Monroe
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Monroe clear sky chart from 2005-11-06 to 2024-01-13.

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	12% 6% 2 5% 5% 3 5% 5% 6% 8% 44%	74785
	Night	12% 5% 2 4 4 3 4 4 5% 7% 49%	74938
Transparency	Day	38% 6% 11% 20% 19% 6%	74510
	Night	34% 6% 11% 20% 21% 8%	74734
Seeing	Day	13% 7% 20% 25% 24% 11%	13986
	Night	14% 6% 23% 32% 21% 4	23878

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% 8% 3 5% 4 3 3 4 4 5% 45%	1707
	11th to 20th	Day	20% 8% 3 5% 5% 2 4 3 3 4 42%	1638
	21st to end	Day	18% 8% 3 4 3 2 3 3 4 5% 47%	1782
February	1st to 10th	Day	19% 8% 4 5% 4 2 4 4 4 6% 40%	1652
	11th to 20th	Day	22% 8% 3 5% 4 3 4 3 4 5% 40%	1748
	21st to end	Day	20% 10% 4 6% 5% 3 3 4 3 5% 37%	1538
March	1st to 10th	Day	17% 8% 3 6% 5% 3 4 4 5% 6% 39%	1980
	11th to 20th	Day	14% 7% 4 6% 5% 4 4 4 6% 7% 39%	1980
	21st to end	Day	12% 6% 3 5% 5% 4 5% 5% 5% 6% 44%	2178
April	1st to 10th	Day	11% 6% 2 5% 5% 4 5% 5% 5% 8% 44%	2160
	11th to 20th	Day	16% 6% 3 6% 4 3 4 4 5% 8% 41%	2134
	21st to end	Day	10% 6% 2 6% 6% 3 5% 4 5% 8% 45%	2160
May	1st to 10th	Day	12% 6% 3 5% 6% 4 4 5% 5% 7% 42%	2160
	11th to 20th	Day	11% 5% 3 5% 6% 4 5% 5% 6% 9% 42%	2124
	21st to end	Day	8% 4 2 5% 6% 4 6% 7% 7% 11% 42%	2530
June	1st to 10th	Day	8% 4 3 5% 6% 3 6% 7% 9% 10% 40%	2340
	11th to 20th	Day	5% 4 2 5% 5% 4 6% 7% 8% 9% 46%	2340
	21st to end	Day	5% 4 2 6% 5% 4 7% 7% 8% 11% 40%	2340
July	1st to 10th	Day	7% 3 2 5% 8% 5% 7% 8% 8% 12% 34%	2340
	11th to 20th	Day	7% 4 2 5% 6% 4 8% 6% 9% 10% 39%	2340
	21st to end	Day	7% 5% 2 6% 5% 5% 7% 8% 8% 11% 37%	2546
August	1st to 10th	Day	5% 3 2 5% 7% 4 5% 6% 7% 11% 44%	2243
	11th to 20th	Day	9% 5% 3 4 6% 4 5% 7% 7% 10% 41%	2125
	21st to end	Day	12% 4 2 5% 5% 4 5% 6% 7% 10% 40%	2376
September	1st to 10th	Day	7% 4 2 5% 7% 4 6% 6% 6% 9% 44%	2160
	11th to 20th	Day	13% 5% 3 5% 5% 3 5% 5% 6% 8% 43%	2160
	21st to end	Day	10% 5% 2 3 4 2 4 4 5% 6% 54%	1897
October	1st to 10th	Day	6% 3 2 4 5% 3 4 4 5% 6% 59%	1800
	11th to 20th	Day	11% 4 2 4 4 2 3 3 4 6% 56%	1800
	21st to end	Day	14% 5% 2 4 4 2 3 3 4 4 54%	1980
November	1st to 10th	Day	10% 6% 2 4 4 2 3 4 4 5% 56%	1858
	11th to 20th	Day	11% 6% 2 4 4 2 4 4 5% 5% 53%	1900
	21st to end	Day	17% 6% 3 4 5% 3 4 4 5% 5% 44%	1835
December	1st to 10th	Day	17% 8% 2 5% 5% 2 4 4 4 5% 42%	1638
	11th to 20th	Day	15% 9% 3 6% 5% 3 4 4 3 6% 42%	2161
	21st to end	Day	16% 8% 2 5% 5% 3 4 4 5% 6% 42%	3135
January	1st to 10th	Night	17% 5% 2 4 4 2 3 4 4 5% 49%	2458
	11th to 20th	Night	19% 7% 3 5% 5% 2 3 3 3 6% 45%	2379
	21st to end	Night	19% 7% 2 5% 4 2 4 4 4 5% 46%	2574
February	1st to 10th	Night	16% 7% 3 5% 4 2 4 4 5% 6% 44%	2304
	11th to 20th	Night	19% 7% 3 5% 4 2 4 4 4 5% 43%	2098
	21st to end	Night	21% 8% 3 4 5% 2 4 4 4 5% 40%	1732
