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 2024-03-01.

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% 5% 2 5% 5% 3 5% 5% 6% 8% 43%	78559
	Night	15% 6% 2 5% 5% 3 4 4 5% 7% 45%	80843
Transparency	Day	39% 6% 11% 23% 17% 4	78280
	Night	39% 6% 10% 22% 18% 4	80641
Seeing	Day	19% 10% 26% 25% 15% 6%	14061
	Night	17% 8% 28% 31% 14% 1	23938

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 2 4 4 5% 5% 48%	2836
	11th to 20th	Day	14% 8% 3 5% 5% 4 5% 4 4 5% 43%	2840
	21st to end	Day	19% 8% 3 5% 4 3 4 4 4 6% 40%	3124
February	1st to 10th	Day	13% 7% 3 5% 5% 4 5% 5% 5% 7% 41%	1710
	11th to 20th	Day	19% 6% 3 5% 4 3 3 4 6% 5% 43%	1668
	21st to end	Day	18% 7% 3 5% 5% 3 5% 4 5% 7% 37%	1632
March	1st to 10th	Day	13% 5% 2 5% 4 2 4 4 4 7% 51%	1980
	11th to 20th	Day	17% 5% 3 6% 5% 3 4 4 6% 6% 41%	1980
	21st to end	Day	17% 6% 3 6% 6% 3 4 4 5% 7% 38%	2178
April	1st to 10th	Day	11% 4 2 4 5% 3 4 4 5% 8% 50%	2132
	11th to 20th	Day	13% 5% 3 4 4 2 4 5% 5% 7% 48%	2134
	21st to end	Day	17% 6% 2 5% 5% 3 4 5% 3 6% 43%	2165
May	1st to 10th	Day	15% 6% 3 4 4 3 5% 6% 6% 9% 40%	2340
	11th to 20th	Day	17% 6% 2 5% 5% 3 5% 5% 6% 8% 37%	2301
	21st to end	Day	15% 5% 2 5% 5% 3 5% 5% 6% 9% 40%	2668
June	1st to 10th	Day	11% 3 3 4 5% 3 6% 5% 7% 9% 44%	2520
	11th to 20th	Day	11% 4 2 6% 6% 4 5% 5% 8% 10% 40%	2520
	21st to end	Day	8% 4 2 5% 5% 3 5% 6% 8% 10% 43%	2520
July	1st to 10th	Day	10% 5% 2 5% 5% 3 7% 6% 8% 10% 39%	2417
	11th to 20th	Day	6% 4 2 4 6% 5% 7% 7% 8% 12% 40%	2340
	21st to end	Day	9% 4 3 5% 6% 4 6% 7% 7% 11% 37%	2547
August	1st to 10th	Day	11% 6% 2 5% 6% 4 6% 5% 7% 11% 36%	2327
	11th to 20th	Day	11% 6% 2 5% 7% 5% 7% 5% 8% 10% 34%	2247
	21st to end	Day	11% 5% 2 5% 5% 4 4 6% 6% 10% 42%	2376
September	1st to 10th	Day	12% 6% 2 5% 4 4 5% 4 6% 7% 46%	2160
	11th to 20th	Day	12% 6% 2 5% 5% 2 4 5% 6% 9% 45%	2102
	21st to end	Day	20% 5% 2 6% 4 3 4 5% 5% 6% 38%	1908
October	1st to 10th	Day	16% 5% 2 5% 4 3 4 4 4 7% 48%	1800
	11th to 20th	Day	16% 4 1 5% 4 2 3 4 5% 5% 51%	1800
	21st to end	Day	14% 5% 2 5% 4 2 3 2 3 6% 52%	1980
November	1st to 10th	Day	13% 4 1 3 4 3 4 4 4 6% 55%	1857
	11th to 20th	Day	14% 5% 2 3 4 2 3 4 4 6% 51%	1696
	21st to end	Day	15% 4 2 3 4 2 3 4 5% 7% 50%	1520
December	1st to 10th	Day	17% 6% 2 4 4 3 4 5% 6% 7% 41%	1520
	11th to 20th	Day	17% 5% 2 3 3 3 3 3 4 5% 51%	1910
