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 2024-11-05.

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% 8% 3 8% 5% 5% 5% 4 6% 8% 35%	100960
	Night	15% 10% 4 8% 5% 4 4 4 6% 7% 35%	98061
Transparency	Day	44% 6% 13% 22% 13% 1	104590
	Night	47% 5% 11% 22% 13% 1	102571
Seeing	Day	16% 4 17% 31% 24% 8%	15444
	Night	19% 5% 24% 32% 17% 3	25400

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	16% 16% 5% 12% 7% 5% 5% 4 4 6% 20%	2527
	11th to 20th	Day	15% 16% 6% 13% 8% 6% 7% 6% 6% 5% 12%	2559
	21st to end	Day	27% 18% 7% 11% 6% 3 4 3 4 4 13%	3124
February	1st to 10th	Day	14% 15% 3 11% 7% 6% 4 3 5% 5% 25%	1710
	11th to 20th	Day	14% 10% 4 13% 7% 5% 6% 3 6% 6% 26%	1807
	21st to end	Day	15% 12% 4 10% 5% 5% 3 4 7% 7% 28%	1570
March	1st to 10th	Day	18% 12% 4 10% 6% 4 4 3 5% 6% 27%	3205
	11th to 20th	Day	12% 10% 3 8% 6% 4 7% 4 5% 7% 34%	3480
	21st to end	Day	19% 10% 4 9% 6% 6% 5% 4 5% 6% 27%	3815
April	1st to 10th	Day	14% 9% 3 8% 6% 6% 5% 4 7% 7% 32%	2199
	11th to 20th	Day	17% 7% 3 7% 6% 5% 5% 3 5% 7% 34%	2399
	21st to end	Day	17% 9% 3 7% 4 4 4 3 5% 8% 35%	2470
May	1st to 10th	Day	17% 8% 3 7% 5% 5% 4 3 6% 7% 34%	4082
	11th to 20th	Day	15% 7% 3 6% 5% 5% 5% 4 7% 9% 33%	4081
	21st to end	Day	9% 5% 2 7% 4 5% 5% 4 6% 8% 44%	4476
June	1st to 10th	Day	10% 6% 2 6% 5% 5% 5% 5% 7% 9% 41%	2598
	11th to 20th	Day	8% 5% 2 6% 4 5% 5% 5% 7% 9% 42%	2660
	21st to end	Day	8% 6% 2 7% 5% 4 6% 5% 8% 10% 39%	2660
July	1st to 10th	Day	10% 6% 2 6% 5% 5% 5% 4 7% 9% 42%	4440
	11th to 20th	Day	7% 4 2 5% 4 4 5% 5% 7% 11% 47%	4440
	21st to end	Day	6% 5% 2 7% 5% 5% 6% 5% 7% 9% 42%	4471
August	1st to 10th	Day	10% 5% 2 5% 4 5% 4 4 7% 9% 45%	4104
	11th to 20th	Day	7% 5% 2 7% 5% 5% 7% 5% 8% 11% 38%	4044
	21st to end	Day	7% 5% 3 6% 5% 5% 6% 5% 7% 10% 41%	4468
September	1st to 10th	Day	11% 6% 2 6% 5% 4 4 3 6% 8% 46%	2142
	11th to 20th	Day	8% 4 2 6% 5% 5% 5% 5% 6% 8% 48%	2090
	21st to end	Day	15% 6% 2 6% 3 4 5% 4 7% 7% 40%	2090
October	1st to 10th	Day	11% 6% 2 7% 5% 4 4 4 6% 7% 45%	2043
	11th to 20th	Day	17% 7% 2 7% 4 5% 5% 4 5% 6% 37%	1900
	21st to end	Day	18% 8% 3 6% 6% 5% 5% 4 6% 7% 32%	1951
November	1st to 10th	Day	10% 8% 3 7% 5% 4 4 4 6% 7% 41%	1708
	11th to 20th	Day	15% 11% 3 9% 5% 5% 5% 3 5% 6% 33%	1710
	21st to end	Day	18% 11% 3 8% 5% 4 4 5% 6% 7% 29%	1692
December	1st to 10th	Day	16% 15% 6% 11% 7% 5% 4 4 4 7% 21%	1520
	11th to 20th	Day	15% 13% 6% 10% 5% 5% 6% 5% 6% 7% 23%	1942
	21st to end	Day	22% 18% 8% 14% 6% 4 3 3 4 5% 12%	2783
January	1st to 10th	Night	16% 15% 6% 10% 6% 5% 4 3 5% 5% 24%	4428
	11th to 20th	Night	14% 19% 7% 12% 6% 5% 5% 4 7% 7% 14%	4407
	21st to end	Night	26% 17% 8% 11% 5% 4 4 3 3 4 16%	4532
February	1st to 10th	Night	17% 14% 4 10% 7% 5% 5% 3 5% 5% 25%	2470
	11th to 20th	Night	14% 13% 5% 8% 6% 5% 5% 4 5% 6% 28%	2256
