% 12% 18% 13% 1	4120
	11th to 20th	Day	47% 8% 12% 21% 11% 1	4085
	21st to end	Day	32% 9% 14% 22% 20% 2	4738
June	1st to 10th	Day	34% 8% 16% 25% 16% 1	2660
	11th to 20th	Day	36% 9% 15% 22% 15% 2	2660
	21st to end	Day	33% 9% 16% 25% 15% 2	2660
July	1st to 10th	Day	31% 10% 23% 19% 11% 6%	4188
	11th to 20th	Day	37% 7% 19% 26% 9% 1	4051
	21st to end	Day	45% 8% 12% 21% 13% 1	4324
August	1st to 10th	Day	44% 7% 17% 24% 7% 1	4091
	11th to 20th	Day	36% 8% 15% 25% 15% 1	3971
	21st to end	Day	30% 6% 18% 27% 17% 1	4180
September	1st to 10th	Day	37% 7% 12% 18% 22% 5%	2280
	11th to 20th	Day	37% 6% 8% 26% 20% 4	2218
	21st to end	Day	47% 5% 9% 18% 17% 3	2014
October	1st to 10th	Day	37% 5% 8% 25% 21% 4	1900
	11th to 20th	Day	35% 4 8% 24% 24% 5%	1900
	21st to end	Day	34% 3 7% 27% 23% 7%	2090
November	1st to 10th	Day	32% 4 8% 23% 28% 5%	1857
	11th to 20th	Day	34% 4 10% 22% 22% 8%	1696
	21st to end	Day	35% 4 9% 24% 23% 5%	1520
December	1st to 10th	Day	42% 5% 10% 23% 15% 4	1520
	11th to 20th	Day	36% 4 7% 29% 16% 7%	1906
	21st to end	Day	45% 5% 10% 25% 14% 1	2804
January	1st to 10th	Night	38% 4 7% 23% 23% 5%	4109
	11th to 20th	Night	41% 4 6% 20% 23% 6%	4120
	21st to end	Night	46% 3 6% 23% 17% 5%	4532
February	1st to 10th	Night	40% 5% 10% 25% 17% 3	2470
	11th to 20th	Night	44% 3 7% 20% 19% 7%	2398
	21st to end	Night	41% 5% 9% 21% 18% 6%	1820
March	1st to 10th	Night	46% 6% 8% 22% 16% 3	3418
	11th to 20th	Night	31% 4 8% 22% 27% 8%	3480
	21st to end	Night	38% 5% 9% 23% 21% 5%	3817
April	1st to 10th	Night	38% 6% 9% 17% 23% 7%	1927
	11th to 20th	Night	33% 6% 13% 20% 23% 6%	1875
	21st to end	Night	37% 6% 12% 23% 17% 6%	1900
May	1st to 10th	Night	47% 7% 14% 19% 11% 2	2850
	11th to 20th	Night	48% 8% 12% 22% 9% 1	2813
	21st to end	Night	35% 9% 15% 25% 15% 2	2833
June	1st to 10th	Night	34% 8% 12% 28% 16% 1	1520
	11th to 20th	Night	36% 10% 17% 21% 15% 2	1520
	21st to end	Night	33% 9% 15% 22% 18% 3	1520
July	1st to 10th	Night	37% 11% 23% 14% 12% 3	2656
	11th to 20th	Night	41% 10% 20% 21% 7% 1	2786
	21st to end	Night	48% 9% 14% 18% 10%	2988
August	1st to 10th	Night	47% 8% 17% 22% 6% 1	2814
	11th to 20th	Night	41% 9% 15% 22% 12% 1	2890
	21st to end	Night	37% 7% 14% 29% 12% 2	3476
September	1st to 10th	Night	38% 7% 12% 20% 16% 7%	1900
	11th to 20th	Night	37% 7% 10% 23% 21% 3	1958
	21st to end	Night	46% 5% 9% 20% 16% 3	2164
October	1st to 10th	Night	38% 5% 9% 24% 19% 4	2280
	11th to 20th	Night	36% 5% 6% 23% 24% 6%	2280
	21st to end	Night	33% 4 8% 25% 24% 6%	2508
November	1st to 10th	Night	36% 4 8% 21% 25% 6%	2228
	11th to 20th	Night	37% 3 8% 20% 24% 8%	2479
	21st to end	Night	35% 4 8% 24% 22% 6%	2660
December	1st to 10th	Night	44% 4 8% 23% 17% 4	2660
	11th to 20th	Night	39% 4 9% 22% 20% 6%	3288
	21st to end	Night	41% 6% 11% 25% 16% 2	4848

