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 2026-01-02.

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% 9% 3 8% 5% 4 4 4 6% 7% 38%	127556
	Night	13% 10% 4 8% 5% 4 4 3 5% 6% 39%	124060
Transparency	Day	27% 39% 8% 16% 9% 1	131038
	Night	28% 39% 7% 15% 10% 1	128651
Seeing	Day	16% 12% 30% 25% 14% 5%	17444
	Night	17% 10% 31% 30% 11% 1	27348

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	8% 11% 8% 15% 8% 7% 5% 3 5% 5% 26%	3625
	11th to 20th	Day	8% 10% 6% 13% 5% 4 4 6% 7% 6% 31%	3620
	21st to end	Day	12% 15% 8% 9% 4 3 3 3 4 6% 34%	4255
February	1st to 10th	Day	12% 14% 5% 11% 5% 4 5% 3 5% 6% 31%	1800
	11th to 20th	Day	13% 12% 4 8% 5% 4 5% 3 5% 6% 35%	1877
	21st to end	Day	12% 13% 4 10% 6% 4 4 2 5% 6% 33%	1650
March	1st to 10th	Day	15% 8% 3 6% 3 3 3 3 4 7% 45%	4480
	11th to 20th	Day	11% 7% 3 7% 4 4 4 4 5% 8% 43%	4842
	21st to end	Day	20% 13% 4 10% 5% 5% 4 3 4 5% 27%	5870
April	1st to 10th	Day	18% 12% 3 8% 5% 3 4 4 5% 6% 31%	2400
	11th to 20th	Day	17% 10% 4 8% 5% 4 5% 3 6% 5% 33%	2374
	21st to end	Day	19% 10% 3 8% 4 4 4 3 5% 6% 33%	2440
May	1st to 10th	Day	14% 8% 3 7% 5% 5% 4 4 6% 7% 38%	6064
	11th to 20th	Day	13% 6% 2 7% 5% 5% 5% 4 6% 6% 42%	6319
	21st to end	Day	14% 6% 2 6% 5% 4 5% 4 7% 8% 38%	6935
June	1st to 10th	Day	11% 4 2 6% 5% 4 6% 5% 7% 8% 43%	2800
	11th to 20th	Day	11% 6% 2 6% 4 5% 5% 4 8% 9% 42%	2800
	21st to end	Day	12% 6% 3 7% 5% 4 5% 5% 6% 9% 38%	2800
July	1st to 10th	Day	9% 6% 3 8% 4 5% 5% 5% 8% 9% 38%	6360
	11th to 20th	Day	8% 6% 2 7% 4 4 5% 4 6% 8% 46%	6360
	21st to end	Day	10% 6% 3 8% 5% 5% 5% 4 7% 9% 38%	6924
August	1st to 10th	Day	9% 5% 2 6% 5% 5% 6% 5% 7% 8% 41%	4437
	11th to 20th	Day	11% 5% 2 6% 4 5% 4 4 6% 8% 46%	3942
	21st to end	Day	9% 5% 2 7% 4 4 4 3 6% 9% 47%	4312
September	1st to 10th	Day	11% 5% 2 6% 5% 5% 5% 3 6% 7% 45%	2400
	11th to 20th	Day	12% 4 2 5% 3 3 4 3 5% 8% 52%	2345
	21st to end	Day	11% 8% 2 7% 4 4 4 4 5% 7% 45%	2200
October	1st to 10th	Day	12% 6% 3 6% 4 3 4 3 5% 6% 49%	2029
	11th to 20th	Day	18% 8% 3 8% 4 3 4 3 6% 6% 37%	2000
	21st to end	Day	18% 10% 3 5% 4 3 3 3 5% 5% 40%	2035
November	1st to 10th	Day	12% 9% 3 7% 4 4 4 3 6% 6% 43%	1852
	11th to 20th	Day	14% 12% 4 9% 5% 5% 4 3 5% 6% 34%	1881
	21st to end	Day	14% 15% 3 10% 5% 3 4 2 4 5% 35%	1680
December	1st to 10th	Day	8% 9% 4 9% 4 4 5% 3 6% 6% 41%	2690
	11th to 20th	Day	13% 15% 5% 13% 6% 5% 5% 4 5% 6% 24%	3088
	21st to end	Day	19% 23% 9% 12% 5% 3 4 4 5% 4 13%	4070
January	1st to 10th	Night	9% 12% 6% 14% 7% 4 4 3 4 4 32%	6363
	11th to 20th	Night	10% 13% 6% 13% 6% 6% 5% 5% 7% 5% 23%	6360
	21st to end	Night	13% 15% 6% 10% 5% 4 4 3 4 5% 31%	6720
February	1st to 10th	Night	13% 13% 5% 9% 6% 5% 4 3 5% 5% 33%	2600
	11th to 20th	Night	11% 12% 3 8% 5% 5% 4 3 5% 6% 39%	2408
	21st to end	Night	16% 12% 4 7% 5% 3 4 3 5% 6% 36%	1980