	21st to end	Night	19% 10% 4 9% 5% 5% 4 4 5% 5% 30%	1884
March	1st to 10th	Night	16% 12% 4 8% 4 3 4 3 4 5% 36%	3647
	11th to 20th	Night	11% 7% 2 6% 5% 4 4 4 6% 7% 44%	3480
	21st to end	Night	17% 8% 4 8% 5% 4 4 3 5% 7% 35%	3817
April	1st to 10th	Night	15% 10% 4 7% 5% 5% 4 4 6% 6% 36%	1995
	11th to 20th	Night	18% 7% 2 6% 5% 5% 5% 4 5% 7% 37%	1729
	21st to end	Night	18% 8% 2 6% 4 4 4 4 5% 7% 38%	1710
May	1st to 10th	Night	17% 8% 3 8% 5% 5% 5% 3 6% 7% 33%	2813
	11th to 20th	Night	16% 8% 3 8% 4 5% 5% 3 6% 7% 38%	2812
	21st to end	Night	10% 5% 2 5% 4 4 5% 4 5% 8% 48%	3079
June	1st to 10th	Night	10% 6% 2 5% 5% 5% 4 4 7% 8% 45%	1577
	11th to 20th	Night	10% 5% 2 6% 4 5% 3 5% 7% 9% 43%	1520
	21st to end	Night	10% 5% 2 4 4 5% 5% 5% 5% 10% 45%	1520
July	1st to 10th	Night	9% 3 1 5% 4 4 4 4 6% 10% 50%	2530
	11th to 20th	Night	8% 4 2 5% 3 3 5% 3 7% 9% 51%	2530
	21st to end	Night	6% 4 2 5% 4 5% 5% 5% 8% 9% 46%	3077
August	1st to 10th	Night	11% 6% 2 6% 3 4 4 4 6% 8% 45%	2825
	11th to 20th	Night	7% 5% 2 5% 4 4 5% 4 7% 8% 48%	2785
	21st to end	Night	7% 5% 2 6% 5% 5% 5% 4 6% 8% 47%	3183
September	1st to 10th	Night	9% 5% 2 6% 5% 5% 4 4 5% 6% 49%	2019
	11th to 20th	Night	9% 5% 2 5% 3 3 3 4 5% 7% 53%	2090
	21st to end	Night	14% 6% 2 7% 5% 5% 4 4 6% 6% 42%	2090
October	1st to 10th	Night	13% 5% 2 5% 4 4 4 3 6% 7% 46%	2137
	11th to 20th	Night	16% 8% 3 7% 5% 4 4 4 5% 6% 38%	2280
	21st to end	Night	20% 8% 3 7% 4 3 4 4 5% 7% 36%	2646
November	1st to 10th	Night	13% 7% 3 6% 4 4 4 3 6% 6% 43%	2470
	11th to 20th	Night	16% 10% 3 8% 6% 5% 5% 4 6% 7% 33%	2470
	21st to end	Night	19% 13% 4 8% 5% 5% 3 3 5% 6% 29%	2479
December	1st to 10th	Night	16% 14% 6% 10% 7% 5% 4 3 5% 6% 24%	2660
	11th to 20th	Night	16% 14% 4 9% 5% 5% 5% 3 6% 6% 27%	3230
	21st to end	Night	27% 19% 6% 10% 6% 4 4 3 4 5% 12%	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	65% 5% 11% 12% 5%	2528
	11th to 20th	Day	71% 10% 8% 8% 3	2559
	21st to end	Day	75% 5% 8% 8% 4 1	3124
February	1st to 10th	Day	59% 5% 12% 16% 7%	1710
	11th to 20th	Day	58% 5% 10% 18% 8% 1	1817
	21st to end	Day	52% 5% 15% 19% 7% 2	1570
March	1st to 10th	Day	57% 4 14% 20% 5%	3205
	11th to 20th	Day	47% 5% 16% 22% 9% 1	3480
	21st to end	Day	54% 4 14% 19% 8% 1	3815
April	1st to 10th	Day	48% 5% 14% 19% 13%	2199
	11th to 20th	Day	47% 5% 12% 22% 12% 2	2399
	21st to end	Day	46% 5% 13% 22% 12% 3	2470
May	1st to 10th	Day	45% 7% 12% 24% 11% 1	4120
	11th to 20th	Day	44% 8% 15% 22% 10% 1	4085
	21st to end	Day	35% 6% 13% 20% 20% 6%	4489
June	1st to 10th	Day	36% 7% 14% 27% 14% 3	2598
	11th to 20th	Day	33% 7% 16% 23% 18% 2	2660
	21st to end	Day	35% 8% 16% 23% 16% 3	2660
July	1st to 10th	Day	38% 5% 14% 23% 19% 2	4371
	11th to 20th	Day	28% 6% 13% 33% 19% 1	4365
	21st to end	Day	33% 7% 16% 20% 22% 2	4329
August	1st to 10th	Day	32% 6% 16% 30% 15% 1	4091