March	1st to 10th	Night	15% 6% 2 5% 4 3 4 3 4 6% 45%	1980
	11th to 20th	Night	15% 6% 2 5% 5% 3 5% 5% 5% 7% 42%	1980
	21st to end	Night	13% 7% 2 5% 4 3 4 4 5% 5% 48%	2175
April	1st to 10th	Night	11% 5% 2 4 3 2 4 4 6% 8% 50%	1800
	11th to 20th	Night	14% 7% 2 4 4 2 4 3 6% 7% 47%	1775
	21st to end	Night	9% 5% 3 5% 5% 3 5% 3 4 6% 53%	1800
May	1st to 10th	Night	9% 4 3 5% 4 3 3 4 6% 9% 50%	1800
	11th to 20th	Night	9% 4 3 5% 5% 3 4 5% 6% 10% 46%	1767
	21st to end	Night	7% 4 2 5% 5% 3 5% 4 6% 11% 49%	1745
June	1st to 10th	Night	7% 4 2 4 5% 3 5% 6% 8% 10% 48%	1620
	11th to 20th	Night	4 3 2 3 3 2 5% 5% 6% 11% 56%	1620
	21st to end	Night	5% 4 3 3 4 3 5% 5% 7% 9% 51%	1620
July	1st to 10th	Night	6% 4 1 4 5% 3 5% 7% 8% 11% 45%	1620
	11th to 20th	Night	6% 3 1 3 4 3 5% 6% 8% 12% 49%	1620
	21st to end	Night	5% 3 1 3 4 3 4 6% 9% 13% 50%	1772
August	1st to 10th	Night	3 2 2 3 4 2 5% 6% 8% 12% 53%	1692
	11th to 20th	Night	6% 4 1 4 3 3 4 5% 8% 14% 47%	1776
	21st to end	Night	9% 3 2 4 4 3 4 5% 7% 10% 47%	1980
September	1st to 10th	Night	6% 4 2 5% 6% 3 5% 5% 7% 8% 50%	1800
	11th to 20th	Night	9% 5% 2 5% 5% 4 4 4 6% 7% 49%	1800
	21st to end	Night	9% 4 1 3 4 2 3 3 5% 6% 59%	2038
October	1st to 10th	Night	6% 4 2 3 5% 2 4 3 5% 7% 60%	2160
	11th to 20th	Night	10% 5% 1 4 5% 2 3 3 4 5% 57%	2160
	21st to end	Night	13% 4 2 4 4 2 3 3 4 5% 57%	2376
November	1st to 10th	Night	12% 4 1 4 3 2 3 4 4 5% 58%	2220
	11th to 20th	Night	12% 5% 2 4 4 2 3 4 3 6% 56%	2280
	21st to end	Night	14% 6% 3 5% 5% 2 4 4 5% 5% 48%	2331
December	1st to 10th	Night	16% 7% 3 5% 4 2 3 3 4 6% 46%	2518
	11th to 20th	Night	16% 7% 2 5% 5% 2 4 4 3 5% 47%	3036
	21st to end	Night	16% 9% 2 5% 4 2 4 3 4 5% 45%	4532

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	42% 3 6% 21% 21% 7%	1708
	11th to 20th	Day	47% 3 4 17% 22% 7%	1638
	21st to end	Day	43% 2 4 18% 26% 7%	1782
February	1st to 10th	Day	47% 4 6% 17% 17% 10%	1652
	11th to 20th	Day	48% 4 6% 17% 19% 7%	1758
	21st to end	Day	52% 4 6% 11% 20% 8%	1538
March	1st to 10th	Day	46% 4 9% 14% 19% 9%	1980
	11th to 20th	Day	45% 6% 9% 16% 17% 6%	1980
	21st to end	Day	39% 6% 10% 18% 23% 3	2178
April	1st to 10th	Day	40% 5% 9% 22% 16% 8%	2160
	11th to 20th	Day	42% 5% 9% 16% 19% 8%	2134
	21st to end	Day	38% 5% 8% 23% 23% 3	2160
May	1st to 10th	Day	42% 6% 9% 20% 18% 5%	2160
	11th to 20th	Day	38% 7% 14% 25% 15% 2	2128
	21st to end	Day	34% 8% 16% 27% 15%	2530
June	1st to 10th	Day	35% 11% 16% 23% 14% 1	2340
	11th to 20th	Day	31% 9% 16% 26% 17% 2	2340
	21st to end	Day	32% 9% 17% 23% 16% 3	2340
July	1st to 10th	Day	37% 11% 22% 21% 8% 1	2276
	11th to 20th	Day	34% 11% 21% 23% 11% 1	2271
	21st to end	Day	36% 11% 20% 21% 11% 1	2405
August	1st to 10th	Day	31% 10% 20% 27% 12%	2229
	11th to 20th	Day	35% 10% 17% 23% 14% 2	2125
	21st to end	Day	36% 8% 18% 21% 13% 3	2376
