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 2024-11-12.

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% 9% 3 8% 5% 4 4 4 6% 7% 37%	101539
	Night	14% 10% 4 7% 5% 4 4 3 5% 6% 39%	97729
Transparency	Day	23% 48% 7% 14% 8% 1	105066
	Night	24% 47% 6% 13% 8% 1	102342
Seeing	Day	16% 11% 29% 25% 14% 5%	15904
	Night	17% 10% 31% 30% 11% 1	25744

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	11% 14% 9% 13% 6% 5% 4 3 4 4 27%	2527
	11th to 20th	Day	10% 12% 4 16% 5% 4 5% 8% 8% 6% 20%	2530
	21st to end	Day	17% 20% 10% 11% 4 4 3 3 3 5% 21%	2972
February	1st to 10th	Day	12% 14% 5% 10% 5% 4 5% 4 6% 6% 31%	1710
	11th to 20th	Day	13% 12% 4 7% 5% 4 5% 3 5% 6% 36%	1780
	21st to end	Day	13% 13% 4 11% 6% 4 4 2 5% 6% 32%	1570
March	1st to 10th	Day	13% 9% 3 6% 4 4 4 3 5% 7% 42%	3120
	11th to 20th	Day	11% 7% 4 8% 4 4 4 4 6% 7% 43%	3384
	21st to end	Day	21% 14% 4 10% 5% 4 4 3 5% 5% 25%	4096
April	1st to 10th	Day	19% 12% 3 8% 5% 3 4 3 5% 6% 31%	2280
	11th to 20th	Day	17% 10% 3 7% 5% 4 5% 3 6% 6% 34%	2254
	21st to end	Day	20% 10% 3 8% 4 4 4 3 5% 6% 33%	2318
May	1st to 10th	Day	16% 8% 3 8% 5% 5% 5% 4 6% 7% 36%	4228
	11th to 20th	Day	13% 7% 2 7% 5% 4 4 3 5% 6% 43%	4399
	21st to end	Day	13% 7% 2 7% 5% 4 5% 4 6% 8% 39%	4824
June	1st to 10th	Day	11% 4 2 6% 5% 4 6% 5% 7% 8% 43%	2660
	11th to 20th	Day	11% 5% 2 6% 4 5% 5% 4 7% 9% 43%	2660
	21st to end	Day	12% 6% 3 7% 5% 4 5% 5% 6% 9% 37%	2660
July	1st to 10th	Day	10% 8% 3 8% 5% 6% 5% 5% 8% 9% 34%	4440
	11th to 20th	Day	5% 4 2 6% 4 4 5% 4 7% 9% 50%	4440
	21st to end	Day	9% 6% 3 7% 5% 5% 5% 5% 6% 9% 40%	4813
August	1st to 10th	Day	9% 6% 2 6% 5% 5% 6% 5% 7% 8% 40%	4301
	11th to 20th	Day	11% 5% 2 6% 4 5% 4 4 6% 8% 46%	3819
	21st to end	Day	9% 6% 2 7% 4 4 4 3 6% 9% 47%	4180
September	1st to 10th	Day	12% 6% 2 6% 5% 4 5% 3 6% 7% 46%	2280
	11th to 20th	Day	12% 4 2 4 3 3 4 3 5% 8% 52%	2228
	21st to end	Day	12% 8% 2 7% 4 4 4 4 4 7% 44%	2090
October	1st to 10th	Day	12% 7% 3 6% 4 3 4 3 5% 6% 48%	1928
	11th to 20th	Day	18% 8% 3 8% 4 3 4 3 6% 6% 37%	1900
	21st to end	Day	18% 10% 3 5% 4 3 3 3 5% 6% 40%	1933
November	1st to 10th	Day	13% 9% 2 7% 5% 3 4 3 5% 6% 43%	1762
	11th to 20th	Day	13% 12% 4 9% 5% 5% 4 3 5% 6% 34%	1712
	21st to end	Day	14% 13% 3 9% 4 3 4 2 4 6% 37%	1520
December	1st to 10th	Day	14% 14% 4 9% 4 4 5% 3 5% 5% 33%	1520
	11th to 20th	Day	13% 14% 4 10% 5% 4 4 3 5% 6% 29%	1918
	21st to end	Day	20% 21% 9% 11% 5% 3 4 4 4 4 15%	2783
January	1st to 10th	Night	12% 14% 8% 11% 6% 4 4 3 4 4 31%	4428
	11th to 20th	Night	12% 17% 6% 13% 5% 5% 4 5% 8% 4 21%	4440
	21st to end	Night	16% 19% 7% 11% 5% 5% 3 3 3 5% 22%	4692
February	1st to 10th	Night	12% 13% 5% 9% 6% 5% 4 3 5% 5% 33%	2470
	11th to 20th	Night	11% 11% 3 8% 5% 5% 4 3 5% 6% 39%	2285