	21st to end	Day	20% 6% 3 5% 5% 3 4 4 6% 7% 38%	2804
January	1st to 10th	Night	13% 7% 3 5% 4 3 4 4 4 6% 48%	4109
	11th to 20th	Night	17% 7% 3 4 4 2 3 3 4 5% 48%	4120
	21st to end	Night	20% 7% 3 5% 4 3 4 3 3 5% 43%	4532
February	1st to 10th	Night	14% 7% 2 4 5% 3 5% 5% 5% 7% 43%	2470
	11th to 20th	Night	20% 7% 2 5% 4 3 4 3 3 7% 43%	2396
	21st to end	Night	16% 7% 2 4 4 3 4 4 5% 6% 44%	1820
March	1st to 10th	Night	13% 4 3 4 3 3 4 4 5% 6% 51%	1987
	11th to 20th	Night	19% 7% 2 4 4 2 4 4 6% 7% 41%	1980
	21st to end	Night	16% 6% 2 5% 5% 3 4 4 4 6% 44%	2178
April	1st to 10th	Night	14% 6% 2 5% 5% 3 4 4 5% 7% 46%	1826
	11th to 20th	Night	12% 4 2 5% 4 2 4 3 5% 8% 49%	1775
	21st to end	Night	16% 4 2 4 5% 3 4 4 5% 8% 46%	1800
May	1st to 10th	Night	15% 6% 3 5% 5% 3 5% 4 5% 9% 42%	1630
	11th to 20th	Night	17% 6% 2 5% 4 3 5% 5% 6% 9% 36%	1592
	21st to end	Night	14% 5% 3 5% 6% 4 5% 5% 5% 8% 41%	1602
June	1st to 10th	Night	10% 5% 2 5% 5% 3 5% 6% 7% 9% 44%	1440
	11th to 20th	Night	10% 5% 3 5% 5% 4 5% 6% 6% 9% 42%	1440
	21st to end	Night	9% 3 1 5% 6% 4 6% 5% 7% 10% 43%	1440
July	1st to 10th	Night	10% 5% 3 5% 5% 4 5% 6% 5% 9% 42%	1537
	11th to 20th	Night	5% 4 2 5% 6% 3 6% 6% 8% 11% 44%	1620
	21st to end	Night	8% 5% 2 5% 6% 4 7% 6% 8% 10% 39%	1771
August	1st to 10th	Night	10% 5% 2 5% 6% 4 6% 7% 7% 10% 38%	1611
	11th to 20th	Night	12% 7% 3 5% 6% 3 5% 6% 6% 8% 38%	1634
	21st to end	Night	10% 6% 2 8% 6% 3 6% 6% 6% 9% 37%	1980
September	1st to 10th	Night	14% 5% 2 5% 4 3 4 5% 6% 8% 44%	1800
	11th to 20th	Night	12% 6% 2 5% 6% 4 4 5% 5% 7% 46%	1854
	21st to end	Night	22% 7% 2 5% 3 2 4 5% 4 6% 40%	2050
October	1st to 10th	Night	17% 5% 2 5% 3 2 4 4 5% 7% 46%	2160
	11th to 20th	Night	16% 5% 2 4 5% 2 3 4 4 6% 48%	2160
	21st to end	Night	14% 4 2 4 4 3 4 3 5% 6% 52%	2376
November	1st to 10th	Night	13% 6% 2 5% 5% 2 3 3 3 5% 53%	2221
	11th to 20th	Night	14% 5% 2 4 5% 3 3 4 4 6% 50%	2479
	21st to end	Night	13% 4 1 4 4 3 4 4 5% 6% 50%	2660
December	1st to 10th	Night	17% 7% 3 5% 5% 3 4 4 4 6% 42%	2660
	11th to 20th	Night	17% 6% 3 4 4 2 4 3 4 5% 47%	3285
	21st to end	Night	17% 6% 2 5% 5% 3 5% 5% 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% 6%	1632
March	1st to 10th	Day	35% 5% 9% 22% 22% 6%	1980
	11th to 20th	Day	42% 5% 12% 18% 16% 7%	1980
	21st to end	Day	46% 6% 8% 19% 16% 5%	2178
April	1st to 10th	Day	33% 5% 12% 22% 19% 9%	2132