September	1st to 10th	Day	34% 9% 13% 20% 18% 6%	2160
	11th to 20th	Day	38% 8% 10% 17% 20% 6%	2160
	21st to end	Day	30% 5% 10% 22% 23% 11%	1897
October	1st to 10th	Day	27% 5% 8% 22% 24% 14%	1800
	11th to 20th	Day	30% 4 5% 19% 27% 14%	1800
	21st to end	Day	35% 3 4 17% 29% 12%	1980
November	1st to 10th	Day	31% 4 8% 18% 29% 10%	1858
	11th to 20th	Day	33% 4 6% 18% 27% 12%	1900
	21st to end	Day	41% 5% 6% 17% 22% 7%	1835
December	1st to 10th	Day	44% 5% 9% 18% 16% 8%	1638
	11th to 20th	Day	45% 4 5% 15% 26% 6%	2159
	21st to end	Day	43% 3 6% 16% 28% 4	3135
January	1st to 10th	Night	38% 3 7% 17% 27% 7%	2458
	11th to 20th	Night	43% 4 6% 18% 21% 8%	2379
	21st to end	Night	43% 4 4 15% 25% 9%	2574
February	1st to 10th	Night	41% 5% 6% 19% 21% 9%	2304
	11th to 20th	Night	45% 3 5% 18% 21% 8%	2099
	21st to end	Night	47% 5% 6% 12% 16% 14%	1732
March	1st to 10th	Night	40% 4 8% 17% 21% 10%	1980
	11th to 20th	Night	42% 7% 11% 16% 18% 8%	1980
	21st to end	Night	38% 6% 8% 19% 25% 6%	2175
April	1st to 10th	Night	32% 5% 12% 21% 20% 10%	1800
	11th to 20th	Night	36% 5% 9% 18% 20% 11%	1775
	21st to end	Night	33% 5% 7% 23% 27% 5%	1800
May	1st to 10th	Night	32% 6% 10% 23% 20% 8%	1800
	11th to 20th	Night	32% 7% 12% 28% 19% 2	1768
	21st to end	Night	30% 6% 15% 27% 21% 1	1746
June	1st to 10th	Night	29% 9% 18% 26% 17% 1	1620
	11th to 20th	Night	22% 7% 19% 30% 19% 3	1620
	21st to end	Night	27% 9% 16% 25% 19% 4	1620
July	1st to 10th	Night	28% 9% 25% 26% 9% 2	1575
	11th to 20th	Night	23% 11% 26% 24% 14% 2	1566
	21st to end	Night	21% 11% 25% 29% 12% 2	1673
August	1st to 10th	Night	20% 9% 27% 30% 14% 1	1682
	11th to 20th	Night	26% 10% 21% 24% 16% 4	1776
	21st to end	Night	30% 9% 18% 22% 16% 4	1980
September	1st to 10th	Night	30% 9% 14% 23% 16% 9%	1800
	11th to 20th	Night	35% 8% 11% 16% 21% 10%	1800
	21st to end	Night	27% 5% 9% 22% 24% 13%	2038
October	1st to 10th	Night	25% 5% 9% 21% 24% 17%	2160
	11th to 20th	Night	30% 4 5% 15% 29% 16%	2160
	21st to end	Night	31% 4 6% 18% 27% 15%	2376
November	1st to 10th	Night	29% 4 8% 18% 26% 14%	2220
	11th to 20th	Night	31% 4 8% 16% 28% 13%	2280
	21st to end	Night	38% 3 7% 17% 25% 11%	2331
December	1st to 10th	Night	40% 5% 9% 20% 20% 7%	2518
	11th to 20th	Night	42% 4 6% 13% 26% 10%	3037
	21st to end	Night	42% 4 6% 18% 24% 6%	4532

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	26% 16% 38% 16% 3 1	270
	11th to 20th	Day	25% 16% 36% 15% 5% 2	246
	21st to end	Day	27% 21% 28% 22% 3	264
February	1st to 10th	Day	25% 16% 36% 18% 5% 1	240
	11th to 20th	Day	34% 17% 36% 12% 1	240
	21st to end	Day	31% 25% 29% 13% 2 1	198
March	1st to 10th	Day	25% 14% 35% 21% 5%	240
	11th to 20th	Day	18% 25% 35% 19% 1 1	240
	21st to end	Day	19% 19% 38% 18% 7%	264
April	1st to 10th	Day	17% 13% 35% 24% 10%	420
	11th to 20th	Day	23% 14% 25% 25% 11% 2	412