	21st to end	Night	16% 12% 4 7% 5% 3 4 3 5% 6% 35%	1884
March	1st to 10th	Night	18% 9% 3 6% 4 3 4 3 4 5% 41%	3733
	11th to 20th	Night	9% 6% 2 6% 5% 4 4 3 5% 8% 47%	3590
	21st to end	Night	24% 13% 5% 10% 4 4 3 2 4 5% 26%	3535
April	1st to 10th	Night	17% 10% 2 6% 5% 3 4 4 5% 5% 38%	1900
	11th to 20th	Night	19% 9% 3 6% 4 4 3 3 4 6% 38%	1875
	21st to end	Night	16% 9% 3 7% 5% 4 4 4 4 8% 37%	1860
May	1st to 10th	Night	17% 8% 2 7% 6% 4 5% 3 6% 7% 36%	2670
	11th to 20th	Night	14% 7% 2 6% 5% 4 5% 4 6% 7% 41%	2506
	21st to end	Night	10% 6% 2 6% 4 4 5% 4 6% 8% 44%	2743
June	1st to 10th	Night	8% 5% 2 4 5% 5% 5% 5% 7% 8% 47%	1520
	11th to 20th	Night	11% 5% 2 5% 3 4 4 3 6% 11% 45%	1520
	21st to end	Night	10% 6% 2 6% 4 4 4 3 7% 8% 47%	1520
July	1st to 10th	Night	14% 7% 2 6% 4 4 4 3 7% 8% 40%	2530
	11th to 20th	Night	4 5% 2 5% 4 4 3 4 6% 9% 55%	2530
	21st to end	Night	7% 5% 2 6% 4 5% 5% 4 6% 9% 48%	2750
August	1st to 10th	Night	8% 4 2 5% 5% 4 5% 3 6% 8% 51%	2635
	11th to 20th	Night	9% 5% 3 5% 3 4 4 3 5% 7% 51%	3012
	21st to end	Night	9% 5% 2 6% 4 4 4 4 5% 8% 50%	3476
September	1st to 10th	Night	9% 4 1 5% 3 3 4 2 4 7% 56%	1900
	11th to 20th	Night	11% 4 2 4 3 3 4 4 5% 7% 53%	1933
	21st to end	Night	10% 6% 2 5% 4 4 4 3 4 7% 50%	2090
October	1st to 10th	Night	12% 6% 2 6% 4 3 3 2 5% 6% 51%	2250
	11th to 20th	Night	16% 8% 2 5% 4 4 4 3 4 6% 45%	2280
	21st to end	Night	18% 9% 3 6% 4 4 4 4 5% 6% 38%	2665
November	1st to 10th	Night	12% 8% 3 6% 4 3 3 4 4 5% 48%	2536
	11th to 20th	Night	14% 11% 3 8% 5% 5% 4 3 4 6% 36%	2488
	21st to end	Night	17% 11% 3 7% 4 3 4 3 4 6% 38%	2660
December	1st to 10th	Night	15% 12% 4 9% 6% 5% 5% 4 5% 5% 31%	2660
	11th to 20th	Night	15% 14% 5% 10% 5% 5% 5% 3 5% 5% 30%	3279
	21st to end	Night	21% 17% 6% 11% 6% 4 4 3 4 5% 19%	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	42% 38% 7% 9% 4	2528
	11th to 20th	Day	35% 41% 10% 8% 6% 1	2530
	21st to end	Day	44% 40% 5% 9% 3	2972
February	1st to 10th	Day	18% 66% 4 5% 7%	1710
	11th to 20th	Day	18% 64% 3 11% 4 1	1789
	21st to end	Day	16% 65% 4 8% 4 2	1570
March	1st to 10th	Day	21% 44% 6% 20% 7% 3	3120
	11th to 20th	Day	21% 43% 7% 21% 8% 1	3384
	21st to end	Day	37% 43% 8% 9% 4 1	4096
April	1st to 10th	Day	21% 65% 4 7% 3	2280
	11th to 20th	Day	18% 66% 4 7% 5% 1	2254
	21st to end	Day	17% 65% 3 6% 7% 1	2318
May	1st to 10th	Day	24% 43% 7% 12% 12% 1	4266
	11th to 20th	Day	23% 43% 6% 21% 7%	4403
	21st to end	Day	21% 44% 8% 15% 10% 3	4837
June	1st to 10th	Day	10% 66% 5% 11% 7% 1	2660
	11th to 20th	Day	16% 66% 5% 8% 4 1	2660
	21st to end	Day	16% 65% 5% 9% 4 1	2660
July	1st to 10th	Day	31% 39% 9% 15% 4 1	4371
	11th to 20th	Day	16% 38% 13% 23% 10%	4365
	21st to end	Day	25% 39% 9% 12% 13% 1	4662
August	1st to 10th	Day	25% 40% 10% 17% 8%	4286
	11th to 20th	Day	22% 40% 10% 21% 8%	3857