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	24% 21% 31% 19% 6%	270
	11th to 20th	Day	26% 29% 29% 13% 3	270
	21st to end	Day	25% 22% 37% 13% 3	297
February	1st to 10th	Day	24% 21% 39% 12% 5%	270
	11th to 20th	Day	38% 23% 27% 10% 2	275
	21st to end	Day	29% 17% 30% 21% 3	382
March	1st to 10th	Day	23% 16% 35% 20% 6%	460
	11th to 20th	Day	22% 20% 34% 18% 6%	460
	21st to end	Day	24% 16% 34% 20% 6% 1	506
April	1st to 10th	Day	22% 19% 31% 19% 8% 1	460
	11th to 20th	Day	19% 15% 30% 22% 10% 5%	452
	21st to end	Day	24% 11% 33% 21% 9% 2	460
May	1st to 10th	Day	20% 15% 31% 21% 10% 3	463
	11th to 20th	Day	22% 9% 28% 25% 11% 5%	487
	21st to end	Day	17% 4 24% 31% 19% 5%	529
June	1st to 10th	Day	12% 7% 24% 31% 21% 5%	490
	11th to 20th	Day	12% 6% 25% 30% 17% 10%	490
	21st to end	Day	10% 4 22% 37% 21% 6%	490
July	1st to 10th	Day	11% 2 17% 32% 28% 10%	485
	11th to 20th	Day	8% 3 13% 36% 30% 11%	484
	21st to end	Day	11% 4 20% 32% 23% 11%	532
August	1st to 10th	Day	14% 3 18% 27% 25% 13%	486
	11th to 20th	Day	12% 2 19% 30% 25% 12%	479
	21st to end	Day	11% 4 15% 30% 24% 16%	539
September	1st to 10th	Day	13% 6% 15% 27% 23% 17%	490
	11th to 20th	Day	16% 3 14% 35% 23% 10%	490
	21st to end	Day	31% 4 23% 26% 11% 5%	490
October	1st to 10th	Day	19% 4 23% 29% 17% 7%	490
	11th to 20th	Day	15% 11% 24% 25% 21% 4	490
	21st to end	Day	16% 11% 34% 27% 10% 3	539
November	1st to 10th	Day	16% 9% 26% 32% 12% 4	455
	11th to 20th	Day	18% 15% 30% 25% 11% 2	334
	21st to end	Day	19% 13% 34% 24% 8% 2	180
December	1st to 10th	Day	22% 17% 40% 13% 7% 2	180
	11th to 20th	Day	25% 14% 31% 21% 7% 2	180
	21st to end	Day	28% 16% 29% 17% 8% 1	207
January	1st to 10th	Night	19% 13% 39% 26% 4	760
	11th to 20th	Night	21% 13% 36% 26% 4	760
	21st to end	Night	18% 14% 40% 24% 3	836
February	1st to 10th	Night	18% 11% 38% 30% 3	760
	11th to 20th	Night	25% 14% 39% 20% 1	743
	21st to end	Night	22% 15% 37% 23% 2	628
March	1st to 10th	Night	18% 14% 38% 26% 4	760
	11th to 20th	Night	21% 15% 35% 23% 6% 1	760
	21st to end	Night	19% 12% 37% 27% 5%	836
April	1st to 10th	Night	16% 16% 40% 23% 6%	760
	11th to 20th	Night	14% 12% 36% 29% 9%	751
	21st to end	Night	17% 8% 33% 33% 8%	760
May	1st to 10th	Night	19% 9% 30% 30% 12% 1	580
	11th to 20th	Night	21% 3 23% 35% 17% 1	561
	21st to end	Night	16% 1 18% 39% 23% 3	467
June	1st to 10th	Night	9% 2 19% 42% 27% 1	380
	11th to 20th	Night	12% 3 15% 42% 26% 1	380
	21st to end	Night	8% 1 21% 48% 21% 2	380
July	1st to 10th	Night	11% 2 15% 36% 31% 4	468
	11th to 20th	Night	7% 2 11% 39% 36% 5%	552
	21st to end	Night	8% 2 16% 42% 28% 4	624
August	1st to 10th	Night	14% 2 10% 40% 32% 3	567
	11th to 20th	Night	15% 2 10% 38% 32% 3	603
	21st to end	Night	11% 2 14% 35% 34% 4	836
September	1st to 10th	Night	16% 1 13% 33% 31% 6%	760
	11th to 20th	Night	14% 3 16% 33% 31% 4	760
	21st to end	Night	25% 4 18% 31% 20% 2	760
October	1st to 10th	Night	20% 5% 17% 31% 23% 5%	760
	11th to 20th	Night	18% 7% 25% 33% 16% 1	760
	21st to end	Night	15% 7% 28% 35% 13% 1	836
November	1st to 10th	Night	15% 7% 28% 35% 13% 2	743
	11th to 20th	Night	17% 10% 34% 30% 9%	760
	21st to end	Night	14% 9% 33% 33% 10% 1	760
December	1st to 10th	Night	21% 9% 36% 26% 8%	760
	11th to 20th	Night	18% 9% 33% 36% 5%	760
	21st to end	Night	20% 10% 31% 36% 4	836

Page generated at 2024-10-29 11:20:46. Version ac07

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