March	1st to 10th	Night	17% 9% 4 7% 4 3 4 3 4 4 42%	5373
	11th to 20th	Night	8% 7% 2 6% 4 4 4 3 5% 8% 48%	5146
	21st to end	Night	21% 14% 6% 10% 5% 4 4 3 4 5% 26%	5059
April	1st to 10th	Night	17% 10% 2 6% 5% 3 3 4 4 6% 39%	2000
	11th to 20th	Night	19% 9% 3 7% 4 4 3 3 4 6% 38%	1975
	21st to end	Night	15% 9% 3 7% 5% 4 4 4 5% 7% 37%	1958
May	1st to 10th	Night	18% 8% 2 6% 5% 4 4 3 6% 6% 39%	3825
	11th to 20th	Night	11% 6% 2 5% 4 4 4 4 6% 8% 45%	3596
	21st to end	Night	14% 7% 2 6% 4 4 5% 4 6% 8% 40%	3942
June	1st to 10th	Night	8% 5% 2 4 5% 5% 5% 5% 7% 8% 47%	1600
	11th to 20th	Night	12% 5% 2 6% 3 4 4 3 7% 11% 44%	1600
	21st to end	Night	10% 6% 2 6% 4 4 3 3 6% 8% 47%	1600
July	1st to 10th	Night	12% 7% 2 6% 4 4 5% 4 7% 8% 41%	3618
	11th to 20th	Night	6% 5% 2 6% 4 4 3 3 5% 8% 53%	3617
	21st to end	Night	9% 5% 2 6% 4 5% 5% 3 5% 8% 48%	3947
August	1st to 10th	Night	8% 4 2 5% 5% 4 5% 3 6% 8% 51%	2719
	11th to 20th	Night	9% 6% 3 5% 3 4 4 3 5% 7% 50%	3109
	21st to end	Night	9% 5% 2 6% 4 4 4 4 5% 8% 50%	3586
September	1st to 10th	Night	9% 4 1 5% 3 3 5% 2 5% 7% 55%	2000
	11th to 20th	Night	10% 4 2 4 3 3 4 4 5% 7% 53%	2035
	21st to end	Night	10% 6% 2 5% 4 4 4 3 4 7% 51%	2200
October	1st to 10th	Night	12% 6% 2 6% 4 3 3 2 5% 6% 51%	2369
	11th to 20th	Night	16% 8% 2 5% 4 4 4 3 4 6% 45%	2400
	21st to end	Night	18% 9% 3 6% 5% 4 4 4 4 5% 38%	2805
November	1st to 10th	Night	12% 8% 3 6% 4 3 3 4 4 5% 48%	2666
	11th to 20th	Night	14% 12% 3 8% 5% 5% 4 3 4 6% 36%	2735
	21st to end	Night	16% 12% 4 8% 4 3 4 3 4 6% 36%	2940
December	1st to 10th	Night	9% 8% 3 7% 5% 6% 5% 4 6% 6% 41%	4720
	11th to 20th	Night	15% 17% 5% 10% 5% 4 5% 3 5% 5% 28%	5339
	21st to end	Night	20% 19% 7% 12% 5% 4 4 3 4 4 17%	7150

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	46% 28% 7% 14% 5%	3626
	11th to 20th	Day	34% 29% 10% 7% 17% 3	3620
	21st to end	Day	36% 28% 10% 15% 10%	4255
February	1st to 10th	Day	20% 63% 4 5% 7%	1800
	11th to 20th	Day	20% 60% 3 11% 4 1	1886
	21st to end	Day	18% 62% 4 9% 5% 2	1650
March	1st to 10th	Day	26% 31% 7% 24% 8% 4	4480
	11th to 20th	Day	25% 31% 10% 24% 9% 1	4842
	21st to end	Day	43% 31% 8% 10% 7% 1	5872
April	1st to 10th	Day	23% 63% 4 7% 3	2400
	11th to 20th	Day	20% 63% 5% 7% 5% 1	2374
	21st to end	Day	19% 62% 4 7% 7% 1	2440
May	1st to 10th	Day	28% 32% 7% 16% 16% 1	6099
	11th to 20th	Day	28% 33% 7% 22% 10% 1	6323
	21st to end	Day	27% 32% 10% 21% 8% 2	6949
June	1st to 10th	Day	11% 63% 6% 13% 7% 1	2800
	11th to 20th	Day	17% 63% 6% 9% 4 1	2800
	21st to end	Day	17% 62% 6% 11% 5% 1	2800
July	1st to 10th	Day	30% 29% 12% 21% 7% 1	6291
	11th to 20th	Day	26% 28% 11% 24% 10%	6285
	21st to end	Day	31% 29% 12% 15% 12% 1	6728
August	1st to 10th	Day	25% 39% 11% 18% 8%	4422
	11th to 20th	Day	22% 38% 11% 21% 8%	3980