	21st to end	Day	23% 38% 10% 19% 9%	4179
September	1st to 10th	Day	16% 62% 5% 10% 7%	2280
	11th to 20th	Day	11% 60% 6% 13% 8% 2	2228
	21st to end	Day	17% 60% 4 10% 7% 1	2090
October	1st to 10th	Day	11% 37% 3 28% 20% 1	3201
	11th to 20th	Day	15% 38% 5% 20% 21% 2	3140
	21st to end	Day	26% 37% 6% 20% 9% 3	3158
November	1st to 10th	Day	22% 56% 6% 9% 6% 1	1762
	11th to 20th	Day	19% 60% 5% 9% 6% 1	1712
	21st to end	Day	22% 59% 7% 8% 3	1520
December	1st to 10th	Day	20% 62% 6% 7% 4 1	1520
	11th to 20th	Day	25% 49% 9% 9% 6% 2	1915
	21st to end	Day	50% 39% 4 4 3	2783
January	1st to 10th	Night	37% 39% 7% 11% 6%	4428
	11th to 20th	Night	41% 38% 6% 8% 6%	4440
	21st to end	Night	43% 40% 4 10% 3	4692
February	1st to 10th	Night	19% 65% 4 5% 6% 1	2470
	11th to 20th	Night	17% 64% 3 9% 6%	2286
	21st to end	Night	16% 64% 4 9% 4 3	1884
March	1st to 10th	Night	26% 42% 6% 15% 6% 4	3733
	11th to 20th	Night	18% 42% 5% 22% 12% 1	3590
	21st to end	Night	38% 42% 4 10% 6% 1	3535
April	1st to 10th	Night	19% 66% 3 9% 3 1	1900
	11th to 20th	Night	17% 66% 3 7% 7% 1	1875
	21st to end	Night	15% 65% 4 9% 7% 1	1860
May	1st to 10th	Night	27% 44% 7% 8% 12% 2	2697
	11th to 20th	Night	23% 44% 7% 17% 8%	2507
	21st to end	Night	18% 45% 8% 12% 13% 3	2751
June	1st to 10th	Night	10% 66% 5% 10% 8% 1	1520
	11th to 20th	Night	13% 66% 5% 9% 6% 1	1520
	21st to end	Night	13% 64% 6% 10% 6% 1	1520
July	1st to 10th	Night	32% 37% 11% 12% 6% 2	2490
	11th to 20th	Night	15% 39% 12% 24% 10% 1	2482
	21st to end	Night	21% 39% 11% 12% 14% 3	2662
August	1st to 10th	Night	21% 38% 9% 18% 13%	2626
	11th to 20th	Night	22% 39% 8% 21% 10%	3040
	21st to end	Night	22% 40% 9% 19% 9% 2	3476
September	1st to 10th	Night	11% 61% 6% 12% 9%	1900
	11th to 20th	Night	12% 61% 6% 13% 7% 2	1933
	21st to end	Night	16% 61% 4 10% 8% 1	2090
October	1st to 10th	Night	14% 36% 3 26% 20% 1	3757
	11th to 20th	Night	17% 37% 6% 19% 19% 2	3779
	21st to end	Night	27% 38% 5% 17% 11% 2	4390
November	1st to 10th	Night	21% 56% 4 10% 7% 1	2536
	11th to 20th	Night	19% 59% 5% 9% 7% 1	2488
	21st to end	Night	21% 60% 5% 10% 4 1	2660
December	1st to 10th	Night	23% 60% 5% 7% 4 1	2660
	11th to 20th	Night	26% 51% 7% 11% 6% 1	3281
	21st to end	Night	43% 39% 6% 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	17% 13% 30% 30% 9% 1	270
	11th to 20th	Day	20% 16% 39% 20% 4 1	270
	21st to end	Day	19% 17% 35% 23% 4 1	297
February	1st to 10th	Day	16% 19% 43% 16% 6% 1	270
	11th to 20th	Day	22% 22% 32% 21% 3	270
	21st to end	Day	23% 20% 41% 14% 2	225
March	1st to 10th	Day	15% 21% 45% 15% 4	270
	11th to 20th	Day	20% 23% 34% 16% 5% 2	270
	21st to end	Day	28% 14% 31% 20% 6% 1	463
April	1st to 10th	Day	25% 16% 33% 20% 5%	460
	11th to 20th	Day	26% 18% 26% 18% 10% 2	452
	21st to end	Day	24% 13% 30% 22% 10% 1	460