	11th to 20th	Day	35% 5% 11% 20% 23% 6%	2134
	21st to end	Day	42% 5% 10% 22% 15% 5%	2165
May	1st to 10th	Day	40% 7% 15% 19% 16% 3	2340
	11th to 20th	Day	43% 9% 14% 22% 11% 2	2305
	21st to end	Day	40% 8% 13% 26% 13%	2668
June	1st to 10th	Day	34% 8% 16% 25% 16% 1	2520
	11th to 20th	Day	37% 10% 15% 21% 15% 2	2520
	21st to end	Day	33% 9% 16% 25% 15% 1	2520
July	1st to 10th	Day	38% 9% 13% 20% 16% 3	2352
	11th to 20th	Day	33% 9% 17% 25% 14% 2	2271
	21st to end	Day	38% 9% 13% 24% 14% 1	2405
August	1st to 10th	Day	42% 9% 15% 24% 10% 1	2314
	11th to 20th	Day	43% 9% 14% 21% 12% 1	2247
	21st to end	Day	36% 8% 17% 24% 13% 3	2376
September	1st to 10th	Day	37% 7% 13% 18% 20% 4	2160
	11th to 20th	Day	36% 6% 8% 26% 20% 4	2102
	21st to end	Day	46% 5% 9% 19% 18% 3	1908
October	1st to 10th	Day	37% 5% 9% 26% 19% 4	1800
	11th to 20th	Day	36% 4 9% 25% 23% 4	1800
	21st to end	Day	36% 3 7% 26% 23% 6%	1980
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% 17% 6%	1820
March	1st to 10th	Night	34% 5% 9% 24% 23% 5%	1987
	11th to 20th	Night	42% 4 9% 21% 20% 4	1980
	21st to end	Night	41% 6% 10% 20% 17% 6%	2178
April	1st to 10th	Night	38% 6% 9% 18% 22% 7%	1826
	11th to 20th	Night	33% 6% 12% 20% 23% 6%	1775
	21st to end	Night	37% 6% 12% 23% 16% 6%	1800
May	1st to 10th	Night	41% 6% 13% 22% 14% 4	1630
	11th to 20th	Night	43% 8% 13% 21% 13% 3	1593
	21st to end	Night	41% 9% 13% 24% 12% 1	1603
June	1st to 10th	Night	34% 8% 13% 29% 16% 1	1440
	11th to 20th	Night	37% 10% 17% 20% 15% 2	1440
	21st to end	Night	33% 10% 14% 22% 17% 3	1440
July	1st to 10th	Night	39% 10% 15% 17% 15% 4	1492
	11th to 20th	Night	31% 11% 20% 24% 12% 2	1566
	21st to end	Night	35% 9% 17% 25% 13% 1	1672
August	1st to 10th	Night	39% 10% 17% 23% 11% 1	1600
	11th to 20th	Night	42% 9% 15% 21% 12% 1	1634
	21st to end	Night	40% 9% 16% 22% 11% 3	1980
September	1st to 10th	Night	38% 7% 13% 21% 15% 6%	1800
	11th to 20th	Night	37% 7% 10% 23% 21% 3	1854
	21st to end	Night	45% 5% 9% 21% 16% 3	2050
October	1st to 10th	Night	38% 5% 9% 24% 19% 4	2160
	11th to 20th	Night	38% 5% 6% 24% 22% 5%	2160
	21st to end	Night	34% 4 9% 24% 24% 6%	2376
November	1st to 10th	Night	36% 4 8% 21% 25% 6%	2221
	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	28% 18% 30% 21% 3	382
March	1st to 10th	Day	22% 17% 35% 21% 5%	420