	11th to 20th	Day	35% 7% 14% 31% 12% 1	4083
	21st to end	Day	33% 6% 15% 31% 13% 1	4467
September	1st to 10th	Day	36% 6% 15% 23% 17% 2	2142
	11th to 20th	Day	33% 6% 11% 32% 17% 1	2090
	21st to end	Day	40% 7% 13% 25% 15%	2090
October	1st to 10th	Day	28% 4 14% 32% 21% 1	3394
	11th to 20th	Day	39% 4 10% 27% 19%	3140
	21st to end	Day	42% 4 14% 25% 14% 1	3188
November	1st to 10th	Day	41% 6% 12% 26% 14% 1	1708
	11th to 20th	Day	52% 5% 13% 19% 10% 1	1710
	21st to end	Day	53% 6% 14% 19% 8%	1692
December	1st to 10th	Day	65% 5% 11% 14% 5%	1520
	11th to 20th	Day	60% 5% 13% 17% 5%	1939
	21st to end	Day	75% 4 9% 7% 3	2783
January	1st to 10th	Night	62% 5% 10% 16% 6% 1	4428
	11th to 20th	Night	69% 9% 9% 9% 4	4407
	21st to end	Night	73% 3 10% 10% 3	4532
February	1st to 10th	Night	60% 5% 12% 15% 7% 1	2470
	11th to 20th	Night	57% 5% 9% 20% 8% 1	2257
	21st to end	Night	57% 4 10% 18% 9% 2	1884
March	1st to 10th	Night	51% 4 11% 24% 9%	3647
	11th to 20th	Night	38% 6% 14% 22% 18% 1	3480
	21st to end	Night	49% 5% 11% 24% 10% 1	3817
April	1st to 10th	Night	48% 4 10% 21% 14% 2	1995
	11th to 20th	Night	46% 5% 9% 21% 18% 2	1729
	21st to end	Night	45% 4 11% 20% 16% 3	1710
May	1st to 10th	Night	50% 6% 9% 20% 14% 2	2840
	11th to 20th	Night	44% 5% 11% 26% 12% 1	2813
	21st to end	Night	34% 4 11% 25% 22% 4	3087
June	1st to 10th	Night	36% 5% 10% 29% 17% 3	1577
	11th to 20th	Night	35% 6% 13% 27% 16% 3	1520
	21st to end	Night	34% 6% 13% 27% 20% 1	1520
July	1st to 10th	Night	30% 5% 12% 31% 17% 6%	2490
	11th to 20th	Night	29% 7% 14% 30% 19% 1	2482
	21st to end	Night	29% 8% 18% 21% 22% 2	2979
August	1st to 10th	Night	36% 6% 13% 27% 16% 2	2814
	11th to 20th	Night	32% 6% 12% 33% 15% 2	2812
	21st to end	Night	34% 6% 11% 30% 16% 1	3183
September	1st to 10th	Night	35% 6% 12% 27% 17% 3	2019
	11th to 20th	Night	31% 5% 9% 30% 22% 2	2090
	21st to end	Night	41% 5% 12% 25% 15% 1	2090
October	1st to 10th	Night	27% 4 8% 32% 28% 1	3566
	11th to 20th	Night	40% 4 10% 26% 19% 1	3779
	21st to end	Night	38% 3 9% 32% 16% 1	4359
November	1st to 10th	Night	42% 5% 12% 24% 16% 1	2470
	11th to 20th	Night	52% 5% 11% 21% 10% 1	2470
	21st to end	Night	58% 3 12% 20% 7%	2479
December	1st to 10th	Night	64% 4 11% 15% 6%	2660
	11th to 20th	Night	58% 6% 14% 14% 7% 1	3232
	21st to end	Night	74% 5% 11% 8% 3	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	19% 9% 30% 31% 9% 1	270
	11th to 20th	Day	20% 5% 39% 27% 6% 3	270
	21st to end	Day	29% 5% 24% 29% 12% 1	297
February	1st to 10th	Day	23% 5% 27% 36% 9% 1	270
	11th to 20th	Day	22% 4 37% 26% 11%	270
	21st to end	Day	20% 5% 35% 33% 7%	225
March	1st to 10th	Day	19% 6% 25% 37% 13%	316
	11th to 20th	Day	18% 5% 25% 37% 15% 1	460
	21st to end	Day	24% 4 29% 32% 10% 2	506
April	1st to 10th	Day	17% 6% 23% 37% 15% 2	460
	11th to 20th	Day	21% 4 24% 32% 14% 4	452