May	1st to 10th	Day	21% 12% 31% 25% 9% 2	544
	11th to 20th	Day	20% 10% 30% 24% 13% 3	675
	21st to end	Day	17% 9% 28% 22% 16% 7%	734
June	1st to 10th	Day	8% 8% 30% 29% 19% 5%	680
	11th to 20th	Day	12% 6% 32% 30% 15% 5%	680
	21st to end	Day	14% 9% 29% 29% 15% 4	680
July	1st to 10th	Day	8% 4 19% 32% 25% 13%	671
	11th to 20th	Day	9% 6% 28% 29% 21% 9%	668
	21st to end	Day	7% 4 25% 33% 22% 8%	739
August	1st to 10th	Day	8% 3 20% 35% 25% 9%	676
	11th to 20th	Day	11% 5% 23% 25% 23% 13%	533
	21st to end	Day	11% 6% 19% 31% 24% 9%	539
September	1st to 10th	Day	13% 6% 24% 26% 24% 7%	490
	11th to 20th	Day	10% 5% 21% 30% 23% 11%	490
	21st to end	Day	14% 12% 26% 25% 17% 6%	490
October	1st to 10th	Day	14% 13% 29% 26% 16% 2	328
	11th to 20th	Day	21% 22% 31% 18% 7%	300
	21st to end	Day	29% 15% 29% 21% 5% 1	330
November	1st to 10th	Day	19% 14% 37% 20% 8% 1	300
	11th to 20th	Day	19% 21% 34% 17% 8% 1	273
	21st to end	Day	24% 12% 41% 19% 4	270
December	1st to 10th	Day	16% 22% 36% 19% 6% 2	270
	11th to 20th	Day	20% 13% 39% 20% 8%	270
	21st to end	Day	26% 17% 41% 15% 2	297
January	1st to 10th	Night	18% 15% 36% 25% 6% 1	950
	11th to 20th	Night	20% 13% 37% 24% 5% 1	950
	21st to end	Night	20% 13% 35% 27% 5%	1045
February	1st to 10th	Night	19% 12% 38% 25% 6%	950
	11th to 20th	Night	16% 15% 39% 25% 4	810
	21st to end	Night	23% 15% 39% 20% 4	628
March	1st to 10th	Night	21% 12% 38% 23% 5%	760
	11th to 20th	Night	16% 11% 36% 29% 7%	641
	21st to end	Night	24% 11% 32% 26% 6% 1	627
April	1st to 10th	Night	21% 14% 36% 24% 4	570
	11th to 20th	Night	25% 14% 27% 28% 6%	563
	21st to end	Night	20% 10% 34% 27% 8% 1	570
May	1st to 10th	Night	17% 8% 36% 30% 8%	570
	11th to 20th	Night	19% 6% 32% 32% 11%	561
	21st to end	Night	12% 4 31% 35% 16% 1	617
June	1st to 10th	Night	8% 6% 26% 44% 14% 1	570
	11th to 20th	Night	14% 4 30% 39% 13% 1	570
	21st to end	Night	11% 5% 24% 44% 15% 1	570
July	1st to 10th	Night	9% 2 16% 38% 32% 4	555
	11th to 20th	Night	7% 3 22% 42% 22% 3	552
	21st to end	Night	7% 1 19% 45% 25% 2	624
August	1st to 10th	Night	6% 2 16% 46% 27% 3	567
	11th to 20th	Night	8% 4 14% 40% 29% 6%	564
	21st to end	Night	10% 2 16% 43% 26% 3	627
September	1st to 10th	Night	9% 3 22% 37% 24% 5%	570
	11th to 20th	Night	11% 3 22% 35% 25% 4	603
	21st to end	Night	12% 8% 25% 34% 19% 1	760
October	1st to 10th	Night	14% 7% 29% 32% 17% 1	760
	11th to 20th	Night	19% 12% 30% 29% 9%	760
	21st to end	Night	22% 11% 33% 28% 6%	836
November	1st to 10th	Night	16% 10% 39% 25% 9% 1	780
	11th to 20th	Night	19% 15% 37% 24% 5%	769
	21st to end	Night	21% 13% 35% 24% 7%	950
December	1st to 10th	Night	19% 13% 38% 23% 6%	950
	11th to 20th	Night	21% 13% 35% 25% 5% 1	950
	21st to end	Night	27% 15% 34% 22% 2	1045

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