	11th to 20th	Day	23% 19% 34% 18% 6%	420
	21st to end	Day	23% 16% 34% 20% 6% 1	462
April	1st to 10th	Day	21% 18% 30% 20% 9% 1	420
	11th to 20th	Day	19% 13% 29% 22% 10% 6%	412
	21st to end	Day	25% 11% 32% 21% 9% 2	420
May	1st to 10th	Day	20% 15% 31% 21% 9% 3	423
	11th to 20th	Day	21% 9% 29% 26% 11% 5%	447
	21st to end	Day	19% 4 22% 31% 20% 5%	485
June	1st to 10th	Day	13% 5% 23% 32% 22% 5%	450
	11th to 20th	Day	14% 6% 26% 29% 15% 10%	450
	21st to end	Day	11% 3 23% 36% 21% 6%	450
July	1st to 10th	Day	11% 2 18% 30% 29% 10%	445
	11th to 20th	Day	7% 3 13% 36% 30% 11%	444
	21st to end	Day	11% 3 19% 32% 24% 11%	488
August	1st to 10th	Day	14% 3 17% 27% 26% 14%	446
	11th to 20th	Day	13% 2 16% 29% 27% 13%	439
	21st to end	Day	12% 3 15% 30% 24% 16%	495
September	1st to 10th	Day	14% 5% 16% 25% 23% 18%	450
	11th to 20th	Day	14% 3 13% 36% 23% 10%	450
	21st to end	Day	28% 4 22% 27% 12% 6%	450
October	1st to 10th	Day	20% 4 23% 28% 18% 7%	450
	11th to 20th	Day	16% 11% 24% 26% 20% 3	450
	21st to end	Day	17% 11% 34% 26% 9% 3	495
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	16% 15% 39% 26% 4	723
	11th to 20th	Night	21% 15% 34% 23% 6% 1	720
	21st to end	Night	19% 11% 36% 27% 6%	792
April	1st to 10th	Night	16% 16% 39% 23% 6%	720
	11th to 20th	Night	14% 12% 35% 30% 9%	711
	21st to end	Night	18% 8% 32% 33% 9%	720
May	1st to 10th	Night	19% 9% 30% 30% 12% 1	550
	11th to 20th	Night	20% 3 23% 35% 17% 1	531
	21st to end	Night	17% 1 17% 39% 22% 3	442
June	1st to 10th	Night	10% 2 18% 42% 28% 1	360
	11th to 20th	Night	13% 3 15% 41% 27% 1	360
	21st to end	Night	9% 1 20% 47% 21% 2	360
July	1st to 10th	Night	11% 2 15% 35% 32% 5%	442
	11th to 20th	Night	7% 2 10% 40% 37% 5%	522
	21st to end	Night	8% 2 16% 41% 29% 5%	591
August	1st to 10th	Night	13% 1 10% 40% 33% 3	537
	11th to 20th	Night	15% 2 10% 36% 33% 3	570
	21st to end	Night	12% 2 15% 34% 34% 4	792
September	1st to 10th	Night	17% 2 13% 30% 32% 6%	720
	11th to 20th	Night	13% 3 16% 33% 30% 4	720
	21st to end	Night	24% 4 18% 32% 21% 2	720
October	1st to 10th	Night	20% 5% 17% 31% 23% 5%	720
	11th to 20th	Night	18% 7% 25% 32% 16% 1	720
	21st to end	Night	16% 7% 29% 34% 12% 1	792
November	1st to 10th	Night	15% 7% 28% 35% 14% 2	740
	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 2024-02-27 06:30:13. Version ac07

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