	21st to end	Day	15% 13% 27% 29% 14% 1	420
May	1st to 10th	Day	14% 9% 32% 27% 15% 3	423
	11th to 20th	Day	15% 4 23% 29% 21% 8%	447
	21st to end	Day	8% 4 19% 33% 26% 9%	678
June	1st to 10th	Day	11% 3 10% 29% 30% 16%	630
	11th to 20th	Day	5% 3 12% 35% 37% 9%	630
	21st to end	Day	8% 1 13% 27% 33% 17%	630
July	1st to 10th	Day	5% 3 8% 25% 39% 20%	621
	11th to 20th	Day	6% 1 5% 22% 40% 25%	618
	21st to end	Day	6% 2 4 25% 44% 19%	684
August	1st to 10th	Day	4 2 6% 20% 47% 22%	541
	11th to 20th	Day	9% 2 4 22% 43% 21%	439
	21st to end	Day	13% 1 5% 18% 35% 27%	495
September	1st to 10th	Day	6% 1 8% 26% 39% 20%	450
	11th to 20th	Day	11% 2 10% 21% 37% 19%	450
	21st to end	Day	13% 4 10% 28% 32% 14%	312
October	1st to 10th	Day	7% 3 18% 35% 27% 10%	270
	11th to 20th	Day	9% 5% 31% 31% 16% 7%	270
	21st to end	Day	20% 9% 28% 23% 15% 4	297
November	1st to 10th	Day	17% 9% 26% 30% 15% 4	270
	11th to 20th	Day	13% 14% 33% 28% 11% 3	270
	21st to end	Day	17% 17% 31% 23% 9% 3	270
December	1st to 10th	Day	20% 10% 38% 22% 8% 1	270
	11th to 20th	Day	24% 13% 34% 20% 9% 1	270
	21st to end	Day	20% 16% 36% 20% 5% 2	297
January	1st to 10th	Night	21% 10% 32% 30% 6%	950
	11th to 20th	Night	23% 10% 32% 28% 8%	915
	21st to end	Night	22% 10% 34% 29% 4	990
February	1st to 10th	Night	20% 11% 34% 30% 5%	864
	11th to 20th	Night	23% 12% 33% 27% 5%	703
	21st to end	Night	25% 14% 32% 25% 3	548
March	1st to 10th	Night	18% 9% 33% 33% 7%	540
	11th to 20th	Night	17% 10% 36% 29% 7% 1	540
	21st to end	Night	15% 11% 34% 30% 10%	594
April	1st to 10th	Night	13% 9% 37% 31% 9%	540
	11th to 20th	Night	16% 10% 32% 30% 12% 1	533
	21st to end	Night	11% 8% 32% 35% 13% 1	540
May	1st to 10th	Night	9% 5% 28% 42% 14% 1	540
	11th to 20th	Night	10% 4 25% 37% 22% 2	531
	21st to end	Night	7% 3 17% 35% 33% 5%	584
June	1st to 10th	Night	8% 2 8% 38% 36% 7%	540
	11th to 20th	Night	4 1 12% 36% 44% 4	540
	21st to end	Night	7% 1 8% 31% 43% 11%	540
July	1st to 10th	Night	5% 1 6% 30% 47% 12%	525
	11th to 20th	Night	6% 2 5% 25% 51% 12%	522
	21st to end	Night	6% 4 31% 47% 12%	591
August	1st to 10th	Night	2 1 5% 26% 50% 16%	537
	11th to 20th	Night	9% 3 29% 49% 10%	534
	21st to end	Night	11% 1 7% 23% 44% 14%	594
September	1st to 10th	Night	7% 1 6% 35% 42% 9%	540
	11th to 20th	Night	12% 2 7% 32% 40% 8%	540
	21st to end	Night	10% 2 10% 36% 38% 4	645
October	1st to 10th	Night	8% 2 16% 35% 33% 6%	720
	11th to 20th	Night	12% 4 24% 35% 23% 3	720
	21st to end	Night	15% 6% 24% 32% 19% 4	792
November	1st to 10th	Night	14% 3 21% 38% 21% 3	740
	11th to 20th	Night	14% 6% 27% 37% 16%	760
	21st to end	Night	16% 8% 29% 31% 14% 1	760
December	1st to 10th	Night	21% 7% 29% 35% 9%	831
	11th to 20th	Night	23% 8% 29% 31% 9%	950
	21st to end	Night	23% 11% 28% 31% 7%	1045

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