	21st to end	Day	23% 37% 10% 21% 9%	4311
September	1st to 10th	Day	17% 59% 5% 12% 7%	2400
	11th to 20th	Day	11% 58% 7% 15% 8% 2	2345
	21st to end	Day	18% 58% 4 11% 9% 1	2200
October	1st to 10th	Day	12% 36% 3 28% 20% 1	3302
	11th to 20th	Day	17% 37% 5% 20% 20% 2	3240
	21st to end	Day	26% 36% 6% 20% 9% 2	3260
November	1st to 10th	Day	22% 54% 6% 10% 7% 1	1852
	11th to 20th	Day	22% 54% 5% 11% 7% 1	1881
	21st to end	Day	26% 54% 7% 10% 3	1680
December	1st to 10th	Day	23% 37% 15% 19% 5% 1	2690
	11th to 20th	Day	40% 32% 8% 13% 5% 2	3085
	21st to end	Day	58% 28% 4 6% 4	4070
January	1st to 10th	Night	40% 28% 8% 16% 8% 1	6363
	11th to 20th	Night	43% 28% 7% 7% 14% 1	6360
	21st to end	Night	39% 29% 9% 14% 8%	6720
February	1st to 10th	Night	21% 62% 5% 5% 6% 1	2600
	11th to 20th	Night	20% 61% 3 10% 6%	2409
	21st to end	Night	17% 61% 5% 9% 5% 2	1980
March	1st to 10th	Night	32% 30% 8% 16% 8% 6%	5373
	11th to 20th	Night	22% 30% 7% 28% 10% 3	5146
	21st to end	Night	44% 30% 6% 11% 7% 1	5059
April	1st to 10th	Night	20% 62% 3 10% 4 1	2000
	11th to 20th	Night	19% 63% 3 8% 6% 1	1975
	21st to end	Night	16% 62% 4 9% 7% 1	1958
May	1st to 10th	Night	31% 32% 8% 12% 16% 1	3852
	11th to 20th	Night	23% 34% 11% 17% 13% 2	3597
	21st to end	Night	28% 33% 9% 18% 10% 2	3950
June	1st to 10th	Night	11% 63% 5% 11% 9% 1	1600
	11th to 20th	Night	15% 63% 6% 9% 6% 1	1600
	21st to end	Night	14% 61% 6% 10% 7% 1	1600
July	1st to 10th	Night	32% 28% 12% 17% 10% 1	3580
	11th to 20th	Night	22% 29% 12% 23% 14%	3572
	21st to end	Night	26% 29% 12% 17% 14% 2	3832
August	1st to 10th	Night	21% 38% 10% 18% 13%	2710
	11th to 20th	Night	23% 38% 9% 21% 10%	3137
	21st to end	Night	22% 39% 8% 20% 9% 2	3586
September	1st to 10th	Night	12% 59% 7% 14% 9%	2000
	11th to 20th	Night	12% 58% 7% 14% 7% 2	2035
	21st to end	Night	17% 58% 4 11% 10% 1	2200
October	1st to 10th	Night	15% 35% 3 26% 20% 1	3876
	11th to 20th	Night	18% 36% 6% 19% 19% 2	3899
	21st to end	Night	27% 37% 5% 17% 11% 2	4530
November	1st to 10th	Night	22% 54% 4 11% 8% 1	2666
	11th to 20th	Night	21% 54% 5% 11% 7% 1	2735
	21st to end	Night	26% 55% 5% 10% 4 1	2940
December	1st to 10th	Night	24% 36% 11% 20% 7% 1	4720
	11th to 20th	Night	40% 32% 8% 11% 8%	5341
	21st to end	Night	53% 28% 6% 8% 4	7150

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	16% 14% 31% 29% 8% 1	303
	11th to 20th	Day	18% 18% 41% 19% 4 1	300
	21st to end	Day	18% 19% 36% 22% 4 1	330
February	1st to 10th	Day	18% 19% 43% 15% 5% 1	300
	11th to 20th	Day	22% 22% 34% 19% 3	300
	21st to end	Day	24% 19% 42% 13% 2	249
March	1st to 10th	Day	16% 22% 44% 15% 4	300
	11th to 20th	Day	21% 22% 34% 16% 5% 2	300
	21st to end	Day	27% 16% 31% 19% 6% 1	505
April	1st to 10th	Day	25% 16% 34% 20% 5%	500
	11th to 20th	Day	26% 19% 25% 17% 10% 2	492
	21st to end	Day	24% 13% 31% 22% 9% 1	500