	21st to end	Day	21% 2 23% 35% 17% 2	460
May	1st to 10th	Day	22% 2 20% 32% 21% 4	463
	11th to 20th	Day	17% 4 15% 31% 26% 7%	487
	21st to end	Day	12% 2 9% 30% 34% 13%	529
June	1st to 10th	Day	11% 2 14% 34% 32% 7%	618
	11th to 20th	Day	10% 2 11% 39% 30% 8%	680
	21st to end	Day	11% 4 11% 36% 30% 8%	680
July	1st to 10th	Day	9% 3 6% 29% 38% 16%	671
	11th to 20th	Day	8% 1 8% 31% 40% 12%	668
	21st to end	Day	8% 3 6% 29% 41% 14%	537
August	1st to 10th	Day	10% 2 6% 28% 37% 17%	486
	11th to 20th	Day	12% 2 6% 29% 39% 11%	479
	21st to end	Day	9% 3 6% 28% 37% 17%	539
September	1st to 10th	Day	11% 3 11% 27% 30% 17%	490
	11th to 20th	Day	10% 2 7% 24% 37% 21%	490
	21st to end	Day	19% 5% 14% 23% 27% 11%	490
October	1st to 10th	Day	11% 3 17% 30% 27% 12%	490
	11th to 20th	Day	18% 9% 21% 30% 17% 4	490
	21st to end	Day	24% 5% 25% 30% 15% 3	400
November	1st to 10th	Day	13% 5% 23% 32% 21% 5%	282
	11th to 20th	Day	21% 11% 25% 29% 12% 2	270
	21st to end	Day	22% 6% 27% 38% 7%	261
December	1st to 10th	Day	21% 9% 32% 28% 8% 1	180
	11th to 20th	Day	19% 8% 38% 25% 8% 1	211
	21st to end	Day	24% 6% 32% 32% 6% 1	297
January	1st to 10th	Night	24% 9% 33% 25% 8% 1	950
	11th to 20th	Night	26% 9% 31% 27% 7%	930
	21st to end	Night	23% 4 31% 35% 7% 1	836
February	1st to 10th	Night	23% 4 33% 34% 6% 1	760
	11th to 20th	Night	20% 6% 33% 34% 6%	743
	21st to end	Night	24% 5% 34% 31% 5%	628
March	1st to 10th	Night	19% 4 31% 34% 11% 1	760
	11th to 20th	Night	18% 6% 31% 33% 10% 2	760
	21st to end	Night	24% 4 25% 33% 12% 1	836
April	1st to 10th	Night	20% 5% 30% 33% 9% 2	665
	11th to 20th	Night	21% 4 28% 32% 12% 2	563
	21st to end	Night	23% 2 24% 35% 15% 1	570
May	1st to 10th	Night	20% 3 24% 34% 16% 3	570
	11th to 20th	Night	21% 3 18% 32% 23% 3	561
	21st to end	Night	11% 2 14% 35% 29% 9%	617
June	1st to 10th	Night	13% 2 16% 40% 25% 3	570
	11th to 20th	Night	13% 2 11% 42% 28% 4	570
	21st to end	Night	12% 1 17% 38% 27% 5%	570
July	1st to 10th	Night	10% 2 8% 33% 37% 10%	555
	11th to 20th	Night	9% 2 11% 39% 30% 9%	552
	21st to end	Night	8% 2 9% 41% 34% 6%	624
August	1st to 10th	Night	8% 2 11% 39% 30% 10%	567
	11th to 20th	Night	10% 2 10% 33% 36% 8%	564
	21st to end	Night	10% 3 11% 33% 34% 9%	627
September	1st to 10th	Night	11% 3 14% 29% 33% 9%	689
	11th to 20th	Night	11% 4 11% 28% 37% 9%	760
	21st to end	Night	17% 3 15% 32% 24% 8%	760
October	1st to 10th	Night	17% 4 20% 32% 21% 7%	760
	11th to 20th	Night	23% 8% 27% 28% 13% 3	760
	21st to end	Night	23% 8% 28% 31% 10% 1	836
November	1st to 10th	Night	17% 9% 27% 30% 15% 2	760
	11th to 20th	Night	22% 11% 32% 25% 9% 2	760
	21st to end	Night	28% 6% 32% 26% 8% 1	760
December	1st to 10th	Night	24% 11% 34% 24% 6% 1	760
	11th to 20th	Night	24% 7% 36% 27% 5%	802
	21st to end	Night	28% 8% 30% 28% 5%	1045

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