May	1st to 10th	Day	20% 11% 32% 26% 9% 3	588
	11th to 20th	Day	20% 10% 29% 24% 13% 4	725
	21st to end	Day	17% 9% 29% 23% 15% 7%	789
June	1st to 10th	Day	8% 9% 31% 29% 18% 5%	730
	11th to 20th	Day	12% 6% 32% 30% 15% 5%	730
	21st to end	Day	13% 9% 30% 29% 15% 4	730
July	1st to 10th	Day	8% 3 19% 32% 24% 13%	721
	11th to 20th	Day	10% 6% 27% 28% 20% 8%	718
	21st to end	Day	8% 5% 25% 34% 21% 8%	794
August	1st to 10th	Day	8% 3 20% 34% 26% 10%	726
	11th to 20th	Day	13% 5% 22% 25% 23% 13%	576
	21st to end	Day	11% 6% 20% 30% 24% 9%	583
September	1st to 10th	Day	13% 7% 24% 26% 23% 7%	530
	11th to 20th	Day	10% 5% 20% 30% 24% 12%	530
	21st to end	Day	13% 11% 26% 25% 18% 7%	530
October	1st to 10th	Day	13% 12% 29% 26% 17% 2	359
	11th to 20th	Day	21% 21% 32% 19% 7%	330
	21st to end	Day	28% 15% 29% 21% 5% 1	363
November	1st to 10th	Day	19% 16% 36% 19% 8% 2	330
	11th to 20th	Day	20% 22% 33% 17% 8% 1	330
	21st to end	Day	23% 15% 39% 18% 4	330
December	1st to 10th	Day	14% 22% 39% 18% 5% 2	330
	11th to 20th	Day	20% 15% 39% 19% 7%	330
	21st to end	Day	25% 18% 40% 14% 3	363
January	1st to 10th	Night	17% 15% 36% 26% 6% 1	1006
	11th to 20th	Night	19% 14% 38% 24% 5% 1	1000
	21st to end	Night	19% 13% 36% 27% 4	1100
February	1st to 10th	Night	19% 13% 38% 25% 6%	1000
	11th to 20th	Night	17% 15% 39% 24% 4	853
	21st to end	Night	23% 15% 40% 19% 3	660
March	1st to 10th	Night	21% 12% 38% 23% 5%	800
	11th to 20th	Night	16% 12% 36% 28% 7%	675
	21st to end	Night	24% 12% 32% 26% 5% 1	660
April	1st to 10th	Night	21% 14% 36% 25% 4	600
	11th to 20th	Night	24% 14% 27% 28% 6%	593
	21st to end	Night	20% 10% 34% 28% 8% 1	600
May	1st to 10th	Night	17% 8% 36% 31% 8%	600
	11th to 20th	Night	18% 7% 32% 31% 12%	591
	21st to end	Night	12% 4 31% 36% 16% 1	650
June	1st to 10th	Night	9% 6% 26% 45% 14% 1	600
	11th to 20th	Night	15% 4 30% 39% 13% 1	600
	21st to end	Night	11% 5% 25% 44% 15% 1	600
July	1st to 10th	Night	9% 2 16% 38% 32% 3	585
	11th to 20th	Night	8% 3 22% 42% 23% 3	582
	21st to end	Night	7% 2 20% 45% 24% 2	657
August	1st to 10th	Night	6% 2 16% 47% 27% 3	597
	11th to 20th	Night	9% 3 14% 39% 29% 6%	594
	21st to end	Night	10% 2 15% 44% 26% 3	660
September	1st to 10th	Night	9% 4 22% 37% 24% 5%	600
	11th to 20th	Night	11% 3 21% 35% 26% 4	635
	21st to end	Night	12% 8% 24% 35% 20% 2	800
October	1st to 10th	Night	14% 7% 29% 32% 18% 1	800
	11th to 20th	Night	19% 12% 30% 30% 9%	800
	21st to end	Night	22% 11% 33% 28% 6%	880
November	1st to 10th	Night	15% 11% 39% 25% 9% 1	820
	11th to 20th	Night	19% 16% 37% 23% 5%	845
	21st to end	Night	21% 14% 34% 24% 6%	1050
December	1st to 10th	Night	19% 13% 38% 23% 6%	1050
	11th to 20th	Night	21% 14% 35% 24% 5%	1050
	21st to end	Night	28% 14% 34% 22% 2	1155

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